text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Neurons from several brain regions, such as the neocortex, substantia nigra, and hippocampus have been found to contain autapses.
Autapses have been observed to be relatively more abundant in GABAergic basket and dendrite-targeting cells of the cat visual cortex compared to spiny stellate, double bouquet, and pyramidal cells, suggesting that the degree of neuron self-innervation is cell-specific. Additionally, dendrite-targeting cell autapses were, on average, further from the soma compared to basket cell autapses.
80% of layer V pyramidal neurons in developing rat neocortices contained autaptic connections, which were located more so on basal dendrites and apical oblique dendrites rather than main apical dendrites. The dendritic positions of synaptic connections of the same cell type were similar to those of autapses, suggesting that autaptic and synaptic networks share a common mechanism of formation. | 1 | Biochemistry |
Kinetic isotope effect (KIE) is a measurement of the reaction rate of isotope-labeled reactants against the more common natural substrate. Kinetic isotope effect values are a ratio of the turnover number and include all steps of the reaction. Intrinsic kinetic isotope values stem from the difference in the bond vibrational environment of an atom in the reactants at ground state to the environment of the atom's transition state. Through the kinetic isotope effect much insight can be gained as to what the transition state looks like of an enzyme-catalyzed reaction and guide the development of transition state analogs. | 1 | Biochemistry |
A generic reaction under Curtin–Hammett can be described by the following parameters:
In order for rapid equilibration to be a good assumption, the rate of conversion from the less stable of A or B to the product C or D must be at least 10 times slower than the rate of equilibration between A and B.
The rate of formation for compound C from A is given as
and that of D from B as
with the second approximate equality following from the assumption of rapid equilibration. Under this assumption, the ratio of the products is then
In other words, because equilibration is fast compared to product formation, throughout the reaction. As a result, also remains roughly constant throughout the reaction. In turn, integration with respect to time implies that likewise takes on an approximately constant value through the course of the reaction, namely .
In terms of the ground state and transition state energies, the product ratio can therefore be written as:
Importantly, inspection of the energy diagram above allows us to identify
with the energy difference of the transition states, giving us a simplified equation that captures the essence of the Curtin-Hammett principle:
Thus, although the product ratio depends on the equilibrium constant between A and B and the difference in energy between the barriers from A to C and from B to D, both of these factors are automatically taken into account by the energy difference of the transition states leading to the products, ΔΔG. | 7 | Physical Chemistry |
Perovskites can be deposited as epitaxial thin films on top of other perovskites, using techniques such as pulsed laser deposition and molecular-beam epitaxy. These films can be a couple of nanometres thick or as small as a single unit cell. The well-defined and unique structures at the interfaces between the film and substrate can be used for interface engineering, where new types properties can arise. This can happen through several mechanisms, from mismatch strain between the substrate and film, change in the oxygen octahedral rotation, compositional changes, and quantum confinement. An example of this is LaAlO grown on SrTiO, where the interface can exhibit conductivity, even though both LaAlO and SrTiO are non-conductive. Another example is SrTiO grown on LSAT ((LaAlO) (SrAlTaO)) or DyScO can morph the incipient ferroelectric into a ferroelectric at room temperature through the means of epitaxially applied biaxial strain. The lattice mismatch of GdScO to SrTiO (+1.0%) applies tensile stress resulting in a decrease of the out-of-plane lattice constant of SrTiO, compared to LSAT (−0.9 %), which epitaxially applies compressive stress leading to an extension of the out-of-plane lattice constant of SrTiO (and subsequent increase of the in-plane lattice constant). | 3 | Analytical Chemistry |
Surround optical-fiber immunoassay (SOFIA) is an ultrasensitive, in vitro diagnostic platform incorporating a surround optical-fiber assembly that captures fluorescence emissions from an entire sample. The technologys defining characteristics are its extremely high limit of detection, sensitivity, and dynamic range. SOFIAs sensitivity is measured at the attogram level (10 g), making it about one billion times more sensitive than conventional diagnostic techniques. Based on its enhanced dynamic range, SOFIA is able to discriminate levels of analyte in a sample over 10 orders of magnitude, facilitating accurate titering.
As a diagnostic platform, SOFIA has a broad range of applications. Several studies have already demonstrated SOFIAs unprecedented ability to detect naturally occurring prions in the blood and urine of disease carriers. This is expected to lead to the first reliable ante mortem screening test for vCJD, BSE, scrapie, CWD, and other transmissible spongiform encephalopathies. Given the technologys extreme sensitivity, additional unique applications are anticipated, including in vitro tests for other neurodegenerative diseases, such as Alzheimers and Parkinsons disease.
SOFIA was developed as a result of a joint-collaborative research project between Los Alamos National Laboratory and State University of New York, and was supported by the Department of Defense's National Prion Research Program. | 1 | Biochemistry |
Phosphaalkynes possess diverse reactivity profiles, and can be utilized in the synthesis of various phosphorus-containing saturated of unsaturated heterocyclic compounds. | 0 | Organic Chemistry |
Counterfeit THC oil has been detected to contain synthetic cannabinoids. Several school kids in Greater Manchester collapsed after vaping Spice mis-sold as natural cannabis. | 7 | Physical Chemistry |
Variant genetic codes used by an organism can be inferred by identifying highly conserved genes encoded in that genome, and comparing its codon usage to the amino acids in homologous proteins of other organisms. For example, the program FACIL infers a genetic code by searching which amino acids in homologous protein domains are most often aligned to every codon. The resulting amino acid (or stop codon) probabilities for each codon are displayed in a genetic code logo.
As of January 2022, the most complete survey of genetic codes is done by Shulgina and Eddy, who screened 250,000 prokaryotic genomes using their Codetta tool. This tool uses a similar approach to FACIL with a larger Pfam database. Despite the NCBI already providing 27 translation tables, the authors were able to find new 5 genetic code variations (corroborated by tRNA mutations) and correct several misattributions. Codetta was later used to analyze genetic code change in ciliates. | 1 | Biochemistry |
Glycogen branching enzyme belongs to the α-amylase family of enzymes, which include α-amylases, pullulanas/isoamylase, cyclodextrin glucanotransferase (CGT), and branching enzyme. Shown by x-ray crystallography, glycogen branching enzyme has four marginally asymmetric units each that are organized into three domains: an amino-terminal domain, involved in determining the length of the chain transfer, a carboxyl-terminal domain, involved in substrate preference and catalytic capacity, and a central (α/β) barrel catalytic domain. The amino-terminal domain consists of 128 residues arranged in seven β-strands, the carboxyl-terminal domain with 116 residues also organized in seven β-strands, and the (α/β) barrel domain with 372 residues. While the central (α/β) barrel domain is common in members of the α-amylase family, numerous variations exist between the various barrel domains. Additionally, there are striking differences between the loops connecting elements of the secondary structure among these various α-amylase members, especially around the active site. In comparison to the other family members, glycogen binding enzyme has shorter loops, which result in a more open cavity, favorable to the binding of a bulkier substrate such as branched sugar. Through primary structure analysis and the x-ray crystallographic structures of the members of the α-amylase family, seven residue were conserved, Asp335, His340, Arg403, Asp 405, Glu458, His525, and Asp526 (E coli. numbering). These residues are implicated in catalysis and substrate binding.
Glycogen binding enzymes in other organisms have also been crystallized and structurally determined, demonstrating both similarity and variation to GBE found in Escherichia coli. | 1 | Biochemistry |
The rigid rotor is a good starting point from which to construct a model of a rotating molecule. It is assumed that component atoms are point masses connected by rigid bonds. A linear molecule lies on a single axis and each atom moves on the surface of a sphere around the centre of mass. The two degrees of rotational freedom correspond to the spherical coordinates θ and φ which describe the direction of the molecular axis, and the quantum state is determined by two quantum numbers J and M. J defines the magnitude of the rotational angular momentum, and M its component about an axis fixed in space, such as an external electric or magnetic field. In the absence of external fields, the energy depends only on J. Under the rigid rotor model, the rotational energy levels, F(J), of the molecule can be expressed as,
where is the rotational constant of the molecule and is related to the moment of inertia of the molecule. In a linear molecule the moment of inertia about an axis perpendicular to the molecular axis is unique, that is, , so
For a diatomic molecule
where m and m are the masses of the atoms and d is the distance between them.
Selection rules dictate that during emission or absorption the rotational quantum number has to change by unity; i.e., . Thus, the locations of the lines in a rotational spectrum will be given by
where denotes the lower level and denotes the upper level involved in the transition.
The diagram illustrates rotational transitions that obey the =1 selection rule. The dashed lines show how these transitions map onto features that can be observed experimentally. Adjacent transitions are separated by 2B in the observed spectrum. Frequency or wavenumber units can also be used for the x axis of this plot. | 7 | Physical Chemistry |
The method has been used in life sciences, material sciences and biosensor development.
In life sciences, the main applications focus on pharmaceutical development including small-molecule, antibody or nanoparticle interactions with target with a biomembrane or with a living cell monolayer. As first in the world, MP-SPR is able to separate transcellular and paracellular drug uptake in real-time and label-free for targeted drug delivery.
In biosensor development, MP-SPR is used for assay development for point-of-care applications. Typical developed biosensors include electrochemical printed biosensors, ELISA and SERS.
In material sciences, MP-SPR is used for optimization of thin solid films from Ångströms to 100 nanometers (graphene, metals, oxides), soft materials up to microns (nanocellulose, polyelectrolyte) including nanoparticles. Applications including thin film solar cells, barrier coatings including anti-reflective coatings, antimicrobial surfaces, self-cleaning glass, plasmonic metamaterials, electro-switching surfaces, layer-by-layer assembly, and graphene. | 7 | Physical Chemistry |
The range and degree of human health effects seems to vary annually and temporally in coastal regions, depending on the red tide density as well as variation in toxicity differences among dinoflagellate strains and their subsequent consumers. The Gulf of Mexico, and in particular the west coast of Florida, is the most heavily impacted by the adverse health and environmental effects of nearly annual K. brevis blooms. This region has suffered significant economic losses in local communities that rely on tourism and recreational fishing along with bad publicity over the years. Shellfish poisonings have been known about in Florida since the 1880s, although the cause was not identified as K. brevis until 1960.
The fishing industry loses around 18 million dollars annually due to brevetoxin exposure and the resulting fish kills. Also, around one million dollars has been spent annually on public health due to shellfish poisoning from 1987 to 1992. A major obstacle for these industries and public health is inability to contain a bloom, and it is undetectable in taste and smell, only chemically. One major concern for exposure is not just illness, but that brevetoxin can alter human DNA in lymphocytes, impacting immune function.
