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A bicyclic molecule () is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (all of the ring atoms are carbons), or heterocyclic (the rings atoms consist of at least two elements), like DABCO. Moreover, the two rings can both be aliphatic (e.g. decalin and norbornane), or can be aromatic (e.g. naphthalene), or a combination of aliphatic and aromatic (e.g.' tetralin).
Three modes of ring junction are possible for a bicyclic compound:
* In spiro compounds, the two rings share only one single atom, the spiro atom, which is usually a quaternary carbon. An example of a spirocyclic compound is the photochromic switch spiropyran.
* In fused/condensed bicyclic compounds, two rings share two adjacent atoms. In other words, the rings share one covalent bond, i.e. the bridgehead atoms are directly connected (e.g. α-thujene and decalin).
* In bridged bicyclic compounds, the two rings share three or more atoms, separating the two bridgehead atoms by a bridge containing at least one atom. For example, norbornane, also known as bicyclo[2.2.1]heptane, can be viewed as a pair of cyclopentane rings each sharing three of their five carbon atoms. Camphor is a more elaborate example. | 4 | Stereochemistry |
Zinc is one of the most common metal ions in biological systems. Small molecule sensors for it include:
*ZX1, a compound comprizing a dipicolylamine (DPA) Zinc binding subunit that has greater affinity for Zinc than other species found in solution such as Ca and Mg.
*Zinpyr-1 (ZP1), a compound containing a dichlorofluorescein fluorescent compound bound to two 2-picolamine (DPA) species that bind Zn(II). ZP1 is part of a family of zinc sensors known as the Zinpyr series, the members of which are variants on ZP1 to enable specific affinities and fluorescence profiles.
*ZnAF-1 sensors that comprise an aryl donor and a xanthenone acceptor and have a large change in fluorescence upon binding Zn(II). They have been used to study uptake of Zn(II) in CA3 pyramidal neurons. | 5 | Photochemistry |
Numerous genes and/or proteins as well as other molecules have been identified that mediate plant defense signal transduction. Cytoskeleton and vesicle trafficking dynamics help to orient plant defense responses toward the point of pathogen attack. | 1 | Biochemistry |
Technically a perfect crystal must be infinite, so a finite size is an imperfection. Real crystals always exhibit imperfections of their order besides their finite size, and these imperfections can have profound effects on the properties of the material. André Guinier proposed a widely employed distinction between imperfections that preserve the long-range order of the crystal that he called disorder of the first kind and those that destroy it called disorder of the second kind. An example of the first is thermal vibration; an example of the second is some density of dislocations.
The generally applicable structure factor can be used to include the effect of any imperfection. In crystallography, these effects are treated as separate from the structure factor , so separate factors for size or thermal effects are introduced into the expressions for scattered intensity, leaving the perfect crystal structure factor unchanged. Therefore, a detailed description of these factors in crystallographic structure modeling and structure determination by diffraction is not appropriate in this article. | 3 | Analytical Chemistry |
Austenite is only stable above in bulk metal form. However, fcc transition metals can be grown on a face-centered cubic (fcc) or diamond cubic. The epitaxial growth of austenite on the diamond (100) face is feasible because of the close lattice match and the symmetry of the diamond (100) face is fcc. More than a monolayer of γ-iron can be grown because the critical thickness for the strained multilayer is greater than a monolayer. The determined critical thickness is in close agreement with theoretical prediction. | 8 | Metallurgy |
The first use of diazonium salts was to produce water-fast dyed fabrics by immersing the fabric in an aqueous solution of the diazonium compound, followed by immersion in a solution of the coupler (the electron-rich ring that undergoes electrophilic substitution). The major applications of diazonium compounds remains in the dye and pigment industry.
The most widely practiced reaction of diazonium salts remains azo coupling, which is exploited in the production of azo dyes. In this process, the diazonium compound is attacked by, i.e., coupled to, electron-rich substrates. When the coupling partners are arenes such as anilines and phenols, the process is an example of electrophilic aromatic substitution:
Another commercially important class of coupling partners are acetoacetic amides, as illustrated by the preparation of Pigment Yellow 12, a diarylide pigment.
The resulting azo compounds are often useful dyes and in fact are called azo dyes. The deep colors of the dyes reflects their extended conjugation. For example, the dye called aniline yellow is produced by mixing aniline and cold solution of diazonium salt and then shaking it vigorously. Aniline yellow is obtained as a yellow solid. Similarly, a cold basic solution of Naphthalen-2-ol (beta-naphthol) give the intensely orange-red precipitate. Methyl orange is an example of an azo dye that is used in the laboratory as a pH indicator. | 0 | Organic Chemistry |
Suppose that trans-cis-trans-2,4,6-octatriene is converted to under thermal conditions. Since the substrate octatriene is a "4n + 2" molecule, the Woodward–Hoffmann rules predict that the reaction happens in a disrotatory mechanism.
Since thermal electrocyclic reactions occur in the HOMO, it is first necessary to draw the appropriate molecular orbitals. Next, the new carbon-carbon bond is formed by taking two of the p-orbitals and rotating them 90 degrees (see diagram). Since the new bond requires constructive overlap, the orbitals must be rotated in a certain way. Performing a disrotation will cause the two black lobes to overlap, forming a new bond. Therefore, the reaction with octatriene happens through a disrotatory mechanism.
In contrast, if a conrotation had been performed then one white lobe would overlap with one black lobe. This would have caused destructive interference and no new carbon-carbon bond would have been formed.
In addition, the cis/trans geometry of the product can also be determined. When the p-orbitals were rotated inwards it also caused the two methyl groups to rotate upwards. Since both methyls are pointing "up", then the product is . | 7 | Physical Chemistry |
Synthesis of morphine-like alkaloids in chemistry describes the total synthesis of the natural morphinan class of alkaloids that includes codeine, morphine, oripavine, and thebaine and the closely related semisynthetic analogs methorphan, buprenorphine, hydromorphone, hydrocodone, isocodeine, naltrexone, nalbuphine, oxymorphone, oxycodone, and naloxone.
The structure of morphine is not particularly complex, however the electrostatic polarization of adjacent bonded atoms does not alternate uniformly throughout the structure. This "dissonant connectivity" makes bond formation more difficult and therefore significantly complicates any synthetic strategy that is applied to this family of molecules.
The first morphine total synthesis, devised by Marshall D. Gates, Jr. in 1952 remains a widely used example of total synthesis. This synthesis took a total of 31 steps and proceeded in 0.06% overall yield. The hydrocodone synthesis of Kenner C. Rice is one of the most efficient and proceeds in 30% overall yield in 14 steps. At 9 steps, the Barriault route is the shortest to date, but contains a number of low-yielding steps and is racemic.
Several other syntheses were reported, notably by the research groups of Evans, Fuchs, Parker, Overman, Mulzer-Trauner, White, Taber, Trost, Fukuyama, Guillou, Stork, Magnus, Smith, and Barriault. | 0 | Organic Chemistry |
Bitumen was used in early photographic technology. In 1826, or 1827, it was used by French scientist Joseph Nicéphore Niépce to make the oldest surviving photograph from nature. The bitumen was thinly coated onto a pewter plate which was then exposed in a camera. Exposure to light hardened the bitumen and made it insoluble, so that when it was subsequently rinsed with a solvent only the sufficiently light-struck areas remained. Many hours of exposure in the camera were required, making bitumen impractical for ordinary photography, but from the 1850s to the 1920s it was in common use as a photoresist in the production of printing plates for various photomechanical printing processes.
Bitumen was the nemesis of many artists during the 19th century. Although widely used for a time, it ultimately proved unstable for use in oil painting, especially when mixed with the most common diluents, such as linseed oil, varnish and turpentine. Unless thoroughly diluted, bitumen never fully solidifies and will in time corrupt the other pigments with which it comes into contact. The use of bitumen as a glaze to set in shadow or mixed with other colors to render a darker tone resulted in the eventual deterioration of many paintings, for instance those of Delacroix. Perhaps the most famous example of the destructiveness of bitumen is Théodore Géricault's Raft of the Medusa (1818–1819), where his use of bitumen caused the brilliant colors to degenerate into dark greens and blacks and the paint and canvas to buckle. | 7 | Physical Chemistry |
Faraday devised the laws of chemical electrodeposition of metals from solutions in 1857. He formulated the second law of electrolysis stating "the amounts of bodies which are equivalent to each other in their ordinary chemical action have equal quantities of electricity naturally associated with them." In other words, the quantities of different elements deposited by a given amount of electricity are in the ratio of their chemical equivalent weights.
An important aspect of the second law of electrolysis is electroplating, which together with the first law of electrolysis has a significant number of applications in industry, as when used to protectively coat metals to avoid corrosion. | 7 | Physical Chemistry |
The protein complex nitrogenase is responsible for catalyzing the reduction of nitrogen gas (N) to ammonia (NH). In cyanobacteria, this enzyme system is housed in a specialized cell called the heterocyst. The production of the nitrogenase complex is genetically regulated, and the activity of the protein complex is dependent on ambient oxygen concentrations, and intra- and extracellular concentrations of ammonia and oxidized nitrogen species (nitrate and nitrite). Additionally, the combined concentrations of both ammonium and nitrate are thought to inhibit N, specifically when intracellular concentrations of 2-oxoglutarate (2-OG) exceed a critical threshold. The specialized heterocyst cell is necessary for the performance of nitrogenase as a result of its sensitivity to ambient oxygen.
Nitrogenase consist of two proteins, a catalytic iron-dependent protein, commonly referred to as MoFe protein and a reducing iron-only protein (Fe protein). There are three different iron dependent proteins, molybdenum-dependent, vanadium-dependent, and iron-only, with all three nitrogenase protein variations containing an iron protein component. Molybdenum-dependent nitrogenase is the most commonly present nitrogenase. The different types of nitrogenase can be determined by the specific iron protein component. Nitrogenase is highly conserved. Gene expression through DNA sequencing can distinguish which protein complex is present in the microorganism and potentially being expressed. Most frequently, the nifH gene is used to identify the presence of molybdenum-dependent nitrogenase, followed by closely related nitrogenase reductases (component II) vnfH and anfH representing vanadium-dependent and iron-only nitrogenase, respectively. In studying the ecology and evolution of nitrogen-fixing bacteria, the nifH gene is the biomarker most widely used. nifH has two similar genes anfH and vnfH that also encode for the nitrogenase reductase component of the nitrogenase complex. | 1 | Biochemistry |
As there are for genes, bioinformatics databases exist for SNPs.
