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The TCF7L2 gene, encoding the TCF7L2 protein, is located on chromosome 10q25.2-q25.3. The gene contains 19 exons. Of the 19 exons, 5 are alternative. The TCF7L2 protein contains 619 amino acids and its molecular mass is 67919 Da. TCF7L2's secondary structure is a helix-turn-helix structure. | 1 | Applied and Interdisciplinary Chemistry |
Neuromelanin is found in higher concentrations in humans than in other primates. Neuromelanin concentration increases with age, suggesting a role in neuroprotection (neuromelanin can chelate metals and xenobiotics) or senescence. | 1 | Applied and Interdisciplinary Chemistry |
Symptoms of M2DS include infantile hypotonia and failure to thrive, delayed psychomotor development, impaired speech, abnormal or absent gait, epilepsy, spasticity, gastrointestinal motility problems, recurrent infections, and genitourinary abnormalities. Many of those affected by M2DS also fit diagnostic criteria for autism. M2DS can be associated with syndromic facies, namely an abnormally flat back of the head, underdevelopment of the midface, ear anomalies, deep-set eyes, prominent chin, pointed nose, and a flat nasal bridge. | 1 | Applied and Interdisciplinary Chemistry |
Consideration of the structure factor (and our assumption about translational invariance) is complicated by the fact that atoms in the crystal may be displaced from their respective lattice sites. Taking the scattering potential to be proportional to the density of scattering matter, we rewrite the structure factor.
The integral from here onwards is understood to be taken over the unit cell. is the density of scattering matter. The angle brackets indicate a temporal average of each unit cell followed by a spatial average over every unit cell. We further assume that each atom is displaced independently of the other atoms.
The number of atoms in the unit cell is and the occupancy factor for atom is . represents the point in the unit cell for which we would like to know the density of scattering matter. is the density of scattering matter from atom at a position separated from the nuclear position by a vector . is the probability density function for displacement. is the reference lattice site from which atom may be displaced to a new position . If is symmetrical enough (e.g. spherically symmetrical), is simply the mean nuclear position. When considering X-ray scattering, the scattering matter density consists of electron density around the nucleus. For neutron scattering, we have -functions weighted by a scattering length for the respective nucleus (see Fermi pseudopotential). Note that in the above discussion, we assumed the atoms were not deformable. With this in mind, (9) may be plugged into expression (8) for the structure factor.
Now we see the overall structure factor may be represented as a weighted sum of structure factors corresponding to each atom. Set the displacement between the location in space for which we would like to know the scattering density and the reference position for the nucleus equal to a new variable . Do the same for the displacement between the displaced and reference nuclear positions . Substitute into (10).
Within the square brackets of (11), we convolve the density of scattering matter of atom with the probability density function for some nuclear displacement. Then, in the curly brackets, we Fourier transform the resulting convolution. The final step is to multiply by a phase depending on the reference (e.g. mean) position of atom . But, according to the convolution theorem, Fourier transforming a convolution is the same as multiplying the two Fourier transformed functions. Set the displacement between the location in space for which we would like to know the scattering density and the position for the nucleus equal to a new variable .
Substitute (12) into (10).
That is:
is the atomic form factor of the atom ; it determines how the distribution of scattering matter about the nuclear position influences scattering. is the atomic Debye–Waller factor; it determines how the propensity for nuclear displacement from the reference lattice position influences scattering. The expression given for in the article's opening is different because of 1) the decision to take the thermal or time average, 2) the arbitrary choice of negative sign in the exponential, and 3) the decision to square the factor (which more directly connects it to the observed intensity). | 0 | Theoretical and Fundamental Chemistry |
A homogeneous electrocatalyst is one that is present in the same phase of matter as the reactants, for example, a water-soluble coordination complex catalyzing an electrochemical conversion in solution. This technology is not practiced commercially, but is of research interest. | 0 | Theoretical and Fundamental Chemistry |
Direct translation from DNA to protein has been demonstrated in a cell-free system (i.e. in a test tube), using extracts from E. coli that contained ribosomes, but not intact cells. These cell fragments could synthesize proteins from single-stranded DNA templates isolated from other organisms (e.g., mouse or toad), and neomycin was found to enhance this effect. However, it was unclear whether this mechanism of translation corresponded specifically to the genetic code. | 1 | Applied and Interdisciplinary Chemistry |
The first reported metallic glass was an alloy (AuSi) produced at Caltech by W. Klement (Jr.), Willens and Duwez in 1960. This and other early glass-forming alloys had to be cooled extremely rapidly (in the order of one mega-kelvin per second, 10 K/s) to avoid crystallization. An important consequence of this was that metallic glasses could only be produced in a limited number of forms (typically ribbons, foils, or wires) in which one or more dimensions were small so that heat could be extracted quickly enough to achieve the necessary cooling rates. As a result, metallic glass specimens (with a few exceptions) were limited to thicknesses of less than one hundred micrometers.
Mg-Zn-Ca based metallic glasses are a relatively new group of amorphous metals, possessing commercial and technical advantages over early compositions. Gu and co-workers produced the first Mg-Zn-Ca BMG in 2005, reporting high glass forming ability, high strength and most importantly exceptional plasticity. This lanthanide-free, Mg-based glass attracted immediate interest due to its low density and cost, and particularly because of its uncharacteristically high ductility. This property was unexpected for such compositions, as the constituent elements are found to be of relatively low Poisson ratio, and hence contribute little to the inherent plasticity of the glass. This unlikely asset was seized upon by Li in 2008, who made use of the Poisson ratio principle and increased Mg content at the expense of Zn to further enhance plasticity. Further improvements were achieved by incremental addition of Ca to the Mg72Zn28 binary composition, producing numerous ternary alloys along the 350 °C isotherm of the Mg-Zn-Ca system.
Ternary Ca-Mg-Zn bulk metallic glasses were also discovered in 2005. Similar to the Mg-Zn-Ca, these two amorphous alloys are both bioresorbable metallic glasses and are based on the same Mg-Zn-Ca ternary system. The elements are displayed in order of decreasing atomic concentration. Hence, the distinction between these two metallic glasses lies in their most dominant element, namely Ca and Mg. These Ca-based bulk glassy alloys had compositions of CaMgZn, CaMgZn, and CaMgZn, where X = 0, 5 and 10; Y = 0, 5, 7.5, 10, and 15; and Z = 0, 5, 7.5, 10, and 15. Critical casting thicknesses of up to 10 mm were achieved. | 1 | Applied and Interdisciplinary Chemistry |
The angular momentum density of a fluid element is written either as an antisymmetric tensor () or, equivalently, as a pseudovector. As a tensor,
the equation for the conservation of angular momentum for a simple fluid with no external forces is written:
where is the fluid velocity and is the total pressure tensor (or, equivalently, the negative of the total stress tensor). Note that the Einstein summation convention is used, where summation is assumed over pairs of matched indices. The angular momentum of a fluid element can be separated into extrinsic angular momentum density due to the flow () and intrinsic angular momentum density due to the rotation of the fluid particles about their center of mass ():
where the extrinsic angular momentum density is:
and is the mass density of the fluid element. The conservation of linear momentum equation is written:
and it can be shown that this implies that:
Subtracting this from the equation for the conservation of angular momentum yields:
Any situation in which this last term is zero will result in the total pressure tensor being symmetric, and the conservation of angular momentum equation will be redundant with the conservation of linear momentum. If, however, the internal rotational degrees of freedom of the particles are coupled to the flow (via the velocity term in the above equation), then the total pressure tensor will not be symmetric, with its antisymmetric component describing the rate of angular momentum exchange between the flow and the particle rotation.
In the linear approximation for this transport of angular momentum, the rate of flow is written:
where is the average angular velocity of the rotating particles (as an antisymmetric tensor rather than a pseudovector) and is the rotational viscosity coefficient. | 1 | Applied and Interdisciplinary Chemistry |
If we know that the relevant physical quantities in a physical system are only , then the Reynolds number is essentially fixed by the Buckingham π theorem.
In detail, since there are 4 quantities , but they have only 3 dimensions (length, time, mass), we can consider , where are real numbers. Setting the three dimensions of to zero, we obtain 3 independent linear constraints, so the solution space has 1 dimension, and it is spanned by the vector .
Thus, any dimensionless quantity constructed out of is a function of , the Reynolds number.
Alternatively, we can take the incompressible Navier–Stokes equations (convective form):Remove the gravity term , then the left side consists of inertial force , and viscous force . Their ratio has the order of , the Reynolds number. This argument is written out in detail on the Scallop theorem page. | 1 | Applied and Interdisciplinary Chemistry |
Joseph Black was a chemist who took interest in the pneumatic field after studying under William Cullen. He was first interested in the topic of magnesia alba, or magnesium carbonate (MgCO), and limestone, or calcium carbonate (CaCO), and wrote a dissertation called "De humore acido a cibis orto, et magnesia alba" on the properties of both. His experiments on magnesium carbonate led him to discover that fixed air, or carbon dioxide (CO), was being given off during reactions with various chemicals, including breathing. Despite him never using the pneumatic trough or other instrumentation invented to collect and analyze the airs, his inferences led to more research into fixed air instead of common air, with the trough actually being used.
Gaseous ammonia was first isolated by Joseph Black in 1756 by reacting sal ammoniac (ammonium chloride) with calcined magnesia (magnesium oxide). It was isolated again by Peter Woulfe in 1767, by Carl Wilhelm Scheele in 1770 | 1 | Applied and Interdisciplinary Chemistry |
Biopolymers can be sustainable, carbon neutral and are always renewable, because they are made from plant or animal materials which can be grown indefinitely. Since these materials come from agricultural crops, their use could create a sustainable industry. In contrast, the feedstocks for polymers derived from petrochemicals will eventually deplete. In addition, biopolymers have the potential to cut carbon emissions and reduce CO quantities in the atmosphere: this is because the CO released when they degrade can be reabsorbed by crops grown to replace them: this makes them close to carbon neutral.