The metabolism of brevetoxins in shellfish is particularly concerning, as certain derivatives have been shown to remain in the animal over extended periods of time. It has been shown that the main toxin produced by K. brevis, PbTx-2, is rapidly metabolized, resulting in the production of metabolites that endure in the animal's system for a significantly longer period of time. This stands in contrast to PbTx-3, which is typically eliminated from the shellfish in more or less its original form within a few weeks.
Brevetoxin concentrations in seafood and the regulation of toxic substance monitoring in the animals is concerning. In Florida, only oysters and clams are monitored for NSP. Scallops are not monitored, although scallop-related NSP does not normally occur because in most cases, the muscle which does not accumulate brevetoxin to dangerous levels is consumed. Additionally, scallops are less tolerant to brevetoxins as compared to other bivalves and die off quickly after exposure to K. brevis red tides. However, smaller bivalves such as chione clams and coquinas can accumulate extremely high levels of brevetoxins and are not monitored, which could potentially impact both human and wildlife health in negative ways. According to evidence from Poli et al., whelks are implicated in an NSP event in 1996.
With respect to ichthyotoxicity, reports of massive fish kills have been reported in the Gulf of Mexico as far back as 1844. Originally, fish bioassay-guided fractionation was used to isolate the toxins, but accumulation in or food-web transfer by fish has not been regarded as a threat. Steidinger hypothesized that the presence of brevetoxin found in dolphin mortalities and prey mortalities in 1987-1988 were in part due to brevetoxin transfer through fish. While dangerous levels of brevetoxins have not been found in the muscles of live fish to date, the internal organs of fish are highly susceptible to dangerous levels of toxicity and should not be eaten. It is conjectured that chronic low-level exposure to brevetoxin metabolites can occur through shellfish and fish, although the effects of this have not been studied in detail and remain largely unknown. | 0 | Organic Chemistry |
The photodegradation of pharmaceuticals is of interest because they are found in many water supplies. They have deleterious effects on aquatic organisms including toxicity, endocrine disruption, genetic damage. But also in the primary packaging material the photodegradation of pharmaceuticals has to be prevented. For this, amber glasses like Fiolax amber and Corning 51-L are commonly used to protect the pharmaceutical from UV radiations. Iodine (in the form of Lugol's solution) and colloidal silver are universally used in packaging that lets through very little UV light so as to avoid degradation. | 5 | Photochemistry |
Gain of function mutation was first discovered in patients with chronic mucocutaneous candidiasis (CMC). This disease is characteristic with its symptoms as persistent infections of the skin, mucosae - oral or genital and nails infections caused by Candida, mostly Candida albicans. CMC may very often result from primary immunodeficiency. Patients with CMC often suffer also with bacterial infections (mostly Staphylococcus aureus), also with infections of the respiratory system and skin. In these patients we can also find viral infections caused mostly by Herpesviridae, that also affect the skin. The mycobacterial infections are often caused by Mycobacterium tuberculosis or environmental bacteria. Very common are also autoimmune symptoms like type 1 diabetes, cytopenia, regression of the thymus or systemic lupus erythematosus. When T-cell deficient, these autoimmune díseases are very common. CMC was also reported as a common symptom in patients with hyper immunoglobulin E syndrome (hyper-IgE) and with autoimmune polyendocrine syndrome type I. There was reported an interleukin 17A role, because of low levels of IL-17A producing T-cells in CMC patients.
With various genomic and genetic methods was discovered, that a heterozygous gain of function mutation of STAT1 is a cause of more than a half CMC cases. This mutation is caused by defect in the coiled-coil domain, domain that binds DNA, N-terminal domain or SH2 domain. Because of this there is increased phosphorylation because of impossible dephosphorylation in nucleus. These processes are dependent on cytokines like interferon alpha or beta, interferon gamma or interleukin 27. As mentioned above, low levels of interleukin 17A were observed, therefore impaired the Th17 polarization of the immune response.
Patients with STAT1 gain of function mutation and CMC poorly or not at all respond to treatment with azole drugs such as Fluconazole, Itraconazole or Posaconazole. Besides common viral and bacterial infections, these patients develop autoimmunities or even carcinomas. It is very complicated to find a treatment because of various symptoms and resistances, inhibitors of JAK/STAT pathway such as Ruxolitinib are being tested and are a possible choice of treatment for these patients. | 1 | Biochemistry |
The spacing d between adjacent (hkℓ) lattice planes is given by:
*Cubic:
*Tetragonal:
*Hexagonal:
*Rhombohedral (primitive setting):
*Orthorhombic:
*Monoclinic:
*Triclinic: | 3 | Analytical Chemistry |
Climate change contributes to warmer waters which makes conditions more favorable for algae growth in more regions and farther north. In general, still, warm, shallow water, combined with high-nutrient conditions in lakes or rivers, increases the risk of harmful algal blooms. Warming of summer surface temperatures of lakes, which rose by 0.34 °C decade per decade between 1985 and 2009 due to global warming, also will likely increase algal blooming by 20% over the next century.
Although the drivers of harmful algal blooms are poorly understood, they do appear to have increased in range expansion and frequency in coastal areas since the 1980s. The is the result of human induced factors such as increased nutrient inputs (nutrient pollution) and climate change (in particular the warming of water temperatures). The parameters that affect the formation of HABs are ocean warming, marine heatwaves, oxygen loss, eutrophication and water pollution. | 3 | Analytical Chemistry |
A branch of the field of multiomics is the analysis of multilevel single-cell data, called single-cell multiomics. This approach gives us an unprecedent resolution to look at multilevel transitions in health and disease at the single cell level. An advantage in relation to bulk analysis is to mitigate confounding factors derived from cell to cell variation, allowing the uncovering of heterogeneous tissue architectures.
Methods for parallel single-cell genomic and transcriptomic analysis can be based on simultaneous amplification or physical separation of RNA and genomic DNA. They allow insights that cannot be gathered solely from transcriptomic analysis, as RNA data do not contain non-coding genomic regions and information regarding copy-number variation, for example. An extension of this methodology is the integration of single-cell transcriptomes to single-cell methylomes, combining single-cell bisulfite sequencing to single cell RNA-Seq. Other techniques to query the epigenome, as single-cell ATAC-Seq and single-cell Hi-C also exist.
A different, but related, challenge is the integration of proteomic and transcriptomic data. One approach to perform such measurement is to physically separate single-cell lysates in two, processing half for RNA, and half for proteins. The protein content of lysates can be measured by proximity extension assays (PEA), for example, which use DNA-barcoded antibodies. A different approach uses a combination of heavy-metal RNA probes and protein antibodies to adapt mass cytometry for multiomic analysis. | 1 | Biochemistry |
In organic chemistry, alkynols (hydroxyalkynes) are organic compounds that contain both alkyne and alcohol functional groups. Thus, as structural features, they have a C≡C triple bond and a hydroxyl group. Some alkynols play a role as intermediates in the chemical industry.
The shortened term ynol typically refers to alkynols with the hydroxyl group affixed to one of the two carbon atoms composing the triple bond (), the triple-bond analogues to enols. Ynols can tautomerize to ketenes.
The deprotonated anions of ynols are known as ynolates, the triple-bond analogues to enolates. | 0 | Organic Chemistry |
The three main side reactions that produce impurities have in common that they decompose urea.
Urea hydrolyzes back to ammonium carbamate in the hottest stages of the synthesis plant, especially in the stripper, so residence times in these stages are designed to be short.
Biuret is formed when two molecules of urea combine with the loss of a molecule of ammonia.
Normally this reaction is suppressed in the synthesis reactor by maintaining an excess of ammonia, but after the stripper, it occurs until the temperature is reduced. Biuret is undesirable in urea fertilizer because it is toxic to crop plants to varying degrees, but it is sometimes desirable as a nitrogen source when used in animal feed.
Isocyanic acid HNCO and ammonia results from the thermal decomposition of ammonium cyanate , which is in chemical equilibrium with urea:
This decomposition is at its worst when the urea solution is heated at low pressure, which happens when the solution is concentrated for prilling or granulation (see below). The reaction products mostly volatilize into the overhead vapours, and recombine when these condense to form urea again, which contaminates the process condensate. | 7 | Physical Chemistry |
Certain constituents of volcanic gases may show very early signs of changing conditions at depth, making them a powerful tool to predict imminent unrest. Used in conjunction with monitoring data on seismicity and deformation, correlative monitoring gains great efficiency. Volcanic gas monitoring is a standard tool of any volcano observatory. Unfortunately, the most precise compositional data still require dangerous field sampling campaigns. However, remote sensing techniques have advanced tremendously through the 1990s. The Deep Earth Carbon Degassing Project is employing Multi-GAS remote sensing to monitor 9 volcanoes on a continuous basis. | 2 | Environmental Chemistry |
Force tuning has recently proven its efficiency with a maximum error of 5% in comparison with standard finite element solvers in mechanics. Accurate validation of results can also be a tedious task since these methods are very different, common issues are:
* Meshes or lattice discretization
* Location of computed fields at elements or nodes
* Hidden information in softwares used for finite element analysis comparison
* Non-linear materials
* Steady state convergence for LBMS | 7 | Physical Chemistry |
Sorrento Therapeutics has been developing RTX as a means to provide pain relief for forms of advanced cancer.
The nerve desensitizing properties of RTX were once thought to be useful to treat overactive bladder (OAB) by preventing the bladder from transmitting "sensations of urgency" to the brain, similar to how they can prevent nerves from transmitting signals of pain; RTX has never received FDA approval for this use. RTX has also previously been investigated as a treatment for interstitial cystitis, rhinitis, and lifelong premature ejaculation (PE). | 0 | Organic Chemistry |
Antanas was born in Tatkonys, Kupiškis, Lithuania (then Empire of Russia). After completing Liepaja gymnasium, he was studying in Tartu in 1902–1904 and in Saint Petersburg from which he graduated in 1912. | 0 | Organic Chemistry |
GC–MS is increasingly used for detection of illegal narcotics, and may eventually supplant drug-sniffing dogs. A simple and selective GC–MS method for detecting marijuana usage was recently developed by the Robert Koch Institute in Germany. It involves identifying an acid metabolite of tetrahydrocannabinol (THC), the active ingredient in marijuana, in urine samples by employing derivatization in the sample preparation. GC–MS is also commonly used in forensic toxicology to find drugs and/or poisons in biological specimens of suspects, victims, or the deceased. In drug screening, GC–MS methods frequently utilize liquid-liquid extraction as a part of sample preparation, in which target compounds are extracted from blood plasma. | 3 | Analytical Chemistry |
Ionic potential is the ratio of the electrical charge (z) to the radius (r) of an ion.
