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Aza-IP 5-azacytidine-mediated RNA immunoprecipitation has been optimized on and used for detecting targets of methyltransferases, particularly NSUN2 and DNMT2 — the two main enzymes responsible for laying down the m5C mark.
First, the cell is made to overexpress an epitope-tagged m5C-RNA methytransferase derivative so that the antibody used later on for immunoprecipitation could recognize the enzyme. Second, 5-aza-C is introduced to the cells so that it could be incorporated into nascent RNA in place of cytosine. Normally, the methyltransferases are released (i.e. covalent bond between cytosine and methyltransferase is broken) following methylation of the residue. For 5-aza-C, due to a nitrogen substitution in the C5 position of cytosine, the RNA methytransferase enzyme remains covalently bound to the target RNA molecule at the C6 position.
Third, the cell is lysed and the m5C-RNA methyltransferase of interest is immunoprecipitated along with the RNA molecules that are covalently linked to the protein. The IP step enabled >200-fold enrichment of RNA targets, which were mainly tRNAs. The enriched molecules were then fragmented and purified. cDNA library is then constructed and sequencing is performed.
An important additional feature is that RNA methyltransferase covalent linkage to the C5 of m-aza-C induces rearrangement and ring opening. This ring opening results in preferential pairing with cytosine and is therefore read as guanosine during sequencing. This C to G transversion allows for base resolution detection of m5C sites.
One caveat is that m5C sites not replaced by 5-azacytosine will be missed. | 1 | Biochemistry |
Goldmans equation seeks to determine the voltage E across a membrane. A Cartesian coordinate system is used to describe the system, with the z direction being perpendicular to the membrane. Assuming that the system is symmetrical in the x and y directions (around and along the axon, respectively), only the z direction need be considered; thus, the voltage E is the integral of the z' component of the electric field across the membrane.
According to Goldmans model, only two factors influence the motion of ions across a permeable membrane: the average electric field and the difference in ionic concentration from one side of the membrane to the other. The electric field is assumed to be constant across the membrane, so that it can be set equal to E/L, where L is the thickness of the membrane. For a given ion denoted A with valence n, its flux j'—in other words, the number of ions crossing per time and per area of the membrane—is given by the formula
The first term corresponds to Ficks law of diffusion, which gives the flux due to diffusion down the concentration gradient, i.e., from high to low concentration. The constant D is the diffusion constant of the ion A. The second term reflects the flux due to the electric field, which increases linearly with the electric field; Formally, it is [A] multiplied by the drift velocity of the ions, with the drift velocity expressed using the Stokes–Einstein relation applied to electrophoretic mobility. The constants here are the charge valence n of the ion A (e.g., +1 for K, +2 for Ca and −1 for Cl), the temperature T (in kelvins), the molar gas constant R, and the faraday F', which is the total charge of a mole of electrons.
This is a first-order ODE of the form y = ay + b, with y = [A] and y = d[A]/dz; integrating both sides from z=0 to z=L with the boundary conditions [A](0) = [A] and [A](L) = [A], one gets the solution
where μ is a dimensionless number
and P is the ionic permeability, defined here as
The electric current density J equals the charge q of the ion multiplied by the flux j
Current density has units of (Amperes/m). Molar flux has units of (mol/(s m)). Thus, to get current density from molar flux one needs to multiply by Faraday's constant F (Coulombs/mol). F will then cancel from the equation below. Since the valence has already been accounted for above, the charge q of each ion in the equation above, therefore, should be interpreted as +1 or -1 depending on the polarity of the ion.
There is such a current associated with every type of ion that can cross the membrane; this is because each type of ion would require a distinct membrane potential to balance diffusion, but there can only be one membrane potential. By assumption, at the Goldman voltage E, the total current density is zero
(Although the current for each ion type considered here is nonzero, there are other pumps in the membrane, e.g. Na/K-ATPase, not considered here which serve to balance each individual ions current, so that the ion concentrations on either side of the membrane do not change over time in equilibrium.) If all the ions are monovalent—that is, if all the n' equal either +1 or -1—this equation can be written
whose solution is the Goldman equation
where
If divalent ions such as calcium are considered, terms such as e appear, which is the square of e; in this case, the formula for the Goldman equation can be solved using the quadratic formula. | 7 | Physical Chemistry |
Critics argue that the technique is inaccurate for comparison of closely related species, as any attempt to measure differences between orthologous sequences between organisms is overwhelmed by the hybridization of paralogous sequences within an organism's genome. DNA sequencing and computational comparisons of sequences is now generally the method for determining genetic distance, although the technique is still used in microbiology to help identify bacteria. | 1 | Biochemistry |
In analytical chemistry, cross-validation is an approach by which the sets of scientific data generated using two or more methods are critically assessed. The cross-validation can be categorized as either method validation or analytical data validation. | 3 | Analytical Chemistry |
Conventional nitrogen removal from ammonium-rich wastewater is accomplished in two separate steps: nitrification, which is mediated by aerobic ammonia- and nitrite-oxidizing bacteria and denitrification carried out by denitrifiers, which reduce nitrate to with the input of suitable electron donors. Aeration and input of organic substrates (typically methanol) show that these two processes are:
# Highly energy consuming.
# Associated with the production of excess sludge.
# Produce significant amounts of green-house gases such as and and ozone-depleting NO.
Because anammox bacteria convert ammonium and nitrite directly to anaerobically, this process does not require aeration and other electron donors. Nevertheless, oxygen is still required for the production of nitrite by ammonia-oxidizing bacteria. However, in partial nitritation/anammox systems, oxygen demand is greatly reduced because only half of the ammonium needs to be oxidized to nitrite instead of full conversion to nitrate. The autotrophic nature of anammox bacteria and ammonia-oxidizing bacteria guarantee a low yield and thus less sludge production. Additionally, anammox bacteria easily form stable self-aggregated biofilm (granules) allowing reliable operation of compact systems characterized by high biomass concentration and conversion rate up to 5–10 kg N m. Overall, it has been shown that efficient application of the anammox process in wastewater treatment results in a cost reduction of up to 60% as well as lower emissions. | 1 | Biochemistry |
DNA nucleotides are held together with hydrogen bonds, which are relatively weak and can be easily broken. Base flipping occurs on a millisecond timescale by breaking the hydrogen bonds between bases and unstacking the base from its neighbors. The base is rotated out of the double helix by 180 degrees., typically via the major groove, and into the active site of an enzyme. This opening leads to small conformational changes in the DNA backbone which are quickly stabilized by the increased enzyme-DNA interactions. Studies looking at the free-energy profiles of base flipping have shown that the free-energy barrier to flipping can be lowered by 17 kcal/mol for M.HhaI in the closed conformation.
There are two mechanisms of DNA base flipping: active and passive. In the active mechanism, an enzyme binds to the DNA and then actively rotates the base, while in the passive mechanism a damaged base rotates out spontaneously first, then is recognized and bound by the enzyme. Research has demonstrated both mechanisms: uracil-DNA glycosylase follows the passive mechanism and Tn10 transposase follows the active mechanism.
Furthermore, studies have shown that DNA base flipping is used by many different enzymes in a variety biological processes such as DNA methylation, various DNA repair mechanisms, RNA transcription and DNA replication. | 1 | Biochemistry |
An initial estimate of the toxicity of CYN in 1985 was that an at 24 hours was 64±5 mg of freeze-dried culture/kg of mouse body weight on intraperitoneal injection. A further experiment in 1997 measured the LD as 52 mg/kg at 24 hours and 32 mg/kg at 7 days, however the data suggested that another toxic compound was present in the isolate of sonicated cells used; predictions made by Ohtani et al. about the 24‑hour toxicity were considerably higher, and it was proposed that another metabolite was present to account for the relatively low 24‑hour toxicity level measured.
Because the most likely human route of uptake of CYN is ingestion, oral toxicity experiments were conducted on mice. The oral LD was found to be 4.4-6.9 mg CYN/kg, and in addition to some ulceration of the oesophageal gastric mucosa, symptoms were consistent with that of intraperitoneal dosing. Stomach contents included culture material, which indicated that these LD figures might be overestimated.
Another means of exposure to CYN is related to alterations in the gut microbiome by artificial sweetners. A study including Aspartame conducted at Cedars-Sinai in Los Angeles by Ruchi Mathur, MD detected CYN in the duodenum at levels four times above baseline in Aspartame users, along with alterations in bacterial species. | 0 | Organic Chemistry |
In low-dimensional systems, for example in dye-solution filled optical microcavities with a distance between the resonator mirrors in the wavelength range where the situation becomes two-dimensional, also photon gases with tunable chemical potential can been realized. Such a photon gas in many respects behaves like a gas of material particles. One consequence of the tunable chemical potential is that at high phase space densities then Bose-Einstein condensation of photons is observed. | 7 | Physical Chemistry |
Pure zirconium dioxide undergoes a phase transformation from monoclinic (stable at room temperature) to tetragonal (at about 1173 °C) and then to cubic (at about 2370 °C), according to the scheme
: monoclinic (1173 °C) ↔ tetragonal (2370 °C) ↔ cubic (2690 °C) ↔ melt.
Obtaining stable sintered zirconia ceramic products is difficult because of the large volume change, about 5%, accompanying the transition from tetragonal to monoclinic. Stabilization of the cubic polymorph of zirconia over wider range of temperatures is accomplished by substitution of some of the Zr ions (ionic radius of 0.82 Å, too small for ideal lattice of fluorite characteristic for the cubic zirconia) in the crystal lattice with slightly larger ions, e.g., those of Y (ionic radius of 0.96 Å). The resulting doped zirconia materials are termed stabilized zirconias.
Materials related to YSZ include calcia-, magnesia-, ceria- or alumina-stabilized zirconias, or partially stabilized zirconias (PSZ). Hafnia-stabilized zirconia has about 25% lower thermal conductivity, making it more suitable for thermal barrier applications.
Although 8–9 mol% YSZ is known to not be completely stabilized in the pure cubic YSZ phase up to temperatures above 1000 °C.
Commonly used abbreviations in conjunction with yttria-stabilized zirconia are:
* Partly stabilized zirconia ZrO:
** PSZ – partially stabilized zirconia
** TZP – tetragonal zirconia polycrystal
** 4YSZ: with 4 mol% YO partially stabilized ZrO, yttria-stabilized zirconia
* Fully stabilized zirconias ZrO:
** FSZ – fully stabilized zirconia
** CSZ – cubic stabilized zirconia
** 8YSZ – with 8 mol% YO fully stabilized ZrO
** 8YDZ – 8–9 mol% YO-doped ZrO: the material is not completely stabilized and decomposes at high application temperatures, see next paragraphs) | 7 | Physical Chemistry |
If there are diffusing particles with different sizes (diffusion coefficients), it is common to fit to a function that is the sum of single component forms:
where the sum is over the number different sizes of particle, indexed by i, and gives the weighting, which is related to the quantum yield and concentration of each type. This introduces new parameters, which makes the fitting more difficult as a higher-dimensional space must be searched. Nonlinear least square fitting typically becomes unstable with even a small number of s. A more robust fitting scheme, especially useful for polydisperse samples, is the Maximum Entropy Method. | 7 | Physical Chemistry |
The first description of an approximately 6.4 kb long LINE-derived sequence was published by J. Adams et al. in 1980. | 1 | Biochemistry |
the US National Institutes of Health state there is insufficient evidence to recommend for or against using vitamin D supplementation to prevent or treat COVID-19. The UK National Institute for Health and Care Excellence (NICE) does not recommend to offer a vitamin D supplement to people solely to prevent or treat COVID-19. Both organizations included recommendations to continue the previous established recommendations on vitamin D supplementation for other reasons, such as bone and muscle health, as applicable. Both organizations noted that more people may require supplementation due to lower amounts of sun exposure during the pandemic.
