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Polarizational bremsstrahlung (sometimes referred to as "atomic bremsstrahlung") is the radiation emitted by the target's atomic electrons as the target atom is polarized by the Coulomb field of the incident charged particle. Polarizational bremsstrahlung contributions to the total bremsstrahlung spectrum have been observed in experiments involving relatively massive incident particles, resonance processes, and free atoms. However, there is still some debate as to whether or not there are significant polarizational bremsstrahlung contributions in experiments involving fast electrons incident on solid targets.
It is worth noting that the term "polarizational" is not meant to imply that the emitted bremsstrahlung is polarized. Also, the angular distribution of polarizational bremsstrahlung is theoretically quite different than ordinary bremsstrahlung. | 7 | Physical Chemistry |
There are two major sources of foreign DNA for molecular cloning is genomic DNA (gDNA) and complementary (or copy) DNA (cDNA). cDNA molecules are DNA copies of mRNA molecules, produced in vitro by action of the enzyme reverse transcriptase. In order to obtain the cDNA for a specific gene, it is first necessary to construct a cDNA library. | 1 | Biochemistry |
In the United States, vancomycin is approved by the Food and Drug Administration for either intravenous or oral administration. | 0 | Organic Chemistry |
Yulia Sister and her family repatriated to Israel in 1990. In 1992–1993 she served as a senior researcher of the Department of Inorganic and Analytical Chemistry at the Hebrew University of Jerusalem, and then she was engaged in the topics related to the analysis of biological objects at the Tel Aviv University. During these years, along with her career in chemistry, Yulia Sister became deeply interested in the study of Russian-Jewish culture.
In 1991 Sister began to write for the Shorter Jewish Encyclopedia (SJE) as a non-staff editor. She served as a research fellow covering the field of history of science and wrote about 90 articles for the encyclopedia. Yulia is the author of the articles "Chemistry" (jointly with P. Smorodnitsky), "Veniamin Levich", "Frederick Reines", "Moise Haissinsky", "Yuri Golfand" and many others.
Yulia Sister's activities in the House of Scientists and Experts of Rehovot started in 1991. Within this forum she organizes lectures, seminars and scientific conferences. She leads the scientific seminars of the House of Scientists that are regularly held at the Weizmann Institute of Science. In 2008, and then in 2014 she organized conferences devoted to the Bilu movement and to the First Aliyah. She also maintains friendly contacts with foreign colleagues, such as the Club of Russian-speaking scientists of Massachusetts.
In 1997 Mikhail Parkhomovsky initiated creation of the Research Center for Russian Jewry Abroad, which aimed to collect and publish information on Jews, who emigrated from the Russian Empire, Soviet Union or Post-Soviet states and made a contribution to world civilization. Parkhomovsky became the Scientific Director and Chief Editor and Yulia Sister Director General of the Center. From 2012 the Center changed its name to Research Centre for Russian Jews abroad and in Israel (Erzi). The collection, processing and publication of materials related to Russian Jewry are organized by Sister. By 2015 the Center published about 30 volumes of collections, including books devoted to Jews in England, France, U.S., Israel and other countries. In addition to her executive functions, Sister is a frequent editor and author of the Center's collective monographs. She is the editor of the 17th volume ("Let Us Build the Walls of Jerusalem. Book 3"), a coeditor of the 11th volume ("Let Us Build the Walls of Jerusalem. Book 1") and of the monograph "Israel, Russian Roots", and a participant in the editing of the 10th volume.
Sister's activities include the organization of seminars and conferences. The following examples are a small sampling of the events organized by the Director General of the Center. In 1999 she was the coordinator of the conference dedicated to the 50th anniversary of the Weizmann Institute in Rehovot. Together with Prof. Aron Cherniak she published a detailed report on the conference and some of its materials in the 8th volume of the "Russian Jewry Abroad" series. In 2003 Sister led a conference in Kiryat Ekron, in which she introduced the contribution of the Russian Aliyah to Israeli science, culture and education. More than 200 scientists from all over the country participated at the tenth-anniversary of the Center conference in 2007. The 2012 conference was devoted to the 130th anniversary of the First Aliyah and the event was covered by the House of Scientists of Rehovot.
Yulia Sister lives with her family in Kiryat Ekron. Her husband, Boris (Bezalel) Iosifovich Gendler, is a physician with an extensive experience in medical practice and education. After his repatriation from Kishinev Bezalel Gendler worked as a doctor in one of the Israeli hospitals and published several articles, some of them in collaboration with Yulia. | 3 | Analytical Chemistry |
Bulk gold exhibits a face-centered cubic (fcc) structure. As gold particle size decreases the fcc structure of gold transforms into a centered-icosahedral structure illustrated by . It can be shown that the fcc structure can be extended by a half unit cell in order to make it look like a cuboctahedral structure. The cuboctahedral structure maintains the cubic-closed pack and symmetry of fcc. This can be thought of as redefining the unit cell into a more complicated cell. Each edge of the cuboctahedron represents a peripheral Au–Au bond. The cuboctahedron has 24 edges while the icosahedron has 30 edges; the transition from cuboctahedron to icosahedron is favored since the increase in bonds contributes to the overall stability of the icosahedron structure.
The centered icosahedral cluster is the basis of constructing large gold nanoclusters. is the endpoint of atom-by-atom growth. In other words, starting with one gold atom up to , each successful cluster is created by adding one additional atom. The icosahedral motif is found in many gold clusters through vertex sharing ( and ), face-fusion ( and ), and interpenetrating biicosahedrons (, , , and ). Large gold nanoclusters can essentially be reduced to a series of icosahedrons connecting, overlapping, and/or surrounding each other. The crystallization process of gold nanoclusters involves the formation of surface segments that grow towards the center of the cluster. The cluster assumes an icosahedral structure because of the associated surface energy reduction. | 7 | Physical Chemistry |
In addition, channeling of ions can also be used to analyze a crystalline sample for lattice damage. If atoms within the target are displaced from their crystalline lattice site, this will result in a higher backscattering yield in relation to a perfect crystal. By comparing the spectrum from a sample being analyzed to that from a perfect crystal, and that obtained at a random (non-channeling) orientation (representative of a spectrum from an amorphous sample), it is possible to determine the extent of crystalline damage in terms of a fraction of displaced atoms. Multiplying this fraction by the density of the material when amorphous then also gives an estimate for the concentration of displaced atoms. The energy at which the increased backscattering occurs can also be used to determine the depth at which the displaced atoms are and a defect depth profile can be built up as a result. | 7 | Physical Chemistry |
Planck held that all "natural processes" (meaning, in present-day terminology, a thermodynamic operation followed by a thermodynamic process) are irreversible and proceed in the sense of increase of entropy sum. In these terms, it would be by thermodynamic operations that, if he could exist, Maxwells demon would conduct unnatural affairs, which include transitions in the sense away from thermodynamic equilibrium. They are physically theoretically conceivable up to a point, but are not natural processes in Plancks sense. The reason is that ordinary thermodynamic operations are conducted in total ignorance of the very kinds of microscopic information that is essential to the efforts of Maxwell's demon. | 7 | Physical Chemistry |
In vitro fertilisation (IVF) is a process of fertilisation where an egg is combined with sperm in vitro ("in glass"). The process involves monitoring and stimulating a womans ovulatory process, removing an ovum or ova (egg or eggs) from their ovaries and letting a mans sperm fertilise them in a culture medium in a laboratory. After the fertilised egg (zygote) undergoes embryo culture for 2–6 days, it is transferred by catheter into the uterus, with the intention of establishing a successful pregnancy.
IVF is a type of assisted reproductive technology used for infertility treatment, gestational surrogacy, and, in combination with pre-implantation genetic testing, avoiding transmission of genetic conditions. A fertilised egg from a donor may implant into a surrogate's uterus, and the resulting child is genetically unrelated to the surrogate. Some countries have banned or otherwise regulate the availability of IVF treatment, giving rise to fertility tourism. Restrictions on the availability of IVF include costs and age, in order for a person to carry a healthy pregnancy to term. Children born through IVF are colloquially called test tube babies.
In July 1978, Louise Brown was the first child successfully born after her mother received IVF treatment. Brown was born as a result of natural-cycle IVF, where no stimulation was made. The procedure took place at Dr Kershaws Cottage Hospital (now Dr Kershaws Hospice) in Royton, Oldham, England. Robert Edwards was awarded the Nobel Prize in Physiology or Medicine in 2010. The physiologist co-developed the treatment together with Patrick Steptoe and embryologist Jean Purdy but the latter two were not eligible for consideration as they had died and the Nobel Prize is not awarded posthumously.
