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Nitrification in nature is a two-step oxidation process of ammonium () or ammonia () to nitrite () and then to nitrate () catalyzed by two ubiquitous bacterial groups growing together. The first reaction is oxidation of ammonium to nitrite by ammonia oxidizing bacteria (AOB) represented by members of Betaproteobacteria and Gammaproteobacteria. Further organisms able to oxidize ammonia are Archaea (AOA).
The second reaction is oxidation of nitrite () to nitrate by nitrite-oxidizing bacteria (NOB), represented by the members of Nitrospinota, Nitrospirota, Pseudomonadota, and Chloroflexota.
This two-step process was described already in 1890 by the Ukrainian microbiologist Sergei Winogradsky.
Ammonia can be also oxidized completely to nitrate by one comammox bacterium. | 1 | Biochemistry |
Similar to ρ values for Hammett plots, the polar sensitivity factor ρ* for Taft plots will describe the susceptibility of a reaction series to polar effects. When the steric effects of substituents do not significantly influence the reaction rate the Taft equation simplifies to a form of the Hammett equation:
The polar sensitivity factor ρ* can be obtained by plotting the ratio of the measured reaction rates (k) compared to the reference reaction () versus the σ* values for the substituents. This plot will give a straight line with a slope equal to ρ*. Similar to the Hammett ρ value:
* If ρ* > 1, the reaction accumulates negative charge in the transition state and is accelerated by electron withdrawing groups.
* If 1 > ρ* > 0, negative charge is built up and the reaction is mildly sensitive to polar effects.
* If ρ* = 0, the reaction is not influenced by polar effects.
* If 0 > ρ* > −1, positive charge is built up and the reaction is mildly sensitive to polar effects.
* If −1 > ρ*, the reaction accumulates positive charge and is accelerated by electron donating groups. | 7 | Physical Chemistry |
The movement of terrestrial carbon in the water cycle is shown in the diagram on the right and explained below:
# Atmospheric particles act as cloud condensation nuclei, promoting cloud formation.
#Raindrops absorb organic and inorganic carbon through particle scavenging and adsorption of organic vapors while falling toward Earth.
#Burning and volcanic eruptions produce highly condensed polycyclic aromatic molecules (i.e. black carbon) that is returned to the atmosphere along with greenhouse gases such as CO.
#Terrestrial plants fix atmospheric CO through photosynthesis, returning a fraction back to the atmosphere through respiration. Lignin and celluloses represent as much as 80% of the organic carbon in forests and 60% in pastures.
#Litterfall and root organic carbon mix with sedimentary material to form organic soils where plant-derived and petrogenic organic carbon is both stored and transformed by microbial and fungal activity.
#Water absorbs plant and settled aerosol-derived dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) as it passes over forest canopies (i.e. throughfall) and along plant trunks/stems (i.e. stemflow). Biogeochemical transformations take place as water soaks into soil solution and groundwater reservoirs and overland flow occurs when soils are completely saturated, or rainfall occurs more rapidly than saturation into soils.
#Organic carbon derived from the terrestrial biosphere and in situ primary production is decomposed by microbial communities in rivers and streams along with physical decomposition (i.e. photo-oxidation), resulting in a flux of CO from rivers to the atmosphere that are the same order of magnitude as the amount of carbon sequestered annually by the terrestrial biosphere. Terrestrially-derived macromolecules such as lignin and black carbon are decomposed into smaller components and monomers, ultimately being converted to CO, metabolic intermediates, or biomass.
#Lakes, reservoirs, and floodplains typically store large amounts of organic carbon and sediments, but also experience net heterotrophy in the water column, resulting in a net flux of CO to the atmosphere that is roughly one order of magnitude less than rivers. Methane production is also typically high in the anoxic sediments of floodplains, lakes, and reservoirs.
#Primary production is typically enhanced in river plumes due to the export of fluvial nutrients. Nevertheless, estuarine waters are a source of CO to the atmosphere, globally.
#Coastal marshes both store and export blue carbon. Marshes and wetlands are suggested to have an equivalent flux of CO to the atmosphere as rivers, globally.
#Continental shelves and the open ocean typically absorb CO from the atmosphere.
#The marine biological pump sequesters a small but significant fraction of the absorbed CO as organic carbon in marine sediments (see below). | 5 | Photochemistry |
Nuclear receptor interacting protein 1 (NRIP1) is a nuclear protein that specifically interacts with the hormone-dependent activation domain AF2 of nuclear receptors. Also known as RIP140, this protein is a key regulator which modulates transcriptional activity of a variety of transcription factors, including the estrogen receptor.
RIP140 has an important role in regulating lipid and glucose metabolism, and regulates gene expression in metabolic tissues including heart, skeletal muscle, and liver. A major role for RIP140 in adipose tissue is to block the expression of genes involved in energy dissipation and mitochondrial uncoupling, including uncoupling protein 1 and carnitine palmitoyltransferase 1b.
Estrogen-related receptor alpha (ERRa) can activate RIP140 during adipogenesis, by means of directly binding to an estrogen receptor element/ERR element and indirectly through Sp1 binding to the proximal promoter.
RIP140 suppresses the expression of mitochondrial proteins succinate dehydrogenase complex b and CoxVb and acts as a negative regulator of glucose uptake in mice. | 1 | Biochemistry |
Invalid if other proteins or immunoglobulins compete with TBG, including familial dysalbuminemic hyperthyroxinemia | 1 | Biochemistry |
Sutula, Chester Louis, Structure, molecular orientation and mechanically induced reorientation of molecules in multimolecular films of long-chain n-hydrocarbon derivatives, 155 (1959) | 3 | Analytical Chemistry |
From 1965 — Associate Research Fellow of the Kiev Institute of Hygiene and Occupational Diseases, where he received a PhD degree in medical sciences. Since 1971, research activities related to Romain Efimovicha connected with VNIIGINTOKS (now the Institute of ecological hygiene and toxicology behalf L. I. Medved). Over 26 years of work at the institute, he has gone from a research assistant to the deputy director for scientific work. The main focus of his activity was the methodology of integrated assessment of chemical risks to human health and the environment. He took an active part in the development of new directions in toxicology and health - a complex hygienic regulation of pesticides, hygienic regulation of pesticides in soil, application of mathematical methods to assess and predict the real risk of accumulation of pesticides in the environment and the human body. He is coauthor of environmental hygiene and classification of pesticides hazard. As a toxicologist Romen E. Sova has made a significant contribution to the development problems of biological standards of laboratory animals, the methodology and methods of studying the combined, integrated and combined effects of chemicals and other factors. Romain Yefimovich established the All-Union Center "Dioxin", commenced research on this problem, developed the first hygienic standards of the most dangerous environmental pollutants. He was an expert of WHO on the issue of dioxin, an expert from Ukraine on the issue of persistent organic pollutants in the United Nations Environment Programme, a member of the committee on the hygienic regulation of MH of Ukraine. Romen Yefimovich prepared 5 Candidates of Medical Sciences, published 6 monographs and more than 230 scientific papers. | 0 | Organic Chemistry |
The Association of Public Analysts (APA) is a UK professional association for public analysts. It was founded in 1954, although an earlier body, the Society of Public Analysts, was founded in 1874, became the Society for Analytical Chemistry, and was one of the bodies which merged to form the Royal Society of Chemistry in 1980.
Through its activities it seeks to serve the public by using analytical chemistry to addressing a wide range of issues including not only the adulteration and contamination of food, drugs and other commercial products but also to adi in their accurrate description. the APA president is Jane White.
It publishes the Journal of the Association of Public Analysts (JAPA), which appeared in print from 1963 to 1997, volumes 1-33 (), and was then relaunched as an online journal from volume 34, 2006 (). | 2 | Environmental Chemistry |
One possible treatment for cancer involves monoclonal antibodies that bind only to cancer-cell-specific antigens and induce an immune response against the target cancer cell. Such mAbs can be modified for delivery of a toxin, radioisotope, cytokine or other active conjugate or to design bispecific antibodies that can bind with their Fab regions both to target antigen and to a conjugate or effector cell. Every intact antibody can bind to cell receptors or other proteins with its Fc region.
MAbs approved by the FDA for cancer include:
* Alemtuzumab
* Bevacizumab
* Cetuximab
* Dostarlimab
* Gemtuzumab ozogamicin
* Ipilimumab
* Nivolumab
* Ofatumumab
* Panitumumab
* Pembrolizumab
* Ranibizumab
* Rituximab
* Trastuzumab | 1 | Biochemistry |
Since a sequence of single-stranded DNA needs to find its complementary strand to reform a double helix, common sequences renature more rapidly than rare sequences. Indeed, the rate at which a sequence will reassociate is proportional to the number of copies of that sequence in the DNA sample. A sample with a highly-repetitive sequence will renature rapidly, while complex sequences will renature slowly.
However, instead of simply measuring the percentage of double-stranded DNA versus time, the amount of renaturation is measured relative to a Ct value. The Ct value is the product of C (the initial concentration of DNA), t (time in seconds), and a constant that depends on the concentration of cations in the buffer. Repetitive DNA will renature at low Ct values, while complex and unique DNA sequences will renature at high Ct values. The fast renaturation of the repetitive DNA is because of the availability of numerous complementary sequences. | 1 | Biochemistry |
Thermogalvanic cells can be used to extract a useful quantity of energy from waste heat sources even when the temperature gradient is less than 100C (sometimes only a few tens of degrees). This is often the case in many industrial areas. | 7 | Physical Chemistry |
The other case of special importance is when a molecule D dissociates into two atoms upon adsorption. Here, the following assumptions would be held to be valid:
# D completely dissociates to two molecules of D upon adsorption.
# The D atoms adsorb onto distinct sites on the surface of the solid and then move around and equilibrate.
# All sites are equivalent.
# Each site can hold at most one atom of D.
# There are no interactions between adsorbate molecules on adjacent sites.
Using similar kinetic considerations, we get
The 1/2 exponent on p</sub> arises because one gas phase molecule produces two adsorbed species. Applying the site balance as done above, | 7 | Physical Chemistry |
Hydrogen is produced by hydrogenases and nitrogenases enzymes in many microorganisms, some of which are being studied for their potential for biofuel production. These H-metabolizing enzymes are found in all three domains of life, and out of known genomes over 30% of microbial taxa contain hydrogenase genes. Fermentation produces H from organic matter as part of the anaerobic microbial food chain via light-dependent or light-independent pathways. | 1 | Biochemistry |
Conduction in a gas requires charge carriers, which can be either electrons or ions. Charge carriers come from ionizing some of the gas molecules. In terms of current flow, glow discharge falls between dark discharge and arc discharge.
