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* Chromatin structure oriented factors:<br />(HMTs (Histone MethylTransferases)):<br /> COMPASS§† – (COMplex of Proteins ASsociated with Set1) – Methylates lysine 4 of histone H3: Is responsible of repression/silencing of transcription. A normal part of cell growth and transcription regulation within RNAP II.
* Set2 – Methylates lysine 36 of histone H3: Set2 is involved in regulation transcription elongation through its direct contact with the CTD.<br /> (interesting irrelevant example: Dot1*‡ – Methylates lysine 79 of histone H3.)
* Bre1 – Ubiquinates (adds ubiquitin to) lysine 123 of histone H2B. Associated with pre-initiation and allowing RNA Pol II binding. | 1 | Biochemistry |
DnaA consists mainly in two different forms, the active ATP-form and the inactive ADP. The level of active DnaA within a cell is low immediately after a cell has divided. Although the active form of DnaA requires ATP, the formation of the oriC/DnaA complex and subsequent DNA unwinding does not require ATP hydrolysis.
The oriC site in E. coli has three AT rich 13 base pair regions (DUEs) followed by four 9 bp regions with the sequence TTAT(C or A)CA(C or A)A. Around 10 DnaA molecules bind to the 9 bp regions, which wrap around the proteins causing the DNA at the AT-rich region to unwind. There are 8 DnaA binding sites within oriC, to which DnaA binds with differential affinity. When DNA replication is about to commence, DnaA occupies all of the high and low affinity binding sites. The denatured AT-rich region allows for the recruitment of DnaB (helicase), which complexes with DnaC (helicase loader). DnaC helps the helicase to bind to and to properly accommodate the ssDNA at the 13 bp region; this is accomplished by ATP hydrolysis, after which DnaC is released. Single-strand binding proteins (SSBs) stabilize the single DNA strands in order to maintain the replication bubble. DnaB is a 5→3 helicase, so it travels on the lagging strand. It associates with DnaG (a primase) to form the only primer for the leading strand and to add RNA primers on the lagging strand. The interaction between DnaG and DnaB is necessary to control the longitude of Okazaki fragments on the lagging strand. DNA polymerase III is then able to start DNA replication.
DnaA is made up of four domains: the first is the N-terminal that associates with regulatory proteins, the second is a helical linker region, the third domain is a AAA+ region that binds to ATP, and the fourth domain is the C-terminal DNA binding region. DnaA contains two conserved regions: the first is located in the central part of the protein and corresponds to the ATP-binding domain, the second is located in the C-terminal half and is involved in DNA-binding. | 1 | Biochemistry |
Consider a binary electrolyte AB which dissociates reversibly into A and B ions. Ostwald noted that the law of mass action can be applied to such systems as dissociating electrolytes. The equilibrium state is represented by the equation:
If is the fraction of dissociated electrolyte, then is the concentration of each ionic species. must, therefore be the fraction of undissociated electrolyte, and the concentration of same. The dissociation constant may therefore be given as
For very weak electrolytes (however, neglecting α for most weak electrolytes yields counterproductive result) , implying that .
This gives the following results;
Thus, the degree of dissociation of a weak electrolyte is proportional to the inverse square root of the concentration, or the square root of the dilution. The concentration of any one ionic species is given by the root of the product of the dissociation constant and the concentration of the electrolyte. | 7 | Physical Chemistry |
The pH of a natural soil depends on the mineral composition of the parent material of the soil, and the weathering reactions undergone by that parent material. In warm, humid environments, soil acidification occurs over time as the products of weathering are leached by water moving laterally or downwards through the soil. In dry climates, however, soil weathering and leaching are less intense and soil pH is often neutral or alkaline. | 9 | Geochemistry |
Enantiomers, also known as optical isomers, are two stereoisomers that are related to each other by a reflection: they are mirror images of each other that are non-superposable. Human hands are a macroscopic analog of this. Every stereogenic center in one has the opposite configuration in the other. Two compounds that are enantiomers of each other have the same physical properties, except for the direction in which they rotate polarized light and how they interact with different optical isomers of other compounds. As a result, different enantiomers of a compound may have substantially different biological effects. Pure enantiomers also exhibit the phenomenon of optical activity and can be separated only with the use of a chiral agent. In nature, only one enantiomer of most chiral biological compounds, such as amino acids (except glycine, which is achiral), is present. An optically active compound shows two forms: -(+) form and -(−) form. | 4 | Stereochemistry |
The IUPAC Gold Book defines an intermediate as a compound that has a lifetime greater than a molecular vibration, is formed (directly or indirectly) from the reactants, and reacts further to give (either directly or indirectly) the products of a chemical reaction. The lifetime condition distinguishes true, chemically distinct intermediates, both from vibrational states and from transition states (which, by definition, have lifetimes close to that of molecular vibration).
The different steps of a multi-step reaction often differ widely in their reaction rates. Where the difference is significant, an intermediate consumed more quickly than another may be described as a relative intermediate. A reactive intermediate is one which due to its short lifetime does not remain in the product mixture. Reactive intermediates are usually high-energy, are unstable and are seldom isolated. | 7 | Physical Chemistry |
Chemical activities should be used to define chemical potentials, where the chemical potential depends on the temperature , pressure and the activity according to the formula:
where is the gas constant and is the value of under standard conditions. Note that the choice of concentration scale affects both the activity and the standard state chemical potential, which is especially important when the reference state is the infinite dilution of a solute in a solvent. Chemical potential has units of joules per mole (J/mol), or energy per amount of matter. Chemical potential can be used to characterize the specific Gibbs free energy changes occurring in chemical reactions or other transformations.
Formulae involving activities can be simplified by considering that:
* For a chemical solution:
** the solvent has an activity of unity (only a valid approximation for rather dilute solutions)
** At a low concentration, the activity of a solute can be approximated to the ratio of its concentration over the standard concentration:
Therefore, it is approximately equal to its concentration.
* For a mix of gas at low pressure, the activity is equal to the ratio of the partial pressure of the gas over the standard pressure: Therefore, it is equal to the partial pressure in atmospheres (or bars), compared to a standard pressure of 1 atmosphere (or 1 bar).
* For a solid body, a uniform, single species solid has an activity of unity at standard conditions. The same thing holds for a pure liquid.
The latter follows from any definition based on Raoult's law, because if we let the solute concentration go to zero, the vapor pressure of the solvent will go to . Thus its activity will go to unity. This means that if during a reaction in dilute solution more solvent is generated (the reaction produces water for example) we can typically set its activity to unity.
Solid and liquid activities do not depend very strongly on pressure because their molar volumes are typically small. Graphite at 100 bars has an activity of only 1.01 if we choose as standard state. Only at very high pressures do we need to worry about such changes. Activity expressed in terms of pressure is called fugacity. | 7 | Physical Chemistry |
CK2 typically appears as a tetramer of two α subunits; α being 42 kDa and α’ being 38 kDa, and two β subunits, each weighing in at 28 kDa. The β regulatory domain only has one isoform and therefore within the tetramer will have two β subunits. The catalytic α domains appear as an α or α’ variant and can either be formed in a homodimer (α & α, or α’ & α’) formation or heterodimer formation (α & α’). It is worth noting that other β isoforms have been found in other organisms but not in humans.
The α subunits do not require the β regulatory subunits to function, this allows dimers to form of the catalytic domains independent of β subunit transcription. The presence of these α subunits does have an effect on the phosphorylation targets of CK2. A functional difference between α and α’ has been found but the exact nature of differences isn't fully understood yet. An example is that Caspase 3 is preferentially phosphorylated by α’ based tetramers over α based tetramers. | 1 | Biochemistry |
Chlorinated paraffins (CPs) are complex mixtures of polychlorinated n-alkanes (paraffin wax). The chlorination degree of CPs can vary between 30 and 70 wt%. CPs are subdivided according to their carbon chain length into short-chain CPs (SCCPs, C), medium-chain CPs (MCCPs, C) and long-chain CPs (LCCPs, C). Depending on chain length and chlorine content, CPs are colorless or yellowish liquids or solids. | 2 | Environmental Chemistry |
Dicyanopolyynes are composed of a chain of carbon atoms with alternating single and triple bonds, terminated by nitrogen atoms. Although not a polyyne dicyanoacetylene () otherwise fits within this series.
* or , (dicyanodiacetylene)
* or , dicyanohexatriyne
* or
* or
* or
* or
* or
* or
* or | 0 | Organic Chemistry |
Just like other short-affinity tags (His-tag, FLAG-tag), the Strep-tag can be easily fused to recombinant proteins during subcloning of its cDNA or gene. For its expression, various vectors for various host organisms (E. coli, yeast, insect, and mammalian cells) are available. A particular benefit of the Strep-tag is its rather small size and the fact that it is biochemically almost inert. Therefore, protein folding or secretion is not influenced and usually it does not interfere with protein function. Strep-tag is especially suited for analysis of functional proteins, because the purification procedure can be kept under physiological conditions. This not only allows the isolation of sensitive proteins in a native state, but it is also possible to purify intact protein complexes, even if just one subunit carries the tag.
In the first step of the Strep-tag purification cycle, the cell lysate containing Strep-tag fusion protein is applied to a column with immobilized Strep-Tactin (step 1). After the tagged protein has specifically bound to Strep-Tactin, a short washing step with a physiological buffer (e.g. phosphate buffered saline, PBS) removes all other host proteins (step 2). This is due to Strep-Tactin's low tendency to bind proteins non specifically. Then, the purified Strep-tag fusion protein is gently eluted with a low concentration of desthiobiotin, which specifically competes for the biotin binding pocket (step 3). To regenerate the column, desthiobiotin is removed by application of a HABA containing solution (a yellow azo dye). The removal of desthiobiotin is indicated by a color change from yellow-orange to red (step 4+5).
Finally, the HABA solution is washed out with a small volume of running buffer, thus making the column ready to use for the next purification run. | 1 | Biochemistry |
In October 2011, the first clinical trial was announced for the treatment of choroideremia. Dr. Robert MacLaren of the University of Oxford, who lead the trial, co-developed the treatment with Dr. Miguel Seabra of the Imperial College, London. This Phase 1/2 trial used subretinal AAV to restore the REP gene in affected patients.
