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The chair conformation is the most stable conformer. At , 99.99% of all molecules in a cyclohexane solution adopt this conformation.
The symmetry group is D. All carbon centers are equivalent. Six hydrogen centers are poised in axial positions, roughly parallel with the C3 axis, and six hydrogen atoms are parallel with the equator of the molecule.
Each carbon bears one "up" and one "down" hydrogen. The C–H bonds in successive carbons are thus staggered so that there is little torsional strain. The chair geometry is often preserved when the hydrogen atoms are replaced by halogens or other simple groups. However, when these hydrogens are substituted for a larger group, strain is imposed upon the molecule due to diaxial interactions. This is an interaction (that is usually repulsive) between two substituents in the axial position on a cyclohexane ring.
If one thinks of a carbon atom as a point with four half-bonds sticking out towards the vertices of a tetrahedron, they can imagine them standing on a surface with one half-bond pointing straight up. Looking from right above, the other three would appear to go outwards towards the vertices of an equilateral triangle, so the bonds would appear to have an angle of 120° between them. Now consider six such atoms standing on the surface so that their non-vertical half-bonds meet up and form a perfect hexagon. If three of the atoms are then reflected to be below the surface, the result will be something very similar to chair-conformation cyclohexane. In this model, the six vertical half-bonds are exactly vertical, and the ends of the six non-vertical half-bonds that stick out from the ring are exactly on the equator (that is, on the surface). Since C–H bonds are actually longer than half a C–C bond, the "equatorial" hydrogen atoms of chair cyclohexane will actually be below the equator when attached to a carbon that is above the equator, and vice versa. This is also true of other substituents. The dihedral angle for a series of four carbon atoms going around the ring in this model alternates between exactly +60° and −60° (called gauche).
The chair conformation cannot deform without changing the bond angles or lengths. We can think of it as two chains, mirror images one of the other, containing atoms (1,2,3,4) and (1,6,5,4), with opposite dihedral angles. The distance from atom 1 to atom 4 depends on the absolute value of the dihedral angle. If these two dihedral angles change (still being opposite one of the other), it is not possible to maintain the correct bond angle at both carbon 1 and carbon 4. | 4 | Stereochemistry |
The laws describing the behaviour of gases under fixed pressure, volume and absolute temperature conditions are called Gas Laws. The basic gas laws were discovered by the end of the 18th century when scientists found out that relationships between pressure, volume and temperature of a sample of gas could be obtained which would hold to approximation for all gases. These macroscopic gas laws were found to be consistent with atomic and kinetic theory. | 7 | Physical Chemistry |
An ideal solid surface is flat, rigid, perfectly smooth, and chemically homogeneous, and has zero contact angle hysteresis. Zero hysteresis implies the advancing and receding contact angles are equal.
In other words, only one thermodynamically stable contact angle exists. When a drop of liquid is placed on such a surface, the characteristic contact angle is formed as depicted in Fig. 1. Furthermore, on an ideal surface, the drop will return to its original shape if it is disturbed. The following derivations apply only to ideal solid surfaces; they are only valid for the state in which the interfaces are not moving and the phase boundary line exists in equilibrium. | 7 | Physical Chemistry |
The HIV protease inhibitor Tipranavir is marketed for the treatment of AIDS. The first enantioselective medicinal chemistry route to Tipranavir included the conjugate addition of an organocuprate reagent to a chiral Michael acceptor. The chiral oxazolidinone in the Michael acceptor controlled the stereochemistry of one of two stereocenters in the molecule. The final, commercial route to Tipranavir does not feature a chiral auxiliary; instead, this stereocenter is set by an asymmetric hydrogenation reaction. | 4 | Stereochemistry |
IUPAC defines the temperature programmed chromatography Kovats index equation:
* & retention times of trailing and heading n-alkanes, respectively.
NOTE: TPGC index does depend on temperature program, gas velocity and the column used !
ASTM method D6730 defines the temperature programmed chromatography Kovats index equation:
Measured Kovats retention index values can be found in ASTM method D 6730 databases.
An extensive Kovats index database is compiled by NIST [https://webbook.nist.gov/chemistry/].
The equations produce significant different Kovats indices. | 3 | Analytical Chemistry |
A [4+2] cycloaddition is exemplified by the Diels-Alder reaction. The simplest case is the reaction of 1,3-butadiene with ethylene to form cyclohexene.
One symmetry element is conserved in this transformation – the mirror plane through the center of the reactants as shown to the left. The molecular orbitals of the reactants are the set {Ψ, Ψ, Ψ, Ψ} of molecular orbitals of 1,3-butadiene shown above, along with π and π of ethylene. Ψ is symmetric, Ψ is antisymmetric, Ψ is symmetric, and Ψ is antisymmetric with respect to the mirror plane. Similarly π is symmetric and π is antisymmetric with respect to the mirror plane.
The molecular orbitals of the product are the symmetric and antisymmetric combinations of the two newly formed σ and σ bonds and the π and π bonds as shown below.
Correlating the pairs of orbitals in the starting materials and product of the same symmetry and increasing energy gives the correlation diagram to the right. As this transforms the ground state bonding molecular orbitals of the starting materials into the ground state bonding orbitals of the product in a symmetry conservative manner this is predicted to not have the great energetic barrier present in the ground state [2+2] reaction above.
To make the analysis precise, one can construct the state correlation diagram for the general [4+2]-cycloaddition. As before, the ground state is the electronic state depicted in the molecular orbital correlation diagram to the right. This can be described as ΨπΨ, of total symmetry SS
A=S. This correlates with the ground state of the cyclohexene σσπ which is also SSA=S. As such this ground state reaction is not predicted to have a high symmetry-imposed barrier.
One can also construct the excited-state correlations as is done above. Here, there is a high energetic barrier to a photo-induced Diels-Alder reaction under a suprafacial-suprafacial bond topology due to the avoided crossing shown below. | 7 | Physical Chemistry |
There are detailed descriptions of the interfacial DL in many books on colloid and interface science and microscale fluid transport. There is also a recent IUPAC technical report on the subject of interfacial double layer and related electrokinetic phenomena.
As stated by Lyklema, "...the reason for the formation of a "relaxed" ("equilibrium") double layer is the non-electric affinity of charge-determining ions for a surface..." This process leads to the buildup of an electric surface charge, expressed usually in C/m. This surface charge creates an electrostatic field that then affects the ions in the bulk of the liquid. This electrostatic field, in combination with the thermal motion of the ions, creates a counter charge, and thus screens the electric surface charge. The net electric charge in this screening diffuse layer is equal in magnitude to the net surface charge, but has the opposite polarity. As a result, the complete structure is electrically neutral.
The diffuse layer, or at least part of it, can move under the influence of tangential stress. There is a conventionally introduced slipping plane that separates mobile fluid from fluid that remains attached to the surface. Electric potential at this plane is called electrokinetic potential or zeta potential (also denoted as ζ-potential).
The electric potential on the external boundary of the Stern layer versus the bulk electrolyte is referred to as Stern potential. Electric potential difference between the fluid bulk and the surface is called the electric surface potential.
Usually zeta potential is used for estimating the degree of DL charge. A characteristic value of this electric potential in the DL is 25 mV with a maximum value around 100 mV (up to several volts on electrodes). The chemical composition of the sample at which the ζ-potential is 0 is called the point of zero charge or the iso-electric point. It is usually determined by the solution pH value, since protons and hydroxyl ions are the charge-determining ions for most surfaces.
Zeta potential can be measured using electrophoresis, electroacoustic phenomena, streaming potential, and electroosmotic flow.
The characteristic thickness of the DL is the Debye length, κ. It is reciprocally proportional to the square root of the ion concentration C. In aqueous solutions it is typically on the scale of a few nanometers and the thickness decreases with increasing concentration of the electrolyte.
The electric field strength inside the DL can be anywhere from zero to over 10 V/m. These steep electric potential gradients are the reason for the importance of the DLs.
The theory for a flat surface and a symmetrical electrolyte is usually referred to as the Gouy-Chapman theory. It yields a simple relationship between electric charge in the diffuse layer σ and the Stern potential Ψ:
There is no general analytical solution for mixed electrolytes, curved surfaces or even spherical particles. There is an asymptotic solution for spherical particles with low charged DLs. In the case when electric potential over DL is less than 25 mV, the so-called Debye-Huckel approximation holds. It yields the following expression for electric potential Ψ in the spherical DL as a function of the distance r from the particle center:
There are several asymptotic models which play important roles in theoretical developments associated with the interfacial DL.
The first one is "thin DL". This model assumes that DL is much thinner than the colloidal particle or capillary radius. This restricts the value of the Debye length and particle radius as following:
This model offers tremendous simplifications for many subsequent applications. Theory of electrophoresis is just one example. The theory of electroacoustic phenomena is another example.
The thin DL model is valid for most aqueous systems because the Debye length is only a few nanometers in such cases. It breaks down only for nano-colloids in solution with ionic strengths close to water.
The opposing "thick DL" model assumes that the Debye length is larger than particle radius:
This model can be useful for some nano-colloids and non-polar fluids, where the Debye length is much larger.
The last model introduces "overlapped DLs". This is important in concentrated dispersions and emulsions when distances between particles become comparable with the Debye length. | 7 | Physical Chemistry |
All data in T3DB is non-proprietary or is derived from a non-proprietary source. It is freely accessible and available to anyone. In addition, nearly every data item is fully traceable and explicitly referenced to the original source. T3DB data is available through a public web interface and downloads. | 1 | Biochemistry |
One of the oldest methods is called the multiple tube method. In this method a measured sub-sample (perhaps 10 ml) is diluted with 100 ml of sterile growth medium and an aliquot of 10 ml is then decanted into each of ten tubes. The remaining 10 ml is then diluted again and the process repeated. At the end of 5 dilutions this produces 50 tubes covering the dilution range of 1:10 through to 1:10000.
