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A thermochemical equation is a balanced stoichiometric chemical equation that represents the energy changes from a system to its surroundings. One such equation involves the enthalpy change, which is denoted with ΔH. In variable form, a thermochemical equation would appear similar to the following:
:A + B → C
:ΔH = (±) #
{A, B, C} are the usual agents of a chemical equation with coefficients and “(±) #” is a positive or negative numerical value, which generally has units of kJ/J. Another equation may include the symbol E to denote energy; E<nowiki/>'s position determines whether the reaction is considered endothermic or exothermic.
A + E → C (endothermic, where E would be considered a positive magnitude)
A → C + E (exothermic, where E would be considered a negative magnitude) | 7 | Physical Chemistry |
Stanley Robert Hart (born 20 June 1935 in Swampscott, Massachusetts) is an American geologist, geochemist, leading international expert on mantle isotope geochemistry, and pioneer of chemical geodynamics. | 9 | Geochemistry |
An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word intron is derived from the term agenic regi, i.e., a region inside a gene. The term intron refers to both the DNA sequence within a gene and the corresponding RNA sequence in RNA transcripts. The non-intron sequences that become joined by this RNA processing to form the mature RNA are called exons.
Introns are found in the genes of most eukaryotes and many eukaryotic viruses and they can be located in both protein-coding genes and genes that function as RNA (noncoding genes). There are four main types of introns: tRNA introns, group I introns, group II introns, and spliceosomal introns (see below). Introns are rare in Bacteria and Archaea (prokaryotes). | 1 | Biochemistry |
A durable plaster intermediate is often used as a stage toward the production of a bronze sculpture or as a pointing guide for the creation of a carved stone. With the completion of a plaster, the work is more durable (if stored indoors) than a clay original which must be kept moist to avoid cracking. With the low cost plaster at hand, the expensive work of bronze casting or stone carving may be deferred until a patron is found, and as such work is considered to be a technical, rather than artistic process, it may even be deferred beyond the lifetime of the artist.
In waste molding a simple and thin plaster mold, reinforced by sisal or burlap, is cast over the original clay mixture. When cured, it is then removed from the damp clay, incidentally destroying the fine details in undercuts present in the clay, but which are now captured in the mold. The mold may then at any later time (but only once) be used to cast a plaster positive image, identical to the original clay. The surface of this plaster may be further refined and may be painted and waxed to resemble a finished bronze casting. | 8 | Metallurgy |
It has been shown that survivin can heterodimerize individually with the two splice variants Survivin-2B and survivin-deltaEx3. Evidence of the heterodimerization of survivin splice variants with survivin was shown with co-immunoprecipitation experiments after cotransfection with the respective survivin variants with survivin. To determine the localization of exogenously expressed survivin-2B and survivin-deltaEx3, fusion constructs of the proteins were made with GFP and HcRed respectively and Daoy cells were transfected with the plasmid constructs. Survivin was also tagged with a fluorescent protein. The fusion of the survivin variants with the fluorescent molecules allows for simple detection of cellular location by fluorescence microscopy. Survivin-2B by itself, localized to both nuclear and cytoplasmic compartments whereas survivin-deltaEx3 localized only in the nucleus. The localization of the three variants (survivin, Survivin-2B, and survivin-deltaEx3) differ, however, when cotransfected together rather than individually.
To see which subcellular compartments contained the survivin splice variants complexes, fluorescent antibody markers for different organelles in the cell were employed. The assumption is that, under fluorescence microscopy, if the particular survivin complex is located in that particular cell compartment, one would observe an overlap from the fluorescence given off by the tagged survivin complex and the tagged compartment as well. Different color fluorescence is used to distinguish compartment from survivin.
* Endoplasmic reticulum and lyosomes: no colocalization
* Mitochondria and golgi: both survivin/survivin-2B and survivin/survivin-deltaEx3 colocalize
To verify these observations, they fractionated the subcellular compartments and performed western blot analysis to definitively say that survivin complexes did indeed localize at these compartments. | 1 | Biochemistry |
2α-Mannobiose is a disaccharide. It is formed by a condensation reaction, when two mannose molecules react together, in the formation of a glycosidic bond. | 1 | Biochemistry |
The sample is dissolved in water, or a mixture of water and ethanol, and a few drops of neutral ferric chloride (FeCl) solution, which is prepared by adding de-ionised water. Add sodium hydroxide to the mixture until a permanent brown precipitate is formed. The formation of a red, blue, green, or purple coloration indicates the presence of phenols. Where the sample is insoluble in water, it may be dissolved in dichloromethane with a small amount of pyridine. | 3 | Analytical Chemistry |
At the time of development in the nineteenth century, the superscript Plimsoll symbol () was adopted to indicate the non-zero nature of the standard state. IUPAC recommends in the 3rd edition of Quantities, Units and Symbols in Physical Chemistry a symbol which seems to be a degree sign (°) as a substitute for the plimsoll mark. In the very same publication the plimsoll mark appears to be constructed by combining a horizontal stroke with a degree sign. A range of similar symbols are used in the literature: a stroked lowercase letter O () or a circle with a horizontal bar either where the bar extends beyond the boundaries of the circle () or is enclosed by the circle, dividing the circle in half (). Compared to the plimsoll symbol used in 1800s text, the U+29B5 glyph is too large and its horizontal line does not sufficiently extend beyond the boundaries of the circle. It is easily confused with the Greek letter theta (uppercase Θ or , lowercase θ ). As of 2024, the character has been proposed for Unicode. It is a regular-sized Unicode symbol meant to be used in superscripted form when denoting standard state, replacing U+29B5 for this purpose.
Ian M. Mills, who was involved in producing a revision of Quantities, Units and Symbols in Physical Chemistry, suggested that a superscript zero () is an equal alternative to indicate "standard state", though a degree symbol (°) is used in the same article. The degree symbol has come into widespread use in general, inorganic, and physical chemistry textbooks in recent years. When read out loud, the symbol is pronounced "naught". | 7 | Physical Chemistry |
GDP-mannose is produced from GTP and mannose-6-phosphate by the enzyme mannose-1-phosphate guanylyltransferase.
One of the enzymes from the family of nucleootidyl-transferases, GDP-Mannose Pyrophosphorylase (GDP-MP) is an pervasive enzyme found in bacteria, fungi, plants, and animals. | 1 | Biochemistry |
A shadow wall is created when a light flashes upon a person or object in front of a phosphorescent screen which temporarily captures the shadow. The screen or wall is painted with a glow-in-the-dark product that contains phosphorescent compounds. Publicly, these shadow walls can be found at certain science museums. | 7 | Physical Chemistry |
This method is based on magnetic resonance imaging of the distribution of ions comprising NMR-active nuclei (usually 1H, 19F, 7Li) in an electrochemical cells upon application of electric current | 7 | Physical Chemistry |
* Phase equilibria data (vapor–liquid, liquid–liquid, solid–liquid), data on azeotropy and zeotropy
* Mixing enthalpies
* Gas solubilities
* Activity coefficients at infinite dilution
* Heat capacities and excess heat capacities
* Volumes, densities, and excess volumes (volume effect of mixing)
* Salt solubilities
* Octanol-water partition coefficients
* Critical data
The mixture data banks contain () approx. 308,000 data sets with 2,157,000 data points for 10,750 components building 84,870 different binary, ternary, and higher systems/combinations. | 7 | Physical Chemistry |
Few rocks were visible on the surface where Opportunity landed, but bedrock that was exposed in craters was examined by the suite of instruments on the Rover. Bedrock rocks were found to be sedimentary rocks with a high concentration of sulfur in the form of calcium and magnesium sulfates. Some of the sulfates that may be present in bedrocks are kieserite, sulfate anhydrate, bassanite, hexahydrite, epsomite, and gypsum. Salts, such as halite, bischofite, antarcticite, bloedite, vanthoffite, or glauberite may also be present.
The rocks contained the sulfates had a light tone compared to isolated rocks and rocks examined by landers/rovers at other locations on Mars. The spectra of these light toned rocks, containing hydrated sulfates, were similar to spectra taken by the Thermal Emission Spectrometer on board the Mars Global Surveyor. The same spectrum is found over a large area, so it is believed that water once appeared over a wide region, not just in the area explored by Opportunity Rover.
The Alpha Particle X-ray Spectrometer (APXS) found rather high levels of phosphorus in the rocks. Similar high levels were found by other rovers at Ares Vallis and Gusev Crater, so it has been hypothesized that the mantle of Mars may be phosphorus-rich. The minerals in the rocks could have originated by acid weathering of basalt. Because the solubility of phosphorus is related to the solubility of uranium, thorium, and rare earth elements, they are all also expected to be enriched in rocks.
When Opportunity rover traveled to the rim of Endeavour crater, it soon found a white vein that was later identified as being pure gypsum. It was formed when water carrying gypsum in solution deposited the mineral in a crack in the rock. A picture of this vein, called "Homestake" formation, is shown below. | 9 | Geochemistry |
* [http://grotrian.nsu.ru/en Electronic structure of atoms]
* [https://physics.nist.gov/PhysRefData/ASD/lines_form.html NIST Atomic Spectra Database Lines Form]
* [https://www.physics.unlv.edu/~jeffery/astro/atomic/grotrian/grotrian.html Grotrian Diagrams] | 7 | Physical Chemistry |
Afovirsen is an oligonucleotide capable of antisense interactions with mRNA of human papillomavirus. It has been investigated as a tool for diagnostics and therapeutics. | 0 | Organic Chemistry |
The effect was first observed by Jencks and Carriuolo in 1960 in a series of chemical kinetics experiments involving the reaction of the ester p-nitrophenyl acetate with a range of nucleophiles. Regular nucleophiles such as the fluoride anion, aniline, pyridine, ethylene diamine and the phenolate ion were found to have pseudo first order reaction rates corresponding to their basicity as measured by their pK. Other nucleophiles however reacted much faster than expected based on this criterion alone. These include hydrazine, hydroxylamine, the hypochlorite ion and the hydroperoxide anion. | 7 | Physical Chemistry |
Dr. Raymond U. Lemieux was born in Lac La Biche, Alberta, Canada. His family moved to Edmonton, Alberta in 1926. He studied chemistry at the University of Alberta and received a BSc with Honours in Chemistry in 1943. He went on to study at McGill University, where he received his PhD in Organic Chemistry in 1946. He won a post-doctoral scholarship at Ohio State University, where Bristol Laboratories Inc. sponsored his research on the structure of streptomycin. He met his future wife, a doctoral student, at Ohio State and they were married in 1948.
