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Topography is "classically" applied to inorganic crystals, such a metals and semiconductors. However, it is nowadays applied more and more often also to organic crystals, most notably proteins. Topographic investigations can help to understand and optimize crystal growth processes also for proteins. Numerous studies have been initiated in the last 5–10 years, using both white-beam and plane-wave topography.
Although considerable progress has been achieved, topography on protein crystals remains a difficult discipline: Due to large unit cells, small structure factors and high disorder, diffracted intensities are weak. Topographic imaging therefore requires long exposure times, which may lead to radiation damage of the crystals, generating in the first place the defects which are then imaged. In addition, the low structure factors lead to small Darwin widths and thus to broad dislocation images, i.e. rather low spatial resolution.
Nevertheless, in some cases, protein crystals were reported to be perfect enough to achieve images of single dislocations.
Literature: | 3 | Analytical Chemistry |
The Kovats index applies to organic compounds. The method interpolates peaks between bracketing n-alkanes. The Kovats index of n-alkanes is 100 times their carbon number, e.g. the Kovats index of n-butane is 400. The Kovats index is dimensionless, unlike retention time or retention volume. For isothermal gas chromatography, the Kovats index is given by the equation:
where the variables used are:
* , the Kováts retention index of peak i
* , the carbon number of n-alkane peak heading peak i
* , the retention time of compound i, minutes
* , the air peak, void time in average velocity , minutes
The Kovats index also applies to packed columns with an equivalent equation: | 3 | Analytical Chemistry |
Many metal sulfides are so insoluble in water that they are probably not very toxic. Some metal sulfides, when exposed to a strong mineral acid, including gastric acids, will release toxic hydrogen sulfide.
Organic sulfides are highly flammable. When a sulfide burns it produces sulfur dioxide (SO) gas.
Hydrogen sulfide, some of its salts, and almost all organic sulfides have a strong and putrid stench; rotting biomass releases these. | 0 | Organic Chemistry |
In organic chemistry, anilides (or phenylamides) are a class of organic compounds with the general structure . They are amide derivatives of aniline (). | 0 | Organic Chemistry |
Roasting is a process of oxidizing zinc sulfide concentrates at high temperatures into an impure zinc oxide, called "Zinc Calcine". The chemical reactions that take place are as follows:
Approximately 90% of zinc in concentrates are oxidized to zinc oxide. However, at the roasting temperatures around 10% of the zinc reacts with the iron impurities of the zinc sulfide concentrates to form zinc ferrite. A byproduct of roasting is sulfur dioxide, which is further processed into sulfuric acid, a commodity. The linked refinery flow sheet shows a schematic of Noranda's eastern Canadian zinc roasting operation
The process of roasting varies based on the type of roaster used. There are three types of roasters: multiple-hearth, suspension, and fluidized-bed. | 8 | Metallurgy |
A hydrogel is a network of polymer chains that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. A three-dimensional solid results from the hydrophilic polymer chains being held together by cross-links. Because of the inherent cross-links, the structural integrity of the hydrogel network does not dissolve from the high concentration of water. Hydrogels are highly absorbent (they can contain over 90% water) natural or synthetic polymeric networks.
Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their significant water content. As responsive "smart materials," hydrogels can encapsulate chemical systems which upon stimulation by external factors such as a change of pH may cause specific compounds such as glucose to be liberated to the environment, in most cases by a gel-sol transition to the liquid state. Chemomechanical polymers are mostly also hydrogels, which upon stimulation change their volume and can serve as actuators or sensors. The first appearance of the term hydrogel in the literature was in 1894. | 7 | Physical Chemistry |
The term (kryptoracemate) was coined by Ivan Bernal who employed this term during a meeting of the American Crystallographic Association in 1995.
The name is made of (from Ancient Greek: κρυπτός, "the hidden one") and racemic. It comes from the fact that the racemic composition is "hidden" in a Sohncke space group (usually enantiomerically pure). | 4 | Stereochemistry |
Liquids are often used in cooking due to their excellent heat-transfer capabilities. In addition to thermal conduction, liquids transmit energy by convection. In particular, because warmer fluids expand and rise while cooler areas contract and sink, liquids with low kinematic viscosity tend to transfer heat through convection at a fairly constant temperature, making a liquid suitable for blanching, boiling, or frying. Even higher rates of heat transfer can be achieved by condensing a gas into a liquid. At the liquid's boiling point, all of the heat energy is used to cause the phase change from a liquid to a gas, without an accompanying increase in temperature, and is stored as chemical potential energy. When the gas condenses back into a liquid this excess heat-energy is released at a constant temperature. This phenomenon is used in processes such as steaming. | 7 | Physical Chemistry |
Most materials shrink as they solidify, but, as the adjacent table shows, a few materials do not, such as gray cast iron. For the materials that do shrink upon solidification the type of shrinkage depends on how wide the freezing range is for the material. For materials with a narrow freezing range, less than , a cavity, known as a pipe, forms in the center of the casting, because the outer shell freezes first and progressively solidifies to the center. Pure and eutectic metals usually have narrow solidification ranges. These materials tend to form a skin in open air molds, therefore they are known as skin forming alloys. For materials with a wide freezing range, greater than , much more of the casting occupies the mushy or slushy zone (the temperature range between the solidus and the liquidus), which leads to small pockets of liquid trapped throughout and ultimately porosity. These castings tend to have poor ductility, toughness, and fatigue resistance. Moreover, for these types of materials to be fluid-tight, a secondary operation is required to impregnate the casting with a lower melting point metal or resin.
For the materials that have narrow solidification ranges, pipes can be overcome by designing the casting to promote directional solidification, which means the casting freezes first at the point farthest from the gate, then progressively solidifies toward the gate. This allows a continuous feed of liquid material to be present at the point of solidification to compensate for the shrinkage. Note that there is still a shrinkage void where the final material solidifies, but if designed properly, this will be in the gating system or riser. | 8 | Metallurgy |
For most chain-growth polymerizations, the propagation steps are much faster than the initiation steps, so that each growing chain is formed in a short time compared to the overall polymerization reaction. During the formation of a single chain, the reactant concentrations and therefore the propagation rate remain effectively constant. Under these conditions, the ratio of the number of propagation steps to the number of initiation steps is just the ratio of reaction rates:
where is the rate of propagation, is the rate of initiation of polymerization, and is the rate of termination of the polymer chain. The second form of the equation is valid at steady-state polymerization, as the chains are being initiated at the same rate they are being terminated ().
An exception is the class of living polymerizations, in which propagation is much slower than initiation, and chain termination does not occur until a quenching agent is added. In such reactions the reactant monomer is slowly consumed and the propagation rate varies and is not used to obtain the kinetic chain length. Instead the length at a given time is usually written as:
where represents the number of monomer units consumed, and the number of radicals that initiate polymerization. When the reaction goes to completion, , and then the kinetic chain length is equal to the number average degree of polymerization of the polymer.
In both cases kinetic chain length is an average quantity, as not all polymer chains in a given reaction are identical in length. The value of ν depends on the nature and concentration of both the monomer and initiator involved. | 7 | Physical Chemistry |
A simple case of diffusion with time in one dimension (taken as the -axis) from a boundary located at position , where the concentration is maintained at a value is
where is the complementary error function. This is the case when corrosive gases diffuse through the oxidative layer towards the metal surface (if we assume that concentration of gases in the environment is constant and the diffusion space – that is, the corrosion product layer – is semi-infinite, starting at 0 at the surface and spreading infinitely deep in the material). If, in its turn, the diffusion space is infinite (lasting both through the layer with , and that with , ), then the solution is amended only with coefficient in front of (as the diffusion now occurs in both directions). This case is valid when some solution with concentration is put in contact with a layer of pure solvent. (Bokstein, 2005) The length is called the diffusion length and provides a measure of how far the concentration has propagated in the -direction by diffusion in time (Bird, 1976).
As a quick approximation of the error function, the first two terms of the Taylor series can be used:
If is time-dependent, the diffusion length becomes
This idea is useful for estimating a diffusion length over a heating and cooling cycle, where varies with temperature. | 7 | Physical Chemistry |
Organometallic compounds containing mercury (e.g., thiomersal) and arsenic (e.g. Salvarsan) had a long history of use in medicine as nonselective antimicrobials before the advent of modern antibiotics.
Titanocene dichloride displays anti-cancer activity, and [[dichloridobis((p-methoxybenzyl)cyclopentadienyl)titanium|dichloridobis[(p-methoxybenzyl)cyclopentadienyl]titanium]] is a current anticancer drug candidate. Arene- and cyclopentadienyl complexes are kinetically inert platforms for the design of new radiopharmaceuticals.
Furthermore, there have been made studies utilizing exogenous semi-synthetic ligands; specifically to the dopamine transporter, observing increased resultant efficacy in regard to reward facilitating behavior (incentive salience) and habituation, namely with the phenyltropane compound [[List of phenyltropanes#η6-3β-(transition metal complexed phenyl)tropanes|[η-(2β-carbomethoxy-3β-phenyl)tropane]tricarbonylchromium]].
Carbon monoxide releasing organometallic compounds are also actively investigated, due to the importance of carbon monoxide as a gasotransmitter. | 0 | Organic Chemistry |
* Electrochemical Society Monograph Series
ECS Monographs provide accounts on specific topics in electrochemistry and solid-state science and technology. Since the 1940s, ECS and publishers have cooperated to publish titles in these fields. | 7 | Physical Chemistry |
Mollapour is widely recognized for his research on post-translation regulation of the molecular chaperone Heat shock protein-90 (Hsp90) and co-chaperones in cancer. His work demonstrated how reversible biochemical reactions can become directional and ordered, and in general, how a house-keeping machine (Hsp90) can be modulated through signaling inputs. Mollapour’s finding on post-translational modifications of the Hsp90 chaperone machinery has also explained the reasons for tumors sensitivity and selectivity towards the Hsp90 inhibitors. | 1 | Biochemistry |
In prokaryotes and eukaryotes, GGT consists of two polypeptide chains, a heavy and a light subunit, processed from a single chain precursor by an autocatalytic cleavage. The active site of GGT is known to be located in the light subunit.
