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See also: Dihydroxylation
In a vicinal diol, the two hydroxyl groups occupy vicinal positions, that is, they are attached to adjacent atoms. These compounds are called glycols. Examples include ethane-1,2-diol or ethylene glycol HO−(CH)−OH, a common ingredient of antifreeze products. Another example is propane-1,2-diol, or alpha propylene glycol, HO−CH−CH(OH)−CH, used in the food and medicine industry, as well as a relatively non-poisonous antifreeze product.
On commercial scales, the main route to vicinal diols is the hydrolysis of epoxides. The epoxides are prepared by epoxidation of the alkene. An example in the synthesis of trans-cyclohexanediol or by microreactor:
For academic research and pharmaceutical areas, vicinal diols are often produced from the oxidation of alkenes, usually with dilute acidic potassium permanganate or Osmium tetroxide. Osmium tetroxide can similarly be used to oxidize alkenes to vicinal diols. The chemical reaction called Sharpless asymmetric dihydroxylation can be used to produce chiral diols from alkenes using an osmate reagent and a chiral catalyst. Another method is the Woodward cis-hydroxylation (cis diol) and the related Prévost reaction (anti diol), which both use iodine and the silver salt of a carboxylic acid.
Other routes to vic-diols are the hydrogenation of acyloins and the pinacol coupling reaction. | 0 | Organic Chemistry |
In 1999 the New Zealand Association of Scientists established the Shorland Medal in Shorland's honour. It is awarded annually in recognition of a "major and continued contribution to basic or applied research that has added significantly to scientific understanding or resulted in significant benefits to society." | 0 | Organic Chemistry |
As SPR allows real-time monitoring, individual steps in sequential binding events can be thoroughly assessed when investigating the suitability between antibodies in a sandwich configuration. Additionally, it allows the mapping of epitopes as antibodies of overlapping epitopes will be associated with an attenuated signal compared to those capable of interacting simultaneously. | 7 | Physical Chemistry |
Calcium stable isotopes have been used to study inputs and outputs of dissolved calcium in marine environments. For example, one study found that calcium levels have decreased between 25 and 50 percent over a 40 million year timespan, suggesting that dissolved Caoutputs have exceeded its inputs. The isotope Calcium-44 can help to indicate variations in calcium carbonate over long timespans and help explain variants in global temperature. Declines in the isotope Calcium-44 usually correlate with periods of cooling, as dissolution of calcium carbonate typically signifies a decrease in temperature. Thus, Calcium isotopes correlate with Earth's climate over long periods of time. | 1 | Biochemistry |
Pol II-transcribed genes contain a region in the immediate vicinity of the transcription start site (TSS) that binds and positions the preinitiation complex. This region is called the core promoter because of its essential role in transcription initiation. Different classes of sequence elements are found in the promoters. For example, the TATA box is the highly conserved DNA recognition sequence for the TATA box binding protein, TBP, whose binding initiates transcription complex assembly at many genes.
Eukaryotic genes also contain regulatory sequences beyond the core promoter. These cis-acting control elements bind transcriptional activators or repressors to increase or decrease transcription from the core promoter. Well-characterized regulatory elements include enhancers, silencers, and insulators. These regulatory sequences can be spread over a large genomic distance, sometimes located hundreds of kilobases from the core promoters.
General transcription factors are a group of proteins involved in transcription initiation and regulation. These factors typically have DNA-binding domains that bind specific sequence elements of the core promoter and help recruit RNA polymerase to the transcriptional start site.
General transcription factors for RNA polymerase II include TFIID, TFIIA, TFIIB, TFIIF, TFIIE, and TFIIH. | 1 | Biochemistry |
In 2013, researchers reported that tramadol was found in relatively high concentrations (1%+) in the roots of the African pin cushion tree (Nauclea latifolia). In 2014, however, it was reported that the presence of tramadol in the tree roots was the result of tramadol having been administered to cattle by farmers in the region: tramadol and its metabolites were present in the animals' excreta, which contaminated the soil around the trees. Therefore, tramadol and its mammalian metabolites were found in tree roots in the far north of Cameroon, but not in the south where it is not administered to farm animals.
A 2014 editorial in Lab Times online contested the notion that tramadol in tree roots was the result of anthropogenic contamination, stating that samples were taken from trees that grew in national parks, where livestock were forbidden; it also quoted researcher Michel de Waard, who stated that "thousands and thousands of tramadol-treated cattle sitting around a single tree and urinating there" would be required to produce the concentrations discovered.
In 2015, radiocarbon analysis confirmed that the tramadol found in N. latifolia roots could not be plant-derived and was of synthetic origin. | 4 | Stereochemistry |
For reactions in aqueous solution, such as an acid dissociation reaction
:AH + HO A + HO
the concentration of water may be taken as being constant and the formation of the hydronium ion is implicit.
:AH A + H
Water concentration is omitted from expressions defining equilibrium constants, except when solutions are very concentrated.
: (K defined as a dissociation constant)
Similar considerations apply to metal ion hydrolysis reactions. | 7 | Physical Chemistry |
Many synthetic supramolecular systems are designed to copy functions of biological systems. These biomimetic architectures can be used to learn about both the biological model and the synthetic implementation. Examples include photoelectrochemical systems, catalytic systems, protein design and self-replication. | 6 | Supramolecular Chemistry |
Robert Edward Corbett (13 June 1923 – 3 February 2018) was a New Zealand organic chemist. He is noted for his contribution to natural product chemistry through the isolation and structural elucidation of compounds from New Zealand native plants. | 0 | Organic Chemistry |
During the period of active colonization of the Urals, which began in the 14th to early 15th centuries, there were rumors about subsurface deposits in Perm land and Yugra. But when conditions were dangerous for the settlers, because of the indigenous population, industrial land development was practically not carried out. In 1491, Ivan III sent an expedition to the Northern Urals, to Pechora, with the task of searching for silver and copper ores. As a result, a small silver ore deposit was discovered on the Tsilma River, which was quickly developed. Ivan IV declared the prospecting and mining of ores a state monopoly and in 1567-1568 he sent an expedition to search for silver and copper ores on the Yayva River. The expedition ended in vain. In 1568, Ivan IV allocated extensive lands to Y. A. Stroganov in the Kama region with permission to use iron ores, but was banned from using silver, copper and tin ores, and he had to immediately report their discovery to Moscow.
The active resettlement of Russians to the Urals was facilitated by the agrarian crisis of the agricultural central part of Russia at the end of the 16th century. From 1579 to 1678 the Russian population of Great Perm increased from 2,197 to 11,811 households (by 463%). By 1724, the population of the Urals was already about 1 million people, while the total population of Russia was about 14 million people.
Until the beginning of the 17th century, all of the Ural and Russian metallurgy was locally handcrafted production in the form of small peasant blast furnaces and forges, in which all the processes of obtaining finished products were concentrated. | 8 | Metallurgy |
Stop codons were historically given many different names, as they each corresponded to a distinct class of mutants that all behaved in a similar manner. These mutants were first isolated within bacteriophages (T4 and lambda), viruses that infect the bacteria Escherichia coli. Mutations in viral genes weakened their infectious ability, sometimes creating viruses that were able to infect and grow within only certain varieties of E. coli. | 1 | Biochemistry |
The excavations at Hammeh are part of the Deir 'Alla Regional Project, a joint undertaking of Yarmouk University in Irbid, Jordan, and Leiden University in the Netherlands, in collaboration with the Jordanian Department of Antiquities.
The site's most intriguing feature is the presence of a substantial and very early iron smelting operation, as evidence by large quantities of slag, technical ceramics, furnace remnants etc. This activity dates to 930 BC.
Fieldwork at Tell Hammeh took place in 1996, 1997, and 2000. The first two (rescue) seasons were directed by Dr E.J. van der Steen; the third season was directed by Dr H.A. Veldhuijzen. A fourth season, planned in 2003, had to be abandoned due to the invasion of Iraq. As with the third season, the focus of new excavation would primarily be on the iron smelting evidence. A new excavation was to start in May 2009. | 8 | Metallurgy |
Combinations of chromatographic methods can be used to purify a target molecule. The purpose of purifying proteins with FPLC is to deliver quantities of the target at sufficient purity in a biologically active state to suit its further use. The quality of the end product varies depending the type and amount of starting material, efficiency of separation, and selectivity of the purification resin. The ultimate goal of a given purification protocol is to deliver the required yield and purity of the target molecule in the quickest, cheapest, and safest way for acceptable results. The range of purity required can be from that required for basic analysis (SDS-PAGE or ELISA, for example), with only bulk impurities removed, to pure enough for structural analysis (NMR or X-ray crystallography), approaching >99% target molecule. Purity required can also mean pure enough that the biological activity of the target is retained. These demands can be used to determine the amount of starting material required to reach the experimental goal. If the starting material is limited and full optimization of purification protocol cannot be performed, then a safe standard protocol that requires a minimum adjustment and optimization steps are expected. This may not be optimal with respect to experimental time, yield, and economy but it will achieve the experimental goal. On the other hand, if the starting material is enough to develop more complete protocol, the amount of work to reach the separation goal depends on the available sample information and target molecule properties. Limits to development of purification protocols many times depends on the source of the substance to be purified, whether from natural sources (harvested tissues or organisms, for example), recombinant sources (such as using prokaryotic or eukaryotic vectors in their respective expression systems), or totally synthetic sources.
No chromatographic techniques provide 100% yield of active material and overall yields depend on the number of steps in the purification protocol. By optimizing each step for the intended purpose and arranging them that minimizes inter step treatments, the number of steps will be minimized.
A typical multistep purification protocol starts with a preliminary capture step which often utilizes ion exchange chromatography (IEC). The media (stationary phase) resin consists of beads, which range in size from being large (good for fast flow rates and little to no sample clarification at the expense of resolution) to small (for best possible resolution with all other factors being equal). Short and wide column geometries are amenable to high flow rates also at the expense of resolution, typically because of lateral diffusion of sample on the column. For techniques such as size exclusion chromatography to be useful, very long, thin columns and minimal sample volumes (maximum 5% of column volume) are required. Hydrophobic interaction chromatography (HIC) can also be used for first and/ or intermediate steps. Selectivity in HIC is independent of running pH and descending salt gradients are used. For HIC, conditioning involves adding ammonium sulfate to the sample to match the buffer A concentration. If HIC is used before IEC, the ionic strength would have to be lowered to match that of buffer A for IEC step by dilution, dialysis or buffer exchange by gel filtration. This is why IEC is usually performed prior to HIC as the high salt elution conditions for IEC are ideal for binding to HIC resins in the next purification step. Polishing is used to achieve the final level of purification required and is commonly performed on a gel filtration column. An extra intermediate purification step can be added or optimization of the different steps is performed for improving purity. This extra step usually involves another round of IEC under completely different conditions.