In following years, he returned to Canada where he spent two years as an assistant professor at the University of Saskatchewan. Next he served as Senior Research Officer at the National Research Council's Prairie Regional Laboratory in Saskatoon. In 1953 he and a fellow researcher, George Huber, were the first scientists to successfully synthesize sucrose. In 1954, he accepted the position of Dean in the Faculty of Pure and Applied Sciences at the University of Ottawa, where he established their Department of Chemistry. In 1961 he returned to the University of Alberta as a professor in the Chemistry Department and to serve as the chairman of the Organic Chemistry Division. He developed a method to make synthetic versions of oligosaccharides, which led to improved treatments for leukemia and hemophilia and the development of new antibiotics, blood reagents, and organ anti-rejection drugs.
While at the University of Alberta, he established a number of biochemical companies, including R&L Molecular Research Ltd. in 1962, Raylo Chemicals Ltd. in 1966 (which purchased R&L) and Chembiomed in 1977 (which has since been taken over by Synsorb Biotech of Calgary, Alberta.) Prof. Lemieux published an autobiography, entitled "Explorations with Sugars: How Sweet It Was," in 1990.
Dr. Raymond Lemieux died of an aneurysm in 2000.
In 1999, the University of Alberta Faculty of Science and Strathcona County established the Strathcona County/R.U. Lemieux Chair in Carbohydrate Chemistry. In 2001, the University of Alberta renamed the building(s) housing the Department of Chemistry to the Gunning/Lemieux Chemistry Centre to acknowledge the contributions of Profs. Raymond Lemieux and Harry Gunning. | 0 | Organic Chemistry |
In a semiconductors, if all oscillations have the same eigenfrequency and the broadening in the imaginary part of the dielectric function results only from a finite damping , the system is said to be homogeneously broadened, and has a Lorentzian profile. If the system contains many oscillators with slightly different frequencies about however, then the system is inhomogeneously broadened. | 7 | Physical Chemistry |
Cyclic AMP-dependent protein kinases (protein kinase A) are activated by the signal chain coming from the G protein (that was activated by the FSH-receptor) via adenylate cyclase and cyclic AMP (cAMP).
These protein kinases are present as tetramers with two regulatory units and two catalytic units. Upon binding of cAMP to the regulatory units, the catalytic units are released and initiate the phosphorylation of proteins, leading to the physiologic action. The cyclic AMP-regulatory dimers are degraded by phosphodiesterase and release 5’AMP. DNA in the cell nucleus binds to phosphorylated proteins through the cyclic AMP response element (CRE), which results in the activation of genes.
The signal is amplified by the involvement of cAMP and the resulting phosphorylation. The process is modified by prostaglandins. Other cellular regulators are participate are the intracellular calcium concentration modified by phospholipase, nitric acid, and other growth factors.
The FSH receptor can also activate the extracellular signal-regulated kinases (ERK). In a feedback mechanism, these activated kinases phosphorylate the receptor. The longer the receptor remains active, the more kinases are activated, the more receptors are phosphorylated. | 1 | Biochemistry |
Although it is difficult to generalize on the toxicity of such a broad class of compounds, simple ketones are, in general, not highly toxic. This characteristic is one reason for their popularity as solvents. Exceptions to this rule are the unsaturated ketones such as methyl vinyl ketone with of 7 mg/kg (oral). | 0 | Organic Chemistry |
Nonclassical describes those carbonyl complexes where ν is higher than that for free carbon monoxide. In nonclassical CO complexes, the C-O distance is shorter than free CO (113.7 pm). The structure of [Fe(CO)], with d = 112.9 pm, illustrates this effect. These complexes are usually cationic, sometimes dicationic. | 0 | Organic Chemistry |
The majority of plants possessing CAM are either epiphytes (e.g., orchids, bromeliads) or succulent xerophytes (e.g., cacti, cactoid Euphorbias), but CAM is also found in hemiepiphytes (e.g., Clusia); lithophytes (e.g., Sedum, Sempervivum); terrestrial bromeliads; wetland plants (e.g., Isoetes, Crassula (Tillaea), Lobelia); and in one halophyte, Mesembryanthemum crystallinum; one non-succulent terrestrial plant, (Dodonaea viscosa) and one mangrove associate (Sesuvium portulacastrum).
The only trees that can do CAM are in the genus Clusia; species of which are found across Central America, South America and the Caribbean. In Clusia, CAM is found in species that inhabit hotter, drier ecological niches, whereas species living in cooler montane forests tend to be . In addition, some species of Clusia can temporarily switch their photosynthetic physiology from to CAM, a process known as facultative CAM. This allows these trees to benefit from the elevated growth rates of photosynthesis, when water is plentiful, and the drought tolerant nature of CAM, when the dry season occurs.
Plants which are able to switch between different methods of carbon fixation include Portulacaria afra, better known as Dwarf Jade Plant, which normally uses C fixation but can use CAM if it is drought-stressed, and Portulaca oleracea, better known as Purslane, which normally uses fixation but is also able to switch to CAM when drought-stressed.
CAM has evolved convergently many times. It occurs in 16,000 species (about 7% of plants), belonging to over 300 genera and around 40 families, but this is thought to be a considerable underestimate. The great majority of plants using CAM are angiosperms (flowering plants) but it is found in ferns, Gnetopsida and in quillworts (relatives of club mosses). Interpretation of the first quillwort genome in 2021 (I. taiwanensis) suggested that its use of CAM was another example of convergent evolution.
The following list summarizes the taxonomic distribution of plants with CAM: | 5 | Photochemistry |
Oxacillin, a derivative of methicillin, was first synthesized in the early 1960s as part of a research initiative led by Peter Doyle and John Naylor of Beecham, in consort with Bristol-Myers. Members of the isoxazolyl penicillin family, which includes cloxacillin, dicloxacillin, and oxacillin, were synthesized to counter the increasing prevalence of infections caused by penicillin-resistant Staphylococcus aureus. While methicillin could only be administered via injection, the isoxazolyl penicillins, including oxacillin, could be given orally or by injection. Following the synthesis of cloxacillin and oxacillin, Beecham retained the right to commercially develop cloxacillin in the United Kingdom while Bristol-Myers was given the marketing rights for oxacillin in the United States. | 4 | Stereochemistry |
The rate and outcome of chemical reactions taking place in water often depends on the acidity of the water, and it is therefore useful to know the acidity of the water, typically measured by means of a pH meter. Knowledge of pH is useful or critical in many situations, including chemical laboratory analyses. pH meters are used for soil measurements in agriculture, water quality for municipal water supplies, swimming pools, environmental remediation; brewing of wine or beer; manufacturing, healthcare and clinical applications such as blood chemistry; and many other applications.
Advances in the instrumentation and in detection have expanded the number of applications in which pH measurements can be conducted. The devices have been miniaturized, enabling direct measurement of pH inside of living cells. In addition to measuring the pH of liquids, specially designed electrodes are available to measure the pH of semi-solid substances, such as foods. These have tips suitable for piercing semi-solids, have electrode materials compatible with ingredients in food, and are resistant to clogging. | 7 | Physical Chemistry |
A centisome is a unit of length defined as one percent of the length of a particular chromosome. This course unit of physical DNA length began to be used in the early exploration of genomes through molecular biology before the resolution of the nucleic acid sequences of chromosomes was possible.
One of the main uses for this unit was for describing the locus of a gene by giving a distance in centisomes from a reference point on the chromosome. For instance, when the complete genome of the bacterium Escherichia coli was finally completed in 1997, it was presented with a scale given in centisomes (as well as one in kilobases). Since bacterial chromosomes are circular, the reference point cannot be an end of the DNA molecule, but must be some point that has some easily determinable unique characteristic. Often this point is the origin of replication, although for E. coli it is the origin of transfer during conjugation. Hence, the reference point for centisome positions is simply a convention established for each individual species of organism.
For the most part, modern scientific literature uses "centisome" as part of a shorthand way of referring to a particular region of interest on the chromosome of particular organisms. For instance, much research has been done on the "Centisome 63" area of the chromosomes of Salmonella species. | 1 | Biochemistry |
Centrifugal partition chromatography does not uses any solid stationary phase, so it guarantees a cost-effective separation for the highest industrial levels. As opposed to countercurrent chromatography, it is possible to get very high flow rates (for example 10 liters / min) with active stationary phase ratio of >80%, which guarantees good separation and high productivity. As in centrifugal partition chromatography, material is dissolved, and loaded the column in mass / volume units, loading capability can be much higher than standard solid-liquid chromatographic techniques, where material is loaded to the active surface area of the stationary phase, which takes up less than 10% of the column.
Industrial instrument like Gilson (Armen Instrument), Kromaton (Rousselet Robatel) and RotaChrom Technologies (RotaChrom) differ from laboratory scale instruments by the applicable flow rate with satisfactory stationary phase retention (70–90%). Industrial instruments have flow rates of multiple liter / minutes, while able to purify materials from 10 kg to tonnes per month.
Operating the production scale equipment requires industrial volume solvent preparation (mixer/settler) and solvent recovery equipment. | 3 | Analytical Chemistry |
Hyperpolarization-activated cyclic nucleotide–gated (HCN) channels are integral membrane proteins that serve as nonselective voltage-gated cation channels in the plasma membranes of heart and brain cells. HCN channels are sometimes referred to as pacemaker channels because they help to generate rhythmic activity within groups of heart and brain cells. HCN channels are activated by membrane hyperpolarization, are permeable to and , and are constitutively open at voltages near the resting membrane potential. HCN channels are encoded by four genes (HCN1, 2, 3, 4) and are widely expressed throughout the heart and the central nervous system.
The current through HCN channels, designated I or I, plays a key role in the control of cardiac and neuronal rhythmicity and is called the pacemaker current or "funny" current. Expression of single isoforms in heterologous systems such as human embryonic kidney (HEK) cells, Chinese hamster ovary (CHO) cells and Xenopus oocytes yield homotetrameric channels able to generate ion currents with properties similar to those of the native I/I current, but with quantitative differences in the voltage-dependence, activation/deactivation kinetics and sensitivity to the nucleotide cyclic AMP (cAMP): HCN1 channels have a more positive threshold for activation, faster activation kinetics, and a lower sensitivity to cAMP, while HCN4 channels are slowly gating and strongly sensitive to cAMP. HCN2 and HCN3 have intermediate properties. | 1 | Biochemistry |
The microdialysis technique has undergone much development since its first use in 1972, when it was first employed to monitor concentrations of endogenous biomolecules in the brain. Today's area of application has expanded to monitoring free concentrations of endogenous as well as exogenous compounds in virtually any tissue. Although microdialysis is still primarily used in preclinical animal studies (e.g. laboratory rodents, dogs, sheep, pigs), it is now increasingly employed in humans to monitor free, unbound drug tissue concentrations as well as interstitial concentrations of regulatory cytokines and metabolites in response to homeostatic perturbations such as feeding and/or exercise.