As such, this ratio is a measure of the charge density at the surface of the ion; usually the denser the charge, the stronger the bond formed by the ion with ions of opposite charge.
The ionic potential gives an indication of how strongly, or weakly, the ion will be electrostatically attracted by ions of opposite charge; and to what extent the ion will be repelled by ions of the same charge.
Victor Moritz Goldschmidt, the father of modern geochemistry found that the behavior of an element in its environment could be predicted from its ionic potential and illustrated this with a diagram (plot of the bare ionic radius as a function of the ionic charge). For instance, the solubility of dissolved iron is highly dependent on its redox state. with a lower ionic potential than is much more soluble because it exerts a weaker interaction force with ion present in water and exhibits a less pronounced trend to hydrolysis and precipitation. Under reducing conditions Fe(II) can be present at relatively high concentration in anoxic water, similar to these encountered for other divalent species such as and . However, once anoxic ground water is pumped from a deep well and is discharged to the surface, it enters in contact with atmospheric oxygen. Then is easily oxidized to and this latter rapidly hydrolyzes and precipitates because of its lower solubility due to a higher z/r ratio.
Millot (1970) also illustrated the importance of the ionic potential of cations to explain the high, or the low, solubility of minerals and the expansive behaviour (swelling/shrinking) of clay materials.
The ionic potential of the different cations (, , and ) present in the interlayer of clay minerals also contribute to explain their swelling/shrinking properties. The more hydrated cations such as and are responsible for the swelling of smectite while the less hydrated and cause the collapse of the interlayer. In illite, the interlayer is totally collapsed because of the presence of the poorly hydrated .
Ionic potential is also a measure of the polarising power of a cation.
Ionic potential could be used as a general criterion for the selection of efficient adsorbents for toxic elements. | 7 | Physical Chemistry |
Glyoxalase I, which is part of the glyoxalase system present in the cytosol, catalyzes the conversion of α-oxoaldehyde (RC(O)CHO) and the thiol glutathione (abbreviated GSH) to S-2-hydroxyacylglutathione derivatives [RCH(OH)CO-SG]. The catalytic mechanism involves an intermediate hemithioacetal adduct [RCOCH(OH)-SG]. The spontaneous reaction forms methylglyoxal-glutathione hemithioacetal and human glyoxalase I.
A hemithioacetal is also invoked in the mechanism of prenylcysteine lyase. In catalytic mechanism, S-farnesylcysteine is oxidized by a flavin to a thiocarbenium ion. The thiocarbenium ion hydrolyzes to form the hemithioacetal:
After formation, the hemithioacetal breaks into hydrogen peroxide, farnesal, and cysteine. | 0 | Organic Chemistry |
In physics, thermal contact conductance is the study of heat conduction between solid or liquid bodies in thermal contact. The thermal contact conductance coefficient, , is a property indicating the thermal conductivity, or ability to conduct heat, between two bodies in contact. The inverse of this property is termed thermal contact resistance. | 7 | Physical Chemistry |
Perfluorinated oxaziridines are known to hydroxylate unactivated hydrocarbons with remarkable regio- and diastereospecificity. This is a highly coveted transformation, and similar reactivity and specificity is seldom rivaled, especially considering the nonmetallic nature of the oxidant. Perfluorinated oxaziridines show high selectivity toward tertiary hydrogens. Hydroxylation of primary carbons and dihydroxylation of a compound with two oxidizable sites have never been observed. Retention of stereochemistry is very high, often 95 to 98%. (Retention of stereochemistry may be further enhanced by the addition of a fluoride salt). | 0 | Organic Chemistry |
An O-acylpseudotropine is any derivative of pseudotropine in which the alcohol group is substituted with an acyl group.
Acylpseudotropines are formed by the action of the enzyme pseudotropine acyltransferase on pseudotropine. | 1 | Biochemistry |
Tetrathionate's structure can be visualized by following three edges of a rectangular cuboid, as in the diagram below. The structure shown is the configuration of in BaSO·2HO and NaSO·2HO. Dihedral S–S–S–S angles approaching 90° are common in polysulfides. | 8 | Metallurgy |
Mining is among the first steps of producing metal and as such is one of the foci of experimental archaeometallurgy. However, experimental research on mining is mostly limited to firesetting and the reproduction and use of mining tools. | 8 | Metallurgy |
In physics, thermalisation (or thermalization) is the process of physical bodies reaching thermal equilibrium through mutual interaction. In general, the natural tendency of a system is towards a state of equipartition of energy and uniform temperature that maximizes the system's entropy. Thermalisation, thermal equilibrium, and temperature are therefore important fundamental concepts within statistical physics, statistical mechanics, and thermodynamics; all of which are a basis for many other specific fields of scientific understanding and engineering application.
Examples of thermalisation include:
* the achievement of equilibrium in a plasma.
* the process undergone by high-energy neutrons as they lose energy by collision with a moderator.
* the process of heat or phonon emission by charge carriers in a solar cell, after a photon that exceeds the semiconductor band gap energy is absorbed.
The hypothesis, foundational to most introductory textbooks treating quantum statistical mechanics, assumes that systems go to thermal equilibrium (thermalisation). The process of thermalisation erases local memory of the initial conditions. The eigenstate thermalisation hypothesis is a hypothesis about when quantum states will undergo thermalisation and why.
Not all quantum states undergo thermalisation. Some states have been discovered which do not (see below), and their reasons for not reaching thermal equilibrium are unclear . | 7 | Physical Chemistry |
Alternative splicing results in two transcript variants encoding the same protein. This gene and the gene that encodes ribonuclease, RNase A family, 4 share promoters and 5' exons. Each gene splices to a unique downstream exon that contains its complete coding region. | 1 | Biochemistry |
The aerodynamic diameter of an irregular particle is defined as the diameter of the spherical particle with a density of 1000 kg/m and the same settling velocity as the irregular particle.
Neglecting the slip correction, the particle settles at the terminal velocity proportional to the square of the aerodynamic diameter, d:
where
: = standard particle density (1000 kg/m).
This equation gives the aerodynamic diameter:
One can apply the aerodynamic diameter to particulate pollutants or to inhaled drugs to predict where in the respiratory tract such particles deposit. Pharmaceutical companies typically use aerodynamic diameter, not geometric diameter, to characterize particles in inhalable drugs. | 7 | Physical Chemistry |
Tellurols are analogues of alcohols and phenols where tellurium replaces oxygen. Tellurols, selenols, and thiols have similar properties, but tellurols are the least stable. Although they are fundamental representatives of organotellurium compounds, tellurols are lightly studied because of their instability. Tellurol derivatives include telluroesters (RC(O)TeR') and tellurocyanates (RTeCN). | 0 | Organic Chemistry |
For batch cross-couplings which use immobilized Pd, the concentration of solution-phase Pd increases dramatically when the reaction commences (as Pd is transferred out of the solid phase), and has decreased dramatically by the time full conversion has been achieved (by readsorption or precipitation onto the solid support). Such a kinetic profile matches the processing requirements of a batch process – although some amount of metal remains in solution post-reaction, the supported Pd catalyst can usually be recycled several times, despite the limitations described above.
In contrast, continuous flow systems do not allow for effective metal redeposition on the solid support; the reaction stream will transport the Pd through the support due to continuous metal leaching/readsorption (Figure 4). Cumulative periods of operation inevitably result in significant metal leaching from the flow system, depleting the supported catalyst's activity and giving low recyclability, with – typically – no particular benefit for reactivity.
In principle, it is possible for the metal leaching inherent to continuous flow cross-coupling to be avoided. Plucinkski and coworkers developed a continuous Mizoroki-Heck and hydrogenation sequence consisting of two separated packed-bed reactors containing Pd/C. Because the Pd/C-catalyzed hydrogenation proceeds via a heterogeneous mechanism, metal leaching due to the second hydrogenation step is minimal, and Pd leached from the first part of the reactor during the Heck coupling can be recaptured by the second packed bed during the hydrogenation. By cycling the direction of flow between forward and reverse, catalytic activity could be maintained over two consecutive experiments, although a greater number of cycles would be desirable in order to vindicate this strategy for increasing turnover in solid-supported flow catalysts for cross-coupling. | 0 | Organic Chemistry |
In order to maintain the solution electroneutrality inside the pit populated by cations released by oxidation in the anodic zone (e.g., in case of steel), anions need to migrate inside the narrow pit. It is worth to notice that the electromobilities of thiosulfate () and chloride () anions are the highest after these of and ions in aqueous solution. Moreover, the molar conductivity of thiosulfate ions is even higher than that of chloride ions because they are twice negatively charged (weak base reluctant to accept a proton). In capillary electrophoresis, thiosulfate moves faster than chloride and eluates before this latter. The high electromobility of both anions could also be one of the many factors explaining their harmful impact for pitting corrosion when compared with other much less damaging ion species such as and . | 8 | Metallurgy |
Examples of well-studied vdW molecules are Ar, H-Ar, HO-Ar, benzene-Ar, (HO), and (HF).
Others include the largest diatomic molecule He, and LiHe. | 7 | Physical Chemistry |
Total soil alkalinity increases with:
* Weathering of silicate, aluminosilicate and carbonate minerals containing , , and ;
* Addition of silicate, aluminosilicate and carbonate minerals to soils; this may happen by deposition of material eroded elsewhere by wind or water, or by mixing of the soil with less weathered material (such as the addition of limestone to acid soils);
* Addition of water containing dissolved bicarbonates (as occurs when irrigating with high-bicarbonate waters).
The accumulation of alkalinity in a soil (as carbonates and bicarbonates of Na, K, Ca and Mg) occurs when there is insufficient water flowing through the soils to leach soluble salts. This may be due to arid conditions, or poor internal soil drainage; in these situations most of the water that enters the soil is transpired (taken up by plants) or evaporates, rather than flowing through the soil.
