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An operon contains one or more structural genes which are generally transcribed into one polycistronic mRNA (a single mRNA molecule that codes for more than one protein). However, the definition of an operon does not require the mRNA to be polycistronic, though in practice, it usually is. Upstream of the structural genes lies a promoter sequence which provides a site for RNA polymerase to bind and initiate transcription. Close to the promoter lies a section of DNA called an operator. | 1 | Biochemistry |
The contact stage is the initial wetting that occurs between the adhesive and membrane. This can occur mechanically by bringing together the two surfaces, or through the bodily systems, like when particles are deposited in the nasal cavity by inhalation. The principles of initial adsorption of small molecule adsorbates can be described by DLVO theory. | 1 | Biochemistry |
This coordination compound is prepared by the reaction of tungsten hexacarbonyl with 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (Hhpp) in o-dichlorobenzene at 200 °C:
The reaction gives W(hpp)Cl. Dichlorobenzene provides the chlorine atoms and is itself reductively coupled to 2,2′-dichlorobiphenyl. The bond order between the tungsten centers in W(hpp)Cl is three.
This dichloride is further reduced by potassium metal to W(hpp). This species has a quadruple bond between the two tungsten centers. Related quadruply bonded complexes include [WCl] and [[Potassium octachlorodimolybdate|[MoCl]]]. Because of its low ionization energy, W(hpp) is easily oxidized back to the dichloride by dichloromethane. It is readily oxidized to the corresponding cation with the oxidants fullerene and with tetracyanoquinodimethane. (hpp) was proposed to be a potentially useful powerful reducing agent akin to CpCo and CpCr, so far this reagent has not become part of the synthetic chemist's armament. grand total of 7 refs in 5 years--> | 7 | Physical Chemistry |
BioModels is developed by the BioModels.net Team at the EMBL-EBI, UK, the Le Novère lab at the Babraham Institute, UK, and the SBML Team in Caltech, USA. | 1 | Biochemistry |
Metal carbene complexes have applications in hetereogeneous and homogeneous catalysis, and as reagents for organic reactions. | 0 | Organic Chemistry |
The Rydberg states of an atom or molecule are electronically excited states with energies that follow the Rydberg formula as they converge on an ionic state with an ionization energy. Although the Rydberg formula was developed to describe atomic energy levels, it has been used to describe many other systems that have electronic structure roughly similar to atomic hydrogen. In general, at sufficiently high principal quantum numbers, an excited electron-ionic core system will have the general character of a hydrogenic system and the energy levels will follow the Rydberg formula. Rydberg states have energies converging on the energy of the ion. The ionization energy threshold is the energy required to completely liberate an electron from the ionic core of an atom or molecule. In practice, a Rydberg wave packet is created by a laser pulse on a hydrogenic atom and thus populates a superposition of Rydberg states. Modern investigations using pump-probe experiments show molecular pathways – e.g. dissociation of (NO) – via these special states. | 7 | Physical Chemistry |
The DrugWipe is a test used to wipe surfaces for traces of drug residue. It may also be used for sweat or saliva testing of individuals. DrugWipe was named a finalist in the 2011 Cygnus Law Enforcement Group Innovation Awards competition. The DrugWipe 6s (saliva only) test was entered under the category of Traffic Enforcement. | 3 | Analytical Chemistry |
Tetraanthraporphyrin exhibit strongly red-shifted and hyperchromic absorption bands. The maximum of absorption is about 830 nm. The molar extinction coefficients reach 10 scale. Very strong red-shift of absorption by about 90 nm upon protonation of nitrogen atoms and blue-shift by 20−40 nm upon metal insertion are observed. | 1 | Biochemistry |
Radical cascades are those in which the
key step constitutes a radical reaction. The high reactivity of free radical
species renders radical-based synthetic approaches decidedly suitable for
cascade reactions.
One of the most widely recognized
examples of the synthetic utility of radical cascades is the cyclization
sequence employed in the total synthesis of (±)-hirsutene, in 1985 (Scheme 6). Herein, alkyl iodide 28 was converted to the primary radical
intermediate 29, which underwent a 5-exo-trig cyclization to afford reactive species 30. A subsequent 5-exo-dig radical cyclization lead to intermediate 31, which upon quenching gave the
target (±)-hirsutene (32) in 80%
overall yield.
A cascade radical process was also
used in one of the total syntheses of (–)-morphine (Scheme 7). Aryl bromide 33 was converted to the corresponding
radical species 34 by treatment with
tri-n-butyltin hydride. A 5-exo-trig cyclization then occurred to
give intermediate 35
stereoselectively in virtue of the stereochemistry of the ether linkage. In the
next step of the cascade, the geometric constraints of 35 forbid the kinetically favored 5-exo-trig cyclization pathway; instead secondary benzylic radical
species 36 was obtained via a
geometrically-allowed 6-endo-trig
cyclization. Subsequent elimination of the phenyl sulfinyl radical afforded
product 37 in 30% overall yield,
which was further elaborated to (–)-morphine (38). | 0 | Organic Chemistry |
A crystal structure is defined as the spatial distribution of the atoms within a crystal, usually modeled by the idea of an infinite crystal pattern. An infinite crystal pattern refers to the infinite 3D periodic array which corresponds to a crystal, in which the lengths of the periodicities of the array may not be made arbitrarily small. The geometrical shift which takes a crystal structure coincident with itself is termed a symmetry translation (translation) of the crystal structure. The vector which is related to this shift is called a translation vector . Since a crystal pattern is periodic, all integer linear combinations of translation vectors are also themselves translation vectors, | 3 | Analytical Chemistry |
A cell saline buffer containing the TIVA tag is added to the coverslip and incubated. During the incubation period, the TIVA tag penetrates the cell membrane via the CPP that is bound to it. Subsequently, the cytosolic environment cleaves the CPP and the TIVA tag is trapped inside the cell. After incubation, the coverslip is rinsed twice with cell saline buffer and then transferred to an imaging chamber. Using a confocal microscope, loading of the tag is confirmed by detecting the Cy5 signal at a wavelength of 561 nm. | 1 | Biochemistry |
Spliceosomal splicing and self-splicing involve a two-step biochemical process. Both steps involve transesterification reactions that occur between RNA nucleotides. tRNA splicing, however, is an exception and does not occur by transesterification.
Spliceosomal and self-splicing transesterification reactions occur via two sequential transesterification reactions. First, the 2OH of a specific branchpoint nucleotide within the intron, defined during spliceosome assembly, performs a nucleophilic attack on the first nucleotide of the intron at the 5 splice site, forming the lariat intermediate. Second, the 3OH of the released 5 exon then performs a nucleophilic attack at the first nucleotide following the last nucleotide of the intron at the 3' splice site, thus joining the exons and releasing the intron lariat. | 1 | Biochemistry |
In most areas of biology a single gene codes for one or a few possible proteins. Through V(D)J recombination a number of organisms take a relatively small number of genes coding for antibodies and T-cell receptors (TCRs) and produce a huge diversity of slightly different antibodies and TCRs. The diversity allows for the recognition of a wide array of antigens. As an immune system reacts to infections and other events, the number of different antibodies and TCRs it contains changes. The makeup and quantity of these proteins is sometimes referred to as an immune repertoire.
Immunosequencing is a technique utilizing multiplex polymerase chain reaction that allows for the sequencing and quantification of the large diversity of antibody and TCR genes composing an individual's immune repertoire. | 1 | Biochemistry |
When a viral gene is introduced into the host cell and is sufficient to induce oncogenesis – the creation of cancerous cells – in the infected cell line, the gene is said to be a "viral transforming gene". When this type of gene is translated to a protein, the protein is called a "transforming protein". Note that since the viral oncogenes originated from a host genome, the transformation event is different from transduction, which describes the process of introducing non-native genes to a host organism via a viral infection. | 1 | Biochemistry |
Schock et al. (2000) identified and named the family AtMRS2 based on the similarity of the genes to the MRS2 gene of yeast. The authors also showed that the AtMRS2-1 gene could complement a Δmrs2 yeast mutant phenotype. Independently, Li et al. (2001) published a report identifying the family and showing that two additional members could complement Mg transport deficient mutants, one in S. typhimurium and the other in S. cerevisiae.
The three genes that have been shown to transport Mg are AtMRS2-1, AtMRS2-10 and AtMRS2-11, and these genes produce proteins 442, 443 and 459 amino acids in size, respectively. Each of the proteins shows significant similarity to Mrs2p of yeast and a weak similarity to CorA of bacteria, contains the conserved GMN amino acid motif at the outside end of the first TM domain, and is predicted to have two TM domains.
The AtMRS2-1 gene, when expressed in yeast from the MRS2 promoter and being fused C-terminally to the first 95 amino acids of the Mrs2p protein, was directed to the mitochondria, where it complemented a Δmrs2 mutant both phenotypically (mitochondrial RNA splicing was restored) and with respect to the Mg content of the organelle. No data on the kinetics of the transport was presented. The AtMRS2-11 gene was analysed in yeast (in the alr1 alr2 strain), where it was shown that expression of the gene significantly increased the rate of Mg uptake into starved cells over the control, as measured using flame atomic absorption spectroscopy of total cellular Mg content. However, Alr1p was shown to be significantly more effective at transporting Mg at low extracellular concentrations, suggesting that the affinity of AtMRS2-11 for Mg is lower than that of Alr1p. An electrophysiological (voltage clamp) analysis of the AtMRS2-11 protein in Xenopus oocytes also showed a Mg-dependent current at membrane potentials (ΔΨ) of –100 – –150 mV inside. These values are physiologically significant, as several membranes in plants maintain ΔΨ in this range. However, the author had difficulty reproducing these results due to an apparent "death" of oocytes containing the AtMRS2-11 protein, and therefore these results should be viewed with caution.
The AtMRS2-10 transporter has been analysed using radioactive tracer uptake analysis. 63Ni was used as the substitute ion and Mg was shown to inhibit the uptake of 63Ni with a Ki of 20 μM. Uptake was also inhibited by Co(III)Hex and by other divalent cations. Only Co and Cu inhibited transport with Ki values less than 1 mM.
