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Made of high gem quality, flawless diamonds, usually with 16 facets, they typically weigh to carat (25 to 70 mg). The culet (tip) is ground and polished to a hexadecagonal surface parallel to the table. The culets of the two diamonds face one another, and must be perfectly parallel in order to produce uniform pressure and to prevent dangerous strains. Specially selected anvils are required for specific measurements – for example, low diamond absorption and luminescence is required in corresponding experiments. | 7 | Physical Chemistry |
Transposable elements have been recognized as good candidates for stimulating gene adaptation, through their ability to regulate the expression levels of nearby genes. Combined with their "mobility", transposable elements can be relocated adjacent to their targeted genes, and control the expression levels of the gene, dependent upon the circumstances.
The study conducted in 2008, "High Rate of Recent Transposable Element–Induced Adaptation in Drosophila melanogaster", used D. melanogaster that had recently migrated from Africa to other parts of the world, as a basis for studying adaptations caused by transposable elements. Although most of the TEs were located on introns, the experiment showed a significant difference in gene expressions between the population in Africa and other parts of the world. The four TEs that caused the selective sweep were more prevalent in D. melanogaster from temperate climates, leading the researchers to conclude that the selective pressures of the climate prompted genetic adaptation. From this experiment, it has been confirmed that adaptive TEs are prevalent in nature, by enabling organisms to adapt gene expression as a result of new selective pressures.
However, not all effects of adaptive TEs are beneficial to the population. In the research conducted in 2009, "A Recent Adaptive Transposable Element Insertion Near Highly Conserved Developmental Loci in Drosophila melanogaster", a TE, inserted between Jheh 2 and Jheh 3, revealed a downgrade in the expression level of both of the genes. Downregulation of such genes has caused Drosophila to exhibit extended developmental time and reduced egg to adult viability. Although this adaptation was observed in high frequency in all non-African populations, it was not fixed in any of them. This is not hard to believe, since it is logical for a population to favor higher egg to adult viability, therefore trying to purge the trait caused by this specific TE adaptation.
At the same time, there have been several reports showing the advantageous adaptation caused by TEs. In the research done with silkworms, "An Adaptive Transposable Element insertion in the Regulatory Region of the EO Gene in the Domesticated Silkworm", a TE insertion was observed in the cis-regulatory region of the EO gene, which regulates molting hormone 20E, and enhanced expression was recorded. While populations without the TE insert are often unable to effectively regulate hormone 20E under starvation conditions, those with the insert had a more stable development, which resulted in higher developmental uniformity.
These three experiments all demonstrated different ways in which TE insertions can be advantageous or disadvantageous, through means of regulating the expression level of adjacent genes. The field of adaptive TE research is still under development and more findings can be expected in the future. | 1 | Biochemistry |
The reciprocal lattice is easily constructed in one dimension: for particles on a line with a period , the reciprocal lattice is an infinite array of points with spacing . In two dimensions, there are only five Bravais lattices. The corresponding reciprocal lattices have the same symmetry as the direct lattice. 2-D lattices are excellent for demonstrating simple diffraction geometry on a flat screen, as below.
Equations (1)–(7) for structure factor apply with a scattering vector of limited dimensionality and a crystallographic structure factor can be defined in 2-D as .
However, recall that real 2-D crystals such as graphene exist in 3-D. The reciprocal lattice of a 2-D hexagonal sheet that exists in 3-D space in the plane is a hexagonal array of lines parallel to the or axis that extend to and intersect any plane of constant in a hexagonal array of points.
The Figure shows the construction of one vector of a 2-D reciprocal lattice and its relation to a scattering experiment.
A parallel beam, with wave vector is incident on a square lattice of parameter . The scattered wave is detected at a certain angle, which defines the wave vector of the outgoing beam, (under the assumption of elastic scattering, ). One can equally define the scattering vector and construct the harmonic pattern . In the depicted example, the spacing of this pattern coincides to the distance between particle rows: , so that contributions to the scattering from all particles are in phase (constructive interference). Thus, the total signal in direction is strong, and belongs to the reciprocal lattice. It is easily shown that this configuration fulfills Bragg's law. | 3 | Analytical Chemistry |
Geologic phenomena such as iron cycling and soil contamination are controlled by the interfaces between minerals and their environment. The atomic-scale structure and chemical properties of mineral-solution interfaces are studied using in situ synchrotron X-ray techniques such as X-ray reflectivity, X-ray standing waves, and X-ray absorption spectroscopy as well as scanning probe microscopy. For example, studies of heavy metal or actinide adsorption onto mineral surfaces reveal molecular-scale details of adsorption, enabling more accurate predictions of how these contaminants travel through soils or disrupt natural dissolution-precipitation cycles. | 7 | Physical Chemistry |
Guido Bargellini (1879–1963) was an Italian organic chemist. He specialized in natural product chemistry, in particular, flavonoid dyes and coumarins, and the compound santonin. He was admitted to the Accademia dei Lincei in 1946. The Bargellini reaction is named for him. | 0 | Organic Chemistry |
Not all biomarkers should be used as surrogate endpoints to assess clinical outcomes. Biomarkers can be difficult to validate and require different levels of validation depending on their intended use. If a biomarker is to be used to measure the success of a therapeutic intervention, the biomarker should reflect a direct effect of that medicine. | 1 | Biochemistry |
Standalone fans are usually powered by an electric motor, often attached directly to the motors output, with no gears or belts. The motor is either hidden in the fans center hub or extends behind it. For big industrial fans, three-phase asynchronous motors are commonly used, may be placed near the fan, and drive it through a belt and pulleys. Smaller fans are often powered by shaded pole AC motors, or brushed or brushless DC motors. AC-powered fans usually use mains voltage, while DC-powered fans typically use low voltage, typically 24V, 12V, or 5 V.
In machines with a rotating part, the fan is often connected to it rather than being powered separately. This is commonly seen in motor vehicles with internal combustion engines, large cooling systems, locomotives, and winnowing machines, where the fan is connected to the drive shaft or through a belt and pulleys. Another common configuration is a dual-shaft motor, where one end of the shaft drives a mechanism, while the other has a fan mounted on it to cool the motor itself. Window air conditioners commonly use a dual-shaft fan to operate separate fans for the interior and exterior parts of the device.
Where electrical power or rotating parts are not readily available, fans may be driven by other methods. High-pressure gases such as steam can be used to drive a small turbine, and high-pressure liquids can be used to drive a pelton wheel, either which can provide the rotational drive for a fan.
Large, slow-moving energy sources such as a flowing river can also power a fan using a water wheel and a series of step-down gears or pulleys to increase the rotational speed to that which is required for efficient fan operation. | 7 | Physical Chemistry |
Water molecules dissociate into equal amounts of HO and OH, so their concentrations are almost exactly at 25 °C and 0.1 MPa. A solution in which the HO and OH concentrations equal each other is considered a neutral solution. In general, the pH of the neutral point is numerically equal to pK.
Pure water is neutral, but most water samples contain impurities. If an impurity is an acid or base, this will affect the concentrations of hydronium ion and hydroxide ion. Water samples that are exposed to air will absorb some carbon dioxide to form carbonic acid (HCO) and the concentration of HO will increase due to the reaction HCO + HO = HCO + HO. The concentration of OH will decrease in such a way that the product [HO][OH] remains constant for fixed temperature and pressure. Thus these water samples will be slightly acidic. If a pH of exactly 7.0 is required, it must be maintained with an appropriate buffer solution. | 7 | Physical Chemistry |
In materials science, intergranular corrosion (IGC), also known as intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides. (Cf. transgranular corrosion.) | 8 | Metallurgy |
In eukaryotes, O-linked glycans are assembled one sugar at a time on a serine or threonine residue of a peptide chain in the Golgi apparatus. Unlike N-linked glycans, there is no known consensus sequence yet. However, the placement of a proline residue at either -1 or +3 relative to the serine or threonine is favourable for O-linked glycosylation. | 0 | Organic Chemistry |
eIF5 is a GTPase-activating protein, which helps the large ribosomal subunit associate with the small subunit. It is required for GTP-hydrolysis by eIF2.
eIF5A is the eukaryotic homolog of EF-P. It helps with elongation and also plays a role in termination. EIF5A contains the unusual amino acid hypusine.
eIF5B is a GTPase, and is involved in assembly of the full ribosome. It is the functional eukaryotic analog of bacterial IF2. | 1 | Biochemistry |
Here, the aglycone is a simple phenolic structure. An example is arbutin found in the Common Bearberry Arctostaphylos uva-ursi. It has a urinary antiseptic effect. | 0 | Organic Chemistry |
Accidentally consuming small quantities of clean seawater is not harmful, especially if the seawater is taken along with a larger quantity of fresh water. However, drinking seawater to maintain hydration is counterproductive; more water must be excreted to eliminate the salt (via urine) than the amount of water obtained from the seawater itself. In normal circumstances, it would be considered ill-advised to consume large amounts of unfiltered seawater.
The renal system actively regulates the levels of sodium and chloride in the blood within a very narrow range around 9 g/L (0.9% by mass).
In most open waters concentrations vary somewhat around typical values of about 3.5%, far higher than the body can tolerate and most beyond what the kidney can process. A point frequently overlooked in claims that the kidney can excrete NaCl in Baltic concentrations of 2% (in arguments to the contrary) is that the gut cannot absorb water at such concentrations, so that there is no benefit in drinking such water. The salinity of Baltic surface water, however, is never 2%. It is 0.9% or less, and thus never higher than that of bodily fluids. Drinking seawater temporarily increases bloods NaCl concentration. This signals the kidney to excrete sodium, but seawaters sodium concentration is above the kidneys maximum concentrating ability. Eventually the bloods sodium concentration rises to toxic levels, removing water from cells and interfering with nerve conduction, ultimately producing fatal seizure and cardiac arrhythmia.