The soil pH usually increases when the total alkalinity increases, but the balance of the added cations also has a marked effect on the soil pH. For example, increasing the amount of sodium in an alkaline soil tends to induce dissolution of calcium carbonate, which increases the pH. Calcareous soils may vary in pH from 7.0 to 9.5, depending on the degree to which or dominate the soluble cations. | 9 | Geochemistry |
In contrast to old H3 and H4, the old H2A and H2B histone proteins are released and degraded; therefore, newly assembled H2A and H2B proteins are incorporated into new nucleosomes. H2A and H2B are assembled into dimers which are then loaded onto nucleosomes by the nucleosome assembly protein-1 (NAP-1) which also assists with nucleosome sliding. The nucleosomes are also spaced by ATP-dependent nucleosome-remodeling complexes containing enzymes such as Isw1 Ino80, and Chd1, and subsequently assembled into higher order structure. | 1 | Biochemistry |
The development of UVGI traces back to 1878 when Arthur Downes and Thomas Blunt found that sunlight, particularly its shorter wavelengths, hindered microbial growth. Expanding upon this work, Émile Duclaux, in 1885, identified variations in sunlight sensitivity among different bacterial species. A few years later, in 1890, Robert Koch demonstrated the lethal effect of sunlight on Mycobacterium tuberculosis, hinting at UVGI's potential for combating diseases like tuberculosis.
Subsequent studies further defined the wavelengths most efficient for germicidal inactivation. In 1892, it was noted that the UV segment of sunlight had the most potent bactericidal effect. Research conducted in the early 1890s demonstrated the superior germicidal efficacy of UV-C compared to UV-A and UV-B.
The mutagenic effects of UV were first unveiled in a 1914 study that observed metabolic changes in Bacillus anthracis upon exposure to sublethal doses of UV. Frederick Gates, in the late 1920s, offered the first quantitative bactericidal action spectra for Staphylococcus aureus and Bacillus coli, noting peak effectiveness at 265 nm. This matched the absorption spectrum of nucleic acids, hinting at DNA damage as the key factor in bacterial inactivation. This understanding was solidified by the 1960s through research demonstrating the ability of UV-C to form thymine dimers, leading to microbial inactivation. These early findings collectively laid the groundwork for modern UVGI as a disinfection tool. | 5 | Photochemistry |
Previous analysis focused only on diffraction from a perfectly flat surface of a crystal surface. However, non-flat surfaces add additional diffraction conditions to RHEED analysis.
Streaked or elongated spots are common to RHEED patterns. As Fig 3 shows, the reciprocal lattice rods with the lowest orders intersect the Ewald sphere at very small angles, so the intersection between the rods and sphere is not a singular point if the sphere and rods have thickness. The incident electron beam diverges and electrons in the beam have a range of energies, so in practice, the Ewald sphere is not infinitely thin as it is theoretically modeled. The reciprocal lattice rods have a finite thickness as well, with their diameters dependent on the quality of the sample surface. Streaks appear in the place of perfect points when broadened rods intersect the Ewald sphere. Diffraction conditions are fulfilled over the entire intersection of the rods with the sphere, yielding elongated points or ‘streaks’ along the vertical axis of the RHEED pattern. In real cases, streaky RHEED patterns indicate a flat sample surface while the broadening of the streaks indicate small area of coherence on the surface.
Surface features and polycrystalline surfaces add complexity or change RHEED patterns from those from perfectly flat surfaces. Growing films, nucleating particles, crystal twinning, grains of varying size and adsorbed species add complicated diffraction conditions to those of a perfect surface. Superimposed patterns of the substrate and heterogeneous materials, complex interference patterns and degradation of the resolution are characteristic of complex surfaces or those partially covered with heterogeneous materials. | 3 | Analytical Chemistry |
Upon heating, DAST converts to the highly explosive (NEt)SF with expulsion of sulfur tetrafluoride. To minimize accidents, samples are maintained below 50 °C. Bis-(2-methoxyethyl)aminosulfur trifluoride (trade name: Deoxo-Fluor) and difluoro(morpholino)sulfonium tetrafluoroborate (trade name: XtalFluor-M) are reagents related to DAST with less explosive potential.
XtalFluor-E has been jointly developed by OmegaChem Inc. and Manchester Organics Ltd. in 2009–2010. | 0 | Organic Chemistry |
In the early 1900s, chemical messengers were crudely extracted from whole animal brains and tissues and studied for their physiological effects. In 1931, von Euler and Gaddum, used a similar method to try and isolate acetylcholine but instead discovered a peptide substance that induced physiological changes including muscle contractions and depressed blood pressure. These effects were not abolished using atropine, ruling out the substance as acetylcholine.
In insects, proctolin was the first neuropeptide to be isolated and sequenced. In 1975, Alvin Starratt and Brian Brown extracted the peptide from hindgut muscles of the cockroach and found that its application enhanced muscle contractions. While Starratt and Brown initially thought of proctolin as an excitatory neurotransmitter, proctolin was later confirmed as a neuromodulatory peptide.
David de Wied first used the term "neuropeptide" in the 1970s to delineate peptides derived from the nervous system. | 1 | Biochemistry |
Foldit attempts to apply the human brain's three-dimensional pattern matching and spatial reasoning abilities to help solve the problem of protein structure prediction. 2016 puzzles are based on well-understood proteins. By analysing how humans intuitively approach these puzzles, researchers hope to improve the algorithms used by protein-folding software.
Foldit includes a series of tutorials where users manipulate simple protein-like structures and a periodically updated set of puzzles based on real proteins. It shows a graphical representation of each protein which users can manipulate using a set of tools. | 1 | Biochemistry |
Electrons leave the cathode with an energy of about 1 eV, which is not enough to ionize or excite atoms, leaving a thin dark layer next to the cathode. | 3 | Analytical Chemistry |
Sinter plants agglomerate iron ore fines (dust) with other fine materials at high temperature, to create a product that can be used in a blast furnace. The final product, a sinter, is a small, irregular nodule of iron mixed with small amounts of other minerals. The process, called sintering, causes the constituent materials to fuse to make a single porous mass with little change in the chemical properties of the ingredients. The purpose of sinter are to be used converting iron into steel.
Sinter plants, in combination with blast furnaces, are also used in non-ferrous smelting. About 70% of the world's primary lead production is still produced using the sinter plant–blast furnace combination, and this combination was formerly often used in copper smelting (at the Electrolytic Refining and Smelting smelter in Wollongong, New South Wales, for example). | 8 | Metallurgy |
Although there is a large number of simple known ABX perovskites, this number can be greatly expanded if the A and B sites are increasingly doubled / complex AA’BB’X. Ordered double perovskites are usually denoted as ABB’O where disordered are denoted as A(BB’)O. In ordered perovskites, three different types of ordering are possible: rock-salt, layered, and columnar. The most common ordering is rock-salt followed by the much more uncommon disordered and very distant columnar and layered. The formation of rock-salt superstructures is dependent on the B-site cation ordering. Octahedral tilting can occur in double perovskites, however Jahn–Teller distortions and alternative modes alter the B–O bond length. | 3 | Analytical Chemistry |
The coffee ring effect is utilized in convective deposition by researchers wanting to order particles on a substrate using capillary-driven assembly, replacing a stationary droplet with an advancing meniscus drawn across the substrate. This process differs from dip-coating in that evaporation drives flow along the substrate as opposed to gravity.
Convective deposition can control particle orientation, resulting in the formation of crystalline monolayer films from nonspherical particles such as hemispherical, dimer, and dumbbell shaped particles. Orientation is afforded by the system trying to reach a state of maximum packing of the particles in the thin meniscus layer over which evaporation occurs. They showed that tuning the volume fraction of particles in solution will control the specific location along the varying meniscus thickness at which assembly occurs. Particles will align with their long axis in- or out-of-plane depending on whether or not their longer dimension of the particle was equal to the thickness of the wetting layer at the meniscus location. Such thickness transitions were established with spherical particles as well. It was later shown that convective assembly could control particle orientation in assembling multi-layers, resulting in long-range 3D colloidal crystals from dumbbell shaped particles. These finds were attractive for the self-assembled of colloidal crystal films for applications such as photonics. Recent advances have increased the application of coffee-ring assembly from colloidal particles to organized patterns of inorganic crystals. | 7 | Physical Chemistry |
TADs have been reported to be relatively constant between different cell types (in stem cells and blood cells, for example), and even between species in specific cases. | 1 | Biochemistry |
Lysergic acid, also known as -lysergic acid and (+)-lysergic acid, is a precursor for a wide range of ergoline alkaloids that are produced by the ergot fungus and found in the seeds of Turbina corymbosa (ololiuhqui), Argyreia nervosa (Hawaiian baby woodrose), and Ipomoea tricolor (morning glories, tlitliltzin).
Amides of lysergic acid, lysergamides, are widely used as pharmaceuticals and as psychedelic drugs, e.g. lysergic acid diethylamide (LSD). Lysergic acid is listed as a Table I precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.
Lysergic acid received its name as it was a product of the lysis of various ergot alkaloids. | 0 | Organic Chemistry |
Phosphopantetheine, also known as 4'-phosphopantetheine, is a prosthetic group of several acyl carrier proteins including the acyl carrier proteins (ACP) of fatty acid synthases, ACPs of polyketide synthases, the peptidyl carrier proteins (PCP), as well as aryl carrier proteins (ArCP) of nonribosomal peptide synthetases (NRPS). It is also present in formyltetrahydrofolate dehydrogenase.
Subsequent to the expression of the apo acyl carrier protein, 4-phosphopantetheine moiety is attached to a serine residue. The coupling involves formation of a phosphodiester linkage. This coupling is mediated by acyl carrier protein synthase (ACPS), a 4-phosphopantetheinyl transferase.
Phosphopantetheine prosthetic group covalently links to the acyl group via a high energy thioester bond. The flexibility and length of the phosphopantetheine chain (approximately 2 nm) allows the covalently tethered intermediates to access spatially distinct enzyme-active sites. This accessibility increases the effective molarity of the intermediate and allows an assembly line-like process. | 1 | Biochemistry |
If a gas is compressed adiabatically, i.e. without outflow of heat from the system, the temperature rises (due to the pressure increase) at a higher rate with respect to isothermal compression, where the performed work is dissipated as heat. The exponent, , with which the expansion of the gas can be calculated by the application of heat is called the isentropic – or adiabatic coefficient. Its value is determined by the Rüchardt experiment.
An adiabatic and reversible running state change is isentropic (entropy S remains the same as temperature T changes). The technique is usually an adiabatic change of state. For example, a steam turbine is not isentropic, as friction, choke and shock processes produce entropy. | 7 | Physical Chemistry |
During its formation, the Earth likely suffered a series of magma oceans resulting from giant impacts, the final one being the Moon-forming impact. The best chemical evidence for the existence of magma oceans on Earth is the abundance of certain siderophile elements in the mantle that record magma ocean depths of approximately 1000 km during accretion. The scientific evidence to support the existence of magma oceans on early Earth is not as developed as the evidence for the Moon because of the recycling of the Earth's crust and mixing of the mantle. Unlike Earth, indications of a magma ocean on the Moon such as the flotation crust, elemental components in rocks, and KREEP have been preserved throughout its lifetime.
