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Title 15, Chapter 8, Section 291 of the United States Code makes it unlawful to stamp goods in the United States with "United States assay" or any similar stamp which gives the impression that the item has been officially assayed by the United States government. | 3 | Analytical Chemistry |
Acetylides are sometimes intermediates in coupling reactions. Examples include Sonogashira coupling, Cadiot-Chodkiewicz coupling, Glaser coupling and Eglinton coupling. | 0 | Organic Chemistry |
For pol II-transcribed genes, and unlike bacterial RNA polymerase, promoter melting requires hydrolysis of ATP and is mediated by TFIIH. TFIIH is a ten-subunit protein, including both ATPase and protein kinase activities. While the upstream promoter DNA is held in a fixed position by TFIID, TFIIH pulls downstream double-stranded DNA into the cleft of the polymerase, driving the separation of DNA strands and the transition of the preinitiation complex from the closed to open state. TFIIB aids in open complex formation by binding the melted DNA and stabilizing the transcription bubble. | 1 | Biochemistry |
Siderophores (Greek: "iron carrier") are small, high-affinity iron-chelating compounds that are secreted by microorganisms such as bacteria and fungi. They help the organism accumulate iron. Although a widening range of siderophore functions is now being appreciated, siderophores are among the strongest (highest affinity) Fe binding agents known. Phytosiderophores are siderophores produced by plants. | 1 | Biochemistry |
According to a research study conducted Hutton, M et al, a missense mutation occurring on the 5 region of the RNA associated with the tau protein was found to be correlated with inherited dementia (known as FTDP-17). The splice-site mutations all destabilize a potential stem–loop structure which is most likely involved in regulating the alternative splicing of exon10 in chromosome 17. Consequently, more usage occurs on the 5 splice site and an increased proportion of tau transcripts that include exon 10 are created. Such drastic increase in mRNA will increase the proportion of Tau containing four microtubule-binding repeats, which is consistent with the neuropathology described in several families with FTDP-17, a type inherited dementia. | 1 | Biochemistry |
Sucrose esters are stable in the pH range of 4 to 8, so they can be used as an additive in most foods. At pH higher than 8, saponification (hydrolysis of the ester bond to release the original sucrose and the salt of fatty acids) might occur. Hydrolysis could also occur at pH lower than 4. | 0 | Organic Chemistry |
The presence of harmful algae blooms can lead to hypoxia or anoxia in a body of water. The depletion of oxygen within a body of water can lead to the creation of a dead zone. Dead zones occur when a body of water has become unsuitable for organism survival in that location. HABs cause dead zones by consuming oxygen in these bodies of water - leaving minimal oxygen available to other marine organisms. When the HABs die, their bodies will sink to the bottom of the body of water - as the decaying of their bodies (through bacteria) is what causes the consumption of oxygen. Once oxygen levels get so low, the HABs have placed the body of water in hypoxia - and these low oxygen levels will cause marine organisms to seek out better suited locations for their survival.
Blooms can harm the environment even without producing toxins by depleting oxygen from the water when growing and while decaying after they die. Blooms can also block sunlight to organisms living beneath it. A record-breaking number and size of blooms have formed in the Pacific coast, in Lake Erie, in the Chesapeake Bay and in the Gulf of Mexico, where a number of dead zones were created as a result. In the 1960s the number of dead zones worldwide was 49; the number rose to over 400 by 2008.
Among the largest dead zones were those in northern Europe's Baltic Sea and the Gulf of Mexico, which affects a $2.8 billion U.S. fish industry. Unfortunately, dead zones rarely recover and usually grow in size. One of the few dead zones to ever recover was in the Black Sea, which returned to normal fairly quickly after the collapse of the Soviet Union in the 1990s due to a resulting reduction in fertilizer use. | 3 | Analytical Chemistry |
The objective of the refinement process is to find equilibrium constant values that give the best fit to the experimental data. This is usually achieved by minimising an objective function, , by the method of non-linear least-squares. First the residuals are defined as
Then the most general objective function is given by
The matrix of weights, , should be, ideally, the inverse of the variance-covariance matrix of the observations. It is rare for this to be known. However, when it is, the expectation value of U is one, which means that the data are fitted within experimental error. Most often only the diagonal elements are known, in which case the objective function simplifies to
with when . Unit weights, , are often used but, in that case, the expectation value of is the root mean square of the experimental errors.
The minimization may be performed using the Gauss–Newton method. Firstly the objective function is linearised by approximating it as a first-order Taylor series expansion about an initial parameter set, .
The increments are added to the corresponding initial parameters such that is less than . At the minimum the derivatives , which are simply related to the elements of the Jacobian matrix,
where is the th parameter of the refinement, are equal to zero. One or more equilibrium constants may be parameters of the refinement. However, the measured quantities (see above) represented by are not expressed in terms of the equilibrium constants, but in terms of the species concentrations, which are implicit functions of these parameters. Therefore, the Jacobian elements must be obtained using implicit differentiation.
The parameter increments are calculated by solving the normal equations, derived from the conditions that at the minimum.
The increments are added iteratively to the parameters
where is an iteration number. The species concentrations and values are recalculated at every data point. The iterations are continued until no significant reduction in is achieved, that is, until a convergence criterion is satisfied. If, however, the updated parameters do not result in a decrease of the objective function, that is, if divergence occurs, the increment calculation must be modified. The simplest modification is to use a fraction, , of calculated increment, so-called shift-cutting.
In this case, the direction of the shift vector, , is unchanged. With the more powerful Levenberg–Marquardt algorithm, on the other hand, the shift vector is rotated towards the direction of steepest descent, by modifying the normal equations,
where is the Marquardt parameter and is an identity matrix. Other methods of handling divergence have been proposed.
A particular issue arises with NMR and spectrophotometric data. For the latter, the observed quantity is absorbance, , and the Beer–Lambert law can be written as
It can be seen that, assuming that the concentrations, c, are known, that absorbance, , at a given wavelength, , and path length , is a linear function of the molar absorbptivities, . With 1 cm path-length, in matrix notation
There are two approaches to the calculation of the unknown molar absorptivities
:(1) The values are considered parameters of the minimization and the Jacobian is constructed on that basis. However, the values themselves are calculated at each step of the refinement by linear least-squares:
:using the refined values of the equilibrium constants to obtain the speciation. The matrix
:is an example of a pseudo-inverse.
:Golub and Pereyra showed how the pseudo-inverse can be differentiated so that parameter increments for both molar absorptivities and equilibrium constants can be calculated by solving the normal equations.
:(2) The Beer–Lambert law is written as
:The unknown molar absorbances of all "coloured" species are found by using the non-iterative method of linear least-squares, one wavelength at a time. The calculations are performed once every refinement cycle, using the stability constant values obtaining at that refinement cycle to calculate species' concentration values in the matrix . | 7 | Physical Chemistry |
There are other proteins that have acetylating abilities but differ in structure to the previously mentioned families. One HAT is called steroid receptor coactivator 1 (SRC1), which has a HAT domain located at the C-terminus end of the protein along with a basic helix-loop-helix and PAS A and PAS B domains with a LXXLL receptor interacting motif in the middle. Another is ATF-2 which contains a transcriptional activation (ACT) domain and a basic zipper DNA-binding (bZip) domain with a HAT domain in-between. The last is TAFII250 which has a Kinase domain at the N-terminus region, two bromodomains located at the C-terminus region and a HAT domain located in-between. | 0 | Organic Chemistry |
In organic chemistry, the Hammett plot provides a means to assess substituent effects on a reaction equilibrium or rate using the Hammett equation (1):
Hammett developed this equation from equilibrium constants from the dissociation of benzoic acid and derivatives (Fig. 1):
Hammett defined the equation based on two parameters: the reaction constant (ρ) and the substituent parameter (σ). When other reactions were studied using these parameters, a correlation was not always found due to the specific derivation of these parameters from the dissociation equilibrium of substituted benzoic acids and the original negligence of resonance effects. Therefore, the effects of substituents on an array of compounds must be studied on an individual reaction basis using the equation Hammett derived either for field or resonance effects, but not both. | 7 | Physical Chemistry |
Spermatozoon is the male gamete. After ejaculation this cell is not mature, so it can not fertilize the oocyte. To have the ability to fertilize the female gamete, this cell suffers capacitation and acrosome reaction in female reproductive tract. The signaling pathways best described for spermatozoon involve these processes. The cAMP/PKA signaling pathway leads to sperm cells capacitation; however, adenylyl cyclase in sperm cells is different from the somatic cells. Adenylyl cyclase in spermatozoon does not recognize G proteins, so it is stimulated by bicarbonate and Ca ions. Then, it converts adenosine triphosphate into cyclic AMP, which activates Protein kinase A. PKA leads to protein tyrosine phosphorylation.
Phospholipase C (PLC) is involved in acrosome reaction. ZP3 is a glycoprotein present in zona pelucida and it interacts with receptors in spermatozoon. So, ZP3 can activate G protein coupled receptors and tyrosine kinase receptors, that leads to production of PLC. PLC cleaves the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) into diacyl glycerol (DAG) and inositol 1,4,5-trisphosphate. IP3 is released as a soluble structure into the cytosol and DAG remains bound to the membrane. IP3 binds to IP3 receptors, present in acrosome membrane. In addition, calcium and DAG together work to activate protein kinase C, which goes on to phosphorylate other molecules, leading to altered cellular activity. These actions cause an increase in cytosolic concentration of Ca that leads to dispersion of actin and consequently promotes plasmatic membrane and outer acrosome membrane fusion.
Progesterone is a steroid hormone produced in cumulus oophorus. In somatic cells it binds to receptors in nucleus; however, in spermatozoon its receptors are present in plasmatic membrane. This hormone activates AKT that leads to activation of other protein kinases, involved in capacitation and acrosome reaction.
When ROS (reactive oxygen species) are present in high concentration, they can affect the physiology of cells, but when they are present in moderated concentration they are important for acrosome reaction and capacitation. ROS can interact with cAMP/PKA and progesterone pathway, stimulating them. ROS also interacts with ERK pathway that leads to activation of Ras, MEK and MEK-like proteins. These proteins activate protein tyrosine kinase (PTK) that phosphorylates various proteins important for capacitation and acrosome reaction. | 7 | Physical Chemistry |
The stereoelectronic effect influences the thermodynamics of equilibrium. For example, the following equilibrium could be achieved via a cascade of pericyclic reactions.
Despite very similar structures, one of the two isomers is strongly favored over the other because of a stereoelectronic effect. Since the σ* orbital adjacent to the electron-withdrawing carbonyl group is lower in energy and is therefore a better acceptor than the σ* orbital adjacent to the methoxy, the isomer in which the n lone pair is able to donate into this lower-energy antibonding orbital will be stabilized (orbital interaction illustrated).