Although this is an example of a common purification protocol for proteins, the buffer conditions, flow rates, and resins used to achieve final goals can be chosen to cover a broad range of target proteins. This flexibility is imperative for a functional purification system as all proteins behave differently and often deviate from predictions. | 3 | Analytical Chemistry |
Vancomycin is made by the soil bacterium Amycolatopsis orientalis.
Vancomycin biosynthesis occurs primarily via three nonribosomal protein syntheses (NRPSs) VpsA, VpsB, and VpsC. The enzymes determine the amino acid sequence during its assembly through its 7 modules. Before vancomycin is assembled through NRPS, the non-proteinogenic amino acids are first synthesized. -tyrosine is modified to become the β-hydroxytyrosine (β-HT) and 4-hydroxyphenylglycine (4-Hpg) residues. 3,5 dihydroxyphenylglycine ring (3,5-DPG) is derived from acetate.
Nonribosomal peptide synthesis occurs through distinct modules that can load and extend the protein by one amino acid per module through the amide bond formation at the contact sites of the activating domains. Each module typically consists of an adenylation (A) domain, a peptidyl carrier protein (PCP) domain, and a condensation (C) domain. In the A domain, the specific amino acid is activated by converting into an aminoacyl adenylate enzyme complex attached to a 4phosphopantetheine cofactor by thioesterification. The complex is then transferred to the PCP domain with the expulsion of AMP. The PCP domain uses the attached 4-phosphopantethein prosthetic group to load the growing peptide chain and their precursors. The organization of the modules necessary to biosynthesize Vancomycin is shown in Figure 1. In the biosynthesis of Vancomycin, additional modification domains are present, such as the epimerization (E) domain, which isomerizes the amino acid from one stereochemistry to another, and a thioesterase domain (TE) is used as a catalyst for cyclization and releases of the molecule via a thioesterase scission.
A set of NRPS enzymes (peptide synthase VpsA, VpsB, and VpsC) are responsible for assembling the heptapeptide. (Figure 2). VpsA codes for modules 1, 2, and 3. VpsB codes for modules 4, 5, and 6, and VpsC codes for module 7. The vancomycin aglycone contains 4 D-amino acids, although the NRPSs only contain 3 epimerization domains. The origin of D-Leu at residue 1 is not known. The three peptide syntheses are located at the start of the region of the bacterial genome linked with antibiotic biosynthesis, and span 27 kb.
β-hydroxytyrosine (β-HT) is synthesized prior to incorporation into the heptapeptide backbone. L-tyrosine is activated and loaded on the NRPS VpsD, hydroxylated by OxyD, and released by the thioesterase Vhp. The timing of the chlorination by halogenase VhaA during biosynthesis is currently undetermined, but is proposed to occur before the complete assembly of the heptapeptide.
After the linear heptapeptide molecule is synthesized, vancomycin has to undergo further modifications, such as oxidative cross-linking and glycosylation, in trans by distinct enzymes, referred to as tailoring enzymes, to become biologically active (Figure 3). To convert the linear heptapeptide to cross-linked, glycosylated vancomycin, six enzymes, are required. The enzymes OxyA, OxyB, OxyC, and OxyD are cytochrome P450 enzymes. OxyB catalyzes oxidative cross-linking between residues 4 and 6, OxyA between residues 2 and 4, and OxyC between residues 5 and 7. This cross-linking occurs while the heptapeptide is covalently bound to the PCP domain of the 7th NRPS module. These P450s are recruited by the X domain present in the 7th NRPS module, which is unique to glycopeptide antibiotic biosynthesis. The cross-linked heptapeptide is then released by the action of the TE domain, and methyltransferase Vmt then N-methylates the terminal leucine residue. GtfE then joins D-glucose to the phenolic oxygen of residue 4, followed by the addition of vancosamine catalyzed by GtfD.
Some of the glycosyltransferases capable of glycosylating vancomycin and related nonribosomal peptides display notable permissivity and have been employed for generating libraries of differentially glycosylated analogs through a process known as glycorandomization. | 0 | Organic Chemistry |
An expansion of TST to the reactions when two spin-states are involved simultaneously is called nonadiabatic transition state theory (NA-TST). | 7 | Physical Chemistry |
The phase diagram explains why liquids do not exist in space or any other vacuum. Since the pressure is essentially zero (except on surfaces or interiors of planets and moons) water and other liquids exposed to space will either immediately boil or freeze depending on the temperature. In regions of space near the Earth, water will freeze if the sun is not shining directly on it and vaporize (sublime) as soon as it is in sunlight. If water exists as ice on the Moon, it can only exist in shadowed holes where the sun never shines and where the surrounding rock does not heat it up too much. At some point near the orbit of Saturn, the light from the Sun is too faint to sublime ice to water vapor. This is evident from the longevity of the ice that composes Saturn's rings. | 7 | Physical Chemistry |
Laser light is sent to the sample and the outcoming transmitted or backscattered light is detected by an optoelectric sensor. The light intensity detected is the result of the interference of all the optical waves coming from the different light paths.
The signal is analysed by calculating the intensity autocorrelation function called g.
For the case of non-interacting particles suspended in a (complex) fluid a direct relation between g-1 and the mean squared displacement of the particles > can be established. Let us note P(s) the probability density function (PDF) of the photon path length s. The relation can be written as follows:
with and is the transport mean free path of scattered light.
For simple cell geometries, it is thus possible to calculate the mean squared displacement of the particles > from the measured g-1 values analytically. For example, for the backscattering geometry, an infinitely thick cell, large laser spot illumination and detection of photons coming from the center of the spot, the relationship between g-1 and > is:
, γ value is around 2.
For less thick cells and in transmission, the relationship depends also on l* (the transport length).
For quasi-transparent cells, an angle-independent variant method called cavity amplified scattering spectroscopy makes use of an integrating sphere to isotropically probe samples from all directions, elongating photon paths through the sample in the process, allowing for the study of low turbidity samples under the DWS formalism. | 7 | Physical Chemistry |
Abortive initiation, also known as abortive transcription, is an early process of genetic transcription in which RNA polymerase binds to a DNA promoter and enters into cycles of synthesis of short mRNA transcripts which are released before the transcription complex leaves the promoter. This process occurs in both eukaryotes and prokaryotes. Abortive initiation is typically studied in the T3 and T7 RNA polymerases in bacteriophages and in E. coli. | 1 | Biochemistry |
Fresh domestic sewage entering a wastewater collection system contains proteins including organic sulfur compounds oxidizable to sulfates and may contain inorganic sulfates. Dissolved oxygen is depleted as bacteria begin to catabolize organic material in sewage. In the absence of dissolved oxygen and nitrates, sulfates are reduced to hydrogen sulfide as an alternative source of oxygen for catabolizing organic waste by sulfate reducing bacteria (SRB), identified primarily from the obligate anaerobic species Desulfovibrio.
Hydrogen sulfide production depends on various physicochemical, topographic and hydraulic parameters such as:
* Sewage oxygen concentration. The threshold is 0.1 mg.l; above this value, sulfides produced in sludge and sediments are oxidized by oxygen; below this value, sulfides are emitted in the gaseous phase.
* Temperature. The higher the temperature, the faster the kinetics of HS production.
* Sewage pH. It must be included between 5.5 and 9 with an optimum at 7.5-8.
* Sulfate concentration.
* Nutrients concentration, associated to the biochemical oxygen demand.
* Conception of the sewage As HS is formed only in anaerobic conditions. Slow flow and long retention time gives more time to aerobic bacteria to consume all available dissolved oxygen in water, creating anaerobic conditions. The flatter the land, the less slope can be given to the sewer network, and this favors slower flow and more pumping stations (where retention time is generally longer) | 8 | Metallurgy |
The discovery of the photoacoustic effect dates back to 1880, when Alexander Graham Bell was experimenting with long-distance sound transmission. Through his invention, called "photophone", he transmitted vocal signals by reflecting sun-light from a moving mirror to a selenium solar cell receiver. As a byproduct of this investigation, he observed that sound waves were produced directly from a solid sample when exposed to beam of sunlight that was rapidly interrupted with a rotating slotted wheel. He noticed that the resulting acoustic signal was dependent on the type of the material and correctly reasoned that the effect was caused by the absorbed light energy, which subsequently heats the sample. Later Bell showed that materials exposed to the non-visible (ultra-violet and infra-red) portions of the solar spectrum can also produce sounds and invented a device, which he called "spectrophone", to apply this effect for spectral identification of materials. Bell himself and later John Tyndall and Wilhelm Röntgen extended these experiments, demonstrating the same effect in liquids and gases. However, the results were too crude, dependent on ear detection, and this technique was soon abandoned. The application of the photoacoustic effect had to wait until the development of sensitive sensors and intense light sources. In 1938 Mark Leonidovitch Veingerov revived the interest in the photoacoustic effect, being able to use it in order to measure very small carbon dioxide concentration in nitrogen gas (as low as 0.2% in volume). Since then research and applications grew faster and wider, acquiring several fold more detection sensitivity.
While the heating effect of the absorbed radiation was considered to be the prime cause of the photoacoustic effect, it was shown in 1978 that gas evolution resulting from a photochemical reaction can also cause a photoacoustic effect. Independently, considering the apparent anomalous behaviour of the photoacoustic signal from a plant leaf, which could not be explained solely by the heating effect of the exciting light, led to the cognition that photosynthetic oxygen evolution is normally a major contributor to the photoacoustic signal in this case. | 7 | Physical Chemistry |
HRM analysis is performed on double stranded DNA samples. Typically the user will use polymerase chain reaction (PCR) prior to HRM analysis to amplify the DNA region in which their mutation of interest lies. In the sample tube there are now many copies of the DNA region of interest. This region that is amplified is known as the amplicon.
After the PCR process the HRM analysis begins. The process is simply a precise warming of the amplicon DNA from around 50 ˚C up to around 95 ˚C. At some point during this process, the melting temperature of the amplicon is reached and the two strands of DNA separate or "melt" apart.
The key to HRM is to monitor this separation of strands in real-time. This is achieved by using a fluorescent dye. The dyes that are used for HRM are known as intercalating dyes and have a unique property. They bind specifically to double-stranded DNA and when they are bound they fluoresce brightly. In the absence of double stranded DNA they have nothing to bind to and they only fluoresce at a low level.