Co-translational N-glycosylation serves a significant role in the proper autocatalytic cleavage and proper folding of GGT. Single site mutations at asparagine residues were shown to result in a functionally active yet slightly less thermally stable version of the enzyme in vitro, while knockout of all asparagine residues resulted in an accumulation of the uncleaved, propeptide form of the enzyme. | 1 | Biochemistry |
Hydroperoxides are mildly acidic. The range is indicated by 11.5 for Methyl hydroperoxide| to 13.1 for .
Hydroperoxides can be reduced to alcohols with lithium aluminium hydride, as described in this idealized equation:
This reaction is the basis of methods for analysis of organic peroxides. Another way to evaluate the content of peracids and peroxides is the volumetric titration with alkoxides such as sodium ethoxide.
The phosphite esters and tertiary phosphines also effect reduction: | 0 | Organic Chemistry |
Scintillators are used by the American government as Homeland Security radiation detectors. Scintillators can also be used in particle detectors, new energy resource exploration, X-ray security, nuclear cameras, computed tomography and gas exploration. Other applications of scintillators include CT scanners and gamma cameras in medical diagnostics, and screens in older style CRT computer monitors and television sets. Scintillators have also been proposed as part of theoretical models for the harnessing of gamma-ray energy through the photovoltaic effect, for example in a nuclear battery.
The use of a scintillator in conjunction with a photomultiplier tube finds wide use in hand-held survey meters used for detecting and measuring radioactive contamination and monitoring nuclear material. Scintillators generate light in fluorescent tubes, to convert the ultra-violet of the discharge into visible light. Scintillation detectors are also used in the petroleum industry as detectors for Gamma Ray logs. | 5 | Photochemistry |
The V. M. Goldschmidt Award is an award given by the Geochemical Society at the V. M. Goldschmidt Conference for achievements in the fields of geochemistry and cosmochemistry. The award in honor of Victor Moritz Goldschmidt, a pioneer in both those fields. | 9 | Geochemistry |
Although seagrass makes up only 0.1% of the area of the ocean floor, it accounts for approximately 10–18% of the total oceanic carbon burial. Currently global seagrass meadows are estimated to store as much as 19.9 Pg (gigaton, or billion tons) of organic carbon. There has been considerable attention to how large-scale seaweed cultivation in the open ocean can act as a form of carbon sequestration. Studies have demonstrated that nearshore seaweed forests constitute a source of blue carbon, as seaweed detritus is carried by wave currents into the middle and deep ocean thereby sequestering carbon.
Carbon primarily accumulates in marine sediments, which are anoxic and thus continually preserve organic carbon from decadal-millennial time scales. High accumulation rates, low oxygen, low sediment conductivity and slower microbial decomposition rates all encourage carbon burial and carbon accumulation in these coastal sediments.
Compared to terrestrial habitats that lose carbon stocks as CO during decomposition or by disturbances like fires or deforestation, marine carbon sinks can retain C for much longer time periods. Carbon sequestration rates in seagrass meadows vary depending on the species, characteristics of the sediment, and depth of the habitats, but on average the carbon burial rate is approximately 138 g C m yr.
Seagrass habitats are threatened by coastal eutrophication, increased seawater temperatures, increased sedimentation and coastal development, and sea level rise which may decrease light availability for photosynthesis. Seagrass loss has accelerated over the past few decades, from 0.9% per year prior to 1940 to 7% per year in 1990, with about 1/3 of global loss since WWII. The decline in seagrasses is due to a number of factors including drought, water quality issues, agricultural practices, invasive species, pathogens, fishing and climate change.
Scientists encourage the protection and continued research of these ecosystems for organic carbon storage, valuable habitat and other ecosystem services.
Restored seagrass meadows were found to start sequestering carbon in sediment within about four years. This was the time needed for the meadow to reach sufficient shoot density to cause sediment deposition. | 9 | Geochemistry |
The scope of organometallic reagents that may be aminated by electrophilic methods is large. Alkyl Grignard reagents, alkylithium compounds, alkylzinc compounds, and alkylcuprates have been aminated with electrophilic reagents successfully. Among sp-centered carbanions, vinyllithium compounds, vinylcuprates, and vinyl Grignard reagents react with electrophilic aminating reagents to afford enamines.
Aryl and heteroaryl organolithium reagents undergo efficient electrophilic amination under copper (I) catalyzed condition mediated by recoverable silicon reagents, termed siloxane transfer agents.
The scope of sp-centered carbanions is limited to alkynylcuprates. Enolates and silyl enol ethers, the most widely used class of carbon nucleophiles in electrophilic amination reactions, participate in amination, adization and hydrazination reactions.
The primary application of alkylmetal reagents in electrophilic amination reactions is the synthesis of hindered amines, many of which are difficult to prepare through nucleophilic displacement with an alkyl halide (nucleophilic amination). For instance, in the presence of a copper(II) catalyst, bulky organozinc reagents react with O-acylhydroxylamines to afford hindered amines.
Allylic metal species can be used to prepare allylic amines through electrophilic amination. Although allylic amines are usually prepared through nucleophilic amination of allylic halides, a few examples of electrophlic amination of allylic substrates are known. In the example below, an allylic zirconium reagent (obtained by hydrozirconation) is trapped with an O-alkylhydroxylamine.
The electrophilic amination of enolates yields α-amino carbonyl compounds. When chiral oxazolidinones are used in conjunction with azo compounds, enantioselectivity is observed (see above). BINAP can also be used for this purpose in the amination of silyl enol ethers.
Aryl and heteroaryl organometallic reagents undergo many of the same transformations as their aliphatic counterparts. Formation of amines, hydrazines, and azides is possible through the use of various electrophilic aminating reagents. An example employing a nitrenoid reagent is shown below.
Intramolecular amination is possible, and has been used to prepare small and medium rings. In the example below, deprotonation of an activated methylene compound containing an O-phosphinoylhydroxylamine led to the cyclic amine shown. | 0 | Organic Chemistry |
Agricola addresses the book to prominent German aristocrats, the most important of whom were Maurice, Elector of Saxony and his brother Augustus, who were his main patrons. He then describes the works of ancient and contemporary writers on mining and metallurgy, the chief ancient source being Pliny the Elder. Agricola describes several books contemporary to him, the chief being a booklet by Calbus of Freiberg in German. The works of alchemists are then described. Agricola does not reject the idea of alchemy, but notes that alchemical writings are obscure and that we do not read of any of the masters who became rich. He then describes fraudulent alchemists, who deserve the death penalty. Agricola completes his introduction by explaining that, since no other author has described the art of metals completely, he has written this work, setting forth his scheme for twelve books. Finally, he again directly addresses his audience of German princes, explaining the wealth that can be gained from this art. | 8 | Metallurgy |
Taq polymerase lacks a 3′ to 5′ exonuclease activity. Thus, Taq has no error-proof-reading activity, which consists of excision of any newly misincorporated nucleotide base from the nascent (i.e., extending) DNA strand that does not match with its opposite base in the complementary DNA strand. The lack in 3′ to 5′ proofreading of the Taq enzyme results in a high error rate (mutations per nucleotide per cycle) of approximately 1 in bases, which affects the fidelity of the PCR, especially if errors occur early in the PCR with low amounts of starting material, causing accumulation of a large proportion of amplified DNA with incorrect sequence in the final product.
Several "high-fidelity" DNA polymerases, having engineered 3′ to 5′ exonuclease activity, have become available that permit more accurate amplification for use in PCRs for sequencing or cloning of products. Examples of polymerases with 3′ to 5′ exonuclease activity include: KOD DNA polymerase, a recombinant form of Thermococcus kodakaraensis KOD1; Vent, which is extracted from Thermococcus litoralis; Pfu DNA polymerase, which is extracted from Pyrococcus furiosus; Pwo, which is extracted from Pyrococcus woesii; Q5 polymerase, with 280x higher fidelity amplification compared with Taq. | 1 | Biochemistry |
The following polyhedra are closo polyhedra, and are the basis for the 4n rules; each of these have triangular faces. The number of vertices in the cluster determines what polyhedron the structure is based on.
Using the electron count, the predicted structure can be found. n is the number of vertices in the cluster. The 4n rules are enumerated in the following table.
When counting electrons for each cluster, the number of valence electrons is enumerated. For each transition metal present, 10 electrons are subtracted from the total electron count. For example, in Rh(CO) the total number of electrons would be = = 26. Therefore, the cluster is a closo polyhedron because , with .
Other rules may be considered when predicting the structure of clusters:
# For clusters consisting mostly of transition metals, any main group elements present are often best counted as ligands or interstitial atoms, rather than vertices.
# Larger and more electropositive atoms tend to occupy vertices of high connectivity and smaller more electronegative atoms tend to occupy vertices of low connectivity.
# In the special case of boron hydride clusters, each boron atom connected to 3 or more vertices has one terminal hydride, while a boron atom connected to two other vertices has two terminal hydrogen atoms. If more hydrogen atoms are present, they are placed in open face positions to even out the coordination number of the vertices.
# For the special case of transition metal clusters, ligands are added to the metal centers to give the metals reasonable coordination numbers, and if any hydrogen atoms are present they are placed in bridging positions to even out the coordination numbers of the vertices.
In general, closo structures with n vertices are n-vertex polyhedra.
To predict the structure of a nido cluster, the closo cluster with n + 1 vertices is used as a starting point; if the cluster is composed of small atoms a high connectivity vertex is removed, while if the cluster is composed of large atoms a low connectivity vertex is removed.
To predict the structure of an arachno cluster, the closo polyhedron with n + 2 vertices is used as the starting point, and the n + 1 vertex nido complex is generated by following the rule above; a second vertex adjacent to the first is removed if the cluster is composed of mostly small atoms, a second vertex not adjacent to the first is removed if the cluster is composed mostly of large atoms.
Example:
:Electron count: 10 × Pb + 2 (for the negative charge) = 10 × 4 + 2 = 42 electrons.
:Since n = 10, 4n + 2 = 42, so the cluster is a closo bicapped square antiprism.