The AtMRS2-10 protein was fused to GFP, and was shown to be localised to the plasma membrane. A similar experiment was attempted in the Schock et al. (2000) paper, but the observed localisation was not significantly different from that seen with unfused GFP. The most likely reason for the lack of a definitive localisation of AtMRS2-1 in the Schock et al. paper is that the authors removed the TM domains from the protein, thereby precluding its insertion into a membrane.
The exact physiological significance of the AtMRS2-1 and AtMRS2-10 proteins in plants has yet to be clarified. The AtMRS2-11 gene has been overexpressed (from the CaMV 35S promoter) in A. thaliana. The transgenic line has been shown to accumulate high levels of the AtMRS2-11 transcript. A strong Mg deficiency phenotype (necrotic spots on the leaves, see Chapter 1.5 below) was recorded during the screening process (in both the T1 and T2 generations) for a homozygote line, but this phenotype was lost in the T3 generation and could not be reproduced when the earlier generations were screened a second time. The author suggested that environmental effects were the most likely cause of the inconsistent phenotype. | 1 | Biochemistry |
AREs are recognized by RNA binding proteins such as tristetraprolin (TTP), AUF1, and Hu Antigen R (HuR). Although the exact mechanism is not very well understood, recent publications have attempted to propose the action of some of these proteins. AUF1, also known as hnRNP D, binds AREs through RNA recognition motifs (RRMs). AUF1 is also known to interact with the translation initiation factor eIF4G and with poly(A)-binding protein, indicating that AUF1 senses the translational status of mRNA and decays accordingly through the excision of the poly(A) tail.
TTP's expression is rapidly induced by insulin. Immunoprecipitation experiments have shown that TTP co-precipitates with an exosome, suggesting that it helps recruit exosomes to the mRNA containing AREs. Alternatively, HuR proteins have a stabilizing effect—their binding to AREs increases the half-life of mRNAs. Similar to other RNA-binding proteins, this class of proteins contain three RRMs, two of which are specific to ARE elements. A likely mechanism for HuR action relies on the idea that these proteins compete with other proteins that normally have a destabilizing effect on mRNAs. HuRs are involved in genotoxic response—they accumulate in the cytoplasm in response to UV exposure and stabilize mRNAs that encode proteins involved in DNA repair. | 1 | Biochemistry |
There was a quarterly report on each research topic presented to the individual research committee and an annual one circulated also to members on request. Final results were compiled as a report that was immediately available to members. After about two years the commercial confidentiality was dropped and a paper was presented at a meeting of the Institute of Metals or other organisation and subsequently published in their Journal. Some researches that had resulted in valuable definitive advancements were then published in book form. | 8 | Metallurgy |
Sodium amide decomposes violently on contact with water, producing ammonia and sodium hydroxide:
When burned in oxygen, it will give oxides of sodium (which react with the produced water, giving sodium hydroxide) along with nitrogen oxides:
In the presence of limited quantities of air and moisture, such as in a poorly closed container, explosive mixtures of peroxides may form. This is accompanied by a yellowing or browning of the solid. As such, sodium amide is to be stored in a tightly closed container, under an atmosphere of an inert gas. Sodium amide samples which are yellow or brown in color represent explosion risks. | 0 | Organic Chemistry |
Although the terms direct and indirect bilirubin are used equivalently with conjugated and unconjugated bilirubin, this is not quantitatively correct, because the direct fraction includes both conjugated bilirubin and δ bilirubin.
Delta bilirubin is albumin-bound conjugated bilirubin. In the other words, delta bilirubin is the kind of bilirubin covalently bound to albumin, which appears in the serum when hepatic excretion of conjugated bilirubin is impaired in patients with hepatobiliary disease. Furthermore, direct bilirubin tends to overestimate conjugated bilirubin levels due to unconjugated bilirubin that has reacted with diazosulfanilic acid, leading to increased azobilirubin levels (and increased direct bilirubin).
δ bilirubin = total bilirubin – (unconjugated bilirubin + conjugated bilirubin) | 1 | Biochemistry |
A nonstop mutation, also called a stop-loss variant, is a point mutation that occurs within a stop codon. Nonstop mutations cause the continued translation of an mRNA strand into what should be an untranslated region. Most polypeptides resulting from a gene with a nonstop mutation lose their function due to their extreme length and the impact on normal folding. Nonstop mutations differ from nonsense mutations in that they do not create a stop codon but, instead, delete one. Nonstop mutations also differ from missense mutations, which are point mutations where a single nucleotide is changed to cause replacement by a different amino acid. Nonstop mutations have been linked with many inherited diseases including endocrine disorders, eye disease, and neurodevelopmental disorders. | 1 | Biochemistry |
An insect repellent (also commonly called "bug spray") is a substance applied to the skin, clothing, or other surfaces to discourage insects (and arthropods in general) from landing or climbing on that surface. Insect repellents help prevent and control the outbreak of insect-borne (and other arthropod-bourne) diseases such as malaria, Lyme disease, dengue fever, bubonic plague, river blindness, and West Nile fever. Pest animals commonly serving as vectors for disease include insects such as flea, fly, and mosquito; and ticks (arachnids).
Some insect repellents are insecticides (bug killers), but most simply discourage insects and send them flying or crawling away. Nearly any would be fatal upon reaching the median lethal dose, but classification as an insecticide implies death even at lower doses. | 1 | Biochemistry |
By local transformations, the weld toe plastically deformed and solidified.
The depth of the aftertreatment track should be between 0.2 and 0.35 mm.
The undercut at the weld toe is no longer recognizable. | 8 | Metallurgy |
Etching has applications in the printed circuit board and semiconductor fabrication industries. It is also used in the aerospace industry to remove shallow layers of material from large aircraft components, missile skin panels, and extruded parts for airframes. Etching is used widely to manufacture integrated circuits and Microelectromechanical systems. In addition to the standard, liquid-based techniques, the semiconductor industry commonly uses plasma etching. | 8 | Metallurgy |
An antibiotic called geldanamycin was separated from media by the capsular perstraction. Geldanamycin is hydrophobic. Outer particle diameter varied from than less 500 to 750 µm. Alginate formed the shell of capsule and its thickness varied from 30 to 90 µm. Dibutyl sebacate or oleic acid as liquid core extracted geldanamycin well. The bigger agitation and thinner capsule membrane were, the faster transfer rate was.
Geldanamycin was back-extracted from capsules. Dibutyl sebacate capsules were disposable because liquid core came out from capsules in the back-extraction. On the contrary, oleic acid remained in capsules during the back-extraction when an extractant was saturated with oleic acid. Nevertheless, the presence of oleic acid in the back-extraction solution demanded more purification steps (precipitation, centrifugation and filtration). Oleic acid was removed because it prevents crystallization of geldanamycin. Therefore, geldanamycin was crystallized and the end product was highly purified.
Enzymes can be immobilized to the capsule membrane. In this case, the capsule external diameter was 500 µm and internal diameter 300 µm. The product of enzyme-catalyzed reaction can be concentrated to capsules and the end-product inhibition is low. Enzyme recycling could be performed by back-extracting the product. The technique has been applied to the hydrolysis of penicillin G. | 3 | Analytical Chemistry |
A phonovoltaic (pV) cell converts vibrational (phonons) energy into a direct current much like the photovoltaic effect in a photovoltaic (PV) cell converts light (photon) into power. That is, it uses a p-n junction to separate the electrons and holes generated as valence electrons absorb optical phonons more energetic than the band gap, and then collects them in the metallic contacts for use in a circuit. The pV cell is an application of heat transfer physics and competes with other thermal energy harvesting devices like the thermoelectric generator.
While the thermoelectric generator converts heat, a broad spectrum of phonon and electron energy, to electricity, the pV cell converts only a narrow band of phonon energy, i.e., only the most energetic optical phonon modes. A narrow band of excited optical phonons has much less entropy than heat. Thus, the pV cell can exceed the thermoelectric efficiency. However, exciting and harvesting the optical phonon poses a challenge. | 7 | Physical Chemistry |
The solidifying behavior depends on the alloy composition. Pure metals solidify at a certain temperature, forming crystals of one phase. Eutectic alloys also solidify at a single temperature, all components precipitating simultaneously in so-called coupled growth. Non-eutectic compositions on cooling start to first precipitate the non-eutectic phase; dendrites when it is a metal, large crystals when it is an intermetallic compound. Such a mixture of solid particles in a molten eutectic is referred to as a mushy state. Even a relatively small proportion of solids in the liquid can dramatically lower its fluidity.
The temperature of total solidification is the solidus of the alloy, the temperature at which all components are molten is the liquidus.
The mushy state is desired where a degree of plasticity is beneficial for creating the joint, allowing filling larger gaps or being wiped over the joint (e.g. when soldering pipes). In hand soldering of electronics it may be detrimental as the joint may appear solidified while it is not yet. Premature handling of such joint then disrupts its internal structure and leads to compromised mechanical integrity. | 8 | Metallurgy |
* According to the Big Bang theory, in the early universe at high temperatures when the universe was only a few tens of microseconds old, the phase of matter took the form of a hot phase of quark matter called the quark–gluon plasma (QGP).
* Compact stars (neutron stars). A neutron star is much cooler than 10 K, but gravitational collapse has compressed it to such high densities, that it is reasonable to surmise that quark matter may exist in the core. Compact stars composed mostly or entirely of quark matter are called quark stars or strange stars.
* QCD matter may exist within the collapsar of a gamma-ray burst, where temperatures as high as 6.7 × 10 K may be generated.
At this time no star with properties expected of these objects has been observed, although some evidence has been provided for quark matter in the cores of large neutron stars.
* Strangelets. These are theoretically postulated (but as yet unobserved) lumps of strange matter comprising nearly equal amounts of up, down and strange quarks. Strangelets are supposed to be present in the galactic flux of high energy particles and should therefore theoretically be detectable in cosmic rays here on Earth, but no strangelet has been detected with certainty.
* Cosmic ray impacts. Cosmic rays comprise a lot of different particles, including highly accelerated atomic nuclei, particularly that of iron.
Laboratory experiments suggests that the inevitable interaction with heavy noble gas nuclei in the upper atmosphere would lead to quark–gluon plasma formation.