Another example of the preference in the equilibrium within the area of pericyclic reaction is shown below. The stereoelectronic effect that affect the equilibrium is the interaction between the delocalized “banana bonds” and the empty p orbital on the boron atom. | 4 | Stereochemistry |
Overdosing experiments in animals showed loss of body control and drooping, difficulty breathing, tremors, and convulsions. Doses in excess of 1500 mg/kg orally and 250 mg/kg IV produced significant mortality in rodents.
In the event of an acute overdosage, authorities recommend unspecific standard procedures such as emptying the stomach, observing the patient and maintaining appropriate hydration. Levofloxacin is not efficiently removed by hemodialysis or peritoneal dialysis. | 4 | Stereochemistry |
Most plant pathogens invade the apoplasm by releasing pectolytic enzymes which facilitate the spread of the invading organism. Bacteria frequently infect plants by gaining entry to the tissue via the stomata. Having entered the plant they spread and multiply in the intercellular spaces. With bacterial vascular diseases, the infection is spread within the plants through the xylem.
Once within the plant, the bacteria need to be able to scavenge iron from the two main iron-transporting ligands, nicotianamine and citrate. To do this they produce siderophores, thus the enterobacterial Erwinia chrysanthemi produces two siderophores, chrysobactin and achromobactin. Xanthomonas group of plant pathogens produce xanthoferrin siderophores to scavenge the iron.
Like in humans, plants also possess siderophore binding proteins involved in host defense, like the major birch pollen allergen, Bet v 1, which are usually secreted and possess a lipocalin-like structure. | 1 | Biochemistry |
AOAC International is a 501(c) non-profit scientific association with headquarters in Rockville, Maryland. It was founded in 1884 as the Association of Official Agricultural Chemists (AOAC) and became AOAC International in 1991. It publishes standardized, chemical analysis methods designed to increase confidence in the results of chemical and microbiological analyses. Government agencies and civil organizations often require that laboratories use official AOAC methods. AOAC is headquartered in Rockville, Maryland, and has approximately 3,000 members based in over 90 countries. | 3 | Analytical Chemistry |
Fumaric acid is an organic compound with the formula HOCCH=CHCOH. A white solid, fumaric acid occurs widely in nature. It has a fruit-like taste and has been used as a food additive. Its E number is E297. The salts and esters are known as fumarates. Fumarate can also refer to the ion (in solution). Fumaric acid is the trans isomer of butenedioic acid, while maleic acid is the cis isomer. | 1 | Biochemistry |
The autocorrelations above assume that the fluctuations are not due to changes in the fluorescent properties of the particles. However, for the majority of (bio)organic fluorophores—e.g. green fluorescent protein, rhodamine, Cy3 and Alexa Fluor dyes—some fraction of illuminated particles are excited to a triplet state (or other non-radiative decaying states) and then do not emit photons for a characteristic relaxation time . Typically is on the order of microseconds, which is usually smaller than the dynamics of interest (e.g. ) but large enough to be measured. A multiplicative term is added to the autocorrelation to account for the triplet state. For normal diffusion:
where is the fraction of particles that have entered the triplet state and is the corresponding triplet state relaxation time. If the dynamics of interest are much slower than the triplet state relaxation, the short time component of the autocorrelation can simply be truncated and the triplet term is unnecessary. | 7 | Physical Chemistry |
The chiral pool is a "collection of abundant enantiopure building blocks provided by nature" used in synthesis. In other words, a chiral pool would be a large quantity of common organic enantiomers. Contributors to the chiral pool are amino acids, sugars, and terpenes. Their use improves the efficiency of total synthesis. Not only does the chiral pool contribute a premade carbon skeleton, their chirality is usually preserved in the remainder of the reaction sequence.
This strategy is especially helpful if the desired molecule resembles cheap enantiopure natural products. Many times, suitable enantiopure starting materials cannot be identified. The alternative to the use of the chiral pool is asymmetric synthesis, whereby achiral precursors are employed or racemic intermediates are resolved. | 0 | Organic Chemistry |
Pure calcium carbide is a colourless solid. The common crystalline form at room temperature is a distorted rock-salt structure with the C</sup> units lying parallel. There are three different polymorphs which appear at room temperature: the tetragonal structure and two different monoclinic structures. | 8 | Metallurgy |
The maximum density of a substance is the highest attainable density of the substance under given conditions. | 7 | Physical Chemistry |
The MCSGP process consists of several, at least two, chromatographic columns which are switched in position opposite to the flow direction. Most of the columns are equipped with a gradient pump to adjust the modifier concentration at the column inlet. Some columns are connected directly, so that non pure product streams are internally recycled. Other columns are short circuited, so that they operate in pure batch mode. The system is split into several sections, from which every section performs a tasks analogous to the tasks of a batch purification. These tasks are loading the feed, running the gradient elution, recycling of weakly adsorbing site fractions, fractionation of the purified product, recycling of strongly adsorbing site fractions, cleaning the column from strongly adsorbing impurities, cleaning in place and re-equilibration of the column to start the next purification run. All of the tasks mentioned here are carried out at the same time in one unit. Recycling of non-pure side fractions is performed in countercurrent movement. | 3 | Analytical Chemistry |
The effects on animals occur very rapidly and strongly, all resulting in death. Exposure to a high concentration of MFA vapor does not show any symptoms in animals until 30–60 minutes. Then violent reactions and death took place in a few hours, according to studies. From intravenous injection mice, rats, and guinea pigs show symptoms after 15 min to 2 hours. The animals become quiet and limp. Rabbits show a similar latent time period and muscle weakness. Dogs show symptoms of hyperactivity. They are more sensitive because of higher rates of metabolism and, eventually, they also fail to respirate. Fish are more resistant because of slow metabolism and therefore it is not expected that the substance will build up in fish. Also, Australian herbivores (e.g. possum and seed-eating birds) that live in a habitat consisting of plants with traces of fluoroacetate, have some tolerance. This can happen by detoxifying fluoroacetate or more resistivity of aconitase to fluorocitrate in the presence of GSH. Some insects can store the toxin in vacuoles and use it later. The highly hazardous MFA cannot be used for poisoning animals without risking human life. | 1 | Biochemistry |
The Annual Review of Physical Chemistry published its first volume in 1950. Its founding editor was University of California chemist Gerhard Krohn Rollefson. Some branches of physical chemistry were designated to be reviewed with each volume, while other branches would be reviewed less frequently. Upon Rollefsons death in 1955, he was succeeded by Henry Eyring. The editorial committee considered changing the name of the journal in the 1980s to the Annual Review of Physical Chemistry and Chemical Physics', though decided against it by 1988. In addition to publishing reviews about physical chemistry, many volumes contain a prefatory chapter with an informal review of a chemist or institution. As of 2020, it was published both in print and electronically.
It defines its scope as covering recent developments in the fields of biophysical chemistry, chemical kinetics, colloids, electrochemistry, geochemistry, cosmochemistry, atmospheric chemistry, laser chemistry and ultrafast processes, the liquid state, magnetic resonance, physical organic chemistry, polymers, and macromolecules. As of 2023, Journal Citation Reports gives it a 2022 impact factor of 14.7, ranking it sixteenth of 161 journal titles in the category "Physical Chemistry". | 7 | Physical Chemistry |
Telomere length varies greatly between species, from approximately 300 base pairs in yeast to many kilobases in humans, and usually is composed of arrays of guanine-rich, six- to eight-base-pair-long repeats. Eukaryotic telomeres normally terminate with 3′ single-stranded-DNA overhang ranging from 75 to 300 bases, which is essential for telomere maintenance and capping. Multiple proteins binding single- and double-stranded telomere DNA have been identified. These function in both telomere maintenance and capping. Telomeres form large loop structures called telomere loops, or T-loops. Here, the single-stranded DNA curls around in a long circle, stabilized by telomere-binding proteins. At the very end of the T-loop, the single-stranded telomere DNA is held onto a region of double-stranded DNA by the telomere strand disrupting the double-helical DNA, and base pairing to one of the two strands. This triple-stranded structure is called a displacement loop or D-loop. | 1 | Biochemistry |
Allosteric modulators of small SK channels work by changing the apparent calcium sensitivity of the channels. Examples include:
* Riluzole
* Non-selective positive modulators of SK channels: EBIO (1-Ethyl-2-BenzimIdazolinOne), NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime)
* SK-2 and SK-3 selective positive modulators : CyPPA (NS6277; Cyclohexyl-(2-(3,5-dimethyl-Pyrazol-1-yl)-6-methyl-Pyrimidin-4-yl)-Amine)
<br /> | 1 | Biochemistry |
Yoon has started his independent career in 2005 in the chemistry department at the University of Wisconsin-Madison where he has been ever since. His group specializes in studying the atomic level of control and molecular shape that can be manipulated by chemical synthesis. He has a research group that studies high energy and reactive molecules which convert into more stable molecules through chemical reactions. Such molecules include radicals and electronically organic triplets to more complex structures. | 0 | Organic Chemistry |
Within the field of molecular biology, a protein-fragment complementation assay, or PCA, is a method for the identification and quantification of protein–protein interactions. In the PCA, the proteins of interest ("bait" and "prey") are each covalently linked to fragments of a third protein (e.g. DHFR, which acts as a "reporter"). Interaction between the bait and the prey proteins brings the fragments of the reporter protein in close proximity to allow them to form a functional reporter protein whose activity can be measured. This principle can be applied to many different reporter proteins and is also the basis for the yeast two-hybrid system, an archetypical PCA assay. | 1 | Biochemistry |
Cytochrome c is a highly conserved protein across the spectrum of eukaryotic species, found in plants, animals, fungi, and many unicellular organisms. This, along with its small size (molecular weight about 12,000 daltons), makes it useful in studies of cladistics. Cytochrome c has been studied for the glimpse it gives into evolutionary biology.
Cytochrome c has a primary structure consisting of a chain of about 100 amino acids. Many higher-order organisms possess a chain of 104 amino acids. The sequence of cytochrome c in humans is identical to that of chimpanzees (our closest relatives), but differs from that of horses.