Example:
:Electron count: 4 × S – 2 (for the positive charge) = 4 × 6 – 2 = 22 electrons.
:Since n = 4, 4n + 6 = 22, so the cluster is arachno.
:Starting from an octahedron, a vertex of high connectivity is removed, and then a non-adjacent vertex is removed.
Example: Os(CO)
:Electron count: 6 × Os + 18 × CO – 60 (for 6 osmium atoms) = 6 × 8 + 18 × 2 – 60 = 24
:Since n = 6, 4n = 24, so the cluster is capped closo.
:Starting from a trigonal bipyramid, a face is capped. The carbonyls have been omitted for clarity.
Example:
:Electron count: 5 × B + 5 × H + 4 (for the negative charge) = 5 × 3 + 5 × 1 + 4 = 24
:Since n = 5, 4n + 4 = 24, so the cluster is nido.
:Starting from an octahedron, one of the vertices is removed.
The rules are useful in also predicting the structure of carboranes.
Example: CBH
:Electron count = 2 × C + 7 × B + 13 × H = 2 × 4 + 7 × 3 + 13 × 1 = 42
:Since n in this case is 9, 4n + 6 = 42, the cluster is arachno.
The bookkeeping for deltahedral clusters is sometimes carried out by counting skeletal electrons instead of the total number of electrons. The skeletal orbital (electron pair) and skeletal electron counts for the four types of deltahedral clusters are:
*n-vertex closo: n + 1 skeletal orbitals, 2n + 2 skeletal electrons
*n-vertex nido: n + 2 skeletal orbitals, 2n + 4 skeletal electrons
*n-vertex arachno: n + 3 skeletal orbitals, 2n + 6 skeletal electrons
*n-vertex hypho: n + 4 skeletal orbitals, 2n + 8 skeletal electrons
The skeletal electron counts are determined by summing the total of the following number of electrons:
*2 from each BH unit
*3 from each CH unit
*1 from each additional hydrogen atom (over and above the ones on the BH and CH units)
*the anionic charge electrons | 7 | Physical Chemistry |
Ractopamine () is an animal feed additive used to promote leanness and increase food conversion efficiency in farmed animals in several countries, but banned in others. Pharmacologically, it is a phenol-based TAAR1 agonist and β adrenoreceptor agonist that stimulates β and β adrenergic receptors.
It is most commonly administered to animals for meat production as ractopamine hydrochloride. It is the active ingredient in products marketed in the US as Paylean for swine, Optaflexx for cattle, and Topmax for turkeys. It was developed by Elanco Animal Health, a division of Eli Lilly and Company.
As of 2014, the use of ractopamine was banned in 160 countries, including the European Union, China and Russia, while 27 other countries, such as Japan, the United States, South Korea, and New Zealand have deemed meat from livestock fed ractopamine safe for human consumption.
Commercial ractopamine is a mixture of all four possible stereoisomers. It is also a positional isomer of dobutamine, a related drug. | 4 | Stereochemistry |
When multiple assays measure the same target their results and utility may or may not be comparable depending on the natures of the assay and their methodology, reliability etc. Such comparisons are possible through study of general quality attributes of the assays e.g. principles of measurement (including identification, amplification and detection), dynamic range of detection (usually the range of linearity of the standard curve), analytic sensitivity, functional sensitivity, analytic specificity, positive, negative predictive values, turn around time i.e. time taken to finish a whole cycle from the preanalytic steps till the end of the last post analytic step (report dispatch/transmission), throughput i.e. number of assays done per unit time (usually expressed as per hour) etc. Organizations or laboratories that perform Assays for professional purposes e.g. medical diagnosis and prognostics, environmental analysis, forensic proceeding, pharmaceutical research and development must undergo well regulated quality assurance procedures including method validation, regular calibration, analytical quality control, proficiency testing, test accreditation, test licensing and must document appropriate certifications from the relevant regulating bodies in order to establish the reliability of their assays, especially to remain legally acceptable and accountable for the quality of the assay results and also to convince customers to use their assay commercially/professionally. | 1 | Biochemistry |
iC3b is a protein fragment that is part of the complement system, a component of the vertebrate immune system. iC3b is produced when complement factor I cleaves C3b. Complement receptors on white blood cells are able to bind iC3b, so iC3b functions as an opsonin. Unlike intact C3b, iC3b cannot associate with factor B, thus preventing amplification of the complement cascade through the alternative pathway. Complement factor I can further cleave iC3b into a protein fragment known as C3d. | 1 | Biochemistry |
* For a polymer to exhibit the thermally induced shape-memory effect, it must have anchor points for temporary and permanent shape. These can be physical (chain entanglements, crystals) or chemical (chemical crosslinking, curing, vulcanization).
* This effect in polymers depends on entropic forces and not on martensitic transitions like metals.
* The most important physical properties are: elastic modulus, recovery speed, temporary shape stability.
* The transition temperature T can be Tm or Tg or a mixture of both.
* All crystalline polymers (except for PP) can exhibit thermally induced shape-memory effect.
* Inelastic mechanisms that decrease the effect are: moisture degradation (for moisture sensitive polymers e.g. polyurethanes), unraveling of the chains, degradation of the bonds that fix the permanent or temporary shape. | 7 | Physical Chemistry |
AMPP offers individual training and certification programs. Many are merged programs that originated as competing programs under the former NACE and SSPC organizations. Other programs are still being administered under the legacy NACE or SSPC frameworks until the merger is complete. | 8 | Metallurgy |
All peroxisomal proteins are synthesized in the cytoplasm and must be directed to the peroxisome. The first step in this process is the binding of the protein to a receptor. The receptor then directs the complex to the peroxisome. Receptors recognize and bind to a region of the peroxisomal protein called a peroxisomal targeting signal, or PTS.
Peroxisomes consist of a matrix surrounded by a specific membrane. Most peroxisomal matrix proteins contain a short sequence, usually three amino acids at the extreme carboxy tail of the protein, that serves as the PTS. The prototypic sequence (many variations exist) is serine-lysine-leucine (-SKL in the one-letter amino acid code). This motif, and its variations, is known as the PTS1, and the receptor is termed the PTS1 receptor.
It was found that the PTS1 receptor is encoded by the PEX5 gene. PEX5 imports folded proteins into the peroxisome, shuttling between the peroxisome and cytosol. PEX5 interacts with a large number of other proteins, including Pex8p, 10p, 12p, 13p, 14p.
A few peroxisomal matrix proteins have a different, and less conserved sequence, at their amino termini. This PTS2 signal is recognized by the PTS2 receptor, encoded by the PEX7 gene.
"PEX" refers to a group of genes that were identified as being important for peroxisomal synthesis. The numerical attributions, such as PEX5, generally refer to the order in which they were first discovered.
A distinct motif is used for proteins destined for the peroxisomal membrane called the "mPTS" motif, which is more poorly defined and may consist of discontinuous subdomains. One of these usually is a cluster of basic amino acids (arginines and lysines) within a loop of protein (i.e., between membrane spans) that will face the matrix. The mPTS receptor is the product of PEX19. | 1 | Biochemistry |
Cast iron has been found in China dating to the 5th century BC, but the earliest extant blast furnaces in China date to the 1st century AD and in the West from the High Middle Ages. They spread from the region around Namur in Wallonia (Belgium) in the late 15th century, being introduced to England in 1491. The fuel used in these was invariably charcoal. The successful substitution of coke for charcoal is widely attributed to English inventor Abraham Darby in 1709. The efficiency of the process was further enhanced by the practice of preheating the combustion air (hot blast), patented by Scottish inventor James Beaumont Neilson in 1828. | 8 | Metallurgy |
Three-letter abbreviations are used to describe phenotypes in bacteria including E. coli.
Examples include:
* Lac (the ability to use lactose),
* His (the ability to synthesize the amino acid histidine)
* Mot (swimming motility)
* Sm (resistance to the antibiotic streptomycin)
In the case of Lac, wild type cells are Lac and are able to use lactose as a carbon and energy source, while Lac mutant derivatives cannot use lactose. The same three letters are typically used (lower-case, italicized) to label the genes involved in a particular phenotype, where each different gene is additionally distinguished by an extra letter. The lac genes encoding enzymes are lacZ, lacY, and lacA. The fourth lac gene is lacI, encoding the lactose repressor—"I" stands for inducibility.
One may distinguish between structural genes encoding enzymes, and regulatory genes encoding proteins that affect gene expression. Current usage expands the phenotypic nomenclature to apply to proteins: thus, LacZ is the protein product of the lacZ gene, β-galactosidase. Various short sequences that are not genes also affect gene expression, including the lac promoter, lac p, and the lac operator, lac o. Although it is not strictly standard usage, mutations affecting lac o are referred to as lac o, for historical reasons. | 1 | Biochemistry |
There are about 20,000 known lichen species. But what is meant by "species" is different from what is meant by biological species in plants, animals, or fungi, where being the same species implies that there is a common ancestral lineage. Because lichens are combinations of members of two or even three different biological kingdoms, these components must have a different ancestral lineage from each other. By convention, lichens are still called "species" anyway, and are classified according to the species of their fungus, not the species of the algae or cyanobacteria. Lichens are given the same scientific name (binomial name) as the fungus in them, which may cause some confusion. The alga bears its own scientific name, which has no relationship to the name of the lichen or fungus.
Depending on context, "lichenized fungus" may refer to the entire lichen, or to the fungus when it is in the lichen, which can be grown in culture in isolation from the algae or cyanobacteria. Some algae and cyanobacteria are found naturally living outside of the lichen. The fungal, algal, or cyanobacterial component of a lichen can be grown by itself in culture. When growing by themselves, the fungus, algae, or cyanobacteria have very different properties than those of the lichen. Lichen properties such as growth form, physiology, and biochemistry, are very different from the combination of the properties of the fungus and the algae or cyanobacteria.
The same fungus growing in combination with different algae or cyanobacteria, can produce lichens that are very different in most properties, meeting non-DNA criteria for being different "species". Historically, these different combinations were classified as different species. When the fungus is identified as being the same using modern DNA methods, these apparently different species get reclassified as the same species under the current (2014) convention for classification by fungal component. This has led to debate about this classification convention. These apparently different "species" have their own independent evolutionary history.
