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Concatenation of the tags, as developed in 2004, is different from that seen in SAGE. The cleavage of the tags with Xho1 and mixture of the different samples, followed by ligation, form the first concatenation step. The second step uses one of the restriction endonucleases with consensus to the adapter molecule attached to the 3’ end. They are again ligated, and PCR is performed to purify samples for the next joining. The concatenation is continued with the second restriction endonuclease, followed by the third and finally the fourth. This results in the concatamer formed by the six endonuclease ligations containing 32 tags, arranged 5’ to 5’ around the Xho1 site. In SAGE, concatenation takes place after ditags are formed and amplified by PCR. The linkers on the outside of the ditags are cleaved with the enzyme that provided their binding and these sticky end ditags are concatenated randomly and placed into a cloning vector. | 1 | Biochemistry |
Fibrin monomers are monomers of fibrin which are formed by the cleavage of fibrinogen by thrombin. Levels of fibrin monomers can be measured using blood tests and can serve as a marker of in vivo fibrinogenesis and coagulation activation. They may be useful in the evaluation hypercoagulability.
Levels of fibrin monomers may be increased with pregnancy and by estrogen-containing combined birth control pills. | 1 | Biochemistry |
RNA polymerase III can terminate transcription efficiently without the involvement of additional factors. The Pol III termination signal consists of a stretch of thymines (on the nontemplate strand) located within 40bp downstream from the 3' end of mature RNAs. The poly-T termination signal pauses Pol III | 1 | Biochemistry |
The word effusion derives from the Latin word, effundo, which means "shed, pour forth, pour out, utter, lavish, waste." | 7 | Physical Chemistry |
Demethylating agents are chemical substances that can inhibit methylation, resulting in the expression of the previously hypermethylated silenced genes (see Methylation#Cancer for more detail). Cytidine analogs such as 5-azacytidine (azacitidine) and 5-azadeoxycytidine (decitabine) are the most commonly used demethylating agents. They work by inhibiting DNA methyltransferases. Both compounds have been approved in the treatment of myelodysplastic syndrome (MDS) by Food and Drug Administration (FDA) in United States. Azacitidine and decitabine are marketed as Vidaza and Dacogen respectively. Azacitidine is the first drug to be approved by FDA for treating MDS and has been given orphan drug status. Procaine is a DNA-demethylating agent with growth-inhibitory effects in human cancer cells. There are many other demethylating agents that can be used to inhibit the growth of other diseases. | 1 | Biochemistry |
Convergent beam electron diffraction (CBED) is an electron diffraction technique where a convergent or divergent beam (conical electron beam) of electrons is used to study materials. | 3 | Analytical Chemistry |
Isoschizomers are pairs of restriction enzymes specific to the same recognition sequence. For example, SphI (CGTAC/G) and BbuI (CGTAC/G) are isoschizomers of each other. The first enzyme discovered which recognizes a given sequence is known as the prototype; all subsequently identified enzymes that recognize that sequence are isoschizomers. Isoschizomers are isolated from different strains of bacteria and therefore may require different reaction conditions.
In some cases, only one out of a pair of isoschizomers can recognize both the methylated as well as unmethylated forms of restriction sites. In contrast, the other restriction enzyme can recognize only the unmethylated form of the restriction site.
This property of some isoschizomers allows identification of methylation state of the restriction site while isolating it from a bacterial strain.
For example, the restriction enzymes HpaII and MspI are isoschizomers, as they both recognize the sequence 5-CCGG-3 when it is unmethylated. But when the second C of the sequence is methylated, only MspI can recognize it while HpaII cannot.
An enzyme that recognizes the same sequence but cuts it differently is a neoschizomer. Neoschizomers are a specific type (subset) of isoschizomer. For example, SmaI (CCC/GGG) and XmaI (C/CCGGG) are neoschizomers of each other. Similarly KpnI (GGTAC/C) and Acc65I (G/GTACC) are neoschizomers of each other.
An enzyme that recognizes a slightly different sequence, but produces the same ends is an isocaudomer. | 1 | Biochemistry |
Phenol red, sometimes labelled with a different name, such as "Guardex Solution #2", is used as a pH indicator in home swimming pool test kits.
Chlorine can result in the bleaching of the dye in the absence of thiosulfate to inhibit the oxidizing chlorine. High levels of bromine can convert phenol red to bromophenol red (dibromophenolsulfonephthalein, whose lowered pK results in an indicator with a range shifted in the acidic direction – water at pH 6.8 will appear to test at 7.5). Even higher levels of bromine (>20 ppm) can result in the secondary conversion of bromophenol red to bromophenol blue with an even lower pK, erroneously giving the impression that the water has an extremely high pH despite being dangerously low. | 3 | Analytical Chemistry |
CKLF like MARVEL transmembrane domain-containing 7 (i.e. CMTM7), previously termed chemokine-like factor superfamily 7 (i.e. CKLFSF7), is a protein that in humans is encoded by the CMTM7 gene. This gene, which is located in band 22 on the short (i.e. "p") arm of chromosome 3, and the protein that it encodes belong to the CKLF-like MARVEL transmembrane domain-containing family. Through the process of alternative splicing, the CMTM7 gene encodes two isoforms, CMTM7-v1 and CMTM7-v2, with CMTM7-v1 being the main form expressed and studied. CMTM7 proteins are widely expressed in normal human tissues. | 1 | Biochemistry |
Significant are also the extensions of the polaron concept: acoustic polaron, piezoelectric polaron, electronic polaron, bound polaron, trapped polaron, spin polaron, molecular polaron, solvated polarons, polaronic exciton, Jahn-Teller polaron, small polaron, bipolarons and many-polaron systems. These extensions of the concept are invoked, e. g., to study the properties of conjugated polymers, colossal magnetoresistance perovskites, high- superconductors, layered MgB superconductors, fullerenes, quasi-1D conductors, semiconductor nanostructures.
The possibility that polarons and bipolarons play a role in high- superconductors has renewed interest in the physical properties of many-polaron systems and, in particular, in their optical properties. Theoretical treatments have been extended from one-polaron to many-polaron systems.
A new aspect of the polaron concept has been investigated for semiconductor nanostructures: the exciton-phonon states are not factorizable into an adiabatic product Ansatz, so that a non-adiabatic treatment is needed. The non-adiabaticity of the exciton-phonon systems leads to a strong enhancement of the phonon-assisted transition probabilities (as compared to those treated adiabatically) and to multiphonon optical spectra that are considerably different from the Franck–Condon progression even for small values of the electron-phonon coupling constant as is the case for typical semiconductor nanostructures.
In biophysics Davydov soliton is a propagating along the protein α-helix self-trapped amide I excitation that is a solution of the Davydov Hamiltonian. The mathematical techniques that are used to analyze Davydovs soliton are similar to some that have been developed in polaron theory. In this context the Davydov soliton corresponds to a polaron that is (i) large so the continuum limit approximation in justified, (ii) acoustic because the self-localization arises from interactions with acoustic modes of the lattice, and (iii) weakly coupled' because the anharmonic energy is small compared with the phonon bandwidth.
It has been shown that the system of an impurity in a Bose–Einstein condensate is also a member of the polaron family. This allows the hitherto inaccessible strong coupling regime to be studied, since the interaction strengths can be externally tuned through the use of a Feshbach resonance. This was recently realized experimentally by two research groups.
The existence of the polaron in a Bose–Einstein condensate was demonstrated for both attractive and repulsive interactions, including the strong coupling regime and dynamically observed. | 7 | Physical Chemistry |
A contig (from contiguous) is a set of overlapping DNA segments that together represent a consensus region of DNA.
In bottom-up sequencing projects, a contig refers to overlapping sequence data (reads); in top-down sequencing projects, contig refers to the overlapping clones that form a physical map of the genome that is used to guide sequencing and assembly. Contigs can thus refer both to overlapping DNA sequences and to overlapping physical segments (fragments) contained in clones depending on the context. | 1 | Biochemistry |
Eutrophication can have the following ecological effects: increased biomass of phytoplankton, changes in macrophyte species composition and biomass, dissolved oxygen depletion, increased incidences of fish kills, loss of desirable fish species. | 2 | Environmental Chemistry |
In other instances, molecular interactions between gas molecules previously adsorbed on a solid surface form significant interactions with gas molecules in the gaseous phases. Hence, adsorption of gas molecules to the surface is more likely to occur around gas molecules that are already present on the solid surface, rendering the Langmuir adsorption isotherm ineffective for the purposes of modelling. This effect was studied in a system where nitrogen was the adsorbate and tungsten was the adsorbent by Paul Kisliuk (1922–2008) in 1957. To compensate for the increased probability of adsorption occurring around molecules present on the substrate surface, Kisliuk developed the precursor state theory, whereby molecules would enter a precursor state at the interface between the solid adsorbent and adsorbate in the gaseous phase. From here, adsorbate molecules would either adsorb to the adsorbent or desorb into the gaseous phase. The probability of adsorption occurring from the precursor state is dependent on the adsorbates proximity to other adsorbate molecules that have already been adsorbed. If the adsorbate molecule in the precursor state is in close proximity to an adsorbate molecule that has already formed on the surface, it has a sticking probability reflected by the size of the S constant and will either be adsorbed from the precursor state at a rate of k or will desorb into the gaseous phase at a rate of k'. If an adsorbate molecule enters the precursor state at a location that is remote from any other previously adsorbed adsorbate molecules, the sticking probability is reflected by the size of the S constant.
These factors were included as part of a single constant termed a "sticking coefficient", k, described below:
As S is dictated by factors that are taken into account by the Langmuir model, S can be assumed to be the adsorption rate constant. However, the rate constant for the Kisliuk model (R’) is different from that of the Langmuir model, as R’ is used to represent the impact of diffusion on monolayer formation and is proportional to the square root of the systems diffusion coefficient. The Kisliuk adsorption isotherm is written as follows, where θ is fractional coverage of the adsorbent with adsorbate, and t' is immersion time:
Solving for θ yields: | 7 | Physical Chemistry |
Particles can deposit in the nose, mouth, pharynx and larynx (the head airways region), deeper within the respiratory tract (from the trachea to the terminal bronchioles), or in the alveolar region. The location of deposition of aerosol particles within the respiratory system strongly determines the health effects of exposure to such aerosols. This phenomenon led people to invent aerosol samplers that select a subset of the aerosol particles that reach certain parts of the respiratory system.
