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A typical optical transfection protocol is as follows:
1) Build an optical tweezers system with a high NA objective
2) Culture cells to 50-60% confluency
3) Expose cells to at least 10 µg/ml of plasmid DNA
4) Dose the plasma membrane of each cell with 10-40 ms of focussed laser, at a power of <100 mW at focus
5) Observe transient transfection 24-96h later
6) Add selective medium if the generation of stable colonies is desired | 1 | Biochemistry |
If analytes are too small to generate a readable signal for determining concentration, the assay matrix can be modified. CD/DVD based assays utilize the optical properties of gold. Gold nanoparticle bioconjugates are tracers used to increase the sensitivity of the assay. The gold nanoparticles can be identified with photometric or plasmonic detectors. The smaller the nanoparticles are, the more sensitive the assay becomes.
Silver enhancer solution is also used to increase the reflective properties of samples. Gold nanoparticles have catalytic properties which cause them to reduce silver ions to silver metal. The silver metal deposits on the analytes and causes signals to be amplified. Silver metal is more easily detectable by cameras, scanners, or other drives than is the analyte alone. Still, this enhancement procedure requires many additional reaction and washing steps which could lead to analytical errors. | 1 | Biochemistry |
Temperature is an important quantity to know for the understanding of the system. Material properties such as density, thermal conductivity, viscosity, and specific heat depend on temperature, and very high or low temperature can bring unexpected changes in the system. In solid, the heat equation can be used to obtain the temperature distribution inside the material with given geometries.
For steady-state and static case, the heat equation can be written as
where Fourier’s law of conduction is applied.
Applying boundary conditions gives a solution for the temperature distribution. | 7 | Physical Chemistry |
Claudins allow for Mg transport via the paracellular pathway; that is, it mediates the transport of the ion through the tight junctions between cells that form an epithelial cell layer. In particular, Claudin-16 allows the selective reuptake of Mg in the human kidney. Some patients with mutations in the CLDN19 gene also have altered magnesium transport.
The gene Claudin-16 was cloned by Simon et al. (1999), but only after a series of reports described the Mg flux itself with no gene or protein. The expression pattern of the gene was determined by RT-PCR, and was shown to be very tightly confined to a continuous region of the kidney tubule running from the medullary thick descending limb to the distal convoluted tubule. This localisation was consistent with the earlier reports for the location of Mg re-uptake by the kidney. Following the cloning, mutations in the gene were identified in patients with familial hypomagnesaemia with hypercalciuria and nephrocalcinosis, strengthening the links between the gene and the uptake of Mg. | 1 | Biochemistry |
The oldest form of mineral processing practiced since the Stone Age is hand-picking. Georgius Agricola also describes hand-picking is his book De re metallica in 1556. Sensor-based sorting is the automation and extension to hand picking. In addition to sensors that measure visible differences like color (and the further interpretation of the data regarding texture and shape), other sensors are available on industrial scale sorters that are able to measure differences invisible for the human eye (EM, XRT, NIR).
The principles of the technology and the first machinery has been developed since the 1920s (. Nevertheless, widely applied and standard technology it is only in the industrial minerals and gemstone segments. Mining is benefiting from the step change developments in sensing and computing technologies and from machine development in the recycling and food processing industries.
In 2002, Cutmore and Eberhard stated that the relatively small installed base of sensor-based sorters in mining is more a result of insufficient industry interest than any technical barriers to their effective use
Nowadays sensor-based sorting is beginning to reveal its potential in various applications in basically all segments of mineral production (industrial minerals, gemstones, base-metals, precious metals, ferrous metals, fuel). Precondition is physical liberation in coarse size ranges (~) to make physical separation possible. Either the product fraction, but more often the waste fraction needs to be liberated. If liberation is present, there is good potential that one of available detection technologies on today's sensor-based sorters can positively or negatively identify one of the two desired fractions. | 3 | Analytical Chemistry |
The Kröhnke pyridine synthesis provides a fairly general method for generating substituted pyridines using pyridine itself as a reagent which does not become incorporated into the final product. The reaction of pyridine with bromomethyl ketones gives the related pyridinium salt, wherein the methylene group is highly acidic. This species undergoes a Michael-like addition to α,β-unsaturated carbonyls in the presence of ammonium acetate to undergo ring closure and formation of the targeted substituted pyridine as well as pyridinium bromide.
The Ciamician–Dennstedt rearrangement entails the ring-expansion of pyrrole with dichlorocarbene to 3-chloropyridine.
In the Gattermann–Skita synthesis, a malonate ester salt reacts with dichloromethylamine.
Other methods include the Boger pyridine synthesis and Diels–Alder reaction of an alkene and an oxazole. | 0 | Organic Chemistry |
In 1698, the English mechanical designer Thomas Savery invented a pumping appliance that used steam to draw water directly from a well by means of a vacuum created by condensing steam. The appliance was also proposed for draining mines, but it could only draw fluid up approximately 25 feet, meaning it had to be located within this distance of the mine floor being drained. As mines became deeper, this was often impractical. It also consumed a large amount of fuel compared with later engines.
The solution to draining deep mines was found by Thomas Newcomen who developed an "atmospheric" engine that also worked on the vacuum principle. It employed a cylinder containing a movable piston connected by a chain to one end of a rocking beam that worked a mechanical lift pump from its opposite end. At the bottom of each stroke, steam was allowed to enter the cylinder below the piston. As the piston rose within the cylinder, drawn upward by a counterbalance, it drew in steam at atmospheric pressure. At the top of the stroke the steam valve was closed, and cold water was briefly injected into the cylinder as a means of cooling the steam. This water condensed the steam and created a partial vacuum below the piston. The atmospheric pressure outside the engine was then greater than the pressure within the cylinder, thereby pushing the piston into the cylinder. The piston, attached to a chain and in turn attached to one end of the "rocking beam", pulled down the end of the beam, lifting the opposite end of the beam. Hence, the pump deep in the mine attached to opposite end of the beam via ropes and chains was driven. The pump pushed, rather than pulled the column of water upward, hence it could lift water any distance. Once the piston was at the bottom, the cycle repeated.
The Newcomen engine was more powerful than the Savery engine. For the first time water could be raised from a depth of over 300 feet. The first example from 1712 was able to replace a team of 500 horses that had been used to pump out the mine. Seventy-five Newcomen pumping engines were installed at mines in Britain, France, Holland, Sweden and Russia. In the next fifty years only a few small changes were made to the engine design. It was a great advancement.
While Newcomen engines brought practical benefits, they were inefficient in terms of the use of energy to power them. The system of alternately sending jets of steam, then cold water into the cylinder meant that the walls of the cylinder were alternately heated, then cooled with each stroke. Each charge of steam introduced would continue condensing until the cylinder approached working temperature once again. So at each stroke part of the potential of the steam was lost. | 7 | Physical Chemistry |
In heterogeneous catalysis the catalyst is in a different phase from the reactants. Heterogeneous photocatalysis is a discipline which includes a large variety of reactions: mild or total oxidations, dehydrogenation, hydrogen transfer, O–O and deuterium-alkane isotopic exchange, metal deposition, water detoxification, and gaseous pollutant removal.
Most heterogeneous photocatalysts are transition metal oxides and semiconductors. Unlike metals, which have a continuum of electronic states, semiconductors possess a void energy region where no energy levels are available to promote recombination of an electron and hole produced by photoactivation in the solid. The difference in energy between the filled valence band and the empty conduction band in the MO diagram of a semiconductor is the band gap. When the semiconductor absorbs a photon with energy equal to or greater than the material's band gap, an electron excites from the valence band to the conduction band, generating a electron hole in the valence band. This electron-hole pair is an exciton. The excited electron and hole can recombine and release the energy gained from the excitation of the electron as heat. Such exciton recombination is undesirable and higher levels cost efficiency. Efforts to develop functional photocatalysts often emphasize extending exciton lifetime, improving electron-hole separation using diverse approaches that may rely on structural features such as phase hetero-junctions (e.g. anatase-rutile interfaces), noble-metal nanoparticles, silicon nanowires and substitutional cation doping. The ultimate goal of photocatalyst design is to facilitate reactions of the excited electrons with oxidants to produce reduced products, and/or reactions of the generated holes with reductants to produce oxidized products. Due to the generation of positive holes (h) and excited electrons (e), oxidation-reduction reactions take place at the surface of semiconductors irradiated with light.
In one mechanism of the oxidative reaction, holes react with the moisture present on the surface and produce a hydroxyl radical. The reaction starts by photo-induced exciton generation in the metal oxide (MO) surface by photon (hv) absorption:
:MO + hν → MO (h + e)
Oxidative reactions due to photocatalytic effect:
:h + HO → H + •OH
:2 h + 2 HO → 2 H + HO
:HO→ 2 •OH
Reductive reactions due to photocatalytic effect:
:e + O → •O
:•O + HO• + H → HO + O
:HO → 2 •OH
Ultimately, both reactions generate hydroxyl radicals. These radicals are oxidative in nature and nonselective with a redox potential of E = +3.06 V. This is significantly greater than many common organic compounds, which typically are not greater than E = +2.00 V. This results in the non-selective oxidative behavior of these radicals.
Titanium dioxide|, a wide band-gap semiconductor, is a common choice for heterogeneous catalysis. Inertness to chemical environment and long-term photostability has made an important material in many practical applications. Investigation of TiO in the rutile (bandgap 3.0 eV) and anatase (bandgap 3.2 eV) phases is common. The absorption of photons with energy equal to or greater than the band gap of the semiconductor initiates photocatalytic reactions. This produces electron-hole (e /h) pairs:
Where the electron is in the conduction band and the hole is in the valence band. The irradiated particle can behave as an electron donor or acceptor for molecules in contact with the semiconductor. It can participate in redox reactions with adsorbed species, as the valence band hole is strongly oxidizing while the conduction band electron is strongly reducing. | 5 | Photochemistry |
While it is important to note that the process of remineralization is a series of complex biochemical pathways [within microbes], it can often be simplified as a series of one-step processes for ecosystem-level models and calculations. A generic form of these reactions is shown by:
The above generic equation starts with two reactants: some piece of organic matter (composed of organic carbon) and an oxidant. Most organic carbon exists in a reduced form which is then oxidized by the oxidant (such as ) into and energy that can be harnessed by the organism. This process generally produces , water and a collection of simple nutrients like nitrate or phosphate that can then be taken up by other organisms. The above general form, when considering as the oxidant, is the equation for respiration. In this context specifically, the above equation represents bacterial respiration though the reactants and products are essentially analogous to the short-hand equations used for multi-cellular respiration. | 9 | Geochemistry |
The Joule expansion (a subset of free expansion) is an irreversible process in thermodynamics in which a volume of gas is kept in one side of a thermally isolated container (via a small partition), with the other side of the container being evacuated. The partition between the two parts of the container is then opened, and the gas fills the whole container.