Cytochrome c has an amino acid sequence that is highly conserved in eukaryotes, varying by only a few residues. In more than thirty species tested in one study, 34 of the 104 amino acids were conserved (identical at their characteristic position). For example, human cytochrome oxidase reacted with wheat cytochrome c, in vitro; which held true for all pairs of species tested. In addition, the redox potential of +0.25 volts is the same in all cytochrome c molecules studied. | 1 | Biochemistry |
In biology, scaffold proteins are crucial regulators of many key signalling pathways. Although scaffolds are not strictly defined in function, they are known to interact and/or bind with multiple members of a signalling pathway, tethering them into complexes. In such pathways, they regulate signal transduction and help localize pathway components (organized in complexes) to specific areas of the cell such as the plasma membrane, the cytoplasm, the nucleus, the Golgi, endosomes, and the mitochondria. | 1 | Biochemistry |
Pyrite (FeS) is a mineral formed by the reaction of hydrogen sulfide (HS) and bioreactive iron (Fe). In oxic bottom waters pyrite can only form in sediments where HS is present. However, in iron-rich euxinic environments, pyrite formation can occur at higher rates in both the water column and in sediments due to higher concentrations of HS. Therefore the presence of euxinic conditions can be inferred by the ratio of pyrite-bound iron to the total iron in sediments. High ratios of pyrite-bound iron can be used as an indicator of past euxinic conditions. Similarly, if >45% of the bioreactive iron in sediments is pyrite-bound, then anoxic or euxinic conditions can be inferred. While useful, these methods do not provide definitive proof of euxinia because not all euxinic waters have the same concentrations of bioreactive iron available. These relationships have been found to be present in the modern euxinic Black Sea. | 9 | Geochemistry |
The presence of fulgurites in an area can be used to estimate the frequency of lightning over a period of time, which can help to understand past regional climates. Paleolightning is the study of various indicators of past lightning strikes, primarily in the form of fulgurites and lightning-induced remanent magnetization (LIRM) signatures. | 9 | Geochemistry |
MFGM bioactive protein components, including the glycoproteins lactadherin, MUC-1, and butyrophilin, have been shown in preclinical studies to affect immune response. These components influence the immune system by several mechanisms, including interference with microbe adhesion to intestinal epithelia, bacteriocidal action, support of beneficial microbiota, and modulation of other parts of the immune system.
MFGM phospholipid components such as phosphatidylcholine are a key constituent of the intestinal mucus barrier, and therefore may contribute to intestinal defense against invasive pathogens. Sphingolipids, including sphingomyelin, are present in the apical membrane of the gut epithelia, and are also important for maintaining membrane structure, modulating growth factor receptors, and serving competitive binding inhibitors for microorganisms, microbial toxins, and viruses. Gangliosides are also present in intestinal mucosa and may possibly contribute to improved gut microflora and antibacterial defense. | 1 | Biochemistry |
In the same year that Brønsted and Lowry published their theory, G. N. Lewis created an alternative theory of acid–base reactions. The Lewis theory is based on electronic structure. A Lewis base is a compound that can give an electron pair to a Lewis acid, a compound that can accept an electron pair. Lewis's proposal explains the Brønsted–Lowry classification using electronic structure.
In this representation both the base, B, and the conjugate base, A, are shown carrying a lone pair of electrons and the proton, which is a Lewis acid, is transferred between them.
Lewis later wrote "To restrict the group of acids to those substances that contain hydrogen interferes as seriously with the systematic understanding of chemistry as would the restriction of the term oxidizing agent to substances containing oxygen." In Lewis theory an acid, A, and a base, B, form an adduct, AB, where the electron pair forms a dative covalent bond between A and B. This is shown when the adduct HN−BF forms from ammonia and boron trifluoride, a reaction that cannot occur in water because boron trifluoride reacts violently with water in a hydrolysis reaction.
These reactions illustrate that BF is an acid in both Lewis and Brønsted–Lowry classifications and show that both theories agree with each other.
Boric acid is recognised as a Lewis acid because of the reaction
In this case the acid does not split up but the base, HO, does. A solution of B(OH) is acidic because hydrogen ions are given off in this reaction.
There is strong evidence that dilute aqueous solutions of ammonia contain minute amounts of the ammonium ion
and that, when dissolved in water, ammonia functions as a Lewis base. | 7 | Physical Chemistry |
In the 1990s, the Niihama copper refinery, owned by Sumitomo Metal Mining Company Limited (“Sumitomo”), treated copper anode slimes generated in-house, together with anode slimes from Sumitomo’s Toyo refinery and lead refinery slime from the Harima Imperial Smelting Process smelter. A total of 1200 tonnes per year (“t/y”) of anode slimes and 400 t/y of lead refinery slimes were treated using a process flow sheet that included a chloridizing step to remove separate the lead as lead chloride (PbCl) and a reverberatory-type doré furnace. It produced about 200 t of silver, 22 t of gold, 1.5 t of palladium, 300 kilograms (“kg”) of platinum and 40 kg of rhodium, as well as 60 t of selenium, 50 t of bismuth, 900 kg of tellurium and 150 t of antimony alloy annually.
The gold production doubled during the decade to 1996, as its concentration in anode slimes and the quantity of anode slimes increased. To enable this, Sumitomo decided in 1990 to upgrade the refinery, and as part of that upgrade, installed a 3.5 t-capacity BBOC to replace its reverberatory doré furnace in October 1992.
Sumitomo reported that, while the old oil-fired reverberatory furnace had served it well for many years, it had the following drawbacks:
* its operation was labor-intensive
* it had a low fuel efficiency
* there was a high waste gas volume
* the reaction rate was low.
Sumitomo investigated both the TBRC and BBOC furnaces before making a selection. It chose the BBOC over the TBRC technology because of the ease of control of the bath temperature, its high oxygen efficiency and its simple maintenance.
Sumitomo found that the impurity contents of BBOC doré anodes was high when the furnace was first commissioned. This was because it was important to determine the endpoint of the oxidation reactions to maximize the quality of the anodes. Sumitomo found that this could be determined by measuring the oxygen content of the off-gas using oxygen sensors based on stabilized zirconia with an Fe/FeO reference electrode.
Sumitomo subsequently adapted the BBOC to allow the chloridizing step to be undertaken in the furnace, thus eliminating the need for a separate chloridizing furnace for lead chloride production. This was done in February 1994 and was reported to be “giving very good results.” | 8 | Metallurgy |
Cecil Czerkinsky first described ELISpot in 1983 as a new way to quantify the production of an antigen-specific immunoglobulin by hybridoma cells.
In 1988, Czerkinsky developed an ELISA spot assay that quantified the secretion of a lymphokine by T cells.
In the same year, dual-color ELISpot was combined with computer imaging for the first time, which allowed for the enumeration and analysis of spots.
1988 also marked the first use of membrane-bottomed plates for performing these assays. | 1 | Biochemistry |
MAO is well known as catalyst activator for olefin polymerizations by homogeneous catalysis. In traditional Ziegler–Natta catalysis, supported titanium trichloride is activated by treatment with trimethylaluminium (TMA). TMA only weakly activates homogeneous precatalysts, such as zirconacene dichloride. In the mid-1970s Kaminsky discovered that metallocene dichlorides can be activated by MAO (see Kaminsky catalyst). The effect was discovered when a small amount of water was found to enhance the activity in the Ziegler–Natta system.
MAO serves multiple functions in the activation process. First it alkylates the metal-chloride pre-catalyst species giving Ti/Zr-methyl intermediates. Second, it abstracts a ligand from the methylated precatalysts, forming an electrophilic, coordinatively unsaturated catalysts that can undergo ethylene insertion. This activated catalyst is an ion pair between a cationic catalyst and an weakly basic MAO-derived anion. MAO also functions as scavenger for protic impurities. | 7 | Physical Chemistry |
In analytical chemistry, glow discharges are usually operated in direct-current mode. For direct-current, the cathode (which is the sample in solids analysis) must be conductive. In contrast, analysis of a non conductive cathode requires the use of a high frequency alternating current.
The potential, pressure, and current are interrelated. Only two can be directly controlled at once, while the third must be allowed to vary. The pressure is most typically held constant, but other schemes may be used. The pressure and current may be held constant, while potential is allowed to vary. The pressure and voltage may be held constant while the current is allowed to vary. The power (product of voltage and current) may be held constant while the pressure is allowed to vary.
Glow discharges may also be operated in radio-frequency. The use of this frequency will establish a negative DC-bias voltage on the sample surface. The DC-bias is the result of an alternating current waveform that is centered about negative potential; as such it more or less represent the average potential residing on the sample surface. Radio-frequency has ability to appear to flow through insulators (non-conductive materials).
Both radio-frequency and direct-current glow discharges can be operated in pulsed mode, where the potential is turned on and off. This allows higher instantaneous powers to be applied without excessively heating the cathode. These higher instantaneous powers produce higher instantaneous signals, aiding detection. Combining time-resolved detection with pulsed powering results in additional benefits. In atomic emission, analyte atoms emit during different portions of the pulse than background atoms, allowing the two to be discriminated. Analogously, in mass spectrometry, sample and background ions are created at different times. | 3 | Analytical Chemistry |
When producers, importers or authorities test a sample for the unintended presence of GMOs, they usually do not know which GMO to expect. While EU authorities prefer an event-specific approach to this problem, US authorities rely on construct-specific test schemes. | 1 | Biochemistry |
Methane has a very light δC signature: biogenic methane of −60‰, thermogenic methane −40‰. The release of large amounts of methane clathrate can impact on global δC values, as at the Paleocene–Eocene Thermal Maximum.
More commonly, the ratio is affected by variations in primary productivity and organic burial. Organisms preferentially take up light C, and have a δC signature of about −25‰, depending on their metabolic pathway. Therefore, an increase in δC in marine fossils is indicative of an increase in the abundance of vegetation.
An increase in primary productivity causes a corresponding rise in δC values as more C is locked up in plants. This signal is also a function of the amount of carbon burial; when organic carbon is buried, more C is locked out of the system in sediments than the background ratio. | 9 | Geochemistry |
In chemistry, hexol is a cation with formula {[Co(NH)(OH)]Co} — a coordination complex consisting of four cobalt cations in oxidation state +3, twelve ammonia molecules , and six hydroxy anions , with a net charge of +6. The hydroxy groups act as bridges between the central cobalt atom and the other three, which carry the ammonia ligands.
Salts of hexol, such as the sulfate {[Co(NH)(OH)]Co}(SO)(HO), are of historical significance as the first synthetic non-carbon-containing chiral compounds. | 4 | Stereochemistry |
The nano guitar is a microscopically small carved guitar. It was developed by Dustin W. Carr in 1997, under the direction of Professor Harold G. Craighead, in the Cornell Nanofabrication Facility. The idea came about as a fun way to illustrate nanotechnology, and captured popular attention. It is disputed as to whether the nano guitar should be classified as a guitar, but it is the common opinion that it is in fact a guitar. | 6 | Supramolecular Chemistry |
There is evidence for high concentrations of over 6,000 ppm between 600 and 400 million years ago, and of over 3,000 ppm between 200 and 150 million years ago.