Several systematic reviews and meta-analyses of multiple studies have described the associations of vitamin D deficiency with adverse outcomes in COVID-19. In the largest analysis, with data from 76 observational studies including almost two million adults, vitamin D deficiency or insufficiency significantly increased the susceptibility to becoming infected with COVID-19 and having severe COVID-19, with odds ratios of 1.5 and 1.9 respectively, but these findings had high risk of bias and heterogeneity. A two-fold greater mortality was found, but this analysis was less robust. These findings confirm smaller, earlier analyses, one of which, in reporting that people with COVID-19 tend to have lower 25(OH)D levels than healthy subjects, stated that the trend for associations with health outcomes was limited by the low quality of the studies and by the possibility of reverse causality mechanisms.
A meta-analysis of three studies on the effect of oral vitamin D or calcifediol supplementation indicated a lower intensive care unit (ICU) admission rate (odds ratio: 0.36) compared to those without supplementation, but without a change in mortality. A Cochrane review, also of three studies, found the evidence for the effectiveness of vitamin D supplementation for the treatment of COVID-19 to be very uncertain. They found there was substantial clinical and methodological heterogeneity in the three studies that were included, mainly because of different supplementation strategies, vitamin D formulations (one using calcifediol), pre-treatment status and reported outcomes. Another meta-analysis stated that the use of high doses of vitamin D in people with COVID-19 is not based on solid evidence although calcifediol supplementation may have a protective effect on ICU admissions. | 1 | Biochemistry |
When samples show elevated levels of indicator bacteria, further analysis is often undertaken to look for specific pathogenic bacteria. Species commonly investigated in the temperate zone include Salmonella typhi and Salmonella Typhimurium.
Depending on the likely source of contamination investigation may also extend to organisms such as Cryptosporidium spp.
In tropical areas analysis of Vibrio cholerae is also routinely undertaken. | 3 | Analytical Chemistry |
European population estimates for A1+ genotype frequencies range from 20.8 to 43.4% (National Center of Biotechnology Information (NCBI), identification number rs1800497). | 1 | Biochemistry |
Salt spalling is a specific type of weathering which occurs in porous building materials, such as brick, natural stone, tiles and concrete. Dissolved salt is carried through the material in water and crystallizes inside the material near the surface as the water evaporates. As the salt crystals expand this builds up shear stresses which break away spall from the surface.
Some engineers believe that porous building materials can be protected against salt spalling by treatment with penetrating sealants which are hydrophobic (water repellent) and will penetrate deeply enough to keep water with dissolved salts well away from the surface. Great care and expert advice must be consulted, however, to ensure that any coating is compatible with the substrate in terms of breathability (ability to allow the release of vapours from inside while preventing water intrusion), or other serious problems can be created.
Chimneys show spalling damage before other portions of buildings because they are more exposed to the elements. | 8 | Metallurgy |
In principle, cis–trans notation should not be used for alkenes with two or more different substituents. Instead the E–Z notation is used based on the priority of the substituents using the Cahn–Ingold–Prelog (CIP) priority rules for absolute configuration. The IUPAC standard designations E and Z are unambiguous in all cases, and therefore are especially useful for tri- and tetrasubstituted alkenes to avoid any confusion about which groups are being identified as cis or trans to each other.
Z (from the German ) means "together". E (from the German ) means "opposed" in the sense of "opposite". That is, Z has the higher-priority groups cis to each other and E has the higher-priority groups trans to each other. Whether a molecular configuration is designated E or Z is determined by the CIP rules; higher atomic numbers are given higher priority. For each of the two atoms in the double bond, it is necessary to determine the priority of each substituent. If both the higher-priority substituents are on the same side, the arrangement is Z; if on opposite sides, the arrangement is E.
Because the cis–trans and E–Z systems compare different groups on the alkene, it is not strictly true that Z corresponds to cis and E corresponds to trans. For example, trans-2-chlorobut-2-ene (the two methyl groups, C1 and C4, on the but-2-ene backbone are trans to each other) is (Z)-2-chlorobut-2-ene (the chlorine and C4 are together because C1 and C4 are opposite). | 4 | Stereochemistry |
Gražvydas Lukinavičius is a Lithuanian biochemist. His scientific interest and main area of research is focused on labeling of biomolecules and visualization using super-resolution microscopy. He is co-invertor of DNA labeling technology known as Methyltransferase-Directed Transfer of Activated Groups (mTAG) and biocompatible and cell permeable fluorophore – silicon-rhodamine (SiR). Both inventions were commercialized. He is studying labeling methods and apply them for chromatin dynamics visualization in living cells. | 1 | Biochemistry |
Bile produced by the liver is made up of water (97%), bile salts, mucus and pigments, 1% fats and inorganic salts. Bilirubin is its major pigment. Bile acts partly as a surfactant which lowers the surface tension between either two liquids or a solid and a liquid and helps to emulsify the fats in the chyme. Food fat is dispersed by the action of bile into smaller units called micelles. The breaking down into micelles creates a much larger surface area for the pancreatic enzyme, lipase to work on. Lipase digests the triglycerides which are broken down into two fatty acids and a monoglyceride. These are then absorbed by villi on the intestinal wall. If fats are not absorbed in this way in the small intestine problems can arise later in the large intestine which is not equipped to absorb fats. Bile also helps in the absorption of vitamin K from the diet.
Bile is collected and delivered through the common hepatic duct. This duct joins with the cystic duct to connect in a common bile duct with the gallbladder.
Bile is stored in the gallbladder for release when food is discharged into the duodenum and also after a few hours. | 1 | Biochemistry |
The radiometric description of the electromagnetic radiative field at a point in space and time is completely represented by the spectral radiance (or specific intensity) at that point. In a region in which the material is uniform and the radiative field is isotropic and homogeneous, let the spectral radiance (or specific intensity) be denoted by , a scalar-valued function of its arguments , , , and , where denotes a unit vector with the direction and sense of the geometrical vector from the source point to the detection point , where denotes the coordinates of , at time and wave frequency . Then, in the region, takes a constant scalar value, which we here denote by . In this case, the value of the vector flux density at is the zero vector, while the scalar or hemispheric flux density at in every direction in both senses takes the constant scalar value . The reason for the value is that the hemispheric integral is half the full spherical integral, and the integrated effect of the angles of incidence of the radiation on the detector requires a halving of the energy flux according to Lambert's cosine law; the solid angle of a sphere is .
The vector definition is suitable for the study of general radiative fields. The scalar or hemispheric spectral flux density is convenient for discussions in terms of the two-stream model of the radiative field, which is reasonable for a field that is uniformly stratified in flat layers, when the base of the hemisphere is chosen to be parallel to the layers, and one or other sense (up or down) is specified. In an inhomogeneous non-isotropic radiative field, the spectral flux density defined as a scalar-valued function of direction and sense contains much more directional information than does the spectral flux density defined as a vector, but the full radiometric information is customarily stated as the spectral radiance (or specific intensity). | 7 | Physical Chemistry |
The term "thermal diode" can refer to:
* a (possibly non-electrical) device which allows heat to flow preferentially in one direction;
* an electrical (semiconductor) diode in reference to a thermal effect or function;
* or it may describe both situations, where an electrical diode is used as a heat pump or thermoelectric cooler. | 7 | Physical Chemistry |
The configuration index is a single digit which is the priority number of the ligand trans to the highest priority ligand. (If there are two possibilities the principle of trans difference is applied). As an example, (acetonitrile)dichlorido(pyridine)platinum(II) complex where the Cl ligands may be trans or cis to one another.<br />
The ligand priority numbers are, applying the CIP rules:
*two chlorides of priority number 1
*acetonitrile priority 2
*pyridine priority 3
In the trans case the configuration index is 1 giving the name(SP-4-1)-(acetonitrile)dichlorido(pyridine)platinum(II).<br />
In the cis case both of the organic ligands are trans to a chloride so to choose the trans difference is considered and the greater is between 1 and three therefore the name is (SP-4-3)-(acetonitrile)dichlorido(pyridine)platinum(II). | 4 | Stereochemistry |
There are two equivalent ways to define the meaning of the Miller indices: via a point in the reciprocal lattice, or as the inverse intercepts along the lattice vectors. Both definitions are given below. In either case, one needs to choose the three lattice vectors a, a, and a that define the unit cell (note that the conventional unit cell may be larger than the primitive cell of the Bravais lattice, as the examples below illustrate). Given these, the three primitive reciprocal lattice vectors are also determined (denoted b, b, and b).
Then, given the three Miller indices denotes planes orthogonal to the reciprocal lattice vector:
That is, (hkℓ) simply indicates a normal to the planes in the basis of the primitive reciprocal lattice vectors. Because the coordinates are integers, this normal is itself always a reciprocal lattice vector. The requirement of lowest terms means that it is the shortest reciprocal lattice vector in the given direction.
Equivalently, (hkℓ) denotes a plane that intercepts the three points a/h, a/k, and a/ℓ, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane, in the basis of the lattice vectors. If one of the indices is zero, it means that the planes do not intersect that axis (the intercept is "at infinity").
Considering only (hkℓ) planes intersecting one or more lattice points (the lattice planes), the perpendicular distance d between adjacent lattice planes is related to the (shortest) reciprocal lattice vector orthogonal to the planes by the formula: .
The related notation [hkℓ] denotes the direction:
That is, it uses the direct lattice basis instead of the reciprocal lattice. Note that [hkℓ] is not generally normal to the (hkℓ) planes, except in a cubic lattice as described below. | 3 | Analytical Chemistry |
Somewhere between 1 and 2 billion years ago,
a free-living cyanobacterium entered an early eukaryotic cell, either as food or as an internal parasite, but managed to escape the phagocytic vacuole it was contained in. The two innermost lipid-bilayer membranes that surround all chloroplasts correspond to the outer and inner membranes of the ancestral cyanobacterium's gram negative cell wall, and not the phagosomal membrane from the host, which was probably lost.
The new cellular resident quickly became an advantage, providing food for the eukaryotic host, which allowed it to live within it. Over time, the cyanobacterium was assimilated, and many of its genes were lost or transferred to the nucleus of the host. From genomes that probably originally contained over 3000 genes only about 130 genes remain in the chloroplasts of contemporary plants. Some of its proteins were then synthesized in the cytoplasm of the host cell, and imported back into the chloroplast (formerly the cyanobacterium). Separately, somewhere about 90–140 million years ago, it happened again and led to the amoeboid Paulinella chromatophora.
This event is called endosymbiosis, or "cell living inside another cell with a mutual benefit for both". The external cell is commonly referred to as the host while the internal cell is called the endosymbiont.
Chloroplasts are believed to have arisen after mitochondria, since all eukaryotes contain mitochondria, but not all have chloroplasts. This is called serial endosymbiosis—an early eukaryote engulfing the mitochondrion ancestor, and some descendants of it then engulfing the chloroplast ancestor, creating a cell with both chloroplasts and mitochondria.