The Joule expansion, treated as a thought experiment involving ideal gases, is a useful exercise in classical thermodynamics. It provides a convenient example for calculating changes in thermodynamic quantities, including the resulting increase in entropy of the universe (entropy production) that results from this inherently irreversible process. An actual Joule expansion experiment necessarily involves real gases; the temperature change in such a process provides a measure of intermolecular forces.
This type of expansion is named after James Prescott Joule who used this expansion, in 1845, in his study for the mechanical equivalent of heat, but this expansion was known long before Joule e.g. by John Leslie, in the beginning of the 19th century, and studied by Joseph-Louis Gay-Lussac in 1807 with similar results as obtained by Joule.
The Joule expansion should not be confused with the Joule–Thomson expansion or throttling process which refers to the steady flow of a gas from a region of higher pressure to one of lower pressure via a valve or porous plug. | 7 | Physical Chemistry |
The atmospheric properties of exoplanets are of particular importance, as atmospheres provide the most likely observables for the near future, including habitability indicators and biosignatures. Over billions of years, the processes of life on a planet would result in a mixture of chemicals unlike anything that could form in an ordinary chemical equilibrium. For example, large amounts of oxygen and small amounts of methane are generated by life on Earth.
An exoplanet's color—or reflectance spectrum—can also be used as a biosignature due to the effect of pigments that are uniquely biologic in origin such as the pigments of phototrophic and photosynthetic life forms. Scientists use the Earth as an example of this when looked at from far away (see Pale Blue Dot) as a comparison to worlds observed outside of our solar system. Ultraviolet radiation on life forms could also induce biofluorescence in visible wavelengths that may be detected by the new generation of space observatories under development.
Some scientists have reported methods of detecting hydrogen and methane in extraterrestrial atmospheres. Habitability indicators and biosignatures must be interpreted within a planetary and environmental context. For example, the presence of oxygen and methane together could indicate the kind of extreme thermochemical disequilibrium generated by life. Two of the top 14,000 proposed atmospheric biosignatures are dimethyl sulfide and chloromethane (). An alternative biosignature is the combination of methane and carbon dioxide.
The detection of phosphine in the atmosphere of Venus is being investigated as a possible biosignature. | 2 | Environmental Chemistry |
A full description of non-linear inverse Compton scattering must include some effects related to the quantization of light and matter. The principal ones are listed below.
* Inclusion of the discretization of the emitted radiation, i.e. the introduction of photons with respect to the continuous description of the classical limit. This effect does not change quantitatively the emission features but changes how the emitted radiation is interpreted. A parameter equivalent to can be introduced for the photon of frequency and it is called photon quantum parameter:where is the photon four-wavevector and is the three-dimensional wavevector. In the limit in which the particle approaches the speed of light, the ratio between and is equal to:From the Frequency distribution of radiated energy one can get a rate of high-energy photon emission distributed in as a function of and but still valid in the classical limit:
where stands for the McDonald functions. The mean energy of the emitted photon is given by . Consequently, a large Lorentz factor and intense fields increase the chance of producing high-energy photons. goes as because of this formula.
* The effect of radiation reaction, due to photon recoil. The electron energy after the interaction process reduces because part of it is delivered to the emitted photon and the maximum energy achievable by the emitted photon cannot be higher than the electron kinetic energy. This effect is not taken into account in non-linear Thomson scattering in which the electron energy is supposed to remain almost unaltered in energy such as in elastic scattering. Quantum radiation reaction effects become important when the emitted photon energy approaches the electron energy. Since , if the classical limit of NICS is a valid description, while for the energy of the emitted photon is of the order of the electron energy and photon recoil is very relevant.
* The quantization of the motion of the electron and spin effects. An accurate description of non-linear inverse Compton scattering is made considering the electron dynamics described with the Dirac equation in presence of an electromagnetic field. | 7 | Physical Chemistry |
Other uses include making custom-shaped apertures and blocks (for example, electron-beam cutouts and lung blocks) for medical radiation treatment, and making casts of keys that are hard to otherwise duplicate.
Like other fusible alloys, e.g. Roses metal, Woods metal can be used as a heat-transfer medium in hot baths. Hot baths with Roses and Woods metals are not used routinely but are employed at temperatures above .
Wood's metal has a modulus of elasticity of 12.7 GPa and a yield strength of 26.2 MPa. | 8 | Metallurgy |
A post–September 11 development, explosive detection systems have become a part of all US airports. These systems run on a host of technologies, many of them based on GC–MS. There are only three manufacturers certified by the FAA to provide these systems, one of which is Thermo Detection (formerly Thermedics), which produces the EGIS, a GC–MS-based line of explosives detectors. The other two manufacturers are Barringer Technologies, now owned by Smith's Detection Systems, and Ion Track Instruments, part of General Electric Infrastructure Security Systems. | 3 | Analytical Chemistry |
There are ten assay offices at:
Polish Assay Offices test and mark precious metal alloy articles (gold, silver and platinum group metals). They also supervise compliance with Hallmarking Law at processing plants and precious metal alloy sales points. All Assay Offices must report to the Central Office of Measures. | 3 | Analytical Chemistry |
ASBMB has hosted a yearly meeting each year since 1956. It has also coordinated the joint ComBio meeting with societies in related research fields since 1999. It also supports smaller special interest group meetings, symposia, workshops, conferences, and school science competitions. | 1 | Biochemistry |
It has been observed that the stereoelectronic environment at the β-carbon of can also direct asymmetric induction. A number of predictive models have evolved over the years to define the stereoselectivity of such reactions. | 4 | Stereochemistry |
Faradaic losses are experienced by both electrolytic and galvanic cells when electrons or ions participate in unwanted side reactions. These losses appear as heat and/or chemical byproducts.
An example can be found in the oxidation of water to oxygen at the positive electrode in electrolysis. Some electrons are diverted to the production of hydrogen peroxide. The fraction of electrons so diverted represent a faradaic loss and vary in different apparatuses.
Even when the proper electrolysis products are produced, losses can still occur if the products are permitted to recombine. During water electrolysis, the desired products (H and O), could recombine to form water. This could realistically happen in the presence of catalytic materials such as platinum or palladium commonly used as electrodes. Failure to account for this Faraday-efficiency effect has been identified as the cause of the misidentification of positive results in cold fusion experiments.
Proton exchange membrane fuel cells provide another example of faradaic losses when some of the electrons separated from hydrogen at the anode leak through the membrane and reach the cathode directly instead of passing through the load and performing useful work. Ideally the electrolyte membrane would be a perfect insulator and prevent this from happening.
An especially familiar example of faradaic loss is the self-discharge that limits battery shelf-life. | 7 | Physical Chemistry |
Resonance has a deeper significance in the mathematical formalism of valence bond theory (VB). Quantum mechanics requires that the wavefunction of a molecule obey its observed symmetry. If a single contributing structure does not achieve this, resonance is invoked.
For example, in benzene, valence bond theory begins with the two Kekulé structures which do not individually possess the sixfold symmetry of the real molecule. The theory constructs the actual wave function as a linear superposition of the wave functions representing the two structures. As both Kekulé structures have equal energy, they are equal contributors to the overall structure – the superposition is an equally weighted average, or a 1:1 linear combination of the two in the case of benzene. The symmetric combination gives the ground state, while the antisymmetric combination gives the first excited state, as shown.
In general, the superposition is written with undetermined coefficients, which are then variationally optimized to find the lowest possible energy for the given set of basis wave functions. When more contributing structures are included, the molecular wave function becomes more accurate and more excited states can be derived from different combinations of the contributing structures. | 7 | Physical Chemistry |
In general, reactions of organic free radicals (•C(CH)(X)R) with metal-centered radicals (M•) either produce an organometallic complex (reaction 1) or a metal hydride (M-H) and an olefin (CH=C(X)R) by the metallo radical M• abstracting a β-hydrogen from the organic radical •C(CH)(X)R (reaction 2).
These organo-radical reactions with metal complexes provides several mechanisms to control radical polymerization of monomers CH=CH(X). A wide range of metal-centered radicals and organo-metal complexes manifest at least a portion of these reactions. Various transition metal species, including complexes of Cr(I), Mo(III), Fe(I), V(0), Ti(III), and Co(II) have been demonstrated to control molecular weights in radical polymerization of olefins.
The olefin generating reaction 2 can become catalytic, and such catalytic chain transfer reactions are generally used to reduce the polymer molecular weight during the radical polymerization process. Mechanistically, catalytic chain transfer involves hydrogen atom transfer from the organic growing polymeryl radical to cobalt(II), thus leaving a polymer vinyl-end group and a cobalt-hydride species. The Co(por)(H) species has no cis-vacant site for direct insertion of a new olefinic monomer into the Co-H bond to finalize the chain-transfer process, and hence the required olefin insertion also proceeds via a radical pathway.
The best recognized chain transfer catalysts are low spin cobalt(II) complexes and organo-cobalt(III) species, which function as latent storage sites for organo-radicals required to obtain living radical polymerization by several pathways.
The major products of catalytic chain transfer polymerization are vinyl terminated polymer chains. One of the major drawbacks of the process is that catalytic chain transfer polymerization does not produce macromonomers of use in free radical polymerizations, but instead produces addition-fragmentation agents. When a growing polymer chain reacts with the addition fragmentation agent the radical end-group attacks the vinyl bond and forms a bond. However, the resulting product is so hindered that the species undergoes fragmentation, leading eventually to telechelic species.
These addition fragmentation chain transfer agents do form graft copolymers with styrenic and acrylate species however they do so by first forming block copolymers and then incorporating these block copolymers into the main polymer backbone. While high yields of macromonomers are possible with methacrylate monomers, low yields are obtained when using catalytic chain transfer agents during the polymerization of acrylate and styrenic monomers. This has been seen to be due to the interaction of the radical centre with the catalyst during these polymerization reactions. | 7 | Physical Chemistry |
Metal whiskering is a phenomenon that occurs in electrical devices when metals form long whisker-like projections over time. Tin whiskers were noticed and documented in the vacuum tube era of electronics early in the 20th century in equipment that used pure, or almost pure, tin solder in their production. It was noticed that small metal hairs or tendrils grew between metal solder pads, causing short circuits. Metal whiskers form in the presence of compressive stress. Germanium, zinc, cadmium, and even lead whiskers have been documented. Many techniques are used to mitigate the problem, including changes to the annealing process (heating and cooling), the addition of elements like copper and nickel, and the inclusion of conformal coatings. Traditionally, lead has been added to slow down whisker growth in tin-based solders.
