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Ultraviolet-visible (UV-Vis) absorption spectroelectrochemistry (SEC) is a multiresponse technique that analyzes the evolution of the absorption spectra in UV-Vis regions during an electrode process. This technique provides information from an electrochemical and spectroscopic point of view. In this way, it enables a better perception about the chemical system of interest. On one hand, molecular information related to the electronic levels of the molecules is obtained from the evolution of the spectra. On the other hand, kinetic and thermodynamic information of the processes is obtained from the electrochemical signal.
UV-Vis absorption SEC allows qualitative analysis, through the characterization of the different present compounds, and quantitative analysis, by determining the concentration of the analytes of interest. Furthermore, it helps to determine different electrochemical parameters such as absorptivity coefficients, standard potentials, diffusion coefficients, electronic transfer rate constants, etc. Throughout history, reversible processes have been studied with colored reagents or electrolysis products. Nowadays, it is possible to study all kinds of electrochemical processes in the entire UV-Vis spectral range, even in the near infrared (NIR). | 7 | Physical Chemistry |
In September 2011, three NASA investigators claimed that they identified tin whiskers on the accelerator position sensors of sampled Toyota Camry models that could contribute to the "stuck accelerator" crashes affecting certain Toyota models during 2005–2010. This contradicted an earlier 10-month joint investigation by the National Highway Traffic Safety Administration (NHTSA) and a large group of other NASA researchers that found no electronic defects.
In 2012, NHTSA maintained: "We do not believe that tin whiskers are a plausible explanation for these incidents...[the likely cause was] pedal misapplication."
Toyota also maintains that tin whiskers were not the cause of any stuck accelerator issues: "In the words of U.S. Transportation Secretary Ray LaHood, 'The verdict is in. There is no electronic-based cause for unintended high-speed acceleration in Toyotas. Period. According to a Toyota press release, "no data indicates that tin whiskers are more prone to occur in Toyota vehicles than any other vehicle in the marketplace." Toyota also states that "their systems are designed to reduce the risk that tin whiskers will form in the first place." | 8 | Metallurgy |
In proteomics, the study of the full set of proteins expressed by a genome, identifying diseases biomarkers can involve the usage of stable isotope labeling by amino acids in cell culture (SILAC), that provides isotopic labeled forms of amino acid used to estimate protein levels. In protein recombinant, manipulated proteins are produced in large quantities and isotope labeling is a tool to test for relevant proteins. The method used to be about selectively enrich nuclei with C or N or deplete H from them. The recombinant would be expressed in E.coli with media containing N-ammonium chloride as a source of nitrogen. The resulting N labeled proteins are then purified by immobilized metal affinity and their percentage estimated. In order to increase the yield of labeled proteins and cut down the cost of isotope labeled media, an alternative procedure primarily increases the cell mass using unlabeled media before introducing it in a minimal amount of labeled media. Another application of isotope labeling would be in measuring DNA synthesis, that is cell proliferation in vitro. Uses H-thymidine labeling to compare pattern of synthesis (or sequence) in cells. | 7 | Physical Chemistry |
In physical organic chemistry, the Grunwald–Winstein equation is a linear free energy relationship between relative rate constants and the ionizing power of various solvent systems, describing the effect of solvent as nucleophile on different substrates. The equation, which was developed by Ernest Grunwald and Saul Winstein in 1948, could be written
where the and are the solvolysis rate constants for a certain compound in different solvent systems and in the reference solvent, 80% aqueous ethanol, respectively. The parameter is a parameter measuring the sensitivity of the solvolysis rate with respect to , the measure of ionizing power of the solvent. | 7 | Physical Chemistry |
When radiation enters the body, it will interact with the atoms and molecules of the cells (mainly made of water) to produce free radicals and molecules that are able to diffuse far enough to reach the critical target in the cell, the DNA, and damage it indirectly through some chemical reaction. This is the main damage mechanism for photons as they are used for example in external beam radiation therapy.
Typically, the radiolytic events that lead to the damage of the (tumor)-cell DNA are subdivided into different stages that take place on different time scales:
* The physical stage (), consists in the energy deposition by the ionizing particle and the consequent ionization of water.
* During the physico-chemical stage () numerous processes occur, e.g. the ionized water molecules may split into a hydroxyl radical and a hydrogen molecule or free electrons may undergo solvation.
* During the chemical stage (), the first products of radiolysis react with each other and with their surrounding, thus producing several reactive oxygen species which are able to diffuse.
* During the bio-chemical stage ( to days) these reactive oxygen species might break the chemical bonds of the DNA, thus triggering the response of enzymes, the immune-system, etc.
* Finally, during the biological stage (days up to years) the chemical damage may translate into biological cell death or oncogenesis when the damaged cells attempt to divide. | 5 | Photochemistry |
Sum-frequency generation (SFG) is a second order nonlinear optical process based on the mixing of two input photons at frequencies and to generate a third photon at frequency . As with any optical phenomenon in nonlinear optics, this can only occur under conditions where:
the light is interacting with matter, that lacks centrosymmetry (for example, surfaces and interfaces);
the light has a very high intensity (typically from a pulsed laser).
Sum-frequency generation is a "parametric process", meaning that the photons satisfy energy conservation, leaving the matter unchanged: | 7 | Physical Chemistry |
In astronomy, the photosphere of a star is defined as the surface where its optical depth is 2/3. This means that each photon emitted at the photosphere suffers an average of less than one scattering before it reaches the observer. At the temperature at optical depth 2/3, the energy emitted by the star (the original derivation is for the Sun) matches the observed total energy emitted.
Note that the optical depth of a given medium will be different for different colors (wavelengths) of light.
For planetary rings, the optical depth is the (negative logarithm of the) proportion of light blocked by the ring when it lies between the source and the observer. This is usually obtained by observation of stellar occultations. | 7 | Physical Chemistry |
Khalil Ahmad Qureshi (Urdu: خليل احمد قريشى; HI, SI), is a Pakistani physical chemist and the professor of physical chemistry at the Punjab University. He has published notable papers in nuclear physical chemistry in international scientific journals as well contributing in the advancement of the scientific applications of the civilian usage of the fuel cycle. | 7 | Physical Chemistry |
The Adams decarboxylation is a chemical reaction that involved the decarboxylation of coumarins which have carboxylic acid group in the third position. The decarboxylation is achieved by aqueous solution of sodium bisulfite, heat and a concentrated solution of sodium hydroxide. | 0 | Organic Chemistry |
Tsumaki described the first metal–salen complexes in 1938. He found that the cobalt(II) complex Co(salen) reversibly binds O, which led to intensive research on cobalt complexes of salen and related ligands for their capacity for oxygen storage and transport, looking for potential synthetic oxygen carriers. Cobalt salen complexes also replicate certain aspects of vitamin B. | 0 | Organic Chemistry |
Nathalie Helene Katsonis (born 22 February 1978 in Vienna, Austria) is a Professor of Active Molecular Systems at the Stratingh Institute for Chemistry, University of Groningen. In 2016 she was awarded the Royal Netherlands Chemical Society Gold Medal. | 0 | Organic Chemistry |
It is the primary reactant in Yamaguchi esterification. 2,4,6-Trichlorobenzoyl chloride readily reacts with alcohols. This newly formed reagent, when mixed with a stoichiometric amount of 4-dimethylaminopyridine, cyclizes and forms esters. This reaction creates 2,4,6-trichlorobenzoic acid as a byproduct. | 0 | Organic Chemistry |
For each amino acid in a gene, the weight of each of its codons represented by a parameter termed relative adaptiveness (), is computed from a reference sequence set, as the ratio between the observed frequency of the codon and the frequency of the most frequent synonymous codon for that amino acid.
The CAI of a gene is simply defined as the geometric mean of the weight associated to each codon over the length () of the gene sequence (measured in codons). | 1 | Biochemistry |
It is possible to perform lateral force measurements using a nc-AFM probe oscillating normal to the surface under study. This method uses a similar method to force spectroscopy except the tip is moved parallel to the surface while the frequency shift is recorded, this is repeated at multiple heights above the surface, starting far from the surface and moving closer. After any change to the surface, for example moving an atom on the surface, the experiment is stopped. This leaves a 2D grid of measured frequency shifts. Using an appropriate force spectroscopy calculation each of the vertical frequency shift vectors can be converted into a vector of forces in the z-direction, thus creating a 2D grid of calculated forces. These forces can be integrated vertically to produce a 2D map of the potential. It is then possible to differentiate the potential horizontally to calculate the lateral forces. As this method relies on heavy mathematical processing, in which each state assumes a vertical motion of the tip, it is critical that the sensor is not angled, and that the tip length is very short compared to the length of the sensor.
A direct measurement of lateral forces is possible by using a torsional mode with a silicon cantilever or by orienting the sensor to oscillate parallel to the surface. Using the latter technique, Weymouth et al. measured the tiny interaction of two CO molecules as well as the lateral stiffness of a CO terminated tip. | 6 | Supramolecular Chemistry |
Shot peening is a cold working process used to finish metal parts. In the process of shot peening, small round shot is blasted against the surface of the part to be finished. This process is used to prolong the product life of the part, prevent stress corrosion failures, and also prevent fatigue. The shot leaves small dimples on the surface like a peen hammer does, which cause compression stress under the dimple. As the shot media strikes the material over and over, it forms many overlapping dimples throughout the piece being treated. The compression stress in the surface of the material strengthens the part and makes it more resistant to fatigue failure, stress failures, corrosion failure, and cracking. | 8 | Metallurgy |
Acetylcholine (ACh) is a neurotransmitter found in the brain, neuromuscular junctions and the autonomic ganglia.
