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Scytovirin is a 95-amino acid antiviral protein isolated from the cyanobacteria Scytonema varium. It has been cultured in E. coli and its structure investigated in detail. Scytovirin is thought to be produced by the bacteria to protect itself from viruses that might otherwise attack it, but as it has broad-spectrum antiviral activity against a range of enveloped viruses, scytovirin has also been found to be useful against a range of major human pathogens, most notably HIV / AIDS but also including SARS coronavirus and filoviruses such as Ebola virus and Marburg virus. While some lectins such as cyanovirin and Urtica dioica agglutinin are thought likely to be too allergenic to be used internally in humans, studies so far on scytovirin and griffithsin have not shown a similar level of immunogenicity. Scytovirin and griffithsin are currently being investigated as potential microbicides for topical use. | 1 | Biochemistry |
Photoreceptor cells are unusual cells in that they depolarize in response to absence of stimuli or scotopic conditions (darkness). In photopic conditions (light), photoreceptors hyperpolarize to a potential of −60 mV.
In the dark, cGMP levels are high and keep cGMP-gated sodium channels open allowing a steady inward current, called the dark current. This dark current keeps the cell depolarized at about −40 mV, leading to glutamate release which inhibits excitation of neurons.
The depolarization of the cell membrane in scotopic conditions opens voltage-gated calcium channels. An increased intracellular concentration of Ca causes vesicles containing glutamate, a neurotransmitter, to merge with the cell membrane, therefore releasing glutamate into the synaptic cleft, an area between the end of one cell and the beginning of another neuron. Glutamate, though usually excitatory, functions here as an inhibitory neurotransmitter.
In the cone pathway, glutamate:
* Hyperpolarizes on-center bipolar cells. Glutamate that is released from the photoreceptors in the dark binds to metabotropic glutamate receptors (mGluR6), which, through a G-protein coupling mechanism, causes non-specific cation channels in the cells to close, thus hyperpolarizing the bipolar cell.
* Depolarizes off-center bipolar cells. Binding of glutamate to ionotropic glutamate receptors results in an inward cation current that depolarizes the bipolar cell. | 1 | Biochemistry |
In order to get a meaningful sulfur signal from the analysis, the buffer should not contain sulfur (i.e. no BES, DDT, HEPES, MES, MOPSO or PIPES compounds). Excessive amounts of chlorine in the buffer should also be avoided, since this will overlap with the sulfur peak; KBr and NaBr are suitable alternatives. | 7 | Physical Chemistry |
Hydrocarbons, primarily paraffins (CH) and lipids but also sugar alcohols.
* Advantages
** Freeze without much supercooling
** Ability to melt congruently
** Self nucleating properties
** Compatibility with conventional material of construction
** No segregation
** Chemically stable
** Safe and non-reactive
* Disadvantages
** Low thermal conductivity in their solid state. High heat transfer rates are required during the freezing cycle. Nano composites were found to yield an effective thermal conductivity increase up to 216%.
** Volumetric latent heat storage capacity can be low
** Flammable. This can be partially alleviated by specialised containment. | 7 | Physical Chemistry |
Liquid is one of the four primary states of matter, with the others being solid, gas and plasma. A liquid is a fluid. Unlike a solid, the molecules in a liquid have a much greater freedom to move. The forces that bind the molecules together in a solid are only temporary in a liquid, allowing a liquid to flow while a solid remains rigid.
A liquid, like a gas, displays the properties of a fluid. A liquid can flow, assume the shape of a container, and, if placed in a sealed container, will distribute applied pressure evenly to every surface in the container. If liquid is placed in a bag, it can be squeezed into any shape. Unlike a gas, a liquid is nearly incompressible, meaning that it occupies nearly a constant volume over a wide range of pressures; it does not generally expand to fill available space in a container but forms its own surface, and it may not always mix readily with another liquid. These properties make a liquid suitable for applications such as hydraulics.
Liquid particles are bound firmly but not rigidly. They are able to move around one another freely, resulting in a limited degree of particle mobility. As the temperature increases, the increased vibrations of the molecules causes distances between the molecules to increase. When a liquid reaches its boiling point, the cohesive forces that bind the molecules closely together break, and the liquid changes to its gaseous state (unless superheating occurs). If the temperature is decreased, the distances between the molecules become smaller. When the liquid reaches its freezing point the molecules will usually lock into a very specific order, called crystallizing, and the bonds between them become more rigid, changing the liquid into its solid state (unless supercooling occurs). | 7 | Physical Chemistry |
Quantities, Units and Symbols in Physical Chemistry, also known as the Green Book, is a compilation of terms and symbols widely used in the field of physical chemistry. It also includes a table of physical constants, tables listing the properties of elementary particles, chemical elements, and nuclides, and information about conversion factors that are commonly used in physical chemistry. The Green Book is published by the International Union of Pure and Applied Chemistry (IUPAC) and is based on published, citeable sources. Information in the Green Book is synthesized from recommendations made by IUPAC, the International Union of Pure and Applied Physics (IUPAP) and the International Organization for Standardization (ISO), including recommendations listed in the IUPAP Red Book Symbols, Units, Nomenclature and Fundamental Constants in Physics and in the ISO 31 standards. | 3 | Analytical Chemistry |
There is one Public Analyst Laboratory in each of Guernsey, Isle of Man and Jersey serving the needs of these islands. | 2 | Environmental Chemistry |
The Caspian Sea is at its South Caspian Basin, like the Black Sea, a remnant of the ancient Paratethys Sea. Its seafloor is, therefore, a standard oceanic basalt and not a continental granite body. It is estimated to be about 30 million years old, and became landlocked in the Late Miocene, about 5.5 million years ago, due to tectonic uplift and a fall in sea level. The Caspian Sea was a comparatively small endorheic lake during the Pliocene, but its surface area increased fivefold around the time of the Pliocene-Pleistocene transition. During warm and dry climatic periods, the landlocked sea almost dried up, depositing evaporitic sediments like halite that were covered by wind-blown deposits and were sealed off as an evaporite sink when cool, wet climates refilled the basin. (Comparable evaporite beds underlie the Mediterranean.) Due to the current inflow of fresh water in the north, the Caspian Sea water is almost fresh in its northern portions, getting more brackish toward the south. It is most saline on the Iranian shore, where the catchment basin contributes little flow. Currently, the mean salinity of the Caspian is one third that of Earth's oceans. The Garabogazköl lagoon, which dried up when water flow from the main body of the Caspian was blocked in the 1980s but has since been restored, routinely exceeds oceanic salinity by a factor of 10. | 2 | Environmental Chemistry |
Accurate detection and quantification are the most vital components of the TOC analysis process. Conductivity and non-dispersive infrared (NDIR) are the two common detection methods used in modern TOC analyzers. | 3 | Analytical Chemistry |
Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) is a spectroanalytical procedure for the quantitative determination of chemical elements by free atoms in the gaseous state. Atomic absorption spectroscopy is based on absorption of light by free metallic ions.
In analytical chemistry the technique is used for determining the concentration of a particular element (the analyte) in a sample to be analyzed. AAS can be used to determine over 70 different elements in solution, or directly in solid samples via electrothermal vaporization, and is used in pharmacology, biophysics,
archaeology and toxicology research.
Atomic emission spectroscopy (AAS) was first used as an analytical technique, and the underlying principles were established in the second half of the 19th century by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff, both professors at the University of Heidelberg, Germany.
The modern form of AAS was largely developed during the 1950s by a team of Australian chemists. They were led by Sir Alan Walsh at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Division of Chemical Physics, in Melbourne, Australia.