Following the Restriction of Hazardous Substances Directive (RoHS), the European Union banned the use of lead in most consumer electronic products from 2006 due to health problems associated with lead and the "high-tech trash" problem, leading to a re-focusing on the issue of whisker formation in lead-free solders. | 8 | Metallurgy |
Radicals are either (1) formed from spin-paired molecules or (2) from other radicals. Radicals are formed from spin-paired molecules through homolysis of weak bonds or electron transfer, also known as reduction. Radicals are formed from other radicals through substitution, addition, and elimination reactions. | 2 | Environmental Chemistry |
DNA extraction is frequently a preliminary step in many diagnostic procedures used to identify environmental viruses and bacteria and diagnose illnesses and hereditary diseases. These methods consist of, but are not limited to:
Fluorescence In Situ Hybridization (FISH) technique was developed in the 1980s. The basic idea is to use a nucleic acid probe to hybridize nuclear DNA from either interphase cells or metaphase chromosomes attached to a microscopic slide. It is a molecular method used, among other things, to recognize and count particular bacterial groupings.
To recognize, define, and quantify the geographical and temporal patterns in marine bacterioplankton communities, researchers employ a technique called terminal restriction fragment length polymorphism (T-RFLP).
Sequencing: Whole or partial genomes and other chromosomal components, ended for comparison with previously published sequences. | 1 | Biochemistry |
PPA is known as a self-immolative material which depolymerizes through endcap cleavage in response to a specific stimulus. For this reason, several PPA polymers with different endcaps have been synthesized and used as self-immolative materials for sensing toxic and specific compounds. | 7 | Physical Chemistry |
Differential static light scatter (DSLS) is a term coined to represent the change in total light scatter of a system over time or temperature in a static environment.
Static light scattering or SLS and its many types are well outlined in literature and is the base principal for DSLS but varies specifically in that the difference (before and after) is the focus of this measurement. Typically the system will commence measurement at T and over the course of time measure the change in light scatter. One of the more practical applications of DSLS is in the area of proteomic research and protein based chemistry. Solution conditions can be varied across samples of a specific protein in a screening scenario and the system can be kept at either a static temperature or be ramped up, or in some cases down. The change will be observed over time and the focus of the calculation is on the amount of change in signal from T to T . This method of analysis provides researchers with data that helps them predict a protein or compound's stability in various conditions and further, in the case of proteomic structural work, can help identify the best protein candidates, and their optimal conditions to crystallize and thereby undergo x-ray crystallography for structural analysis.
There are other technologies or techniques using similar concepts such as DLS (dynamic light scattering) to obtain this information with the help of fluorophores and the use of lasers for excitation however the primary focus in this arena is on particle sizing. Also DLS has a greater focus in flow-based instrumentation. Many proteins are discovered on an annual basis and in the field of drug discovery it is very important characterize the structure of a novel peptides as well as the best conditions to keep them in solution. Because of this staggering number of potential therapeutics churning out of this research sector today there is a strong need for instrumentation to best capture this data and to date there are a few solutions that are DSLS focused. One such oriented instrument designed for high throughput scenarios utilizing standard HTS (high-throughput screening) SBS standard type plates (or automation friendly) is the StarGazer2.
There are other solutions also available that have either wider focus to include particular sizing and Zeta potential but are limited but are limited by how many samples can be run at once, thus, non-HTS. As DSLS in principal measures particles as they either aggregate (or grow larger) or, in theory, breakdown and grow smaller, this technology and method of measurement will pull in a number of great applications in the future in the food and beverage, or environmental sector as the technology is stretched into new applications beyond proteomics. | 7 | Physical Chemistry |
Pdr1p and Pdr3p is a part of Gal4 transcription factor family due to their zinc-finger DNA binding motif, which is located in N-terminus end of Pdr1p. Pdr1p also contains a long internal region of many inhibitory domains and possess a C-terminal transcription activation domain (amino acids 879–1036). The transcriptional activation domain is rich in glutamine and asparagine, which is theorized to facilitate in protein-protein interaction via hydrogen bonding. A study found that DNA-binding domain of Pdr1p was sufficient for recognizing its endogenous target genes. Strong drug resistance phenotype of yeasts with pdr1-3 is speculated due to its inability to bind to ligands that otherwise cause conformational change to inhibit the transcriptional activity of Pdr1p. | 1 | Biochemistry |
Zinc finger nucleases are genetically engineered enzymes that combine fusing a zinc finger DNA-binding domain on a DNA-cleavage domain. These are also combined with CRISPR-CAS9 or TALENs to gain a sequence-specific addition, or deletion, within the genome of more complex cells and organisms. | 1 | Biochemistry |
Stopped-flow is an experimental technique for studying chemical reactions with a half time of the order of 1 ms, introduced by Britton Chance and extended by Quentin Gibson (Other techniques, such as the temperature-jump method, are available for much faster processes.) | 7 | Physical Chemistry |
A DNA microarray is a collection of spots attached to a solid support such as a microscope slide where each spot contains one or more single-stranded DNA oligonucleotide fragments. Arrays make it possible to put down large quantities of very small (100 micrometre diameter) spots on a single slide. Each spot has a DNA fragment molecule that is complementary to a single DNA sequence. A variation of this technique allows the gene expression of an organism at a particular stage in development to be qualified (expression profiling). In this technique the RNA in a tissue is isolated and converted to labeled complementary DNA (cDNA). This cDNA is then hybridized to the fragments on the array and visualization of the hybridization can be done. Since multiple arrays can be made with exactly the same position of fragments, they are particularly useful for comparing the gene expression of two different tissues, such as a healthy and cancerous tissue. Also, one can measure what genes are expressed and how that expression changes with time or with other factors.
There are many different ways to fabricate microarrays; the most common are silicon chips, microscope slides with spots of ~100 micrometre diameter, custom arrays, and arrays with larger spots on porous membranes (macroarrays). There can be anywhere from 100 spots to more than 10,000 on a given array. Arrays can also be made with molecules other than DNA. | 1 | Biochemistry |
For high energy photons it is useful to distinguish between small and large angle scattering. For large angles, where , the scatter ratio is large and
showing that the (large angle) differential cross section is inversely proportional to the photon energy.
The differential cross section has a constant peak in the forward direction:
independent of . From the large angle analysis it follows that this peak can only extend to about . The forward peak is thus confined to a small solid angle of approximately , and we may conclude that the total small angle cross section decreases with . | 7 | Physical Chemistry |
Interference of atom matter waves was first observed by Esterman and Stern in 1930, when a Na beam was diffracted off a surface of NaCl. The short de Broglie wavelength of atoms prevented progress for many years until two technological breakthroughs revived interest: microlithography allowing precise small devices and laser cooling allowing atoms to be slowed, increasing their de Broglie wavelength.
Until 2006, the resolution of imaging systems based on atomic beams was not better than that of an optical microscope, mainly due to the poor performance of the focusing elements. Such elements use small numerical aperture; usually, atomic mirrors use grazing incidence, and the reflectivity drops drastically with increase of the grazing angle; for efficient normal reflection, atoms should be ultracold, and dealing with such atoms usually involves magnetic, magneto-optical or optical traps.
At the beginning of the 21st century scientific publications about "atom nano-optics", evanescent field lenses and ridged mirrors
showed significant improvement.
In particular, an atomic hologram can be realized. | 7 | Physical Chemistry |
Cap analysis of gene expression (CAGE) is a gene expression technique used in molecular biology to produce a snapshot of the 5′ end of the messenger RNA population in a biological sample (the transcriptome). The small fragments (historically 27 nucleotides long, but now limited only by sequencing technologies) from the very beginnings of mRNAs (5' ends of capped transcripts) are extracted, reverse-transcribed to cDNA, PCR amplified (if needed) and sequenced. CAGE was first published by Hayashizaki, Carninci and co-workers in 2003.
CAGE has been extensively used within the FANTOM research projects. | 1 | Biochemistry |
The letters s,t,u are also used in the terms s-channel (timelike channel), t-channel, and u-channel (both spacelike channels). These channels represent different Feynman diagrams or different possible scattering events where the interaction involves the exchange of an intermediate particle whose squared four-momentum equals s,t,u, respectively.
For example, the s-channel corresponds to the particles 1,2 joining into an intermediate particle that eventually splits into 3,4: The t-channel represents the process in which the particle 1 emits the intermediate particle and becomes the final particle 3, while the particle 2 absorbs the intermediate particle and becomes 4. The u-channel is the t-channel with the role of the particles 3,4 interchanged.
When evaluating a Feynman amplitude one often finds scalar products of the external four momenta. One can use the Mandelstam variables to simplify these:
Where is the mass of the particle with corresponding momentum . | 7 | Physical Chemistry |
Plasmid copies are paired around a centromere-like site and then separated in the two daughter cells. Partition systems involve three elements, organized in an auto-regulated operon:
* A centromere-like DNA site
* Centromere binding proteins (CBP)
* The motor protein
The centromere-like DNA site is required in cis for plasmid stability. It often contains one or more inverted repeats which are recognized by multiple CBPs. This forms a nucleoprotein complex termed the partition complex. This complex recruits the motor protein, which is a nucleotide triphosphatase (NTPase). The NTPase uses energy from NTP binding and hydrolysis to directly or indirectly move and attach plasmids to specific host location (e.g. opposite bacterial cell poles).
The partition systems are divided in four types, based primarily on the type of NTPases:
* Type I : Walker type P-loop ATPase
* Type II : Actin-like ATPase
* Type III : tubulin-like GTPase
* Type IV : No NTPase | 1 | Biochemistry |
Researchers have extensively investigated the use of hematite (α-FeO) in PEC water-splitting devices due to its low cost, ability to be n-type doped, and band gap (2.2eV). However, performance is plagued by poor conductivity and crystal anisotropy. Some researchers have enhanced catalytic activity by forming a layer of co-catalysts on the surface. Co-catalysts include cobalt-phosphate and iridium oxide, which is known to be a highly active catalyst for the oxygen evolution reaction. | 5 | Photochemistry |
The azo-transfer compounds, trifluoromethanesulfonyl azide and imidazole-1-sulfonyl azide react with amines to give the corresponding azides. Diazo transfer onto amines using trifluoromethanesulfonyl azide () and Tosyl azide () has been reported. | 0 | Organic Chemistry |
Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites. The oldest preserved chitin dates to the Oligocene, about , consisting of a beetle encased in amber. | 1 | Biochemistry |
HDAC8 has been found to be most similar to HDAC3. Its major feature is its catalytic domain which contains an NLS region in the center. Two transcripts of this HDAC have been found which include a 2.0kb transcript and a 2.4kb transcript. Unlike the other HDAC molecules, when purified, this HDAC showed to be enzymatically active. At this point, due to its recent discovery, it is not yet known if it is regulated by co-repressor protein complexes. Northern blots have revealed that different tissue types show varying degrees of HDAC8 expression but has been observed in smooth muscles and is thought to contribute to contractility. | 0 | Organic Chemistry |
Spectrophotometry is an important technique used in many biochemical experiments that involve DNA, RNA, and protein isolation, enzyme kinetics and biochemical analyses. Since samples in these applications are not readily available in large quantities, they are especially suited to be analyzed in this non-destructive technique. In addition, precious sample can be saved by utilizing a micro-volume platform where as little as 1uL of sample is required for complete analyses.