Examples of these subsets of the particle-size distribution of an aerosol, important in occupational health, include the inhalable, thoracic, and respirable fractions. The fraction that can enter each part of the respiratory system depends on the deposition of particles in the upper parts of the airway. The inhalable fraction of particles, defined as the proportion of particles originally in the air that can enter the nose or mouth, depends on external wind speed and direction and on the particle-size distribution by aerodynamic diameter. The thoracic fraction is the proportion of the particles in ambient aerosol that can reach the thorax or chest region. The respirable fraction is the proportion of particles in the air that can reach the alveolar region. To measure the respirable fraction of particles in air, a pre-collector is used with a sampling filter. The pre-collector excludes particles as the airways remove particles from inhaled air. The sampling filter collects the particles for measurement. It is common to use cyclonic separation for the pre-collector, but other techniques include impactors, horizontal elutriators, and large pore membrane filters.
Two alternative size-selective criteria, often used in atmospheric monitoring, are PM and PM. PM is defined by ISO as particles which pass through a size-selective inlet with a 50% efficiency cut-off at 10 μm aerodynamic diameter and PM as particles which pass through a size-selective inlet with a 50% efficiency cut-off at 2.5 μm aerodynamic diameter. PM corresponds to the "thoracic convention" as defined in ISO 7708:1995, Clause 6; PM corresponds to the "high-risk respirable convention" as defined in ISO 7708:1995, 7.1. The United States Environmental Protection Agency replaced the older standards for particulate matter based on Total Suspended Particulate with another standard based on PM in 1987 and then introduced standards for PM (also known as fine particulate matter) in 1997. | 7 | Physical Chemistry |
A perfectly immobile fluorescent moiety when exited with polarized light will emit light which is also polarized. However, if a molecule is moving, it will tend to "scramble" the polarization of the light by radiating at a different direction from the incident light. | 1 | Biochemistry |
While the Kastle–Meyer test has been reported as being able to detect blood dilutions down to 1:10, there are a number of important limitations to the test. Chemical oxidants such as copper and nickel salts will cause the Kastle–Meyer reagent to turn pink before the addition of the hydrogen peroxide, thus it is vitally important to add the reagent first, then wait a few seconds, then add the hydrogen peroxide.
The Kastle–Meyer test has the same reaction with human blood as it does with any other hemoglobin-based blood, so a confirmatory test such as the Ouchterlony test must be performed to definitively conclude from which species the blood originated.
Color catalytic tests are very sensitive, but not specific. The positive color test alone should not be interpreted as positive proof of blood. A negative result is generally proof of the absence of detectable quantities of heme, however a false negative can be generated in the presence of a reducing agent. The test is unable to give specific evidence as to what is in the blood. | 3 | Analytical Chemistry |
Photolithographic methods are useful in patterning SAMs. SAMs are also useful in depositing nanostructures, because each adsorbate molecule can be tailored to attract two different materials. Current techniques utilize the head to attract to a surface, like a plate of gold. The terminal group is then modified to attract a specific material like a particular nanoparticle, wire, ribbon, or other nanostructure. In this way, wherever the SAM is patterned to a surface there will be nanostructures attached to the tail groups. One example is the use of two types of SAMs to align single wall carbon nanotubes, SWNTs. Dip pen nanolithography was used to pattern a 16-mercaptohexadecanoic acid (MHA)SAM and the rest of the surface was passivated with 1-octadecanethiol (ODT) SAM. The polar solvent that is carrying the SWNTs is attracted to the hydrophilic MHA; as the solvent evaporates, the SWNTs are close enough to the MHA SAM to attach to it due to Van der Waals forces. The nanotubes thus line up with the MHA-ODT boundary. Using this technique Chad Mirkin, Schatz and their co-workers were able to make complex two-dimensional shapes, a representation of a shape created is shown to the right.
Another application of patterned SAMs is the functionalization of biosensors. The tail groups can be modified so they have an affinity for cells, proteins, or molecules. The SAM can then be placed onto a biosensor so that binding of these molecules can be detected. The ability to pattern these SAMs allows them to be placed in configurations that increase sensitivity and do not damage or interfere with other components of the biosensor. | 6 | Supramolecular Chemistry |
GenePattern is a freely available computational biology open-source software package originally created and developed at the Broad Institute for the analysis of genomic data. Designed to enable researchers to develop, capture, and reproduce genomic analysis methodologies, GenePattern was first released in 2004. GenePattern is currently developed at the University of California, San Diego. | 1 | Biochemistry |
Resonance Raman spectroscopy explains the huge enhancement of Raman scattering intensity. Intermolecular and intramolecular charge transfers significantly enhance Raman spectrum peaks. In particular, the enhancement is huge for species adsorbing the metal surface due to the high-intensity charge transfers from the metal surface with wide band to the adsorbing species. This resonance Raman enhancement is dominant in SERS for species on small nanoclusters with considerable band gaps, because surface plasmon appears only in metal surface with near-zero band gaps. This chemical mechanism probably occurs in concert with the electromagnetic mechanism for metal surface. | 7 | Physical Chemistry |
Some industrial-level sprays (with teflon or leather needle packing, variable speed agitator in pressure pot, separate air and fluid pressure regulators) can also be used for Dimetcote. | 8 | Metallurgy |
Self-healing hydrogels are a specialized type of polymer hydrogel. A hydrogel is a macromolecular polymer gel constructed of a network of crosslinked polymer chains. Hydrogels are synthesized from hydrophilic monomers by either chain or step growth, along with a functional crosslinker to promote network formation. A net-like structure along with void imperfections enhance the hydrogel's ability to absorb large amounts of water via hydrogen bonding. As a result, hydrogels, self-healing alike, develop characteristic firm yet elastic mechanical properties. Self-healing refers to the spontaneous formation of new bonds when old bonds are broken within a material. The structure of the hydrogel along with electrostatic attraction forces drive new bond formation through reconstructive covalent dangling side chain or non-covalent hydrogen bonding. These flesh-like properties have motivated the research and development of self-healing hydrogels in fields such as reconstructive tissue engineering as scaffolding, as well as use in passive and preventive applications. | 7 | Physical Chemistry |
El-Shall was born in Cairo, Egypt, and spent his early life in Cairo. He is the grandson of Sheikh Mahmud Shaltut. He earned his B.S. degree in chemistry in 1976, and M.S. degree in physical chemistry in 1980 both from Cairo University. El-Shall earned his doctoral degree in physical chemistry from Georgetown University in 1985. | 7 | Physical Chemistry |
pVIII is the main coat protein of Ff phages. Peptides are usually fused to the N-terminus of pVIII. Usually peptides that can be fused to pVIII are 6-8 amino acids long. The size restriction seems to have less to do with structural impediment caused by the added section and more to do with the size exclusion caused by pIV during coat protein export. Since there are around 2700 copies of the protein on a typical phages, it is more likely that the protein of interest will be expressed polyvalently even if a phagemid is used. This makes the use of this protein unfavorable for the discovery of high affinity binding partners.
To overcome the size problem of pVIII, artificial coat proteins have been designed. An example is Weiss and Sidhus inverted artificial coat protein (ACP) which allows the display of large proteins at the C-terminus. The ACPs could display a protein of 20kDa, however, only at low levels (mostly only monovalently). | 1 | Biochemistry |
Tollens' reagent is also used to apply a silver mirror to glassware; for example the inside of an insulated vacuum flask. The underlying chemical process is called silver mirror reaction. The reducing agent is glucose (an aldehyde) for such applications. Clean glassware is required for a high quality mirror. To increase the speed of deposition, the glass surface may be pre-treated with tin(II) chloride stabilised in hydrochloric acid solution.
For applications requiring the highest optical quality, such as in telescope mirrors, the use of tin(II) chloride is problematic, since it creates nanoscale roughness and reduces the reflectivity.
Methods to produce telescope mirrors include additional additives to increase adhesion and film resilience, such as in Martin's method, which includes tartaric acid and ethanol. | 3 | Analytical Chemistry |
A 2011 study reported the detection of prions in urine from naturally and orally infected sheep with clinical scrapie agent and orally infected preclinical and infected white-tailed deer with clinical chronic wasting disease (CWD). This is the first report on prion detection of PrP from the urine of naturally or preclinical prion-diseased ovines or cervids.
A 2010 study demonstrated a moderate amount of protein misfolding cyclic amplification (PMCA) coupled to a novel SOFIA detection scheme, can be used to detect PrP in protease-untreated plasma from preclinical and clinical scrapie sheep, and white-tailed deer with chronic wasting disease, following natural and experimental infection. The disease-associated form of the prion protein (PrP), resulting from a conformational change of the normal (cellular) form of prion protein (PrP), is considered central to neuropathogenesis and serves as the only reliable molecular marker for prion disease diagnosis. While the highest levels of PrP are present in the CNS, the development of a reasonable diagnostic assay requires the use of body fluids which characteristically contains extremely low levels of PrP. PrP has been detected in the blood of sick animals by means of PMCA technology. However, repeated cycling over several days, which is necessary for PMCA of blood material, has been reported to result in decreased specificity (false positives). To generate an assay for PrP in blood that is both highly sensitive and specific, the researchers used limited serial PMCA (sPMCA) with SOFIA. They did not find any enhancement of sPMCA with the addition of polyadenylic acid, nor was it necessary to match the genotypes of the PrP and PrP sources for efficient amplification.