Today Earths outer core is a liquid layer about thick, composed mostly of molten iron and molten nickel that lies above Earths solid inner core and below its mantle. This layer may be considered as an ocean of molten iron and nickel inside Earth. | 9 | Geochemistry |
The antitubercular agent Ethambutol contains two constitutionally symmetrical stereogenic centers in its structure and exists in three stereoisomeric forms. An enantiomeric pair (S,S)- and (R,R)-ethambutol, along with the achiral stereoisomer called meso-form, it holds a diastereomeric relationship with the optically active stereoisomers. The activity of the drug resides in the (S,S)-enantiomer which is 500 and 12 fold more potent than the (R,R)-ethambutol and the meso-form. The drug had initially been introduced for clinical use as the racemate and was changed to the (S,S)-enantiomer, as a result of optic neuritis leading to blindness. Toxicity is related to both dose and duration of treatment. All the three stereoisomers were almost equipotent with respect to side effects. Hence the use of S,S)-enantiomer greatly enhanced the risk/benefit ratio. | 4 | Stereochemistry |
The Coulter Counter was created by Wallace H. Coulter in 1949. The Coulter counter consists of two electrolyte reservoirs that are connected by a small channel, through which a current of ions flow. Each particle drawn through the channel causes a brief change to the electrical resistance of the liquid. The change in the electrical resistance causes a disturbance in the electric field. The counter detects these changes in electrical resistance; the size of the particles in the field is proportional to magnitude of the disturbance in the electric field. | 7 | Physical Chemistry |
In organic chemistry, a staggered conformation is a chemical conformation of an ethane-like moiety abcX–Ydef in which the substituents a, b, and c are at the maximum distance from d, e, and f; this requires the torsion angles to be 60°. It is the opposite of an eclipsed conformation, in which those substituents are as close to each other as possible.
Such a conformation exists in any open chain single chemical bond connecting two sp-hybridised atoms, and is normally a conformational energy minimum. For some molecules such as those of n-butane, there can be special versions of staggered conformations called gauche and anti; see first Newman projection diagram in Conformational isomerism.
Staggered/eclipsed configurations also distinguish different crystalline structures of e.g. cubic/hexagonal boron nitride, and diamond/lonsdaleite. | 4 | Stereochemistry |
Karl Norris pioneered the field of near-infrared spectroscopy. He began by using log(1/R) as a metric of absorption. While often the samples examined were “infinitely thick”, partially transparent samples were analyzed (especially later) in cells that had a rear reflecting surface (reflector) in a mode called "transflectance". Therefore, the remission from the sample contained light that was back-scattered from the sample, as well as light that was transmitted through the sample, then reflected back to be transmitted through the sample again, thereby doubling the path length. Having no sound theoretical basis for data treatment, Norris used the same electronic processing that was used for absorption data collected in transmission. He pioneered the use of multiple linear regression for analysis of data.
Gerry Birth was the founder of the International Diffuse Reflectance Conference (IDRC). He also worked at the USDA. He was known to have a deep desire to have a better understanding of the process of light scattering. He teamed up with Harry Hecht (who was active in the early meetings of IDRC) to write the Physics theory chapter, with many photographic illustrations, in an influential Handbook edited by Phil Williams and Karl Norris: Nearinfrared Technology in the Agriculture and Food Industries. | 7 | Physical Chemistry |
Christy F. Landes is an American physical chemist who is the Jerry A. Walker Endowed Chair in chemistry at the University of Illinois Urbana-Champaign. She previously was the Kenneth S. Pitzer-Schlumberger Chair at Rice University. She seeks to understand the structure-function relationships in biological processes and materials. She was appointed a National Academy of Sciences Kavli Fellow in 2019. | 7 | Physical Chemistry |
An illustrative example: There are two types of Zintl ions in KSi; 2x (pseudo P,
or according to Wades rules, 12 = 2n + 4 skeletal-electrons corresponding to a nido'-form of a trigonal-bipyramid) and 1x
(according to Wades rules, 22 = 2n + 4 skeletal-electrons corresponding to a nido'-form of a bicapped square antiprism)
Examples from Müller's 1973 review paper with known structures are listed in the table below. | 7 | Physical Chemistry |
Ecdysteroids are arthropod steroid hormones that are mainly responsible for molting, development and, to a lesser extent, reproduction; examples of ecdysteroids include ecdysone, ecdysterone, turkesterone and 2-deoxyecdysone. These compounds are synthesized in arthropods from dietary cholesterol upon metabolism by the Halloween family of cytochrome P450s. Phytoecdysteroids also appear in many plants mostly as a protection agents (toxins or antifeedants) against herbivore insects.
Ecdysterone has been tested on mammals due to the interest in its potential hypertrophic effect. It has been found to increase hypertrophy in rats at a similar level to some anabolic androgenic steroids and SARM S 1. This is proposed to be through increase of Calcium leading to activation of Akt and protein synthesis in skeletal muscles. | 1 | Biochemistry |
Chromatin assembly factor-1 (CAF-1) is a protein complex — including Chaf1a (p150), Chaf1b (p60), and p48 subunits in humans, or Cac1, Cac2, and Cac3, respectively, in yeast— that assembles histone tetramers onto replicating DNA during the S phase of the cell cycle. | 1 | Biochemistry |
Modafinil and/or its major metabolite, modafinil acid, may be quantified in plasma, serum, or urine to monitor dosage in those receiving the drug therapeutically, to confirm a diagnosis of poisoning in hospitalized patients, or to assist in the forensic investigation of a vehicular traffic violation. Instrumental techniques involving gas or liquid chromatography are usually employed for these purposes. In 2011, modafinil was not tested for by common drug screens (except for anti-doping screens) and is unlikely to cause false positives for other chemically unrelated drugs such as substituted amphetamines.
Reagent testing can screen for the presence of modafinil in samples. | 4 | Stereochemistry |
Like LTR retrotransposons, non-LTR retrotransposons contain genes for reverse transcriptase, RNA-binding protein, nuclease, and sometimes ribonuclease H domain but they lack the long terminal repeats. RNA-binding proteins bind the RNA-transposition intermediate and nucleases are enzymes that break phosphodiester bonds between nucleotides in nucleic acids. Instead of LTRs, non-LTR retrotransposons have short repeats that can have an inverted order of bases next to each other aside from direct repeats found in LTR retrotransposons that is just one sequence of bases repeating itself.
Although they are retrotransposons, they cannot carry out reverse transcription using an RNA transposition intermediate in the same way as LTR retrotransposons. Those two key components of the retrotransposon are still necessary but the way they are incorporated into the chemical reactions is different. This is because unlike LTR retrotransposons, non-LTR retrotransposons do not contain sequences that bind tRNA.
They mostly fall into two types – LINEs (Long interspersed nuclear elements) and SINEs (Short interspersed nuclear elements). SVA elements are the exception between the two as they share similarities with both LINEs and SINEs, containing Alu elements and different numbers of the same repeat. SVAs are shorter than LINEs but longer than SINEs.
While historically viewed as "junk DNA", research suggests in some cases, both LINEs and SINEs were incorporated into novel genes to form new functions. | 1 | Biochemistry |
A metal salen complex is a coordination compound between a metal cation and a ligand derived from N,N′-bis(salicylidene)ethylenediamine, commonly called salen. The classical example is salcomine, the complex with divalent cobalt , usually denoted as Co(salen). These complexes are widely investigated as catalysts and enzyme mimics.
The metal-free salen compound (Hsalen or salenH) has two phenolic hydroxyl groups. The salen ligand is usually its conjugate base (salen), resulting from the loss of protons from those hydroxyl groups. The metal atom usually makes four coordination bonds to the oxygen and nitrogen atoms. | 0 | Organic Chemistry |
The parent hydride compound is the hypothetical molecule PH.
Pentaphenylphosphorane (PhP) is stable.
Pentaalkoxyphosphoranes are more common with electronegative substituents. Examples of P(OR) (R = alkyl), have however been prepared by reaction of phosphites with benzene alkyl sulfenates: | 0 | Organic Chemistry |
Transcriptomics allows identification of genes and pathways that respond to and counteract biotic and abiotic environmental stresses. The non-targeted nature of transcriptomics allows the identification of novel transcriptional networks in complex systems. For example, comparative analysis of a range of chickpea lines at different developmental stages identified distinct transcriptional profiles associated with drought and salinity stresses, including identifying the role of transcript isoforms of AP2-EREBP. Investigation of gene expression during biofilm formation by the fungal pathogen Candida albicans revealed a co-regulated set of genes critical for biofilm establishment and maintenance.
Transcriptomic profiling also provides crucial information on mechanisms of drug resistance. Analysis of over 1000 isolates of Plasmodium falciparum, a virulent parasite responsible for malaria in humans, identified that upregulation of the unfolded protein response and slower progression through the early stages of the asexual intraerythrocytic developmental cycle were associated with artemisinin resistance in isolates from Southeast Asia.
The use of transcriptomics is also important to investigate responses in the marine environment. In marine ecology, "stress" and "adaptation" have been among the most common research topics, especially related to anthropogenic stress, such as global change and pollution. Most of the studies in this area have been done in animals, although invertebrates have been underrepresented. One issue still is a deficiency in functional genetic studies, which hamper gene annotations, especially for non-model species, and can lead to vague conclusions on the effects of responses studied. | 1 | Biochemistry |
Before TFH identified it, it had several names. It was isolated in 1989 isolated from rat liver, known by factor transcription delta. When identified from cancer cells it was known that time as Basic transcription factor 2. Also, when isolated from yeast it was termed transcription factor B. Finally, in 1992 known as TFH. | 1 | Biochemistry |
In particular to building materials, moisture sorption has significant implications for cements, woods, insulation materials, and fibers. Moisture damage is a significant factor limiting a buildings lifespan. As well, moisture infusion through a buildings outer structure can have a significant effect on indoor air quality and air-conditioning load. | 7 | Physical Chemistry |
The critical heat flux is an important point on the boiling curve and it may be desirable to operate a boiling process near this point. However, one could become cautious of dissipating heat in excess of this amount. Zuber, through a hydrodynamic stability analysis of the problem has developed an expression to approximate this point.
Units: critical flux: kW/m; h: kJ/kg; σ: N/m; ρ: kg/m; g: m/s.
It is independent of the surface material and is weakly dependent upon the heated surface geometry described by the constant C. For large horizontal cylinders, spheres and large finite heated surfaces, the value of the Zuber constant . For large horizontal plates, a value of is more suitable.