Muscarinic receptors are used in the following roles: | 1 | Biochemistry |
In response to the arrival of food in the stomach and small intestine, the activity of the parasympathetic nervous system increases and the activity of the sympathetic nervous system decreases. This shift in the balance of autonomic tone towards the parasympathetic system results in a subjective state of low energy and a desire to be at rest, the opposite of the fight-or-flight state induced by high sympathetic tone. The larger the meal, the greater the shift in autonomic tone towards the parasympathetic system, regardless of the composition of the meal. | 1 | Biochemistry |
The phrase pseudokinase was first coined in 2002. They were subsequently sub-classified into different classes. Several pseudokinase-containing families are found in the human kinome, including the Tribbles pseudokinases, which are at the interface between kinase and ubiquitin E3 ligase signalling.
The human pseudokinases (and their pseudophosphatase cousins) are implicated in a wide variety of diseases, which has made them potential drug targets and antitargets). Pseudokinases are made up of an evolutionary mixture of eukaryotic protein kinase (ePK) and non ePK-related pseudoenzyme proteins (e.g., FAM20A, which binds ATP and is pseudokinase due to a conserved glutamate to glutamine swap in the alpha-C helix. FAM20A is implicated in periodontal disease, and serves to control the catalytic activity of FAM20C, an important physiological casein kinase that controls phosphorylation of proteins in the Golgi apparatus that are destined for secretion, such as the milk protein casein.
A comprehensive evolutionary analysis confirms that pseudokinases group into multiple subfamilies, and these are found in the annotated kinome of organisms across the kingdoms of life, including prokaryotes, archaea and all eukaryotic lineages with an annotated proteome; this data is searchable in ProKino (http://vulcan.cs.uga.edu/prokino/about/browser). | 1 | Biochemistry |
NADH-coenzyme Q oxidoreductase, also known as NADH dehydrogenase or complex I, is the first protein in the electron transport chain. Complex I is a giant enzyme with the mammalian complex I having 46 subunits and a molecular mass of about 1,000 kilodaltons (kDa). The structure is known in detail only from a bacterium; in most organisms the complex resembles a boot with a large "ball" poking out from the membrane into the mitochondrion. The genes that encode the individual proteins are contained in both the cell nucleus and the mitochondrial genome, as is the case for many enzymes present in the mitochondrion.
The reaction that is catalyzed by this enzyme is the two electron oxidation of NADH by coenzyme Q10 or ubiquinone (represented as Q in the equation below), a lipid-soluble quinone that is found in the mitochondrion membrane:
The start of the reaction, and indeed of the entire electron chain, is the binding of a NADH molecule to complex I and the donation of two electrons. The electrons enter complex I via a prosthetic group attached to the complex, flavin mononucleotide (FMN). The addition of electrons to FMN converts it to its reduced form, FMNH. The electrons are then transferred through a series of iron–sulfur clusters: the second kind of prosthetic group present in the complex. There are both [2Fe–2S] and [4Fe–4S] iron–sulfur clusters in complex I.
As the electrons pass through this complex, four protons are pumped from the matrix into the intermembrane space. Exactly how this occurs is unclear, but it seems to involve conformational changes in complex I that cause the protein to bind protons on the N-side of the membrane and release them on the P-side of the membrane. Finally, the electrons are transferred from the chain of iron–sulfur clusters to a ubiquinone molecule in the membrane. Reduction of ubiquinone also contributes to the generation of a proton gradient, as two protons are taken up from the matrix as it is reduced to ubiquinol (QH). | 1 | Biochemistry |
In type I reactions, the photoactivated Sens* interacts with the substrate to yield a radical substrate, usually through the homolytic bond breaking of a hydrogen bond on the substrate. This substrate radical then interacts with O (ground state) to yield a substrate-O radical. Such a radical is generally quenched by abstracting a hydrogen from another substrate molecule or from the solvent. This process allows for chain propagation of the reaction. | 5 | Photochemistry |
To work out which wallpaper group corresponds to a given design, one may use the following table.
See also this overview with diagrams. | 3 | Analytical Chemistry |
Calcineurin is a heterodimer of a 61-kD calmodulin-binding catalytic subunit, calcineurin A and a 19-kD Ca-binding regulatory subunit, calcineurin B. There are three isozymes of the catalytic subunit, each encoded by a separate gene (PPP3CA, PPP3CB, and PPP3CC) and two isoforms of the regulatory, also encoded by separate genes (PPP3R1, PPP3R2). | 1 | Biochemistry |
Trifluoromethanesulfonic acid is produced industrially by electrochemical fluorination (ECF) of methanesulfonic acid:
The resulting CFSOF is hydrolyzed, and the resulting triflate salt is reprotonated. Alternatively, trifluoromethanesulfonic acid arises by oxidation of trifluoromethylsulfenyl chloride:
Triflic acid is purified by distillation from triflic anhydride. | 0 | Organic Chemistry |
Using mesophilic bacteria requires the fermentation process to occur below 40 °C, which can cause bacterial contamination due to the low temperature. On the industrial scale, this requires sterilization steps which means a special facility must be built, more employees are needed to run this extra step, and more energy is consumed at the plant. A novel aerobic Geobacillus strain XT15 has been shown to produce 2,3-butanediol at a temperature between 45 and 55 °C. This higher temperature will avoid the risk of contamination because microorganisms that live in normal environments cannot reproduce above 45 °C. The Geobacillus strain XT15 is thermophilic, which allows it to be able to operate fermentation at this higher temperature. Sterilization would not be necessary using this alternative strain making the manufacturing process more efficient and cost-effective. | 1 | Biochemistry |
The quinhydrone electrode may be used to measure the hydrogen ion concentration (pH) of a solution containing an acidic substance. | 3 | Analytical Chemistry |
In 1941, in the midst of World War II, Prelog was invited to lecture in Germany by Richard Kuhn. Shortly afterwards, Lavoslav Ružička, whom Prelog asked for help, invited Prelog to visit him on his way to Germany. He and his wife used those invitations to escape to Zürich in Switzerland. With Ružičkas help, he gained support from CIBA Ltd. and started to work in the Organic Chemistry Laboratory in the Swiss Federal Institute of Technology (ETH, or Eidgenössische Technische Hochschule). Prelog was able to separate the chiral enantiomers of Trögers base in 1944 by chromatography on an optically active substrate.
With this chiral resolution, he was able to prove that not only carbon but also nitrogen atoms can be the chiral centre in a molecule, which had been speculated for several years. His relationship with Ružička helped him climb up the academic hierarchical ladder. Starting as an assistant, he became Privat-Dozent, Titularprofessor, associate professor, and in 1952 full professor. In 1957 he succeeded Ružička as head of the Laboratory. Since Prelog disliked administrative duties, he implemented rotating chairmanship in the ETH. Prelog joined the ETH at the right time, since Ružička's Jewish co-workers left the country and went to the United States, so Prelog filled the vacuum they left. | 4 | Stereochemistry |
Control of an operon is a type of gene regulation that enables organisms to regulate the expression of various genes depending on environmental conditions. Operon regulation can be either negative or positive by induction or repression.
Negative control involves the binding of a repressor to the operator to prevent transcription.
* In negative inducible operons, a regulatory repressor protein is normally bound to the operator, which prevents the transcription of the genes on the operon. If an inducer molecule is present, it binds to the repressor and changes its conformation so that it is unable to bind to the operator. This allows for expression of the operon. The lac operon is a negatively controlled inducible operon, where the inducer molecule is allolactose.
* In negative repressible operons, transcription of the operon normally takes place. Repressor proteins are produced by a regulator gene, but they are unable to bind to the operator in their normal conformation. However, certain molecules called corepressors are bound by the repressor protein, causing a conformational change to the active site. The activated repressor protein binds to the operator and prevents transcription. The trp operon, involved in the synthesis of tryptophan (which itself acts as the corepressor), is a negatively controlled repressible operon.
Operons can also be positively controlled. With positive control, an activator protein stimulates transcription by binding to DNA (usually at a site other than the operator).
* In positive inducible operons, activator proteins are normally unable to bind to the pertinent DNA. When an inducer is bound by the activator protein, it undergoes a change in conformation so that it can bind to the DNA and activate transcription. Examples of positive inducible operons include the MerR family of transcriptional activators.
* In positive repressible operons, the activator proteins are normally bound to the pertinent DNA segment. However, when an inhibitor is bound by the activator, it is prevented from binding the DNA. This stops activation and transcription of the system. | 1 | Biochemistry |
Columnar structures have also been studied intensively in the context of nanotubes. Their physical or chemical properties can be altered by trapping identical particles inside them. These are usually done by self-assembling fullerenes such as C60, C70, or C78 into carbon nanotubes, but also boron nitride nanotubes
Such structures also assemble when particles are coated on the surface of a spherocylinder as in the context of pharmaceutical research. Lazáro et al. examined the morphologies of virus capsid proteins self-assembled around metal nanorods. Drug particles were coated as densely as possible on a spherocylinder to provide the best medical treatment.
Wu et al. built rods of the size of several microns. These microrods are created by densely packing silica colloidal particles inside cylindrical pores. By solidifying the assembled structures the microrods were imaged and examined using scanning electron microscopy (SEM).