A 2009 study found SOFIA, in its current format, is capable of detecting less than 10 attogram (ag) of hamster, sheep and deer recombinant PrP. About 10 ag of PrP from 263K-infected hamster brains can be detected with similar lower limits of PrP detection from the brains of scrapie-infected sheep and deer infected with chronic wasting disease. These detection limits allow protease-treated and untreated material to be diluted beyond the point where PrP, nonspecific proteins or other extraneous material may interfere with PrP signal detection and/or specificity. This not only eliminates the issue of specificity of PrP detection, but also increases sensitivity, since the possibility of partial PrP proteolysis is no longer a concern. SOFIA will likely lead to early ante mortem detection of transmissible encephalopathies and is also amenable for use with additional target amplification protocols. SOFIA represents a sensitive means for detecting specific proteins involved in disease pathogenesis and/or diagnosis that extends beyond the scope of the transmissible spongiform encephalopathies. | 1 | Biochemistry |
For black body emitters where photon recirculation is achieved via filters, Planck's law states that a black body emits light with a spectrum given by:
where I′ is the light flux of a specific wavelength, λ, given in units of 1 m⋅s. h is the Planck constant, k is the Boltzmann constant, c is the speed of light, and T is the emitter temperature. Thus, the light flux with wavelengths in a specific range can be found by integrating over the range. The peak wavelength is determined by the temperature, T based on Wien's displacement law:
where b is Wien's displacement constant. For most materials, the maximum temperature an emitter can stably operate at is about 1800 °C. This corresponds to an intensity that peaks at or an energy of ~0.75 eV. For more reasonable operating temperatures of 1200 °C, this drops to ~0.5 eV. These energies dictate the range of bandgaps that are needed for practical TPV converters (though the peak spectral power is slightly higher). Traditional PV materials such as Si (1.1 eV) and GaAs (1.4 eV) are substantially less practical for TPV systems, as the intensity of the black body spectrum is low at these energies for emitters at realistic temperatures. | 7 | Physical Chemistry |
Breaking C–F bonds is of interest as a way to decompose and destroy organofluorine "forever chemicals" such as PFOA and perfluorinated compounds (PFCs). Candidate methods include catalysts, such as platinum atoms; photocatalysts; UV, iodide, and sulfite, radicals; etc. | 0 | Organic Chemistry |
The ability of pioneer factors to respond to extracellular signals to differentiate cell type has been studied as a potential component of hormone-dependent cancers. Hormones such as estrogen and IGFI are shown to increase pioneer factor concentration leading to a change in transcription. Known pioneer factors such as FoxA1, PBX1, TLE, AP2, GATA factors 2/3/4, and PU.1 have been associated with hormone-dependent cancer . FoxA1 is necessary for estrogen and androgen mediated hepatocarcinogenesis and is a defining gene for ER luminal breast cancer, as is another pioneer factor GATA3. FOXA1 particularly is expressed in 90% of breast cancer metastases and 89% of metastic prostate cancers. In the breast cancer cell line, MCF-7, it was found that FoxA1 was bound to 50% of estrogen receptor binding sites independent of estrogen presence. High expression of pioneer factors is associated with poor prognosis with the exception of breast cancer where FoxA1 is associated with a stronger outcome.
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The correlation between pioneer factors and cancer has led to prospective therapeutic targeting. In knockdown studies in the MCF-7 breast cancer cell line it was found that decreasing pioneer factors FoxA1 and AP2 decreased ER signalling. Other fork head proteins have been associated with cancer, including FoxO3 and FoxM that repress the cell survival pathways Ras and PPI3K/AKT/IKK. Drugs such as Paclitaxel, Imatinib, and doxorubicin which activate FoxO3a or its targets are being used. Modification to modulate related factors with pioneer activity is a topic of interest in the early stages as knocking down pioneer factors may have toxic effects through alteration of the lineage pathways of healthy cells. | 1 | Biochemistry |
Public Analyst Laboratories in Cork, Dublin and Galway provide an analytical service to the Food Safety Authority. | 2 | Environmental Chemistry |
PKA phosphorylates proteins that have the motif Arginine-Arginine-X-Serine exposed, in turn (de)activating the proteins. Many possible substrates of PKA exist; a list of such substrates is available and maintained by the NIH.
As protein expression varies from cell type to cell type, the proteins that are available for phosphorylation will depend upon the cell in which PKA is present. Thus, the effects of PKA activation vary with cell type: | 1 | Biochemistry |
The light harvesting materials employed in biological photovoltaic devices can be categorised by their complexity; more complex materials are typically less efficient but more robust. | 7 | Physical Chemistry |
Conjugated systems form the basis of chromophores, which are light-absorbing parts of a molecule that can cause a compound to be colored. Such chromophores are often present in various organic compounds and sometimes present in polymers that are colored or glow in the dark. Chromophores often consist of a series of conjugated bonds and/or ring systems, commonly aromatic, which can include C–C, C=C, C=O, or N=N bonds.
Conjugated chromophores are found in many organic compounds including azo dyes (also artificial food additives), compounds in fruits and vegetables (lycopene and anthocyanidins), photoreceptors of the eye, and some pharmaceutical compounds such as the following:
Conjugated polymer nanoparticles (PDots) are assembled from hydrophobic fluorescent conjugated polymers, along with amphiphilic polymers to provide water solubility. Pdots are important labels for single-molecule fluorescence microscopy, based on high brightness, lack of blinking or dark fraction, and slow photobleaching. | 7 | Physical Chemistry |
Free hydride anions exist only under extreme conditions and are not invoked for homogeneous solution. Instead, many compounds have hydrogen centres with hydridic character.
Aside from electride, the hydride ion is the simplest possible anion, consisting of two electrons and a proton. Hydrogen has a relatively low electron affinity, 72.77 kJ/mol and reacts exothermically with protons as a powerful Lewis base.
The low electron affinity of hydrogen and the strength of the H–H bond () means that the hydride ion would also be a strong reducing agent | 0 | Organic Chemistry |
Because of limited computing power, specialized simulation models have been developed for various purposes depending on the time scale:
a) Electronic scale simulations (density function theory, ab-initio molecular dynamics): sub-atomic length scale in femto-second time scale
b) Atomic scale simulations (MD): nano to micro-meter length scale in nano-second time scale
c) Film scale simulation (KMC): micro-meter length scale in micro to hour time scale.
d) Reactor scale simulation (phase field model): meter length scale in year time scale.
Multiscale modeling techniques have also been developed to deal with overlapping time scales. | 7 | Physical Chemistry |
Chromosome jumping enables two ends of a DNA sequence to be cloned without the middle section. Genomic DNA may be partially digested using restriction endonuclease and with the aid of DNA ligase, the fragments are circularized at low concentration. From a known sequence, a primer is designed to sequence across the circularized junction. This primer is used to jump 100 kb-300 kb intervals: a sequence 100 kb away would have come near the known sequence on circularization, it permits jumping and sequencing in an alternative manner. Thus, sequences not reachable by chromosome walking can be sequenced. Chromosome walking can also be used from the new jump position (in either direction) to look for gene-like sequences, or additional jumps can be used to progress further along the chromosome. Combining chromosome jumping to chromosome walking through the chromosome allows bypassing repetitive DNA for the search of the target gene. | 1 | Biochemistry |
* As a mordant when performing a Gram stain. It is applied for 1 minute after staining with crystal violet, but before ethanol to ensure that gram positive organisms' peptidoglycan remains stained, easily identifying it as a gram positive in microscopy.
* This solution is used as an indicator test for the presence of starches in organic compounds, with which it reacts by turning a dark-blue/black. Elemental iodine solutions like Lugols will stain starches due to iodines interaction with the coil structure of the polysaccharide. Starches include the plant starches amylose and amylopectin and glycogen in animal cells. Lugol's solution will not detect simple sugars such as glucose or fructose. In the pathologic condition amyloidosis, amyloid deposits (i.e., deposits that stain like starch, but are not) can be so abundant that affected organs will also stain grossly positive for the Lugol reaction for starch.
* It can be used as a cell stain, making the cell nuclei more visible and for preserving phytoplankton samples.
* Lugol's solution can also be used in various experiments to observe how a cell membrane uses osmosis and diffusion.
* Lugols solution is also used in the marine aquarium industry. Lugols solution provides a strong source of free iodine and iodide to reef inhabitants and macroalgae. Although the solution is thought to be effective when used with stony corals, systems containing xenia and soft corals are assumed to be particularly benefited by the use of Lugols solution. Used as a dip for stony and soft or leather corals, Lugols may help rid the animals of unwanted parasites and harmful bacteria. The solution is thought to foster improved coloration and possibly prevent bleaching of corals due to changes in light intensity, and to enhance coral polyp expansion. The blue colors of Acropora spp. are thought to be intensified by the use of potassium iodide. Specially packaged supplements of the product intended for aquarium use can be purchased at specialty stores and online. | 3 | Analytical Chemistry |
The glyoxylate cycle, a variation of the tricarboxylic acid cycle, is an anabolic pathway occurring in plants, bacteria, protists, and fungi. The glyoxylate cycle centers on the conversion of acetyl-CoA to succinate for the synthesis of carbohydrates. In microorganisms, the glyoxylate cycle allows cells to use two carbons (C2 compounds), such as acetate, to satisfy cellular carbon requirements when simple sugars such as glucose or fructose are not available. The cycle is generally assumed to be absent in animals, with the exception of nematodes at the early stages of embryogenesis. In recent years, however, the detection of malate synthase (MS) and isocitrate lyase (ICL), key enzymes involved in the glyoxylate cycle, in some animal tissue has raised questions regarding the evolutionary relationship of enzymes in bacteria and animals and suggests that animals encode alternative enzymes of the cycle that differ in function from known MS and ICL in non-metazoan species.
Plants as well as some algae and bacteria can use acetate as the carbon source for the production of carbon compounds. Plants and bacteria employ a modification of the TCA cycle called the glyoxylate cycle to produce four carbon dicarboxylic acid from two carbon acetate units. The glyoxylate cycle bypasses the two oxidative decarboxylation reactions of the TCA cycle and directly converts isocitrate through isocitrate lyase and malate synthase into malate and succinate.