At the beginning of the HRM analysis there is a high level of fluorescence in the sample because of the billions of copies of the amplicon. But as the sample is heated up and the two strands of the DNA melt apart, presence of double stranded DNA decreases and thus fluorescence is reduced. The HRM machine has a camera that watches this process by measuring the fluorescence. The machine then simply plots this data as a graph known as a melt curve, showing the level of fluorescence vs the temperature: | 1 | Biochemistry |
The measurement of heat changes is performed using calorimetry, usually an enclosed chamber within which the change to be examined occurs. The temperature of the chamber is monitored either using a thermometer or thermocouple, and the temperature plotted against time to give a graph from which fundamental quantities can be calculated. Modern calorimeters are frequently supplied with automatic devices to provide a quick read-out of information, one example being the differential scanning calorimeter. | 7 | Physical Chemistry |
The ouzo effect ( ), also known as the louche effect ( ) and spontaneous emulsification, is the phenomenon of formation of a milky oil-in-water emulsion when water is added to ouzo and other anise-flavored liqueurs and spirits, such as pastis, rakı, arak, sambuca and absinthe. Such emulsions occur with only minimal mixing and are highly stable. | 7 | Physical Chemistry |
* Cocaine, for example, blocks the reuptake of dopamine, leaving these neurotransmitters in the synaptic gap for longer.
* AMPT prevents the conversion of tyrosine to L-DOPA, the precursor to dopamine; reserpine prevents dopamine storage within vesicles; and deprenyl inhibits monoamine oxidase (MAO)-B and thus increases dopamine levels. | 1 | Biochemistry |
The most confirmed function of plastid terminal oxidase in developed chloroplasts is its role in chlororespiration. In this process, NADPH dehydrogenase (NDH) reduces the quinone pool and the terminal oxidase oxidizes it, serving the same function as cytochrome c oxidase from mitochondrial electron transport. In Chlamydomonas, there are two copies of the gene for the oxidase. PTOX2 significantly contributes to the flux of electrons through chlororespiration in the dark. There is also evidence from experiments with tobacco that it functions in plant chlororespiration as well.
In fully developed chloroplasts, prolonged exposure to light increases the activity of the oxidase. Because the enzyme acts at the plastoquinone pool in between photosystem II and photosystem I, it may play a role in controlling electron flow through photosynthesis by acting as an alternative electron sink. Similar to its role in carotenoid synthesis, its oxidase activity may prevent the over-reduction of photosystem I electron acceptors and damage by photoinhibition. A recent analysis of electron flux through the photosynthetic pathway shows that even when activated, the electron flux plastid terminal oxidase diverts is two orders of magnitude less than the total flux through photosynthetic electron transport. This suggests that the protein may play less of a role than previously thought in relieving the oxidative stress in photosynthesis. | 5 | Photochemistry |
In materials science parlance, dislocations are defined as line defects in a material's crystal structure. The bonds surrounding the dislocation are already elastically strained by the defect compared to the bonds between the constituents of the regular crystal lattice. Therefore, these bonds break at relatively lower stresses, leading to plastic deformation.
The strained bonds around a dislocation are characterized by lattice strain fields. For example, there are compressively strained bonds directly next to an edge dislocation and tensilely strained bonds beyond the end of an edge dislocation. These form compressive strain fields and tensile strain fields, respectively. Strain fields are analogous to electric fields in certain ways. Specifically, the strain fields of dislocations obey similar laws of attraction and repulsion; in order to reduce overall strain, compressive strains are attracted to tensile strains, and vice versa.
The visible (macroscopic) results of plastic deformation are the result of microscopic dislocation motion. For example, the stretching of a steel rod in a tensile tester is accommodated through dislocation motion on the atomic scale. | 8 | Metallurgy |
Salting in refers to the effect where increasing the ionic strength of a solution increases the solubility of a solute, such as a protein. This effect tends to be observed at lower ionic strengths.
Protein solubility is a complex function of physicochemical nature of the protein, pH, temperature, and the concentration of the salt used. It also depends on whether the salt is kosmotropic, whereby the salt will stabilize water. The solubility of proteins usually increases slightly in the presence of salt, referred to as "salting in". However, at high concentrations of salt, the solubility of the proteins drop sharply and proteins can precipitate out, referred to as "salting out". | 3 | Analytical Chemistry |
The Sommelet reaction is an organic reaction in which a benzyl halide is converted to an aldehyde by action of hexamine and water. It is named after the French chemist Marcel Sommelet, who first reported the reaction in 1913.
One example, thiophene-2-carboxaldehyde is prepared by the reaction of hexamine with 2-chloromethylthiophene. The reaction is formally an oxidation of the carbon. | 0 | Organic Chemistry |
A faster method of log P determination makes use of high-performance liquid chromatography. The log P of a solute can be determined by correlating its retention time with similar compounds with known log P values.
An advantage of this method is that it is fast (5–20 minutes per sample). However, since the value of log P is determined by linear regression, several compounds with similar structures must have known log P values, and extrapolation from one chemical class to another—applying a regression equation derived from one chemical class to a second one—may not be reliable, since each chemical classes will have its characteristic regression parameters. | 7 | Physical Chemistry |
A total synthesis of enantiopure phorbol was developed in 2015. While this synthesis will not replace natural isolation products, it will enable researchers to create phorbol analogs for use in research, especially creating phorbol derivatives that can be evaluated for anti-cancer activity. Previously, the difficulty with synthesizing phorbol had been creating C–C bonds, especially in the six-membered ring at the top of the molecule. This synthesis starts from (+)-3-carene, and uses a series of 19 steps to eventually create (+)-phorbol. | 0 | Organic Chemistry |
The sample of a material (analyte) is brought into the flame as a gas, sprayed solution, or directly inserted into the flame by use of a small loop of wire, usually platinum. The heat from the flame evaporates the solvent and breaks intramolecular bonds to create free atoms. The thermal energy also excites the atoms into excited electronic states that subsequently emit light when they return to the ground electronic state. Each element emits light at a characteristic wavelength, which is dispersed by a grating or prism and detected in the spectrometer.
A frequent application of the emission measurement with the flame is the regulation of alkali metals for pharmaceutical analytics. | 3 | Analytical Chemistry |
RNA can also be transfected into cells to transiently express its coded protein, or to study RNA decay kinetics. RNA transfection is often used in primary cells that do not divide.
siRNAs can also be transfected to achieve RNA silencing (i.e. loss of RNA and protein from the targeted gene). This has become a major application in research to achieve "knock-down" of proteins of interests (e.g. Endothelin-1) with potential applications in gene therapy. Limitation of the silencing approach are the toxicity of the transfection for cells and potential "off-target" effects on the expression of other genes/proteins.
RNA can be purified from cells after lysis or synthesized from free nucleotides either chemically, or enzymatically using an RNA polymerase to transcribe a DNA template. As with DNA, RNA can be delivered to cells by a variety of means including microinjection, electroporation, and lipid-mediated transfection. If the RNA encodes a protein, transfected cells may translate the RNA into the encoded protein. If the RNA is a regulatory RNA (such as a miRNA), the RNA may cause other changes in the cell (such as RNAi-mediated knockdown).
Encapsulating the RNA molecule in lipid nanoparticles was a breakthrough for producing viable RNA vaccines, solving a number of key technical barriers in delivering the RNA molecule into the human cell.
RNA molecules shorter than about 25nt (nucleotides) largely evade detection by the innate immune system, which is triggered by longer RNA molecules. Most cells of the body express proteins of the innate immune system, and upon exposure to exogenous long RNA molecules, these proteins initiate signaling cascades that result in inflammation. This inflammation hypersensitizes the exposed cell and nearby cells to subsequent exposure. As a result, while a cell can be repeatedly transfected with short RNA with few non-specific effects, repeatedly transfecting cells with even a small amount of long RNA can cause cell death unless measures are taken to suppress or evade the innate immune system (see "Long-RNA transfection" below).
Short-RNA transfection is routinely used in biological research to knock down the expression of a protein of interest (using siRNA) or to express or block the activity of a miRNA (using short RNA that acts independently of the cells RNAi machinery, and therefore is not referred to as siRNA). While DNA-based vectors (viruses, plasmids) that encode a short RNA molecule can also be used, short-RNA transfection does not risk modification of the cells DNA, a characteristic that has led to the development of short RNA as a new class of macromolecular drugs.
Long-RNA transfection is the process of deliberately introducing RNA molecules longer than about 25nt into living cells. A distinction is made between short- and long-RNA transfection because exogenous long RNA molecules elicit an innate immune response in cells that can cause a variety of nonspecific effects including translation block, cell-cycle arrest, and apoptosis. | 1 | Biochemistry |
In 2015, the United Nations adopted the 2030 Agenda and a set of 17 Sustainable Development Goals (SDG), including a goal dedicated to the ocean, Sustainable Development Goal 14, which calls to "conserve and sustainably use the oceans, seas and marine resources for sustainable development". Ocean acidification is directly addressed by the target SDG 14.3. The full title of Target 14.3 is: "Minimize and address the impacts of ocean acidification, including through enhanced scientific cooperation at all levels". This target has one indicator: Indicator 14.3.1 which calls for the "Average marine acidity (pH) measured at agreed suite of representative sampling stations".
The Intergovernmental Oceanographic Commission (IOC) of UNESCO was identified as the custodian agency for the SDG 14.3.1 Indicator. In this role, IOC-UNESCO is tasked with developing the SDG 14.3.1 Indicator Methodology, the annual collection of data towards the SDG 14.3.1 Indicator and the reporting of progress to the United Nations. | 9 | Geochemistry |
Solomons ground-breaking work on free radical polymerization was initiated through observations made in industry. For example, anomalies that were not explained by polymerization theory at the time, and the observation that during the production of polymer/mineral composites some batches underwent spontaneous combustion. This led to discoveries that had significant influence on the future directions of radical chemistry. It led to the development of Nitroxide Mediated Polymerization (NMP), the first example of a controlled, or living, radical polymerization technique. This research also produced early examples of what was to become known as RAFT, or Reversible addition−fragmentation chain-transfer polymerization. Solomons work rewrote the theory on free radical polymerization, and he was co-author with Graeme Moad on the definitive reference book: The Chemistry of Radical Polymerization (Moad & Solomon, 2006). Previous theories attempted to explain radical polymerization on the basis of thermodynamic stability controlling structure. Solomon's work showed that kinetics was the major factor in controlling the way polymer chains formed. | 7 | Physical Chemistry |
The Dole effect, named after Malcolm Dole, describes an inequality in the ratio of the heavy isotope O (a "standard" oxygen atom with two additional neutrons) to the lighter O, measured in the atmosphere and seawater. This ratio is usually denoted δO.