Indeed, higher CO concentrations are thought to have prevailed throughout most of the Phanerozoic Eon, with concentrations four to six times current concentrations during the Mesozoic era, and ten to fifteen times current concentrations during the early Palaeozoic era until the middle of the Devonian period, about 400 million years ago. The spread of land plants is thought to have reduced CO concentrations during the late Devonian, and plant activities as both sources and sinks of CO have since been important in providing stabilizing feedbacks.
Earlier still, a 200-million year period of intermittent, widespread glaciation extending close to the equator (Snowball Earth) appears to have been ended suddenly, about 550 Ma, by a colossal volcanic outgassing that raised the concentration of the atmosphere abruptly to 12%, about 350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm per day. This episode marked the close of the Precambrian Eon, and was succeeded by the generally warmer conditions of the Phanerozoic, during which multicellular animal and plant life evolved. No volcanic CO emission of comparable scale has occurred since. In the modern era, emissions to the atmosphere from volcanoes are approximately 0.645 billion tons of per year, whereas humans contribute 29 billion tons of each year. | 2 | Environmental Chemistry |
Boyle, Charles and Gay-Lussac laws, together with Avogadro's law, were combined by Émile Clapeyron in 1834, giving rise to the ideal gas law. At the end of the 19th century, later developments from scientists like August Krönig, Rudolf Clausius, James Clerk Maxwell and Ludwig Boltzmann, gave rise to the kinetic theory of gases, a microscopic theory from which the ideal gas law can be derived as an statistical result from the movement of atoms/molecules in a gas. | 7 | Physical Chemistry |
Amoxicillin is used to treat odontogenic infections, infections of the tongue, lips, and other oral tissues. It may be prescribed following a tooth extraction, particularly in those with compromised immune systems. | 4 | Stereochemistry |
Plant disease resistance is crucial to the reliable production of food, and it provides significant reductions in agricultural use of land, water, fuel and other inputs. Plants in both natural and cultivated populations carry inherent disease resistance, but this has not always protected them.
The late blight Great Famine of Ireland of the 1840s was caused by the oomycete Phytophthora infestans. The worlds first mass-cultivated banana cultivar Gros Michel was lost in the 1920s to Panama disease caused by the fungus Fusarium oxysporum. The current wheat stem rust, leaf rust and yellow stripe rust epidemics spreading from East Africa into the Indian subcontinent are caused by rust fungi Puccinia graminis and P. striiformis'. Other epidemics include chestnut blight, as well as recurrent severe plant diseases such as rice blast, soybean cyst nematode, and citrus canker.
Plant pathogens can spread rapidly over great distances, vectored by water, wind, insects, and humans. Across large regions and many crop species, it is estimated that diseases typically reduce plant yields by 10% every year in more developed nations or agricultural systems, but yield loss to diseases often exceeds 20% in less developed settings.
However, disease control is reasonably successful for most crops. Disease control is achieved by use of plants that have been bred for good resistance to many diseases, and by plant cultivation approaches such as crop rotation, pathogen-free seed, appropriate planting date and plant density, control of field moisture, and pesticide use. | 1 | Biochemistry |
A chemical system is said to be in equilibrium when the quantities of the chemical entities involved do not and cannot change in time without the application of an external influence. In this sense a system in chemical equilibrium is in a stable state. The system at chemical equilibrium will be at a constant temperature, pressure or volume and a composition. It will be insulated from exchange of heat with the surroundings, that is, it is a closed system. A change of temperature, pressure (or volume) constitutes an external influence and the equilibrium quantities will change as a result of such a change. If there is a possibility that the composition might change, but the rate of change is negligibly slow, the system is said to be in a metastable state. The equation of chemical equilibrium can be expressed symbolically as
:reactant(s) product(s)
The sign means "are in equilibrium with". This definition refers to macroscopic properties. Changes do occur at the microscopic level of atoms and molecules, but to such a minute extent that they are not measurable and in a balanced way so that the macroscopic quantities do not change. Chemical equilibrium is a dynamic state in which forward and backward reactions proceed at such rates that the macroscopic composition of the mixture is constant. Thus, equilibrium sign symbolizes the fact that reactions occur in both forward and backward directions.
A steady state, on the other hand, is not necessarily an equilibrium state in the chemical sense. For example, in a radioactive decay chain the concentrations of intermediate isotopes are constant because the rate of production is equal to the rate of decay. It is not a chemical equilibrium because the decay process occurs in one direction only.
Thermodynamic equilibrium is characterized by the free energy for the whole (closed) system being a minimum. For systems at constant volume the Helmholtz free energy is minimum and for systems at constant pressure the Gibbs free energy is minimum. Thus a metastable state is one for which the free energy change between reactants and products is not minimal even though the composition does not change in time.
The existence of this minimum is due to the free energy of mixing of reactants and products being always negative. For ideal solutions the enthalpy of mixing is zero, so the minimum exists because the entropy of mixing is always positive. The slope of the reaction free energy, δG with respect to the reaction coordinate, ξ, is zero when the free energy is at its minimum value. | 7 | Physical Chemistry |
VMATs are found in a variety of cell types throughout the body, however, VMAT1 is found exclusively in neuroendocrine cells, in contrast to VMAT2, which is also found in the PNS and CNS. Specifically, VMAT1 is found in chromaffin cells, enterochromaffin cells, and small intensely fluorescent cells (SIFs). Chromaffin cells are responsible for releasing the catecholamines (norepinephrine and epinephrine) into systemic circulation. Enterochromaffin cells are responsible for storing serotonin in the gastrointestinal tract. SIFs are interneurons associated with the sympathetic nervous system which are managed by dopamine. | 1 | Biochemistry |
In the years up to 1960 the following approximate division of Fulmer's income applied: about 25% of project work was for UK Government defence agencies; 25% for the Atomic Energy Authority and another 10% for other Government agencies. About 10% was for US Government agencies (the US Air Force and the Office of Aerospace Research); 30% was for British Industry. | 8 | Metallurgy |
In most open ocean ecosystems only a small fraction of organic matter reaches the seafloor. Biological activity in the photic zone of most water bodies tends to recycle material so well that only a small fraction of organic matter ever sinks out of that top photosynthetic layer. Remineralisation within this top layer occurs rapidly and due to the higher concentrations of organisms and the availability of light, those remineralised nutrients are often taken up by autotrophs just as rapidly as they are released.
What fraction does escape varies depending on the location of interest. For example, in the North Sea, values of carbon deposition are ~1% of primary production while that value is <0.5% in the open oceans on average. Therefore, most of nutrients remain in the water column, recycled by the biota. Heterotrophic organisms will utilize the materials produced by the autotrophic (and chemotrophic) organisms and via respiration will remineralise the compounds from the organic form back to inorganic, making them available for primary producers again.
For most areas of the ocean, the highest rates of carbon remineralisation occur at depths between in the water column, decreasing down to about 1,200 m where remineralisation rates remain pretty constant at 0.1 μmol kg yr. As a result of this, the pool of remineralised carbon (which generally takes the form of carbon dioxide) tends to increase in the photic zone.
Most remineralisation is done with dissolved organic carbon (DOC). Studies have shown that it is larger sinking particles that transport matter down to the sea floor while suspended particles and dissolved organics are mostly consumed by remineralisation. This happens in part due to the fact that organisms must typically ingest nutrients smaller than they are, often by orders of magnitude. With the microbial community making up 90% of marine biomass, it is particles smaller than the microbes (on the order of ) that will be taken up for remineralisation. | 9 | Geochemistry |
The PFA-100 (Platelet Function Assay or Platelet Function Analyser) is a platelet function analyser that aspirates blood in vitro from a blood specimen into disposable test cartridges through a microscopic aperture cut into a biologically active membrane at the end of a capillary. The membrane of the cartridges are coated with collagen and adenosine diphosphate (ADP) or collagen and epinephrine inducing a platelet plug to form which closes the aperture.
The PFA test result is dependent on platelet function, plasma von Willebrand Factor level, platelet
number, and (to some extent) the hematocrit (that is, the percent composition of red blood cells in the sample).
The PFA test is initially performed with the Collagen/Epinepherine membrane. A normal Col/Epi closure time
(<180 seconds) excludes the presence of a significant platelet function defect.
If the Col/Epi closure time is prolonged (>180 seconds), the Col/ADP test is automatically
performed. If the Col/ADP result is normal (<120 seconds), aspirin-induced platelet dysfunction is
most likely.
Prolongation of both test results (Col/Epi >180 seconds, Col/ADP >120 seconds) may indicate
the following;
* Anemia (hematocrit <0.28)
* Thrombocytopenia (platelet count < 100 x 10/L)
* A significant platelet function defect other than aspirin
Once anemia and thrombocytopenia have been excluded, further evaluation to exclude von
Willebrand disease and inherited/acquired platelet dysfunction can be made. | 1 | Biochemistry |
CD96 (Cluster of Differentiation 96) or Tactile (T cell activation, increased late expression) is a protein that in humans is encoded by the CD96 gene. CD96 is a receptor protein which is expressed on T cells and NK cells and shares sequence similarity with CD226 (also known as DNAM-1). The protein encoded by this gene belongs to the immunoglobulin superfamily. It is a type I membrane protein. The protein may play a role in the adhesion of activated T and NK cells to their target cells during the late phase of the immune response. It may also function in antigen presentation. Alternative splicing occurs at this locus and two transcript variants encoding distinct isoforms have been identified. CD96 is a transmembrane glycoprotein that has three extracellular immunoglobulin-like domains and is expressed by all resting human and mouse NK cells. CD96 main ligand is CD155. CD 96 has approximately 20% homology with CD226 and competed for binding to CD155 with CD226. | 1 | Biochemistry |
A thiophosphonate group is a functional group related to phosphonate by substitution of an oxygen atom for a sulphur. They are a reactive component of many pesticides and nerve agents. Substituted thiophosphonates can have 2 main structural isomers bonding though either O or S groups to give thione and thiol forms respectively. This is a property they share with related functional groups such as thiocarboxylic acids and organothiophosphates. | 0 | Organic Chemistry |
Inhalation of sulfuryl fluoride is hazardous and may result in respiratory irritation, pulmonary edema, nausea, abdominal pain, central nervous system depression, numbness in the extremities, muscle twitching, seizures, and death. These high exposures occurred when people entered into structures illegally during fumigation or after insufficient aeration. Epidemiological studies showed that fumigation workers who used sulfuryl fluoride showed neurological effects, which included reduced performance on cognitive tests and pattern memory tests, and reduced olfactory function. | 2 | Environmental Chemistry |
Biological signaling networks incorporate a wide array of reversible interactions, post-translational modifications and conformational changes. Furthermore, it is common for a protein to be composed of several - identical or nonidentical - subunits, and for several proteins and/or nucleic acid species to assemble into larger complexes. A molecular species with several of those features can therefore exist in a large number of possible states.