Atomic absorption spectrometry has many uses in different areas of chemistry such as clinical analysis of metals in biological fluids and tissues such as whole blood, plasma, urine, saliva, brain tissue, liver, hair, muscle tissue. Atomic absorption spectrometry can be used in qualitative and quantitative analysis. | 3 | Analytical Chemistry |
Organic ionic plastic crystals – are a type organic salts exhibiting mesophases (i.e. a state of matter intermediate between liquid and solid), in which mobile ions are orientationally or rotationally disordered while their centers are located at the ordered sites in the crystal structure. They have various forms of disorder due to one or more solid–solid phase transitions below the melting point and have therefore plastic properties and good mechanical flexibility as well as improved electrode|electrolyte interfacial contact. In particular, protic organic ionic plastic crystals (POIPCs), which are solid protic organic salts formed by proton transfer from a Brønsted acid to a Brønsted base and in essence are protic ionic liquids in the molten state, have found to be promising solid-state proton conductors for fuel cells. Examples include 1,2,4-triazolium perfluorobutanesulfonate and imidazolium methanesulfonate. | 7 | Physical Chemistry |
The endothelial protease vasohibin uses a cysteine as the nucleophile, but a serine to coordinate the histidine base. Despite the serine being a poor acid, it is still effective in orienting the histidine in the catalytic triad. Some homologues alternatively have a threonine instead of serine at the acid location. | 1 | Biochemistry |
A thermodynamic system consisting of a single phase, in the absence of external forces, in its own state of internal thermodynamic equilibrium, is homogeneous. This means that the material in any region of the system can be interchanged with the material of any congruent and parallel region of the system, and the effect is to leave the system thermodynamically unchanged. The thermodynamic operation of scaling is the creation of a new homogeneous system whose size is a multiple of the old size, and whose intensive variables have the same values. Traditionally the size is stated by the mass of the system, but sometimes it is stated by the entropy, or by the volume. For a given such system , scaled by the real number to yield a new one , a state function, , such that , is said to be extensive. Such a function as is called a homogeneous function of degree 1. There are two different concepts mentioned here, sharing the same name: (a) the mathematical concept of degree-1 homogeneity in the scaling function; and (b) the physical concept of the spatial homogeneity of the system. It happens that the two agree here, but that is not because they are tautologous. It is a contingent fact of thermodynamics. | 7 | Physical Chemistry |
Sucrose esters were first mentioned in 1880 by Herzfeld who described the preparation of sucrose octaacetate. The substance is still in use today as a food additive. In 1921, Hess and Messner synthesized sucrose octapalmitate and sucrose octastearate. Both are sucrose fatty acid esters.
Rosenthal, in 1924, synthesized highly substituted sucrose fatty acid esters using the classical condensation reaction between sucrose and the acid chloride of the drying oil fatty acid; pyridine was used as a solvent. Rheineck, Rabin, and Long followed the same procedure using alternative polyhydroxyl molecules such as mannitol. These condensation gave low yields, and the products, which were dark in color, needed extensive purification. Moreover, pyridine is a toxic solvent, so the synthesis was not commercially successful.
In 1939, Cantor, who patented a production route of sucrose fatty acid esters from starch factory by-products, claimed that the products could be used as emulsifying agents or fats. The classical esterification was used with a mixture of pyridine and either chloroform or carbontetrachloride as a solvent.
Later, the concept of synthesizing sucrose ester from sucrose and fatty acids was patented in 1952. The new synthesis pathway, which involved transesterification of triglycerides and sucrose in the new solvent dimethylformamide or DMF, was invented and seemed promising.
In 1950s, Foster Snell and his team conducted research on the production of several mono- and di-substituted sucrose esters. Many processes are still used in commercial production today. | 0 | Organic Chemistry |
The reaction mechanism of allylic C-H acetoxylation has been studied. The first step in the catalytic cycle is cleavage of the allylic C-H bond. The sulfoxide ligand is thought to promote this step by generating a highly electrophilic, possibly cationic palladium species in situ. This species coordinates to the alkene and acidifies the adjacent C-H bond, which allows acetate to abstract the proton and forms a π-allyl palladium complex (II). Subsequently, a π-acid such as benzoquinone coordinates to the palladium, activating the π-allyl complex to nucleophilic attack (III). A nucleophile, in this case acetate, attacks to reductively eliminate palladium, generating the product and palladium(0) (IV). The palladium(0) is reoxidized to palladium(II) by benzoquinone and the sulfoxide ligand reassociates, closing the catalytic cycle. | 0 | Organic Chemistry |
The word pesticide derives from the Latin pestis (plague) and caedere (kill).
The Food and Agriculture Organization (FAO) has defined pesticide as:
: any substance or mixture of substances intended for preventing, destroying, or controlling any pest, including vectors of human or animal disease, unwanted species of plants or animals, causing harm during or otherwise interfering with the production, processing, storage, transport, or marketing of food, agricultural commodities, wood and wood products or animal feedstuffs, or substances that may be administered to animals for the control of insects, arachnids, or other pests in or on their bodies. The term includes substances intended for use as a plant growth regulator, defoliant, desiccant, or agent for thinning fruit or preventing the premature fall of fruit. Also used as substances applied to crops either before or after harvest to protect the commodity from deterioration during storage and transport. | 2 | Environmental Chemistry |
In discussing these figures, it should be kept in mind that both the radon distribution in dwelling and its effect at low exposures are not precisely known, and the radon health effect has to be computed (deaths caused by radon domestic exposure cannot be observed as such). These estimations are strongly dependent on the model retained.
According to these models, radon exposure is thought to be the second major cause of lung cancer after smoking.
Iowa has the highest average radon concentration in the United States; studies performed there have demonstrated a 50% increased lung cancer risk with prolonged radon exposure above the EPA's action level of 4 pCi/L.
Based on studies carried out by the National Academy of Sciences in the United States, radon would thus be the second leading cause of lung cancer after smoking, and accounts for 15,000 to 22,000 cancer deaths per year in the US alone.
The United States Environmental Protection Agency (EPA) says that radon is the number one cause of lung cancer among non-smokers.
The general population is exposed to small amounts of polonium as a radon daughter in indoor air; the isotopes Po and Po are thought to cause the majority of the estimated 15,000–22,000 lung cancer deaths in the US every year that have been attributed to indoor radon.
The Surgeon General of the United States has reported that over 20,000 Americans die each year of radon-related lung cancer.
In the United Kingdom, residential radon would be, after cigarette smoking, the second most frequent cause of lung cancer deaths: according to models, 83.9% of deaths are attributed to smoking only, 1.0% to radon only, and 5.5% to a combination of radon and smoking.
The World Health Organization has recommended a radon reference concentration of 100 Bq/m (2.7 pCi/L). The European Union recommends that action should be taken starting from concentrations of 400 Bq/m (11 pCi/L) for older dwellings and 200 Bq/m (5 pCi/L) for newer ones. After publication of the North American and European Pooling Studies, Health Canada proposed a new guideline that lowers their action level from 800 to 200 Bq/m (22 to 5 pCi/L).
The United States Environmental Protection Agency (EPA) strongly recommends action for any dwelling with a concentration higher than 148 Bq/m (4 pCi/L),
and encourages action starting at 74 Bq/m (2 pCi/L).
EPA recommends that all homes should be monitored for radon. If testing shows levels less than 4 picocuries radon per liter of air (160 Bq/m), then no action is necessary. For levels of 20 picocuries radon per liter of air (800 Bq/m) or higher, the home owner should consider some type of procedure to decrease indoor radon levels. For instance, as radon has a half-life of four days, opening the windows once a day can cut the mean radon concentration to one fourth of its level.
The United States Environmental Protection Agency (EPA) recommends homes be fixed if an occupant's long-term exposure will average 4 picocuries per liter (pCi/L) that is 148 Bq/m. EPA estimates that one in 15 homes in the United States has radon levels above the recommended guideline of 4 pCi/L.
EPA radon risk level tables including comparisons to other risks encountered in life are available in their citizen's guide.
The EPA estimates that nationally, 8% to 12% of all dwellings are above their maximum "safe levels" (four picocuries per liter—the equivalent to roughly 200 chest x-rays). The United States Surgeon General and the EPA both recommend that all homes be tested for radon.