A brief explanation of the procedure of spectrophotometry includes comparing the absorbency of a blank sample that does not contain a colored compound to a sample that contains a colored compound. This coloring can be accomplished by either a dye such as Coomassie Brilliant Blue G-250 dye measured at 595 nm or by an enzymatic reaction as seen between β-galactosidase and ONPG (turns sample yellow) measured at 420 nm. The spectrophotometer is used to measure colored compounds in the visible region of light (between 350 nm and 800 nm), thus it can be used to find more information about the substance being studied.
In biochemical experiments, a chemical and/or physical property is chosen and the procedure that is used is specific to that property to derive more information about the sample, such as the quantity, purity, enzyme activity, etc.
Spectrophotometry can be used for a number of techniques such as determining optimal wavelength absorbance of samples, determining optimal pH for absorbance of samples, determining concentrations of unknown samples, and determining the pKa of various samples. Spectrophotometry is also a helpful process for protein purification and can also be used as a method to create optical assays of a compound. Spectrophotometric data can also be used in conjunction with the Beer–Lambert Equation, , to determine various relationships between transmittance and concentration, and absorbance and concentration. Because a spectrophotometer measures the wavelength of a compound through its color, a dye-binding substance can be added so that it can undergo a color change and be measured. It is possible to know the concentrations of a two-component mixture using the absorption spectra of the standard solutions of each component. To do this, it is necessary to know the extinction coefficient of this mixture at two wavelengths and the extinction coefficients of solutions that contain the known weights of the two components. In addition to the traditional Beer-Lamberts law model, cuvette based label free spectroscopy can be used, which add an optical filter in the pathways of the light, enabling the spectrophotometer to quantify concentration, size and refractive index of samples following the hands law. Spectrophotometers have been developed and improved over decades and have been widely used among chemists. Additionally, Spectrophotometers are specialized to measure either UV or Visible light wavelength absorbance values. It is considered to be a highly accurate instrument that is also very sensitive and therefore extremely precise, especially in determining color change. This method is also convenient for use in laboratory experiments because it is an inexpensive and relatively simple process. | 7 | Physical Chemistry |
Advantages of HPTLC:
* Provides straightforward information about effects arising from individual compounds in complex or natural samples separated in parallel.
* Combines chromatographic separation with effect-directed detection using enzymatic or biological assays.
* Helps to select important compounds from a sample for further characterization using high-resolution mass spectrometry.
* Offers unique benefits such as super-hyphenation, minimum sample preparation requirements, detection of multi-modulating compounds, and distinguishing agonistic versus antagonistic effects. | 3 | Analytical Chemistry |
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Water () is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue. It is by far the most studied chemical compound and is described as the "universal solvent" and the "solvent of life". It is the most abundant substance on the surface of Earth and the only common substance to exist as a solid, liquid, and gas on Earth's surface. It is also the third most abundant molecule in the universe (behind molecular hydrogen and carbon monoxide).
Water molecules form hydrogen bonds with each other and are strongly polar. This polarity allows it to dissociate ions in salts and bond to other polar substances such as alcohols and acids, thus dissolving them. Its hydrogen bonding causes its many unique properties, such as having a solid form less dense than its liquid form, a relatively high boiling point of 100 °C for its molar mass, and a high heat capacity.
Water is amphoteric, meaning that it can exhibit properties of an acid or a base, depending on the pH of the solution that it is in; it readily produces both hydron (chemistry)| and hydroxide| ions. Related to its amphoteric character, it undergoes self-ionization. The product of the activities, or approximately, the concentrations of and is a constant, so their respective concentrations are inversely proportional to each other. | 2 | Environmental Chemistry |
Helmchens Postulates are the theoretical models used to predict the elution order and extent of separation of diastereomers (including those formed from CDAs) that are adsorbed onto a surface. Although Helmchens postulates are specific for amides on silica gel using liquid chromatography, the postulates provide fundamental guidelines for other molecules. Helmchen's Postulates are:
#Conformations are the same in solution and when adsorbed.
#Diastereomers bind to surfaces (silica gel in normal phase chromatography) mainly with hydrogen bonding.
#Significant resolution of diastereomers is only expected when molecules can adsorb to silica through two contact points (two hydrogen bonds). This interaction can be perturbed by substituents.
#Diastereomers with bulky substituents on the alpha carbon (R2) and on the nitrogen (R1) can shield the hydrogen bonding with the surface, thus the molecule will be eluted before similar molecules with smaller substituents.
Helmchen's postulates have been proven to be applicable to other functional groups such as: carbamates, esters, and epoxides. | 4 | Stereochemistry |
The discovery of plant viruses causing disease is often accredited to A. Mayer (1886) working in the Netherlands demonstrated that the sap of mosaic obtained from tobacco leaves developed mosaic symptom when injected in healthy plants. However the infection of the sap was destroyed when it was boiled. He thought that the causal agent was bacteria. However, after larger inoculation with a large number of bacteria, he failed to develop a mosaic symptom.
In 1898, Martinus Beijerinck, who was a Professor of Microbiology at the Technical University the Netherlands, put forth his concepts that viruses were small and determined that the "mosaic disease" remained infectious when passed through a Chamberland filter-candle. This was in contrast to bacteria microorganisms, which were retained by the filter. Beijerinck referred to the infectious filtrate as a "contagium vivum fluidum", thus the coinage of the modern term "virus".
After the initial discovery of the viral concept there was need to classify any other known viral diseases based on the mode of transmission even though microscopic observation proved fruitless. In 1939 Holmes published a classification list of 129 plant viruses. This was expanded and in 1999 there were 977 officially recognized, and some provisional, plant virus species.
The purification (crystallization) of TMV was first performed by Wendell Stanley, who published his findings in 1935, although he did not determine that the RNA was the infectious material. However, he received the Nobel Prize in Chemistry in 1946. In the 1950s a discovery by two labs simultaneously proved that the purified RNA of the TMV was infectious which reinforced the argument. The RNA carries genetic information to code for the production of new infectious particles.
More recently virus research has been focused on understanding the genetics and molecular biology of plant virus genomes, with a particular interest in determining how the virus can replicate, move and infect plants. Understanding the virus genetics and protein functions has been used to explore the potential for commercial use by biotechnology companies. In particular, viral-derived sequences have been used to provide an understanding of novel forms of resistance. The recent boom in technology allowing humans to manipulate plant viruses may provide new strategies for production of value-added proteins in plants. | 1 | Biochemistry |
The solute carrier family 18 member 2 (SLC18A2) also known as vesicular monoamine transporter 2 (VMAT2) is a protein that in humans is encoded by the SLC18A2 gene. SLC18A2 is an integral membrane protein that transports monoamines—particularly neurotransmitters such as dopamine, norepinephrine, serotonin, and histamine—from cellular cytosol into synaptic vesicles. In nigrostriatal pathway and mesolimbic pathway dopamine-releasing neurons, SLC18A2 function is also necessary for the vesicular release of the neurotransmitter GABA. | 1 | Biochemistry |
GGT is predominantly used as a diagnostic marker for liver disease. Elevated serum GGT activity can be found in diseases of the liver, biliary system, pancreas and kidneys. Latent elevations in GGT are typically seen in patients with chronic viral hepatitis infections often taking 12 months or more to present.
Individual test results should always be interpreted using the reference range from the laboratory that performed the test, though example reference ranges are 15–85 IU/L for men, and 5–55 IU/L for women. GGT is similar to alkaline phosphatase (ALP) in detecting disease of the biliary tract. Indeed, the two markers correlate well, though there are conflicting data about whether GGT has better sensitivity. In general, ALP is still the first test for biliary disease. The main value of GGT is in verifying that ALP elevations are, in fact, due to biliary disease; ALP can also be increased in certain bone diseases, but GGT is not. | 1 | Biochemistry |
Thiols, or more specific their conjugate bases, are readily alkylated to give sulfides:
:RSH + R′Br + B → RSR′ + [HB]Br (B = base) | 0 | Organic Chemistry |
C5a is a protein fragment released from cleavage of complement component C5 by protease C5-convertase into C5a and C5b fragments. C5b is important in late events of the complement cascade, an orderly series of reactions which coordinates several basic defense mechanisms, including formation of the membrane attack complex (MAC), one of the most basic weapons of the innate immune system, formed as an automatic response to intrusions from foreign particles and microbial invaders. It essentially pokes microscopic pinholes in these foreign objects, causing loss of water and sometimes death. C5a, the other cleavage product of C5, acts as a highly inflammatory peptide, encouraging complement activation, formation of the MAC, attraction of innate immune cells, and histamine release involved in allergic responses. The origin of C5 is in the hepatocyte, but its synthesis can also be found in macrophages, where it may cause local increase of C5a. C5a is a chemotactic agent and an anaphylatoxin; it is essential in the innate immunity but it is also linked with the adaptive immunity. The increased production of C5a is connected with a number of inflammatory diseases. | 1 | Biochemistry |
Rhamnolipids are a class of glycolipid produced by Pseudomonas aeruginosa, amongst other organisms, frequently cited as bacterial surfactants. They have a glycosyl head group, in this case a rhamnose moiety, and a 3-(hydroxyalkanoyloxy)alkanoic acid (HAA) fatty acid tail, such as 3-hydroxydecanoic acid.
Specifically there are two main classes of rhamnolipids: mono-rhamnolipids and di-rhamnolipids, which consist of one or two rhamnose groups respectively. Rhamnolipids are also heterogeneous in the length and degree of branching of the HAA moiety, which varies with the growth media used and the environmental conditions. | 0 | Organic Chemistry |
The material may be solid, liquid, gas, a material of some intermediate characteristics such as gel or sputum, tissue, organism, or a combination of these. Even if a material sample is not countable as individual items, the quantity of the sample may still be describable in terms of its volume, mass, size, or other such dimensions. A solid sample can come in one or a few discrete pieces, or it can be fragmented, granular, or powdered. A section of a rod, wire, cord, sheeting, or tubing may be considered a sample. Samples which are not a solid piece are commonly kept in a container of some sort.