For instance, it has been estimated that the yeast scaffold protein Ste5 can be a part of 25666 unique protein complexes. In E. coli, chemotaxis receptors of four different kinds interact in groups of three, and each individual receptor can exist in at least two possible conformations and has up to eight methylation sites, resulting in billions of potential states. The protein kinase CaMKII is a dodecamer of twelve catalytic subunits, arranged in two hexameric rings. Each subunit can exist in at least two distinct conformations, and each subunit features various phosphorylation and ligand binding sites. A recent model incorporated conformational states, two phosphorylation sites and two modes of binding calcium/calmodulin, for a total of around one billion possible states per hexameric ring. A model of coupling of the EGF receptor to a MAP kinase cascade presented by Danos and colleagues accounts for distinct molecular species, yet the authors note several points at which the model could be further extended. A more recent model of ErbB receptor signalling even accounts for more than one googol () distinct molecular species. The problem of combinatorial explosion is also relevant to synthetic biology, with a recent model of a relatively simple synthetic eukaryotic gene circuit featuring 187 species and 1165 reactions.
Of course, not all of the possible states of a multi-state molecule or complex will necessarily be populated. Indeed, in systems where the number of possible states is far greater than that of molecules in the compartment (e.g. the cell), they cannot be. In some cases, empirical information can be used to rule out certain states if, for instance, some combinations of features are incompatible. In the absence of such information, however, all possible states need to be considered a priori. In such cases, computational modeling can be used to uncover to what extent the different states are populated.
The existence (or potential existence) of such large numbers of molecular species is a combinatorial phenomenon: It arises from a relatively small set of features or modifications (such as post-translational modification or complex formation) that combine to dictate the state of the entire molecule or complex, in the same way that the existence of just a few choices in a coffee shop (small, medium or large, with or without milk, decaf or not, extra shot of espresso) quickly leads to a large number of possible beverages (24 in this case; each additional binary choice will double that number). Although it is difficult for us to grasp the total numbers of possible combinations, it is usually not conceptually difficult to understand the (much smaller) set of features or modifications and the effect each of them has on the function of the biomolecule. The rate at which a molecule undergoes a particular reaction will usually depend mainly on a single feature or a small subset of features. It is the presence or absence of those features that dictates the reaction rate. The reaction rate is the same for two molecules that differ only in features which do not affect this reaction. Thus, the number of parameters will be much smaller than the number of reactions. (In the coffee shop example, adding an extra shot of espresso will cost 40 cent, no matter what size the beverage is and whether or not it has milk in it). It is such "local rules" that are usually discovered in laboratory experiments. Thus, a multi-state model can be conceptualised in terms of combinations of modular features and local rules. This means that even a model that can account for a vast number of molecular species and reactions is not necessarily conceptually complex. | 1 | Biochemistry |
As the environment is altered through physical means (dredging), the occurring reactions change resulting in a decrease of the availability of nutrients and chemical species to plant species and the ecosystem. This then further changes the physical environment as these species are no longer able to survive. The loss of species then results in further changes to the chemical environment, as they are no longer present to remove excess nutrients. This also changes the physical environment further as the lack of survival of plant species results in open land and increased erosion. The change of the chemical environment also affects the mitigation techniques to be applied for rebuilding of wetlands as the survival of plant species that could potentially be planted depends on the chemical environment, and changes must be monitored for effective mitigation to take place. | 9 | Geochemistry |
Addition-elimination reactions are addition reactions immediately followed by elimination reactions. In general, these reactions take place when esters (or related functional groups) react with nucleophiles. In fact, the only requirement for an addition-elimination reaction to proceed is that the group being eliminated is a better leaving group than the incoming nucleophile. | 0 | Organic Chemistry |
YwIE is a member of the low-molecular-weight protein tyrosine phosphatase (LMW-PTP). It is the only active PAP present in B.subtilis, and PAPs exhibits almost no activity against Protein Serine, Protein Tyrosine, and Protein Threonine peptides. Also, YwIE has been shown to play a role in B.Subtilis's resistance to stress. Elsholz et al. (2012), reported in their paper that protein arginine phosphorylation likely plays a critical physiological and regulatory role in bacteria. They showed that protein arginine phosphorylation is involved in the regulation of homeostasis, biofilm formation, motility, competence, stress, and stringent responses by regulating gene expression and protein activity in Bacillus Subtilis. Their results suggested that the combined action of protein arginine phosphatase and kinase allows for rapid and reversible regulation of protein activity. Also, that protein-arginine-phosphatases reverse the effect of protein arginine kinases (PAKs) in living organisms. In B.Subtilis, YwIE, a PAP, counteracts the action of McsB, a protein arginine kinase (PAK). McsB phosphorylates arginine residues in the winged helix-turn-helix domain of CtsR4, preventing it from binding to DNA, allowing for the expression of the repressed gene. However, YwIE is capable of restoring the DNA-binding ability of the CtsR repressor, a stress response & heat shock regulator in B.Subtilis, by reversing the McsB-mediated phosphorylation4. It accomplishes this by dephosphorylating the CtsR Protein. Additionally, McsB and YwIE are capable of differentiating between phosphoarginine and other amino acid residues | 1 | Biochemistry |
Although the sequestration of marine carbon is a primary outcome of the biological pump, the recycling of nutrients such as N and P in organic matter plays a comparatively important role in maintaining the processes that facilitate this carbon export without removing nutrients for primary production. One key difference between the lipid pump and biological pump is that the ratios of nutrients such as nitrogen and phosphorus relative to carbon are minimal or zero in lipids, whereas the exported POC in the biological pump retains the standard Redfield ratios found throughout the world's oceans. This is primarily due to zooplankton in their copepodite stages releasing an excessive amount of nitrogen and phosphorus from excretion back into the surface. Thus, the production, transport, and metabolism of lipid carbon during overwintering do not contribute to a net consumption or removal of essential nutrients in the surface ocean, which is unlike many components of the biological pump. This process creates what is known as a "lipid shunt" in the biological pump, as the carbon sequestration of the lipid pump is decoupled from nutrient removal. | 9 | Geochemistry |
The increased complexity of the phosphorelay system compared to orthodox two-component signaling provides additional opportunities for regulation and improves the specificity of the response. Although there is very little cross-talk between orthodox two-component systems, phosphorelays allow more complex signaling pathways; examples include a bifurcated pathway with multiple downstream outputs, as in the case of the Caulobacter crescentus ChpT HPt involved in cell cycle regulation, or, alternatively, pathways in which more than one histidine kinase controls a single response regulator, such as the sporulation pathway in Bacillus subtilis, which can give rise to complex temporal variations. In some known cases, there is an additional form of regulation in phosphohistidine phosphatase enzymes that act on HPt, such as the Escherichia coli protein SixA which targets ArcB. | 1 | Biochemistry |
Flammability is the ease with which a combustible substance can be ignited, causing fire or combustion or even an explosion. The degree of difficulty required to cause the combustion of a substance is quantified through fire testing. Internationally, a variety of test protocols exist to quantify flammability. The ratings achieved are used in building codes, insurance requirements, fire codes and other regulations governing the use of building materials as well as the storage and handling of highly flammable substances inside and outside of structures and in surface and air transportation. For instance, changing an occupancy by altering the flammability of the contents requires the owner of a building to apply for a building permit to make sure that the overall fire protection design basis of the facility can take the change into account. | 7 | Physical Chemistry |
Moroidin is a biologically active compound found in the plants Dendrocnide moroides and Celosia argentea. It is a peptide composed of eight amino acids, with unusual leucine-tryptophan and tryptophan-histidine cross-links that form its two rings. Moroidin has been shown to be at least one of several bioactive compounds responsible for the painful sting of the Dendrocnide moroides plant. It also has demonstrated anti-mitotic properties, specifically by inhibition of tubulin polymerization. Anti-mitotic activity gives moroidin potential as a chemotherapy drug, and this property combined with its unusual chemical structure has made it a target for organic synthesis. | 0 | Organic Chemistry |
The Krupp–Renn process was a direct reduction steelmaking process used from the 1930s to the 1970s. It used a rotary furnace and was one of the few technically and commercially successful direct reduction processes in the world, acting as an alternative to blast furnaces due to their coke consumption. The Krupp-Renn process consumed mainly hard coal and had the unique characteristic of partially melting the charge. This method is beneficial for processing low-quality or non-melting ores, as their waste material forms a protective layer that can be easily separated from the iron. It generates Luppen, nodules of pre-reduced iron ore, which can be easily melted down.
The first industrial furnaces emerged in the 1930s, firstly in Nazi Germany and then in the Japanese Empire. During the 1950s, new facilities were constructed, notably in Czechoslovakia and West Germany. The process was discontinued in the early 1970s, with a few nuances.
It was unproductive, intricate to master, and only pertinent to certain ores. In the beginning of the 21st century, Japan modernized the process to manufacture ferronickel, which is the sole surviving variant. | 8 | Metallurgy |
Lee (1977) designed a seepage meter, which consists of a chamber which is connected to a sampling port and a plastic bag. The chamber is inserted into the sediment and water discharging through the sediments is caught within the plastic bag. The change in volume of water which is caught in the plastic bag over time represents the freshwater flux. | 9 | Geochemistry |
The journal is abstracted and indexed in:
* Academic Search
* Aquatic Sciences & Fisheries Abstracts
* Chemical Abstracts Service
* Current Contents/Physical, Chemical & Earth Sciences
* GeoRef
* Science Citation Index
According to the Journal Citation Reports, the journal has a 2018 impact factor of 4.256, ranking it 11th out of 84 journals in the category "Geochemistry and Geophysics". | 9 | Geochemistry |
Aerosol is defined as a suspension system of solid or liquid particles in a gas. An aerosol includes both the particles and the suspending gas, which is usually air. Meteorologists usually refer them as particle matter - PM2.5 or PM10, depending on their size. Frederick G. Donnan presumably first used the term aerosol during World War I to describe an aero-solution, clouds of microscopic particles in air. This term developed analogously to the term hydrosol, a colloid system with water as the dispersed medium. Primary aerosols contain particles introduced directly into the gas; secondary aerosols form through gas-to-particle conversion.
Key aerosol groups include sulfates, organic carbon, black carbon, nitrates, mineral dust, and sea salt, they usually clump together to form a complex mixture. Various types of aerosol, classified according to physical form and how they were generated, include dust, fume, mist, smoke and fog.