Whether or not primary chloroplasts came from a single endosymbiotic event, or many independent engulfments across various eukaryotic lineages, has long been debated. It is now generally held that organisms with primary chloroplasts share a single ancestor that took in a cyanobacterium 600–2000 million years ago. It has been proposed this the closest living relative of this bacterium is Gloeomargarita lithophora. The exception is the amoeboid Paulinella chromatophora, which descends from an ancestor that took in a Prochlorococcus cyanobacterium 90–500 million years ago.
These chloroplasts, which can be traced back directly to a cyanobacterial ancestor, are known as primary plastids ("plastid" in this context means almost the same thing as chloroplast). All primary chloroplasts belong to one of four chloroplast lineages—the glaucophyte chloroplast lineage, the amoeboid Paulinella chromatophora lineage, the rhodophyte (red algal) chloroplast lineage, or the chloroplastidan (green) chloroplast lineage. The rhodophyte and chloroplastidan lineages are the largest, with chloroplastidan (green) being the one that contains the land plants. | 5 | Photochemistry |
Ketones that have at least one alpha-hydrogen, undergo keto-enol tautomerization; the tautomer is an enol. Tautomerization is catalyzed by both acids and bases. Usually, the keto form is more stable than the enol. This equilibrium allows ketones to be prepared via the hydration of alkynes. | 0 | Organic Chemistry |
ChIP-on-chip (also known as ChIP-chip) is a technology that combines chromatin immunoprecipitation (ChIP) with DNA microarray ("chip"). Like regular ChIP, ChIP-on-chip is used to investigate interactions between proteins and DNA in vivo. Specifically, it allows the identification of the cistrome, the sum of binding sites, for DNA-binding proteins on a genome-wide basis. Whole-genome analysis can be performed to determine the locations of binding sites for almost any protein of interest. As the name of the technique suggests, such proteins are generally those operating in the context of chromatin. The most prominent representatives of this class are transcription factors, replication-related proteins, like origin recognition complex protein (ORC), histones, their variants, and histone modifications.
The goal of ChIP-on-chip is to locate protein binding sites that may help identify functional elements in the genome. For example, in the case of a transcription factor as a protein of interest, one can determine its transcription factor binding sites throughout the genome. Other proteins allow the identification of promoter regions, enhancers, repressors and silencing elements, insulators, boundary elements, and sequences that control DNA replication. If histones are subject of interest, it is believed that the distribution of modifications and their localizations may offer new insights into the mechanisms of regulation.
One of the long-term goals ChIP-on-chip was designed for is to establish a catalogue of (selected) organisms that lists all protein-DNA interactions under various physiological conditions. This knowledge would ultimately help in the understanding of the machinery behind gene regulation, cell proliferation, and disease progression. Hence, ChIP-on-chip offers both potential to complement our knowledge about the orchestration of the genome on the nucleotide level and information on higher levels of information and regulation as it is propagated by research on epigenetics.
__TOC__ | 1 | Biochemistry |
The intense color from which the compound gets its name results from irradiation and subsequent excitation and relaxation of the extended π electron system across the R-N=N-R linked phenols. Absorption of these electrons falls in the visible region of the electromagnetic spectrum. Azo violets intense indigo color (λ 432 nm) approximates Pantone R: 102 G: 15 B: 240. | 3 | Analytical Chemistry |
A growing trend in the world of elemental analysis has revolved around the speciation, or determination of oxidation state of certain metals such as chromium and arsenic. The toxicity of those elements varies with the oxidation state, so new regulations from food authorities requires speciation of some elements. One of the primary techniques to achieve this is to separate the chemical species with high-performance liquid chromatography (HPLC) or field flow fractionation (FFF) and then measure the concentrations with ICP-MS. | 3 | Analytical Chemistry |
Proteins without signal peptides can also be secreted by unconventional mechanisms. E.g. Interleukin, Galectin. The process by which such secretory proteins gain access to the cell exterior is termed unconventional protein secretion (UPS). In plants, even 50% of secreted proteins can be UPS dependent. | 1 | Biochemistry |
PAMPs, conserved molecules that inhabit multiple pathogen genera, are referred to as MAMPs by many researchers. The defenses induced by MAMP perception are sufficient to repel most pathogens. However, pathogen effector proteins (see below) are adapted to suppress basal defenses such as PTI. Many receptors for MAMPs (and DAMPs) have been discovered. MAMPs and DAMPs are often detected by transmembrane receptor-kinases that carry LRR or LysM extracellular domains. | 1 | Biochemistry |
Over the years, concerns over population declines of the northern white rhinoceros (Ceratotherium simum cottoni) have increased with the increasing value of their horns to poachers. Specifically, the population has declined nearly seventy percent from 2011 to 2019. Processes like SCNT can help aid in conservation efforts towards the revival of their population. Researchers are looking towards induced pluripotent stem cells (iPSC), as they hold limitless possibilities. With the lack of natural mating occurring within the species due to the limited number of them, this sub-species provides researchers the opportunity for iPSC intervention. Other methods, including artificial insemination with fresh semen (AI), have been used successfully in another sub-species, the Southern White Rhinoceros (Ceratotherium simum simum). Frozen-thawed semen has been tested and has seen some successes, helping solve issues with reproduction of the species as a whole. | 1 | Biochemistry |
A conditional gene knockout allows gene deletion in a tissue in a tissue specific manner. This is required in place of a gene knockout if the null mutation would lead to embryonic death, or a specific tissue or cell type is of specific interest. This is done by introducing short sequences called loxP sites around the gene. These sequences will be introduced into the germ-line via the same mechanism as a knockout. This germ-line can then be crossed to another germline containing Cre-recombinase which is a viral enzyme that can recognize these sequences, recombines them and deletes the gene flanked by these sites.
Genes not involved in early development have been effectively studied using knockout approaches that use gene deletion. However, it is typically not possible to knock off genes that are active during early development without the organism suffering a fatal outcome. One method around this is conditional knockout. Utilizing a site-specific recombinase called Cre, the original conditional knockout technique recombined short target sequences known as LoxP. Since then, other recombinases have been created and employed in conditional knockout experiments. | 1 | Biochemistry |
Some types of [http://www.epilepsy.com/ epilepsy] may be brought on due to a splice site mutation.
In addition to a mutation in a stop codon, a splice site mutation on the 3' strand was found in a gene coding for cystatin B in Progressive Myoclonus Epilepsy patients. This combination of mutations was not found in unaffected individuals. By comparing sequences with and without the splice site mutation, investigators were able to determine that a G-to-C nucleotide transversion occurs at the last position of the first intron. This transversion occurs in the region that codes for the cystatin B gene. Individuals suffering from Progressive Myoclonus Epilepsy possess a mutated form of this gene, which results in decreased output of mature mRNA, and subsequently decreases in protein expression.
A study has also shown that a type of Childhood Absence Epilepsy (CAE) causing febrile seizures may be linked to a splice site mutation in the sixth intron of the [https://www.ncbi.nlm.nih.gov/gene/2566 GABRG2 gene]. This splice site mutation was found to cause a nonfunctional GABRG2 subunit in affected individuals. According to this study, a point mutation was the culprit for the splice-donor site mutation, which occurred in intron 6. A nonfunctional protein product is produced, leading to the also nonfunctional subunit. | 1 | Biochemistry |
Martha spent much of her scientific career interested in the quantitative analysis of various elements. Specifically, she studied the composition of ammonium phosphates in magnesium, zinc, and cadmium. Her study of ammonium phosphates was later used as a tool in her later analytical work. Martha spent much of her research career developing several analytical procedures for metal estimations and separations, with a special focus on gravimetric estimations of manganese and magnesium. Her other work included the analysis of prehistoric bronzes without major disruption to the metal composition and the study of organic esters.
While in graduate school at Yale, she worked for Andrew Gooch in the Kent Chemical Laboratory. Throughout her time in graduate school, she published nine papers in the American Journal of Science and in Zeitschrift für anorganische und allgemeine Chemie for her work in analytical chemistry. Four of the nine papers she published individually and the other five in collaboration with Gooch. After her marriage to Issac King Phelps in 1904, she collaborated with her husband to study ester synthesis. The work resulted in six more publications. In total, she published fifteen papers throughout the span of her ten year career as a chemist.
Martha's work is primarily recognized for her development of a protocol estimating arsenic as ammonium magnesium arsenate. The paper detailing the procedure was published in 1900. The protocol became a standard method of arsenic estimation in quantitative analysis studies and was written into textbooks for several years. | 3 | Analytical Chemistry |
Phosphate groups can exist in three different forms depending on a solution's pH. Phosphorus atoms can bind three oxygen atoms with single bonds and a fourth oxygen atom using a double/dative bond. The pH of the solution, and thus the form of the phosphate group determines its ability to bind to other molecules. The binding of phosphate groups to the inositol ring is accomplished by phosphor-ester binding (see phosphoric acids and phosphates). This bond involves combining a hydroxyl group from the inositol ring and a free phosphate group through a dehydration reaction. Considering that the average physiological pH is approximately 7.4, the main form of the phosphate groups bound to the inositol ring in vivo is PO. This gives IP a net negative charge, which is important in allowing it to dock to its receptor, through binding of the phosphate groups to positively charged residues on the receptor. IP has three hydrogen bond donors in the form of its three hydroxyl groups. The hydroxyl group on the 6th carbon atom in the inositol ring is also involved in IP docking. | 1 | Biochemistry |
These oxidize the hydrogen to water. Examples include:
* Nitric acid, used in the Grove cell and Bunsen cell
* Chromic acid, used in the Chromic acid cell
* Manganese dioxide, used in the Leclanché cell and Dry cell
Nitric and chromic acids are powerful oxidizing agents, and effective depolarizers, but their hazardous nature makes them unsuitable for general use. Manganese dioxide is, therefore, the most widely used depolarizer. | 7 | Physical Chemistry |
Motility is a key virulence determinant in Pseudomonas aeruginosa. Pseudomonas aeruginosa has three distinct methods of moving across or through a medium. Rhamnolipids are particularly important in swarming motility where they are postulated to lower the surface tension of the surface through their surfactant properties, allowing the bacterial cell to swarm. New evidence suggests that rhamnolipids are necessary to allow Pseudomonas aeruginosa cells to overcome attachment mediated by type IV pili. There is some discrepancy between the role of HAAs and RHLs in swarming motility. Some studies use a rhlA mutation to assess the effect on motility, which prevents the formation of HAAs and rhamnolipids. Studies that use a rhlB mutant show that Pseudomonas aeruginosa can swarm in the absence of rhamnolipids, but HAAs are absolutely necessary for swarming. Rhamnolipids have been proposed to be important in regulating swarm tendril formation.
Rhamnolipids and HAAs are also implicated in twitching motility, similarly the surfactant is thought to lower the surface tension allowing cells to move across the substratum. However, the role of rhamnolipids in twitching motility may be nutritionally conditional. | 0 | Organic Chemistry |
* [http://www.mikomma.de/schroe/quantumjumps.htm Are there quantum jumps?]
* «[http://www.rzuser.uni-heidelberg.de/~as3/no-quantum-jumps.pdf There are no quantum jumps, nor are there particles!]» by H. D. Zeh, Physics Letters A172, 189 (1993).