Survival manuals consistently advise against drinking seawater. A summary of 163 life raft voyages estimated the risk of death at 39% for those who drank seawater, compared to 3% for those who did not. The effect of seawater intake on rats confirmed the negative effects of drinking seawater when dehydrated.
The temptation to drink seawater was greatest for sailors who had expended their supply of fresh water and were unable to capture enough rainwater for drinking. This frustration was described famously by a line from Samuel Taylor Coleridges The Rime of the Ancient Mariner':
Although humans cannot survive on seawater, some people claim that up to two cups a day, mixed with fresh water in a 2:3 ratio, produces no ill effect. The French physician Alain Bombard survived an ocean crossing in a small Zodiak rubber boat using mainly raw fish meat, which contains about 40% water (like most living tissues), as well as small amounts of seawater and other provisions harvested from the ocean. His findings were challenged, but an alternative explanation was not given. In his 1948 book The Kon-Tiki Expedition, Thor Heyerdahl reported drinking seawater mixed with fresh in a 2:3 ratio during the 1947 expedition. A few years later, another adventurer, William Willis, claimed to have drunk two cups of seawater and one cup of fresh per day for 70 days without ill effect when he lost part of his water supply.
During the 18th century, Richard Russell advocated the medical use of this practice in the UK, and René Quinton expanded the advocation of this practice to other countries, notably France, in the 20th century. Currently, it is widely practiced in Nicaragua and other countries, supposedly taking advantage of the latest medical discoveries.
Most oceangoing vessels desalinate potable water from seawater using processes such as vacuum distillation or multi-stage flash distillation in an evaporator, or, more recently, reverse osmosis. These energy-intensive processes were not usually available during the Age of Sail. Larger sailing warships with large crews, such as Nelson's , were fitted with distilling apparatus in their galleys.
Animals such as fish, whales, sea turtles, and seabirds, such as penguins and albatrosses, have adapted to living in a high-saline habitat. For example, sea turtles and saltwater crocodiles remove excess salt from their bodies through their tear ducts. | 9 | Geochemistry |
There are many applications in technology and lab work for this process to create desired morphologies of polymers. One of these applications is inscribing secondary nanostructures onto electrospun fibers. The use of poly(ε‐caprolactone) fibers, known as PCL, allows using solvents like acetone to move the amorphous chains of block polymers onto a pre-existing crystal, making the inscribed secondary structure. When the PCL is annealed with acetone, the amorphous chains can be mobilized to a given desired region, while the overall integrity of the fully crystallized regions stays intact. With a careful approach to the semi-crystalline polymer chosen and looking for appropriate solvent vapor, this simple process can be applied to many different systems and allows for the creation of many types of hierarchical polymer material.
Another application of SVA is its use in helping create and improve photovoltaic device efficiency through the annealing of perovskite materials. For the greater performance of these energy cells, the keys lie with higher quality perovskite materials and on the use of SVA to create these higher quality films that can retain energy more efficiently. Solvent engineering is the key to make the perovskite material and improving their quality through SVA in an anhydrous isopropanol environment, where the crystalline polymer has low solubility, which causes the performance to increase greatly. The use of SVA here leads to a more energy-efficient and promising path of using specific polymers to help move forward with the improvement of energy storage. | 7 | Physical Chemistry |
Thioamides are typically prepared by treating amides with phosphorus sulfides such as phosphorus pentasulfide, a reaction first described in the 1870s. Alternative routes include the use of Lawesson's reagent or the reaction of nitriles with hydrogen sulfide:
The Willgerodt-Kindler reaction also gives benzylthioamides.
The C(R)(N)(S) core of thioamides is planar. Using thioacetamide as representative: the C-S, C-N, and C-C distances are 1.68, 1.31, and 1.50 Å, respectively. The short C-S and C-N distances indicate multiple bonding. | 0 | Organic Chemistry |
An atom or a molecule can absorb light and undergo a transition from
one quantum state to another.
The oscillator strength of a transition from a lower state
to an upper state may be defined by
where is the mass of an electron and is
the reduced Planck constant. The quantum states 1,2, are assumed to have several
degenerate sub-states, which are labeled by . "Degenerate" means
that they all have the same energy .
The operator is the sum of the x-coordinates
of all electrons in the system, i.e.
The oscillator strength is the same for each sub-state .
The definition can be recast by inserting the Rydberg energy and Bohr radius
In case the matrix elements of are the same, we can get rid of the sum and of the 1/3 factor | 7 | Physical Chemistry |
Many natural (or biological) materials are complex composites with remarkable mechanical properties. These complex structures, which have risen from hundreds of million years of evolution, are inspiring materials scientists in the design of novel materials. Their defining characteristics include structural hierarchy, multifunctionality and self-healing capability. Self-organization is also a fundamental feature of many biological materials and the manner by which the structures are assembled from the molecular level up. Thus, self-assembly is emerging as a new strategy in the chemical synthesis of high performance biomaterials. | 7 | Physical Chemistry |
Paracrine signaling through fibroblast growth factors and its respective receptors utilizes the receptor tyrosine pathway. This signaling pathway has been highly studied, using Drosophila eyes and human cancers.
Binding of FGF to FGFR phosphorylates the idle kinase and activates the RTK pathway. This pathway begins at the cell membrane surface, where a ligand binds to its specific receptor. Ligands that bind to RTKs include fibroblast growth factors, epidermal growth factors, platelet-derived growth factors, and stem cell factor. This dimerizes the transmembrane receptor to another RTK receptor, which causes the autophosphorylation and subsequent conformational change of the homodimerized receptor. This conformational change activates the dormant kinase of each RTK on the tyrosine residue. Due to the fact that the receptor spans across the membrane from the extracellular environment, through the lipid bilayer, and into the cytoplasm, the binding of the receptor to the ligand also causes the trans phosphorylation of the cytoplasmic domain of the receptor.
An adaptor protein (such as SOS) recognizes the phosphorylated tyrosine on the receptor. This protein functions as a bridge which connects the RTK to an intermediate protein (such as GNRP), starting the intracellular signaling cascade. In turn, the intermediate protein stimulates GDP-bound Ras to the activated GTP-bound Ras. GAP eventually returns Ras to its inactive state. Activation of Ras has the potential to initiate three signaling pathways downstream of Ras: Ras→Raf→MAP kinase pathway, PI3 kinase pathway, and Ral pathway. Each pathway leads to the activation of transcription factors which enter the nucleus to alter gene expression. | 1 | Biochemistry |
Rotavirus is the most common cause of acute gastroenteritis in infants and young children worldwide. This virus contains a dsRNA genome and is a member of the Reoviridae family. The genome of rotavirus consists of eleven segments of dsRNA. Each genome segment codes for one protein with the exception of segment 11, which codes for two proteins. Among the twelve proteins, six are structural and six are non-structural proteins.
It is a double-stranded RNA non-enveloped virus. | 1 | Biochemistry |
There are many different effective medium approximations, each of them being more or less accurate in distinct conditions. Nevertheless, they all assume that the macroscopic system is homogeneous and, typical of all mean field theories, they fail to predict the properties of a multiphase medium close to the percolation threshold due to the absence of long-range correlations or critical fluctuations in the theory.
The properties under consideration are usually the conductivity or the dielectric constant of the medium. These parameters are interchangeable in the formulas in a whole range of models due to the wide applicability of the Laplace equation. The problems that fall outside of this class are mainly in the field of elasticity and hydrodynamics, due to the higher order tensorial character of the effective medium constants.
EMAs can be discrete models, such as applied to resistor networks, or continuum theories as applied to elasticity or viscosity. However, most of the current theories have difficulty in describing percolating systems. Indeed, among the numerous effective medium approximations, only Bruggeman's symmetrical theory is able to predict a threshold. This characteristic feature of the latter theory puts it in the same category as other mean field theories of critical phenomena. | 7 | Physical Chemistry |
The ethyl ester of propionic acid (1) was brominated and then converted to the Wittig reagent using triphenylphosphine. Aldehyde 6 was obtained from allyl alcohol (4) by protection as the tert-butyldiphenylsilyl ether (5) followed by ozonolysis. Wittig reagent 3 and aldehyde 6 reacted in a Wittig reaction to give unsaturated ester 7, which was deprotected to give dienophile 8 (Scheme 1, compound 1). | 0 | Organic Chemistry |
The simplest case refers to the formation of a strictly linear polymer by the reaction (usually by condensation) of two monomers in equimolar quantities. An example is the synthesis of nylon-6,6 whose formula is
from one mole of hexamethylenediamine, , and one mole of adipic acid, . For this case
In this equation
* is the number-average value of the degree of polymerization, equal to the average number of monomer units in a polymer molecule. For the example of nylon-6,6 ( diamine units and diacid units).
* is the extent of reaction (or conversion to polymer), defined by
** is the number of molecules present initially as monomer
** is the number of molecules present after time . The total includes all degrees of polymerization: monomers, oligomers and polymers.
This equation shows that a high monomer conversion is required to achieve a high degree of polymerization. For example, a monomer conversion, , of 98% is required for = 50, and = 99% is required for = 100. | 7 | Physical Chemistry |
Isocyanates can present respiratory hazards as particulates, vapors or aerosols. Autobody shop workers are a very commonly examined population for isocyanate exposure as they are repeatedly exposed when spray painting automobiles and can be exposed when installing truck bed liners. Hypersensitivity pneumonitis has slower onset and features chronic inflammation that can be seen on imaging of the lungs. Occupational asthma is a worrisome outcome of respiratory sensitization to isocyanates as it can be acutely fatal. Diagnosis of occupational asthma is generally performed using pulmonary function testing (PFT) and performed by pulmonology or occupational medicine physicians. Occupational asthma is much like asthma in that it causes episodic shortness of breath and wheezing. Both the dose and duration of exposure to isocyanates can lead to respiratory sensitization. Dermal exposures to isocyanates can sensitize an exposed person to respiratory disease.