Assisted by egg donation and IVF, there are many women who may be past their reproductive years, have infertile partners, have idiopathic female-fertility issues, or have reached menopause, that can still become pregnant. After the IVF treatment, some couples get pregnant without any fertility treatments. In 2023, it was estimated that twelve million children had been born worldwide using IVF and other assisted reproduction techniques. A 2019 study that explores 10 adjuncts with IVF (screening hysteroscopy, DHEA, testosterone, GH, aspirin, heparin, antioxidants, seminal plasma and PRP) suggests that until more evidence is done to show that these adjuncts are safe and effective, they should be avoided. | 1 | Biochemistry |
Several pathways exist for the halogenation of organic compounds, including free radical halogenation, ketone halogenation, electrophilic halogenation, and halogen addition reaction. The nature of the substrate determines the pathway. The facility of halogenation is influenced by the halogen. Fluorine and chlorine are more electrophilic and are more aggressive halogenating agents. Bromine is a weaker halogenating agent than both fluorine and chlorine, while iodine is the least reactive of them all. The facility of dehydrohalogenation follows the reverse trend: iodine is most easily removed from organic compounds, and organofluorine compounds are highly stable. | 0 | Organic Chemistry |
Due to a sustained drug release, a prolonged therapeutic level of drugs exhibiting a short elimination half-life can be maintained. Consequently the frequency of dosing can be reduced contributing to an improved compliance. The release of drugs out of polymeric carrier systems can be controlled by a simple diffusion process. So far the efficacy of such delivery systems, however, was limited by a too rapid disintegration and/or erosion of the polymeric network. By using thiolated polymers this essential shortcoming can be overcome. Because of the formation of inter- and intrachain disulfide bonds during the swelling process, the stability of the polymeric drug carrier matrix is strongly improved. Hence, a controlled drug release for numerous hours is guaranteed. There are numerous drug delivery systems making use of this technology. | 7 | Physical Chemistry |
Ultrafast X-ray diffraction (time-resolved X-ray diffraction) can surpass ultrashortpulse visible techniques, which are limited to detecting structures on the level of valence and free electrons. Ultrashort pulse X-ray techniques are able to resolve atomic scales, where dynamic structural changes and reactions occur in the interior of a material. | 7 | Physical Chemistry |
The extraction cell is filled with the solid sample to be examined and placed in a temperature-controllable oven. After adding the solvent, the cell is heated at constant pressure (adjustable between 0.3 and 20 MPa) up to a maximum temperature of 200°C and kept at constant conditions for a while so that equilibrium can be established. The extract is then transferred to a sample tube. A sample often goes through several extraction cycles. Finally, the extraction cell is rinsed with solvent, the rinsing valve is opened and the cell and all lines are rinsed with nitrogen and the apparatus is prepared for further extractions. | 3 | Analytical Chemistry |
The electrochemical equivalent of a substance is the mass of the substance deposited to one of the electrodes when a current of 1 ampere is passed for 1 second, i.e. a quantity of electricity of one coulomb is passed.
The formula for finding electrochemical equivalent is as follows:
where is the mass of substance and is the charge passed. Since , where is the current applied and is time, we also have | 7 | Physical Chemistry |
In the light-independent reactions (also known as the Calvin-Benson cycle), two 3-phosphoglycerate molecules are synthesized. RuBP, a 5-carbon sugar, undergoes carbon fixation, catalyzed by the rubisco enzyme, to become an unstable 6-carbon intermediate. This intermediate is then cleaved into two, separate 3-carbon molecules of 3-PGA. One of the resultant 3-PGA molecules continues through the Calvin-Benson cycle to be regenerated into RuBP while the other is reduced to form one molecule of glyceraldehyde 3-phosphate (G3P) in two steps: the phosphorylation of 3-PGA into 1,3-bisphosphoglyceric acid via the enzyme phosphoglycerate kinase (the reverse of the reaction seen in glycolysis) and the subsequent catalysis by glyceraldehyde 3-phosphate dehydrogenase into G3P. G3P eventually reacts to form the sugars such as glucose or fructose or more complex starches. | 5 | Photochemistry |
Generally, two kinds of reactions occur with xylenes: those involving the methyl groups and those involving the ring C–H bonds. Being benzylic and hence weakened, the C–H bonds of the methyl groups are susceptible to free-radical reactions, including halogenation to the corresponding xylene dichlorides (bis(chloromethyl)benzenes), while mono-bromination yields xylyl bromide, a tear gas agent. Oxidation and ammoxidation also target the methyl groups, affording dicarboxylic acids and the dinitriles. Electrophiles attack the aromatic ring, leading to chloro- and nitroxylenes. | 2 | Environmental Chemistry |
Several factors influence the energy penalty associated with the allylic strain. In order to relieve strain caused by interaction between the two methyl groups, the cyclohexanes will often exhibit a boat or twist-boat conformation. The boat conformation tends to be the major conformation to the strain. The effect of allylic strain on cis alkenes creates a preference for more linear structures. | 4 | Stereochemistry |
A range of analysis techniques are in use by drug checking services. The most common are reagent testing, fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, raman spectroscopy, mass spectrometry and gas chromatography mass spectrometry.
Reagent testing uses chemical indicators that show a colour change in the presence of particular drugs. These tests are widely available and affordable. The use of several reagents is generally necessary to positively identify a substance with Marquis, Mandelin, and Mecke reagents being used to detect MDMA and Ehrlich's reagent common for detecting LSD. However, reagent testing only indicates the presence of a substance, not the absence of contaminants or other substances. This can provide a false sense of security when illicit drugs are deliberately adulterated to fool reagent tests.
The presence of specific drugs can also be detected through immunoassay testing strips. Testing strips for fentanyl can detect a few tens of nanograms of the substance at a price of a few dollars per test. Recent increased demand for immunoassay test strips, lack of regulation, and approval to use federal funding for test strip purchasing in the US have led to a boom in test strip manufacturers creating concern in drug checking programs and harm reduction organizations about the lack of validation, consistency, and accuracy of results.
Fourier transform infrared spectroscopy is a rapid test using robust hardware that can be carried out in the field. It provides sample identification and mixture analysis, allowing the detection of impurities and adulterants. It is highly sensitive and can carry out analysis using only a few milligrams of a sample. It is semi-quantitative and can provide an indication of purity. For these reasons, it is widely used by both fixed and mobile testing services and considered the best technology to use.
Gas chromatography mass spectrometry provides very sensitive and quantified information about substances. However, the high price and delicate equipment generally limit the use of this technique to fixed sites.
The RADIAN ASAP is a novel, dedicated direct analysis system specifically designed for rapid, easy and low-cost analysis of liquids and solids. Engineered using proven and robust single quadrupole mass spectrometry technology combined with the Atmospheric Pressure Solids Analysis Probe (ASAP), the RADIAN ASAP delivers quality and ease of use in a compact footprint. RADIAN ASAP screens samples in less than 5 minutes against a library of known compounds for rapid, confident identification of illicit drugs. The sensitivity and selectivity of mass spectrometry provides confidence in detecting drugs with an easy, efficient triage workflow. | 3 | Analytical Chemistry |
The consumption of the bioluminescent POC by fish can lead to the emission of bioluminescent fecal pellets (repackaging), which can also be produced with non-bioluminescent POC if the fish gut is already charged with bioluminescent bacteria.
In the diagram on the right, the sinking POC is moving downward followed by a chemical plume. The plain white arrows represent the carbon flow. Panel (a) represents the classical view of a non-bioluminescent particle. The length of the plume is identified by the scale on the side. Panel (b) represents the case of a glowing particle in the bioluminescence shunt hypothesis. Bioluminescent bacteria are represented aggregated onto the particle. Their light emission is shown as a bluish cloud around it. Blue dotted arrows represent the visual detection and the movement toward the particle of the consumer organisms. Increasing the visual detection allows a better detection by upper trophic levels, potentially leading to the fragmentation of sinking POC into suspended POC due to sloppy feeding. | 9 | Geochemistry |
In 1850, T. J. Mulvany was probably the first investigator to use mathematical modeling in a stream hydrology context, although there was no chemistry involved. By 1892 M.E. Imbeau had conceived an event model to relate runoff to peak rainfall, again still with no chemistry. Robert E. Horton’s seminal work on surface runoff along with his coupling of quantitative treatment of erosion laid the groundwork for modern chemical transport hydrology. | 2 | Environmental Chemistry |
The Australian cattle industry is responsible for producing 3.9% of world beef productivity and due to 60% of the nation's entire beef production being exported, Australia operates alongside America and Brazil as one of the largest beef exporters worldwide. Slaughter rates in the Australian feedlot sector tend to increase during drought periods which can last for a number of years. This is due to the limited availability of grain which the onset of drought brings with it, meaning that feedlots are generally lacking in activity during this time. The Southern rangelands typically operate their feedlots by running smaller herds via more intense operations compared to the Northern rangeland sector.
The vast majority of Australian feedlot production falls in Queensland and the Northern Territory. The use of these feedlots has grown substantially since 1980 and the industry is currently able to feed over 1 million cattle in feedlots at once. The increasing use of feedlots in Australia is due to a consumerist demand for grass fed beef. Feedlot sectors are typically characterised by climates where crops and pastures are able to survive and typically consist of vegetation where short term crops such as wheat, oats and barley and long term crops such as clover can survive Australia's subterranean climate where conditions will endure for over 5 months. Further, this also encompasses those months where the ratio of rainfall and evaporation exceeds 1 cm and where the average monthly temperature exceeds 7 degrees. | 2 | Environmental Chemistry |
Through competitive fellowship stipends, ECS supports students and young professionals as they pursue new ideas and forge connections with professionals both within and outside the field. | 7 | Physical Chemistry |
Acute lymphoblastic leukemia (ALL) is a blood cancer of malignant B lymphocytes (termed B-cell ALL) or T lymphocytes (termed T-cell ALL) that typically occurs in infants and young children. In a three population-representative cohort study, NUTM1 gene rearrangements (i.e. fusion genes) occurred in 0.28 to 0.86% of pediatric patients with B-cell ALL. Among a total of 71 NUTM1-rearranged cases, 10 fusion partners of NUTM1 were identified: ACIN1-NUTM1 (24 cases), BRD9-NUTM1 (10 cases), CUX1-NUTM1 (15 cases), ZNF618-NUTM1 (9 cases; ZNF618 is the zinc finger protein 618 gene) fusion genes, and (in 1 to 4 cases each) AFF1-NUTM1, C17orf78-NUTM1 (C17orf78 is also termed ATAD5), CHD4-NUTM1, RUNX1-NUTM1, IKZF1-NUTM1, and SLC12A6-NUTM1 fusion genes. Individuals with these NUTM1 fusion gene-associated leukemias had appreciably better prognoses than those who had NUTM1 fusion gene negative B-cell acute lymphoblastic leukemias. It is thought that the cited fusion genes contribute to the development and/or progression of these NUTM1 fusion gene-associated ALL cases but the molecular mechanism(s) for this is unknown. Some HOXA genes, particularly HOXA9, are upregulated in these NUTM1 fusion gene-associated ALL cases as well as in cases of NUTM1 fusion gene-negative ALL. Further studies are required to determine if the overexpression of one or more HOXA genes contributes to NUTM1 fusion gene-associated B-cell ALL. | 1 | Biochemistry |
Asymmetric hydrogenations are used in the production of several drugs, such as the antibacterial levofloxin, the antibiotic carbapenem, and the antipsychotic agent BMS181100.