It was noticed in 1935 that air contained more O than seawater; this was quantified in 1975 to 23.5‰, but later refined as 23.88‰ in 2005. The imbalance arises mainly as a result of respiration in plants and in animals. Due to thermodynamics of isotope reactions, respiration removes the lighter—hence more reactive—O in preference to O, increasing the relative amount of O in the atmosphere.
The inequality is balanced by photosynthesis. Photosynthesis emits oxygen with the same isotopic composition (i.e. the ratio between O and O) as the water (HO) used in the reaction, which is independent of the atmospheric ratio. Thus when atmospheric O levels are high enough, photosynthesis will act as a reducing factor. However, as a complicating factor, the degree of fractionation (i.e. change in isotope ratio) occurring due to photosynthesis is not entirely dependent on the water drawn up by the plant, as fractionation can occur as a result of preferential evaporation of and other small but significant processes. | 5 | Photochemistry |
Benzenediazonium chloride heated with cuprous chloride or cuprous bromide respectively dissolved in HCl or HBr yield chlorobenzene or bromobenzene, respectively. | 0 | Organic Chemistry |
In organic chemistry, crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups (). The most common crown ethers are cyclic oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., . Important members of this series are the tetramer (n = 4), the pentamer (n = 5), and the hexamer (n = 6). The term "crown" refers to the resemblance between the structure of a crown ether bound to a cation, and a crown sitting on a persons head. The first number in a crown ethers name refers to the number of atoms in the cycle, and the second number refers to the number of those atoms that are oxygen. Crown ethers are much broader than the oligomers of ethylene oxide; an important group are derived from catechol.
Crown ethers strongly bind certain cations, forming complexes. The oxygen atoms are well situated to coordinate with a cation located at the interior of the ring, whereas the exterior of the ring is hydrophobic. The resulting cations often form salts that are soluble in nonpolar solvents, and for this reason crown ethers are useful in phase transfer catalysis. The denticity of the polyether influences the affinity of the crown ether for various cations. For example, 18-crown-6 has high affinity for potassium cation, 15-crown-5 for sodium cation, and 12-crown-4 for lithium cation. The high affinity of 18-crown-6 for potassium ions contributes to its toxicity. The smallest crown ether still capable of binding cations is 8-crown-4, with the largest experimentally confirmed crown ether being 81-crown-27. Crown ethers are not the only macrocyclic ligands that have affinity for the potassium cation. Ionophores such as valinomycin also display a marked preference for the potassium cation over other cations.
Crown ethers have been shown to coordinate to Lewis acids through electrostatic, σ-hole (see halogen bond) interactions, between the Lewis basic oxygen atoms of the crown ether and the electrophilic Lewis acid center. | 6 | Supramolecular Chemistry |
NASBA was developed by J Compton in 1991, who defined it as "a primer-dependent technology that can be used for the continuous amplification of nucleic acids in a single mixture at one temperature". Immediately after the invention of NASBA it was used for the rapid diagnosis and quantification of HIV-1 in patient sera. Although RNA can also be amplified by PCR using a reverse transcriptase (in order to synthesize a complementary DNA strand as a template), NASBA's main advantage is that it works under isothermal conditions – usually at a constant temperature of 41 °C or two different temperatures, depending on the primers and enzymes used. Even when two different temperatures are applied, it is still considered isothermal, because it does not cycle back and forth between those temperatures. NASBA can be used in medical diagnostics as an alternative to PCR that is quicker and more sensitive in some circumstances. | 1 | Biochemistry |
Light detectors, such as photographic plates or CCDs, measure only the intensity of the light that hits them. This measurement is incomplete (even when neglecting other degrees of freedom such as polarization and angle of incidence) because a light wave has not only an amplitude (related to the intensity), but also a phase (related to the direction), and polarization which are systematically lost in a measurement. In diffraction or microscopy experiments, the phase part of the wave often contains valuable information on the studied specimen. The phase problem constitutes a fundamental limitation ultimately related to the nature of measurement in quantum mechanics.
In X-ray crystallography, the diffraction data when properly assembled gives the amplitude of the 3D Fourier transform of the molecule's electron density in the unit cell. If the phases are known, the electron density can be simply obtained by Fourier synthesis. This Fourier transform relation also holds for two-dimensional far-field diffraction patterns (also called Fraunhofer diffraction) giving rise to a similar type of phase problem. | 3 | Analytical Chemistry |
Alvircept sudotox is a form of recombinant CD4 derived from Pneumonas aeruginosa exotoxin A, or 'PE40, which has a size of 59,187 daltons and is an anti-viral agent. | 1 | Biochemistry |
Carbon dioxide has unique long-term effects on climate change that are nearly "irreversible" for a thousand years after emissions stop (zero further emissions). The greenhouse gases methane and nitrous oxide do not persist over time in the same way as carbon dioxide. Even if human carbon dioxide emissions were to completely cease, atmospheric temperatures are not expected to decrease significantly in the short term. This is because the air temperature is determined by a balance between heating, due to greenhouse gases, and cooling due to heat transfer to the ocean. If emissions were to stop, CO levels and the heating effect would slowly decrease, but simultaneously the cooling due to heat transfer would diminish (because sea temperatures would get closer to the air temperature), with the result that the air temperature would decrease only slowly. Sea temperatures would continue to rise, causing thermal expansion and some sea level rise. Lowering global temperatures more rapidly would require carbon sequestration or geoengineering.
Various techniques have been proposed for removing excess carbon dioxide from the atmosphere. | 2 | Environmental Chemistry |
Work done on, and work done by, a thermodynamic system need to be distinguished, through consideration of their precise mechanisms. Work done on a thermodynamic system, by devices or systems in the surroundings, is performed by actions such as compression, and includes shaft work, stirring, and rubbing. Such work done by compression is thermodynamic work as here defined. But shaft work, stirring, and rubbing are not thermodynamic work as here defined, in that they do not change the volume of the system against its resisting pressure. Work without change of volume is known as isochoric work, for example when an agency, in the surroundings of the system, drives a frictional action on the surface or in the interior of the system.
In a process of transfer of energy from or to a thermodynamic system, the change of internal energy of the system is defined in theory by the amount of adiabatic work that would have been necessary to reach the final from the initial state, such adiabatic work being measurable only through the externally measurable mechanical or deformation variables of the system, that provide full information about the forces exerted by the surroundings on the system during the process. In the case of some of Joule's measurements, the process was so arranged that some heating that occurred outside the system (in the substance of the paddles) by the frictional process also led to heat transfer from the paddles into the system during the process, so that the quantity of work done by the surrounds on the system could be calculated as shaft work, an external mechanical variable.
The amount of energy transferred as work is measured through quantities defined externally to the system of interest, and thus belonging to its surroundings. In an important sign convention, preferred in chemistry, work that adds to the internal energy of the system is counted as positive. On the other hand, for historical reasons, an oft-encountered sign convention, preferred in physics, is to consider work done by the system on its surroundings as positive. | 7 | Physical Chemistry |
In 1999, Meléndez et al claimed that the structure of glycogen is optimal under a particular metabolic constraint model, where the structure was suggested to be "fractal" in nature. However, research by Besford et al used small angle X-ray scattering experiments accompanied by branching theory models to show that glycogen is a randomly hyperbranched polymer nanoparticle. Glycogen is not fractal in nature. This has been subsequently verified by others who have performed Monte Carlo simulations of glycogen particle growth, and shown that the molecular density reaches a maximum near the centre of the nanoparticle structure, not at the periphery (contradicting a fractal structure that would have greater density at the periphery). | 1 | Biochemistry |
The immune system uses the lethal effects of oxidants by making the production of oxidizing species a central part of its mechanism of killing pathogens; with activated phagocytes producing both reactive oxygen and nitrogen species. These include superoxide , nitric oxide (•NO) and their particularly reactive product, peroxynitrite (ONOO-). Although the use of these highly reactive compounds in the cytotoxic response of phagocytes causes damage to host tissues, the non-specificity of these oxidants is an advantage since they will damage almost every part of their target cell. This prevents a pathogen from escaping this part of immune response by mutation of a single molecular target. | 1 | Biochemistry |
An ideal surface is flat, rigid, perfectly smooth, chemically homogeneous, and has zero contact angle hysteresis. Zero hysteresis implies the advancing and receding contact angles are equal. In other words, only one thermodynamically stable contact angle exists. When a drop of liquid is placed on such a surface, the characteristic contact angle is formed as depicted in Figure 1. Furthermore, on an ideal surface, the drop will return to its original shape if it is disturbed. The following derivations apply only to ideal solid surfaces; they are only valid for the state in which the interfaces are not moving and the phase boundary line exists in equilibrium. | 7 | Physical Chemistry |
Different applications move over their particular map along different paths. An example map with no operating lines is shown as a pictorial reference with the stall/surge line on the left and the steepening speed lines towards choke and overload on the right.
Maps have similar features and general shape because they all apply to machines with spinning vanes which use similar principles for pumping a compressible fluid. Not all machines have stationary vanes (centrifugal compressors may have either vaned or vaneless diffusers). However a compressor operating as part of a gas turbine or turbocharged engine behaves differently to an industrial compressor because its flow and pressure characteristics have to match those of its driving turbine and other engine components, such as power turbine or jet nozzle for a gas turbine, and, for a turbocharger the engine airflow which depends on engine speed and charge pressure. A link between a gas turbine compressor and its engine can be shown with lines of constant engine temperature ratio, ie the effect of fuelling/increased turbine temperature which raises the running line as the temperature ratio increases.
One manifestation of different behaviour appears in the choke region on the right-hand side of a map. It is a no-load condition in a gas turbine, turbocharger or industrial axial compressor but overload in an industrial centrifugal compressor. Hiereth et al. shows a turbocharger compressor full-load, or maximum fuelling, curve runs up close to the surge line. A gas turbine compressor full-load line also runs close to the surge line. The industrial compressor overload is a capacity limit and requires high power levels to pass the high flow rates required. Excess power is available to inadvertently take the compressor beyond the overload limit to a hazardous condition on cold days if it is driven by a gas turbine. | 7 | Physical Chemistry |
McGraw-Hill Dictionary of Scientific & Technical Terms (6. ed.). The McGraw-Hill Companies, Inc. 2003. [http://encyclopedia2.thefreedictionary.com/aquametry] (online May 6, 2011) | 3 | Analytical Chemistry |
Anthraquinone glycosides are found in senna, rhubarb, and Aloe.