There is also debate as to the appropriateness of giving the same binomial name to the fungus, and to the lichen that combines that fungus with an alga or cyanobacterium (synecdoche). This is especially the case when combining the same fungus with different algae or cyanobacteria produces dramatically different lichen organisms, which would be considered different species by any measure other than the DNA of the fungal component. If the whole lichen produced by the same fungus growing in association with different algae or cyanobacteria, were to be classified as different "species", the number of "lichen species" would be greater. | 2 | Environmental Chemistry |
A chemolithotroph is able to use inorganic reduced compounds in its energy-producing reactions. This process involves the oxidation of inorganic compounds coupled to ATP synthesis. The majority of chemolithotrophs are chemolithoautotrophs, able to fix carbon dioxide (CO) through the Calvin cycle, a metabolic pathway in which CO is converted to glucose. This group of organisms includes sulfur oxidizers, nitrifying bacteria, iron oxidizers, and hydrogen oxidizers.
The term "chemolithotrophy" refers to a cell's acquisition of energy from the oxidation of inorganic compounds, also known as electron donors. This form of metabolism is believed to occur only in prokaryotes and was first characterized by Ukrainian microbiologist Sergei Winogradsky. | 1 | Biochemistry |
Quoted values sunlight-to-biomass efficiency
The following is a breakdown of the energetics of the photosynthesis process from Photosynthesis by Hall and Rao:
Starting with the solar spectrum falling on a leaf,
* 47% lost due to photons outside the 400–700 nm active range (chlorophyll uses photons between 400 and 700 nm, extracting the energy of one 700 nm photon from each one)
* 30% of the in-band photons are lost due to incomplete absorption or photons hitting components other than chloroplasts
* 24% of the absorbed photon energy is lost due to degrading short wavelength photons to the 700 nm energy level
* 68% of the used energy is lost in conversion into d-glucose
* 35–45% of the glucose is consumed by the leaf in the processes of dark and photo respiration
Stated another way:
* 100% sunlight → non-bioavailable photons waste is 47%, leaving
* 53% (in the 400–700 nm range) → 30% of photons are lost due to incomplete absorption, leaving
* 37% (absorbed photon energy) → 24% is lost due to wavelength-mismatch degradation to 700 nm energy, leaving
* 28.2% (sunlight energy collected by chlorophyll) → 68% is lost in conversion of ATP and NADPH to d-glucose, leaving
* 9% (collected as sugar) → 35–40% of sugar is recycled/consumed by the leaf in dark and photo-respiration, leaving
* 5.4% net leaf efficiency.
Many plants lose much of the remaining energy on growing roots. Most crop plants store ~0.25% to 0.5% of the sunlight in the product (corn kernels, potato starch, etc.).
Photosynthesis increases linearly with light intensity at low intensity, but at higher intensity this is no longer the case (see Photosynthesis-irradiance curve). Above about 10,000 lux or ~100 watts/square meter the rate no longer increases. Thus, most plants can only use ~10% of full mid-day sunlight intensity. This dramatically reduces average achieved photosynthetic efficiency in fields compared to peak laboratory results. However, real plants (as opposed to laboratory test samples) have many redundant, randomly oriented leaves. This helps to keep the average illumination of each leaf well below the mid-day peak enabling the plant to achieve a result closer to the expected laboratory test results using limited illumination.
Only if the light intensity is above a plant specific value, called the compensation point the plant assimilates more carbon and releases more oxygen by photosynthesis than it consumes by cellular respiration for its own current energy demand.<br>
Photosynthesis measurement systems are not designed to directly measure the amount of light absorbed by the leaf. Nevertheless, the light response curves that the class produces do allow comparisons in photosynthetic efficiency between plants. | 5 | Photochemistry |
Early diffusion models postulated that atomic motion in substitutional alloys occurs via a direct exchange mechanism, in which atoms migrate by switching positions with atoms on adjacent lattice sites. Such a mechanism implies that the atomic fluxes of two different materials across an interface must be equal, as each atom moving across the interface causes another atom to move across in the other direction.
Another possible diffusion mechanism involves lattice vacancies. An atom can move into a vacant lattice site, effectively causing the atom and the vacancy to switch places. If large-scale diffusion takes place in a material, there will be a flux of atoms in one direction and a flux of vacancies in the other.
The Kirkendall effect arises when two distinct materials are placed next to each other and diffusion is allowed to take place between them. In general, the diffusion coefficients of the two materials in each other are not the same. This is only possible if diffusion occurs by a vacancy mechanism; if the atoms instead diffused by an exchange mechanism, they would cross the interface in pairs, so the diffusion rates would be identical, contrary to observation. By Fick's 1st law of diffusion, the flux of atoms from the material with the higher diffusion coefficient will be larger, so there will be a net flux of atoms from the material with the higher diffusion coefficient into the material with the lower diffusion coefficient. To balance this flux of atoms, there will be a flux of vacancies in the opposite direction—from the material with the lower diffusion coefficient into the material with the higher diffusion coefficient—resulting in an overall translation of the lattice relative to the environment in the direction of the material with the lower diffusion constant.
Macroscopic evidence for the Kirkendall effect can be gathered by placing inert markers at the initial interface between the two materials, such as molybdenum markers at an interface between copper and brass. The diffusion coefficient of zinc is higher than the diffusion coefficient of copper in this case. Since zinc atoms leave the brass at a higher rate than copper atoms enter, the size of the brass region decreases as diffusion progresses. Relative to the molybdenum markers, the copper-brass interface moves toward the brass at an experimentally measurable rate. | 8 | Metallurgy |
The 5' UTRs of mouse L1s contain a variable number of GC-rich tandemly repeated monomers of around 200 bp, followed by a short non-monomeric region. Human 5’ UTRs are ~900 bp in length and do not contain repeated motifs. All families of human L1s harbor in their most 5’ extremity a binding motif for the transcription factor YY1. Younger families also have two binding sites for SOX-family transcription factors, and both YY1 and SOX sites were shown to be required for human L1 transcription initiation and activation. Both mouse and human 5’ UTRs also contain a weak antisense promoter of unknown function. | 1 | Biochemistry |
LaNi is a hexagonal intermetallic compound composed of rare earth element lanthanum and transition metal nickel. It presents a calcium pentacopper (CaCu) crystal structure. It is a melting compound with the same composition and has hydrogen storage capacity. | 8 | Metallurgy |
The variable region rearrangements happen in an orderly sequence in the bone marrow. Usually, the assortment of these gene segments occurs at B cell maturation. | 1 | Biochemistry |
Thermodynamic potentials for the reduction of CO to various products is given in the following table versus NHE at pH = 7. Single electron reduction of CO to CO radical occurs at E° = −1.90 V versus NHE at pH = 7 in an aqueous solution at 25 °C under 1 atm gas pressure. The reason behind the high negative thermodynamically unfavorable single electron reduction potential of CO is the large reorganization energy between the linear molecule and bent radical anion. Proton-coupled multi-electron steps for CO reductions are generally more favorable than single electron reductions, as thermodynamically more stable molecules are produced. | 5 | Photochemistry |
Only certain combinations of symmetry elements are possible in a space group. Translations are always present, and the space group P1 has only translations and the identity element. The presence of mirrors implies glide planes as well, and the presence of rotation axes implies screw axes as well, but the converses are not true. An inversion and a mirror implies two-fold screw axes, and so on. | 4 | Stereochemistry |
Racemic crystallography is a technique used in structural biology where crystals of a protein molecule are developed from an equimolar mixture of an L-protein molecule of natural chirality and its D-protein mirror image. L-protein molecules consist of left-handed L-amino acids and the achiral amino acid glycine, whereas the mirror image D-protein molecules consist of right-handed D-amino acids and glycine. Typically, both the L-protein and the D-protein are prepared by total chemical synthesis. | 3 | Analytical Chemistry |
An episome is a special type of plasmid, which remains as a part of the eukaryotic genome without integration. Episomes manage this by replicating together with the rest of the genome and subsequently associating with metaphase chromosomes during mitosis. Episomes do not degrade, unlike standard plasmids, and can be designed so that they are not epigenetically silenced inside the eukaryotic cell nucleus. Episomes can be observed in nature in certain types of long-term infection by adeno-associated virus or Epstein-Barr virus. In 2004, it was proposed that non-viral episomes might be used in genetic therapy for long-term change in gene expression.
As of 1999, there were many known sequences of DNA (deoxyribonucleic acid) that allow a standard plasmid to become episomally retained. One example is the S/MAR sequence.
The length of episomal retention is fairly variable between different genetic constructs and there are many known features in the sequence of an episome which will affect the length and stability of genetic expression of the carried transgene. Among these features is the number of CpG sites which contribute to epigenetic silencing of the transgene carried by the episome. | 1 | Biochemistry |
Dexmedetomidine is a highly selective α-adrenergic agonist. It possesses an α:α selectivity ratio of 1620:1, making it eight times more selective for the α-receptor than clonidine. Unlike opioids and other sedatives such as propofol, dexmedetomidine is able to achieve its effects without causing respiratory depression. Dexmedetomidine induces sedation by decreasing activity of noradrenergic neurons in the locus ceruleus in the brain stem, thereby increasing the downstream activity of inhibitory gamma-aminobutyric acid (GABA) neurons in the ventrolateral preoptic nucleus. In contrast, other sedatives like propofol and benzodiazepines directly increase activity of gamma-aminobutyric acid neurons. Through action on this endogenous sleep-promoting pathway the sedation produced by dexmedetomidine more closely mirrors natural sleep (specifically stage 2 non-rapid eye movement sleep), as demonstrated by EEG studies. As such, dexmedetomidine provides less amnesia than benzodiazepines. Dexmedetomidine also has analgesic effects at the spinal cord level and other supraspinal sites. | 4 | Stereochemistry |
Polanyis deliverance' (as he described it) from these rejections and criticism of his model occurred in 1930, when Fritz London proposed a new theory of cohesive forces founded on the theories of quantum mechanics on the polarization of electronic systems. Polanyi wrote to London asking,
After computational analysis, a joint publication was made between Polanyi and London claiming that the adsorptive forces behaved similarly to the model that Polanyi had proposed. | 7 | Physical Chemistry |
The combination of atoms into molecules leads to the creation of unique types of energetic states and therefore unique spectra of the transitions between these states. Molecular spectra can be obtained due to electron spin states (electron paramagnetic resonance), molecular rotations, molecular vibration, and electronic states. Rotations are collective motions of the atomic nuclei and typically lead to spectra in the microwave and millimeter-wave spectral regions. Rotational spectroscopy and microwave spectroscopy are synonymous. Vibrations are relative motions of the atomic nuclei and are studied by both infrared and Raman spectroscopy. Electronic excitations are studied using visible and ultraviolet spectroscopy as well as fluorescence spectroscopy.