Dermal exposures can occur via mixing, spraying coatings or applying and spreading coatings manually. Dermal exposures to isocyanates is known to lead to respiratory sensitization. Even when the right personal protective equipment (PPE) is used, exposures can occur to body areas not completely covered. Isocyanates can also permeate improper PPE, necessitating frequent changes of both disposable gloves and suits if they become over exposed. | 0 | Organic Chemistry |
Standard ellipsometry (or just short ellipsometry) is applied, when no s polarized light is converted into p polarized light nor vice versa. This is the case for optically isotropic samples, for instance, amorphous materials or crystalline materials with a cubic crystal structure. Standard ellipsometry is also sufficient for optically uniaxial samples in the special case, when the optical axis is aligned parallel to the surface normal. In all other cases, when s polarized light is converted into p polarized light and/or vice versa, the generalized ellipsometry approach must be applied. Examples are arbitrarily aligned, optically uniaxial samples, or optically biaxial samples. | 7 | Physical Chemistry |
UV light is electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays. UV is categorised into several wavelength ranges, with short-wavelength UV (UV-C) considered "germicidal UV". Wavelengths between about 200 nm and 300 nm are strongly absorbed by nucleic acids. The absorbed energy can result in defects including pyrimidine dimers. These dimers can prevent replication or can prevent the expression of necessary proteins, resulting in the death or inactivation of the organism. Recently, it has been shown that these dimers are fluorescent.
* Mercury-based lamps operating at low vapor pressure emit UV light at the 253.7 nm line.
* Ultraviolet light-emitting diode (UV-C LED) lamps emit UV light at selectable wavelengths between 255 and 280 nm.
* Pulsed-xenon lamps emit UV light across the entire UV spectrum with a peak emission near 230 nm.
This process is similar to, but stronger than, the effect of longer wavelengths (UV-B) producing sunburn in humans. Microorganisms have less protection against UV and cannot survive prolonged exposure to it.
A UVGI system is designed to expose environments such as water tanks, rooms and forced air systems to germicidal UV. Exposure comes from germicidal lamps that emit germicidal UV at the correct wavelength, thus irradiating the environment. The forced flow of air or water through this environment ensures exposure of that air or water. | 5 | Photochemistry |
These are based upon study of the terminal velocity acquired by particles suspended in a viscous liquid. Sedimentation time is longest for the finest particles, so this technique is useful for sizes below 10 μm, but sub-micrometer particles cannot be reliably measured due to the effects of Brownian motion. Typical apparatus disperses the sample in liquid, then measures the density of the column at timed intervals. Other techniques determine the optical density of successive layers using visible light or x-rays.
Advantages: this technique determines particle size as a function of settling velocity.
Disadvantages: Sample must be dispersed in a liquid medium... some particles may (partially or fully) dissolve in the medium altering the size distribution, requiring careful selection of the dispersion media.
Density is highly dependent upon fluid temperature remaining constant.
X-Rays will not count carbon (organic) particles.
Many of these instruments can require a bulk sample (e.g. two to five grams). | 7 | Physical Chemistry |
An example of such an enantiomer is the sedative thalidomide, which was sold in a number of countries around the world from 1957 until 1961. It was withdrawn from the market when it was found to cause birth defects. One enantiomer caused the desirable sedative effects, while the other, unavoidably present in equal quantities, caused birth defects.
The herbicide mecoprop is a racemic mixture, with the (R)-(+)-enantiomer ("Mecoprop-P", "Duplosan KV") possessing the herbicidal activity.
Another example is the antidepressant drugs escitalopram and citalopram. Citalopram is a racemate [1:1 mixture of (S)-citalopram and (R)-citalopram]; escitalopram [(S)-citalopram] is a pure enantiomer. The dosages for escitalopram are typically 1/2 of those for citalopram. Here, (S)-citalopram is called a chiral switch of Citalopram. | 4 | Stereochemistry |
When ortho substitution occurs in benzoic acid, steric hindrance causes the carboxyl group to twist out of the plane of the benzene ring. The twisting inhibits the resonance of the carboxyl group with the phenyl ring, leading to increased acidity of the carboxyl group. This increased acidity contrasts with the reduced acidity caused by destabilizing cross-conjugation. The destabilizing cross-conjugation causes decreased acidity of benzoic acid compared to formic acid. | 4 | Stereochemistry |
Indolyl-3-acryloylglycine, also known as trans-indolyl-3-acryloylglycine, or IAG for short, is a compound consisting of an indole group attached to an acrylic acid moiety, which is in turn attached to a glycine molecule. This compound has been shown to isomerize when exposed to light. It is likely a metabolic intermediate in the biosynthesis of tryptophan, and is synthesized from tryptophan via indolepropionic acid and indoleacrylicacid (IAcrA). It is also likely that IAcrA is converted into IAG in the gut wall. It may also be produced by certain elements of the mammalian gut microbiota by phenylalanine ammonia-lyase. Identifiable in the urine by high-performance liquid chromatography, it may be a biomarker for autism spectrum disorders, as demonstrated by the research of Paul Shattock and other researchers from Australia. These researchers have reported that urinary levels of IAG are much higher in autistic children than in controls; however, other researchers have found no association between IAG concentrations in the urine and autism. Its excretion in the urine may also be changed in Hartnup disease and celiac disease, as well as photodermatosis, muscular dystrophy, and liver cirrhosis. | 0 | Organic Chemistry |
The microscopic structure of liquids is complex and historically has been the subject of intense research and debate. A few of the key ideas are explained below. | 7 | Physical Chemistry |
Synthetic elements are excluded from the classification, as they do not occur naturally.
Trace radioactive elements (namely Tc, Pm, Po, At, Rn, Fr, Ra, Ac, Pa, Np, Pu) are also treated as synthetic. Although these do occur in nature, their occurrence is entirely dependent on their long-lived parents Th and U, and they are not very mobile. For instance, polonium's chemistry would predict it to be a chalcophile, but it tends to occur instead as a lithophile along with its parent uranium. Even radon, which is a gas, does not usually have time to travel very far from the original uranium source before decaying. When needed, these elements are typically produced synthetically in nuclear reactors instead of using the tedious and laborious process of extraction from uranium ores. | 9 | Geochemistry |
The applications of synthetic nucleotides vary widely and include disease diagnosis, treatment, or precision medicine.
# Antiviral or Antiretroviral agents: several nucleotide derivatives have been used in the treatment against infection with Hepatitis and HIV. Examples of direct nucleoside analog reverse-transcriptase inhibitors (NRTIs) include Tenofovir disoproxil, Tenofovir alafenamide, and Sofosbuvir. On the other hand, agents such as Mericitabine, Lamivudine, Entecavir and Telbivudine must first undergo metabolization via phosphorylation to become activated.
# Antisense oligonucleotides (ASO): synthetic oligonucleotides have been used in the treatment of rare heritable diseases since they can bind specific RNA transcripts and ultimately modulate protein expression. Spinal muscular atrophy, amyotrophic lateral sclerosis, homozygous familial hypercholesterolemia, and primary hyperoxaluria type 1 are all amenable to ASO-based therapy. The application of oligonucleotides is a new frontier in precision medicine and management of conditions which are untreatable.
# Synthetic guide RNA (gRNA): synthetic nucleotides can be used to design gRNA which are essential for the proper function of gene-editing technologies such as CRISPR-Cas9. | 1 | Biochemistry |
The most important operating parameters of disc filters are the height of the slurry tank, agitation and the intensity and rotation speed of the disc as these will determine the cake formation and drying times. It is important to continuously agitate the slurry in order to prevent sedimentation of the solids. Excessively high agitation intensity may affect cake formation or change the particle size distribution of the product. One of the most commonly used agitators for filtration using vacuum disc filters is an oscillating cradle-type agitator located in the bottom of the basin, which requires fairly high rotation speeds to form homogeneous slurry. For processing rapidly settling high concentration slurries, bottom-feed rotary disc filters are usually used.
Stage 1: Filtration
The filtrate from the internal passages of the discs is removed by the low vacuum used in the filter, while the small pressure differential across the disc causes cake formation. With a thicker cake produced in this stage, more effective washing is achieved at higher wash liquor flows. However, this causes larger air volumes to be consumed at discharge due to reduced resistance and marginally lower cake moisture.
Stage 2: Dewatering
In rare cases, due to the even structure of the cakes formed, the steady flow profile of the ceramic filter media and the gas free filtrate flow cake, washing has proved to be efficient in ceramic disc filters. The formation of thicker cakes during filtration and higher vacuum level leads to greater removal of solute.
Stage 3: Discharge
The basic scraper works well when the cakes are relatively thick and non-sticky. The final cakes are discharged by blade or wire scrapers on either side of the discs However, other types of agitators should be considered and installed if the cake is sticky or thin. An air blow-back system is often employed to aid cake removal where wetter cakes are discharged from disc filter. | 3 | Analytical Chemistry |
In 1905, both Goldberg and Ullman moved to Technische Hochschule in Berlin. Goldbergs research, along with that of the Ullmann-Goldberg collaborative, was also a part of Germanys synthetic dye industry. Their research helped with the creation of the synthetic alizarin industry, or the process of replacing natural dye obtained from madder. In 1909, Goldberg also collaborated with Hermann Friedman to review German patents under BASF (Badische Anilin und Soda Fabrik) and Bayer & Co. Farbenfabriken, providing notes on preparation for 114 dyes. | 0 | Organic Chemistry |
Aromatic polyamides and polyamides are practical compounds due to their temperature resistance, electrical or insulating characteristics, and their mechanical strength. Some of the polyamides and polyimides that can be synthesized by o-Cresophthalein are polycarbonate, polyacrylate, and epoxy-resin.