Columnar arrangements are also investigated as a possible candidate of optical metamaterials (i.e. materials with a negative refractive index) which find applications in super lenses or optical cloaking. Tanjeem et al. are constructing such a resonator by self-assembling nanospheres on the surface of the cylinder. The nanospheres are suspended in an SDS solution together with a cylinder of diameter , much larger than the diameter of the nanospheres (). The nanospheres then stick to the surface of the cylinders by a depletion force. | 3 | Analytical Chemistry |
Ferrier was elected Fellow of the Royal Society of New Zealand (1977) and the New Zealand Institute of Chemistry (1972) and awarded a DSc (London, 1968). | 0 | Organic Chemistry |
2-methylisocitric acid, an intermediate of the methylcitrate cycle, was first synthesized in 1886 as a mixture of four isomers. The pathway of the methylcitrate cycle was not discovered until 1973 in fungi, though it was not yet fully understood. Originally, the methylcitrate cycle was thought to be present only in fungal species, such as Candida lipolytica and Aspergillus nidulans. In 1999, it was discovered that the methylcitrate cycle was also present in bacteria Salmonella enterica and Escherichia coli. Much research has been done on the methylcitrate cycle's role in the development and function of various fungi and strains of bacteria, as well as its virulent properties in conjunction with the glyoxylate cycle. | 1 | Biochemistry |
Sulfonyl halides have tetrahedral sulfur centres attached to two oxygen atoms, an organic radical, and a halide. In a representative example, methanesulfonyl chloride, the S=O, S−C, and S−Cl bond distances are respectively 142.4, 176.3, and 204.6 pm. | 0 | Organic Chemistry |
*Order "For Merit to the Fatherland", 4th class
*Two Orders of Lenin
*Order of the Patriotic War, 2nd class
*Order of the Red Star
*Order of the October Revolution
*Two Orders of the Red Banner of Labour
*Medal of Zhukov
* USSR State Prize | 0 | Organic Chemistry |
Due to a color change from blue to red at pH 3.0–5.2, Congo red can be used as a pH indicator. Since this color change is an approximate inverse of that of litmus, it can be used with litmus paper in a simple parlor trick: add a drop or two of Congo red to both an acid solution and a base solution. Dipping red litmus paper in the red solution will turn it blue, while dipping blue litmus paper in the blue solution will turn it red. This property gives Congo red a metachromatic property as a dye, both in strongly acidic solutions and with strongly acidophilic tissue.
Congo red has a propensity to aggregate in aqueous and organic solutions. The proposed mechanisms suggest hydrophobic interactions between the aromatic rings of the dye molecules, leading to a π–π stacking phenomenon. Although these aggregates are present under various sizes and shapes, the "ribbon-like micelles" of a few molecules seem to be the predominant form (even if the "micelle" term is not an entirely appropriate name for it). This aggregation phenomenon is more prevalent in high Congo red concentrations, at high salinity and/or low pH. | 3 | Analytical Chemistry |
The structure of a polymeric material can be described at different length scales, from the sub-nm length scale up to the macroscopic one. There is in fact a hierarchy of structures, in which each stage provides the foundations for the next one.
The starting point for the description of the structure of a polymer is the identity of its constituent monomers. Next, the microstructure essentially describes the arrangement of these monomers within the polymer at the scale of a single chain. The microstructure determines the possibility for the polymer to form phases with different arrangements, for example through crystallization, the glass transition or microphase separation.
These features play a major role in determining the physical and chemical properties of a polymer. | 7 | Physical Chemistry |
A receptor modulator, or receptor ligand, is a general term for a substance, endogenous or exogenous, that binds to and regulates the activity of chemical receptors. They are ligands that can act on different parts of receptors and regulate activity in a positive, negative, or neutral direction with varying degrees of efficacy. Categories of these modulators include receptor agonists and receptor antagonists, as well as receptor partial agonists, inverse agonists, orthosteric modulators, and allosteric modulators, Examples of receptor modulators in modern medicine include CFTR modulators, selective androgen receptor modulators (SARMs), and muscarinic ACh receptor modulators. | 1 | Biochemistry |
CFCs were phased out via the Montreal Protocol due to their part in ozone depletion.
The atmospheric impacts of CFCs are not limited to their role as ozone-depleting chemicals. Infrared absorption bands prevent heat at that wavelength from escaping Earth's atmosphere. CFCs have their strongest absorption bands from C-F and C-Cl bonds in the spectral region of 7.8–15.3 µm—referred to as the "atmospheric window" due to the relative transparency of the atmosphere within this region.
The strength of CFC absorption bands and the unique susceptibility of the atmosphere at wavelengths where CFCs (indeed all covalent fluorine compounds) absorb radiation creates a "super" greenhouse effect from CFCs and other unreactive fluorine-containing gases such as perfluorocarbons, HFCs, HCFCs, bromofluorocarbons, SF, and NF. This "atmospheric window" absorption is intensified by the low concentration of each individual CFC. Because CO is close to saturation with high concentrations and few infrared absorption bands, the radiation budget and hence the greenhouse effect has low sensitivity to changes in CO concentration; the increase in temperature is roughly logarithmic. Conversely, the low concentration of CFCs allow their effects to increase linearly with mass, so that chlorofluorocarbons are greenhouse gases with a much higher potential to enhance the greenhouse effect than CO.
Groups are actively disposing of legacy CFCs to reduce their impact on the atmosphere.
According to NASA in 2018, the hole in the ozone layer has begun to recover as a result of CFC bans. However, research released in 2019 reports an alarming increase in CFCs, pointing to unregulated use in China. | 2 | Environmental Chemistry |
The salt ammonium carbamate is generated by treatment of ammonia with carbon dioxide:
:2 NH + CO → NH[HNCO] | 0 | Organic Chemistry |
Ro-vibrational spectra are usually measured at high spectral resolution. In the past, this was achieved by using an echelle grating as the spectral dispersion element in a grating spectrometer. This is a type of diffraction grating optimized to use higher diffraction orders. Today at all resolutions the preferred method is FTIR. The primary reason for this is that infrared detectors are inherently noisy, and FTIR detects summed signals at multiple wavelengths simultaneously achieving a higher signal to noise by virtue of Fellgett's advantage for multiplexed methods. The resolving power of an FTIR spectrometer depends on the maximum retardation of the moving mirror. For example, to achieve a resolution of 0.1 cm, the moving mirror must have a maximum displacement of 10 cm from its position at zero path difference. Connes measured the vibration-rotation spectrum of Venusian CO at this resolution. A spectrometer with 0.001 cm resolution is now available commercially. The throughput advantage of FTIR is important for high-resolution spectroscopy as the monochromator in a dispersive instrument with the same resolution would have very narrow entrance and exit slits.
When measuring the spectra of gases it is relatively easy to obtain very long path-lengths by using a multiple reflection cell. This is important because it allows the pressure to be reduced so as to minimize pressure broadening of the spectral lines, which may degrade resolution. Path lengths up to 20m are commercially available. | 7 | Physical Chemistry |
As with any piece of instrumentation or equipment, there are many aspects of maintenance that need to be encompassed by daily, weekly and annual procedures. The frequency of maintenance is typically determined by the sample volume and cumulative run time that the instrument is subjected to.
One of the first things that should be carried out before the calibration of the ICP-MS is a sensitivity check and optimization. This ensures that the operator is aware of any possible issues with the instrument and if so, may address them before beginning a calibration. Typical indicators of sensitivity are Rhodium levels, Cerium/Oxide ratios and DI water blanks. One common standard practice is to measure a standard tuning solution provided by the ICP manufacturer every time the plasma torch is started. Then the instrument is auto-calibrated for optimum sensitivity and the operator obtains a report providing certain parameters such as sensitivity, mass resolution and estimated amount of oxidized species and double-positive charged species.
One of the most frequent forms of routine maintenance is replacing sample and waste tubing on the peristaltic pump, as these tubes can get worn fairly quickly resulting in holes and clogs in the sample line, resulting in skewed results. Other parts that will need regular cleaning and/or replacing are sample tips, nebulizer tips, sample cones, skimmer cones, injector tubes, torches and lenses. It may also be necessary to change the oil in the interface roughing pump as well as the vacuum backing pump, depending on the workload put on the instrument. | 3 | Analytical Chemistry |
The term "half-life" is almost exclusively used for decay processes that are exponential (such as radioactive decay or the other examples above), or approximately exponential (such as biological half-life discussed below). In a decay process that is not even close to exponential, the half-life will change dramatically while the decay is happening. In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc., where the first half-life is defined as the time required for decay from the initial value to 50%, the second half-life is from 50% to 25%, and so on. | 7 | Physical Chemistry |
Prokaryotes have diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct prokaryotic types. For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide. This enables prokaryotes to thrive in harsh environments as cold as the snow surface of Antarctica, studied in cryobiology, or as hot as undersea hydrothermal vents and land-based hot springs.
Prokaryotes live in nearly all environments on Earth. Some archaea and bacteria are extremophiles, thriving in harsh conditions, such as high temperatures (thermophiles) or high salinity (halophiles). Many archaea grow as plankton in the oceans. Symbiotic prokaryotes live in or on the bodies of other organisms, including humans. Prokaryote have high populations in the soil - including the rhizosphere and rhizosheath. Soil prokaryotes are still heavily undercharacterized despite their easy proximity to humans and their tremendous economic importance to agriculture. | 1 | Biochemistry |
The haloacid dehalogenase (HAD) superfamily is a further PP group that uses Asp as a nucleophile and was recently shown to have dual-specificity. These PPs can target both Ser and Tyr, but are thought to have greater specificity towards Tyr. A subfamily of HADs, the Eyes Absent Family (Eya), are also transcription factors and can therefore regulate their own phosphorylation and that of transcriptional cofactor/s, and contribute to the control of gene transcription. The combination of these two functions in Eya reveals a greater complexity of transcriptional gene control than previously thought . A further member of this class is the RNA polymerase II C-terminal domain phosphatase. While this family remains poorly understood, it is known to play important roles in development and nuclear morphology. | 1 | Biochemistry |
The principal source of 5β-coprostanol in the environment is from human wastes. The concentration of 5β-coprostanol in raw, untreated sewage is around 2-6% of the dry solids. This relatively high concentration and its stability allows it to be used in the assessment of the faecal matter in samples, especially sediments. | 2 | Environmental Chemistry |
Titrations are often recorded on graphs called titration curves, which generally contain the volume of the titrant as the independent variable and the pH of the solution as the dependent variable (because it changes depending on the composition of the two solutions).