Studies in molecular spectroscopy led to the development of the first maser and contributed to the subsequent development of the laser. | 7 | Physical Chemistry |
Stars known as white dwarfs have mass comparable to the Sun, but have about a hundredth of its radius. The high densities mean that the electrons are no longer bound to single nuclei and instead form a degenerate electron gas. The number density of electrons in a white dwarf is of the order of 10 electrons/m. This means their Fermi energy is: | 7 | Physical Chemistry |
Thermolysin is an enzyme produced by Bacillus thermoproteolyticus that catalyses the hydrolysis of peptides containing hydrophobic amino acids. Therefore, it is also a target for antibacterial agents. The enzymatic reaction mechanism starts form the small peptide molecule and replaces the zinc binding water molecule towards Glu143 of thermolysin. The water molecule is then activated by both the zinc ion and the Glu143 residue and attacks the carbonyl carbon to form a tetrahedral transition state (see figure). Holden and coworkers then mimicked that tetrahedral transition state to design a series of phosphonamidate peptide analogues. Among the synthesized analogues, R = -Leu possesses the most potent inhibitory activity (K = 9.1 nM). | 1 | Biochemistry |
Two major modifications of the biuret test are commonly applied in modern colorimetric analysis of peptides: the bicinchoninic acid (BCA) assay and the Lowry assay. In these tests, the Cu formed during the biuret reaction reacts further with other reagents, leading to a deeper color.
In the BCA test, Cu forms a deep purple complex with bicinchoninic acid (BCA), which absorbs around 562 nm, producing the signature mauve color. The water-soluble BCA/copper complex absorbs much more strongly than the peptide/copper complex, increasing the sensitivity of the biuret test by a factor of around 100: the BCA assay allows to detect proteins in the range of 0.0005 to 2 mg/mL). Additionally, the BCA protein assay gives the important benefit of compatibility with substances such as up to 5% surfactants in protein samples.
In the Lowry protein assay Cu is oxidized back to Cu by Mo in the Folin–Ciocalteu reagent, which forms molybdenum blue (Mo). Tyrosine residues in the protein also form molybdenum blue under these circumstances. In this way, proteins can be detected in concentrations between 0.005 and 2 mg/mL. Molybdenum blue in turn can bind certain organic dyes such as malachite green and Auramine O, resulting in further amplification of the signal. | 3 | Analytical Chemistry |
Magnetic particles loaded with vectors are concentrated on the target cells by the influence of an external magnetic field. The cells then take up genetic material naturally via endocytosis and pinocytosis. Consequently, membrane architecture and structure stays intact, in contrast to other physical transfection methods such as electroporation or gene guns that damage the cell membrane.
The nucleic acids are then released into the cytoplasm by different mechanisms depending upon the formulation used:
# the proton sponge effect caused by cationic polymers coated on the nanoparticles that promote endosome osmotic swelling, disruption of the endosome membrane and intracellular release of DNA form,
# the destabilization of endosome by cationic lipids coated on the particles that release the nucleic acid into cells by flip-flop of cell negative lipids and charge neutralization and
# the viral infection mechanism.
Magnetofection works with cells that are not dividing or slowly dividing, meaning that the genetic materials can go to the cell nucleus without cell division. | 1 | Biochemistry |
DNA editing proteins edit and permanently change gene sequence, and subsequently the gene expression of the cell. All progenies of the cell will inherit the edited gene sequence. DNA editing proteins often take part in the immune response system of both prokaryotes and eukaryotes, providing high variance in gene expression in adaptation to various pathogens.
Specific examples include:
* RAG1/RAG2
* TdT
* Cas1/Cas2 | 1 | Biochemistry |
Before 1830, few Americans used ice to refrigerate foods due to a lack of ice-storehouses and iceboxes. As these two things became more widely available, individuals used axes and saws to harvest ice for their storehouses. This method proved to be difficult, dangerous, and certainly did not resemble anything that could be duplicated on a commercial scale.
Despite the difficulties of harvesting ice, Frederic Tudor thought that he could capitalize on this new commodity by harvesting ice in New England and shipping it to the Caribbean islands as well as the southern states. In the beginning, Tudor lost thousands of dollars, but eventually turned a profit as he constructed icehouses in Charleston, Virginia and in the Cuban port town of Havana. These icehouses as well as better insulated ships helped reduce ice wastage from 66% to 8%. This efficiency gain influenced Tudor to expand his ice market to other towns with icehouses such as New Orleans and Savannah. This ice market further expanded as harvesting ice became faster and cheaper after one of Tudors suppliers, Nathaniel Wyeth, invented a horse-drawn ice cutter in 1825. This invention as well as Tudors success inspired others to get involved in the ice trade and the ice industry grew.
Ice became a mass-market commodity by the early 1830s with the price of ice dropping from six cents per pound to a half of a cent per pound. In New York City, ice consumption increased from 12,000 tons in 1843 to 100,000 tons in 1856. Boston's consumption leapt from 6,000 tons to 85,000 tons during that same period. Ice harvesting created a "cooling culture" as majority of people used ice and iceboxes to store their dairy products, fish, meat, and even fruits and vegetables. These early cold storage practices paved the way for many Americans to accept the refrigeration technology that would soon take over the country. | 7 | Physical Chemistry |
Perovskite materials exhibit many interesting and intriguing properties from both the theoretical and the application point of view. Colossal magnetoresistance, ferroelectricity, superconductivity, charge ordering, spin dependent transport, high thermopower and the interplay of structural, magnetic and transport properties are commonly observed features in this family. These compounds are used as sensors and catalyst electrodes in certain types of fuel cells and are candidates for memory devices and spintronics applications.
Many superconducting ceramic materials (the high temperature superconductors) have perovskite-like structures, often with 3 or more metals including copper, and some oxygen positions left vacant. One prime example is yttrium barium copper oxide which can be insulating or superconducting depending on the oxygen content.
Chemical engineers are considering a cobalt-based perovskite material as a replacement for platinum in catalytic converters for diesel vehicles. | 3 | Analytical Chemistry |
The ASTM D6866 method has been developed to certify the biologically derived content of bioplastics. Cosmic rays colliding with the atmosphere mean that some of the carbon is the radioactive isotope carbon-14. CO from the atmosphere is used by plants in photosynthesis, so new plant material will contain both carbon-14 and carbon-12. Under the right conditions, and over geological timescales, the remains of living organisms can be transformed into fossil fuels. After ~100,000 years all the carbon-14 present in the original organic material will have undergone radioactive decay leaving only carbon-12. A product made from biomass will have a relatively high level of carbon-14, while a product made from petrochemicals will have no carbon-14. The percentage of renewable carbon in a material (solid or liquid) can be measured with an accelerator mass spectrometer.
There is an important difference between biodegradability and biobased content. A bioplastic such as high-density polyethylene (HDPE) can be 100% biobased (i.e. contain 100% renewable carbon), yet be non-biodegradable. These bioplastics such as HDPE nonetheless play an important role in greenhouse gas abatement, particularly when they are combusted for energy production. The biobased component of these bioplastics is considered carbon-neutral since their origin is from biomass. | 7 | Physical Chemistry |
Shq1p is a protein involved in the rRNA processing pathway. It was discovered by Pok Yang in the Chanfreau laboratory at UCLA. Depletion of Shq1p has led to decreased level of various H/ACA box snoRNAs (H/ACA box snoRNAs are responsible for pseuduridylation of pre-rRNA) and certain pre-rRNA intermediates. | 1 | Biochemistry |
Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
Errors in compilations concerning equilibrium and/or data elaboration. Data not recommended. Strongly suggested to refer to the original papers. | 7 | Physical Chemistry |
Knock out of AK1 disrupts the synchrony between inorganic phosphate and turnover at ATP-consuming sites and ATP synthesis sites. This reduces the energetic signal communication in the post-ischemic heart and precipitates inadequate coronary reflow following ischemia-reperfusion. | 1 | Biochemistry |
The study of spinor condensates was initiated in 1998 by experimental groups at JILA
and MIT. These experiments utilised
Na and Rb atoms, respectively.
In contrast to most prior experiments on ultracold gases, these experiments utilised a purely
optical trap, which is spin-insensitive. Shortly thereafter, theoretical work appeared
which described the possible mean-field phases of spin-one spinor condensates. | 7 | Physical Chemistry |
It is possible to use this technique to study the overall degree of translation in cells (for examples), but it can be used much more specifically to study individual proteins and their mRNAs. As an example shown in the lower portion of the figure, a protein that composes part of the small subunit can first be detected in the 40S fraction, then nearly disappears from the 60S fraction (the separations on these gradients are not absolute), then reappears in the 80S and polysome fractions. This indicates that there is at most very little of the protein found in the cell that is not part of the small subunit. In contrast, in the upper row of the immunoblot figure, a soluble protein appears in the soluble fractions and associated with ribosomes and polysomes. The particular protein is a chaperone protein, which (in brief) helps to fold the nascent peptide as it is being extruded from the ribosome. As other work in the paper showed, there is a direct association of the chaperone with the ribosome.
The technique can also be used to study the degree of translation of a particular mRNA In these experiments, 5 and 3 sequences of an mRNA were investigated for their effects on amount of mRNA produced and how well the mRNAs were translated. As shown, not all mRNA isoforms are translated with the same efficiency even though their coding sequences are the same. | 1 | Biochemistry |
Protein–protein interaction networks are an important ingredient for the system-level understanding of cellular processes.