*In a dark discharge, the gas is ionized (the carriers are generated) by a radiation source such as ultraviolet light or Cosmic rays. At higher voltages across the anode and cathode, the freed carriers can gain enough energy so that additional carriers are freed during collisions; the process is a Townsend avalanche or multiplication.
*In a glow discharge, the carrier generation process reaches a point where the average electron leaving the cathode allows another electron to leave the cathode. For example, the average electron may cause dozens of ionizing collisions via the Townsend avalanche; the resulting positive ions head toward the cathode, and a fraction of those that cause collisions with the cathode will dislodge an electron by secondary emission.
*In an arc discharge, electrons leave the cathode by thermionic emission and field emission, and the gas is ionized by thermal means.
Below the breakdown voltage there is little to no glow and the electric field is uniform. When the electric field increases enough to cause ionization, the Townsend discharge starts. When a glow discharge develops, the electric field is considerably modified by the presence of positive ions; the field is concentrated near the cathode. The glow discharge starts as a normal glow. As the current is increased, more of the cathode surface is involved in the glow. When the current is increased above the level where the entire cathode surface is involved, the discharge is known as an abnormal glow. If the current is increased still further, other factors come into play and an arc discharge begins. | 3 | Analytical Chemistry |
In some compounds the metal-ligand bonds may not all be at the same distance. For example in PbCl, the coordination number of Pb could be said to be seven or nine, depending on which chlorides are assigned as ligands. Seven chloride ligands have Pb-Cl distances of 280–309 pm. Two chloride ligands are more distant, with a Pb-Cl distances of 370 pm.
In some cases a different definition of coordination number is used that includes atoms at a greater distance than the nearest neighbours. The very broad definition adopted by the International Union of Crystallography, IUCR, states that the coordination number of an atom in a crystalline solid depends on the chemical bonding model and the way in which the coordination number is calculated.
Some metals have irregular structures. For example, zinc has a distorted hexagonal close packed structure. Regular hexagonal close packing of spheres would predict that each atom has 12 nearest neighbours and a triangular orthobicupola (also called an anticuboctahedron or twinned cuboctahedron) coordination polyhedron. In zinc there are only 6 nearest neighbours at 266 pm in the same close packed plane with six other, next-nearest neighbours, equidistant, three in each of the close packed planes above and below at 291 pm. It is considered to be reasonable to describe the coordination number as 12 rather than 6. Similar considerations can be applied to the regular body centred cube structure where in addition to the 8 nearest neighbors there 6 more, approximately 15% more distant, and in this case the coordination number is often considered to be 14.
Many chemical compounds have distorted structures. Nickel arsenide, NiAs has a structure where nickel and arsenic atoms are 6-coordinate. Unlike sodium chloride where the chloride ions are cubic close packed, the arsenic anions are hexagonal close packed. The nickel ions are 6-coordinate with a distorted octahedral coordination polyhedron where columns of octahedra share opposite faces. The arsenic ions are not octahedrally coordinated but have a trigonal prismatic coordination polyhedron. A consequence of this arrangement is that the nickel atoms are rather close to each other. Other compounds that share this structure, or a closely related one are some transition metal sulfides such as FeS and CoS, as well as some intermetallics. In cobalt(II) telluride, CoTe, the six tellurium and two cobalt atoms are all equidistant from the central Co atom.
Two other examples of commonly-encountered chemicals are FeO and TiO. FeO has a crystal structure that can be described as having a near close packed array of oxygen atoms with iron atoms filling two thirds of the octahedral holes. However each iron atom has 3 nearest neighbors and 3 others a little further away. The structure is quite complex, the oxygen atoms are coordinated to four iron atoms and the iron atoms in turn share vertices, edges and faces of the distorted octahedra. TiO has the rutile structure. The titanium atoms 6-coordinate, 2 atoms at 198.3 pm and 4 at 194.6 pm, in a slightly distorted octahedron. The octahedra around the titanium atoms share edges and vertices to form a 3-D network. The oxide ions are 3-coordinate in a trigonal planar configuration. | 4 | Stereochemistry |
The dissociation degree is the fraction of original solute molecules that have dissociated. It is usually indicated by the Greek symbol α. More accurately, degree of dissociation refers to the amount of solute dissociated into ions or radicals per mole. In case of very strong acids and bases, degree of dissociation will be close to 1. Less powerful acids and bases will have lesser degree of dissociation. There is a simple relationship between this parameter and the van 't Hoff factor . If the solute substance dissociates into ions, then
For instance, for the following dissociation
As , we would have that . | 7 | Physical Chemistry |
The molar concentration is defined as the amount of a constituent (in moles) divided by the volume of the mixture :
The SI unit is mol/m. However, more commonly the unit mol/L (= mol/dm) is used. | 3 | Analytical Chemistry |
An example is the auxin mediated derepression of the auxin response factor family of transcription factors in plants. These auxin response factors are repressed by Aux/IAA repressors. In the presence of auxin, these Aux/AII proteins undergo ubiquitination and are then degraded. This derepresses the auxin response factors so they may carry out their functions in the cell. | 1 | Biochemistry |
When drained, soils containing Reduced Inorganic Sulfides such as pyrite may become extremely acidic (pH SO):
The product Fe(OH), iron(III) hydroxide (orange), precipitates as a solid, insoluble mineral by which the alkalinity component is immobilized, while the acidity remains active in the sulfuric acid. The process of acidification is accompanied by the formation of high amounts of aluminium (Al, released from clay minerals under influence of the acidity), which are harmful to vegetation. Other products of the chemical reaction are:
# Hydrogen sulfide (HS), a foul-smelling gas
# Sulfur (S), a yellow solid
# Iron(II) sulfide (FeS), a black/gray/blue solid
# Hematite (FeO), a red solid
# Goethite (), a brown mineral
# Iron sulfate compounds (e.g., jarosite, schwertmannite, gypsum, and epsomite)
# H-Clay (hydrogen clay, with a large fraction of adsorbed H ions, a stable mineral, but poor in nutrients)
The iron can be present in bivalent and trivalent forms (Fe, the ferrous ion, and Fe, the ferric ion respectively). The ferrous form is soluble in a relatively wide range of pH conditions whereas the ferric form is not soluble except in an extremely acidic environment such as muriatic acid rust remover. The more oxidized the soil becomes, the more the ferric forms dominate. Acid sulfate soils exhibit an array of colors ranging from black, brown, blue-gray, red, orange and yellow. The hydrogen clay can be improved by admitting sea water: the magnesium (Mg) and sodium (Na) in the sea water replaces the adsorbed hydrogen and other exchangeable acidic cations such as aluminium (Al). However this can create additional risks when the hydrogen ions and exchangeable metals are mobilised. | 9 | Geochemistry |
There are relatively few published examples of demonstrations or recreation of the experiment. Two physicists in the University of Washington system reported on demonstrations to students and colleagues and produced directions for re-creating the experiment in 1985 as part of an investigation into the role of the experiment in the history of physics. Physicists at Sofia University in Bulgaria reported on reproducing the experiment for high school students in 2017. | 7 | Physical Chemistry |
Iron stress repressed RNA (IsrR) is a cis-encoded antisense RNA which regulates the expression of the photosynthetic protein isiA. IsiA expression is activated by the Ferric uptake regulator protein (Fur) under iron stress conditions. IsiA enhances photosynthesis by forming a ring around photosystem I which acts as an additional antenna complex.
IsrR is abundant when there is a sufficient iron concentration. IsrR is encoded for within the opposite stand of isiA gene and contains a conserved stem loop secondary structure. Under sufficient iron conditions IsrR binds to its complementary region which corresponds to the central third of the isiA mRNA. The resulting duplex RNA is then targeted for degradation. This allows the antisense RNA to act as a reversible switch that responds to changes in environmental conditions to modulate the expression of the isiA protein.
IsrR was originally identified within cyanobacteria but may be conserved throughout a number of photosynthetic species from multiple kingdoms. At present, IsrR is the only non coding RNA identified that has a regulatory role on photosynthetic proteins. | 1 | Biochemistry |
Born on September 16, 1944, in the village of Novachene, Sofia Province. In 1969 he graduated from Sofia University "St. Kliment Ohridski”, Faculty of Geology and Geography, specialty geology-geochemistry. From 1969 to 1975 he worked in the uranium mine "Eleshnitsa" as a deputy director. In 1975 he won a competition for a research associate and was employed at the Institute of Oceanology - BAS. In 1979 he defended his dissertation on "Genesis of marine sediments in the peripheral region of the western part of the Black Sea shelf in the Quaternary" under the guidance of Academician Yastrebov and Prof. Aksenov at the Shirshov Institute of Oceanology, Moscow.
* He introduced new scientific disciplines for the Bulgaria - "Marine Geology" and "Geoarchaeology".
* Scientific Secretary of IO-BAS, Varna, 1977 - 1984; Deputy Director of IO-BAS, Varna, 1984 - 1993; Head of the Department "Marine Geology and Archaeology" of IO-BAS, Varna, 1997 - 2009.
* There is original research related to the "Black Sea deluge hypothesis"
* Leader and participant in over 30 international scientific expeditions in the Black Sea (with Dr. Robert Ballard 2001, 2002; Woods Hole Oceanographic Institution 2006; Prof. William Ryan 2009, 2011 – project 02–337 "Ancient coastlines of the Black Sea and conditions for human presence", funded by the Bulgarian National Science Fund at the Ministry of Education and Science of Bulgaria ). His is the most sensational, but also the most controversial find in Bulgarian archeology, the so-called "Noahs Plate". It was discovered on July 15, 1985 at a depth of about 93 m and 65 km inland from Varna. There is still no one to acknowledge its authenticity.'
* He participated in international scientific expeditions to the Pacific Ocean (1982), the Atlantic Ocean and the Mediterranean Sea (1984).
* The first Bulgarian scientist studied Manganese nodule in Pacific Ocean.
* Membership in scientific organizations: Member of Union of Scientists - Varna, Bulgarian Geological Society, Bulgarian Geographical Society, Foreign member of the National Academy of Sciences of Ukraine.
* Honorary citizen of the city of Varna, 2013
* Research interests: Black Sea, Geology, Geochemistry, Marine geology, Black Sea deluge hypothesis, alternative sources and energy resources from the bottom of the Black Sea, Maritime history, archeology and geoarcheology, uranium minerals and uranium mining.
* Teaching activity: Lecturer in Marine Geology, Lithology and Geochemistry in Nikola Vaptsarov Naval Academy and Varna Free University. Lecturer at the University of Bologna and the University Consortium in Underwater Archeology - Sicily, Italy.