The critical heat flux depends strongly on pressure. At low pressures (including atmospheric pressure), the pressure dependence is mainly through the change in vapor density leading to an increase in the critical heat flux with pressure. However, as pressures approach the critical pressure, both the surface tension and the heat of vaporization converge to zero, making them the dominant sources of pressure dependency.
For water at 1atm, the above equation calculates a critical heat flux of approximately 1000 kW/m. | 7 | Physical Chemistry |
Sulfate transported through the roots and SO diffusing into leaves becomes the pool for plants to assimilate sulfur throughout their tissues. Though there is minimal fractionation from the source sulfur of the total plant organic matter, in wheat, roots and stems are depleted from soil by 2‰ and leaves and grain are 2‰ enriched. The S enrichment in leaf whole matter is not caused by S-enriched sulfate present in the leaf, but is the result of the S-enrichment arriving at sink organs causing proteins in the leaves to be S-enriched. In rice, translocation from root to shoot does not discriminate S isotopes, however, the sulfate pools of the shoot are significantly S-enriched with respect to the sulfate pools of both root and sap. As sulfate moves through the plant system and is incorporated into biomass, the pool becomes enriched, giving organs such as leaves and grains higher δS values than earlier tissues. | 9 | Geochemistry |
This process was developed by the National Smelting Company at Avonmouth Docks, England, in order to increase production, increase efficiency, and decrease labour and maintenance costs. L. J. Derham proposed using a spray of molten lead droplets to rapidly cool and absorb the zinc vapour, despite the high concentration of carbon dioxide. The mixture is then cooled, where the zinc separates from the lead. The first plant using this design opened up in 1950. One of the advantages of this process is that it can co-produce lead bullion and copper dross. In 1990, it accounted for 12% of the world's zinc production.
The process starts by charging solid sinter and heated coke into the top of the blast furnace. Preheated air at is blown into the bottom of the furnace. Zinc vapour and sulfides leave through the top and enter the condenser. Slag and lead collect at the bottom of the furnace and are tapped off regularly. The zinc is scrubbed from the vapour in the condenser via liquid lead. The liquid zinc is separated from the lead in the cooling circuit. Approximately of lead are required each year for this process, however this process recovers 25% more lead from the starting ores than other processes. | 8 | Metallurgy |
In addition to the NUTM1 fusion genes in the above cited carcinomas, recent studies have found NUTM1 fusion genes in malignancies with undifferentiated spindle cell, round cell, and epithelioid cell-like features which are regarded as sarcomas. Sarcomas with NUTM1 fusion genes typically a) occur in some sites were sarcomas otherwise rarely develop and b) consist of tumor cells that express a NUTM1 gene fused to one of the MADS-box gene family genes (i.e. a MXD4, MGA, or MXD1 gne), or, alternatively, a BRD4, ZNF532, or CIC gene. A recent review listed the follow NUTM1 fusion gene-associated sarcomas:
* Colorectal sarcomas: Six cases, all with a MXD4-NUTM1 fusion gene.
* Lung sarcomas: Four cases, one each with a BRD4-NUTM1, MDX4-NUTM1, CIC-NUTM1, or MGA-NUTM1 fusion gene.
* Kidney sarcomas: Three cases, two with a BRD4-NUTM1 and one with a CIC-NUTM1 fusion gene.
* Sarcomas of the extremities: Two cases of foot sarcomas, one with a MGA-NUTM1 and one with a X-NUTM1 (i.e. X indicates the fusion partner is not identified) fusion gene; two cases of thigh sarcomas, one with a BRD4-NUTM1 and the other with a MGA-NUTM1 fusion gene; and one case of an arm sarcoma with a BCORL1-NUTM1 fusion gene (BCORL1 is the BCL6 corepressor like 1 gene).
* Bone sarcomas: One case of mandible sarcoma with a ZNF532-NUTM1 fusion gene and one case each of temporal bone and occipital bone sarcomas (both of which were also in nearby brain tissues) with a CIC-NUTM1 fusion gene.
* Other sites: One case each of: stomach sarcoma with a MXD1-NUTM1 fusion gene; brain parietal cortex sarcoma with a BRD4-NUTM1 fusion gene; brain dura sarcoma with a MGA-NUTM1 fusion gene; sarcoma of the scalp with a CIC-NUTM1 fusion gene; paravertebral sarcoma with a CIC-NUTM1 gene; pleural sarcoma with the MGA-NUTM1 fusion gene; epidural sarcoma with CIC-NUTM1 gene; brain lateral ventricle sarcoma with the CIC-NUTM1 fusion gene; brain parietal cortex sarcoma with a BRD4-NUTM1 fusion gene; and ovary with a MXD4-NUTM1 fusion gene.
In general, these NUTM1 fusion gene-associated sarcomas have very poor prognoses and require further study to determine of role of these fusion genes in the development and progression of their corresponding sarcomas. | 1 | Biochemistry |
A direct electron ionization liquid chromatography–mass spectrometry interface (Direct-EI LC-MS interface) is a technique for coupling liquid chromatography and mass spectrometry (LC-MS) based on the direct introduction of the liquid effluent into an electron ionization (EI) source. Library searchable mass spectra are generated. Gas-phase EI has many applications for the detection of HPLC amenable compounds showing minimal adverse matrix effects. The direct-EI LC-MS interface provides access to well-characterized electron ionization data for a variety of LC applications and readily interpretable spectra from electronic libraries for environmental, food safety, pharmaceutical, biomedical, and other applications. | 3 | Analytical Chemistry |
The increase in use of Terfenol-D in transducers required new production techniques that increased production rates and quality because the original methods were unreliable and small scale. There are four methods that are used to produce Terfenol-D, which are free stand zone melting, modified Bridgman, sintered powder compact, and polymer matrix composites.
The first two methods, free stand zone melting (FSZM) and modified Bridgman (MB), are capable of producing Terfenol-D that has high magnetostrictive properties and energy densities. However, FSZM cannot produce a rod larger than 8 mm in diameter due to the surface tension of the Terfenol-D and how the FSZM process has no container to restrict the material. The MB process offers a minimum of 10 mm diameter size and is only restricted due to the wall interfering with the crystal growth. Both methods create solid crystals that require later manufacturing if a geometry other than a right-angle cylinder is needed. The solid crystals produced have a fine lamellar structure.
The other two techniques, sintered powder compact and polymer matrix composites, are powder based. These techniques allow for intricate geometry and detail. However, the size is limited to 10mm in diameter and 100mm in length due to the molds used. The resulting microstructures of these powder based methods differ from the solid crystal ones because they do not have a lamellar structure and have a lower density. However, all methods have similar magnetostrictive properties.
Due to size restriction, MB is the best process to produce Terfenol-D, however it is a labor-intensive method. A newer process like MB is ET-Ryma crystal growth (ECG) that results in larger diameter Terfenol-D crystals and increased magnetostrictive performance. The reliability of magnetostrictive properties of the Terfenol-D throughout the life of the material is increased by using ET-Ryma.
Terfenol-D has some minor drawbacks which stem from its material properties. Terfenol-D has low ductility and low fracture resistance. To solve this, Terfenol-D has been added to polymers and other metals to create composites. When added to polymers, the stiffness of the resulting composite is low. When composites of Terfenol-D with ductile metal binders are created, the resulting material has increased stiffness and ductility with reduced magnetostrictive properties. These metal composites may be formed by explosion compaction. In a study done on processing Terfenol-D alloys, the resulting alloys created using copper and Terfenol-D had increased strength and hardness values, which supports the theory that the composites of ductile metal binders and Terfenol-D result in a stronger and more ductile material. | 8 | Metallurgy |
Electrowinning and electrorefining respectively involve the recovery and purification of metals using electrodeposition of metals at the cathode, and either metal dissolution or a competing oxidation reaction at the anode. | 8 | Metallurgy |
The majority of sperm donors who donate their sperm through a sperm bank receive some kind of payment, although this is rarely a significant amount. A review including 29 studies from nine countries came to the result that the amount of money actual donors received for their donation varied from $10 to €70 per donation or sample. The payments vary from the situation in the United Kingdom where donors are only entitled to their expenses in connection with the donation, to the situation with some US sperm banks where a donor receives a set fee for each donation plus an additional amount for each vial stored. At one prominent California sperm bank for example, TSBC, donors receive roughly $50 for each donation (ejaculation) which has acceptable motility/survival rates both at donation and at a test-thaw a couple of days later. Because of the requirement for the two-day celibacy period before donation, and geographical factors which usually require the donor to travel, it is not a viable way to earn a significant income—and is far less lucrative than selling human eggs. Some private donors may seek remuneration although others donate for altruistic reasons. According to the EU Tissue Directive donors in EU may only receive compensation, which is strictly limited to making good the expenses and inconveniences related to the donation. | 1 | Biochemistry |
Whole genome sequencing studies enable the assessment of associations between complex traits and both coding and noncoding rare variants (minor allele frequency (MAF) < 1%) across the genome. Single-variant analyses typically have low power to identify associations with rare variants, and variant set tests have been proposed to jointly test the effects of given sets of multiple rare variants. SNP annotations help to prioritize rare functional variants, and incorporating these annotations can effectively boost the power of genetic association of rare variants analysis of whole genome sequencing studies. Some tools have been specifically developed to provide all-in-one rare variant association analysis for whole-genome sequencing data, including integration of genotype data and their functional annotations, association analysis, result summary and visualization.
Meta-analysis of whole genome sequencing studies provides an attractive solution to the problem of collecting large sample sizes for discovering rare variants associated with complex phenotypes. Some methods have been developed to enable functionally informed rare variant association analysis in biobank-scale cohorts using efficient approaches for summary statistic storage. | 1 | Biochemistry |
Biotin PEG2 amine (biotine PEG2 amine) is a water-soluble pegylated biotin derivative used as linker in biotechnology and molecular biology applications. | 1 | Biochemistry |
ER oxidoreductin 1 (Ero1) is an oxidoreductase enzyme that catalyses the formation and isomerization of protein disulfide bonds in the endoplasmic reticulum (ER) of eukaryotes. ER Oxidoreductin 1 (Ero1) is a conserved, luminal, glycoprotein that is tightly associated with the ER membrane, and is essential for the oxidation of protein dithiols. Since disulfide bond formation is an oxidative process, the major pathway of its catalysis has evolved to utilise oxidoreductases, which become reduced during the thiol-disulfide exchange reactions that oxidise the cysteine thiol groups of nascent polypeptides. Ero1 is required for the introduction of oxidising equivalents into the ER and their direct transfer to protein disulfide isomerase (PDI), thereby ensuring the correct folding and assembly of proteins that contain disulfide bonds in their native state.