Such networks can be used for filtering and assessing functional genomics data and for providing an intuitive platform for annotating structural, functional and evolutionary properties of proteins.
Exploring the predicted interaction networks can suggest new directions for future experimental research and provide cross-species predictions for efficient interaction mapping. | 1 | Biochemistry |
In cattle and swine tissue, it was found in 2007 that a procedure for the analysis of ractopamine residues in liver or muscle can be performed by high performance liquid chromatography (HPLC) with fluorescence detection. The confirmatory method include reversed-phase HPLC/electrospray ionization triple tandem quadrupole mass spectrometry. The limit of quantification of the drug using this LC/MS instrument was shown to be 1 ng/g (1 ppb). In cattle, a 2018 Chinese study promoted the use of hair as an indelible test of feed containing ractopamine. | 4 | Stereochemistry |
Coating components are subject to particle-particle, particle-solvent, and particle-polymer interactions. Van der Waals forces, electrostatic repulsions, and steric stabilization are the reasons for these interactions. Importantly, the characteristics of adhesion and cohesion between the components form the base coating structure. Calcium carbonate and kaolin are commonly used pigments. Pigments support a structure of fine porosity and form a light scattering surface. The surface charge of the pigment plays an important role in dispersion consistency. The surface charge of calcium carbonate is negative and not dependent on pH, however it can decompose under acidic conditions. Kaolin has negatively charged faces while the charge of its laterals depend on pH, being positive in acidic conditions and negative in basic conditions with an isoelectric point at 7.5. The equation for determining the isoelectric point is as follows:
In the papermaking process, the pigment dispersions are generally kept at a pH above 8.0. | 7 | Physical Chemistry |
Particulate organic matter (POM) includes steadily decomposing plant litter and animal faeces, and the detritus from the activity of microorganisms. Most of it continually undergoes decomposition by microorganisms (when conditions are sufficiently moist) and usually has a turnover time of less than 10 years. Less active parts may take 15 to 100 years to turnover. Where it is still at the soil surface and relatively fresh, particulate organic matter intercepts the energy of raindrops and protects physical soil surfaces from damage. As it is decomposes, particulate organic matter provides much of the energy required by soil organisms as well as providing a steady release of nutrients into the soil environment.
The decomposition of POM provides energy and nutrients. Nutrients not taken up by soil organisms may be available for plant uptake. The amount of nutrients released (mineralized) during decomposition depends on the biological and chemical characteristics of the POM, such as the C:N ratio. In addition to nutrient release, decomposers colonizing POM play a role in improving soil structure. Fungal mycelium entangle soil particles and release sticky, cement-like, polysaccharides into the soil; ultimately forming soil aggregates
Soil POM content is affected by organic inputs and the activity of soil decomposers. The addition of organic materials, such as manure or crop residues, typically results in an increase in POM. Alternatively, repeated tillage or soil disturbance increases the rate of decomposition by exposing soil organisms to oxygen and organic substrates; ultimately, depleting POM. Reduction in POM content is observed when native grasslands are converted to agricultural land. Soil temperature and moisture also affect the rate of POM decomposition. Because POM is a readily available (labile) source of soil nutrients, is a contributor to soil structure, and is highly sensitive to soil management, it is frequently used as an indicator to measure soil quality. | 9 | Geochemistry |
* [http://www.maizegdb.org/cgi-bin/displaylocusrecord.cgi?id=12097 MaizeGDB]
* [https://www.ncbi.nlm.nih.gov/gene?cmd=search&term=542117 NCBI]
* [https://www.uniprot.org/uniprot/P42390 Uniprot] | 1 | Biochemistry |
This derivation
based on statistical mechanics was originally provided by Volmer and Mahnert in 1925. The partition function of the finite number of adsorbents adsorbed on a surface, in a canonical ensemble, is given by
where is the partition function of a single adsorbed molecule, is the number of adsorption sites (both occupied and unoccupied), and is the number of adsorbed molecules which should be less than or equal to . The terms in the bracket give the total partition function of the adsorbed molecules by taking a product of the individual partition functions (refer to Partition function of subsystems). The factor accounts for the overcounting arising due to the indistinguishable nature of the adsorbates. The grand canonical partition function is given by
is the chemical potential of an adsorbed molecule. As it has the form of binomial series, the summation is reduced to
where
The grand canonical potential is
based on which the average number of occupied sites is calculated
which gives the coverage
Now, invoking the condition that the system is in equilibrium, that is, the chemical potential of the adsorbed molecules is equal to that of the molecules in gas phase, we have
The chemical potential of an ideal gas is
where is the Helmholtz free energy of an ideal gas with its partition function
is the partition function of a single particle in the volume of (only consider the translational freedom here).
We thus have , where we use Stirling's approximation.
Plugging to the expression of , we have
which gives the coverage
By defining
and using the identity , finally, we have
It is plotted in the figure alongside demonstrating that the surface coverage increases quite rapidly with the partial pressure of the adsorbants, but levels off after P reaches P. | 7 | Physical Chemistry |
At higher energies ionization tends to occur more than chemical dissociations. In a typical reactive gas, 1 in 100 molecules form free radicals whereas only 1 in 10 ionizes. The predominant effect here is the forming of free radicals.
Ionic effects can predominate with selection of process parameters and if necessary the use of noble gases. | 8 | Metallurgy |
The continuous process of applying up to three separate coating layers onto one or both sides of a metal strip substrate occurs on a coil coating line. These lines vary greatly in size, with widths from and speeds from ; however, all coil-coating lines share the same basic process steps.
A typical organic coil coating line consists of decoilers, entry strip accumulator, cleaning, chemical pretreatment, primer coat application, curing, final coat application, curing, exit accumulator and recoilers.
The following steps take place on a modern coating line:
* Mechanical stitching of the strip to its predecessor
* Cleaning the strip
* Power brushing
* Surface treatment by chemical conversion
* Drying the strip
* Application of primer on one or both sides
* Passage through the first curing oven (between 15 and 60 seconds)
* Cooling the strip
* Coating the finish on one or both sides
* Passage through the second curing oven (between 15 and 60 seconds)
* Cooling down to room temperature
* Rewinding of the coated coil | 8 | Metallurgy |
The specific biochemical mechanism of lithium action in stabilizing mood is unknown.
Upon ingestion, lithium becomes widely distributed in the central nervous system and interacts with a number of neurotransmitters and receptors, decreasing norepinephrine release and increasing serotonin synthesis.
Unlike many other psychoactive drugs, typically produces no obvious psychotropic effects (such as euphoria) in normal individuals at therapeutic concentrations.
Lithium may also increase the release of serotonin by neurons in the brain. In vitro studies performed on serotonergic neurons from rat raphe nuclei have shown that when these neurons are treated with lithium, serotonin release is enhanced during a depolarization compared to no lithium treatment and the same depolarization.
Lithium both directly and indirectly inhibits GSK3β (glycogen synthase kinase 3β) which results in the activation of mTOR. This leads to an increase in neuroprotective mechanisms by facilitating the Akt signaling pathway. GSK-3β is a downstream target of monoamine systems. As such, it is directly implicated in cognition and mood regulation. During mania, GSK-3β is activated via dopamine overactivity. GSK-3β inhibits the transcription factors β-catenin and cyclic AMP (cAMP) response element binding protein (CREB), by phosphorylation. This results in a decrease in the transcription of important genes encoding for neurotrophins. In addition, several authors proposed that pAp-phosphatase could be one of the therapeutic targets of lithium. This hypothesis was supported by the low Ki of lithium for human pAp-phosphatase compatible within the range of therapeutic concentrations of lithium in the plasma of people (0.8–1 mM). The Ki of human pAp-phosphatase is ten times lower than that of GSK3β (glycogen synthase kinase 3β). Inhibition of pAp-phosphatase by lithium leads to increased levels of pAp (3′-5′ phosphoadenosine phosphate), which was shown to inhibit PARP-1.
Another mechanism proposed in 2007 is that lithium may interact with nitric oxide (NO) signalling pathway in the central nervous system, which plays a crucial role in neural plasticity. The NO system could be involved in the antidepressant effect of lithium in the Porsolt forced swimming test in mice. It was also reported that NMDA receptor blockage augments antidepressant-like effects of lithium in the mouse forced swimming test, indicating the possible involvement of NMDA receptor/NO signaling in the action of lithium in this animal model of learned helplessness.
Lithium possesses neuroprotective properties by preventing apoptosis and increasing cell longevity.
Although the search for a novel lithium-specific receptor is ongoing, the high concentration of lithium compounds required to elicit a significant pharmacological effect leads mainstream researchers to believe that the existence of such a receptor is unlikely. | 1 | Biochemistry |
The first glycosynthase was a retaining exoglycosidase that catalyzed the formation of β 1-4 linked glycosides of glucose and galactose. Glycosynthase enzymes have since been expanded to include mutants of endoglycosidase, as well as mutants of inverting glycosidase. Substrates of glycosynthase include glucose, galactose, mannose, xylose, and glucuronic acid.
Modern methods to prepare glycosynthase use directed evolution to introduce modifications, which improve the enzymes function. This process was made available due to the development of high throughput screens for glycosynthase activity. | 0 | Organic Chemistry |
Mixer settlers are a class of mineral process equipment used in the solvent extraction process. A mixer settler consists of a first stage that mixes the phases together followed by a quiescent settling stage that allows the phases to separate by gravity. | 3 | Analytical Chemistry |
Many lawsuits have been filed against Bayer, the manufacturer of drospirenone, due to the higher risk of venous thromboembolism (VTE) that has been observed with combined birth control pills containing drospirenone and certain other progestins relative to the risk with levonorgestrel-containing combined birth control pills.
In July 2012, Bayer notified its stockholders that there were more than 12,000 such lawsuits against the company involving Yaz, Yasmin, and other birth control pills with drospirenone. They also noted that the company by then had settled 1,977 cases for US$402.6 million, for an average of US$212,000 per case, while setting aside US$610.5 million to settle the others.