The cardiac glycosides are phytochemicals from plants including foxglove and lily of the valley. They include digoxin and digitoxin which act as diuretics. | 1 | Biochemistry |
Color change materials have been used in several very common outlets but also in an increasing number of new ones. Commercial applications include photochromics in ophthalmics, fashion/cosmetics, security, sensors, optical memory and optical switches, thermochromics in paints, inks, plastics and textiles as indicators/sensors and in architecture, ionochromics in copy paper, direct thermal printing and textile sensors, electrochromics in car mirrors, smart windows, flexible devices and solar protection, solvatochromics in biological probes and sensors, gasochromics in windows and gas sensors. | 5 | Photochemistry |
The importance of an antiparallel DNA double helix structure is because of its hydrogen bonding between the complementary nitrogenous base pairs. If the DNA structure were to be parallel, the hydrogen bonding would not be possible, as the base pairs would not be paired in the known way. The four base pairs are: adenine, guanine, cytosine, and thymine, where adenine complements thymine, and guanine complements cytosine. Transcription would be another problem if the DNA structure were to be parallel, making no sense of the information being read from the DNA. This would further lead to the production of incorrect proteins. | 1 | Biochemistry |
Cheonggukjang, doenjang, fermented bean curd, miso, natto, soy sauce, stinky tofu, tempeh, oncom, soybean paste, Beijing mung bean milk, kinama, iru, thua nao | 1 | Biochemistry |
ortho-Substituted aryl aldehyde complexes undergo diastereoselective nucleophilic addition with organometallic reagents and other nucleophiles. Equation (8) is an example of a diastereoselective Morita-Baylis-Hillman reaction.
Pinacol coupling and the corresponding diamine coupling are possible in the presence of a one-electron reducing agent such as samarium(II) iodide.
Benzylic cations of chromium arene complexes are conformationally stable, and undergo only exo attack to afford S1 products stereospecifically, with retention of configuration. Propargyl and oxonium cations undergo retentive substitution reactions, and even β carbocations react with a significant degree of retention.
Benzylic anions of chromium arene complexes exhibit similar reactivity to cations. They are also conformationally restricted and undergo substitution reactions with retention of stereochemistry at the benzylic carbon. In the example below, complexation of the pyridine nitrogen to lithium is essential for high stereoselectivity.
Nucleophilic addition to styrenes followed by quenching with an electrophile leads to cis products with essentially complete stereoselectivity.
Diastereoselective reduction of styrenes is possible with samarium(II) iodide. A distant alkene is untouched during this reaction, which provides the reduced alkylarene product in high yield.
Complexation of a haloarene to chromium increases its propensity to undergo oxidative addition. Suzuki cross coupling of a planar chiral chromium haloarene complex with an aryl boronic acid is thus a viable method for the synthesis of axially chiral biaryls. In the example below, the syn isomer is formed in preference to the anti isomer; when R is the formyl group, the selectivity reverses.
Tetralones complexed to chromium may be deprotonated without side reactions. Alkylation of the resulting enolate proceeds with complete diastereoselectivity to afford the exo product. | 0 | Organic Chemistry |
The reaction of an organic substrate with phosgene is called phosgenation. Phosgenation of diols give carbonates (R = H, alkyl, aryl), which can be either linear or cyclic:
An example is the reaction of phosgene with bisphenol A to form polycarbonates. Phosgenation of diamines gives di-isocyanates, like toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). In these conversions, phosgene is used in excess to increase yield and minimize side reactions. The phosgene excess is separated during the work-up of resulting end products and recycled into the process, with any remaining phosgene decomposed in water using activated carbon as the catalyst. Diisocyanates are precursors to polyurethanes. More than 90% of the phosgene is used in these processes, with the biggest production units located in the United States (Texas and Louisiana), Germany, Shanghai, Japan, and South Korea. The most important producers are Dow Chemical, Covestro, and BASF. Phosgene is also used to produce monoisocyanates, used as pesticide precursors (e.g. methyl isocyanate (MIC).
Aside from the widely used reactions described above, phosgene is also used to produce acyl chlorides from carboxylic acids:
For this application, thionyl chloride is commonly used instead of phosgene. | 0 | Organic Chemistry |
Ketones give positive results in Bradys test, the reaction with 2,4-dinitrophenylhydrazine to give the corresponding hydrazone. Ketones may be distinguished from aldehydes by giving a negative result with Tollens reagent or with Fehlings solution. Methyl ketones give positive results for the iodoform test. Ketones also give positive results when treated with m'-dinitrobenzene in presence of dilute sodium hydroxide to give violet coloration. | 0 | Organic Chemistry |
The journal includes:
* reviews
* full papers
* communications
* working methods papers
* crystallographic reports
It also includes occasional reports on:
* relevant conferences of applied work in the field of organometallics
* including bioorganometallic chemistry
* metal/organic ligand coordination chemistry. | 0 | Organic Chemistry |
Leonard P. Guarente is recognized as the leading proponent of the hypothesis that caloric restriction slows aging by activation of Sirtuins.
STACs have been discovered by Konrad Howitz of Biomol Inc and biologist David Sinclair. In September 2003, Howitz and Sinclair et al. published a highly cited paper reporting that polyphenols such as resveratrol activate human SIRT1 and extend the lifespan of budding yeast (Howitz et al., Nature, 2003). Other examples of such products are butein, piceatannol, isoliquiritigenin, fisetin, and quercetin.
Sirtuins depend on the crucial cellular molecule called nicotinamide adenine dinucleotide (NAD+) for their function. Falling NAD+ levels during aging may adversely impact sirtuin maintenance of DNA integrity and ability to combat oxidative stress-induced cell damage. Increasing cellular NAD+ levels with supplements like nicotinamide mononucleotide (NMN) during aging may slow or reverse certain aging processes with sirtuin function enhancement.
Some STACs can cause artificial effects in the assay initially used for their identification, but it has been shown that STACs also activate SIRT1 against regular polypeptide substrates, with an influence of the substrate sequence.
Sirtris Pharmaceuticals, Sinclair's company, was purchased by GlaxoSmithKline (GSK) in 2008, and subsequently shut down as a separate entity within GSK. | 1 | Biochemistry |
Karl Söllner (9 January 1903 – 14 June 1986) was an Austrian-American chemist, primarily active in the field of physical chemistry and biophysics. | 7 | Physical Chemistry |
The history of spectroscopy began with Isaac Newton's optics experiments (1666–1672). According to Andrew Fraknoi and David Morrison, "In 1672, in the first paper that he submitted to the Royal Society, Isaac Newton described an experiment in which he permitted sunlight to pass through a small hole and then through a prism. Newton found that sunlight, which looks white to us, is actually made up of a mixture of all the colors of the rainbow." Newton applied the word "spectrum" to describe the rainbow of colors that combine to form white light and that are revealed when the white light is passed through a prism.
Fraknoi and Morrison state that "In 1802, William Hyde Wollaston built an improved spectrometer that included a lens to focus the Sun's spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the spectrum." During the early 1800s, Joseph von Fraunhofer made experimental advances with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics, and astronomy. Per Fraknoi and Morrison, "Later, in 1815, German physicist Joseph Fraunhofer also examined the solar spectrum, and found about 600 such dark lines (missing colors), are now known as Fraunhofer lines, or Absorption lines."
In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy of a photon is related to its frequency by where is Planck's constant, and so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can also excite resonant interactions.
Spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first successfully explained by the Rutherford–Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be a single transition if the density of energy states is high enough. Named series of lines include the principal, sharp, diffuse and fundamental series. | 7 | Physical Chemistry |
Organelle biogenesis is the biogenesis, or creation, of cellular organelles in cells. Organelle biogenesis includes the process by which cellular organelles are split between daughter cells during mitosis; this process is called organelle inheritance. | 1 | Biochemistry |
Flutamide has been used in case reports to decrease the frequency of spontaneous orgasms, for instance in men with post-orgasmic illness syndrome. | 4 | Stereochemistry |
In the Mohr method, named after Karl Friedrich Mohr, potassium chromate is an indicator, giving red silver chromate after all chloride ions have reacted:
: 2Ag (aq) + CrO (aq) → AgCrO (s) (K = 1.1 × 10)
The solution needs to be near neutral, because silver hydroxide forms at high pH, while the chromate forms AgCrO or AgHCrO4 at low pH, reducing the concentration of chromate ions, and delaying the formation of the precipitate. Carbonates and phosphates precipitate with silver, and need to be absent to prevent inaccurate results.
The Mohr method may be adapted to determine the total chlorine content of a sample by igniting the sample with calcium, then ferric acetate. Calcium acetate "fixes" free chlorine, precipitates carbonates, and neutralizes the resultant solution. Ferric acetate removes phosphates. All chlorides are dissolved out of the residue, and titrated. | 3 | Analytical Chemistry |
Hydrostatic CCC or centrifugal partition chromatography (CPC) was invented in the 1980s by the Japanese company Sanki Engineering Ltd, whose president was Kanichi Nunogaki. CPC has been extensively developed in France starting from the late 1990s. In France, they initially optimized the stacked disc concept initiated by Sanki. More recently, in France and UK, non-stacked disc CPC configurations have been developed with PTFE, stainless steel or titanium rotors. These have been designed to overcome possible leakages between the stacked discs of the original concept, and to allow steam cleaning for good manufacturing practice. The volumes ranging from a 100 ml to 12 liters are available in different rotor materials. The 25-liter rotor CPC has a titanium rotor. This technique is sometimes sold under the name "fast" CPC or "high-performance" CPC. | 3 | Analytical Chemistry |
UVGI can be used to disinfect air with prolonged exposure. In the 1930s and 40s, an experiment in public schools in Philadelphia showed that upper-room ultraviolet fixtures could significantly reduce the transmission of measles among students. In 2020, UVGI is again being researched as a possible countermeasure against COVID-19.
UV and violet light are able to neutralize the infectivity of SARS-CoV-2. Viral titers usually found in the sputum of COVID-19 patients are completely inactivated by levels of UV-A and UV-B irradiation that are similar to those levels experienced from natural sun exposure. This finding suggests that the reduced incidence of SARS-COV-2 in the summer may be, in part, due to the neutralizing activity of solar UV irradiation.