* dbSNP is a SNP database from the National Center for Biotechnology Information (NCBI). , dbSNP listed 149,735,377 SNPs in humans.
* [http://db.systemsbiology.net/kaviar/ Kaviar] is a compendium of SNPs from multiple data sources including dbSNP.
* SNPedia is a wiki-style database supporting personal genome annotation, interpretation and analysis.
* The OMIM database describes the association between polymorphisms and diseases (e.g., gives diseases in text form)
* dbSAP – single amino-acid polymorphism database for protein variation detection
* The Human Gene Mutation Database provides gene mutations causing or associated with human inherited diseases and functional SNPs
* The International HapMap Project, where researchers are identifying Tag SNPs to be able to determine the collection of haplotypes present in each subject.
* GWAS Central allows users to visually interrogate the actual summary-level association data in one or more genome-wide association studies.
The International SNP Map working group mapped the sequence flanking each SNP by alignment to the genomic sequence of large-insert clones in Genebank. These alignments were converted to chromosomal coordinates that is shown in Table 1. This list has greatly increased since, with, for instance, the Kaviar database now listing 162 million single nucleotide variants (SNVs). | 1 | Biochemistry |
Specifically, in the basal state Perilipin A allows a low level of basal lipolysis by reducing the access of cytosolic lipases to stored triacylglycerol in LDs. It is found at their surface in a complex with CGI-58, the co-activator of ATGL. ATGL might also be in this complex but it is quiescent.
Under lipolytically stimulated conditions, PKA is activated and phosphorylates up to 6 Serine residues on Perilipin A (Ser81, 222, 276, 433, 492, and 517) and 2 on HSL (Ser659, and 660). Although PKA also phosphorylates HSL, which can increase its activity, the more than 50-fold increase in fat mobilization (triggered by epinephrine) is primarily due to Perilipin phosphorylation.
Then, Phosphorylated HSL translocates to the LD surface and associates with Perilipin A and Adipocyte fatty acid-binding protein (AFABP). Consequently, HSL gains access to triacylglycerol (TAG) and diacylglycerol (DAG), substrates in LDs. Also, CGI-58 separates from the LD outer layer which leads to a redistribution of ATGL. In particular, ATGL interacts with Perilipin A through phosphorylated Ser517.
As a result, PKA phosphorylation implies an enriched colocation of HLS and ATGL which facilitates maximal lipolysis by the two lipases. | 1 | Biochemistry |
Cis-action or cis-acting is a vague term that, in general, means "an action on the same" in contrast to trans-action "an action on a different". In other words, the initiator of the action is affected by it. Cis-actions occur wherever circular dependencies are present. Most notably in:
* biology, where it refers to life itself as in the selfish gene, cis-acting genetic elements and self-maintenance as a trait of self-replicating entities;
* chemistry, where it is known as autocatalytic set.
* Software engineering, as in computer viruses. | 1 | Biochemistry |
To perform immunofluorescence staining, a fluorophore must be conjugated (“tagged”) to an antibody. Staining procedures can be applied to both retained intracellular expressed antibodies, or to cell surface antigens on living cells. There are two general classes of immunofluorescence techniques: primary (direct) and secondary (indirect). The following descriptions will focus primarily on these classes in terms of conjugated antibodies. | 1 | Biochemistry |
Besides inhibiting human acetylcholinesterase (although to a lesser degree than the insect enzyme), carbamate insecticides also target human melatonin receptors. The human health effects of carbamates are well documented in the list of known endocrine disruptor compounds. Clinical effects of carbamate exposure can vary from slightly toxic to highly toxic depending on a variety of factors including such as dose and route of exposure with ingestion and inhalation resulting in the most rapid clinical effects. These clinical manifestations of carbamate intoxication are muscarinic signs, nicotinic signs, and in rare cases central nervous system signs. | 0 | Organic Chemistry |
After graduating, Smolková-Keulemansová joined the Faculty of Sciences at Charles University and focused on analytical chemistry. In the early 1950s, she built a team focused on modern analytical separation methods such as gas chromatography, high-performance liquid chromatography and electromigration. At this same time, she attended an analytical conference in Prague, leading to her finding a volumetric chromatographic device. Her team began to prepare its own device with volumetric detection, and constructed a more universal glass thermal conductivity detector, allowing them to analyze a larger variety of gas. Little did she know that this was a new idea and, soon after, this detector became part of a commercially available instrument. Because of her innovation and dedication to the field, people started telling her that she was "the first lady of chromatography". | 3 | Analytical Chemistry |
This identification of the 's as asymptotic states is the justification for the in the denominator of the Lippmann–Schwinger equations. | 7 | Physical Chemistry |
The reactions between oxides in the solid or liquid state are excluded in Brønsted–Lowry theory. For example, the reaction
is not covered in the Brønsted–Lowry definition of acids and bases. On the other hand, magnesium oxide acts as a base when it reacts with an aqueous solution of an acid.
Dissolved SiO,silicon dioxide has been predicted to be a weak acid in the Brønsted–Lowry sense.
According to the Lux–Flood theory, oxides like MgO and SiO in the solid state may be called acids or bases. For example, the mineral olivine may be known as a compound of a basic oxide, MgO, and silicon dioxide, SiO, as an acidic oxide. This is important in geochemistry. | 7 | Physical Chemistry |
Given the above definitions the interaction Hamiltonian is
as stated. The next step is to find the Hamiltonian in the interaction picture, . The required unitary transformation is
where the 3rd step can be proved by using a Taylor series expansion, and using the orthogonality of the states and . Note that a multiplication by an overall phase of on a unitary operator does not affect the underlying physics, so in the further usages of we will neglect it. Applying gives:
Now we apply the RWA by eliminating the counter-rotating terms as explained in the previous section:
Finally, we transform the approximate Hamiltonian back to the Schrödinger picture:
The atomic Hamiltonian was unaffected by the approximation, so the total Hamiltonian in the Schrödinger picture under the rotating wave approximation is | 7 | Physical Chemistry |
Bracken is known to have various biological effects, such as carcinogenicity and its well-defined syndromes in livestock and laboratory animals. Ptaquiloside is proved to be responsible for several of these biological effects, some of which are species specific. | 0 | Organic Chemistry |
Egap was born in Athens, Ohio, and went to school in New York City. She started her academic career at Stony Brook University as a philosophy major, but was inspired by her chemistry professor and switched to chemistry. She graduated from Stony Brook University in 2005. She completed her postgraduate studies in 2011 at the University of Washington under the supervision of Samson Jenekhe. Her doctoral work focused on the design and synthesis of organic macromolecules. She examined the structure–property relationships of these macromolecules in next generation electronic devices, including organic field-effect transistors, organic photovoltaics and light-emitting diodes. She investigated how charge carriers and excitons are confined in 0D and 1D nanostructures. This included benzobisthiazole-thiophene copolymers, which can be used for OFETs and OPVs. She worked on oligothiophene-functionalised naphthalene dimide nanowires that can form in solution. Whilst at the University of Washington she developed electron-transport materials for efficient blue phosphorescent OLEDs, using FIrpic and oligoquinolines.
Ahmed joined Massachusetts Institute of Technology as a postdoctoral fellow with Timothy M. Swager. She was a Martin Luther King Jr. Visiting Scholar between 2011 and 2013. She developed a platform that used polymer nanoparticles for in vivo imaging. She won the Gordon Research Conferences Carl Storm Award in 2013 and a graduate award at the MIT Polymer Day in 2014. | 0 | Organic Chemistry |
R/S and E/Z descriptors are assigned by using a system for ranking priority of the groups attached to each stereocenter. This procedure, often known as the sequence rules, is the heart of the CIP system. The overview in this section omits some rules that are needed only in rare cases.
#Compare the atomic number (Z) of the atoms directly attached to the stereocenter; the group having the atom of higher atomic number Z receives higher priority (i.e. number 1).
#If there is a tie, the atoms at distance 2 from the stereocenter have to be considered: a list is made for each group of further atoms bonded to the one directly attached to the stereocenter. Each list is arranged in order of decreasing atomic number Z. Then the lists are compared atom by atom; at the earliest difference, the group containing the atom of higher atomic number Z receives higher priority.
#If there is still a tie, each atom in each of the two lists is replaced with a sublist of the other atoms bonded to it (at distance 3 from the stereocenter), the sublists are arranged in decreasing order of atomic number Z, and the entire structure is again compared atom by atom. This process is repeated recursively, each time with atoms one bond farther from the stereocenter, until the tie is broken. | 4 | Stereochemistry |
In organic chemistry, the term "reagent" denotes a chemical ingredient (a compound or mixture, typically of inorganic or small organic molecules) introduced to cause the desired transformation of an organic substance. Examples include the Collins reagent, Fenton's reagent, and Grignard reagents. | 0 | Organic Chemistry |
The original Bürgi-Dunitz measurements were of a series of intramolecular amine-ketone carbonyl interactions, in crystals of compounds bearing both functionalities—e.g., methadone and protopine. These gave a narrow range of BD angle values (105 ± 5°); corresponding computations—molecular orbital calculations of the SCF-LCAO-type—describing the approach of the s-orbital of a hydride anion (H) to the pi-system of the simplest aldehyde, formaldehyde (HC=O), gave a BD angle value of 107°.
Hence, Bürgi, Dunitz, and thereafter many others noted that the crystallographic measurements of the aminoketones and the computational estimate for the simplest nucleophile-electrophile system were quite close to a theoretical ideal, the tetrahedral angle (internal angles of a tetrahedron, 109.5°), and so consistent with a geometry understood to be important to developing transition states in nucleophilic attacks at trigonal centers.
In the structure of -methadone (above, left), note the tertiary amine projecting to the lower right, and the carbonyl (CO) group at the center, which engage in an intramolecular interaction in the crystal structure (after rotation around the single bonds connecting them, during the crystallization process).