As of 17 July 2015, there have been at least 4,000 lawsuits and claims still pending regarding VTE related to drospirenone. This is in addition to around 10,000 claims that Bayer has already settled without admitting liability. These claims of VTE have amounted to US$1.97 billion. Bayer also reached a settlement for arterial thromboembolic events, including stroke and heart attacks, for US$56.9 million. | 4 | Stereochemistry |
An example reference range for transferrin is 204–360 mg/dL. Laboratory test results should always be interpreted using the reference range provided by the laboratory that performed the test.
A high transferrin level may indicate an iron deficiency anemia. Levels of serum iron and total iron binding capacity (TIBC) are used in conjunction with transferrin to specify any abnormality. See interpretation of TIBC. Low transferrin likely indicates malnutrition. | 1 | Biochemistry |
In a gas of finite-sized particles there are collisions among particles that depend on their cross-sectional size. The average distance that a particle travels between collisions depends on the density of gas particles. These quantities are related by
where
: is the cross section of a two-particle collision (SI units: m),
: is the mean free path between collisions (SI units: m),
: is the number density of the target particles (SI units: m).
If the particles in the gas can be treated as hard spheres of radius that interact by direct contact, as illustrated in Figure 1, then the effective cross section for the collision of a pair is
If the particles in the gas interact by a force with a larger range than their physical size, then the cross section is a larger effective area that may depend on a variety of variables such as the energy of the particles.
Cross sections can be computed for atomic collisions but also are used in the subatomic realm. For example, in nuclear physics a "gas" of low-energy neutrons collides with nuclei in a reactor or other nuclear device, with a cross section that is energy-dependent and hence also with well-defined mean free path between collisions. | 7 | Physical Chemistry |
Because BIK1 is a possible regulator of the FLS2-BAK1 complex, it is speculated that in vitro, BAK1 phosphorylates BIK1, which then phosphorylates both FLS2 and BAK1. However, in vivo, BIK1 is not phosphorylated until about 5-10 minutes after the addition of FS2, and the peak phosphorylation occurs just after the phosphorylation of the FS2-BAK1 complex. It is speculated that BIK1 activation might be enhanced through transphosphorylation by BAK1 rather than by FLS2 because FLS2 more likely serves as a scaffold protein for the arrangement of the BAK1-FLS2 complex. This hypothesis will require more testing in vivo. Research has shown that BIK1 and BAK1 are signaling partners for the flagellin receptor FLS2 and that the three together initiate defense response. However, BIK1 and BAK1 phosphorylate different residues of the FLS2 receptor with the exception of only a select few. This suggests that both BAK1 and BIK1 play unique roles in defense response by a series of phosphorylation reactions with one another and the flagellin receptor FLS2. | 1 | Biochemistry |
* Gold. 1990. Organic Compounds in Biological Systems, 2nd ed. John Wiley & Sons, Inc.
* [https://web.archive.org/web/20100213004815/http://faculty.mansfield.edu/bganong/biochemistry/reagents.htm Chemical Reagents] | 3 | Analytical Chemistry |
If the polymeric system is amorphous, then the anchor points of the crystalline structure are not available and the only way to ensure the stability of the temporary shape is through chain entanglements (physical entanglements and not chemical crosslinking), in addition to the possibility of crosslinking. | 7 | Physical Chemistry |
Iron or steel, when heated to above 460 °C (900 °F), glows with a red color. The color of heated iron changes predictably (due to black-body radiation) from dull red through orange and yellow to white, and can be a useful indicator of its temperature. Good quality iron or steel at and above this temperature becomes increasingly malleable and plastic. Iron or steel having too much sulfur, on the other hand, becomes crumbly and brittle. This is due to the sulfur forming iron sulfide/iron mixtures in the grain boundaries of the metal which have a lower melting point than the steel.
When the steel is heated up and worked, the mechanical energy added to the workpiece increases the temperature further. The iron sulfide (FeS) or iron/iron sulfide alloy (which has an even lower melting point) begins to melt, and the steel starts to separate at the grain boundaries. Steelmakers add manganese (Mn) to the steel when it is produced, to form manganese sulfide (MnS). Manganese sulfide inclusions have a higher melting point and do not concentrate at the grain boundaries. Thus, when the steel is later heated up and worked, the melting at the grain boundaries does not occur. | 8 | Metallurgy |
The pterobranchia mitochondrial code (translation table 24) is a genetic code used by the mitochondrial genome of Rhabdopleura compacta (Pterobranchia). The Pterobranchia are one of the two groups in the Hemichordata which together with the Echinodermata and Chordata form the three major lineages of deuterostomes. AUA translates to isoleucine in Rhabdopleura as it does in the Echinodermata and Enteropneusta while AUA encodes methionine in the Chordata. The assignment of AGG to lysine is not found elsewhere in deuterostome mitochondria but it occurs in some taxa of Arthropoda. This code shares with many other mitochondrial codes the reassignment of the UGA STOP to tryptophan, and AGG and AGA to an amino acid other than arginine. The initiation codons in Rhabdopleura compacta are ATG and GTG.
Code 24 is very similar to the mitochondrial code 33 for the Pterobranchia. | 1 | Biochemistry |
Some metals, particularly nickel and nickel alloys, can be made into nanocrystalline foils using electrodeposition. | 8 | Metallurgy |
SCARLET (site-specific cleavage and radioactive-labeling followed by ligation-assisted extraction and thin-layer chromatography) is used determining the fraction of RNA in a sample that carries a methylated adenine at a specific site. One can start with total RNA without having to enrich for the target RNA molecule. Therefore, it is an especially suitable method for quantifying methylation status in low abundance RNAs such as tRNAs. However, it is not suitable or practical for large-scale location of m6A sites.
The procedure begins with a chimeric DNA oligonucleotide annealing to the target RNA around the candidate modification site. The chimeric ssDNA has 2’OMe/2’H modifications and is complementary to the target sequence. The chimeric oligonucleotide serves as a guide to allow RNase H to cleave the RNA strand precisely at the 5’-end of the candidate site. The cut site is then radiolabeled with phosphorus-32 and splint-ligated to a 116nt ssDNA oligonucleotide using DNA ligase. RNase T1/A is introduced to the sample to digest all RNA, except for the RNA molecules with the 116-mers DNA attached. This radiolabeled product is then isolated and digested by nuclease to generate a mixture of modified and unmodified adenosines (5’P-m6A and 5’-P-A) which is separated using thin layer chromatography. The relative proportions of the two groups can be determined using UV absorption levels. | 1 | Biochemistry |
Catalyst poisons lower catalyst activity. They are usually impurities in the synthesis gas. Permanent poisons cause irreversible loss of catalytic activity, while temporary poisons lower the activity while present. Sulfur compounds, phosphorus compounds, arsenic compounds, and chlorine compounds are permanent poisons. Oxygenic compounds like water, carbon monoxide, carbon dioxide, and oxygen are temporary poisons.
Although chemically inert components of the synthesis gas mixture such as noble gases or methane are not strictly poisons, they accumulate through the recycling of the process gases and thus lower the partial pressure of the reactants, which in turn slows conversion. | 7 | Physical Chemistry |
The first approved gene therapy clinical research in the US took place on 14 September 1990, at the National Institutes of Health (NIH), under the direction of William French Anderson. Four-year-old Ashanti DeSilva received treatment for a genetic defect that left her with adenosine deaminase deficiency (ADA-SCID), a severe immune system deficiency. The defective gene of the patients blood cells was replaced by the functional variant. Ashantis immune system was partially restored by the therapy. Production of the missing enzyme was temporarily stimulated, but the new cells with functional genes were not generated. She led a normal life only with the regular injections performed every two months. The effects were successful, but temporary.
Cancer gene therapy was introduced in 1992/93 (Trojan et al. 1993). The treatment of glioblastoma multiforme, the malignant brain tumor whose outcome is always fatal, was done using a vector expressing antisense IGF-I RNA (clinical trial approved by NIH protocol no.1602 24 November 1993, and by the FDA in 1994). This therapy also represents the beginning of cancer immunogene therapy, a treatment which proves to be effective due to the anti-tumor mechanism of IGF-I antisense, which is related to strong immune and apoptotic phenomena.
In 1992, Claudio Bordignon, working at the Vita-Salute San Raffaele University, performed the first gene therapy procedure using hematopoietic stem cells as vectors to deliver genes intended to correct hereditary diseases. In 2002, this work led to the publication of the first successful gene therapy treatment for ADA-SCID. The success of a multi-center trial for treating children with SCID (severe combined immune deficiency or "bubble boy" disease) from 2000 and 2002, was questioned when two of the ten children treated at the trial's Paris center developed a leukemia-like condition. Clinical trials were halted temporarily in 2002, but resumed after regulatory review of the protocol in the US, the United Kingdom, France, Italy, and Germany.
In 1993, Andrew Gobea was born with SCID following prenatal genetic screening. Blood was removed from his mothers placenta and umbilical cord immediately after birth, to acquire stem cells. The allele that codes for adenosine deaminase (ADA) was obtained and inserted into a retrovirus. Retroviruses and stem cells were mixed, after which the viruses inserted the gene into the stem cell chromosomes. Stem cells containing the working ADA gene were injected into Andrews blood. Injections of the ADA enzyme were also given weekly. For four years T cells (white blood cells), produced by stem cells, made ADA enzymes using the ADA gene. After four years more treatment was needed.
In 1996, Luigi Naldini and Didier Trono developed a new class of gene therapy vectors based on HIV capable of infecting non-dividing cells that have since then been widely used in clinical and research settings, pioneering lentivirals vector in gene therapy.
Jesse Gelsinger's death in 1999 impeded gene therapy research in the US. As a result, the FDA suspended several clinical trials pending the reevaluation of ethical and procedural practices. | 1 | Biochemistry |
The active zone or synaptic active zone is a term first used by Couteaux and Pecot-Dechavassinein in 1970 to define the site of neurotransmitter release. Two neurons make near contact through structures called synapses allowing them to communicate with each other. As shown in the adjacent diagram, a synapse consists of the presynaptic bouton of one neuron which stores vesicles containing neurotransmitter (uppermost in the picture), and a second, postsynaptic neuron which bears receptors for the neurotransmitter (at the bottom), together with a gap between the two called the synaptic cleft (with synaptic adhesion molecules, SAMs, holding the two together). When an action potential reaches the presynaptic bouton, the contents of the vesicles are released into the synaptic cleft and the released neurotransmitter travels across the cleft to the postsynaptic neuron (the lower structure in the picture) and activates the receptors on the postsynaptic membrane.