The equivalence point on the graph is where all of the starting solution (usually an acid) has been neutralized by the titrant (usually a base). It can be calculated precisely by finding the second derivative of the titration curve and computing the points of inflection (where the graph changes concavity); however, in most cases, simple visual inspection of the curve will suffice. In the curve given to the right, both equivalence points are visible, after roughly 15 and 30 mL of NaOH solution has been titrated into the oxalic acid solution. To calculate the logarithmic acid dissociation constant (pK), one must find the volume at the half-equivalence point, that is where half the amount of titrant has been added to form the next compound (here, sodium hydrogen oxalate, then disodium oxalate). Halfway between each equivalence point, at 7.5 mL and 22.5 mL, the pH observed was about 1.5 and 4, giving the pK.
In weak monoprotic acids, the point halfway between the beginning of the curve (before any titrant has been added) and the equivalence point is significant: at that point, the concentrations of the two species (the acid and conjugate base) are equal. Therefore, the Henderson-Hasselbalch equation can be solved in this manner:
Therefore, one can easily find the pK of the weak monoprotic acid by finding the pH of the point halfway between the beginning of the curve and the equivalence point, and solving the simplified equation. In the case of the sample curve, the acid dissociation constant K = 10 would be approximately 1.78×10 from visual inspection (the actual K is 1.7×10)
For polyprotic acids, calculating the acid dissociation constants is only marginally more difficult: the first acid dissociation constant can be calculated the same way as it would be calculated in a monoprotic acid. The pK of the second acid dissociation constant, however, is the pH at the point halfway between the first equivalence point and the second equivalence point (and so on for acids that release more than two protons, such as phosphoric acid). | 3 | Analytical Chemistry |
In animals, it has been shown that different cell types maintain different concentrations of magnesium. It seems likely that the same is true for plants. This suggests that different cell types may regulate influx and efflux of magnesium in different ways based on their unique metabolic needs. Interstitial and systemic concentrations of free magnesium must be delicately maintained by the combined processes of buffering (binding of ions to proteins and other molecules) and muffling (the transport of ions to storage or extracellular spaces).
In plants, and more recently in animals, magnesium has been recognized as an important signaling ion, both activating and mediating many biochemical reactions. The best example of this is perhaps the regulation of carbon fixation in chloroplasts in the Calvin cycle.
Magnesium is very important in cellular function. Deficiency of the nutrient causes disease of the affected organism. In single-cell organisms such as bacteria and yeast, low levels of magnesium manifests in greatly reduced growth rates. In magnesium transport knockout strains of bacteria, healthy rates are maintained only with exposure to very high external concentrations of the ion. In yeast, mitochondrial magnesium deficiency also leads to disease.
Plants deficient in magnesium show stress responses. The first observable signs of both magnesium starvation and overexposure in plants is a decrease in the rate of photosynthesis. This is due to the central position of the Mg ion in the chlorophyll molecule. The later effects of magnesium deficiency on plants are a significant reduction in growth and reproductive viability. Magnesium can also be toxic to plants, although this is typically seen only in drought conditions.
In animals, magnesium deficiency (hypomagnesemia) is seen when the environmental availability of magnesium is low. In ruminant animals, particularly vulnerable to magnesium availability in pasture grasses, the condition is known as grass tetany. Hypomagnesemia is identified by a loss of balance due to muscle weakness. A number of genetically attributable hypomagnesemia disorders have also been identified in humans.
Overexposure to magnesium may be toxic to individual cells, though these effects have been difficult to show experimentally. Hypermagnesemia, an overabundance of magnesium in the blood, is usually caused by loss of kidney function. Healthy animals rapidly excrete excess magnesium in the urine and stool. Urinary magnesium is called magnesuria. Characteristic concentrations of magnesium in model organisms are: in E. coli 30-100mM (bound), 0.01-1mM (free), in budding yeast 50mM, in mammalian cell 10mM (bound), 0.5mM (free) and in blood plasma 1mM. | 1 | Biochemistry |
Nucleosome Remodeling Factor (NURF) is an ATP-dependent chromatin remodeling complex first discovered in Drosophila melanogaster (fruit fly) that catalyzes nucleosome sliding in order to regulate gene transcription. It contains an ISWI ATPase, making it part of the ISWI family of chromatin remodeling complexes. NURF is highly conserved among eukaryotes and is involved in transcriptional regulation of developmental genes. | 1 | Biochemistry |
The concentration of malonyl-CoA depends on the balance between acetyl-CoA carboxylase (ACC) and malonyl-CoA decarboxylase (MCD). AMP-activated protein kinase (AMPK) is reported to phosphorylate and inactivate liver ACC. This in turn decreases malonyl-CoA concentrations which stimulates fatty acid oxidation and ketogenesis by glucagon in the liver. AMPK phosphorylates and inactivates ACC in the liver and other tissues. | 1 | Biochemistry |
Diazomethane is an organic chemical compound with the formula CHN, discovered by German chemist Hans von Pechmann in 1894. It is the simplest diazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellow gas; thus, it is almost universally used as a solution in diethyl ether. The compound is a popular methylating agent in the laboratory, but it is too hazardous to be employed on an industrial scale without special precautions. Use of diazomethane has been significantly reduced by the introduction of the safer and equivalent reagent trimethylsilyldiazomethane. | 0 | Organic Chemistry |
Copper phosphide, , also copper(I) phosphide, cuprous phosphide, cuprophosphorus and phosphor copper, is a compound of copper and phosphorus, a phosphide of copper. It has the appearance of yellowish-grey very brittle mass of crystalline structure. It does not react with water.
Recent crystallographic investigations have proven CuP to be copper deficient, which means that the sum formula of this compound is more accurately expressed as CuP.
Copper phosphide has a role in copper alloys, namely in phosphor bronze. It is a very good deoxidizer of copper.
Copper phosphide can be produced in a reverberatory furnace or in a crucible, e.g. by a reaction of red phosphorus with a copper-rich material. It can also be prepared photochemically, by irradiating cupric hypophosphite with ultraviolet radiation. It can also be produced by reducing copper(II) phosphate with aluminum.
When subjected to ultraviolet light, copper phosphide shows fluorescence.
A blue-black film of copper phosphide forms on white phosphorus when subjected to a solution of copper salt; wounds containing particles of phosphorus therefore have to be washed with 1% solution of copper sulfate. The particles then can be easily removed, which is helped by their fluorescence. Formation of protective layer of copper phosphide is also used in cases of phosphorus ingestion, when gastric lavage with copper sulfate is employed as part of the cure. | 8 | Metallurgy |
As an antibiotic, benzylpenicillin is noted to possess effectiveness mainly against gram-positive organisms. Some gram-negative organisms such as Neisseria gonorrhoeae and Leptospira weilii are also reported to be susceptible to benzylpenicillin. | 4 | Stereochemistry |
While statins may reduce CoQ in the blood it is unclear if they reduce CoQ in muscle. Evidence does not support that supplementation improves side effects from statins. However, a more recent metanalysis conducted in China, one of the world's largest producers of this supplement, concluded that, "CoQ supplementation ameliorated SAMSs [statin‐associated muscle symptoms], implying that CoQ supplementation might be a complementary approach to ameliorate statin‐induced myopathy." | 1 | Biochemistry |
CRP binds to the phosphocholine expressed on the surface of bacterial cells such as pneumococcus bacteria. This activates the complement system, promoting phagocytosis by macrophages, which clears necrotic and apoptotic cells and bacteria. With this mechanism, CRP also binds to ischemic/hypoxic cells, which could regenerate with more time. However, the binding of CRP causes them to be disposed of prematurely. CRP is a prehistoric antibody and binds to the Fc-gamma receptor IIa, to which antibodies also bind. In addition, CRP activates the classical complement pathway via C1q binding. CRP thus forms immune complexes in the same way as IgG antibodies.
This so-called acute phase response occurs as a result of increasing concentrations of interleukin-6 (IL-6), which is produced by macrophages as well as adipocytes in response to a wide range of acute and chronic inflammatory conditions such as bacterial, viral, or fungal infections; rheumatic and other inflammatory diseases; malignancy; and tissue injury and necrosis. These conditions cause release of IL-6 and other cytokines that trigger the synthesis of CRP and fibrinogen by the liver.
CRP binds to phosphocholine on micro-organisms. It is thought to assist in complement binding to foreign and damaged cells and enhances phagocytosis by macrophages (opsonin-mediated phagocytosis), which express a receptor for CRP. It plays a role in innate immunity as an early defense system against infections. | 1 | Biochemistry |
It once was a popular solvent in organic chemistry, but because of its adverse health effects, it is rarely used today. It is sometimes useful as a solvent for infrared spectroscopy, because there are no significant absorption bands above 1600 cm. Because carbon tetrachloride does not have any hydrogen atoms, it was historically used in proton NMR spectroscopy. In addition to being toxic, its dissolving power is low. Its use in NMR spectroscopy has been largely superseded by deuterated solvents (mainly deuterochloroform). The use of carbon tetrachloride in the determination of oil has been replaced by various other solvents, such as tetrachloroethylene. Because it has no C–H bonds, carbon tetrachloride does not easily undergo free-radical reactions. It is a useful solvent for halogenations either by the elemental halogen or by a halogenation reagent such as N-bromosuccinimide (these conditions are known as Wohl–Ziegler bromination). | 2 | Environmental Chemistry |
A metallurgical assay is a compositional analysis of an ore, metal, or alloy, usually performed in order to test for purity or quality.
Some assay methods are suitable for raw materials; others are more appropriate for finished goods. Raw precious metals (bullion) are assayed by an assay office. Silver is assayed by titration, gold by cupellation and platinum by inductively coupled plasma optical emission spectrometry (ICP OES).