There are several measures of aerosol concentration. Environmental science and environmental health often use the mass concentration (M), defined as the mass of particulate matter per unit volume, in units such as μg/m. Also commonly used is the number concentration (N), the number of particles per unit volume, in units such as number per m or number per cm.
Particle size has a major influence on particle properties, and the aerosol particle radius or diameter (d) is a key property used to characterise aerosols.
Aerosols vary in their dispersity. A monodisperse aerosol, producible in the laboratory, contains particles of uniform size. Most aerosols, however, as polydisperse colloidal systems, exhibit a range of particle sizes. Liquid droplets are almost always nearly spherical, but scientists use an equivalent diameter to characterize the properties of various shapes of solid particles, some very irregular. The equivalent diameter is the diameter of a spherical particle with the same value of some physical property as the irregular particle. The equivalent volume diameter (d) is defined as the diameter of a sphere of the same volume as that of the irregular particle. Also commonly used is the aerodynamic diameter, d. | 7 | Physical Chemistry |
With the advent of the high-throughput DNA and RNA sequence identification methods (such as Illumina sequencing), it became possible to efficiently analyse nucleotide sequences of large numbers of relatively short DNA and RNA fragments. Sequences of these fragments can be superimposed to reconstruct the source. Alternatively, if the source sequence is already known, the fragments can be found within it (“mapped”), and their individual numbers counted. Thus, if an initial stage exists whereby the fragments are differentially present or selected (“enriched”), this approach can be used to quantitatively describe such stage over even a very large number or length of the input sequences, most usually encompassing the entire DNA or RNA of the cell.
TCP-seq is based on these capabilities of the high-throughput RNA sequencing and further uses the nucleic acid protection phenomenon. The protection is manifested as resistance to depolymerisation or modification of stretches of nucleic acids (particularly, RNA) that are tightly bound to or engulfed with other biomolecules, which thus leave their “footprints” over the nucleic acid strand. These “footprint” fragments therefore represent location on nucleic acid chain where the interaction occurs. By sequencing and mapping the fragments back to the source sequence, it is possible to precisely identify the locations and counts of these intermolecular contacts.
In case of TCP-seq, ribosomes and ribosomal subunits engaged in interaction with mRNA are first fast chemically crosslinked to it with formaldehyde to preserve existing state of interactions (“snapshot” of distribution) and to block any possible non-equilibrium processes. The crosslinking can be performed directly in, but not restricted to, live cells. The RNA is then partially degraded (e.g. with ribonuclease) so that only fragments protected by the ribosomes or ribosomal subunits are left. The protected fragments are then purified according to the sedimentation dynamics of the attached ribosomes or ribosomal subunits, de-blocked, sequenced and mapped to the source transcriptome, giving the original locations of the translation complexes over mRNA.
TCP-seq merges several elements typical to other transcriptome-wide analyses of its kind. In particular, polysome profiling and ribosome (translation) profiling approaches are also employed to identify mRNA involved in polysome formation and locations of elongating ribosomes over coding regions of transcripts, correspondingly. These methods, however, do not use chemical stabilisation of translation complexes and purification of the covalently bound intermediates from the live cells. TCP-seq thus can be considered more as a functional equivalent of ChIP-seq and similar methods of investigating momentary interactions of DNA that are redesigned to be applicable for translation. | 1 | Biochemistry |
When used as a fully supported roof covering, copper is half the weight (including substrate) of lead and only a quarter of tiled roofs. This generally provides savings in supporting structure and materials costs. Copper cladding offers additional opportunities to reduce the weight of copper structures (For more details, see: Copper cladding and Wall cladding). | 8 | Metallurgy |
In haloalkanes and haloarenes (), Halogen functional groups are prefixed with the bonding position and take the form of fluoro-, chloro-, bromo-, iodo-, etc., depending on the halogen. Multiple groups are dichloro-, trichloro-, etc., and dissimilar groups are ordered alphabetically as before. For example, (chloroform) is trichloromethane. The anesthetic halothane () is 2-bromo-2-chloro-1,1,1-trifluoroethane. | 0 | Organic Chemistry |
As a form of energy, heat has the unit joule (J) in the International System of Units (SI). In addition, many applied branches of engineering use other, traditional units, such as the British thermal unit (BTU) and the calorie. The standard unit for the rate of heating is the watt (W), defined as one joule per second.
The symbol for heat was introduced by Rudolf Clausius and Macquorn Rankine in .
Heat released by a system into its surroundings is by convention a negative quantity (); when a system absorbs heat from its surroundings, it is positive (). Heat transfer rate, or heat flow per unit time, is denoted by , but it is not a time derivative of a function of state (which can also be written with the dot notation) since heat is not a function of state. Heat flux is defined as rate of heat transfer per unit cross-sectional area (watts per square metre). | 7 | Physical Chemistry |
Media for 3D optical data storage have been suggested in several form factors: disk, card and crystal.
A disc media offers a progression from CD/DVD, and allows reading and writing to be carried out by the familiar spinning disc method.
A credit card form factor media is attractive from the point of view of portability and convenience, but would be of a lower capacity than a disc.
Several science fiction writers have suggested small solids that store massive amounts of information, and at least in principle this could be achieved with 5D optical data storage. | 5 | Photochemistry |
Wohl model may refer to:
* Wohl equation of state: an empirical model for a real gas proposed by A. Wohl
* an empirical model for the excess Gibbs free energy of mixing which has been formulated for ternary solutions by K. Wohl (1946, 1953) | 7 | Physical Chemistry |
The resistivity of solvent extract (ROSE) test is a test for the presence and average concentration of soluble ionic contaminants, for example on a printed circuit board (PCB). It was developed in the early 1970s. Some manufacturers use it as part of Six Sigma processes.
Some modern fluxes have low solubility in traditional ROSE solvents such as water and isopropyl alcohol, and therefore require the use of different solvents. | 3 | Analytical Chemistry |
The technique has been used to evolve aptamers of extremely high binding affinity to a variety of target ligands, including small molecules such as ATP and adenosine and proteins such as prions and vascular endothelial growth factor (VEGF). Moreover, SELEX has been used to select high-affinity aptamers for complex targets such as tumor cells, tumor exosomes, or tumor tissue. Clinical uses of the technique are suggested by aptamers that bind tumor markers, GFP-related fluorophores, and a VEGF-binding aptamer trade-named Macugen has been approved by the FDA for treatment of macular degeneration. Additionally, SELEX has been utilized to obtain highly specific catalytic DNA or DNAzymes. Several metal-specific DNAzymes have been reported including the GR-5 DNAzyme (lead-specific), the CA1-3 DNAzymes (copper-specific), the 39E DNAzyme (uranyl-specific) and the NaA43 DNAzyme (sodium-specific).
These developed aptamers have seen diverse application in therapies for macular degeneration and various research applications including biosensors, fluorescent labeling of proteins and cells, and selective enzyme inhibition. | 1 | Biochemistry |
In chemistry, the standard state of a material (pure substance, mixture or solution) is a reference point used to calculate its properties under different conditions. A degree sign (°) or a superscript Plimsoll symbol () is used to designate a thermodynamic quantity in the standard state, such as change in enthalpy (ΔH°), change in entropy (ΔS°), or change in Gibbs free energy (ΔG°). The degree symbol has become widespread, although the Plimsoll is recommended in standards, see discussion about typesetting below.
In principle, the choice of standard state is arbitrary, although the International Union of Pure and Applied Chemistry (IUPAC) recommends a conventional set of standard states for general use. The standard state should not be confused with standard temperature and pressure (STP) for gases, nor with the standard solutions used in analytical chemistry. STP is commonly used for calculations involving gases that approximate an ideal gas, whereas standard state conditions are used for thermodynamic calculations.
For a given material or substance, the standard state is the reference state for the material's thermodynamic state properties such as enthalpy, entropy, Gibbs free energy, and for many other material standards. The standard enthalpy change of formation for an element in its standard state is zero, and this convention allows a wide range of other thermodynamic quantities to be calculated and tabulated. The standard state of a substance does not have to exist in nature: for example, it is possible to calculate values for steam at 298.15 K and , although steam does not exist (as a gas) under these conditions. The advantage of this practice is that tables of thermodynamic properties prepared in this way are self-consistent. | 7 | Physical Chemistry |
Benzene is an organic chemical compound with the molecular formula CH. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.
Benzene is a natural constituent of petroleum and is one of the elementary petrochemicals. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma of gasoline. It is used primarily as a precursor to the manufacture of chemicals with more complex structures, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. Although benzene is a major industrial chemical, it finds limited use in consumer items because of its toxicity. Benzene is a volatile organic compound.
Benzene is classified as a carcinogen.[https://emergency.cdc.gov/agent/benzene/basics/facts.asp] | 2 | Environmental Chemistry |
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction, facilitating multistep organic synthesis.
*Boc for the t-butoxycarbonyl group
*Cbz or Z for the carboxybenzyl group
*Fmoc for the fluorenylmethoxycarbonyl group
*Alloc for the allyloxycarbonyl group
*Troc for the trichloroethoxycarbonyl group
*TMS, TBDMS, TES, TBDPS, TIPS, ... for various silyl ether groups
*PMB for the 4-methoxybenzyl group
*MOM for the methoxymethyl group
*THP for the 2-tetrahydropyranyl group | 0 | Organic Chemistry |
Type I restriction enzymes were the first to be identified and were first identified in two different strains (K-12 and B) of E. coli. These enzymes cut at a site that differs, and is a random distance (at least 1000 bp) away, from their recognition site. Cleavage at these random sites follows a process of DNA translocation, which shows that these enzymes are also molecular motors. The recognition site is asymmetrical and is composed of two specific portions—one containing 3–4 nucleotides, and another containing 4–5 nucleotides—separated by a non-specific spacer of about 6–8 nucleotides. These enzymes are multifunctional and are capable of both restriction digestion and modification activities, depending upon the methylation status of the target DNA. The cofactors S-Adenosyl methionine (AdoMet), hydrolyzed adenosine triphosphate (ATP), and magnesium (Mg) ions, are required for their full activity. Type I restriction enzymes possess three subunits called HsdR, HsdM, and HsdS; HsdR is required for restriction digestion; HsdM is necessary for adding methyl groups to host DNA (methyltransferase activity), and HsdS is important for specificity of the recognition (DNA-binding) site in addition to both restriction digestion (DNA cleavage) and modification (DNA methyltransferase) activity. | 1 | Biochemistry |
Chiral switch, a re-engineering approach, has enabled in the remarketing of a number of racemic drugs as chiral specific enantiomer products. Chiral switching strategy is the way most blockbuster drugs have entered the market as enantiopure drugs. A more appropriate term may be unichiral. But the alternate route is de novo (anew) synthesis of chiral specific drugs. The chiral switches may have the same, very similar, therapeutic indications as the original racemic drug. But, there are instances where new indications for the old drug have been reported. The table below gives a brief list of launched chiral switches. | 4 | Stereochemistry |
The entrance to the active site for this enzyme is made up mainly of several arginine, histidine, serine, and aspartate side-chains, with a glutamate side-chain playing a secondary role. These side-chains, to be specific Arg359, Arg528, His469, and Ser386, are conserved within each transketolase enzyme and interact with the phosphate group of the donor and acceptor substrates. Because the substrate channel is so narrow, the donor and acceptor substrates cannot be bound simultaneously. Also, the substrates conform into a slightly extended form upon binding in the active site to accommodate this narrow channel.