Various UV-emitting devices can be used for SARS-CoV-2 disinfection, and these devices may help in reducing the spread of infection. SARS-CoV-2 can be inactivated by a wide range of UVC wavelengths, and the wavelength of 222 nm provides the most effective disinfection performance.
Disinfection is a function of UV intensity and time. For this reason, it is in theory not as effective on moving air, or when the lamp is perpendicular to the flow, as exposure times are dramatically reduced. However, numerous professional and scientific publications have indicated that the overall effectiveness of UVGI actually increases when used in conjunction with fans and HVAC ventilation, which facilitate whole-room circulation that exposes more air to the UV source. Air purification UVGI systems can be free-standing units with shielded UV lamps that use a fan to force air past the UV light. Other systems are installed in forced air systems so that the circulation for the premises moves microorganisms past the lamps. Key to this form of sterilization is placement of the UV lamps and a good filtration system to remove the dead microorganisms. For example, forced air systems by design impede line-of-sight, thus creating areas of the environment that will be shaded from the UV light. However, a UV lamp placed at the coils and drain pans of cooling systems will keep microorganisms from forming in these naturally damp places. | 5 | Photochemistry |
Small molecule sensors are an effective way to detect the presence of metal ions in solution. Although many types exist, most small molecule sensors comprise a subunit that selectively binds to a metal that in turn induces a change in a fluorescent subunit. This change can be observed in the small molecule sensor's spectrum, which can be monitored using a detection system such as a microscope or a photodiode. Different probes exist for a variety of applications, each with different dissociation constants with respect to a particular metal, different fluorescent properties, and sensitivities. They show great promise as a way to probe biological processes by monitoring metal ions at low concentrations in biological systems. Since they are by definition small and often capable of entering biological systems, they are conducive to many applications for which other more traditional bio-sensing are less effective or not suitable. | 5 | Photochemistry |
Hydrazones are oxidized (dehydrogenation) for example with silver oxide or mercury oxide for example the synthesis of from acetone hydrazone. Other oxidizing reagents are lead tetraacetate, manganese dioxide and the Swern reagent. Tosyl hydrazones RRC=N-NHTs are reacted with base for example triethylamine in the synthesis of crotyl diazoacetate and in the synthesis of phenyldiazomethane from PhCHNHTs and sodium methoxide.
Reaction of a carbonyl group with the hydrazine 1,2-bis(tert-butyldimethylsilyl)hydrazine to form the hydrazone is followed by reaction with the iodane difluoroiodobenzene yields the diazo compound: | 0 | Organic Chemistry |
The mechanisms of carcinogenesis are not completely clear in humans. NMOR and its metabolites may induce DNA damage by directly forming reactive oxygen species or compounds which crosslink DNA. In a rat model in 2013, it was observed that NMOR is hydroxylated, probably by a P450 enzyme, alpha to the N-nitroso moiety. This then decomposes into a diazonium-containing aldehyde which is capable of crosslinking DNA.
Endogenous synthesis from morpholine in the digestive system is observed. NMOR can be generated from N-nitrosating species formed by salivary nitrite and stomach acid, potentially leading to more damage in individuals with acid reflux. H. pylori does not induce NMOR formation in vitro, though this has yet to be confirmed in vivo.
NMOR is in fact used to generate liver cancer models in rats. Along with N-diethylnitrosamine, it is the gold standard for producing hepatocarcinoma with 100% lung metastasis. | 0 | Organic Chemistry |
Since the industrial revolution, and especially since the end of WWII, human activity has substantially disturbed the global carbon cycle by redistributing massive amounts of carbon from the geosphere. Humans have also continued to shift the natural component functions of the terrestrial biosphere with changes to vegetation and other land use. Man-made (synthetic) carbon compounds have been designed and mass-manufactured that will persist for decades to millennia in air, water, and sediments as pollutants. Climate change is amplifying and forcing further indirect human changes to the carbon cycle as a consequence of various positive and negative feedbacks. | 5 | Photochemistry |
"Ternatin" is a term used for two unrelated categories of biochemical compounds:
* The ternatin heptapeptide derived from the mushroom Coriolus versicolor
* Delphinidin ternatins derivatives of delphinidin, an anthocyanidin | 1 | Biochemistry |
Plastid terminal oxidase is an integral membrane protein, or more specifically, an integral monotopic protein and is bound to the thylakoid membrane facing the stroma. Based on sequence homology, the enzyme is predicted to contain four alpha helix domains that encapsulate a di-iron center. The two iron atoms are ligated by six essential conserved histidine and glutamate residues – Glu136, Glu175, His171, Glu227, Glu296, and His299. The predicted structure is similar to that of the alternative oxidase, with an additional Exon 8 domain that is required for the plastid oxidase's activity and stability. The enzyme is anchored to the membrane by a short fifth alpha helix that contains a Tyr212 residue hypothesized to be involved in substrate binding. | 5 | Photochemistry |
Morpholinos have become a standard knockdown tool in animal embryonic systems, which have a broader range of gene expression than adult cells and can be strongly affected by an off-target interaction. Following initial injections into frog or fish embryos at the single-cell or few-cell stages, Morpholino effects can be measured up to five days later, after most of the processes of organogenesis and differentiation are past, with observed phenotypes consistent with target-gene knockdown. Control oligos with irrelevant sequences usually produce no change in embryonic phenotype, evidence of the Morpholino oligo's sequence-specificity and lack of non-antisense effects. The dose required for a knockdown can be reduced by coinjection of several Morpholino oligos targeting the same mRNA, which is an effective strategy for reducing or eliminating dose-dependent off-target RNA interactions.
mRNA rescue experiments can sometimes restore the wild-type phenotype to the embryos and provide evidence for the specificity of a Morpholino. In an mRNA rescue, a Morpholino is co-injected with an mRNA that codes for the morphlinos protein. However, the rescue mRNA has a modified 5-UTR (untranslated region) so that the rescue mRNA contains no target for the Morpholino. The rescue mRNAs coding region encodes the protein of interest. Translation of the rescue mRNA replaces production of the protein that was knocked down by the Morpholino. Since the rescue mRNA would not affect phenotypic changes due to the Morpholinos off-target gene expression modulation, this return to wild-type phenotype is further evidence of Morpholino specificity. In some cases, ectopic expression of the rescue RNA makes recovery of the wild-type phenotype impossible.
In embryos, Morpholinos can be tested in null mutants to check for unexpected RNA interactions, then used in a wild-type embryo to reveal the acute knockdown phenotype. The knockdown phenotype is often more extreme than the mutant phenotype; in the mutant, effects of losing the null gene can be concealed by genetic compensation.
Because of their completely unnatural backbones, Morpholinos are not recognized by cellular proteins. Nucleases do not degrade Morpholinos, nor are they degraded in serum or in cells.
Up to 18% of Morpholinos appear to induce nontarget-related phenotypes including cell death in the central nervous system and somite tissues of zebrafish embryos. Most of these effects are due to activation of p53-mediated apoptosis and can be suppressed by co-injection of an anti-p53 Morpholino along with the experimental Morpholino. Moreover, the p53-mediated apoptotic effect of a Morpholino knockdown has been phenocopied using another antisense structural type, showing the p53-mediated apoptosis to be a consequence of the loss of the targeted protein and not a consequence of the knockdown oligo type. It appears that these effects are sequence-specific; as in most cases, if a Morpholino is associated with non-target effects, the 4-base mismatch Morpholino will not trigger these effects.
A cause for concern in the use of Morpholinos is the potential for "off-target" effects. Whether an observed morphant phenotype is due to the intended knockdown or an interaction with an off-target RNA can often be addressed in embryos by running another experiment to confirm that the observed morphant phenotype results from the knockdown of the expected target. This can be done by recapitulating the morphant phenotype with a second, non-overlapping Morpholino targeting the same mRNA, by confirmation of the observed phenotypes by comparing with a mutant strain (though compensation will obscure a phenotype in some mutants), by testing the Morpholino in a null mutant background to detect additional phenotypic changes or by dominant-negative methods. As mentioned above, rescue of observed phenotypes by coinjecting a rescue mRNA is, when feasible, a reliable test of specificity of a Morpholino. | 1 | Biochemistry |
1,3-Bisphosphoglycerate is the conjugate base of 1,3-bisphosphoglyceric acid. It is phosphorylated at the number 1 and 3 carbons. The result of this phosphorylation gives 1,3BPG important biological properties such as the ability to phosphorylate ADP to form the energy storage molecule ATP. | 5 | Photochemistry |
Haloalkanes are diverse in their properties, making generalizations difficult. Few are acutely toxic, but many pose risks from prolonged exposure. Some problematic aspects include carcinogenicity and liver damage (e.g., carbon tetrachloride). Under certain combustion conditions, chloromethanes convert to phosgene, which is highly toxic. | 2 | Environmental Chemistry |
In mammals there are several structures that have been implicated as oxygen sensing structures; however, all of these structures are situated to detect aortic or internal hypoxia since mammals rarely run into environmental hypoxia. These structures include the type I cells of the carotid body, the neuroepithelial bodies of the lungs as well as some central and peripheral neurons and vascular smooth muscle cells.
In fish, the neuroepithelial cells (NEC) have been implicated as the major oxygen sensing cells. NEC have been found in all teleost fish studied to date, and are likely a highly conserved structure within many taxa of fish. NEC are also found in all four gill arches within several different structures, such as along the filaments, at the ends of the gill rakers and throughout the lamellae. Two separate neural pathways have been identified within the zebrafish gill arches both the motor and sensory nerve fibre pathways. Since neuroepithelial cells are distributed throughout the gills, they are often ideally situated to detect both arterial as well as environmental oxygen. | 9 | Geochemistry |
* 2023: Yoshida Prize, International Organic Chemistry Foundation
* 2022: Sang-Chul Shim Academic Award, Korean Chemical Society
* 2007: NUS Young Investigator Award
* 2005: Career Award, National Science Foundation | 0 | Organic Chemistry |
Alkalimetry and acidimetry are types of volumetric analyses in which the fundamental reaction is a neutralization reaction. They involve the controlled addition of either an acid or a base (titrant) of known concentration to the solution of the unknown concentration (titrate) until the reaction reaches its stoichiometric equivalence point. At this point, the moles of acid and base are equal, resulting in a neutral solution:
:acid + base → salt + water
For example:
:HCl + NaOH → NaCl + HO
Acidimetry is the specialized analytical use of acid-base titration to determine the concentration of a basic (alkaline) substance using standard acid. This can be used for weak bases and strong bases. An example of an acidimetric titration involving a strong base is as follows:
:Ba(OH) + 2 H → Ba + 2 HO
In this case, the strong base (Ba(OH)) is neutralized by the acid until all of the base has reacted. This allows the viewer to calculate the concentration of the base from the volume of the standard acid that is used.