When employed in brain research, microdialysis is commonly used to measure neurotransmitters (e.g. dopamine, serotonin, norepinephrine, acetylcholine, glutamate, GABA) and their metabolites, as well as small neuromodulators (e.g. cAMP, cGMP, NO), amino acids (e.g. glycine, cysteine, tyrosine), and energy substrates (e.g. glucose, lactate, pyruvate). Exogenous drugs to be analyzed by microdialysis include new antidepressants, antipsychotics, as well as antibiotics and many other drugs that have their pharmacological effect site in the brain. The first non-metabolite to be analyzed by microdialysis in vivo in the human brain was rifampicin.
Applications in other organs include the skin (assessment of bioavailability and bioequivalence of topically applied dermatological drug products), and monitoring of glucose concentrations in patients with diabetes (intravascular or subcutaneous probe placement). The latter may even be incorporated into an artificial pancreas system for automated insulin administration.
Microdialysis has also found increasing application in environmental research, sampling a diversity of compounds from waste-water and soil solution, including saccharides, metal ions, micronutrients, organic acids, and low molecular weight nitrogen. Given the destructive nature of conventional soil sampling methods, microdialysis has potential to estimate fluxes of soil ions that better reflect an undisturbed soil environment. | 1 | Biochemistry |
While the high-selectivity and tight-binding of RNA aptamers have generated interest in their use as pharmaceuticals, there are many problems which have prevented them from being successful in vivo. For one, without modifications RNA aptamers are degraded after being introduced into the body by nucleases in the span of a few minutes. Also, due to their small size, RNA aptamers can be removed from the bloodstream by the renal system. Because of their negative charge, RNA aptamers are additionally known to bind proteins in the bloodstream, leading to non-target tissue delivery and toxicity. Care must also be taken when isolating the RNA aptamers, as aptamers which contain repeated Cytosine-Phosphate-Guanine (CpG) sequences will cause immune system activation through the Toll-like receptor pathway.
In order to combat some of the in vivo limitations of RNA aptamers, various modifications can be added to the nucleotides to aid in efficacy of the aptamer. For instance, a polyethylene glycol (PEG) moiety can be attached to increase the size of the aptamer, thereby preventing its removal from the bloodstream by the renal glomerulus. However, PEG has been implicated in allergic reactions during in vivo testing. Furthermore, modifications can be added to prevent nuclease degradation, such as a 2’ fluoro or amino group as well as a 3’ inverted thymidine. Additionally, the aptamer can be synthesized so that the ribose sugar is in the L-form instead of the D-form, further preventing nuclease recognition. Such aptamers are known as Spiegelmers. In order to prevent Toll-like receptor pathway activation, the cytosine nucleobases within the aptamer can be methylated. Nevertheless, despite these potential solutions to reduced in vivo efficacy, it is possible that chemically modifying the aptamer may weaken its binding affinity towards its target. | 1 | Biochemistry |
HVAF coating technology is the combustion of propane in a compressed air stream. Like HVOF, this produces a uniform high velocity jet. HVAF differs by including a heat baffle to further stabilize the thermal spray mechanisms. Material is injected into the air-fuel stream and coating particles are propelled toward the part. HVAF has a maximum flame temperature of 3,560° to 3,650 °F and an average particle velocity of 3,300 ft/sec. Since the maximum flame temperature is relatively close to the melting point of most spray materials, HVAF results in a more uniform, ductile coating. This also allows for a typical coating thickness of 0.002–0.050". HVAF coatings also have a mechanical bond strength of greater that 12,000 psi. Common HVAF coating materials include, but are not limited to; tungsten carbide, chrome carbide, stainless steel, hastelloy, and inconel. Due to its ductile nature hvaf coatings can help resist cavitation damage. | 8 | Metallurgy |
Glasses are amorphous solids, which are usually fabricated when the molten material cools very rapidly to below its glass transition temperature, without sufficient time for a regular crystal lattice to form. Solids are characterised by a high degree of connectivity between their molecules, and fluids have lower connectivity of their structural blocks. Melting of a solid material can also be considered as a percolation via broken connections between particles e.g. connecting bonds. In this approach melting of an amorphous material occurs, when the broken bonds form a percolation cluster with T dependent on quasi-equilibrium thermodynamic parameters of bonds e.g. on enthalpy (H) and entropy (S) of formation of bonds in a given system at given conditions:
where f is the percolation threshold and R is the universal gas constant.
Although H and S are not true equilibrium thermodynamic parameters and can depend on the cooling rate of a melt, they can be found from available experimental data on viscosity of amorphous materials.
Even below its melting point, quasi-liquid films can be observed on crystalline surfaces. The thickness of the film is temperature-dependent. This effect is common for all crystalline materials. This pre-melting shows its effects in e.g. frost heave, the growth of snowflakes, and, taking grain boundary interfaces into account, maybe even in the movement of glaciers. | 7 | Physical Chemistry |
The 6 of the 11 metabolic intermediates in reverse Krebs cycle promoted by Fe, Zn, and Cr in acidic conditions imply that protocells possibly emerged in locally metal-rich and acidic terrestrial hydrothermal fields. The acidic conditions are seemingly consistent with the stabilization of RNA. These hydrothermal fields would have exhibited cycling of freezing and thawing and a variety of temperature gradients that would promote nonenzymatic reactions of gluconeogenesis, nucleobase synthesis, nonenzymatic polymerization, and RNA replication. ATP synthesis and oxidation of ferrous iron via photochemical reactions or oxidants such as nitric oxide derived from lightning strikes, meteorite impacts, or volcanic emissions could have also occurred at hydrothermal fields.
Wet-dry cycling of hydrothermal fields would polymerize RNA and peptides, protocell aggregation in a moist gel phase during wet-dry cycling would allow diffusion of metabolic products across neighboring protocells. Protocell aggregation could be described as a primitive version of horizontal gene transfer. Fatty acid vesicles would be stabilized by polymers in the presence of Mg required for ribozyme activity. These prebiotic processes might have occurred in shaded areas that protect the emergence of early cellular life under ultraviolet irradiation. Long chain alcohols and monocarboxylic acids would have also been synthesized via Fischer–Tropsch synthesis. Hydrothermal fields would also have precipitates of transition metals and concentrated many elements including CHNOPS. Geothermal convection could also be a source of energy for the emergence of the proton motive force, phosphoryl group transfer, coupling between oxidation-reduction, and active transport. Its noted by David Deamer and Bruce Damer that these environments seemingly resemble Charles Darwins idea of a "warm little pond".
The problems with the hypothesis of a subaerial hydrothermal field of abiogenesis is that the proposed chemistry doesnt resemble known biochemical reactions. The abundance of subaerial hydrothermal fields would have been rare and offered no protection from either meteorites or ultraviolet irradiation. Clay minerals at subaerial hydrothermal fields would absorb organic reactants. Pyrophosphate has low solubility in water and cant be phosphorylated without a phosphorylating agent. It doesn't offer explanations for the origin of chemiosmosis and differences between Archaea and Bacteria. | 1 | Biochemistry |
Hydrogen forms whenever molten aluminium comes into contact with water vapor, and easily dissolves into the melt. The gas tends to come out of the solution and forms bubbles when the melt solidifies.
The detrimental effects arising from the presence of an excess of dissolved hydrogen in aluminium are numerous. Hydrogen causes porosity in aluminum products leading to many casting defects, reduced mechanical properties like fatigue and lower corrosion resistance. Several methods are used to reduce the amount of dissolved hydrogen from the melt, such as furnace fluxing prior to the casting process or using in-line degassing equipment during the casting process. | 8 | Metallurgy |
The first step in analysis is the introduction of the sample. This has been achieved in ICP-MS through a variety of means.
The most common method is the use of analytical nebulizers. Nebulizer converts liquids into an aerosol, and that aerosol can then be swept into the plasma to create the ions. Nebulizers work best with simple liquid samples (i.e. solutions). However, there have been instances of their use with more complex materials like a slurry. Many varieties of nebulizers have been coupled to ICP-MS, including pneumatic, cross-flow, Babington, ultrasonic, and desolvating types. The aerosol generated is often treated to limit it to only smallest droplets, commonly by means of a Peltier cooled double pass or cyclonic spray chamber. Use of autosamplers makes this easier and faster, especially for routine work and large numbers of samples. A Desolvating Nebuliser (DSN) may also be used; this uses a long heated capillary, coated with a fluoropolymer membrane, to remove most of the solvent and reduce the load on the plasma. Matrix removal introduction systems are sometimes used for samples, such as seawater, where the species of interest are at trace levels, and are surrounded by much more abundant contaminants.
Laser ablation is another method. While being less common in the past, is rapidly becoming popular has been used as a means of sample introduction, thanks to increased ICP-MS scanning speeds. In this method, a pulsed UV laser is focused on the sample and creates a plume of ablated material which can be swept into the plasma. This allows geochemists to spacially map the isotope composition in cross-sections of rock samples, a tool which is lost if the rock is digested and introduced as a liquid sample. Lasers for this task are built to have highly controllable power outputs and uniform radial power distributions, to produce craters which are flat bottomed and of a chosen diameter and depth.
For both Laser Ablation and Desolvating Nebulisers, a small flow of Nitrogen may also be introduced into the Argon flow. Nitrogen exists as a dimer, so has more vibrational modes and is more efficient at receiving energy from the RF coil around the torch.
Other methods of sample introduction are also utilized. Electrothermal vaporization (ETV) and in torch vaporization (ITV) use hot surfaces (graphite or metal, generally) to vaporize samples for introduction. These can use very small amounts of liquids, solids, or slurries. Other methods like vapor generation are also known. | 3 | Analytical Chemistry |
In addition to the operations of the point group, the space group of the crystal structure contains translational symmetry operations. These include:
*Pure translations, which move a point along a vector
*Screw axes, which rotate a point around an axis while translating parallel to the axis.
*Glide planes, which reflect a point through a plane while translating it parallel to the plane.
There are 230 distinct space groups. | 3 | Analytical Chemistry |
Practical applications of the respiratory quotient can be found in severe cases of chronic obstructive pulmonary disease, in which patients spend a significant amount of energy on respiratory effort. By increasing the proportion of fats in the diet, the respiratory quotient is driven down, causing a relative decrease in the amount of CO produced. This reduces the respiratory burden to eliminate CO, thereby reducing the amount of energy spent on respirations.
Respiratory Quotient can be used as an indicator of over or underfeeding. Underfeeding, which forces the body to utilize fat stores, will lower the respiratory quotient, while overfeeding, which causes lipogenesis, will increase it. Underfeeding is marked by a respiratory quotient below 0.85, while a respiratory quotient greater than 1.0 indicates overfeeding. This is particularly important in patients with compromised respiratory systems, as an increased respiratory quotient significantly corresponds to increased respiratory rate and decreased tidal volume, placing compromised patients at a significant risk.