Where goods are sold or supplied by reference to a sample, relevant sale of goods legislation may dictate the supplier's legal obligations in ensuring that the bulk of the goods corresponds with the goods comprising the sample, for example in the UK, the Sale of Goods Act 1979, section 15, the Supply of Goods and Services Act 1982, section 5, and the Consumer Rights Act 2015, section 13. | 3 | Analytical Chemistry |
A speciation calculation is one in which concentrations of all the species in an equilibrium system are calculated, knowing the analytical concentrations, T, T etc. of the reactants A, B etc. This means solving a set of nonlinear equations of mass-balance
for the free concentrations [A], [B] etc. When the pH (or equivalent e.m.f., E).is measured, the free concentration of hydrogen ions, [H], is obtained from the measured value as or </blockquote>and only the free concentrations of the other reactants are calculated. The concentrations of the complexes are derived from the free concentrations via the chemical model.
Some authors include the free reactant terms in the sums by declaring identity (unit) constants for which the stoichiometric coefficients are 1 for the reactant concerned and zero for all other reactants. For example, with 2 reagents, the mass-balance equations assume the simpler form.
In this manner, all chemical species, including the free reactants, are treated in the same way, having been formed from the combination of reactants that is specified by the stoichiometric coefficients.
In a titration system the analytical concentrations of the reactants at each titration point are obtained from the initial conditions, the burette concentrations and volumes. The analytical (total) concentration of a reactant R at the th titration point is given by
where R is the initial amount of R in the titration vessel, is the initial volume, [R] is the concentration of R in the burette and is the volume added. The burette concentration of a reactant not present in the burette is taken to be zero.
In general, solving these nonlinear equations presents a formidable challenge because of the huge range over which the free concentrations may vary. At the beginning, values for the free concentrations must be estimated. Then, these values are refined, usually by means of Newton–Raphson iterations. The logarithms of the free concentrations may be refined rather than the free concentrations themselves. Refinement of the logarithms of the free concentrations has the added advantage of automatically imposing a non-negativity constraint on the free concentrations. Once the free reactant concentrations have been calculated, the concentrations of the complexes are derived from them and the equilibrium constants.
Note that the free reactant concentrations can be regarded as implicit parameters in the equilibrium constant refinement process. In that context the values of the free concentrations are constrained by forcing the conditions of mass-balance to apply at all stages of the process. | 7 | Physical Chemistry |
Reaction dynamics is a field within physical chemistry, studying why chemical reactions occur, how to predict their behavior, and how to control them. It is closely related to chemical kinetics, but is concerned with individual chemical events on atomic length scales and over very brief time periods. It considers state-to-state kinetics between reactant and product molecules in specific quantum states, and how energy is distributed between translational, vibrational, rotational, and electronic modes.
Experimental methods of reaction dynamics probe the chemical physics associated with molecular collisions. They include crossed molecular beam and infrared chemiluminescence experiments, both recognized by the 1986 Nobel Prize in Chemistry awarded to Dudley Herschbach, Yuan T. Lee, and John C. Polanyi "for their contributions concerning the dynamics of chemical elementary processes", In the crossed beam method used by Herschbach and Lee, narrow beams of reactant molecules in selected quantum states are allowed to react in order to determine the reaction probability as a function of such variables as the translational, vibrational and rotational energy of the reactant molecules and their angle of approach. In contrast the method of Polanyi measures vibrational energy of the products by detecting the infrared chemiluminescence emitted by vibrationally excited molecules, in some cases for reactants in defined energy states.
Spectroscopic observation of reaction dynamics on the shortest time scales is known as femtochemistry, since the typical times studied are of the order of 1 femtosecond = 10 s. This subject has been recognized by the award of the 1999 Nobel Prize in Chemistry to Ahmed Zewail.
In addition, theoretical studies of reaction dynamics involve calculating the potential energy surface for a reaction as a function of nuclear positions, and then calculating the trajectory of a point on this surface representing the state of the system. A correction can be applied to include the effect of quantum tunnelling through the activation energy barrier, especially for the movement of hydrogen atoms. | 7 | Physical Chemistry |
A direct indicating dial thermometer, common in household devices (such as a patio thermometer or a meat thermometer), uses a bimetallic strip wrapped into a coil in its most common design. The coil changes the linear movement of the metal expansion into a circular movement thanks to the helicoidal shape it draws. One end of the coil is fixed to the housing of the device as a fix point and the other drives an indicating needle inside a circular indicator. A bimetallic strip is also used in a recording thermometer. Breguet's thermometer consists of a tri-metallic helix in order to have a more accurate result. | 8 | Metallurgy |
Changeable optics filters are used in the colorimeter to select the wavelength which the solute absorbs the most, in order to maximize accuracy. The usual wavelength range is from 400 to 700 nm. If it is necessary to operate in the ultraviolet range then some modifications to the colorimeter are needed. In modern colorimeters the filament lamp and filters may be replaced by several (light-emitting diode) of different colors. | 7 | Physical Chemistry |
XPS detects only electrons that have actually escaped from the sample into the vacuum of the instrument. In order to escape from the sample, a photoelectron must travel through the sample. Photo-emitted electrons can undergo inelastic collisions, recombination, excitation of the sample, recapture or trapping in various excited states within the material, all of which can reduce the number of escaping photoelectrons. These effects appear as an exponential attenuation function as the depth increases, making the signals detected from analytes at the surface much stronger than the signals detected from analytes deeper below the sample surface. Thus, the signal measured by XPS is an exponentially surface-weighted signal, and this fact can be used to estimate analyte depths in layered materials. | 7 | Physical Chemistry |
For the simple reaction, the change in Gibbs energy is:
where a and a are the activities at equilibrium. The activities a are related to the concentrations c by a=γc where γ is the activity coefficient. The equilibrium potential is given by the Nernst equation:
where is the standard potential
Defining the formal potential:
the equilibrium potential is then:
Substituting this equilibrium potential into the Butler–Volmer equation yields:
which may also be written in terms of the standard rate constant k as:
The standard rate constant is an important descriptor of electrode behavior, independent of concentrations. It is a measure of the rate at which the system will approach equilibrium. In the limit as , the electrode becomes an ideal polarizable electrode and will behave electrically as an open circuit (neglecting capacitance). For nearly ideal electrodes with small k, large changes in the overpotential are required to generate a significant current. In the limit as , the electrode becomes an ideal non-polarizable electrode and will behave as an electrical short. For a nearly ideal electrodes with large k, small changes in the overpotential will generate large changes in current. | 7 | Physical Chemistry |
*AkzoNobel Coil Coatings Europe, https://web.archive.org/web/20130528041259/http://www.akzonobel.com/CCE/coil_coatings/ourindustry/ecca/,
*ArcelorMittal, http://www.constructalia.com/francais/actualites/plus_dactus/plus_dactus100/magazine_ecca_2012_une_source_d_inspiration_pour_les_architectes,
*Shingels, https://web.archive.org/web/20140714204231/http://shingels.com/?page_id=657&lang=en,
*Precoat Metals, http://www.precoat.com/links.htm,
*Spooner Industries, http://www.spooner.co.uk/products/36/coil-coating ,
*Novacel, http://www.novacel.fr/fr/novacel/partenariat.html ,
*The Plan "Architecture and Technologies in details", https://web.archive.org/web/20140714212808/http://www.theplan.it/J/index.php?option=com_content&view=article&id=2366:alcoa&Itemid=1&lang=en,
*Union of International Associations, http://www.uia.be/s/or/en/1100007909,
*Tata Steel, http://www.tatasteel.com/,
*BASF, http://www.basf.com/ | 8 | Metallurgy |
Hydrazines and hydroxylamines displace carbonyl oxygens much more readily than amines. Their equilibria strongly favor the dehydrated product, and the carbonyl is recovered only with difficulty. | 0 | Organic Chemistry |
The DeMayo reaction is a photochemical reaction in which the enol of a 1,3-diketone reacts with an alkene (or another species with a C=C bond) and the resulting cyclobutane ring undergoes a retro-aldol reaction to yield a 1,5-diketone:
The net effect is to add the two carbon atoms in the C=C double bond between the two carbonyl groups of the diketone. It is thus useful in syntheses both as a relatively selective way to join two parts of a molecule and as a way to apply the more developed chemistry of 1,3-diketone synthesis to 1,5-diketones. The first part is a [2+2] cycloaddition. The ensuing retro-aldol cleavage is favored by the relative instability of the cyclobutane ring. | 0 | Organic Chemistry |
Cucurbit[n]urils have similar size of γ-CD, which also behave similarly (e.g., 1 cucurbit[n]uril can thread onto 2 PEG chains). | 6 | Supramolecular Chemistry |
Luminol is synthesized in a two-step process, beginning with 3-nitrophthalic acid. First, hydrazine (NH) is heated with the 3-nitrophthalic acid in a high-boiling solvent such as triethylene glycol and glycerol. An acyl substitution condensation reaction occurs, with loss of water, forming 3-nitrophthalhydrazide. Reduction of the nitro group to an amino group with sodium dithionite (NaSO), via a transient hydroxylamine intermediate, produces luminol.
The compound was first synthesized in Germany in 1902, but was not named "luminol" until 1934. | 3 | Analytical Chemistry |
Polymersomes are synthetic versions of liposomes (vesicles with a lipid bilayer), made of amphiphilic block copolymers. They can encapsulate either hydrophilic or hydrophobic contents and can be used to deliver cargo such as DNA, proteins, or drugs to cells. Advantages of polymersomes over liposomes include greater stability, mechanical strength, blood circulation time, and storage capacity. | 1 | Biochemistry |
The PPM family, which includes PP2C and pyruvate dehydrogenase phosphatase, are enzymes with Mn/Mg metal ions that are resistant to classic inhibitors and toxins of the PPP family. Unlike most PPPs, PP2C exists in only one subunit but, like PTPs, it displays a wide variety of structural domains that confer unique functions. In addition, PP2C does not seem to be evolutionarily related to the major family of Ser/Thr PPs and has no sequence homology to ancient PPP enzymes. The current assumption is that PPMs evolved separately from PPPs but converged during evolutionary development. | 1 | Biochemistry |
Ratsimamanga started working at the French National Centre for Scientific Research (CNRS) in 1945 after he was approached by Frédéric Joliot-Curie, CNRS's research director and Nobel prize laureate in Chemistry (1935). At CNRS, he pioneered the study of Human blood group systems, and treatments for leprosy and tuberculosis. Ratsimamanga work showed the presence of hormones in the diet and their role in the development of the body, while eliminating the factors of cellular detoxification, especially in the liver.