Precious metal items of art or jewelry are frequently hallmarked (depending upon the requirements of the laws of either the place of manufacture or the place of import). Where required to be hallmarked, semi-finished precious metal items of art or jewelry pass through the official testing channels where they are analyzed or assayed for precious metal content. While different nations permit a variety of legally acceptable finenesses, the assayer is actually testing to determine that the fineness of the product conforms with the statement or claim of fineness that the maker has claimed (usually by stamping a number such as 750 for 18k gold) on the item. In the past the assay was conducted by using the touchstone method but currently (most often) it is done using X-ray fluorescence (XRF). XRF is used because this method is more than the touchstone test. The most exact method of assay is known as fire assay or cupellation. This method is better suited for the assay of bullion and gold stocks rather than works of art or jewelry because it is a completely destructive method. | 8 | Metallurgy |
Vitamin A is a fat-soluble vitamin and an essential nutrient for animals. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin (precursor) carotenoids, most notably beta-carotene. Vitamin A has multiple functions: it is essential for embryo development and growth, for maintenance of the immune system, and for vision, where it combines with the protein opsin to form rhodopsin the light-absorbing molecule necessary for both low-light (scotopic vision) and color vision.
Vitamin A occurs as two principal forms in foods: A) retinol, found in animal-sourced foods, either as retinol or bound to a fatty acid to become a retinyl ester, and B) the carotenoids alpha-carotene, β-carotene, gamma-carotene, and the xanthophyll beta-cryptoxanthin (all of which contain β-ionone rings) that function as provitamin A in herbivore and omnivore animals which possess the enzymes that cleave and convert provitamin carotenoids to retinal and then to retinol. Some carnivore species lack this enzyme. The other carotenoids have no vitamin activity.
Dietary retinol is absorbed from the digestive tract via passive diffusion. Unlike retinol, β-carotene is taken up by enterocytes by the membrane transporter protein scavenger receptor B1 (SCARB1), which is upregulated in times of vitamin A deficiency. Storage of retinol is in lipid droplets in the liver. A high capacity for long-term storage of retinol means that well-nourished humans can go months on a vitamin A- and β-carotene-deficient diet, while maintaining blood levels in the normal range. Only when the liver stores are nearly depleted will signs and symptoms of deficiency show. Retinol is reversibly converted to retinal, then irreversibly to retinoic acid, which activates hundreds of genes.
Vitamin A deficiency is common in developing countries, especially in Sub-Saharan Africa and Southeast Asia. Deficiency can occur at any age but is most common in pre-school age children and pregnant women, the latter due to a need to transfer retinol to the fetus. Vitamin A deficiency is estimated to affect approximately one-third of children under the age of five around the world, resulting in hundreds of thousands of cases of blindness and deaths from childhood diseases because of immune system failure. Reversible night blindness is an early indicator of low vitamin A status. Plasma retinol is used as a biomarker to confirm vitamin A deficiency. Breast milk retinol can indicate a deficiency in nursing mothers. Neither of these measures indicates the status of liver reserves.
The European Union and various countries have set recommendations for dietary intake, and upper limits for safe intake. Vitamin A toxicity also referred to as hypervitaminosis A, occurs when there is too much vitamin A accumulating in the body. Symptoms may include nervous system effects, liver abnormalities, fatigue, muscle weakness, bone and skin changes, and others. The adverse effects of both acute and chronic toxicity are reversed after consumption of high dose supplements is stopped. | 1 | Biochemistry |
The Danheiser benzannulation is a chemical reaction used in organic chemistry to generate highly substituted phenols in a single step. It is named after Rick L. Danheiser who developed the reaction. | 0 | Organic Chemistry |
The Knudsen effusion cell is used to measure the vapor pressures of a solid with very low vapor pressure. Such a solid forms a vapor at low pressure by sublimation. The vapor slowly effuses through a pinhole, and the loss of mass is proportional to the vapor pressure and can be used to determine this pressure. The heat of sublimation can also be determined by measuring the vapor pressure as a function of temperature, using the Clausius–Clapeyron relation. | 7 | Physical Chemistry |
FLiNaK is the name of the ternary eutectic alkaline metal fluoride salt mixture LiF-NaF-KF (46.5-11.5-42 mol %). It has a melting point of 462 °C and a boiling point of 1570 °C. It is used as electrolyte for the electroplating of refractory metals and compounds like titanium, tantalum, hafnium, zirconium and their borides. FLiNaK also could see potential use as a coolant in the very high temperature reactor, a type of nuclear reactor. | 7 | Physical Chemistry |
* Elected a Fellow of the Royal Society of Medicine (FRSM)
* Awarded Fellowship of the International Society for Science and Religion
* 2010 James Gregory Medal
* 2010 Agilent Thought Leader Award
* 2012 Waters Corporation Center of Innovation Program Honors
* 2014 University of Gothenburg Sahlgrenska institute Honorary Doctorate
* 2016 The Analytical Scientist Power List
* 2017 International glycoconjugate organisation award | 1 | Biochemistry |
It is possible to envision three-dimensional (3D) graphs showing three thermodynamic quantities. For example, for a single component, a 3D Cartesian coordinate type graph can show temperature (T) on one axis, pressure (p) on a second axis, and specific volume (v) on a third. Such a 3D graph is sometimes called a p–v–T diagram. The equilibrium conditions are shown as curves on a curved surface in 3D with areas for solid, liquid, and vapor phases and areas where solid and liquid, solid and vapor, or liquid and vapor coexist in equilibrium. A line on the surface called a triple line is where solid, liquid and vapor can all coexist in equilibrium. The critical point remains a point on the surface even on a 3D phase diagram.
An orthographic projection of the 3D p–v–T graph showing pressure and temperature as the vertical and horizontal axes collapses the 3D plot into the standard 2D pressure–temperature diagram. When this is done, the solid–vapor, solid–liquid, and liquid–vapor surfaces collapse into three corresponding curved lines meeting at the triple point, which is the collapsed orthographic projection of the triple line. | 7 | Physical Chemistry |
The first observations of an autoinducer-controlled phenotype in bacteria were reported in 1970, by Kenneth Nealson, Terry Platt, and J. Woodland Hastings, who observed what they described as a conditioning of the medium in which they had grown the bioluminescent marine bacterium Aliivibrio fischeri. These bacteria did not synthesize luciferase—and therefore did not luminesce—in freshly inoculated culture but only after the bacterial population had increased significantly. Because they attributed this conditioning of the medium to the growing population of cells itself, they referred to the phenomenon as autoinduction. In 1994, after study of the autoinduction phenomenon had expanded into several additional bacteria, the term "quorum sensing" was coined in a review by W. Claiborne Fuqua, Stephen C. Winans, and E. Peter Greenberg.
Dr. Stephen Winnans did not believe the word "autoinducer" fully enveloped the true process, so introduced the world to the term "Quorum Sensing" in 1994 through his article review of autoinduction in bacteria. This new phrase helped relieve confusion between 'autoinduction" and "autoregulation". The phrase "Quorum Sensing" was not stumbled onto, but rather created through trial and error. Dr. Winnans created many options, such as "gridlockins", "communiolins", and "quoromones". Eventually, it was "Quorum Sensing that stuck, and Dr. Stephen Winnans phrase spread quickly into the world. Quorum Sensing is now involved in practically every article written about autoinduction throughout the scientific community. | 1 | Biochemistry |
Non-essential nutrients are substances within foods that can have a significant impact on health. Dietary fiber is not absorbed in the human digestive tract. Soluble fiber is metabolized to butyrate and other short-chain fatty acids by bacteria residing in the large intestine. Soluble fiber is marketed as serving a prebiotic function with claims for promoting "healthy" intestinal bacteria. | 9 | Geochemistry |
There are many ways to accurately manipulate single molecules. Prominent among these are optical or magnetic tweezers, atomic-force-microscope (AFM) cantilevers and acoustic force spectroscopy. In all of these techniques, a biomolecule, such as protein or DNA, or some other biopolymer has one end bound to a surface or micrometre-sized bead and the other to a force sensor. The force sensor is usually a micrometre-sized bead or a cantilever, whose displacement can be measured to determine the force. | 7 | Physical Chemistry |
In practice, the term is usually used more specifically to indicate that non-carbon atoms have replaced carbon in the backbone of the molecular structure. Typical heteroatoms are nitrogen (N), oxygen (O), sulfur (S), phosphorus (P), chlorine (Cl), bromine (Br), and iodine (I), as well as the metals lithium (Li) and magnesium (Mg). | 0 | Organic Chemistry |
In geometry, a glide reflection or transflection is a geometric transformation that consists of a reflection across a hyperplane and a translation ("glide") in a direction parallel to that hyperplane, combined into a single transformation. Because the distances between points are not changed under glide reflection, it is a motion or isometry. When the context is the two-dimensional Euclidean plane, the hyperplane of reflection is a straight line called the glide line or glide axis. When the context is three-dimensional space, the hyperplane of reflection is a plane called the glide plane. The displacement vector of the translation is called the glide vector.
When some geometrical object or configuration appears unchanged by a transformation, it is said to have symmetry, and the transformation is called a symmetry operation. Glide-reflection symmetry is seen in frieze groups (patterns which repeat in one dimension, often used in decorative borders), wallpaper groups (regular tessellations of the plane), and space groups (which describe e.g. crystal symmetries). Objects with glide-reflection symmetry are in general not symmetrical under reflection alone, but two applications of the same glide reflection result in a double translation, so objects with glide-reflection symmetry always also have a simple translational symmetry.
When a reflection is composed with a translation in a direction perpendicular to the hyperplane of reflection, the composition of the two transformations is a reflection in a parallel hyperplane. However, when a reflection is composed with a translation in any other direction, the composition of the two transformations is a glide reflection, which can be uniquely described as a reflection in a parallel hyperplane composed with a translation in a direction parallel to the hyperplane.
A single glide is represented as frieze group p11g. A glide reflection can be seen as a limiting rotoreflection, where the rotation becomes a translation. It can also be given a Schoenflies notation as S, Coxeter notation as [∞,2], and orbifold notation as ∞×. | 3 | Analytical Chemistry |
The Mountain Pass Rare Earth Mine and Processing Facility, owned by MP Materials, is an open-pit mine of rare-earth elements on the south flank of the Clark Mountain Range in California, southwest of Las Vegas, Nevada. In 2020 the mine supplied 15.8% of the world's rare-earth production. It is the only rare-earth mining and processing facility in the United States.