The glyoxylate cycle was discovered in 1957 at the University of Oxford by Sir Hans Kornberg and his mentor Hans Krebs, resulting in a Nature paper Synthesis of Cell Constituents from C-Units by a Modified Tricarboxylic Acid Cycle. | 1 | Biochemistry |
Once the presence of a carbonyl group has been identified using 2,4-dinitrophenylhydrazine (also known as Bradys reagent or 2,4-DNPH or 2,4-DNP), Tollens reagent can be used to distinguish ketone vs aldehyde. Tollens' reagent gives a negative test for most ketones, with alpha-hydroxy ketones being one exception.
The test rests on the premise that aldehydes are more readily oxidized compared with ketones; this is due to the carbonyl-containing carbon in aldehydes having attached hydrogen. The diamine silver(I) complex in the mixture is an oxidizing agent and is the essential reactant in Tollens' reagent. The test is generally carried out in a test tube in a warm water bath.
In a positive test, the diamine silver(I) complex oxidizes the aldehyde to a carboxylate ion and in the process is reduced to elemental silver and aqueous ammonia. The elemental silver precipitates out of solution, occasionally onto the inner surface of the reaction vessel, giving a characteristic "silver mirror". The carboxylate ion on acidification will give its corresponding carboxylic acid. The carboxylic acid is not directly formed in the first place as the reaction takes place under alkaline conditions. The ionic equations for the overall reaction are shown below; R refers to an alkyl group.
Tollens' reagent can also be used to test for terminal alkynes (). A white precipitate of the acetylide () is formed in this case. Another test relies on reaction of the furfural with phloroglucinol to produce a colored compound with high molar absorptivity. It also gives a positive test with hydrazines, hydrazones, α-hydroxy ketones and 1,2-dicarbonyls.
Both Tollens reagent and Fehlings reagent give positive results with formic acid. | 3 | Analytical Chemistry |
Negative thermal expansion is usually observed in non-close-packed systems with directional interactions (e.g. ice, graphene, etc.) and complex compounds (e.g. , , beta-quartz, some zeolites, etc.). However, in a paper, it was shown that negative thermal expansion (NTE) is also realized in single-component close-packed lattices with pair central force interactions. The following sufficient condition for potential giving rise to NTE behavior is proposed for the interatomic potential, , at the equilibrium distance :
where is shorthand for the third derivative of the interatomic potential at the equilibrium point:
This condition is (i) necessary and sufficient in 1D and (ii) sufficient, but not necessary in 2D and 3D. An approximate necessary and sufficient condition is derived in a paper
where is the space dimensionality. Thus in 2D and 3D negative thermal expansion in close-packed systems with pair interactions is realized even when the third derivative of the potential is zero or even negative. Note that one-dimensional and multidimensional cases are qualitatively different. In 1D thermal expansion is caused by anharmonicity of interatomic potential only. Therefore, the sign of thermal expansion coefficient is determined by the sign of the third derivative of the potential. In multidimensional case the geometrical nonlinearity is also present, i.e. lattice vibrations are nonlinear even in the case of harmonic interatomic potential. This nonlinearity contributes to thermal expansion. Therefore, in multidimensional case both and are present in the condition for negative thermal expansion. | 7 | Physical Chemistry |
In the field of clinical imaging, with sufficient exposure, solarization of certain screen-film systems can occur which obscures details within the X-ray image and degrades the accuracy of the diagnosis. Even though degradation can occur this was found to be a rare phenomenon. | 7 | Physical Chemistry |
The technique is applied to conversions that proceed via unimolecular pathways. 2-Acetoxydioxane, when heated at 425 °C converts to the highly reactive dioxene, via loss of acetic acid.
2-Furonitrile has been prepared by flash-dehydration of 2-furoic acid amide or oxime over molecular sieves. The strained ring benzocyclobutenone has been prepared by FVP from a simple benzoyl chloride precursor. | 0 | Organic Chemistry |
The measurement volume is a convolution of illumination (excitation) and detection geometries, which result from the optical elements involved. The resulting volume is described mathematically by the point spread function (or PSF), it is essentially the image of a point source. The PSF is often described as an ellipsoid (with unsharp boundaries) of few hundred nanometers in focus diameter, and almost one micrometer along the optical axis. The shape varies significantly (and has a large impact on the resulting FCS curves) depending on the quality of the optical elements (it is crucial to avoid astigmatism and to check the real shape of the PSF on the instrument). In the case of confocal microscopy, and for small pinholes (around one Airy unit), the PSF is well approximated by Gaussians:
where is the peak intensity, r and z are radial and axial position, and and are the radial and axial radii, and . This Gaussian form is assumed in deriving the functional form of the autocorrelation.
Typically is 200–300 nm, and is 2–6 times larger. One common way of calibrating the measurement volume parameters is to perform FCS on a species with known diffusion coefficient and concentration (see below). Diffusion coefficients for common fluorophores in water are given in a later section.
The Gaussian approximation works to varying degrees depending on the optical details, and corrections can sometimes be applied to offset the errors in approximation. | 7 | Physical Chemistry |
Sepro designs and builds modular and mobile processing plants for a wide range of mineral applications. Complete plants can be assembled using Sepro manufactured equipment along with equipment from third-party vendors and sub-contractors.
Sepro Mobile Plants are designed to be easily re-locatable as they are mounted on road transportable custom built trailer assemblies. These include the Sepro Mobile Mill Plant and Sepro Mobile Flotation Plant, both of which were installed by Banks Island Gold Ltd at the company's Yellow Giant Gold Property on the coast of British Columbia. They can be designed to encompass a wide variety of process options from crushing through to the final concentrate collection.
Sepro Modular and Skid Mounted Plants are engineered around structural elements that are simple and easy to erect on site. These plants can be designed with larger equipment for higher tonnage applications than that of the Sepro Mobile Plants. One example is a 360 TPD Gold Processing Plant Sepro supplied to ProEurasia LCC for the Vladimirskaya Project in Russia. This included milling, gravity and smelting circuits.
Sepro also offers standard process modules which are designed around a single recovery or procession option. Dense Media Separation and Gravity Concentration are two examples of standard Sepro process modules. | 8 | Metallurgy |
Mutations that affect the functioning of the integrated stress response may have debilitating effects on cells. For example, cells lacking the ATF4 gene are unable to elicit proper gene expression in response to stressors. This results in cells exhibiting issues with amino acid transport, glutathione biosynthesis and oxidative stress resistance. When a mutation inhibits the functioning of PERK, endogenous peroxides accumulate when the cell experiences endoplasmic reticulum stress. In mice and humans lacking PERK, there have been observed destruction of secretory cells undergoing high endoplasmic reticulum stress. | 1 | Biochemistry |
Hollywood is a RNA splicing database containing data for the splicing of orthologous genes in different species. | 1 | Biochemistry |
Corrin is a heterocyclic compound. Although not known to exist on its own, the molecule is of interest as the parent macrocycle related to the cofactor and chromophore in vitamin B. Its name reflects that it is the "core" of vitamin B (cobalamins). Compounds with a corrin core are known as "corrins".
There are two chiral centres, which in natural compounds like cobalamin have the same stereochemistry. | 1 | Biochemistry |
Isodesmosine is a lysine derivative found in elastin. Isodesmosine is an isomeric pyridinium-based amino acid resulting from the condensation of four lysine residues between elastin proteins by lysyl-oxidase. These represent ideal biomarkers for monitoring elastin turnover because these special cross-links are only found in mature elastin in mammals. | 1 | Biochemistry |
Isolation of the FeMo cofactor from nitrogenase is done through centrifugal sedimentation of nitrogenase into the MoFe protein and the Fe protein. The FeMo cofactor is extracted by treating the MoFe protein with acids. The first extraction is done with N,N-dimethylformamide and the second by a mixture of N-methylformamide and NaHPO before final sedimentation by centrifugation. | 7 | Physical Chemistry |
The G-less cassette technique is used to determine promoter strength beyond basal levels of transcription (i.e. in the presence of transcription activators or transcription factors). For example, to measure the effects of a TATA box consensus sequence modification in Saccharomyces cerevisiae in the presence of TFIID, G-less cassettes were implemented to measure the relative strength of each promoter. | 1 | Biochemistry |
Negative-sense (3′-to-5′) viral RNA is complementary to the viral mRNA, thus a positive-sense RNA must be produced by an RNA-dependent RNA polymerase from it prior to translation. Like DNA, negative-sense RNA has a nucleotide sequence complementary to the mRNA that it encodes; also like DNA, this RNA cannot be translated into protein directly. Instead, it must first be transcribed into a positive-sense RNA that acts as an mRNA. Some viruses (e.g. influenza viruses) have negative-sense genomes and so must carry an RNA polymerase inside the virion. | 1 | Biochemistry |
Masking is the process of applying the maskant material to the surface to ensure that only desired areas are etched. Liquid maskants may be applied via dip-masking, in which the part is dipped into an open tank of maskant and then the maskant dried. Maskant may also be applied by flow coating: liquid maskant is flowed over the surface of the part. Certain conductive maskants may also be applied by electrostatic deposition, where electrical charges are applied to particles of maskant as it is sprayed onto the surface of the material. The charge causes the particles of maskant to adhere to the surface. | 8 | Metallurgy |
The Journal of Photochemistry and Photobiology C: Photochemistry Reviews is abstracted and indexed in BIOSIS Previews, Chemistry & Chemical Engineering, Chemistry Citation Index, Current Contents/Physical, Chemical & Earth Sciences, Science Citation Index and Scopus. According to the Journal Citation Reports, the journal has a 2014 impact factor of 16.094. | 5 | Photochemistry |
Instrumentation of supercritical fluid chromatography SFC has a similar setup to an HPLC instrument. The stationary phases are similar, and are packed inside similar column types. However, there are special features in these systems, because of the need to keep the mobile phase at supercritical fluidic state over the entire system. Temperature is critical to keep the fluids in a supercritical state, so there should be a heat control tool in the system, similar to that of GC. Also, there should be a precise pressure control mechanism, a restrictor to keep the pressure above a certain point, because pressure is another essential parameter to keep the mobile phase in a supercritical fluid state, so it is kept at the required minimal level. A microprocessor mechanism is placed in the instrument for SFC. This unit collects data for pressure, oven temperature, and detector performance to control the related pieces of the instrument.