Initial results of the trial were reported in January 2014 as promising as all six patients had better vision. | 1 | Biochemistry |
A methyl group may rotate around the axis. This is a free rotation only in the simplest cases like gaseous methyl chloride . In most molecules, the remainder R breaks the C symmetry of the axis and creates a potential V(φ) that restricts the free motion of the three protons. For the model case of ethane , this is discussed under the name ethane barrier.
In condensed phases, neighbour molecules also contribute to the potential. Methyl group rotation can be experimentally studied using quasielastic neutron scattering. | 0 | Organic Chemistry |
In chemistry, the alkoxy group is an alkyl group which is singularly bonded to oxygen; thus . Denoted usually with apostrophe('). The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the organic compound ethyl phenyl ether (, also known as ethoxybenzene).
Related to alkoxy groups are aryloxy groups, which have an aryl group singularly bonded to oxygen such as the phenoxy group ().
An alkoxy or aryloxy group bonded to an alkyl or aryl () is an ether. If bonded to H it is an alcohol.
An alkoxide can refer to salts of alcohols, and they are ionic compounds containing an alkoxide ions ; it is a derivative of an alcohol where the hydrogen of the –OH group is replaced by a metal, for example sodium salt of ethanol () is sodium ethoxide, containing ethoxide anions and sodium cations . | 0 | Organic Chemistry |
Like organolithium compounds, Grignard reagents are useful for forming carbon–heteroatom bonds.
Grignard reagents react with many metal-based electrophiles. For example, they undergo transmetallation with cadmium chloride (CdCl) to give dialkylcadmium: | 0 | Organic Chemistry |
Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis, organic reactions are used in the construction of new organic molecules. The production of many man-made chemicals such as drugs, plastics, food additives, fabrics depend on organic reactions.
The oldest organic reactions are combustion of organic fuels and saponification of fats to make soap. Modern organic chemistry starts with the Wöhler synthesis in 1828. In the history of the Nobel Prize in Chemistry awards have been given for the invention of specific organic reactions such as the Grignard reaction in 1912, the Diels–Alder reaction in 1950, the Wittig reaction in 1979 and olefin metathesis in 2005. | 0 | Organic Chemistry |
Currently, it is highly unlikely that the presence of unexpected or even unknown GMOs will be detected, since either the DNA sequence of the transgene or its product, the protein, must be known for detection. In addition, even testing for known GMOs is time-consuming and costly, as current reliable detection methods can test for only one GMO at a time. Therefore, research programmes such as Co-Extra are developing improved and alternative testing methods, for example DNA microarrays. | 1 | Biochemistry |
A Townsend discharge can be sustained only over a limited range of gas pressure and electric field intensity. The accompanying plot shows the variation of voltage drop and the different operating regions for a gas-filled tube with a constant pressure, but a varying current between its electrodes. The Townsend avalanche phenomena occurs on the sloping plateau B-D. Beyond D the ionisation is sustained.
At higher pressures, discharges occur more rapidly than the calculated time for ions to traverse the gap between electrodes, and the streamer theory of spark discharge of Raether, Meek, and Loeb is applicable. In highly non-uniform electric fields, the corona discharge process is applicable. See Electron avalanche for further description of these mechanisms.
Discharges in vacuum require vaporization and ionisation of electrode atoms. An arc can be initiated without a preliminary Townsend discharge; for example when electrodes touch and are then separated. | 7 | Physical Chemistry |
Kudernac et al. described a specially designed molecule that has four motorized "wheels". By depositing the molecule on a copper surface and providing them with sufficient energy from electrons of a scanning tunnelling microscope they were able to drive some of the molecules in a specific direction, much like a car, being the first single molecule capable to continue moving in the same direction across a surface. Inelastic electron tunnelling induces conformational changes in the rotors and propels the molecule across a copper surface. By changing the direction of the rotary motion of individual motor units, the self-propelling molecular four-wheeler structure can follow random or preferentially linear trajectories. This design provides a starting point for the exploration of more sophisticated molecular mechanical systems, perhaps with complete control over their direction of motion.
This electrically driven nanocar was built under supervision of University of Groningen chemist Bernard L. Feringa, who was awarded the Nobel Prize for Chemistry in 2016 for his pioneering work on nanomotors, together with Jean-Pierre Sauvage and J. Fraser Stoddart. | 6 | Supramolecular Chemistry |
Involvement of mediator in various human diseases has been reviewed. Since inhibiting one interaction of a disease-causing signaling pathway with a subunit of mediator may not inhibit general transcription needed for normal function, mediator subunits are attractive candidates for therapeutic drugs. | 1 | Biochemistry |
Energy associated with the transfer of electrons down the electron transport chain is used to pump protons from the mitochondrial matrix into the intermembrane space, creating an electrochemical proton gradient (ΔpH) across the inner mitochondrial membrane. This proton gradient is largely but not exclusively responsible for the mitochondrial membrane potential (ΔΨ). It allows ATP synthase to use the flow of H through the enzyme back into the matrix to generate ATP from adenosine diphosphate (ADP) and inorganic phosphate. Complex I (NADH coenzyme Q reductase; labeled I) accepts electrons from the Krebs cycle electron carrier nicotinamide adenine dinucleotide (NADH), and passes them to coenzyme Q (ubiquinone; labeled Q), which also receives electrons from Complex II (succinate dehydrogenase; labeled II). Q passes electrons to Complex III (cytochrome bc complex; labeled III), which passes them to cytochrome c (cyt c). Cyt c passes electrons to Complex IV (cytochrome c oxidase; labeled IV).
Four membrane-bound complexes have been identified in mitochondria. Each is an extremely complex transmembrane structure that is embedded in the inner membrane. Three of them are proton pumps. The structures are electrically connected by lipid-soluble electron carriers and water-soluble electron carriers. The overall electron transport chain can be summarized as follows:
NADH, H → Complex I → Q → Complex III → cytochrome c → Complex IV → HO
Complex II
Succinate | 1 | Biochemistry |
The enzymology of proteases provides some of the clearest known examples of convergent evolution. The same geometric arrangement of triad residues occurs in over 20 separate enzyme superfamilies. Each of these superfamilies is the result of convergent evolution for the same triad arrangement within a different structural fold. This is because there are limited productive ways to arrange three triad residues, the enzyme backbone and the substrate. These examples reflect the intrinsic chemical and physical constraints on enzymes, leading evolution to repeatedly and independently converge on equivalent solutions. | 1 | Biochemistry |
Once through the observation cell the mixture enters a third syringe that contains a piston that is driven by the flow to activate a switch to stop the flow and activate the observation. | 7 | Physical Chemistry |
In the Science journal article, GFAJ-1 is referred to as a strain of Halomonadaceae and not as a new species. The International Code of Nomenclature of Bacteria, the set of regulations which govern the taxonomy of bacteria, and certain articles in the International Journal of Systematic and Evolutionary Microbiology contain the guidelines and minimal standards to describe a new species, e.g. the minimal standards to describe a member of the Halomonadaceae. Organisms are described as new species if they meet certain physiological and genetic conditions, such as generally less than 97% 16S rRNA sequence identity to other known species and metabolic differences allowing them to be discerned apart. In addition to indicators to tell the novel species from other species, other analyses are required, such as fatty acid composition, respiratory quinone used and tolerance ranges and deposition of the strain in at least two microbiological repositories. New proposed names are given in italics followed by sp. nov. (and gen. nov. if it is a novel genus according to the descriptions of that clade).
In the instance of the GFAJ-1 strain these criteria are not met, and the strain is not claimed to be a new species. When a strain is not assigned to a species (e.g. due to insufficient data or choice) it is often labeled as the genus name followed by "sp." (i.e., undetermined species of that genus) and the strain name. In the case of GFAJ-1 the authors chose to refer to the strain by strain designation only. Strains closely related to GFAJ-1 include Halomonas sp. GTW and Halomonas sp. G27, neither of which were described as valid species. If the authors had formally assigned strain GFAJ-1 to the genus Halomonas, the name would be given as Halomonas sp. GFAJ-1.
The Genome Taxonomy Database assigns GFAJ-1 its own tentative species, Halomonas sp002966495. This means that the strain falls into Halomonas phylogenetically, and its whole-genome similarity compared to other defined species of the genus is low enough. Neither strain GTW nor strain G27 has a genome available for the database to run its classification. | 1 | Biochemistry |
MCAT is also involved in bacterial polyketide biosynthesis. The enzyme MCAT together with an acyl carrier protein (ACP), and a polyketide synthase (PKS) and chain-length factor heterodimer, constitutes the minimal PKS of type II polyketides. | 1 | Biochemistry |
The following is a list of structural features that can be elucidated by NMR:
* Chemical structure of each carbohydrate residue in a molecule, including
** carbon skeleton size and sugar type (aldose/ketose)
** cycle size (pyranose/furanose/linear)
** stereo configuration of all carbons (monosaccharide identification)
** stereo configuration of anomeric carbon (α/β)
** absolute configuration (D/L)
** location of amino-, carboxy-, deoxy- and other functions
* Chemical structure of non-carbohydrate residues in molecule (amino acids, fatty acids, alcohols, organic aglycons etc.)
* Substitution positions in residues
* Sequence of residues
* Stoichiometry of terminal residues and side chains
* Location of phosphate and sulfate diester bonds
* Polymerization degree and frame positioning (for polysaccharides) | 0 | Organic Chemistry |
Counter-immunoelectrophoresis and its modification
In comparison to other conventional methods of diagnosis e.g. for viral infection testing, counter-immunoelectrophoresis is a highly specific, simple, and speedy method that does not require sophisticated, expensive tools, input materials, or long-term capacity building. Considering the high informativeness of counter-immunoelectrophoresis, the results in practice can be dubious at times. As a result, by using a manufactured amphiphilic fluorescein-containing copolymer to increase the antigen and antibody interaction, counter-immunoelectrophoresis procedures can be improved. The use of the fluorescein copolymer-antigen mixture improved the association with plasma levels antibodies of animals immunized against hemorrhage illness and enhanced protein concentration in the precipitated zone, according to the findings. The capability of the amphiphilic fluorescein copolymer to boost antigen-antibody association and see the fluorescent accumulation domain may improve the efficiency of counter-immunoelectrophoresis for infectious disease rapid diagnosis.