The limits retained do not correspond to a known threshold in the biological effect, but are determined by a cost-efficiency analysis. EPA believes that a 150 Bq/m level (4 pCi/L) is achievable in the majority of homes for a reasonable cost, the average cost per life saved by using this action level is about $700,000.
For radon concentration in drinkable water, the World Health Organization issued as guidelines (1988) that remedial action should be considered when the radon activity exceeded 100 kBq/m in a building, and remedial action should be considered without long delay if exceeding 400 kBq/m. | 2 | Environmental Chemistry |
Steroid 21-hydroxylase is a cytochrome P450 enzyme that is notable for its substrate specificity and relatively high catalytic efficiency.
Like other cytochrome P450 enzymes, steroid 21-hydroxylase participates in the cytochrome P450 catalytic cycle and engages in one-electron transfer with NADPH-P450 reductase. Steroid 21-hydroxylase is highly specific for hydroxylation of progesterone and 17-hydroxyprogesterone. This is in marked contrast to the evolutionarily and functionally related P450 enzyme 17-hydroxylase, which has a broad range of substrates.
The chemical reaction in which steroid 21-hydroxylase catalyzes the addition of hydroxyl (-OH) to the C21 position of progesterone, 17α-hydroxyprogesterone and 21-desoxycortisone was first described in 1952.
Studies of the human enzyme expressed in yeast initially classified 17-hydroxyprogesterone as the preferred substrate for steroid 21-hydroxylase, however, later analysis of the purified human enzyme found a lower K and greater catalytic efficiency for progesterone over 17-hydroxyprogesterone.
The catalytic efficiency of steroid 21-hydroxylase for conversion of progesterone in humans is approximately 1.3 x 10 Ms at 37 °C. This makes it the most catalytically efficient P450 enzyme of those reported to date, and catalytically more efficient than the closely related bovine steroid 21-hydroxylase enzyme. C-H bond breaking to create a primary carbon radical is thought to be the rate-limiting step in the hydroxylation. | 1 | Biochemistry |
In the field of energetics, an energy carrier is produced by human technology from a primary energy source. Only the energy sector uses primary energy sources. Other sectors of society use an energy carrier to perform useful activities (end-uses). The distinction between "Energy Carriers" (EC) and "Primary Energy Sources" (PES) is extremely important. An energy carrier can be more valuable (have a higher quality) than a primary energy source. For example 1 megajoule (MJ) of electricity produced by a hydroelectric plant is equivalent to 3 MJ of oil. Sunlight is a main source of primary energy, which can be transformed into plants and then into coal, oil and gas. Solar power and wind power are other derivatives of sunlight. Note that although coal, oil and natural gas are derived from sunlight, they are considered primary energy sources which are extracted from the earth (fossil fuels). Natural uranium is also a primary energy source extracted from the earth but does not come from the decomposition of organisms (mineral fuel). | 7 | Physical Chemistry |
A primary alcohol is an alcohol in which the hydroxy group is bonded to a primary carbon atom. It can also be defined as a molecule containing a “–CHOH” group.
In contrast, a secondary alcohol has a formula “–CHROH” and a tertiary alcohol has a formula “–CROH”, where “R” indicates a carbon-containing group.
Examples of primary alcohols include ethanol and 1-butanol.
Methanol is also generally regarded as a primary alcohol, including by the 1911 edition of the Encyclopædia Britannica. | 0 | Organic Chemistry |
In theoretical electrolysis of water, a voltage of only 1.23 V is required to split water into hydrogen and oxygen, The formation of an EDL increases this to its thermo-neutral voltage of 1.45 V. Minimising the EDL formed during pulse electrolysis is advantageous, as it can reduce the thermo-neutral voltage and the energy input required, increasing energy efficiency. | 7 | Physical Chemistry |
The calcium cycle is a transfer of calcium between dissolved and solid phases. There is a continuous supply of calcium ions into waterways from rocks, organisms, and soils. Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as calcium carbonate and calcium silicate, which can deposit to form sediments or the exoskeletons of organisms. Calcium ions can also be utilized biologically, as calcium is essential to biological functions such as the production of bones and teeth or cellular function. The calcium cycle is a common thread between terrestrial, marine, geological, and biological processes. Calcium moves through these different media as it cycles throughout the Earth. The marine calcium cycle is affected by changing atmospheric carbon dioxide due to ocean acidification. | 1 | Biochemistry |
When discussing the properties of acids it is usual to specify equilibrium constants as acid dissociation constants, denoted by K, with numerical values given the symbol pK.
On the other hand, association constants are used for bases.
However, general purpose computer programs that are used to derive equilibrium constant values from experimental data use association constants for both acids and bases. Because stability constants for a metal-ligand complex are always specified as association constants, ligand protonation must also be specified as an association reaction. The definitions show that the value of an acid dissociation constant is the reciprocal of the value of the corresponding association constant:
Notes
# For a given acid or base in water, , the self-ionization constant of water.
# The association constant for the formation of a supramolecular complex may be denoted as K; in such cases "a" stands for "association", not "acid".
# For polyprotic acids, the numbering of stepwise association constants is the reverse of the numbering of the dissociation constants. For example, for phosphoric acid (details in the polyprotic acids section below): | 7 | Physical Chemistry |
The siRNA-induced post transcriptional gene silencing is initiated by the assembly of the RNA-induced silencing complex (RISC). The complex silences certain gene expression by cleaving the mRNA molecules coding the target genes. To begin the process, one of the two siRNA strands, the guide strand (anti-sense strand), will be loaded into the RISC while the other strand, the passenger strand (sense strand), is degraded. Certain Dicer enzymes may be responsible for loading the guide strand into RISC. Then, the siRNA scans for and directs RISC to perfectly complementary sequence on the mRNA molecules. The cleavage of the mRNA molecules is thought to be catalyzed by the Piwi domain of Argonaute proteins of the RISC. The mRNA molecule is then cut precisely by cleaving the phosphodiester bond between the target nucleotides which are paired to siRNA residues 10 and 11, counting from the 5end. This cleavage results in mRNA fragments that are further degraded by cellular exonucleases. The 5 fragment is degraded from its 3 end by exosome while the 3 fragment is degraded from its 5 end by 5 -3' exoribonuclease 1(XRN1). Dissociation of the target mRNA strand from RISC after the cleavage allow more mRNA to be silenced. This dissociation process is likely to be promoted by extrinsic factors driven by ATP hydrolysis.
Sometimes cleavage of the target mRNA molecule does not occur. In some cases, the endonucleolytic cleavage of the phosphodiester backbone may be suppressed by mismatches of siRNA and target mRNA near the cleaving site. Other times, the Argonaute proteins of the RISC lack endonuclease activity even when the target mRNA and siRNA are perfectly paired. In such cases, gene expression will be silenced by an miRNA induced mechanism instead
Piwi-interacting RNAs are responsible for the silencing of transposons and are not siRNAs. PIWI-interacting RNAs (piRNAs) are a recently-discovered class of small non-coding RNAs (ncRNAs) with a length of 21-35 nucleotides. They play a role in gene expression regulation, transposon silencing, and viral infection inhibition. Once considered as "dark matter" of ncRNAs, piRNAs emerged as important players in multiple cellular functions in different organisms. | 1 | Biochemistry |
Hydrogels have the remarkable ability to swell in water and aqueous solvents. During the process of swelling, surface instability can occur. This instability depends on the thickness of the hydrogel layers and the surface tension. A higher surface tension stabilizes the flat surface of the hydrogel, which is the outer-most layer. The swelling ratio of the flat layer can be calculated using the following equation derived from the Flory–Huggins theory of free surface energy in hydrogels:
Where λ is the swelling ratio, μ is the chemical potential, p is pressure, k is the Boltzmann constant, and χ and N are unitless hydrogel constants.