As of 2022, work is ongoing to restore processing capabilities for domestic light rare-earth elements (LREEs) and work has been funded by the United States Department of Defense to restore processing capabilities for heavy rare-earth metals (HREEs) to alleviate supply chain risk. | 8 | Metallurgy |
Lithium has been associated with several forms of kidney injury. It is estimated that impaired urinary concentrating ability is present in at least half of individuals on chronic lithium therapy, a condition called lithium-induced nephrogenic diabetes insipidus. Continued use of lithium can lead to more serious kidney damage in an aggravated form of diabetes insipidus. Chronic kidney disease caused by lithium has not been proven with various contradicting results presented by a 2018 review. In rare cases, some forms of lithium-caused kidney damage may be progressive and lead to end-stage kidney failure with a reported incidence of 0.2% to 0.7%. | 1 | Biochemistry |
CooA is a heme-containing transcription factor that responds to the presence of carbon monoxide. This protein forms homodimers and is a homolog of cAMP receptor protein. CooA regulates the expression of carbon monoxide dehydrogenase, an enzyme that catalyzes the oxidation of CO to CO. The most well-studied CooA homolog comes from Rhodospirillum rubrum (RrCooA), but the CooA homolog from Carboxydothermus hydrogenoformans (ChCooA) has been studied as well. The main difference between these two CooA homologs is the ferric heme coordination. For RrCooA, the ferric heme iron is bound to a cysteine and the amine of the N-terminal proline, while, in the ferrous state, a ligand switch occurs where a nearby histidine displaces the thiolate. For ChCooA, the heme iron is ligated by a histidine and the N-terminal amine in both the ferric and ferrous states. For both homologs, CO displaces the amine ligand and activates the protein to bind to its target DNA sequence. Several structures of CooA exist: RrCooA in the ferrous state (1FT9), ChCooA in the ferrous, imidazole-bound state (2FMY), and ChCooA in the ferrous, CO-bound state (2HKX). | 1 | Biochemistry |
Noyori has also demonstrated the kinetic resolution of allylic alcohols by asymmetric hydrogenation of the olefin.
Utilizing the Ru[BINAP] complex, selective hydrogenation can give high ees of the unsaturated alcohol in addition to the hydrogenated alcohol, as shown below. Thus, a second hydrogenation of the enantioenriched allylic alcohol remaining will give enantiomerically pure samples of both enantiomers of the saturated alcohol. Noyori has resolved a number of allylic alcohols with good to excellent yields and good to excellent ees (up to >99%). | 4 | Stereochemistry |
DDM is based on an algorithm proposed in Croccolo et al. and Alaimo et al., which is conveniently named differential dynamic algorithm (DDA). DDA works by subtracting images acquired at different times and taking advantage that, as the delay between two subtracted images gets large, the energy content of the difference image increases correspondingly. A two-dimensional fast Fourier transform (FFT) analysis of the difference images allows to quantify the growth of the signal contains for each wave vector and one can calculate the Fourier power spectrum of the difference images for different delays to obtain the so-called image structure function . Calculation shows that for both scattering- and fluorescence-based DDM
where is the normalized intermediate scattering function that would be measured in a dynamic light scattering (DLS) experiment, the sample scattering intensity that would be measured in a static light scattering (SLS) experiment, a background term due to the noise along the detection chain a transfer function that depends on the microscope details. Equation () shows that DDM can be used for DLS experiments, provided that a model for the normalized intermediate scattering function is available. For instance, in the case of Brownian motion one has where is the diffusion coefficient of the Brownian particles. If the transfer function is determined by calibrating the microscope with a suitable sample, DDM can be employed also for SLS experiments. Alternative algorithms for data analysis are suggested in.
Running DDM on a series of frames smaller than the full-frame has been called multi-DDM. This is analogous to changing the scattering volume in a light scattering experiment, but is readily carried out by selecting out of the full-frame movie. The coherence lengthscale of the dynamics can be picked up from a multi-DDM analysis. | 7 | Physical Chemistry |
The definition of thermodynamic work is in terms of the changes of the system's extensive deformation (and chemical constitutive and certain other) state variables, such as volume, molar chemical constitution, or electric polarisation. Examples of state variables that are not extensive deformation or other such variables are temperature and entropy , as for example in the expression . Changes of such variables are not actually physically measureable by use of a single simple adiabatic thermodynamic process; they are processes that occur neither by thermodynamic work nor by transfer of matter, and therefore are said occur by heat transfer. The quantity of thermodynamic work is defined as work done by the system on its surroundings. According to the second law of thermodynamics, such work is irreversible. To get an actual and precise physical measurement of a quantity of thermodynamic work, it is necessary to take account of the irreversibility by restoring the system to its initial condition by running a cycle, for example a Carnot cycle, that includes the target work as a step. The work done by the system on its surroundings is calculated from the quantities that constitute the whole cycle. A different cycle would be needed to actually measure the work done by the surroundings on the system. This is a reminder that rubbing the surface of a system appears to the rubbing agent in the surroundings as mechanical, though not thermodynamic, work done on the system, not as heat, but appears to the system as heat transferred to the system, not as thermodynamic work. The production of heat by rubbing is irreversible; historically, it was a piece of evidence for the rejection of the caloric theory of heat as a conserved substance. The irreversible process known as Joule heating also occurs through a change of a non-deformation extensive state variable.
Accordingly, in the opinion of Lavenda, work is not as primitive concept as is heat, which can be measured by calorimetry. This opinion does not negate the now customary thermodynamic definition of heat in terms of adiabatic work.
Known as a thermodynamic operation, the initiating factor of a thermodynamic process is, in many cases, a change in the permeability of a wall between the system and the surroundings. Rubbing is not a change in wall permeability. Kelvin's statement of the second law of thermodynamics uses the notion of an "inanimate material agency"; this notion is sometimes regarded as puzzling. The triggering of a process of rubbing can occur only in the surroundings, not in a thermodynamic system in its own state of internal thermodynamic equilibrium. Such triggering may be described as a thermodynamic operation. | 7 | Physical Chemistry |
*Glutamine is the most abundant amino acid in the plasma and an additional energy source in tumor cells especially when glycolytic energy production is low due to a high amount of the dimeric form of M2-PK.
*Glutamine and its degradation products glutamate and aspartate are precursors for nucleic acid and serine synthesis.
*Glutaminolysis is insensitive to high concentrations of reactive oxygen species (ROS).
*Due to the truncation of the citric acid cycle the amount of acetyl-CoA infiltrated in the citric acid cycle is low and acetyl-CoA is available for de novo synthesis of fatty acids and cholesterol. The fatty acids can be used for phospholipid synthesis or can be released.
*Fatty acids represent an effective storage vehicle for hydrogen. Therefore, the release of fatty acids is an effective way to get rid of cytosolic hydrogen produced within the glycolytic glyceraldehyde 3-phosphate dehydrogenase (GAPDH; EC 1.2.1.9) reaction.
*Glutamate and fatty acids are immunosuppressive. The release of both metabolites may protect tumor cells from immune attacks.
*It has been discussed that the glutamate pool may drive the endergonic uptake of other amino acids by system ASC.
*Glutamine can be converted to citrate without NADH production, uncoupling NADH production from biosynthesis. | 1 | Biochemistry |
A paracrystalline lattice, or paracrystal, is a molecular or atomic lattice with significant amounts (e.g., larger than a few percent) of partial disordering of molecular arrangements. Limiting cases of the paracrystal model are nanostructures, such as glasses, liquids, etc., that may possess only local ordering and no global order. A simple example of a paracrystalline lattice is shown in the following figure for a silica glass:
Liquid crystals also have paracrystalline rather than crystalline structures.
Highly hydrated B-DNA occurs naturally in living cells in such a paracrystalline state, which is a dynamic one despite the relatively rigid DNA double helix stabilized by parallel hydrogen bonds between the nucleotide base-pairs in the two complementary, helical DNA chains (see figures). For simplicity most DNA molecular models omit both water and ions dynamically bound to B-DNA, and are thus less useful for understanding the dynamic behaviors of B-DNA in vivo. The physical and mathematical analysis of X-ray and spectroscopic data for paracrystalline B-DNA is thus far more complex than that of crystalline, A-DNA X-ray diffraction patterns. The paracrystal model is also important for DNA technological applications such as DNA nanotechnology. Novel methods that combine X-ray diffraction of DNA with X-ray microscopy in hydrated living cells are now also being developed. | 4 | Stereochemistry |
Big dynorphin is an endogenous opioid peptide of the dynorphin family that is composed of both dynorphin A and dynorphin B. Big dynorphin has the amino acid sequence: Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys-Trp-Asp-Asn-Gln-Lys-Arg-Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Gln-Phe-Lys-Val-Val-Thr. It has nociceptive and anxiolytic-like properties, as well as effects on memory in mice.
Big dynorphin is a principal endogenous, agonist at the human kappa-opioid receptor. | 1 | Biochemistry |
After rearranging the expression defining K, and putting , one obtains
This is the Henderson–Hasselbalch equation, from which the following conclusions can be drawn.
* At half-neutralization the ratio ; since , the pH at half-neutralization is numerically equal to pK. Conversely, when , the concentration of HA is equal to the concentration of A.
* The buffer region extends over the approximate range pK ± 2. Buffering is weak outside the range pK ± 1. At pH ≤ pK − 2 the substance is said to be fully protonated and at pH ≥ pK + 2 it is fully dissociated (deprotonated).
* If the pH is known, the ratio may be calculated. This ratio is independent of the analytical concentration of the acid.