Almost all biopolymers are biodegradable in the natural environment: they are broken down into CO and water by microorganisms. These biodegradable biopolymers are also compostable: they can be put into an industrial composting process and will break down by 90% within six months. Biopolymers that do this can be marked with a compostable symbol, under European Standard EN 13432 (2000). Packaging marked with this symbol can be put into industrial composting processes and will break down within six months or less. An example of a compostable polymer is PLA film under 20μm thick: films which are thicker than that do not qualify as compostable, even though they are "biodegradable". In Europe there is a home composting standard and associated logo that enables consumers to identify and dispose of packaging in their compost heap. | 1 | Applied and Interdisciplinary Chemistry |
Only one example is known, bis(trifluoromethyl)phosphinous acid, (CF)POH. It is prepared in several steps from phosphorus trichloride (Et = ethyl):
:PCl + 2 EtNH → PClNEt + EtNHCl
:2 P(NEt) + PClNEt + 2 CFBr → P(CF)NEt + 2 BrClP(NEt)
:P(CF)NEt + HO → P(CF)OH + HNEt | 0 | Theoretical and Fundamental Chemistry |
The rate of living theory postulates that the faster an organism’s metabolism, the shorter its lifespan. First proposed by Max Rubner in 1908, the theory was based on his observation that smaller animals had faster metabolisms and shorter lifespans compared to larger animals with slower metabolisms. The theory gained further credibility through the work of Raymond Pearl, who conducted experiments on drosophila and cantaloupe seeds, which supported Rubners initial observation. Pearls findings were later published in his book, The Rate of Living, in 1928, in which he expounded upon Rubner's theory and demonstrated a causal relationship between the slowing of metabolism and an increase in lifespan.
The theory gained additional credibility with the discovery of Max Kleibers law in 1932. Kleiber found that an organisms basal metabolic rate could be predicted by taking 3/4 the power of the organism's body weight. This finding was noteworthy because the inversion of the scaling exponent, between 0.2 and 0.33, also demonstrated the scaling for both lifespan and metabolic rate, and was colloquially called the "mouse-to-elephant" curve. | 1 | Applied and Interdisciplinary Chemistry |
The crystalline sponges can be viewed as the extension of organometallic cage compounds. They can not only accommodate guest molecules, but also provide non-covalent interactions with the guest. To exploit these properties, the Fujita group demonstrates [(Co(NCS))(TPT)] can enrich C, C, or other higher fullerenes from C mixtures as normal cage compounds did in precedent research. | 0 | Theoretical and Fundamental Chemistry |
According to the Carothers equation number-average degree of polymerization is given by
where is the extent of the reaction and is the average functionality of reaction mixture. For the gel can be considered to be infinite, thus the critical extent of the reaction at the gel point is found as
If is greater or equal to , gelation occurs. | 0 | Theoretical and Fundamental Chemistry |
Iron metallurgy in Africa developed within Africa; though initially assumed to be of external origin, this assumption has been rendered untenable; archaeological evidence has increasingly supported an indigenous origin. Some recent studies date the inception of iron metallurgy in Africa between 3000 BCE and 2500 BCE. Archaeometallurgical scientific knowledge and technological development originated in numerous centers of Africa; the centers of origin were located in West Africa, Central Africa, and East Africa; consequently, as these origin centers are located within inner Africa, these archaeometallurgical developments are thus native African technologies.
Iron metallurgical development occurred 2631 BCE – 2458 BCE at Lejja, in Nigeria, 2136 BCE – 1921 BCE at Obui, in Central Africa Republic, 1895 BCE – 1370 BCE at Tchire Ouma 147, in Niger, and 1297 BCE – 1051 BCE at Dekpassanware, in Togo. Evidence exists for early iron metallurgy in parts of Nigeria, Cameroon, and Central Africa, possibly from as early as around 2,000 BCE. Iron metallurgy may have been independently developed in the Nok culture between the 9th century BCE and 550 BCE. The nearby Djenné-Djenno culture of the Niger Valley in Mali shows evidence of iron production from 250 BCE. The Bantu expansion spread the technology to Eastern and Southern Africa between 500 BCE and 400 CE, as shown in the Urewe culture. | 1 | Applied and Interdisciplinary Chemistry |
Through her experiences carrying out domestic chores, especially dishwashing, Pockels became interested in the effect of soaps on water and more generally on the effect of impurities on water and soapy water. By age 18, she began conducting experiments in her home to understand the physical properties of water and impurities, as an amateur chemist.
As a result of her interests, by age 20, Pockels devised a slide trough for making quantitative measurements on the surface properties of soapy water and related substances. Specifically, this consisted of a trough, made of metal and rectangular in shape, roughly 70 centimeters (cm) long, 5 cm wide, and 2 cm deep. The trough was filled with water. A metal strip of about 1.5 cm width was laid on top of the water across the width of the trough so as to divide the surface of the water in two parts. There was a ruler along the length of the trough so that the position of the metal strip, and therefore the surface area of each of the two parts of the trough, could be determined as the strip was moved along the length of the trough.
Pockels further developed her apparatus by placing a small disk (typically 6 millimeters in diameter), such as a button, on the surface of the water in the trough. She then used a weighing scale (typically an apothecary's balance) to determine the force (weight) necessary to lift the disk from the water. By comparing the forces required to lift the disk from pure water to water containing impurities, she devised a direct measure of surface tension. This apparatus enabled her to investigate the surface forces of mono-molecular films, the surface tension of emulsions and solutions, the effect of impurities on the physical properties of water, and providing an understanding of surfactancy.
Pockels sliding trough design built on the prior findings of Ludwig Wilhelmys plate method of measuring surface tension. Pockels' design influenced later investigators who improved on the method, leading to the modern Langmuir-Blodgett trough which is in extensive use in colloid and surface science in contemporary times. | 0 | Theoretical and Fundamental Chemistry |
In 1681, Samuel Pepys (then serving as Admiralty Secretary) agreed to the removal of lead sheathing from English Royal Navy vessels to prevent the mysterious disintegration of their rudder-irons and bolt-heads, though he confessed himself baffled as to the reason the lead caused the corrosion.
The problem recurred when vessels were sheathed in copper to reduce marine weed accumulation and protect against shipworm. In an experiment, the Royal Navy in 1761 had tried fitting the hull of the frigate HMS Alarm with 12-ounce copper plating. Upon her return from a voyage to the West Indies, it was found that although the copper remained in fine condition and had indeed deterred shipworm, it had also become detached from the wooden hull in many places because the iron nails used during its installation "were found dissolved into a kind of rusty Paste". To the surprise of the inspection teams, however, some of the iron nails were virtually undamaged. Closer inspection revealed that water-resistant brown paper trapped under the nail head had inadvertently protected some of the nails: "Where this covering was perfect, the Iron was preserved from Injury". The copper sheathing had been delivered to the dockyard wrapped in the paper which was not always removed before the sheets were nailed to the hull. The conclusion therefore reported to the Admiralty in 1763 was that iron should not be allowed direct contact with copper in sea water. | 1 | Applied and Interdisciplinary Chemistry |
Force spectroscopy is a set of techniques for the study of the interactions and the binding forces between individual molecules. These methods can be used to measure the mechanical properties of single polymer molecules or proteins, or individual chemical bonds. The name "force spectroscopy", although widely used in the scientific community, is somewhat misleading, because there is no true matter-radiation interaction.
Techniques that can be used to perform force spectroscopy include atomic force microscopy, optical tweezers, magnetic tweezers, acoustic force spectroscopy, microneedles, and biomembranes.
Force spectroscopy measures the behavior of a molecule under stretching or torsional mechanical force. In this way a great deal has been learned in recent years about the mechanochemical coupling in the enzymes responsible for muscle contraction, transport in the cell, energy generation (F1-ATPase), DNA replication and transcription (polymerases), DNA unknotting and unwinding (topoisomerases and helicases).
As a single-molecule technique, as opposed to typical ensemble spectroscopies, it allows a researcher to determine properties of the particular molecule under study. In particular, rare events such as conformational change, which are masked in an ensemble, may be observed. | 0 | Theoretical and Fundamental Chemistry |
Pasteur observed that fermentation does not require oxygen, but needs yeast, which is alive. Fermentation is a biological process, not a reduction and oxygen chemical process. He used two slender bottles. One of the bottles had a curved neck; this is called a swan neck. Pasteur poured liquid broth into the two bottles, and heated in the bottom of the bottles. When the liquid boiled, he let them cool. Pasteur observed that the broth in the curved bottle stayed clear, except when the bottle was shaken.
Pasteur explained that the two bottles were filled with air, but the curved bottle could stop most of the particles in the air, and it kept its nature. However, the liquid in the other bottle degenerated. Therefore, he concluded that fermentation does not require oxygen, but needs the yeast. When yeast is allowed to grow over time, the substance will spoil or rot.
Pasteur's viewed fermentation as a type of vitalism. He observed that living organisms were responsible for the process of fermentation. | 1 | Applied and Interdisciplinary Chemistry |
Inherent within this model, the following assumptions are valid specifically for the simplest case: the adsorption of a single adsorbate onto a series of equivalent sites onto the surface of the solid.
# The surface containing the adsorbing sites is a perfectly flat plane with no corrugations (assume the surface is homogeneous). However, chemically heterogeneous surfaces can be considered to be homogeneous if the adsorbate is bound to only one type of functional groups on the surface.
# The adsorbing gas adsorbs into an immobile state.
# All sites are energetically equivalent, and the energy of adsorption is equal for all sites.
# Each site can hold at most one molecule (mono-layer coverage only).
# No (or ideal) interactions between adsorbate molecules on adjacent sites. When the interactions are ideal, the energy of side-to-side interactions is equal for all sites regardless of the surface occupancy. | 0 | Theoretical and Fundamental Chemistry |
In general, δZn values of various rocks and minerals do not appear to significantly vary. The δZn value of bulk silicate Earth (BSE) is +0.28 + 0.05‰. Fractionation of Zn isotopes by igneous processes is generally insignificant, and δZn values of basalt fall within the range of +0.2 to +0.3‰, encompassing the value for BSE. δZn values of clay minerals from diverse environments and of diverse ages have been found to fall within the same range as basalts, suggesting negligible fractionation between the basaltic precursors and sedimentary materials. Carbonates appear to be more Zn-enriched than other sedimentary and igneous rocks. For example, the δZn value of a limestone core taken from the Central Pacific was +0.6‰ at the surface and increased to +1.2‰ with depth The Zn isotopic compositions of various ores are not well-characterized, but smithsonites and sphalerites (Zn carbonates and Zn sulfides, respectively) collected from various localities in Europe had δZn values ranging from -0.06 to +0.69‰, with smithsonite potentially slightly heavier by 0.3‰ than sphalerite. | 0 | Theoretical and Fundamental Chemistry |
In a cell, there are several non-canonical bases present: CpG islands in DNA (often methylated), all eukaryotic mRNA (capped with a methyl-7-guanosine), and several bases of rRNAs (methylated). Often, tRNAs are heavily modified postranscriptionally in order to improve their conformation or base pairing, in particular in or near the anticodon: inosine can base pair with C, U, and even with A, whereas thiouridine (with A) is more specific than uracil (with a purine). Other common tRNA base modifications are pseudouridine (which gives its name to the TΨC loop), dihydrouridine (which does not stack as it is not aromatic), queuosine, wyosine, and so forth. Nevertheless, these are all modifications to normal bases and are not placed by a polymerase. | 1 | Applied and Interdisciplinary Chemistry |
The Rehbinder effect in physics is the reduction in the hardness and ductility of a material, particularly metals, by a surfactant film. The effect is named for Soviet scientist , who discovered the effect in 1928.