* Scientific publications: Author and co-author of over 150 scientific articles and books. Citations: over 1300.
* He is the creator of the idea for the application of sapropel sediments from the bottom of the Black Sea as a natural ecological fertilizer and biological products. Patent BG No. 63868, Register No. 104106.
* Scientific awards: Medal for scientific contributions "St. St. Cyril and Methodius”- II degree, for realization of the project "Correlation of Geological, Climatic and Historical Events in the Black Sea, Marmara Sea and Mediterranean Sea during the last 25000 years (Noahs Flood Project')".
* Participation in films about the Black Sea Flood (Black Sea deluge hypothesis) – „BBC–Horizon–1996 – Noah's Flood“, ZDF „Terra X 56 Die Sintflut“, UFOTV „Dark Secrets of Black Sea“, „Ancient X-Files: Season 2 Episode 8 - Great Flood and Scottish Stone Mystery - National Geographic“ etc.
* Collaborator of the Institute of Ancient Civilizations in Sofia.
* He was a member of the High Attestation Commission (Scientific Commission for Geological and Geographical Sciences) - 2 mandate.
* OUR MEMORY ON LIFE AND SCIENTIFIC ACTIVITY BY PROFESSOR DIMITROV PETKO STOYANOV. | 9 | Geochemistry |
In the physical sciences, an interface is the boundary between two spatial regions occupied by different matter, or by matter in different physical states. The interface between matter and air, or matter and vacuum, is called a surface, and studied in surface science. In thermal equilibrium, the regions in contact are called phases, and the interface is called a phase boundary. An example for an interface out of equilibrium is the grain boundary in polycrystalline matter.
The importance of the interface depends on the type of system: the bigger the quotient area/volume, the greater the effect the interface will have. Consequently, interfaces are very important in systems with large interface area-to-volume ratios, such as colloids.
Interfaces can be flat or curved. For example, oil droplets in a salad dressing are spherical but the interface between water and air in a glass of water is mostly flat.
Surface tension is the physical property which rules interface processes involving liquids. For a liquid film on flat surfaces, the liquid-vapor interface keeps flat to minimize interfacial area and system free energy. For a liquid film on rough surfaces, the surface tension tends to keep the meniscus flat, while the disjoining pressure makes the film conformal to the substrate. The equilibrium meniscus shape is a result of the competition between the capillary pressure and disjoining pressure.
Interfaces may cause various optical phenomena, such as refraction. Optical lenses serve as an example of a practical application of the interface between glass and air.
One topical interface system is the gas-liquid interface between aerosols and other atmospheric molecules. | 7 | Physical Chemistry |
To make this kind of race possible, a considerable number of problems had to be solved beforehand, such as the choice of the track and its preparation, the improvement of monitoring and control devices, in particular the sensitivity of current measurements, the evaporation of a large number of very different molecules on the same surface and microscope validation
Among the benefits, the CNRS cites the development molecular motors and Tech-Atoms, that will make possible in the future the preparation of quantum electronic circuits on the surface of an insulator, atom by atom, whose calculating parts will measure less than 1 nm. | 6 | Supramolecular Chemistry |
Iron oxides are reduced in the following sequence:
O → FeO → FeO
Each transition from one oxide to the next is due to two simultaneous high-temperature reduction reactions by carbon monoxide CO or dihydrogen H:
These temperatures differ from those predicted by the Ellingham diagram. In reality, there is a coupling between carbon monoxide reduction and dihydrogen, so that these reactions work together, with hydrogen significantly improving the efficiency of CO reduction. | 8 | Metallurgy |
* 2021, ACS Carothers Award
* 2019, DuPont Company Lavoisier Medal
* 2018, elected to the National Academy of Engineering
* 2018, named Fellow of the SPIE
* 2016, Perkin Medal, from the Society of Chemical Industry
* 2014, ACS Heroes of Chemistry, from the American Chemical Society (one of thirteen scientists from the Dow Chemical Company credited with the development of Dow AR Fast Etch Organic Bottom Antireflectant Coatings)
* 2013, SPIE C. Grant Willson Best Paper Award in Patterning Materials and Processes jointly with researchers at Dow and Texas A&M University, from SPIE for the paper "Bottom-up / top-down high-resolution, high-throughput lithography using vertically assembled block brush polymers". | 5 | Photochemistry |
Tenuifolins are bio-active terpenoids. Tenuifolins inhibit beta-amyloid synthesis in vitro. Tenuifolins have nootropic activity in vivo via acetylcholinesterase inhibition and increased norepinephrine and dopamine production. | 0 | Organic Chemistry |
Ferrotitanium is a ferroalloy, an alloy of iron and titanium with between 10 and 20% iron and 45–75% titanium and sometimes a small amount of carbon. It is used in steelmaking as a cleansing agent for iron and steel; the titanium is highly reactive with sulfur, carbon, oxygen, and nitrogen, forming insoluble compounds and sequestering them in slag, and is therefore used for deoxidizing, and sometimes for desulfurization and denitrogenation. In steelmaking, the addition of titanium yields metal with finer grain structure. Ferrotitanium can be manufactured by mixing titanium sponge and scrap with iron and melting them together in an induction furnace. Ferrotitanium powder can be also used as a fuel in some pyrotechnic compositions. | 8 | Metallurgy |
As shown in the diagram, a number of baffles are used throughout to remove possible stray light being reflected off the sides of the beamline tube. The use of only one mirror minimizes the loss of photon flux which is most important in the VUV region where reflectivity is poor relative to the visible wavelength range.
The first constructed SRCD beamlines initially tried to utilize the intrinsic properties of the SR radiation produced, whereby there exists a "central" linearly-polarized component with, above and below this, equally opposing regions of circularly-polarized components. The premise for this was that the overall signal produced from a chiral sample would be enhanced by the absorption difference (the signal) derived from these circularly polarized features of the beam. In an ideal situation this approach would work; however, this setup was modified such that all beamlines now include a linear polarizer (as shown) to remove these circularly polarized components. This was because even the minutest of movements in beam position (beam drift) led to unequal matching of the contributions of the circularly polarized components striking the sample and this, in turn, meant the SRCD signal produced was inaccurate and unreliable; often being irreproducible as a result.
Whereas cCD machines are purged throughout with nitrogen to minimize the absorption by oxygen of the light from the source xenon arc lamp, in an SRCD arrangement the beam passes through a calcium fluoride (CaF), or similar "VUV-wavelengths transparent", window where everything before this point is in vacuum, and everything beyond is in nitrogen. The beam interacts with a photoelastic modulator (PEM) which consequently produces an alternating right- then left-circularly polarized beam and these now interact with the sample. The resultant absorption difference by the sample is measured and amplified by a photomultiplier tube (PMT) and from this the SRCD spectrum is recorded.
The wavelength range that is utilized for SRCD studies is typically in the UV to VUV region and can go to below this; potentially from ~100 nm, up to the visible region, ~400 nm. The exact range over which data can be collected relies on the beamline set up, the sample preparation and the wavelength range of the PMT detector used. One of the primary factors limiting the lower wavelength cut off is the sample usually being in solution as a large water absorption band exists centred ~167 nm. This high absorption background swamps any possibility of measuring the very small CD difference signal, although use of deuterated water (DO) as the solvent reduces the solvent absorption increasing the lower wavelength data collection range by ~10 nm. Removing the solvating water completely, creating a film as a result, means that data can be recorded to significantly lower wavelengths, down to around ~130 nm. | 7 | Physical Chemistry |
Bragg diffraction occurs when radiation of a wavelength comparable to atomic spacings is scattered in a specular fashion (mirror-like reflection) by planes of atoms in a crystalline material, and undergoes constructive interference. When the scattered waves are incident at a specific angle, they remain in phase and constructively interfere. The glancing angle (see figure on the right, and note that this differs from the convention in Snells law where is measured from the surface normal), the wavelength , and the "grating constant" of the crystal are connected by the relation:where is the diffraction order ( is first order, is second order, is third order). This equation, Braggs law, describes the condition on θ for constructive interference.
A map of the intensities of the scattered waves as a function of their angle is called a diffraction pattern. Strong intensities known as Bragg peaks are obtained in the diffraction pattern when the scattering angles satisfy Bragg condition. This is a special case of the more general Laue equations, and the Laue equations can be shown to reduce to the Bragg condition with additional assumptions. | 3 | Analytical Chemistry |
Two-dimensional chromatography represents the most thorough and rigorous approach to evaluation of the proteome. While previously accepted approaches have utilized elution mode chromatographic approaches such as cation exchange to reversed phase HPLC, yields are typically very low requiring analytical sensitivities in the picomolar to femtomolar range. As displacement chromatography offers the advantage of concentration of trace components, two dimensional chromatography utilizing displacement rather than elution mode in the upstream chromatography step represents a potentially powerful tool for analysis of trace components, modifications, and identification of minor expressed components of the proteome. | 3 | Analytical Chemistry |
Stable isotope labeling involves the use of non-radioactive isotopes that can act as a tracers used to model several chemical and biochemical systems. The chosen isotope can act as a label on that compound that can be identified through nuclear magnetic resonance (NMR) and mass spectrometry (MS). Some of the most common stable isotopes are H, C, and N, which can further be produced into NMR solvents, amino acids, nucleic acids, lipids, common metabolites and cell growth media. The compounds produced using stable isotopes are either specified by the percentage of labeled isotopes (i.e. 30% uniformly labeled C glucose contains a mixture that is 30% labeled with carbon isotope and 70% naturally labeled carbon) or by the specifically labeled carbon positions on the compound (i.e. 1-C glucose which is labeled at the first carbon position of glucose).