Immunomethods
The terminologies, immune-methods and immune-chemical techniques refer to a variety of immunoelectrophoresis processes whose results are identified using antibodies and immunological methodologies. As a result, immunomethods' great sensitivity is a beneficial compared to the great expense of utilizing antibodies. Many different types of agarose electrophoresis are used to see how proteins travel under diverse circumstances. Proteins are recognized after the timer has expired by incubating gels with certain antibodies, which are then stained with Comassie blue.
Radial immunodiffusion
The radial immunodiffusion is an immunoassay technique for determining the concentration of a particular protein in a mixture including other modules. It is made up of an agarose gel, just like the others. Furthermore, in this procedure, the materials are placed into round wells in the gel's core part and disperse through it, generating a deposition ring with a diameter relation to the number of unbound protein that has diffused.
Identification of nanomaterial interaction with C3 protein complement and 2D immunoelectrophoresis
2D immunoelectrophoresis is a potential method that can be used for a range of functions involving protein flow of migrants, such as the deep examination of protein opsonization, in succession of first dimension as an activity of protein molar mass and the second dimension as a role of the isoelectric point. Despite the fact that it contains a large number of proteins, each spot on the 2D gel will symbolize a particular protein with a specific molecular mass and feature.
2D immunoelectrophoresis is also provided as a valuable implement for examining the stimulation of the signal transduction pathway, which is an essential factor in researching nanoparticles before in vivo delivery, because it will impact nanoparticle longevity, destination, and bio-distribution. This method employs two-dimensional horizontally agarose protein electrophoresis to specifically identify the association of nanoparticles with the C3 protein. Proteins can be separated in the first dimension according to their molecular mass (the shorter the protein, the far it drifts), and in the second dimension according to their abundance
Some limitations of immunoelectrophoresis
Though immunoelectrophoresis has a number of benefits, it also has certain drawbacks, such as when compared to other methods of electrophoresis, such as immunofixation, this method is sluggish and less precise. It can be difficult to interpret the results. Several tiny monoclonal proteins may be harder to identify. The accessibility of particular antibodies limits its utility in analytical techniques. Traditional (classical or conventional) immunoelectrophoresis has a number of drawbacks, including the fact that it is time consuming and the protocol might take up to 3 days to finish, has limited specificity and sensitivity, and the results can be difficult to read. As a result, newer immunoelectrophoresis techniques have largely supplanted the conventional immunoelectrophoresis. | 1 | Biochemistry |
Sphingosine can be phosphorylated in vivo via two kinases, sphingosine kinase type 1 and sphingosine kinase type 2. This leads to the formation of sphingosine-1-phosphate, a potent signaling lipid.
Sphingolipid metabolites, such as ceramides, sphingosine and sphingosine-1-phosphate, are lipid signaling molecules involved in diverse cellular processes. | 1 | Biochemistry |
Rhabdoviruses are a diverse family of single stranded, negative sense RNA viruses that infect a wide range of hosts, from plants and insects, to fish and mammals. The Rhaboviridae family consists of six genera, two of which, cytorhabdoviruses and nucleorhabdoviruses, only infect plants. Novirhabdoviruses infect fish, and vesiculovirus, lyssavirus and ephemerovirus infect mammals, fish and invertebrates. The family includes pathogens such as rabies virus, vesicular stomatitis virus and potato yellow dwarf virus that are of public health, veterinary, and agricultural significance. | 1 | Biochemistry |
NIM811 is a mitochondrial permeability transition inhibitor. Also known as N-methyl-4-isoleucine cyclosporin, it is a four-substituted cyclosporine analogue that binds to cyclophilin, however this binary complex cannot bind to calcineurin, and therefore lacks immunosuppressive activity.
NIM811 is a form of treatment for patients with the hepatitis C virus (HCV). Studies indicate a strong relationship between a treatments cyclophilin binding affinity and suppression of HCV activity. NIM811 is also being studied as a potential treatment to genetic muscular diseases such as Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM) disease, diseases altering the genes for collagen VI production. | 1 | Biochemistry |
The enantiomers of axially chiral compounds are usually given the stereochemical labels (R) and (S), sometimes abbreviated (R) and (S). The designations are based on the same Cahn–Ingold–Prelog priority rules used for tetrahedral stereocenters. The chiral axis is viewed end-on and the two "near" and two "far" substituents on the axial unit are ranked, but with the additional rule that the two near substituents have higher priority than the far ones. | 4 | Stereochemistry |
This method is limited to the measurement of the oxygen consumption due only to carbonaceous oxidation. Ammonia oxidation is inhibited.
The sample is kept in a sealed container fitted with a pressure sensor. A substance that absorbs carbon dioxide (typically lithium hydroxide) is added in the container above the sample level. The sample is stored in conditions identical to the dilution method. Oxygen is consumed and, as ammonia oxidation is inhibited, carbon dioxide is released. The total amount of gas, and thus the pressure, decreases because carbon dioxide is absorbed. From the drop of pressure, the sensor electronics computes and displays the consumed quantity of oxygen.
The main advantages of this method compared to the dilution method are:
* simplicity: no dilution of sample required, no seeding, no blank sample.
* direct reading of BOD value.
* continuous display of BOD value at the current incubation time. | 3 | Analytical Chemistry |
can be considered as temperature dependent. It was postulated as the basic expansion the reciprocal-activation reciprocal-temperature relationship, for which can provide a formal mathematical justification by Tolman Theorem. The function when written as the logarithmic derivative of the rate constants with respect to , Eq. (7), the concept to an activation energy represents an energetic obstacle to the progress of the reaction: therefore its reciprocal can be interpreted as a measure of the propensity for the reaction to proceed and defined as the specific transitivity () of the process:
This notation emphasizes the fact that in general the transitivity can take a gamma of values, but not including abrupt changes e.g. in the mechanism or in the phases of reactants. If it is admit a Laurent expansion in a neighbourhood around a reference value, it is possible recover the Eqs. (6) and (8).
What it is call the sub-Arrhenius behaviour would be accounted for traditionally by introducing a tunnelling parameter () in the conventional Transition-State-Theory. In the -TST formulation, it is replace the factor in the TST rate constant by the deformed exponential function, Eq. (3), yielding:
where is Planck constant, is Boltzmann constant and is the (translational, vibrational and rotational) partition functions of the reactants, and is the partition function of the activated complex. In Ref., the significance of the parameter and an explicit procedure for its calculation were proposed, which it is inversely proportional to the square of the barrier height ()and directly proportional to the square of the frequency for crossing the barrier () at a saddle point in the potential energy surface: | 7 | Physical Chemistry |
In genomics, DNA–DNA hybridization is a molecular biology technique that measures the degree of genetic similarity between DNA sequences. It is used to determine the genetic distance between two organisms and has been used extensively in phylogeny and taxonomy. | 1 | Biochemistry |
The set of all lines through the origin in three-dimensional space forms a space called the real projective plane. This plane is difficult to visualize, because it cannot be embedded in three-dimensional space.
However, one can visualize it as a disk, as follows. Any line through the origin intersects the southern hemisphere ≤ 0 in a point, which can then be stereographically projected to a point on a disk in the XY plane. Horizontal lines through the origin intersect the southern hemisphere in two antipodal points along the equator, which project to the boundary of the disk. Either of the two projected points can be considered part of the disk; it is understood that antipodal points on the equator represent a single line in 3 space and a single point on the boundary of the projected disk (see quotient topology). So any set of lines through the origin can be pictured as a set of points in the projected disk. But the boundary points behave differently from the boundary points of an ordinary 2-dimensional disk, in that any one of them is simultaneously close to interior points on opposite sides of the disk (just as two nearly horizontal lines through the origin can project to points on opposite sides of the disk).
Also, every plane through the origin intersects the unit sphere in a great circle, called the trace of the plane. This circle maps to a circle under stereographic projection. So the projection lets us visualize planes as circular arcs in the disk. Prior to the availability of computers, stereographic projections with great circles often involved drawing large-radius arcs that required use of a beam compass. Computers now make this task much easier.
Further associated with each plane is a unique line, called the planes pole', that passes through the origin and is perpendicular to the plane. This line can be plotted as a point on the disk just as any line through the origin can. So the stereographic projection also lets us visualize planes as points in the disk. For plots involving many planes, plotting their poles produces a less-cluttered picture than plotting their traces.
This construction is used to visualize directional data in crystallography and geology, as described below. | 3 | Analytical Chemistry |
TISAB is very commonly applied to fluoride ion analysis such as in fluoride ion selective electrodes.
There are four main constituents to TISAB, namely CDTA (cyclohexylenedinitrilotetraacetate), sodium hydroxide, sodium chloride and acetic acid (ethanoic acid), which are all dissolved in deionised water. Hence, TISAB has a density ~1.0 kg/L, though this can vary to 1.18 kg/L. Each constituent plays an important role in controlling the ionic strength and pH of the analyte solution, which may otherwise cause error and inaccuracy.
The activity of a substance in solution depends on the product of its concentration and the activity coefficient in that solution. The activity coefficient depends on the ionic strength of the solution in which the potentiometric measurements are made. This can be calculated for dilute solutions using the Debye–Hückel equation; for more concentrated solutions other approximations must be used. In most cases, the analyst's goal is simply to make sure that the activity coefficient is constant across a set of solutions, with the assumption that no significant ion pairing exists in the solutions.
Example: An ion-selective electrode might be calibrated using dilute solutions of the analyte in distilled water. If this calibration is used to calculate the concentration of the analyte in sea water (high ionic strength), significant error is introduced by the difference between the activity of the analyte in the dilute solutions and the concentrated sample. This can be avoided by adding a small amount of ionic-strength buffer to the standards, so that the activity coefficients match more closely.
Adding a TISAB buffer to increase the ionic strength of the solution helps to "fix" the ionic strength at a stable level, making a linear correlation between the logarithm of the concentration of analyte and the measured voltage. By also adding the TISAB buffer to the samples from which the potentiometric equipment are calibrated, the linear correlation can be used to calculate the concentration of analyte in the solution.
where is measured voltage, is the gas constant, the temperature measured in kelvins, is the Faraday constant and the charge of the analyte. is the concentration of analyte.