A proposed explanation for this effect is the disruption of surface oxide films, and the reduction of surface energy by surfactants.
The effect is of particular importance in machining, as lubricants reduce cutting forces. | 0 | Theoretical and Fundamental Chemistry |
CcrM is a type II DNA Methyltransferase, that transfer a methyl group from the methyl donor SAM to the N6 of an adenine in a 5-GANTC-3 recognition sites of hemimethylated DNA. Based on the order of the conserved motifs that form the SAM binding, the active site and the target recognition domain in the sequence of CcrM it can be classified as a β-class adenine N6 Methyltransferase. CcrM homologs in Alphaproteobacteria have an 80 residues C terminal domain, with non well characterized function.
CcrM is characterized by a high degree of sequence discrimination, showing a very high specificity for GANTC sites over AANTC sites , being able to recognize and methylate this sequence in both double and single strand DNA. CcrM in complex with a dsDNA structure was resolved, showing that the enzyme presents a novel DNA interaction mechanism, opening a bubble in the DNA recognition site (The concerted mechanism of Methyltransferases relies in the flip of the target base), the enzyme interacts with DNA forming an homodimer with differential monomer interactions.
CcrM is a highly efficient enzyme capable of methylating a high number of 5-GANTC-3 sites in low time, however if the enzyme is processive (the enzyme binds to the DNA and methylate several methylation sites before dissociation) or distributive (the enzyme dissociates from DNA after each methylation) it is still in discussion. First reports indicated the second case, however more recent characterisation of CcrM indicate that it is a processive enzyme. | 1 | Applied and Interdisciplinary Chemistry |
The x-ray beam used for topography is generated by an x-ray source, typically either a laboratory x-ray tube (fixed or rotating) or a synchrotron source. The latter offers advantages due to its higher beam intensity, lower divergence, and its continuous wavelength spectrum. X-ray tubes are still useful, however, due to easier access and continuous availability, and are often used for initial screening of samples and/or training of new staff.
For white beam topography, not much more is required: most often, a set of slits to precisely define the beam shape and a (well polished) vacuum exit window will suffice. For those topography techniques requiring a monochromatic x-ray beam, an additional crystal monochromator is mandatory. A typical configuration at synchrotron sources is a combination of two Silicon crystals, both with surfaces oriented parallel to [111]-lattice planes, in geometrically opposite orientation. This guarantees relatively high intensity, good wavelength selectivity (about 1 part in 10000) and the possibility to change the target wavelength without having to change the beam position ("fixed exit"). | 0 | Theoretical and Fundamental Chemistry |
A foundational discourse on the field of chemometrics by Kowalski, "Chemometrics: Views and Propositions," was published in 1975. In it he defines chemometrics as "any and all methods that can be used to extract useful chemical information from raw data." Kowalski takes up the question of what constitutes "new and viable research" in the field and goes on to explain how his training as an analytical chemist and experience with pattern recognition as a tool for chemical analysis has influenced his opinion about this. The included letter to a "prospective chemometrician," signed by Kowalski and Svante Wold, asserts "chemometrics should not involve theoretical calculations, but should deal primarily with the extraction of useful chemical information from measured data." The letter announces that an informal "Chemometrics Society" was begun on June 10, 1974, describes the purposes of the society and invites the interested researcher to join. Kowalskis research group was given as the Laboratory for Chemometrics, Department of Chemistry, University of Washington, and Wolds research group was given as Research Group for Chemometrics, Institute of Chemistry, Umea University, Sweden. This society, formed from Kowalksis and Wolds two research groups, eventually became the International Chemometrics Society.
Wold had coined the term "chemometrics" for a grant application in 1971. He and Kowalski first met in 1973 at a symposium in Tucson, Arizona, and after discussion, Kowalski agreed to use the term to describe his own research as well. Wold says Kowalski became "both a strong proponent and spokesman for this new field." | 0 | Theoretical and Fundamental Chemistry |
The experimental determination of reaction rates involves measuring how the concentrations of reactants or products change over time. For example, the concentration of a reactant can be measured by spectrophotometry at a wavelength where no other reactant or product in the system absorbs light.
For reactions which take at least several minutes, it is possible to start the observations after the reactants have been mixed at the temperature of interest. | 0 | Theoretical and Fundamental Chemistry |
Olefin metathesis has several industrial applications. Almost all commercial applications employ heterogeneous catalysts using catalysts developed well before the Nobel-Prize winning work on homogeneous complexes. Representative processes include:
*The Phillips Triolefin and the Olefin conversion technology. This process interconverts propylene with ethylene and 2-butenes. Rhenium and molybdenum catalysts are used. Nowadays, only the reverse reaction, i.e., the conversion of ethylene and 2-butene to propylene is industrially practiced, however.
*Shell higher olefin process (SHOP) produces (alpha-olefins) for conversion to detergents. The process recycles certain olefin fractions using metathesis.
*Neohexene production, which involves ethenolysis of isobutene dimers. The catalyst is derived from tungsten trioxide supported on silica and MgO.
*1,5-Hexadiene and 1,9-decadiene, useful crosslinking agents and synthetic intermediates, are produced commercially by ethenolysis of 1,5-cyclooctadiene and cyclooctene. The catalyst is derived from ReO on alumina.
*Synthesis of pharmaceutical drugs, | 0 | Theoretical and Fundamental Chemistry |
The development of high-speed and high-sensitivity pump–probe imaging techniques has enabled applications in several fields, such as materials science, biology, and art. | 0 | Theoretical and Fundamental Chemistry |
*ALAS1 Aminolevulinic Acid Synthase type 1 (type 2 is erythroid and associated with porphyria)
*ARHGEF2 Rho guanine nucleotide exchange factor
*ARMET Mesencephalic astrocyte-derived neurotrophic factor
*AES amino terminal enhancer of split
*BECN1 involved in autophagy and partners with PI3K
*BUD31 formerly Maternal G10 transcript
*Creatine kinase CKB (ATP reservoir)
*Cytidine deaminase questionable: not present in very high levels at all
*CPNE1
*ENSA (gene)
*FTH1 Heavy chain of Ferritin
*GDI2 rab/ras vesicular trafficking
*GUK1 Guanylate kinase transfers phosphate from ATP to GMP
*HPRT Hypoxanthine-guanine phosphoribosyltransferase
*IFITM1 Induced by interferon, transmembrane protein
*JTB (gene) Jumping translocation breakpoint
*MMPL2
*NME2 (formerly NM23B) Nucleoside diphosphate kinase
*NONO
*P4HB
*PRDX1 peroxiredoxin (reduces peroxides)
*PTMA Prothymosin
*RPA2 Binds DNA during replication to keep it straightened out
*SULT1A3 Sulfate conjugation (note: SULT1C is cited in earlier literature as being ubiquitous but this may be an example of different tags being used to refer to a common area of 2 closely related genes. If the tag is too short, then it may not be specific enough to truly specify one member of a gene family from another)
*SYNGR2 Synaptogyrin (may participate in vesicle translocation)
*Tetratricopeptide, TTC1 small glutamine rich tetratricopeptide | 1 | Applied and Interdisciplinary Chemistry |
Palladium(II) acetate has been described as being "among the most extensively used transition metal complexes in metal-mediated organic synthesis". Many coupling reactions utilize this reagent, which is soluble in organic solvents and which contains a built-in Bronsted base (acetate). | 0 | Theoretical and Fundamental Chemistry |
Lucie Blanquies was a woman scientist who worked in Madame Curie's laboratory in Paris from 1908 to 1910. She measured the power of the alpha particles emitted by different radioactive materials. | 0 | Theoretical and Fundamental Chemistry |
Polymers with an all-carbon backbone, such as polyolefins, are usually resistant to hydrolysis. Condensation polymers like polyesters, polyamides, polyurethanes and polycarbonates can be degraded by hydrolysis of their carbonyl groups, to give lower molecular weight molecules. Such reactions are exceedingly slow at ambient temperatures, however, they remain a significant source of degradation for these materials, particularly in the marine environment. Swelling caused by the absorption of minute amounts of water can also cause environmental stress cracking, which accelerates degradation. | 0 | Theoretical and Fundamental Chemistry |
On March 28, 2013, a team of bioengineers from Stanford University led by Drew Endy announced that they had created the biological equivalent of a transistor, which they named a "transcriptor". That is, they created a three-terminal device with a logic system that can control other components. The transcriptor regulates the flow of RNA polymerase across a strand of DNA using special combinations of enzymes to control movement. According to project member Jerome Bonnet, "The choice of enzymes is important. We have been careful to select enzymes that function in bacteria, fungi, plants and animals, so that bio-computers can be engineered within a variety of organisms."