* [http://www.mikomma.de/fh/hydrod/h71.html Der Quantensprung im Bohrschen Atommodell] Frühe Quantenphysik
* [http://www.zeit.de/1996/19/quanten.txt.19960503.xml Der Quantensprung] Die zweifelhafte Karriere eines Fachausdrucks (ZEIT 1996)
* [http://www.arxiv.org/abs/quant-ph/9702007 M.B. Plenio und P.L. Knight The Quantum Jump Approach to Dissipative Dynamics in Quantum Optics], vgl. auch Rev. Mod. Phys. 70 101–144 (1998). (Beschreibung der Dynamik offener Systeme mittels Quantensprüngen)
* [http://www.mikomma.de/soqsp/soqsp.htm Historisches zum Quantensprung], Sommerfeld und Einstein 1911 | 7 | Physical Chemistry |
Very common effects (>10% incidence) include:
* Headache (24%)
* Nausea (18%)
* Ejaculation disorder (9–14%)
* Somnolence (4–13%)
* Insomnia (7–12%) | 4 | Stereochemistry |
Senescence in cells is a state in which cells are metabolically active but are no longer able to replicate. pRb is an important regulator of senescence in cells and since this prevents proliferation, senescence is an important antitumor mechanism. pRb may occupy E2F-regulated promoters during senescence. For example, pRb was detected on the cyclin A and PCNA promoters in senescent cells. | 1 | Biochemistry |
In order to have a practical microscope or diffractometer, just having an electron beam was not enough, it needed to be controlled. Many developments laid the groundwork of electron optics; see the paper by Chester J. Calbick for an overview of the early work. One significant step was the work of Heinrich Hertz in 1883 who made a cathode-ray tube with electrostatic and magnetic deflection, demonstrating manipulation of the direction of an electron beam. Others were focusing of electrons by an axial magnetic field by Emil Wiechert in 1899, improved oxide-coated cathodes which produced more electrons by Arthur Wehnelt in 1905 and the development of the electromagnetic lens in 1926 by Hans Busch.
Building an electron microscope involves combining these elements, similar to an optical microscope but with magnetic or electrostatic lenses instead of glass ones. To this day the issue of who invented the transmission electron microscope is controversial, as discussed by Thomas Mulvey and more recently by Yaping Tao. Extensive additional information can be found in the articles by Martin Freundlich, Reinhold Rüdenberg and Mulvey.
One effort was university based. In 1928, at the Technical University of Berlin, (Professor of High Voltage Technology and Electrical Installations) appointed Max Knoll to lead a team of researchers to advance research on electron beams and cathode-ray oscilloscopes. The team consisted of several PhD students including Ernst Ruska. In 1931, Max Knoll and Ernst Ruska successfully generated magnified images of mesh grids placed over an anode aperture. The device, a replicate of which is shown in Figure 5, used two magnetic lenses to achieve higher magnifications, the first electron microscope. (Max Knoll died in 1969, so did not receive a share of the Nobel Prize in Physics in 1986.)
Apparently independent of this effort was work at Siemens-Schuckert by Reinhold Rudenberg. According to patent law (U.S. Patent No. 2058914 and 2070318, both filed in 1932), he is the inventor of the electron microscope, but it is not clear when he had a working instrument. He stated in a very brief article in 1932 that Siemens had been working on this for some years before the patents were filed in 1932, so his effort was parallel to the university effort. He died in 1961, so similar to Max Knoll, was not eligible for a share of the Nobel Prize.
These instruments could produce magnified images, but were not particularly useful for electron diffraction; indeed, the wave nature of electrons was not exploited during the development. Key for electron diffraction in microscopes was the advance in 1936 where showed that they could be used as micro-diffraction cameras with an aperture—the birth of selected area electron diffraction.
Less controversial was the development of LEED—the early experiments of Davisson and Germer used this approach. As early as 1929 Germer investigated gas adsorption, and in 1932 Harrison E. Farnsworth probed single crystals of copper and silver. However, the vacuum systems available at that time were not good enough to properly control the surfaces, and it took almost forty years before these became available. Similarly, it was not until about 1965 that Peter B. Sewell and M. Cohen demonstrated the power of RHEED in a system with a very well controlled vacuum. | 7 | Physical Chemistry |
Electrochemical engineering is applied in industrial water electrolysis, electrolysis, electrosynthesis, electroplating, fuel cells, flow batteries, decontamination of industrial effluents, electrorefining, electrowinning, etc. The primary example of an electrolysis-based process is the Chloralkali process for caustic soda and chlorine production. Other inorganic chemicals produced by electrolysis include:
* Ammonium persulfate
* Chlorine
* Electrowinning
* Fluorine
* Hydrogen peroxide
* Manganese dioxide
* Ozone
* Potassium dichromate
* Potassium permanganate
* Sodium chlorate
* Sodium hypochlorite
* Sodium persulfate
* Silver nitrate
* White lead (Basic lead carbonate) | 7 | Physical Chemistry |
Dendrites form in unary (one-component) systems as well as multi-component systems. The requirement is that the liquid (the molten material) be undercooled, aka supercooled, below the freezing point of the solid. Initially, a spherical solid nucleus grows in the undercooled melt. As the sphere grows, the spherical morphology becomes unstable and its shape becomes perturbed. The solid shape begins to express the preferred growth directions of the crystal. This growth direction may be due to anisotropy in the surface energy of the solid–liquid interface, or to the ease of attachment of atoms to the interface on different crystallographic planes, or both (for an example of the latter, see hopper crystal). In metallic systems, interface attachment kinetics is usually negligible (for non-negligible cases, see dendrite (crystal)). In metallic systems, the solid then attempts to minimize the area of those surfaces with the highest surface energy. The dendrite thus exhibits a sharper and sharper tip as it grows. If the anisotropy is large enough, the dendrite may present a faceted morphology. The microstructural length scale is determined by the interplay or balance between the surface energy and the temperature gradient (which drives the heat/solute diffusion) in the liquid at the interface.
As solidification proceeds, an increasing number of atoms lose their kinetic energy, making the process exothermic. For a pure material, latent heat is released at the solid–liquid interface so that the temperature remains constant until the melt has completely solidified. The growth rate of the resultant crystalline substance will depend on how fast this latent heat can be conducted away. A dendrite growing in an undercooled melt can be approximated as a parabolic needle-like crystal that grows in a shape-preserving manner at constant velocity. Nucleation and growth determine the grain size in equiaxed solidification while the competition between adjacent dendrites decides the primary spacing in columnar growth. Generally, if the melt is cooled slowly, nucleation of new crystals will be less than at large undercooling. The dendritic growth will result in dendrites of a large size. Conversely, a rapid cooling cycle with a large undercooling will increase the number of nuclei and thus reduce the size of the resulting dendrites (and often lead to small grains).
Smaller dendrites generally lead to higher ductility of the product. One application where dendritic growth and resulting material properties can be seen is the process of welding. The dendrites are also common in cast products, where they may become visible by etching of a polished specimen.
As dendrites develop further into the liquid metal, they get hotter because they continue to extract heat. If they get too hot, they will remelt. This remelting of the dendrites is called recalescence. Dendrites usually form under non-equilibrium conditions. | 8 | Metallurgy |
True vapor pressure (TVP) is a common measure of the volatility of petroleum distillate fuels. It is defined as the
equilibrium partial pressure exerted by a volatile organic liquid as a function of temperature as determined by the test method ASTM D 2879.
The true vapor pressure (TVP) at 100 °F differs slightly from the Reid vapor pressure (RVP) (per definition also at 100 °F), as it excludes dissolved fixed gases such as air. Conversions between the two can be found in [https://www.epa.gov/sites/default/files/2020-10/documents/ch07s01.pdf AP 42, Fifth Edition, Volume I Chapter 7: Liquid Storage Tanks] (p 7.1-54 and onwards) | 7 | Physical Chemistry |
Born in Moscow to a Russian-Jewish family, she later traveled to Geneva in the 1890s to study chemistry at Geneva University. | 0 | Organic Chemistry |
Hyperactive mTOR pathways have been identified in certain lymphoproliferative diseases such as autoimmune lymphoproliferative syndrome (ALPS), multicentric Castleman disease, and post-transplant lymphoproliferative disorder (PTLD). | 1 | Biochemistry |
In the U.S. it is marketed as Zinacef by Covis Pharmaceuticals since the company acquired the U.S. rights to the product from GSK. GSK had continued marketing a pediatric oral suspension as Ceftin; however, this presentation was discontinued as of 24 June 2017.
In Bangladesh, it is available as Kilbac by Incepta, Axim by Aristopharma, Rofurox by Radiant and Xorimax by Sandoz. In India, it is available as Ceftum and "Cefuall" by Allencia Biosciences in tablet form and Supacef in injection form by GSK. In Poland, it is available as Zamur by Mepha, subsidiary of Teva Pharmaceutical Industries. In Australia, the "first generic" form of Cefuroxime axetil, Pharmacor Cefuroxime (tablets) from Pharmacor Pty Ltd, was registered on 27 March 2017, by the Therapeutic Goods Administration. Cefuroxime axetil is sold in tablet form in Turkey inder the brand names Aksef and Cefaks. Cefuroxime axetil is also available (in two strengths) as granules for oral suspension from Aspen Pharmacare Australia Pty Ltd under the brand name Zinnat cefuroxime. | 4 | Stereochemistry |
The correct (extensive) formulas for systems A and B were obtained because we included all the possible ways that the two systems could exchange particles. The use of combinations (i.e. N particles choose N) was used to ascertain the number of ways N particles can be divided into system A containing n particles and system B containing n particles. This counting is not justified on physical grounds, but on the need to integrate over phase space. As will be illustrated below, phase space contains not a single n-sphere and a single n-sphere, but instead
pairs of n-spheres, all situated in the same -dimensional velocity space. The integral over accessible phase space must include all of these n-spheres, as can be seen in the figure, which shows the actual velocity phase space associated with a gas that consists of three particles. Moreover, this gas has been divided into two systems, A and B.
If we ignore the spatial variables, the phase space of a gas with three particles is three dimensional, which permits one to sketch the n-spheres over which the integral over phase space must be taken. If all three particles are together, the split between the two gases is 3|0. Accessible phase space is delimited by an ordinary sphere (2-sphere) with a radius that is either or (depending which system has the particles).
If the split is 2|1, then phase space consists of circles and points. Each circle occupies two dimensions, and for each circle, two points lie on the third axis, equidistant from the center of the circle. In other words, if system A has 2 particles, accessible phase space consists of 3 pairs of n-spheres, each pair being a 1-sphere and a 0-sphere:
Note that | 7 | Physical Chemistry |
Bacteria are often viewed as the main consumers of DOC, but they can also produce DOC during cell division and viral lysis. The biochemical components of bacteria are largely the same as other organisms, but some compounds from the cell wall are unique and are used to trace bacterial derived DOC (e.g., peptidoglycan). These compounds are widely distributed in the ocean, suggesting that bacterial DOC production could be important in marine systems. Viruses are the most abundant life forms in the oceans infecting all life forms including algae, bacteria and zooplankton. After infection, the virus either enters a dormant (lysogenic) or productive (lytic) state. The lytic cycle causes disruption of the cell(s) and release of DOC. | 2 | Environmental Chemistry |
The reaction can be demonstrated by starting with solutions of potassium cyanate and ammonium chloride which are mixed, heated and cooled again. An additional proof of the chemical transformation is obtained by adding a solution of oxalic acid which forms urea oxalate as a white precipitate.