Knowles' research into asymmetric hydrogenation and its application to the production scale synthesis of L-Dopa gave asymmetric hydrogenation a strong start in the industrial world. A 2001 review indicated that asymmetric hydrogenation accounted for 50% of production scale, 90% of pilot scale, and 74% of bench scale catalytic, enantioselective processes in industry, with the caveat that asymmetric catalytic methods in general were not yet widely used.
Asymmetric hydrogenation has replaced kinetic resolution based methods has resulted in substantial improvements in the processs efficiency. can be seen in a number of specific cases where the For example, Roches Catalysis Group was able to achieve the synthesis of (S,S)-Ro 67-8867 in 53% overall yield, a dramatic increase above the 3.5% that was achieved in the resolution based synthesis. Roche's synthesis of mibefradil was likewise improved by replacing resolution with asymmetric hydrogenation, reducing the step count by three and increasing the yield of a key intermediate to 80% from the original 70%.
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Noyori-inspired hydrogenation catalysts have been applied to the commercial synthesis of number of fine chemicals. (R)-1,2-Propandiol, precursor to the antibacterial levofloxacin, can be efficiently synthesized from hydroxyacetone using Noyori asymmetric hydrogenation:
Newer routes focus on the hydrogenation of (R)-methyl lactate.
An antibiotic carbapenem is also prepared using Noyori asymmetric hydrogenation via (2S,3R)-methyl 2-(benzamidomethyl)-3-hydroxybutanoate, which is synthesized from racemic methyl 2-(benzamidomethyl)-3-oxobutanoate by dynamic kinetic resolution.
An antipsychotic agent BMS 181100 is synthesized using BINAP/diamine-Ru catalyst. | 0 | Organic Chemistry |
Diazenes may extrude nitrogen to provide discrete TMM intermediates. Generally, bridged diazenes are used to avoid competitive closure to MCPs and dimerization reactions. In combination with an alkenic acceptor, cyclization to either fused or bridged products takes place. Fused products are generally favored, unless the diazene precursor is substituted with electron-donating groups at the methylene carbon atom. The configuration of the alkene is maintained as long as the reaction is proceeding through a singlet TMM.
When stabilizing groups are present, MCPs may open to the corresponding zwitterionic TMMs. Acetal 1 has been used in this context, and provides cyclopentanes with the acetal functionality exo to the newly formed ring with high selectivity. This reaction is also stereospecific with respect to alkene geometry, and exhibits high selectivity for endo products in most cases.
MCPs lacking stabilizing groups may generate TMM synthons in the presence of palladium(0) or nickel(0) catalysts. Formal insertion of the catalyst into either of the two chemically distinct cyclopropane bonds (called "distal" and "proximal" to reflect their distance from the double bond) has the potential to generate isomeric products. Generally, palladium catalysts cause formal distal bond cleavage. This process is believed to occur through direct attack of the distal bond on the coordinated alkene. The reaction is stepwise and lacks stereospecificity under both palladium and nickel catalysis.
Silylated allylic acetates, carbonates and other substituted allyl compounds may form TMM synthons under palladium catalysis. The reaction is highly regioselective, providing only the substitution pattern shown below regardless of the position of the R' group on the starting allylic acetate. However, cyclization takes place in a stepwise fashion and does not exhibit stereospecificity. Rapid racemization of chiral pi-allyl palladium complexes occurs, and only moderate diastereoselectivity is observed in reactions of chiral allylic acetates. Chiral non-racemic alkenes, however, may exhibit moderate to high diastereoselectivity. | 0 | Organic Chemistry |
Vanillin is most prominent as the principal flavor and aroma compound in vanilla. Cured vanilla pods contain about 2% by dry weight vanillin. On cured pods of high quality, relatively pure vanillin may be visible as a white dust or "frost" on the exterior of the pod.
It is also found in Leptotes bicolor, a species of orchid native to Paraguay and southern Brazil, and the Southern Chinese red pine.
At lower concentrations, vanillin contributes to the flavor and aroma profiles of foodstuffs as diverse as olive oil, butter, raspberry, and lychee fruits.
Aging in oak barrels imparts vanillin to some wines, vinegar, and spirits.
In other foods, heat treatment generates vanillin from other compounds. In this way, vanillin contributes to the flavor and aroma of coffee, maple syrup, and whole-grain products, including corn tortillas and oatmeal. | 0 | Organic Chemistry |
Lovelock started defining the idea of a self-regulating Earth controlled by the community of living organisms in September 1965, while working at the Jet Propulsion Laboratory in California on methods of detecting life on Mars. The first paper to mention it was Planetary Atmospheres: Compositional and other Changes Associated with the Presence of Life, co-authored with C.E. Giffin. A main concept was that life could be detected in a planetary scale by the chemical composition of the atmosphere. According to the data gathered by the Pic du Midi observatory, planets like Mars or Venus had atmospheres in chemical equilibrium. This difference with the Earth atmosphere was considered to be a proof that there was no life in these planets.
Lovelock formulated the Gaia Hypothesis in journal articles in 1972 and 1974, followed by a popularizing 1979 book Gaia: A new look at life on Earth. An article in the New Scientist of February 6, 1975, and a popular book length version of the hypothesis, published in 1979 as The Quest for Gaia, began to attract scientific and critical attention.
Lovelock called it first the Earth feedback hypothesis, and it was a way to explain the fact that combinations of chemicals including oxygen and methane persist in stable concentrations in the atmosphere of the Earth. Lovelock suggested detecting such combinations in other planets' atmospheres as a relatively reliable and cheap way to detect life.
Later, other relationships such as sea creatures producing sulfur and iodine in approximately the same quantities as required by land creatures emerged and helped bolster the hypothesis.
In 1971 microbiologist Dr. Lynn Margulis joined Lovelock in the effort of fleshing out the initial hypothesis into scientifically proven concepts, contributing her knowledge about how microbes affect the atmosphere and the different layers in the surface of the planet. The American biologist had also awakened criticism from the scientific community with her advocacy of the theory on the origin of eukaryotic organelles and her contributions to the endosymbiotic theory, nowadays accepted. Margulis dedicated the last of eight chapters in her book, The Symbiotic Planet, to Gaia. However, she objected to the widespread personification of Gaia and stressed that Gaia is "not an organism", but "an emergent property of interaction among organisms". She defined Gaia as "the series of interacting ecosystems that compose a single huge ecosystem at the Earths surface. Period". The books most memorable "slogan" was actually quipped by a student of Margulis'.
James Lovelock called his first proposal the Gaia hypothesis but has also used the term Gaia theory. Lovelock states that the initial formulation was based on observation, but still lacked a scientific explanation. The Gaia hypothesis has since been supported by a number of scientific experiments and provided a number of useful predictions. | 9 | Geochemistry |
The effects of transforming growth factor-β (TGF-β) are determined by cellular context. There are three kinds of contextual factors that determine the shape the TGF-β response: the signal transduction components, the transcriptional cofactors and the epigenetic state of the cell. The different ligands and receptors of TGF-β are significant as well in the composition signal transduction pathway.
* the signal transduction components: ligand isoforms, ligand traps, co-receptors, receptor sub-types, inhibitory SMAD proteins, crosstalk inputs
* the transcriptional cofactors of SMAD proteins: pluripotency factors, lineage regulators, DNA-binding cofactors, HATs and HDACs, SNF, chromatin readers
* the epigenetic factors: heterochromatin, pluripotency marks, lineage marks, EMT marks, iPS cell marks, oncogenic marks. | 1 | Biochemistry |
In biological systems, oxocarbenium ions are mostly seen during reactions of carbohydrates. Since sugars are present in the structure of nucleic acids, with a ribose sugar present in RNA and a deoxyribose present in the structure of DNA, their chemistry plays an important role in wide range of cellular functions of nucleic acids. In addition to their functions in nucleotides, sugars are also used for structural components of organisms, as energy storage molecules, cell signaling molecules, protein modification and play key roles in the immune system, fertilization, preventing pathogenesis, blood clotting, and development. The abundance of sugar chemistry in biological processes leads many reaction mechanisms to proceed through oxocarbenium ions. Several important biological reactions that utilize oxocarbenium ions are outlined in this section. | 0 | Organic Chemistry |
Methyllysine is derivative of the amino acid residue lysine where the sidechain ammonium group has been methylated one or more times.
Such methylated lysines play an important role in epigenetics; the methylation of specific lysines of certain histones in a nucleosome alters the binding of the surrounding DNA to those histones, which in turn affects the expression of genes on that DNA. The binding is affected because the effective radius of the positive charge is increased (methyl groups are larger than the hydrogen atoms they replace), reducing the strongest potential electrostatic attraction with the negatively charged DNA.
It is thought that the methylation of lysine (and arginine) on histone tails does not directly affect their binding to DNA. Rather, such methyl marks recruit other proteins that modulate chromatin structure.
In Protein Data Bank files, methylated lysines are indicated by the MLY or MLZ acronyms. | 1 | Biochemistry |
Dexmedetomidine may be useful for the treatment of the negative cardiovascular effects of acute amphetamines and cocaine intoxication and overdose. Dexmedetomidine has also been used as an adjunct to neuroaxial anesthesia for lower limb procedures. It has been successfully used to treat opioid withdrawal symptoms.
In 2022 it was approved by the FDA for the treatment of agitation in schizophrenia and bipolar disorder. | 4 | Stereochemistry |
There have been reports of incidents of abuse regarding forced insemination with sperm samples bought online.