* Quark matter with baryon number over about 300 may be more stable than nuclear matter. This form of baryonic matter could possibly form a continent of stability. | 7 | Physical Chemistry |
Three major classes of charge transfer reactions can be studied at an ITIES:
*Ion transfer reactions
*Assisted ion transfer reactions
*Heterogeneous electron transfer reactions
The Nernst equation for an ion transfer reaction reads
where is the standard transfer potential defined as the Gibbs energy of transfer expressed in a voltage scale.
The Nernst equation for a single heterogeneous electron transfer reaction reads
where is the standard redox potential for the interfacial transfer of electrons defined as the difference the standard redox potentials of the two redox couples but referred to the aqueous standard hydrogen electrode (SHE). | 7 | Physical Chemistry |
'Jose H. Zagal Moya (born in Talca Chile, December 19, 1949) is a Chilean scientist educated at the University of Chile with postgraduate training in the United States of America with a Ph.D. degree from Case Western Reserve University, Cleveland Ohio and postdoctoral training at Brookhaven National Laboratory , Upton, New York. At present he is a Distinguished Professor, Department of Chemistry and Materials, Faculty of Chemistry and Biology, Universidad de Santiago de Chile (USACH) where he directs the Laboratory of Electrocatalysis since 1982. He got his Ph.D. in chemistry Case Western Reserve University, US (1978) and was postdoctoral fellow at Brookhaven National Laboratory, Upton, New York, in 1982. His main research efforts are focused on the fundamentals of electron transfer reactions that are relevant for energy conversion and sensors. He has contributed in the area of electrocatalysis, electrodes modified with metal macrocyclics, electrochemistry of biological molecules, the catalysis of the reduction of molecular oxygen and many other reactions of relevance, conductive polymers, electrochemical sensors and in pioneering work in the establishment of non-linear correlations between thermodynamic properties of molecular catalysts and their electrochemical reactivity. These contributions are essential in the development of non-precious metal catalysts for energy conversion devices and electrochemical sensors. [1][2][3]
He also has contributed in the field of corrosion, conductive polymers and his well-known volcano correlations for the electrocatalytic properties of surface-confined molecular catalysts | 7 | Physical Chemistry |
A scoring matrix or a table of values is required for evaluating the significance of a sequence alignment, such as describing the probability of a biologically meaningful amino-acid or nucleotide residue-pair occurring in an alignment. Typically, when two nucleotide sequences are being compared, all that is being scored is whether or not two bases are the same at one position. All matches and mismatches are respectively given the same score (typically +1 or +5 for matches, and -1 or -4 for mismatches). But it is different for proteins. Substitution matrices for amino acids are more complicated and implicitly take into account everything that might affect the frequency with which any amino acid is substituted for another. The objective is to provide a relatively heavy penalty for aligning two residues together if they have a low probability of being homologous (correctly aligned by evolutionary descent). Two major forces drive the amino-acid substitution rates away from uniformity: substitutions occur with the different frequencies, and lessen functionally tolerated than others. Thus, substitutions are selected against.
Commonly used substitution matrices include the blocks substitution (BLOSUM) and point accepted mutation (PAM) matrices. Both are based on taking sets of high-confidence alignments of many homologous proteins and assessing the frequencies of all substitutions, but they are computed using different methods.
Scores within a BLOSUM are log-odds scores that measure, in an alignment, the logarithm for the ratio of the likelihood of two amino acids appearing with a biological sense and the likelihood of the same amino acids appearing by chance. The matrices are based on the minimum percentage identity of the aligned protein sequence used in calculating them. Every possible identity or substitution is assigned a score based on its observed frequencies in the alignment of related proteins. A positive score is given to the more likely substitutions while a negative score is given to the less likely substitutions.
To calculate a BLOSUM matrix, the following equation is used:
Here, is the probability of two amino acids and replacing each other in a homologous sequence, and and are the background probabilities of finding the amino acids and in any protein sequence. The factor is a scaling factor, set such that the matrix contains easily computable integer values. | 1 | Biochemistry |
There is no electron repulsion in a d complex, and the single electron resides in the t orbital ground state. A d octahedral metal complex, such as [Ti(HO)], shows a single absorption band in a UV-vis experiment. The term symbol for d is D, which splits into the T and E states. The t orbital set holds the single electron and has a T state energy of -4Dq. When that electron is promoted to an e orbital, it is excited to the E state energy, +6Dq. This is in accordance with the single absorption band in a UV-vis experiment. The prominent shoulder in this absorption band is due to a Jahn–Teller distortion which removes the degeneracy of the two E states. However, since these two transitions overlap in a UV-vis spectrum, this transition from T to E does not require a Tanabe–Sugano diagram. | 7 | Physical Chemistry |
As with many signal transduction pathways, plant gene expression during immune responses can be regulated by degradation. This often occurs when hormone binding to hormone receptors stimulates ubiquitin-associated degradation of repressor proteins that block expression of certain genes. The net result is hormone-activated gene expression. Examples:
* Auxin: binds to receptors that then recruit and degrade repressors of transcriptional activators that stimulate auxin-specific gene expression.
* Jasmonic acid: similar to auxin, except with jasmonate receptors impacting jasmonate-response signaling mediators such as JAZ proteins.
* Gibberellic acid: Gibberellin causes receptor conformational changes and binding and degradation of Della proteins.
* Ethylene: Inhibitory phosphorylation of the EIN2 ethylene response activator is blocked by ethylene binding. When this phosphorylation is reduced, EIN2 protein is cleaved and a portion of the protein moves to the nucleus to activate ethylene-response gene expression. | 1 | Biochemistry |
In chemistry, chromism is a process that induces a change, often reversible, in the colors of compounds. In most cases, chromism is based on a change in the electron states of molecules, especially the π- or d-electron state, so this phenomenon is induced by various external stimuli which can alter the electron density of substances. It is known that there are many natural compounds that have chromism, and many artificial compounds with specific chromism have been synthesized to date. It is usually synonymous with chromotropism, the (reversible) change in color of a substance due to the physical and chemical properties of its ambient surrounding medium, such as temperature and pressure, light, solvent, and presence of ions and electrons.
Chromism is classified by what kind of stimuli are used. Examples of the major kinds of chromism are as follows.
* thermochromism is chromism that is induced by heat, that is, a change of temperature. This is the most common chromism of all.
* photochromism is induced by light irradiation. This phenomenon is based on the isomerization between two different molecular structures, light-induced formation of color centers in crystals, precipitation of metal particles in a glass, or other mechanisms.
* electrochromism is induced by the gain and loss of electrons. This phenomenon occurs in compounds with redox active sites, such as metal ions or organic radicals.
*solvatochromism depends on the polarity of the solvent. Most solvatochromic compounds are metal complexes.
There are many more chromisms and these are listed below in .
The output from the chromisms described above is observed by a change in the absorption spectra of the chromic material. An increasingly important group of chromisms are those where changes are displayed in their emission spectra. Hence they are called fluorochromisms, exemplified by solvatofluorochromism, electrofluorochromism and mechanofluorochromism. | 5 | Photochemistry |
Viral epitranscriptomics is the field that studies RNA modifications in viral transcripts that do not affect the sequence of the transcript but that are functionally relevant. So far, the studies have been focused on viral transcripts of mammalian viruses. Mammalian viral transcripts must function in a mammalian cell, so they must acquire the same epigenetic marks as the host cell. For this, viruses make use of the numerous mRNA modifying enzymes found in the host cells. | 1 | Biochemistry |
Sulfur concrete has a low porosity and is a poorly permeable material. Its low hydraulic conductivity slows down water ingress in its low porosity matrix and so decreases the transport of harmful chemical species, such as chloride (pitting corrosion), towards the steel reinforcements (physical protection of steel as long as no microcracks develop in the sulfur concrete matrix). It is resistant to some compounds like acids which attack normal concrete.
Beside its impermeability, Loov et al. (1974) also consider amongst the beneficial characteristics of sulfur concrete its low thermal and electrical conductivities. Sulfur concrete does not cause adverse reaction with glass (no alkali–silica reaction), does not produce efflorescences, and also presents a smooth surface finish. They also mention amongst its main limitations, its high coefficient of thermal expansion, the possible formation of acid under the action of water and sunlight. It also reacts with copper and produces a smell when melted. | 8 | Metallurgy |
Recognizing that approximately 50% of commercial pharmaceuticals are salts, ionic liquid forms of a number of pharmaceuticals have been investigated. Combining a pharmaceutically active cation with a pharmaceutically active anion leads to a Dual Active ionic liquid in which the actions of two drugs are combined.
ILs can extract specific compounds from plants for pharmaceutical, nutritional and cosmetic applications, such as the antimalarial drug artemisinin from the plant Artemisia annua. | 7 | Physical Chemistry |
A crucible and its lid are pre-weighed after thorough drying. The sample is added to the completely dry crucible and lid and together they are weighed to determine the mass of the sample by difference. The sample is placed in the hot furnace long enough so that complete combustion of the sample occurs. The crucible, lid and ash then are re-weighed. | 3 | Analytical Chemistry |
The phosphatases in the PHLPP family, PHLPP1 and PHLPP2 have been shown to directly dephosphorylate, and therefore inactivate, distinct Akt isoforms, at one of the two critical phosphorylation sites required for activation: Serine473. PHLPP2 dephosphorylates AKT1 and AKT3, whereas PHLPP1 is specific for AKT2 and AKT3. Lack of PHLPP appears to have effects on growth factor-induced Akt phosphorylation. When both PHLPP1 and PHLPP2 are knocked down using siRNA and cells are stimulated using epidermal growth factor, peak Akt phosphorylation at both Serine473 and Threonine308 (the other site required for full Akt activation) is increased dramatically. | 1 | Biochemistry |
A rich source of inorganic nitrate in the human diets come from leafy green foods, such as spinach and arugula. (inorganic nitrate) is the viable active component within beetroot juice and other vegetables. Drinking water is also a dietary source.
Dietary nitrate supplementation delivers positive results when testing endurance exercise performance.