The tubes are then incubated at a pre-set temperature for a specified time and at the end of the process the number of tubes with growth in is counted for each dilution. Statistical tables are then used to derive the concentration of organisms in the original sample. This method can be enhanced by using indicator medium which changes colour when acid forming species are present and by including a tiny inverted tube called a Durham tube in each sample tube. The Durham inverted tube catches any gas produced. The production of gas at 37 degrees Celsius is a strong indication of the presence of Escherichia coli. | 3 | Analytical Chemistry |
To produce hydrogel fiber, the solidification of the pregel solution is the most important step. The pregel solution needs to be solidified while maintaining its fibrous shape. To achieve this, several methods based on chemical crosslinking, phase change, rheological property change have been developed. | 7 | Physical Chemistry |
Polyester resin has the following disadvantages:
# Strong styrene odour
# More difficult to mix than other resins, such as a two-part epoxy
# The toxic nature of its fumes, and especially of its catalyst, MEKP, pose a safety risk if proper protection isn't used
# Not appropriate for bonding many substrates
# The finished cure is most likely weaker than an equal amount of an epoxy resin | 7 | Physical Chemistry |
This response was first identified in E. coli. The E. coli adaptive response constitutes of four genes: ada, alkA, alkB, and aidB, each one working in specific residues, all regulated by the E. coli Ada protein.
The E. coli adaptive response is mediated by the Ada protein, which covalently transfers methylation damage from DNA to one of its two active methyl acceptor cysteine residues: Cys38 and Cys321. The Ada protein can repair damage by transferring methyl groups from O6-methylguanine or O4-methylthymine to Cys321 and also from methylphosphotriesters to Cys38 residue through an irreversible process. It can also convert the protein from a weak to a strong activator of transcription, increasing alkylation repair activity. | 1 | Biochemistry |
C/EBPβ levels are increased in cortical samples of Alzheimers and Parkinsons disease victims at autopsy. Cell culture studies in mice and human microglia lines also find increased C/EBPβ activity associated with pathogenic inflammation and cytokine responses. Downstream analysis of genes regulated by C/EBPβ have significance in immune response, mitochondrial health, and autophagy. Molecular interference of these cellular processes have been shown to play a role in neurodegenerative pathogenesis. Genetic and molecular pathways with degenerative implications involving C/EBPβ and its homologs are conserved across multiple model organisms including Mus musculus, Drosophila melanogaster, Caenorhabditis elegans, and Danio rerio'. Upstream regulators of C/EBPβ include genes known to be associated with neurodegenerative and neurodevelopmental disease when mutated or dysregulated. This includes a well characterized cellular stress response pathway involving p38 and JNK. | 1 | Biochemistry |
The Global Ocean Data Analysis Project (GLODAP) is a synthesis project bringing together oceanographic data, featuring two major releases as of 2018. The central goal of GLODAP is to generate a global climatology of the World Ocean's carbon cycle for use in studies of both its natural and anthropogenically forced states. GLODAP is funded by the National Oceanic and Atmospheric Administration, the U.S. Department of Energy, and the National Science Foundation.
The first GLODAP release (v1.1) was produced from data collected during the 1990s by research cruises on the World Ocean Circulation Experiment, Joint Global Ocean Flux Study and Ocean-Atmosphere Exchange Study programmes. The second GLODAP release (v2) extended the first using data from cruises from 2000 to 2013. The data are available both as individual "bottle data" from sample sites, and as interpolated fields on a standard longitude, latitude, depth grid. | 9 | Geochemistry |
In eukaryotic transcription of mRNAs, terminator signals are recognized by protein factors that are associated with the RNA polymerase II and which trigger the termination process. The genome encodes one or more polyadenylation signals. Once the signals are transcribed into the mRNA, the proteins cleavage and polyadenylation specificity factor (CPSF) and cleavage stimulation factor (CstF) transfer from the carboxyl terminal domain of RNA polymerase II to the poly-A signal. These two factors then recruit other proteins to the site to cleave the transcript, freeing the mRNA from the transcription complex, and add a string of about 200 A-repeats to the 3' end of the mRNA in a process known as polyadenylation. During these processing steps, the RNA polymerase continues to transcribe for several hundred to a few thousand bases and eventually dissociates from the DNA and downstream transcript through an unclear mechanism; there are two basic models for this event known as the torpedo and allosteric models. | 1 | Biochemistry |
AUFS is an arbitrary but ubiquitous unit of UV absorbance intensity. It can be used in chemical analysis to quantify components in a mixture, as each components' integrated peak area correspond to their relative abundance. | 3 | Analytical Chemistry |
The slightly curved, near vertical, lines on the main part of the map are the (constant rotational) corrected speed lines. They are a measure of rotor blade tip Mach number.
Note on the illustration that the speed lines are not distributed linearly with flow. This is because this particular compressor is fitted with variable stators, which open progressively as speed increases, causing an exaggerated increase in flow in the medium to high speed region. At low speed, the variable stators are locked, causing a more linear relationship between speed and flow.
Also note that beyond 100% flow, the speed lines close up rapidly, due to choking. Beyond choke, any further increase in speed will generate no further increase in airflow. | 7 | Physical Chemistry |
Biopolymers are natural polymers produced by the cells of living organisms. Like other polymers, biopolymers consist of monomeric units that are covalently bonded in chains to form larger molecules. There are three main classes of biopolymers, classified according to the monomers used and the structure of the biopolymer formed: polynucleotides, polypeptides, and polysaccharides. The Polynucleotides, RNA and DNA, are long polymers of nucleotides. Polypeptides include proteins and shorter polymers of amino acids; some major examples include collagen, actin, and fibrin. Polysaccharides are linear or branched chains of sugar carbohydrates; examples include starch, cellulose, and alginate. Other examples of biopolymers include natural rubbers (polymers of isoprene), suberin and lignin (complex polyphenolic polymers), cutin and cutan (complex polymers of long-chain fatty acids), melanin, and polyhydroxyalkanoates (PHAs).
In addition to their many essential roles in living organisms, biopolymers have applications in many fields including the food industry, manufacturing, packaging, and biomedical engineering. | 1 | Biochemistry |
The Max Planck Institute for Terrestrial Microbiology () is a research institute for terrestrial microbiology in Marburg, Germany. It was founded in 1991 by Rudolf K. Thauer and is one of 80 institutes in the Max Planck Society (Max-Planck-Gesellschaft). Its sister institute is the Max Planck Institute for Marine Microbiology, which was founded a year later in 1992 in Bremen. | 9 | Geochemistry |
The analysis of slag is based on its shape, texture, isotopic signature, chemical and mineralogical characteristics. Analytical tools like Optical Microscope, scanning electron microscope (SEM), X-ray Fluorescence (XRF), X-ray diffraction (XRD) and inductively coupled plasma-mass spectrometry (ICP-MS) are widely employed in the study of slag. | 8 | Metallurgy |
Omega-alicyclic fatty acids typically contain an omega-terminal propyl or butyryl cyclic group and are some of the major membrane fatty acids found in several species of bacteria. The fatty acid synthetase used to produce omega-alicyclic fatty acids is also used to produce membrane branched-chain fatty acids. In bacteria with membranes composed mainly of omega-alicyclic fatty acids, the supply of cyclic carboxylic acid-CoA esters is much greater than that of branched-chain primers. The synthesis of cyclic primers is not well understood but it has been suggested that mechanism involves the conversion of sugars to shikimic acid which is then converted to cyclohexylcarboxylic acid-CoA esters that serve as primers for omega-alicyclic fatty acid synthesis | 1 | Biochemistry |
Ion suppression in LC-MS and LC-MS/MS refers to reduced detector response, or signal:noise as a manifested effect of competition for ionisation efficiency in the ionisation source, between the analyte(s) of interest and other endogenous or exogenous (e.g. plasticisers extracted from plastic tubes, mobile phase additives) species which have not been removed from the sample matrix during sample preparation. Ion suppression is not strictly a problem unless interfering compounds elute at the same time as the analyte of interest. In cases where ion suppressing species do co-elute with an analyte, the effects on the important analytical parameters including precision, accuracy and limit of detection (analytical sensitivity) can be extensive, severely limiting the validity of an assay's results. | 3 | Analytical Chemistry |
The research conducted by Otto and his research group is focused on various fields, varying from the origin of life (self-replicating systems and the Darwinian evolution thereof), to materials chemistry (self-synthesizing fibres, hydrogels and nanoparticle surfaces).
Specific interests include self-replicating molecules, foldamers, catalysis, molecular recognition of biomolecules and self-synthesizing materials (materials of which their self-assembly drives the synthesis of the molecules that assemble). The complex chemical mixtures that are designed, made and researched often display new properties that are relevant to understanding how new traits are able to arise in nature. The final goal of all of this research is the de novo synthesis of new forms of life via the integration of self-replicating systems with metabolism and compartmentalization. His 114 publications have been cited a total of 8,873 times by other scientists. His h-index is 51. | 0 | Organic Chemistry |
Atmospheric chemists often define the Henry solubility as
Here is the concentration of a species in the aqueous phase, and is the partial pressure of that species in the gas phase under equilibrium conditions.
The SI unit for is mol/(m·Pa); however, often the unit M/atm is used, since is usually expressed in M (1M = 1 mol/dm) and in atm (1atm = 101325Pa). | 7 | Physical Chemistry |
Recently it was pointed out that, in the same way that electric polarisation can be generated by spatially varying magnetic order, magnetism can be generated by a temporally varying polarisation. The resulting phenomenon was called Dynamical Multiferroicity. The magnetisation, is given by
where is the polarisation and the indicates the vector product. The dynamical multiferroicity formalism underlies the following diverse range of phenomena:
* The phonon Zeeman effect, in which phonons of opposite circular polarisation have different energies in a magnetic field. This phenomenon awaits experimental verification.
* Resonant magnon excitation by optical driven phonons.
* Dzylaoshinskii-Moriya-type electromagnons.
* The inverse Faraday effect.
* Exotic flavours of quantum criticality. | 7 | Physical Chemistry |
Adenosine triphosphate (ATP) is a major "energy currency" of the cell. The high energy bonds between the phosphate groups can be broken to power a variety of reactions used in all aspects of cell function.