CO utilized in carbon dioxide dedicated pumps, which require that the incoming CO and pump heads be kept cold, in order to maintain the carbon dioxide at a temperature and pressure fit for supercritical fluidic state, where it can be effectively metered at a specified flow rate range. The CO subsequently becomes supercritical fluid throughout the injector and the column oven, when the temperature and pressure it is subjected to, are raised above the critical point of the liquid, thus the supercritical state is achieved.
Supercritical fluids combine useful properties of gas and liquid phases, as it can behave like both a gas and a liquid in various aspects. A supercritical fluid provides a gas-like characteristic when it fills a container and it takes the shape of the container. The motion and kinetics of the molecules are quite similar to gas molecules. On the other hand, a supercritical fluid behaves like a liquid because its density property is near liquid; thus, a supercritical fluid shows a similarity to the dissolving effect of a liquid. The result is that one can load masses, similar to those used in HPLC, on column per injection, and still maintain a high chromatographic efficiency similar to those attained in GC. Typically, gradient elution is employed in analytical SFC using a polar co-solvent such as methanol, possibly with a weak acid or base at low concentrations ~1%. The apparent plate count per analysis can be observed to exceed 500K plates per meter routinely with 5 um stationary phases. The operator uses software to set mobile phase flow rate, co-solvent composition, system back pressure and column oven temperature, which must exceed 40 °C for supercritical conditions needed to be achieved with CO. In addition, SFC provides an additional control parameter – pressure – by using an automated static and dynamic back pressure regulator. From an operational standpoint, SFC is as simple and robust as HPLC, but fraction collection is more convenient because the primary mobile phase evaporates leaving only the analyte and a small volume of polar co-solvent. If the outlet CO is captured, it can be re-compressed and recycled, allowing for >90% reuse of CO.
Similar to HPLC, SFC uses a variety of detection methods including UV/VIS, mass spectrometry, FID (unlike HPLC) and evaporative light scattering. | 3 | Analytical Chemistry |
A provitamin is a substance that may be converted within the body to a vitamin. The term previtamin is a synonym.
The term "provitamin" is used when it is desirable to label a substance with little or no vitamin activity, but which can be converted to an active form by normal metabolic processes. | 1 | Biochemistry |
In addition to diagnosis and classification, EPIC-seq holds promise in predicting patient response to various cancer therapies, including immune-checkpoint inhibition (ICI). By analyzing changes in gene expression patterns captured through EPIC-seq, researchers can forecast patient response to PD-(L)1 blockade therapy, which can provide great help in personalized cancer treatment. EPIC-seq-derived indices have shown significant correlation with treatment response, offering potential prognostic markers for therapy outcome prediction. | 1 | Biochemistry |
In organic synthesis, vinyl oxocarbenium ions (structure on right) can be utilized in a wide range of cycloaddition reactions. They are commonly employed as dienophiles in the Diels–Alder reaction. An electron withdrawing ketone is often added to the dienophile to increase the rate of the reaction, and these ketones are often converted to vinyl oxocarbenium ions during the reaction It is not clear that an oxocarbenium ion necessarily will form, but Roush and co-workers demonstrated the oxocarbenium intermediate in the cyclization shown below. Two products were observed in this reaction, which could only form if the oxocarbenium ring is present as an intermediate. [4+3], [2+2], [3+2] and [5+2] cycloadditions with oxocarbenium intermediates have also been reported. | 0 | Organic Chemistry |
The absorption of flutamide is complete upon oral ingestion. Food has no effect on the bioavailability of flutamide. Steady-state levels of hydroxyflutamide, the active form of flutamide, are achieved after 2 to 4 days administration. Levels of hydroxyflutamide are approximately 50-fold higher than those of flutamide at steady-state.
The plasma protein binding of flutamide and hydroxyflutamide are high; 94 to 96% and 92 to 94%, respectively. Flutamide and its metabolite hydroxyflutamide are known to be transported by the multidrug resistance-associated protein 1 (MRP1; ABCC1).
Flutamide is metabolized by CYP1A2 (via α-hydroxylation) in the liver during first-pass metabolism to its main metabolite hydroxyflutamide (which accounts for 23% of an oral dose of flutamide one hour post-ingestion), and to at least five other, minor metabolites. Flutamide has at least 10 inactive metabolites total, including 4-nitro-3-fluoro-methylaniline.
Flutamide is excreted in various forms in the urine, the primary form being 2-amino-5-nitro-4-(trifluoromethyl)phenol.
Flutamide and hydroxyflutamide have elimination half-lives of 4.7 hours and 6 hours in adults, respectively. However, the half-life of hydroxyflutamide is extended to 8 hours after a single dose and to 9.6 hours at steady state) in elderly individuals. The elimination half-lives of flutamide and hydroxyflutamide are regarded as too short to allow for once-daily dosing, and for this reason, flutamide is instead administered three times daily at 8-hour intervals. In contrast, the newer NSAAs nilutamide, bicalutamide, and enzalutamide all have much longer half-lives, and this allows for once-daily administration in their cases. | 4 | Stereochemistry |
In analytical chemistry, ashing or ash content determination is the process of mineralization by complete combustion for preconcentration of trace substances prior to a chemical analysis, such as chromatography, or optical analysis, such as spectroscopy. | 3 | Analytical Chemistry |
The term "pyrometer" was coined in the 1730s by Pieter van Musschenbroek, better known as the inventor of the Leyden jar. His device, of which no surviving specimens are known, may be now called a dilatometer because it measured the dilation of a metal rod.
The earliest example of a pyrometer thought to be in existence is the [https://collection.sciencemuseumgroup.org.uk/objects/co1668/hindleys-pyrometer-pyrometers-dilatometers Hindley Pyrometer] held by the London Science Museum, dating from 1752, produced for the Royal collection. The pyrometer was a well known enough instrument that it was described in some detail by the mathematician Euler in 1760.
Around 1782 potter Josiah Wedgwood invented a different type of pyrometer (or rather a pyrometric device) to measure the temperature in his kilns, which first compared the color of clay fired at known temperatures, but was eventually upgraded to measuring the shrinkage of pieces of clay, which depended on kiln temperature (see Wedgwood scale for details). Later examples used the expansion of a metal bar.
In 1860s–1870s brothers William and Werner Siemens developed a platinum resistance thermometer, initially to measure temperature in undersea cables, but then adapted for measuring temperatures in metallurgy up to 1000 °C, hence deserving a name of a pyrometer.
The first disappearing-filament pyrometer was built by L. Holborn and F. Kurlbaum in 1901. This device had a thin electrical filament between an observer's eye and an incandescent object. The current through the filament was adjusted until it was of the same colour (and hence temperature) as the object, and no longer visible; it was calibrated to allow temperature to be inferred from the current.
The temperature returned by the vanishing-filament pyrometer and others of its kind, called brightness pyrometers, is dependent on the emissivity of the object. With greater use of brightness pyrometers, it became obvious that problems existed with relying on knowledge of the value of emissivity. Emissivity was found to change, often drastically, with surface roughness, bulk and surface composition, and even the temperature itself.
To get around these difficulties, the ratio or two-color pyrometer was developed. They rely on the fact that Plancks law, which relates temperature to the intensity of radiation emitted at individual wavelengths, can be solved for temperature if Plancks statement of the intensities at two different wavelengths is divided. This solution assumes that the emissivity is the same at both wavelengths and cancels out in the division. This is known as the gray-body assumption. Ratio pyrometers are essentially two brightness pyrometers in a single instrument. The operational principles of the ratio pyrometers were developed in the 1920s and 1930s, and they were commercially available in 1939.
As the ratio pyrometer came into popular use, it was determined that many materials, of which metals are an example, do not have the same emissivity at two wavelengths. For these materials, the emissivity does not cancel out, and the temperature measurement is in error. The amount of error depends on the emissivities and the wavelengths where the measurements are taken. Two-color ratio pyrometers cannot measure whether a material's emissivity is wavelength-dependent.
To more accurately measure the temperature of real objects with unknown or changing emissivities, multiwavelength pyrometers were envisioned at the US National Institute of Standards and Technology and described in 1992. Multiwavelength pyrometers use three or more wavelengths and mathematical manipulation of the results to attempt to achieve accurate temperature measurement even when the emissivity is unknown, changing or differs according to wavelength of measurement. | 8 | Metallurgy |
High-valent iron commonly denotes compounds and intermediates in which iron is found in a formal oxidation state > 3 that show a number of bonds > 6 with a coordination number ≤ 6. The term is rather uncommon for hepta-coordinate compounds of iron. It has to be distinguished from the terms hypervalent and hypercoordinate, as high-valent iron compounds neither necessarily violate the 18-electron rule nor necessarily show coordination numbers > 6. The ferrate(VI) ion [FeO] was the first structure in this class synthesized. The synthetic compounds discussed below contain highly oxidized iron in general, as the concepts are closely related. | 7 | Physical Chemistry |
The ortho effect occurs in Diels-Alder reactions when the Z-substituted dienophiles react with 1-substituted butadienes to give 3,4-disubstituted cyclohexenes, independent of the nature of diene substituents. | 4 | Stereochemistry |
The size of the substituents interacting at the 1 and 3 positions of an allylic group is often the largest factor contributing to the magnitude of the strain. As a rule, larger substituents will create a larger magnitude of strain. Proximity of bulky groups causes an increase in repulsive Van der Waals forces. This quickly increases the magnitude of the strain. The interactions between the hydrogen and methyl group in the allylic system cause a change in enthalpy equal to 3.6 kcal/mol. The strain energy in this system was calculated to be 7.6 kcal/mol due to interactions between the two methyl groups. | 4 | Stereochemistry |
British Organic Geochemical Society (BOGS) is an organization that aims to promote, exchange and discuss all aspects of organic geochemistry. It also aims to facilitate academic and social networking between British organic geochemists. | 9 | Geochemistry |
Featuring divalent carbon, vinylidenes are unusual species in organic chemistry. They are unstable as solids or liquids but can be generated as stable dilute gases. The parent member of this series is methylidenecarbene. With the formula :C=CH), it is a carbene. | 0 | Organic Chemistry |
The Achmatowicz reaction, also known as the Achmatowicz rearrangement, is an organic synthesis in which a furan is converted to a dihydropyran. In the original publication by the Polish Chemist Osman Achmatowicz Jr. (b. 20 December 1931 in Vilnius) in 1971 furfuryl alcohol is reacted with bromine in methanol to 2,5-dimethoxy-2,5-dihydrofuran which rearranges to the dihydropyran with dilute sulfuric acid. Additional reaction steps, alcohol protection with methyl orthoformate and boron trifluoride) and then ketone reduction with sodium borohydride produce an intermediate from which many monosaccharides can be synthesised.