Ingestion of large doses of nitrate either in the form of pure sodium nitrate or beetroot juice in young healthy individuals rapidly increases plasma nitrate concentration by a factor of 2 to 3, and this elevated nitrate concentration can be maintained for at least 2 weeks. Increased plasma nitrate stimulates the production of nitric oxide, NO. Nitric oxide is an important physiological signaling molecule that is used in, among other things, regulation of muscle blood flow and mitochondrial respiration. | 0 | Organic Chemistry |
Dissolution of an organic solid can be described as an equilibrium between the substance in its solid and dissolved forms. For example, when sucrose (table sugar) forms a saturated solution
An equilibrium expression for this reaction can be written, as for any chemical reaction (products over reactants):
where K</sup> is called the thermodynamic solubility constant. The braces indicate activity. The activity of a pure solid is, by definition, unity. Therefore
The activity of a substance, A, in solution can be expressed as the product of the concentration, [A], and an activity coefficient, γ. When K,
is obtained. This is equivalent to defining the standard state as the saturated solution so that the activity coefficient is equal to one. The solubility constant is a true constant only if the activity coefficient is not affected by the presence of any other solutes that may be present. The unit of the solubility constant is the same as the unit of the concentration of the solute. For sucrose K = 1.971 mol dm at 25 °C. This shows that the solubility of sucrose at 25 °C is nearly 2 mol dm (540 g/L). Sucrose is unusual in that it does not easily form a supersaturated solution at higher concentrations, as do most other carbohydrates. | 7 | Physical Chemistry |
The cellular reproduction process of meiosis was discovered by Oscar Hertwig in 1876. Mitosis was discovered several years later in 1882 by Walther Flemming.
Hertwig studied sea urchins, and noticed that each egg contained one nucleus prior to fertilization and two nuclei after. This discovery proved that one spermatozoon could fertilize an egg, and therefore proved the process of meiosis. Hermann Fol continued Hertwig's research by testing the effects of injecting several spermatozoa into an egg, and found that the process did not work with more than one spermatozoon.
Flemming began his research of cell division starting in 1868. The study of cells was an increasingly popular topic in this time period. By 1873, Schneider had already begun to describe the steps of cell division. Flemming furthered this description in 1874 and 1875 as he explained the steps in more detail. He also argued with Schneider's findings that the nucleus separated into rod-like structures by suggesting that the nucleus actually separated into threads that in turn separated. Flemming concluded that cells replicate through cell division, to be more specific mitosis.
Matthew Meselson and Franklin Stahl are credited with the discovery of DNA replication. Watson and Crick acknowledged that the structure of DNA did indicate that there is some form of replicating process. However, there was not a lot of research done on this aspect of DNA until after Watson and Crick. People considered all possible methods of determining the replication process of DNA, but none were successful until Meselson and Stahl. Meselson and Stahl introduced a heavy isotope into some DNA and traced its distribution. Through this experiment, Meselson and Stahl were able to prove that DNA reproduces semi-conservatively. | 1 | Biochemistry |
Zhong Zhong (, born 27 November 2017) and Hua Hua (, born 5 December 2017) are a pair of identical crab-eating macaques (also referred to as cynomolgus monkeys) that were created through somatic cell nuclear transfer (SCNT), the same cloning technique that produced Dolly the sheep in 1996. They are the first cloned primates produced by this technique. Unlike previous attempts to clone monkeys, the donated nuclei came from fetal cells, not embryonic cells. The primates were born from two independent surrogate pregnancies at the Institute of Neuroscience of the Chinese Academy of Sciences in Shanghai. | 1 | Biochemistry |
Long non-coding RNA (LncRNA) are a type of RNA which is usually defined as transcripts which are greater than 200 base-pairs in length and not translated into proteins. This limitation distinguishes lncRNA from small non-coding RNAs which encompasses microRNAs (miRNAs), small interfering RNAs (siRNAs), Piwi-interacting RNAs (piRNAs), small nucleolar RNAs (snoRNAs), and other short RNAs. Long non-coding RNAs include lincRNAs, intronic ncRNAs, circular and linear ncRNA. | 1 | Biochemistry |
In crystalline materials, Umklapp scattering (also U-process or Umklapp process) is a scattering process that results in a wave vector (usually written k) which falls outside the first Brillouin zone. If a material is periodic, it has a Brillouin zone, and any point outside the first Brillouin zone can also be expressed as a point inside the zone. So, the wave vector is then mathematically transformed to a point inside the first Brillouin zone. This transformation allows for scattering processes which would otherwise violate the conservation of momentum: two wave vectors pointing to the right can combine to create a wave vector that points to the left. This non-conservation is why crystal momentum is not a true momentum.
Examples include electron-lattice potential scattering or an anharmonic phonon-phonon (or electron-phonon) scattering process, reflecting an electronic state or creating a phonon with a momentum k-vector outside the first Brillouin zone. Umklapp scattering is one process limiting the thermal conductivity in crystalline materials, the others being phonon scattering on crystal defects and at the surface of the sample.
The left panel of Figure 1 schematically shows the possible scattering processes of two incoming phonons with wave-vectors (k-vectors) k and k (red) creating one outgoing phonon with a wave vector k (blue). As long as the sum of k and k stay inside the first Brillouin zone (grey squares), k is the sum of the former two, thus conserving phonon momentum. This process is called normal scattering (N-process).
With increasing phonon momentum and thus larger wave vectors k and k, their sum might point outside the first Brillouin zone (k). As shown in the right panel of Figure 1, k-vectors outside the first Brillouin zone are physically equivalent to vectors inside it and can be mathematically transformed into each other by the addition of a reciprocal lattice vector G'. These processes are called Umklapp scattering and change the total phonon momentum.
Umklapp scattering is the dominant process for electrical resistivity at low temperatures for low defect crystals (as opposed to phonon-electron scattering, which dominates at high temperatures, and high-defect lattices which lead to scattering at any temperature.)
Umklapp scattering is the dominant process for thermal resistivity at high temperatures for low defect crystals. The thermal conductivity for an insulating crystal where the U-processes are dominant has 1/T dependence. | 7 | Physical Chemistry |
A clinical trial in cardiac arrest patients showed that hypothermia improved neurological outcome and reduced mortality. A retrospective study of the use of hypothermia for cardiac arrest patients showed favorable neurological outcome and survival. Osborn waves on electrocardiogram (ECG) are frequent during TTM after cardiac arrest, particularly in patients treated with 33 °C. Osborn waves are not associated with increased risk of ventricular arrhythmia, and may be considered a benign physiological phenomenon, associated with lower mortality in univariable analyses. | 1 | Biochemistry |
When the single bond between the two centres is free to rotate, cis/trans descriptors become invalid. Two widely accepted prefixes used to distinguish diastereomers on sp³-hybridised bonds in an open-chain molecule are syn and anti. Masamune proposed the descriptors which work even if the groups are not attached to adjacent carbon atoms. It also works regardless of CIP priorities. Syn describes groups on the same face while anti describes groups on opposite faces. The concept applies only to the Zigzag projection. The descriptors only describe relative stereochemistry rather than absolute stereochemistry.
All isomers are same. | 4 | Stereochemistry |
Ferrocene-containing dendrimers can be synthesized by both convergent and divergent methods. Some of the first dendrimers of this type, were made by attaching ferrocene units to small silicon containing dendrimers.
Dendrimers with peripheral ferrocene groups are usually synthesized by attaching ferrocene to the core by either olefin metathesis or by hydrosilylation. As an example, tetraallylsilane undergoes Pt-catalyzed hydrosilylation to form the core. This core was then reacted with ferrocenyllithium to form 1. Convergent approaches can also be used to make dendrimers with peripheral ferrocene. As an example, figure 1 shows a 54-ferrocene dendrimer which was synthesized by a fast convergent approach.
Dendrimers with ferrocene cores have been synthesized by decorating suitably functionalized ferrocenes, e.g., decaallylferrocene.
synthesis
Ferrocene-containing dendrimers can be synthesized by convergence and diffusion methods. By linking ferrocene units to small silicon-containing dendrimers, some of these first-type dendrimers can be made. [3]
Dendritic macromolecules with peripheral ferrocene groups are usually synthesized by linking ferrocene to the core through olefin metathesis or hydrosilylation [1]. For example, tetraallyl silane undergoes Pt-catalyzed hydrosilylation to form a core. The core is then reacted with ferrocenyl lithium to form 1. [4]. The convergence method can also be used to make dendrimers with peripheral ferrocene.
en.china.cn is a good place to supply polymer resin | 6 | Supramolecular Chemistry |
Recent excavations in Middle Ganges Valley show iron working in India may have begun as early as 1800 BCE. In the 5th century BCE, the Greek historian Herodotus observed that "Indian and the Persian army used arrows tipped with iron." Ancient Romans used armour and cutlery made of Indian iron. Pliny the Elder also mentioned Indian iron. Muhammad al-Idrisi wrote the Hindus excelled in the manufacture of iron, and that it would be impossible to find anything to surpass the edge from Hindwani steel. Quintus Curtius wrote about an Indian present of steel to Alexander. Ferrum indicum appeared in the list of articles subject to duty under Marcus Aurelius and Commodus. Indian Wootz steel was held in high regard in Europe, and Indian iron was often considered to be the best. | 8 | Metallurgy |
While α-galactose as a part of glycoprotein glycans from vertebrates other than higher apes was known for a long time as being a prominent xeno-antigen, its implication in allergy only began to materialize when complications during treatment with a recombinant monoclonal antibody (Erbitux) were attributed to IgE directed against α-Gal containing N-glycans on this antibody. The incidencies of anaphylaxis due to Erbitux were confined to a certain area in the eastern United States, which raised speculations about the involvement of a particular type of tick endemic in this area. However, IgE antibodies against the α-Gal epitope should be taken into account in the diagnosis of milk and meat allergy. It is currently largely unexplored whether this type of CCD is generally also clinically irrelevant such as the plant/insect CCDs. The very localized case of Erbitux complications points at a possible if rare clinical significance of α-Gal.
Yet other potentially immunogenic carbohydrates with widespread occurrence such as N-Glycolylneuraminic acid, which does not occur in humans, or plant O-glycans (arabinogalactans and arabinans) may be mentioned but have so far not qualified as either IgE or as cross-reactive determinants.