Substrate-level phosphorylation occurs in the cytoplasm of cells during glycolysis and in mitochondria either during the Krebs cycle or by MTHFD1L ([https://www.uniprot.org/uniprot/Q6UB35 EC 6.3.4.3]), an enzyme interconverting ADP + phosphate + 10-formyltetrahydrofolate to ATP + formate + tetrahydrofolate (reversibly), under both aerobic and anaerobic conditions. In the pay-off phase of glycolysis, a net of 2 ATP are produced by substrate-level phosphorylation. | 1 | Biochemistry |
Duplex sequencing is a library preparation and analysis method for next-generation sequencing (NGS) platforms that employs random tagging of double-stranded DNA to detect mutations with higher accuracy and lower error rates.
This method uses degenerate molecular tags in addition to sequencing adapters to recognize reads originating from each strand of DNA. The generated sequencing reads then will be analyzed using two methods: single-strand consensus sequences (SSCS) and duplex consensus sequences (DCS) assembly. Duplex sequencing theoretically can detect mutations with frequencies as low as 5 x 10 --that is more than 10,000 times higher in accuracy compared to the conventional next-generation sequencing methods.
The estimated error rate of standard next-generation sequencing platforms is 10 to 10 per base call. With this error rate, billions of base calls that are produced by NGS will result in millions of errors. The errors are introduced during sample preparation and sequencing such as polymerase chain reaction, sequencing, and image analysis errors. While the NGS platforms' error rate is acceptable in some applications such as detection of clonal variants, it is a major limitation for applications that require higher accuracy for detection of low-frequency variants such as detection of intra-organismal mosaicism, subclonal variants in genetically heterogeneous cancers, or circulating tumor DNA.
Several library preparation strategies have been developed that increase accuracy of NGS platforms such as molecular barcoding and circular consensus sequencing method. Like NGS platforms, the data generated by these methods originates from a single strand of DNA, and therefore the errors that are introduced during PCR amplification, tissue processing, DNA extraction, hybridization capture (where used) or DNA sequencing itself can still be distinguished as a true variant. The duplex sequencing method addresses this problem by taking advantage of the complementary nature of two strands of DNA and confirming only variants that are present in both strands of DNA. Because the probability of two complementary errors arising at the same location in both strands is exceedingly low, duplex sequencing increases the accuracy of sequencing significantly. | 1 | Biochemistry |
Synthetic hydrocarbons can be produced in chemical reactions between carbon dioxide, which can be captured from power plants or the air, and hydrogen. The fuel, often referred to as electrofuel, stores the energy that was used in the production of the hydrogen.
Hydrogen fuel is typically prepared by the electrolysis of water in a power to gas process. To minimize emissions, the electricity is produced using a low-emission energy source such as wind, solar, or nuclear power.
Through the Sabatier reaction methane can then be produced which may then be stored to be burned later in power plants (as a synthetic natural gas), transported by pipeline, truck, or tanker ship, or be used in gas to liquids processes such as the Fischer–Tropsch process to make traditional fuels for transportation or heating.
There are a few more fuels that can be created using hydrogen. Formic acid for example can be made by reacting the hydrogen with . Formic acid combined with can form isobutanol.
Methanol can be made from a chemical reaction of a carbon-dioxide molecule with three hydrogen molecules to produce methanol and water. The stored energy can be recovered by burning the methanol in a combustion engine, releasing carbon dioxide, water, and heat. Methane can be produced in a similar reaction. Special precautions against methane leaks are important since methane is nearly 100 times as potent as CO, regarding the 20-year global warming potential. More energy can be used to combine methanol or methane into larger hydrocarbon fuel molecules.
Researchers have also suggested using methanol to produce dimethyl ether. This fuel could be used as a substitute for diesel fuel due to its ability to self ignite under high pressure and temperature. It is already being used in some areas for heating and energy generation. It is nontoxic, but must be stored under pressure. Larger hydrocarbons and ethanol can also be produced from carbon dioxide and hydrogen.
All synthetic hydrocarbons are generally produced at temperatures of 200–300 °C, and at pressures of 20 to 50 bar. Catalysts are usually used to improve the efficiency of the reaction and create the desired type of hydrocarbon fuel. Such reactions are exothermic and use about 3 mol of hydrogen per mole of carbon dioxide involved. They also produce large amounts of water as a byproduct. | 0 | Organic Chemistry |
It is believed that an alternative visual cycle exists, which uses Müller glial cells instead of Retinal Pigment Epithelium. In this pathway, cones reduce all-trans retinal to all-trans retinol via all-trans Retinol Dehydrogenase, then transport all-trans retinol to Müller cells. There, it is transformed into 11-cis retinol by all-trans retinol isomerase, and can either be stored as retinyl esters within Müller cells, or transported back to the cone photoreceptors, where it is transformed from 11-cis retinol to 11-cis retinal by 11-cis Retinal Dehydrogenase. This pathway helps explain the rapid dark adaptation in the cone system, and the presence of 11-cis Retinal Dehydrogenase in cone photoreceptors, as it is not found in rods, only in the RPE. | 1 | Biochemistry |
A figure is achiral with an orthogonal matrix and a vector . The determinant of is either 1 or −1 then. If it is −1 the isometry is orientation-reversing, otherwise it is orientation-preserving.
A general definition of chirality based on group theory exists. It does not refer to any orientation concept: an isometry is direct if and only if it is a product of squares of isometries, and if not, it is an indirect isometry. The resulting chirality definition works in spacetime. | 4 | Stereochemistry |
In the mitochondrion, pyruvate is oxidized by the pyruvate dehydrogenase complex to the acetyl group, which is fully oxidized to carbon dioxide by the citric acid cycle (also known as the Krebs cycle). Every "turn" of the citric acid cycle produces two molecules of carbon dioxide, one equivalent of ATP guanosine triphosphate (GTP) through substrate-level phosphorylation catalyzed by succinyl-CoA synthetase, as succinyl-CoA is converted to succinate, three equivalents of NADH, and one equivalent of FADH. NADH and FADH are recycled (to NAD and FAD, respectively) by oxidative phosphorylation, generating additional ATP. The oxidation of NADH results in the synthesis of 2–3 equivalents of ATP, and the oxidation of one FADH yields between 1–2 equivalents of ATP. The majority of cellular ATP is generated by this process. Although the citric acid cycle itself does not involve molecular oxygen, it is an obligately aerobic process because O is used to recycle the NADH and FADH. In the absence of oxygen, the citric acid cycle ceases.
The generation of ATP by the mitochondrion from cytosolic NADH relies on the malate-aspartate shuttle (and to a lesser extent, the glycerol-phosphate shuttle) because the inner mitochondrial membrane is impermeable to NADH and NAD. Instead of transferring the generated NADH, a malate dehydrogenase enzyme converts oxaloacetate to malate, which is translocated to the mitochondrial matrix. Another malate dehydrogenase-catalyzed reaction occurs in the opposite direction, producing oxaloacetate and NADH from the newly transported malate and the mitochondrion's interior store of NAD. A transaminase converts the oxaloacetate to aspartate for transport back across the membrane and into the intermembrane space.
In oxidative phosphorylation, the passage of electrons from NADH and FADH through the electron transport chain releases the energy to pump protons out of the mitochondrial matrix and into the intermembrane space. This pumping generates a proton motive force that is the net effect of a pH gradient and an electric potential gradient across the inner mitochondrial membrane. Flow of protons down this potential gradient – that is, from the intermembrane space to the matrix – yields ATP by ATP synthase. Three ATP are produced per turn.
Although oxygen consumption appears fundamental for the maintenance of the proton motive force, in the event of oxygen shortage (hypoxia), intracellular acidosis (mediated by enhanced glycolytic rates and ATP hydrolysis), contributes to mitochondrial membrane potential and directly drives ATP synthesis.
Most of the ATP synthesized in the mitochondria will be used for cellular processes in the cytosol; thus it must be exported from its site of synthesis in the mitochondrial matrix. ATP outward movement is favored by the membrane's electrochemical potential because the cytosol has a relatively positive charge compared to the relatively negative matrix. For every ATP transported out, it costs 1 H. Producing one ATP costs about 3 H. Therefore, making and exporting one ATP requires 4H The inner membrane contains an antiporter, the ADP/ATP translocase, which is an integral membrane protein used to exchange newly synthesized ATP in the matrix for ADP in the intermembrane space. | 1 | Biochemistry |
Tetrathionate is a product of the oxidation of thiosulfate, , by iodine, I:
:2 + I → + 2I
The use of bromine instead of iodine is dubious as excess bromine will oxidize the thiosulfate to sulfate. | 8 | Metallurgy |
The fecal pellets of zooplankton can be important vehicles for the transfer of particulate organic carbon (POC) to the deep ocean, often making large contributions to the carbon sequestration. The size distribution of the copepod community indicates high numbers of small fecal pellets are produced in the epipelagic. However, small fecal pellets are rare in the deeper layers, suggesting they are not transferred efficiently to depth. This means small fecal pellets make only minor contributions to fecal pellet fluxes in the meso- and bathypelagic, particularly in terms of carbon. In a study is focussed on the Scotia Sea, which contains some of the most productive regions in the Southern Ocean, the dominant fecal pellets in the upper mesopelagic were cylindrical and elliptical, while ovoid fecal pellets were dominant in the bathypelagic. The change in fecal pellet morphology, as well as size distribution, points to the repacking of surface fecal pellets in the mesopelagic and in situ production in the lower meso- and bathypelagic, which may be augmented by inputs of fecal pellets via zooplankton vertical migrations. This suggests the flux of carbon to the deeper layers within the Southern Ocean is strongly modulated by meso- and bathypelagic zooplankton, meaning that the community structure in these zones has a major impact on the efficiency of the fecal pellet transfer to ocean depths.