As swelling increases, mechanical properties generally suffer. | 7 | Physical Chemistry |
It has been suggested certain microbial dark matter genetic material could belong to a new (i.e., fourth) domain of life, although other explanations (e.g., viral origin) are also possible, which has ties with the issue of a hypothetical shadow biosphere. | 1 | Biochemistry |
Catherine E. Costello is the William Fairfield Warren distinguished professor in the department of biochemistry, Cell Biology and Genomics, and the director of the Center for Biomedical Mass Spectrometry at the Boston University School of Medicine. | 1 | Biochemistry |
In 1756 Thomas Melvill observed the emission of distinct patterns of colour when salts were added to alcohol flames. By 1785 James Gregory discovered the principles of diffraction grating and American astronomer David Rittenhouse made the first engineered diffraction grating. In 1821 Joseph von Fraunhofer solidified this significant experimental leap of replacing a prism as the source of wavelength dispersion improving the spectral resolution and allowing for the dispersed wavelengths to be quantified.
In 1835, Charles Wheatstone reported that different metals could be distinguished by bright lines in the emission spectra of their sparks, thereby introducing an alternative to flame spectroscopy.
In 1849, J. B. L. Foucault experimentally demonstrated that absorption and emission lines at the same wavelength are both due to the same material, with the difference between the two originating from the temperature of the light source.
In 1853, the Swedish physicist Anders Jonas Ångström presented observations and theories about gas spectra. Ångström postulated that an incandescent gas emits luminous rays of the same wavelength as those it can absorb. At the same time George Stokes and William Thomson (Kelvin) were discussing similar postulates. Ångström also measured the emission spectrum from hydrogen later labeled the Balmer lines.
In 1854 and 1855, David Alter published observations on the spectra of metals and gases, including an independent observation of the Balmer lines of hydrogen.
By 1859, Gustav Kirchhoff and Robert Bunsen noticed that several Fraunhofer lines (lines in the solar spectrum) coincide with characteristic emission lines identified in the spectra of heated elements. It was correctly deduced that dark lines in the solar spectrum are caused by absorption by chemical elements in the solar atmosphere. | 7 | Physical Chemistry |
Reports on the "classical" pharmacology of pempidine have been published. The Spinks group, at ICI, compared pempidine, its N-ethyl analogue, and mecamylamine in considerable detail, with additional data related to several structurally simpler compounds. | 0 | Organic Chemistry |
An inexact differential or imperfect differential is a differential whose integral is path dependent. It is most often used in thermodynamics to express changes in path dependent quantities such as heat and work, but is defined more generally within mathematics as a type of differential form. In contrast, an integral of an exact differential is always path independent since the integral acts to invert the differential operator. Consequently, a quantity with an inexact differential cannot be expressed as a function of only the variables within the differential. I.e., its value cannot be inferred just by looking at the initial and final states of a given system. Inexact differentials are primarily used in calculations involving heat and work because they are path functions, not state functions. | 7 | Physical Chemistry |
The mother liquor (or spent liquor) is the solution remaining after a component has been removed by a some process such as filtration or more commonly crystallization. It is encountered in chemical processes including sugar refining.
In crystallization, a solid (usually impure) is dissolved in a solvent at high temperature, taking advantage of the fact that most solids are more soluble at higher temperatures. As the solution cools, the solubility of the solute in the solvent will gradually become smaller. The resultant solution is described as supersaturated, meaning that there is more solute dissolved in the solution than would be predicted by its solubility at that temperature. Crystallization can then be induced from this supersaturated solution and the resultant pure crystals removed by such methods as filtration and centrifugal separators. The remaining solution, once the crystals have been filtered out, is known as the mother liquor, and will contain a portion of the original solute (as predicted by its solubility at that temperature) as well as any impurities that were not filtered out. Second and third crops of crystals can then be harvested from the mother liquor.
An alternative to second cropping is continuous recycle of a portion of the mother liquors from one batch into in subsequent batches in which an increased product yield is expected, and also leads to an accumulation of impurities. It can be shown that the impurity profile of the mother liquors, at moderate recycle levels (i.e. when x>1), quickly reaches a steady state according to (1 − x)/(1 − x), where n is the number of times the process is operated and x is the fraction of mother liquors recycled (Fig. 1). The aforementioned approach is idealised and assumes that the build up of impurities in the mother liquor does not exceed the impurity/impurities solubility. The approach has been confirmed experimentally. | 3 | Analytical Chemistry |
Amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's disease, is a motor neuron disease that affects the brain and spinal cord. The disease causes motor neurons to degenerate, which eventually leads to neuron death and muscular degeneration. Hundreds of mutations in the Cu/Zn superoxide dismutase (SOD1) gene have been found to cause ALS. Gene silencing has been used to knock down the SOD1 mutant that is characteristic of ALS. In specific, siRNA molecules have been successfully used to target the SOD1 mutant gene and reduce its expression through allele-specific gene silencing. | 1 | Biochemistry |
Third-generation Glycoazodyes are synthesized using amino sugars such as 6-amino-6-deoxy-D-galactose or 6 amino-6-deoxylactose. The point of the amide bond is controlled by protecting the alcohol groups on the sugar and allowing the free amine to react. The point of the ester group is controlled by choosing a azo dye with a different alcohol group position. Either the dye or the sugar is reacted with succinic anhydride. This forms an amide group with the sugar or an ester group with the dye. The free carboxylic acid may then react with the alcohol group or amine group on the corresponding dye or sugar. The condensation product is then deprotected. | 0 | Organic Chemistry |
Few commercial applications exist for bioplastics. Cost and performance remain problematic. Typical is the example of Italy, where biodegradable plastic bags are compulsory for shoppers since 2011 with the introduction of a specific law. Beyond structural materials, electroactive bioplastics are being developed that promise to carry electric current.
Bioplastics are used for disposable items, such as packaging, crockery, cutlery, pots, bowls, and straws.
Biopolymers are available as coatings for paper rather than the more common petrochemical coatings.
Bioplastics called drop-in bioplastics are chemically identical to their fossil-fuel counterparts but made from renewable resources. Examples include bio-PE, bio-PET, bio-propylene, bio-PP, and biobased nylons. Drop-in bioplastics are easy to implement technically, as existing infrastructure can be used. A dedicated bio-based pathway allows to produce products that cannot be obtained through traditional chemical reactions and can create products which have unique and superior properties, compared to fossil-based alternatives. | 7 | Physical Chemistry |
In metallurgy, gas flushing removes dissolved gases from the molten metal prior to the material being processed. For example, before casting aluminium alloys, argon bubbles are injected into liquid aluminium using a rotary degasser. The argon bubbles rise to the surface, bringing with them some of the dissolved hydrogen. The degassing step reduces the occurrence of hydrogen gas porosity. In the steel making process, this method is used very commonly for duplex steel and some high reactivity metals. | 8 | Metallurgy |
For an isolated spherical solid particle of diameter in its own liquid, the Gibbs–Thomson equation for the structural melting point depression can be written:
where:
* T = bulk melting temperature
* σ = solid–liquid interface energy (per unit area)
* H = bulk enthalpy of fusion (per gram of material)
* ρ = density of solid
* r = radius of the nanoparticle | 7 | Physical Chemistry |
The dithiodialkyphosphinic acids (RPSH) are related to the diorganodithiophosphates with the formula (RO)PSH, which are also used as complexing agents in the purification of metals. The phosphates are more prone to hydrolysis owing to the greater lability of the RO-P linkage vs the direct C-P bond. | 0 | Organic Chemistry |
As illustrated in Retrosynthetic Scheme I, Taxol was derived from diol 7.2 by an ester bond formation, according to the Ojima-Holton method. This diol comes from carbonate 6.3 by the addition of phenyllithium. The oxetane ring in compound 6.3 was obtained via an S2 reaction involving a mesylate derived from acetal 4.9. Ring B was closed via a McMurry reaction involving dialdehyde 4.8 which ultimately was derived from aldehyde 4.2 and hydrazone 3.6 using a Shapiro coupling reaction.