Literature: | 0 | Organic Chemistry |
In 1956, Lev Landau developed the Fermi liquid theory, where he treated the case of a Fermi liquid, i.e., a system with repulsive, not necessarily small, interactions between fermions. The theory shows that the thermodynamic properties of an ideal Fermi gas and a Fermi liquid do not differ that much. It can be shown that the Fermi liquid is equivalent to a Fermi gas composed of collective excitations or quasiparticles, each with a different effective mass and magnetic moment. | 7 | Physical Chemistry |
The dysfunction of potassium channels, including SK channels, is thought to play a role in the pathogenesis of Parkinson's disease (PD), a progressive neurodegenerative disorder.
SK channel blockers control the firing rate (the number of action potentials produced by a neuron in a given time) and the firing pattern (the way action potentials are allocated throughout time) through their production of m-AHP. SK channel activators decrease the firing rate, neuron sensitivity to excitatory stimuli, mediating neuroprotection, whereas SK channel blockers increase the firing rate and sensitivity to excitatory stimuli. This has important implications as to the function of dopaminergic neurons. For example, the amount of dopamine released by midbrain dopaminergic neurons is much higher when the frequency of firing increases than when they fire at a constant rate.
SK channels are widely expressed in midbrain dopaminergic neurons. Multiple pharmacological techniques have been used to adjust SK affinity for calcium ions, thereby modulating the excitability of substantia nigra dopaminergic neurons. Blockage of SK channels in vivo increases the firing rate of substantia nigra cells, which increases the amount of dopamine released from the synaptic terminals. When a large amount of dopamine accumulates in the cytosol, cell damage is induced due to the build-up of free radicals and damage to mitochondria.
In addition, techniques have been used to modulate SK channels in order to alter the dopamine phenotype of neurons. After the loss of TH+ (tyrosine hydroxylase-positive) substantia nigra compacta (SNc) neurons due to Parkinson’s-induced neurodegeneration, the number of these neurons can partially recover via a cell phenotype "shift" from TH- (tyrosine hydroxylase-negative) to TH+. The number of TH+ neurons can be altered by SK channel modulation; to be specific, the infusion of SK agonists into substantia nigra increases the number of TH+ neurons, whereas the infusion of SK antagonist decreases the number of TH+ neurons. The reason for this relationship between SK channels and TH expression may be due to neuroprotection against dopamine toxicity.
Two contradictory methods have been suggested as therapeutic options for the improvement of PD symptoms:
Inhibition of SK channels
*Inhibition of SK channels, to be specific the blockage of SK3 channels, increases the frequency of firing in dopaminergic neurons, thereby increasing the release of dopamine. It is, therefore, thought that the application of SK3 channels blockers in PD patients may alleviate short-term motor symptoms.
*However, inhibition also results in a decreased number of TH+ substantia nigra compacta (SNc) neurons in the cell, which results in a decrease in dopamine synthesis over the long term.
Facilitation of SK channels
*Enhancing the function of SK channels increases the number of TH+ substantia nigra compacta (SNc) neurons in the cell, thereby maintaining dopamine synthesis over the long term.
*However, the facilitation of SK channels decreases the firing frequency in dopaminergic neurons over the short term. | 1 | Biochemistry |
People can be exposed to halothane in the workplace by breathing it in as waste anaesthetic gas, skin contact, eye contact, or swallowing it. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 2 ppm (16.2 mg/m) over 60 minutes. | 4 | Stereochemistry |
In an inversion through a centre of symmetry, (the element), we imagine taking each point in a molecule and then moving it out the same distance on the other side. In summary, the inversion operation projects each atom through the centre of inversion and out to the same distance on the opposite side. The inversion center is a point in space that lies in the geometric center of the molecule. As a result, all the cartesian coordinates of the atoms are inverted (i.e. to ). The symbol used to represent inversion center is . When the inversion operation is carried out times, it is denoted by , where when is even and when is odd.
Examples of molecules that have an inversion center include certain molecules with octahedral geometry (general formula ), square planar geometry (general formula ), and ethylene (). Examples of molecules without inversion centers are cyclopentadienide () and molecules with trigonal pyramidal geometry (general formula ). | 7 | Physical Chemistry |
The stockpiles, which have been maintained for more than 50 years, are now considered obsolete. Public Law 99-145, contains section 1412, which directs the Department of Defense (DOD) to dispose of the stockpiles. This directive fell upon the DOD with joint cooperation from the Federal Emergency Management Agency (FEMA). The Congressional directive has resulted in the present Chemical Stockpile Disposal Program.
Historically, chemical munitions have been disposed of by land burial, open burning, and ocean dumping (referred to as Operation CHASE). However, in 1969, the National Research Council (NRC) recommended that ocean dumping be discontinued. The Army then began a study of disposal technologies, including the assessment of incineration as well as chemical neutralization methods. In 1982, that study culminated in the selection of incineration technology, which is now incorporated into what is known as the baseline system. Construction of the Johnston Atoll Chemical Agent Disposal System (JACADS) began in 1985.
This was to be a full-scale prototype facility using the baseline system. The prototype was a success but there were still many concerns about CONUS operations. To address growing public concern over incineration, Congress, in 1992, directed the Army to evaluate alternative disposal approaches that might be "significantly safer", more cost effective, and which could be completed within the established time frame. The Army was directed to report to Congress on potential alternative technologies by the end of 1993, and to include in that report: "any recommendations that the National Academy of Sciences makes ..." In June 2007, the disposal program achieved the milestone of reaching 45% destruction of the chemical weapon stockpile. The Chemical Materials Agency (CMA) releases regular updates to the public regarding the status of the disposal program. On July 7, 2023, the program completed destruction of all declared chemical weapons. | 1 | Biochemistry |
DNA microarray studies done on different fish species exposed to low-oxygen conditions have shown that at the genetic level fish respond to hypoxia by changing the expression of genes involved in oxygen transport, ATP production, and protein synthesis. In the liver of mudsuckers exposed to hypoxia there were changes in the expression of genes involved in heme metabolism such as hemopexin, heme oxygenase 1, and ferritin. Changes in the sequestration and metabolism of iron may suggest hypoxia induced erythropoiesis and increased demand for hemoglobin synthesis, leading to increased oxygen uptake and transport. Increased expression of myoglobin, which is normally only found in muscle tissue, has also been observed after hypoxia exposure in the gills of zebrafish and in non-muscle tissue of the common carp suggesting increased oxygen transport throughout fish tissues.
Microarray studies done on fish species exposed to hypoxia typically show a metabolic switch, that is, a decrease in the expression of genes involved in aerobic metabolism and an increase in expression of genes involved in anaerobic metabolism. Zebrafish embryos exposed to hypoxia decreased expression of genes involved in the citric acid cycle including, succinate dehydrogenase, malate dehydrogenase, and citrate synthase, and increased expression of genes involved in glycolysis such as phosphoglycerate mutase, enolase, aldolase, and lactate dehydrogenase. A decrease in protein synthesis is an important response to hypoxia to decrease ATP demand for whole organism metabolic suppression. Decreases in the expression of genes involved in protein synthesis, such as elongation factor-2 and several ribosomal proteins, have been shown in the muscle of the mudsucker and gills of adult zebrafish after hypoxia exposure .
Research in mammals has implicated hypoxia inducible factor (HIF) as a key regulator of gene expression changes in response to hypoxia However, a direct link between fish HIFs and gene expression changes in response to hypoxia has yet to be found. Phylogenetic analysis of available fish, tetrapod, and bird HIF-α and -β sequences shows that the isoforms of both subunits present in mammals are also represented in fish Within fish, HIF sequences group close together and are distinct from tetrapod and bird sequences. As well, amino acid analysis of available fish HIF-α and -β sequences reveals that they contain all functional domains shown to be important for mammalian HIF function, including the basic helix-loop-helix (bHLH) domain, Per-ARNT-Sim (PAS) domain, and the oxygen-dependent degradation domain (ODD), which render the HIF-α subunit sensitive to oxygen levels. The evolutionary similarity between HIF sequences in fish, tetrapods and birds, as well as the conservation of important functional domains suggests that HIF function and regulation is similar between fish and mammalian species. There is also evidence of novel HIF mechanisms present in fish not found in mammals. In mammals, HIF-α protein is continuously synthesized and regulated post-translationally by changing oxygen conditions, but it has been shown in different fish species that HIF-α mRNA levels are also responsive to hypoxia. In the hypoxia tolerant grass carp, substantial increases in HIF-1α and HIF-3α mRNA were observed in all tissues after hypoxia exposure. Likewise, mRNA levels of HIF-1α and HIF-2α were hypoxia-responsive in the ovaries of the Atlantic croaker during both short and long term hypoxia. | 9 | Geochemistry |
KAP1 forms a complex with MDM2 (a ubiquitin E3 ligase) that binds to p53. The complex marks the bound p53 for degradation. p53 is a known precursor of apoptosis that facilitates the synthesis of proteins necessary for cell death so its degradation results in apoptosis inhibition. | 1 | Biochemistry |
A Folch solution is a solution containing chloroform and methanol, usually in a 2:1 (vol/vol) ratio. One of its uses is in separating polar from nonpolar compounds, for example separating nonpolar lipids from polar proteins and carbohydrates in blood serum. | 0 | Organic Chemistry |
Silicon carbide can be used in the production of graphene because of its chemical properties that promote the production of graphene on the surface of SiC nanostructures.
When it comes to its production, silicon is used primarily as a substrate to grow the graphene. But there are actually several methods that can be used to grow the graphene on the silicon carbide. The confinement controlled sublimation (CCS) growth method consists of a SiC chip that is heated under vacuum with graphite. Then the vacuum is released very gradually to control the growth of graphene. This method yields the highest quality graphene layers. But other methods have been reported to yield the same product as well.
Another way of growing graphene would be thermally decomposing SiC at a high temperature within a vacuum. But this method turns out to yield graphene layers that contain smaller grains within the layers. So there have been efforts to improve the quality and yield of graphene. One such method is to perform ex situ graphitization of silicon terminated SiC in an atmosphere consisting of argon. This method has proved to yield layers of graphene with larger domain sizes than the layer that would be attainable via other methods. This new method can be very viable to make higher quality graphene for a multitude of technological applications.