Absorption efficiency (AE) is the proportion of food absorbed by plankton that determines how available the consumed organic materials are in meeting the required physiological demands. Depending on the feeding rate and prey composition, variations in AE may lead to variations in fecal pellet production, and thus regulates how much organic material is recycled back to the marine environment. Low feeding rates typically lead to high AE and small, dense pellets, while high feeding rates typically lead to low AE and larger pellets with more organic content. Another contributing factor to DOM release is respiration rate. Physical factors such as oxygen availability, pH, and light conditions may affect overall oxygen consumption and how much carbon is loss from zooplankton in the form of respired CO. The relative sizes of zooplankton and prey also mediate how much carbon is released via sloppy feeding. Smaller prey are ingested whole, whereas larger prey may be fed on more “sloppily”, that is more biomatter is released through inefficient consumption. There is also evidence that diet composition can impact nutrient release, with carnivorous diets releasing more dissolved organic carbon (DOC) and ammonium than omnivorous diets. | 9 | Geochemistry |
The selection rule for rotational transitions, derived from the symmetries of the rotational wave functions in a rigid rotor, is ΔJ = ±1, where J is a rotational quantum number. | 7 | Physical Chemistry |
The rate of electrons being passed from P700* to the subsequent electron acceptors is high, preventing the electron from being transferred back to P700. Consequently, in most cases, the electrons transferring within photosystem I follow a linear pathway, from the excitation of the P700 special pair to the production of NADPH. | 5 | Photochemistry |
SBPase is a homodimeric protein, meaning that it is made up of two identical subunits. The size of this protein varies between species, but is about 92,000 Da (two 46,000 Da subunits) in cucumber plant leaves. The key functional domain controlling SBPase function involves a disulfide bond between two cysteine residues. These two cysteine residues, Cys52 and Cys57, appear to be located in a flexible loop between the two subunits of the homodimer, near the active site of the enzyme. Reduction of this regulatory disulfide bond by thioredoxin incites a conformational change in the active site, activating the enzyme. Additionally, SBPase requires the presence of magnesium (Mg) to be functionally active. SBPase is bound to the stroma-facing side of the thylakoid membrane in the chloroplast in a plant. Some studies have suggested the SBPase may be part of a large (900 kDa) multi-enzyme complex along with a number of other photosynthetic enzymes. | 5 | Photochemistry |
Pepper spray is banned for use in war by Article I.5 of the Chemical Weapons Convention, which bans the use of all riot control agents in warfare whether lethal or less-than-lethal. Depending on the location, it may be legal to use for self-defense. | 1 | Biochemistry |
SBO has benefited from the funds of the European Molecular Biology Laboratory and the National Institute of General Medical Sciences. | 1 | Biochemistry |
An Interpenetrating polymer network (IPN) is a polymer comprising two or more networks which are at least partially interlaced on a polymer scale but not covalently bonded to each other. The network cannot be separated unless chemical bonds are broken.
The two or more networks can be envisioned to be entangled in such a way that they are concatenated and cannot be pulled apart, but not bonded to each other by any chemical bond.
Simply mixing two or more polymers does not create an interpenetrating polymer network (polymer blend), nor does creating a polymer network out of more than one kind of monomers which are bonded to each other to form one network (heteropolymer or copolymer).
There are semi-interpenetrating polymer networks (SIPN) and pseudo-interpenetrating polymer networks.
To prepare IPNs and SIPNs, the different components are formed simultaneously or sequentially. | 7 | Physical Chemistry |
7-nt primer ligates in the open state of the hairpin, which will block rezipping of the last seven nucleotides and increase the distance between the surface and the magnetic bead by ~5 nm. If the ligation is not successful, no change in the hairpin length is observed. | 1 | Biochemistry |
* Current Contents/Physical, Chemical and Earth Sciences
* Reaction Citation Index
* Science Citation Index Expanded
* Journal Citation Reports/Science Edition
* Chemical Abstracts Service
* Scopus
* Inspec | 7 | Physical Chemistry |
The lower limit of the hot working temperature is determined by its recrystallization temperature. As a guideline, the lower limit of the hot working temperature of a material is 60% its melting temperature (on an absolute temperature scale). The upper limit for hot working is determined by various factors, such as: excessive oxidation, grain growth, or an undesirable phase transformation. In practice materials are usually heated to the upper limit first to keep forming forces as low as possible and to maximize the amount of time available to hot work the workpiece.
The most important aspect of any hot working process is controlling the temperature of the workpiece. 90% of the energy imparted into the workpiece is converted into heat. Therefore, if the deformation process is quick enough the temperature of the workpiece should rise, however, this does not usually happen in practice. Most of the heat is lost through the surface of the workpiece into the cooler tooling. This causes temperature gradients in the workpiece, usually due to non-uniform cross-sections where the thinner sections are cooler than the thicker sections. Ultimately, this can lead to cracking in the cooler, less ductile surfaces. One way to minimize the problem is to heat the tooling. The hotter the tooling the less heat lost to it, but as the tooling temperature rises, the tool life decreases. Therefore the tooling temperature must be compromised; commonly, hot working tooling is heated to 500–850 °F (325–450 °C). | 8 | Metallurgy |
Electrophilic, soluble alkylating agents are often toxic and carcinogenic, due to their tendency to alkylate DNA. This mechanism of toxicity is relevant to the function of anti-cancer drugs in the form of alkylating antineoplastic agents. Some chemical weapons such as mustard gas (sulfide of dichloroethyl) function as alkylating agents. Alkylated DNA either does not coil or uncoil properly, or cannot be processed by information-decoding enzymes. | 0 | Organic Chemistry |
A possible mechanism for Leber's congenital amaurosis has been proposed as the deficiency of RPE65. Without the RPE65 protein, the RPE is unable to store retinyl esters, and the visual cycle is therefore interrupted. At the beginning stages of the disease, the cone cells are unaffected, as they can rely on the alternate Muller cell visual cycle. However, rods do not have access to this alternative and are rendered inert. LCA therefore manifests as nyctalopia (night blindness). In the later stages of the disease, general retinopathy is observed as the rod cells lose their ability to signal. As a result, the rods continually secrete glutamate, a neurotransmitter, at a rate the Muller cells are unable to absorb. The glutamate levels will build up within the retina, where they will reach neurotoxic levels. The RPE65 deficiency would be genetic in origin, and is only one of many proposed possible pathophysiologies of the disease. However, there is a retinal gene therapy to reintroduce normal RPE65 genes that has been approved by the FDA since 2017. | 1 | Biochemistry |
The process of peak-fitting high energy resolution XPS spectra is a mixture of scientific knowledge and experience. The process is affected by instrument design, instrument components, experimental settings and sample variables. Before starting any peak-fit effort, the analyst performing the peak-fit needs to know if the topmost 15 nm of the sample is expected to be a homogeneous material or is expected to be a mixture of materials. If the top 15 nm is a homogeneous material with only very minor amounts of adventitious carbon and adsorbed gases, then the analyst can use theoretical peak area ratios to enhance the peak-fitting process. Peak fitting results are affected by overall peak widths (at half maximum, FWHM), possible chemical shifts, peak shapes, instrument design factors and experimental settings, as well as sample properties:
* The full width at half maximum (FWHM) values are useful indicators of chemical state changes and physical influences. Their increase may indicate a change in the number of chemical bonds, a change in the sample condition (x-ray damage) or differential charging of the surface (localised differences in the charge state of the surface). However, the FWHM also depends on the detector, and can also increase due to the sample getting charged. When using high energy resolution experiment settings on an XPS equipped with a monochromatic Al K-alpha X-ray source, the FWHM of the major XPS peaks range from 0.3 eV to 1.7 eV. The following is a simple summary of FWHM from major XPS signals: Main metal peaks (e.g. 1s, 2p3, 3d5, 4f7) from pure metals have FWHMs that range from 0.30 eV to 1.0 eV Main metal peaks (e.g. 1s, 2p3, 3d5, 4f7) from binary metal oxides have FWHMs that range from 0.9 eV to 1.7 eV The O (1s) peak from binary metal oxides have FWHMs that, in general, range from 1.0 eV to 1.4 eV The C (1s) peak from adventitious hydrocarbons have FWHMs that, in general, range from 1.0 eV to 1.4 eV
* Chemical shift values depend on the degree of electron bond polarization between nearest-neighbor atoms. A specific chemical shift is the difference in BE values of one specific chemical state versus the BE of one form of the pure element, or of a particular agreed-upon chemical state of that element. Component peaks derived from peak-fitting a raw chemical state spectrum can be assigned to the presence of different chemical states within the sampling volume of the sample.
* Peak shapes depend on instrument parameters, experimental parameters and sample characteristics.
* Instrument design factors include linewidth and purity of X-rays used (monochromatic Al, non-monochromatic Mg, Synchrotron, Ag, Zr), as well as properties of the electron analyzer.
* Settings of the electron analyzer (e.g. pass energy, step size)
* Sample factors that affect the peak fitting are the number of physical defects within the analysis volume (from ion etching, or laser cleaning), and the very physical form of the sample (single crystal, polished, powder, corroded) | 7 | Physical Chemistry |
Excessive exposure or intake may lead to a condition known as manganism, a neurodegenerative disorder that causes dopaminergic neuronal death and symptoms similar to Parkinson's disease. | 1 | Biochemistry |
Rain is generally mildly acidic, with a pH between 5.2 and 5.8 if not having any acid stronger than carbon dioxide. If high amounts of nitrogen and sulfur oxides are present in the air, they too will dissolve into the cloud and raindrops, producing acid rain. | 2 | Environmental Chemistry |
In these cycles and engines the working fluid are always like liquid:
*Stirling cycle (Malone engine)
*Heat Regenerative Cyclone | 7 | Physical Chemistry |
High-tensile steels are low-carbon, or steels at the lower end of the medium-carbon range, which have additional alloying ingredients in order to increase their strength, wear properties or specifically tensile strength. These alloying ingredients include chromium, molybdenum, silicon, manganese, nickel, and vanadium. Impurities such as phosphorus and sulfur have their maximum allowable content restricted.