The diether-diamine 3,3-bis[4-(4-amino-phenoxy)-3-methylphenyl]phthalide, or BNMP, is synthesized by 12 g o-cresophthalein, 11.5 g p-chloronitrobenzene, 5.1 g anhydrous potassium carbonate, and 55 mL of DMF. The compounds should be refluxed together at 160 °C for eight hours. Once it is done and has cooled, it should be mixed with 0.3 L methanol. A precipitate should form and be vacuum filtered to obtain a solid. It should then be washed with water and dried, yielding a yellow product. It should then be recrystallized from glacial acetic acid to yield yellow needles. The product is BNMP. The reaction can go further by combining 15.5 g of BNMP with 0.18 g 10% Pd/C and 50 mL ethanol. They should be stirred at 80 °C. 7 mL of hydrazine monohydrate should be added drop by drop for one hour. The solution should then be mixed for eight hours. It should then be filtered to separated from the Pd/C and concentrated. The concentrated solution should be added to water, and a precipitate should be formed. It should then be vacuum filtered to isolate the solid, yelding 3,3-Bis[4-(4-aminophenoxy)-3-methylphenyl]pthalide, or BAMP, as a white solid. It should then be purified by water and ethanol. | 3 | Analytical Chemistry |
Tholins (after the Greek () "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon dioxide (), methane () or ethane (), often in combination with nitrogen () or water (). Tholins are disordered polymer-like materials made of repeating chains of linked subunits and complex combinations of functional groups, typically nitriles and hydrocarbons, and their degraded forms such as amines and phenyls. Tholins do not form naturally on modern-day Earth, but they are found in great abundance on the surfaces of icy bodies in the outer Solar System, and as reddish aerosols in the atmospheres of outer Solar System planets and moons.
In the presence of water, tholins could be raw materials for prebiotic chemistry (i.e., the non-living chemistry that forms the basic chemicals of which life is made). Their existence has implications for the origins of life on Earth and possibly on other planets. As particles in an atmosphere, tholins scatter light, and can affect habitability.
Tholins may be produced in a laboratory, and are usually studied as a heterogeneous mixture of many chemicals with many different structures and properties. Using techniques like thermogravimetric analysis, astrochemists analyze the composition of these tholin mixtures, and the exact character of the individual chemicals within them. | 9 | Geochemistry |
Oceans take up 15 – 40% of anthropogenic CO, and so far roughly 40% of the carbon from fossil fuel combustion has been taken up into the oceans. Because the Revelle factor increases with increasing CO, a smaller fraction of the anthropogenic flux will be taken up by the ocean in the future. Current annual increase in atmospheric CO is approximately 4 gigatons of carbon. This induces climate change that drives carbon concentration and carbon-climate feedback processes that modifies ocean circulation and the physical and chemical properties of seawater, which alters CO uptake. Overfishing and the plastic pollution of the oceans contribute to the degraded state of the world's biggest carbon sink. | 9 | Geochemistry |
Edward Frankland first reported the compound in 1848 from zinc and ethyl iodide, the first organozinc compound discovered. He improved the synthesis by using diethyl mercury as starting material. The contemporary synthesis consists of the reaction of a 1:1 mixture of ethyl iodide and ethyl bromide with a zinc-copper couple, a source of reactive zinc. | 0 | Organic Chemistry |
The chromium atom is surrounded by six nitrogen atoms in an octahedral geometry. The NH ligands are mutually trans and the Cr–NCS groups are linear. The salt crystallizes with one molecule of water.
It was first reported in 1863. NH[Cr(NCS)(NH)] is prepared by treatment of molten NHSCN (melting point around 145–150 °C) with (NH)CrO.
This salt was once widely used to precipitate primary and secondary amines as their ammonium salts. Included in the amines that effectively form crystalline precipitates are those derived from the amino acids, including proline and hydroxyproline. It also reacts with Hg compounds, giving a red color or a red precipitate. | 0 | Organic Chemistry |
Stable carbon isotope composition is another widely used proxy for interpreting paleoenvironment conditions. The Surface temperature fluctuation from the Paleocene to Miocene has been established based on carbon isotope data from foraminifera in Antarctic region. The organic matter preserved in sediments records paleoecosystems, and its carbon isotope composition has been also utilized to reconstruct paleoclimatic evolution. For example, Rogers and Koons (1969) have reported that the carbon isotope ratios, derived from organic matter in Quaternary marine sediments in the Gulf of Mexico, correlate well with Pleistocene climate changes.
Chen et al. (2011) have documented ancient climate fluctuations since the last glacial maximum based on soil samples in Tibet. Other sources for organic carbon isotope used as proxies for paleoenvironment reconstruction include lacustrine deposits for lake level variations, fossilized vertebrates for precipitation fluctuations, oil shales for paleoecological and paleoclimate conditions. | 9 | Geochemistry |
N-Nitrosamines, including the carcinogenic variety, arise from the reaction of nitrite sources with amino compounds, which can happen during the curing of meat. Typically, this reaction occurs when the nucleophilic nitrogen of a secondary amine attacks the nitrogen of the electrophilic nitrosonium ion:
:NO + 2 H → NO + HO
:RNH + NO → RN-NO + H
Formation of an N-nitrosamine:
The nitrosamine can then lose water through protonation to form diazonium cation, which is a very useful intermediate to form different compounds. | 0 | Organic Chemistry |
This parameter is often used in biomechanics, when describing the motion of joints of the body. For any period of time, joint motion can be seen as the movement of a single point on one articulating surface with respect to the adjacent surface (usually distal with respect to proximal). The total translation and rotations along the path of motion can be defined as the time integrals of the instantaneous translation and rotation velocities at the IHA for a given reference time.
In any single plane, the path formed by the locations of the moving instantaneous axis of rotation (IAR) is known as the centroid, and is used in the description of joint motion. | 3 | Analytical Chemistry |
In electrochemistry, exchange current density is a parameter used in the Tafel equation, Butler–Volmer equation and other electrochemical kinetics expressions. The Tafel equation describes the dependence of current for an electrolytic process to overpotential.
The exchange current density is the current in the absence of net electrolysis and at zero overpotential. The exchange current can be thought of as a background current to which the net current observed at various overpotentials is normalized. For a redox reaction written as a reduction at the equilibrium potential, electron transfer processes continue at electrode/solution interface in both directions. The cathodic current is balanced by the anodic current. This ongoing current in both directions is called the exchange current density. When the potential is set more negative than the formal potential, the cathodic current is greater than the anodic current. Written as a reduction, cathodic current is positive. The net current density is the difference between the cathodic and anodic current density.
Exchange current densities reflect intrinsic rates of electron transfer between an analyte and the electrode. Such rates provide insights into the structure and bonding in the analyte and the electrode. For example, the exchange current densities for platinum and mercury electrodes for reduction of protons differ by a factor of 10, indicative of the excellent catalytic properties of platinum. Owing to this difference, mercury is the preferred electrode material at reducing (cathodic) potentials in aqueous solution. | 7 | Physical Chemistry |
Metallodendrimers are investigated as equivalents to nanoparticles. Applications can be expected in the fields of catalysis, as chemical sensors in molecular recognition - for example of bromine and chloride anions - or as materials capable of binding metals. Metallodendrimers can also mimic certain biomolecules for example haemoprotein in dendrimer with a porphyrin core. Further uses are reported as electrocatalyst.
Examples of metallodendrimer heterogeneous catalysis are a nickel-containing dendrimer active in the Kharasch addition, palladium-containing dendrimers active in ethylene polymerization and in the Heck reaction. | 6 | Supramolecular Chemistry |
In placebo-controlled studies, the most commonly observed side effects were headache, xerostomia (dry mouth), nausea, dizziness, and insomnia. Possible side effects also include depression, anxiety, hallucinations, euphoria, extreme increase in activity and talking, anorexia, tremor, thirst, rash, suicidal thoughts, and aggression. Symptoms of an overdose on armodafinil include trouble sleeping, restlessness, confusion, disorientation, feeling excited, mania, hallucinations, nausea, diarrhea, severely increased or decreased heart beat, chest pain, and increased blood pressure. Serious rashes can develop in rare cases, and require immediate medical attention due to the possibility of Steven's-Johnson Syndrome, or other hypersensitivities to armodafinil. | 4 | Stereochemistry |
Comprehensive two-dimensional gas chromatography is an analytical technique that separates and analyzes complex mixtures. It has been utilized in fields such as: flavor, fragrance, environmental studies, pharmaceuticals, petroleum products and forensic science. GCxGC provides a high range of sensitivity and produces a greater separation power due to the increased peak capacity. | 3 | Analytical Chemistry |
Urea was first noticed by Herman Boerhaave in the early 18th century from evaporates of urine. In 1773, Hilaire Rouelle obtained crystals containing urea from human urine by evaporating it and treating it with alcohol in successive filtrations. This method was aided by Carl Wilhelm Scheeles discovery that urine treated by concentrated nitric acid precipitated crystals. Antoine François, comte de Fourcroy and Louis Nicolas Vauquelin discovered in 1799 that the nitrated crystals were identical to Rouelles substance and invented the term "urea." Berzelius made further improvements to its purification and finally William Prout, in 1817, succeeded in obtaining and determining the chemical composition of the pure substance. In the evolved procedure, urea was precipitated as urea nitrate by adding strong nitric acid to urine. To purify the resulting crystals, they were dissolved in boiling water with charcoal and filtered. After cooling, pure crystals of urea nitrate form. To reconstitute the urea from the nitrate, the crystals are dissolved in warm water, and barium carbonate added. The water is then evaporated and anhydrous alcohol added to extract the urea. This solution is drained off and evaporated, leaving pure urea. | 0 | Organic Chemistry |
Homosynaptic plasticity (or also homotropic modulation) is a change in the synaptic strength that results from the history of activity at a particular synapse. This can result from changes in presynaptic calcium as well as feedback onto presynaptic receptors, i.e. a form of autocrine signaling. Homosynaptic plasticity can affect the number and replenishment rate of vesicles or it can affect the relationship between calcium and vesicle release. Homosynaptic plasticity can also be postsynaptic in nature. It can result in either an increase or decrease in synaptic strength.