Alkalimetry follows uses same concept of specialized analytic acid-base titration, but to determine the concentration of an acidic substance using standard base. An example of an alkalimetric titration involving a strong acid is as follows:
:HSO + 2 OH → SO + 2 HO
In this case, the strong acid (HSO) is neutralized by the base until all of the acid has reacted. This allows the viewer to calculate the concentration of the acid from the volume of the standard base that is used.
The standard solution (titrant) is stored in the burette, while the solution of unknown concentration (analyte/titrate) is placed in the Erlenmeyer flask below it with an indicator. | 3 | Analytical Chemistry |
In specific acid catalysis, protonated solvent is the catalyst. The reaction rate is proportional to the concentration of the protonated solvent molecules SH. The acid catalyst itself (AH) only contributes to the rate acceleration by shifting the chemical equilibrium between solvent S and AH in favor of the SH species. This kind of catalysis is common for strong acids in polar solvents, such as water.
For example, in an aqueous buffer solution the reaction rate for reactants R depends on the pH of the system but not on the concentrations of different acids.
This type of chemical kinetics is observed when reactant R is in a fast equilibrium with its conjugate acid RH which proceeds to react slowly with R to the reaction product; for example, in the acid catalysed aldol reaction. | 7 | Physical Chemistry |
A classic route to carbodiimides involves dehydrosulfurization of thioureas. A typical reagent for this process is mercuric oxide:
:(R(H)N)CS + HgO → (RN)C + HgS + HO
This reaction can often be conducted as stated, even though carbodiimides react with water. In some cases, a dehydrating agent is added to the reaction mixture.
The dehydration of N,N'-dialkylureas gives carbodiimides:
:(R(H)N)CO → (RN)C + HO
Phosphorus pentoxide and p-Toluenesulfonyl chloride have been used as a dehydrating agents. | 0 | Organic Chemistry |
A diffuse series of triplet lines is designated by series letter d and formula 1p-md. The diffuse series of singlet lines has series letter S and formula 1P-mS. | 7 | Physical Chemistry |
Persephin has the potential to be used as a therapeutic treatment for neurodegenerative diseases, such as Parkinson's disease and other diseases that affect motor neurons. Because persephin acts more selectively compared to other GFLs, such as GDNF, it may produce fewer mechanism-based complications, making it a stronger therapeutic target. | 1 | Biochemistry |
* Conversion coating
** Autophoretic, the registered trade name of a proprietary series of auto-depositing coatings specifically for ferrous metal substrates
** Anodising
** Chromate conversion coating
** Plasma electrolytic oxidation
** Phosphate (coating)
* Ion beam mixing
* Pickled and oiled, a type of plate steel coating
* Plating
** Electroless plating
** nickel plating coating using a different material to preserve mechanical properties
** Electroplating | 8 | Metallurgy |
Calcium is a necessary ion in the formation of the mitotic spindle. Without the mitotic spindle, cellular division cannot occur. Although young leaves have a higher need for calcium, older leaves contain higher amounts of calcium because calcium is relatively immobile through the plant. It is not transported through the phloem because it can bind with other nutrient ions and precipitate out of liquid solutions. | 1 | Biochemistry |
For transition metals, oxidative reaction results in the decrease in the d to a configuration with fewer electrons, often 2e fewer. Oxidative addition is favored for metals that are (i) basic and/or (ii) easily oxidized. Metals with a relatively low oxidation state often satisfy one of these requirements, but even high oxidation state metals undergo oxidative addition, as illustrated by the oxidation of Pt(II) with chlorine:
:[PtCl] + Cl → [PtCl]
In classical organometallic chemistry, the formal oxidation state of the metal and the electron count of the complex both increase by two. One-electron changes are also possible and in fact some oxidative addition reactions proceed via series of 1e changes. Although oxidative additions can occur with the insertion of a metal into many different substrates, oxidative additions are most commonly seen with H–H, H–X, and C–X bonds because these substrates are most relevant to commercial applications.
Oxidative addition requires that the metal complex have a vacant coordination site. For this reason, oxidative additions are common for four- and five-coordinate complexes.
Reductive elimination is the reverse of oxidative addition. Reductive elimination is favored when the newly formed X–Y bond is strong. For reductive elimination to occur the two groups (X and Y) should be mutually adjacent on the metal's coordination sphere. Reductive elimination is the key product-releasing step of several reactions that form C–H and C–C bonds. | 0 | Organic Chemistry |
In the early 1940s, Bradley reported the observation of sidebands around the Bragg peaks in the X-ray diffraction pattern of a Cu-Ni-Fe alloy that had been quenched and then annealed inside the miscibility gap. Further observations on the same alloy were made by Daniel and Lipson, who demonstrated that the sidebands could be explained by a periodic modulation of composition in the <100> directions. From the spacing of the sidebands, they were able to determine the wavelength of the modulation, which was of the order of 100 angstroms (10 nm).
The growth of a composition modulation in an initially homogeneous alloy implies uphill diffusion or a negative diffusion coefficient. Becker and Dehlinger had already predicted a negative diffusivity inside the spinodal region of a binary system. But their treatments could not account for the growth of a modulation of a particular wavelength, such as was observed in the Cu-Ni-Fe alloy. In fact, any model based on Fick's law yields a physically unacceptable solution when the diffusion coefficient is negative.
The first explanation of the periodicity was given by Mats Hillert in his 1955 Doctoral Dissertation at MIT. Starting with a regular solution model, he derived a flux equation for one-dimensional diffusion on a discrete lattice. This equation differed from the usual one by the inclusion of a term, which allowed for the effect of the interfacial energy on the driving force of adjacent interatomic planes that differed in composition. Hillert solved the flux equation numerically and found that inside the spinodal it yielded a periodic variation of composition with distance. Furthermore, the wavelength of the modulation was of the same order as that observed in the Cu-Ni-Fe alloys.
Building on Hillert's work, a more flexible continuum model was subsequently developed by John W. Cahn and John Hilliard, who included the effects of coherency strains as well as the gradient energy term. The strains are significant in that they dictate the ultimate morphology of the decomposition in anisotropic materials. | 7 | Physical Chemistry |
General health hazards associated with solvent exposure include toxicity to the nervous system, reproductive damage, liver and kidney damage, respiratory impairment, cancer, hearing loss, and dermatitis. | 2 | Environmental Chemistry |
There are no regulations regarding SF6 currently in China, even though some measures for reducing emissions were taken by the government. The emissions of this gas are currently on the rise in China (and in other countries defined as non-Annex-I by the United Nations Framework Convention on Climate Change) "due to their rapid expansion of power demand and fast adoption of renewable energy technologies". In China, they are now close to total greenhouse gas emissions from the Netherlands or Nigeria. | 2 | Environmental Chemistry |
In terms of input and output, ICP-MS instrument consumes prepared sample material and translates it into mass-spectral data. Actual analytical procedure takes some time; after that time the instrument can be switched to work on the next sample. Series of such sample measurements requires the instrument to have plasma ignited, meanwhile a number of technical parameters has to be stable in order for the results obtained to have feasibly accurate and precise interpretation. Maintaining the plasma requires a constant supply of carrier gas (usually, pure argon) and increased power consumption of the instrument. When these additional running costs are not considered justified, plasma and most of auxiliary systems can be turned off. In such standby mode only pumps are working to keep proper vacuum in mass-spectrometer.
The constituents of ICP-MS instrument are designed to allow for reproducible and/or stable operation. | 3 | Analytical Chemistry |
Monosaccharides can be linked together by glycosidic bonds, which can be cleaved by hydrolysis. Two, three, several or many monosaccharides thus linked form disaccharides, trisaccharides, oligosaccharides, or polysaccharides, respectively. Enzymes that hydrolyze glycosidic bonds are called "glycoside hydrolases" or "glycosidases".
The best-known disaccharide is sucrose (table sugar). Hydrolysis of sucrose yields glucose and fructose. Invertase is a sucrase used industrially for the hydrolysis of sucrose to so-called invert sugar. Lactase is essential for digestive hydrolysis of lactose in milk; many adult humans do not produce lactase and cannot digest the lactose in milk.