Retrosynthetic Scheme II indicates that both the aldehyde and the hydrazone used in the Shapiro coupling reaction were synthesized using Diels-Alder reactions. | 0 | Organic Chemistry |
In cancers, loss of expression of genes occurs about 10 times more frequently by transcription silencing (caused by promoter hypermethylation of CpG islands) than by mutations. As Vogelstein et al. point out, in a colorectal cancer there are usually about 3 to 6 driver mutations and 33 to 66 hitchhiker or passenger mutations. In contrast, in colon tumors compared to adjacent normal-appearing colonic mucosa, there are about 600 to 800 heavily methylated CpG islands in promoters of genes in the tumors while these CpG islands are not methylated in the adjacent mucosa.
Using gene set enrichment analysis, 569 out of 938 gene sets were hypermethylated and 369 were hypomethylated in cancers. Hypomethylation of CpG islands in promoters results in increased transcription of the genes or gene sets affected.
One study listed 147 specific genes with colon cancer-associated hypermethylated promoters and 27 with hypomethylated promoters, along with the frequency with which these hyper/hypo-methylations were found in colon cancers. At least 10 of those genes had hypermethylated promoters in nearly 100% of colon cancers. They also indicated 11 microRNAs whose promoters were hypermethylated in colon cancers at frequencies between 50% and 100% of cancers. MicroRNAs (miRNAs) are small endogenous RNAs that pair with sequences in messenger RNAs to direct post-transcriptional repression. On average, each microRNA represses or inhibits transcriptional expression of several hundred target genes. Thus microRNAs with hypermethylated promoters may be allowing enhanced transcription of hundreds to thousands of genes in a cancer. | 1 | Biochemistry |
McCrones work as a microscopist first attracted widespread public attention when he helped exonerate Lloyd Eldon Miller, a cabdriver who had been sentenced to death for the 1955 murder of an 8-year-old girl in Canton, Illinois. McCrone was able to show that the stains in a pair of undershorts that the prosecution had presented to the jury as blood were actually red paint. Millers conviction was overturned by the US Supreme Court in 1967. In later life, McCrone microscopically examined the physical evidence (hairs, fibers, blood, etc.) that led to the conviction of Wayne Williams as the Atlanta child killer. That work earned him the 1982 Certificate of Merit from the Forensic Sciences Foundation.
On occasion, McCrone was given hair samples of famous people to analyze. Based on such analysis, he rejected the hypothesis that Napoleon had been poisoned with arsenic, but concluded that Beethoven had suffered from lead poisoning. | 3 | Analytical Chemistry |
Different rules (4n, 5n, or 6n) are invoked depending on the number of electrons per vertex.
The 4n rules are reasonably accurate in predicting the structures of clusters having about 4 electrons per vertex, as is the case for many boranes and carboranes. For such clusters, the structures are based on deltahedra, which are polyhedra in which every face is triangular. The 4n clusters are classified as closo-, nido-, arachno- or hypho-, based on whether they represent a complete (closo-) deltahedron, or a deltahedron that is missing one (nido-), two (arachno-) or three (hypho-) vertices.
However, hypho clusters are relatively uncommon due to the fact that the electron count is high enough to start to fill antibonding orbitals and destabilize the 4n structure. If the electron count is close to 5 electrons per vertex, the structure often changes to one governed by the 5n rules, which are based on 3-connected polyhedra.
As the electron count increases further, the structures of clusters with 5n electron counts become unstable, so the 6n rules can be implemented. The 6n clusters have structures that are based on rings.
A molecular orbital treatment can be used to rationalize the bonding of cluster compounds of the 4n, 5n, and 6n types. | 7 | Physical Chemistry |
In polymerase chain reaction (PCR) experiments, the GC-content of short oligonucleotides known as primers is often used to predict their annealing temperature to the template DNA. A higher GC-content level indicates a relatively higher melting temperature.
Many sequencing technologies, such as Illumina sequencing, have trouble reading high-GC-content sequences. Bird genomes are known to have many such parts, causing the problem of "missing genes" expected to be present from evolution and phenotype but never sequenced — until improved methods were used. | 1 | Biochemistry |
* Nesmeyanov A.N. D.I. Mendeleev's Periodic Table of Elements and Organic Chemistry. Series: Reports at the plenary session/ VIII Mendeleev Congress on General and Applied Chemistry. Moscow: Publishing House Acad. Sciences of the USSR, 1959.
* Nesmeyanov A.N. Ed. acad. A. V. Topchiev Selected Works. Moscow: Publishing House Acad. Sciences of the USSR, 1959.
* Ioffe S.T. and Nesmeyanov A.N. Ed. A. N. Nesmeyanova and К. A. Kocheshkova Magnesium, beryllium, calcium, strontium, barium. Series: Methods of elemental organic chemistry. Moscow: Publishing House Acad. Sciences of the USSR, 1963.
* Nesmeyanov A.N. and Sokolik R.A. Ed. A. N. Nesmeyanova and К. A. Kocheshkova Bor. Aluminum. Gallium. Indium. Thallium. Series: Methods of elemental organic chemistry. Moscow: Publishing House Acad. Sciences of the USSR, 1964.
* Makarova L.G. and Nesmeyanov A.N. Ed. A. N. Nesmeyanova and К. A. Kocheshkova Mercury. Series: Methods of elemental organic chemistry. Moscow: Publishing House Acad. Sciences of the USSR, 1965.
* Nesmeyanov A.N., Belikov V.M.Problem of food synthesis. Series: Report at the plenary session / XI Mendeleev Congress on General and Applied Chemistry. Moscow: Nauka, 1965.
* Nesmeyanov A.N.Research in Organic Chemistry. Selected works 1959-1969. Moscow: Nauka, 1971.
* Nesmeyanov A.N. and Nesmeyanov N.A. The Beginnings of Organic Chemistry. In two books. Moscow: Chemistry, 1969.
* Nesmeyanov A.N. and Nesmeyanov N.A. The Beginnings of Organic Chemistry. In two books. Moscow: Chemistry, 1970. | 0 | Organic Chemistry |
Conventional SNP typing methods are typically time-consuming and expensive, requiring several probe based assays to be multiplexed together or the use of DNA microarrays. HRM is more cost-effective and reduces the need to design multiple pairs of primers and the need to purchase expensive probes. The HRM method has been successfully used to detect a single G to A substitution in the gene Vssc (Voltage Sensitive Sodium Channel) which confers resistance to the acaricide permethrin in Scabies mite. This mutation results in a coding change in the protein (G1535D). The analysis of scabies mites collected from suspected permethrin susceptible and tolerant populations by HRM showed distinct melting profiles. The amplicons from the sensitive mites were observed to have a higher melting temperature relative to the tolerant mites, as expected from the higher thermostability of the GC base pair
In a field more relevant to clinical diagnostics, HRM has been shown to be suitable in principle for the detection of mutations in the breast cancer susceptibility genes BRCA1 and BRCA2. More than 400 mutations have been identified in these genes.<br />The sequencing of genes is the gold standard for identifying mutations. Sequencing is time-consuming and labour-intensive and is often preceded by techniques used to identify heteroduplex DNA, which then further amplify these issues. HRM offers a faster and more convenient closed-tube method of assessing the presence of mutations and gives a result which can be further investigated if it is of interest. In a study carried out by Scott et al. in 2006, 3 cell lines harbouring different BRCA mutations were used to assess the HRM methodology. It was found that the melting profiles of the resulting PCR products could be used to distinguish the presence or absence of a mutation in the amplicon. Similarly in 2007 Krypuy et al. showed that the careful design of HRM assays (with regards to primer placement) could be successfully employed to detect mutations in the TP53 gene, which encodes the tumour suppressor protein p53 in clinical samples of breast and ovarian cancer. Both these studies highlighted the fact that changes in the melting profile can be in the form of a shift in the melting temperature or an obvious difference in the shape of the melt curve. Both of these parameters are a function of the amplicon sequence.