The active zone is the region in the presynaptic bouton that mediates neurotransmitter release and is composed of the presynaptic membrane and a dense collection of proteins called the cytomatrix at the active zone (CAZ). The CAZ is seen under the electron microscope to be a dark (electron dense) area close to the membrane. Proteins within the CAZ tether synaptic vesicles to the presynaptic membrane and mediate synaptic vesicle fusion, thereby allowing neurotransmitter to be released reliably and rapidly when an action potential arrives. | 1 | Biochemistry |
The existence of charged particles causes the plasma to generate, and be affected by, magnetic fields. Plasma with a magnetic field strong enough to influence the motion of the charged particles is said to be magnetized. A common quantitative criterion is that a particle on average completes at least one gyration around the magnetic-field line before making a collision, i.e., , where is the electron gyrofrequency and is the electron collision rate. It is often the case that the electrons are magnetized while the ions are not. Magnetized plasmas are anisotropic, meaning that their properties in the direction parallel to the magnetic field are different from those perpendicular to it. While electric fields in plasmas are usually small due to the plasma high conductivity, the electric field associated with a plasma moving with velocity in the magnetic field is given by the usual Lorentz formula , and is not affected by Debye shielding. | 7 | Physical Chemistry |
Thalidomide is a classical example highlighting the alleged role of chirality in drug toxicity. Thalidomide was a racemic therapeutic and prescribed to pregnant women to control nausea and vomiting. The drug was withdrawn from world market when it became evident that the use in pregnancy causes phocomelia (clinical conditions where babies are born with deformed hand and limbs). Later in late 1970s studies indicated that the (R)- enantiomer is an effective sedative, the (S)-enantiomer harbors teratogenic effect and causes fetal abnormalities. Later studies established that under biological conditions the (R)-thalidomide, good partner, undergoes an in vivo metabolic inversion to the (S)-thalidomide, evil partner and vice versa. It is a bidirectional chiral inversion. Hence the argument that the thalidomide tragedy could have been avoided by using a single enantiomer is ambiguous and pointless.
The salient features are presented in the table below. | 4 | Stereochemistry |
Hydrolysis of DNA occurs at a significant rate in vivo. For example, it is estimated that in each human cell 2,000 to 10,000 DNA purine bases turn over every day due to hydrolytic depurination, and that this is largely counteracted by specific rapid DNA repair processes. Hydrolytic DNA damages that fail to be accurately repaired may contribute to carcinogenesis and ageing. | 7 | Physical Chemistry |
Carboranes of intermediate nuclearity are most efficiently generated by degradations from larger clusters. In contrast, smaller carboranes are usually prepared by building-up routes, e.g. from pentaborane + alkyne, etc.
For example ortho-carborane can be degraded to give , which can be manipulated with oxidants, protonation, and thermolysis.
Chromate oxidation of 11-vertex clusters results in deboronation, giving . From that species, other clusters result by pyrolysis, sometimes in the presence of diborane: .
In general, isomers having non-adjacent cage carbon atoms are more thermally stable than those with adjacent carbons. Thus, heating tends to induce mutual separation of the carbon atoms in the framework. | 7 | Physical Chemistry |
The waste product was allowed to cool in the hearth and removed as a "mosser". In the Furness district they were often left as the capstone of a wall, particularly near Spark Bridge and Nibthwaite forges. | 8 | Metallurgy |
A riboside is any glycoside of ribose. Ribosides in the form of ribonucleosides and ribonucleotides play an important role in biochemistry. | 1 | Biochemistry |
The largest risk when using a separating funnel is that of pressure build-up. Pressure accumulates during mixing if a gas evolving reaction or physical change occurs. This problem can be easily handled by simply opening the stopper at the top of the funnel routinely while mixing. More standard procedure is to invert the separating funnel upside down, and open the stopcock to release the pressure, a step done repeatedly known as venting. This should be done with the tip of the funnel pointed away from the body. | 3 | Analytical Chemistry |
Analytical Chemistry is a biweekly peer-reviewed scientific journal published since 1929 by the American Chemical Society. Articles address general principles of chemical measurement science and novel analytical methodologies. Topics commonly include chemical reactions and selectivity, chemometrics and data processing, electrochemistry, elemental and molecular characterization, imaging, instrumentation, mass spectrometry, microscale and nanoscale systems, -omics, sensing, separations, spectroscopy, and surface analysis. It is abstracted and indexed in Chemical Abstracts Service, CAB International, EBSCOhost, ProQuest, PubMed, Scopus, and the Science Citation Index Expanded. According to the Journal Citation Reports, it has a 2022 impact factor of 7.4. The editor-in-chief is Jonathan V. Sweedler (University of Illinois). | 3 | Analytical Chemistry |
In a GC-O analysis, various methods are used to determine the odour contribution of a compound or the relative importance of each odorant. The methods can be categorised as (i) detection frequency, (ii) dilution to threshold and (iii) direct intensity. | 3 | Analytical Chemistry |
Bents rule is able to characterize molecule geometry with accuracy. Bents rule provides a reliable and robust framework for predicting the bond angles of molecules. Bents rule accuracy and precision in predicting the geometry of real-world molecules continues to demonstrate its credibility. Beyond bond angle prediction, Bents rule has some significant applications and is of considerable interest to chemists. Bent's rule can be applied to analyzing bonding interactions and molecular syntheses.
Bents rule can be used to predict which products are favored in an organic synthesis depending on the starting materials. Wang et. al. considered how the substituents affected the silabenzenes equilibrium and found that Bents rule played a significant role in the results. The study conducted by Wang et. al. demonstrates how Bents rule can be used to predict the route of a synthesis and the stability of products. Showing a similar application, Dubois et. al were able to justify some of their findings using Bents rule when they found a reaction to be irreversible. Both these studies show how Bents rule can be used to aid synthetic chemistry. Knowing how molecular geometry accurately due to Bents rule allows synthetic chemists to predict relative product stability. Additionally, Bents rule can help chemists choose their starting materials to drive the reaction towards a particular product. Hence, Bent's rule allows synthetic chemists to exert more control over reactions of interest. | 4 | Stereochemistry |
conversion of carbon dioxide| into gaseous hydrocarbons. The proposed reaction mechanisms involve the creation of a highly reactive carbon radical from carbon monoxide and carbon dioxide which then reacts with photogenerated protons to ultimately form methane. Efficiencies of -based photocatalysts are low, although nanostructures such as carbon nanotubes and metallic nanoparticles help. | 5 | Photochemistry |
Epigenetics refers to the study of heritable changes in genetic activities that are distinct from changes in DNA sequences. Epigenetic analysis involves studying DNA-protein interactions, histone modifications, and DNA methylation. Linked-read sequencing has been used for studying DNA methylation patterns by many studies. For example, in 2021, a study investigated the DNA methylation differences in peripheral blood cells between twins, in which one twin had Alzheimer’s Disease and the other was cognitively normal. Linked-read sequencing technology allowed researchers to identify more than 3000 differentially methylated regions between these twins discordant for Alzheimer’s Disease, and investigation of these differentially methylated regions eventually led to identification of genes enriched in neurodevelopmental processes, neuronal signalling, and immune system functions | 1 | Biochemistry |
Bilirubin (BR) (from the Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the destruction of aged or abnormal red blood cells. In the first step of bilirubin synthesis, the heme molecule is stripped from the hemoglobin molecule. Heme then passes through various processes of porphyrin catabolism, which varies according to the region of the body in which the breakdown occurs. For example, the molecules excreted in the urine differ from those in the feces. The production of biliverdin from heme is the first major step in the catabolic pathway, after which the enzyme biliverdin reductase performs the second step, producing bilirubin from biliverdin.
Ultimately, bilirubin is broken down within the body, and its metabolites excreted through bile and urine; elevated levels may indicate certain diseases. It is responsible for the yellow color of healing bruises and the yellow discoloration in jaundice. The bacterial enzyme bilirubin reductase is responsible for the breakdown of bilirubin in the gut. One breakdown product, urobilin, is the main component of the straw-yellow color in urine. Another breakdown product, stercobilin, causes the brown color of feces.
Although bilirubin is usually found in animals rather than plants, at least one plant species, Strelitzia nicolai, is known to contain the pigment. | 1 | Biochemistry |
The cecum is a pouch marking the division between the small intestine and the large intestine. It lies below the ileocecal valve in the lower right quadrant of the abdomen. The cecum receives chyme from the last part of the small intestine, the ileum, and connects to the ascending colon of the large intestine. At this junction there is a sphincter or valve, the ileocecal valve which slows the passage of chyme from the ileum, allowing further digestion. It is also the site of the appendix attachment. | 1 | Biochemistry |
Zeba was married to Toufiq M Seraj, a Bangladeshi businessman who was the founder and managing director of Sheltech. They have two daughters. | 1 | Biochemistry |
Thermal radiation is an important factor of many engineering applications, especially for those dealing with high temperatures. | 7 | Physical Chemistry |
A western blot is used for the detection of specific proteins in complex samples. Proteins are first separated by size using electrophoresis before being transferred to an appropriate blotting matrix (usually polyvinylidene fluoride or nitrocellulose) and subsequent detection with antibodies. | 1 | Biochemistry |
Many elegant structural mimics have been synthesized reproducing the atomic content and connectivity of the active site. The work by Pickett is a prime example of this field. The catalytic activity of these mimics do not however compare to the native enzyme. In contrast, functional mimics, also known as bio-inspired catalysts, aim to reproduce only the functional features of an enzyme often through the use of different atomic content and connectivity from that found in the native enzymes. Functional mimics have made advances in the reactive chemistry and have implications on the mechanistic activity of the enzyme as well as acting as catalysts in their own right. | 1 | Biochemistry |
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