Although this enzyme is able to bind numerous types of substrates, such as phosphorylated and nonphosphorylated monosaccharides including the keto and aldosugars fructose, ribose, etc., it has a high specificity for the stereoconfiguration of the hydroxyl groups of the sugars. These hydroxyl groups at C-3 and C-4 of the ketose donor must be in the D-threo configuration in order to correctly correspond to the C-1 and C-2 positions on the aldose acceptor. Also they stabilize the substrate in the active site by interacting with the Asp477, His30, and His263 residues. Disruption of this configuration, both the placement of hydroxyl groups or their stereochemistry, would consequently alter the H-bonding between the residues and substrates thus causing a lower affinity for the substrates.
In the first half of this pathway, His263 is used to effectively abstract the C3 hydroxyl proton, which thus allows a 2-carbon segment to be cleaved from fructose 6-phosphate. The cofactor necessary for this step to occur is thiamin pyrophosphate (TPP). The binding of TPP to the enzyme incurs no major conformational change to the enzyme; instead, the enzyme has two flexible loops at the active site that make TPP accessible and binding possible. Thus, this allows the active site to have a "closed" conformation rather than a large conformational change. Later in the pathway, His263 is used as a proton donor for the substrate acceptor-TPP complex, which can then generate erythrose-4-phosphate.
The histidine and aspartate side-chains are used to effectively stabilize the substrate within the active site and also participate in deprotonation of the substrate. To be specific, the His 263 and His30 side-chains form hydrogen bonds to the aldehyde end of the substrate, which is deepest into the substrate channel, and Asp477 forms hydrogen bonds with the alpha hydroxyl group on the substrate, where it works to effectively bind the substrate and check for proper stereochemistry. It is also thought that Asp477 could have important catalytic effects because of its orientation in the middle of the active site and its interactions with the alpha hydroxyl group of the substrate. Glu418, which is located in the deepest region of the active site, plays a critical role in stabilizing the TPP cofactor. To be specific, it is involved in the cofactor-assisted proton abstraction from the substrate molecule.
The phosphate group of the substrate also plays an important role in stabilizing the substrate upon its entrance into the active site. The tight ionic and polar interactions between this phosphate group and the residues Arg359, Arg528, His469, and Ser386 collectively work to stabilize the substrate by forming H-bonds to the oxygen atoms of the phosphate. The ionic nature is found in the salt bridge formed from Arg359 to the phosphate group. | 5 | Photochemistry |
Phosphonium iodide is prepared by mixing diphosphorus tetraiodide () with elemental phosphorus and water at 80 °C and allowing the salt to sublime. | 0 | Organic Chemistry |
Mature messenger RNA, often abbreviated as mature mRNA is a eukaryotic RNA transcript that has been spliced and processed and is ready for translation in the course of protein synthesis. Unlike the eukaryotic RNA immediately after transcription known as precursor messenger RNA, mature mRNA consists exclusively of exons and has all introns removed.
Mature mRNA is also called "mature transcript", "mature RNA" or "mRNA".
The production of a mature mRNA molecule occurs in 3 steps:
# Capping of the 5' end
# Polyadenylation of the 3' end
# RNA Splicing of the introns | 1 | Biochemistry |
Source:
If a solid body is modeled by a constant field and the structure of the field is such that it has a penetrable core, then
Here is the position of the dividing surface, is the external force field, simulating a solid, is the field value deep in the solid, , is the Boltzmann constant, and is the temperature.
Introducing "the surface of zero adsorption"
where
and
we get
and the problem of determination is reduced to the calculation of .
Taking into account that for Henry absorption constant we have
where is the number density inside the solid, we arrive at the parametric dependence
where | 7 | Physical Chemistry |
RiAFP refers to an antifreeze protein (AFP) produced by the Rhagium inquisitor longhorned beetle. It is a type V antifreeze protein with a molecular weight of 12.8 kDa; this type of AFP is noted for its hyperactivity. R. inquisitor is a freeze-avoidant species, meaning that, due to its AFP, R. inquisitor prevents its body fluids from freezing altogether. This contrasts with freeze-tolerant species, whose AFPs simply depress levels of ice crystal formation in low temperatures. Whereas most insect antifreeze proteins contain cysteines at least every sixth residue, as well as varying numbers of 12- or 13-mer repeats of 8.3-12.5kDa, RiAFP is notable for containing only one disulfide bridge. This property of RiAFP makes it particularly attractive for recombinant expression and biotechnological applications. | 1 | Biochemistry |
Dialysis is generally performed in clipped bags of dialysis tubing or in a variety of formatted dialyzers. The choice of the dialysis set up used is largely dependent on the size of the sample and the preference of the user.
Dialysis tubing is the oldest and generally the least expensive format used for dialysis in the lab. Tubing is cut and sealed with a clip at one end, then filled and sealed with a clip on the other end. Tubing provides flexibility but has increased concerns regarding handling, sealing and sample recovery. Dialysis tubing is typically supplied either wet or dry in rolls or pleated telescoped tubes.
A wide variety of dialysis devices (or dialyzers) are available from several vendors. Dialyzers are designed for specific sample volume ranges and provide greater sample security and improved ease of use and performance for dialysis experiments over tubing. The most common preformatted dialyzers are Slide-A-Lyzer, Float-A-Lyzer, and the Pur-A-lyzer/D-Tube/GeBAflex Dialyzers product lines. | 1 | Biochemistry |
Orcein, also archil, orchil, lacmus and C.I. Natural Red 28, are names for dyes extracted from several species of lichen, commonly known as "orchella weeds", found in various parts of the world. A major source is the archil lichen, Roccella tinctoria. Orcinol is extracted from such lichens. It is then converted to orcein by ammonia and air. In traditional dye-making methods, urine was used as the ammonia source. If the conversion is carried out in the presence of potassium carbonate, calcium hydroxide, and calcium sulfate (in the form of potash, lime, and gypsum in traditional dye-making methods), the result is litmus, a more complex molecule. The manufacture was described by Cocq in 1812 and in the UK in 1874. Edmund Roberts noted orchilla as a principal export of the Cape Verde islands, superior to the same kind of "moss" found in Italy or the Canary Islands, that in 1832 was yielding an annual revenue of $200,000. Commercial archil is either a powder (called cudbear) or a paste. It is red in acidic pH and blue in alkaline pH. | 3 | Analytical Chemistry |
β-Lysine (3,6-diaminohexanoic acid) is an amino acid produced by platelets during coagulation and is directly antibacterial by causing lysis of many Gram positive bacteria by acting as a cationic detergent. | 1 | Biochemistry |
Phosphorylated amino acids are crucial for the modulation of the binding of transcription factors and other gene regulatory proteins. Pin1s effect on isomerization of proline residues leads to an increase or decrease in recruitment of phosphatases, namely Scp1 and Ssu72 and their recruitment to the RNAP II CTD. The cis-Pro formation is associated with an increase in Ssu72. Scp1 on recognizes trans'-Pro formations, and is not affected by such isomerization. Pin1 also triggers the activation of the DSIF complex and NELF, which are responsible for pausing RNAP II in mammalian cells, and their conversion into positive elongation factors, facilitating elongation. This potentially could be an isomerization dependent process. | 4 | Stereochemistry |
A Markov process is called a reversible Markov process or reversible Markov chain if it satisfies the detailed balance equations. These equations require that the transition probability matrix P for the Markov process possess a stationary distribution (i.e. equilibrium probability distribution) π such that
where P is the Markov transition probability from state i to state j, i.e. , and π and π are the equilibrium probabilities of being in states i and j, respectively. When for all i, this is equivalent to the joint probability matrix, being symmetric in i and j; or symmetric in and t.
The definition carries over straightforwardly to continuous variables, where π becomes a probability density, and a transition kernel probability density from state s′ to state s:
The detailed balance condition is stronger than that required merely for a stationary distribution; that is, there are Markov processes with stationary distributions that do not have detailed balance. Detailed balance implies that, around any closed cycle of states, there is no net flow of probability. For example, it implies that, for all a, b and c,
This can be proved by substitution from the definition. In the case of a positive transition matrix, the "no net flow" condition implies detailed balance. Indeed, a necessary and sufficient condition for the reversibility condition is Kolmogorov's criterion, which demands that for the reversible chains the product of transition rates over any closed loop of states must be the same in both directions.
Transition matrices that are symmetric or always have detailed balance. In these cases, a uniform distribution over the states is an equilibrium distribution. For continuous systems with detailed balance, it may be possible to continuously transform the coordinates until the equilibrium distribution is uniform, with a transition kernel which then is symmetric. In the case of discrete states, it may be possible to achieve something similar by breaking the Markov states into appropriately-sized degenerate sub-states.
For a Markov transition matrix and a stationary distribution, the detailed balance equations may not be valid. However, it can be shown that a unique Markov transition matrix exists which is closest according to the stationary distribution and a given norm. The closest Matrix can be computed by solving a quadratic-convex optimization problem. For more details see Closest reversible Markov chain | 7 | Physical Chemistry |
Ibuprofen is practically insoluble in water, but very soluble in most organic solvents like ethanol (66.18g/100mL at 40°C for 90% EtOH), methanol, acetone and dichloromethane.