Transcriptors can replicate traditional AND, OR, NOR, NAND, XOR, and XNOR gates with equivalents, which Endy dubbed "Boolean Integrase Logic (BIL) gates", in a single-layer process (i.e., without requiring multiple instances of the simpler gates to build up more complex ones). Like a traditional transistor, a transcriptor can amplify an input signal. A group of transcriptors can do almost any type of computing, including counting and comparison. | 1 | Applied and Interdisciplinary Chemistry |
Whole cell and tissue analysis is possible using a microPIXE beam, this method is also referred to as nuclear microscopy. | 0 | Theoretical and Fundamental Chemistry |
Organelle biogenesis is the biogenesis, or creation, of cellular organelles in cells. Organelle biogenesis includes the process by which cellular organelles are split between daughter cells during mitosis; this process is called organelle inheritance. | 1 | Applied and Interdisciplinary Chemistry |
General transcription factors (GTFs) or basal transcription factors are protein transcription factors that have been shown to be important in the transcription of class II genes to mRNA templates. Many of them are involved in the formation of a preinitiation complex, which, together with RNA polymerase II, bind to and read the single-stranded DNA gene template. The cluster of RNA polymerase II and various transcription factors is known as a basal transcriptional complex (BTC). | 1 | Applied and Interdisciplinary Chemistry |
Contrary to bacteria and fungi, most plant metabolic pathways are not grouped into biosynthetic gene clusters, but instead are scattered as individual genes. Some exceptions have been discovered: steroidal glycoalkaloids in Solanum, polyketides in Pooideae, benzoxazinoids in Zea mays, triterpenes in Avena sativa, Cucurbitaceae, Arabidopsis, and momilactone diterpenes in Oryza sativa. | 1 | Applied and Interdisciplinary Chemistry |
Hydrothermal vents contribute dissolved Si to the ocean Si reservoir. Currently, it is challenging to determine the magnitude of hydrothermal Si fluxes, due to lack of data on the δSi values associated with this flux. There are only two published data points of the δSi value of hydrothermal vents (−0.4‰ and −0.2‰). | 0 | Theoretical and Fundamental Chemistry |
The binding of the negatively charged nucleic acids to the positively charged iron particles occurs relatively fast. After complex formation, the loaded particles are incubated together with the target cells on a magnetic plate. The magnetic field causes the iron particles to be rapidly drawn towards the surface of the cell membrane. Cellular uptake occurs by either endocytosis or pinocytosis. Once delivered to the target cells, the DNA is released into the cytoplasm. The magnetic particles are accumulated in endosomes and/or vacuoles. Over time, the nanoparticles are degraded and the iron enters the normal iron metabolism. Influence of cellular functions by iron particles has not been reported yet. In most cases the increased iron concentration in culture media does not lead to cytotoxic effects. | 1 | Applied and Interdisciplinary Chemistry |
Because most deoxyribozymes suffer from product inhibition and thus exhibit single-turnover behavior, it is sometimes argued that deoxyribozymes do not exhibit "true" catalytic behavior since they cannot undergo multiple-turnover catalysis like most biological enzymes. However, the general definition of a catalyst requires only that the substance speeds up the rate of a chemical reaction without being consumed by the reaction (i.e. it is not permanently chemically altered and can be recycled). Thus, by this definition, single-turnover deoxyribozymes are indeed catalysts. Furthermore, many endogenous enzymes (both proteins and ribozymes) also exhibit single-turnover behavior, and so the exclusion of deoxyribozymes from the rank of "catalyst" simply because it does not feature multiple-turnover behavior seems unjustified. | 0 | Theoretical and Fundamental Chemistry |
Phosphoenolpyruvate and erythrose-4-phosphate condense to form 3-deoxy--arabinoheptulosonate-7-phosphate (DAHP), in a reaction catalyzed by the enzyme DAHP synthase. DAHP is then transformed to 3-dehydroquinate (DHQ), in a reaction catalyzed by DHQ synthase. Although this reaction requires nicotinamide adenine dinucleotide (NAD) as a cofactor, the enzymic mechanism regenerates it, resulting in the net use of no NAD.
DHQ is dehydrated to 3-dehydroshikimic acid by the enzyme 3-dehydroquinate dehydratase, which is reduced to shikimic acid by the enzyme shikimate dehydrogenase, which uses nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor. | 1 | Applied and Interdisciplinary Chemistry |
In contact with water, hydrogen is created. Hence, sodium–potassium alloys are used as desiccants in drying solvents prior to distillation. | 1 | Applied and Interdisciplinary Chemistry |
Phage λ is a double-stranded DNA virus that infects E. coli. The λ chromosome is 48.5kb long and can carry inserts up to 25kb. These inserts replace non-essential viral sequences in the λ chromosome, while the genes required for formation of viral particles and infection remain intact. The insert DNA is replicated with the viral DNA; thus, together they are packaged into viral particles. These particles are very efficient at infection and multiplication leading to a higher production of the recombinant λ chromosomes. However, due to the smaller insert size, libraries made with λ phage may require many clones for full genome coverage. | 1 | Applied and Interdisciplinary Chemistry |
Topical administration to the eye is usually characterised by very poor drug bioavailability due to several natural defence mechanisms, including nasolacrymal drainage, blinking, and poor permeability of the cornea. Enhancement of the corneal permeability to drug molecules is one of the strategies to improve the efficiency of topical drug delivery to the eye. Several classes of compounds have been researched as potential penetration enhancers through ocular membranes. These include chelating agents, cyclodextrins, surfactants, bile acids and salts, and crown ethers. There are also reports on the use of cell penetrating peptides and chitosan as penetration enhancers in ocular drug delivery. The most commonly used penetration enhancers in ocular formulations are benzalkonium chloride and ethylenediamine tetraacetate (EDTA). Benzalkonium chloride is often used as an antimicrobial preservative in eye drops and EDTA is used as a chelating agent. | 1 | Applied and Interdisciplinary Chemistry |
Electromagnetic devices with a vortex layer were proposed in 1967 by D.D. Logvinenko and O.P. Shelyakov. The monograph "intensification of technological processes on devices with a vortex layer", written by these authors, showed the effective use of these devices in:
* mixing of liquids and gases
* mixing of loose materials
* dry grinding of solids (micro-resin)
* grinding and dispersion of solids in liquid media
* activation of substance surface
* implementation of chemical reactions
* changes in the physical and chemical properties of substances
Following this research, these intensifiers found their application in many researches and developments. | 1 | Applied and Interdisciplinary Chemistry |
Similar to imprint nanolithography, capillary nanolithography employs a patterned elastomeric mold. However, instead of utilizing high pressure, when the temperature is raised above the Tg, capillary forces enable the polymer to fill the voids within the mold. Suh and Jon used molds made from (PUA). These were placed on spin coated, water-soluble polymer, polyethylene glycol (PEG), which was raised above PEG's Tg. This study found that the addition of nanotopography increased the contact angle, and this increase was dependent on the height of the nanotopography. Often, this technique produces a meniscus on the tip of the protruding nanostructures, characteristic of capillary action. The mold can later be dissolved away. Combinatorial lithography approaches are also used. One study used capillarity to fill PDMS molds with PUA, first partially curing the polymer resin with UV light. After microstructures were formed, pressure was applied to fabricate nanostructures, and UV curing was used again. This study is a good example of the use of hierarchical structures to increase surface hydrophobicity. | 0 | Theoretical and Fundamental Chemistry |
Mass-analyzed ion kinetic-energy spectrometry (MIKES) is a mass spectrometry technique by which mass spectra are obtained from a sector instrument that incorporates at least one magnetic sector plus one electric sector in reverse geometry (the beam first enters the magnetic sector). The accelerating voltage V, and the magnetic field B, are set to select the precursor ions of a particular m/z. The precursor ions then dissociate or react in an electric field-free region between the two sectors. The ratio of the kinetic energy to charge of the product ions are analyzed by scanning the electric sector field E. The width of the product ion spectrum peaks is related to the kinetic energy release distribution for the dissociation process. | 0 | Theoretical and Fundamental Chemistry |
In synaptic vesicle fusion, the vesicle must be within a few nanometers of the target membrane for the fusion process to begin. This closeness allows the cell membrane and the vesicle to exchange lipids which is mediated by certain proteins which remove water that comes between the forming junction. Once the vesicle is in position it must wait until Ca enters the cell by the propagation of an action potential to the presynaptic membrane. Ca binds to specific proteins, one of which is Synaptotagmin, in neurons which triggers the complete fusion of the vesicle with the target membrane.
SNARE proteins are also thought to help mediate which membrane is the target of which vesicle. | 1 | Applied and Interdisciplinary Chemistry |
Heterotrimeric G protein complexes are composed of three distinct protein subunits named alpha (α), beta (β) and gamma (γ) subunits. The alpha subunits contain the GTP binding/GTPase domain flanked by long regulatory regions, while the beta and gamma subunits form a stable dimeric complex referred to as the beta-gamma complex. When activated, a heterotrimeric G protein dissociates into activated, GTP-bound alpha subunit and separate beta-gamma subunit, each of which can perform distinct signaling roles. The α and γ subunit are modified by lipid anchors to increase their association with the inner leaflet of the plasma membrane.
Heterotrimeric G proteins act as the transducers of G protein-coupled receptors, coupling receptor activation to downstream signaling effectors and second messengers. In unstimulated cells, heterotrimeric G proteins are assembled as the GDP bound, inactive trimer (G-GDP-G complex). Upon receptor activation, the activated receptor intracellular domain acts as GEF to release GDP from the G protein complex and to promote binding of GTP in its place. The GTP-bound complex undergoes an activating conformation shift that dissociates it from the receptor and also breaks the complex into its component G protein alpha and beta-gamma subunit components. While these activated G protein subunits are now free to activate their effectors, the active receptor is likewise free to activate additional G proteins – this allows catalytic activation and amplification where one receptor may activate many G proteins.
G protein signaling is terminated by hydrolysis of bound GTP to bound GDP. This can occur through the intrinsic GTPase activity of the α subunit, or be accelerated by separate regulatory proteins that act as GTPase-activating proteins (GAPs), such as members of the Regulator of G protein signaling (RGS) family). The speed of the hydrolysis reaction works as an internal clock limiting the length of the signal. Once G is returned to being GDP bound, the two parts of the heterotrimer re-associate to the original, inactive state.
The heterotrimeric G proteins can be classified by sequence homology of the α unit and by their functional targets into four families: G family, G family, G family and G family. Each of these G protein families contains multiple members, such that the mammals have 16 distinct -subunit genes. The G and G are likewise composed of many members, increasing heterotrimer structural and functional diversity. Among the target molecules of the specific G proteins are the second messenger-generating enzymes adenylyl cyclase and phospholipase C, as well as various ion channels. | 1 | Applied and Interdisciplinary Chemistry |
The rate for the hydrolysis of cobalt(III) ammine halide complexes are deceptive, appearing to be associative but proceeding by an alternative pathway. The hydrolysis of [Co(NH)Cl] follows second order kinetics: the rate increases linearly with concentration of hydroxide as well as the starting complex. Based on this information, the reactions would appear to proceed via nucleophilic attack of hydroxide at cobalt. Studies show, however, that the hydroxide deprotonates one NH ligand to give the conjugate base of the starting complex, i.e., [Co(NH)(NH)Cl]. In this monovalent cation, the chloride spontaneously dissociates. This pathway is called the S1cB mechanism. | 0 | Theoretical and Fundamental Chemistry |
Alus are the most common SINE in primates. They are approximately 350 base pairs long, do not encode proteins and can be recognized by the restriction enzyme AluI (hence the name). Their distribution may be important in some genetic diseases and cancers. Copy and pasting Alu RNA requires the Alu's adenine-rich end and the rest of the sequence bound to a signal. The signal-bound Alu can then associate with ribosomes. LINE RNA associates on the same ribosomes as the Alu. Binding to the same ribosome allows Alus of SINEs to interact with LINE. This simultaneous translation of Alu element and LINE allows SINE copy and pasting. | 1 | Applied and Interdisciplinary Chemistry |
Previous efforts to understand how sulfur metabolism and biosynthetic pathways relied on expensive labeling experiments using radioactive S. By leveraging natural assimilatory processes, stable isotope ratios can be used to track the sources of sulfur for plants, plant organs used in sulfur acquisition, the movement of sulfur through plants.