Because of its role in metabolism, respiratory quotient can be used in analysis of liver function and diagnosis of liver disease. In patients with liver cirrhosis, non-protein respiratory quotient (npRQ) values act as good indicators in the prediction of overall survival rate. Patients having a npRQ < 0.85 show considerably lower survival rates as compared to patients with a npRQ > 0.85. A decrease in npRQ corresponds to a decrease in glycogen storage by the liver. Similar research indicates that non-alcoholic fatty liver diseases are also accompanied by a low respiratory quotient value, and the non protein respiratory quotient value was a good indication of disease severity.
Recently the respiratory quotient is also used from aquatic scientists to illuminate its environmental applications. Experimental studies with natural bacterioplankton using different single substrates suggested that RQ is linked to the elemental composition of the respired compounds. By this way, it is demonstrated that bacterioplankton RQ is not only a practical aspect of Bacterioplankton Respiration determination, but also a major ecosystem state variable that provides unique information about aquatic ecosystem functioning. Based on the stoichiometry of the different metabolized substrates, the scientists can predict that dissolved oxygen (O) and carbon dioxide (CO) in aquatic ecosystems should covary inversely due to the processing of photosynthesis and respiration. Using this quotient we could shed light on the metabolic behavior and the simultaneous roles of chemical and physical forcing that shape the biogeochemistry of aquatic ecosystems. | 1 | Biochemistry |
Lipotropic compounds are those that help catalyse the breakdown of fat during metabolism in the body. A lipotropic nutrient promotes or encourages the export of fat from the liver. Lipotropics are necessary for maintenance of a healthy liver, and for burning the exported fat for additional energy. Without lipotropics, such as choline and inositol, fats and bile can become trapped in the liver, causing severe problems such as cirrhosis and blocking fat metabolism.
Choline is the major lipotrope in mammals and other known lipotropes are important only insofar as they contribute to the synthesis of choline. Choline is essential for fat metabolism. Choline functions as a methyl donor and it is required for proper liver function. Though choline can be synthesized from methionine or serine, mammals don't produce a sufficient amount on their own. Liver, eggs, wheat bran, meat, and broccoli are dietary sources of choline.
Inositol exerts lipotropic effects as well. Oranges and cantaloupe are high in inositol.
Methionine, an essential amino acid, is a major lipotropic compound in humans. When estrogen levels are high, the body requires more methionine. Estrogens reduce bile flow through the liver and increase bile cholesterol levels. Methionine helps deactivate estrogens. Egg whites are high in methionine.
Methionine levels also affect the amount of sulfur-containing compounds, such as glutathione, in the liver. Glutathione and other sulfur-containing peptides play a critical role in defending against toxic compounds. Supplementation with vitamin C, vitamin D, and NAC can increase glutathione levels.
Betaine hydrochloride is a lipotropic and increases gastric acid. Betaine itself (in a non-hydrochloric form, also known as TMG or Trimethylglycine) also has a lipotropic effect. Quinoa is high in betaine. | 1 | Biochemistry |
A model put forward by Lee Kump, Alexander Pavlov and Michael Arthur in 2005 suggests that oceanic anoxic events may have been characterized by upwelling of water rich in highly toxic hydrogen sulfide gas, which was then released into the atmosphere. This phenomenon would probably have poisoned plants and animals and caused mass extinctions. Furthermore, it has been proposed that the hydrogen sulfide rose to the upper atmosphere and attacked the ozone layer, which normally blocks the deadly ultraviolet radiation of the Sun. The increased UV radiation caused by this ozone depletion would have amplified the destruction of plant and animal life. Fossil spores from strata recording the Permian–Triassic extinction event show deformities consistent with UV radiation. This evidence, combined with fossil biomarkers of green sulfur bacteria, indicates that this process could have played a role in that mass extinction event, and possibly other extinction events. The trigger for these mass extinctions appears to be a warming of the ocean caused by a rise of carbon dioxide levels to about 1000 parts per million. | 9 | Geochemistry |
Assuming a two state denaturation as stated above, one can derive the fundamental thermodynamic parameters namely, , and provided one has knowledge on the of the system under investigation.
The thermodynamic observables of denaturation can be described by the following equations:
where , and indicate the enthalpy, entropy and Gibbs free energy of unfolding under a constant pH and pressure. The temperature, is varied to probe the thermal stability of the system and is the temperature at which half of the molecules in the system are unfolded. The last equation is known as the Gibbs–Helmholtz equation. | 7 | Physical Chemistry |
Minipreparation of plasmid DNA is a rapid, small-scale isolation of plasmid DNA from bacteria. Commonly used miniprep methods include alkaline lysis and spin-column based kits. It is based on the alkaline lysis method. The extracted plasmid DNA resulting from performing a miniprep is itself often called a "miniprep".
Minipreps are used in the process of molecular cloning to analyze bacterial clones. A typical plasmid DNA yield of a miniprep is 5 to 50 µg depending on the cell strain.
Miniprep of a large number of plasmids can also be done conveniently on filter paper by lysing the cell and eluting the plasmid on to filter paper. | 1 | Biochemistry |
Proteins are biomolecules that are composed of amino acid subunits. Each amino acid has a side chain that gains or loses charge depending on the pH of the surrounding environment, as well as its own individual polar/nonpolar qualities. Charged regions can greatly contribute to how that protein interacts with other molecules and surfaces, as well as its own tertiary structure (protein folding). As a result of their hydrophilicity, charged amino acids tend to be located on the outside of proteins, where they are able to interact with surfaces. It is the unique combination of amino acids that gives a protein its properties. In terms of surface chemistry, protein adsorption is a critical phenomenon that describes the aggregation of these molecules on the exterior of a material. The tendency for proteins to remain attached to a surface depends largely on the material properties such as surface energy, texture, and relative charge distribution. Larger proteins are more likely to adsorb and remain attached to a surface due to the higher number of contact sites between amino acids and the surface (Figure 1). | 1 | Biochemistry |
Feline leukemia virus and Feline immunodeficiency virus infections are treated with biologics, including the only immunomodulator currently licensed for sale in the United States, Lymphocyte T-Cell Immune Modulator (LTCI). | 1 | Biochemistry |
An old standing dynamic problem is how DNA "self-replication" takes place in living cells that should involve transient uncoiling of supercoiled DNA fibers. Although DNA consists of relatively rigid, very large elongated biopolymer molecules called fibers or chains (that are made of repeating nucleotide units of four basic types, attached to deoxyribose and phosphate groups), its molecular structure in vivo undergoes dynamic configuration changes that involve dynamically attached water molecules and ions. Supercoiling, packing with histones in chromosome structures, and other such supramolecular aspects also involve in vivo DNA topology which is even more complex than DNA molecular geometry, thus turning molecular modeling of DNA into an especially challenging problem for both molecular biologists and biotechnologists. Like other large molecules and biopolymers, DNA often exists in multiple stable geometries (that is, it exhibits conformational isomerism) and configurational, quantum states which are close to each other in energy on the potential energy surface of the DNA molecule.
Such varying molecular geometries can also be computed, at least in principle, by employing ab initio quantum chemistry methods that can attain high accuracy for small molecules, although claims that acceptable accuracy can be also achieved for polynuclelotides, and DNA conformations, were recently made on the basis of vibrational circular dichroism (VCD) spectral data. Such quantum geometries define an important class of ab initio molecular models of DNA which exploration has barely started, especially related to results obtained by VCD in solutions. More detailed comparisons with such ab initio quantum computations are in principle obtainable through 2D-FT NMR spectroscopy and relaxation studies of polynucleotide solutions or specifically labeled DNA, as for example with deuterium labels.
In an interesting twist of roles, the DNA molecule was proposed to be used for quantum computing via DNA. Both DNA nanostructures and DNA computing biochips have been built. | 4 | Stereochemistry |
Daily light integral (DLI) describes the number of photosynthetically active photons (individual particles of light in the 400-700 nm range) that are delivered to a specific area over a 24-hour period. This variable is particularly useful to describe the light environment of plants. | 5 | Photochemistry |
Some carbon removal techniques add alkalinity to the ocean and therefore immediately buffer pH changes which might help the organisms in the region that the extra alkalinity is added to. The two technologies that fall into this category are ocean alkalinity enhancement and electrochemical methods. Eventually, due to diffusion, that alkalinity addition will be quite small to distant waters. This is why the term local ocean acidification mitigation is used. Both of these technologies have the potential to operate on a large scale and to be efficient at removing carbon dioxide. However, they are expensive, have many risks and side effects and currently have a low technology readiness level. | 9 | Geochemistry |
TFD is itself composed of TBP and several subunits called TATA-binding protein Associated Factors (TBP-associated factors, or TAFs). In a test tube, only TBP is necessary for transcription at promoters that contain a TATA box. TAFs, however, add promoter selectivity, especially if there is no TATA box sequence for TBP to bind to. TAFs are included in two distinct complexes, TFD and B-TFD. The TFD complex is composed of TBP and more than eight TAFs. But, the majority of TBP is present in the B-TFD complex, which is composed of TBP and TAFII170 (BTAF1) in a 1:1 ratio. TFD and B-TFD are not equivalent, since transcription reactions utilizing TFD are responsive to gene specific transcription factors such as SP1, while reactions reconstituted with B-TFD are not.
Subunits in the TFD complex include:
* TBP (TATA binding protein), or:
** TBP-related factors in animals (TBPL1; TBPL2)
* TAF1 (TAFII250)
* TAF2 (CIF150)
* TAF3 (TAFII140)
* TAF4 (TAFII130/135)
* TAF4B (TAFII105)
* TAF5 (TAFII100)
* TAF6 (TAFII70/80)
* TAF7 (TAFII55)
* TAF8 (TAFII43)
* TAF9 (TAFII31/32)
* TAF9B (TAFII31L)
* TAF10 (TAFII30)
* TAF11 (TAFII28)
* TAF12 (TAFII20/15)
* TAF13 (TAFII18)
* TAF15 (TAFII68) | 1 | Biochemistry |
Several studies of diets supplemented with MFGM and its components, including gangliosides and sphingomyelin, have aimed to address measures of cognitive development in pediatric populations. In some of the studies, MFGM supplementation to infant formula was shown to narrow the gap in cognitive development between breastfed and formula-fed infants.
Tanaka et al. (2013) studied the neurobehavioral effects of feeding formula supplemented with sphingomyelin-enriched phospholipid in 24 very low birth weight preterm infants (birth weight <1500 g).