One example is neurons of the sympathetic nervous system (SNS), which release noradrenaline, which, besides affecting postsynaptic receptors, also affects presynaptic α2-adrenergic receptors, inhibiting further release of noradrenaline. This effect is utilized with clonidine to perform inhibitory effects on the SNS. | 1 | Biochemistry |
The adenylate energy charge is an index used to measure the energy status of biological cells.
ATP or Mg-ATP is the principal molecule for storing and transferring energy in the cell : it is used for biosynthetic pathways, maintenance of transmembrane gradients, movement, cell division, etc... More than 90% of the ATP is produced by phosphorylation of ADP by the ATP synthase. ATP can also be produced by “substrate level phosphorylation” reactions (ADP phosphorylation by (1,3)-bisphosphoglycerate, phosphoenolpyruvate, phosphocreatine), by the succinate-CoA ligase and phosphoenolpyruvate carboxylkinase, and by adenylate kinase, an enzyme that maintains the three adenine nucleotides in equilibrium ().
The energy charge is related to ATP, ADP and AMP concentrations. It was first defined by Atkinson and Walton who found that it was necessary to take into account the concentration of all three nucleotides, rather than just ATP and ADP, to account for the energy status in metabolism. Since the adenylate kinase maintains two ADP molecules in equilibrium with one ATP (), Atkinson defined the adenylate energy charge as:
The energy charge of most cells varies between 0.7 and 0.95 - oscillations in this range are quite frequent. Daniel Atkinson showed that when the energy charge increases from 0.6 to 1.0, the citrate lyase and phosphoribosyl pyrophosphate synthetase, two enzymes controlling anabolic (ATP-demanding) pathways are activated, while the phosphofructokinase and the pyruvate dehydrogenase, two enzymes controlling amphibolic pathways (supplying ATP as well as important biosynthetic intermediates) are inhibited He concluded that control of these pathways has evolved to maintain the energy charge within rather narrow limits - in other words, that the energy charge, like the pH of a cell, must be buffered at all times. We now know that most if not all anabolic and catabolic pathways are indeed controlled, directly and indirectly, by the energy charge. In addition to direct regulation of several enzymes by adenyl nucleotides, an AMP-activated protein kinase known as AMP-K phosphorylates and thereby regulates key enzymes when the energy charge decreases. This results in switching off anabolic pathways while switching on catabolic pathways when AMP increases.
Life depends on an adequate energy charge. If ATP synthesis is momentarily insufficient to maintain an adequate energy charge, AMP can be converted by two different pathways to hypoxanthine and ribose-5P, followed by irreversible oxidation of hypoxanthine to uric acid. This helps to buffer the adenylate energy charge by decreasing the total {ATP+ADP+AMP} concentration. | 1 | Biochemistry |
Insertion of a SINE upstream of a coding region may result in exon shuffling or changes to the regulatory region of the gene. Insertion of a SINE into the coding sequence of a gene can have deleterious effects and unregulated transposition can cause genetic disease. The transposition and recombination of SINEs and other active nuclear elements is thought to be one of the major contributions of genetic diversity between lineages during speciation. | 1 | Biochemistry |
Photobiology is the scientific study of the beneficial and harmful interactions of non-ionizing radiation in living organisms, conventionally demarcated around 10 eV, the first ionization energy of oxygen. UV ranges roughly from 3 to 30 eV in energy. Hence photobiology entertains some, but not all, of the UV spectrum. | 5 | Photochemistry |
One might expect that larger side chains would result in more restrictions and consequently a smaller allowable region in the Ramachandran plot, but the effect of side chains is small. In practice, the major effect seen is that of the presence or absence of the methylene group at Cβ. Glycine has only a hydrogen atom for its side chain, with a much smaller van der Waals radius than the CH, CH, or CH group that starts the side chain of all other amino acids. Hence it is least restricted, and this is apparent in the Ramachandran plot for glycine (see Gly plot in gallery) for which the allowable area is considerably larger. In contrast, the Ramachandran plot for proline, with its 5-membered-ring side chain connecting Cα to backbone N, shows a limited number of possible combinations of ψ and φ (see Pro plot in gallery). The residue preceding proline ("pre-proline") also has limited combinations compared to the general case. | 1 | Biochemistry |
Enzyme-based DNA computers are usually of the form of a simple Turing machine; there is analogous hardware, in the form of an enzyme, and software, in the form of DNA.
Benenson, Shapiro and colleagues have demonstrated a DNA computer using the FokI enzyme and expanded on their work by going on to show automata that diagnose and react to prostate cancer: under expression of the genes PPAP2B and GSTP1 and an over expression of PIM1 and HPN. Their automata evaluated the expression of each gene, one gene at a time, and on positive diagnosis then released a single strand DNA molecule (ssDNA) that is an antisense for MDM2. MDM2 is a repressor of protein 53, which itself is a tumor suppressor. On negative diagnosis it was decided to release a suppressor of the positive diagnosis drug instead of doing nothing. A limitation of this implementation is that two separate automata are required, one to administer each drug. The entire process of evaluation until drug release took around an hour to complete. This method also requires transition molecules as well as the FokI enzyme to be present. The requirement for the FokI enzyme limits application in vivo, at least for use in "cells of higher organisms". It should also be pointed out that the software molecules can be reused in this case. | 1 | Biochemistry |
The discreteness condition means that there is some positive real number ε, such that for every translation T in the group, the vector v has length at least ε (except of course in the case that v is the zero vector, but the independent translations condition prevents this, since any set that contains the zero vector is linearly dependent by definition and thus disallowed).
The purpose of this condition is to ensure that the group has a compact fundamental domain, or in other words, a "cell" of nonzero, finite area, which is repeated through the plane. Without this condition, one might have for example a group containing the translation T for every rational number x, which would not correspond to any reasonable wallpaper pattern.
One important and nontrivial consequence of the discreteness condition in combination with the independent translations condition is that the group can only contain rotations of order 2, 3, 4, or 6; that is, every rotation in the group must be a rotation by 180°, 120°, 90°, or 60°. This fact is known as the crystallographic restriction theorem, and can be generalised to higher-dimensional cases. | 3 | Analytical Chemistry |
Side chain polyrotaxanes are formed by host–guest interactions of polymer side chains with cyclic molecules that are interlocked by bulky stoppers.
There are mainly three types of side chain polyrotaxanes:
(1) Polyaxis/rotor: Comb-like polymers assembled with the cyclic molecules that are not interlocked on the side chain.
(2) Polyrotor/axis: polymers possess cyclic molecules on the side chain, which assemble with guest molecules to form polypseudorotaxanes.
(3) Polyrotor/polyaxis: polymers possess covalently bonded cyclic molecule-moieties assembled with polymers possess guested in the side chain.
Similar to the synthesis routes to main chain polyrotaxanes, there are mainly six approaches to side chain polyrotaxane.
(1) Ring-threading of performed graft polymer
(2) Ring-grafting
(3) Rotaxane-grafting
(4) Polymerization of macromonomer with rings
(5) Polymerization of rotaxane-monomer
(6) Chemical conversion
Similarly, the positions of chain and rings can be switched, which results in corresponding side-chain polyrotaxanes. | 6 | Supramolecular Chemistry |
Ortho lithiation can be used to generate many of the same structures as lateral lithiation; however, reactivity differences between aryl- and benzyllithium species may suggest the use of one method over the other. A useful alternative method for stereoselective functionalization of the benzylic position involves the use of chromium arene complexes. Substitution at the benzylic position is much better tolerated in methods that employ benzylic lithiation of chromium arene complexes than lateral lithiations; however, the chromium byproducts of these reactions pose waste disposal difficulties. The use of mixed zinc/copper organometallic reagents generated from benzyl bromides represents a second alternative to lateral lithiation. The functional group compatibility of this method is greater than lateral lithiation, but more steps are required to generate the reactive organometallic species from an unfunctionalized benzylic position. | 0 | Organic Chemistry |
A prehormone is a biochemical substance secreted by glandular tissue and has minimal or no significant biological activity, but it is converted in peripheral tissues into an active hormone. Calcifediol is an example of a prehormone which is produced by hydroxylation of vitamin D (cholecalciferol) in the liver. Another example is adrenal androgens like dehydroepiandrosterone and androstenedione, which can be converted into testosterone and dihydrotestosterone. | 1 | Biochemistry |
In the field of molecular biology, trans-acting (trans-regulatory, trans-regulation), in general, means "acting from a different molecule" (i.e., intermolecular). It may be considered the opposite of cis-acting (cis-regulatory, cis-regulation), which, in general, means "acting from the same molecule" (i.e., intramolecular).
In the context of transcription regulation, a trans-acting factor is usually a regulatory protein that binds to DNA. The binding of a trans-acting factor to a cis-regulatory element in DNA can cause changes in transcriptional expression levels. microRNAs or other diffusible molecules are also examples of trans-acting factors that can regulate target sequences.
The trans-acting gene may be on a different chromosome to the target gene, but the activity is via the intermediary protein or RNA that it encodes. Cis-acting elements, on the other hand, do not code for protein or RNA. Both the trans-acting gene and the protein/RNA that it encodes are said to "act in trans" on the target gene. | 1 | Biochemistry |
In healthy adults, the normal concentrations of CRP varies between 0.8 mg/L and 3.0 mg/L. However, some healthy adults show elevated CRP at 10 mg/L. CRP concentrations also increase with age, possibly due to subclinical conditions. There are also no seasonal variations of CRP concentrations. Gene polymorphism of interleukin-1 family, interleukin 6, and polymorphic GT repeat of the CRP gene do affect the usual CRP concentrations when a person does not have any medical illnesses. | 1 | Biochemistry |
Like chemists, chemical engineers use the unit mole extensively, but different unit multiples may be more suitable for industrial use. For example, the SI unit for volume is the cubic metre, a much larger unit than the commonly used litre in the chemical laboratory. When amount of substance is also expressed in kmol (1000 mol) in industrial-scaled processes, the numerical value of molarity remains the same, as . Chemical engineers once used the kilogram-mole (notation kg-mol), which is defined as the number of entities in 12 kg of C, and often referred to the mole as the gram-mole (notation g-mol), then defined as the number of entities in 12 g of C, when dealing with laboratory data.