Sulfur (S) stable isotope composition measurements are often performed using an Elemental Analysis-Isotope Ratio Mass Spectrometer, (EA-IRMS) in which organic sulfur from biological samples is oxidized to sulfur dioxide (SO) and analyzed on a mass spectrometer. The mass spectrometer is used to quantify the ratio of the lighter (SO) to the heavier (SO) isotopologue of SO, and this ratio is then compared to sulfur isotope standards in order to standardize data to the VSMOW scale. In biological materials, sulfur is scarce relative to other organic elements like carbon and oxygen, introducing some additional difficulty in measuring its stable isotope composition. The elemental S composition of plant matter is ≈0.2%, accounting for approximately 2 mmol/m in most leaf tissue. In order to reach detectable levels of 30 ng to 3 µg of elemental S to calculate reliable δS values, leaf tissue samples need to be between 2–5 mg.
Improvements in detection have been made in recent years in the utilization of gas chromatography coupled with multicollector ICP-MS (GC/MC-ICP-MS) to be able to measure pmol quantities of organic S. Additionally, ICP-MS has been used to measure nanomolar quantities of dissolved sulfate. Most studies have focused on measuring the bulk δS value of plant tissues and few studies have been performed on measuring the δS values of individual S-containing compounds. The coupling of high-performance liquid chromatography (HPLC) with ICP-MS has been proposed as a way to test individual S-containing compounds. | 0 | Theoretical and Fundamental Chemistry |
Seraj studied at the University of Dhaka, Bangladesh obtaining a B.Sc. in 1980. She completed her M.Sc. from the same university in 1982. She obtained her PhD in biochemistry from University of Glasgow in 1986 and went to University of Liverpool for post-doctoral work in the following year. After completing her post-doc., she joined the Department of Biochemistry and Molecular Biology, University of Dhaka in 1988. She became an associate professor in 1991 and later a professor in 1997 at the same university. She has been supervising plant biotechnology projects funded by foreign and local grants as a principal investigator since 1991. She is a visiting researcher with UT Austin since 2013 | 1 | Applied and Interdisciplinary Chemistry |
Oxygen isotopic ratios are commonly compared to both the VSMOW and the VPDB references. Traditionally oxygen in water is reported relative to VSMOW while oxygen liberated from carbonate rocks or other geologic archives is reported relative to VPDB. As in the case of hydrogen, the oxygen isotopic scale is defined by two materials, VSMOW2 and SLAP2. Measurements of sample δO vs. VSMOW can be converted to the VPDB reference frame through the following equation: δO = 0.97001*δO - 29.99‰ (Brand et al., 2014). | 0 | Theoretical and Fundamental Chemistry |
By analyzing the isotopic compositions of stable and radiogenic nuclides in meteorites, Dauphas investigates the timing and processes that lead to the formation of Solar System bodies and the establishment of habitable conditions on Earth and Mars. He used iron isotopes to study how the iron biogeochemical cycle of the Earth changed through time. He established that Mars was formed rapidly, within the first 2~4 million years of the birth of the Solar System, which explains the much smaller size of Mars compared to Earth and Venus. He first identified the mineralogical carrier of the Cr isotopic anomalies in meteorites as Cr-rich nano-sized spinels from supernovae. He constrained the nature of Earths accreting materials through time, using a novel approach that relies on the different affinities of elements with Earths core, and showed that the materials formed Earth are from an isotopically homogeneous reservoir.
Dauphas was part of the preliminary examination team for JAXA's Hayabusa2 mission, which returned a fragment of Ryugu carbonaceous asteroid to Earth for scientific research. He was selected as a member of the Mars Sample Return Campaign Science Group in 2022. | 0 | Theoretical and Fundamental Chemistry |
Conservative replacements in proteins often have a better effect on function than non-conservative replacements. The reduced effect of conservative replacements on function can also be seen in the occurrence of different replacements in nature. Non-conservative replacements between proteins are far more likely to be removed by natural selection due to their deleterious effects. | 1 | Applied and Interdisciplinary Chemistry |
Upon illumination of a dark-adapted leaf, there is a rapid rise in fluorescence from Photosystem II (PSII), followed by a slow decline. First observed by Kautsky et al., 1932, this is called the Kautsky Effect. This variable rise in chlorophyll fluorescence is due to photosystem II. Fluorescence from photosystem I is not variable, but constant.
The increase in fluorescence is due to PSII reaction centers being in a "closed" or chemically reduced state. Reaction centers are "closed" when unable to accept further electrons. This occurs when electron acceptors downstream of PSII have not yet passed their electrons to a subsequent electron carrier, so are unable to accept another electron. Closed reaction centres reduce the overall photochemical efficiency, and so increases the level of fluorescence. Transferring a leaf from dark into light increases the proportion of closed PSII reaction centres, so fluorescence levels increase for 1–2 seconds. Subsequently, fluorescence decreases over a few minutes. This is due to; 1. more "photochemical quenching" in which electrons are transported away from PSII due to enzymes involved in carbon fixation; and 2. more "non-photochemical quenching" in which more energy is converted to heat. | 0 | Theoretical and Fundamental Chemistry |
Parvoviruses are a family of DNA viruses that have single-stranded DNA (ssDNA) genomes enclosed in rugged, icosahedral protein capsids 18–26 nanometers (nm) in diameter. Unlike most other ssDNA viruses, which have circular genomes that form a loop, parvoviruses have linear genomes with short terminal sequences at each end of the genome. These termini are capable of being formed into structures called hairpins or hairpin loops and consist of short, imperfect palindromes. Varying from virus to virus, the coding region of the genome is 4–6 kilobases (kb) in length, and the termini are 116–550 nucleotides (nt) in length each. The hairpin sequences provide most of the cis-acting information needed for DNA replication and packaging.
Parvovirus genomes may be either positive-sense or negative-sense. Some species, such as adeno-associated viruses (AAV) like AAV2, package a roughly equal number of positive-sense and negative-sense strands into virions, others, such as minute virus of mice (MVM), show preference toward packaging negative-sense strands, and others have varying proportions. Because of this disparity, the 5′-end (usually pronounced "five prime end") of the strand that encodes the non-structural proteins is called the "left end", and the 3′-end (usually pronounced "three prime end") is called the "right end". In reference to the negative-sense strand, the 3′-end is the left side and the 5′-end is the right side.
Parvoviruses replicate their genomes through a process called rolling hairpin replication (RHR), which is a unidirectional, strand displacement form of DNA replication. Before replication, the coding portion of the ssDNA genome is converted to a double-strand DNA (dsDNA) form, which is then cleaved by a viral protein to initiate replication. Sequential unfolding and refolding of the hairpin termini acts to reverse the direction of synthesis, which allows replication to go back and forth along the genome to synthesize a continuous duplex replicative form (RF) DNA intermediate. Progeny ssDNA genomes are then excised from the RF intermediate. While the general aspects of RHR are conserved across genera and species, the exact details likely vary.
Parvovirus genomes have distinct starting points of replication that contain palindromic DNA sequences. These sequences are able to alternate between inter- and intrastrand basepairing throughout replication, and they serve as self-priming telomeres at each end of the genome. They also contain two key sites necessary for replication used by the initiator protein: a binding site and a cleavage site. Telomere sequences have significant complexity and diversity, suggesting that they perform additional functions for many species. In MVM, for example, the left-end hairpin contains binding sites for transcription factors that modulate gene expression from an adjacent promoter. For AAV, the hairpins can bind to MRE11/Rad50/NBS1 (MRN) complexes and Ku70/80 heterodimers, which are involved in sensing and repairing DNA. In general, however, they have the same basic structure: imperfect palindromes in which a fully or primarily basepaired region terminates into an axial symmetry. These palindromes can fold into a variety of structures such as a Y-shaped structure and a cruciform-shaped structure. During replication, the termini act as hinges in which the imperfectly basepaired or partial cruciform regions surrounding the axis provide a favorable environment for unfolding and refolding of the hairpin.
Some parvoviruses, such as AAV2, are homotelomeric, meaning the two palindromic telomeres are similar or identical and form part of larger (inverted) terminal repeat sequences. Replication at each terminal ending is therefore similar. Other parvoviruses, such as MVM, are heterotelomeric, meaning they have two physically different telomeres. As a result, heterotelomeric parvoviruses tend to have a more complex replication process since the two telomeres have different replication processes. In general, homotelomeric parvoviruses replicate both ends via a process called terminal resolution, whereas heterotelomeric parvoviruses replicate one end by terminal resolution and the other end by an asymmetric process called junction resolution. Whether a genus is hetero- or homotelomeric, along with other genomic characteristics, is shown in the following table. | 1 | Applied and Interdisciplinary Chemistry |
Wood is a natural organic material consisting primarily of cellulose fibers embedded in a matrix of lignin. Regarding mechanical properties, the fibers are strong in tension, and the lignin matrix resists compression. Thus wood has been an important construction material since humans began building shelters and using boats. Wood to be used for construction work is commonly known as lumber or timber. In construction, wood is not only a structural material, but is also used to form the mould for concrete.
Wood-based materials are also extensively used for packaging (e.g. cardboard) and paper, which are both created from the refined pulp. The chemical pulping processes use a combination of high temperature and alkaline (kraft) or acidic (sulfite) chemicals to break the chemical bonds of the lignin before burning it out. | 0 | Theoretical and Fundamental Chemistry |
In 2005, Meyers et al. Proposed the following mechanism for the decarboxylative cross-coupling reaction. The initial and rate determining step is the decarboxylation. The ipso carbon of the arene ring is thought to coordinate to the palladium centre initially and is followed by the expulsion of carbon dioxide, forming an aryl–palladium intermediate. The olefin then inserts between the arene and palladium center, which then undergoes beta elimination to form the desired vinyl halide, as well as a palladium hydride. This proton is abstracted by silver carbonate, which acts as both a base and an oxidant to regenerate the starting palladium complex completing the catalytic cycle. | 0 | Theoretical and Fundamental Chemistry |
The rotational friction factors are rarely observed directly. Rather, one measures the exponential rotational relaxation(s) in response to an orienting force (such as flow, applied electric field, etc.). The time constant for relaxation of the axial direction vector is
whereas that for the equatorial direction vectors is
These time constants can differ significantly when the axial ratio deviates significantly from 1, especially for prolate spheroids. Experimental methods for measuring these time constants include fluorescence anisotropy, NMR, flow birefringence and dielectric spectroscopy.