In this double-blind RCT, the preterm infants were fed either control formula containing phospholipids derived from egg yolk lecithin with sphingomyelin at 13% of total phospholipid or a supplemented formula with milk-derived phospholipids containing 20% sphingomyelin. Infants fed the supplemented formula had significantly higher percentages of sphingomyelin in total plasma phospholipids after 4, 6, and 8 weeks of feeding compared to those fed the control formula. The infants fed the supplemented formula also showed improvements across multiple developmental measures at 18 months, with significantly better scores on the Behavior Rating Scale of the Bayley Scales of Infant Development II (BSID-II), the Fagan test (novelty preference rate), the latency of visual evoked potentials (VEP), and sustained attention test than in the control group.
Gurnida et al. (2012) assessed the cognitive effects of formula supplemented with a ganglioside-enriched, MFGM-derived complex milk lipid in term infants. In this double-blind RCT, healthy infants (2–8 weeks of age) were fed until 6 months of age, either control infant formula (n=30), or a supplemented infant formula (n=29) with added complex milk lipids to increase ganglioside concentration to approximately 11-12 μg/mL to be within the human milk range. A breastfed reference group (n=32) was also included. Results showed that serum ganglioside levels in the supplemented group were significantly higher compared to the control group at 6 months, but did not significantly differ from levels in the breastfed group. The cognitive outcomes measured using the Griffiths Mental Development Scale showed that the supplemented group had significantly increased scores for Hand and Eye Coordination, Performance, and Total Score (General Quotient) at 6 months compared to the control group, and there were no significant differences in cognitive performance compared to the breastfed reference group.
Timby et al. (2014) also assessed the potential impact of MFGM supplementation on cognitive development in term infants. In this double-blind RCT, term infants (<2 months old) were fed until 6 months of age either a control formula (n=64) or an MFGM-supplemented formula (n=71). A breastfed reference group (n=70) was also included. Cognitive assessment done using the BSID-III at 12 months of age showed that the MFGM-fed infants exhibited significantly higher mean cognitive scores than the control group (105.8 vs 101.8; P<0.008), and not significantly different from the breastfed reference group. In contrast, there were no significant differences in motor domain scores between the three groups, and both experimental and control formula groups scored lower than the reference group in the verbal domain.
Veereman-Wauters et al. (2012) assessed the potential behavioral benefits of MFGM supplementation in young children. In this double-blind RCT, healthy preschool children (2.5 to 6 years of age) consumed for 4 months, either a control formula (n=97) providing 60 mg/day of endogenous phospholipid, or an MFGM-supplemented formula (n=85) providing a total of 500 mg/day of dairy-derived phospholipids. At the end of the trial, parents and teachers completed the Achenbach System of Empirically Based Assessment (ASEBA), a validated questionnaire considered to be a gold standard for assessing emotion and behavior in preschool children. Significant differences in internal, external, and total behavioral problem scores were observed in favor of the supplemented formula group, as reported by parents (but not by teachers). | 1 | Biochemistry |
Aside from virtually all saturated organic compounds, most compounds of Si, Ge, and Sn are tetrahedral. Often tetrahedral molecules feature multiple bonding to the outer ligands, as in xenon tetroxide (XeO), the perchlorate ion (), the sulfate ion (), the phosphate ion (). Thiazyl trifluoride () is tetrahedral, featuring a sulfur-to-nitrogen triple bond.
Other molecules have a tetrahedral arrangement of electron pairs around a central atom; for example ammonia () with the nitrogen atom surrounded by three hydrogens and one lone pair. However the usual classification considers only the bonded atoms and not the lone pair, so that ammonia is actually considered as pyramidal. The H–N–H angles are 107°, contracted from 109.5°. This difference is attributed to the influence of the lone pair which exerts a greater repulsive influence than a bonded atom. | 4 | Stereochemistry |
In nature, carbon fixation is done by green plants using the enzyme RuBisCO as a part of the Calvin cycle. RuBisCO is a rather slow catalyst compared to the vast majority of other enzymes, incorporating only a few molecules of carbon dioxide into ribulose-1,5-bisphosphate per minute, but does so at atmospheric pressure and in mild, biological conditions. The resulting product is further reduced and eventually used in the synthesis of glucose, which in turn is a precursor to more complex carbohydrates, such as cellulose and starch. The process consumes energy in the form of ATP and NADPH.
Artificial CO reduction for fuel production aims mostly at producing reduced carbon compounds from atmospheric CO. Some transition metal polyphosphine complexes have been developed for this end; however, they usually require previous concentration of CO before use, and carriers (molecules that would fixate CO) that are both stable in aerobic conditions and able to concentrate CO at atmospheric concentrations haven't been yet developed. The simplest product from CO reduction is carbon monoxide (CO), but for fuel development, further reduction is needed (for example, to multi-carbon products), and a key step also needing further development is the transfer of hydride anions to CO. | 5 | Photochemistry |
* Coordinates in square brackets such as denote a direction vector (in real space).
* Coordinates in angle brackets or chevrons such as <100> denote a family of directions which are related by symmetry operations. In the cubic crystal system for example, or the negative of any of those directions.
* Miller indices in parentheses such as (100) denote a plane of the crystal structure, and regular repetitions of that plane with a particular spacing. In the cubic system, the normal to the (hkl) plane is the direction [hkl], but in lower-symmetry cases, the normal to (hkl) is not parallel to [hkl].
* Indices in curly brackets or braces such as denote a family of planes and their normals. In cubic materials the symmetry makes them equivalent, just as the way angle brackets denote a family of directions. In non-cubic materials, <hkl> is not necessarily perpendicular to {hkl}. | 3 | Analytical Chemistry |
Loss of gene activity leads to a nutritional requirement (auxotrophy) not exhibited by the wildtype (prototrophy).
Amino acids:
*ala = alanine
*arg = arginine
*asn = asparagine
Some pathways produce metabolites that are precursors of more than one pathway. Hence, loss of one of these enzymes will lead to a requirement for more than one amino acid. For example:
*ilv: isoleucine and valine
Nucleotides:
*gua = guanine
*pur = purines
*pyr = pyrimidine
*thy = thymine
Vitamins:
*bio = biotin
*nad = NAD
*pan = pantothenic acid | 1 | Biochemistry |
Electrofusion welding employs fittings that are placed around the joint to be welded. Metal coils are implanted into the fittings, and electric current is run through the coils to generate heat and melt part of the pipes, forming a joint upon solidification. There are two possible fittings used in electrofusion welding: couplers and tapping tees (saddles). Coupler fittings contain two separate regions of coils, creating two distinct fusion zones during welding. The inner diameter of the coupler is typically slightly larger than the outer diameter of the pipes. This is to increase the ease of assembly in the field and allows for minor inconsistencies in pipe diameter. Proper insertion of the pipes in the coupler is critical for the creation of a strong joint. Incorrect placement of the coupler can cause the coils to move and lead to the extrusion of molten polymer material from the joint, reducing the joint's strength. Tapping tees, or saddles, are less common but operate under the same principles as a coupler. They require clamping to ensure a proper fit up with the pipes. | 7 | Physical Chemistry |
Diphoterine is a decontamination solution used in first aid for the emergency treatment of chemical spills to the eyes and body. | 7 | Physical Chemistry |
Phosphorylation is the main post-translational modification predicted for FAM227B due to its predicted localization to the nucleus. There are many experimentally predicted phosphorylation sites, the most highly rated included in the conceptual translation. Glycosylation sites and SUMOylation sites were also predicted. | 1 | Biochemistry |
The forms of sulfur available in aquatic environments depends on whether it is a marine or freshwater environment. Freshwater environments are more varied and subject to a multitude of sulfur inputs and outputs, including atmospheric deposition, runoff, diagenesis of bedrock and the presence of microbial sulfate reducers (MSR). Overall, the main species of sulfur in freshwater environments are hydrogen sulfide and sulfate. In estuaries, plant roots extend into sulfide-rich, S-depleted sediments created by MSR, and incorporate that sulfide into their biomass. However, levels of sulfide produced by MSR can be toxic, and it has been proposed that these plants pump oxygen into their roots to oxidize sulfide into the less toxic sulfate. In these environments algae will preferentially acquire sulfur from HS if present, rather than the more abundant sulfate, as sulfide can be readily incorporated into the direct formation of cysteine. This is consistent with cyanobacteria being able to carry out anoxygenic photosynthesis using sulfide.
In marine environments, the main forms of sulfur available is in sulfate at ~29 mM and a δS of 21‰ in seawater. At the surface of the sea, this excess in sulfur is subsequently converted into dimethylsulfoniopropionate (DMSP) by algae as an osmolyte and a repellent against grazing. DMSP also accounts for 50–100% of bacterial sulfur demand, making it the most important source of reduced sulfur for marine bacteria. DMSP's cleavage product dimethyl sulfide (DMS) is highly volatile, escaping the ocean into the atmosphere with emissions ranging between 15 and 33 Tg S year and accounting for 50–60% of the total natural reduced sulfur flux to the atmosphere. In seafloor sediments, microbial sulfate reduction is a major biogeochemical process that consumes organic carbon. Microbial sulfate reduction can completely use up sulfate from the seawater and accumulate hydrogen sulfide in the sediment. Sulfide reoxidation and disproportionation are also thought to be major processes affecting the sulfur isotopic compositions of marine minerals and sediment porewater. | 9 | Geochemistry |
A typical amphiphilic flexible surfactant can form aggregates through a self-assembly process that results of specific interactions between the molecules of the amphiphilic mesogen and those of the non-mesogenic solvent.
In aqueous media, the driving force of the aggregation is the "hydrophobic effect". The aggregates formed by amphiphilic molecules are characterised by structures in which the hydrophilic head-groups expose their surface to aqueous solution, shielding the hydrophobic chains from contact with water.
For most lyotropic systems aggregation occurs only when the concentration of the amphiphile exceeds a critical concentration (known variously as the critical micelle concentration (CMC) or the critical aggregation concentration (CAC)).
At very low amphiphile concentration, the molecules will be dispersed randomly without any ordering. At slightly higher (but still low) concentration, above the CMC, self-assembled amphiphile aggregates exist as independent entities in equilibrium with monomeric amphiphiles in solution, but with no long ranged orientational or positional (translational) order. As a result, phases are isotropic (i.e. not liquid crystalline). These dispersions are generally referred to as micellar solutions, often denoted by the symbol L, while the constituent spherical aggregates are known as micelles.