* 41xx steel
** 4140 steel
** 4145 steel
* 4340 steel
** 300M steel
* EN25 steel – 2.521% nickel-chromium-molybdenum steel
* EN26 steel | 8 | Metallurgy |
IUPAC defines resolution in optical spectroscopy as the minimum wavenumber, wavelength or frequency difference between two lines in a spectrum that can be distinguished. Resolving power, R, is given by the transition wavenumber, wavelength or frequency, divided by the resolution. | 7 | Physical Chemistry |
The photopigments used to carry out anaerobic photosynthesis are similar to chlorophyll but differ in molecular detail and peak wavelength of light absorbed. Bacteriochlorophylls a through g absorb electromagnetic radiation maximally in the near-infrared within their natural membrane milieu. This differs from chlorophyll a, the predominant plant and cyanobacteria pigment, which has peak absorption wavelength approximately 100 nanometers shorter (in the red portion of the visible spectrum). | 5 | Photochemistry |
With reference to the definitions, above, a magma chamber will tend to cool down and crystallize minerals according to the liquid line of descent. When this occurs, especially in conjunction with zonation and crystal accumulation, and the melt portion is removed, this can change the composition of a magma chamber. In fact, this is basically fractional crystallization, except in this case we are observing a magma chamber which is the remnant left behind from which a daughter melt has been extracted.
If such a magma chamber continues to cool, the minerals it forms and its overall composition will not match a sample liquid line of descent or a parental magma composition. | 9 | Geochemistry |
In polymer science, the side chain of an oligomeric or polymeric offshoot extends from the backbone chain of a polymer. Side chains have noteworthy influence on a polymer's properties, mainly its crystallinity and density. An oligomeric branch may be termed a short-chain branch, and a polymeric branch may be termed a long-chain branch. Side groups are different from side chains; they are neither oligomeric nor polymeric. | 0 | Organic Chemistry |
Some drugs enhance or inhibit the response to NMBAs which require the dosage adjustment guided by monitoring. | 1 | Biochemistry |
The RM system was first discovered by Salvatore Luria and Mary Human in 1952 and 1953. They found that a bacteriophage growing within an infected bacterium could be modified, so that upon their release and re-infection of a related bacterium the bacteriophages growth is restricted (inhibited; also described by Luria in his autobiography on pages 45 and 99 in 1984). In 1953, Jean Weigle and Giuseppe Bertani reported similar examples of host-controlled modification using different bacteriophage system. Later work by Daisy Roulland-Dussoix and Werner Arber in 1962 and many other subsequent workers led to the understanding that restriction was due to attack and breakdown of the modified bacteriophages DNA by specific enzymes of the recipient bacteria. Further work by Hamilton O. Smith isolated HinDII, the first of the class of enzymes now known as restriction enzymes, while Daniel Nathans showed that it can be used for restriction mapping. When these enzymes were isolated in the laboratory they could be used for controlled manipulation of DNA, thus providing the foundation for the development of genetic engineering. Werner Arber, Daniel Nathans, and Hamilton Smith were awarded the Nobel Prize in Physiology or Medicine in 1978 for their work on restriction-modification. | 1 | Biochemistry |
The flow of currents within an axon can be described quantitatively by cable theory and its elaborations, such as the compartmental model. Cable theory was developed in 1855 by Lord Kelvin to model the transatlantic telegraph cable and was shown to be relevant to neurons by Hodgkin and Rushton in 1946. In simple cable theory, the neuron is treated as an electrically passive, perfectly cylindrical transmission cable, which can be described by a partial differential equation
where V(x, t) is the voltage across the membrane at a time t and a position x along the length of the neuron, and where λ and τ are the characteristic length and time scales on which those voltages decay in response to a stimulus. Referring to the circuit diagram on the right, these scales can be determined from the resistances and capacitances per unit length.
These time and length-scales can be used to understand the dependence of the conduction velocity on the diameter of the neuron in unmyelinated fibers. For example, the time-scale τ increases with both the membrane resistance r and capacitance c. As the capacitance increases, more charge must be transferred to produce a given transmembrane voltage (by the equation Q = CV); as the resistance increases, less charge is transferred per unit time, making the equilibration slower. In a similar manner, if the internal resistance per unit length r is lower in one axon than in another (e.g., because the radius of the former is larger), the spatial decay length λ becomes longer and the conduction velocity of an action potential should increase. If the transmembrane resistance r is increased, that lowers the average "leakage" current across the membrane, likewise causing λ to become longer, increasing the conduction velocity. | 7 | Physical Chemistry |
An oxygen diffusion-enhancing compound is any substance that increases the availability of oxygen in body tissues by influencing the molecular structure of water in blood plasma and thereby promoting the movement (diffusion) of oxygen through plasma. Oxygen diffusion-enhancing compounds have shown promise in the treatment of conditions associated with hypoxia (a lack of oxygen in tissues) and ischemia (a lack of oxygen in the circulating blood supply). Such conditions include hemorrhagic shock, myocardial infarction (heart attack), and stroke. | 1 | Biochemistry |
Back titration is a titration done in reverse; instead of titrating the original sample, a known excess of standard reagent is added to the solution, and the excess is titrated. A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration, as with precipitation reactions. Back titrations are also useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in a non-soluble solid. | 3 | Analytical Chemistry |
In viruses and bacteriophages, the DNA or RNA is surrounded by a protein capsid, sometimes further enveloped by a lipid membrane. Double-stranded DNA is stored inside the capsid in the form of a spool, which can have different types of coiling leading to different types of liquid-crystalline packing. This packing can change from hexagonal to cholesteric to isotropic at different stages of the phage functioning. Although the double helices are always locally aligned, the DNA inside viruses does not represent real liquid crystals, because it lacks fluidity. On the other hand, DNA condensed in vitro, e.g., with the help of polyamines also present in viruses, is both locally ordered and fluid. | 1 | Biochemistry |
Studies have demonstrated seaweed's potential to improve nitrogen levels. Seaweed aquaculture offers an opportunity to mitigate, and adapt to climate change. Seaweed, such as kelp, also absorbs phosphorus and nitrogen and is thus useful to remove excessive nutrients from polluted parts of the sea. Some cultivated seaweeds have very high productivity and could absorb large quantities of N, P, , producing large amounts of having an excellent effect on decreasing eutrophication. It is believed that seaweed cultivation in large scale should be a good solution to the eutrophication problem in coastal waters. | 2 | Environmental Chemistry |
As a successor to the HSEES program, ATSDR launched the National Toxic Substance Incidents Program (NTSIP) in 2009. One aspect of NTSIP is a national database of information related to chemical spills. NTSIP also has Assessment of Chemical Exposure teams to assist state and local health departments in the aftermath of toxic spills. These teams interview people who were exposed to the hazardous substances and collect samples to test the level of contamination in the environment and in people. | 1 | Biochemistry |
An osmometer is a device for measuring the osmotic strength of a solution, colloid, or compound.
There are several different techniques employed in osmometry:
* Freezing point depression osmometers may also be used to determine the osmotic strength of a solution, as osmotically active compounds depress the freezing point of a solution. This is the most common method in clinical laboratories because it is the most accurate and simple method.
* Vapor pressure osmometers determine the concentration of osmotically active particles that reduce the vapor pressure of a solution.
* Membrane osmometers measure the osmotic pressure of a solution separated from pure solvent by a semipermeable membrane.
Osmometers are useful for determining the total concentration of dissolved salts and sugars in blood or urine samples. Osmometry is also useful in determining the molecular weight of unknown compounds and polymers.
Osmometry is the measurement of the osmotic strength of a substance. This is often used by chemists for the determination of average molecular weight.
Osmometry is also useful for estimating the drought tolerance of plant leaves. | 7 | Physical Chemistry |
Abé (1996) explores the record of iron and steel firms in Victorian England by analyzing Bolckow Vaughan & Company. It was wedded for too long to obsolescent technology and was a very late adopter of the open hearth furnace method. Abé concludes that the firm—and the British steel industry—suffered from a failure of entrepreneurship and planning.
Blair (1997) explores the history of the British Steel industry since the Second World War to evaluate the impact of government intervention in a market economy. Entrepreneurship was lacking in the 1940s; the government could not persuade the industry to upgrade its plants. For generations the industry had followed a patchwork growth pattern which proved inefficient in the face of world competition. In 1946 the first steel development plan was put into practice with the aim of increasing capacity; the Iron and Steel Act 1949 meant nationalization of the industry in the form of the Iron and Steel Corporation of Great Britain. However, the reforms were dismantled by the Conservative Party governments in the 1950s. In 1967, under Labour Party control again, the industry was again nationalized. But by then twenty years of political manipulation had left companies such as the British Steel Corporation with serious problems: a complacency with existing equipment, plants operating under capacity (low efficiency), poor quality assets, outdated technology, government price controls, higher coal and oil costs, lack of funds for capital improvement, and increasing world market competition. By the 1970s the Labour government had its main goal to keep employment high in the declining industry. Since British Steel was a main employer in depressed regions, it had kept many mills and facilities that were operating at a loss. In the 1980s, Conservative Prime Minister Margaret Thatcher re-privatized BSC as British Steel plc. | 8 | Metallurgy |
Thioacetic acid is prepared by the reaction of acetic anhydride with hydrogen sulfide:
It has also been produced by the action of phosphorus pentasulfide on glacial acetic acid, followed by distillation.
Thioacetic acid is typically contaminated by acetic acid.
The compound exists exclusively as the thiol tautomer, consistent with the strength of the double bond. Reflecting the influence of hydrogen-bonding, the boiling point (93 °C) and melting points are 20 and 75 K lower than those for acetic acid. | 0 | Organic Chemistry |
Semidiones are radical anions analogous to semiquinones, obtained from the one-electron reduction of non-quinone conjugated dicarbonyls.
The simplest possible semidiones are derived from 1,2-dicarbonyls and have structure , making them the second member of a homologous series starting with ketyl radicals.
They are often transient intermediates, appearing in reactions such as the final reduction step of the acyloin condensation.
Benzil semidione (), synthesized by Auguste Laurent in 1836, is believed to have been the first radical ion ever characterized.