TISAB buffers often include chelators which bind ions that could otherwise interfere with the analyte. | 3 | Analytical Chemistry |
Galvanic corrosion (also called bimetallic corrosion or dissimilar metal corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A similar galvanic reaction is exploited in primary cells to generate a useful electrical voltage to power portable devices. This phenomenon is named after Italian physician Luigi Galvani (1737–1798). | 8 | Metallurgy |
Memory and naïve B cells normally exist in relatively small numbers. As the body needs to be able to respond to a large number of potential pathogens, it maintains a pool of B cells with a wide range of specificities. Consequently, while there is almost always at least one B (naive or memory) cell capable of responding to any given epitope (of all that the immune system can react against), there are very few exact duplicates. However, when a single B cell encounters an antigen to which it can bind, it can proliferate very rapidly. Such a group of cells with identical specificity towards the epitope is known as a clone, and is derived from a common "mother" cell. All the "daughter" B cells match the original "mother" cell in their epitope specificity, and they secrete antibodies with identical paratopes. These antibodies are monoclonal antibodies, since they derive from clones of the same parent cell. A polyclonal response is one in which clones of multiple B cells react to the same antigen. | 1 | Biochemistry |
A protocell (or protobiont) is a self-organized, endogenously ordered, spherical collection of lipids proposed as a rudimentary precursor to cells during the origin of life. A central question in evolution is how simple protocells first arose and how their progeny could diversify, thus enabling the accumulation of novel biological emergences over time (i.e. biological evolution). Although a functional protocell has not yet been achieved in a laboratory setting, the goal to understand the process appears well within reach.
A protocell is a pre-cell in abiogenesis, and was a contained system consisting of simple biologically relevant molecules like ribozymes, and encapsulated in a simple membrane structure – isolating the entity from the environment and other individuals – thought to consist of simple fatty acids, mineral structures, or rock-pore structures. | 9 | Geochemistry |
Untranslated regions (UTRs) are sections of the mRNA before the start codon and after the stop codon that are not translated, termed the five prime untranslated region (5 UTR) and three prime untranslated region (3 UTR), respectively. These regions are transcribed with the coding region and thus are exonic as they are present in the mature mRNA. Several roles in gene expression have been attributed to the untranslated regions, including mRNA stability, mRNA localization, and translational efficiency. The ability of a UTR to perform these functions depends on the sequence of the UTR and can differ between mRNAs. Genetic variants in 3' UTR have also been implicated in disease susceptibility because of the change in RNA structure and protein translation.
The stability of mRNAs may be controlled by the 5 UTR and/or 3 UTR due to varying affinity for RNA degrading enzymes called ribonucleases and for ancillary proteins that can promote or inhibit RNA degradation. (See also, C-rich stability element.)
Translational efficiency, including sometimes the complete inhibition of translation, can be controlled by UTRs. Proteins that bind to either the 3 or 5 UTR may affect translation by influencing the ribosomes ability to bind to the mRNA. MicroRNAs bound to the 3 UTR also may affect translational efficiency or mRNA stability.
Cytoplasmic localization of mRNA is thought to be a function of the 3 UTR. Proteins that are needed in a particular region of the cell can also be translated there; in such a case, the 3 UTR may contain sequences that allow the transcript to be localized to this region for translation.
Some of the elements contained in untranslated regions form a characteristic secondary structure when transcribed into RNA. These structural mRNA elements are involved in regulating the mRNA. Some, such as the SECIS element, are targets for proteins to bind. One class of mRNA element, the riboswitches, directly bind small molecules, changing their fold to modify levels of transcription or translation. In these cases, the mRNA regulates itself. | 1 | Biochemistry |
The Curtin–Hammett principle has been invoked to explain selectivity in a variety of synthetic pathways. One example is observed en route to the antitumor antibiotic AT2433-A1, in which a Mannich-type cyclization proceeds with excellent regioselectivity. Studies demonstrate that the cyclization step is irreversible in the solvent used to run the reaction, suggesting that Curtin–Hammett kinetics can explain the product selectivity. | 7 | Physical Chemistry |
After the molecules travel the length of the column, pass through the transfer line and enter into the mass spectrometer they are ionized by various methods with typically only one method being used at any given time. Once the sample is fragmented it will then be detected, usually by an electron multiplier, which essentially turns the ionized mass fragment into an electrical signal that is then detected.
The ionization technique chosen is independent of using full scan or SIM. | 3 | Analytical Chemistry |
As far back as 1966, the ETH group had started to explore, once again in a model system, an alternative strategy of corrin synthesis in which the corrin ring would be closed between rings A and D. The project was inspired by the conceivable existence of a thus far unknown bond reorganization process. This if existing would make possible the construction of cobyric acid from one single starting material. Importantly, the hypothetical process, being interpreted as implying two sequential rearrangements, was recognized to be formally covered by the new reactivity classifications of sigmatropic rearrangements and electrocyclizations propounded by Woodward and Hoffmann in the context of their orbital symmetry rules!
By May 1968, the ETH group had demonstrated in a model study that the envisaged process, a photochemical A/D-seco-corrinate→corrinate cycloisomerization, does in fact exist. This process was first found to proceed with the Pd complex, but not at all with corresponding Ni(II)- or cobalt(III)-A/D-seco-corrinate complexes. It also went smoothly in complexes of metal ions such as zinc and other photochemically inert and loosely bound metal ions. These, after ring closure, could easily be replaced by cobalt. These discoveries opened the door to what eventually became the photochemical A/D approach of cobyric acid synthesis.
Starting in fall of 1969 with the B-C-component of the A/B approach and a ring-D precursor prepared from the enantiomer of the starting material leading to the ring-B precursor, it took PhD student Walter Fuhrer less than one and a half years to translate the photochemical model corrin synthesis into a synthesis of dicyano-cobalt(III)-5,15-bisnor-a,b,d,e,g-pentamethyl-cobyrinate-c-N,N-dimethylamide-f-nitrile 2 (fig. 4), the common corrinoid intermediate on the way to cobyric acid. At Harvard, the very same intermediate 2 was obtained around the same time by coupling the ring-D differentiated Harvard A-D-component (available in spring 1971) with the ETH B-C-component, applying the condensation methods developed earlier using the undifferentiated A-D-component.
Thus, in spring 1971, two different routes to a common corrinoid intermediate 2 (fig. 4) along the way to cobyric acid had become available, one requiring 62 chemical steps (Harvard/ETH A/B approach), the other 42 (ETH A/D approach). In both approaches, the four peripheral rings derived from enantiopure precursors possessing the correct sense of chiral, thereby circumventing major stereochemical problems in the buildup of the ligand system. In the construction of the A/D-junction by the A/D-secocorrin→corrin cycloisomerization, formation of two A/D-diastereomers had to be expected. Using cadmium(II) as the coordinating metal ion led to a very high diastereoselectivity in favor of the natural A/D--isomer.
Once the corrin structure was formed by either approach, the three C-H-chirogenic centers at the periphery adjacent to the chromophore system turned out to be prone to epimerizations with exceptional ease. This required a separation of diastereomers after most of the chemical steps in this advanced stage of the syntheses. It was fortunate indeed that, just around that time, the technique of high pressure liquid chromatography (HPLC) had been developed in analytical chemistry. HPLC became an indispensable tool in both laboratories; its use in the B project, pioneered by Jakob Schreiber at ETH, was the earliest application of the technique in natural product synthesis. | 0 | Organic Chemistry |
Ostromislensky died at the age 58. His scientific work did not receive appropriate recognition during his lifetime, but was widely praised afterwards. He was among the first 5 scientists inducted into the International Rubber Science Hall of Fame. | 0 | Organic Chemistry |
Whereas hyperspectral imaging acquires data as many contiguous spectral bands, full spectral imaging acquires data as spectral curves. A significant advantage of FSI over hyperspectral imaging is a significant reduction in data rate and volume. FSI extracts and saves only the information that is in the raw data. The information is contained in the shape of the spectral curves. The rate at which data is produced by an FSI system is proportional to the amount of information in the scene/image. | 7 | Physical Chemistry |
Depending on the dosage form and route of administration, mucoadhesives may be used for either local or systemic drug delivery. An overview on the mucoadhesive properties of mucoadhesives is provided by Vjera Grabovac and Andreas Bernkop-Schnürch. The bioavailability of such drugs is affected by many factors unique to each route of application. In general, mucoadhesives work to increase the contact time at these sites, prolonging the residence time and maintaining an effective release rate. These polymeric coatings may be applied to a wide variety of liquid and solid dosages, each specially suited for the route of administration. | 1 | Biochemistry |
The Old Copper Complex in North America has been radiometrically dated to 9500 BP—i.e., about 7480 BCE—making it one of the oldest known examples of copper extraction in the world. The earliest evidence of the cold-hammering of native copper comes from the excavation at Çayönü Tepesi in eastern Anatolia, which dates between 7200 to 6600 BCE. Among the various items considered to be votive or amulets, there was one that looked like a fishhook and one like an awl. Another find, at Shanidar Cave in Mergasur, Iraq, contained copper beads, and dates back to 8,700 BCE.
One of the world's oldest known copper mines, as opposed to usage of surface deposits, is at Timna Valley, Israel, and has been used since the fourth millennium BC, with surface deposit usage occurring in the fifth and sixth millennium.
The Pločnik archaeological site in southeastern Europe (Serbia) contains the oldest securely dated evidence of copper making at high temperature, from 5,000 BCE. The find in June 2010 extends for an additional 500 years, dated to 5th millennium BCE, representing the earlier record of copper smelting from Rudna Glava (Serbia). | 8 | Metallurgy |
In wire and fiber, all crystals tend to have nearly identical orientation in the axial direction, but nearly random radial orientation. The most familiar exceptions to this rule are fiberglass, which has no crystal structure, and carbon fiber, in which the crystalline anisotropy is so great that a good-quality filament will be a distorted single crystal with approximately cylindrical symmetry (often compared to a jelly roll). Single-crystal fibers are also not uncommon.