Further abuse of sperm banks comes from the fertility clinic staff themselves. There have been a number of reports of staff at sperm banks and fertility clinics providing their own sperm in place of donor sperm. There have also been cases in which men have claimed their sperm sample was used by a clinic to inseminate a woman without his consent. This has led to cases of malpractice, and in some states, lobbying to create fertility fraud laws. These incidents have also led to outcry by people who had been conceived by such incidents, raising concerns of consanguinity, as well as the simple right to know who their siblings and biologic parents are. | 1 | Biochemistry |
Each half-reaction has a standard electrode potential (E), which is equal to the potential difference or voltage at equilibrium under standard conditions of an electrochemical cell in which the cathode reaction is the half-reaction considered, and the anode is a standard hydrogen electrode where hydrogen is oxidized:
:H → H + e
The electrode potential of each half-reaction is also known as its reduction potential (E), or potential when the half-reaction takes place at a cathode. The reduction potential is a measure of the tendency of the oxidizing agent to be reduced. Its value is zero for H + e → H by definition, positive for oxidizing agents stronger than H (e.g., +2.866 V for F) and negative for oxidizing agents that are weaker than H (e.g., −0.763V for Zn).
For a redox reaction that takes place in a cell, the potential difference is:
:E = E – E
However, the potential of the reaction at the anode is sometimes expressed as an oxidation potential:
:E = –E
The oxidation potential is a measure of the tendency of the reducing agent to be oxidized but does not represent the physical potential at an electrode. With this notation, the cell voltage equation is written with a plus sign
:E = E + E | 9 | Geochemistry |
Hot blast refers to the preheating of air blown into a blast furnace or other metallurgical process. As this considerably reduced the fuel consumed, hot blast was one of the most important technologies developed during the Industrial Revolution.
Hot blast also allowed higher furnace temperatures, which increased the capacity of furnaces.
As first developed, it worked by alternately storing heat from the furnace flue gas in a firebrick-lined vessel with multiple chambers, then blowing combustion air through the hot chamber. This is known as regenerative heating. Hot blast was invented and patented for iron furnaces by James Beaumont Neilson in 1828 at Wilsontown Ironworks in Scotland, but was later applied in other contexts, including late bloomeries. Later the carbon monoxide in the flue gas was burned to provide additional heat. | 8 | Metallurgy |
Pyrolysis of iodomethyltrimethylammonium iodide affords the desired salt:
An alternative route starts with bis(dimethylamino)methane: | 0 | Organic Chemistry |
* TsOH may be converted to p-toluenesulfonic anhydride by heating with phosphorus pentoxide.
* When heated with acid and water, TsOH undergoes hydrolysis to toluene:
:CHCHSOH + HO → CHCH + HSO
This reaction is general for aryl sulfonic acids. | 0 | Organic Chemistry |
The mass average molar mass (often loosely termed weight average molar mass) is another way of describing the molar mass of a polymer. Some properties are dependent on molecular size, so a larger molecule will have a larger contribution than a smaller molecule. The mass average molar mass is calculated by
where is the number of molecules of molecular mass .
The mass average molecular mass can be determined by static light scattering, small angle neutron scattering, X-ray scattering, and sedimentation velocity.
The ratio of the mass average to the number average is called the dispersity or the polydispersity index.
The mass-average molecular mass, , is also related to the fractional monomer conversion, , in step-growth polymerization (for the simplest case of linear polymers formed from two monomers in equimolar quantities) as per Carothers' equation:
where is the molecular mass of the repeating unit. | 7 | Physical Chemistry |
According to the United States National Library of Medicines medical subject headings, the term neurotrophin may be used as a synonym for neurotrophic factor, but the term neurotrophin is more generally reserved for four structurally related factors: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). The term neurotrophic factor' generally refers to these four neurotrophins, the GDNF family of ligands, and ciliary neurotrophic factor (CNTF), among other biomolecules. Neurotrophin-6 and neurotrophin-7 also exist, but are only found in zebrafish. | 1 | Biochemistry |
The toxicity of PCBs varies considerably among congeners. The coplanar PCBs, known as nonortho PCBs because they are not substituted at the ring positions ortho to (next to) the other ring, (such as PCBs 77, 126 and 169), tend to have dioxin-like properties, and generally are among the most toxic congeners. Because PCBs are almost invariably found in complex mixtures, the concept of toxic equivalency factors (TEFs) has been developed to facilitate risk assessment and regulation, where more toxic PCB congeners are assigned higher TEF values on a scale from 0 to 1. One of the most toxic compounds known, [[2,3,7,8-tetrachlorodibenzodioxin|2,3,7,8-tetrachlorodibenzo[p]dioxin]], a PCDD, is assigned a TEF of 1. In June 2020, State Impact of Pennsylvania stated that "In 1979, the EPA banned the use of PCBs, but they still exist in some products produced before 1979. They persist in the environment because they bind to sediments and soils. High exposure to PCBs can cause birth defects, developmental delays, and liver changes." | 2 | Environmental Chemistry |
Protein Ser/Thr phosphatases were originally classified using biochemical assays as either, type 1 (PP1) or type 2 (PP2), and were further subdivided based on metal-ion requirement (PP2A, no metal ion; PP2B, Ca stimulated; PP2C, Mg dependent) (Moorhead et al., 2007). The protein Ser/Thr phosphatases PP1, PP2A and PP2B of the PPP family, together with PP2C of the PPM family, account for the majority of Ser/Thr PP activity in vivo (Barford et al., 1998). In the brain, they are present in different subcellular compartments in neuronal and glial cells, and contribute to different neuronal functions. | 1 | Biochemistry |
A domestic refrigerator is an example of a heat pump: a heat engine in reverse. Work is used to create a heat differential. Many cycles can run in reverse to move heat from the cold side to the hot side, making the cold side cooler and the hot side hotter. Internal combustion engine versions of these cycles are, by their nature, not reversible.
Refrigeration cycles include:
*Air cycle machine
*Gas-absorption refrigerator
*Magnetic refrigeration
*Stirling cryocooler
*Vapor-compression refrigeration
*Vuilleumier cycle | 7 | Physical Chemistry |
The fluorescence signals emitted from phycoerythrin and phycocyanin have made them suitable for use as indicators to detect cyanotoxins such as microcystins in drinking water. A study examined the nature of the biliproteins fluorescence signals regarding their real-time character, sensitivity and the biliproteins behaviour in different treatment stages (of water) in comparison to microcystins. The fluorescence signals' real-time character was confirmed by fluorescence measurements, as they can be carried out without having to pre-concentrate the biliproteins. If the ratio of biliprotein to microcystin is above 1, the fluorescence signals can estimate very low concentrations of microcystins. A test conducted in 2009 compared the behaviour of both biliproteins and selected microcystins MC-LR and MC-RR during water treatment. The test results showed that the biliproteins have an early warning function against microcystins in conventional treatment stages that use pre-oxidation with permanganate, activated carbon and chlorination. However, the early warning function does not occur when chlorine dioxide is used as a pre-oxidant or final disinfectant. It is important for the biliprotein/toxin ratio of raw water to be known in order to use the biliproteins for control measurements in drinking water treatment. | 1 | Biochemistry |
A carrier-powered radio is a batteryless radio which "leeches" its power from the incoming electromagnetic wave. A simple circuit (very similar to a crystal set) rectifies the incoming signal and this DC current is then used to power a small transistor amplifier. Typically a strong local station is tuned in to provide power, leaving the listener free to listen to weaker and more distant stations. | 7 | Physical Chemistry |
Keith Christopher Rowley , (born 24 October 1949) is a Trinidadian politician serving as the seventh prime minister of Trinidad and Tobago, first elected into office on 9 September 2015 and again following the 2020 general election. He has led the People's National Movement (PNM) since May 2010 and was Leader of the Opposition from 2010 to 2015. He has also served as the Member of the House of Representatives for Diego Martin West since 1991. He is a volcanologist by profession, holding a doctorate in geology, specializing in geochemistry. | 9 | Geochemistry |
In biological systems, only manganese (Mn) is readily capable of replacing Mg, but only in a limited set of circumstances. Mn is very similar to Mg in terms of its chemical properties, including inner and outer shell complexation. Mn effectively binds ATP and allows hydrolysis of the energy molecule by most ATPases. Mn can also replace Mg as the activating ion for a number of Mg-dependent enzymes, although some enzyme activity is usually lost. Sometimes such enzyme metal preferences vary among closely related species: For example, the reverse transcriptase enzyme of lentiviruses like HIV, SIV and FIV is typically dependent on Mg, whereas the analogous enzyme for other retroviruses prefers Mn. | 1 | Biochemistry |
Following the laser cooling proposals, in 1978 two research groups that Wineland, Drullinger and Walls of NIST, and Neuhauser, Hohenstatt, Toscheck and Dehmelt of the University of Washington succeeded in laser cooling atoms. The NIST group wanted to reduce the effect of Doppler broadening on spectroscopy. They cooled magnesium ions in a Penning trap to < 40 Kelvin. The Washington group cooled barium ions.
The research from both groups served to illustrate the mechanical properties of light. Around this time, laser cooling techniques had allowed for temperatures lowered to around 40 kelvins.
Influenced by the Wineland's work on laser cooling ions, William Phillips applied the same principles to laser cool neutral atoms. In 1982, he published the first paper where neutral atoms were laser cooled. The process used is now known as the Zeeman slower and is a standard technique for slowing an atomic beam. | 7 | Physical Chemistry |
Tetrakis(hexahydropyrimidinopyrimidine)ditungsten(II), known as ditungsten tetra(hpp), is the name of the coordination compound with the formula W(hpp). This material consists of a pair of tungsten centers linked by the conjugate base of four hexahydropyrimidopyrimidine (hpp) ligands. It adopts a structure sometimes called a Chinese lantern structure or paddlewheel compound, the prototype being copper(II) acetate.