Semidehydroascorbate is a stable semidione produced by the one-electron oxidation of Vitamin C. | 0 | Organic Chemistry |
*ABCB10 NM_012089
*ABCB7 NM_004299
*ABCD3 NM_002857
*ABCE1 NM_002939
*ABCF1 NM_001090
*ABCF2 NM_005692
*ABCF3 NM_018358
*CALM1 Calmodulin grasps calcium ions
*MFSD11 NM_024311 similar to MSFD10 aka TETRAN or tetracycline transporter-like protein
*MFSD12 NM_174983
*MFSD3 NM_138431
*MFSD5 NM_032889
*SLC15A4 NM_145648
*SLC20A1 NM_005415
*SLC25A11 mitochondrial oxoglutarate/malate carrier
*SLC25A26 NM_173471
*SLC25A28 NM_031212
*SLC25A3 NM_002635
*SLC25A32 NM_030780
*SLC25A38 NM_017875
*SLC25A39 NM_016016
*SLC25A44 NM_014655
*SLC25A46 NM_138773
*SLC25A5 NM_001152
*SLC27A4 NM_005094
*SLC30A1 NM_021194
*SLC30A5 NM_022902
*SLC30A9 NM_006345
*SLC35A2 NM_005660
*SLC35A4 NM_080670
*SLC35B1 NM_005827
*SLC35B2 NM_178148
*SLC35C2 NM_015945
*SLC35E1 NM_024881
*SLC35E3 NM_018656
*SLC35F5 NM_025181
*SLC38A2 NM_018976
*SLC39A1 NM_014437
*SLC39A3 NM_144564
*SLC39A7 NM_006979
*SLC41A3 NM_017836
*SLC46A3 NM_181785
*SLC48A1 NM_017842 | 1 | Biochemistry |
# The effector of both the G and G pathways is the cyclic-adenosine monophosphate (cAMP)-generating enzyme adenylate cyclase, or AC. While there are ten different AC gene products in mammals, each with subtle differences in tissue distribution or function, all catalyze the conversion of cytosolic adenosine triphosphate (ATP) to cAMP, and all are directly stimulated by G-proteins of the G class. In contrast, however, interaction with Gα subunits of the G type inhibits AC from generating cAMP. Thus, a GPCR coupled to G counteracts the actions of a GPCR coupled to G, and vice versa. The level of cytosolic cAMP may then determine the activity of various ion channels as well as members of the ser/thr-specific protein kinase A (PKA) family. Thus cAMP is considered a second messenger and PKA a secondary effector.
# The effector of the G pathway is phospholipase C-β (PLCβ), which catalyzes the cleavage of membrane-bound phosphatidylinositol 4,5-bisphosphate (PIP2) into the second messengers inositol (1,4,5) trisphosphate (IP3) and diacylglycerol (DAG). IP3 acts on IP3 receptors found in the membrane of the endoplasmic reticulum (ER) to elicit Ca release from the ER, while DAG diffuses along the plasma membrane where it may activate any membrane localized forms of a second ser/thr kinase called protein kinase C (PKC). Since many isoforms of PKC are also activated by increases in intracellular Ca, both these pathways can also converge on each other to signal through the same secondary effector. Elevated intracellular Ca also binds and allosterically activates proteins called calmodulins, which in turn tosolic small GTPase, Rho. Once bound to GTP, Rho can then go on to activate various proteins responsible for cytoskeleton regulation such as Rho-kinase (ROCK). Most GPCRs that couple to G also couple to other sub-classes, often G. | 1 | Biochemistry |
Naphthenic hydrocarbons are saturated cyclic hydrocarbons, and are very important in the refining of liquid crude oil.
Also known as cyclic alkanes, they are represented by the formula CH, where n is a positive integer. | 9 | Geochemistry |
Salting out (also known as salt-induced precipitation, salt fractionation, anti-solvent crystallization, precipitation crystallization, or drowning out) is a purification technique that utilizes the reduced solubility of certain molecules in a solution of very high ionic strength. Salting out is typically used to precipitate large biomolecules, such as proteins or DNA. Because the salt concentration needed for a given protein to precipitate out of the solution differs from protein to protein, a specific salt concentration can be used to precipitate a target protein. This process is also used to concentrate dilute solutions of proteins. Dialysis can be used to remove the salt if needed. | 3 | Analytical Chemistry |
The prediction of crystal properties by numerical simulation has become commonplace in the last 20 years as computers have grown more powerful and theoretical techniques more sophisticated. High accuracy prediction of elastic, electronic, transport and phase properties is possible with modern methods. | 3 | Analytical Chemistry |
The grid complexes exhibit pH-dependent changes in the optical absorption, electronic spin states and reversible redox states. The latticial metal complexes may thus be used theoretically for information storage and processing in the future. | 6 | Supramolecular Chemistry |
In 1993 the silicon carbide was considered a semiconductor in both research and early mass production providing advantages for fast, high-temperature and/or high-voltage devices. The first devices available were Schottky diodes, followed by junction-gate FETs and MOSFETs for high-power switching. Bipolar transistors and thyristors were described.
A major problem for SiC commercialization has been the elimination of defects: edge dislocations, screw dislocations (both hollow and closed core), triangular defects and basal plane dislocations. As a result, devices made of SiC crystals initially displayed poor reverse blocking performance, though researchers have been tentatively finding solutions to improve the breakdown performance.
Apart from crystal quality, problems with the interface of SiC with silicon dioxide have hampered the development of SiC-based power MOSFETs and insulated-gate bipolar transistors. Although the mechanism is still unclear, nitriding has dramatically reduced the defects causing the interface problems.
In 2008, the first commercial JFETs rated at 1200 V were introduced to the market, followed in 2011 by the first commercial MOSFETs rated at 1200 V. JFETs are now available rated 650 V to 1700 V with resistance as low as 25 mΩ. Beside SiC switches and SiC Schottky diodes (also Schottky barrier diode, SBD) in the popular TO-247 and TO-220 packages, companies started even earlier to implement the bare chips into their power electronic modules.
SiC SBD diodes found wide market spread being used in PFC circuits and IGBT power modules.
Conferences such as the International Conference on Integrated Power Electronics Systems (CIPS) report regularly about the technological progress of SiC power devices.
Major challenges for fully unleashing the capabilities of SiC power devices are:
* Gate drive: SiC devices often require gate drive voltage levels that are different from their silicon counterparts and may be even unsymmetric, for example, +20 V and −5 V.
* Packaging: SiC chips may have a higher power density than silicon power devices and are able to handle higher temperatures exceeding the silicon limit of 150 °C. New die attach technologies such as sintering are required to efficiently get the heat out of the devices and ensure a reliable interconnection.
Beginning with Tesla Model 3 the inverters in the drive unit use 24 pairs of silicon carbide (SiC) MOSFET chips rated for 650 volts each. Silicon carbide in this instance gave Tesla a significant advantage over chips made of silicon in terms of size and weight. A number of automobile manufacturers are planning to incorporate silicon carbide into power electronic devices in their products. A significant increase in production of silicon carbide is projected, beginning with a large plant opened 2022 by Wolfspeed in upstate New York. | 8 | Metallurgy |
Plasmids are often used to purify a specific sequence, since they can easily be purified away from the rest of the genome. For their use as vectors, and for molecular cloning, plasmids often need to be isolated.
There are several methods to isolate plasmid DNA from bacteria, ranging from the miniprep to the maxiprep or bulkprep. The former can be used to quickly find out whether the plasmid is correct in any of several bacterial clones. The yield is a small amount of impure plasmid DNA, which is sufficient for analysis by restriction digest and for some cloning techniques.
In the latter, much larger volumes of bacterial suspension are grown from which a maxi-prep can be performed. In essence, this is a scaled-up miniprep followed by additional purification. This results in relatively large amounts (several hundred micrograms) of very pure plasmid DNA.
Many commercial kits have been created to perform plasmid extraction at various scales, purity, and levels of automation. | 1 | Biochemistry |
A racemate is optically inactive (achiral), meaning that such materials do not rotate the polarization of plane-polarized light. Although the two enantiomers rotate plane-polarized light in opposite directions, the rotations cancel each other out because they are present in equal amounts of negative (-) counterclockwise (levorotatory) and positive (+) clockwise (dextrorotatory) enantiomers.
In contrast to the two pure enantiomers, which have identical physical properties except for the direction of rotation of plane-polarized light, a racemate sometimes has different properties from either of the pure enantiomers. Different melting points are most common, but different solubilities and boiling points are also possible.
Pharmaceuticals may be available as a racemate or as the pure enantiomer, which might have different potencies. Because biological systems have many chiral asymmetries, pure enantiomers frequently have very different biological effects; examples include glucose and methamphetamine. | 4 | Stereochemistry |
Filling a clean bottle with river water is a very simple task, but a single sample is only representative of that point along the river the sample was taken from and at that point in time. Understanding the chemistry of a whole river, or even a significant tributary, requires prior investigation to understand how homogeneous or mixed the flow is and to determine if the quality changes during the course of a day and during the course of a year. Almost all natural rivers will have very significant patterns of change through the day and through the seasons. Water remote sensing offers a spatially continuous tool to improve understanding of spatial and temporal river water quality. Many rivers also have a very large flow that is unseen. This flows through underlying gravel and sand layers and is called hyporheic flow. How much mixing there is between the hyporheic zone and the water in the open channel will depend on a variety of factors, some of which relate to flows leaving aquifers which may have been storing water for many years. | 2 | Environmental Chemistry |
A quasiperiodic crystal, or quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. While crystals, according to the classical crystallographic restriction theorem, can possess only two-, three-, four-, and six-fold rotational symmetries, the Bragg diffraction pattern of quasicrystals shows sharp peaks with other symmetry orders—for instance, five-fold.
Aperiodic tilings were discovered by mathematicians in the early 1960s, and, some twenty years later, they were found to apply to the study of natural quasicrystals. The discovery of these aperiodic forms in nature has produced a paradigm shift in the field of crystallography. In crystallography the quasicrystals were predicted in 1981 by a five-fold symmetry study of Alan Lindsay Mackay,—that also brought in 1982, with the crystallographic Fourier transform of a Penrose tiling, the possibility of identifying quasiperiodic order in a material through diffraction.
Quasicrystals had been investigated and observed earlier, but, until the 1980s, they were disregarded in favor of the prevailing views about the atomic structure of matter. In 2009, after a dedicated search, a mineralogical finding, icosahedrite, offered evidence for the existence of natural quasicrystals.