It may seem paradoxical that involves . This arises because re-orientations of the axial direction vector occur through rotations about the perpendicular axes, i.e., about the equatorial axes. Similar reasoning pertains to . | 1 | Applied and Interdisciplinary Chemistry |
Ethanol is formed in E. coli by the reduction of acetyl coenzyme A using NADH. This two-step reaction requires the enzyme alcohol dehydrogenase (ADHE).
acetyl-CoA + NADH + H → acetaldehyde + NAD + CoA
acetaldehyde + NADH + H → ethanol + NAD | 1 | Applied and Interdisciplinary Chemistry |
If good health physics controls are maintained in a laboratory where radionuclides are used, it is unlikely that the overall radiation dose received by workers will be of much significance. Nevertheless, the effects of low doses are mostly unknown so many regulations exist to avoid unnecessary risks, such as skin or internal exposure. Due to the low penetration power and many variables involved it is hard to convert a radioactive concentration to a dose.
1 μCi of P-32 on a square centimetre of skin (through a dead layer of a thickness of 70 μm) gives 7961 rads (79.61 grays) per hour . Similarly a mammogram gives an exposure of 300 mrem (3 mSv) on a larger volume (in the US, the average annual dose is 620 mrem or 6.2 mSv ). | 0 | Theoretical and Fundamental Chemistry |
He is a founding scientist and current director of 908 Devices incorporated, a company which focuses on building handheld mass spectrometry devices for applications in laboratory analysis, safety and security, as well as for use in the life sciences. In 2017 908 Devices Inc. received the Federal Laboratory Consortium Excellence in Technology Transfer Award. The company is known for several products, including the zipchip ™ separations platform for quick and high quality separation and mass spectrometry analysis of biological samples and the M908 ™ handheld High Pressure Mass Spectrometry tool for analysis of chemical warfare agents. Dr. Ramsey is also a founding scientist and former scientific advisory board member of Caliper Technologies incorporated, later renamed Caliper Life Sciences, a company that commercializes microfluidics and lab-on-a-chip technologies. Caliper Life Sciences was acquired by PerkinElmer in 2011 for $650M.
Between 1979 and 2004, Ramsey worked as a Eugene P. Wigner Fellow, research associate, and eventually a group leader for Oak Ridge National Laboratory. | 0 | Theoretical and Fundamental Chemistry |
Cucurbiturils are amidals (less precisely aminals) and synthesized from urea 1 and a dialdehyde (e.g., glyoxal 2) via a nucleophilic addition to give the intermediate glycoluril 3. This intermediate is condensed with formaldehyde to give hexamer cucurbit[6]uril above 110 °C. Ordinarily, multifunctional monomers such as 3 would undergo a step-growth polymerization that would give a distribution of products, but due to favorable strain and an abundance of hydrogen bonding, the hexamer is the only reaction product isolated after precipitation.
Decreasing the temperature of the reaction to between 75 and 90 °C can be used to access other sizes of cucurbiturils including CB[5], CB[7], CB[8], and CB[10]. CB[6] is still the major product; the other ring sizes are formed in smaller yields. The isolation of sizes other than CB[6] requires fractional crystallization and dissolution. CB[5], CB[6], CB[7], and CB[8] are all currently commercially available. The larger sizes are a particularly active area of research since they can bind larger and more interesting guest molecules, thus expanding their potential applications.
Cucurbit[10]uril is particularly difficult to isolate. It was first discovered by Day and coworkers in 2002 as an inclusion complex containing CB[5] by fractional crystallization of the cucurbituril reaction mixture. The CB[10]·CB[5] was unambiguously identified by single crystal X-ray structural analysis that revealed the complex resembled a molecular gyroscope. In this case, the free rotation of the CB[5] within the CB[10] cavity mimics the independent rotation of a flywheel within the frame of a gyroscope.
Isolation of pure CB[10] could not be accomplished by direct separation methods since the compound has such a high affinity for CB[5]. The strong binding affinity for the CB[5] can be understood since it has a complementary size and shape to the cavity of the CB[10]. Pure CB[10] was isolated by Isaacs and coworkers in 2005 by introducing a more strongly binding melamine diamine guest that is capable of displacing the CB[5]. The melamine diamine guest was then separated from the CB[10] by reaction with acetic anhydride that converted the positively charged amine groups to neutrally charged amides. Cucurbiturils strongly bind cationic guests, but by removing the positive charge from the melamine diamine guest reduces the association constant to the point it can be removed by washing with methanol, DMSO, and water. The CB[10] has an unusually large cavity (870 Å) that's free and capable of binding extraordinarily large guests including a cationic [[calixarene|calix[4]arene]]. | 0 | Theoretical and Fundamental Chemistry |
MIRO Analytical is a Swiss manufacturer of laser-based gas analyzers and isotope analyzers.
The company is based in Zurich, Switzerland and was founded 2018. | 0 | Theoretical and Fundamental Chemistry |
Dimetcote should be applied by specific sprays. Here is a list of several suitable items of equipment typically used by manufacturers. | 1 | Applied and Interdisciplinary Chemistry |
The formose reaction is of importance to the question of the origin of life, as it leads from simple formaldehyde to complex sugars like ribose, a building block of RNA. In one experiment simulating early Earth conditions, pentoses formed from mixtures of formaldehyde, glyceraldehyde, and borate minerals such as colemanite (CaBO5HO) or kernite (NaBO). However, issues remain with both the thermodynamic and kinetic feasibility of binding pre-made sugars to a pre-made nucleobase, as well as a method to selectively employ ribose from the mixture. Both formaldehyde and glycolaldehyde have been observed spectroscopically in outer space, making the formose reaction of particular interest to the field of astrobiology. | 0 | Theoretical and Fundamental Chemistry |
Toc34 is an integral protein in the outer chloroplast membrane that's anchored into it by its hydrophobic C-terminal tail. Most of the protein, however, including its large guanosine triphosphate (GTP)-binding domain projects out into the stroma.
Toc34s job is to catch some chloroplast preproteins in the cytosol and hand them off to the rest of the TOC complex. When GTP, an energy molecule similar to ATP attaches to Toc34, the protein becomes much more able to bind to many chloroplast preproteins in the cytosol. The chloroplast preproteins presence causes Toc34 to break GTP into guanosine diphosphate (GDP) and inorganic phosphate. This loss of GTP makes the Toc34 protein release the chloroplast preprotein, handing it off to the next TOC protein. Toc34 then releases the depleted GDP molecule, probably with the help of an unknown GDP exchange factor. A domain of Toc159 might be the exchange factor that carry out the GDP removal. The Toc34 protein can then take up another molecule of GTP and begin the cycle again.
Toc34 can be turned off through phosphorylation. A protein kinase drifting around on the outer chloroplast membrane can use ATP to add a phosphate group to the Toc34 protein, preventing it from being able to receive another GTP molecule, inhibiting the protein's activity. This might provide a way to regulate protein import into chloroplasts.
Arabidopsis thaliana has two homologous proteins, AtToc33 and AtToc34 (The At stands for Arabidopsis thaliana), which are each about 60% identical in amino acid sequence to Toc34 in peas (called psToc34). AtToc33 is the most common in Arabidopsis, and it is the functional analogue of Toc34 because it can be turned off by phosphorylation. AtToc34 on the other hand cannot be phosphorylated. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, a Haworth projection is a common way of writing a structural formula to represent the cyclic structure of monosaccharides with a simple three-dimensional perspective. Haworth projection approximate the shapes of the actual molecules better for furanoses—which are in reality nearly planar—than for pyranoses which exist in solution in the chair conformation. Organic chemistry and especially biochemistry are the areas of chemistry that use the Haworth projection the most.
The Haworth projection was named after the British chemist Sir Norman Haworth.
A Haworth projection has the following characteristics:
* Carbon is the implicit type of atom. In the example on the right, the atoms numbered from 1 to 6 are all carbon atoms. Carbon 1 is known as the anomeric carbon.
* Hydrogen atoms on carbon are implicit. In the example, atoms 1 to 6 have extra hydrogen atoms not depicted.
* A thicker line indicates atoms that are closer to the observer. In the example on the right, atoms 2 and 3 (and their corresponding OH groups) are the closest to the observer. Atoms 1 and 4 are farther from the observer. Atom 5 and the other atoms are the farthest.
*The groups below the plane of the ring in Haworth projections correspond to those on the right-hand side of a Fischer projection. This rule does not apply to the groups on the two ring carbons bonded to the endocyclic oxygen atom. combined with hydrogen. | 0 | Theoretical and Fundamental Chemistry |
The presence of a charged impermeant ion (for example, a protein) on one side of a membrane will result in an asymmetric distribution of permeant charged ions. The Gibbs–Donnan equation at equilibrium states (assuming permeant ions are Na and Cl):Equivalently, | 0 | Theoretical and Fundamental Chemistry |
For most substrates, in the absence of an oxidant, the dihydrophenanthrene intermediate may reversibly open to the corresponding cis-stilbene. However, suitably substituted stilbenes cyclize irreversibly if an aromatizing elimination or hydrogen shift process can take place. Examples of these transformations are provided below. | 0 | Theoretical and Fundamental Chemistry |
Plant roots acidify soil by releasing protons and organic acids so as to chemically weather soil minerals. Decaying remains of dead plants on soil may also form organic acids which contribute to soil acidification. Acidification from leaf litter on the O-horizon is more pronounced under coniferous trees such as pine, spruce and fir, which return fewer base cations to the soil, rather than under deciduous trees; however, soil pH differences attributed to vegetation often preexisted that vegetation, and help select for species which tolerate them. Calcium accumulation in existing biomass also strongly affects soil pH - a factor which can vary from species to species. | 0 | Theoretical and Fundamental Chemistry |
Heat can be used to trigger the electrocyclization topochemical polymerization. For example, Kana M. Sureshan et al. have developed a series of bio-compatible polymer crystals based on [3+2] Topochemical Azide-Alkyne Cycloaddition (TAAC) reaction and [3+2] topochemical ene-azide cycloaddition (TEAC) reaction. The monomers are polymerized by heating for a few days. Contrary to the light-initiated topochemical polymerization, the lower temperature and slower reaction rate would produce high quality polymer crystals. This is due to the fact that heat expansion is not obvious in lower temperature. | 0 | Theoretical and Fundamental Chemistry |
A variety of heteroatom-containing substituents promote lateral lithiation of an ortho methyl group. Generally, better results are obtained when the heteroatom is in the β position rather than the α position, as the latter tends to promote ortho lithiation. Lithation of primary benzylic positions is slower than lithiation of methyl groups due to inductive electron donation from the additional alkyl group (rather than steric effects). Electrophiles that react with the benzylic anions formed by these methods include aldehydes and ketones, activated (primary, allylic, or benzylic) halides, molecular oxygen, and silyl chlorides. This section describes the scope of directing groups that may be used to effect site-selective lithiation in substituted benzenes and heterocycles. | 0 | Theoretical and Fundamental Chemistry |
The phenomenon of upstream contamination could be relevant to industrial and biotechnological processes, and may be connected even to movements of the protoplasm. It could imply that some of the good practices in industrial and biotechnological procedures need revision. | 1 | Applied and Interdisciplinary Chemistry |
Industrial process imaging, or industrial process tomography or process tomography are methods used to form an image of a cross-section of vessel or pipe in a chemical engineering or mineral processing, or petroleum extraction or refining plant.