The molecule is of research interest because it has the lowest ionization energy (3.51 eV) of all stable chemical elements or chemical compounds as of the year 2005. This value is even lower than of caesium with 3.89 eV (or 375 kJ/mol) located at the extreme left lower corner of the periodic table (although francium is at a lower position in the periodic table compared to caesium, it has a higher ionization energy and is radioactive) or known metallocene reducing agents such as decamethylcobaltocene with 4.71 eV. | 7 | Physical Chemistry |
Transcription initiation at the P promoter occurs in the presence of high arabinose and low glucose concentrations. Upon arabinose binding to AraC, the N-terminal arm of AraC is released from its DNA binding domain via a “light switch” mechanism. This allows AraC to dimerize and bind the I and I operators. The AraC-arabinose dimer at this site contributes to activation of the Ppromoter. Additionally, CAP binds to two CAP binding sites upstream of the I and I operators and helps activate the P promoter. In the presence of both high arabinose and high glucose concentrations however, low cAMP levels prevent CAP from activating the P promoter. It is hypothesized that P promoter activation by CAP and AraC is mediated through contacts between the C-terminal domain of the α-subunit of RNA polymerase and the CAP and AraC proteins.
Without arabinose, and regardless of glucose concentration, the P and Ppromoters are repressed by AraC. The N-terminal arm of AraC interacts with its DNA binding domain, allowing two AraC proteins to bind to the O and I operator sites. The Ooperator is situated within the araC gene. An AraC dimer also binds to the O operator and represses the P promoter via a negative autoregulatory feedback loop. The two bound AraC proteins dimerize and cause looping of the DNA. The looping prevents binding of CAP and RNA Polymerase, which normally activate the transcription of both P and P.
The spacing between the O and I operator sites is critical. Adding or removing 5 base pairs between the O and I operator sites abrogates AraC mediated repression of the P promoter. The spacing requirement arises from the double helix nature of DNA, in which a complete turn of the helix is about 10.5 nucleotides. Therefore, adding or removing 5 base pairs between the O and I operator sites rotates the helix roughly 180 degrees. This reverses the direction that the Ooperator faces when the DNA is looped and prevents dimerization of the O bound AraC with the bound I araC. | 1 | Biochemistry |
Dipole-dipole interactions are electrostatic interactions between permanent dipoles in molecules. These interactions tend to align the molecules to increase attraction (reducing potential energy). Normally, dipoles are associated with electronegative atoms, including oxygen, nitrogen, sulfur, and fluorine.
For example, acetone, the active ingredient in some nail polish removers, has a net dipole associated with the carbonyl (see figure 2). Since oxygen is more electronegative than the carbon that is covalently bonded to it, the electrons associated with that bond will be closer to the oxygen than the carbon, creating a partial negative charge (δ) on the oxygen, and a partial positive charge (δ) on the carbon. They are not full charges because the electrons are still shared through a covalent bond between the oxygen and carbon. If the electrons were no longer being shared, then the oxygen-carbon bond would be an electrostatic interaction.
Often molecules contain dipolar groups, but have no overall dipole moment. This occurs if there is symmetry within the molecule that causes the dipoles to cancel each other out. This occurs in molecules such as tetrachloromethane. Note that the dipole-dipole interaction between two individual atoms is usually zero, since atoms rarely carry a permanent dipole. See atomic dipoles. | 6 | Supramolecular Chemistry |
The largest use of bitumen is for making asphalt concrete for road surfaces; this accounts for approximately 85% of the bitumen consumed in the United States. There are about 4,000 asphalt concrete mixing plants in the US, and a similar number in Europe.
Asphalt concrete pavement mixes are typically composed of 5% bitumen (known as asphalt cement in the US) and 95% aggregates (stone, sand, and gravel). Due to its highly viscous nature, bitumen must be heated so it can be mixed with the aggregates at the asphalt mixing facility. The temperature required varies depending upon characteristics of the bitumen and the aggregates, but warm-mix asphalt technologies allow producers to reduce the temperature required.
The weight of an asphalt pavement depends upon the aggregate type, the bitumen, and the air void content. An average example in the United States is about 112 pounds per square yard, per inch of pavement thickness.
When maintenance is performed on asphalt pavements, such as milling to remove a worn or damaged surface, the removed material can be returned to a facility for processing into new pavement mixtures. The bitumen in the removed material can be reactivated and put back to use in new pavement mixes. With some 95% of paved roads being constructed of or surfaced with asphalt, a substantial amount of asphalt pavement material is reclaimed each year. According to industry surveys conducted annually by the Federal Highway Administration and the National Asphalt Pavement Association, more than 99% of the bitumen removed each year from road surfaces during widening and resurfacing projects is reused as part of new pavements, roadbeds, shoulders and embankments or stockpiled for future use.
Asphalt concrete paving is widely used in airports around the world. Due to the sturdiness and ability to be repaired quickly, it is widely used for runways. | 7 | Physical Chemistry |
Peroxin-7 is a receptor associated with Refsum's disease and rhizomelic chondrodysplasia punctata type 1. | 1 | Biochemistry |
Stainless steel contains additives which are highly oxidizable, such as chromium and molybdenum. Such steels can only be decarburized by reacting with dry hydrogen, which has no water content, unlike wet hydrogen, which is produced in a way that includes some water and can otherwise be used for decarburization. | 8 | Metallurgy |
Half-sandwich compounds employing Ru(II), such as (cymene)ruthenium dichloride dimer, have been mainly investigated as catalysts for transfer hydrogenation. These complexes feature three coordination sites that are susceptible to substitution, while the arene ligand is tightly bonded and protects the metal against oxidation to Ru(III). They are prepared by reaction of RuCl·x(HO) with 1,3-cyclohexadienes. Work is also conducted on their potential as anticancer drugs.
(η-CH)RuCl readily undergoes ligand exchange via cleavage of the chloride bridges, making this complex a versatile precursor to Ru(II) piano stool derivatives. | 0 | Organic Chemistry |
* Barker, George Frederick. [https://books.google.com/books?id=5CrCQwJ2su8C&dq=Memoir+of+John+William+Draper:+1811-1882&source=gbs_summary_s&cad=0 Memoir of John William Draper: 1811–1882.] Washington, D.C., 1886.
* Miller, Lillian B., Frederick Voss, and Jeannette M. Hussey. The Lazzaroni: Science and Scientists in Mid-Nineteenth-Century America. Washington, D.C.: Smithsonian Institution Press, 1972.
* Ungureanu, James C. [https://upittpress.org/books/9780822945819/ Science, Religion, and the Protestant Tradition: Retracing the Origins of Conflict]. Pittsburgh: University of Pittsburgh Press, 2019. | 5 | Photochemistry |
An example of undesirable work hardening is during machining when early passes of a cutter inadvertently work-harden the workpiece surface, causing damage to the cutter during the later passes. Certain alloys are more prone to this than others; superalloys such as Inconel require machining strategies that take it into account.
For metal objects designed to flex, such as springs, specialized alloys are usually employed in order to avoid work hardening (a result of plastic deformation) and metal fatigue, with specific heat treatments required to obtain the necessary characteristics. | 8 | Metallurgy |
Different processes and techniques have been developed around melt spinning which offer advantages to the industrial applications and product consistency. | 8 | Metallurgy |
Hexahydroxybenzene triscarbonate is a chemical compound, an oxide of carbon with formula . Its molecular structure consists of a benzene core with the six hydrogen atoms replaced by three carbonate groups. It can be seen as a sixfold ester of hexahydroxybenzene (benzenehexol) and carbonic acid.
The compound was obtained by C. Nallaiah in 1984, as a tetrahydrofuran solvate. | 0 | Organic Chemistry |
A DamID variant known as RNA-DamID can be used to detect interactions between RNA molecules and DNA. This method relies on the expression of a Dam-MCP fusion protein which is able to bind to an RNA that has been modified with MS2 stem-loops. Binding of the Dam-fusion protein to the RNA results in detectable methylation at sites of RNA binding to the genome. | 1 | Biochemistry |
DESs are fluids generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form eutectic mixtures with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C, and they exhibit similar physico-chemical properties to traditional ILs, while being much cheaper and environmentally friendlier. Most of them are mixtures of choline chloride and a hydrogen-bond donor (e.g., urea, ethylene glycol, malonic acid) or mixtures of choline chloride with a hydrated metal salt. Other choline salts (e.g. acetate, citrate, nitrate) have a much higher costs or need to be synthesised, and the DES formulated from these anions are typically much more viscous and can have higher conductivities than for choline chloride. This results in lower plating rates and poorer throwing power and for this reason chloride-based DES systems are still favoured. For instance, Reline (a 1:2 mixture of choline chloride and urea) has been used to selectively recover Zn and Pb from a mixed metal oxide matrix. Similarly, Ethaline (a 1: 2 mixture of choline chloride and ethylene glycol) facilitates metal dissolution in electropolishing of steels. DESs have also demonstrated promising results to recover metals from complex mixtures such Cu/Zn and Ga/As, and precious metals from minerals. It has also been demonstrated that metals can be recovered from complex mixtures by electrocatalysis using a combination of DESs as lixiviants and an oxidising agent, while metal ions can be simultaneously separated from the solution by electrowinning. | 8 | Metallurgy |
In macromolecular chemistry, a catenane () is a mechanically interlocked molecular architecture consisting of two or more interlocked macrocycles, i.e. a molecule containing two or more intertwined rings. The interlocked rings cannot be separated without breaking the covalent bonds of the macrocycles. They are conceptually related to other mechanically interlocked molecular architectures, such as rotaxanes, molecular knots or molecular Borromean rings. Recently the terminology "mechanical bond" has been coined that describes the connection between the macrocycles of a catenane. Catenanes have been synthesised in two different ways: statistical synthesis and template-directed synthesis. | 6 | Supramolecular Chemistry |
RT is the product of the molar gas constant, R, and the temperature, T. This product is used in physics and chemistry as a scaling factor for energy values in macroscopic scale (sometimes it is used as a pseudo-unit of energy), as many processes and phenomena depend not on the energy alone, but on the ratio of energy and RT, i.e. E/RT. The SI units for RT are joules per mole (J/mol).