A network of reactions adopted from the glycolysis pathway and the pentose phosphate pathway is shown in which the labeled carbon isotope rearranges to different carbon positions throughout the network of reactions. The network starts with fructose 6-phosphate (F6P), which has 6 carbon atoms with a label C at carbon position 1 and 2. 1,2-C F6P becomes two glyceraldehyde 3-phosphate (G3P), one 2,3-C T3P and one unlabeled T3P. The 2,3-C T3P can now be reacted with sedoheptulose 7-phosphate (S7P) to form an unlabeled erythrose 4-phosphate(E4P) and a 5,6-C F6P. The unlabeled T3P will react with the S7P to synthesize unlabeled products. The figure demonstrates the use of stable isotope labeling to discover the carbon atom rearrangement through reactions using position specific labeled compounds. | 7 | Physical Chemistry |
Some trans-spliced snRNAs have been observed to have a N,N,7-trimethylguanosine cap. This particular modification to the guanosine cap is rare in snRNAs. Trans-splicing is a phenomenon in which exons from two different primary RNA transcripts are ligated together. These rare variants have been seen during development in C.elegans and are associated with polysomes. How this modification is regulated in certain cell types and the exact function of this modification remains largely unknown, although it has been speculated that this modification may help define a special subset of trimethylguanosine-regulated RNAs. | 1 | Biochemistry |
Spectral hemispherical transmittance in frequency and spectral hemispherical transmittance in wavelength of a surface, denoted T and T respectively, are defined as
where
*Φ is the spectral radiant flux in frequency transmitted by that surface;
*Φ is the spectral radiant flux in frequency received by that surface;
*Φ is the spectral radiant flux in wavelength transmitted by that surface;
*Φ is the spectral radiant flux in wavelength received by that surface. | 7 | Physical Chemistry |
Liquids are sometimes used in measuring devices. A thermometer often uses the thermal expansion of liquids, such as mercury, combined with their ability to flow to indicate temperature. A manometer uses the weight of the liquid to indicate air pressure.
The free surface of a rotating liquid forms a circular paraboloid and can therefore be used as a telescope. These are known as liquid-mirror telescopes. They are significantly cheaper than conventional telescopes, but can only point straight upward (zenith telescope). A common choice for the liquid is mercury. | 7 | Physical Chemistry |
In protic solution exchangeable protons such as those in hydroxyl or amine group exchange protons with the solvent. If DO is solvent, deuterons will be incorporated at these positions. The exchange reaction can be followed using a variety of methods (see Detection). Since this exchange is an equilibrium reaction, the molar amount of deuterium should be high compared to the exchangeable protons of the substrate. For instance, deuterium is added to a protein in HO by diluting the HO solution with DO (e.g. tenfold). Usually exchange is performed at physiological pH (7.0–8.0) where proteins are in their most native ensemble of conformational states.
The H/D exchange reaction can also be catalysed, by acid, base or metal catalysts such as platinum. For the backbone amide hydrogen atoms of proteins, the minimum exchange rate occurs at approximately pH 2.6, on average. By performing the exchange at neutral pH and then rapidly changing the pH, the exchange rates of the backbone amide hydrogens can be dramatically slowed, or quenched. The pH at which the reaction is quenched depends on the analysis method. For detection by NMR, the pH may be moved to around 4.0–4.5. For detection by mass spectrometry, the pH is dropped to the minimum of the exchange curve, pH 2.6. In the most basic experiment, the reaction is allowed to take place for a set time before it is quenched.
The deuteration pattern of a molecule that has undergone H/D exchange can be maintained in aprotic environments. However, some methods of deuteration analysis for molecules such as proteins, are performed in aqueous solution, which means that exchange will continue at a slow rate even after the reaction is quenched. Undesired deuterium-hydrogen exchange is referred to as back-exchange and various methods have been devised to correct for this. | 7 | Physical Chemistry |
Some examples of biologically important molecular motors:
* Cytoskeletal motors
** Myosins are responsible for muscle contraction, intracellular cargo transport, and producing cellular tension.
** Kinesin moves cargo inside cells away from the nucleus along microtubules, in anterograde transport.
** Dynein produces the axonemal beating of cilia and flagella and also transports cargo along microtubules towards the cell nucleus, in retrograde transport.
* Polymerisation motors
** Actin polymerization generates forces and can be used for propulsion. ATP is used.
** Microtubule polymerization using GTP.
** Dynamin is responsible for the separation of clathrin buds from the plasma membrane. GTP is used.
*Rotary motors:
**FF-ATP synthase family of proteins convert the chemical energy in ATP to the electrochemical potential energy of a proton gradient across a membrane or the other way around. The catalysis of the chemical reaction and the movement of protons are coupled to each other via the mechanical rotation of parts of the complex. This is involved in ATP synthesis in the mitochondria and chloroplasts as well as in pumping of protons across the vacuolar membrane.
** The bacterial flagellum responsible for the swimming and tumbling of E. coli and other bacteria acts as a rigid propeller that is powered by a rotary motor. This motor is driven by the flow of protons across a membrane, possibly using a similar mechanism to that found in the F motor in ATP synthase.
* Nucleic acid motors:
** RNA polymerase transcribes RNA from a DNA template.
** DNA polymerase turns single-stranded DNA into double-stranded DNA.
** Helicases separate double strands of nucleic acids prior to transcription or replication. ATP is used.
** Topoisomerases reduce supercoiling of DNA in the cell. ATP is used.
** RSC and SWI/SNF complexes remodel chromatin in eukaryotic cells. ATP is used.
** SMC proteins responsible for chromosome condensation in eukaryotic cells.
** Viral DNA packaging motors inject viral genomic DNA into capsids as part of their replication cycle, packing it very tightly. Several models have been put forward to explain how the protein generates the force required to drive the DNA into the capsid. An alternative proposal is that, in contrast with all other biological motors, the force is not generated directly by the protein, but by the DNA itself. In this model, ATP hydrolysis is used to drive protein conformational changes that alternatively dehydrate and rehydrate the DNA, cyclically driving it from B-DNA to A-DNA and back again. A-DNA is 23% shorter than B-DNA, and the DNA shrink/expand cycle is coupled to a protein-DNA grip/release cycle to generate the forward motion that propels DNA into the capsid.
* Enzymatic motors: The enzymes below have been shown to diffuse faster in the presence of their catalytic substrates, known as enhanced diffusion. They also have been shown to move directionally in a gradient of their substrates, known as chemotaxis. Their mechanisms of diffusion and chemotaxis are still debated. Possible mechanisms include solutal buoyancy, phoresis or conformational changes leading to change in effective diffusivity and kinetic asymmetry.
**Catalase
**Urease
**Aldolase
**Hexokinase
**Phosphoglucose isomerase
**Phosphofructokinase
**Glucose Oxidase
A recent study has also shown that certain enzymes, such as Hexokinase and Glucose Oxidase, are aggregating or fragmenting during catalysis. This changes their hydrodynamic size that can affect enhanced diffusion measurements.
*Synthetic molecular motors have been created by chemists that yield rotation, possibly generating torque. | 6 | Supramolecular Chemistry |
Ascorbic acid can also react with organic acids as an alcohol forming esters such as ascorbyl palmitate and ascorbyl stearate. | 1 | Biochemistry |
For binary mixtures of two chemically independent components, so that . In addition to temperature and pressure, the other degree of freedom is the composition of each phase, often expressed as mole fraction or mass fraction of one component.
As an example, consider the system of two completely miscible liquids such as toluene and benzene, in equilibrium with their vapours. This system may be described by a boiling-point diagram which shows the composition (mole fraction) of the two phases in equilibrium as functions of temperature (at a fixed pressure).
Four thermodynamic variables which may describe the system include temperature (T), pressure (p), mole fraction of component 1 (toluene) in the liquid phase (x), and mole fraction of component 1 in the vapour phase (x). However, since two phases are present () in equilibrium, only two of these variables can be independent (). This is because the four variables are constrained by two relations: the equality of the chemical potentials of liquid toluene and toluene vapour, and the corresponding equality for benzene.
For given T and p, there will be two phases at equilibrium when the overall composition of the system (system point) lies in between the two curves. A horizontal line (isotherm or tie line) can be drawn through any such system point, and intersects the curve for each phase at its equilibrium composition. The quantity of each phase is given by the lever rule (expressed in the variable corresponding to the x-axis, here mole fraction).
For the analysis of fractional distillation, the two independent variables are instead considered to be liquid-phase composition (x) and pressure. In that case the phase rule implies that the equilibrium temperature (boiling point) and vapour-phase composition are determined.
Liquid–vapour phase diagrams for other systems may have azeotropes (maxima or minima) in the composition curves, but the application of the phase rule is unchanged. The only difference is that the compositions of the two phases are equal exactly at the azeotropic composition. | 7 | Physical Chemistry |
Although the Caspian Sea is endorheic, its main tributary, the Volga, is connected by important shipping canals with the Don River (and thus the Black Sea) and with the Baltic Sea, with branch canals to Northern Dvina and to the White Sea.
Another Caspian tributary, the Kuma River, is connected by an irrigation canal with the Don basin as well.
Scheduled ferry services (including train ferries) across the sea chiefly are between:
*Türkmenbaşy in Turkmenistan, (formerly Krasnovodsk) and Baku.
*Aktau, Kazakhstan and Baku.
*Cities in Iran and Russia (chiefly for cargo.) | 2 | Environmental Chemistry |
The disulfide chain allows the mono-BOC-cystamine to be easily cleaved, allowing removal of the tagging residue when desired.
Mono-BOC-cystamine is used as a crosslinker for the synthesis of cleavable photo-cross-linking reagent.
Mono-BOC-cystamine is used as a crosslinker for the synthesis of a biodegradable cystamine spacer in PGA-cystamine-Gd-DO3A, which shows improved MRI contrast for breast carcinoma imaging in mice. | 1 | Biochemistry |
Industrial facilities are utilizing light-activated resin as a sealant for leaks and cracks. Some light-activated resins have unique properties that make them ideal as a pipe repair product. These resins cure rapidly on any wet or dry surface. | 5 | Photochemistry |
This method uses in vivo and silico ctDNA fragment length selection to enrich the variant proportion in the plasma. The method is decided on size selection criteria based on blood ctDNA fragment length properties, so it may not generalize well for other non-invasive sampling methods. Furthermore, it employs supervised machine learning methods like Random Forest and Logistic Regression on shallow WGS to classify cancer and healthy patients. The method can be used for different cancer types. | 1 | Biochemistry |
Mechanically interlocked molecular architectures consist of molecules that are linked only as a consequence of their topology. Some non-covalent interactions may exist between the different components (often those that were used in the construction of the system), but covalent bonds do not. Supramolecular chemistry, and template-directed synthesis in particular, is key to the efficient synthesis of the compounds. Examples of mechanically interlocked molecular architectures include catenanes, rotaxanes, molecular knots, molecular Borromean rings and ravels. | 6 | Supramolecular Chemistry |
Wood is a natural growth material that possesses excellent mechanical properties, including high strength, good durability, high moisture content, and high specific gravity. Wood can be classified in two types of wood, softwood and hardwood. While each type is different—e.g., the longitudinal cells in softwood are shorter in length when compared to hardwood—both types have a similar hierarchical structure, meaning the orientation of the cells is identical in the wood. This unique anisotropic structure, the properties with distinctive values when measured in several directions, allows it to pump ions and water for photosynthesis in the wood. Similarly, in transparent wood composites, removing the lignin and maintaining the cellulose fiber tubes it allows it to become a clear wood that can get soaked in a glue-like epoxy that makes it a robust and transparent material. An excellent raw material with high transmittance and enhanced mechanical properties.