The consensus is that HRM is a cost efficient method that can be employed as an initial screen for samples suspected of harbouring polymorphisms or mutations. This would reduce the number of samples which need to be investigated further using more conventional methods. | 1 | Biochemistry |
The thylakoid lumen is a continuous aqueous phase enclosed by the thylakoid membrane. It plays an important role for photophosphorylation during photosynthesis. During the light-dependent reaction, protons are pumped across the thylakoid membrane into the lumen making it acidic down to pH 4. | 5 | Photochemistry |
Wu was born 1 January 1928 in Jinan, Shandong, Republic of China. He graduated from the Department of Chemistry of Fudan University in 1951, and was hired as a faculty member by the university. In September 1954, he began his graduate studies in the Department of Chemistry of the Moscow State University, and earned his associate doctor degree (Ph.D. equivalent) in June 1958.
After returning to China, Wu was assigned to the newly founded Zhengzhou University to help establish its chemistry department, where he worked for the rest of his career. He later served as chairman of the department and a doctoral advisor.
Wu published more than 160 research articles. He won a National Science Congress Award in 1978, and the Henan Science and Technology Progress Award (First Class) in 2001. He was elected an academician of the Chinese Academy of Sciences in 2003. | 0 | Organic Chemistry |
He briefly taught physical chemistry at the London University before moving to Pakistan. Upon his return, he joined the Pakistan Atomic Energy Commission (PAEC) and took the professorship of nuclear chemistry at the Pakistan Institute of Nuclear Science and Technology (PINSTECH). Subsequently, he joined the clandestine atomic bomb project's chemistry section led by fellow chemist Iqbal Hussain Qureshi.
Munir Ahmad Khan, chairman PAEC, had him partially take over the "R-Labs" at PAEC to engage research in chemical explosives. Initially, the research was concentrated towards development of the HMX, a non-toxic explosive that was produced as a by-product of the RDX process. In the 1970s, he founded the Metallurgical Laboratory (ML) where he also moved majority of the staff to undertake research in metallurgy. He then led a team of chemists who supervised the physical conversion of UF into solid metal before coating and machining the metal. During this time, he also led the research on using chemical and metallurgical industrial techniques and reduction furnaces to produce metal from the Highly enriched uranium. Due to the sensitivity of the project and concerns of fellow theorist Dr. AQ Khan, the program was moved to KRL in the 1980s. | 7 | Physical Chemistry |
* Weber et al. 2005 determined that the inactive X-chromosome in females is hypermethylated on a chromosome wide level using MeDIP coupled with microarray.
* Keshet et al. 2006 performed a study on colon and prostate cancer cells using MeDIP-chip. The result is a genome-wide analysis of genes lying in hypermethylated regions as well as conclude that there is an instructive mechanism of de novo methylation in cancer cells.
* Zhang et al. 2006 obtained a high resolution methylome mapping in Arabidopsis using MeDIP-chip.
* Novak et al. 2006 used the MeDIP-chip approach to investigate human breast cancer for methylation associated silencing and observed the inactivation of the HOXA gene cluster | 1 | Biochemistry |
The structural changes that occur during 72-hour hypothermic storage of previously uninjured kidneys have been described by Mackay who showed how there was progressive vacuolation of the cytoplasm of the cells which particularly affected the proximal tubules. On electron microscopy the mitochondria were seen to become swollen with early separation of the internal cristal membranes and later loss of all internal structure. Lysosomal integrity was well preserved until late, and the destruction of the cell did not appear to be caused by lytic enzymes because there was no more injury immediately adjacent to the lysosomes than in the rest of the cell.
Woods and Liu – when describing successful 5 and 7 day kidney storage - described the light microscopic changes seen at the end of perfusion and at post mortem, but found few gross abnormalities apart from some infiltration with lymphocytes and occasional tubular atrophy.
The changes during short perfusions of human kidneys prior to reimplantation have been described by Hill who also performed biopsies 1 hour after reimplantation. On electron microscopy Hill found endothelial damage which correlated with the severity of the fibrin deposition after reimplantation. The changes that Hill saw in the glomeruli on light microscopy were occasional fibrin thrombi and infiltration with polymorphs. Hill suspected that these changes were an immunologically induced lesion, but found that there was no correlation between the severity of the histological lesion and the presence or absence of immunoglobulin deposits.
There are several reports of the analysis of urine produced by kidneys during perfusion storage. Kastagir analysed urine produced during 24-hour perfusion and found it to be an ultrafiltrate of the perfusate, Scott found a trace of protein in the urine during 24-hour storage, and Pederson found only a trace of protein after 36 hours perfusion storage. Pederson mentioned that he had found heavy proteinuria during earlier experiments. Woods noted protein casts in the tubules of viable kidneys after 5 day storage, but he did not analyse the urine produced during perfusion. In Cohen's study there was a progressive increase in urinary protein concentration during 8 day preservation until the protein content of the urine equalled that of the perfusate. This may have been related to the swelling of the glomerular basement membranes and the progressive fusion of epithelial cell foot processes that was also observed during the same period of perfusion storage. | 1 | Biochemistry |
SLS has been proposed as a potentially effective topical microbicide, for intravaginal use, to inhibit and possibly prevent infection by various enveloped and non-enveloped viruses such as the herpes simplex viruses, HIV, and the Semliki Forest virus.
Liquid membranes formed from SDS in water have been demonstrated to work as unusual particle separators. The device acts as a reverse filter, allowing large particles to pass while capturing smaller particles. | 1 | Biochemistry |
In general, prehistoric extraction of metals, particularly copper, involved two fundamental stages: first, the smelting of copper ore at temperatures exceeding 700 °C is needed to separate the gangue from the copper; second, melting the copper, which requires temperatures exceeding its melting point of 1080 °C. Given the available technology at the time, accomplishing these extreme temperatures posed a significant challenge. Early smelters developed ways to effectively increase smelting temperatures by feeding the fire with forced flows of oxygen.
Copper extraction in particular is of great interest in archeometallurgical studies since it dominated other metals in Mesopotamia from the early Chalcolithic until the mid-to-late sixth century BC. There is a lack of consensus among archaeometallurgists on the origin of non-ferrous extractive metallurgy. Some scholars believe that extractive metallurgy may have been simultaneously or independently discovered in several parts of the world. The earliest known use of pyrometallurgical extraction of copper occurred in Belovode, eastern Serbia, from the late sixth to early fifth millennium BC. However, there is also evidence of copper smelting in Tal-i-Iblis, southeastern Iran, which dates back to around the same period. During this period, copper smelters used large in-grown pits filled with coal, or crucibles to extract copper, but by the fourth millennium BC this practice had begun to phase out in favor of the smelting furnace, which had a larger production capacity. From the third millennium onward, the invention of the reusable smelting furnace was crucial to the success of large-scale copper production and the robust expansion of the copper trade through the Bronze Age.
The earliest silver objects began appearing in the late fourth millennium BC in Anatolia, Turkey. Prehistoric silver extraction is strongly associated with the extraction of the less valuable metal, lead; although evidence of lead extraction technology predates silver by at least 3 millennia. Silver and lead extractions are also associated because the argentiferous (silver-bearing) ores used in the process often contains both elements.
In general, prehistoric silver recovery was broken down into three phases: First, the silver-lead ore is roasted to separate the silver and lead from the gangue. The metals are then melted at high temperature ( greater than 1100 °C) in the crucible while air is blown over the molten metal (cupellation). Finally, lead is oxidized to form lead monoxide (PbO) or is absorbed into the walls of the crucible, leaving the refined silver behind.
The silver-lead cupellation method was first used in Mesopotamia between 4000 and 3500 BC. Silver artifacts, dating around 3600 BC, were discovered in Naqada, Egypt. Some of these cast silver artifacts contained less than 0.5% lead, which strongly indicates cupellation. | 8 | Metallurgy |
The use of equivalent weights in general chemistry has largely been superseded by the use of molar masses. Equivalent weights may be calculated from molar masses if the chemistry of the substance is well known:
*sulfuric acid has a molar mass of 98.078(5) , and supplies two moles of hydrogen ions per mole of sulfuric acid, so its equivalent weight is 98.078(5) /2 = 49.039(3) .