It differs from kT only by a factor of the Avogadro constant, N. Its dimension is energy or MLT, expressed in SI units as joules (J):
:kT = RT/N | 7 | Physical Chemistry |
Chimpanzee age impacts the frequency of alarm signalling. Chimpanzees over 80 months of age are more likely to produce an alarm call than those less than 80 months of age. There are several hypotheses for this lack of alarm calling in infants zero to four years of age. The first hypothesis is a lack of motivation to produce alarm calls because of mothers in close proximity that minimize the infants perception of a threat or that respond to a threat before the infant can. Infants may also be more likely to use distress calls to catch their mothers attention in order for her to produce an alarm call. Infants might also lack the physical ability to produce alarm calls or lack the necessary experience to classify unfamiliar objects as dangerous and worthy of an alarm signal. Therefore, alarm calling may require advanced levels of development, perception, categorization, and social cognition. | 1 | Biochemistry |
The term "autapse" was first coined in 1972 by Van der Loos and Glaser, who observed them in Golgi preparations of the rabbit occipital cortex while originally conducting a quantitative analysis of neocortex circuitry. Also in the 1970s, autapses have been described in dog and rat cerebral cortex, monkey neostriatum, and cat spinal cord.
In 2000, they were first modeled as supporting persistence in recurrent neural networks. In 2004, they were modeled as demonstrating oscillatory behavior, which was absent in the same model neuron without autapse. More specifically, the neuron oscillated between high firing rates and firing suppression, reflecting the spike bursting behavior typically found in cerebral neurons. In 2009, autapses were, for the first time, associated with sustained activation. This proposed a possible function for excitatory autapses within a neural circuit. In 2014, electrical autapses were shown to generate stable target and spiral waves in a neural model network. This indicated that they played a significant role in stimulating and regulating the collective behavior of neurons in the network. In 2016, a model of resonance was offered.
Autapses have been used to simulate "same cell" conditions to help researchers make quantitative comparisons, such as studying how N-methyl-D-aspartate receptor (NMDAR) antagonists affect synaptic versus extrasynaptic NMDARs. | 1 | Biochemistry |
A simple buffer solution consists of a solution of an acid and a salt of the conjugate base of the acid. For example, the acid may be acetic acid and the salt may be sodium acetate.
The Henderson–Hasselbalch equation relates the pH of a solution containing a mixture of the two components to the acid dissociation constant, K of the acid, and the concentrations of the species in solution.
To derive the equation a number of simplifying assumptions have to be made.
Assumption 1: The acid, HA, is monobasic and dissociates according to the equations
C is the analytical concentration of the acid and C is the concentration the hydrogen ion that has been added to the solution. The self-dissociation of water is ignored. A quantity in square brackets, [X], represents the concentration of the chemical substance X. It is understood that the symbol H stands for the hydrated hydronium ion. K is an acid dissociation constant.
The Henderson–Hasselbalch equation can be applied to a polybasic acid only if its consecutive pK values differ by at least 3. Phosphoric acid is such an acid.
Assumption 2. The self-ionization of water can be ignored.
This assumption is not, strictly speaking, valid with pH values close to 7, half the value of pK, the constant for self-ionization of water. In this case the mass-balance equation for hydrogen should be extended to take account of the self-ionization of water.
However, the term can be omitted to a good approximation.
Assumption 3: The salt MA is completely dissociated in solution. For example, with sodium acetate
the concentration of the sodium ion, [Na] can be ignored. This is a good approximation for 1:1 electrolytes, but not for salts of ions that have a higher charge such as magnesium sulphate, MgSO, that form ion pairs.
Assumption 4: The quotient of activity coefficients, , is a constant under the experimental conditions covered by the calculations.
The thermodynamic equilibrium constant, ,
is a product of a quotient of concentrations and a quotient, , of activity coefficients .
In these expressions, the quantities in square brackets signify the concentration of the undissociated acid, HA, of the hydrogen ion H, and of the anion A; the quantities are the corresponding activity coefficients. If the quotient of activity coefficients can be assumed to be a constant which is independent of concentrations and pH, the dissociation constant, K can be expressed as a quotient of concentrations.
Rearrangement of this expression and taking logarithms provides the Henderson–Hasselbalch equation | 7 | Physical Chemistry |
Countercurrent chromatography and related liquid-liquid separation techniques have been used on both industrial and laboratory scale to purify a wide variety of chemical substances. Separation realizations include proteins, DNA, Cannabidiol (CBD) from Cannabis Sativa antibiotics, vitamins, natural products, pharmaceuticals, metal ions, pesticides, enantiomers, polyaromatic hydrocarbons from environmental samples, active enzymes, and carbon nanotubes. Countercurrent chromatography is known for its high dynamic range of scalability: milligram to kilogram quantities purified chemical components may be obtained with this technique. It also has the advantage of accommodating chemically complex samples with undissolved particulates. | 3 | Analytical Chemistry |
Paschen's law requires that:
* There are already free electrons at the cathode () which can be accelerated to trigger impact ionization. Such so-called seed electrons can be created by ionization by natural radioactivity or cosmic rays.
* The creation of further free electrons is only achieved by impact ionization. Thus Paschen's law is not valid if there are external electron sources. This can, for example, be a light source creating secondary electrons by the photoelectric effect. This has to be considered in experiments.
* Each ionized atom leads to only one free electron. However, multiple ionizations occur always in practice.
* Free electrons at the cathode surface are created by the impacting ions. The problem is that the number of thereby created electrons strongly depends on the material of the cathode, its surface (roughness, impurities) and the environmental conditions (temperature, humidity etc.). The experimental, reproducible determination of the factor is therefore nearly impossible.
* The electrical field is homogeneous. | 7 | Physical Chemistry |
Carcinoembryonic antigen peptide-1 is a nine amino acid peptide fragment of carcinoembryonic antigen (CEA), a protein that is overexpressed in several cancer cell types, including gastrointestinal, breast, and non-small-cell lung.
Synonyms:
* CAP-1
* Carcinoembryonic Antigen Peptide-1
* Carcinoembryonic Peptide-1
* CEA Peptide 1
* CEA Peptide 9-mer | 1 | Biochemistry |
Domain walls are spatially extended regions of transition mediating the transfer of the order parameter from one domain to another. In comparison to the domains the domain walls are not homogeneous and they can have a lower symmetry. This may modify the properties of a multiferroic and the coupling of its order parameters. Multiferroic domain walls may display particular static and dynamic properties.
Static properties refer to stationary walls. They can result from
*The reduced dimensionality
*The finite width of the wall
*The different symmetry of the wall
*The inherent chemical, electronic, or order-parameter inhomogeneity within the walls and the resulting gradient effects. | 7 | Physical Chemistry |
# The critical temperature of the fluid should be well above the highest temperature existing in the proposed cycle. Evaporation of the working fluid — and thus the significant addition of heat — can then ensue at the maximum temperature of the cycle. This results in a relatively high cycle efficiency.
# The slope ds/dT of the saturated vapour line in T–s diagram (see Chapter Classification of pure (single-component) working fluids) should be nearly zero in the applied pressure ratio of the expander. This prevents significant moisture (liquid droplet) formation or excessive superheat occurring during the expansion. It also ensures that all the heat rejection in the condenser occurs at the minimum cycle temperature, which increases the thermal efficiency.
# A low value for the specific heat of the liquid or, alternatively, a low ratio of number of atoms per molecule divided by the molecular weight and a high ratio of the latent heat of vaporisation to the liquids specific heat should appertain. This reduces the amount of the heat required to raise the temperature of the subcooled liquid of the working fluid to the saturation temperature corresponding to the pressure in the Rankinecycles evaporator. So most of the heat is added at the maximum cycle temperature, and the Rankine cycle can approach more closely the Carnot cycle. | 7 | Physical Chemistry |
Julia was born in 1922 in Paris as son of the renowned mathematician Gaston Julia. Julia studied physics at the École Normale Supérieure. After receiving his diploma he joined the group of Ian Heilbron and David G. Jones at the Imperial College London where he received his first PhD in 1948. Back to France he changed his subject to chemistry and subsequently received his second PhD for work with . | 0 | Organic Chemistry |
It may cause dizziness, and patients should not, therefore, drive or operate heavy machinery or vehicles until they are familiar with how dexketoprofen affects them. Concomitant use of alcohol and other sedatives may potentiate this effect. In a small subset of individuals the dizziness may be intolerable and require transition to an alternative treatment. | 4 | Stereochemistry |
* Magnesium aluminide, MgAl
* Titanium aluminide, TiAl
* Iron aluminides, including FeAl and FeAl
* Nickel aluminide, NiAl
See category for a list. | 8 | Metallurgy |
ORs, which are located on the membranes of the cilia have been classified as a complex type of ligand-gated metabotropic channels. There are approximately 1000 different genes that code for the ORs, making them the largest gene family. An odorant will dissolve into the mucus of the olfactory epithelium and then bind to an OR. ORs can bind to a variety of odor molecules, with varying affinities. The difference in affinities causes differences in activation patterns resulting in unique odorant profiles. The activated OR in turn activates the intracellular G-protein, GOLF (GNAL), adenylate cyclase and production of cyclic AMP (cAMP) opens ion channels in the cell membrane, resulting in an influx of sodium and calcium ions into the cell, and an efflux of chloride ions. This influx of positive ions and efflux of negative ions causes the neuron to depolarize, generating an action potential. | 1 | Biochemistry |
Once monoclonal antibodies for a given substance have been produced, they can be used to detect the presence of this substance. Proteins can be detected using the Western blot and immuno dot blot tests. In immunohistochemistry, monoclonal antibodies can be used to detect antigens in fixed tissue sections, and similarly, immunofluorescence can be used to detect a substance in either frozen tissue section or live cells. | 1 | Biochemistry |
Lithium diisopropylamide (commonly abbreviated LDA) is a chemical compound with the molecular formula . It is used as a strong base and has been widely utilized due to its good solubility in non-polar organic solvents and non-nucleophilic nature. It is a colorless solid, but is usually generated and observed only in solution. It was first prepared by Hamell and Levine in 1950 along with several other hindered lithium diorganylamides to effect the deprotonation of esters at the α position without attack of the carbonyl group. | 0 | Organic Chemistry |
For the analysis of volatile compounds, a purge and trap (P&T) concentrator system may be used to introduce samples. The target analytes are extracted by mixing the sample with water and purge with inert gas (e.g. Nitrogen gas) into an airtight chamber, this is known as purging or sparging. The volatile compounds move into the headspace above the water and are drawn along a pressure gradient (caused by the introduction of the purge gas) out of the chamber. The volatile compounds are drawn along a heated line onto a trap. The trap is a column of adsorbent material at ambient temperature that holds the compounds by returning them to the liquid phase. The trap is then heated and the sample compounds are introduced to the GC–MS column via a volatiles interface, which is a split inlet system. P&T GC–MS is particularly suited to volatile organic compounds (VOCs) and BTEX compounds (aromatic compounds associated with petroleum).