Researchers have successfully tested an eco-friendly alternative: limonene acrylate, a monomer made from limonene, into an acrylate. Limonene is a common cyclic terpene that can be extracted from industrial waste, via isomerization of α‐pinene (from wood) or from citrus peel oil. The bio-based polymers can offer advantages compared to conventional non‐renewable polymers from fossil resources, and still retain a high mechanical performance and it is lightweight, stemming from its porous and anisotropic cellulosic structure; and is of great interest for large-scale sustainable nanotechnologies. Succinylation of the delignified wood substrate using succinic anhydride results in a nanostructured and mechanically strong biocomposite. The polymer matrix usually accounts for ≈70 vol%, results in nanostructured biocomposites combining an excellent optical transmittance of 90% at 1.2 mm thickness and a remarkably low haze of 30%, with a high mechanical performance (strength 174 MPa, Young's modulus 17 GPa). | 7 | Physical Chemistry |
Modern applications of the Wilfley table (and other wet shaking tables) are predominantly observed in the following roles:
# Laboratories. Small shaking tables are an excellent tool for see if a material will be responsive to gravity separation techniques
# Gold rooms. Wilfley tables typically act as rougher tables on gravity gold concentrate ahead final concentration methods (e.g. panning)
# High value heavy mineral concentrate cleaners. In mining, the vast majority of Wilfley-type tables are installed globally to concentrate (e.g.) tin, tungsten, tantalum, niobium, zircon, rutile, leucoxene, xenotime, monazite
# Zircon finishing table – a specialist application
Tables are now also being used in the recycling of electronic scrap to recover precious metals. | 8 | Metallurgy |
Hermann Senftleben (April 8, 1890, in Bremen – 1975 in Recklinghausen) was a German physicist and physical chemist. | 7 | Physical Chemistry |
In organic chemistry, endo–exo isomerism is a special type of stereoisomerism found in organic compounds with a substituent on a bridged ring system. The prefix endo is reserved for the isomer with the substituent located closest, or "syn", to the longest bridge. The prefix exo is reserved for the isomer with the substituent located farthest, or "anti", to the longest bridge. Here "longest" and "shortest" refer to the number of atoms that comprise the bridge. This type of molecular geometry is found in norbornane systems such as dicyclopentadiene.
The terms endo and exo are used in a similar sense in discussions of the stereoselectivity in Diels–Alder reactions. | 4 | Stereochemistry |
* Till early 1970s, it was often recommended for use in victims of rape in order to avoid pregnancy. The idea stemmed from the fact that, in the laboratory, Lugols iodine appeared to kill sperm cells even in such great dilutions as 1:32. Thus it was thought that an intrauterine application of Lugols iodine, immediately after the event, would help avoid pregnancy. | 3 | Analytical Chemistry |
The ultrasensitivity (sigmoidality) of a Goldbeter–Koshland module can be measured by its Hill Coefficient:
where EC90 and EC10 are the input values needed to produce the 10% and 90% of the maximal response, respectively.
In a living cell, Goldbeter–Koshland modules are embedded in a bigger network with upstream and downstream components. This components may constrain the range of inputs that the module will receive as well as the range of the module’s outputs that network will be able to detect. Altszyler et al. (2014) studied how the effective ultrasensitivity of a modular system is affected by these restrictions. They found that Goldbeter–Koshland modules are highly sensitive to dynamic range limitations imposed by downstream components. However, in the case of asymmetric Goldbeter–Koshland modules, a moderate downstream constrain can produce effective sensitivities much larger than that of the original module when considered in isolation. | 7 | Physical Chemistry |
Tertiary alcohols react with hydrochloric acid to produce tertiary alkyl chloride. Primary and secondary alcohols are converted to the corresponding chlorides using thionyl chloride and various phosphorus chloride reagents.
Primary and secondary alcohols, likewise, convert to alkyl bromides phosphorus tribromide, for example:
In the Barton-McCombie deoxygenation an alcohol is deoxygenated to an alkane with tributyltin hydride or a trimethylborane-water complex in a radical substitution reaction. | 0 | Organic Chemistry |
Pyruvate kinase isozymes M1/M2 (PKM1/M2), also known as pyruvate kinase muscle isozyme (PKM), pyruvate kinase type K, cytosolic thyroid hormone-binding protein (CTHBP), thyroid hormone-binding protein 1 (THBP1), or opa-interacting protein 3 (OIP3), is an enzyme that in humans is encoded by the PKM2 gene.
PKM2 is an isoenzyme of the glycolytic enzyme pyruvate kinase. Depending upon the different metabolic functions of the tissues, different isoenzymes of pyruvate kinase are expressed. PKM2 is expressed in some differentiated tissues, such as lung, fat tissue, retina, and pancreatic islets, as well as in all cells with a high rate of nucleic acid synthesis, such as normal proliferating cells, embryonic cells, and especially tumor cells. | 1 | Biochemistry |
Melid, also known as Arslantepe, was an ancient city on the Tohma River, a tributary of the upper Euphrates rising in the Taurus Mountains. It has been identified with the modern archaeological site of Arslantepe near Malatya, Turkey.
It was named a UNESCO World Heritage Site under the name Arslantepe Mound on 26 July 2021. | 8 | Metallurgy |
H–D exchange was measured originally by the father of hydrogen exchange Kaj Ulrik Linderstrøm-Lang using density gradient tubes. In modern times, H–D exchange has primarily been monitored by the methods: NMR spectroscopy, mass spectrometry and neutron crystallography. Each of these methods have their advantages and drawbacks. | 7 | Physical Chemistry |
One primary application of the Bland–Altman plot is to compare two clinical measurements each of which produced some error in their measures. It can also be used to compare a new measurement technique or method with a gold standard, as even a gold standard does not—and should not—imply it to be without error. See Analyse-it, MedCalc, NCSS, GraphPad Prism, R, StatsDirect, or JASP for software providing Bland–Altman plots.
Bland–Altman plots are extensively used to evaluate the agreement among two different instruments or two measurements techniques. Bland–Altman plots allow identification of any systematic difference between the measurements (i.e., fixed bias) or possible outliers. The mean difference is the estimated bias, and the SD of the differences measures the random fluctuations around this mean. If the mean value of the difference differs significantly from 0 on the basis of a 1-sample t-test, this indicates the presence of fixed bias. If there is a consistent bias, it can be adjusted for by subtracting the mean difference from the new method. It is common to compute 95% limits of agreement for each comparison (average difference ± 1.96 standard deviation of the difference), which tells us how far apart measurements by two methods were more likely to be for most individuals. If the differences within mean ± 1.96 SD are not clinically important, the two methods may be used interchangeably. The 95% limits of agreement can be unreliable estimates of the population parameters especially for small sample sizes so, when comparing methods or assessing repeatability, it is important to calculate confidence intervals for 95% limits of agreement. This can be done by Bland and Altman's approximate method or by more precise methods.
Bland–Altman plots were also used to investigate any possible relationship of the discrepancies between the measurements and the true value (i.e., proportional bias). The existence of proportional bias indicates that the methods do not agree equally through the range of measurements (i.e., the limits of agreement will depend on the actual measurement). To evaluate this relationship formally, the difference between the methods should be regressed on the average of the 2 methods. When a relationship between the differences and the true value was identified (i.e., a significant slope of the regression line), regression-based 95% limits of agreement should be provided. | 3 | Analytical Chemistry |
After earning her PhD, Simon was offered a position at DuPont’s Pioneer Research Lab in Buffalo, New York. Here, she worked to develop new catalysts to change the properties of synthetic polymers. This work led to the development of two polymers which would later be named Dacron and Orlon.
After completing her work with DuPont, Simon transferred to Oak Ridge National Laboratory, in Oak Ridge, Tennessee. Here, she made discoveries in the field of radiochemistry in studying the triple-fission of uranium. While at ORNL, Simon also became the first to discover a new isotope of calcium. For a short period of time after leaving ORNL, she continued with similar research regarding uranium at Argonne National Laboratory in Chicago, Illinois.
In 1949, Simon began work at Lewis Research Center in Cleveland, Ohio, a division of the National Advisory Committee for Aeronautics (NACA), the predecessor of NASA. Once here, she was assigned to the fuels and combustion division, where she conducted research regarding flame velocities and types of fuel for aerospace applications. She also conducted studies to determine the minimum diameter of tubing necessary to maintain an engine flame. This led to Simon being credited in numerous technical publications and research papers for her work, and led to improvements in engine designs for aeronautic and spaceflight purposes.
As a result of her work at NACA, Simon was given the Rockefeller Federal Service Award, which entailed a $10,000 (~$110,000 in 2022) grant from the Rockefeller Foundation. She used this award to travel to Europe to further her education at the University of Cambridge in Cambridge, England. Simon also toured around Europe where she met with scientists from Germany, England, France, and Italy to examine their research regarding physical chemistry and radiochemistry. Upon returning from her tour, she was promoted to assistant chief of NACA’s combustion branch, where she became a pioneer in female corporate management. Throughout the 1950’s she served as an advocate for women in science and education, appearing in several radio shows and magazines.
Once leaving NACA, Simon briefly held a position at Magnolia Petroleum in Texas, where she did work regarding oil sands.
In 1956, Simon took a position at AVCO corporation, an aviation conglomerate in New England. There, she applied her previous experience with polymer construction and physical chemistry to develop the technology for early aerospace heat shields, which were critical to NASA’s crewed spacecraft endeavors. This technology would go on to be used most notably during NASA’s Apollo program, and later was applied to ballistic missiles at the height of the Cold War. Simon remained at AVCO for 30 years, during which she held the titles of vice president and director of research at the company, becoming the company’s first female corporate officer. | 7 | Physical Chemistry |
The first successful solid-hybrid dye-sensitized solar cells were reported.
To improve electron transport in these solar cells, while maintaining the high surface area needed for dye adsorption, two researchers have designed alternate semiconductor morphologies, such as arrays of nanowires and a combination of nanowires and nanoparticles, to provide a direct path to the electrode via the semiconductor conduction band. Such structures may provide a means to improve the quantum efficiency of DSSCs in the red region of the spectrum, where their performance is currently limited.