Ratsimamanga was the founding director of the (IMRA) in 1957. IMRA was focused on Phytotherapy to use local plants and traditional practices to cure diseases, i.e., traditional pharmacopoeia. IMRA succeeded in using the Syzygium cumini tree as an anti-diabetic agent, and creating alternative medicines against malaria, leprosy, asthma, lithiasis, blood pressure, hepatitis and other common conditions.
Ratsimamanga was the head of Malagasy National Academy, and a Professor Emeritus of the Faculty of Medicine, University of Antananarivo. He was one of the founders of the World Academy of Sciences in 1983, and the African Academy of Sciences in 1985. He was a member of the Royal Academy for Overseas Sciences, Institut de France (1966), and the Académie Nationale de Médecine (1967). | 1 | Biochemistry |
Transduction with viral vectors can be used to insert or modify genes in mammalian cells. It is often used as a tool in basic research and is actively researched as a potential means for gene therapy. | 1 | Biochemistry |
Genes encoding the MuvB complex were originally identified from loss-of-function mutation studies in C. elegans. When mutated, these genes produced worms with multiple vulva-like organs, hence the name ‘Muv’. Three classes of Muv genes were classified, with class B genes encoding homologues of mammalian RB, E2F, and DP1, and others such as LIN-54, LIN-37, LIN-7 and LIN-52, whose functions were not yet understood.
Studies in Drosophila melanogaster ovarian follicle cells identified a protein complex that bound to repeatedly amplifying chorion genes. The complex included genes that had close homology with the MuvB genes such as Mip130, Mip120 and Mip40. These Mip genes were identified as homologues of the MuvB genes LIN9, LIN54, and LIN37 respectively. Further studies in the fly embryo nuclear extracts confirmed the coexistence of these proteins with others such as the RB homologues Rbf1 and Rbf2, and others like E2f and Dp. The protein complex was thus termed as the Drosophila RBF, E2f2 and Mip (dREAM) complex. Disruption of the dREAM complex through RNAi knockdown of the components of dREAM complex led to higher expression of E2f regulated genes that are typically silenced, implicating dREAM’s role in gene down-regulation. Later in Drosophila melanogaster, there was also found a testis-specific paralog of the Myb-MuvB/DREAM complex known as tMAC (testis-specific meiotic arrest complex), which is involved in meiotic arrest.
A protein complex similar to dREAM was subsequently identified in C. elegans extract containing DP, RB, and MuvB, and was named as DRM. This complex included mammalian homologues of RB and DP, and other members of the MuvB complex.
The mammalian DREAM complex was identified following immunoprecipitation of p130 with mass-spectrometry analysis. The results showed that p130 was associated with E2F4, E2F5, the dimerization partner DP, and LIN9, LIN54, LIN37, LIN52, and RBBP4 that make up the MuvB complex. Immunoprecipitation of MuvB factors also revealed association of BMYB. Subsequent immunoprecipitation with BMYB yielded all the MuvB core proteins, but not other members of the DREAM complex – p130, p107, E2F4/5 and DP. This indicated that MuvB associated with BMYB to form the BMYB-MuvB complex or with p130/p107, E2F4/5 and DP to form the DREAM complex. The DREAM complex was found prevalent in quiescent or starved cells, and the BMYB-MuvB complex was found in actively dividing cells, hinting at separate functionalities of these two complexes.
MuvB-like complexes were also recently discovered in Arabidoposis that include E2F and MYB orthologs combined with LIN9 and LIN54 orthologs. | 1 | Biochemistry |
This has an interesting consequence on the electric dipole moment (EDM) of any particle. The EDM is defined through the shift in the energy of a state when it is put in an external electric field: , where d is called the EDM and δ, the induced dipole moment. One important property of an EDM is that the energy shift due to it changes sign under a parity transformation. However, since d is a vector, its expectation value in a state |ψ⟩ must be proportional to ⟨ψ| J |ψ⟩, that is the expected spin. Thus, under time reversal, an invariant state must have vanishing EDM. In other words, a non-vanishing EDM signals both P and T symmetry-breaking.
Some molecules, such as water, must have EDM irrespective of whether T is a symmetry. This is correct; if a quantum system has degenerate ground states that transform into each other under parity, then time reversal need not be broken to give EDM.
Experimentally observed bounds on the electric dipole moment of the nucleon currently set stringent limits on the violation of time reversal symmetry in the strong interactions, and their modern theory: quantum chromodynamics. Then, using the CPT invariance of a relativistic quantum field theory, this puts strong bounds on strong CP violation.
Experimental bounds on the electron electric dipole moment also place limits on theories of particle physics and their parameters. | 7 | Physical Chemistry |
Gelation occurs when a polymer forms large interconnected polymer molecules through cross-linking. In other words, polymer chains are cross-linked with other polymer chains to form an infinitely large molecule, interspersed with smaller complex molecules, shifting the polymer from a liquid to a network solid or gel phase. The Carothers equation is an effective method for calculating the degree of polymerization for stoichiometrically balanced reactions. However, the Carothers equation is limited to branched systems, describing the degree of polymerization only at the onset of cross-linking. The Flory–Stockmayer Theory allows for the prediction of when gelation occurs using percent conversion of initial monomer and is not confined to cases of stoichiometric balance. Additionally, the Flory–Stockmayer Theory can be used to predict whether gelation is possible through analyzing the limiting reagent of the step-growth polymerization. | 7 | Physical Chemistry |
* CDC14s: CDC14A, CDC14B, CDC14C, CDKN3
* Phosphatase and tensin homologs: PTEN
* slingshot: SSH1, SSH2, SSH3 | 1 | Biochemistry |
A key issue in bacterial phylogeny is to understand how different bacterial species are related to each other and their branching order from a common ancestor. Currently most phylogenetic trees are based on 16S rRNA or other genes/proteins. These trees are not always able to resolve key phylogenetic questions with a high degree of certainty. However in recent years the discovery and analyses of conserved indels (CSIs) in many universally distributed proteins have aided in this quest. The genetic events leading to them are postulated to have occurred at important evolutionary branch points and their species distribution patterns provide valuable information regarding the branching order and interrelationships among different bacterial phyla. | 1 | Biochemistry |
Accidental or inadvertent poisoning of agricultural workers due to exposure to pesticides is a very serious matter resulting in many deaths and hospitalizations. The effects of pesticides at high concentrations on human health is a thus a matter of much study, resulting in many publications on the toxicology of pesticides. However the maximum residue limits of pesticides in food are low, and are carefully set by the authorities to ensure, to their best judgement, no health impacts.
According to the American Cancer Society there is no evidence that pesticide residues increase the risk of people getting cancer. The ACA advises washing fruit and vegetables before eating to remove both pesticide residue and other undesirable contaminants.
There are many studies on the health differences between consumers of organic foods vs consumers of organically grown foods. When the American Academy of Pediatrics reviewed the literature on organic foods in 2012, they found that "current evidence does not support any meaningful nutritional benefits or deficits from eating organic compared with conventionally grown foods, and there are no well-powered human studies that directly demonstrate health benefits or disease protection as a result of consuming an organic diet." | 2 | Environmental Chemistry |
Photothermal deflection spectroscopy is a kind of spectroscopy that measures the change in refractive index due to heating of a medium by light. It works via a sort of "mirage effect" where a refractive index gradient exists adjacent to the test sample surface. A probe laser beam is refracted or bent in a manner proportional to the temperature gradient of the transparent medium near the surface. From this deflection, a measure of the absorbed excitation radiation can be determined. The technique is useful when studying optically thin samples, because sensitive measurements can be obtained of whether absorption is occurring. It is of value in situations where "pass through" or transmission spectroscopy can't be used.
There are two main forms of PDS: Collinear and Transverse. Collinear PDS was introduced in a 1980 paper by A.C. Boccara, D. Fournier, et al. In collinear, two beams pass through and intersect in a medium. The pump beam heats the material and the probe beam is deflected. This technique only works for transparent media. In transverse, the pump beam heats come in normal to the surface, and the probe beam passes parallel. In a variation on this, the probe beam may reflect off the surface, and measure buckling due to heating. Transverse PDS can be done in Nitrogen, but better performance is gained in a liquid cell: usually an inert, non-absorbing material such as a perfluorocarbon is used.
In both collinear and transverse PDS, the surface is heated using a periodically modulated light source, such as an optical beam passing through a mechanical chopper or regulated with a function generator. A lock-in amplifier is then used to measure deflections found at the modulation frequency. Another scheme uses a pulsed laser as the excitation source. In that case, a boxcar average can be used to measure the temporal deflection of the probe beam to the excitation radiation. The signal falls off exponentially as a function of frequency, so frequencies around 1-10 hertz are frequently used. A full theoretical analysis of the PDS system was published by Jackson, Amer, et al. in 1981. The same paper also discussed the use of PDS as a form of microscopy, called "Photothermal Deflection Microscopy", which can yield information about impurities and the surface topology of materials.
PDS analysis of thin films can also be performed using a patterned substrate that supports optical resonances, such as guided-mode resonance and whispering-gallery modes. The probe beam is coupled into a resonant mode and the coupling efficiency is highly sensitive to the incidence angle. Due to the photoheating effect, the coupling efficiency is changed and characterized to indicate the thin film absorption. | 7 | Physical Chemistry |
Bis(chloromethyl) ether has been extensively used in chemical synthesis, primarily as a crosslinking agent in the manufacture of ion-exchange resins and in the textile industry. It was also used as a linker in the synthesis of certain nerve agent antidotes (asoxime chloride, obidoxime).