Alternatively the reaction can be carried out with lead cyanate and ammonia. The actual reaction taking place is a double displacement reaction to form ammonium cyanate:
Ammonium cyanate decomposes to ammonia and cyanic acid which in turn react to produce urea:
Complexation with oxalic acid drives this chemical equilibrium to completion. | 0 | Organic Chemistry |
The most common mammalian expression systems are Chinese Hamster ovary (CHO) and Human embryonic kidney (HEK) cells.
* Chinese hamster ovary cell
* Mouse myeloma lymphoblstoid (e.g. NS0 cell)
* Fully Human
** Human embryonic kidney cells (HEK-293)
** Human embryonic retinal cells (Crucell's Per.C6)
** Human amniocyte cells (Glycotope and CEVEC) | 1 | Biochemistry |
The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public health agency within the United States Department of Health and Human Services. The agency focuses on minimizing human health risks associated with exposure to hazardous substances. It works closely with other federal, state, and local agencies; tribal governments; local communities; and healthcare providers. Its mission is to "Serve the public through responsive public health actions to promote healthy and safe environments and prevent harmful exposures." ATSDR was created as an advisory, nonregulatory agency by the Superfund legislation and was formally organized in 1985.
Although ATSDR is an independent operating agency within the Department of Health and Human Services, the Centers for Disease Control and Prevention (CDC) performs many of its administrative functions. The CDC director also serves as the ATSDR administrator, and ATSDR has a joint Office of the Director with the National Center for Environmental Health (NCEH). The ATSDR headquarters are located in Atlanta, Georgia, at the CDC Chamblee campus. In fiscal year 2010, ATSDR had an operating budget of $76.8 million and had roughly 300 full-time employees (not including contractors).
The ATSDR is formally and administratively overseen by the Director of the Centers for Disease Control and Prevention (CDC), currently Dr. Mandy Cohen since July 10, 2023 Direction is provided by ATSDRs Director, currently Dr. Patrick N. Breysse, who ranks below the Administrator, and ATSDRs Associate Director, currently Dr. Christopher M. Reh. | 1 | Biochemistry |
After the first bond is synthesized, the RNA polymerase must escape the promoter. During this time there is a tendency to release the RNA transcript and produce truncated transcripts. This is called abortive initiation, and is common for both eukaryotes and prokaryotes. Abortive initiation continues to occur until an RNA product of a threshold length of approximately 10 nucleotides is synthesized, at which point promoter escape occurs and a transcription elongation complex is formed.
Mechanistically, promoter escape occurs through DNA scrunching, providing the energy needed to break interactions between RNA polymerase holoenzyme and the promoter.
In bacteria, it was historically thought that the sigma factor is definitely released after promoter clearance occurs. This theory had been known as the obligate release model. However, later data showed that upon and following promoter clearance, the sigma factor is released according to a stochastic model known as the stochastic release model.
In eukaryotes, at an RNA polymerase II-dependent promoter, upon promoter clearance, TFIIH phosphorylates serine 5 on the carboxy terminal domain of RNA polymerase II, leading to the recruitment of capping enzyme (CE). The exact mechanism of how CE induces promoter clearance in eukaryotes is not yet known. | 1 | Biochemistry |
Consider the bimolecular elementary reaction:
:A + B → C
In collision theory it is considered that two particles A and B will collide if their nuclei get closer than a certain distance. The area around a molecule A in which it can collide with an approaching B molecule is called the cross section (σ) of the reaction and is, in simplified terms, the area corresponding to a circle whose radius () is the sum of the radii of both reacting molecules, which are supposed to be spherical.
A moving molecule will therefore sweep a volume per second as it moves, where is the average velocity of the particle. (This solely represents the classical notion of a collision of solid balls. As molecules are quantum-mechanical many-particle systems of electrons and nuclei based upon the Coulomb and exchange interactions, generally they neither obey rotational symmetry nor do they have a box potential. Therefore, more generally the cross section is defined as the reaction probability of a ray of A particles per areal density of B targets, which makes the definition independent from the nature of the interaction between A and B. Consequently, the radius is related to the length scale of their interaction potential.)
From kinetic theory it is known that a molecule of A has an average velocity (different from root mean square velocity) of , where is the Boltzmann constant, and is the mass of the molecule.
The solution of the two-body problem states that two different moving bodies can be treated as one body which has the reduced mass of both and moves with the velocity of the center of mass, so, in this system must be used instead of .
Thus, for a given molecule A, it travels before hitting a molecule B if all B is fixed with no movement, where is the average traveling distance. Since B also moves, the relative velocity can be calculated using the reduced mass of A and B.
Therefore, the total collision frequency, of all A molecules, with all B molecules, is
From Maxwell–Boltzmann distribution it can be deduced that the fraction of collisions with more energy than the activation energy is . Therefore, the rate of a bimolecular reaction for ideal gases will be
: in unit number of molecular reactions s⋅m,
where:
* Z is the collision frequency with unit s⋅m. The z is Z without [A][B].
* is the steric factor, which will be discussed in detail in the next section,
* E is the activation energy (per mole) of the reaction in unit J/mol,
*T is the absolute temperature in unit K,
* R is the gas constant in unit J/mol/K.
* [A] is molar concentration of A in unit mol/L,
* [B] is molar concentration of B in unit mol/L.
The product zρ is equivalent to the preexponential factor of the Arrhenius equation. | 7 | Physical Chemistry |
Especially when determining the exposure of a population rather than individuals, indirect methods can often make use of relevant statistics about the activities that can lead to an exposure. These statistics are called exposure factors. They are generally drawn from the scientific literature or governmental statistics. For example, they may report informations such as amount of different food eaten by specific populations, divided by location or age, breathing rates, time spent for different modes of commuting, showering or vacuuming, as well as information on types of residences. Such information can be combined with contaminant concentrations from ad-hoc studies or monitoring network to produce estimates of the exposure in the population of interest. These are especially useful in establishing protective standards.
Exposure factor values can be used to obtain a range of exposure estimates such as average, high-end and bounding estimates. For example, to calculate the lifetime average daily dose one would use the equation below:
All of the variables in the above equation, with the exception of contaminant concentration, are considered exposure factors. Each of the exposure factors involves humans, either in terms of their characteristics (e.g., body weight) or behaviors (e.g., amount of time spent in a specific location, which affects exposure duration). These characteristics and behaviors can carry a great deal of variability and uncertainty. In the case of lifetime average daily dose, variability pertains to the distribution and range of LADDs amongst individuals in the population. The uncertainty, on the other hand, refers to exposure analyst's lack of knowledge of the standard deviation, mean, and general shape when dealing with calculating LADD.
The U.S. Environmental Protection Agencys Exposure Factors Handbook' provides solutions when confronting variability and reducing uncertainty. The general points are summarized below: | 2 | Environmental Chemistry |
Translation starts with a chain-initiation codon or start codon. The start codon alone is not sufficient to begin the process. Nearby sequences such as the Shine-Dalgarno sequence in E. coli and initiation factors are also required to start translation. The most common start codon is AUG, which is read as methionine or as formylmethionine (in bacteria, mitochondria, and plastids). Alternative start codons depending on the organism include "GUG" or "UUG"; these codons normally represent valine and leucine, respectively, but as start codons they are translated as methionine or formylmethionine.
The three stop codons have names: UAG is amber, UGA is opal (sometimes also called umber), and UAA is ochre. Stop codons are also called "termination" or "nonsense" codons. They signal release of the nascent polypeptide from the ribosome because no cognate tRNA has anticodons complementary to these stop signals, allowing a release factor to bind to the ribosome instead. | 1 | Biochemistry |
After the end of the Hittite empire, from the 12th to 7th century BC, the city became the center of an independent Luwian Neo-Hittite state of Kammanu, also known as Malizi. A palace was built and monumental stone sculptures of lions and the ruler erected.
In the 12th century, Melid was probably dependent on Karkemiš, where king Kuzi-Tešub ruled. His two grandsons, Runtyas (Runtiya) and Arnuwantis, were at first appointed as “Country Lords” of Melid, but later they also became kings of Melid.
The encounter with the Assyrian king Tiglath-Pileser I (1115–1077 BC) resulted in the kingdom of Melid being forced to pay tribute to Assyria. Melid remained able to prosper until the Assyrian king Sargon II (722–705 BC) sacked the city in 712 BC. At the same time, the Cimmerians and Scythians invaded Anatolia and the city declined.
According to Igor Diakonoff and John Greppin, there was likely an Armenian presence in Melid by 1200 BCE. | 8 | Metallurgy |
Magnetic nanoparticles do not aggregate easily once the magnet is removed, and therefore are unlikely to block capillaries or cause thrombosis. In addition, iron oxide is biodegradable, and the iron can be reused in hemoglobin or iron metabolism pathways. | 1 | Biochemistry |
Epoxides react with a broad range of nucleophiles, for example, alcohols, water, amines, thiols, and even halides. With two often nearly equivalent sites of attack, epoxides are examples "ambident substrates." The regioselectivity of ring-opening in asymmetric epoxides generally follows the S2 pattern of attack at the least-substituted carbon, but can be affected by carbocation stability under acidic conditions. This class of reactions is the basis of epoxy glues and the production of glycols. | 0 | Organic Chemistry |
Early iron smelting used charcoal as both the heat source and the reducing agent. By the 18th century, the availability of wood for making charcoal was limiting the expansion of iron production, so that England became increasingly dependent for a considerable part of the iron required by its industry, on Sweden (from the mid-17th century) and then from about 1725 also on Russia.
Smelting with coal (or its derivative coke) was a long sought objective. The production of pig iron with coke was probably achieved by Dud Dudley around 1619, and with a mixed fuel made from coal and wood again in the 1670s. However this was probably only a technological rather than a commercial success. Shadrach Fox may have smelted iron with coke at Coalbrookdale in Shropshire in the 1690s, but only to make cannonballs and other cast iron products such as shells. However, in the peace after the Nine Years War, there was no demand for these. | 8 | Metallurgy |
Consider two uniform distributions, with the support of enclosed within (). Then the information gain is:
Intuitively, the information gain to a times narrower uniform distribution contains bits. This connects with the use of bits in computing, where bits would be needed to identify one element of a long stream. | 7 | Physical Chemistry |
In addition to temperature and pressure, other thermodynamic properties may be graphed in phase diagrams. Examples of such thermodynamic properties include specific volume, specific enthalpy, or specific entropy. For example, single-component graphs of temperature vs. specific entropy (T vs. s) for water/steam or for a refrigerant are commonly used to illustrate thermodynamic cycles such as a Carnot cycle, Rankine cycle, or vapor-compression refrigeration cycle.
Any two thermodynamic quantities may be shown on the horizontal and vertical axes of a two-dimensional diagram. Additional thermodynamic quantities may each be illustrated in increments as a series of lines – curved, straight, or a combination of curved and straight. Each of these iso-lines represents the thermodynamic quantity at a certain constant value. | 7 | Physical Chemistry |
It is not certain when the pillar was moved to Delhi from its original location. Alexander Cunningham attributed the relocation to the Tomara king Anangpal, based on the short pillar inscription ascribed to this king. Pasanaha Chariu, an 1132 CE Jain Apabhramsha text composed by Vibudh Shridhar, states that "the weight of his pillar caused the Lord of the Snakes to tremble". The identification of this pillar with the iron pillar lends support to the theory that the pillar was already in Delhi during Anangpal's reign.