In August 2006, to prove the chemical and thermal robustness of the 1-ethyl-3 methylimidazolium tetracyanoborate solar cell, the researchers subjected the devices to heating at 80 °C in the dark for 1000 hours, followed by light soaking at 60 °C for 1000 hours. After dark heating and light soaking, 90% of the initial photovoltaic efficiency was maintained – the first time such excellent thermal stability has been observed for a liquid electrolyte that exhibits such a high conversion efficiency. Contrary to silicon solar cells, whose performance declines with increasing temperature, the dye-sensitized solar-cell devices were only negligibly influenced when increasing the operating temperature from ambient to 60 °C. | 5 | Photochemistry |
The Henry adsorption constant is the constant appearing in the linear adsorption isotherm, which formally resembles Henrys law; therefore, it is also called Henrys adsorption isotherm. It is named after British chemist William Henry. This is the simplest adsorption isotherm in that the amount of the surface adsorbate is represented to be proportional to the partial pressure of the adsorptive gas:
where:
* X - surface coverage,
* P - partial pressure,
* K - Henry's adsorption constant.
For solutions, concentrations, or activities, are used instead of the partial pressures.
The linear isotherm can be used to describe the initial part of many practical isotherms. It is typically taken as valid for low surface coverages, and the adsorption energy being independent of the coverage (lack of inhomogeneities on the surface).
The Henry adsorption constant can be defined as:
where:
* is the number density at free phase,
* is the surface number density, | 7 | Physical Chemistry |
The four most common Maxwell's relations are:
More relations include the following.
Other differential equations are: | 7 | Physical Chemistry |
The inductive effect can be explained with Bents rule. The inductive effect is the transmission of charge through covalent bonds and Bents rule provides a mechanism for such results via differences in hybridisation. In the table below, as the groups bonded to the central carbon become more electronegative, the central carbon becomes more electron-withdrawing as measured by the polar substituent constant. The polar substituent constants are similar in principle to σ values from the Hammett equation, as an increasing value corresponds to a greater electron-withdrawing ability. Bent's rule suggests that as the electronegativity of the groups increase, more p character is diverted towards those groups, which leaves more s character in the bond between the central carbon and the R group. As s orbitals have greater electron density closer to the nucleus than p orbitals, the electron density in the C−R bond will more shift towards the carbon as the s character increases. This will make the central carbon more electron-withdrawing to the R group. Thus, the electron-withdrawing ability of the substituents has been transferred to the adjacent carbon, as the inductive effect predicts. | 4 | Stereochemistry |
Molecular-weight size markers can be broken up into two categories: molecular weight markers vs. molecular ladder markers. Markers are either stained or unstained, and depending on the circumstance, one may be more appropriate than another. Molecular-weight size markers can also be biochemically altered. The conjugation with biotin is the most common. Molecular-weight size markers are most commonly used in SDS-polyacrylamide gel electrophoresis and western blotting.
With all the different types and uses of molecular-weight size markers, it is important to choose the appropriate protein standard. Besides the most common use, as a way to calculate the molecular weight of the samples, other uses include allowing visual evidence of protein migration and transfer efficiency and are sometimes even used for positive control. | 1 | Biochemistry |
In the laboratory, triflic acid is useful in protonations because the conjugate base of triflic acid is nonnucleophilic. It is also used as an acidic titrant in nonaqueous acid-base titration because it behaves as a strong acid in many solvents (acetonitrile, acetic acid, etc.) where common mineral acids (such as HCl or HSO) are only moderately strong.
With a K = , pK = , triflic acid qualifies as a superacid. It owes many of its useful properties to its great thermal and chemical stability. Both the acid and its conjugate base CFSO, known as triflate, resist oxidation/reduction reactions, whereas many strong acids are oxidizing, such as perchloric or nitric acid. Further recommending its use, triflic acid does not sulfonate substrates, which can be a problem with sulfuric acid, fluorosulfuric acid, and chlorosulfonic acid. Below is a prototypical sulfonation, which triflic acid does not undergo:
Triflic acid fumes in moist air and forms a stable solid monohydrate, CFSOH·HO, melting point 34 °C. | 0 | Organic Chemistry |
Some cyanobacteria, the so-called cyanobionts (cyanobacterial symbionts), have a symbiotic relationship with other organisms, both unicellular and multicellular. As illustrated on the right, there are many examples of cyanobacteria interacting symbiotically with land plants. Cyanobacteria can enter the plant through the stomata and colonize the intercellular space, forming loops and intracellular coils. Anabaena spp. colonize the roots of wheat and cotton plants. Calothrix sp. has also been found on the root system of wheat. Monocots, such as wheat and rice, have been colonised by Nostoc spp., In 1991, Ganther and others isolated diverse heterocystous nitrogen-fixing cyanobacteria, including Nostoc, Anabaena and Cylindrospermum, from plant root and soil. Assessment of wheat seedling roots revealed two types of association patterns: loose colonization of root hair by Anabaena and tight colonization of the root surface within a restricted zone by Nostoc.
The relationships between cyanobionts (cyanobacterial symbionts) and protistan hosts are particularly noteworthy, as some nitrogen-fixing cyanobacteria (diazotrophs) play an important role in primary production, especially in nitrogen-limited oligotrophic oceans. Cyanobacteria, mostly pico-sized Synechococcus and Prochlorococcus, are ubiquitously distributed and are the most abundant photosynthetic organisms on Earth, accounting for a quarter of all carbon fixed in marine ecosystems. In contrast to free-living marine cyanobacteria, some cyanobionts are known to be responsible for nitrogen fixation rather than carbon fixation in the host. However, the physiological functions of most cyanobionts remain unknown. Cyanobionts have been found in numerous protist groups, including dinoflagellates, tintinnids, radiolarians, amoebae, diatoms, and haptophytes. Among these cyanobionts, little is known regarding the nature (e.g., genetic diversity, host or cyanobiont specificity, and cyanobiont seasonality) of the symbiosis involved, particularly in relation to dinoflagellate host. | 5 | Photochemistry |
Bioactivity databases correlate structures or other chemical information to bioactivity results taken from bioassays in literature, patents, and screening programs. | 1 | Biochemistry |
Mg is essential for plant growth and is present in higher plants in amounts on the order of 80 μmol g dry weight. The amounts of Mg vary in different parts of the plant and are dependent upon nutritional status. In times of plenty, excess Mg may be stored in vascular cells (Stelzer et al., 1990; and in times of starvation Mg is redistributed, in many plants, from older to newer leaves.
Mg is taken up into plants via the roots. Interactions with other cations in the rhizosphere can have a significant effect on the uptake of the ion.(Kurvits and Kirkby, 1980; The structure of root cell walls is highly permeable to water and ions, and hence ion uptake into root cells can occur anywhere from the root hairs to cells located almost in the centre of the root (limited only by the Casparian strip). Plant cell walls and membranes carry a great number of negative charges, and the interactions of cations with these charges is key to the uptake of cations by root cells allowing a local concentrating effect. Mg binds relatively weakly to these charges, and can be displaced by other cations, impeding uptake and causing deficiency in the plant.
Within individual plant cells, the Mg requirements are largely the same as for all cellular life; Mg is used to stabilise membranes, is vital to the utilisation of ATP, is extensively involved in the nucleic acid biochemistry, and is a cofactor for many enzymes (including the ribosome). Also, Mg is the coordinating ion in the chlorophyll molecule. It is the intracellular compartmentalisation of Mg in plant cells that leads to additional complexity. Four compartments within the plant cell have reported interactions with Mg. Initially, Mg will enter the cell into the cytoplasm (by an as yet unidentified system), but free Mg concentrations in this compartment are tightly regulated at relatively low levels (≈2 mmol/L) and so any excess Mg is either quickly exported or stored in the second intracellular compartment, the vacuole. The requirement for Mg in mitochondria has been demonstrated in yeast and it seems highly likely that the same will apply in plants. The chloroplasts also require significant amounts of internal Mg, and low concentrations of cytoplasmic Mg. In addition, it seems likely that the other subcellular organelles (e.g., Golgi, endoplasmic reticulum, etc.) also require Mg. | 1 | Biochemistry |
* Discrete dipole approximation codes
* Codes for electromagnetic scattering by cylinders
* Codes for electromagnetic scattering by spheres | 7 | Physical Chemistry |
Inhaled anesthetics inhibit nicotinic acetylcholine receptors (nAChRs) and potentiate neuromuscular blockage with nondepolarising NMBAs. It depends on the type of volatile anesthetic (desflurane > sevoflurane > isoflurane > nitrous oxide), the concentration and the duration of exposure. | 1 | Biochemistry |
Photoreceptor proteins are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria. They mediate light responses as varied as visual perception, phototropism and phototaxis, as well as responses to light-dark cycles such as circadian rhythm and other photoperiodisms including control of flowering times in plants and mating seasons in animals. | 1 | Biochemistry |
Sulfuric acid is used in large quantities by the iron and steelmaking industry to remove oxidation, rust, and scaling from rolled sheet and billets prior to sale to the automobile and major appliances industry. Used acid is often recycled using a spent acid regeneration (SAR) plant. These plants combust spent acid with natural gas, refinery gas, fuel oil or other fuel sources. This combustion process produces gaseous sulfur dioxide () and sulfur trioxide () which are then used to manufacture "new" sulfuric acid. SAR plants are common additions to metal smelting plants, oil refineries, and other industries where sulfuric acid is consumed in bulk, as operating a SAR plant is much cheaper than the recurring costs of spent acid disposal and new acid purchases.
Hydrogen peroxide () can be added to sulfuric acid to produce piranha solution, a powerful but very toxic cleaning solution with which substrate surfaces can be cleaned. Piranha solution is typically used in the microelectronics industry, and also in laboratory settings to clean glassware. | 7 | Physical Chemistry |
Incongruent melting occurs when a solid substance being partially melted does not melt uniformly, so that the chemical composition of neither the resulting liquid nor the resulting solid is the same as that of the original solid. For example, melting of orthoclase (KAlSiO) produces leucite (KAlSiO) in addition to a melt. The melt produced is richer in silica (SiO). The proportions of leucite and melt formed can be recombined to yield the bulk composition of the starting feldspar. Another mineral that can melt incongruently is enstatite (MgSiO), which produces forsterite (MgSiO) in addition to a melt richer in SiO when melting at low pressure. Enstatite melts congruently at higher pressures between 2.5 and 5.5 kilobars. | 9 | Geochemistry |
*AMPP Annual Conference
*Area Conferences
*Coatings+ (will retire after 2021)
*CORROSION (will retire after 2022) | 8 | Metallurgy |
ISO 31-8 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to physical chemistry and molecular physics. | 7 | Physical Chemistry |
Due to its high abundance in plants (generally 40% of the total protein content), RuBisCO often impedes analysis of important signaling proteins such as transcription factors, kinases, and regulatory proteins found in lower abundance (10-100 molecules per cell) within plants. For example, using mass spectrometry on plant protein mixtures would result in multiple intense RuBisCO subunit peaks that interfere and hide those of other proteins.