Similarly, in the structure of protopine (above, center), note the tertiary amine at the center of the molecule, part of a ten-membered ring, and the CO group opposite it on the ring; these engage in an intramolecular interaction allowed by changes in the torsion angles of the atoms of the ring. | 7 | Physical Chemistry |
Crystal chemistry is the study of the principles of chemistry behind crystals and their use in describing structure-property relations in solids, as well as the chemical properties of periodic structures. The principles that govern the assembly of crystal and glass structures are described, models of many of the technologically important crystal structures (alumina, quartz, perovskite) are studied, and the effect of crystal structure on the various fundamental mechanisms responsible for many physical properties are discussed.
The objectives of the field include:
#identifying important raw materials and minerals as well as their names and chemical formulae.
#describing the crystal structure of important materials and determining their atomic details
#learning the systematics of crystal and glass chemistry.
#understanding how physical and chemical properties are related to crystal structure and microstructure.
#studying the engineering significance of these ideas and how they relate to foreign products: past, present, and future.
Topics studied are:
#Chemical bonding, Electronegativity
#Fundamentals of crystallography: crystal systems, Miller Indices, symmetry elements, bond lengths and radii, theoretical density
#Crystal and glass structure prediction: Pauling's and Zachariasen’s rules
#Phase diagrams and crystal chemistry (including solid solutions)
#Imperfections (including defect chemistry and line defects)
#Phase transitions
#Structure – property relations: Neumann's law, melting point, mechanical properties (hardness, slip, cleavage, elastic moduli), wetting, thermal properties (thermal expansion, specific heat, thermal conductivity), diffusion, ionic conductivity, refractive index, absorption, color, Dielectrics and Ferroelectrics, and Magnetism
#Crystal structures of representative metals, semiconductors, polymers, and ceramics | 3 | Analytical Chemistry |
Dye-ligand affinity chromatography is one of the Affinity chromatography techniques used for protein purification of a complex mixture. Like general chromatography, but using dyes to apply on a support matrix of a column as the stationary phase that will allow a range of proteins with similar active sites to bind to, refers to as pseudo-affinity. Synthetic dyes are used to mimic substrates or cofactors binding to the active sites of proteins which can be further enhanced to target more specific proteins. Follow with washing, the process of removing other non-target molecules, then eluting out target proteins out by changing pH or manipulate the salt concentration. The column can be reused many times due to the stability of immobilized dyes. It can carry out in a conventional way by using as a packed column, or in high-performance liquid chromatography (HPLC) column. | 3 | Analytical Chemistry |
Thiourea per se has few applications. It is mainly consumed as a precursor to thiourea dioxide, which is a common reducing agent in textile processing. | 0 | Organic Chemistry |
In spite of the second law of thermodynamics, crystallization of pure liquids usually begins at a lower temperature than the melting point, due to high activation energy of homogeneous nucleation. The creation of a nucleus implies the formation of an interface at the boundaries of the new phase. Some energy is expended to form this interface, based on the surface energy of each phase. If a hypothetical nucleus is too small, the energy that would be released by forming its volume is not enough to create its surface, and nucleation does not proceed. Freezing does not start until the temperature is low enough to provide enough energy to form stable nuclei. In presence of irregularities on the surface of the containing vessel, solid or gaseous impurities, pre-formed solid crystals, or other nucleators, heterogeneous nucleation may occur, where some energy is released by the partial destruction of the previous interface, raising the supercooling point to be near or equal to the melting point. The melting point of water at 1 atmosphere of pressure is very close to 0 °C (32 °F, 273.15 K), and in the presence of nucleating substances the freezing point of water is close to the melting point, but in the absence of nucleators water can supercool to before freezing. Under high pressure (2,000 atmospheres) water will supercool to as low as before freezing. | 1 | Biochemistry |
A fixed bed of porous materials (e.g. activated carbons and zeolites) is pressurized and purged with a carrier gas. After becoming stationary one or more adsorptives are added to the carrier gas, resulting in a step-wise change of the inlet concentration. This is in contrast to chromatographic separation processes, where pulse-wise changes of the inlet concentrations are used. The course of the adsorptive concentrations at the outlet of the fixed bed are monitored. | 7 | Physical Chemistry |
Polymers, especially conductive ones, have been widely researched to coat electrode surfaces. Conductive polymers are organic materials that have properties similar to metals and semiconductors in their ability conduct electricity and attractive optical properties. These materials have rough surfaces, resulting in large surface area and charge density. Conducting polymer coatings have been shown to improve the performance and stability of neural electrode.
Conductive polymers have been shown to lower the impedance of electrodes (an important property as mentioned above), increase the charge density, and improve the mechanical interface between the soft tissue and hard electrode. The porous (rough) structure of many conductive polymer coatings on the electrode increases the surface area. The high surface area of conductive polymers is directly related to decreased impedance and charge transfer improvement at the tissue-electrode interface. This improved charge transfer allows for better recording and stimulating in neural application. Table 2 below shows some common impedance and charge density values of different electrodes at a frequency of 1 kHz, which is the characteristic of neural biological activity. The porous, high surface area of the conductive polymer coatings allows for target cell adhesion (increased cell and tissue integration), which increase the bio-compatibility and stability of the device.
Conducting polymer coatings as mentioned above can greatly improve the interface between the soft tissue in the body and the hard electrode surface. Polymers are softer, which reduces the inflammation from strain mismatch between tissue and electrode surface. The reduced inflammatory reaction causes a decrease in thickness of the glial encapsulation which causes signal degeneration. The elastic modulus of silicon (a common material that electrodes are made from) is around 100 GPa and the tissue in the brain is about 100 kPa. The electrode modulus (stiffness) is about 100 times greater than that of the tissue in the brain. For the best device integration in the body, it is important to get the stiffness between the two to be as similar as possible. To improve this interface, a conductive polymer coating (smaller modulus than the electrode) can be applied to the electrode surface which causes a gradient of mechanical properties to act as a mediator between the hard and soft surfaces. The added polymer coating reduces the stiffness of the electrode and allows for better integration of the electrode. The figure to the right shows a graph of how the modulus changes when integrating the polymer coating onto the electrode. | 7 | Physical Chemistry |
Transforming C-H bonds into C-B bonds through borylation has been thoroughly investigated due to their utility in synthesis (i.e. for cross-coupling reactions). John F. Hartwig reported a highly regioselective arene and alkane borylation catalyzed by a rhodium complex. In the case of alkanes, exclusive terminal functionalization was observed.
Later, ruthenium catalysts were discovered to have higher activity and functional group compatibility.
Other borylation catalysts have also been developed, including iridium-based catalysts, which successfully activate C-H bonds with high compatibility.
For more information, consult borylation. | 0 | Organic Chemistry |
The sea hare A californica is a model organism in neurobiology to study among others the molecular mechanisms of long-term memory. To study interactions, important in neurology, in a more native environment a two-hybrid system has been developed in A californica neurons. A GAL4 AD and BD are used in this system. | 1 | Biochemistry |
Reductive elimination is often seen in higher oxidation states, and can involve a two-electron change at a single metal center (mononuclear) or a one-electron change at each of two metal centers (binuclear, dinuclear, or bimetallic).
For mononuclear reductive elimination, the oxidation state of the metal decreases by two, while the d-electron count of the metal increases by two. This pathway is common for d metals Ni(II), Pd(II), and Au(III) and d metals Pt(IV), Pd(IV), Ir(III), and Rh(III). Additionally, mononuclear reductive elimination requires that the groups being eliminated must be cis to one another on the metal center.
For binuclear reductive elimination, the oxidation state of each metal decreases by one, while the d-electron count of each metal increases by one. This type of reactivity is generally seen with first row metals, which prefer a one-unit change in oxidation state, but has been observed in both second and third row metals. | 0 | Organic Chemistry |
Because of their wide needs, the overall chelating agents growth was 4 % annually during 2009-2014 and the trend is likely to increase. Aminopolycarboxylic acids chelators are the most widely consumed chelating agents; however, the percentage of the greener alternative chelators in this category continues to grow. The consumption of traditional aminopolycarboxylates chelators, in particular the EDTA (ethylenediaminetetraacetic acid) and NTA (nitrilotriacetic acid), is declining (–6% annually), because of the persisting concerns over their toxicity and negative environmental impact. In 2013, these greener alternative chelants represented approximately 15% of the total aminopolycarboxylic acids demand. This is expected to rise to around 21% by 2018, replacing and aminophosphonic acids used in cleaning applications. Examples of some Greener alternative chelating agents include ethylenediamine disuccinic acid (EDDS), polyaspartic acid (PASA), methylglycinediacetic acid (MGDA), glutamic diacetic acid (L-GLDA), citrate, gluconic acid, amino acids, plant extracts etc. | 7 | Physical Chemistry |
Distribution of stop codons within the genome of an organism is non-random and can correlate with GC-content. For example, the E. coli K-12 genome contains 2705 TAA (63%), 1257 TGA (29%), and 326 TAG (8%) stop codons (GC content 50.8%). Also the substrates for the stop codons release factor 1 or release factor 2 are strongly correlated to the abundance of stop codons. Large scale study of bacteria with a broad range of GC-contents shows that while the frequency of occurrence of TAA is negatively correlated to the GC-content and the frequency of occurrence of TGA is positively correlated to the GC-content, the frequency of occurrence of the TAG stop codon, which is often the minimally used stop codon in a genome, is not influenced by the GC-content. | 1 | Biochemistry |
The system equation can be analyzed by looking at the linear response of the equation around the steady-state with respect to the parameter . At steady-state, the system equation is set to zero and given by:
Differentiating the equation with respect to and rearranging gives:
This derivation assumes that the stoichiometry matrix has full rank. If this is not the case, then the inverse won't exist. | 1 | Biochemistry |
The slow processing speed of a DNA computer (the response time is measured in minutes, hours or days, rather than milliseconds) is compensated by its potential to make a high amount of multiple parallel computations. This allows the system to take a similar amount of time for a complex calculation as for a simple one. This is achieved by the fact that millions or billions of molecules interact with each other simultaneously. However, it is much harder to analyze the answers given by a DNA computer than by a digital one. | 1 | Biochemistry |
Berlin is a member of the New York Academy of Science, the American Chemical Society, and the Royal Society of Chemistry. He is a member of the International Society for the Study of the Origin of Life, an honor Member of the European Molecular Liquids Group, a fellow of the Mendeleev Chemical Society and the Russian Physical Society. His work has earned him many awards, including EU Erasmus Mundus Professorship Award (2009) and Scientific Award of Hans Veilberth Foundation, Germany (2007). Most recently, Yuri Berlin was awarded the Maria Sklodowska-Curie Medal (2019) in recognition of his distinguished achievements in radiation research as well as the long-lasting and productive cooperation with Polish scientists. | 7 | Physical Chemistry |
Both Kohlrausch's law and the Debye–Hückel–Onsager equation break down as the concentration of the electrolyte increases above a certain value. The reason for this is that as concentration increases the average distance between cation and anion decreases, so that there is more interactions between close ions. Whether this constitutes ion association is a moot point. However, it has often been assumed that cation and anion interact to form an ion pair. So, an "ion-association" constant , can be derived for the association equilibrium between ions A and B:
: A + B AB with =
Davies describes the results of such calculations in great detail, but states that should not necessarily be thought of as a true equilibrium constant, rather, the inclusion of an "ion-association" term is useful in extending the range of good agreement between theory and experimental conductivity data. Various attempts have been made to extend Onsager's treatment to more concentrated solutions.