In water, measurable pK values range from about −2 for a strong acid to about 12 for a very weak acid (or strong base).
A buffer solution of a desired pH can be prepared as a mixture of a weak acid and its conjugate base. In practice, the mixture can be created by dissolving the acid in water, and adding the requisite amount of strong acid or base. When the pK and analytical concentration of the acid are known, the extent of dissociation and pH of a solution of a monoprotic acid can be easily calculated using an ICE table. | 7 | Physical Chemistry |
Elizabeth Kujawinski is an American oceanographer who is Senior Scientist at the Woods Hole Oceanographic Institution, where she works as Program Director of the Center for Chemical Currencies of a Microbial Planet. Her research considers analytical chemistry, chemical oceanography, microbiology and microbial ecology. She is interested in what controls the composition of organic materials in aquatic systems. | 9 | Geochemistry |
In organic chemistry, a bipolaron is a molecule or part of a macromolecular chain containing two positive charges in a conjugated system. The charges can be located in the centre of the chain or at its termini. Bipolarons and polarons are encountered in doped conducting polymers such as polythiophene.
It is possible to synthesize and isolate bipolaron model compounds for X-ray diffraction studies. The diamagnetic bis(triaryl)amine dication 2 in scheme 1 is prepared from the neutral precursor 1 in dichloromethane by reaction with 4 equivalents of antimony pentachloride. Two resonance structures exist for the dication. Structure 2a is a (singlet) diradical and 2b is the closed shell quinoid. The experimental bond lengths for the central vinylidene group in 2 are 141 pm and 137 pm compared to 144 pm and 134 pm for the precursor 1 implying some contribution from the quinoid structure.
On the other hand, when a thiophene unit is added to the core in the structure depicted in scheme 2, these bond lengths are identical (around 138 pm) making it a true hybrid. | 7 | Physical Chemistry |
Since scientists produced the first cloned mammal Dolly the sheep in 1996 using the somatic cell nuclear transfer (SCNT) technique, 23 mammalian species have been successfully cloned, including cattle, cats, dogs, horses and rats. Using this technique for primates had never been successful and no pregnancy had lasted more than 80 days. The main difficulty was likely the proper programming of the transferred nuclei to support the growth of the embryo. Tetra (born October 1999), a female rhesus macaque, was created by a team led by Gerald Schatten of the Oregon National Primate Research Center using a different technique, called "embryo splitting". She is the first cloned primate by artificial twinning, which is a much less complex procedure than the DNA transfer used for the creation of Zhong Zhong and Hua Hua.
In January 2019, scientists in China reported the creation of five identical cloned gene-edited monkeys, using the same cloning technique that was used with Zhong Zhong and Hua Hua, and the same gene-editing CRISPR-Cas9 technique allegedly used by He Jiankui in creating the first ever gene-modified human babies Lulu and Nana. The monkey clones were made in order to study several medical diseases. | 1 | Biochemistry |
This intuitive picture is not quite right, because is an eigenfunction of the Hamiltonian and so at different times only differs by a phase. Thus, in particular, the physical state does not evolve and so it cannot become noninteracting. This problem is easily circumvented by assembling and into wavepackets with some distribution of energies over a characteristic scale . The uncertainty principle now allows the interactions of the asymptotic states to occur over a timescale and in particular it is no longer inconceivable that the interactions may turn off outside of this interval. The following argument suggests that this is indeed the case.
Plugging the Lippmann–Schwinger equations into the definitions
and
of the wavepackets we see that, at a given time, the difference between the and wavepackets is given by an integral over the energy . | 7 | Physical Chemistry |
* The Physics and Chemistry of Wave Packets, with John Yeazell [https://books.google.com/books?id=_sScnHz1kfsC&dq=Turgay+Uzer&pg=PP9 at books.google]
* Lecture Notes on Atomic and Molecular Physics with Şakir Erkoç [https://books.google.com/books?id=KWssMj81fpkC&q=Lecture+Notes+on+Atomic+and+Molecular+Physics at books.google] | 7 | Physical Chemistry |
While most chloroplasts originate from that first set of endosymbiotic events, Paulinella chromatophora is an exception that acquired a photosynthetic cyanobacterial endosymbiont more recently. It is not clear whether that symbiont is closely related to the ancestral chloroplast of other eukaryotes. Being in the early stages of endosymbiosis, Paulinella chromatophora can offer some insights into how chloroplasts evolved. Paulinella cells contain one or two sausage-shaped blue-green photosynthesizing structures called chromatophores, descended from the cyanobacterium Synechococcus. Chromatophores cannot survive outside their host. Chromatophore DNA is about a million base pairs long, containing around 850 protein-encoding genes—far less than the three million base pair Synechococcus genome, but much larger than the approximately 150,000 base pair genome of the more assimilated chloroplast. Chromatophores have transferred much less of their DNA to the nucleus of their host. About 0.3–0.8% of the nuclear DNA in Paulinella is from the chromatophore, compared with 11–14% from the chloroplast in plants. | 5 | Photochemistry |
In the 1780s for the French Academy of Sciences, Lavoisier, Laplace, and Seguin investigated and published relationships between direct calorimetry and respiratory gas exchanges from mammalian subjects. 100 years later in the 19th century for the Connecticut-based Wesleyan University, Professors Atwater and Rosa provided ample evidence of nitrogen, carbon dioxide, and oxygen transport during the metabolism of amino acids, glucose, and fatty acids in human subjects, further establishing the value of indirect calorimetry in determining bioenergetics of free-living humans. The work of Atwater and Rosa also made it possible to calculate the caloric values of foods, which eventually became the criteria adopted by the USDA to create the food calorie library.
In the early 20th century at Oxford University, physiology researcher Claude Gordon Douglas developed an inexpensive and mobile method of collecting exhaled breath (partly in preparation for experiments to be conducted on Pike's Peak, Colorado). In this method, the subject exhales into a nearly impermeable and large volume collection bag over a recorded period of time. The entire volume is measured, the oxygen and carbon dioxide content are analyzed, and the differences from inspired "ambient" air are calculated to determine the rates of oxygen uptake and carbon dioxide output.
To estimate energy expenditure from the exhaled gases, several algorithms were developed. One of the most widely used was developed in 1949 at University of Glasgow by research physiologist J. B. de V. Weir. His abbreviated equation for estimating metabolic rate was written with rates of gas exchange being volume/time, excluded urinary nitrogen, and allowed for the inclusion of a time conversion factor of 1.44 to extrapolate to 24-hour energy expenditure from 'kcal per minute" to "kcal per day." Weir used the Douglas Bag method in his experiments, and in support of neglecting the effect of protein metabolism under normal physiological conditions and eating patterns of ~12.5% protein calories, he wrote:
:"...In fact if the percentage of protein calories [consumed] lies between 10 and 14 the maximum error in using [the equation] is less than 1 in 500." | 1 | Biochemistry |
* Estimating dissolved organic carbon concentration
* Specific ultraviolet absorbance for metric of aromaticity
* Bial's test for concentration of pentoses | 7 | Physical Chemistry |
Inspired by enzymes with deep active site pocket, List and coworkers designed and constructed a set of confined Bronsted acids with an extremely sterically demanding chiral pocket based on a C-symmetric bis(binapthyl) imidodiphosphoric acid. Within the chiral microenvironment, the catalysts has a geometrically fixed bifunctional active site that activates both an electrophilic part and a nucleophilic part of a substrate. This catalyst enables stereoselective spiroacetal formation with high enantiomeric excess for a variety of substrates. | 6 | Supramolecular Chemistry |
The SFA has more recently been extended to perform dynamic measurements, thereby determining viscous and viscoelastic properties of fluids, frictional and tribological properties of surfaces, and the time-dependent interaction between biological structures. | 6 | Supramolecular Chemistry |
The synthesis of ring C also required hydroxygeranyl acetate 2. Subsequent steps were allylic oxidation (SeO, tBuOH, salicylic acid) to aldehyde 13, then carbonyl reduction (NaBH) to alcohol 14, then epoxidation (VO(acac), tBuOH) to 15, then alcohol protection (MPM trichloroacetimidate) to MPM ether 16, then radical cyclisation (titanocene dichloride, manganese, triethylborane, TMSCl, KCO) to alcohol 17, alcohol protection (BOMCl, DIPEA) to benzyloxymethyl ether 18, acetate hydrolysis (NaOH) and Ley oxidation to aldehyde 19. | 0 | Organic Chemistry |
In order to reap the benefits of working in this small-angle regime, one must take into consideration:
* The characteristic length scale of the polymer, e.g.
* The wavelength of the scattered particles
The ratio will determine the available angular spectrum of this regime. To see this one may consider the case of elastic scattering (even approximately elastic ). If the scattering angle is , we may express as:
so the small-angle condition becomes , determining the relevant angles. | 7 | Physical Chemistry |
The enduring contributions of Zervas were made together with Bergmann and involved the first successful synthesis of substantial length oligopeptides. They achieved this using the carboxybenzyl amine protecting group for the masking of the N-terminus of the growing oligopeptide chain to which amino acid residues are added in a serial manner. The carboxybenzyl group discovered by Zervas is introduced by reaction with benzyl chloroformate, originally in aqueous sodium carbonate solution at 0 °C:
The protecting group is abbreviated Cbz or, in honour of Zervas, simply Z. The typical route for deprotection involves hydrogenolysis under mild conditions e.g. with hydrogen gas and a catalyst such as palladium on charcoal.
The discovery of the Bergmann-Zervas synthesis has been characterised as "epoch-making" as it allowed the advent of controlled synthetic peptide chemistry, completing the work started in the early 20th century by Bergmann's mentor Emil Fischer. Previously impossible to synthesise oligopeptides with a highly specific sequence and reactive side chains were consequently produced in the 1930s by Bergmann and Zervas. The ability of Z-protection to prevent racemization of activated derivatives of the protected amino acids and the importance thereof were also noted by the two chemists.