The Achmatowitz protocol has been used in total synthesis, including those of desoxoprosophylline, pyrenophorin Recently it has been used in diversity oriented synthesis
and in enantiomeric scaffolding. | 0 | Organic Chemistry |
Photodissociation is used to detect electromagnetic activity of ions, compounds, and clusters when spectroscopy cannot be directly applied. Low concentrations of analyte can be one inhibiting factor to spectroscopy esp. in the gas phase. Mass spectrometers, time-of-flight and ion cyclotron resonance have been used to study hydrated ion clusters. Instruments are able to use ESI to effectively form hydrated ion clusters. Laser ablation and corona discharge have also been used to form ion clusters. Complexes are directed through a mass spectrometer where they are irradiated with infrared light, Nd:YAG laser. | 7 | Physical Chemistry |
The BASIC assembly strategy was developed in 2015 and sought to address the limitations of previous assembly techniques, incorporating six key concepts from them: standard reusable parts; single-tier format (all parts are in the same format and are assembled using the same process); idempotent cloning; parallel (multipart) DNA assembly; size independence; automatability.
DNA parts and linker design
The DNA parts are designed and cloned into storage plasmids, with the part flanked by an integrated prefix (iP) and an integrated suffix (iS) sequence. The iP and iS sequences contain inward facing BsaI restriction sites, which contain overhangs complementary to the BASIC linkers. Like in MODAL, the 7 standard linkers used in BASIC were designed with the R2oDNA Designer software, and screened to ensure that they do not contain sequences with homology to chassis genomes, and that they do not contain unwanted sequences like secondary structure sequences, restriction sites or ribosomal binding sites. Each linker sequence is split into two halves, each with a 4 bp overhang complementary to the BsaI restriction site, a 12 bp double stranded sequence and sharing a 21 bp overlap sequence with the other half. The half that is will bind to the upstream DNA part is known as the suffix linker part (e.g. L1S) and the half that binds to the downstream part is known as the prefix linker part (e.g. L1P). These linkers form the basis of assembling the DNA parts together.
Besides directing the order of assembly, the standard BASIC linkers can also be modified to carry out other functions. To allow for idempotent assembly, linkers were also designed with additional methylated iP and iS sequences inserted to protect them from being recognised by BsaI. This methylation is lost following transformation and in vivo plasmid replication, and the plasmids can be extracted, purified, and used for further reactions.
Because the linker sequence are relatively long (45bp for a standard linker), there is an opportunity to incorporate functional DNA sequences to reduce the number of DNA parts needed during assembly. The BASIC assembly standard provides several linkers embedded with RBS of different strengths. Similarly to facilitate the construction of fusion proteins containing multiple protein domains, several fusion linkers were also designed to allow for full read-through of the DNA construct. These fusion linkers code for a 15 amino acid glycine and serine polypeptide, which is an ideal linker peptide for fusion proteins with multiple domains.
Assembly
There are three main steps in the assembly of the final construct.
# First, the DNA parts are excised from the storage plasmid, giving a DNA fragment with BsaI overhangs on the 3 and 5 end.
# Next, each linker part is attached to its respective DNA part by incubating with T4 DNA ligase. Each DNA part will have a suffix and prefix linker part from two different linkers to direct the order of assembly. For example, the first part in the sequence will have L1P and L2S, while the second part will have L2P and L3S attached. The linker parts can be changed to change the sequence of assembly.
# Finally, the parts with the attached linkers are assembled into a plasmid by incubating at 50 °C. The 21 bp overhangs of the P and S linkers anneal and the final construct can be transformed into bacteria cells for cloning. The single stranded nicks are repaired in vivo following transformation, producing a stable final construct cloned into plasmids. | 1 | Biochemistry |
Plants have mechanisms that protect against adverse effects of strong light. The most studied biochemical protective mechanism is non-photochemical quenching of excitation energy. Visible-light-induced photoinhibition is ~25% faster in an Arabidopsis thaliana mutant lacking non-photochemical quenching than in the wild type. It is also apparent that turning or folding of leaves, as occurs, e.g., in Oxalis species in response to exposure to high light, protects against photoinhibition. | 5 | Photochemistry |
FDA launched HIVE Open Source as a platform to support end to end needs for NGS analytics.
https://github.com/FDA/fda-hive
HIVE biocompute harmonization platform is at the core of High-throughput Sequencing Computational Standards for Regulatory Sciences (HTS-CSRS) project. Its mission is to provide the scientific community with a framework to harmonize biocomputing, promote interoperability, and verify bioinformatics protocols (https://hive.biochemistry.gwu.edu/htscsrs). For more information, see the project description on the FDA Extramural Research page (https://www.fda.gov/ScienceResearch/SpecialTopics/RegulatoryScience/ucm491893.htm | 1 | Biochemistry |
The depolarized voltage opens additional voltage-dependent potassium channels, and some of these do not close right away when the membrane returns to its normal resting voltage. In addition, further potassium channels open in response to the influx of calcium ions during the action potential. The intracellular concentration of potassium ions is transiently unusually low, making the membrane voltage V even closer to the potassium equilibrium voltage E. The membrane potential goes below the resting membrane potential. Hence, there is an undershoot or hyperpolarization, termed an afterhyperpolarization, that persists until the membrane potassium permeability returns to its usual value, restoring the membrane potential to the resting state. | 7 | Physical Chemistry |
While the definition of sublimation is simple, there is often confusion as to what counts as a sublimation. | 3 | Analytical Chemistry |
For a system of diameter and volume , at constant temperature , the classical canonical partition function
with a scaled coordinate, the free energy is given by:
Combining the above equation with the definition of chemical potential,
we get the chemical potential of a sufficiently large system from (and the fact that the smallest allowed change in the particle number is )
wherein the chemical potential of an ideal gas can be evaluated analytically.
Now let's focus on since the potential energy of an system can be separated into the potential energy of an system and the potential of the excess particle interacting with the system, that is,
and
Thus far we converted the excess chemical potential into an ensemble average, and the integral in the above equation can be sampled by the brute force Monte Carlo method.
The calculating of excess chemical potential is not limited to homogeneous systems, but has also been extended to inhomogeneous systems by the Widom insertion method, or other ensembles such as NPT and NVE. | 7 | Physical Chemistry |
Plasmids may be classified in a number of ways. Plasmids can be broadly classified into conjugative plasmids and non-conjugative plasmids. Conjugative plasmids contain a set of transfer genes which promote sexual conjugation between different cells. In the complex process of conjugation, plasmids may be transferred from one bacterium to another via sex pili encoded by some of the transfer genes (see figure). Non-conjugative plasmids are incapable of initiating conjugation, hence they can be transferred only with the assistance of conjugative plasmids. An intermediate class of plasmids are mobilizable, and carry only a subset of the genes required for transfer. They can parasitize a conjugative plasmid, transferring at high frequency only in its presence.
Plasmids can also be classified into incompatibility groups. A microbe can harbour different types of plasmids, but different plasmids can only exist in a single bacterial cell if they are compatible. If two plasmids are not compatible, one or the other will be rapidly lost from the cell. Different plasmids may therefore be assigned to different incompatibility groups depending on whether they can coexist together. Incompatible plasmids (belonging to the same incompatibility group) normally share the same replication or partition mechanisms and can thus not be kept together in a single cell.
Another way to classify plasmids is by function. There are five main classes:
* Fertility F-plasmids, which contain tra genes. They are capable of conjugation and result in the expression of sex pili.
* Resistance (R) plasmids, which contain genes that provide resistance against antibiotics or antibacterial agents. Historically known as R-factors, before the nature of plasmids was understood.
* Col plasmids, which contain genes that code for bacteriocins, proteins that can kill other bacteria.
* Degradative plasmids, which enable the digestion of unusual substances, e.g. toluene and salicylic acid.
* Virulence plasmids, which turn the bacterium into a pathogen. e.g. Ti plasmid in Agrobacterium tumefaciens
Plasmids can belong to more than one of these functional groups. | 1 | Biochemistry |
Eszopiclone, sold under the brand name Lunesta among others, is a medication used in the treatment of insomnia. Evidence supports slight to moderate benefit up to six months. It is taken by mouth.
Common side effects include headache, dry mouth, nausea, and dizziness. Severe side effects may include suicidal thoughts, hallucinations, and angioedema. Rapid decreasing of the dose may result in withdrawal. Eszopiclone is classified as a nonbenzodiazepine or Z-drug and a sedative and hypnotic of the cyclopyrrolone group. It is the S-stereoisomer of zopiclone. It works by interacting with the GABA receptors.
Approved for medical use in the United States in 2004, eszopiclone is available as a generic medication. In 2020, it was the 232nd most commonly prescribed medication in the United States, with more than 1million prescriptions. Eszopiclone is not sold in the European Union, as of 2009, the European Medicines Agency (EMA) ruled that it was too similar to zopiclone to be considered a new active substance. | 4 | Stereochemistry |
Historians debate whether bloomery-based ironworking ever spread to China from the Middle East. One theory suggests that metallurgy was introduced through Central Asia. In 2008, two iron fragments were excavated at the Mogou site, in Gansu. They have been dated to the 14th century BC, belonging to the period of Siwa culture, suggesting an independent Chinese origin. One of the fragments was made of bloomery iron rather than meteoritic iron.