The hydrolysis of polysaccharides to soluble sugars can be recognized as saccharification. Malt made from barley is used as a source of β-amylase to break down starch into the disaccharide maltose, which can be used by yeast to produce beer. Other amylase enzymes may convert starch to glucose or to oligosaccharides. Cellulose is first hydrolyzed to cellobiose by cellulase and then cellobiose is further hydrolyzed to glucose by beta-glucosidase. Ruminants such as cows are able to hydrolyze cellulose into cellobiose and then glucose because of symbiotic bacteria that produce cellulases. | 7 | Physical Chemistry |
Cytochrome b was synthesized with photo-methionine to map the protein-protein interactions while also identifying its structure to study the mammalian mixed function oxidase system (also known as the MFO). This system is located in the membrane of the endoplasmic reticulum and it is composed of cytochrome P450, NADPH: cytochrome P450 reductase, and cytochrome b along with NADH: cytochrome b reductase. Once the cytochrome b complex had photo-methionine incorporated (meaning photo-met was substituted in place of methionine and now photo-cyt b), photo-cyt b and cytochrome P450 were put under UV-light and the products were able to be studied using SDS-Page; this method had shown three cross-links. The photo-methionine had proven successful in mapping photo-cyt b as the MALDI-TOF method shown three oligomers (from chymotryptic peptides) that were composed of photo-cyt b and cytochrome P450 in molecular weight ratio's of 1:1, 1:2, and 2:1. What makes photo-methionine here so useful in studying cytochrome P450 and cytochrome b is that this method not only mapped protein-protein interfaces not only in regions exposed to solvent, but also in the native environment; the membrane. A typical cross-linking method can only work in solvent exposed regions, proving once again that photo-methionine is useful to map these protein-protein interactions with the protein in their native environment. | 5 | Photochemistry |
*[http://www.google.com/patents?id=l5wdAAAAEBAJ&dq=ininventor:%22heinz+falk%22&as_drrb_ap=q&as_minm_ap=1&as_miny_ap=2008&as_maxm_ap=1&as_maxy_ap=2008&as_drrb_is=q&as_minm_is=1&as_miny_is=2008&as_maxm_is=1&as_maxy_is=2008 Process for the N-alkylation or ureas] US Pat. 5124451 - Filed Jul 10, 1991 - Chemie Linz GmbH
*[http://www.google.com/patents?id=va8fAAAAEBAJ&dq=ininventor:%22heinz+falk%22&as_drrb_ap=q&as_minm_ap=1&as_miny_ap=2008&as_maxm_ap=1&as_maxy_ap=2008&as_drrb_is=q&as_minm_is=1&as_miny_is=2008&as_maxm_is=1&as_maxy_is=2008 Process for the N-alkylation of ureas] US Pat. 5169954 - Filed Dec 16, 1991 - Chemie Linz GmbH
*[http://www.google.com/patents?id=K7ccAAAAEBAJ&dq=ininventor:%22heinz+falk%22&as_drrb_ap=q&as_minm_ap=1&as_miny_ap=2008&as_maxm_ap=1&as_maxy_ap=2008&as_drrb_is=q&as_minm_is=1&as_miny_is=2008&as_maxm_is=1&as_maxy_is=2008 Process for the preparation of pure N,N'-asymmetrically substituted phenylureas] US Pat. 5283362 - Filed Jul 31, 1992 - Chemie Linz GmbH
*[http://www.google.com/patents?id=XU4aAAAAEBAJ&dq=5360601 Process for the preparation of Isocyanic Acid by Decomposition of N,N-trisubstituted Ureas] Eur. Pat. EP 0582863A2 - Filed Feb 16, 1994 - US Pat. Nr. 5360601 Filed Nov 1, 1994 - Chemie Linz GmbH
*Isocyanates by Decomposition of N,N,N-trisubstituted Ureas Eur. Pat. EP 0583637A1 - Filed Feb 23, 1994 - Chemie Linz GmbH
*[http://www.google.com/patents?id=XBUbAAAAEBAJ&dq=ininventor:%22heinz+falk%22&as_drrb_ap=q&as_minm_ap=1&as_miny_ap=2008&as_maxm_ap=1&as_maxy_ap=2008&as_drrb_is=q&as_minm_is=1&as_miny_is=2008&as_maxm_is=1&as_maxy_is=2008 Amine-oxides] US Pat. 5409532 - Filed Jan 21, 1993 - Lenzing AG | 0 | Organic Chemistry |
Dendritic molecules are characterized by structural perfection. Dendrimers and dendrons are monodisperse and usually highly symmetric, spherical compounds. The field of dendritic molecules can be roughly divided into low-molecular weight and high-molecular weight species. The first category includes dendrimers and dendrons, and the latter includes dendronized polymers, hyperbranched polymers, and the polymer brush.
The properties of dendrimers are dominated by the functional groups on the molecular surface, however, there are examples of dendrimers with internal functionality. Dendritic encapsulation of functional molecules allows for the isolation of the active site, a structure that mimics that of active sites in biomaterials. Also, it is possible to make dendrimers water-soluble, unlike most polymers, by functionalizing their outer shell with charged species or other hydrophilic groups. Other controllable properties of dendrimers include toxicity, crystallinity, tecto-dendrimer formation, and chirality.
Dendrimers are also classified by generation, which refers to the number of repeated branching cycles that are performed during its synthesis. For example, if a dendrimer is made by convergent synthesis (see below), and the branching reactions are performed onto the core molecule three times, the resulting dendrimer is considered a third generation dendrimer. Each successive generation results in a dendrimer roughly twice the molecular weight of the previous generation. Higher generation dendrimers also have more exposed functional groups on the surface, which can later be used to customize the dendrimer for a given application. Dendrimers may have a single surface functional group, or may be modified to allow for multiple functional groups on the surface. | 6 | Supramolecular Chemistry |
A major improvement to the product imaging technique was achieved by Eppink and Parker. A difficulty that limits the resolution in the position-sensing version is that the spot on the detector is no smaller than the cross-sectional area of the ions excited. For example, if the volume of interaction of the molecular beam, photolysis laser, and ionization laser is, say 1 mm x 1 mm x 1 mm, then the spot for an ion moving with a single velocity would still span 1mm x 1mm at the detector. This dimension is much larger than the limit of a channel width (10 μm) and is substantial compared to the radius of a typical detector (25 mm). Without some further improvement, the velocity resolution for a position-sensing apparatus would be limited to about one part in twenty-five. Eppink and Parker found a way around this limit. Their version of the product imaging technique is called velocity map imaging.
Velocity map imaging is based on the use of an electrostatic lens to accelerate the ions toward the detector. When the voltages are properly adjusted, this lens has the advantage that it focuses ions with the same velocity to a single spot on the detector regardless where the ion was created. This technique thus overcomes the blurring caused by the finite overlap of the laser and molecular beams.
In addition to ion imaging, velocity map imaging is also used for electron kinetic energy analysis in photoelectron photoion coincidence spectroscopy. | 7 | Physical Chemistry |
Photosynthetic pigments convert light into biochemical energy. Examples for photosynthetic pigments are chlorophyll, carotenoids and phycobilins. These pigments enter a high-energy state upon absorbing a photon which they can release in the form of chemical energy. This can occur via light-driven pumping of ions across a biological membrane (e.g. in the case of the proton pump bacteriorhodopsin) or via excitation and transfer of electrons released by photolysis (e.g. in the photosystems of the thylakoid membranes of plant chloroplasts). In chloroplasts, the light-driven electron transfer chain in turn drives the pumping of protons across the membrane. | 1 | Biochemistry |
Analyst is a biweekly peer-reviewed scientific journal covering all aspects of analytical chemistry, bioanalysis, and detection science. It is published by the Royal Society of Chemistry and the editor-in-chief is Norman Dovichi (University of Notre Dame). The journal was established in 1877 by the Society for Analytical Chemistry. | 3 | Analytical Chemistry |
Index inducer or just inducer predictably induce metabolism via a given pathway and are commonly used in prospective clinical drug-drug interaction studies.
Strong, moderate, and weak inducers are drugs that decreases the AUC of sensitive index substrates of a given metabolic pathway by ≥80%, ≥50% to <80%, and ≥20% to <50%, respectively. | 0 | Organic Chemistry |
It can be shown that there are four types of Euclidean plane isometries. (Note: the notations for the types of isometries listed below are not completely standardised.) | 3 | Analytical Chemistry |
Zintl compounds feature naked anionic clusters that are generated by reduction of heavy main group p elements, mostly metals or semimetals, with alkali metals, often as a solution in anhydrous liquid ammonia or ethylenediamine. Examples of Zintl anions are [Bi], [Sn], [Pb], and [Sb]. Although these species are called "naked clusters," they are usually strongly associated with alkali metal cations. Some examples have been isolated using cryptate complexes of the alkali metal cation, e.g., [Pb] anion, which features a capped square antiprismatic shape. According to Wade's rules (2n+2) the number of cluster electrons is 22 and therefore a closo cluster. The compound is prepared from oxidation of KPb by Au in PPhAuCl (by reaction of tetrachloroauric acid and triphenylphosphine) in ethylene diamine with 2.2.2-crypt. This type of cluster was already known as is the endohedral Ni@Pb (the cage contains one nickel atom). The icosahedral tin cluster Sn or stannaspherene anion is another closed shell structure observed (but not isolated) with photoelectron spectroscopy. With an internal diameter of 6.1 Ångstrom, it is of comparable size to fullerene and should be capable of containing small atoms in the same manner as endohedral fullerenes, and indeed exists a Sn cluster that contains an Ir atom: [Ir@Sn]. | 7 | Physical Chemistry |
Polyunsaturated aldehydes (PUAs) are a group of allelopathic chemicals typically associated with diatom-copepod predator-prey interactions. These compounds are classified by an aldehyde group covalently bound to long carbon chains containing two or more carbon-carbon double bonds. Examples include isomers of heptadienal, octadienal, octatrienal, and decatrienal. | 1 | Biochemistry |
The physical principles of ion traps were first explored by F. M. Penning (1894–1953), who observed that electrons released by the cathode of an ionization vacuum gauge follow a long cycloidal path to the anode in the presence of a sufficiently strong magnetic field.
A scheme for confining charged particles in three dimensions without the use of magnetic fields was developed by W. Paul based on his work with quadrupole mass spectrometers.
Ion traps were used in television receivers prior to the introduction of aluminized CRT faces around 1958, to protect the phosphor screen from ions. The ion trap must be delicately adjusted for maximum brightness. | 7 | Physical Chemistry |
As the reaction proceeds with the passage of time, the species' activities, and hence the reaction quotient, change in a way that reduces the free energy of the chemical system. The direction of the change is governed by the Gibbs free energy of reaction by the relation
where K is a constant independent of initial composition, known as the equilibrium constant. The reaction proceeds in the forward direction (towards larger values of Q) when ΔG ) when ΔG > 0. Eventually, as the reaction mixture reaches chemical equilibrium, the activities of the components (and thus the reaction quotient) approach constant values. The equilibrium constant is defined to be the asymptotic value approached by the reaction quotient:
: and .
The timescale of this process depends on the rate constants of the forward and reverse reactions. In principle, equilibrium is approached asymptotically at t → ∞; in practice, equilibrium is considered to be reached, in a practical sense, when concentrations of the equilibrating species no longer change perceptibly with respect to the analytical instruments and methods used.
If a reaction mixture is initialized with all components having an activity of unity, that is, in their standard states, then
: and .
This quantity, ΔG°, is called the standard Gibbs free energy of reaction.
All reactions, regardless of how favorable, are equilibrium processes, though practically speaking, if no starting material is detected after a certain point by a particular analytical technique in question, the reaction is said to go to completion. | 7 | Physical Chemistry |
Hexamethylenetetramine was first introduced into the medical setting in 1895 as a urinary antiseptic. It was officially approved by the FDA for medical use in the United States in 1967. However, it was only used in cases of acidic urine, whereas boric acid was used to treat urinary tract infections with alkaline urine. Scientist De Eds found that there was a direct correlation between the acidity of hexamethylenetetramine's environment and the rate of its decomposition. Therefore, its effectiveness as a drug depended greatly on the acidity of the urine rather than the amount of the drug administered. In an alkaline environment, hexamethylenetetramine was found to be almost completely inactive.
Hexamethylenetetramine was also used as a method of treatment for soldiers exposed to phosgene in World War I. Subsequent studies have shown that large doses of hexamethylenetetramine provide some protection if taken before phosgene exposure but none if taken afterwards. | 0 | Organic Chemistry |
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