When it comes to understanding how or when to use these methods of graphene production, most of them mainly produce or grow this graphene on the SiC within a growth enabling environment. It is utilized most often at rather higher temperatures (such as 1300 °C) because of SiC thermal properties. However, there have been certain procedures that have been performed and studied that could potentially yield methods that use lower temperatures to help manufacture graphene. More specifically this different approach to graphene growth has been observed to produce graphene within a temperature environment of around 750 °C. This method entails the combination of certain methods like chemical vapor deposition (CVD) and surface segregation. And when it comes to the substrate, the procedure would consist of coating a SiC substrate with thin films of a transition metal. And after the rapid heat treating of this substance, the carbon atoms would then become more abundant at the surface interface of the transition metal film which would then yield graphene. And this process was found to yield graphene layers that were more continuous throughout the substrate surface. | 8 | Metallurgy |
The experimental set-up used to carry out UV-Vis absorption SEC measurements depends on the chosen configuration and the characteristics of the analyte. The experimental set-up is composed of a light source, a spectrometer, a potentiostat/galvanostat, a SEC cell, a three-electrode system, optical elements to conduct the light beam, and a computer for data collection and analysis. Currently, there are commercial devices that integrate all these elements in a single instrument, simplifying significantly the SEC experiments.
* Light source: provides the electromagnetic radiation that interacts with the sample while the electrochemical process is taking place. A specific source is required for the UV-Vis spectral region, being the most common the deuterium/halogen lamp.
* Spectrometer: instrument that allows measuring the properties of the light in a certain region of the electromagnetic spectrum. It uses a monochromator to separate the different spectral wavelengths of interest emitted by the light source. A diode-array detector can be used to obtain time-resolved spectra. For UV-Vis spectroelectrochemistry, spectrometer must be specific for UV-Vis spectral region.
* Potentiostat/Galvanostat: electronic device that allows controlling the working electrode potential regarding to the reference electrode or controlling the current that passes respect to the auxiliary electrode.
* Three electrode system: consists of a working electrode, a reference electrode and an auxiliary electrode. This system can be simplified by using screen-printed electrodes that include the three electrodes on a single holder.
* Spectroelectrochemical cell: device in which the solution and the system of three electrodes is located, avoiding possible interference in the optical path. It is the link between the electrochemistry and the UV-Vis absorption spectroscopy.
* Devices to conduct the radiation beam: lenses, mirrors and/or optical fibers. The last ones conduct electromagnetic radiation over great distances with hardly any losses. In addition, they simplify the optical configurations because they allow working with a small amount of solution. Optical fibers make easier to conduct and collect light near the electrode.
* Analysis and data collection devices: a computer collects the signals provided by the spectrometer and potentiostat that, using a suitable software, treats, analyzes and interprets the signals. | 7 | Physical Chemistry |
It may cause irritation. Its toxicological properties have not been fully investigated. Harmful if swallowed, Acute Toxicity. Only Hazardous when percent values are above 10%. | 3 | Analytical Chemistry |
Hydrothermal ore minerals, which typically form from high temperature aqueous solutions, trap tiny bubbles of liquids or gases when cooling and forming solid rock. The trapped fluid in an inclusion preserves a record of the composition, temperature and pressure of the mineralizing environment. An inclusion often contains two or more phases. If a vapor bubble is present in the inclusion along with a liquid phase, simple heating of the inclusion to the point of resorption of the vapor bubble gives a likely temperature of the original fluid. If minute crystals, such as halite, sylvite, hematite or sulfides, are present in the inclusion, they provide direct clues as to the composition of the original fluid. | 9 | Geochemistry |
Fatty acid oxidation also occurs in peroxisomes when the fatty acid chains are too long to be processed by the mitochondria. The same enzymes are used in peroxisomes as in the mitochondrial matrix and acetyl-CoA is generated. Very long chain (greater than C-22) fatty acids, branched fatty acids, some prostaglandins and leukotrienes undergo initial oxidation in peroxisomes until octanoyl-CoA is formed, at which point it undergoes mitochondrial oxidation.
One significant difference is that oxidation in peroxisomes is not coupled to ATP synthesis. Instead, the high-potential electrons are transferred to O, which yields hydrogen peroxide. The enzyme catalase, found primarily in peroxisomes and the cytosol of erythrocytes (and sometimes in mitochondria), converts the hydrogen peroxide into water and oxygen.
Peroxisomal β-oxidation also requires enzymes specific to the peroxisome and to very long fatty acids. There are four key differences between the enzymes used for mitochondrial and peroxisomal β-oxidation:
# The NADH formed in the third oxidative step cannot be reoxidized in the peroxisome, so reducing equivalents are exported to the cytosol.
# β-oxidation in the peroxisome requires the use of a peroxisomal carnitine acyltransferase (instead of carnitine acyltransferase I and II used by the mitochondria) for transport of the activated acyl group into the mitochondria for further breakdown.
# The first oxidation step in the peroxisome is catalyzed by the enzyme acyl-CoA oxidase.
# The β-ketothiolase used in peroxisomal β-oxidation has an altered substrate specificity, different from the mitochondrial β-ketothiolase.
Peroxisomal oxidation is induced by a high-fat diet and administration of hypolipidemic drugs like clofibrate. | 1 | Biochemistry |
The maximum power principle or Lotka's principle has been proposed as the fourth principle of energetics in open system thermodynamics. According to American ecologist Howard T. Odum, "The maximum power principle can be stated: During self-organization, system designs develop and prevail that maximize power intake, energy transformation, and those uses that reinforce production and efficiency." | 7 | Physical Chemistry |
In polymer chemistry, there are several mechanisms by which a polymerization reaction can terminate depending on the mechanism and circumstances of the reaction. A method of termination that applies to all polymer reactions is the depletion of monomer. In chain growth polymerization, two growing chains can collide head to head causing the growth of both of the chains to stop. In the case of radical or anionic polymerization, chain transfer can occur where the radical at the end of the growing chain can be transferred from the chain to an individual monomer unit causing a new chain to start growing and the previous chain to stop growing. With step-growth polymerization, the reaction can be terminated by adding a monofunctional species containing the same functionality as one or more of the types of monomer used in the reaction. For example, an alcohol can be used to stop a reaction between a polyisocyanate and a polyol because it will react with the isocyanate functionality to produce which is then no longer reactive with the polyol. | 7 | Physical Chemistry |
Amlodipine blocks the transmembrane influx of calcium into the vascular and cardiac smooth muscles resulting in vasodilation and hence a fall in blood pressure. Levamlodipine is an allosteric modulator and acts on the L-type of calcium channels. Receptor binding studies have shown that out of the two forms only the (S)-enantiomer of amlodipine binds to and blocks L-type calcium channels whereas the (R)-enantiomer has no activity on these channels.
The precise mechanisms by which levamlodipine relieves angina have not been fully explored, but are thought to include the following:
* Decreases peripheral resistance by arteriolar vasodilatation leading to the reduction in oxygen requirement and energy consumption of cardiac smooth muscles.
* Decreases coronary vascular resistance and can lead to an increase in coronary blood flow. | 4 | Stereochemistry |
Non-systematic, less-recognized and often unverified syntheses of silicon carbide include:
* César-Mansuète Despretz's passing an electric current through a carbon rod embedded in sand (1849)
* Robert Sydney Marsden's dissolution of silica in molten silver in a graphite crucible (1881)
* Paul Schuetzenberger's heating of a mixture of silicon and silica in a graphite crucible (1881)
* Albert Colson's heating of silicon under a stream of ethylene (1882). | 8 | Metallurgy |
In the medical field, nitrates, such as glyceryl trinitrate, isosorbide dinitrate, and isosorbide mononitrate, are used in the prophylaxis and management of acute coronary syndrome, myocardial infarction, acute pulmonary oedema. These class of drugs are also known as nitrovasodilators. | 0 | Organic Chemistry |
The electronic density functional is explicitly used in the calculation of the electronic ground state. Packages such as VASP have an option to calculate the electronic density of states per eV to facilitate the prediction of conduction bands and band gaps. | 3 | Analytical Chemistry |
The origin of the stereographic projection is not known, but it is believed to have been discovered by Ancient Greek astronomers and used for projecting the celestial sphere to the plane so that the motions of stars and planets could be analyzed using plane geometry. Its earliest extant description is found in Ptolemys Planisphere (2nd century AD), but it was ambiguously attributed to Hipparchus (2nd century BC) by Synesius (), and Apolloniuss Conics () contains a theorem which is crucial in proving the property that the stereographic projection maps circles to circles. Hipparchus, Apollonius, Archimedes, and even Eudoxus (4th century BC) have sometimes been speculatively credited with inventing or knowing of the stereographic projection, but some experts consider these attributions unjustified. Ptolemy refers to the use of the stereographic projection in a "horoscopic instrument", perhaps the described by Vitruvius (1st century BC).
By the time of Theon of Alexandria (4th century), the planisphere had been combined with a dioptra to form the planispheric astrolabe ("star taker"), a capable portable device which could be used for measuring star positions and performing a wide variety of astronomical calculations. The astrolabe was in continuous use by Byzantine astronomers, and was significantly further developed by medieval Islamic astronomers. It was transmitted to Western Europe during the 11th–12th century, with Arabic texts translated into Latin.
In the 16th and 17th century, the equatorial aspect of the stereographic projection was commonly used for maps of the Eastern and Western Hemispheres. It is believed that already the map created in 1507 by Gualterius Lud was in stereographic projection, as were later the maps of Jean Roze (1542), Rumold Mercator (1595), and many others. In star charts, even this equatorial aspect had been utilised already by the ancient astronomers like Ptolemy.
François dAguilon gave the stereographic projection its current name in his 1613 work Opticorum libri sex philosophis juxta ac mathematicis utiles' (Six Books of Optics, useful for philosophers and mathematicians alike).