Roughly, an ordering is non-periodic if it lacks translational symmetry, which means that a shifted copy will never match exactly with its original. The more precise mathematical definition is that there is never translational symmetry in more than n – 1 linearly independent directions, where n is the dimension of the space filled, e.g., the three-dimensional tiling displayed in a quasicrystal may have translational symmetry in two directions. Symmetrical diffraction patterns result from the existence of an indefinitely large number of elements with a regular spacing, a property loosely described as long-range order. Experimentally, the aperiodicity is revealed in the unusual symmetry of the diffraction pattern, that is, symmetry of orders other than two, three, four, or six. In 1982, materials scientist Dan Shechtman observed that certain aluminium–manganese alloys produced the unusual diffractograms which today are seen as revelatory of quasicrystal structures. Due to fear of the scientific community's reaction, it took him two years to publish the results for which he was awarded the Nobel Prize in Chemistry in 2011.
On 25 October 2018, Luca Bindi and Paul Steinhardt were awarded the Aspen Institute 2018 Prize for collaboration and scientific research between Italy and the United States, after they discovered icosahedrite, the first quasicrystal known to occur naturally. | 3 | Analytical Chemistry |
Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of crystal structure beneath the surface. This will generally leave some material stuck or even friction welded to the adjacent surface, whereas the galled material may appear gouged with balled-up or torn lumps of material stuck to its surface.
Galling is most commonly found in metal surfaces that are in sliding contact with each other. It is especially common where there is inadequate lubrication between the surfaces. However, certain metals will generally be more prone to galling, due to the atomic structure of their crystals. For example, aluminium is a metal that will gall very easily, whereas annealed (softened) steel is slightly more resistant to galling. Steel that is fully hardened is very resistant to galling.
Galling is a common problem in most applications where metals slide in contact with other metals. This can happen regardless of whether the metals are the same or different. Alloys such as brass and bronze are often chosen for bearings, bushings, and other sliding applications because of their resistance to galling, as well as other forms of mechanical abrasion. | 7 | Physical Chemistry |
Soft chemistry (also known as chimie douce) is a type of chemistry that uses reactions at ambient temperature in open reaction vessels with reactions similar to those occurring in biological systems. | 1 | Biochemistry |
Each radioligand therapy requires significant patient testing and eligibility requirements before administration. Radioligand therapies for cancer treatment are not the first course of action and generally require the patient to have undergone other previous treatments and many diagnostic imagings (i.e. seeing if specific receptors/antigens exist) to determine the benefit vs. adverse effect of undergoing the radioligand therapy.
For example, the PSMA radioligand therapy (Pluvicto) requires the patient to have end-stage prostate cancer that has metastasized in other organs, the PSMA ligand (confirmed through diagnostic imaging), and gone through hormonal therapies and chemotherapies. For patient eligibility to get Lutathera radioligand therapy the patient must have disease progression despite receiving somatostatin analog therapy (octreotide or lanreotide), have a locally advanced, inoperable, or metastatic well-differentiated disease, and have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2. | 1 | Biochemistry |
The upper limit for efficiency in TPVs (and all systems that convert heat energy to work) is the Carnot efficiency, that of an ideal heat engine. This efficiency is given by:
where T is the temperature of the PV converter. Practical systems can achieve T= ~300 K and T= ~1800 K, giving a maximum possible efficiency of ~83%. This assumes the PV converts the radiation into electrical energy without losses, such as thermalization or Joule heating, though in reality the photovoltaic inefficiency is quite significant. In real devices, as of 2021, the maximum demonstrated efficiency in the laboratory was 35% with an emitter temperature of 1,773 K. This is the efficiency in terms of heat input being converted to electrical power. In complete TPV systems, a necessarily lower total system efficiency may be cited including the source of heat, so for example, fuel-based TPV systems may report efficiencies in terms of fuel-energy to electrical energy, in which case 5% is considered a "world record" level of efficiency. Real-world efficiencies are reduced by such effects as heat transfer losses, electrical conversion efficiency (TPV voltage outputs are often quite low), and losses due to active cooling of the PV cell. | 7 | Physical Chemistry |
The basic setup in electrosynthesis is a galvanic cell, a potentiostat and two electrodes. Typical solvent and electrolyte combinations minimizes electrical resistance. Protic conditions often use alcohol-water or dioxane-water solvent mixtures with an electrolyte such as a soluble salt, acid or base. Aprotic conditions often use an organic solvent such as acetonitrile or dichloromethane with electrolytes such as lithium perchlorate or tetrabutylammonium salts. The choice of electrodes with respect to their composition and surface area can be decisive. For example, in aqueous conditions the competing reactions in the cell are the formation of oxygen at the anode and hydrogen at the cathode. In this case a graphite anode and lead cathode could be used effectively because of their high overpotentials for oxygen and hydrogen formation respectively. Many other materials can be used as electrodes. Other examples include platinum, magnesium, mercury (as a liquid pool in the reactor), stainless steel or reticulated vitreous carbon. Some reactions use a sacrificial electrode that is consumed during the reaction like zinc or lead. Cell designs can be undivided cell or divided cell type. In divided cells the cathode and anode chambers are separated with a semiporous membrane. Common membrane materials include sintered glass, porous porcelain, polytetrafluoroethene or polypropylene. The purpose of the divided cell is to permit the diffusion of ions while restricting the flow of the products and reactants. This separation simplifies workup. An example of a reaction requiring a divided cell is the reduction of nitrobenzene to phenylhydroxylamine, where the latter chemical is susceptible to oxidation at the anode. | 7 | Physical Chemistry |
Further alloys with low melting points are at , at and at . The alloy consisting of 40.8 % caesium, 11.8 % sodium and 47.4 % potassium has a melting point of . | 8 | Metallurgy |
Infection does not kill the host bacteria, in contrast to most other families of phage. Progeny phage are assembled as they extrude through the membrane of growing bacteria, probably at adhesion sites joining inner and outer membranes. The five phage proteins that form the coat of the completed phage enter the inner membrane; for p8 and p3, N-terminal leader sequences (later removed) help the proteins to enter the bacterial membrane, with their N-termini directed away from the cytoplasm towards the periplasm. Three other phage membrane proteins that are not present in the phage, p1, p11, and p4, are also involved in assembly. Replication of RF DNA is converted to production of phage ssDNA by coating of the DNA with p5 to form an elongated p5/DNA replication/assembly complex, which then interacts with the membrane-bound phage proteins. The extrusion process picks up the p7 and p9 proteins which form the outer tip of the progeny phage. As the p5 is stripped off the DNA, the progeny DNA is extruded across the membrane and wrapped in a helical casing of p8, to which p3 and p6 are added at the end of assembly. The p4 protein may form an extrusion pore in the outer membrane.
Interaction of the double-stranded packaging DNA signal with the p1-thioredoxin complex at the host inner membrane triggers the formation of a pore. The p1 protein contains Walker motifs which are essential for phage assembly, suggesting that p1 is a molecular motor involved in phage assembly. The p1 protein has a membrane-spanning hydrophobic domain with the N-terminal portion in the cytoplasm and the C-terminal portion in the periplasm (the reverse of the orientation of p8). Adjacent to the cytoplasmic side of the membrane-spanning domain is a 13- residue sequence of p1 having a pattern of basic residues closely matching the pattern of basic residues near the C terminus of p8, but inverted with respect to that sequence.
Intermediate assemblies of p8 can be generated by treating the phage with chloroform. The helical content of p8 in these intermediate forms is similar to that in the phage, suggesting that the structural change during assembly may involve just a sliding of the shingled p8 subunits with respect to their neighbours in the assembly. | 1 | Biochemistry |
One of the problems of both the glutamate–glutamine cycle and the GABA-glutamine cycle is ammonia homeostasis. When one molecule of glutamate or GABA is converted to glutamine in the astrocytes, one molecule of ammonia is absorbed. Also, for each molecule of glutamate or GABA cycled into the astrocytes from the synapse, one molecule of ammonia will be produced in the neurons. This ammonia will obviously have to be transported out of the neurons and back into the astrocytes for detoxification, as an elevated ammonia concentration has detrimental effects on a number of cellular functions and can cause a spectrum of neuropsychiatric and neurological symptoms (impaired memory, shortened attention span, sleep-wake inversions, brain edema, intracranial hypertension, seizures, ataxia and coma). | 1 | Biochemistry |
Arsenic removal technologies are traditional treatment processes which have been tailored to improve removal of arsenic from drinking water. Although some of the removal processes, such as precipitative processes, adsorption processes, ion exchange processes, and separation (membrane) processes, may be technically feasible, their cost may be prohibitive.
For underdeveloped countries, the challenge is finding the means to fund such technologies. The Environmental Protection Agency, for example, has estimated the total national annualized cost of treatment, monitoring, reporting, record keeping, and administration to enforce the MCL rule to be approximately $181 million. Most of the cost is due to the installation and operation of the treatment technologies needed to reduce arsenic in public water systems. | 1 | Biochemistry |
The state of an amount of gas is determined by its pressure, volume, and temperature. The modern form of the equation relates these simply in two main forms. The temperature used in the equation of state is an absolute temperature: the appropriate SI unit is the kelvin. | 7 | Physical Chemistry |
Fulgurites are formed when lightning strikes the ground, fusing and vitrifying mineral grains. The primary SiO phase in common tube fulgurites is lechatelierite, an amorphous silica glass. Many fulgurites show some evidence of crystallization: in addition to glasses, many are partially protocrystalline or microcrystalline. Because fulgurites are generally amorphous in structure, fulgurites are classified as mineraloids.
Material properties (size, color, texture) of fulgurites vary widely, depending on the size of the lightning bolt and composition and moisture content of the surface struck by lightning. Most natural fulgurites fall on a spectrum from white to black. Iron is a common impurity that can result in a deep brownish-green coloration. Lechatelierite similar to fulgurites can also be produced via controlled (or uncontrolled) arcing of artificial electricity into a medium. Downed high voltage power lines have produced brightly colored lechatelierites, due to the incorporation of copper or other materials from the power lines themselves. Brightly colored lechatelierites resembling fulgurites are usually synthetic and reflect the incorporation of synthetic materials. However, lightning can strike man-made objects, resulting in colored fulgurites.