Another theory is that the relocation happened during the Muslim rule in Delhi. Some scholars have assumed that it happened around 1200 CE, when Qutb al-Din Aibak commenced the construction of the Qutb complex as a general of Muhammad of Ghor.
Finbarr Barry Flood (2009) theorizes that it was Qutb al-Din's successor Iltutmish (r. 1210–1236 CE), who moved the pillar to Delhi. According to this theory, the pillar was originally erected in Vidisha and that the pillar was moved to the Qutb complex, by Iltutmish when he attacked and sacked Vidisha in the thirteenth century. | 8 | Metallurgy |
Prime editor 4 utilizes the same machinery as PE2, but also includes a plasmid that encodes for dominant negative MMR protein MLH1. Dominant negative MLH1 is able to essentially knock out endogenous MLH1 by inhibition, thereby reducing cellular MMR response and increasing prime editing efficiency. | 1 | Biochemistry |
Electrochemical sensors can be used for label-free sensing of biomolecules. They detect changes and measure current between a probed metal electrode and an electrolyte containing the target analyte. A known potential to the electrode is then applied from a feedback current and the resulting current can be measured. For example, one technique using electrochemical sensing includes slowly raising the voltage causing chemical species at the electrode to be oxidized or reduced. Cell current vs voltage is plotted which can ultimately identify the quantity of chemical species consumed or produced at the electrode. Fluorescent tags can be used in conjunction with electrochemical sensors for ease of detection in a biological system. | 1 | Biochemistry |
In E-AB sensors, the signal between electrochemical response and absence of target is small. The aptamer can be reengineered to a large-scale, conformational change. Long flexible loops or complementary strands can also force a change in the aptamers conformation. These techniques to modify aptamers increase the signal ratio, but does not guarantee that it is sufficient enough to be measured.
E-AB sensors are only as sensitive as the aptamer deployed. The selectivity of the aptamer can be a concern when there are similar compounds in the blood or other bodily fluids. cross-reactivity causes interference in in-vivo monitoring and requires understanding of how the aptamer reacts with similar compounds that may be in the sample. | 7 | Physical Chemistry |
Despite the reduced efficiency verses reversed phase HPLC, hundreds of applications have been reported using MLC. One of the most advantageous is the ability to directly inject physiological fluids. Micelles have an ability to solubilize proteins which enables MLC to be useful in analyzing untreated biological fluids such as plasma, serum, and urine. Martinez et al. found MLC to be highly useful in analyzing a class of drugs called b-antagonists, so called beta-blockers, in urine samples. The main advantage of the use of MLC with this type of sample, is the great time savings in sample preparation. Alternative methods of analysis including reversed phase HPLC require lengthy extraction and sample work up procedures before analysis can begin. With MLC, direct injection is often possible, with retention times of less than 15 minutes for the separation of up to nine b-antagonists.
Another application compared reversed phase HPLC with MLC for the analysis of desferrioxamine in serum. Desferrioxamine (DFO) is a commonly used drug for removal of excess iron in patients with chronic and acute levels. The analysis of DFO along with its chelated complexes, Fe(III) DFO and Al(III) DFO has proven to be difficult at best in previous attempts. This study found that direct injection of the serum was possible for MLC, verses an ultrafiltration step necessary in HPLC. This analysis proved to have difficulties with the separation of the chelated DFO compounds and with the sensitivity levels for DFO itself when MLC was applied. The researcher found that, in this case, reverse phase HPLC, was a better, more sensitive technique despite the time savings in direct injection.
Analysis of pharmaceuticals by MLC is also gaining popularity. The selectivity and peak shape of MLC over commonly used ion-pair chromatography is much enhanced. MLC mimics, yet enhances, the selectivity offered by ion-pairing reagents for the separation of active ingredients in pharmaceutical drugs. For basic drugs, MLC improves the excessive peak tailing frequently observed in ion-pairing. Hydrophilic drugs are often unretained using conventional HPLC, are retained by MLC due to solubilization into the micelles. Commonly found drugs in cold medications such as acetaminophen, L-ascorbic acid, phenylpropanolamine HCL, tipepidine hibenzate, and chlorpheniramine maleate have been successfully separated with good peak shape using MLC. Additional basic drugs like many narcotics, such as codeine and morphine, have also been successfully separated using MLC.
Another novel application of MLC involves the separation and analysis of inorganic compounds, mostly simple ions. This is a relatively new area for MLC, but has seen some promising results. MLC has been observed to provide better selectivity of inorganic ions that ion-exchange or ion-pairing chromatography. While this application is still in the beginning stages of development, the possibilities exist for novel, much enhanced separations of inorganic species.
Since the technique was first reported on in 1980, micellar liquid chromatography has been used in hundreds of applications. This micelle controlled technique provides for unique opportunities for solving complicated separation problems. Despite the poor efficiency of MLC, it has been successfully used in many applications. The use of MLC in the future appears to be extremely advantages in the areas of physiological fluids, pharmaceuticals, and even inorganic ions. The technique has proven to be superior over ion-pairing and ion-exchange for many applications. As new approaches are developed to combat the poor efficiency of MLC, its application is sure to spread and gain more acceptance. | 3 | Analytical Chemistry |
Of the 25 known isotopes of sulfur, four are stable. In order of their abundance, those isotopes are S (94.93%), S (4.29%), S (0.76%), and S (0.02%). The δS value refers to a measure of the ratio of the two most common stable sulfur isotopes, S:S, as measured in a sample against that same ratio as measured in a known reference standard. The lowercase delta character is used by convention, to be consistent with use in other areas of stable isotope chemistry. That value can be calculated in per mil (‰, parts per thousand) as:
Less commonly, if the appropriate isotope abundances are measured, similar formulae can be used to quantify ratio variations between S and S, and S and S, reported as δS and δS, respectively. | 9 | Geochemistry |
The most common dye used to make DNA or RNA bands visible for agarose gel electrophoresis is ethidium bromide, usually abbreviated as EtBr. It fluoresces under UV light when intercalated into the major groove of DNA (or RNA). By running DNA through an EtBr-treated gel and visualizing it with UV light, any band containing more than ~20 ng DNA becomes distinctly visible. EtBr is a known mutagen, and safer alternatives are available, such as GelRed, produced by Biotium, which binds to the minor groove.
SYBR Green I is another dsDNA stain, produced by Invitrogen. It is more expensive, but 25 times more sensitive, and possibly safer than EtBr, though there is no data addressing its mutagenicity or toxicity in humans.
SYBR Safe is a variant of SYBR Green that has been shown to have low enough levels of mutagenicity and toxicity to be deemed nonhazardous waste under U.S. Federal regulations. It has similar sensitivity levels to EtBr, but, like SYBR Green, is significantly more expensive. In countries where safe disposal of hazardous waste is mandatory, the costs of EtBr disposal can easily outstrip the initial price difference, however.
Since EtBr stained DNA is not visible in natural light, scientists mix DNA with negatively charged loading buffers before adding the mixture to the gel. Loading buffers are useful because they are visible in natural light (as opposed to UV light for EtBr stained DNA), and they co-sediment with DNA (meaning they move at the same speed as DNA of a certain length). Xylene cyanol and Bromophenol blue are common dyes found in loading buffers; they run about the same speed as DNA fragments that are 5000 bp and 300 bp in length respectively, but the precise position varies with percentage of the gel. Other less frequently used progress markers are Cresol Red and Orange G which run at about 125 bp and 50 bp, respectively.
Visualization can also be achieved by transferring DNA after SDS-PAGE to a nitrocellulose membrane followed by exposure to a hybridization probe. This process is termed Southern blotting.
For fluorescent dyes, after electrophoresis the gel is illuminated with an ultraviolet lamp (usually by placing it on a light box, while using protective gear to limit exposure to ultraviolet radiation). The illuminator apparatus mostly also contains imaging apparatus that takes an image of the gel, after illumination with UV radiation. The ethidium bromide fluoresces reddish-orange in the presence of DNA, since it has intercalated with the DNA. The DNA band can also be cut out of the gel, and can then be dissolved to retrieve the purified DNA.
The gel can then be photographed usually with a digital or polaroid camera. Although the stained nucleic acid fluoresces reddish-orange, images are usually shown in black and white (see figures). UV damage to the DNA sample can reduce the efficiency of subsequent manipulation of the sample, such as ligation and cloning. Shorter wavelength UV radiations (302 or 312 nm) cause greater damage, for example exposure for as little as 45 seconds can significantly reduce transformation efficiency. Therefore if the DNA is to be use for downstream procedures, exposure to a shorter wavelength UV radiations should be limited, instead higher-wavelength UV radiation (365 nm) which cause less damage should be used. Higher wavelength radiations however produces weaker fluorescence, therefore if it is necessary to capture the gel image, a shorter wavelength UV light can be used a short time. Addition of Cytidine or guanosine to the electrophoresis buffer at 1 mM concentration may protect the DNA from damage. Alternatively, a blue light excitation source with a blue-excitable stain such as SYBR Green or GelGreen may be used.
Gel electrophoresis research often takes advantage of software-based image analysis tools, such as ImageJ. | 1 | Biochemistry |
Ordered Two-Template Relay (OTTR) is a library preparation technique used to improve quantitation of highly modified non-coding RNA (ncRNA) species, which have been difficult to characterize using traditional cDNA sequencing approaches. OTTR leverages a retroelement reverse transcriptase (RT), termed BoMoC, with template jumping properties and high processivity across modified RNA templates, to generate cDNA products for next-generation sequencing (NGS). Overall, OTTR offers a streamlined approach for cDNA library production of full-length and modified ncRNA targets. | 1 | Biochemistry |
Plastic crystals behave like true plastic metals under mechanical stress.
For example, closer to melting, plastic crystals show high ductility and/or malleability. Plastic crystals can flow through a hole under pressure. For example, aminoborane plastic crystals bend, twist and stretch with characteristic necking, under appropriate stress. These crystals can be literally shaped into any possible way, like copper or silver metals.
This way, they are very unique compared to other molecular crystals, which are generally brittle and fragile. | 7 | Physical Chemistry |
The broad scope of the Kröhnke pyridine synthesis has made it particularly useful for the synthesis of poly aryl systems including pyridyl, thienyl, and furanyl moieties as well. The method tolerates a broad array of aryl substitiuents on both the α-pyridinium methyl ketone fragment and the α, β-unsaturated carbonyl compounds and can thus be used to generate a wide catalog of poly-aryl systems. Additionally, electron-withdrawing groups and electron-donating groups on the incoming aryl substituents are both well tolerated. The Kröhnke synthesis can also employ alkyl and vinyl substituents giving moderated to good yields as well. Due to its broad scope, the Kröhnke method has seen wide applicability to for the synthesis of bipyridines (16), terpyridines (17), quaterpyridines (18) and even up to septipyridines (19) as shown below. | 0 | Organic Chemistry |
Splat quenching is a metallurgical, metal morphing technique used for forming metals with a particular crystal structure by means of extremely rapid quenching, or cooling.
A typical technique for splat quenching involves casting molten metal by pouring it between two massive, cooled copper rollers that are constantly chilled by the circulation of water. These provide a near-instant quench because of the large surface area in close contact with the melt. The thin sheet formed has a low ratio of volume relative to the area used for cooling.