A faster alternative is the "purge-closed loop" system. In this system the inert gas is bubbled through the water until the concentrations of organic compounds in the vapor phase are at equilibrium with concentrations in the aqueous phase. The gas phase is then analysed directly. | 3 | Analytical Chemistry |
Born and raised in countryside China, Yu obtained his B.Sc. (Chemistry) from Shandong University in 1991 at an age of 20. He then received his joint M.Sc. from Shandong University and Dalian Institute of Chemical Physics (Chemical Physics) in 1994, and his Ph.D. from Peking University (Materials Chemistry, with Prof. Zhong-Fan Liu) in 1997. He did his postdoctoral research with Nobel Laureate Ahmed Zewail and electrochemist Fred Anson at the California Institute of Technology from 1997 to 1999. | 3 | Analytical Chemistry |
Duplex sequencing and the significant increase of sequencing accuracy has had an important impact on applications such as detection of rare human genetic variants, detection of subclonal mutations involved in mechanisms of resistance to therapy in genetically heterogeneous cancers, screening variants in circulating tumor DNA as a non-invasive biomarker, and prenatal screening for genetic abnormalities in a fetus. | 1 | Biochemistry |
eIF1 and eIF1A both bind to the 40S ribosome subunit-mRNA complex. Together they induce an "open" conformation of the mRNA binding channel, which is crucial for scanning, tRNA delivery, and start codon recognition. In particular, eIF1 dissociation from the 40S subunit is considered to be a key step in start codon recognition.
eIF1 and eIF1A are small proteins (13 and 16 kDa, respectively in humans) and are both components of the 43S PIC. eIF1 binds near the ribosomal P-site, while eIF1A binds near the A-site, in a manner similar to the structurally and functionally related bacterial counterparts IF3 and IF1, respectively. | 1 | Biochemistry |
Among the neurons in the human brain, somatically derived copy number variations are frequent. Copy number variations show wide variability (9 to 100% of brain neurons in different studies). Most alterations are between 2 and 10 Mb in size with deletions far outnumbering amplifications. Copy number variations appear to be higher in brain cells than in other cell types. A likely source of copy number variation is incorrect repair of DNA damage.
Genomic duplication and triplication of the gene appear to be a rare cause of Parkinson's disease, although more common than point mutations.
Copy number variants in RCL1 gene are associated with a range of neuropsychiatric phenotypes in children. | 1 | Biochemistry |
Experiments led by Randall Hulet at Rice University from 1995 through 2000 showed that lithium condensates with attractive interactions could stably exist up to a critical atom number. Quench cooling the gas, they observed the condensate to grow, then subsequently collapse as the attraction overwhelmed the zero-point energy of the confining potential, in a burst reminiscent of a supernova, with an explosion preceded by an implosion.
Further work on attractive condensates was performed in 2000 by the JILA team, of Cornell, Wieman and coworkers. Their instrumentation now had better control so they used naturally attracting atoms of rubidium-85 (having negative atom–atom scattering length). Through Feshbach resonance involving a sweep of the magnetic field causing spin flip collisions, they lowered the characteristic, discrete energies at which rubidium bonds, making their Rb-85 atoms repulsive and creating a stable condensate. The reversible flip from attraction to repulsion stems from quantum interference among wave-like condensate atoms.
When the JILA team raised the magnetic field strength further, the condensate suddenly reverted to attraction, imploded and shrank beyond detection, then exploded, expelling about two-thirds of its 10,000 atoms. About half of the atoms in the condensate seemed to have disappeared from the experiment altogether, not seen in the cold remnant or expanding gas cloud. Carl Wieman explained that under current atomic theory this characteristic of Bose–Einstein condensate could not be explained because the energy state of an atom near absolute zero should not be enough to cause an implosion; however, subsequent mean-field theories have been proposed to explain it. Most likely they formed molecules of two rubidium atoms; energy gained by this bond imparts velocity sufficient to leave the trap without being detected.
The process of creation of molecular Bose condensate during the sweep of the magnetic field throughout the Feshbach resonance, as well as the reverse process, are described by the exactly solvable model that can explain many experimental observations. | 7 | Physical Chemistry |
The computation method Saltmod is based on seasonal water balances of agricultural lands. Four seasons in one year can be distinguished, e.g. dry, wet, cold, hot, irrigation or fallow seasons. The number of seasons (Ns) can be chosen between a minimum of one and a maximum of four. The larger the number of seasons becomes, the larger is the number of input data required. The duration of each season (Ts) is given in number of months (0 < Ts < 12). Day to day water balances are not considered for several reasons:
#daily inputs would require much information, which may not be readily available;
#the method is especially developed to predict long term, not day-to-day, trends and predictions for the future are more reliably made on a seasonal (long term) than on a daily (short term) basis, due to the high variability of short-term data;
#even though the precision of the predictions for the future may still not be very high, a lot is gained when the trend is sufficiently clear; for example, it need not be a major constraint to design appropriate soil salinity control measures when a certain salinity level, predicted by Saltmod to occur after 20 years, will in reality occur after 15 or 25 years. | 9 | Geochemistry |
The condition to get a partially ideal solution on mixing is that the volume of the resulting mixture V to equal double the volume V of each solution mixed in equal volumes due to the additivity of volumes. The resulting volume can be found from the mass balance equation involving densities of the mixed and resulting solutions and equalising it to 2:
implies
Of course for real solutions inequalities appear instead of the last equality. | 3 | Analytical Chemistry |
The Generalized Steno Law states that the interfacial angles between identical faces of any single crystal of the same material are, by nature, restricted to the same value. This offers the opportunity to fingerprint crystalline materials on the basis of optical goniometry, which is also known as crystallometry. In order to employ this technique successfully, one must consider the observed point group symmetry of the measured faces and creatively apply the rule that "crystal morphologies are often combinations of simple (i.e. low multiplicity) forms where the individual faces have the lowest possible Miller indices for any given zone axis". This shall ensure that the correct indexing of the crystal faces is obtained for any single crystal.
It is in many cases possible to derive the ratios of the crystal axes for crystals with low symmetry from optical goniometry with high accuracy and precision and to identify a crystalline material on their basis alone employing databases such as Crystal Data. Provided that the crystal faces have been correctly indexed and the interfacial angles were measured to better than a few fractions of a tenth of a degree, a crystalline material can be identified quite unambiguously on the basis of angle comparisons to two rather comprehensive databases: the Bestimmungstabellen für Kristalle (Определитель Кристаллов) and the Barker Index of Crystals.
Since Stenos Law can be further generalized for a single crystal of any material to include the angles between either all identically indexed net planes (i.e. vectors of the reciprocal lattice, also known as potential reflections in diffraction experiments') or all identically indexed lattice directions (i.e. vectors of the direct lattice, also known as zone axes), opportunities exist for morphological fingerprinting of nanocrystals in the transmission electron microscope (TEM) by means of transmission electron goniometry.
The specimen goniometer of a TEM is thereby employed analogously to the goniometer head of an optical goniometer. The optical axis of the TEM is then analogous to the reference direction of an optical goniometer. While in optical goniometry net-plane normals (reciprocal lattice vectors) need to be successively aligned parallel to the reference direction of an optical goniometer in order to derive measurements of interfacial angles, the corresponding alignment needs to be done for zone axes (direct lattice vector) in transmission electron goniometry. (Note that such alignments are by their nature quite trivial for nanocrystals in a TEM after the microscope has been aligned by standard procedures.)
Since transmission electron goniometry is based on Braggs Law for the transmission (Laue) case (diffraction of electron waves), interzonal angles (i.e. angles between lattice directions) can be measured by a procedure that is analogous to the measurement of interfacial angles in an optical goniometer on the basis of Snells Law, i.e. the reflection of light. The complements to interfacial angles of external crystal faces can, on the other hand, be directly measured from a zone-axis diffraction pattern or from the Fourier transform of a high resolution TEM image that shows crossed lattice fringes. | 7 | Physical Chemistry |
Josef Fried was born in the town of Przemyśl, Poland, on July 21, 1914.
Fried received his Ph.D. in organic chemistry from Columbia University in 1940.
Fried joined the Squibb Institute in 1944 as a head of its antibiotics and steroids department. He was later promoted to director of the organic chemistry section in 1959.