The existence of a so-called conductance minimum in solvents having the relative permittivity under 60 has proved to be a controversial subject as regards interpretation. Fuoss and Kraus suggested that it is caused by the formation of ion triplets, and this suggestion has received some support recently.
Other developments on this topic have been done by Theodore Shedlovsky, E. Pitts, R. M. Fuoss, Fuoss and Shedlovsky, Fuoss and Onsager. | 7 | Physical Chemistry |
Binding of targeting sequence elements by CTCF can block the interaction between enhancers and promoters, therefore limiting the activity of enhancers to certain functional domains. Besides acting as enhancer blocking, CTCF can also act as a chromatin barrier by preventing the spread of heterochromatin structures. | 1 | Biochemistry |
It appears that growth factors, amino acids, ATP, and oxygen levels regulate mTOR signaling. Several downstream pathways that regulate cell-cycle progression, translation, initiation, transcriptional stress responses, protein stability, and survival of cells are signaling through mTOR.
The serine/threonine kinase mTOR is a downstream effector of the PI3K/AKT pathway, and forms two distinct multiprotein complexes, mTORC1 and mTORC2. These two complexes have a separate network of protein partners, feedback loops, substrates, and regulators. mTORC1 consists of mTOR and two positive regulatory subunits, raptor and mammalian LST8 (mLST8), and two negative regulators, proline-rich AKT substrate 40 (PRAS40) and DEPTOR. mTORC2 consists of mTOR, mLST8, mSin1, protor, rictor, and DEPTOR.
mTORC1 is sensitive to rapamycin but mTORC2 is considered to be resistant and is generally insensitive to nutrients and energy signals. mTORC2 is activated by growth factors, phosphorylates PKCα, AKT and paxillin, and regulates the activity of the small GTPase, Rac, and Rho related to cell survival, migration and regulation of the actin cytoskeleton.
The mTORC1 signaling cascade is activated by phosphorylated AKT and results in phosphorylation of S6K1, and 4EBP1, which lead to mRNA translation. | 1 | Biochemistry |
The company was founded on June 15, 1917, with Spanish-French financial support, with a capital stock of 25 million pesetas. It was born in the context of a boom in Spanish industry, in the heat of the First World War. Two foreign capital companies were involved in its creation, the Sociedad Minera y Metalúrgica de Peñarroya (SMMP) and the Rio Tinto Company Limited (RTC), both of which became shareholders of the new company. The SECEM owned an important plant in Cordoba dedicated to copper metallurgy, brass production, manufacture of motors and electric transformers, etc. Over the years it ended up becoming one of the main companies in the sector, having also a great importance in the local context of Cordoba.
The company came to manufacture nearly 40% of all the electrolytic copper produced in Spain, being supplied to a large extent by the material coming from the Rio Tinto-Nerva mining basin. In this sense, SECEM became an important client of the Compañía Española de Minas de Río Tinto (CEMRT), and later the companies Río Tinto Patiño and Río Tinto Minera would have an important shareholding in SECEM. In spite of this privileged situation, the lack of internal competition meant that the machinery and technology of the Cordovan factory were not modernized, which in the long term would end up causing serious problems for SECEM's economic viability. Towards the end of the 1970s, the industrial crisis had a considerable impact on the copper sector. Taking advantage of this context, in May 1978 SECEM —with the financial support of Banco de Bilbao and Banco Hispano Americano— proceeded to acquire the companies Pradera Hermanos, Sociedad Industrial Asturiana and Earle; at the end of the year, all of these companies formed the conglomerate Ibercobre, which controlled 60% of the copper market.
The SECEM complex in Cordoba remained intact until 1989–1990, after the purchase of Ibercobre by the Finnish company Outokumpu, which decided to split it into three separate industries. | 8 | Metallurgy |
Glyceroneogenesis can be regulated at two reaction pathways. First, it can be held at the decarboxylation of oxaloacetate to phosphoenolpyruvate. Secondly, the TCA cycle can affect glyceroneogenesis when the glutamate or substrates in the TCA cycle are being used as a precursor.
Decarboxylation of oxaloacetate to phosphoenolpyruvate is catalyzed by PEPC-K, the essential enzyme which regulates glyceroneogenesis. Increases in PEPC-K levels or overexpression of the gene that codes for PEPC-K will increase glyceroneogenesis. Also, oxaloacetate can be decarboxylated to phosphoenolpyruvate when more PEPC-K can catalyze the reaction.
Gene expression of PEPC-K can be suppressed by norepinephrine, glucocorticoids, and insulin. Norepinephrine is a neurotransmitter which decreases the activity of PEPC-K when the cell is in a cold environment. Glucocorticoids are steroid hormones involved in the reciprocal regulation of glyceroneogenesis in the liver and adipose tissues. Through a poorly-understood mechanism, they induce transcription of PEPC-K in the liver while decreasing transcription in adipose tissues. Insulin is a peptide hormone that causes cells to take in glucose. Through glyceroneogenesis, insulin down-regulates the expression of PEPC-K in both liver and adipose tissues. | 1 | Biochemistry |
Possible reactivity at aldehydes include nucleophilic attack and addition of allylmetals. The stereoselectivity of nucleophilic attack at alpha-chiral aldehydes may be described by the Felkin–Anh or polar Felkin Anh models and addition of achiral allylmetals may be described by Cram’s rule. | 4 | Stereochemistry |
Sequence-based classifications are one of the most powerful predictive methods for suggesting function for newly sequenced enzymes for which function has not been biochemically demonstrated. A classification system for glycosyl hydrolases, based on sequence similarity, has led to the definition of more than 100 different families. This classification is available on the CAZy (CArbohydrate-Active EnZymes) web site. The database provides a series of regularly updated sequence based classification that allow reliable prediction of mechanism (retaining/inverting), active site residues and possible substrates. The online database is supported by CAZypedia, an online encyclopedia of carbohydrate active enzymes. Based on three-dimensional structural similarities, the sequence-based families have been classified into clans of related structure. Recent progress in glycosidase sequence analysis and 3D structure comparison has allowed the proposal of an extended hierarchical classification of the glycoside hydrolases. | 0 | Organic Chemistry |
AGEs have been implicated in Alzheimer's Disease, cardiovascular disease, and stroke. The mechanism by which AGEs induce damage is through a process called cross-linking that causes intracellular damage and apoptosis. They form photosensitizers in the crystalline lens, which has implications for cataract development. Reduced muscle function is also associated with AGEs. | 1 | Biochemistry |
Calcareous is used as an adjectival term applied to anatomical structures which are made primarily of calcium carbonate, in animals such as gastropods, i.e., snails, specifically in relation to such structures as the operculum, the clausilium, and the love dart. The term also applies to the calcium carbonate tests of, often, more-or-less microscopic Foraminifera. Not all tests are calcareous; diatoms and radiolaria have siliceous tests.
The molluscs are calcareous organisms, as are the calcareous sponges (Calcarea), that have spicules which are made of calcium carbonate.
Additionally, reef-building corals, or Scleractinia, are calcareous organisms that form their rigid skeletal structure through the precipitation of aragonite (i.e., a polymorph of calcium carbonate). | 9 | Geochemistry |
Phosphorescence is a type of photoluminescence related to fluorescence. When exposed to light (radiation) of a shorter wavelength, a phosphorescent substance will glow, absorbing the light and reemitting it at a longer wavelength. Unlike fluorescence, a phosphorescent material does not immediately reemit the radiation it absorbs. Instead, a phosphorescent material absorbs some of the radiation energy and reemits it for a much longer time after the radiation source is removed.
In a general sense, there is no distinct boundary between the emission times of fluorescence and phosphorescence (i.e.: if a substance glows under a black light it is generally considered fluorescent, and if it glows in the dark it is often simply called phosphorescent). In a modern, scientific sense, the phenomena can usually be classified by the three different mechanisms that produce the light, and the typical timescales during which those mechanisms emit light. Whereas fluorescent materials stop emitting light within nanoseconds (billionths of a second) after the excitation radiation is removed, phosphorescent materials may continue to emit an afterglow ranging from a few microseconds to many hours after the excitation is removed.
There are two separate mechanisms that may produce phosphorescence, called triplet phosphorescence (or simply phosphorescence) and persistent phosphorescence (or persistent luminescence). Triplet phosphorescence occurs when an atom absorbs a high-energy photon, and the energy becomes locked in the spin multiplicity of the electrons, generally changing from a fluorescent "singlet state" to a slower emitting "triplet state". The slower timescales of the reemission are associated with "forbidden" energy state transitions in quantum mechanics. As these transitions occur relatively slowly in certain materials, absorbed radiation is reemitted at a lower intensity, ranging from a few microseconds to as much as one second after the excitation is removed.