Products that are formed through this process have a crystal structure that is near-amorphous, or non-crystalline. They are commonly used for their valuable magnetic properties, specifically high magnetic permeability. This makes them useful for magnetic shielding and for low-loss transformer cores in electrical grids. | 8 | Metallurgy |
Tic56 is also a nuclear encoded protein. The preprotein its gene encodes is 527 amino acids long, weighing close to 62 thousand daltons; the mature form probably undergoes processing that trims it down to something that weighs 56 thousand daltons when it gets imported into the chloroplast. Tic56 is largely embedded inside the 1 million dalton complex.
Tic56 and Tic100 are highly conserved among land plants, but they don't resemble any protein whose function is known. Neither has any transmembrane domains. | 5 | Photochemistry |
After completing his PhD at Purdue University, Atalla was employed at Bell Telephone Laboratories (BTL) in 1949. In 1950, he began working at Bell's New York City operations, where he worked on problems related to the reliability of electromechanical relays, and worked on circuit-switched telephone networks. With the emergence of transistors, Atalla was moved to the Murray Hill lab, where he began leading a small transistor research team in 1956. Despite coming from a mechanical engineering background and having no formal education in physical chemistry, he proved himself to be a quick learner in physical chemistry and semiconductor physics, eventually demonstrating a high level of skill in these fields. He researched, among other things, the surface properties of silicon semiconductors and the use of silica as a protective layer of silicon semiconductor devices. He eventually adopted the alias pseudonyms "Martin" M. Atalla or "John" M. Atalla for his professional career.
Between 1956 and 1960, Atalla led a small team of several BTL researchers, including Eileen Tannenbaum, Edwin Joseph Scheibner and Dawon Kahng. They were new recruits at BTL, like himself, with no senior researchers on the team. Their work was initially not taken seriously by senior management at BTL and its owner AT&T, due to the team consisting of new recruits, and due to the team leader Atalla himself coming from a mechanical engineering background, in contrast to the physicists, physical chemists and mathematicians who were taken more seriously, despite Atalla demonstrating advanced skills in physical chemistry and semiconductor physics.
Despite working mostly on their own, Atalla and his team made significant advances in semiconductor technology. According to Fairchild Semiconductor engineer Chih-Tang Sah, the work of Atalla and his team during 19561960 was "the most important and significant technology advance" in silicon semiconductor technology. | 7 | Physical Chemistry |
In materials science, segregation is the enrichment of atoms, ions, or molecules at a microscopic region in a materials system. While the terms segregation and adsorption are essentially synonymous, in practice, segregation is often used to describe the partitioning of molecular constituents to defects from solid solutions, whereas adsorption is generally used to describe such partitioning from liquids and gases to surfaces. The molecular-level segregation discussed in this article is distinct from other types of materials phenomena that are often called segregation, such as particle segregation in granular materials, and phase separation or precipitation, wherein molecules are segregated in to macroscopic regions of different compositions. Segregation has many practical consequences, ranging from the formation of soap bubbles, to microstructural engineering in materials science, to the stabilization of colloidal suspensions.
Segregation can occur in various materials classes. In polycrystalline solids, segregation occurs at defects, such as dislocations, grain boundaries, stacking faults, or the interface between two phases. In liquid solutions, chemical gradients exist near second phases and surfaces due to combinations of chemical and electrical effects.
Segregation which occurs in well-equilibrated systems due to the instrinsic chemical properties of the system is termed equilibrium segregation. Segregation that occurs due to the processing history of the sample (but that would disappear at long times) is termed non-equilibrium segregation. | 7 | Physical Chemistry |
AOAC International has 18 active [https://www.aoac.org/membership/sections/ sections]; eight in North America, and ten in the rest of the world, China, India, Japan, Southeast Asia (excluding Thailand), Taiwan, Thailand, Europe (excluding Belgium, Netherlands, and Luxembourg), the Low Countries, Sub-Saharan Africa, and Latin America and the Caribbean. | 3 | Analytical Chemistry |
Henry Walter Bates (1825–1892) was an English explorer-naturalist who surveyed the Amazon rainforest with Alfred Russel Wallace in 1848. While Wallace returned in 1852, Bates remained for over a decade. Batess field research included collecting almost a hundred species of butterflies from the families Ithomiinae and Heliconiinae, as well as thousands of other insects specimens. In sorting these butterflies into similar groups based on appearance, inconsistencies began to arise. Some appeared superficially similar to others, so much so that even Bates could not tell some species apart based only on wing appearance. However, closer examination of less obvious morphological characters seemed to show that they were not even closely related. Shortly after his return to England, he read a paper on his theory of mimicry at a meeting of the Linnean Society of London on 21 November 1861, which was then published in 1862 as Contributions to an Insect Fauna of the Amazon Valley in the societys Transactions. He elaborated on his experiences further in The Naturalist on the River Amazons.
Bates put forward the hypothesis that the close resemblance between unrelated species was an antipredator adaptation. He noted that some species showed very striking coloration and flew in a leisurely manner, almost as if taunting predators to eat them. He reasoned that these butterflies were unpalatable to birds and other insectivores, and were thus avoided by them. He extended that logic to forms that closely resembled such protected species and mimicked their warning coloration but not their toxicity.
This naturalistic explanation fitted well with the recent account of evolution by Wallace and Charles Darwin, as outlined in his famous 1859 book The Origin of Species. Because the Darwinian explanation required no supernatural forces, it met with considerable criticism from anti-evolutionists, both in academic circles and in the broader social realm. | 1 | Biochemistry |
Transitions between rotational states can be observed in molecules with a permanent electric dipole moment. A consequence of this rule is that no microwave spectrum can be observed for centrosymmetric linear molecules such as (dinitrogen) or HCCH (ethyne), which are non-polar. Tetrahedral molecules such as (methane), which have both a zero dipole moment and isotropic polarizability, would not have a pure rotation spectrum but for the effect of centrifugal distortion; when the molecule rotates about a 3-fold symmetry axis a small dipole moment is created, allowing a weak rotation spectrum to be observed by microwave spectroscopy.
With symmetric tops, the selection rule for electric-dipole-allowed pure rotation transitions is , . Since these transitions are due to absorption (or emission) of a single photon with a spin of one, conservation of angular momentum implies that the molecular angular momentum can change by at most one unit. Moreover, the quantum number K is limited to have values between and including +J to -J. | 7 | Physical Chemistry |
Proteolysis is widely used in biochemistry and cell biology to probe protein structure. In "limited trypsin proteolysis", low amounts of protease digest both folded and unfolded protein but at largely different rates: unstructured proteins are cut more rapidly, while structured proteins are cut at a slower rate (sometimes by orders of magnitude). Recently, several other assays of protein stability based on proteolysis have been proposed, exploiting other proteases with high specificity for cleaving unfolded proteins. These include Pulse Proteolysis, Proteolytic Scanning Calorimetry and FASTpp. | 1 | Biochemistry |
The visual cycle is a process in the retina that replenishes the molecule retinal for its use in vision. Retinal is the chromophore of most visual opsins, meaning it captures the photons to begin the phototransduction cascade. When the photon is absorbed, the 11-cis retinal photoisomerizes into all-trans retinal as it is ejected from the opsin protein. Each molecule of retinal must travel from the photoreceptor cell to the RPE and back in order to be refreshed and combined with another opsin. This closed enzymatic pathway of 11-cis retinal is sometimes called Wald's visual cycle after George Wald (1906–1997), who received the Nobel Prize in 1967 for his work towards its discovery. | 1 | Biochemistry |
Olympiadane is a mechanically interlocked molecule composed of five interlocking macrocycles that resembles the Olympic rings. The molecule is a linear pentacatenane or a [5]catenane. It was synthesized and named by Fraser Stoddart and coworkers in 1994. The molecule was designed without any practical use in mind, although other catenanes may have possible application to the construction of a molecular computer. | 6 | Supramolecular Chemistry |
Thiomicrospira denitrificans, Candidatus Arcobacter, and Chlorobaculum tepidum have been shown to utilize the rTCA cycle to turn CO into carbon compounds. The ability of these bacteria, among others, to use the rTCA cycle, supports the idea that they are derived from an ancestral proteobacterium, and that other organisms using this cycle are much more abundant than previously believed. | 1 | Biochemistry |
Femtochemistry is the area of physical chemistry that studies chemical reactions on extremely short timescales (approximately 10 seconds or one femtosecond, hence the name) in order to study the very act of atoms within molecules (reactants) rearranging themselves to form new molecules (products). In a 1988 issue of the journal Science, Ahmed Hassan Zewail published an article using this term for the first time, stating "Real-time femtochemistry, that is, chemistry on the femtosecond timescale...". Later in 1999, Zewail received the Nobel Prize in Chemistry for his pioneering work in this field showing that it is possible to see how atoms in a molecule move during a chemical reaction with flashes of laser light.
Application of femtochemistry in biological studies has also helped to elucidate the conformational dynamics of stem-loop RNA structures.
Many publications have discussed the possibility of controlling chemical reactions by this method, but this remains controversial. The steps in some reactions occur in the femtosecond timescale and sometimes in attosecond timescales, and will sometimes form intermediate products. These reaction intermediates cannot always be deduced from observing the start and end products. | 7 | Physical Chemistry |
Scientists began to wonder about the energetic of cluster formation early in the 19th century. Henry Eyring developed the activated-complex theory describing kinetics of reactions. Interest in studying the weak interactions of molecules and ions(e.g. van der Waals) in clusters encouraged gas phase spectroscopy, in 1962 D.H. Rank studied weak interactions in the gas phase using traditional infrared spectroscopy. D.S. Bomse used IRPD with an ICR to study isotopic compounds in 1980 at California Institute of Technology. Spectroscopy for weak bonding clusters was limited by low cluster concentration and the variety of accessible cluster states. Cluster states vary in part due to frequent collisions with other species, to reduce collisions in gas phase IRPD forms clusters in low pressure ion traps (e.g. FT-ICR). Nitrogen and water were one of the first complexes studied with the aid of a mass spectrometer by A. Good at University of Alberta in the 1960s. | 7 | Physical Chemistry |
* University Faculty Scholar, The University of Western Ontario: 2005–2007
* Professor of Chemistry, The University of Western Ontario: 2005–present
* Associate Professor, The University of Western Ontario: 2000–2005
* Assistant Professor, The University of Western Ontario: 1995–2000
* Associate Research Officer, National Research Council: 1994–1995
** Steacie Institute For Molecular Sciences
** Organic Reactions Dynamic Group
* Research Associate, National Research Council: 1992–1994 | 0 | Organic Chemistry |
Rieke zinc has attracted the greatest attention of all the Rieke metals. Interest is motivated by the ability of Rieke Zn to convert 2,5-dibromothiophenes to the corresponding polythiophene. Rieke-Zn also reacts with bromoesters to give organozinc reagents of value for the Reformatsky reaction.
Rieke magnesium reacts with aryl halides, some even at −78 °C, to afford the corresponding Grignard reagents, often with considerable selectivity. Rieke magnesium is famous for enabling the formation of "impossible Grignard reagents" such as those derived from aryl fluorides and from 2-chloronorbornane. | 0 | Organic Chemistry |
The restoration of the plant began immediately after the end of the battles for the city, and on February 14, 1944, the plant carried out the first steel smelting from the flat furnace; in March 1944, the rolling mill and the first blast furnace were put into operation; between 1944 and 1946, the enterprise was awarded the Red flag ten times by the Soviet Defense Committee for the successful restoration of the facility.