In 1963 Fried was appointed professor at the Ben May Laboratory for Cancer Research at the University of Chicago. | 0 | Organic Chemistry |
These mechanistic mimetics do not directly recapitulate the side chains or conformation of a peptide but mimic its mode-of-action. Class D peptidomimetics can be directly designed from a small peptide sequence or identified the screening of compound libraries. For example, Nirmatrelvir is an orally-active small molecule drug derived from lufotrelvir, a modified L-peptide. | 0 | Organic Chemistry |
There are many GFP-like proteins that, despite being in the same protein family as GFP, are not directly derived from Aequorea victoria. These include dsRed, eqFP611, Dronpa, TagRFPs, KFP, EosFP/IrisFP, Dendra, and so on. Having been developed from proteins in different organisms, these proteins can sometimes display unanticipated approaches to chromophore formation. Some of these, such as KFP, are developed from naturally non- or weakly-fluorescent proteins to be greatly improved upon by mutagenesis. When GFP-like barrels of different spectra characteristics are used, the excitation spectra of one chromophore can be used to power another chromophore (FRET), allowing for conversion between wavelengths of light.
FMN-binding fluorescent proteins (FbFPs) were developed in 2007 and are a class of small (11–16 kDa), oxygen-independent fluorescent proteins that are derived from blue-light receptors. They are intended especially for the use under anaerobic or hypoxic conditions, since the formation and binding of the Flavin chromophore does not require molecular oxygen, as it is the case with the synthesis of the GFP chromophore.
Fluorescent proteins with other chromophores, such as UnaG with bilirubin, can display unique properties like red-shifted emission above 600 nm or photoconversion from a green-emitting state to a red-emitting state. They can have excitation and emission wavelengths far enough apart to achieve conversion between red and green light.
A new class of fluorescent protein was evolved from a cyanobacterial (Trichodesmium erythraeum) phycobiliprotein, α-allophycocyanin, and named small ultra red fluorescent protein (smURFP) in 2016. smURFP autocatalytically self-incorporates the chromophore biliverdin without the need of an external protein, known as a lyase. Jellyfish- and coral-derived GFP-like proteins require oxygen and produce a stoichiometric amount of hydrogen peroxide upon chromophore formation. smURFP does not require oxygen or produce hydrogen peroxide and uses the chromophore, biliverdin. smURFP has a large extinction coefficient (180,000 M cm) and has a modest quantum yield (0.20), which makes it comparable biophysical brightness to eGFP and ~2-fold brighter than most red or far-red fluorescent proteins derived from coral. smURFP spectral properties are similar to the organic dye Cy5.
Reviews on new classes of fluorescent proteins and applications can be found in the cited reviews. | 1 | Biochemistry |
The basic structure of [https://web.archive.org/web/20110720035915/http://metpetdb.rpi.edu/ MetPetDB] is based on a geologic sample and derivative subsamples. Geochemical data are linked to subsamples and the minerals within them, while image data can relate to samples or subsamples. MetPetDB is designed to store the distinct spatial/textural context of mineral analysis that is a crucial to petrologic interpretation. A web-based user interface allows a user to become members and download their search results. Approved members may become contributors and upload data to catalogue and share with the public. More information about the data model and the design of the database is available on the MetPetDB Support Wiki. | 9 | Geochemistry |
A different technique to simulate the metabolic network is to perform flux balance analysis. This method uses linear programming, but in contrast to elementary mode analysis and extreme pathways, only a single solution results in the end. Linear programming is usually used to obtain the maximum potential of the objective function that you are looking at, and therefore, when using flux balance analysis, a single solution is found to the optimization problem. In a flux balance analysis approach, exchange fluxes are assigned to those metabolites that enter or leave the particular network only. Those metabolites that are consumed within the network are not assigned any exchange flux value. Also, the exchange fluxes along with the enzymes can have constraints ranging from a negative to positive value (ex: -10 to 10).
Furthermore, this particular approach can accurately define if the reaction stoichiometry is in line with predictions by providing fluxes for the balanced reactions. Also, flux balance analysis can highlight the most effective and efficient pathway through the network in order to achieve a particular objective function. In addition, gene knockout studies can be performed using flux balance analysis. The enzyme that correlates to the gene that needs to be removed is given a constraint value of 0. Then, the reaction that the particular enzyme catalyzes is completely removed from the analysis. | 1 | Biochemistry |
There are numerous classes of natural products for which total synthesis is applied to. These include (but are not limited to): terpenes, alkaloids, polyketides and polyethers. Total synthesis targets are sometimes referred to by their organismal origin such as plant, marine, and fungal. The term total synthesis is less frequently but still accurately applied to the synthesis of natural polypeptides and polynucleotides. The peptide hormones oxytocin and vasopressin were isolated and their total syntheses first reported in 1954. It is not uncommon for natural product targets to feature multiple structural components of several natural product classes. | 0 | Organic Chemistry |
The multiple hearth furnaces consist of several circular hearths or kilns superimposed on each other. Material is fed from the top and is moved by the action of rotating "rabble arms", and the revolving mechanical rabbles attached to the arms move over the surface of each hearth to continuously shift the ore. The arms are attached to a rotating central shaft that passes through the center of the roaster. As the material is moved, the ore that is charged at the top hearth gradually moves downward as it passes through windows in the floor of each hearth or through alternate passages around the shaft and the periphery until it finally emerges at the bottom. | 8 | Metallurgy |
The ratio average (RA) plot is an integer-based version of an MA plot for visualizing two-condition count data. Its distinctive arrow-like shape derives from the way it includes condition-unique (0,n) or (n,0) points into the plot via an epsilon factor. | 1 | Biochemistry |
Opacity broadening is an example of a non-local broadening mechanism. Electromagnetic radiation emitted at a particular point in space can be reabsorbed as it travels through space. This absorption depends on wavelength. The line is broadened because the photons at the line center have a greater reabsorption probability than the photons at the line wings. Indeed, the reabsorption near the line center may be so great as to cause a self reversal in which the intensity at the center of the line is less than in the wings. This process is also sometimes called self-absorption. | 7 | Physical Chemistry |
Boiling point is the temperature at which the vapor pressure of a liquid is equal to the surrounding pressure, causing the liquid to rapidly evaporate, or boil. It is closely related to vapor pressure, but is dependent on pressure. The normal boiling point is the boiling point at atmospheric pressure, but it can also be reported at higher and lower pressures. | 7 | Physical Chemistry |
James Cullen Kirkcaldie (18 April 1875 – 16 August 1931) was a New Zealand cricketer. He played in one first-class match for Wellington in 1903/04.
Kirkcaldie was an analytical chemist. | 3 | Analytical Chemistry |
In the late 1990s, evidence began accumulating to suggest that some GPCRs are able to signal without G proteins. The ERK2 mitogen-activated protein kinase, a key signal transduction mediator downstream of receptor activation in many pathways, has been shown to be activated in response to cAMP-mediated receptor activation in the slime mold D. discoideum despite the absence of the associated G protein α- and β-subunits.
In mammalian cells, the much-studied β-adrenoceptor has been demonstrated to activate the ERK2 pathway after arrestin-mediated uncoupling of G-protein-mediated signaling. Therefore, it seems likely that some mechanisms previously believed related purely to receptor desensitisation are actually examples of receptors switching their signaling pathway, rather than simply being switched off.
In kidney cells, the bradykinin receptor B2 has been shown to interact directly with a protein tyrosine phosphatase. The presence of a tyrosine-phosphorylated ITIM (immunoreceptor tyrosine-based inhibitory motif) sequence in the B2 receptor is necessary to mediate this interaction and subsequently the antiproliferative effect of bradykinin. | 1 | Biochemistry |
Microanalysis is the chemical identification and quantitative analysis of very small amounts of chemical substances (generally less than 10 mg or 1 ml) or very small surfaces of material (generally less than 1 cm). One of the pioneers in the microanalysis of chemical elements was the Austrian Nobel Prize winner Fritz Pregl. | 3 | Analytical Chemistry |
Starting from the 1950s, Schwab was allowed to return to West Germany, with his first post being guest professor at the Technical University of Darmstadt (1949) before he was appointed to the illustrious Professorship of Physical Chemistry at the University of Munich in 1950. While holding the corresponding seat in Athens, Schwab continued visiting Greece to offer lectures on his course.
Meanwhile, he engaged in notable novel research regarding surface catalytic interactions. In the 1955–1956 academic year he was Dean of the Faculty of Natural Sciences of the University of Munich. He retired in 1967 with the title of Emeritus Professor of Physical Chemistry, which he held until his death in 1984. | 7 | Physical Chemistry |
The variation of specific rotation with wavelength is called optical rotatory dispersion (ORD). ORD can be used in conjunction with computational methods to determine the absolute configuration of certain compounds. | 4 | Stereochemistry |
A tertiary carbon atom is a carbon atom bound to three other carbon atoms. For this reason, tertiary carbon atoms are found only in hydrocarbons containing at least four carbon atoms. They are called saturated hydrocarbons because they only contain carbon-carbon single bonds. Tertiary carbons have a hybridization of sp3. Tertiary carbon atoms can occur, for example, in branched alkanes, but not in linear alkanes. | 0 | Organic Chemistry |
While semi-synthetic ion channels, often based on modified peptidic channels like gramicidin, had been prepared since the 1970s, the first attempt to prepare a synthetic ion channel was made in 1982 using a substituted β-cyclodextrin.
Inspired by gramicidin, this molecule was designed to be a barrel-shaped entity spanning a single leaflet of a bilayer membrane, becoming "active" only when two molecules in opposite leaflets come together in an end-to-end fashion. While the compound does induce ion-fluxes in vesicles, the data does not unambiguously show channel formation (as opposed to other transport mechanisms; see Mechanism).
Na transport by such channels was first reported by two groups of investigators in 1989–1990.
With the adoption of voltage clamp technique to synthetic channel research in the early 1990s, researchers were able to observe quantized electrical activities from synthetic molecules, often considered the signature evidence for ion channels. This led to a sustained increase in research activity over the next two decades. In 2009, over 25 peer-reviewed papers were published on the topic, and a series of comprehensive reviews are available. | 6 | Supramolecular Chemistry |
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