The making of metal sheet often involves compression in one direction and, in efficient rolling operations, tension in another, which can orient crystallites in both axes by a process known as grain flow. However, cold work destroys much of the crystalline order, and the new crystallites that arise with annealing usually have a different texture. Control of texture is extremely important in the making of silicon steel sheet for transformer cores (to reduce magnetic hysteresis) and of aluminium cans (since deep drawing requires extreme and relatively uniform plasticity).
Texture in ceramics usually arises because the crystallites in a slurry have shapes that depend on crystalline orientation, often needle- or plate-shaped. These particles align themselves as water leaves the slurry, or as clay is formed.
Casting or other fluid-to-solid transitions (i.e., thin-film deposition) produce textured solids when there is enough time and activation energy for atoms to find places in existing crystals, rather than condensing as an amorphous solid or starting new crystals of random orientation. Some facets of a crystal (often the close-packed planes) grow more rapidly than others, and the crystallites for which one of these planes faces in the direction of growth will usually out-compete crystals in other orientations. In the extreme, only one crystal will survive after a certain length: this is exploited in the Czochralski process (unless a seed crystal is used) and in the casting of turbine blades and other creep-sensitive parts. | 8 | Metallurgy |
Chromosome III is the third smallest chromosome in S. cerevisiae; its size was estimated from pulsed-field gel electro- phoresis studies to be 300–360 kb
This chromosome has been the subject of intensive study, not least because it contains the three genetic loci involved in mating-type control: MAT, HML and HMR.
In March 2014, Jef Boeke of the Langone Medical Centre at New York University, published that his team has synthesized one of the S. cerevisiae 16 yeast chromosomes, the chromosome III, that he named synIII. The procedure involved replacing the genes in the original chromosome with synthetic versions and the finished synthesized chromosome was then integrated into a yeast cell. It required designing and creating 273,871 base pairs of DNA - fewer than the 316,667 pairs in the original chromosome. | 1 | Biochemistry |
The differential diagnosis for berylliosis includes:
* Sarcoidosis
* Granulomatous lung diseases
** Tuberculosis
** Fungal infections (e.g., histoplasmosis)
** Granulomatosis with polyangiitis
* Idiopathic pulmonary fibrosis
* Hypersensitivity pneumonitis
* Asthma
Diagnosis of berylliosis is based on history of beryllium exposures, documented beryllium sensitivity, and granulomatous inflammation on lung biopsy. Given the invasive nature of a lung biopsy, diagnosis can also be based on clinical history consistent with berylliosis, abnormal chest x-ray or CT scan findings, and abnormalities in pulmonary function tests.
The radiologic and pathologic features of berylliosis are very similar to sarcoidosis. Due to the strong clinical and histopathological resemblance of sarcoidosis and berylliosis, patients are sometimes misdiagnosed with sarcoidosis until the history of exposure to beryllium is elicited and beryllium hypersensitivity demonstrated with specific testing. Some studies suggest that up to 6% of all cases of sarcoidosis are actually berylliosis.
The beryllium lymphocyte proliferation test (BeLPT) is the standard way of determining sensitivity to beryllium. The test is performed by acquiring either peripheral blood or fluid from a bronchial alveolar lavage, and lymphocytes are cultured with beryllium sulfate. Cells are then counted and those with elevated number of cells are considered abnormal. Those exposed persons with two abnormal BeLPT tested with peripheral blood, or one abnormal and one borderline result, are considered beryllium sensitized. Also, those with one abnormal BeLPT tested with fluid from a bronchial alveolar lavage are considered sensitized.
Chest radiography findings of berylliosis are non-specific. Early in the disease radiography findings are usually normal. In later stages interstitial fibrosis, pleural irregularities, hilar lymphadenopathy and ground-glass opacities have been reported. Findings on CT are also not specific to berylliosis. Findings that are common in CT scans of people with berylliosis include parenchymal nodules in early stages. One study found that ground-glass opacities were more commonly seen on CT scan in berylliosis than in sarcoidosis. In later stages hilar lymphadenopathy, interstitial pulmonary fibrosis and pleural thickening. | 1 | Biochemistry |
The proof that a spatial displacement can be decomposed into a rotation around, and translation along, a line in space is attributed to Michel Chasles in 1830. Recently the work of Giulio Mozzi has been identified as presenting a similar result in 1763. | 3 | Analytical Chemistry |
Hyper Rayleigh scattering optical activity (HRS OA) is arguably the most fundamental nonlinear chiral optical (chiroptical) effect; since other nonlinear chiroptical effects have additional requirements, which make them conceptually more involved, i.e. less fundamental. HRS OA is a scattering effect and therefore it does not require the frequency conversion process to be coherent, contrary to other nonlinear chiroptical effects, such as second harmonic generation circular dichroism or second harmonic generation optical rotation. Moreover, HRS OA is a parametric process: the initial and final quantum mechanical states of the excited electron are the same. Because the excitation proceeds via virtual states, there is no restriction on the frequency of incident light. By contrast, other nonlinear scattering effects, such as two-photon circular dichroism and hyper-Raman are non-parametric: they require real energy states that restrict the frequencies at which these effects can be observed. | 4 | Stereochemistry |
Acid rain is rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists between 6.5 and 8.5, but acid rain has a pH level lower than this and ranges from 4–5 on average. The more acidic the acid rain is, the lower its pH is. Acid rain can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids.
Acid rain has been shown to have adverse impacts on forests, freshwaters, soils, microbes, insects and aquatic life-forms. In ecosystems, persistent acid rain reduces tree bark durability, leaving flora more susceptible to environmental stressors such as drought, heat/cold and pest infestation. Acid rain is also capable of detrimenting soil composition by stripping it of nutrients such as calcium and magnesium which play a role in plant growth and maintaining healthy soil. In terms of human infrastructure, acid rain also causes paint to peel, corrosion of steel structures such as bridges, and weathering of stone buildings and statues as well as having impacts on human health.
Some governments, including those in Europe and North America, have made efforts since the 1970s to reduce the release of sulfur dioxide and nitrogen oxide into the atmosphere through air pollution regulations. These efforts have had positive results due to the widespread research on acid rain starting in the 1960s and the publicized information on its harmful effects. The main source of sulfur and nitrogen compounds that result in acid rain are anthropogenic, but nitrogen oxides can also be produced naturally by lightning strikes and sulfur dioxide is produced by volcanic eruptions. | 2 | Environmental Chemistry |
The process of space corrosion is being actively investigated. One of the efforts aims to design a sensor based on zinc oxide, able to measure the amount of atomic oxygen in the vicinity of the spacecraft; the sensor relies on drop of electrical conductivity of zinc oxide as it absorbs further oxygen. | 8 | Metallurgy |
Voltage-gated ion channels open and close in response to membrane potential.
*Voltage-gated sodium channels: This family contains at least 9 members and is largely responsible for action potential creation and propagation. The pore-forming α subunits are very large (up to 4,000 amino acids) and consist of four homologous repeat domains (I-IV) each comprising six transmembrane segments (S1-S6) for a total of 24 transmembrane segments. The members of this family also coassemble with auxiliary β subunits, each spanning the membrane once. Both α and β subunits are extensively glycosylated.
*Voltage-gated calcium channels: This family contains 10 members, though these are known to coassemble with αδ, β, and γ subunits. These channels play an important role in both linking muscle excitation with contraction as well as neuronal excitation with transmitter release. The α subunits have an overall structural resemblance to those of the sodium channels and are equally large.
**Cation channels of sperm: This small family of channels, normally referred to as Catsper channels, is related to the two-pore channels and distantly related to TRP channels.
*Voltage-gated potassium channels (K): This family contains almost 40 members, which are further divided into 12 subfamilies. These channels are known mainly for their role in repolarizing the cell membrane following action potentials. The α subunits have six transmembrane segments, homologous to a single domain of the sodium channels. Correspondingly, they assemble as tetramers to produce a functioning channel.
*Some transient receptor potential channels: This group of channels, normally referred to simply as TRP channels, is named after their role in Drosophila phototransduction. This family, containing at least 28 members, is incredibly diverse in its method of activation. Some TRP channels seem to be constitutively open, while others are gated by voltage, intracellular Ca, pH, redox state, osmolarity, and mechanical stretch. These channels also vary according to the ion(s) they pass, some being selective for Ca while others are less selective, acting as cation channels. This family is subdivided into 6 subfamilies based on homology: classical (TRPC), vanilloid receptors (TRPV), melastatin (TRPM), polycystins (TRPP), mucolipins (TRPML), and ankyrin transmembrane protein 1 (TRPA).
*Hyperpolarization-activated cyclic nucleotide-gated channels: The opening of these channels is due to hyperpolarization rather than the depolarization required for other cyclic nucleotide-gated channels. These channels are also sensitive to the cyclic nucleotides cAMP and cGMP, which alter the voltage sensitivity of the channel's opening. These channels are permeable to the monovalent cations K and Na. There are 4 members of this family, all of which form tetramers of six-transmembrane α subunits. As these channels open under hyperpolarizing conditions, they function as pacemaking channels in the heart, particularly the SA node.
*Voltage-gated proton channels: Voltage-gated proton channels open with depolarization, but in a strongly pH-sensitive manner. The result is that these channels open only when the electrochemical gradient is outward, such that their opening will only allow protons to leave cells. Their function thus appears to be acid extrusion from cells. Another important function occurs in phagocytes (e.g. eosinophils, neutrophils, macrophages) during the "respiratory burst." When bacteria or other microbes are engulfed by phagocytes, the enzyme NADPH oxidase assembles in the membrane and begins to produce reactive oxygen species (ROS) that help kill bacteria. NADPH oxidase is electrogenic, moving electrons across the membrane, and proton channels open to allow proton flux to balance the electron movement electrically. | 1 | Biochemistry |
The relation between a probe and the mRNA that it is expected to detect is not trivial. Some mRNAs may cross-hybridize probes in the array that are supposed to detect another mRNA. In addition, mRNAs may experience amplification bias that is sequence or molecule-specific. Thirdly, probes that are designed to detect the mRNA of a particular gene may be relying on genomic EST information that is incorrectly associated with that gene. | 1 | Biochemistry |
In astronomy, the curve of growth describes the equivalent width of a spectral line as a function of the column density of the material from which the spectral line is observed. | 7 | Physical Chemistry |
An ultrasonic flow meter measures the velocity of a liquid or gas through a pipe using acoustic sensors. This has some advantages over other measurement techniques. The results are slightly affected by temperature, density or conductivity. Maintenance is inexpensive because there are no moving parts.