The original synthesis of ibuprofen by the Boots Group started with the compound isobutylbenzene. The synthesis took six steps. A modern, greener technique with fewer waste byproducts for the synthesis involves only three steps was developed in the 1980s by the Celanese Chemical Company. The synthesis is initiated with the acylation of isobutylbenzene using the recyclable Lewis acid catalyst hydrogen fluoride. The following catalytic hydrogenation of isobutylacetophenone is performed with either Raney nickel or palladium on carbon to lead into the key-step, the carbonylation of 1-(4-isobutylphenyl)ethanol. This is achieved by a PdCl(PPh) catalyst, at around 50 bar of CO pressure, in the presence of HCl (10%). The reaction presumably proceeds through the intermediacy of the styrene derivative (acidic elimination of the alcohol) and (1-chloroethyl)benzene derivative (Markovnikow addition of HCl to the double bond). | 4 | Stereochemistry |
By definition, antagonists display no efficacy to activate the receptors they bind. Antagonists do not maintain the ability to activate a receptor. Once bound, however, antagonists inhibit the function of agonists, inverse agonists, and partial agonists. In functional antagonist assays, a dose-response curve measures the effect of the ability of a range of concentrations of antagonists to reverse the activity of an agonist. The potency of an antagonist is usually defined by its half maximal inhibitory concentration (i.e., IC value). This can be calculated for a given antagonist by determining the concentration of antagonist needed to elicit half inhibition of the maximum biological response of an agonist. Elucidating an IC value is useful for comparing the potency of drugs with similar efficacies, however the dose-response curves produced by both drug antagonists must be similar. The lower the IC the greater the potency of the antagonist, and the lower the concentration of drug that is required to inhibit the maximum biological response. Lower concentrations of drugs may be associated with fewer side-effects. | 1 | Biochemistry |
Terphthalaldehyde is used in the preparation of imines, which are also commonly referred to as Schiff bases, following a condensation reaction with amines. During this reaction, water is also formed. This reaction is also reversible. However, due to aromatic conjugation with the benzene ring, the imines are relatively stable and will not easily hydrolyse back to the aldehyde. When in an acidic aqueous environment, the imines will start to hydrolyse more easily. Typically, an equilibrium between the imine and aldehyde is formed, which is dependent on the concentration of the relevant compounds and the pH of the solution.
Imines from terephthalaldehyde find use in the preparation of metal-organic coordination complexes. In addition, terepthaldehyde is a commonly used monomer in the production of imine polymers (polyimines), covalent organic frameworks (COFs), and molecular cages. Terephthalaldehyde is also used as an intermediate for the preparation of dyes and fluorescent whitening agents. | 0 | Organic Chemistry |
In 1989 and 1993, Yamada and co-workers reported the first enantioselective total synthesis of both the enantiomers of ptaquilosin, the aglycone of ptaquiloside. In the first step, the menthyl ester of cyclopentane-1,2-dicarboxylic acid 1 was partially hydrolyzed to afford the monomenthyl ester, which was later alkylated with methallyl bromide in the presence of HMPA to selectively produce 2. The product 2 was then converted to the acid chloride and treated with stannic chloride to effect Friedel-Crafts acylation to give enone 3. Hydride reduction, selective oxidation of the allylic alcohol, and silylation were then performed to provide compound 4. On treatment with base and a chloroethyl sulfonium salt, a mixture of spirocyclopropanes was obtained. The minor product 5a can be isomerized with p-toluenesulfonic acid to 5b with 81% yield. Desaturation by selenylation/dehydroselenation and basic peroxide oxidation afforded epoxide 6. Mild reduction, methyl Grignard addition, and oxidation gave compound 7. Methylation of the cyclopentanone under Noyoris condition using the TASF enolate produced a mixture of isomers. The undesired isomer 8a can be equilibriumed with potassium tert-butoxide in 81% yield to exclusively generate 8b. Reduction, deprotection, and oxidation afforded 9. On treatment with oxygen in warm ethyl acetate, the aldehyde on 9 was oxidized to the acyl radical for decarbonylation. Stereoselective trapping of the tertiary radical by oxygen gave the hydroperoxide 10. Under mild reduction, the naturally occurred (-)-ptaquilosin 11 was obtained. The Yamadas synthesis proceeded in 20 steps with an overall yield of 2.9%. Similarly, the unnatural (+)-enantiomer of ptaquilosin was synthesized from the diastereomer of 2.
Multiple synthetic studies directed towards ptaquilosin 11 have been reported since 1989. In 1994, Padwa and co-workers described the synthesis of the core skeleton of ptaquilosin by a highly convergent approach. In 1995, Cossy and co-workers reported novel routes to the racemic and optically active ptaquilosin skeleton. Their properly functionalized tricyclic compound would be of great utility for the synthesis of 11. | 0 | Organic Chemistry |
Radial chromatography is a form of chromatography, a preparatory technique for separating chemical mixtures. It can also be referred to as centrifugal thin-layer chromatography. It is a common technique for isolating compounds and can be compared to column chromatography as a similar process. A common device used for this technique is a Chromatotron.
Here the solvent travels from the center of the circular chromatography silica layered on a plate towards the periphery. The entire system is kept covered in order to prevent evaporation of solvent while developing a chromatogram.
The wick at the center of system drips solvent into the system which the provides the mobile phase and moves the sample radially to form the sample spots of different compounds as concentric rings.
Continuous annular chromatography uses a stationary phase which is filled into an annular gap. The eluent is continuously fed across the whole bed interface also the feed is continuously fed at the top of the stationary however only at a certain point and not a cross the whole bed. The stationary phase is then rotated with a certain rotation speed. The rotation speed, eluent and feed flow rates have to be defined precisely such that the collector vessels only collect the correct substance. The retention times are transformed into the respective retention angles. | 3 | Analytical Chemistry |
An alloy of NiAl, known as IC-221M, is made up of nickel aluminide combined with several other metals including chromium, molybdenum, zirconium and boron. Adding boron increases the ductility of the alloy by positively altering the grain boundary chemistry and promoting grain refinement. The Hall-Petch parameters for this material were σ = 163 MPa and k = 8.2 MPaˑcm. Boron increases the hardness of bulk NiAl by a similar mechanism.
This alloy is extremely strong for its weight, five times stronger than common SAE 304 stainless steel. Unlike most alloys, IC-221M increases in strength from room temperature up to .
The alloy is very resistant to heat and corrosion, and finds use in heat-treating furnaces and other applications where its longer lifespan and reduced corrosion give it an advantage over stainless steel. It has been found that the microstructure of this alloy includes NiZr eutectic phase and therefore solution treatment is effective for hot working without cracking. | 8 | Metallurgy |
Enzymes responsible for AMPylation, called AMPylators or Adenylyltransferase, fall into two different families, all depending on their structural properties and mechanism used. AMPylator is created by two catalytic homologous halves. One half is responsible for catalyzing the adenylylation reaction, while the other half catalyzes the phosphorolytic deadenylylation reaction. These two families are the DNA-β-polymerase-like and the Fic family.
DNA-β-polymerase-like, is a family of Nucleotidyltransferase. It more specifically is known as the GlnE family. There is a specific motif that is used to clarify this particular family. The motif consists of a three stranded β-sheet which is part of magnesium ion coordination and phosphate binding. Aspartate is essential for the activity to occur in this family.
The Fic domain belongs to Fido (Fic/Doc) superfamilyFic family, which is a filamentation induced by cyclic AMP domain, is known to perform AMPylation. This term was coined when VopS from Vibrio parahaemolyticus was discovered to modify RhoGTPases with AMP on a serine.
This family of proteins are found in all domains of life on earth. It is mediated via a mechanism of ATP-binding-site alpha helix motif. Infectious bacteria use this domain to interrupt phagocytosis and cause cell death. Fic domains are evolutionarily conserved domains in prokaryotes and eukaryotes that belong to the Fido domain superfamily.
AMPylators have been shown to be comparable to kinases due to their ATP hydrolysis activity and reversible transfer of the metabolite to a hydroxyl side chain of the protein substrate. However, AMPylation catalyse a nucleophilic attack on the α-phosphate group, while kinase in the phosphorylation reaction targets γ-phosphate. The nucleophilic attack of AMPylation leads to release Pyrophosphate and the AMP-modified protein are the products of the AMPylation reaction. | 1 | Biochemistry |
The milk fat globule is surrounded by a phospholipid trilayer containing associated proteins, carbohydrates, and lipids derived primarily from the membrane of the secreting mammary epithelial cell (lactocyte). This trilayer is collectively known as MFGM. While MFGM makes up only an estimated 2% to 6% of the total milk fat globule, it is an especially rich phospholipid source, accounting for the majority of total milk phospholipids. In contrast, the inner core of the milk fat globule is composed predominantly of triacylglycerols.
The MFGM structure is complex and comprises a variety of phospholipids, glycolipids, proteins, and glycoproteins, along with cholesterol and other lipids. Specific lipids and proteins are localized to different layers of the membrane, with carbohydrate chains of glycoproteins and glycolipids directed toward the outer surface of the milk fat globule; the lipid-to-protein weight ratio in MFGM is approximately 1:1.
However, the nutritional significance of these components is defined not only by their structure or macronutrient category, but also by the physiological role that each nutrient serves. As a quantitatively minor presence within milk, MFGM likely contributes little to energy production, but its constituents may confer structural and functional benefits. Many of these nutrients are known to play important functional roles within the gut, brain, and elsewhere in the body; the functions of other components are still being elucidated. | 1 | Biochemistry |
The first device which used a scintillator was built in 1903 by Sir William Crookes and used a ZnS screen. The scintillations produced by the screen were visible to the naked eye if viewed by a microscope in a darkened room; the device was known as a spinthariscope. The technique led to a number of important discoveries but was obviously tedious. Scintillators gained additional attention in 1944, when Curran and Baker replaced the naked eye measurement with the newly developed PMT. This was the birth of the modern scintillation detector. | 5 | Photochemistry |
Structures of eIF4F components have been solved individually and as partial complexes by a variety of methods, but no complete structure of eIF4F is currently available. | 1 | Biochemistry |
Plane-wave topography is in some sense the opposite of white-beam topography, making use of monochromatic (single-wavelength) and parallel incident beam. In order to achieve diffraction conditions, the sample under study must be precisely aligned. The contrast observed strongly depends on the exact position of the angular working point on the rocking curve of the sample, i.e. on the angular distance between the actual sample rotation position and the theoretical position of the Bragg peak. A sample rotation stage is therefore an essential instrumental precondition for controlling and varying the contrast conditions. | 3 | Analytical Chemistry |
N-Linked glycosylation involves oligosaccharide attachment to asparagine via a beta linkage to the amine nitrogen of the side chain. The process of N-linked glycosylation occurs cotranslationally, or concurrently while the proteins are being translated. Since it is added cotranslationally, it is believed that N-linked glycosylation helps determine the folding of polypeptides due to the hydrophilic nature of sugars. All N-linked oligosaccharides are pentasaccharides: five monosaccharides long.
In N-glycosylation for eukaryotes, the oligosaccharide substrate is assembled right at the membrane of the endoplasmatic reticulum. For prokaryotes, this process occurs at the plasma membrane. In both cases, the acceptor substrate is an asparagine residue. The asparagine residue linked to an N-linked oligosaccharide usually occurs in the sequence Asn-X-Ser/Thr, where X can be any amino acid except for proline, although it is rare to see Asp, Glu, Leu, or Trp in this position. | 0 | Organic Chemistry |
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