The earliest iron artifacts made from bloomeries in China date to end of the 9th century BC. Cast iron was used in ancient China for warfare, agriculture and architecture. Around 500 BC, metalworkers in the southern state of Wu achieved a temperature of 1130 °C. At this temperature, iron combines with 4.3% carbon and melts. The liquid iron can be cast into molds, a method far less laborious than individually forging each piece of iron from a bloom.
Cast iron is rather brittle and unsuitable for striking implements. It can be decarburized to steel or wrought iron by heating it in air for several days. In China, these iron working methods spread northward, and by 300 BC, iron was the material of choice throughout China for most tools and weapons. A mass grave in Hebei province, dated to the early 3rd century BC, contains several soldiers buried with their weapons and other equipment. The artifacts recovered from this grave are variously made of wrought iron, cast iron, malleabilized cast iron, and quench-hardened steel, with only a few, probably ornamental, bronze weapons.
During the Han Dynasty (202 BC–220 AD), the government established ironworking as a state monopoly, repealed during the latter half of the dynasty and returned to private entrepreneurship, and built a series of large blast furnaces in Henan province, each capable of producing several tons of iron per day. By this time, Chinese metallurgists had discovered how to fine molten pig iron, stirring it in the open air until it lost its carbon and could be hammered (wrought). In modern Mandarin-Chinese, this process is now called chao, literally stir frying. Pig iron is known as raw iron, while wrought iron is known as cooked iron. By the 1st century BC, Chinese metallurgists had found that wrought iron and cast iron could be melted together to yield an alloy of intermediate carbon content, that is, steel.
According to legend, the sword of Liu Bang, the first Han emperor, was made in this fashion. Some texts of the era mention "harmonizing the hard and the soft" in the context of ironworking; the phrase may refer to this process. The ancient city of Wan (Nanyang) from the Han period forward was a major center of the iron and steel industry. Along with their original methods of forging steel, the Chinese had also adopted the production methods of creating Wootz steel, an idea imported from India to China by the 5th century AD.
During the Han Dynasty, the Chinese were also the first to apply hydraulic power (i.e. a waterwheel) in working the bellows of the blast furnace. This was recorded in the year 31 AD, as an innovation by the Chinese mechanical engineer and politician Du Shi, Prefect of Nanyang. Although Du Shi was the first to apply water power to bellows in metallurgy, the first drawn and printed illustration of its operation with water power appeared in 1313 AD, in the Yuan Dynasty era text called the Nong Shu.
In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, heterogeneous steel and a precursor to the modern Bessemer process that utilized partial decarbonization via repeated forging under a cold blast. By the 11th century, there was a large amount of deforestation in China due to the iron industry's demands for charcoal. By this time however, the Chinese had learned to use bituminous coke to replace charcoal, and with this switch in resources many acres of prime timberland in China were spared. | 8 | Metallurgy |
Cryptococcus neoformans is a basidiomycetous fungus that grows as a budding yeast in culture and in an infected host. C. neoformans causes life-threatening meningoencephalitis in immune compromised patients. It undergoes a filamentous transition during the sexual cycle to produce spores, the suspected infectious agent. The vast majority of environmental and clinical isolates of C. neoformans are mating type α. Filaments ordinarily have haploid nuclei, but these can undergo a process of diploidization (perhaps by endoduplication or stimulated nuclear fusion) to form diploid cells termed blastospores. The diploid nuclei of blastospores can then undergo meiosis, including recombination, to form haploid basidiospores that can then be dispersed. This process is referred to as monokaryotic fruiting. Required for this process is a gene designated dmc1, a conserved homologue of genes RecA in bacteria, and RAD51 in eukaryotes. Dmc1 mediates homologous chromosome pairing during meiosis and repair of double-strand breaks in DNA (see Meiosis; also Michod et al.). Lin et al. suggested that one benefit of meiosis in C. neoformans could be to promote DNA repair in a DNA damaging environment that could include the defensive responses of the infected host. | 1 | Biochemistry |
Octanoyl-coenzyme A is the endpoint of beta oxidation in peroxisomes. It is produced alongside acetyl-CoA and transferred to the mitochondria to be further oxidized into acetyl-CoA. | 1 | Biochemistry |
The Endocare PerCryo Percutaneous Cryoablation device utilizes argon as a coolant and can be used with four different single cryoprobe configurations with a diameter of either 1.7 mm (~16 gauge) or 2.4 mm (~13 gauge) in diameter .
The Myoscience Iovera is a handheld device that uses nitrous oxide as a coolant and can be used with a three-probe configuration with a probe diameter of 0.4 mm (~27 gauge). | 1 | Biochemistry |
*Albert Hewett Coons (1912-1978), physician, pathologist and immunologist.
*Cornelia Mitchell Downs (1892–1987), microbiologist and journalist | 1 | Biochemistry |
Most traditional HPLC is performed with the stationary phase attached to the outside of small spherical silica particles (very small beads). These particles come in a variety of sizes with 5 µm beads being the most common. Smaller particles generally provide more surface area and better separations, but the pressure required for optimum linear velocity increases by the inverse of the particle diameter squared.
According to the equations of the column velocity, efficiency and backpressure, reducing the particle diameter by half and keeping the size of the column the same, will double the column velocity and efficiency; but four times increase the backpressure. And the small particles HPLC also can decrease the width broadening. Larger particles are used in preparative HPLC (column diameters 5 cm up to >30 cm) and for non-HPLC applications such as solid-phase extraction. | 3 | Analytical Chemistry |
There are two principal classes of fatty acid synthases.
* Type I systems utilise a single large, multifunctional polypeptide and are common to both animals and fungi (although the structural arrangement of fungal and animal syntheses differ). A Type I fatty acid synthase system is also found in the CMN group of bacteria (corynebacteria, mycobacteria, and nocardia). In these bacteria, the FAS I system produces palmitic acid, and cooperates with the FAS II system to produce a greater diversity of lipid products.
* Type II is found in archaea, bacteria and plant plastids, and is characterized by the use of discrete, monofunctional enzymes for fatty acid synthesis. Inhibitors of this pathway (FASII) are being investigated as possible antibiotics.
The mechanism of FAS I and FAS II elongation and reduction is the same, as the domains of the FAS II enzymes are largely homologous to their domain counterparts in FAS I multienzyme polypeptides. However, the differences in the organization of the enzymes - integrated in FAS I, discrete in FAS II - gives rise to many important biochemical differences.
The evolutionary history of fatty acid synthases are very much intertwined with that of polyketide synthases (PKS). Polyketide synthases use a similar mechanism and homologous domains to produce secondary metabolite lipids. Furthermore, polyketide synthases also exhibit a Type I and Type II organization. FAS I in animals is thought to have arisen through modification of PKS I in fungi, whereas FAS I in fungi and the CMN group of bacteria seem to have arisen separately through the fusion of FAS II genes. | 1 | Biochemistry |
Photoacids are molecules that upon light absorption undergo a proton transfer to form the photobase.
In these reactions the dissociation occurs in the electronically excited state. After proton transfer and relaxation to the electronic ground state, the proton and acid recombine to form the photoacid again.
Photoacids are a convenient source to induce pH jumps in ultrafast laser spectroscopy experiments. | 5 | Photochemistry |
*Scorpion® probes
*Molecular Beacon probes
*TaqMan® probes
*LNA® (Locked Nucleic Acid) probes
*Cycling Probe Technology (CPT) | 1 | Biochemistry |
Transforming growth factor (, or TGF) is used to describe two classes of polypeptide growth factors, TGFα and TGFβ.
The name "Transforming Growth Factor" is somewhat arbitrary, since the two classes of TGFs are not structurally or genetically related to one another, and they act through different receptor mechanisms. Furthermore, they do not always induce cellular transformation, and are not the only growth factors that induce cellular transformation. | 1 | Biochemistry |
The alkylation of tropanes with methyl iodide is a classic example of a Curtin–Hammett scenario in which a major product can arise from a less stable conformation. Here, the less stable conformer reacts via a more stable transition state to form the major product. Therefore, the ground state conformational distribution does not reflect the product distribution. | 7 | Physical Chemistry |
Total selenium in selenium yeast can be reliably determined using open acid digestion to extract selenium from the yeast matrix followed by flame atomic absorption spectrometry. Determination of the selenium species selenomethionine can be achieved via proteolytic digestion of selenium yeast followed by high-performance liquid chromatography with inductively coupled plasma mass spectrometry. | 1 | Biochemistry |
RegulonDB is a database of the regulatory network of gene expression in Escherichia coli K-12. RegulonDB also models the organization of the genes in transcription units, operons and regulons. A total of 120 sRNAs with 231 total interactions which all together regulate 192 genes are also included. RegulonDB was founded in 1998 and also contributes data to the EcoCyc database. | 1 | Biochemistry |
Station ALOHA is a deep water (~4,800 m) location approximately 100 km north of the Hawaiian Island of Oahu. Thus, the region is far enough from land to be free of coastal ocean dynamics and terrestrial inputs, but close enough to a major port (Honolulu) to make relatively short duration (less than five days) near-monthly cruises logistically and financially feasible. Sampling at this site occurs within a 10 km radius around the center of the station.