The interior of Type I (sand) fulgurites normally is smooth or lined with fine bubbles, while their exteriors are coated with rough sedimentary particles or small rocks. Other types of fulgurites are usually vesicular, and may lack an open central tube; their exteriors can be porous or smooth. Branching fulgurites display fractal-like self-similarity and structural scale invariance as a macroscopic or microscopic network of root-like branches, and can display this texture without central channels or obvious divergence from morphology of context or target (e.g. sheet-like melt, rock fulgurites). Fulgurites are usually fragile, making the field collection of large specimens difficult.
Fulgurites can exceed 20 centimeters in diameter and can penetrate deep into the subsoil, sometimes occurring as far as below the surface that was struck, although they may also form directly on a sedimentary surface. One of the longest fulgurites to have been found in modern times was a little over in length, and was found in northern Florida. The Yale University Peabody Museum of Natural History displays one of the longest known preserved fulgurites, approximately in length. Charles Darwin in The Voyage of the Beagle recorded that tubes such as these found in Drigg, Cumberland, UK reached a length of . The Winans Lake fulgurite[s] (Winans Lake, Livingston County, Michigan), extended discontinuously throughout a 30 m range, and arguably includes the largest reported fulgurite mass ever recovered and described: its largest section extending approximately 16 ft (4.88 m) in length by 1 ft in diameter (30 cm).
Peak temperatures within a lightning channel exceed 30,000 K, with sufficient pressure to produce planar deformation features in SiO, a kind of polymorphism. This is also known colloquially as shocked quartz. | 9 | Geochemistry |
Restriction enzymes are used to excise the gene of interest (the insert) from the parent. The insert is purified in order to isolate it from other DNA molecules. A common purification method is gel isolation. The number of copies of the gene is then amplified using polymerase chain reaction (PCR).
Simultaneously, the same restriction enzymes are used to digest (cut) the destination. The idea behind using the same restriction enzymes is to create complementary sticky ends, which will facilitate ligation later on. A phosphatase, commonly calf-intestinal alkaline phosphatase (CIAP), is also added to prevent self-ligation of the destination vector. The digested destination vector is isolated/purified.
The insert and the destination vector are then mixed together with DNA ligase. A typical molar ratio of insert genes to destination vectors is 3:1; by increasing the insert concentration, self-ligation is further decreased. After letting the reaction mixture sit for a set amount of time at a specific temperature (dependent upon the size of the strands being ligated; for more information see DNA ligase), the insert should become successfully incorporated into the destination plasmid. | 1 | Biochemistry |
The COLUMBUS PROGRAMS were started in 1980 in the Department of Chemistry of Ohio State University by Isaiah Shavitt, Hans Lischka and Ron Shepard. The programs pioneered the Graphical Unitary Group Approach (GUGA) for configuration interaction calculations, which is now available in many other program suites. The programs are named after Columbus, OH. | 7 | Physical Chemistry |
In general, patches consist of three separate layers that contribute and control the release of medicine. The outer impermeable backing layer controls the direction of release and reduces drug loss away from the site of contact. It also protects the other layers and acts as a mechanical support. The middle reservoir layer holds the drug and is tailored to provide the specified dosage. The final inner layer consists of the mucoadhesive, allowing the patch to adhere to the specified mucosa. | 1 | Biochemistry |
Lanthanide organometallic complexes have been synthesized by RT and RTLE. Lanthanides are very electropositive elements.
Organomercurials, such as HgPh, are common kinetically inert RT and RTLE reagents that allow functionalized
derivatives to be synthesized, unlike organolithiums and Grignard reagents. Diarylmercurials are often used to synthesize lanthanide organometallic complexes. Hg(CF) is a better RT reagent to use with lanthanides than HgPh because it does not require a step to activate the metal. However, phenyl-substituted lanthanide complexes are more thermally stable than the pentafluorophenyl complexes. The use of HgPh led to the synthesis of a ytterbium complex with different oxidation states on the two Yb atoms:
:Yb(CH)(THF) + HgPh → YbYbPh(THF)
In the Ln(CF) complexes, where Ln = Yb, Eu, or Sm, the Ln–C bonds are very reactive, making them useful in RTLE reactions. Protic substrates have been used as a reactant with the Ln(CF) complex as shown: Ln(CF) + 2LH → Ln(L) + 2CFH. It is possible to avoid the challenges of working with the unstable Ln(CF) complex by forming it in situ by the following reaction:
:Ln + HgR + 2 LH → Ln(L) + Hg + 2 RH
Organotins are also kinetically inert RT and RTLE reagents that have been used in a variety of organometallic reactions. They have applications to the synthesis of lanthanide complexes, such as in the following reaction:
:Yb + Sn(N(SiMe)) → Yb(N(SiMe)) + Sn | 0 | Organic Chemistry |
Cellular noise is random variability in quantities arising in cellular biology. For example, cells which are genetically identical, even within the same tissue, are often observed to have different expression levels of proteins, different sizes and structures. These apparently random differences can have important biological and medical consequences.
Cellular noise was originally, and is still often, examined in the context of gene expression levels – either the concentration or copy number of the products of genes within and between cells. As gene expression levels are responsible for many fundamental properties in cellular biology, including cells' physical appearance, behaviour in response to stimuli, and ability to process information and control internal processes, the presence of noise in gene expression has profound implications for many processes in cellular biology. | 1 | Biochemistry |
In crystallography and solid state physics, the Laue equations relate incoming waves to outgoing waves in the process of elastic scattering, where the photon energy or light temporal frequency does not change upon scattering by a crystal lattice. They are named after physicist Max von Laue (1879–1960).
The Laue equations can be written as as the condition of elastic wave scattering by a crystal lattice, where is the scattering vector, , are incoming and outgoing wave vectors (to the crystal and from the crystal, by scattering), and is a crystal reciprocal lattice vector. Due to elastic scattering , three vectors. , , and , form a rhombus if the equation is satisfied. If the scattering satisfies this equation, all the crystal lattice points scatter the incoming wave toward the scattering direction (the direction along ). If the equation is not satisfied, then for any scattering direction, only some lattice points scatter the incoming wave. (This physical interpretation of the equation is based on the assumption that scattering at a lattice point is made in a way that the scattering wave and the incoming wave have the same phase at the point.) It also can be seen as the conservation of momentum as since is the wave vector for a plane wave associated with parallel crystal lattice planes. (Wavefronts of the plane wave are coincident with these lattice planes.)
The equations are equivalent to Braggs law; the Laue equations are vector equations while Braggs law is in a form that is easier to solve, but these tell the same content. | 3 | Analytical Chemistry |
The Eastern Analytical Symposium and Exposition is sponsored by the following organizations: the Analytical Division of the American Chemical Society, the American Chemical Society New York and New Jersey Sections, the American Microchemical Society, the Chromatography Forum of Delaware Valley, the Coblentz Society, the New York Microscopical Society, the Society for Applied Spectroscopy's Delaware Valley, New York, and New England Sections, the Association of Laboratory Managers (ALMA), and the New Jersey Association of Forensic Scientists. | 7 | Physical Chemistry |
* Chester (closed 24 August 1962)
* Dublin (1801-1922 part of UK system – see Dublin Assay Office)
* Exeter (closed 1883)
* Glasgow (closed 31 March 1964)
* Newcastle (closed 1884)
* Norwich (closed 1702)
* York (closed 1857) | 3 | Analytical Chemistry |
It is important to distinguish molecularity from order of reaction. The order of reaction is an empirical quantity determined by experiment from the rate law of the reaction. It is the sum of the exponents in the rate law equation. Molecularity, on the other hand, is deduced from the mechanism of an elementary reaction, and is used only in context of an elementary reaction. It is the number of molecules taking part in this reaction.
This difference can be illustrated on the reaction between nitric oxide and hydrogen:
where the observed rate law is , so that the reaction is third order. Since the order does not equal the sum of reactant stoichiometric coefficients, the reaction must involve more than one step. The proposed two-step mechanism has a rate-limiting first step whose molecularity corresponds to the overall order of 3:
Slow:
Fast:
On the other hand, the molecularity of this reaction is undefined, because it involves a mechanism of more than one step. However, we can consider the molecularity of the individual elementary reactions that make up this mechanism: the first step is trimolecular because it involves three reactant molecules, while the second step is bimolecular because it involves two reactant molecules. | 7 | Physical Chemistry |
A non-Kekulé molecule is a conjugated hydrocarbon that cannot be assigned a classical Kekulé structure.
Since non-Kekulé molecules have two or more formal charges or
radical centers, their spin-spin interactions can cause electrical conductivity or ferromagnetism (molecule-based magnets), and applications to functional materials are expected. However, as these molecules are quite reactive and most of them are easily decomposed or polymerized at room temperature, strategies for stabilization are needed for their practical use. Synthesis and observation of these reactive molecules are generally accomplished by matrix-isolation methods. | 0 | Organic Chemistry |
The kinetic process of destabilisation can be rather long (up to several months or years for some products). Thus, it is often required for the formulator to use further accelerating methods to reach reasonable development time for new product design. Thermal methods are the most commonly used and consist of increasing temperature to accelerate destabilisation (below critical temperatures of phase inversion or chemical degradation). Temperature affects not only viscosity, but also interfacial tension in the case of non-ionic surfactants or more generally interactions forces inside the system. Storing a dispersion at high temperatures enables to simulate real life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times.
Mechanical acceleration including vibration, centrifugation and agitation are sometimes used. They subject the product to different forces that pushes the particles / droplets against one another, hence helping in the film drainage. Some emulsions would never coalesce in normal gravity, while they do under artificial gravity. Segregation of different populations of particles have been highlighted when using centrifugation and vibration. | 7 | Physical Chemistry |
The mole fraction is defined as the amount of a constituent (in moles) divided by the total amount of all constituents in a mixture :
The SI unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole fractions. | 3 | Analytical Chemistry |
Examples of enzymes capable of arene dearomatization are toluene dixoyhydrogenase, naphthalene dixoyhydrogenase and benzoyl CoA reductase. | 0 | Organic Chemistry |
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