Ero1 exists in two isoforms: Ero1-α and Ero1-β. Ero1-α is mainly induced by hypoxia (HIF-1), whereas Ero1-β is mainly induced by the unfolded protein response (UPR).
During endoplasmic reticulum stress (such as occurs in beta cells of the pancreas or in macrophages causing atherosclerosis), CHOP can induce activation of Ero1, causing calcium release from the endoplasmic reticulum into the cytoplasm, resulting in apoptosis.
Homologues of the Saccharomyces cerevisiae Ero1 proteins have been found in all eukaryotic organisms examined, and contain seven cysteine residues that are absolutely conserved, including three that form the sequence Cys–X–X–Cys–X–X–Cys (where X can be any residue). | 1 | Biochemistry |
An aromatic (or aryl) compound contains a set of covalently bound atoms with specific characteristics:
# A delocalized conjugated π system, most commonly an arrangement of alternating single and double bonds
# Coplanar structure, with all the contributing atoms in the same plane
# Contributing atoms arranged in one or more rings
# A number of π delocalized electrons that is even, but not a multiple of 4. That is, 4n + 2 number of π electrons, where n=0, 1, 2, 3, and so on. This is known as Hückel's Rule.
Whereas benzene is aromatic (6 electrons, from 3 double bonds), cyclobutadiene is not, since the number of π delocalized electrons is 4, which of course is a multiple of 4. The cyclobutadienide (2−) ion, however, is aromatic (6 electrons). An atom in an aromatic system can have other electrons that are not part of the system, and are therefore ignored for the 4n + 2 rule. In furan, the oxygen atom is sp² hybridized. One lone pair is in the π system and the other in the plane of the ring (analogous to C-H bond on the other positions). There are 6 π electrons, so furan is aromatic.
Aromatic molecules typically display enhanced chemical stability, compared to similar non-aromatic molecules. A molecule that can be aromatic will tend to alter its electronic or conformational structure to be in this situation. This extra stability changes the chemistry of the molecule. Aromatic compounds undergo electrophilic aromatic substitution and nucleophilic aromatic substitution reactions, but not electrophilic addition reactions as happens with carbon-carbon double bonds.
Many of the earliest-known examples of aromatic compounds, such as benzene and toluene, have distinctive pleasant smells. This property led to the term "aromatic" for this class of compounds, and hence the term "aromaticity" for the eventually discovered electronic property.
The circulating π electrons in an aromatic molecule produce ring currents that oppose the applied magnetic field in NMR. The NMR signal of protons in the plane of an aromatic ring are shifted substantially further down-field than those on non-aromatic sp² carbons. This is an important way of detecting aromaticity. By the same mechanism, the signals of protons located near the ring axis are shifted up-field.
Aromatic molecules are able to interact with each other in so-called π-π stacking: The π systems form two parallel rings overlap in a "face-to-face" orientation. Aromatic molecules are also able to interact with each other in an "edge-to-face" orientation: The slight positive charge of the substituents on the ring atoms of one molecule are attracted to the slight negative charge of the aromatic system on another molecule.
Planar monocyclic molecules containing 4n π electrons are called antiaromatic and are, in general, destabilized. Molecules that could be antiaromatic will tend to alter their electronic or conformational structure to avoid this situation, thereby becoming non-aromatic. For example, cyclooctatetraene (COT) distorts itself out of planarity, breaking π overlap between adjacent double bonds. Relatively recently, cyclobutadiene was discovered to adopt an asymmetric, rectangular configuration in which single and double bonds indeed alternate; there is no resonance and the single bonds are markedly longer than the double bonds, reducing unfavorable p-orbital overlap. This reduction of symmetry lifts the degeneracy of the two formerly non-bonding molecular orbitals, which by Hund's rule forces the two unpaired electrons into a new, weakly bonding orbital (and also creates a weakly antibonding orbital). Hence, cyclobutadiene is non-aromatic; the strain of the asymmetric configuration outweighs the anti-aromatic destabilization that would afflict the symmetric, square configuration. | 7 | Physical Chemistry |
In cyclohexane, the two chair conformations have the same energy. The situation becomes more complex with substituted derivatives. | 4 | Stereochemistry |
Flux in geochemical cycles is the movement of material between the deep Earth and the surface reservoirs. This occurs through two different processes: volcanism and subduction of tectonic plates.
Subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge. This leads to the sinking of one plate into the mantle which creates a broad range of geochemical transformations or cycling.
Volcanism is the process that takes place at divergent boundaries by which one tectonic plate separates from another creating a rift in which molten rock (magma) erupts onto the surface of the Earth. This molten rock magma then cools and crystallizes, forming igneous rocks. If crystallization occurs at the Earths surface, extrusive igneous rocks are formed; if crystallization occurs within the Earths lithosphere, intrusive igneous rocks are formed which can then be brought to Earth's surface by denudation | 9 | Geochemistry |
Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, canaries, flamingos, salmon, lobster, shrimp, and daffodils. Over 1,100 identified carotenoids can be further categorized into two classes xanthophylls (which contain oxygen) and carotenes (which are purely hydrocarbons and contain no oxygen).
All are derivatives of tetraterpenes, meaning that they are produced from 8 isoprene units and contain 40 carbon atoms. In general, carotenoids absorb wavelengths ranging from 400 to 550 nanometers (violet to green light). This causes the compounds to be deeply colored yellow, orange, or red. Carotenoids are the dominant pigment in autumn leaf coloration of about 15-30% of tree species, but many plant colors, especially reds and purples, are due to polyphenols.
Carotenoids serve two key roles in plants and algae: they absorb light energy for use in photosynthesis, and they provide photoprotection via non-photochemical quenching. Carotenoids that contain unsubstituted beta-ionone rings (including β-carotene, α-carotene, β-cryptoxanthin, and γ-carotene) have vitamin A activity (meaning that they can be converted to retinol). In the eye, lutein, meso-zeaxanthin, and zeaxanthin are present as macular pigments whose importance in visual function, as of 2016, remains under clinical research. | 5 | Photochemistry |
The earliest measurements combining AFM with infrared spectroscopy were performed in 1999 by Hammiche et al. at the University of Lancaster in the United Kingdom, in an EPSRC-funded project led by M Reading and H M Pollock. Separately, Anderson at the Jet Propulsion Laboratory in the United States made a related measurement in 2000. Both groups used a conventional Fourier transform infrared spectrometer (FTIR) equipped with a broadband thermal source, the radiation was focused near the tip of a probe that was in contact with a sample. The Lancaster group obtained spectra by detecting the absorption of infrared radiation using a temperature sensitive thermal probe. Anderson took the different approach of using a conventional AFM probe to detect the thermal expansion. He reported an interferogram but not a spectrum; the first infrared spectrum obtained in this way was reported by Hammiche et al. in 2004: this represented the first proof that spectral information about a sample could be obtained using this approach.
Both of these early experiments used a broadband source in conjunction with an interferometer; these techniques could, therefore, be referred to as AFM-FTIR although Hammiche et al. coined the more general term photothermal microspectroscopy or PTMS in their first paper. PTMS has various subgroups; including techniques that measure temperature measure thermal expansion use broadband sources. use lasers excite the sample using evanescent waves, illuminate the sample directly from above etc. and different combinations of these. Fundamentally, they all exploit the photothermal effect. Different combinations of sources, methods, methods of detection and methods of illumination have benefits for different applications. Care should be taken to ensure that it is clear which form of PTMS is being used in each case. Currently there is no universally accepted nomenclature. The original technique dubbed AFM-IR that induced resonant motion in the probe using a Free Electron Laser has developed by exploiting the foregoing permutations so that it has evolved into various forms.
The pioneering experiments of Hammiche et al and Anderson had limited spatial resolution due to thermal diffusion - the spreading of heat away from the region where the infrared light was absorbed. The thermal diffusion length (the distance the heat spreads) is inversely proportional to the root of the modulation frequency. Consequently, the spatial resolution achieved by the early AFM-IR approaches was around one micron or more, due to the low modulation frequencies of the incident radiation created by the movement of the mirror in the interferometer. Also, the first thermal probes were Wollaston wire devices that were developed originally for Microthermal analysis (in fact PTMS was originally considered to be one of a family of microthermal techniques). The comparatively large size of these probes also limited spatial resolution. Bozec et al. and Reading et al. used thermal probes with nanoscale dimensions and demonstrated higher spatial resolution. Ye et al described a MEM-type thermal probe giving sub-100 nm spatial resolution, which they used for nanothermal analysis. The process of exploring laser sources began in 2001 by Hammiche et al when they acquired the first spectrum using a tuneable laser (see Resolution improvement with pulsed laser source).
A significant development was the creation by Reading et al. in 2001 of a custom interface that allowed measurements to be made while illuminating the sample from above; this interface focused the infrared beam to a spot of circa 500μm diameter, close to the theoretical maximum. The use of top-down or top-side illumination has the important benefit that samples of arbitrary thickness can be studied on arbitrary substrates. In many cases this can be done without any sample preparation. All subsequent experiments by Hammiche, Pollock, Reading and their co-workers were made using this type of interface including the instrument constructed by Hill et al. for nanoscale imaging using a pulsed laser. The work of the University of Lancaster group in collaboration with workers from the University of East Anglia led to the formation of a company, Anasys Instruments, to exploit this and related technologies (see Commercialization). | 3 | Analytical Chemistry |
Glaciers are large bodies of ice and snow formed in cold climates by processes involving the compaction of fallen snow. While snowy glaciers appear white from a distance, the long path lengths of internal reflected light causes glaciers to appear a deep blue when viewed up close and when shielded from direct ambient light.
Relatively small amounts of regular ice appear white because plenty of air bubbles are present, and also because small quantities of water appear to be colorless. In glaciers, on the other hand, the pressure causes the air bubbles, trapped in the accumulated snow, to be squeezed out increasing the density of the created ice. Large quantities of water appear cyan, therefore a large piece of compressed ice, or a glacier, would also appear cyan. | 3 | Analytical Chemistry |
*Johnson thermoelectric energy converter
*Thermoelectric (Peltier–Seebeck effect)
*Thermogalvanic cell
*Thermionic emission
*Thermotunnel cooling | 7 | Physical Chemistry |
In the 1989 Queen's Birthday Honours, Campbell was appointed an Officer of the Order of the British Empire, for services to science. | 3 | Analytical Chemistry |
* The reduction of nitrate to nitrogen in the presence of an acid (denitrification):
* The combustion of hydrocarbons, such as in an internal combustion engine, produces water, carbon dioxide, some partially oxidized forms such as carbon monoxide, and heat energy. Complete oxidation of materials containing carbon produces carbon dioxide.