At higher concentration, the assemblies will become ordered. True lyotropic liquid crystalline phases are formed as the concentration of amphiphile in water is increased beyond the point where the micellar aggregates are forced to be disposed regularly in space. For amphiphiles that consist of a single hydrocarbon chain the concentration at which the first liquid crystalline phases are formed is typically in the range 25–30 wt%. | 7 | Physical Chemistry |
The Federal Government of Canada defines brownfields as "abandoned, idle or underutilized commercial or industrial properties [typically located in urban areas] where past actions have caused environmental contamination, but which still have potential for redevelopment or other economic opportunities." | 2 | Environmental Chemistry |
The GLD-2 protein together with 136 proteins more, is involved in the molecular process of hematopoietic progenitor cell differentiation, in the human proteome. This is the process in which precursor cell type acquires the specialized features of a hematopoietic progenitor cell, a kind of cell types including myeloid progenitor cells and lymphoid progenitor cells. | 1 | Biochemistry |
Superhydrophilicity refers to the phenomenon of excess hydrophilicity, or attraction to water; in superhydrophilic materials, the contact angle of water is equal to zero degrees. This effect was discovered in 1995 by the Research Institute of Toto Ltd. for titanium dioxide irradiated by sunlight. Under light irradiation, water dropped onto titanium dioxide forms no contact angle (almost 0 degrees).
Superhydrophilic material has various advantages. For example, it can defog glass, and it can also enable oil spots to be swept away easily with water. Such materials are already commercialized as door mirrors for cars, coatings for buildings, self-cleaning glass, etc.
Several mechanisms of this superhydrophilicity have been proposed by researchers. One is the change of the surface structure to a metastable structure, and another is cleaning the surface by the photodecomposition of dirt such as organic compounds adsorbed on the surface, after either of which water molecules can adsorb to the surface. The mechanism is still controversial, and it is too soon to decide which suggestion is correct. To decide, atomic scale measurements and other studies will be necessary. | 7 | Physical Chemistry |
ρ: Actual particle density (g/cm)
ρ: Gas or sample matrix density (g/cm)
r: Least-squares coefficient of determination. The closer this value is to 1.0, the better the data fit to a hyperplane representing the relationship between the response variable and a set of covariate variables. A value equal to 1.0 indicates all data fit perfectly within the hyperplane.
λ: Gas mean free path (cm)
D: Mass-median-diameter (MMD). The log-normal distribution mass median diameter. The MMD is considered to be the average particle diameter by mass.
σ: Geometric standard deviation. This value is determined mathematically by the equation:
:σ = D/D = D/D
The value of σ determines the slope of the least-squares regression curve.
α: Relative standard deviation or degree of polydispersity. This value is also determined mathematically. For values less than 0.1, the particulate sample can be considered to be monodisperse.
:α = σ/D
Re : Particle Reynolds Number.
In contrast to the large numerical values noted for flow Reynolds number, particle Reynolds number for fine particles in gaseous mediums is typically less than 0.1.
Re : Flow Reynolds number.
Kn: Particle Knudsen number. | 7 | Physical Chemistry |
This method is an acid heap leaching method like that of the copper method in that it utilises sulfuric acid instead of cyanide solution to dissolve the target minerals from crushed ore. The amount of sulfuric acid required is much higher than for copper ores, as high as 1,000 kg of acid per tonne of ore, but 500 kg is more common. The method was originally patented by Australian miner BHP and is being commercialized by Cerro Matoso in Colombia, a wholly owned subsidiary of BHP; Vale in Brazil; and European Nickel for the rock laterite deposits of Turkey, Talvivaara mine in Finland, the Balkans, and the Philippines. There currently are no operating commercial scale nickel laterite heap leach operations, but there is a sulphide HL operating in Finland.
Nickel recovery from the leach solutions is much more complex than for copper and requires various stages of iron and magnesium removal, and the process produces both leached ore residue ("ripios") and chemical precipitates from the recovery plant (principally iron oxide residues, magnesium sulfate and calcium sulfate) in roughly equal proportions. Thus, a unique feature of nickel heap leaching is the need for a tailings disposal area.
The final product can be nickel hydroxide precipitates (NHP) or mixed metal hydroxide precipitates (MHP), which are then subject to conventional smelting to produce metallic nickel. | 8 | Metallurgy |
To stop the electron transfer chain completing, producing output signals, the input of a photon, , is used to produce a pump probe spectroscopy effect by promoting an electron in an electron transfer chain. The fall of the pump probe promoted electron produces an output that is quenched down an electron transfer chain.
An alternative is similar to the AND gate alternative; an input causes a change in molecule structure breaking the electron transfer chain by not allowing the smooth energy transfer of electrons. | 5 | Photochemistry |
There are different enzymes to remove the glycans from the proteins or remove some part of the sugar chain.
* α2-3,6,8,9-Neuraminidase (from Arthrobacter ureafaciens): cleaves all non-reducing terminal branched and unbranched sialic acids.
* β1,4-Galactosidase (from Streptococcus pneumoniae): releases only β1,4-linked, nonreducing terminal galactose from complex carbohydrates and glycoproteins.
* β-N-Acetylglucosaminidase (from Streptococcus pneumoniae): cleaves all non-reducing terminal β-linked N-acetylglucosamine residues from complex carbohydrates and glycoproteins.
* endo-α-N-Acetylgalactosaminidase (O-glycosidase from Streptococcus pneumoniae): removes O-glycosylation. This enzyme cleaves serine- or threonine-linked unsubstituted Galβ1,3GalNAc
* PNGase F: cleaves asparagine-linked oligosaccharides unless α1,3-core fucosylated. | 0 | Organic Chemistry |
Basaltic magma is the most abundant in iron, magnesium, and calcium but the lowest in silica, potassium, and sodium. The composition of silica within basaltic magma ranges from 45-55 weight percent (wt.%), or mass fraction of a species. It forms in temperatures ranging from approximately 1830 °F to 2200 °F. Basaltic magma has the lowest viscosity and volatiles content, yet still may be up to 100,000 times more viscous than water. Because of its low viscosity, this is the least explosive form of magma. Basaltic magma may found in regions such as Hawaii, known for its shield volcanoes.
Basaltic magma forms minerals such as calcium-rich plagioclase feldspar and pyroxene. The water composition of basaltic magma varies dependent on the evolution of the magma chamber. Arc magmas, such as Izarú in Costa Rica, range from 3.2-3.5 wt.%. | 9 | Geochemistry |
Enzymes and enzymatic complexes able to break down difficult-to-transform macromolecules such as cellulose, hemicelluloses, pectin and proteins. Solid state fermentation is well suited for the production of various enzymatic complexes composed of multiple enzymes. Enzymatic compounds generated by SSF find outlets in all sectors where digestibility, solubility or viscosity is needed.
This is why SSF enzymes are widely used in the following industries:
* fruit and vegetable transformation (pectinases)
* baking (hemicellulases)
* animal feeding (hemicellulases and cellulases)
* bio ethanol (cellulases and hemicellulases)
* brewing and distilling (hemicellulases) | 1 | Biochemistry |
Polymers are of great importance when considering protein adsorption in the biomedical arena. Polymers are composed of one or more types of "mers" bound together repeatedly, typically by directional covalent bonds. As the chain grows by the addition of mers, the chemical and physical properties of the material are dictated by the molecular structure of the monomer. By carefully selecting the type or types of mers in a polymer and its manufacturing process, the chemical and physical properties of a polymer can be highly tailored to adsorb specific proteins and cells for a particular application. | 1 | Biochemistry |
Electroosmotic flow is caused by the Coulomb force induced by an electric field on net mobile electric charge in a solution. Because the chemical equilibrium between a solid surface and an electrolyte solution typically leads to the interface acquiring a net fixed electrical charge, a layer of mobile ions, known as an electrical double layer or Debye layer, forms in the region near the interface. When an electric field is applied to the fluid (usually via electrodes placed at inlets and outlets), the net charge in the electrical double layer is induced to move by the resulting Coulomb force. The resulting flow is termed electroosmotic flow. | 7 | Physical Chemistry |
CDC Director Mandy Cohen serves concurrently/ex officio as ATSDR administrator and CDC director, heading the Office of the Administrator. Patrick N. Breysse, PhD. serves as director of NCEH/ATSDR, heading the Office of the Director. The ATSDR administrator/CDC director, who provides overall leadership of the agency, is appointed by the president of the United States; the appointment does not require Senate approval. The ATSDR administrator appoints the NCEH/ATSDR director, who is responsible for managing the agency's programs and activities. | 1 | Biochemistry |
Current researchers have developed gene transfer systems on the basis of conservative transposition which can integrate new DNA in both invertebrates and vertebrate genomes. Scientists alter the genetic sequence of a transposon in a laboratory setting, then insert this sequence into a vector which is then inserted into a target cell. The transposase coding region of these transposons is replaced by a gene of interest intended to be integrated into the genome. Conservative transposition is induced by the expression of transposase from another source within the cell, since the transposon no longer contains the transposase coding region to be self sufficient. Generally a second vector is prepared and inserted into the cell for expression of transposase. This technique is used in transgenesis and insertional mutagenesis research fields. The Sleeping Beauty transposon system is an example of gene transfer system developed for use in vertebrates. Further development in integration site preferences of transposable elements is expected to advance the technologies of human gene therapy. | 1 | Biochemistry |
Hattori has made contributions to the field of earth sciences, utilizing trace element geochemistry and stable and radiogenic isotopes to understand the earth processes. During the early stages of her career, she focused on studying active volcanoes and associated hydrothermal activity. However, a tragic accident atop a Colombian volcano, resulting in the loss of several colleagues, prompted her to shift her research focus to ancient volcanic terranes in Canada. Over the past 14 years, she has conducted research in various regions of subduction zones worldwide, where oceanic crust subducts and forms arc volcanoes and mountain belts. Her investigations involve examining rocks and collecting samples to analyze the intricate processes of subduction and the subsequent return of materials to the surface through volcanoes. Her research areas have included the Himalayas (Northern Pakistan, Northern India), Italian and French Alps, Turkey, China, Japan, Philippines, Peru, and the Dominican Republic.
Hattoris contributions to the earth sciences primarily center on utilizing the abundance of redox-sensitive elements and their isotopic compositions to interpret processes from the surface to the mantle. Her discoveries include the timing of the abrupt rise in atmospheric oxygen content at around 2.2 billion years ago during Earths evolution, the definition of osmium isotope evolution in the mantle, the identification of serpentine as the reservoir of water and fluid-mobile elements in the mantle, and the provision of evidence that oxidized mafic magmas bring base metals and sulfur from the mantle to form giant copper deposits that supply many critical metals for society. In addition, her work has contributed to the discovery of such critical metal deposits through the mobility of metals in surface waters. | 9 | Geochemistry |
The prostaglandin E (PGE) receptors are G protein-coupled receptors that bind and are activated by prostaglandin E. They are members of the prostaglandin receptors class of receptors and include the following Protein isoforms:
* Prostaglandin E receptor 1 (EP) -
* Prostaglandin E receptor 2 (EP) -
* Prostaglandin E receptor 3 (EP) -
* Prostaglandin E receptor 4 (EP) - | 1 | Biochemistry |
The avalanche occurs in a gaseous medium that can be ionised (such as air). The electric field and the mean free path of the electron must allow free electrons to acquire an energy level (velocity) that can cause impact ionisation. If the electric field is too small, then the electrons do not acquire enough energy. If the mean free path is too short, the electron gives up its acquired energy in a series of non-ionising collisions. If the mean free path is too long, then the electron reaches the anode before colliding with another molecule.