On the other hand, persistent phosphorescence occurs when a high-energy photon is absorbed by an atom and its electron becomes trapped in a defect in the lattice of the crystalline or amorphous material. A defect such as a missing atom (vacancy defect) can trap an electron like a pitfall, storing that electron's energy until released by a random spike of thermal (vibrational) energy. Such a substance will then emit light of gradually decreasing intensity, ranging from a few seconds to up to several hours after the original excitation.
Everyday examples of phosphorescent materials are the glow-in-the-dark toys, stickers, paint, and clock dials that glow after being charged with a bright light such as in any normal reading or room light. Typically, the glow slowly fades out, sometimes within a few minutes or up to a few hours in a dark room.
The study of phosphorescent materials led to the discovery of radioactive decay. | 7 | Physical Chemistry |
The roles of regulatory agencies also continue to evolve with respect to the development of chiral switches. An interesting concept brought up in the FDA policy is that of "bridging studies". When a sponsor/innovator seeks to develop a single enantiomer from a racemic drug, the regulatory agencies demand them to conduct bridging studies. Bridging studies are tests (pharmacological and toxicological evaluations) to connect what is known about the already approved racemate and what is unknown about the single enantiomer under study, without going back to square one as for a completely new chemical entity. The intent of the bridging studies is to make sure that the companies are not scarifying some protective effect conferred by the other" isomer when they develop a chiral drug as single enantiomer rather than a racemate. "Bridging" procedure will help to reduce the number of studies required on the "new" enantiopure drug. | 4 | Stereochemistry |
Robert S. Mulliken proposed that the arithmetic mean of the first ionization energy (E) and the electron affinity (E) should be a measure of the tendency of an atom to attract electrons:
As this definition is not dependent on an arbitrary relative scale, it has also been termed absolute electronegativity, with the units of kilojoules per mole or electronvolts. However, it is more usual to use a linear transformation to transform these absolute values into values that resemble the more familiar Pauling values. For ionization energies and electron affinities in electronvolts,
and for energies in kilojoules per mole,
The Mulliken electronegativity can only be calculated for an element whose electron affinity is known. Measured values are available for 72 elements, while approximate values have been estimated or calculated for the remaining elements.
The Mulliken electronegativity of an atom is sometimes said to be the negative of the chemical potential. By inserting the energetic definitions of the ionization potential and electron affinity into the Mulliken electronegativity, it is possible to show that the Mulliken chemical potential is a finite difference approximation of the electronic energy with respect to the number of electrons., i.e., | 3 | Analytical Chemistry |
In science, a representative liquid sample taken from a larger amount of liquid is sometimes called an aliquot or aliquot part where the sample is an exact divisor of the whole. For example, 10mL would be an aliquot part of a 100mL sample. | 3 | Analytical Chemistry |
Compactin and lovastatin, natural products with a powerful inhibitory effect on HMG-CoA reductase, were discovered in the 1970s, and taken into clinical development as potential drugs for lowering LDL cholesterol.
In 1982, some small-scale clinical investigations of lovastatin, a polyketide-derived natural product isolated from Aspergillus terreus, in very high-risk patients were undertaken, in which dramatic reductions in LDL cholesterol were observed, with very few adverse effects. After the additional animal safety studies with lovastatin revealed no toxicity of the type thought to be associated with compactin, clinical studies continued.
Large-scale trials confirmed the effectiveness of lovastatin. Observed tolerability continued to be excellent, and lovastatin was approved by the US FDA in 1987. It was the first statin approved by the FDA.
Lovastatin is also naturally produced by certain higher fungi, such as Pleurotus ostreatus (oyster mushroom) and closely related Pleurotus spp. Research into the effect of oyster mushroom and its extracts on the cholesterol levels of laboratory animals has been extensive, although the effect has been demonstrated in a very limited number of human subjects.
In 1998, the FDA placed a ban on the sale of dietary supplements derived from red yeast rice, which naturally contains lovastatin, arguing that products containing prescription agents require drug approval. Judge Dale A. Kimball of the United States District Court for the District of Utah, granted a motion by Cholestins manufacturer, Pharmanex, that the agencys ban was illegal under the 1994 Dietary Supplement Health and Education Act because the product was marketed as a dietary supplement, not a drug.
The objective is to decrease excess levels of cholesterol to an amount consistent with maintenance of normal body function. Cholesterol is biosynthesized in a series of more than 25 separate enzymatic reactions that initially involves three successive condensations of acetyl-CoA units to form the six-carbon compound 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA). This is reduced to mevalonate and then converted in a series of reactions to the isoprenes that are building-blocks of squalene, the immediate precursor to sterols, which cyclizes to lanosterol (a methylated sterol) and further metabolized to cholesterol. A number of early attempts to block the synthesis of cholesterol resulted in agents that inhibited late in the biosynthetic pathway between lanosterol and cholesterol. A major rate-limiting step in the pathway is at the level of the microsomal enzyme that catalyzes the conversion of HMG CoA to mevalonic acid, and that has been considered to be a prime target for pharmacologic intervention for several years.
HMG CoA reductase occurs early in the biosynthetic pathway and is among the first committed steps to cholesterol formulation. Inhibition of this enzyme could lead to accumulation of HMG CoA, a water-soluble intermediate that is, then, capable of being readily metabolized to simpler molecules. This inhibition of reductase would lead to accumulation of lipophylic intermediates with a formal sterol ring.
Lovastatin was the first specific inhibitor of HMG CoA reductase to receive approval for the treatment of hypercholesterolemia. The first breakthrough in efforts to find a potent, specific, competitive inhibitor of HMG CoA reductase occurred in 1976, when Endo et al. reported the discovery of mevastatin, a highly functionalized fungal metabolite, isolated from cultures of Penicillium citrium. | 0 | Organic Chemistry |
Since its introduction in 1977, Northern blot has been used extensively for RNA quantification despite its shortcomings: (a) time-consuming technique, (b) requires a large quantity of RNA for detection, and (c) quantitatively inaccurate in the low abundance of RNA content. However, since PCR was invented by Kary Mullis in 1983, RT PCR has since displaced Northern blot as the method of choice for RNA detection and quantification.
RT-PCR has risen to become the benchmark technology for the detection and/or comparison of RNA levels for several reasons: (a) it does not require post PCR processing, (b) a wide range (>10-fold) of RNA abundance can be measured, and (c) it provides insight into both qualitative and quantitative data. Due to its simplicity, specificity and sensitivity, RT-PCR is used in a wide range of applications from experiments as simple as quantification of yeast cells in wine to more complex uses as diagnostic tools for detecting infectious agents such as the avian flu virus and SARS-CoV-2. | 1 | Biochemistry |
The Royal Commission on River Pollution, established in 1865, and the formation of the Royal Commission on Sewage Disposal in 1898 led to the selection in 1908 of BOD as the definitive test for organic pollution of rivers. Five days was chosen as an appropriate test period because this is supposedly the longest time that river water takes to travel from source to estuary in the U.K. In its sixth report the Royal Commission recommended that the standard set should be 15 parts by weight per million of water. However, in the Ninth report the commission had revised the recommended standard: This was the cornerstone 20:30 (BOD:Suspended Solids) + full nitrification standard which was used as a yardstick in the U.K. up to the 1970s for sewage works effluent quality.
The United States includes BOD effluent limitations in its secondary treatment regulations. Secondary sewage treatment is generally expected to remove 85 percent of the BOD measured in sewage and produce effluent BOD concentrations with a 30-day average of less than 30 mg/L and a 7-day average of less than 45 mg/L. The regulations also describe "treatment equivalent to secondary treatment" as removing 65 percent of the BOD and producing effluent BOD concentrations with a 30-day average less than 45 mg/L and a 7-day average less than 65 mg/L. | 3 | Analytical Chemistry |
A phosphoramidite (RO)PNR is a monoamide of a phosphite diester. The key feature of phosphoramidites is their markedly high reactivity towards nucleophiles catalyzed by weak acids e.c., triethylammonium chloride or 1H-tetrazole. In these reactions, the incoming nucleophile replaces the NR moiety. | 0 | Organic Chemistry |
In LS AAS background absorption can only be corrected using instrumental techniques, and all of them are based on two sequential measurements: firstly, total absorption (atomic plus background), secondly, background absorption only. The difference of the two measurements gives the net atomic absorption. Because of this, and because of the use of additional devices in the spectrometer, the signal-to-noise ratio of background-corrected signals is always significantly inferior compared to uncorrected signals. It should also be pointed out that in LS AAS there is no way to correct for (the rare case of) a direct overlap of two atomic lines. In essence there are three techniques used for background correction in LS AAS: | 3 | Analytical Chemistry |
Investment casting (known as lost-wax casting in art) is a process that has been practiced for thousands of years, with the lost-wax process being one of the oldest known metal forming techniques. From 5000 years ago, when beeswax formed the pattern, to today's high technology waxes, refractory materials, and specialist alloys, the castings ensure high-quality components are produced with the key benefits of accuracy, repeatability, versatility, and integrity.
Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting is that the wax can be reused.
The process is suitable for repeatable production of net shape components from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 300 kg and aluminium castings of up to 30 kg. Compared to other casting processes such as die casting or sand casting, it can be an expensive process. However, the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so require little or no rework once cast. | 8 | Metallurgy |
The Journal of Photochemistry and Photobiology A: Chemistry is abstracted and indexed in BIOSIS Previews, Chemical Abstracts, Chemical Citation Index, Current Contents/Physics, Chemistry & Engineering, Engineering Index, Metals Abstracts, PASCAL, Physics Abstracts, Physikalische Berichte, Polymer Contents, Science Citation Index and Scopus. According to the Journal Citation Reports, the journal has a 2019 impact factor of 3.261. | 5 | Photochemistry |
Parasitoids have successfully been incorporated into biological pest control programs for many years. Plants can influence the effect of parasitoids on herbivores by releasing chemical cues that attract parasitoids and by providing food sources or domatia. Certain parasitoids may be dependent on this plant relationship. Therefore, in agricultural areas where parasitoid presence is desired, ensuring the crops being grown meet all of these requirements is likely to promote higher parasitoid populations and better pest control.