Bis(chloromethyl) was also effective for chloromethylation of aromatic substrates. | 0 | Organic Chemistry |
Photoexcitation is the first step in a photochemical process where the reactant is elevated to a state of higher energy, an excited state. The first law of photochemistry, known as the Grotthuss–Draper law (for chemists Theodor Grotthuss and John W. Draper), states that light must be absorbed by a chemical substance in order for a photochemical reaction to take place. According to the second law of photochemistry, known as the Stark–Einstein law (for physicists Johannes Stark and Albert Einstein), for each photon of light absorbed by a chemical system, no more than one molecule is activated for a photochemical reaction, as defined by the quantum yield. | 5 | Photochemistry |
Fluoride salts are commonly used in biological assay processing to inhibit the activity of phosphatases, such as serine/threonine phosphatases. Fluoride mimics the nucleophilic hydroxide ion in these enzymes' active sites. Beryllium fluoride and aluminium fluoride are also used as phosphatase inhibitors, since these compounds are structural mimics of the phosphate group and can act as analogues of the transition state of the reaction. | 1 | Biochemistry |
Almost all amine oxides are prepared by the oxidation of either tertiary aliphatic amines or aromatic N-heterocycles. Hydrogen peroxide is the most common reagent both industrially and in academia, however peracids are also important. More specialised oxidising agents can see niche use, for instance Caros acid or m'CPBA. Spontaneous or catalysed reactions using molecular oxygen are rare. Certain other reactions will also produce amine oxides, such as the retro-Cope elimination, however they are rarely employed. | 0 | Organic Chemistry |
Ribulose 1,5-bisphosphate (RuBP) is an organic substance that is involved in photosynthesis, notably as the principal acceptor in plants. It is a colourless anion, a double phosphate ester of the ketopentose (ketone-containing sugar with five carbon atoms) called ribulose. Salts of RuBP can be isolated, but its crucial biological function happens in solution. RuBP occurs not only in plants but in all domains of life, including Archaea, Bacteria, and Eukarya. | 5 | Photochemistry |
To become functional, the 4-phospho-pantetheine sidechain of acyl-CoA molecules has to be attached to the PCP-domain by 4PP transferases (Priming) and the S-attached acyl group has to be removed by specialized associated thioesterases (TE-II) (Deblocking). | 1 | Biochemistry |
In a zeta-potential titration, the Zeta potential is the indicator. Measurement of the zeta potential can be performed using microelectrophoresis, or electrophoretic light scattering, or electroacoustic phenomena. The last method makes possible to perform titrations in concentrated systems, with no dilution. | 7 | Physical Chemistry |
Because many reagents exist for radical generation and trapping, establishing a single prevailing mechanism is not possible. However, once a radical is generated, it can react with multiple bonds in an intramolecular fashion to yield cyclized radical intermediates. The two ends of the multiple bond constitute two possible sites of reaction. If the radical in the resulting intermediate ends up outside of the ring, the attack is termed "exo"; if it ends up inside the newly formed ring, the attack is called "endo." In many cases, exo cyclization is favored over endo cyclization (macrocyclizations constitute the major exception to this rule). 5-hexenyl radicals are the most synthetically useful intermediates for radical cyclizations, because cyclization is extremely rapid and exo selective. Although the exo radical is less thermodynamically stable than the endo radical, the more rapid exo cyclization is rationalized by better orbital overlap in the chair-like exo transition state (see below).
Substituents that affect the stability of these transition states can have a profound effect on the site selectivity of the reaction. Carbonyl substituents at the 2-position, for instance, encourage 6-endo ring closure. Alkyl substituents at positions 2, 3, 4, or 6 enhance selectivity for 5-exo closure.
Cyclization of the homologous 6-heptenyl radical is still selective, but is much slower—as a result, competitive side reactions are an important problem when these intermediates are involved. Additionally, 1,5-shifts can yield stabilized allylic radicals at comparable rates in these systems. In 6-hexenyl radical substrates, polarization of the reactive double bond with electron-withdrawing functional groups is often necessary to achieve high yields. Stabilizing the initially formed radical with electron-withdrawing groups provides access to more stable 6-endo cyclization products preferentially.
Cyclization reactions of vinyl, aryl, and acyl radicals are also known. Under conditions of kinetic control, 5-exo cyclization takes place preferentially. However, low concentrations of a radical scavenger establish thermodynamic control and provide access to 6-endo products—not via 6-endo cyclization, but by 5-exo cyclization followed by 3-exo closure and subsequent fragmentation (Dowd-Beckwith rearrangement). Whereas at high concentrations of the exo product is rapidly trapped preventing subsequent rearrangement to the endo product Aryl radicals exhibit similar reactivity.
Cyclization can involve heteroatom-containing multiple bonds such as nitriles, oximes, and carbonyls. Attack at the carbon atom of the multiple bond is almost always observed. In the latter case attack is reversible; however alkoxy radicals can be trapped using a stannane trapping agent. | 0 | Organic Chemistry |
Epoxidations of alkynes and allenes proceed by concerted mechanisms analogous to epoxidations of simple alkenes. Often, these epoxidized products are unstable and undergo further oxidation reactions via different mechanisms, such as Y-H insertion.
Kinetic studies of heteroatom oxidations have demonstrated that their mechanisms likely proceed by an S2 process, rather than a single-electron-transfer pathway. An example of heteroatom oxidation is the nucleophilic decomposition of DMD by N-oxides, a side reaction that regenerates the reduced starting material and converts the oxidizing agent to dioxygen and acetone.
Concerning the mechanism of C-H and Si-H oxidations, two mechanisms have been proposed. The debate centers on whether the oxidation takes place via concerted oxenoid-type insertion or via radical intermediates. A large body of evidence (including analogous oxidations of alkenes and peracid epoxidation) supports the concerted mechanism; however, recent observations of radical reactivity have been made. Complete retention of configuration in oxidations of chiral alkanes rules out the involvement of free, uncaged radicals. However, products of radical decomposition pathways have been observed in some DMD oxidations, suggesting radical intermediates. | 0 | Organic Chemistry |
These luxurious products were most often sold in important jewellery stores. Sometimes the retailer's paper labels survived the cleaning attempts of the last decades, and these labels are always a keen addition for any collector. They confirm that silver overlay porcelain and glass was sold all over Germany.
Friedrich Deusch, the oldest and biggest firm, also sold internationally and even produced a large amount of silver overlay tableware for the Royal House of Saudi Arabia. Deusch is the only firm that has survived (as of 2013), although the focus of production has
changed from fine art to galvanizing parts for the automobile industry. In 1976, after three generations, the Deusch family relinquished interest in the firm of Friedrich Deusch and Company Today, there is scant knowledge and interest about this firm's history.
Veyhl (father and son) traveled a lot offering their newest items to different jewellery stores. Later, they opened their own shop in Plüderhausen (close to Schwäbisch Gmünd). Friedrich Wilhelm Spahr created timeless designs which can be found today all over Europe and even in the United States. These are rare, desirable and mostly exquisite.
Silver overlay was a very exclusive luxury ware from the beginning because of the very complicated and time-consuming steps of manufacturing. Silver overlay items were never mass-produced and were made in limited numbers. The development of silver overlay was forged by a technical alliance between artists, artisans and advances in chemistry, physics, electronics and, ultimately, the industrialized techniques of the late 19th century. The arts movements of the day were philosophically against industrialized techniques. Yet, ironically, many delightfully decorated pieces of silver overlay porcelain and glass can be seen with superb handicraft and Art Nouveau-inspired designs. Thus, while the handicraft movement died after a single incandescent generation, their designs live on, as do the stunning works of Friedrich Deusch, Friedrich Wilhelm Spahr, and Alfred & Manfred Vehyl. | 8 | Metallurgy |
LC–MS is frequently used in drug development because it allows quick molecular weight confirmation and structure identification. These features speed up the process of generating, testing, and validating a discovery starting from a vast array of products with potential application. LC–MS applications for drug development are highly automated methods used for peptide mapping, glycoprotein mapping, lipodomics, natural products dereplication, bioaffinity screening, in vivo drug screening, metabolic stability screening, metabolite identification, impurity identification, quantitative bioanalysis, and quality control. | 3 | Analytical Chemistry |
The Noyori asymmetric hydrogenation of ketones is an excellent example of dynamic kinetic resolution at work. The enantiomeric β-ketoesters can undergo epimerization, and the choice of chiral catalyst, typically of the form Ru[(R)-BINAP]X, where X is a halogen, leads to one of the enantiomers reacting preferentially faster. The relative free energy for a representative reaction is shown below. As can be seen, the epimerization intermediate is lower in free energy than the transition states for hydrogenation, resulting in rapid racemization and high yields of a single enantiomer of the product.
The enantiomers interconvert through their common enol, which is the energetic minimum located between the enantiomers. The shown reaction yields a 93% ee sample of the anti product shown above. Solvent choice appears to have a major influence on the diastereoselectivity, as dichloromethane and methanol both show effectiveness for certain substrates. Noyori and others have also developed newer catalysts which have improved on both ee and diastereomeric ratio (dr).
Genêt and coworkers developed SYNPHOS, a BINAP analogue which forms ruthenium complexes, which perform highly selective asymmetric hydrogenations. Enantiopure Ru[SYNPHOS]Br was shown to selectively hydrogenate racemic α-amino-β-ketoesters to enantiopure aminoalcohols, as shown below utilizing (R)-SYNPHOS. 1,2-syn amino alcohols were prepared from benzoyl protected amino compounds, whereas anti products were prepared from hydrochloride salts of the amine. | 4 | Stereochemistry |
Ion pairs are formed when a cation and anion, which are present in a solution of an ionizable substance, come together to form a discrete chemical species. There are three distinct types of ion pairs, depending on the extent of solvation of the two ions. For example, magnesium sulfate exists as both contact and solvent-shared ion-pairs in seawater.
In the schematic representation above, the circles represent spheres. The sizes are arbitrary and not necessarily similar as illustrated. The cation is coloured red and the anion is coloured blue. The green area represents solvent molecules in a primary solvation shell; secondary solvation is ignored. When both ions have a complete primary solvation sphere, the ion pair may be termed fully solvated (separated ion pair, SIP). When there is about one solvent molecule between cation and anion, the ion pair may be termed solvent-shared. Lastly, when the ions are in contact with each other, the ion pair is termed a contact ion pair (CIP). Even in a contact ion pair, however, the ions retain most of their solvation shell. The nature of this solvation shell is generally not known with any certainty. In aqueous solution and in other donor solvents, metal cations are surrounded by between 4 and 9 solvent molecules in the primary solvation shell,
An alternative name for a solvent-shared ion pair is an outer-sphere complex. This usage is common in coordination chemistry and denotes a complex between a solvated metal cation and an anion. Similarly, a contact ion pair may be termed an inner-sphere complex. The essential difference between the three types is the closeness with which the ions approach each other: fully solvated > solvent-shared > contact. With fully solvated and solvent-shared ion pairs the interaction is primarily electrostatic, but in a contact ion pair some covalent character in the bond between cation and anion is also present.
An ion triplet may be formed from one cation and two anions or from one anion and two cations. Higher aggregates, such as a tetramer , may be formed.
Ternary ion associates involve the association of three species. Another type, named intrusion ion pair, has also been characterized. | 7 | Physical Chemistry |
Although TSS appears to be a straightforward measure of particulate weight obtained by separating particles from a water sample using a filter, it suffers as a defined quantity from the fact that particles occur in nature in essentially a continuum of sizes. At the lower end, TSS relies on a cut-off established by properties of the filter being used. At the upper end, the cut-off should be the exclusion of all particulates too large to be "suspended" in water. However, this is not a fixed particle size but is dependent upon the energetics of the situation at the time of sampling: moving water suspends larger particles than does still water. Usually it is the case that the additional suspended material caused by the movement of the water is of interest.