Process imaging is used for the development of process equipment such as filters, separators and conveyors, as well as monitoring of production plant including flow rate measurement. As well as conventional tomographic methods widely used in medicine such as X-ray computed tomography, magnetic resonance imaging and gamma ray tomography, and ultra-sound tomography, new and emerging methods such as electrical capacitance tomography and magnetic induction tomography and electrical resistivity tomography (similar to medical electrical impedance tomography) are also used.
Although such techniques are not in widespread deployment in industrial plant there is an active research community, including a Virtual Center for industrial Process Tomography, and a regular World Congress on Industrial Process Tomography, now organized by a learned society for this area, the International Society for Industrial Process Tomography
A number of applications of tomography of process equipment were described in the 1970s, using Ionising Radiation from X-ray or isotope sources but routine use was limited by the high cost involved and safety constraints. Radiation-based methods used long exposure times which meant that dynamic measurements of the real-time behaviour of process systems were not feasible. The use of electrical methods to image industrial processes was pioneered by Maurice Beck at the UMIST in the mid-1980s | 1 | Applied and Interdisciplinary Chemistry |
In organic chemistry and organometallic chemistry, carbon–hydrogen bond activation ( activation) is a type of organic reaction in which a carbon–hydrogen bond is cleaved and replaced with a bond (X ≠ H is typically a main group element, like carbon, oxygen, or nitrogen). Some authors further restrict the term C–H activation to reactions in which a C–H bond, one that is typically considered to be "unreactive", interacts with a transition metal center M, resulting in its cleavage and the generation of an organometallic species with an M–C bond. The intermediate of this step (sometimes known as the activation step) could then undergo subsequent reactions with other reagents, either in situ or in a separate step, to produce the functionalized product.
The alternative term functionalization is used to describe any reaction that converts a relatively inert bond into a bond, irrespective of the reaction mechanism (or with an agnostic attitude towards it). In particular, this definition does not require the cleaved C–H bond to initially interact with the transition metal in the reaction mechanism. This broader definition encompasses all reactions that would fall under the restricted definition of C–H activation given above. However, it also includes iron-catalyzed alkane C–H hydroxylation reactions that proceed through the oxygen rebound mechanism (e.g. cytochrome P450 enzymes and their synthetic analogues), in which a metal–carbon bond is not believed to be involved. Likewise, the ligand-based reactivity of many metal carbene species with hydrocarbons in which the carbene carbon inserts into a C–H bond, again without interaction of the hydrocarbon C–H bond with the metal, also falls under this category. Often, when authors make the distinction between C–H functionalization and activation, they will restrict the latter to the narrow sense. | 0 | Theoretical and Fundamental Chemistry |
Rydberg ionization spectroscopy is a spectroscopy technique in which multiple photons are absorbed by an atom causing the removal of an electron to form an ion. | 0 | Theoretical and Fundamental Chemistry |
The most basic optical tweezer setup will likely include the following components: a laser (usually Nd:YAG), a beam expander, some optics used to steer the beam location in the sample plane, a microscope objective and condenser to create the trap in the sample plane, a position detector (e.g. quadrant photodiode) to measure beam displacements and a microscope illumination source coupled to a CCD camera.
An Nd:YAG laser (1064 nm wavelength) is a common choice of laser for working with biological specimens. This is because such specimens (being mostly water) have a low absorption coefficient at this wavelength. A low absorption is advisable so as to minimise damage to the biological material, sometimes referred to as opticution. Perhaps the most important consideration in optical tweezer design is the choice of the objective. A stable trap requires that the gradient force, which is dependent upon the numerical aperture (NA) of the objective, be greater than the scattering force. Suitable objectives typically have an NA between 1.2 and 1.4.
While alternatives are available, perhaps the simplest method for position detection involves imaging the trapping laser exiting the sample chamber onto a quadrant photodiode. Lateral deflections of the beam are measured similarly to how it is done using atomic force microscopy (AFM).
Expanding the beam emitted from the laser to fill the aperture of the objective will result in a tighter, diffraction-limited spot. While lateral translation of the trap relative to the sample can be accomplished by translation of the microscope slide, most tweezer setups have additional optics designed to translate the beam to give an extra degree of translational freedom. This can be done by translating the first of the two lenses labelled as "Beam Steering" in the figure. For example, translation of that lens in the lateral plane will result in a laterally deflected beam from what is drawn in the figure. If the distance between the beam steering lenses and the objective is chosen properly, this will correspond to a similar deflection before entering the objective and a resulting lateral translation in the sample plane. The position of the beam waist, that is the focus of the optical trap, can be adjusted by an axial displacement of the initial lens. Such an axial displacement causes the beam to diverge or converge slightly, the result of which is an axially displaced position of the beam waist in the sample chamber.
Visualization of the sample plane is usually accomplished through illumination via a separate light source coupled into the optical path in the opposite direction using dichroic mirrors. This light is incident on a CCD camera and can be viewed on an external monitor or used for tracking the trapped particle position via video tracking. | 1 | Applied and Interdisciplinary Chemistry |
Perdeuteration of one component of a multi-component system can provide contrast for neutron scattering experiments, where the contrast obtained by using deuterated solvents is insufficient. | 0 | Theoretical and Fundamental Chemistry |
Chymosin (EC 3.4.23.4) is an aspartic protease that specifically hydrolyzes the peptide bond in Phe105-Met106 of κ- casein and is considered to be the most efficient protease for the cheesemaking industry. However, there are milk-clotting proteases able to cleave other peptide bonds in the κ-casein chain, such as the endothiapepsin produced by Endothia parasitica. There are also several milk-clotting proteases that, being able to cleave the Phe105-Met106 bond in the κ-casein molecule, also cleave other peptide bonds in other caseins, such as those produced by Cynara cardunculus or even bovine chymosin. This allows the manufacture of different cheeses with a variety of rheological and organoleptic properties.
The milk-clotting process consists of three main phases:
# Enzymatic degradation of κ-casein.
# Micellar flocculation.
# Gel formation.
Each step follows a different kinetic pattern, the limiting step in milk-clotting being the degradation rate of κ-casein. The kinetic pattern of the second step of the milk-clotting process is influenced by the cooperative nature of micellar flocculation, whereas the rheological properties of the gel formed depend on the type of action of the proteases, the type of milk, and the patterns of casein proteolysis. The overall process is influenced by several different factors, such as pH or temperature.
The conventional way of quantifying a given milk-clotting enzyme employs milk as the substrate and determines the time elapsed before the appearance of milk clots. However, milk clotting may take place without the participation of enzymes because of variations in physicochemical factors, such as low pH or high temperature. Consequently, this may lead to confusing and irreproducible results, particularly when the enzymes have low activity. At the same time, the classical method is not specific enough, in terms of setting the precise onset of milk gelation, such that the determination of the enzymatic units involved becomes difficult and unclear. Furthermore, although it has been reported that κ-casein hydrolysis follows typical Michaelis–Menten kinetics, it is difficult to determine with the classic milk-clotting assay.
To overcome this, several alternative methods have been proposed, such as the determination of halo diameter in agar-gelified milk, colorimetric measurement, or determination of the rate of degradation of casein previously labeled with either a radioactive tracer or a fluorochrome compound. All these methods use casein as the substrate to quantify proteolytic or milk-clotting activities. | 1 | Applied and Interdisciplinary Chemistry |
The method combines a standard and efficient technique of mutagenesis using a chemical mutagen such as ethyl methanesulfonate (EMS) with a sensitive DNA screening-technique that identifies single base mutations (also called point mutations) in a target gene. The TILLING method relies on the formation of DNA heteroduplexes that are formed when multiple alleles are amplified by PCR and are then heated and slowly cooled. A “bubble” forms at the mismatch of the two DNA strands, which is then cleaved by a single stranded nuclease. The products are then separated by size on several different platforms (see below).
Mismatches may be due to induced mutation, heterozygosity within an individual, or natural variation between individuals.
EcoTILLING is a method that uses TILLING techniques to look for natural mutations in individuals, usually for population genetics analysis. DEcoTILLING is a modification of TILLING and EcoTILLING which uses an inexpensive method to identify fragments. Since the advent of NGS sequencing technologies, TILLING-by-sequencing has been developed based on Illumina sequencing of target genes amplified from multidimensionally pooled templates to identify possible single-nucleotide changes. | 1 | Applied and Interdisciplinary Chemistry |
In a 1988 study conducted by Hugo Scheer and Harmut Kayser, biliproteins were extracted from the large white butterfly and puss moth and their respective properties were examined. Their properties were compared to those of plant and algae biliproteins, and their distinguishing features were taken into account.
Unlile plant and algae biliproteins whose bilins are generally only derived from the IXα biliverdin isomer, the bilins of insect biliproteins are also derived from the IXγ isomer, which is almost exclusively found in Lepidoptera. The study cited from M. Bois-Choussy and M. Barbier that these IXγ-series bile pigments are derived from cleavage of the porphyrin precursors at the C-15 (formerly γ) methine bridge, which is uncharacteristic of other mammalian and plant biliproteins. When the scientists examined biliproteins from both the large white butterfly and puss moth, they found that their polypeptides had a low α-helix content in comparison to phycobiliproteins.
It was hypothesised that the role of biliproteins in insects would also have a role related to light-absorption similar to that in plant and algae biliproteins. However, when the photochemical properties required for light-absorption were found absent in the biliprotein of the large white butterfly, this hypothesis was eliminated, followed by the assumption that those photochemical properties also do not occur in any other insect biliproteins.