In a sugar beet crop, when only beets were grown, few aphids were parasitized. However, when collard crops were grown next to the sugar beets, parasitism of aphids increased. Collard crops release more VOCs than sugar beets. As a result, the companion collard plants attract more aphid parasitoids, which kill aphids in both the collard and the nearby sugar beets.
In a related study, ethylene and other compounds released by rice plants in response to brown planthopper feeding attracted a facultative parasitoid that parasitizes brown planthopper eggs.
In another study, the presence of plant extrafloral nectaries in cotton crops caused parasitoids to spend more time in the cotton and led to the parasitization of more moth larva than in cotton crops with no nectaries. Since the publication of this study, most farmers have switched to cotton varieties with nectaries. A separate study found that a naturalized cotton variety emitted seven times more VOCs than cultivated cotton varieties when experiencing feeding damage. It is unknown whether this generalizes to other crops; there are cases of other crops that do not show the same trend.
These findings reveal the specific variables a farmer can manipulate to influence parasitoid populations and illustrate the potential impact parasitoid habitat management can have on pest control. In the case of cotton and other similar high-VOC crop scenarios, there is interest in genetically engineering the chemical pathways of cultivated varieties to selectively produce the high VOC's that were observed in the naturalized varieties in order to attract greater natural enemy populations. This presents challenges but could produce promising pest control opportunities. | 1 | Biochemistry |
Source: [http://www.asbmb.org/awards/cohn/ American Society for Biochemistry and Molecular Biology]
*2020 - Carol Fierke
*2019 - Angela Gronenborn
*2018 – Leemor Joshua-Tor
*2017 – Wei Yang
*2016 – Eva Nogales
*2015 – Judith P. Klinman
*2014 – Lila M. Gierasch
*2013 – Jennifer A. Doudna | 1 | Biochemistry |
At the neurological level, behavior can be inferred based on hormone concentration, which in turn are influenced by hormone-release patterns; the numbers and locations of hormone receptors; and the efficiency of hormone receptors for those involved in gene transcription. Hormone concentration does not incite behavior, as that would undermine other external stimuli; however, it influences the system by increasing the probability of a certain event to occur.
Not only can hormones influence behavior, but also behavior and the environment can influence hormone concentration. Thus, a feedback loop is formed, meaning behavior can affect hormone concentration, which in turn can affect behavior, which in turn can affect hormone concentration, and so on. For example, hormone-behavior feedback loops are essential in providing constancy to episodic hormone secretion, as the behaviors affected by episodically secreted hormones directly prevent the continuous release of said hormones.
Three broad stages of reasoning may be used to determine if a specific hormone-behavior interaction is present within a system:
* The frequency of occurrence of a hormonally dependent behavior should correspond to that of its hormonal source.
* A hormonally dependent behavior is not expected if the hormonal source (or its types of action) is non-existent.
* The reintroduction of a missing behaviorally dependent hormonal source (or its types of action) is expected to bring back the absent behavior. | 1 | Biochemistry |
An expression vector must have elements necessary for gene expression. These may include a promoter, the correct translation initiation sequence such as a ribosomal binding site and start codon, a termination codon, and a transcription termination sequence. There are differences in the machinery for protein synthesis between prokaryotes and eukaryotes, therefore the expression vectors must have the elements for expression that are appropriate for the chosen host. For example, prokaryotes expression vectors would have a Shine-Dalgarno sequence at its translation initiation site for the binding of ribosomes, while eukaryotes expression vectors would contain the Kozak consensus sequence.
The promoter initiates the transcription and is therefore the point of control for the expression of the cloned gene. The promoters used in expression vector are normally inducible, meaning that protein synthesis is only initiated when required by the introduction of an inducer such as IPTG. Gene expression however may also be constitutive (i.e. protein is constantly expressed) in some expression vectors. Low level of constitutive protein synthesis may occur even in expression vectors with tightly controlled promoters. | 1 | Biochemistry |
Chloropolymers are macromolecules synthesized from alkenes in which one or more hydrogens of the polymer were replaced by chlorine. A common example of a chloropolymer is polyvinyl chloride (PVC) and poly(dichlorophosphazene) which has a polymer formula of (PNCl), the precursor of which is hexachlorophosphazene, which itself has been called chloropolymer. | 7 | Physical Chemistry |
Lactic acid fermentation is a metabolic process by which glucose or other six-carbon sugars (also, disaccharides of six-carbon sugars, e.g. sucrose or lactose) are converted into cellular energy and the metabolite lactate, which is lactic acid in solution. It is an anaerobic fermentation reaction that occurs in some bacteria and animal cells, such as muscle cells.
If oxygen is present in the cell, many organisms will bypass fermentation and undergo cellular respiration; however, facultative anaerobic organisms will both ferment and undergo respiration in the presence of oxygen. Sometimes even when oxygen is present and aerobic metabolism is happening in the mitochondria, if pyruvate is building up faster than it can be metabolized, the fermentation will happen anyway.
Lactate dehydrogenase catalyzes the interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD.
In homolactic fermentation, one molecule of glucose is ultimately converted to two molecules of lactic acid. Heterolactic fermentation, by contrast, yields carbon dioxide and ethanol in addition to lactic acid, in a process called the phosphoketolase pathway. | 1 | Biochemistry |
For species A:
For species B:
:Here the first (positive) term represents the formation of B by the first step , whose rate depends on the initial reactant A. The second (negative) term represents the consumption of B by the second step , whose rate depends on B as the reactant in that step.
For species C: | 7 | Physical Chemistry |
Several Bioconductor packages, for the R software, provide the facility for creating MA plots. These include affy (ma.plot, mva.pairs), limma (plotMA), marray (maPlot), and edgeR(maPlot)
Similar "RA" plots can be generated using the raPlot function in the caroline [https://cran.r-project.org/ CRAN] R package.
An interactive MA plot to filter genes by M, A and p-values, search by names or with a lasso, and save selected genes, is available as an R-Shiny code [https://github.com/alisheharyar/Enhanced_MA_Plot Enhanced-MA-Plot]. | 1 | Biochemistry |
* Office of the Administrator (also CDC Director)
* Office of the Director (also NCEH (National Center for Environmental Health) head)
** Office of Communications
** Office of Science
** Office of Management and Analytics
** Office of Policy, Partnerships, and Planning
* Office of the Associate Director
** Office of Innovation and Analytics (OIA)
** Office of Community Health Hazard Assessment (OCHHA)
** Office of Capacity Development and Applied Prevention Science (OCDAPS)
The Office of the Director (of ASTDR) is joint with that of NCEH; it also contains seven functional units, five offices, five program-specific divisions to support and implement six program areas:
* [https://wwwn.cdc.gov/TSP/PHA/PHALanding.aspx Public Health Assessments]
* [https://www.atsdr.cdc.gov/toxprofiledocs/index.html Toxicological Profiles]
* [https://www.atsdr.cdc.gov/emergencyresponse/index.html Emergency Response]
* [https://www.atsdr.cdc.gov/dataresources.html Exposure and Disease Registries]
* [https://www.atsdr.cdc.gov/dataresources.html Health Effects Research]
* [https://www.atsdr.cdc.gov/environmentaleducation.html Health Education] | 1 | Biochemistry |
Although lichens had been recognized as organisms for quite some time, it was not until 1867, when Swiss botanist Simon Schwendener proposed his dual theory of lichens, that lichens are a combination of fungi with algae or cyanobacteria, whereby the true nature of the lichen association began to emerge. Schwendeners hypothesis, which at the time lacked experimental evidence, arose from his extensive analysis of the anatomy and development in lichens, algae, and fungi using a light microscope. Many of the leading lichenologists at the time, such as James Crombie and Nylander, rejected Schwendeners hypothesis because the consensus was that all living organisms were autonomous.
Other prominent biologists, such as Heinrich Anton de Bary, Albert Bernhard Frank, Beatrix Potter, Melchior Treub and Hermann Hellriegel, were not so quick to reject Schwendeners ideas and the concept soon spread into other areas of study, such as microbial, plant, animal and human pathogens. When the complex relationships between pathogenic microorganisms and their hosts were finally identified, Schwendeners hypothesis began to gain popularity. Further experimental proof of the dual nature of lichens was obtained when Eugen Thomas published his results in 1939 on the first successful re-synthesis experiment.
In the 2010s, a new facet of the fungi–algae partnership was discovered. Toby Spribille and colleagues found that many types of lichen that were long thought to be ascomycete–algae pairs were actually ascomycete–basidiomycete–algae trios The third symbiotic partner in many lichens is a basidiomycete yeast. | 2 | Environmental Chemistry |
Photoelectrochemistry is a subfield of study within physical chemistry concerned with the interaction of light with electrochemical systems. It is an active domain of investigation. One of the pioneers of this field of electrochemistry was the German electrochemist Heinz Gerischer. The interest in this domain is high in the context of development of renewable energy conversion and storage technology. | 5 | Photochemistry |
In a highly basic solution, phenolphthalein's slow change from pink to colorless as it is converted to its Ph(OH) form is used in chemistry classes for the study of reaction kinetics. | 3 | Analytical Chemistry |
Evaluating an individuals rate of bone turnover, termed bone remodeling, directly may be important in assessing his or her potential nonsurgical treatment response as well as evaluating his or her risk of developing complications during healing following surgical intervention. To determine an individuals rate of bone turnover, numerous biomarkers are available in the body fluids that can be correlated to this rate, and one such biomarker is NTX.
However, while NTX does fluctuate in a very sensitive manner in line with bone resorption patterns, they are not very specific, in that they may vary spontaneously without physiologic intervention. For example, NTX levels may drop by 50% from day to day with no treatment, thus, making NTX levels unconvincing evidence of treatment effect.