Indeed, their method became the standard in the field for the following two decades until further developments in the early 1950s with the introduction of mixed anhydrides (e.g. the Boc group).
Zervas continued his research on peptide synthesis in New York and later in Greece. The first topic of his research once in Greece was the synthesis of N- or O-phosphorylated amino acids, in which he demonstrated the utility of dibenzyl chlorophosphonate. He continued his efforts on the development of new methods within peptide chemistry, including the introduction of the o-nitrophenylsulfenyl (NPS) amino protecting group and peptide synthesis using N-tritylamino acids.
One of the major issues which occupied his interests was the chemical synthesis of insulin after its characterisation by Frederick Sanger (1951). The insulin peptide hormone features two protein chains cross-linked by disulfide bridges from cysteine thiols. For this reason, Zervas undertook a systematic study on asymmetric cysteine-containing peptides. In his attempts he introduced new mercaptan protecting groups (e.g. trityl, benzhydryl or benzoyl), which finally made it possible to produce disulfide bridges in a controlled manner. This was a triumph for peptide chemistry in the lab, but could not be possibly scaled to industrial procedures. Building on this work, the first complete synthesis of insulin was simultaneously achieved in 1963 in RWTH Aachen University by Helmut Zahn and in the University of Pittsburgh by Panayotis Katsoyannis, a student of Zervas. Further work on asymmetrical cysteine polypeptides was also done in Athens by Iphigenia Photaki, another student of his.
Overall, the research work of Zervas spans across six decades (1925–1979) and amounts to 96 publications in international chemistry journals. | 0 | Organic Chemistry |
GUIDE-Seq has been shown to miss some off-targets, when compared to the genome-wide sequencing DIGENOME-Seq method, due to the nature of its targeting. Another caveat is that GUIDE-Seq has been observed to generate slightly different off-target sites depending on the cell line. This could be due to cell lines having different parental genetic origins, cell line specific mutations, or, in the case of some immortal cell lines such as K562s, having aneuploidy. This suggests that it would be pertinent for researchers to test multiple cell lines to validate efficacy and accuracy. GUIDE-Seq cannot be used to identify off-targets in vivo. | 1 | Biochemistry |
*[https://www.bgc-jena.mpg.de/paleo-biogeochem/HallmannLab_%40_MPI-BGC_Jena/Home.html Organic Paleobiogeochemistry] (Christian Hallmann)
*[https://www.bgc-jena.mpg.de/index.php/BTM/Home?jahr=&id=&gruppe=KLEI&limit=limit Biospheric Theory and Modelling] (Axel Kleidon)
*[https://www.bgc-jena.mpg.de/bgp/index.php/EmeritusEDS/EmeritusEDS Carbon Balance and Ecosystem Research] (Ernst-Detlef Schulze)
*[https://www.bgc-jena.mpg.de/functionalbiogeography/index.php/Main/HomePage Functional Biogeography] (Christian Wirth & Jens Kattge) | 9 | Geochemistry |
There are two types of bronze smelting techniques in early China, namely the section mold process and the lost-wax process. The earliest bronze ware found in China is the bronze knife (F20: 18) unearthed at the Majiayao in Linjia, Dongxiang, Gansu, and dated to about 3000 BC. This bronze knife uses the section mold process, which is spliced by two molds.
The section mold process is a commonly used bronze casting method in the Shang Dynasty, that is, the mud is selected, and after selecting, filtration, showering, deposition and other procedures, the mud is cooled to a moderate hardness as a backup, and then the mud is made according to the shape of the vessel to be made. There are two types of molds, which is inner mold and outer mold. The inner mold is only the shape of the bronze ware, without decoration; the outer model should consider the division of the bronze ware after casting in the future, that is, the block during the production of the clay model, and also engrave the inscriptions and inscriptions of the bronze ware decoration on the clay model. After the clay mold are done, put it in a cool place to dry in the shade, and then put it into the furnace for roasting. After the mold are heated, they become pottery molds unearthed during modern archaeological discoveries.
After the pottery mold is fired, do not rush out of the furnace. After the copper furnace has liquefied the required copper, the pottery mold that still has residual temperature is taken out and poured. In this way, the temperature difference between the copper liquid and the pottery mold is not large, and the pottery mold is not easy to burst. The quality of the finished product is relatively high. After the copper liquid is poured, remove the pottery molds and molds according to the blocks they were made. If they can't be removed, they can be broken with a hammer. The bronze will come out, and after grinding, it is the finished product. | 8 | Metallurgy |
Moroidin is one of several biologically active compounds isolated from the venom of Dendrocnide moroides, a member of the stinging nettle family. The plant stores its venom in silica hairs that break off when touched, delivering the toxins through the skin and inducing extreme pain. Moroidin also produces a similar pain response when injected subdermally, so it is thought to be partially responsible for the plant’s toxicity. However, moroidin injections are not as potent as injections of crude matter isolated from Dendrocnide moroides, suggesting that there are additional stinging toxins in the venom. | 0 | Organic Chemistry |
A fractional synthetic rate (FSR) is the rate at which a precursor compound is incorporated into a product per unit of product mass. The metric has been used to estimate the rate at which proteins, lipids, and lipoproteins are synthesized within humans and other animals. The formula used to calculate the FSR from a stable isotope tracer experiment is: | 1 | Biochemistry |
Internal conversion is a transition from a higher to a lower electronic state in a molecule or atom. It is sometimes called "radiationless de-excitation", because no photons are emitted. It differs from intersystem crossing in that, while both are radiationless methods of de-excitation, the molecular spin state for internal conversion remains the same, whereas it changes for intersystem crossing.
The energy of the electronically excited state is given off to vibrational modes of the molecule. The excitation energy is transformed into heat. | 7 | Physical Chemistry |
Water has an unusually high surface tension of 71.99 mN/m at 25 °C which is caused by the strength of the hydrogen bonding between water molecules. This allows insects to walk on water. | 2 | Environmental Chemistry |
In stereochemistry, the Klyne–Prelog system (named for William Klyne and Vladimir Prelog) for describing conformations about a single bond offers a more systematic means to unambiguously name complex structures, where the torsional or dihedral angles are not found to occur in 60° increments. Klyne notation views the placement of the substituent on the front atom as being in regions of space called anti/syn and clinal/periplanar relative to a reference group on the rear atom. A plus (+) or minus (−) sign is placed at the front to indicate the sign of the dihedral angle. Anti or syn indicates the substituents are on opposite sides or the same side, respectively. Clinal substituents are found within 30° of either side of a dihedral angle of 60° (from 30° to 90°), 120° (90°–150°), 240° (210°–270°), or 300° (270°–330°). Periplanar substituents are found within 30° of either 0° (330°–30°) or 180° (150°–210°). Juxtaposing the designations produces the following terms for the conformers of butane (see Alkane stereochemistry for an explanation of conformation nomenclature): gauche butane is syn-clinal (+sc or −sc, depending on the enantiomer), anti butane is anti-periplanar, and eclipsed butane is syn-periplanar. | 4 | Stereochemistry |
Van der Waals strain is strain resulting from Van der Waals repulsion when two substituents in a molecule approach each other with a distance less than the sum of their Van der Waals radii.
Van der Waals strain is also called Van der Waals repulsion and is related to steric hindrance. One of the most common forms of this strain is eclipsing hydrogen, in alkanes. | 4 | Stereochemistry |
Basic aluminium (or basic aluminum) is the name of more than one functional group consisting of aluminium with one or two hydroxy groups attached.
Dihydroxyaluminium, Al(OH), also known as dibasic aluminium, is monovalent, and known in these compounds:
*Dihydroxyaluminium acetate, (HO)AlCHCO, also known as aluminium monoacetate, basic aluminium monoacetate, dibasic aluminium acetate
*Dihydroxyaluminium sodium carbonate
*Aloglutamol, tris(hydroxymethyl)aminomethanegluconate dihydroxyaluminate
*Aluminium monostearate
*Carafate
*Sucralfate
Hydroxyaluminium, Al(OH), also known as monobasic aluminium or basic aluminium, is divalent, and known in these compounds:
*Hydroxyaluminium diacetate, HOAl(CHCO), also known as aluminium diacetate, basic aluminium diacetate, basic aluminium acetate, monobasic aluminium acetate
Aluminium, Al, is trivalent. Aluminium triacetate, Al(CHCO), is a complete molecule without any hydroxy groups, so it is not a "basic aluminium" compound.
Aluminium hydroxide, Al(OH), aluminium with three hydroxy groups attached, is a complete molecule, so it is not a "basic aluminium" compound.
Aluminium acetate is a name for three salts in the solid state: dihydroxyaluminium aluminium acetate, hydroxyaluminium diacetate, and aluminium triacetate, Al(CHCO). In aqueous solution, aluminium triacetate hydrolyses to form a mixture of the other two, so all solutions of all three can be referred to simply as "aluminium acetate", as the species co-exist and inter-convert in chemical equilibrium. | 0 | Organic Chemistry |
The coordination numbers are well defined for atoms in the interior of a crystal lattice: one counts the nearest neighbors in all directions. The number of neighbors of an interior atom is termed the bulk coordination number. For surfaces, the number of neighbors is more limited, so the surface coordination number is smaller than the bulk coordination number. Often the surface coordination number is unknown or variable. The surface coordination number is also dependent on the Miller indices of the surface. In a body-centered cubic (BCC) crystal, the bulk coordination number is 8, whereas, for the (100) surface, the surface coordination number is 4. | 4 | Stereochemistry |
Recombinant DNA vectors function as carriers of the foreign DNA. Plasmids are small, closed-circular DNA molecules that exist from the chromosomes of their host. Their replication is to be under stringent control (low copy number) or relaxed (high copy number). The restriction sites, called the multiple cloning site or polylinker, give a wide choice of restriction site for use in the cloning step. | 1 | Biochemistry |
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