Late 20th-century chemical engineering practice came to use the kilomole (kmol), which was numerically identical to the kilogram-mole (until the 2019 redefinition of SI units, which redefined the mole by fixing the value of the Avogadro constant, making it very nearly equivalent to but no longer exactly equal to the gram-mole), but whose name and symbol adopt the SI convention for standard multiples of metric units – thus, kmol means 1000 mol. This is equivalent to the use of kg instead of g. The use of kmol is not only for "magnitude convenience" but also makes the equations used for modelling chemical engineering systems coherent. For example, the conversion of a flowrate of kg/s to kmol/s only requires dividing by the molar mass in g/mol (as ) without multiplying by 1000 unless the basic SI unit of mol/s were to be used, which would otherwise require the molar mass to be converted to kg/mol.
For convenience in avoiding conversions in the imperial (or US customary units), some engineers adopted the pound-mole (notation lb-mol or lbmol), which is defined as the number of entities in 12 lb of C. One lb-mol is equal to , which is the same numerical value as the number of grams in an international avoirdupois pound.
Greenhouse and growth chamber lighting for plants is sometimes expressed in micromoles per square metre per second, where 1 mol photons ≈ photons. The obsolete unit einstein is variously defined as the energy in one mole of photons and also as simply one mole of photons. | 3 | Analytical Chemistry |
In photoredox catalysis, the photon is absorbed by a sensitizer (antenna molecule or ion) which then effects redox reactions on the organic substrate. A common sensitizer is ruthenium(II) tris(bipyridine). Illustrative of photoredox catalysis are some aminotrifluoromethylation reactions. | 5 | Photochemistry |
Push–pull technology was developed at the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya in collaboration with Rothamsted Research, UK. and national partners in the 1990s. Research and development for the push-pull strategy was funded by a number of partners including the Gatsby Charitable Foundation of the UK, the Rockefeller Foundation, the UK’s Department for International Development, and the Global Environment Facility of the UNEP, among others. | 1 | Biochemistry |
Polyphenols of several classes are widespread in plants, including anthocyanins, phytoestrogens, and tannins. Polyphenols are secondary metabolites produced by almost every part of plants, including fruits, flowers, leaves and bark. | 1 | Biochemistry |
The first contribution to van der Waals forces is due to electrostatic interactions between rotating permanent dipoles, quadrupoles (all molecules with symmetry lower than cubic), and multipoles. It is termed the Keesom interaction, named after Willem Hendrik Keesom. These forces originate from the attraction between permanent dipoles (dipolar molecules) and are temperature dependent.
They consist of attractive interactions between dipoles that are ensemble averaged over different rotational orientations of the dipoles. It is assumed that the molecules are constantly rotating and never get locked into place. This is a good assumption, but at some point molecules do get locked into place. The energy of a Keesom interaction depends on the inverse sixth power of the distance, unlike the interaction energy of two spatially fixed dipoles, which depends on the inverse third power of the distance. The Keesom interaction can only occur among molecules that possess permanent dipole moments, i.e., two polar molecules. Also Keesom interactions are very weak van der Waals interactions and do not occur in aqueous solutions that contain electrolytes. The angle averaged interaction is given by the following equation:
where d = electric dipole moment, = permitivity of free space, = dielectric constant of surrounding material, T = temperature, = Boltzmann constant, and r = distance between molecules. | 6 | Supramolecular Chemistry |
The main areas of use are the conversion of ketones to esters (Baeyer-Villiger oxidation), epoxidation of alkenes (Prilezhaev reaction), conversion of silyl enol ethers to silyl α-hydroxy ketones (Rubottom oxidation), oxidation of sulfides to sulfoxides and sulfones, and oxidation of amines to produce amine oxides. The following scheme shows the epoxidation of cyclohexene with mCPBA.
The epoxidation mechanism is concerted: the cis or trans geometry of the alkene starting material is retained in the epoxide ring of the product. The transition state of the Prilezhaev reaction is given below:
The geometry of the transition state, with the peracid bisecting the C-C double bond, allows the two primary frontier orbital interactions to occur: π (HOMO) to σ* (LUMO) and n (HOMO, regarded as a filled p orbital on a sp hybridized oxygen) to π* (LUMO), corresponding, in arrow-pushing terms, to formation of one C-O bond and cleavage of the O-O bond and formation of the other C-O bond and cleavage of the C=C π bond. | 0 | Organic Chemistry |
CARS spectroscopy can be used for temperature measurements; because the CARS signal is temperature dependent. The strength of the signal scales (non-linearly) with the difference in the ground state population and the vibrationally excited state population. Since the population of states follows the temperature dependent Boltzmann distribution, the CARS signal carries an intrinsic temperature dependence as well. This temperature dependence makes CARS a popular technique for monitoring the temperature of hot gases and flames. | 3 | Analytical Chemistry |
Breath analysis is a convenient and non-invasive way to detect chemicals in a bodily system such as alcohol content to determine intoxication, monitor the levels of anesthetics in the body during surgical procedures, and identify performance-enhancing substances in the system of athletes. However, conventional techniques are ineffective at low concentrations. An electrospray ionization interface assisted by an ion funnel used in a linear trap quadrupole Fourier-transform ion cyclotron resonance mass spectrometer was shown to greatly increase sensitivity with high resolution. | 7 | Physical Chemistry |
LAGP-based membranes have been applied as separators in lithium-sulfur batteries. LAGP allows the transfer of lithium ions from anode to cathode but, at the same time, prevents the diffusion of polysulfides from the cathode, suppressing the polysulfide shuttle effect and enhancing the overall performance of the battery. Typically, all-solid-state lithium-sulfur batteries are not fabricated because of high interfacial resistance; therefore, hybrid electrolytes are usually realized, in which LAGP acts as a barrier against polysulfide diffusion but it is combined with liquid or polymer electrolytes to promote fast lithium diffusion and to improve the interfacial contact with electrodes. | 7 | Physical Chemistry |
There are three classes of multiple sclerosis: relapsing-remitting (RRMS), primary progressive (PPMS) and secondary progressive (SPMS). Gene regulatory network (GRN) plays a vital role to understand the disease mechanism across these three different multiple sclerosis classes. | 1 | Biochemistry |
Bottles of di-tert-butyl dicarbonate buildup of internal pressure in sealed containers caused by its slow decomposition to di-tert-butyl carbonate and ultimately tert-butanol and CO in the presence of moisture. For this reason, it is usually sold and stored in plastic bottles rather than glass ones.
The main hazard of the reagent is its inhalational toxicity. Its median lethal concentration of 100 mg/m over 4 hours in rats is comparable to that of phosgene (49 mg/m over 50 min in rats). | 0 | Organic Chemistry |
Finally, fluids with an even higher molecular complexity can exhibit non-classical behavior in the single-phase vapor region near saturation. They are called Bethe-Zel’dovich-Thompson (BZT) fluids, from the name of physicists Hans Bethe, Yakov Zel'dovich, and Philip Thompson, who first worked on these kinds of fluids.
For thermodynamic conditions lying in the non-classical regime, the non-monotone evolution of the Mach number in isentropic expansions can be found even in subsonic conditions. In fact, for values of , positive values of can be reached also in subsonic flows (). In other words, the non-monotone Mach number evolution is also possible in the convergent section of an isentropic nozzle.
Moreover, a peculiar phenomenon of the non-classical regime is the so-called inverted gas-dynamics. In the classical regime, expansions are smooth isentropic processes, while compressions occur through shock waves, which are discontinuities in the flow. If gas-dynamics is inverted, the opposite occurs, namely rarefaction shock waves are physically admissible and compressions occur through smooth isentropic processes.
As a consequence of the negative value of , two other peculiar phenomena can occur for BZT fluids: shock splitting and composite waves. Shock splitting occurs when an inadmissible pressure discontinuity evolves in time by generating two weaker shock waves. Composite waves, instead, are referred to as phenomena in which two elementary waves propagate as a single entity.