Ultrasonic flow meters come in three different types: transmission (contrapropagating transit time) flowmeters, reflection (Doppler) flowmeters, and open-channel flowmeters. Transit time flowmeters work by measuring the time difference between an ultrasonic pulse sent in the flow direction and an ultrasound pulse sent opposite the flow direction. Doppler flowmeters measure the doppler shift resulting in reflecting an ultrasonic beam off either small particles in the fluid, air bubbles in the fluid, or the flowing fluid's turbulence. Open channel flow meters measure upstream levels in front of flumes or weirs.
Optical time-of-flight sensors consist of two light beams projected into the fluid whose detection is either interrupted or instigated by the passage of small particles (which are assumed to be following the flow). This is not dissimilar from the optical beams used as safety devices in motorized garage doors or as triggers in alarm systems. The speed of the particles is calculated by knowing the spacing between the two beams. If there is only one detector, then the time difference can be measured via autocorrelation. If there are two detectors, one for each beam, then direction can also be known. Since the location of the beams is relatively easy to determine, the precision of the measurement depends primarily on how small the setup can be made. If the beams are too far apart, the flow could change substantially between them, thus the measurement becomes an average over that space. Moreover, multiple particles could reside between them at any given time, and this would corrupt the signal since the particles are indistinguishable. For such a sensor to provide valid data, it must be small relative to the scale of the flow and the seeding density. MOEMS approaches yield extremely small packages, making such sensors applicable in a variety of situations. | 7 | Physical Chemistry |
Faced with competition from cheaper British iron production, the Swedish iron industry needed to find a new cheaper method of making iron. In the 1810s, experiments were made with puddling, but this proved unsatisfactory, as it needed coal of which Sweden had none. After visited Britain, he published a report of his observations. He had seen closed finery hearths in south Wales and near Ulverston, then in Lancashire (now Cumbria). Those in south Wales were similar to puddling furnaces, but in Lancashire, he saw closed furnaces, where the metal was in contact with the fuel. On his return to Sweden, Ekman experimented and built furnaces similar to what he had seen near Ulverston, most probably at Newland ironworks.
In 1829-30, Waern installed a furnace of the south Wales type at Backefors ironworks, while independently Ekman built Lancashire hearths at Dormsjö and Söderfors. From there the process spread to other forges. Charcoal consumption by the metallurgical industry in Sweden peaked about 1885. In 1887, 406 hearths made 210,500 tons of iron. The last Lancashire forge in Sweden was at Ramnäs, closed in 1964.
In Shropshire, charcoal iron production continued on a significant scale, but declined after 1870, rods for wire-drawing being a significant product. However most charcoal forges were probably closed by 1890. | 8 | Metallurgy |
For a reversible reaction, the equilibrium constant can be measured at a variety of temperatures. This data can be plotted on a graph with on the -axis and on the axis. The data should have a linear relationship, the equation for which can be found by fitting the data using the linear form of the Van 't Hoff equation
This graph is called the "Van 't Hoff plot" and is widely used to estimate the enthalpy and entropy of a chemical reaction. From this plot, is the slope, and is the intercept of the linear fit.
By measuring the equilibrium constant, , at different temperatures, the Van t Hoff plot can be used to assess a reaction when temperature changes. Knowing the slope and intercept from the Van t Hoff plot, the enthalpy and entropy of a reaction can be easily obtained using
The Van t Hoff plot can be used to quickly determine the enthalpy of a chemical reaction both qualitatively and quantitatively. This change in enthalpy can be positive or negative, leading to two major forms of the Van t Hoff plot. | 7 | Physical Chemistry |
Understanding of electrical matters began in the sixteenth century. During this century, the English scientist William Gilbert spent 17 years experimenting with magnetism and, to a lesser extent, electricity. For his work on magnets, Gilbert became known as the "Father of Magnetism." He discovered various methods for producing and strengthening magnets.
In 1663, the German physicist Otto von Guericke created the first electric generator, which produced static electricity by applying friction in the machine. The generator was made of a large sulfur ball cast inside a glass globe, mounted on a shaft. The ball was rotated by means of a crank and an electric spark was produced when a pad was rubbed against the ball as it rotated. The globe could be removed and used as source for experiments with electricity.
By the mid-18th century the French chemist Charles François de Cisternay du Fay had discovered two types of static electricity, and that like charges repel each other whilst unlike charges attract. Du Fay announced that electricity consisted of two fluids: "vitreous" (from the Latin for "glass"), or positive, electricity; and "resinous," or negative, electricity. This was the two-fluid theory of electricity, which was to be opposed by Benjamin Franklins one-fluid theory' later in the century.
In 1785, Charles-Augustin de Coulomb developed the law of electrostatic attraction as an outgrowth of his attempt to investigate the law of electrical repulsions as stated by Joseph Priestley in England.
In the late 18th century the Italian physician and anatomist Luigi Galvani marked the birth of electrochemistry by establishing a bridge between chemical reactions and electricity on his essay "De Viribus Electricitatis in Motu Musculari Commentarius" (Latin for Commentary on the Effect of Electricity on Muscular Motion) in 1791 where he proposed a "nerveo-electrical substance" on biological life forms.
In his essay Galvani concluded that animal tissue contained a here-to-fore neglected innate, vital force, which he termed "animal electricity," which activated nerves and muscles spanned by metal probes. He believed that this new force was a form of electricity in addition to the "natural" form produced by lightning or by the electric eel and torpedo ray as well as the "artificial" form produced by friction (i.e., static electricity).
Galvanis scientific colleagues generally accepted his views, but Alessandro Volta rejected the idea of an "animal electric fluid," replying that the frogs legs responded to differences in metal temper, composition, and bulk. Galvani refuted this by obtaining muscular action with two pieces of the same material. Nevertheless, Volta's experimentation led him to develop the first practical battery, which took advantage of the relatively high energy (weak bonding) of zinc and could deliver an electrical current for much longer than any other device known at the time. | 7 | Physical Chemistry |
The Miller process is an industrial-scale chemical procedure used to refine gold to a high degree of purity (99.5%). It was patented by Francis Bowyer Miller in 1867. This chemical process involves blowing chlorine gas through molten, but (slightly) impure, gold. Nearly all metal contaminants react to form chlorides but gold does not at these high temperatures. The other metals volatilize or form a low density slag on top of the molten gold.
When all impurities have been removed from the gold (observable by a change in flame color) the gold is removed and processed in the manner required for sale or use. The resulting gold is 99.5% pure, but of lower purity than gold produced by the other common refining method, the Wohlwill process, which produces gold of up to 99.999% purity.
The Wohlwill process is commonly used for producing high-purity gold, such as in electronics work, where exacting standards of purity are required. When highest purity gold is not required, refiners use the Miller process due to its relative ease, quicker turnaround times, and because it does not tie up the large amount of gold in the form of chloroauric acid which the Wohlwill process permanently requires for the electrolyte. | 8 | Metallurgy |
Schmiegel is listed as an inventor on all eighteen of his patents, and his patents are assigned to his company, Eli Lilly. Schmiegel's chemical work concentrated on supplements to bolster the health of animals (growth promotion), weight control agents, and antidepressants. | 0 | Organic Chemistry |
Solid ceramic electrolytes – ions migrate through the ceramic phase by means of vacancies or interstitials within the lattice. There are also glassy-ceramic electrolytes. | 7 | Physical Chemistry |
PAR1, PAR3, and PAR4 are activated by thrombin. There are species-specific differences in thrombin receptor expression in platelets and other cell types, in which differences in thrombin concentrations may considerably affect platelet activation of distinct PARs. As seen in human platelets, PAR1 and PAR4 are the functional thrombin receptors, whereas PAR3 and PAR4 are functional thrombin receptors in mouse platelets
Thrombin receptors are also differentially expressed in cell types, e.g. PAR1 is expressed in fibroblasts, smooth muscle cells, sensory neurons and glial cells, whereas the other two are less clearly defined.
There are various roles depending on location of activation. Fibroblasts and smooth muscle cells induces growth factor and matrix production, migration and proliferation. Sensory neurons induces proliferation and release of neuroactive agents. | 1 | Biochemistry |
A common nitrate test, known as the brown ring test can be performed by adding iron(II) sulfate to a solution of a nitrate, then slowly adding concentrated sulfuric acid such that the acid forms a layer below the aqueous solution. A brown ring will form at the junction of the two layers, indicating the presence of the nitrate ion. Note that the presence of nitrite ions will interfere with this test.
The overall reaction is the reduction of the nitrate ion to nitric oxide by iron(II), which is oxidised to iron(III), followed by the formation of nitrosyl ferrous sulfate between the nitric oxide and the remaining iron(II), where nitric oxide is reduced to NO.
:2HNO + 3HSO + 6FeSO → 3Fe(SO) + 2NO + 4HO
:[Fe(HO)]SO + NO → [Fe(HO)(NO)]SO + HO
This test is sensitive up to 2.5 micrograms and a concentration of 1 in 25,000 parts. | 3 | Analytical Chemistry |
Deulinoleate ethyl (also known as di-deuterated ethyl linoleate, di-deuterated linoleic acid ethyl ester, 11,11-d-ethyl linoleate, or ethyl 11,11-d-linoleate) is an experimental, orally-bioavailable synthetic deuterated polyunsaturated fatty acid (PUFA), a part of reinforced lipids. It is an isotopologue of linoleic acid, an essential omega-6 PUFA. The deuterated compound, while identical to natural linoleic acid except for the presence of deuterium, is resistant to lipid peroxidation which makes studies of its cell-protective properties worthwhile. | 1 | Biochemistry |
MCEF or Major Cdk9-interacting elongation factor is a transcription factor related to Af4. It is the fourth member of the Af4 family (AFF) of transcription factors, involved in numerous pathologies, including Acute Lymphoblastic Leukemia (ALL), abnormal CNS development, breast cancer and azoospermia.
Because it apparently interacts with the species-specific human co-factor (P-TEFb) for HIV-1 transcription, and because it can repress HIV-1 replication, MCEF (also known as AFF4 or AF5q31) may have future therapeutic uses.