These problems in no way invalidate the use of TSS; consistency in method and technique can overcome short-comings in most cases. But comparisons between studies may require a careful review of the methodologies used to establish that the studies are in fact measuring the same thing.
TSS in mg/L can be calculated as:
: (dry weight of residue and filter − dry weight of filter alone, in grams)/ mL of sample * 1,000,000 | 3 | Analytical Chemistry |
Dimer acids, or dimerized fatty acids, are dicarboxylic acids prepared by dimerizing unsaturated fatty acids obtained from tall oil, usually on clay catalysts. The CAS number of the material is [61788-89-4]. Dimer acids are used primarily for synthesis of polyamide resins and polyamide hot melt adhesives. They are also used in alkyd resins, adhesives, surfactants, as fuel oil additives, lubricants, etc. It is a light yellow or yellow viscous transparent liquid.
Dimer acid usually contains predominantly a dimer of oleic acid. It is also called C36 dimer acid.
Trimer acid is a corresponding material where the resulting molecule consists of three fatty acid molecules. Its CAS number is [68937-90-6].
Dimer acids can be converted to dimer amines by reaction with ammonia and subsequent reduction. | 0 | Organic Chemistry |
Persistent triplet state carbenes are likely to have very similar reactivity as other non-persistent triplet state carbenes. | 0 | Organic Chemistry |
Since the outer conductor layer is low-impedance copper, and only the center is higher impedance steel, the skin effect gives RF transmission lines with heavy copper-cladding a low impedance at high frequencies, equivalent to that of a solid copper wire.
Tensile strength of copper-clad steel conductors is greater than that of ordinary copper conductors permitting greater span lengths than with copper.
Another advantage is that smaller diameter copper-clad steel conductors may be used in coaxial cables, permitting higher impedance and smaller cable diameter than with copper conductors of similar strength.
Due to the inseparable union of the two metals and the low amount of the more costly one, it deters theft since copper recovery is impractical and thus has very little scrap value.
Installations with copper-clad steel conductors are generally accepted as fulfilling the legal specifications for a good electrical ground. For this reason its use is preferred by industrial companies and utilities when cost is a concern. | 8 | Metallurgy |
In biophysics, the Kautsky effect (also fluorescence transient, fluorescence induction or fluorescence decay) is a phenomenon consisting of a typical variation in the behavior of a plant fluorescence when exposed to light. It was discovered in 1931 by H. Kautsky and A. Hirsch.
When dark-adapted photosynthesising cells are illuminated with continuous light, chlorophyll fluorescence displays characteristic changes in intensity accompanying the induction of photosynthetic activity. | 5 | Photochemistry |
S. pyogenes causes diseases ranging from pharyngitis to life-threatening impetigo including necrotizing fasciitis. An MLST scheme for S. pyogenes has been developed. At present, the database ([http://www.mlst.net mlst.net]) contains the allelic profiles of isolates that represent the worldwide diversity of the organism and isolates from serious invasive disease. | 1 | Biochemistry |
As outlined above, the Kidd Process did not use wax on its permanent cathodes. This highlighted disadvantages associated with the use of wax by the Isa Process. Cathode copper consumers applied pressure to producers to remove residual wax from the cathode copper, and the use of wax also created “housekeeping” problems for Isa Process operators.
Consequently, MIM commenced a development program in 1997 aimed at eliminating the use of wax. This resulted in a new process called the Isa 2000 technology, which was able to produce single-sheet cathode (as opposed to the Kidd taco shell cathode) without using wax.
This was achieved by machining a 90° “V”-groove into the bottom edge of the cathode. The groove weakens the structure of the copper growing at the bottom edge of the cathode plate because the copper crystals grow perpendicular to the cathode plate from opposite sides of the groove, causing them to intersect at right angles to each other. A discontinuity in the structure is formed at the intersection that results in a weak zone, along which the copper splits during stripping.
Figure 4 is a microscope view of the cross-section a copper cathode growing at the tip of a cathode plate. The yellow lines show the orientation and direction of crystal growth. | 8 | Metallurgy |
Multiferroic composite structures in bulk form are explored for high-sensitivity ac magnetic field sensors and electrically tunable microwave devices such as filters, oscillators and phase shifters (in which the ferri-, ferro- or antiferro-magnetic resonance is tuned electrically instead of magnetically). | 7 | Physical Chemistry |
Rapamycin and rapalogs (rapamycin derivatives) are small molecule inhibitors, which have been evaluated as anticancer agents. The rapalogs have more favorable pharmacokinetic profile compared to rapamycin, the parent drug, despite the same binding sites for mTOR and FKBP12. | 1 | Biochemistry |
Nonferrous archaeometallurgy in the southern Levant is the archaeological study of non-iron-related metal technology in the region of the Southern Levant during the Chalcolithic period and Bronze Age from approximately 4500BC to 1000BC. | 8 | Metallurgy |
Woollins reagent is an organic compound containing phosphorus and selenium. Analogous to Lawessons reagent, it is used mainly as a selenation reagent. It is named after John Derek Woollins. | 0 | Organic Chemistry |
A mesophilic start in surface bodies of waters hypothesis has evolved from Darwins concept of a warm little pond' and the Oparin-Haldane hypothesis. Freshwater bodies under temperate climates can accumulate prebiotic materials while providing suitable environmental conditions conducive to simple life forms. The climate during the Archaean is still a highly debated topic, as there is uncertainty about what continents, oceans, and the atmosphere looked like then. Atmospheric reconstructions of the Archaean from geochemical proxies and models state that sufficient greenhouse gases were present to maintain surface temperatures between 0-40 °C. Under this assumption, there is a greater abundance of moderate temperature niches in which life could begin.
Strong lines of evidence for mesophily from biomolecular studies include Galtiers G+C nucleotide thermometer. G+C are more abundant in thermophiles due to the added stability of an additional hydrogen bond not present between A+T nucleotides. rRNA sequencing on a diverse range of modern lifeforms show that LUCAs reconstructed G+C content was likely representative of moderate temperatures.
Although most modern phylogenies are thermophilic or hyperthermophilic, it is possible that their widespread diversity today is a product of convergent evolution and horizontal gene transfer rather than an inherited trait from LUCA. The reverse gyrase topoisomerase is found exclusively in thermophiles and hyperthermophiles as it allows for coiling of DNA. The reverse gyrase enzyme requires ATP to function, both of which are complex biomolecules. If an origin of life is hypothesised to involve a simple organism that had not yet evolved a membrane, let alone ATP, this would make the existence of reverse gyrase improbable. Moreover, phylogenetic studies show that reverse gyrase had an archaeal origin, and that it was transferred to bacteria by horizontal gene transfer. This implies that reverse gyrase was not present in the LUCA. | 9 | Geochemistry |
One of the remarkable features of plasma electrolyte coatings is the presence of micro pores and cracks on the coating surface. Plasma electrolytic oxide coatings are generally recognized for high hardness, wear resistance, and corrosion resistance. However, the coating properties are highly dependent on the substrate used, as well as on the composition of the electrolyte and the electrical regime used (see Equipment used section, above).
Even on aluminium, the coating properties can vary strongly according to the exact alloy composition. For instance, the hardest coatings can be achieved on 2XXX series aluminium alloys, where the highest proportion of crystalline phase corundum (α-AlO) is formed, resulting in hardnesses of ~2000 HV, whereas coatings on the 5XXX series have less of this important constituent and are hence softer. Extensive work is being pursued by Prof. T. W. Clyne at the University of Cambridge to investigate the fundamental electrical and plasma physical processes involved in this process, having previously elucidated some of the micromechanical (& pore architectural), mechanical and thermal characteristics of PEO coatings. | 8 | Metallurgy |
Transcriptional adaptation is a recently described type of genetic compensation by which a mutation in one gene leads to the transcriptional modulation of related genes, termed adapting genes or modifiers. | 1 | Biochemistry |
Leucopelargonidin is a colorless chemical compound related to leucoanthocyanins. It can be found in Albizia lebbeck (East Indian walnut), in the fruit of Anacardium occidentale (Cashew), in the fruit of Areca catechu (Areca nut), in the fruit of Hydnocarpus wightiana (Hindi Chaulmoogra), in the rhizome of Rumex hymenosepalus (Arizona dock), in Zea mays (Corn) and in Ziziphus jujuba (Chinese date).
(+)-Leucopelargonidin can be synthesized from (+)-aromadendrin by sodium borohydride reduction. | 1 | Biochemistry |
The pioneering work of chemical kinetics was done by German chemist Ludwig Wilhelmy in 1850. He experimentally studied the rate of inversion of sucrose and he used integrated rate law for the determination of the reaction kinetics of this reaction. His work was noticed 34 years later by Wilhelm Ostwald. After Wilhelmy, Peter Waage and Cato Guldberg published 1864 the law of mass action, which states that the speed of a chemical reaction is proportional to the quantity of the reacting substances.
Van t Hoff studied chemical dynamics and in 1884 published his famous "Études de dynamique chimique". In 1901 he was awarded by the first Nobel Prize in Chemistry "in recognition of the extraordinary services he has rendered by the discovery of the laws of chemical dynamics and osmotic pressure in solutions". After van t Hoff, chemical kinetics deals with the experimental determination of reaction rates from which rate laws and rate constants are derived. Relatively simple rate laws exist for zero order reactions (for which reaction rates are independent of concentration), first order reactions, and second order reactions, and can be derived for others. Elementary reactions follow the law of mass action, but the rate law of stepwise reactions has to be derived by combining the rate laws of the various elementary steps, and can become rather complex. In consecutive reactions, the rate-determining step often determines the kinetics. In consecutive first order reactions, a steady state approximation can simplify the rate law. The activation energy for a reaction is experimentally determined through the Arrhenius equation and the Eyring equation. The main factors that influence the reaction rate include: the physical state of the reactants, the concentrations of the reactants, the temperature at which the reaction occurs, and whether or not any catalysts are present in the reaction.
Gorban and Yablonsky have suggested that the history of chemical dynamics can be divided into three eras. The first is the van 't Hoff wave searching for the general laws of chemical reactions and relating kinetics to thermodynamics. The second may be called the Semenov-Hinshelwood wave with emphasis on reaction mechanisms, especially for chain reactions. The third is associated with Aris and the detailed mathematical description of chemical reaction networks. | 7 | Physical Chemistry |
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