Experimental evidence of a non-classical gas-dynamic regime is not available yet. The main reasons are the complexity of performing experiments in such challenging thermodynamic conditions and the thermal stability of these very complex molecules. | 7 | Physical Chemistry |
The bond coat adheres the thermal barrier to the substrate. Additionally, the bond coat provides oxidation protection and functions as a diffusion barrier against the motion of substrate atoms towards the environment. The five major types of bond coats are: the aluminides, the platinum-aluminides, MCrAlY, cobalt-cermets, and nickel-chromium. For aluminide bond coatings, the coatings final composition and structure depends on the substrate composition. Aluminides lack ductility below 750 °C, and exhibit limited thermomechanical fatigue strength. Pt-aluminides are similar to the aluminide bond coats except for a layer of Pt (5—10 μm) deposited on the blade. The Pt aids in oxide adhesion and contributes to hot corrosion, increasing blade lifespan. MCrAlY does not strongly interact with the substrate. Normally applied by plasma spraying, MCrAlY coatings from secondary aluminum oxides. This means that the coatings form an outer chromia layer and a secondary alumina layer underneath. These oxide formations occur at high temperatures in the range of those that superalloys usually encounter. The chromia provides oxidation and hot-corrosion resistance. The alumina controls oxidation mechanisms by limiting oxide growth by self-passivating. The yttrium enhances oxide adherence to the substrate, and limits the growth of grain boundaries (which can lead to coat flaking). Addition of rhenium and tantalum increases oxidation resistance. Cobalt-cermet-based coatings consisting of materials such as tungsten carbide/cobalt can be used due to excellent resistance to abrasion, corrosion, erosion, and heat. These cermet coatings perform well in situations where temperature and oxidation damage are significant concerns, such as boilers. One of cobalt cermets unique advantages is minimal loss of coating mass over time, due to the strength of carbides. Overall, cermet coatings are useful in situations where mechanical demands are equal to chemical demands. Nickel-chromium coatings are used most frequently in boilers fed by fossil fuels, electric furnaces, and waste incineration furnaces, where the danger of oxidizing agents and corrosive compounds in the vapor must be addressed. The specific method of spray-coating depends on the coating composition. Nickel-chromium coatings that also contain iron or aluminum provide better corrosion resistance when they are sprayed and laser glazed, while pure nickel-chromium coatings perform better when thermally sprayed exclusively. | 8 | Metallurgy |
The method is proposed as an assay that employs both cfDNA whole genome methylation sequencing and fragmentomic feature information for multicancer classification. Copy number ratios calculated for healthy and cancerous tissues are used as a cancer type and cancer existence identifier. As done in EPIC-seq, the method also utilizes fragment lengths. Short fragment over long fragment ratio is used in the method as an identifier score. Using the single base or region level methylation percentages on detected cancer methylation markers for each cancer type, copy number ratios, and short/long fragment ratios; the method employs a custom Support Vector Machines algorithm to classify the cancer type if there exists one. This method reports the cancer detection and tissue-of-origin of 4 cancer types. However, it requires detection of specific methylation sites/regions of interest for cancer types | 1 | Biochemistry |
Instrumentation in time-domain diffuse optics consists of three fundamental components namely, a pulsed laser source, a single photon detector and a timing electronics. | 7 | Physical Chemistry |
µSR requires a particle accelerator for the production of a muon beam. This is presently achieved at few large scale facilities in the world: the CMMS continuous source at TRIUMF in Vancouver, Canada; the SµS continuous source at the Paul Scherrer Institut (PSI) in Villigen, Switzerland; the ISIS Neutron and Muon Source and RIKEN-RAL pulsed sources at the Rutherford Appleton Laboratory in Chilton, United Kingdom; and the J-PARC facility in Tokai, Japan, where a new pulsed source is being built to replace that at KEK in Tsukuba, Japan.
Muon beams are also available at the Laboratory of Nuclear Problems, Joint Institute for Nuclear Research (JINR) in Dubna, Russia.
The International Society for µSR Spectroscopy (ISMS) exists to promote the worldwide advancement of µSR. Membership in the society is open free of charge to all individuals in academia, government laboratories and industry who have an interest in the society's goals. | 7 | Physical Chemistry |
Cyclohexenone is an organic compound which is a versatile intermediate used in the synthesis of a variety of chemical products such as pharmaceuticals and fragrances. It is colorless liquid, but commercial samples are often yellow.
Industrially, cyclohexenone is prepared from phenol by Birch reduction.
Cyclohexenone is a ketone, or more precisely an enone. Common reactions include nucleophilic conjugate addition with organocopper reagents, Michael reactions and Robinson annulations. | 0 | Organic Chemistry |
Despite the low oxygen conditions, organisms have evolved to live in and around OMZs. For those organisms, like the vampire squid, special adaptations are needed to either make do with lesser amounts of oxygen or to extract oxygen from the water more efficiently. For example, the giant red mysid (Gnathophausia ingens) continues to live aerobically (using oxygen) in OMZs. They have highly developed gills with large surface area and thin blood-to-water diffusion distance that enables effective removal of oxygen from the water (up to 90% O removal from inhaled water) and an efficient circulatory system with high capacity and high blood concentration of a protein (hemocyanin) that readily binds oxygen.
Another strategy used by some classes of bacteria in the oxygen minimum zones is to use nitrate rather than oxygen, thus drawing down the concentrations of this important nutrient. This process is called denitrification. The oxygen minimum zones thus play an important role in regulating the productivity and ecological community structure of the global ocean. For example, giant bacterial mats floating in the oxygen minimum zone off the west coast of South America may play a key role in the region's extremely rich fisheries, as bacterial mats the size of Uruguay have been found there. | 9 | Geochemistry |
Some other methods to produce LAGP materials have been reported in literature works, including liquid-based techniques, spark plasma sintering, and co-precipitation.
In the following table, some ionic conductivity values are reported for LAGP materials produced with different synthesis routes, in the case of optimized production and annealing conditions. | 7 | Physical Chemistry |
Protocell research has created controversy and opposing opinions, including criticism of vague definitions of "artificial life". The creation of a basic unit of life is the most pressing ethical concern, although the most widespread worry about protocells is their potential threat to human health and the environment through uncontrolled replication.
Additionally, postulation into the conditions for protocellular origins of life on Earth remain debated. Scientists in the field emphasize the importance of further hypothesis based experimentation over theoretical conjecture to more concretely constrain the prebiotic plausibility of different protocell morphologies, geologic conditions, and synthetic schemes. | 9 | Geochemistry |
Diastereomeric recrystallisation is a method of chiral resolution of enantiomers from a racemic mixture. It differs from asymmetric synthesis, which aims to produce a single enantiomer from the beginning, in that diastereomeric recrystallisation separates two enantiomers that have already mixed into a single solution.
The strategy of diastereomeric recrystallisation involves two steps. The first step is to convert the enantiomers into diastereomers by way of a chemical reaction. A mixture of enantiomers may contain two isomers of a molecule with one chiral center. After adding a second chiral center in a determined location, the two isomers are still different, but they are no longer mirror images of each other; rather, they become diastereomers.
In a prototypical example, a mixture of R and S enantiomers with one chiral center would become a mixture of (R,S) and (S,S) diastereomers. (The R-S notation is explained here.) The conversion of the enantiomeric mixture into a diastereomer pair, depending on the nature of the chemicals, can be via covalent bond formation with the enantiopure resolving agent, or by salt formation, the latter being particularly convenient since acid base chemistry is typically quite operationally simple and high yielding.
The second step, once the diastereomers have formed, is to separate them using recrystallisation. This is possible because enantiomers have shared physical properties such as melting point and boiling point, but diastereomers have different chemical properties, so they can be separated like any two different molecules. It is these, now different, physical properties e.g. Melting point & Enthalpy of fusion which determine the eutectic composition (see Eutectic system) which correlates with the maximum yield of pure diastereomer in the crystallization (R, see example melting point phase diagram of a diastereomeric system across all compositions in Figure 1). Various methods have been developed to screening diastereomeric resolutions by determining the eutectic composition as a means of ranking for yield efficiency. | 4 | Stereochemistry |
The TSH index is reduced in patients with secondary hypothyroidism resulting from thyrotropic insufficiency. For this indication, it has, however, up to now only been validated in adults. JTI was also found reduced in cases of TACITUS syndrome (non-thyroidal illness syndrome) as an example of type 1 thyroid allostasis. Conversely, an elevated thyroid function index may serve as a biomarker for type 2 allostasis and contextual stress.
Jostel's TSH index may decrease under therapy with the antidiabetic drug metformin, especially in women under oral contraceptives.
In two large population-based cohorts included in the Study of Health in Pomerania differentially correlated to some markers of body composition. Correlation was positive to body mass index (BMI), waist circumference and fat mass, but negative to body cell mass. With the exception of fat mass all correlations were age-dependent. Very similar observations have been made earlier in the NHANES dataset.
In Parkinson's disease, JTI is significantly elevated in early sub-types of the disease compared to an advanced group.
A longitudinal study in euthyroid subjects with structural heart disease found that JTI predicts the risk of malignant arrhythmia including ventricular fibrillation and ventricular tachycardia. This applies to both incidence and event-free survival. It was therefore concluded that an elevated set point of thyroid homeostasis may contribute to cardiovascular risk. A positive correlation of JTI to SIQALS 2, a score for allostatic load, suggests that thyroid hormones are among the mediators linking stress to major cardiovascular endpoints.
Another study demonstrated the TSH index to inversely correlate to thyroid's secretory capacity and thyroid volume. It is unclear if this finding reflects shortcomings of the index (i.e. low specificity in the setting of subclinical hypothyroidism) or plastic responses of the pituitary gland to beginning hypothyroidism.
In subjects with type 2 diabetes, treatment with beta blockers resulted in increased TSH index, but the mechanism is unclear.
Negative correlation of Jostel's TSH index to the urinary excretion of certain phthalates suggests that endocrine disruptors may affect the central set point of thyroid homeostasis. | 1 | Biochemistry |
Storeys research includes studies of enzyme properties, gene expression, protein phosphorylation, epigenetics, and cellular signal transduction mechanisms to seek out the basic principles of how organisms endure and flourish under extreme conditions. He is particularly known within the field of cryobiology for his studies of animals that can survive freezing, especially the frozen "frog-sicles" (Rana sylvatica) that have made his work popular with multiple TV shows and magazines. Storeys studies of the adaptations that allow frogs, insects, and other animals to survive freezing have made major advances in the understanding of how cells, tissues and organs can endure freezing. Storey was also responsible for the discovery that some turtle species are freeze tolerant: newly hatched painted turtles that spend their first winter on land (Chrysemys picta marginata & C. p. bellii). These turtles are unique as they are the only reptiles, and highest vertebrate life form, known to tolerate prolonged natural freezing of extracellular body fluids during winter hibernation. These advances may aid the development of organ cryopreservation technology. A second area of his research is metabolic rate depression - understanding the mechanisms by which some animals can reduce their metabolism and enter a state of hypometabolism or torpor that allows them to survive prolonged environmental stresses. His studies have identified molecular mechanisms that underlie metabolic arrest across phylogeny and that support phenomena including mammalian hibernation, estivation, and anoxia- and ischemia-tolerance. These studies hold key applications for medical science, particularly for preservation technologies that aim to extend the survival time of excised organs in cold or frozen storage. Additional applications include insights into hyperglycemia in metabolic syndrome and diabetes, and anoxic and ischemic damage caused by heart attack and stroke. Furthermore, Storey's lab has created several web based programs freely available for [http://www.kenstoreylab.com/research-tools/ data management, data plotting, and microRNA analysis]. | 1 | Biochemistry |
Current U.S. assay offices include the following:
* The Philadelphia Mint – 1792 to date
* The Denver Mint – 1862 to date. It served as an assay office until 1906, when coinage operations began.