Recently, one efficient method for precipitating out RuBisCO involves the usage of protamine sulfate solution. Other existing methods for depleting RuBisCO and studying lower abundance proteins include fractionation techniques with calcium and phytate, gel electrophoresis with polyethylene glycol, affinity chromatography, and aggregation using DTT, though these methods are more time-consuming and less efficient when compared to protamine sulfate precipitation. | 5 | Photochemistry |
Several general trends are recognized in determining the structure of Fe–Ni clusters. Larger clusters, containing both iron and nickel, are most stable with Fe atoms located in the inner parts of the cluster and Ni metals on outside. In other terms, when iron and nickel form body-centered cubic structures the preferred position of Ni atoms is at the surface, instead of at the center of the cluster, as it is energetically unfavorable for two nickel atoms to occupy nearest-neighbor positions.
Metal–metal bonds, being d-orbital interactions, happen at larger distances. More stable metal–metal bonds are expected to be longer than unstable bonds. This is shown by the fact that the Fe–Ni bond length is in between Ni–Ni and Fe–Fe bond lengths. For example, in Fe–Ni four-atom clusters (FeNi) which are most stable in a tetrahedral structure, the bond length of metal–metal Fe–Ni bond is 2.65Å and Fe–Fe bond is 2.85 Å. When bonding in these structures is examined, it follows that lowest energy cluster structures of iron and nickel are given by geometries with a maximum number of Fe–Fe bonds, and a small number of Ni–Ni bonds.
The simplest Fe–Ni clusters are of one iron atom and one nickel atom bonded together. More complex clusters can be added through the addition of another atom. Some pictures of sample geometries are shown in Fig. 2.
All Fe–Ni clusters exhibit some degree of distortion from usual geometry. This distortion generally becomes more pronounced as the number of Fe atoms increases.
Notice how in the above cluster diagrams, as calculated by Rollmann and colleagues, the symmetry of the cluster changes from a pure octahedron (D) to a square pyramid (C) as more iron atoms are added. | 7 | Physical Chemistry |
The first CGC was reported by Shapiro and Bercaw for a scandium complex. The following year patents were issued to The Dow Chemical Company and Exxon for applications in alkene polymerization. and today are made at the billion pound scale. | 0 | Organic Chemistry |
Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms and small molecules. In practice, a tunable laser can be used to access an excited intermediate state. The selection rules associated with a two-photon or other multiphoton photoabsorption are different from the selection rules for a single photon transition. The REMPI technique typically involves a resonant single or multiple photon absorption to an electronically excited intermediate state followed by another photon which ionizes the atom or molecule. The light intensity to achieve a typical multiphoton transition is generally significantly larger than the light intensity to achieve a single photon photoabsorption. Because of this, subsequent photoabsorption is often very likely. An ion and a free electron will result if the photons have imparted enough energy to exceed the ionization threshold energy of the system. In many cases, REMPI provides spectroscopic information that can be unavailable to single photon spectroscopic methods, for example rotational structure in molecules is easily seen with this technique.
REMPI is usually generated by a focused frequency tunable laser beam to form a small-volume plasma. In REMPI, first m photons are simultaneously absorbed by an atom or molecule in the sample to bring it to an excited state. Other n photons are absorbed afterwards to generate an electron and ion pair. The so-called m+n REMPI is a nonlinear optical process, which can only occur within the focus of the laser beam. A small-volume plasma is formed near the laser focal region. If the energy of m photons does not match any state, an off-resonant transition can occur with an energy defect ΔE, however, the electron is very unlikely to remain in that state. For large detuning, it resides there only during the time Δt. The uncertainty principle is satisfied for Δt, where ћ=h/2π and h is the Planck constant (6.6261×10^-34 J∙s). Such transition and states are called virtual, unlike real transitions to states with long lifetimes. The real transition probability is many orders of magnitude higher than the virtual transition one, which is called resonance enhanced effect. | 7 | Physical Chemistry |
Foxfire is the bioluminescence created by some species of fungi present in decaying wood. While there may be multiple different luciferins within the kingdom of fungi, 3-hydroxy hispidin was determined to be the luciferin in the fruiting bodies of several species of fungi, including Neonothopanus nambi, Omphalotus olearius, Omphalotus nidiformis, and Panellus stipticus. | 1 | Biochemistry |
The expressions for the T-matrix resulting from both methods can be related to certain class of variational principles. In the case of first iteration of MCFV method we get the same result as from Schwinger variational principle with trial function . The higher iterations with N-terms in the continuous fraction reproduce exactly 2N terms (2N + 1) of Born series for the MCFV (or MCFG) method respectively. The method was tested on calculation of collisions of electrons from hydrogen atom in static-exchange approximation. In this case the method reproduces exact results for scattering cross-section on 6 significant digits in 4 iterations. It can also be shown that both methods reproduce exactly the solution of the Lippmann-Schwinger equation with the potential given by finite-rank operator. The number of iterations is then equal to the rank of the potential. The method has been successfully used for solution of problems in both nuclear and molecular physics. | 7 | Physical Chemistry |
Nonclassical carbocations are stabilized by charge delocalization from contributions of neighbouring or bonds, which can form bridged intermediates or transition states. Nonclassical ions have been extensively studied with the 2-norbornyl system, which as “naked” ion unambiguously exhibit such a bridged structure. The landmark of nonclassical ions are unexpectedly fast solvolysis rates and large differences between epimeric esters. Such behaviour is not restricted to 2-norbornyl esters, as has been shown with some cyclopentyl and steroidal esters with the tosyloxy leaving group.
Substitution reactions of secondary esters occur by S2- or S1-like mechanisms. Only in highly polar solvents such as hexafluoroisopropanol (HFIP) of low nucleophilicity one can expect a nearly same uniform S1-like mechanism. The solvolysis of several cyclopentyl and steroidal esters show that large solvolysis rates and differences between epimers can occur which surpass those of the 2-norbornyl system. In these cases a vicinal C–C or C–H bond can lead to significant delocalization of the positive charge, if these bonds are close to antiperiplanar to the leaving group, and the migration leads to a more stable tertiary carbocation. The reaction products in these cases always result from the migration of the neighbouring bond.
The reaction of epimeric esters can be severely slowed by steric hindrance of solvation.
Solvolysis of cyclopropylcarbinyl, cyclobutyl and homoallyl esters are also characterized by very large rates, and have been shown to occur via a common nonclassical ion structure in the form of a bicyclobutonium ion. | 7 | Physical Chemistry |
To calculate the elastic response of a rubber sample, the three chain force models (regimes Ia, Ib and II) and the network morphology must be combined in a micro-mechanical network model. Using the joint probability distribution in equation () and the force extension models, it is possible to devise numerical algorithms to both construct a faithful representative volume element of a network and to simulate the resulting mechanical stress as it is subjected to strain. An iterative relaxation algorithm is used to maintain approximate force equilibrium at each network node as strain is imposed. When the force constant obtained for kinks having 2 or 3 isoprene units (approximately one Kuhn length) is used in numerical simulations, the predicted stress is found to be consistent with experiments. The results of such a calculation are shown in Fig. 1 (dashed red line) for sulfur cross-linked natural rubber and compared with experimental data (solid blue line). These simulations also predict a steep upturn in the stress as network chains become taut and, ultimately, material failure due to bond rupture. In the case of sulfur cross-linked natural rubber, the S-S bonds in the cross-link are much weaker than the C-C bonds on the chain backbone and are the network failure points. The plateau in the simulated stress, starting at a strain of about 7, is the limiting value for the network. Stresses greater than about 7 MPa cannot be supported and the network fails. Near this stress limit, the simulations predict that less than 10% of the chains are taut, i.e. in the high chain extension regime and less than 0.1% of the chains have ruptured. While the very low rupture fraction may seem surprising, it is not inconsistent with our experience of stretching a rubber band until it breaks. The elastic response of the rubber after breaking is not noticeably different from the original. | 7 | Physical Chemistry |
In ion exchange chromatography, the Gibbs–Donnan effect is observed when the pH of the applied buffer and the ion exchanger differ, even up to one pH unit. For example, in anion-exchange columns, the ion exchangers repeal protons so the pH of the buffer near the column differs is higher than the rest of the solvent. As a result, an experimenter has to be careful that the protein(s) of interest is stable and properly charged in the "actual" pH.
This effect comes as a result of two similarly charged particles, one from the resin and one from the solution, failing to distribute properly between the two sides; there is a selective uptake of one ion over another. For example, in a sulphonated polystyrene resin, a cation exchange resin, the chlorine ion of a hydrochloric acid buffer should equilibrate into the resin. However, since the concentration of the sulphonic acid in the resin is high, the hydrogen of HCl has no tendency to enter the column. This, combined with the need of electroneutrality, leads to a minimum amount of hydrogen and chlorine entering the resin. | 3 | Analytical Chemistry |
Computations in continuum mechanics often require that the regular time derivation operator
is replaced by the substantive derivative operator
This can be seen as follows.
Consider a bug that is moving through a volume where there is some scalar,
e.g. pressure, that varies with time and position:
If the bug during the time interval from
to
moves from
to
then the bug experiences a change in the scalar value,
(the total differential). If the bug is moving with a velocity
the change in particle position is
and we may write
where is the gradient of the scalar field p. So:
If the bug is just moving with the flow, the same formula applies, but now the velocity vector,v, is that of the flow, u.
The last parenthesized expression is the substantive derivative of the scalar pressure.
Since the pressure p in this computation is an arbitrary scalar field, we may abstract it and write the substantive derivative operator as | 7 | Physical Chemistry |
Although the problem was first found in brass, any alloy containing copper will be susceptible to the problem. It includes copper itself (as used in pipe for example), bronzes and other alloys with a significant copper content. Like all problems with hairline cracks, detection in the early stages of attack is difficult, but the characteristic blue coloration may give a clue to attack. Microscopic inspection will often reveal the cracks, and x-ray analysis using the EDX facility on the scanning electron microscope or SEM should reveal the presence of elemental nitrogen from ammoniacal traces. | 8 | Metallurgy |
Rearrangement reaction of 6-membered cyclic dienones generate phenols through the dienone–phenol rearrangement: | 0 | Organic Chemistry |
Walden was born in Rozulas in the Russian Empire (now Stalbe parish, Pārgauja municipality, Latvia) in a large Latvian peasant family. At the age of four, he lost his father and later his mother. Thanks to financial support from his two older brothers who lived in Riga (one was a merchant and another served as a lieutenant in the military) Walden managed to complete his education – first graduated with honors from the district school in the town of Cēsis (1876), and then from the Riga Technical High School (1882).