Based on these examinations, it was concluded that insect biliproteins are only loosely related to those from plants and algae, due to the large number of differences they have regarding structure, chemical composition, derivation of bilins and general functions. | 1 | Applied and Interdisciplinary Chemistry |
The operon must respond to changes in the metabolic state of the cell. It is subject to growth rate dependent control, stringent control (control during the various stresses the cell is exposed to) and other forms of control. Hence it stops biosynthesis if guanine can be obtained from the external medium, increases its expression if nucleotides are needed (for example during DNA replication) and balances the production of GMP with respect to AMP and the pyrimidine nucleotides.
The branch point at IMP mentioned above is tightly controlled rigid node so as to have a balanced production of AMP and GMP. The gua operon is repressed by GMP and is induced by AMP. Similarly AMP synthesis is repressed by AMP itself while it is activated by GMP. This dual control ensures that there is a balance of flux between AMP and GMP and the flux partition remains relatively constant even in the face of perturbations. Some mechanisms by which this control is achieved are discussed below. | 1 | Applied and Interdisciplinary Chemistry |
The heteronuclear single quantum coherence or heteronuclear single quantum correlation experiment, normally abbreviated as HSQC, is used frequently in NMR spectroscopy of organic molecules and is of particular significance in the field of protein NMR. The experiment was first described by Geoffrey Bodenhausen and D. J. Ruben in 1980. The resulting spectrum is two-dimensional (2D) with one axis for proton (H) and the other for a heteronucleus (an atomic nucleus other than a proton), which is usually C or N. The spectrum contains a peak for each unique proton attached to the heteronucleus being considered. The 2D HSQC can also be combined with other experiments in higher-dimensional NMR experiments, such as NOESY-HSQC or TOCSY-HSQC. | 0 | Theoretical and Fundamental Chemistry |
Amable Liñán introduced a modified mixture fraction in 1991 that is appropriate for systems where the fuel and oxidizer have different Lewis numbers. If and are the Lewis number of the fuel and oxidizer, respectively, then Liñán's mixture fraction is defined as
where
The stoichiometric mixture fraction is given by | 1 | Applied and Interdisciplinary Chemistry |
The combination of vancomycin powder and povidone-iodine lavage has shown promise in reducing the risk of periprosthetic joint infection in hip and knee arthroplasties. In several studies, this combination was found to be more effective than vancomycin alone in preventing joint infection, with lower rates of infection and fewer adverse events. However, there is still a need for prospective randomized studies to confirm these findings and assess the long-term efficacy and safety of this treatment approach. The research directions are to determine the optimal dosage and timing of vancomycin and povidone-iodine lavage, as well as their potential synergistic effect, safety, and efficiency of this possible future treatment option in reducing the risk of periprosthetic joint infection in hip and knee arthroplasties. | 0 | Theoretical and Fundamental Chemistry |
The system size expansion, also known as van Kampen's expansion or the Ω-expansion, is a technique pioneered by Nico van Kampen used in the analysis of stochastic processes. Specifically, it allows one to find an approximation to the solution of a master equation with nonlinear transition rates. The leading order term of the expansion is given by the linear noise approximation, in which the master equation is approximated by a Fokker–Planck equation with linear coefficients determined by the transition rates and stoichiometry of the system.
Less formally, it is normally straightforward to write down a mathematical description of a system where processes happen randomly (for example, radioactive atoms randomly decay in a physical system, or genes that are expressed stochastically in a cell). However, these mathematical descriptions are often too difficult to solve for the study of the systems statistics (for example, the mean and variance of the number of atoms or proteins as a function of time). The system size expansion allows one to obtain an approximate statistical description that can be solved much more easily than the master equation. | 0 | Theoretical and Fundamental Chemistry |
This is the hybrid of both of the above techniques. The upper part of ascending chromatography can be folded over a rod in order to allow the paper to become descending after crossing the rod. | 0 | Theoretical and Fundamental Chemistry |
The following provides a simple example for computing the steady-state give a simple mathematical model.
Consider the open chemical system composed of two reactions with rates and :
We will assume that the chemical species and are fixed external species and is an internal chemical species that is allowed to change. The fixed boundaries is to ensure the system can reach a steady-state. If we assume simple irreversible mass-action kinetics, the differential equation describing the concentration of is given by:
To find the steady-state the differential equation is set to zero and the equation rearranged to solve for
This is the steady-state concentration of .
The stability of this system can be determined by making a perturbation in This can be expressed as:
Note that the will elicit a change in the rate of change.
At steady-state , therefore the rate of change of as a result of this perturbation is:
This shows that the perturbation, decays exponetially, hence the system is stable. | 0 | Theoretical and Fundamental Chemistry |
For a sphere in a fluid, the characteristic length-scale is the diameter of the sphere and the characteristic velocity is that of the sphere relative to the fluid some distance away from the sphere, such that the motion of the sphere does not disturb that reference parcel of fluid. The density and viscosity are those belonging to the fluid. Note that purely laminar flow only exists up to = 10 under this definition.
Under the condition of low , the relationship between force and speed of motion is given by Stokes' law.
At higher Reynolds numbers the drag on a sphere depends on surface roughness. Thus, for example, adding dimples on the surface of a golf ball causes the boundary layer on the upstream side of the ball to transition from laminar to turbulent. The turbulent boundary layer is able to remain attached to the surface of the ball much longer than a laminar boundary and so creates a narrower low-pressure wake and hence less pressure drag. The reduction in pressure drag causes the ball to travel farther. | 1 | Applied and Interdisciplinary Chemistry |
Microdialysis is a minimally-invasive sampling technique that is used for continuous measurement of free, unbound analyte concentrations in the extracellular fluid of virtually any tissue. Analytes may include endogenous molecules (e.g. neurotransmitter, hormones, glucose, etc.) to assess their biochemical functions in the body, or exogenous compounds (e.g. pharmaceuticals) to determine their distribution within the body. The microdialysis technique requires the insertion of a small microdialysis catheter (also referred to as microdialysis probe) into the tissue of interest. The microdialysis probe is designed to mimic a blood capillary and consists of a shaft with a semipermeable hollow fiber membrane at its tip, which is connected to inlet and outlet tubing. The probe is continuously perfused with an aqueous solution (perfusate) that closely resembles the (ionic) composition of the surrounding tissue fluid at a low flow rate of approximately 0.1-5μL/min. Once inserted into the tissue or (body)fluid of interest, small solutes can cross the semipermeable membrane by passive diffusion. The direction of the analyte flow is determined by the respective concentration gradient and allows the usage of microdialysis probes as sampling as well as delivery tools. The solution leaving the probe (dialysate) is collected at certain time intervals for analysis. | 1 | Applied and Interdisciplinary Chemistry |
The simplest propagating wave of unchanging form is a sine wave. A sine wave with water surface elevation η( x, t ) is given by:
where a is the amplitude (in metres) and θ = θ( x, t ) is the phase function (in radians), depending on the horizontal position ( x , in metres) and time ( t , in seconds):
: with and
where:
* λ is the wavelength (in metres),
* T is the period (in seconds),
* k is the wavenumber (in radians per metre) and
* ω is the angular frequency (in radians per second).
Characteristic phases of a water wave are:
* the upward zero-crossing at θ = 0,
* the wave crest at θ = ½ π,
* the downward zero-crossing at θ = π and
* the wave trough at θ = 1½ π.
A certain phase repeats itself after an integer m multiple of 2π: sin(θ) = sin(θ+m•2π).
Essential for water waves, and other wave phenomena in physics, is that free propagating waves of non-zero amplitude only exist when the angular frequency ω and wavenumber k (or equivalently the wavelength λ and period T ) satisfy a functional relationship: the frequency dispersion relation
The dispersion relation has two solutions: ω = +Ω(k) and ω = −Ω(k), corresponding to waves travelling in the positive or negative x–direction. The dispersion relation will in general depend on several other parameters in addition to the wavenumber k. For gravity waves, according to linear theory, these are the acceleration by gravity g and the water depth h. The dispersion relation for these waves is:
an implicit equation with tanh denoting the hyperbolic tangent function.
An initial wave phase θ = θ propagates as a function of space and time. Its subsequent position is given by:
This shows that the phase moves with the velocity:
which is called the phase velocity. | 1 | Applied and Interdisciplinary Chemistry |
Bivalent ligands consist of two drug-like molecules (pharmacophores or ligands) connected by an inert linker. There are various kinds of bivalent ligands and are often classified based on what the pharmacophores target. Homobivalent ligands target two of the same receptor types. Heterobivalent ligands target two different receptor types. Bitopic ligands target an orthosteric binding sites and allosteric binding sites on the same receptor.
In scientific research, bivalent ligands have been used to study receptor dimers and to investigate their properties. This class of ligands was pioneered by Philip S. Portoghese and coworkers while studying the opioid receptor system. Bivalent ligands were also reported early on by Micheal Conn and coworkers for the gonadotropin-releasing hormone receptor. Since these early reports, there have been many bivalent ligands reported for various G protein-coupled receptor (GPCR) systems including cannabinoid, serotonin, oxytocin, and melanocortin receptor systems, and for GPCR-LIC systems (D2 and nACh receptors).
Bivalent ligands usually tend to be larger than their monovalent counterparts, and therefore, not drug-like as in Lipinski's rule of five. Many believe this limits their applicability in clinical settings. In spite of these beliefs, there have been many ligands that have reported successful pre-clinical animal studies. Given that some bivalent ligands can have many advantages compared to their monovalent counterparts (such as tissue selectivity, increased binding affinity, and increased potency or efficacy), bivalents may offer some clinical advantages as well. | 1 | Applied and Interdisciplinary Chemistry |
Dorothy Martin Simon (September 18 1919 – March 25 2016) was an American physical chemist known for her work with aerospace combustion and development of polymers. She made important contributions while at NACA regarding heat shield construction and improvement of rocket engine designs. Her work with DuPont resulted in the creation of synthetic polymers Dacron and Orlon. | 0 | Theoretical and Fundamental Chemistry |
A spectral energy distribution (SED) is a plot of energy versus frequency or wavelength of light (not to be confused with a spectrum of flux density vs frequency or wavelength). It is used in many branches of astronomy to characterize astronomical sources. For example, in radio astronomy they are used to show the emission from synchrotron radiation, free-free emission and other emission mechanisms. In infrared astronomy, SEDs can be used to classify young stellar objects. | 0 | Theoretical and Fundamental Chemistry |
*Scorpion® probes
*Molecular Beacon probes
*TaqMan® probes
*LNA® (Locked Nucleic Acid) probes
*Cycling Probe Technology (CPT) | 1 | Applied and Interdisciplinary Chemistry |
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