In 1950, the plant returned to prewar levels of steel production and rolled metal production.
In 1952, the plant was the first in the world to implement a steam evaporation system for cooling flat furnace elements, the development and implementation of which earned two employees of the plant the Stalin Prize.
The plant also specialized in the production of strip valve profiles and spring strips for Pobeda cars in the Fourth Five-Year Plan.
In 1955, the Museum of the History of the DMZ (DMP) was opened.
In 1960, a four-jet continuous casting machine for steel blanks was put into operation at the plant. Also, in 1960, the plant, among the first enterprises of the USSR, mastered the smelting of iron on natural gas (for this achievement, the director of the plant I. M. Ektov and the head of the blast furnace shop of the plant G. A. Panev were awarded the Lenin Prize in 1960).
February 7, 1966 the plant was awarded the Order of Lenin.
In 1967, the plant received a new name: “named after V. I. Lenin.”
In 1970, the plant produced 5.9 times more iron, 5.3 times more steel, and produced 5.5 times more rolled metal than in 1913. Also, in 1970, the Living Memorial was built - immortal, in honor of the workers of the DMZ who died in the Great Patriotic War.
In 1972, the plant was awarded the Order of the October Revolution.
In 1974, a swaging mill 950/900 was built at the plant.
From the early 1980s, DMZ'smain products were rolled bars and rolled sheets of cast iron, steel, high-grade and alloy steel.
By early 1986, the plant was one of the largest industrial enterprises in Donetsk, whose main products were steel, cast iron, sheet metal and long products. | 8 | Metallurgy |
Chlorprothixene has a strong sedative activity with a high incidence of anticholinergic side effects. The types of side effects encountered (dry mouth, massive hypotension and tachycardia, hyperhidrosis, substantial weight gain etc.) normally do not allow a full effective dose for the remission of psychotic disorders to be given. So cotreatment with another, more potent, antipsychotic agent is needed.
Chlorprothixene is structurally related to chlorpromazine, with which it shares, in principle, all side effects. Allergic side effects and liver damage seem to appear with an appreciable lower frequency. The elderly are particularly sensitive to anticholinergic side effects of chlorprothixene (precipitation of narrow angle glaucoma, severe obstipation, difficulties in urinating, confusional and delirant states). In patients >60 years the doses should be particularly low.
Early and late extrapyramidal side effects may occur but have been noted with a low frequency (one study with a great number of participants has delivered a total number of only 1%). | 4 | Stereochemistry |
Joseph Knoll and his team are credited with having developed selegiline. Although selegelines development as a potential treatment for Parkinsons, Alzheimers, and major depressive disorder was headed by other teams, Knoll remained at the forefront of research into the potential longevity enhancing effects of selegiline up until his death in 2018. Knoll published How Selegiline ((-)-Deprenyl) Slows Brain Aging (2018) wherein he claims that:The mechanism of selegilines longevity-promoting effect has been researched by several groups, including Joseph Knoll and his associates at Semmelweis University, Budapest. The drug has been determined to be a catecholaminergic activity enhancer when present in minuscule concentrations far below those at which monoamine oxidase inhibitory activity can be observed, thereby potentiating the release of catecholamine neurotransmitters in response to stimuli. Knoll maintains that micro-doses of selegiline act as a synthetic analogue to a known or unknown trace amine in order to preserve the brain catecholaminergic system, which he perceives as integral to the organism's ability to function in an adaptive, goal-directed and motivated manner during advancing physical age: | 4 | Stereochemistry |
A protocrystalline phase is a distinct phase occurring during crystal growth, which evolves into a microcrystalline form. The term is typically associated with silicon films in optical applications such as solar cells. | 3 | Analytical Chemistry |
In proteins, which are composed of amino acid residues, the side chains are attached to the alpha-carbon atoms of the amide backbone. The side chain connected to the alpha-carbon is specific for each amino acid and is responsible for determining charge and polarity of the amino acid. The amino acid side chains are also responsible for many of the interactions that lead to proper protein folding and function. Amino acids with similar polarity are usually attracted to each other, while nonpolar and polar side chains usually repel each other. Nonpolar/polar interactions can still play an important part in stabilizing the secondary structure due to the relatively large amount of them occurring throughout the protein. Spatial positions of side-chain atoms can be predicted based on protein backbone geometry using computational tools for side-chain reconstruction. | 0 | Organic Chemistry |
Certain combinations of alloys have become popular as industry standards. Selection of the combination is driven by cost, availability, convenience, melting point, chemical properties, stability, and output. Different types are best suited for different applications. They are usually selected on the basis of the temperature range and sensitivity needed. Thermocouples with low sensitivities (B, R, and S types) have correspondingly lower resolutions. Other selection criteria include the chemical inertness of the thermocouple material and whether it is magnetic or not. Standard thermocouple types are listed below with the positive electrode (assuming ) first, followed by the negative electrode. | 8 | Metallurgy |
After World War II ended in 1945, Bruno Tesch and Karl Weinbacher of Tesch & Stabenow were tried in a British military court and executed for knowingly providing Zyklon B to the SS for use on humans. Gerhard Peters, who served as principal operating officer of Degesch and Heli and also held posts in the Nazi government, served two years and eight months in prison as an accessory before being released due to amendments to the penal code.
Use of hydrogen cyanide as a pesticide or cleaner has been banned or restricted in some countries. Most hydrogen cyanide is used in industrial processes, made by companies in Germany, Japan, the Netherlands and the US. Degesch resumed production of Zyklon B after the war. The product was sold as Cyanosil in Germany and Zyklon in other countries. It was still produced as of 2008. Degussa sold Degesch to Detia-Freyberg GmbH in 1986. The company is now called Detia-Degesch. Up until around 2015, a fumigation product similar to Zyklon B was in production by Lučební závody Draslovka of the Czech Republic, under the trade name Uragan D2. Uragan means "hurricane" or "cyclone" in Czech.
Subsequent use of the word "Zyklon" in trade names has prompted angry reactions in English-speaking countries. The name "Zyklon" on portable roller coasters made since 1965 by Pinfari provoked protests among Jewish groups in the U.S. in 1993 and 1999. In 2002, British sportswear and football equipment supplier Umbro issued an apology and stopped using the name "Zyklon", which had appeared since 1999 on the box for one of its trainers, after receiving complaints from the Simon Wiesenthal Center and the Beth Shalom Holocaust Centre. Also in 2002, Siemens withdrew its application for an American trademark of the word "Zyklon", which their subsidiary BSH Bosch und Siemens Hausgeräte had proposed to use for a new line of home appliances in the United States. (The firm was already using the name in Germany for one of their vacuum cleaners.) Protests were lodged by the Simon Wiesenthal Center after the trademark application was reported to BBC News Online by one of their readers. French company IPC's product names used "Cyclone" for degreasers and suffix "B" for biodegradable: "Cyclone B" was renamed ("green cap") in 2013 after protests from Jewish groups. A rabbi said the name was "horrible ignorance at best, and a Guinness record in evil and cynicism if the company did know the history of the name of its product."
Holocaust deniers claim that Zyklon B gas was not used in the gas chambers, relying for evidence on the discredited research of Fred A. Leuchter, who found low levels of Prussian blue in samples of the gas chamber walls and ceilings. Leuchter attributed its presence to general delousing of the buildings. Leuchters negative control, a sample of gasket material taken from a different camp building, had no cyanide residue. In 1999, James Roth, the chemist who had analyzed Leuchters samples, stated that the test was flawed because the material that was sent for testing included large chunks, and the chemical would only be within 10 microns of the surface. The surface that had been exposed to the chemical was not identified, and the large size of the specimens meant that any chemical present was diluted by an undeterminable amount. In 1994, the Institute for Forensic Research in Kraków re-examined Leuchter's claim, stating that formation of Prussian blue by exposure of bricks to cyanide is not a highly probable reaction. Using microdiffusion techniques, they tested 22 samples from the gas chambers and delousing chambers (as positive controls) and living quarters (as negative controls). They found cyanide residue in both the delousing chambers and the gas chambers but none in the living quarters. | 1 | Biochemistry |
Cyclodextrin (CD) chiral stationary phase is produced by partial degradation of starch by the enzyme cyclodextrin glycosyltransferase, followed by enzymatic coupling of the glucose units, forming a toroidal structure. CDs are cyclic oligosaccharides consisting of six (α CDs), seven (β CDs) and eight (γ CDs) glucopyranose units. The chiral recognition mechanism is based on a sort of inclusion complexation. Complexation involves the interaction of the hydrophobic portion of an analyte enantiomer with the non-polar interior of the cavity, while the polar functional groups can form a hydrogen bond with the polar hydroxyl chiral cavity space. The most important factor that determines whether the analyte molecule will fit into the cyclodextrin cavity is its size. The α-CD consists of 30 stereo-selective centers, β-CD consists of 35 stereo-selective centers and γ-CD consists of 40 stereo-selective centers. When the hydrophobic portion of the analyte is larger or smaller than the toroid's cavity size, inclusion will not occur. | 4 | Stereochemistry |
Usually hydrolysis is a chemical process in which a molecule of water is added to a substance. Sometimes this addition causes both the substance and water molecule to split into two parts. In such reactions, one fragment of the target molecule (or parent molecule) gains a hydrogen ion. It breaks a chemical bond in the compound. | 7 | Physical Chemistry |
Isotope-ratio mass spectrometry (IRMS) is a specialization of mass spectrometry, in which mass spectrometric methods are used to measure the relative abundance of isotopes in a given sample.
This technique has two different applications in the earth and environmental sciences. The analysis of stable isotopes is normally concerned with measuring isotopic variations arising from mass-dependent isotopic fractionation in natural systems. On the other hand, radiogenic isotope analysis involves measuring the abundances of decay-products of natural radioactivity, and is used in most long-lived radiometric dating methods. | 9 | Geochemistry |
The nucleolus within the nucleus can be targeted with a sequence called a nucleolar localization signal (abbreviated NoLS or NOS). | 1 | Biochemistry |
The equilibrium concentrations of the products and reactants do not directly depend on the total pressure of the system. They may depend on the partial pressure of the products and reactants, but if the number of moles of gaseous reactants is equal to the number of moles of gaseous products, pressure has no effect on equilibrium.
Changing total pressure by adding an inert gas at constant volume does not affect the equilibrium concentrations (see Effect of adding an inert gas below).
Changing total pressure by changing the volume of the system changes the partial pressures of the products and reactants and can affect the equilibrium concentrations (see §Effect of change in volume below). | 7 | Physical Chemistry |
It is possible to build a basic optical spectrometer using an optical disc grating and a basic webcam, using a CFL lamp for calibrating the wavelengths. A calibration using a source of known spectrum can then turn the spectrometer into a spectroradiometer by interpreting the brightness of photo pixels. A DIY build is affected by some extra error sources in the photo-to-value conversion: photographic noise (requiring dark frame subtraction) and non-linearity in the CCD-to-photograph conversion (possibly solved by a raw image format). | 7 | Physical Chemistry |
The coenzyme is a substrate for coenzyme F hydrogenase, 5,10-methylenetetrahydromethanopterin reductase and methylenetetrahydromethanopterin dehydrogenase.
A long list of other enzymes use F to oxidize (dehydrogenate) or F-H to reduce substrates. | 1 | Biochemistry |
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