Each HOT cruise begins with a stop at a coastal station south of the island of Oahu, approximately 10 km off Kahe Point (21° 20.6N, 158° 16.4W) in 1500 m of water. Station Kahe (termed Station 1) is used to test equipment and train new personnel before departing for Station ALOHA. Since August 2004, Station ALOHA has also been home to a surface mooring outfitted for meteorological and upper ocean measurements; this mooring, named WHOTS (also termed Station 50), is a collaborative project between Woods Hole Oceanographic Institution and HOT. WHOTS provides long-term, high-quality air-sea fluxes as a coordinated part of HOT, contributing to the program’s goals of observing heat, fresh water and chemical fluxes. In 2011, the ALOHA Cabled Observatory (ACO) became operational. This instrumented fiber optic cabled observatory provides power and communications to the seabed (4728 m). The ACO is currently configured with an array of thermistors, current meters, conductivity sensors, two hydrophones, and a video camera. | 9 | Geochemistry |
The composition of the human body can be classified as follows:
*Water
*Proteins
*Fats (or lipids)
*Hydroxyapatite in bones
*Carbohydrates such as glycogen and glucose
*DNA and RNA
*Inorganic ions such as sodium, potassium, chloride, bicarbonate, phosphate
*Gases mainly being oxygen, carbon dioxide
*Many cofactors.
The estimated contents of a typical 20-micrometre human cell is as follows: | 1 | Biochemistry |
In 1929, Rinkel proposed a different method to calculate while using the Rüchardt apparatus: he noted that it may be shown that the vertical distance L which the sphere falls before it begin to rise is: , so may be calculated from measured values of L, m, V, P and A.
In 1951, Koehler and later, in 1972 Flammersfeld introduced a trick in the original Rüchardt setup, to increase the number of oscillations that are limited by the unavoidable friction-damping and gas leak (through the piston-tube seal): they made a thin hole on the tube (at half-height) and provided a gas-feeding pump to keep the pressure inside the vessel constant. By properly trimming the gas inlet flux (through a throttling valve) they obtained the following result: during the oscillations the piston is pushed-up by the gas overpressure until it crosses the hole position; then the gas leakage through the hole reduces the pressure, and the piston falls back. The force acting onto the piston varies at a rate that is regulated by the piston oscillation frequency leading to forced oscillation; fine adjustment of the throttle valve allows to achieve maximum amplitude at resonance.
In 1958, Christy and Rieser used only a gas-feeding pump to stabilize the gas pressure.
A slightly different solution was found in 1964 by Hafner who used a tapered tube (conical: slightly larger at the top).
In 1959, Taylor used a column of mercury oscillating inside a U-shaped tube instead of the Rüchardt sphere.
In 1964, Donnally and Jensen used a variable load attached to the Rüchardt sphere in order to allows frequency measurements with different oscillating mass.
In 1967, Lerner suggested a modified version of the Taylor method (with mercury replaced by water).
In 1979, Smith reported a simplified version of the complex Rüchardt-resonance method, originally invented by Clark and Katz, in which an oscillating magnetic piston is driven into resonance by an external coil.
In 1988, Connolly suggested the use of a photogate to measure more precisely the frequency of the Rüchardt sphere.
In 2001, Severn and Steffensen used a pressure transducer to monitor the pressure oscillations in the original Rüchardt setup.
In 2001, Torzo, Delfitto, Pecori and Scatturin implemented the version of Rüchardt apparatus (shown in the top picture) using three sensors: a sonar that monitors the breast-pump oscillations, and pressure and temperature sensors that monitor the changes in pressure and temperature inside the glass vessel. | 7 | Physical Chemistry |
Modafinil has been studied in the treatment of major depressive disorder. In a 2021 systematic review and meta-analysis of randomized controlled trials of psychostimulants for depression, modafinil and other stimulants such as methylphenidate and amphetamines improved depression in traditional meta-analysis. However, when subjected to network meta-analysis, modafinil and most other stimulants did not significantly improve depression, with only methylphenidate remaining effective. Modafinil and other stimulants likewise did not improve quality of life in the meta-analysis, although there was evidence for reduced fatigue and sleepiness with modafinil and other stimulants. While significant effectiveness of modafinil for depression has been reported by particular trials, reviews and meta-analyses note that the effectiveness of modafinil for depression is limited, the quality of available evidence is low, and the results are inconclusive. | 4 | Stereochemistry |
Innate immune system senses intact peptidoglycan and peptidoglycan fragments using numerous PRRs (pattern recognition receptors) that are secreted, expressed intracellularly or expressed on the cell surface. | 1 | Biochemistry |
The enzyme rhodanase (thiosulfate sulfurtransferase) catalyzes the detoxification of cyanide ion by thiosulfate ion by transforming them into thiocyanate ion and sulfite ion:
Sodium thiosulfate has been considered as an empirical treatment for cyanide poisoning, along with hydroxocobalamin. It is most effective in a pre-hospital setting, since immediate administration by emergency personnel is necessary to reverse rapid intracellular hypoxia caused by the inhibition of cellular respiration, at complex IV.
It activates thiosulfate sulfurtransferase (TST) in mitochondria. TST is associated with protection against obesity and type II (insulin resistant) diabetes.
Thiosulfate can also work as electron donor for growth of bacteria oxidizing sulfur, such as Chlorobium limicola forma thiosulfatophilum. These bacteria use electrons from thiosulfate (and other sources) and carbon from carbon dioxide to synthesize carbon compounds through reverse Krebs cycle. | 8 | Metallurgy |
Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem, enzymes capture photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol. The energized electrons are replaced by oxidizing water to form hydrogen ions and molecular oxygen.
By replenishing lost electrons with electrons from the splitting of water, photosystem II provides the electrons for all of photosynthesis to occur. The hydrogen ions (protons) generated by the oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP. The energized electrons transferred to plastoquinone are ultimately used to reduce to NADPH or are used in non-cyclic electron flow. DCMU is a chemical often used in laboratory settings to inhibit photosynthesis. When present, DCMU inhibits electron flow from photosystem II to plastoquinone. | 5 | Photochemistry |
Hsalen may be synthesized by the condensation of ethylenediamine and salicylaldehyde.
Complexes of salen with metal cations may be made without isolating it from the reaction mixture. This is possible because the stability constant for the formation of the metal complexes are very high, due to the chelate effect.
:HL + M → ML + 2 H
where L stands for the ligand. The pyridine adduct of the cobalt(II) complex Co(salen)(py) (salcomine) has a square-pyramidal structure; it can act as a dioxygen carrier by forming a labile, octahedral O complex.
The name "salen ligands" is used for tetradentate ligands which have similar structures. For example, in salpn there is a methyl substituent on the bridge. It is used as a metal deactivation additive in fuels. The presence of bulky groups near the coordination site may enhance the catalytic activity of a metal complex and prevent its dimerization. Salen ligands derived from 3,5-di-tert-butylsalicylaldehyde fulfill these roles, and also increase the solubility of the complexes in non-polar solvents like pentane. Chiral "salen" ligands may be created by proper substitution of the diamine backbone, the phenyl ring, or both. An example is the ligand obtained by condensation of the C-symmetric trans-1,2-diaminocyclohexane with 3,5-di-tert-butylsalicylaldehyde. Chiral ligands may be used in asymmetric synthesis reactions, such as the Jacobsen epoxidation: | 0 | Organic Chemistry |
Using the relationships defined by this equation, the diffusion coefficient of the electroactive species can be determined. Linear plots of i vs. ν provide evidence for a chemically reversible redox process vs the cases where redox causes major structural change in the analyte. For species where the diffusion coefficient is known (or can be estimated), the slope of the plot of i vs. ν provides information into the stoichiometry of the redox process. | 3 | Analytical Chemistry |
On 16 December 2014, NASA reported the Curiosity rover detected a "tenfold spike", likely localized, in the amount of methane in the Martian atmosphere. Sample measurements taken "a dozen times over 20 months" showed increases in late 2013 and early 2014, averaging "7 parts of methane per billion in the atmosphere." Before and after that, readings averaged around one-tenth that level.
In addition, high levels of organic chemicals, particularly chlorobenzene, were detected in powder drilled from one of the rocks, named "Cumberland", analyzed by the Curiosity rover. | 9 | Geochemistry |
In humans, DNA methylation occurs at the 5' position of the pyrimidine ring of the cytosine residues within CpG sites to form 5-methylcytosines. The presence of multiple methylated CpG sites in CpG islands of promoters causes stable silencing of genes. Silencing of a gene may be initiated by other mechanisms, but this is often followed by methylation of CpG sites in the promoter CpG island to cause the stable silencing of the gene. | 1 | Biochemistry |
Heather D. Willauer (born 1974) is an American analytical chemist and inventor working in Washington, D.C., at the United States Naval Research Laboratory (NRL). Leading a research team, Willauer has patented a method for removing dissolved carbon dioxide (CO) from seawater, in parallel with hydrogen (H) recovered by conventional water electrolysis. Willauer is also searching to improve the catalysts required to enable a continuous Fischer–Tropsch process to recombine carbon monoxide (CO) and hydrogen gases into complex hydrocarbon liquids to synthesize jet fuel for Navy aircraft.
Especially significant for the Navy is the possibility of maintaining naval air operations in remote areas without depending too much on long-distance transport of jet fuel across oceans. The Navy is also studying the feasibility of constructing on-shore facilities capable of synthesizing kerosene from hydrogen and CO, both extracted from seawater constituents. Because of the very high electrical power required by water electrolysis to produce considerable amounts of hydrogen, nuclear power plants or ocean thermal energy conversion (OTEC) are necessary to fuel the industrial installations built on-shore on remote islands close to the sea in strategic locations. | 3 | Analytical Chemistry |
Common adverse drug reactions (ADRs) associated with the use of dicloxacillin include: diarrhea, nausea, rash, urticaria, pain and inflammation at injection site, superinfection (including candidiasis), allergy, and transient increases in liver enzymes and bilirubin.
On rare occasions, cholestatic jaundice (also referred to as cholestatic hepatitis) has been associated with dicloxacillin therapy. The reaction may occur up to several weeks after treatment has stopped, and takes weeks to resolve. The estimated incidence is 1 in 15,000 exposures, and is more frequent in people over 55 years old, females, and those with treatment longer than 2 weeks.
It should be used with caution and monitored in the elderly, particularly with intravenous administration, due to a risk of thrombophlebitis.
Dicloxacillin can also lower the effectiveness of birth control pills and pass into breast milk. | 4 | Stereochemistry |
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