MCEF was originally cloned and named by Mario Clemente Estable of Ryerson University, while he was a post-doctoral fellow in the laboratory of Robert G. Roeder, at the Rockefeller University. | 1 | Biochemistry |
The third paper of 1864 was concerned with the kinetics of the same equilibrium system. Writing the dissociated active mass at some point in time as x, the rate of reaction was given as
Likewise the reverse reaction of A with B proceeded at a rate given by
The overall rate of conversion is the difference between these rates, so at equilibrium (when the composition stops changing) the two rates of reaction must be equal. Hence | 7 | Physical Chemistry |
The advantages of reverse transfection (over conventional transfection) are:
*The addition and attachment of target cells to the DNA-loaded surface can lead to a higher probability of cell-DNA contact, potentially leading to higher transfection efficiency.
*Labour-saving materials (less DNA is required)
*High-throughput screening; hundreds of genes may be expressed in cells on a single microarray for studying gene expression and regulation.
*Parallel cell seeding in a single chamber for 384 experiments, with no physical separation between experiments, increases screening data quality. Well-to-well variations occur in experiments performed in multi-wall dishes.
*Exact-replicate arrays may be produced, since the same sample source plate may be dried and printed on different slides for at least 15 months' storage without apparent loss of transfection efficiency.
The disadvantages of reverse transfection are:
*Reverse transfection is more expensive because a highly accurate and efficient microarray printing system is needed to print the DNA-gelatin solution onto the slides.
*Applications with different cell lines have (so far) required protocol variations to manufacture siRNA or plasmid arrays, which involve considerable development and testing.
*Increased possibility of array-spot cross-contamination as spot density increases; therefore, optimization of the array layout is important. | 1 | Biochemistry |
In the case of an insertion or a deletion, mapping of the paired-end is consistent with the reference genome. But the read are disconcordant in apparent size. The apparent size is the distance of the BAC sequenced-ends mapped in the reference genome. If a BAC has an insert of length (l), a concordant mapping will show a fragment of size (l) in the reference genome. If the paired-ends are closer than distance (l), an insertion is suspected in the sampled DNA. A distance of (l< μ-3σ) can be used as a cut-off to detect an insertion, where μ is the mean length of the insert and σ is the standard deviation. In case of a deletion, the paired-ends are mapped further away in the reference genome compared to the expected distance (l> μ-3σ). | 1 | Biochemistry |
mtDNA can be obtained from such material as hair shafts and old bones/teeth. Control mechanism based on interaction point with data. This can be determined by tooled placement in sample. | 1 | Biochemistry |
The overwhelming majority of aromatic compounds are compounds of carbon, but they need not be hydrocarbons. | 7 | Physical Chemistry |
AMGs employ diverse functions including pathways not involved in metabolism despite what the name suggests. They are categorized in two classes based on their presence in the Kyoto Encyclopedia of Genes and Genomes (KEGG). AMGs do not encompass metabolic genes involved in typical viral functions, such as nucleotide and protein metabolism since their functions achieve direct viral reproduction, rather than augmenting host function to indirectly enhance it. | 1 | Biochemistry |
The valley or wadi of Nahal Mishmar begins in the Hebron hills, running east towards the Dead Sea. Its western part is shallow, at an altitude of approximately 270 m above sea level, and it proceeds to fall more than 300 meters into the Jordan Rift Valley before emptying into the Dead Sea, over . Nahal Mishmar runs north of the Tze'elim Stream, between Ein Gedi and Masada.
Access is from Highway 90. | 8 | Metallurgy |
A particularly common α-substitution reaction in the laboratory is the halogenation of aldehydes and ketones at their α positions by reaction Cl, Br or I in acidic solution. Bromine in acetic acid solvent is often used.
Remarkably, ketone halogenation also occurs in biological systems, particularly in marine alga, where , bromoacetone, , and other related compounds have been found.
The halogenation is a typical α-substitution reaction that proceeds by acid catalyzed formation of an enol intermediate. | 0 | Organic Chemistry |
Trifluoromethyl sulfone (PhSOCF) and trifluoromethyl sulfoxide (PhSOCF) can be used for trifluoromethylations of electrophiles | 0 | Organic Chemistry |
The connectivity theorems are specific relationships between elasticities and control coefficients. They are useful because they highlight the close relationship between the kinetic properties of individual reactions and the system properties of a pathway. Two basic sets of theorems exists, one for flux and another for concentrations. The concentration connectivity theorems are divided again depending on whether the system species is different from the local species . | 1 | Biochemistry |
In spectroscopy a band head is the abrupt edge of a spectroscopic band. When a band is described as degrading to the violet, it means that for wavelengths above the band head wavelength, the spectrum is dark as the band comes to a sudden stop(just above/after the head), and below the wavelength the brightness of the band weakens gradually. A band that degrades to the red, conversely means that the band head is a lower limit on wavelength for the band, and it fades off toward longer wavelengths, which in visible light is the red end of the spectrum.
If a band spectrum is examined at high resolution it consists of many lines. At a band head the numbers often increase to a limit, or otherwise a series of lines may approach from one side and then reverse at the band head. The lines pile up on top of each other at the band head, and may not be viewed separately. They have become unresolvable. | 7 | Physical Chemistry |
In 1974 Becky Schroeder was given a US patent for her invention of the "Glow Sheet" which used phosphorescent lines under writing paper to help people write in low-light conditions.
Glow in the dark material is added to the plastic blend used in injection molds to make some disc golf discs, which allow the game to be played at night.
Often clock faces of watches are painted with phosphorescent colours. Therefore, they can be used in absolute dark environments for several hours after having been exposed to bright light.
A common use of phosphorescence is decoration. Stars made of glow-in-the-dark plastic are placed on walls, ceilings, or hanging from strings make a room look like the night sky. Other objects like figurines, cups, posters, lamp fixtures, toys and bracelet beads may also glow. Using blacklights makes these things glow brightly, common at raves, bedrooms, theme parks, and festivals. | 7 | Physical Chemistry |
DEAD is an efficient component in Diels-Alder reactions and in click chemistry, for example the synthesis of bicyclo[2.1.0]pentane, which originates from Otto Diels. It has also been used to generate aza-Baylis-Hillman adducts with acrylates.
DEAD can be used for synthesis of heterocyclic compounds. Thus, pyrazoline derivatives convert by condensation to α,β-unsaturated ketones:
Another application is the use of DEAD as an enophile in ene reactions: | 0 | Organic Chemistry |
Transitions between scales are always fluent. There is no sharp cut that defines the end of small- and the beginning of medium/pilot scale. However, chromatography columns with an inner diameter (ID) of up to 5 cm are generally considered small scale or laboratory scale columns.
Small scale chromatography columns are mostly intended for design of experiments (DoE); proof of concept; validation (drug manufacture) or research and development experiments. Columns of this scale category are distinguished by their small dimensions in comparison to chromatography columns intended for larger scales as well as relatively high pressure tolerance and selection of materials in contact with the liquid phase. This is especially important for applications in the biopharmaceutical industry which underlie close scrutiny by regulatory agencies (U.S. Food and Drug Administration; European Medicines Agency). | 3 | Analytical Chemistry |
Epilepsy is a neurological condition marked by recurring seizures. It occurs when the brain's electrical activity becomes unbalanced, leading to repeated seizures. These seizures disrupt the normal electrical patterns in the brain, causing sudden and synchronized bursts of electrical energy. As a result, individuals may experience temporary changes in consciousness, movements, or sensations.
Glutamate excitotoxicity is thought to play an important role in the initiation and maintenance of epileptic seizures. The seizure-induced high flux of glutamate overstimulated glutamate receptors, which triggered a chain reaction of excitation in glutamatergic networks. | 1 | Biochemistry |
An N-body treatment accounting for all impact parameters can be performed by taking into account a few simple facts. The main two ones are: (i) The above change in perpendicular velocity is the lowest order approximation in 1/b of a full Rutherford deflection. Therefore, the above perturbative theory can also be done by using this full deflection. This makes the calculation correct up to the smallest impact parameters where this full deflection must be used. (ii) The effect of Debye shielding for large impact parameters can be accommodated by using a Debye-shielded Coulomb potential (Screening effect Debye length). This cancels the above divergence at large impact parameters. The above Coulomb logarithm turns out to be modified by a constant of order unity. | 7 | Physical Chemistry |
Structural variations, such as deletions, duplications, inversions, translocations, and other rearrangements, are common in human genomes. These variations can have significant impacts on genome functions, and have been implicated in many diseases. Linked-read sequencing technology labels all reads that originate from the same long DNA fragment with the same barcode, so it enables the detection of a large number of structural variants. Complexity of structural variants can be resolved with linked-read sequencing, and provide a complete picture of the genomic landscape. Many scientists have already been using linked-read sequencing to identify and characterise structural variants in diverse populations, including people with genetic disorders or cancers | 1 | Biochemistry |
In 1891, at the Académie des Sciences in Paris, Gabriel Lippmann presented a colour photograph of the Sun's spectrum obtained with his new photographic plate. Later, in 1894, he published an article on how his plate was able to record colour information in the depth of photographic grainless gelatin and how the same plate after processing could restore the original colour image merely through light reflection. He was thus the inventor of true interferential colour photography. He received the Nobel Prize in Physics in 1908 for this breakthrough. Unfortunately, this principle was too complex to use. The method was abandoned a few years after its discovery.