In the late 16th century, Thomas Harriot proved that the stereographic projection is conformal; however, this proof was never published and sat among his papers in a box for more than three centuries. In 1695, Edmond Halley, motivated by his interest in star charts, was the first to publish a proof. He used the recently established tools of calculus, invented by his friend Isaac Newton. | 3 | Analytical Chemistry |
Surface conductivity may refer to the electrical conduction across a solid surface measured by surface probes. Experiments may be done to test this material property as in the n-type surface conductivity of p-type. Additionally, surface conductivity is measured in coupled phenomena such as photoconductivity, for example, for the metal oxide semiconductor ZnO. Surface conductivity differs from bulk conductivity for analogous reasons to the electrolyte solution case, where the charge carriers of holes (+1) and electrons (-1) play the role of ions in solution. | 7 | Physical Chemistry |
Levonorgestrel is a hormonal medication which is used in a number of birth control methods. It is combined with an estrogen to make combination birth control pills. As an emergency birth control, sold under the brand names Plan B One-Step and Julie, among others, it is useful within 72 hours of unprotected sex. The more time that has passed since sex, the less effective the medication becomes, and it does not work after pregnancy (implantation) has occurred. Levonorgestrel works by preventing ovulation or fertilization from occurring. It decreases the chances of pregnancy by 57–93%. In an intrauterine device (IUD), such as Mirena among others, it is effective for the long-term prevention of pregnancy. A levonorgestrel-releasing implant is also available in some countries.
Common side effects include nausea, breast tenderness, headaches, and increased, decreased, or irregular menstrual bleeding. When used as an emergency contraceptive, if pregnancy occurs, there is no evidence that its use harms the fetus. It is safe to use during breastfeeding. Birth control that contains levonorgestrel will not change the risk of sexually transmitted infections. It is a progestin and has effects similar to those of the hormone progesterone. It works primarily by preventing ovulation and closing off the cervix to prevent the passage of sperm.
Levonorgestrel was patented in 1960 and introduced for medical use together with ethinylestradiol in 1970. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In the United States, levonorgestrel-containing emergency contraceptives are available over the counter (OTC) for all ages. In 2020, it was the 323rd most commonly prescribed medication in the United States, with more than 800thousand prescriptions. | 4 | Stereochemistry |
Methylaluminoxane, commonly called MAO, is a mixture of organoaluminium compounds with the approximate formula (Al(CH)O). It is usually encountered as a solution in (aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene, Used in large excess, it activates precatalysts for alkene polymerization. | 7 | Physical Chemistry |
Synthesis of vitamin D in nature is dependent on the presence of UV radiation and subsequent activation in the liver and in the kidneys. Many animals synthesize vitamin D from 7-dehydrocholesterol, and many fungi synthesize vitamin D from ergosterol. | 1 | Biochemistry |
First-generation TSH assays were done by radioimmunoassay and were introduced in 1965. There were variations and improvements upon TSH radioimmunoassay, but their use declined as a new immunometric assay technique became available in the middle of the 1980s. The new techniques were more accurate, leading to the second, third, and even fourth generations of TSH assay, with each generation possessing ten times greater functional sensitivity than the last. Third generation immunometric assay methods are typically automated. Fourth generation TSH immunometric assay has been developed for use in research. | 1 | Biochemistry |
MECP2 duplication syndrome (M2DS) is a rare disease that is characterized by severe intellectual disability and impaired motor function. It is an X-linked genetic disorder caused by the overexpression of MeCP2 protein. | 1 | Biochemistry |
If a mixture of gases is being considered, and each gas has its own (attraction between molecules) and (volume occupied by molecules) values, then and for the mixture can be calculated as
: = total number of moles of gas present,
: for each , = number of moles of gas present, and
: or
: or
and the rule of adding partial pressures becomes invalid if the numerical result of the equation is significantly different from the ideal gas equation . | 7 | Physical Chemistry |
Pewter was first used around the beginning of the Bronze Age in the Near East. The earliest known piece of pewter was found in an Egyptian tomb, , but it is unlikely that this was the first use of the material. Pewter was used for decorative metal items and tableware in ancient times by the Egyptians and later the Romans, and came into extensive use in Europe from the Middle Ages until the various developments in pottery and glass-making during the 18th and 19th centuries. Pewter was the chief material for producing plates, cups, and bowls until the making of porcelain. Mass production of pottery, porcelain and glass products have almost universally replaced pewter in daily life, although pewter artifacts continue to be produced, mainly as decorative or specialty items. Pewter was also used around East Asia. Although some items still exist, Ancient Roman pewter is rare.
Lidless mugs and lidded tankards may be the most familiar pewter artifacts from the late 17th and 18th centuries, although the metal was also used for many other items including porringers (shallow bowls), plates, dishes, basins, spoons, measures, flagons, communion cups, teapots, sugar bowls, beer steins (tankards), and cream jugs. In the early 19th century, changes in fashion caused a decline in the use of pewter flatware. At the same time, production increased of both cast and spun pewter tea sets, whale-oil lamps, candlesticks, and so on. Later in the century, pewter alloys were often used as a base metal for silver-plated objects.
In the late 19th century, pewter came back into fashion with the revival of medieval objects for decoration. New replicas of medieval pewter objects were created, and collected for decoration. Today, pewter is used in decorative objects, mainly collectible statuettes and figurines, game figures, aircraft and other models, (replica) coins, pendants, plated jewellery and so on. Certain athletic contests, such as the United States Figure Skating Championships, award pewter medals to fourth-place finishers. | 8 | Metallurgy |
The glycosidic bond can be formed between any hydroxy group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and stereochemistry (alpha- or beta-) result in disaccharides that are diastereoisomers with different chemical and physical properties. Depending on the monosaccharide constituents, disaccharides are sometimes crystalline, sometimes water-soluble, and sometimes sweet-tasting and sticky-feeling. Disaccharides can serve as functional groups by forming glycosidic bonds with other organic compounds, forming glycosides. | 0 | Organic Chemistry |
Retriever is used to insert and retrieve coupons and probes without interrupting the process. They can be provided in hydraulic and mechanical types. | 8 | Metallurgy |
Rosocyanine is a dark green solid with a glossy, metallic shine that forms red colored solutions. It is almost insoluble in water and some organic solvents, very slightly soluble (up to 0.01%) in ethanol, and somewhat soluble (approximately 1%) in pyridine, sulfuric acid, and acetic acid. An alcoholic solution of rosocyanine temporarily turns deeply blue on treatment with alkali.
In rubrocurcumin one molecule of curcumin is replaced with oxalic acid. Rubrocurcumin produces a similar red colored solution. Rosocyanine is an ionic compound, while rubrocurcumin is a neutral complex. | 3 | Analytical Chemistry |
The presence of ANAs in blood can be confirmed by a screening test. Although there are many tests for the detection of ANAs, the most common tests used for screening are indirect immunofluorescence and enzyme-linked immunosorbent assay (ELISA). Following detection of ANAs, various subtypes are determined. | 1 | Biochemistry |
Microbial Prospecting for oil and gas (MPOG) can be used to identify prospective areas for oil and gas occurrences. In many cases, oil and gas is known to seep toward the surface as a hydrocarbon reservoir will usually leak or have leaked towards the surface through buoyancy forces overcoming sealing pressures. These hydrocarbons can alter the chemical and microbial occurrences found in the near-surface soils or can be picked up directly. Techniques used for MPOG include DNA analysis, simple bug counts after culturing a soil sample in a hydrocarbon-based medium or by looking at the consumption of hydrocarbon gases in a culture cell. | 2 | Environmental Chemistry |
Neoantigens are those that are entirely absent from the normal human genome. As compared with nonmutated self-proteins, neoantigens are of relevance to tumor control, as the quality of the T cell pool that is available for these antigens is not affected by central T cell tolerance. Technology to systematically analyze T cell reactivity against neoantigens became available only recently. Neoantigens can be directly detected and quantified. | 1 | Biochemistry |
In a real detector setup, some photons can and will undergo one or potentially more Compton scattering processes (e.g. in the housing material of the radioactive source, in shielding material or material otherwise surrounding the experiment) before entering the detector material. This leads to a peak structure that can be seen in the above shown energy spectrum of (Figure 1, the first peak left of the Compton edge), the so-called backscatter peak. The detailed shape of backscatter peak structure is influenced by many factors, such as the geometry of the experiment (source geometry, relative position of source, shielding and detector) or the type of the surrounding material (giving rise to different ratios of the cross sections of Photo- and Compton-effect).
The basic principle, however, is as follows:
* Gamma-ray sources emit photons isotropically
* Some photons will undergo a Compton scattering process in e.g. the shielding material or the housing of the source with a scattering angle close to 180° and some of these photons will subsequently be detected by the detector.
* The result is a peak structure with approximately the energy of the incident photon minus the energy of the Compton edge.
The backscatter peak usually appears wide and occurs at lower than 250 keV. | 7 | Physical Chemistry |
A neuromuscular non-depolarizing agent is a form of neuromuscular blocker that does not depolarize the motor end plate.
The quaternary ammonium muscle relaxants belong to this class. Quaternary ammonium muscle relaxants are quaternary ammonium salts used as drugs for muscle relaxation, most commonly in anesthesia. It is necessary to prevent spontaneous movement of muscle during surgical operations. Muscle relaxants inhibit neuron transmission to muscle by blocking the nicotinic acetylcholine receptor. What they have in common, and is necessary for their effect, is the structural presence of quaternary ammonium groups, usually two. Some of them are found in nature and others are synthesized molecules.
Below are some more common agents that act as competitive antagonists against acetylcholine at the site of postsynaptic acetylcholine receptors.
Tubocurarine, found in curare of the South American plant Pareira, Chondrodendron tomentosum, is the prototypical non-depolarizing neuromuscular blocker. It has a slow onset (>5 min) and a long duration of action (30 mins). Side-effects include hypotension, which is partially explained by its effect of increasing histamine release, a vasodilator, as well as its effect of blocking autonomic ganglia. It is excreted in the urine.
This drug needs to block about 70–80% of the ACh receptors for neuromuscular conduction to fail, and hence for effective blockade to occur. At this stage, end-plate potentials (EPPs) can still be detected, but are too small to reach the threshold potential needed for activation of muscle fiber contraction.
The speed of onset depends on the potency of the drug, greater potency is associated with slower onset of block. Rocuronium, with an ED of 0.3 mg/kg IV has a more rapid onset than Vecuronium with an ED of 0.05mg/kg. Steroidal compounds, such as rocuronium and vecuronium, are intermediate-acting drugs while Pancuronium and pipecuronium are long-acting drugs.