The avalanche mechanism is shown in the accompanying diagram. The electric field is applied across a gaseous medium; initial ions are created with ionising radiation (for example, cosmic rays). An original ionisation event produces an ion pair; the positive ion accelerates towards the cathode while the free electron accelerates towards the anode. If the electric field is strong enough, the free electron can gain sufficient velocity (energy) to liberate another electron when it next collides with a molecule. The two free electrons then travel towards the anode and gain sufficient energy from the electric field to cause further impact ionisations, and so on. This process is effectively a chain reaction that generates free electrons. Initially, the number of collisions grows exponentially. The total number of electrons reaching the anode is equal to 2 with n the number of collisions, plus the single initiating free electron. Eventually, this relationship will break down - the limit to the multiplication in an electron avalanche is known as the Raether limit.
The Townsend avalanche can have a large range of current densities. In common gas-filled tubes, such as those used as gaseous ionisation detectors, magnitudes of currents flowing during this process can range from about 10 amperes to about 10 amperes. | 7 | Physical Chemistry |
Activity-regulated cytoskeleton-associated protein is a plasticity protein that in humans is encoded by the ARC gene. The gene is believed to derive from a retrotransposon. The protein is found in the neurons of tetrapods and other animals where it can form virus-like capsids that transport RNA between neurons.
ARC mRNA is localized to activated synaptic sites in an NMDA receptor-dependent manner, where the newly translated protein is believed to play a critical role in learning and memory-related molecular processes. Arc protein is widely considered to be important in neurobiology because of its activity regulation, localization, and utility as a marker for plastic changes in the brain. Dysfunction in the production of Arc protein has been implicated as an important factor in understanding various neurological conditions, including amnesia, Alzheimer's disease, Autism spectrum disorders, and Fragile X syndrome.
ARC was first characterized in 1995 and is a member of the immediate-early gene (IEG) family, a rapidly activated class of genes functionally defined by their ability to be transcribed in the presence of protein synthesis inhibitors. Along with other IEGs such as ZNF268 and HOMER1, ARC is a significant tool for systems neuroscience as illustrated by the development of the cellular compartment analysis of temporal activity by fluorescence in situ hybridization, or catFISH technique (see fluorescent in situ hybridization). | 1 | Biochemistry |
In addition to the electrical potential difference, the presence of moisture is a driving factor in the ECM. If there is a sufficient film of moisture with condensation and even at low electrical voltage, the ECM can form a bridging structure between the contacts after just a few minutes.
In general, the process can be broken down into the following steps:
* Adsorption of water through condensation on the surface between the contacts (often promoted by hygroscopic ionic impurities)
* Alkalization of the water due to the applied potential difference and thus lowering of the pH value in the water film (initiates the corrosion of (contact) metallizations e.g. silver, copper, tin)
* Dissolution of the anode material (silver, copper, tin etc.)
* Migration of the metal cations to the cathode
* Reduction of the migrated cations and deposition on the cathode with the formation of a metallic dendrite
* Dendrite growth in the opposite direction, towards the anode
* Reduction of the resistance between the contacts up to a permanent short circuit
* There is also bridge formation through interaction with impurities that run from the anode to the cathode
This mechanism impairs the reliability and longevity of electronic assemblies. This means that electrochemical migration is often the focus of failure root cause analyzes as a possible trigger for malfunctions in the field. | 7 | Physical Chemistry |
The Rehbinder effect in physics is the reduction in the hardness and ductility of a material, particularly metals, by a surfactant film. The effect is named for Soviet scientist , who discovered the effect in 1928.
A proposed explanation for this effect is the disruption of surface oxide films, and the reduction of surface energy by surfactants.
The effect is of particular importance in machining, as lubricants reduce cutting forces. | 7 | Physical Chemistry |
PSII also relies on light to drive the formation of proton gradients in chloroplasts, however, PSII utilizes vectorial redox chemistry to achieve this goal. Rather than physically transporting protons through the protein, reactions requiring the binding of protons will occur on the extracellular side while reactions requiring the release of protons will occur on the intracellular side. Absorption of photons of 680nm wavelength is used to excite two electrons in P to a higher energy level. These higher energy electrons are transferred to protein-bound plastoquinone (PQ) and then to unbound plastoquinone (PQ). This reduces plastoquinone (PQ) to plastoquinol (PQH) which is released from PSII after gaining two protons from the stroma. The electrons in P are replenished by oxidizing water through the oxygen-evolving complex (OEC). This results in release of O and H into the lumen, for a total reaction of
After being released from PSII, PQH travels to the cytochrome bf complex, which then transfers two electrons from PQH to plastocyanin in two separate reactions. The process that occurs is similar to the Q-cycle in Complex III of the electron transport chain. In the first reaction, PQH binds to the complex on the lumen side and one electron is transferred to the iron-sulfur center which then transfers it to cytochrome f which then transfers it to plastocyanin. The second electron is transferred to heme b which then transfers it to heme b which then transfers it to PQ. In the second reaction, a second PQH gets oxidized, adding an electron to another plastocyanin and PQ. Both reactions together transfer four protons into the lumen. | 7 | Physical Chemistry |
The Descriptions of Plant Viruses (DPVs) were first published by the Association of Applied Biologists in 1970 as a series of leaflets, each one written by an expert describing a particular plant virus. In 1998 all of the 354 DPVs published in paper were scanned, and converted into an electronic format in a database and distributed on CDROM. In 2001 the descriptions were made available on the new DPVweb site, providing open access to the now 400+ DPVs (currently 415) as well as taxonomic and sequence data on all plant viruses. | 1 | Biochemistry |
In thermodynamics, a temperature–entropy (T–s) diagram is a thermodynamic diagram used to visualize changes to temperature () and specific entropy () during a thermodynamic process or cycle as the graph of a curve. It is a useful and common tool, particularly because it helps to visualize the heat transfer during a process. For reversible (ideal) processes, the area under the T–s curve of a process is the heat transferred to the system during that process.
Working fluids are often categorized on the basis of the shape of their T–s diagram.
An isentropic process is depicted as a vertical line on a T–s diagram, whereas an isothermal process is a horizontal line. | 7 | Physical Chemistry |
Adenylate cyclase (EC 4.6.1.1, also commonly known as adenyl cyclase and adenylyl cyclase, abbreviated AC) is an enzyme with systematic name ATP diphosphate-lyase (cyclizing; 3′,5′-cyclic-AMP-forming). It catalyzes the following reaction:
:ATP = 3′,5′-cyclic AMP + diphosphate
It has key regulatory roles in essentially all cells. It is the most polyphyletic known enzyme: six distinct classes have been described, all catalyzing the same reaction but representing unrelated gene families with no known sequence or structural homology. The best known class of adenylyl cyclases is class III or AC-III (Roman numerals are used for classes). AC-III occurs widely in eukaryotes and has important roles in many human tissues.
All classes of adenylyl cyclase catalyse the conversion of adenosine triphosphate (ATP) to 3,5-cyclic AMP (cAMP) and pyrophosphate. Magnesium ions are generally required and appear to be closely involved in the enzymatic mechanism. The cAMP produced by AC then serves as a regulatory signal via specific cAMP-binding proteins, either transcription factors, enzymes (e.g., cAMP-dependent kinases), or ion transporters. | 1 | Biochemistry |
The École Nationale Supérieure dÉlectrochimie et dÉlectrométallurgie de Grenoble, or ENSEEG, was one of the French Grandes écoles of engineering (engineering schools). It has been created in 1921 under the name Institut d’électrochimie et d’électrométallurgie (IEE) (Institute of Electrochemistry and Electrometallurgy). The name ENSEEG has been chosen in 1948 and ENSEEG has been part of Grenoble Institute of Technology (INPG or GIT) since its creation in 1971. Therefore, the name INPG-ENSEEG has also been commonly used.
ENSEEG delivered a multidisciplinary education in physical chemistry. The ENSEEG engineers are especially competent in materials science, process engineering and electrochemistry. From September 2008, ENSEEG merged with two other Grandes écoles to create Phelma. | 8 | Metallurgy |
SPEARpesticides has been first developed for Central Germany and updated. SPEARpesticides was adapted and validated for streams and mesocosms worldwide and provides the first ecotoxicological approach to specifically determine the ecological effects of pesticides on aquatic invertebrate communities. Denmark, Finland, France, Germany, Switzerland
Australia
Russia
Mesocosms | 2 | Environmental Chemistry |
* Birch, Alan. Economic History of the British Iron and Steel Industry (Routledge, 2013).
* Burn, D. L. “Recent Trends in the History of the Steel Industry.” Economic History Review, 17#2 1947, pp. 95–102. [https://www.jstor.org/stable/2590552 online].
* Burn, Duncan. The Steel Industry, 1939–1959: A Study in Competition and Planning (1961)
* Burn, Duncan. The Economic History of Steelmaking, 1867–1939: A Study in Competition. Cambridge University Press, 1961
* Carr, J. C. and W. Taplin; History of the British Steel Industry Harvard University Press, 1962
* Tweedale, Geoffrey. Steel City: Entrepreneurship, Strategy, and Technology in Sheffield, 1743–1993. (Oxford U.P. 1995)
* Vaizy, John. The history of British steel (1974), well illustrated
* Warren, Kenneth. British Iron and Sheet Steel Industry since 1840 (1970) Economic geography. | 8 | Metallurgy |
Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid or the liquid content of a substance, usually due to cooling.
For most substances, the melting and freezing points are the same temperature; however, certain substances possess differing solid-liquid transition temperatures. For example, agar displays a hysteresis in its melting point and freezing point. It melts at 85 °C (185 °F) and solidifies from 32 °C to 40 °C (89.6 °F to 104 °F). | 1 | Biochemistry |
Together with the benzyltriethylammonium salt, benzyltrimethylammonium hydroxide is a popular phase-transfer catalyst.
It is used in aldol condensation reactions and base-catalyzed dehydration reactions. It is also used as a base in Ando's Z-selective variant of Horner-Wadsworth-Emmons Olefination reactions.