Conversely, the serum CTX biomarker, described in 2000 by Rosen, appears to be a much more effective and valuable indicator of bone resorption rate. | 1 | Biochemistry |
The Downdraft skimmer is both a proprietary skimmer design and a style of protein skimmer that injects water under high pressure into tubes that have a foam or bubble generating mechanism and carry the air/water mixture down into the skimmer and into a separate chamber. The proprietary design is protected in the United States with patents and commercial skimmer products in the US are limited to that single company. Their design uses one or more tubes with plastic media such as bio balls inside to mix water under high pressure and air in the body of the skimmer resulting in foam that collects protein waste in a collection cup. This was one of the earlier high performance protein skimmer designs and large models were produced that saw success in large and public aquariums. | 3 | Analytical Chemistry |
Major changes in comparison to the previous GOSAT are:
* Improved measurement precision.
* FTS-2 can also monitor carbon monoxide (CO) and nitrogen dioxide (NO).
* FTS-2 can select cloud-free point automatically for observation.
* While GOSATs CAI was observing nadir view, GOSAT-2s CAI-2 observes forward (20 degree) and backward (20 degree) simultaneously.
* CAI-2 can also monitor PM2.5 and black carbon. | 2 | Environmental Chemistry |
Much effort has been placed on understanding iron–carbon alloy system, which includes steels and cast irons. Plain carbon steels (those that contain essentially only carbon as an alloying element) are used in low-cost, high-strength applications, where neither weight nor corrosion are a major concern. Cast irons, including ductile iron, are also part of the iron-carbon system. Iron-Manganese-Chromium alloys (Hadfield-type steels) are also used in non-magnetic applications such as directional drilling.
Other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. These metals are most often used as alloys with the noted exception of silicon, which is not a metal. Other forms include:
* Stainless steel, particularly Austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important.
* Aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications.
* Copper-nickel alloys (such as Monel) are used in highly corrosive environments and for non-magnetic applications.
* Nickel-based superalloys like Inconel are used in high-temperature applications such as gas turbines, turbochargers, pressure vessels, and heat exchangers.
* For extremely high temperatures, single crystal alloys are used to minimize creep. In modern electronics, high purity single crystal silicon is essential for metal-oxide-silicon transistors (MOS) and integrated circuits. | 8 | Metallurgy |
A heavily deformed metal contains a huge number of dislocations predominantly caught up in tangles or forests. Dislocation motion is relatively difficult in a metal with a low stacking fault energy and so the dislocation distribution after deformation is largely random. In contrast, metals with moderate to high stacking fault energy, e.g. aluminum, tend to form a cellular structure where the cell walls consist of rough tangles of dislocations. The interiors of the cells have a correspondingly reduced dislocation density. | 8 | Metallurgy |
The typical composition of KREEP includes about one percent, by mass, of potassium and phosphorus oxides, 20 to 25 parts per million of rubidium, and a concentration of the element lanthanum that is 300 to 350 times the concentrations found in carbonaceous chondrites. Most of potassium, phosphorus and rare-earth elements in KREEP basalts are incorporated in the grains of the phosphate minerals apatite and merrillite. | 9 | Geochemistry |
Deoxyribonucleic acid (DNA) is a nucleic acid containing the genetic instructions used in the development and functioning of all known living organisms. The chemical DNA was discovered in 1869, but its role in genetic inheritance was not demonstrated until 1943. The DNA segments that carry this genetic information are called genes. Other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. Along with RNA and proteins, DNA is one of the three major macromolecules that are essential for all known forms of life.
DNA consists of two long polymers of monomer units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands are oriented in opposite directions to each other and are, therefore, antiparallel. Attached to each sugar is one of four types of molecules called nucleobases (informally, bases). It is the sequence of these four nucleobases along the backbone that encodes genetic information. This information specifies the sequence of the amino acids within proteins according to the genetic code. The code is read by copying stretches of DNA into the related nucleic acid RNA in a process called transcription.
Within cells, DNA is organized into long sequences called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, providing each cell its own complete set of chromosomes. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. | 1 | Biochemistry |
The simplest polymetallic system, the [FeS] cluster, is constituted by two iron ions bridged by two sulfide ions and coordinated by four cysteinyl ligands (in FeS ferredoxins) or by two cysteines and two histidines (in Rieske proteins). The oxidized proteins contain two Fe ions, whereas the reduced proteins contain one Fe and one Fe ion. These species exist in two oxidation states, (Fe) and FeFe. CDGSH iron sulfur domain is also associated with 2Fe-2S clusters.
The Rieske proteins contain Fe–S clusters that coordinate as a 2Fe–2S structure and can be found in the membrane bound cytochrome bc1 complex III in the mitochondria of eukaryotes and bacteria. They are also a part of the proteins of the chloroplast such as the cytochrome bf complex in photosynthetic organisms. These photosynthetic organisms include plants, green algae, and cyanobacteria, the bacterial precursor to chloroplasts. Both are part of the electron transport chain of their respective organisms which is a crucial step in the energy harvesting for many organisms. | 7 | Physical Chemistry |
*5.B.1 The Phagocyte (gp91phox) NADPH Oxidase Family
*5.B.2 The Eukaryotic Cytochrome b561 (Cytb561) Family
*5.B.3 The Geobacter Nanowire Electron Transfer (G-NET) Family
*5.B.4 The Plant Photosystem I Supercomplex (PSI) Family
*5.B.5 The Extracellular Metal Oxido-Reductase (EMOR) Family
*5.B.6 The Transmembrane Epithelial Antigen Protein-3 Ferric Reductase (STEAP) Family
*5.B.7 The YedZ (YedZ) Family
*5.B.8 The Trans-Outer Membrane Electron Transfer Porin/Cytochrome Complex (ET-PCC) Family
*5.B.9 The Porin-Cytochrome c (Cyc2) Family | 1 | Biochemistry |
Pedocal is a subdivision of the zonal soil order. It is a class of soil which forms in semiarid and arid regions. It is rich in calcium carbonate and has low soil organic matter. With only a thin A horizon (topsoil), and intermittent precipitation calcite, other soluble minerals ordinarily removed by water may build up in the B horizon (subsoil) forming a cemented layer known as caliche. It is not used in the current United States system of soil classification but the term commonly shows up in college geology texts. | 9 | Geochemistry |
Boyle's law states that:
The concept can be represented with these formulae:
*, meaning "Volume is inversely proportional to Pressure", or
*, meaning "Pressure is inversely proportional to Volume", or
*, or
where is the pressure, is the volume of a gas, and is the constant in this equation (and is not the same as the proportionality constants in the other equations). | 7 | Physical Chemistry |
When laser cooling of atoms was first proposed in 1975, the only cooling mechanism considered was Doppler cooling. As such the limit on the temperature was predicted to be the Doppler limit:
Here k is the Boltzmann constant, T is the temperature of the atoms, and Γ is the inverse of the excited state's radiative lifetime.
Early experiments seemed to be in agreement with this limit. However, in 1988 experiments began to report temperatures below the Doppler limit. These observations would take the theory of PG cooling to explain. | 7 | Physical Chemistry |
Gas chromatography-mass spectrometry (GC-MS) is a two-dimensional chromatography technique that combines the separation technique of gas chromatography with the identification technique of mass spectrometry. GC-MS is the single most important analytical tool for the analysis of volatile and semi-volatile organic compounds in complex mixtures. It works by first injecting the sample into the GC inlet where it is vaporized and pushed through a column by a carrier gas, typically helium. The analytes in the sample are separated based upon their interaction with the coating of the column, or the stationary phase, and the carrier gas, or the mobile phase. The compounds eluted from the column are converted into ions via electron impact (EI) or chemical ionization (CI) before traveling through the mass analyzer. The mass analyzer serves to separate the ions on a mass-to-charge basis. Popular choices perform the same function but differ in the way that they accomplish the separation. The analyzers typically used with GC-MS are the time-of-flight mass analyzer and the quadrupole mass analyzer. After leaving the mass analyzer, the analytes reach the detector and produce a signal that is read by a computer and used to create a gas chromatogram and mass spectrum. Sometimes GC-MS utilizes two gas chromatographers in particularly complex samples to obtain considerable separation power and be able to unambiguously assign the specific species to the appropriate peaks in a technique known as GCxGC-(MS). Ultimately, GC-MS is a technique utilized in many analytical laboratories and is a very effective and adaptable analytical tool. | 3 | Analytical Chemistry |
The absorbance pattern responsible for the red color of anthocyanins may be complementary to that of green chlorophyll in photosynthetically active tissues such as young Quercus coccifera leaves. It may protect the leaves from attacks by herbivores that may be attracted by green color. | 3 | Analytical Chemistry |
Ty5 is a relative of the Retroviridae family of retroviruses, which includes the human pathogen HIV. Ty5 is a tractable system in which to study the biology of retrovirus integration. | 1 | Biochemistry |
• DIN EN ISO 6988 Metallic and other inorganic coatings - Test with sulfur dioxide with general moisture condensation, March 1997.
• DIN 50018 testing in an alternating condensation climate with an atmosphere containing sulfur dioxide, June 1997.
• The importance of corrosion test procedures with special consideration of the SO test according to DIN 50018, Wilhelm Kesternich, published in Materials and Corrosion Volume 16, Issue 3, pages 193-201, March 1965. | 8 | Metallurgy |
Miraculin was first sequenced in 1989 and was found to be a 24.6 kilodalton glycoprotein consisting of 191 amino acids and 13.9% by weight of various sugars.
The sugars consist of a total of 3.4 kDa, composed of a molar ratio of glucosamine (31%), mannose (30%), fucose (22%), xylose (10%), and galactose (7%).
The native state of miraculin is a tetramer consisting of two dimers, each held together by a disulfide bridge. Both tetramer miraculin and native dimer miraculin in its crude state have the taste-modifying activity of turning sour tastes into sweet tastes. Miraculin belongs to the Kunitz STI protease inhibitor family. | 1 | Biochemistry |
The classical acetoacetatic ester synthesis utilizes the 1:1 conjugate base. Ethyl acetoacetate is however diprotic:
:CHC(O)CHCOEt + NaH → CHC(O)CH(Na)COEt + H
:CHC(O)CH(Na)COEt + BuLi → LiCHC(O)CH(Na)COEt + BuH
The dianion (i.e., LiCHC(O)CH(Na)COEt) adds electrophile to the terminal carbon as depicted in the following simplified form:
:LiCHC(O)CH(Na)COEt + RX → RCHC(O)CH(Na)COEt + LiX | 0 | Organic Chemistry |
The trematode mitochondrial code (translation table 21) is a genetic code found in the mitochondria of Trematoda. | 1 | Biochemistry |
Numerous desorber types are available today. Some of the more common types are listed below.