* The stepwise oxidation of a hydrocarbon by oxygen, in organic chemistry, produces water and, successively: an alcohol, an aldehyde or a ketone, a carboxylic acid, and then a peroxide. | 9 | Geochemistry |
Bisson (2000) thought that because of coppers redness, luminosity and sound, it was valued by Africans. For many African cultures, the redness could be with life giving powers. Bisson (2000) also noted that the redness is a symbol of transition and it association with transition could explain why the wide use of copper in rituals in various African states. Also, its ability to reflect sunlight is suggested represent aggression and liminal boundaries between states, thus emphasizing its transformative properties. Finally, because of coppers use in bells and drums, it is thought to aid in the summoning spirits, when the instruments are played. | 8 | Metallurgy |
Within computational biology, an MA plot is an application of a Bland–Altman plot for visual representation of genomic data. The plot visualizes the differences between measurements taken in two samples, by transforming the data onto M (log ratio) and A (mean average) scales, then plotting these values. Though originally applied in the context of two channel DNA microarray gene expression data, MA plots are also used to visualise high-throughput sequencing analysis. | 1 | Biochemistry |
The amplitude of an action potential is often thought to be independent of the amount of current that produced it. In other words, larger currents do not create larger action potentials. Therefore, action potentials are said to be all-or-none signals, since either they occur fully or they do not occur at all. This is in contrast to receptor potentials, whose amplitudes are dependent on the intensity of a stimulus. In both cases, the frequency of action potentials is correlated with the intensity of a stimulus.
Despite the classical view of the action potential as a stereotyped, uniform signal having dominated the field of neuroscience for many decades, newer evidence does suggest that action potentials are more complex events indeed capable of transmitting information through not just their amplitude, but their duration and phase as well, sometimes even up to distances originally not thought to be possible. | 7 | Physical Chemistry |
While all the metals of antiquity but tin and lead occur natively, only gold and silver are commonly found as the native metal.
* Gold and silver occur frequently in their native form
* Mercury compounds are reduced to elemental mercury simply by low-temperature heating (500 °C).
* Tin and iron occur as oxides and can be reduced with carbon monoxide (produced by, for example, burning charcoal) at 900 °C.
* Copper and lead compounds can be roasted to produce the oxides, which are then reduced with carbon monoxide at 900 °C.
* Meteoric iron is often found as the native metal and it was the earliest source for iron objects known to humanity | 8 | Metallurgy |
In organic chemistry, the Myers deoxygenation reaction is an organic redox reaction that reduces an alcohol into an alkyl position by way of an arenesulfonylhydrazine as a key intermediate. This name reaction is one of four discovered by Andrew Myers that are named after him; this reaction and the Myers allene synthesis reaction involve the same type of intermediate. The other reactions are Myers' asymmetric alkylation and Myers-Saito Cycloaromatization.
:R–CHOH + HNNHSOAr → R–CHN(SOAr)NH → R–CHN=NH → R–CH + N
The reaction is a three-step one-pot process in which the alcohol first undergoes a Mitsunobu reaction with ortho-nitrobenzenesulfonylhydrazine in the presence of triphenylphosphine and diethyl azodicarboxylate. Unlike hydrazone-synthesis reactions, this reaction occurs on the same nitrogen of the hydrazine that has the arenesulfonyl substituent. Upon warming, this product undergoes an elimination of arylsulfinic acid to give an unstable diazene as a reactive intermediate. A radical process then promptly occurs with loss of dinitrogen to give the final alkyl product.
The alkyl-radical intermediate can instead undergo an intramolecular reaction with various other suitably-positioned functional groups within the molecule, such as alkenes or cyclopropanes, leading to alternate products.
If the diazene intermediate is able to undergo a sigmatropic rearrangement, this process occurs in preference to the simple radical reduction to give a hydrocarbon with a transposed π bond. For example, in the Myers allene synthesis, one of the two π bonds of the alkyne of a propargyl alcohol shifts, forming an allene. Likewise, the benzylic alcohol 1-naphthylmethanol rearranges to give a methylene-cyclohexyl product with loss of aromaticity. | 0 | Organic Chemistry |
The Herges compound (6 in the image below) was synthesized in several photochemical cycloaddition reactions from tetradehydrodianthracene 1 and the ladderane syn-tricyclooctadiene 2 as a substitute for cyclooctatetraene.
Intermediate 5 was a mixture of 2 isomers and the final product 6 a mixture of 5 isomers with different cis and trans configurations. One of them was found to have a C molecular symmetry corresponding to a Möbius aromatic and another Hückel isomer was found with C symmetry. Despite having 16 electrons in its pi system (making it a 4n antiaromatic compound) the Heilbronner prediction was borne out because according to Herges the Möbius compound was found to have aromatic properties. With bond lengths deduced from X-ray crystallography a HOMA value was obtained of 0.50 (for the polyene part alone) and 0.35 for the whole compound which qualifies it as a moderate aromat.
It was pointed out by Henry Rzepa that the conversion of intermediate 5 to 6 can proceed by either a Hückel or a Möbius transition state.
The difference was demonstrated in a hypothetical pericyclic ring opening reaction to cyclododecahexaene. The Hückel TS (left) involves 6 electrons (arrow pushing in red) with C molecular symmetry conserved throughout the reaction. The ring opening is disrotatory and suprafacial and both bond length alternation and NICS values indicate that the 6 membered ring is aromatic. The Möbius TS with 8 electrons on the other hand has lower computed activation energy and is characterized by C symmetry, a conrotatory and antarafacial ring opening and 8-membered ring aromaticity.
Another interesting system is the cyclononatetraenyl cation explored for over 30 years by Paul v. R. Schleyer et al. This reactive intermediate is implied in the solvolysis of the bicyclic chloride 9-deutero-9-chlorobicyclo[6.1.0]-nonatriene 1 to the indene dihydroindenol 4. The starting chloride is deuterated in only one position but in the final product deuterium is distributed at every available position. This observation is explained by invoking a twisted 8-electron cyclononatetraenyl cation 2 for which a NICS value of -13.4 (outsmarting benzene) is calculated. A more recent study, however, suggests that the stability of trans-CH is not much different in energy compared to a Hückel topology isomer. The same study suggested that for [13]annulenyl cation, the Möbius topology penta-trans'-CH is a global energy minimum and predicts that it may be directly observable.
In 2005 the same P. v. R. Schleyer questioned the 2003 Herges claim: he analyzed the same crystallographic data and concluded that there was indeed a large degree of bond length alternation resulting in a HOMA value of -0.02, a computed NICS value of -3.4 ppm also did not point towards aromaticity and (also inferred from a computer model) steric strain would prevent effective pi-orbital overlap.
A Hückel-Möbius aromaticity switch (2007) has been described based on a 28 pi-electron porphyrin system:
The phenylene rings in this molecule are free to rotate forming a set of conformers: one with a Möbius half-twist and another with a Hückel double-twist (a figure-eight configuration) of roughly equal energy.
In 2014, Zhu and Xia (with the help of Schleyer) synthesized a planar Möbius system that consisted of two pentene rings connected with an osmium atom. They formed derivatives where osmium had 16 and 18 electrons and determined that Craig–Möbius aromaticity is more important for the stabilization of the molecule than the metal's electron count. | 7 | Physical Chemistry |
A primary standard in metrology is a standard that is sufficiently accurate such that it is not calibrated by or subordinate to other standards. Primary standards are defined via other quantities like length, mass and time. Primary standards are used to calibrate other standards referred to as working standards. See Hierarchy of Standards. | 3 | Analytical Chemistry |
If an electrical potential is applied to an electrolytic solution, a positive ion will move towards the negative electrode and drag along an entourage of negative ions with it. The more concentrated the solution, the closer these negative ions are to the positive ion and thus the greater the resistance experienced by the positive ion. This influence on the speed of an ion is known as the "Asymmetry effect" because the ionic atmosphere moving around the ion is not symmetrical; the charge density behind is greater than in the front, slowing the motion of the ion. The time required to form a new ionic atmosphere on the right or time required for ionic atmosphere on the left to fade away is known as time of relaxation. The asymmetrization of ionic atmosphere does not occur in the case of Debye Falkenhagen effect due to high frequency dependence of conductivity. | 7 | Physical Chemistry |
Noting that digitisers and related electronics technology had significantly progressed since the inception of FTMW spectroscopy, B.H. Pate at the University of Virginia designed a spectrometer which retains many advantages of the Balle-Flygare FT-MW spectrometer while innovating in (i) the use of a high speed (>4 GS/s) arbitrary waveform generator to generate a "chirped" microwave polarisation pulse that sweeps up to 12 GHz in frequency in less than a microsecond and (ii) the use of a high speed (>40 GS/s) oscilloscope to digitise and Fourier transform the molecular free induction decay. The result is an instrument that allows the study of weakly bound molecules but which is able to exploit a measurement bandwidth (12 GHz) that is greatly enhanced compared with the Balle-Flygare FTMW spectrometer. Modified versions of the original CP-FTMW spectrometer have been constructed by a number of groups in the United States, Canada and Europe. The instrument offers a broadband capability that is highly complementary to the high sensitivity and resolution offered by the Balle-Flygare design. | 7 | Physical Chemistry |
Sundström studied chemistry at Umeå University, obtaining his PhD in 1977. During his study, he visited Bell Labs and worked under Peter Rentzepis. Upon his return to Sweden, he started building the first ultrafast spectroscopy laboratory in Scandinavia at Umeå University and later at Lund University in Sweden. In 1994, Sundström was appointed professor of Chemical Dynamics and head of the Chemical Physics Department at Lund University. His group's research centers on the photophysics and photochemical processes in model systems of natural and artificial photosynthetic light harvesting, such as bacteriochlorophyll, carotenoids, transition metal complexes, organic and perovskite solar cells.
Sundström was an editor of the journal Chemical Physics Letters. | 5 | Photochemistry |
The Marschalk reaction in chemistry is the sodium dithionite promoted reaction of a phenolic anthraquinone with an aldehyde to yield a substituted phenolic anthraquinone after the addition of acid.
The mechanism can be found in the book Named Reactions in Organic Chemistry, and its more intuitive version is provided below:
One of the first applications of this reaction was reported in 1985. | 0 | Organic Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.