*potassium permanganate has a molar mass of 158.034(1) , and reacts with five moles of electrons per mole of potassium permanganate, so its equivalent weight is 158.034(1) /5 = 31.6068(3) .
Historically, the equivalent weights of the elements were often determined by studying their reactions with oxygen. For example, 50 g of zinc will react with oxygen to produce 62.24 g of zinc oxide, implying that the zinc has reacted with 12.24 g of oxygen (from the Law of conservation of mass): the equivalent weight of zinc is the mass which will react with eight grams of oxygen, hence 50 g × 8 g/12.24 g = 32.7 g.
Some contemporary general chemistry textbooks make no mention of equivalent weights. Others explain the topic, but point out that it is merely an alternate method of doing calculations using moles. | 7 | Physical Chemistry |
Crucibles used for copper smelting were generally wide shallow vessels made from clay that lacks refractory properties which is similar to the types of clay used in other ceramics of the time. During the Chalcolithic period, crucibles were heated from the top by using blowpipes. Ceramic crucibles from this time had slight modifications to their designs such as handles, knobs or pouring spouts allowing them to be more easily handled and poured. Early examples of this practice can be seen in Feinan, Jordan. These crucibles have added handles to allow for better manipulation, however, due to the poor preservation of the crucibles there is no evidence of a pouring spout. The main purpose of the crucible during this period was to keep the ore in the area where the heat was concentrated to separate it from impurities before shaping.
A crucible furnace dating to 2300–1900 BC for bronze casting has been found at a religious precinct of Kerma. | 3 | Analytical Chemistry |
In Europe, the Water Framework Directive (WFD) went into effect on October 23, 2000. It requires all EU member states to show that all surface and groundwater bodies are in good status. The WFD requires member states to implement monitoring systems to estimate the integrity of biological stream components for specific sub-surface water categories. This requirement increased the incidence of biometrics applied to ascertain stream health in Europe A remote online biomonitoring system was designed in 2006. It is based on bivalve molluscs and the exchange of real-time data between a remote intelligent device in the field (able to work for more than 1 year without in-situ human intervention) and a data centre designed to capture, process and distribute the web information derived from the data. The technique relates bivalve behaviour, specifically shell gaping activity, to water quality changes. This technology has been successfully used for the assessment of coastal water quality in various countries (France, Spain, Norway, Russia, Svalbard (Ny-Ålesund) and New Caledonia).
In the United States, the Environmental Protection Agency (EPA) published Rapid Bioassessment Protocols, in 1999, based on measuring macroinvertebrates, as well as periphyton and fish for assessment of water quality.
In South Africa, the Southern African Scoring System (SASS) method is based on benthic macroinvertebrates, and is used for the assessment of water quality in South African rivers. The SASS aquatic biomonitoring tool has been refined over the past 30 years and is now on the fifth version (SASS5) in accordance with the ISO/IEC 17025 protocol. The SASS5 method is used by the South African Department of Water Affairs as a standard method for River Health Assessment, which feeds the national River Health Programme and the national Rivers Database.
The imposex phenomenon in the dog conch species of sea snail leads to the abnormal development of a penis in females, but does not cause sterility. Because of this, the species has been suggested as a good indicator of pollution with organic man-made tin compounds in Malaysian ports. | 2 | Environmental Chemistry |
The Barbier–Wieland degradation is a procedure for shortening the carbon chain of a carboxylic acid by one carbon. It only works when the carbon adjacent to the carboxyl is a simple methylene bridge (an aliphatic carbon with no substituents). The reaction sequence involves conversion of the carboxyl and alpha carbon into an alkene, which is then cleaved by oxidation to convert the former alpha position into a carboxyl itself. | 0 | Organic Chemistry |
Some forms of mutations are hereditary (germline mutations), or passed on from a parent to its offspring. Such mutated coding regions are present in all cells within the organism. Other forms of mutations are acquired (somatic mutations) during an organisms lifetime, and may not be constant cell-to-cell. These changes can be caused by mutagens, carcinogens, or other environmental agents (ex. UV). Acquired mutations can also be a result of copy-errors during DNA replication and are not passed down to offspring. Changes in the coding region can also be de novo (new); such changes are thought to occur shortly after fertilization, resulting in a mutation present in the offsprings DNA while being absent in both the sperm and egg cells. | 1 | Biochemistry |
The Hoopes process is a metallurgical process, used to obtain aluminium metal of very high purity (about 99.99% pure). The process was patented by William Hoopes, a chemist of the Aluminum Company of America (ALCOA), in 1925. | 8 | Metallurgy |
The radio spectrum scope (also radio panoramic receiver, panoramic adapter, pan receiver, pan adapter, panadapter, panoramic radio spectroscope, panoramoscope, panalyzor and band scope) was invented by Marcel Wallace - and measures and shows the magnitude of an input signal versus frequency within one or more radio bands - e.g. shortwave bands. A spectrum scope is normally a lot cheaper than a spectrum analyzer, because the aim is not high quality frequency resolution - nor high quality signal strength measurements.
The spectrum scope use can be to:
* find radio channels quickly of known and unknown signals when receiving.
* find radio amateurs activity quickly e.g. with the intent of communicating with them.
Modern spectrum scopes, like the Elecraft P3, also plot signal frequencies and amplitudes over time, in a rolling format called a waterfall plot. | 7 | Physical Chemistry |
Metal carbonyls are used in a number of industrially important carbonylation reactions. In the oxo process, an alkene, hydrogen gas, and carbon monoxide react together with a catalyst (such as dicobalt octacarbonyl) to give aldehydes. Illustrative is the production of butyraldehyde from propylene:
:CHCH=CH + H + CO → CHCHCHCHO
Butyraldehyde is converted on an industrial scale to 2-ethylhexanol, a precursor to PVC plasticizers, by aldol condensation, followed by hydrogenation of the resulting hydroxyaldehyde. The "oxo aldehydes" resulting from hydroformylation are used for large-scale synthesis of fatty alcohols, which are precursors to detergents. The hydroformylation is a reaction with high atom economy, especially if the reaction proceeds with high regioselectivity.
Another important reaction catalyzed by metal carbonyls is the hydrocarboxylation. The example below is for the synthesis of acrylic acid and acrylic acid esters:
Also the cyclization of acetylene to cyclooctatetraene uses metal carbonyl catalysts:
In the Monsanto and Cativa processes, acetic acid is produced from methanol, carbon monoxide, and water using hydrogen iodide as well as rhodium and iridium carbonyl catalysts, respectively. Related carbonylation reactions afford acetic anhydride. | 0 | Organic Chemistry |
The glyoxylate cycle uses five of the eight enzymes associated with the tricarboxylic acid cycle: citrate synthase, aconitase, succinate dehydrogenase, fumarase, and malate dehydrogenase. The two cycles differ in that in the glyoxylate cycle, isocitrate is converted into glyoxylate and succinate by isocitrate lyase (ICL) instead of into α-ketoglutarate. This bypasses the decarboxylation steps that take place in the citric acid cycle (TCA cycle), allowing simple carbon compounds to be used in the later synthesis of macromolecules, including glucose. Glyoxylate is subsequently combined with acetyl-CoA to produce malate, catalyzed by malate synthase. Malate is also formed in parallel from succinate by the action of succinate dehydrogenase and fumarase. | 1 | Biochemistry |
Electrophilic amination is a chemical process involving the formation of a carbon–nitrogen bond through the reaction of a nucleophilic carbanion with an electrophilic source of nitrogen. | 0 | Organic Chemistry |
Mesembrine was first isolated and characterized by Bodendorf, et al. in 1957. It is a tricyclic molecule and has two bridgehead chiral carbons between the five-membered ring and the six-membered ring (highlighted in green in the figure below). Because of its structure and bioactivity, mesembrine has been a target for total synthesis over the past 40 years. Over 40 total syntheses have been reported for mesembrine, most of which focused on different approaches and strategies for the construction of the bicyclic ring system and the quaternary carbon.