In December 1882, he enrolled into the Riga Technical University and became seriously interested in chemistry. In 1886, he published his first scientific study on the color evaluation of the reactions of nitric and nitrous acid with various reagents and establishing the limits of sensitivity of the color method to detection of nitric acid.
In April 1887, Walden became an active member of the Russian Physico-chemical Society. During this time, Walden started his collaboration with Wilhelm Ostwald (Nobel Prize in Chemistry 1909) which greatly influenced his development as a scientist. Their first work together was published in 1887 and was devoted to the dependence of the electrical conductivity of aqueous solutions of salts on their molecular weight. | 4 | Stereochemistry |
Methylene blue has been used as a placebo; physicians would tell their patients to expect their urine to change color and view this as a sign that their condition had improved. This same side effect makes methylene blue difficult to use in traditional placebo-controlled clinical studies, including those testing for its efficacy as a treatment. | 3 | Analytical Chemistry |
B. Jill Venton is a professor of chemistry at University of Virginia, where she serves as the department chair since 2019. Venton's research focuses on developing analytical chemistry methods to enable detection of molecules in the brain. | 3 | Analytical Chemistry |
A heat number is an identification coupon number that is stamped on a material plate after it is removed from the ladle and rolled at a steel mill.
Industry quality standards require materials to be tested at the manufacturer and the results of these tests be submitted through a report, also called a mill sheet, mill certificate or mill test certificate (MTC). The only way to trace a steel plate back to its mill sheet is the heat number. A heat number is similar to a lot number, which is used to identify production runs of any other product for quality control purposes. | 8 | Metallurgy |
In obstructive jaundice, no bilirubin reaches the small intestine, meaning that there is no formation of stercobilinogen. The lack of stercobilin and other bile pigments causes feces to become clay-colored. | 1 | Biochemistry |
CAPS is the common name for N-cyclohexyl-3-aminopropanesulfonic acid, a chemical used as buffering agent in biochemistry. The similar substance N-cyclohexyl-2-hydroxyl-3-aminopropanesulfonic acid (CAPSO) is also used as buffering agent in biochemistry. Its useful pH range is 9.7-11.1. | 1 | Biochemistry |
Metal-alkene complexes can be viewed as the smallest metallacycles, but they usually are not classified as metallacycles. In the Dewar–Chatt–Duncanson model, one resonance structure for the M(η-alkene) center is the metallacyclopropane. | 0 | Organic Chemistry |
An Ion Gun typically refers to an instrument that generates a beam of heavy ions with a well defined energy distribution. The ion beam is produced from a plasma that has been confined within a volume. Ions of a particular energy are extracted, accelerated, collimated and/or focused. The ion gun is composed of an ion source, extraction grid structure and a collimation/lensing structure. The plasma can be made up of an inert or reactive gas (e.g. N and O) or an easily condensable substance (e.g. C and B). The plasma can be formed from molecules that contain the substance which will form the beam, in which case, these molecules must be fragmented then ionized (e.g. H and CH can together be fragmented and ionized to create a beam for depositing diamond-like carbon films).
The ion current density (or similarly the ion flux), the ion energy spread, and the resolution of the ion beam are key factors in ion gun design. The ion current density is controlled by the ion source, the energy spread is determined primarily by the extraction grid, and the resolution is determined primarily by the optical column.
The ion gun is an important component in surface science in that it provides the scientist with a means to sputter etch a surface and generate an elemental or chemical depth profile. Modern ion guns can produce beam energies from 10eV to more than 10keV. | 7 | Physical Chemistry |
Steven M. Bachrach is an organic chemist who took up the position of Dean of Science at Monmouth University in 2016. Bachrach had previously been the Dr D. R. Semmes Distinguished Professor of Chemistry at Trinity University in San Antonio, Texas. Bachrach is the author of the textbook Computational Organic Chemistry. | 0 | Organic Chemistry |
A hormone response element (HRE) is a short sequence of DNA within the promoter of a gene, that is able to bind to a specific hormone receptor complex and therefore regulate transcription. The sequence is most commonly a pair of inverted repeats separated by three nucleotides, which also indicates that the receptor binds as a dimer. Specifically, HRE responds to steroid hormones, as the activated steroid receptor is the transcription factor binding HRE. This regulates the transcription of genes signalled by the steroid hormone.
A gene may have many different response elements, allowing complex control to be exerted over the level and rate of transcription.
HRE are used in transgenic animal cells as inducers of gene expression.
Examples of HREs include estrogen response elements and androgen response elements. | 1 | Biochemistry |
Temperatures throughout the Jurassic and Cretaceous are generally thought to have been relatively warm, and consequently dissolved oxygen levels in the ocean were lower than today—making anoxia easier to achieve. However, more specific conditions are required to explain the short-period (less than a million years) oceanic anoxic events. Two hypotheses, and variations upon them, have proved most durable.
One hypothesis suggests that the anomalous accumulation of organic matter relates to its enhanced preservation under restricted and poorly oxygenated conditions, which themselves were a function of the particular geometry of the ocean basin: such a hypothesis, although readily applicable to the young and relatively narrow Cretaceous Atlantic (which could be likened to a large-scale Black Sea, only poorly connected to the World Ocean), fails to explain the occurrence of coeval black shales on open-ocean Pacific plateaus and shelf seas around the world. There are suggestions, again from the Atlantic, that a shift in oceanic circulation was responsible, where warm, salty waters at low latitudes became hypersaline and sank to form an intermediate layer, at depth, with a temperature of .
The second hypothesis suggests that oceanic anoxic events record a major change in the fertility of the oceans that resulted in an increase in organic-walled plankton (including bacteria) at the expense of calcareous plankton such as coccoliths and foraminifera. Such an accelerated flux of organic matter would have expanded and intensified the oxygen minimum zone, further enhancing the amount of organic carbon entering the sedimentary record. Essentially this mechanism assumes a major increase in the availability of dissolved nutrients such as nitrate, phosphate and possibly iron to the phytoplankton population living in the illuminated layers of the oceans.
For such an increase to occur would have required an accelerated influx of land-derived nutrients coupled with vigorous upwelling, requiring major climate change on a global scale. Geochemical data from oxygen-isotope ratios in carbonate sediments and fossils, and magnesium/calcium ratios in fossils, indicate that all major oceanic anoxic events were associated with thermal maxima, making it likely that global weathering rates, and nutrient flux to the oceans, were increased during these intervals. Indeed, the reduced solubility of oxygen would lead to phosphate release, further nourishing the ocean and fuelling high productivity, hence a high oxygen demand—sustaining the event through a positive feedback.
Another way to explain anoxic events is that the Earth releases a huge volume of carbon dioxide during an interval of intense volcanism; global temperatures rise due to the greenhouse effect; global weathering rates and fluvial nutrient flux increase; organic productivity in the oceans increases; organic-carbon burial in the oceans increases (OAE begins); carbon dioxide is drawn down due to both burial of organic matter and weathering of silicate rocks (inverse greenhouse effect); global temperatures fall, and the ocean–atmosphere system returns to equilibrium (OAE ends).
In this way, an oceanic anoxic event can be viewed as the Earth's response to the injection of excess carbon dioxide into the atmosphere and hydrosphere. One test of this notion is to look at the age of large igneous provinces (LIPs), the extrusion of which would presumably have been accompanied by rapid effusion of vast quantities of volcanogenic gases such as carbon dioxide. The age of three LIPs (Karoo-Ferrar flood basalt, Caribbean large igneous province, Ontong Java Plateau) correlates well with that of the major Jurassic (early Toarcian) and Cretaceous (early Aptian and Cenomanian–Turonian) oceanic anoxic events, indicating that a causal link is feasible. | 9 | Geochemistry |
Chloroeremomycin was discovered by Eli Lilly in the 1980s. In the 1990s, researchers at Eli Lilly developed biphenyl-chloroeremomycin, now known as oritavancin, as a functionalized derivative of chloroeremomycin to combat rising antibacterial resistance to vancomycin. The chloroeremomycin gene cluster was sequenced by van Wageningen et al in 1998. After the publication, many groups expressed the genes and conducted experiments to understand how chloroeremomycin and, by extension, vancomycin are biosynthesized. | 0 | Organic Chemistry |
The vast majority of cyclic compounds are organic, and of these, a significant and conceptually important portion are composed of rings made only of carbon atoms (i.e., they are carbocycles). | 4 | Stereochemistry |
In chemistry, chemical stability is the thermodynamic stability of a chemical system.
Thermodynamic stability occurs when a system is in its lowest energy state, or in chemical equilibrium with its environment. This may be a dynamic equilibrium in which individual atoms or molecules change form, but their overall number in a particular form is conserved. This type of chemical thermodynamic equilibrium will persist indefinitely unless the system is changed. Chemical systems might undergo changes in the phase of matter or a set of chemical reactions.
State A is said to be more thermodynamically stable than state B if the Gibbs free energy of the change from A to B is positive. | 7 | Physical Chemistry |
The chemical synthesis of tramadol is described in the literature. Tramadol has two stereogenic centers at the cyclohexane ring. Thus, may exist in four different configurational forms:
* (1R,2R)-isomer
* (1S,2S)-isomer
* (1R,2S)-isomer
* (1S,2R)-isomer
The synthetic pathway leads to the racemate (1:1 mixture) of (1R,2R)-isomer and the (1S,2S)-isomer as the main products. Minor amounts of the racemic mixture of the (1R,2S)-isomer and the (1S,2R)-isomer are formed as well. The isolation of the (1R,2R)-isomer and the (1S,2S)-isomer from the diastereomeric minor racemate [(1R,2S)-isomer and (1S,2R)-isomer] is realized by the recrystallization of the hydrochlorides.
The drug tramadol is a racemate of the hydrochlorides of the (1R,2R)-(+)- and the (1S,2S)-(−)-enantiomers.
The resolution of the racemate [(1R,2R)-(+)-isomer / (1S,2S)-(−)-isomer] was described employing (R)-(−)- or (S)-(+)-mandelic acid. This process does not find industrial application, since tramadol is used as a racemate, despite known different physiological effects of the (1R,2R)- and (1S,2S)-isomers, because the racemate showed higher analgesic activity than either enantiomer in animals and in humans. | 4 | Stereochemistry |
Ouabain can be found in the roots, stems, leaves, and seeds of the Acokanthera schimperi and Strophanthus gratus plants, both of which are native to eastern Africa. | 0 | Organic Chemistry |
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