In larger clinical dose, some of the blocking agent can access the pore of the ion channel and cause blockage. This weakens neuromuscular transmission and diminishes the effect of acetylcholinesterase inhibitors (e.g. neostigmine). Nondepolarizing NBAs may also block prejunctional sodium channels which interfere with the mobilization of acetylcholine at the nerve ending. | 1 | Biochemistry |
__NOTOC__
Binary chemical weapons or munitions are chemical weapons which contain the toxic agent in its active state as chemical precursors that are significantly less toxic than the agent. This improves the safety of storing, transporting, and disposing of the weapon. Commonly, firing the munition removes a barrier between two precursors. These react to form the intended agent which is then aerosolized and distributed by a bursting charge.
Binary chemical weapons are chemical weapons within the scope of the Chemical Weapons Convention and therefore their production, use and stockpiling is forbidden in most countries, as at least one of the individual chemicals is likely to be a Schedule 1 chemical for which large scale production is forbidden. | 1 | Biochemistry |
In the thermodynamic stream of thinking, the specified mechanisms of heat transfer are conduction and radiation. These mechanisms presuppose recognition of temperature; empirical temperature is enough for this purpose, though absolute temperature can also serve. In this stream of thinking, quantity of heat is defined primarily through calorimetry.
Though its definition of them differs from that of the mechanical stream of thinking, the empirical stream of thinking nevertheless presupposes the existence of adiabatic enclosures. It defines them through the concepts of heat and temperature. These two concepts are coordinately coherent in the sense that they arise jointly in the description of experiments of transfer of energy as heat. | 7 | Physical Chemistry |
Isolated photosystems and sub-cellular photosynthetic fractions may be able to directly reduce the anode if the biological redox components are close enough to the electrode for electron transfer to occur. In contrast to organisms such as dissimilatory metal reducing bacteria, algae and cyanobacteria are poorly adapted for extracellular electron export - no molecular mechanisms enabling direct reduction of an insoluble extracellular electron acceptor have been conclusively identified. Nevertheless, a low rate of anode reduction has been observed from whole photosynthetic organisms without the addition of exogenous redox-active compounds. It has been speculated that electron transfer occurs through the release of low concentrations of endogenous redox mediator compounds. Improving the electron export activity of cyanobacteria for use in biological photovoltaic systems is a topic of current research. | 7 | Physical Chemistry |
Lanthanide probes displays unique fluorescence properties, including long lifetime of fluorescence, large Stokes shift and narrow emission peak. These properties is highly advantageous to develop analytical probes for receptor-ligand interactions. Many lanthanide-based fluorescence studies have been developed for GPCRs, including CXCR1, insulin-like family peptide receptor 2, protease-activated receptor 2, β2-adrenergic receptor and C3a receptor. | 1 | Biochemistry |
Fretting examples include wear of drive splines on driveshafts, wheels at the lug bolt interface, and cylinder head gaskets subject to differentials in thermal expansion coefficients.
There is currently a focus on fretting research in the aerospace industry. The dovetail blade-root connection and the spline coupling of gas turbine aero engines experience fretting.
Another example in which fretting corrosion may occur are the pitch bearings of modern wind turbines, which operate under oscillation motion to control the power and loads of the turbine.
Fretting can also occur between reciprocating elements in the human body. Especially implants, for example hip implants, are often affected by fretting effects. | 8 | Metallurgy |
Entropy also plays a role in a substituent's preference for the equatorial position. The entropic component is determined by the following formula:
Where σ is equal to the number of microstates available for each conformation.
Due to the larger number of possible conformations of ethyl cyclohexane, the A value is reduced from what would be predicted based purely on enthalpic terms. Due to these favorable entropic conditions, the steric relevance of an ethyl group is similar to that of a methyl substituent. | 4 | Stereochemistry |
Optical rotatory dispersion is the variation of the specific rotation of a medium with respect to the wavelength of light. Usually described Drude's empirical relation,
where is the specific rotation at temperature and wavelength , and and are constants that depend on the properties of the medium.
Optical rotatory dispersion has applications in organic chemistry regarding determining the structure of organic compounds. | 4 | Stereochemistry |
Stable isotope labeling by/with amino acids in cell culture (SILAC) is a technique based on mass spectrometry that detects differences in protein abundance among samples using non-radioactive isotopic labeling. It is a popular method for quantitative proteomics. | 1 | Biochemistry |
The presence of hydrothermal fluids is essential as a medium for geochemical reactions during silicification. In the silicification of different materials, different mechanisms are involved. In the silicification of rock materials like carbonates, replacement of minerals through hydrothermal alteration is common; while the silicification of organic materials such as woods is solely a process of permeation. | 9 | Geochemistry |
For chronic diseases, whose treatment may require patients to take medications for years, accurate diagnosis is particularly important, especially when strong side effects are expected from the treatment. In these cases, biomarkers are becoming more and more important, because they can confirm a difficult diagnosis or even make it possible in the first place.
A number of diseases, such as Alzheimer's disease or rheumatoid arthritis, often begin with an early, symptom-free phase. In such symptom-free patients there may be more or less probability of actually developing symptoms. In these cases, biomarkers help to identify high-risk individuals reliably and in a timely manner so that they can either be treated before onset of the disease or as soon as possible thereafter.
In order to use a biomarker for diagnostics, the sample material must be as easy to obtain as possible. This may be a blood sample taken by a doctor, a urine or saliva sample, or a drop of blood like those diabetes patients extract from their own fingertips for regular blood-sugar monitoring.
For rapid initiation of treatment, the speed with which a result is obtained from the biomarker test is critical. A rapid test, which delivers a result after only a few minutes, is optimal. This makes it possible for the physician to discuss with the patient how to proceed and if necessary to start treatment immediately after the test.
Naturally, the detection method for a biomarker must be accurate and as easy to carry out as possible. The results from different laboratories may not differ significantly from each other, and the biomarker must naturally have proven its effectiveness for the diagnosis, prognosis, and risk assessment of the affected diseases in independent studies.
A biomarker for clinical use needs good sensitivity and specificity e.g. ≥0.9, and good specificity e.g. ≥0.9 although they should be chosen with the population in mind so positive predictive value and negative predictive value are more relevant. | 1 | Biochemistry |
Huntington's disease occurs when the cytosolic protein Huntingtin (Htt) has an additional 35 glutamine residues added to its amino terminal region. This modified form of Htt is called Htt. Htt makes Type 1 IP receptors more sensitive to IP, which leads to the release of too much Ca from the ER. The release of Ca from the ER causes an increase in the cytosolic and mitochondrial concentrations of Ca. This increase in Ca is thought to be the cause of GABAergic MSN degradation. | 1 | Biochemistry |
Quantification of VOCs is based on the peak area measured on the chromatogram and compared to the peak area of a chemical standard:
* Internal calibration: a known quantity of a specific chemical standard is injected together with the VOCs, the measured area on the chromatogram is proportional to the injected quantity. Because the chemical properties of VOCs alter their affinity to the solid phase (the chromatographic column) and subsequently the peak area on the chromatogram, it is best to use several standards that reflect the best chemical diversity of the floral scent sample. This method allows a more robust comparison among samples.
* External calibration: calibration curves (quantity vs. peak area) are established independently by the injection of a range of quantities of chemical standard. This method is best when the relative and absolute amount of VOCs in floral scent samples varies from sample to sample and from VOC to VOC and when the chemical diversity of VOCs in the sample is high. However, it is more time-consuming and may be a source of errors (e.g. matrix effects due to solvent or very abundant VOCs compared to trace VOCs). | 1 | Biochemistry |
The carbonate pump is sometimes referred to as the “hard tissue” component of the biological pump. Some surface marine organisms, like coccolithophores, produce hard structures out of calcium carbonate, a form of particulate inorganic carbon, by fixing bicarbonate. This fixation of DIC is an important part of the oceanic carbon cycle.
Ca + 2 HCO → CaCO + CO + HO
While the biological carbon pump fixes inorganic carbon (CO) into particulate organic carbon in the form of sugar (CHO), the carbonate pump fixes inorganic bicarbonate and causes a net release of CO. In this way, the carbonate pump could be termed the carbonate counter pump. It works counter to the biological pump by counteracting the CO flux into the biological pump. | 9 | Geochemistry |
Since ca. 2000 methanesulfonic acid has become a popular replacement for other acids in numerous industrial and laboratory applications, because it:
* is a strong acid,
* has a low vapor pressure (see boiling points in the "Properties" inset),
* is not an oxidant or explosive, like nitric, sulfuric or perchloric acids.
* is a liquid at room temperature,
* is soluble in many organic solvents,
* forms water-soluble salts with all inorganic cations and with most organic cations,
* does not form complexes with metal ions in water,
* its anion, mesylate, is non-toxic and suitable for pharmaceutical preparations.
The closely related p-toluenesulfonic acid (PTSA) is solid.
Methanesulfonic acid can be used in the generation of borane (BH) by reacting methanesulfonic acid with NaBH in an aprotic solvent such as THF or DMSO, the complex of BH and the solvent is formed. | 0 | Organic Chemistry |
The son of the radical Protestant theologian Gustav Wislicenus, Johannes was born on 24 June 1835 in Kleineichstedt (now part of Querfurt, Saxony-Anhalt) in Prussian Saxony, and entered University of Halle-Wittenberg in 1853. In October 1853 he immigrated to the United States with his family. For a brief time he acted as assistant to Harvard chemist Eben Horsford, and in 1855 was appointed lecturer at the Mechanics' Institute in New York. Returning to Europe in 1856, he continued to study chemistry with Wilhelm Heinrich Heintz at the University of Halle. In 1860, he began lecturing at the University of Zürich, and at the Swiss Polytechnical Institute and by 1868 he was Professor of Chemistry at the university. In 1870, he was chosen to succeed Georg Staedeler as Professor of General Chemistry at the Swiss Polytechnical Institute in Zürich, retaining also the position of full professor at the University of Zürich. In 1872, he succeeded Adolph Strecker in the chair of chemistry at University of Würzburg, and in 1885, he succeeded Hermann Kolbe as Professor of Chemistry at the University of Leipzig, where he died on 6 December 1902. | 4 | Stereochemistry |
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