Relative to tetramethylammonium hydroxide, benzyltriethylammonium hydroxide is more labile. In 6M NaOH at 160 °C their half-lives are 61.9 and 4 h, respectively. | 0 | Organic Chemistry |
The acylurea functional group is also found in some pharmaceutical drugs such as the anticonvulsants phenacemide, pheneturide, chlorphenacemide, and acetylpheneturide (which are phenylureides), and the sedatives acecarbromal, bromisoval, and carbromal (which are bromoureides). Others include apronal (apronalide), capuride, and ectylurea. Barbiturates (a class of cyclic ureas) are structurally and mechanistically related to them. The phenylureides are also closely related to the hydantoins, such as phenytoin, and may be considered ring-opened analogues of them. | 0 | Organic Chemistry |
In reproducing, most plants inherit their plastids from only one parent. In general, angiosperms inherit plastids from the female gamete, where many gymnosperms inherit plastids from the male pollen. Algae also inherit plastids from just one parent. Thus the plastid DNA of the other parent is completely lost.
In normal intraspecific crossingsresulting in normal hybrids of one speciesthe inheriting of plastid DNA appears to be strictly uniparental; i.e., from the female. In interspecific hybridisations, however, the inheriting is apparently more erratic. Although plastids are inherited mainly from the female in interspecific hybridisations, there are many reports of hybrids of flowering plants producing plastids from the male.
Approximately 20% of angiosperms, including alfalfa (Medicago sativa), normally show biparental inheriting of plastids. | 5 | Photochemistry |
The importance and versatility of depolarization within cells can be seen in the relationship between rod cells in the eye and their associated neurons. When rod cells are in the dark, they are depolarized. In the rod cells, this depolarization is maintained by ion channels that remain open due to the higher voltage of the rod cell in the depolarized state. The ion channels allow calcium and sodium to pass freely into the cell, maintaining the depolarized state. Rod cells in the depolarized state constantly release neurotransmitters which in turn stimulate the nerves associated with rod cells. This cycle is broken when rod cells are exposed to light; the absorption of light by the rod cell causes the channels that had facilitated the entry of sodium and calcium into the rod cell to close. When these channels close, the rod cells produce fewer neurotransmitters, which is perceived by the brain as an increase in light. Therefore, in the case of rod cells and their associated neurons, depolarization actually prevents a signal from reaching the brain as opposed to stimulating the transmission of the signal. | 7 | Physical Chemistry |
Different protecting groups on either the glycosyl donor or the glycosyl acceptor may affect the reactivity and yield of the glycosylation reaction. Typically, electron-withdrawing groups such as acetyl or benzoyl groups are found to decrease the reactivity of the donor/acceptor and are therefore termed "disarming" groups. Electron-donating groups such as the benzyl group, are found to increase the reactivity of the donor/acceptor and are therefore called "arming" groups. | 0 | Organic Chemistry |
Arsenicals are chemical compounds that contain arsenic. In a military context, the term arsenical refer to toxic arsenic compounds that are used as chemical warfare agents. This include blister agents, blood agents and vomiting agents. Historically, they were used extensively as insecticides, especially lead arsenate. | 1 | Biochemistry |
Novec 649/1230 does not deplete ozone (ODP 0) and has a global warming potential of 1 (over 100 years), equivalent to that of carbon dioxide. The Globally Harmonized System of Classification and Labeling of Chemicals (GHS) classifies this chemical as H412 - Harmful to aquatic life with long lasting effects. Photolysis in sunlight, hydrolysis and hydration may be a significant sink of Novec 649/1230 in the environment. It has very short estimated atmospheric lifetime of around 4 to 15 days.
Novec 649/1230 is classified as a PFAS substance. In December 2022, 3M announced that it would cease production of all PFAS products by 2025, including Novec 649/1230. It degrades to Trifluoroacetic acid (TFA) via photolytic degradation in sunlight. | 2 | Environmental Chemistry |
An important example of chemisorption is in heterogeneous catalysis which involves molecules reacting with each other via the formation of chemisorbed intermediates. After the chemisorbed species combine (by forming bonds with each other) the product desorbs from the surface. | 7 | Physical Chemistry |
In polymer chemistry and polymer physics, the Flory–Fox equation is a simple empirical formula that relates molecular weight to the glass transition temperature of a polymer system. The equation was first proposed in 1950 by Paul J. Flory and Thomas G. Fox while at Cornell University. Their work on the subject overturned the previously held theory that the glass transition temperature was the temperature at which viscosity reached a maximum. Instead, they demonstrated that the glass transition temperature is the temperature at which the free space available for molecular motions achieved a minimum value. While its accuracy is usually limited to samples of narrow range molecular weight distributions, it serves as a good starting point for more complex structure-property relationships.
Recent molecular simulations have demonstrated that while the functional form of the Flory-Fox relation holds for a wide range of molecular architectures (linear chain, bottlebrush, star, and ring polymers), however, the central free-volume argument of the Flory-Fox relation does not hold since branched polymers, despite having more free ends, form materials of higher density and glass transition temperature increases. | 7 | Physical Chemistry |
The yeast mitochondrial code (translation table 3) is a genetic code used by the mitochondrial genome of yeasts, notably Saccharomyces cerevisiae, Candida glabrata, Hansenula saturnus, and Kluyveromyces thermotolerans. | 1 | Biochemistry |
A 4n electron electrocyclic ring opening reaction can be considered to have 2 components – the π-system and the breaking σ-bond. With respect to the π-system, the reaction is suprafacial. However, with a conrotatory mechanism, as shown in the figure above, the reaction is antarafacial with respect to the σ-bond. Conversely with a disrotatory mechanism it is suprafacial with respect to the breaking σ-bond.
By the above rules, for a 4n electron pericyclic reaction of 2 components, there must be one antarafacial component. Thus the reaction must proceed through a conrotatory mechanism. This agrees with the result derived in the correlation diagrams above. | 7 | Physical Chemistry |
In this type of reaction, a metal atom in a compound or solution is replaced by an atom of another metal. For example, copper is deposited when zinc metal is placed in a copper(II) sulfate solution:
In the above reaction, zinc metal displaces the copper(II) ion from copper sulfate solution and thus liberates free copper metal. The reaction is spontaneous and releases 213 kJ per 65 g of zinc.
The ionic equation for this reaction is:
As two half-reactions, it is seen that the zinc is oxidized:
And the copper is reduced: | 9 | Geochemistry |
Light harvesting in photosynthesis employs both classical and quantum mechanical processes with an energy efficiency of almost 100 percent. For light to produce energy in classical processes, photons must reach reaction sites before their energy dissipates in less than one nanosecond. In photosynthetic processes, this is not possible. Because energy can exist in a superposition of states, it can travel all routes within a material at the same time. When a photon finds the correct destination, the superposition collapses, making the energy available. However, no purely quantum process can be wholly responsible, because some quantum processes slow down the movement of quantized objects through networks. Anderson localization prevents the spread of quantum states in random media. Because the state acts like a wave, it is vulnerable to disruptive interference effects. Another issue is the quantum zeno effect, in which an unstable state never changes if it is continuously measured/watched, because watching constantly nudges the state, preventing it from collapsing.
Interactions between quantum states and the environment act like measurements. The classical interaction with the environment changes the wave-like nature of the quantum state just enough to prevent Anderson localisation, while the quantum zeno effect extends the quantum states lifetime, allowing it to reach the reaction centre. The proposed long lifetime of quantum coherence in the FMO influenced many scientists to investigate quantum coherence in the system, with Engels 2007 paper being cited over 1500 times within 5 years of its publication. The proposal of Engel is still debated in literature with the suggestion that the original experiments were interpreted incorrectly assigning the spectral oscillations to electronic coherences instead of ground-state vibrational coherences, which will naturally be expected to live longer due to the narrower spectral width of vibrational transitions. | 5 | Photochemistry |
Catalytic chain transfer (CCT) is a process that can be incorporated into radical polymerization to obtain greater control over the resulting products. | 7 | Physical Chemistry |
The majority of organic compounds introduced on Earth by interstellar dust particles have helped to form complex molecules, thanks to their peculiar surface-catalytic activities. Studies of the C/C isotopic ratios of organic compounds in the Murchison meteorite suggest that the RNA component uracil and related molecules, including xanthine, were formed extraterrestrially. NASA studies of meteorites suggest that all four DNA nucleobases (adenine, guanine and related organic molecules) have been formed in outer space. The cosmic dust permeating the universe contains complex organics ("amorphous organic solids with a mixed aromatic–aliphatic structure") that could be created rapidly by stars. Glycolaldehyde, a sugar molecule and RNA precursor, has been detected in regions of space including around protostars and on meteorites. | 9 | Geochemistry |
Huang was born in Putian, Fujian, China on December 15, 1921. He graduated from Fukien Christian University in 1943 with a bachelor's degree in chemistry. After earning his MS in 1949 from Lingnan University in Guangzhou, he entered Harvard University and received his Ph.D. in 1952. His graduate advisor was the organic chemist Louis Fieser. | 0 | Organic Chemistry |
Photochromic, thermochromic, solvatochromic and electrochromic characteristics of spiropyrans make them especially important in the technology area. Most of their applications are based on their photochromic properties.
Photochromic compounds based on spiropyrans, spirooxazines, and [2H]chromenes are being investigated because of their silver-free light-sensitive properties that could be used for optical recording data, including thin films, photoswitches (sensors that discern light of certain wavelength), light filters with modulated transmission and miniature hybrid multifunctional materials.
Thanks to the creation of novel media sensitive to IR radiation and the potential of spiropyrans for optical recording data, semiconductor lasers as activating source of radiation are possible.
Spiropyrans with ion complexes and spiropyran copolymers which are part of powdered and film materials have been used too to record optical data and increase the length of time of its storage.
Another group of spiropyrans which contain indoline or nitrogen heterocycles and the indolinospirothiapyrans found their application in film forms of photochromic materials using polyester resins. Those resins with a high refractive index were used to make photochromic lenses. Moreover, spiropyrans are being used in cosmetics.
New types of modified spiropyrans polymers contained in photochromic compounds found their use in the creation of photoreceptors. The ones with rhodopsin as a compound are adopted to raise the level of the photosignal.
Another collection of spiropyrans characterized for their sensitivity to UV radiation are detectors for the protection of organs, for the production of light filters with modulated transmission, or photochromic lenses.
The determination of peroxidase activity and NO levels in the atmosphere are applications of carboxylated spiropyrans.
Today, spiropyrans are most used as molecular logic devices, photochromic and electrooptical devices, molecular and supramolecular logic switches, photoswitches and multifunctional artificial receptors.
Spiropyrans can be used to probe the conformational state of DNA, as certain derivatives can intercalate into DNA when in the open form.
Spiropyrans are used in photo controlled transfer of amino acids across bilayers and membranes because of nucleophilic interaction between zwitterionic merocyanine and polar amino acids. Certain types of spiropyrans display ring opening upon recognition of an analyte, for example zinc ions. | 5 | Photochemistry |
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