One aspect of the Lippmann concept that was ignored at that time relates to spectroscopic applications. Early in 1933, Herbert E. Ives proposed to use a photoelectric device to probe stationary waves to make spectrometric measurements. In 1995, P. Connes proposed to use the emerging new technology of detectors for three-dimensional Lippmann-based spectrometry. Following this, a first realization of a very compact spectrometer based on a microoptoelectromechanical system (MOEMS) was reported by Knipp et al. in 2005, but it had a very limited spectral resolution. In 2004, two French researchers, Etienne Le Coarer from Joseph Fourier University and Pierre Benech from INP Grenoble, coupled sensing elements to the evanescent part of standing waves within a single-mode waveguide. In 2007, those two researchers reported a near-field method to probe the interferogram within a waveguide. The first SWIFTS-based spectrometers appeared in 2011 based on a SWIFTS linear configuration. | 7 | Physical Chemistry |
The quantitative estimation of stabilization from conjugation is notoriously contentious and depends on the implicit assumptions that are made when comparing reference systems or reactions. The energy of stabilization is known as the resonance energy when formally defined as the difference in energy between the real chemical species and the hypothetical species featuring localized π bonding that corresponds to the most stable resonance form. This energy cannot be measured, and a precise definition accepted by most chemists will probably remain elusive. Nevertheless, some broad statements can be made. In general, stabilization is more significant for cationic systems than neutral ones. For buta-1,3-diene, a crude measure of stabilization is the activation energy for rotation of the C2-C3 bond. This places the resonance stabilization at around 6 kcal/mol. Comparison of heats of hydrogenation of 1,4-pentadiene and 1,3-pentadiene estimates a slightly more modest value of 3.5 kcal/mol. For comparison, allyl cation has a gas-phase rotation barrier of around 38 kcal/mol, a much greater penalty for loss of conjugation. Comparison of hydride ion affinities of propyl cation and allyl cation, corrected for inductive effects, results in a considerably lower estimate of the resonance energy at 20–22 kcal/mol. Nevertheless, it is clear that conjugation stabilizes allyl cation to a much greater extent than buta-1,3-diene. In contrast to the usually minor effect of neutral conjugation, aromatic stabilization can be considerable. Estimates for the resonance energy of benzene range from around 36–73 kcal/mol. | 7 | Physical Chemistry |
Nucleation is the formation and growth of a new phase with or without the presence of external surface. The presence of this surface results in heterogeneous nucleation whereas in its absence homogeneous nucleation occurs. Heterogeneous nucleation occurs in cases where there are pre-existing nuclei present, such as tiny dust particles suspended in a liquid or gas or reacting with a glass surface containing . For the process of Hoffman nucleation and its progression to Lauritzen–Hoffman growth theory, homogeneous nucleation is the main focus. Homogeneous nucleation occurs where no such contaminants are present and is less commonly seen. Homogeneous nucleation begins with small clusters of molecules forming from one phase to the next. As the clusters grow, they aggregate through the condensation of other molecules. The size continues to increase and ultimately form macroscopic droplets (or bubbles depending on the system).
Nucleation is often described mathematically through the change in Gibbs free energy of n moles of vapor at vapor pressure P that condenses into a drop. Also the nucleation barrier, in polymer crystallization, consists of both enthalpic and entropic components that must be over come. This barrier consists of selection processes taking place in different length and time scales which relates to the multiple regimes later on. This barrier is the free energy required to overcome in order to form nuclei. It is the formation of the nuclei from the bulk to a surface that is the interfacial free energy. The interfacial free energy is always a positive term and acts to destabilize the nucleus allowing the continuation of the growing polymer chain. The nucleation continues as a favorable reaction. | 7 | Physical Chemistry |
Rhodopin (1,2-dihydro-ψ,ψ-caroten-1-ol) is a carotenoid. It is a major carotenoid of phototropic bacteria such as Rhodomicrobium vannielii and Rhodopseudomonas acidophila strain 7050. | 1 | Biochemistry |
Heterogeneous metal catalyzed cross-coupling is a subset of metal catalyzed cross-coupling in which a heterogeneous metal catalyst is employed. Generally heterogeneous cross-coupling catalysts consist of a metal dispersed on an inorganic surface or bound to a polymeric support with ligands. Heterogeneous catalysts provide potential benefits over homogeneous catalysts in chemical processes in which cross-coupling is commonly employed—particularly in the fine chemical industry—including recyclability and lower metal contamination of reaction products. However, for cross-coupling reactions, heterogeneous metal catalysts can suffer from pitfalls such as poor turnover and poor substrate scope, which have limited their utility in cross-coupling reactions to date relative to homogeneous catalysts. Heterogeneous metal catalyzed cross-couplings, as with homogeneous metal catalyzed ones, most commonly use Pd as the cross-coupling metal. | 0 | Organic Chemistry |
In the United States, overall availability of IVF in 2005 was 2.5 IVF physicians per 100,000 population, and utilisation was 236 IVF cycles per 100,000. 126 procedures are performed per million people per year. Utilisation highly increases with availability and IVF insurance coverage, and to a significant extent also with percentage of single persons and median income. In the US, an average cycle, from egg retrieval to embryo implantation, costs $12,400, and insurance companies that do cover treatment, even partially, usually cap the number of cycles they pay for. As of 2015, more than 1 million babies had been born utilising IVF technologies.
In the US, nineteen states have laws requiring insurance coverage for infertility treatment, and thirteen of those specifically include IVF. These states that mandate IVF coverage are: Arkansas, California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Louisiana, Maryland, Massachusetts, Montana, New Hampshire, New Jersey, New York, Ohio, Rhode Island, Texas, Utah, and West Virginia. These laws differ by state but many require an egg be fertilised with sperm from a spouse and that in order to be covered you must show you cannot become pregnant through penile-vaginal sex. These requirements are not possible for a same-sex couple to meet. No state Medicaid program, however, covers for IVF according to a 2020 report.
Many fertility clinics in the United States limit the upper age at which people are eligible for IVF to 50 or 55 years. These cut-offs make it difficult for people older than fifty-five to utilise the procedure. | 1 | Biochemistry |
Naming alkanes per standards listed in the IUPAC Gold Book is done according to the Klyne–Prelog system for specifying angles (called either torsional or dihedral angles) between substituents around a single bond:
* a torsion angle between 0° and ±90° is called syn (s)
* a torsion angle between ±90° and 180° is called anti (a)
* a torsion angle between 30° and 150° or between −30° and −150° is called clinal (c)
* a torsion angle between 0° and ±30° or ±150° and 180° is called periplanar (p)
* a torsion angle between 0° and ±30° is called synperiplanar (sp), also called syn- or cis- conformation
* a torsion angle between 30° to 90° and −30° to −90° is called synclinal (sc), also called gauche or skew
* a torsion angle between 90° and 150° or −90° and −150° is called anticlinal (ac)
* a torsion angle between ±150° and 180° is called antiperiplanar (ap), also called anti- or trans- conformation
Torsional strain or "Pitzer strain" refers to resistance to twisting about a bond. | 4 | Stereochemistry |
In 1983, Philip P. Power synthesized a transition-metal complex containing P=P double bond (trans–{[2}) via a simple one-step procedure. They mixed Na[Fe(CO)] and dichlorobis(trimethylsilyl)methylphosphine and got dark red-brown crystals, which was the first complex that contained an unbridged P-P double bond. Each phosphorus exhibited terminal coordination nature and the P-P distance was essentially unchanged. Later in 1983, A. H. Cowley reported ArP=PArFe(CO) (with Ar=2,4,6-tri-tert-butylphenyl) by treating diphosephene with Fe(CO) or NaFe(CO). In this synthesis procedure, there was only one terminal P-coordination and P-P double bond had Z configuration. Apart from iron, other similar transition metal complexes by reacting diphosphenes with transition metal carbonyls of nickel, tungsten, and chromium were discovered and they all exhibited Z configuration. M. Yoshifuji proved E/Z isomerization can take place under lighting, probably via migration of the metal moiety from one side to the other. | 0 | Organic Chemistry |
The Tolman cone angle method assumes empirical bond data and defines the perimeter as the maximum possible circumscription of an idealized free-spinning substituent. The metal-ligand bond length in the Tolman model was determined empirically from crystal structures of tetrahedral nickel complexes. In contrast, the solid-angle concept derives both bond length and the perimeter from empirical solid state crystal structures. There are advantages to each system.
If the geometry of a ligand is known, either through crystallography or computations, an exact cone angle (θ) can be calculated. No assumptions about the geometry are made, unlike the Tolman method. | 4 | Stereochemistry |
The nitronium ion is isoelectronic with carbon dioxide and nitrous oxide, and has the same linear structure and bond angle of 180°. For this reason it has a similar vibrational spectrum to carbon dioxide. Historically, the nitronium ion was detected by Raman spectroscopy, because its symmetric stretch is Raman-active but infrared-inactive. The Raman-active symmetrical stretch was first used to identify the ion in nitrating mixtures. | 0 | Organic Chemistry |
Robert Sidney Cahn (9 June 1899 – 15 June 1981) was a British chemist, best known for his contributions to chemical nomenclature and stereochemistry, particularly by the Cahn–Ingold–Prelog priority rules, which he proposed in 1956 with Christopher Kelk Ingold and Vladimir Prelog. Cahn was the first to report the structure of Cannabinol (CBN) found in Cannabis in the early 1930s.
Cahn was born in Hampstead, London. He became a fellow of the Royal Institute of Chemistry and was editor of the Journal of the Chemical Society from 1949 until 1963, and he remained with the Society as Director of Publications Research until his retirement in 1965. | 4 | Stereochemistry |
The use of ion beams as a particle-beam weapon is theoretically possible, but has not been demonstrated. Electron beam weapons have been tested by the U.S. Navy in the early 20th century, but the hose instability effect prevents these from being accurate at a distance of over approximately 30 inches. See particle-beam weapon for more information on this type of weapon. | 7 | Physical Chemistry |
Organolithium reagents, including n-BuLi are used in synthesis of specific aldehydes and ketones. One such synthetic pathway is the reaction of an organolithium reagent with disubstituted amides:
: RLi + RCONMe → LiNMe + RC(O)R | 0 | Organic Chemistry |
Drugs receive regulatory approval and are granted patents for only a single polymorph.
In a classic patent dispute, the GlaxoSmithKline defended its patent for the Type II polymorph of the active ingredient in Zantac against competitors while that of the Type I polymorph had already expired.
Polymorphism in drugs can also have direct medical implications since dissolution rates depend on the polymorph. Polymorphic purity of drug samples can be checked using techniques such as powder X-ray diffraction, IR/Raman
spectroscopy, and utilizing the differences in their optical properties in some cases. | 3 | Analytical Chemistry |
The first attempt of LBMS tried to use a Boltzmann-like equation for force (vectorial) distributions. The approach requires more computational memory but results are obtained in fracture and solid cracking. | 7 | Physical Chemistry |
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