* Indirect fired rotary
* Direct fired rotary
* Heated screw (hot oil, molten salt, electric)
* Infrared
* Microwave
Most indirect fired rotary systems use an inclined rotating metallic cylinder to heat the feed material. The heat transfer mechanism is usually conduction through the cylinder wall. In this type of system neither the flame nor the products of combustion can contact the feed solids or the offgas. Think of it as a rotating pipe inside a furnace with both ends sticking outside of the furnace. The cylinder for full-scale transportable systems is typically five to eight feet in diameter with heated lengths ranging from twenty to fifty feet. With a carbon steel shell, the maximum solids temperature is around 1,000 °F, while temperatures of 1,800 °F with special alloy cylinders are attainable. Total residence time in this type of desorber normally ranges from 30 to 120 minutes. Treatment capacities can range from 2 to 30 tons per hour for transportable units.
Direct-fired rotary desorbers have been used extensively over the years for petroleum contaminated soils and soils contaminated with Resource Conservation and Recovery Act hazardous wastes as defined by the United States Environmental Protection Agency. A 1992 paper on treating petroleum contaminated soils estimated that between 20 and 30 contractors have 40 to 60 rotary dryer systems available. Today, it is probably closer to 6 to 10 contractors with 15 to 20 portable systems commercially available. The majority of these systems utilize a secondary combustion chamber (afterburner) or catalytic oxidizer to thermally destroy the volatilized organics. A few of these systems also have a quench and scrubber after the oxidizer which allows them to treat soils containing chlorinated organics such as solvents and pesticides. The desorbing cylinder for full-scale transportable systems is typically four to ten feet in diameter with heated lengths ranging from twenty to fifty feet. The maximum practical solids temperature for these systems is around 750 to 900 °F depending on the material of construction of the cylinder. Total residence time in this type of desorber normally ranges from 3 to 15 minutes. Treatment capacities can range from 6 to over 100 tons per hour for transportable units.
Heated screw systems are also an indirect heated system. Typically they use a jacketed trough with a double auger that intermeshes. The augers themselves frequently contain passages for the heating medium to increase the heat transfer surface area. Some systems use electric resistance heaters instead of a heat transfer media and may employ a single auger in each housing. The augers can range from 12 to 36 inches in diameter for full-scale systems, with lengths up to 20 feet. The auger/trough assemblies can be connected in parallel and/or series to increase throughput. Full scale capabilities up to 4 tons per hour have been demonstrated. This type of system has been most successful treating refinery wastes.
In the early days, there was a continuous infrared system that is no longer in common use. In theory, microwaves would be an excellent technical choice since uniform and accurately controlled heating can be achieved with no heat transfer surface fouling problems. One can only guess that capital and/or energy costs have prevented the development of a microwave thermal desorber at the commercial scale. | 2 | Environmental Chemistry |
Adhesion GPCRs are found in fungi. They are believed to have evolved from the cAMP receptor family, arising approximately 1275 million years ago before the split of Unikonts from a common ancestor. Several fungi have novel adhesion GPCRs that have both short, 2–66 amino acid residues, and long, 312–4202 amino acid residues. Analysis of fungi showed that there were no secretin receptor family GPCRs, which suggests that they evolved from adhesion GPCRs in a later organism.
Genome analysis of the Teleost Takifugu rubripes has revealed that it has only two adhesion GPCRs that showed homology to Ig-hepta/GPR116. While the Fugu genome is relatively compact and limited with the number of adhesion GPCRs, Tetraodon nigroviridis, another species of puffer fish, has considerably more, totaling 29 adhesion GPCRs. | 1 | Biochemistry |
Johannes Wislicenus (; 24 June 18355 December 1902) was a German chemist, most famous for his work in early stereochemistry. | 4 | Stereochemistry |
Normal modes are generated in the Earth from long wavelength seismic waves from large earthquakes interfering to form standing waves.
For an elastic, isotropic, homogeneous sphere, spheroidal, toroidal and radial (or breathing) modes arise. Spheroidal modes only involve P and SV waves (like Rayleigh waves) and depend on overtone number n and angular order l but have degeneracy of azimuthal order m. Increasing l concentrates fundamental branch closer to surface and at large l this tends to Rayleigh waves. Toroidal modes only involve SH waves (like Love waves) and do not exist in fluid outer core. Radial modes are just a subset of spheroidal modes with l=0. The degeneracy does not exist on Earth as it is broken by rotation, ellipticity and 3D heterogeneous velocity and density structure.
It may be assumed that each mode can be isolated, the self-coupling approximation, or that many modes close in frequency resonate, the cross-coupling approximation. Self-coupling will solely change the phase velocity and not the number of waves around a great circle, resulting in a stretching or shrinking of standing wave pattern. Modal cross-coupling occurs due to the rotation of the Earth, from aspherical elastic structure, or due to Earth's ellipticity and leads to a mixing of fundamental spheroidal and toroidal modes. | 7 | Physical Chemistry |
Sperm banks make information available about the sperm donors whose donations they hold to enable customers to select the donor whose sperm they wish to use. This information is often available by way of an online catalog. Subscription fees to be able to view the sperm donor through California Cryobank, for example, start at $145. This cost could potentially be a barrier for many on limited income and may not have discretionary income to spend on sperm donor services.
A sperm bank will also usually have facilities to help customers to make their choice and they will be able to advise on the suitability of donors for individual donors and their partners.
Where the recipient has a partner, they may prefer to use sperm from a donor whose physical features are similar to those of their partner if they have one. In some cases, the choice of a donor with the correct blood group will be paramount, with particular considerations for the protection of recipients with negative blood groups. If a surrogate is to be used, such as where the customer is not intending to carry the child, considerations about their blood group etc. will also need to be taken into account. Similar considerations will apply where both partners in a lesbian couple intend to have a child using the same donor.
Information made available by a sperm bank will usually include the race, height, weight, blood group, health and eye color of the donor. Sometimes information about the donors age, family history and educational achievements will also be given. Some sperm banks make a personal profile of a donor available and occasionally more information may be purchased about a donor, either in the form of a DVD or in written form. Catalogs usually state whether samples supplied by a particular donor have already given rise to pregnancies, but this is not necessarily a guide to the fecundity of the sperm since a donor may not have been in the program long enough for any pregnancies to have been recorded. The donors educational qualification is also taken into account when choosing a donor.
If an individual intends to have more than one child, they may wish to have the additional child or children by the same donor. Sperm banks will usually advise whether sufficient stocks of sperm are available from a particular donor for subsequent pregnancies, and they normally have facilities available so that the woman may purchase and store additional vials from that donor on payment of an appropriate fee. These will be stored until required for subsequent pregnancies or they may be on-sold if they become surplus to the woman's requirements.
The catalogue will also state whether samples of sperm are available for ICI, IUI, or IVF use. | 1 | Biochemistry |
Flakes and shatter cracks are internal fissures seen in large forgings. Hydrogen picked up during melting and casting segregates at internal voids and discontinuities and produces these defects during forging. Fish-eyes are bright patches named for their appearance seen on fracture surfaces, generally of weldments. Hydrogen enters the metal during fusion-welding and produces this defect during subsequent stressing. Steel containment vessels exposed to extremely high hydrogen pressures develop small fissures or micro perforations through which fluids may leak. | 8 | Metallurgy |
Phytomining, sometimes called agromining, is the concept of extracting heavy metals from the soil using plants. Specifically, phytomining is for the purpose of economic gain. The approach exploits the existence of hyperaccumulators, proteins or compounds secreted by plants to bind certain metal ions. These extracted ores are called bio-ores. The approach has little practical value ("its commercial viability is limited") because it is slow and inefficient. | 2 | Environmental Chemistry |
Niyazi Serdar Sarıçiftçi (born 1961 in Konya, Turkey) is a Turkish-Austrian physicist. He is professor for physical chemistry at the Johannes Kepler University (JKU) Linz. There, he leads the Institut for Physical Chemistry as well as the Institut for Organic Solar Cells (LIOS). | 7 | Physical Chemistry |
A solar hydrogen panel is a device for artificial photosynthesis that produces photohydrogen directly from sunlight and water vapor utilizing photocatalytic water splitting and thus bypasses the conversion losses of the classical solar–hydrogen energy cycle where solar power is first harvested with solar panels and only then converted to hydrogen with electrolysis plants.
In the solar hydrogen panel the hydrogen and oxygen evolution reactions are performed in the gas phase in cathode and anode compartments separated by a membrane. Anion exchange membranes provide an alkaline environment enabling the use of earth abundant materials as electrocatalysts.
Scientists at KU Leuven's Center for Surface Chemistry and Catalysis in Leuven, Belgium have managed to produce a solar hydrogen panel, which is able to directly convert no less than 15 per cent of sunlight into hydrogen gas, which according to them is a world record. According to IEEE Spectrum in 2019 this is a giant leap from 0.1% efficiency 10 years earlier. On 19 February 2021, exactly 2 years after their original reveal of the panel, KU Leuven launched the Solhyd Project and website.
Solar hydrogen panels seem very promising for the green hydrogen economy as this method of producing hydrogen fuel emits no Carbon dioxide|, unlike steam reforming from natural gas and then utilizing the water-gas shift reaction to produce hydrogen. As of 2015 the majority of worldwide was produced via steam methane reforming, at prices down to $1 / kg . In 2019 the IEA reported that electrolysis of water, another green way to produce hydrogen, accounts for less than 0.1% of global hydrogen production.
The power-to-gas process of producing methane from hydrogen and CO or is called methanation and produces substitute natural gas. Due to the challenges in hydrogen storage, other methods of energy storage and delivery may be useful, despite the conversion losses in power-to-gas. | 5 | Photochemistry |
Literature references (chronological) to case studies after 2000:
Older examples of application can be found in:
#Salinity in the Nile Delta
#Integration of irrigation and drainage management | 9 | Geochemistry |
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