* The San Francisco Mint – 1852 to date. Coinage operations were suspended in March 1955, but the plant continued to operate as an assay office. In 1962, its official designation was changed from mint to assay office. Coinage operations were again authorized in 1965.
* The West Point, New York Bullion Depository – 1938 to date. It is operated as an adjunct of the New York Assay Office. | 3 | Analytical Chemistry |
Lawessons reagent (LR) is a chemical compound used in organic synthesis as a thiation agent. Lawessons reagent was first made popular by Sven-Olov Lawesson, who did not, however, invent it. Lawesson's reagent was first made in 1956 during a systematic study of the reactions of arenes with PS. | 0 | Organic Chemistry |
Isotopic effect expressed with the equations given above only refer to reactions that can be described with first-order kinetics. In all instances in which this is not possible, transient kinetic isotope effects should be taken into account using the GEBIK and GEBIF equations. | 7 | Physical Chemistry |
The compound with empirical formula FeSn is the first known kagome magnet. It is an intermetallic compound composed of iron (Fe) and tin (Sn), with alternating planes of FeSn and Sn. | 8 | Metallurgy |
Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in natural gas for stoves or heating; butane in torches and lighters; various aliphatic (as well as aromatic) hydrocarbons in liquid transportation fuels like petrol/gasoline, diesel, and jet fuel; and other uses such as ethyne (acetylene) in welding. | 0 | Organic Chemistry |
The P-N bond is susceptible to attack by protic reagents. Alcoholysis occurs readily:
:PhPNEt + ROH → PhPOR + HNEt
The P-N bond reverts to the chloride upon treatment with anhydrous hydrogen chloride:
:PhPNEt + 2 HCl → PhPCl + [HNEt]Cl
Similarly, transamination is used in the conversion of one aminophosphine to another:
:P(NMe) + RNH P(NR)(NMe) + HNMe
With tris(dimethylamino)phosphine is a reactant, the equilibrium can be driven by evaporation of dimethylamine.
Since the P-NR bond is not attacked by Grignard reagents, aminophosphine chlorides are useful reagents in the preparation of unsymmetrical tertiary phosphines. Illustrative is the conversion of dimethylaminophosphorus dichloride to chlorodimethylphosphine:
:2 MeMgBr + MeNPCl → MeNPMe + 2 MgBrCl
:MeNPMe + 2 HCl → ClPMe + MeNHCl
Illustrative also is the chemistry of 1,2-bis(dichlorophosphino)benzene, a versatile precursor to diphosphine ligands, is prepared using aminophosphine reagents. It is prepared from 1,2-dibromobenzene via lithiation and treatment with (EtN)PCl (Et = ethyl). This route gives CH[P(NEt)], which is treated with hydrogen chloride:
:CH[P(NEt)] + 8 HCl → CH(PCl) + 4 EtNHCl | 0 | Organic Chemistry |
Naturally occurring polymers such as cotton, starch, and rubber were familiar materials for years before synthetic polymers such as polyethene and perspex appeared on the market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur. Ways in which polymers can be modified include oxidation, cross-linking, and end-capping. | 7 | Physical Chemistry |
Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production.
Coenzyme A (CoASH or CoA) consists of a β-mercaptoethylamine group linked to pantothenic acid (vitamin B5) through an amide linkage and 3'-phosphorylated ADP. The acetyl group (indicated in blue in the structural diagram on the right) of acetyl-CoA is linked to the sulfhydryl substituent of the β-mercaptoethylamine group. This thioester linkage is a "high energy" bond, which is particularly reactive. Hydrolysis of the thioester bond is exergonic (−31.5 kJ/mol).
CoA is acetylated to acetyl-CoA by the breakdown of carbohydrates through glycolysis and by the breakdown of fatty acids through β-oxidation. Acetyl-CoA then enters the citric acid cycle, where the acetyl group is oxidized to carbon dioxide and water, and the energy released is captured in the form of 11 ATP and one GTP per acetyl group.
Konrad Bloch and Feodor Lynen were awarded the 1964 Nobel Prize in Physiology or Medicine for their discoveries linking acetyl-CoA and fatty acid metabolism. Fritz Lipmann won the Nobel Prize in 1953 for his discovery of the cofactor coenzyme A. | 1 | Biochemistry |
Polanyis model of adsorption was met with much criticism for several decades after publication years. His simplistic model for determining adsorption was formed during the time of the discovery of Debyes fixed dipoles, Bohr's atomic model, and well as the developing theory of intermolecular forces and electrostatic forces by key figures in the chemistry world including W.H. Bragg, W.L. Bragg, and Willem Hendrik Keesom.
Opponents of his model claimed that Polanyis theory did not take into account these emerging theories. Criticism included that the model did not take into account the electrical interactions of the gas and the surface, and that the presence of other molecules would screen off the attraction of the gas to the surface. Polanyis model was furthermore put under scrutiny following the experimental claims of Irving Langmuir from 1916 to 1918 through whose research would eventually win the Nobel Prize in 1932.
However, Polanyi was not able to participate in many of these discussions because he served as a medical officer for the Austro-Hungarian army in the Serbian front during World War I. Polanyi wrote about this experience saying: | 7 | Physical Chemistry |
Most metal carbonyl complexes contain a mixture of ligands. Examples include the historically important IrCl(CO)(P(CH)) and the antiknock agent (CHCH)Mn(CO). The parent compounds for many of these mixed ligand complexes are the binary carbonyls, those species of the formula [M(CO)], many of which are commercially available. The formulae of many metal carbonyls can be inferred from the 18-electron rule. | 0 | Organic Chemistry |
Bina Shaheen Siddiqui is a Pakistani chemist and the Director of the H.E.J. Research Institute of Chemistry at the University of Karachi. Siddiqui graduated from the University of Karachi with an MPhil in 1978. In 1980, she graduated from the same university with a PhD in organic chemistry.
She specialises in the chemical components of Pakistan's indigenous plants. She was elected to The World Academy of Sciences in 1989, and was elected a Fellow of the Pakistan Academy of Sciences in 1997. She is also a Fellow of the Chemical Society of Pakistan. | 0 | Organic Chemistry |
For historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates (excluding carbonate esters), simple oxides of carbon (for example, CO and carbon dioxide|) and cyanides are generally considered inorganic compounds. Different forms (allotropes) of pure carbon, such as diamond, graphite, fullerenes and carbon nanotubes are also excluded because they are simple substances composed of a single element and so not generally considered chemical compounds.
The word "organic" in this context does not mean "natural". | 0 | Organic Chemistry |
The bx1 gene encodes a protein, BX1, that forms indol from indol-3-glycerol phosphate in the plastid. It is the first step in the pathway and determines much of the natural variation in levels of DIMBOA in maize. The next steps in the pathway occur in the endoplasmic reticulum, also referred to as the microsomes in cell fractionation experiments, and are carried by proteins encoded by genes bx2, bx3, bx4, and bx5. | 1 | Biochemistry |
In chemistry, a nucleofuge () is a leaving group which retains the lone pair of electrons from its previous bond with another species. For example, in the S2 mechanism, a nucleophile attacks an organic compound containing the nucleofuge (the bromo group) which simultaneously breaks the bond with the nucleofuge.
After a reaction nucleofuges may contain either a negative or a neutral charge; this is governed by the nature of the specific reaction.
The word nucleofuge is commonly found in older literature, but its use is less common in current literature in which the term leaving group dominates. | 0 | Organic Chemistry |
A suggestion has been made that in the early stages of the Earths development when its radioactivity was almost two orders of magnitude higher than at present, radiolysis could have been the principal source of atmospheric oxygen, which ensured the conditions for the origin and development of life. Molecular hydrogen and oxidants produced by the radiolysis of water may also provide a continuous source of energy to subsurface microbial communities (Pedersen, 1999). Such speculation is supported by a discovery in the Mponeng Gold Mine in South Africa, where the researchers found a community dominated by a new phylotype of Desulfotomaculum', feeding on primarily radiolytically produced H. | 5 | Photochemistry |
A submitochondrial particle (SMP) is an artificial vesicle made from the inner mitochondrial membrane. They can be formed by subjecting isolated mitochondria to sonication, freezing and thawing, high pressure, or osmotic shock. SMPs can be used to study the electron transport chain in a cell-free context.
The process of SMP formation forces the inner mitochondrial membrane inside out, meaning that the matrix-facing leaflet becomes the outer surface of the SMP, and the intermembrane space-facing leaflet faces the lumen of the SMP. As a consequence, the F particles which normally face the matrix are exposed. Chaotropic agents can destabilize F particles and cause them to dissociate from the membrane, thereby uncoupling the final step of oxidative phosphorylation from the rest of the electron transport chain. | 1 | Biochemistry |
Immunoelectrophoresis is a general name for a number of biochemical methods for separation and characterization of proteins based on electrophoresis and reaction with antibodies. All variants of immunoelectrophoresis require immunoglobulins, also known as antibodies, reacting with the proteins to be separated or characterized. The methods were developed and used extensively during the second half of the 20th century. In somewhat chronological order: Immunoelectrophoretic analysis (one-dimensional immunoelectrophoresis ad modum Grabar), crossed immunoelectrophoresis (two-dimensional quantitative immunoelectrophoresis ad modum Clarke and Freeman or ad modum Laurell), rocket-immunoelectrophoresis (one-dimensional quantitative immunoelectrophoresis ad modum Laurell), fused rocket immunoelectrophoresis ad modum Svendsen and Harboe, affinity immunoelectrophoresis ad modum Bøg-Hansen. | 1 | Biochemistry |
Photolithotrophs such as plants obtain energy from light and therefore use inorganic electron donors such as water only to fuel biosynthetic reactions (e. g., carbon dioxide fixation in lithoautotrophs). | 1 | Biochemistry |
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