The first total synthesis of mesembrine was reported by Shamma, et al. in 1965. This route has 21 steps, which was among the longest synthetic routes for mesembrine. Key steps involve the construction of the six-membered ketone ring by Diels-Alder reaction, α-allylation for synthesis of the quaternary carbon, and conjugate addition reaction for the final five-membered ring closure. The final product from this route is a racemic mixture of (+)- and (-)-mesembrine.
In 1971, Yamada, et al. reported the first asymmetric total synthesis of (+)-mesembrine. The quaternary carbon was introduced by asymmetric Robinson annulation reaction mediated by an -proline derivative. | 0 | Organic Chemistry |
Thymidylate synthase inhibitors are chemical agents which inhibit the enzyme thymidylate synthase and have potential as an anticancer chemotherapy. This inhibition prevents the methylation of C5 of deoxyuridine monophosphate (dUMP) thereby inhibiting the synthesis of deoxythymidine monophosphate (dTMP). The downstream effect is promotion of cell death because cells would not be able to properly undergo DNA synthesis if they are lacking dTMP, a necessary precursor to dTTP.
Five agents were in clinical trials in 2002: raltitrexed, pemetrexed, nolatrexed, Plevitrexed( ZD9331/BGC9331), and GS7904L.
Examples include
* Raltitrexed, used for colorectal cancer since 1998
* Fluorouracil, used for colorectal cancer
* BGC 945/ ONX-0801
* OSI-7904L | 1 | Biochemistry |
Abiotic sources of hydrogen gas include water-rock and photochemical reactions. Exothermic serpentinization reactions between water and olivine minerals produce H in the marine or terrestrial subsurface. In the ocean, hydrothermal vents erupt magma and altered seawater fluids including abundant H, depending on the temperature regime and host rock composition. Molecular hydrogen can also be produced through photooxidation (via solar UV radiation) of some mineral species such as siderite in anoxic aqueous environments. This may have been an important process in the upper regions of early Earth's Archaean oceans. | 1 | Biochemistry |
In order to conduct DNA separation by silica adsorption, a sample (this may be anything from purified cells to a tissue specimen) is lysed, releasing proteins, DNA, phospholipids, etc. from the cells. The remaining tissue is discarded. The supernatant containing the DNA is then exposed to silica in a solution with high ionic strength. The highest DNA adsorption efficiencies occur in the presence of buffer solution with a pH at or below the pKa of the surface silanol groups.
The mechanism behind DNA adsorption onto silica is not fully understood; one possible explanation involves reduction of the silica surface's negative charge due to the high ionic strength of the buffer. This decrease in surface charge leads to a decrease in the electrostatic repulsion between the negatively charged DNA and the negatively charged silica. Meanwhile, the buffer also reduces the activity of water by formatting hydrated ions. This leads to the silica surface and DNA becoming dehydrated. These conditions lead to an energetically favorable situation for DNA to adsorb to the silica surface.
A further explanation of how DNA binds to silica is based on the action of guanidinium chloride (GuHCl), which acts as a chaotrope. A chaotrope denatures biomolecules by disrupting the shell of hydration around them. This allows positively charged ions to form a salt bridge between the negatively charged silica and the negatively charged DNA backbone in high salt concentration. The DNA can then be washed with high salt and ethanol, and ultimately eluted with low salt.
After the DNA is bound to the silica it is then washed to remove contaminants and finally eluted using an elution buffer or distilled water. | 1 | Biochemistry |
Plants secrete a variety of chemicals to help seal off damaged areas. For example, the grape vine Vitis vinifera is able to block the xylem water-transport tubes in its stems using the chemical tylose in summertime, and gels in wintertime when the plant is dormant. Tylose helps to prevent pathogens such as wood-rotting fungi and the bacterium Xylella fastidiosa from spreading through the plant: the chemical is produced as a response both to the bacterium and to mechanical damage such as viticultural pruning. | 1 | Biochemistry |
A J-aggregate is a type of dye with an absorption band that shifts to a longer wavelength (bathochromic shift) of increasing sharpness (higher absorption coefficient) when it aggregates under the influence of a solvent or additive or concentration as a result of supramolecular self-organisation. The dye can be characterized further by a small Stokes shift with a narrow band. The J in J-aggregate refers to E.E. Jelley who discovered the phenomenon in 1936. The dye is also called a Scheibe aggregate after G. Scheibe who also independently published on this topic in 1937.
Scheibe and Jelley independently observed that in ethanol the dye PIC chloride has two broad absorption maxima at around 19,000 cm and 20,500 cm (526 and 488 nm respectively) and that in water a third sharp absorption maximum appears at 17,500 cm (571 nm). The intensity of this band further increases on increasing concentration and on adding sodium chloride. In the oldest aggregation model for PIC chloride the individual molecules are stacked like a roll of coins forming a supramolecular polymer but the true nature of this aggregation phenomenon is still under investigation. Analysis is complicated because PIC chloride is not a planar molecule. The molecular axis can tilt in the stack creating a helix pattern. In other models the dye molecules orient themselves in a brickwork, ladder, or staircase fashion. In various experiments the J-band was found to split as a function of temperature, liquid crystal phases were found with concentrated solutions and CryoTEM revealed aggregate rods 350 nm long and 2.3 nm in diameter.
J-aggregate dyes are found with polymethine dyes in general, with cyanines, merocyanines, squaraine and perylene bisimides. Certain π-conjugated macrocycles, reported by Swager and co-workers at MIT, were also found to form J-aggregates and exhibited exceptionally high photoluminescence quantum yields. In 2020, a famous cyanine dye (TDBC) was reported with enhanced photoluminescence quantum yield (> 50%) in the solution at room-temperature.
Molecular PIC aggregates exhibiting J-like properties have been shown to spontaneously template into sequence specific DNA duplex strands. These DNA based J-aggregates, known as J-bits, have been sought after as a bottom-up method of self-assembling PIC J-aggregates into large scale multi-functional DNA scaffolds. Critically, J-bits have been observed to engage in energy transfer when in proximity to quantum dots as well as organic dyes such as Alexa Fluor dyes. Prototypical DNA energy transfer arrays, which are based on the molecular photonic wire design, use FRET to transfer excitons step-wise down an energy gradient. Since the FRET efficiency between two Fluorophores decays by their separation distance to the 6th power, the spatial limitations of these systems are highly constrained. It is hypothesized that integrating J-bit relays between FRET nodes would allow some of this energy loss to be recouped. In theory, dense packing and rigid alignment of the PIC monomers enables superposition of the transition dipoles allowing excitons to propagate through the length of the aggregate with low loss. | 6 | Supramolecular Chemistry |
Deficiency of expression of a DNA repair gene occurs in many cancers (see DNA repair defect and cancer risk and microRNA and DNA repair). Altered microRNA (miRNA) expression that either decreases accurate DNA repair or increases inaccurate microhomology-mediated end joining (MMEJ) DNA repair is often observed in cancers. Deficiency of accurate DNA repair may be a major source of the high frequency of mutations in cancer (see mutation frequencies in cancers). Repression of DNA repair genes in cancers by changes in the levels of microRNAs may be a more frequent cause of repression than mutation or epigenetic methylation of DNA repair genes.
For instance, BRCA1 is employed in the accurate homologous recombinational repair (HR) pathway. Deficiency of BRCA1 can cause breast cancer. Down-regulation of BRCA1 due to mutation occurs in about 3% of breast cancers. Down-regulation of BRCA1 due to methylation of its promoter occurs in about 14% of breast cancers. However, increased expression of miR-182 down-regulates BRCA1 mRNA and protein expression, and increased miR-182 is found in 80% of breast cancers.
In another example, a mutated constitutively (persistently) expressed version of the oncogene c-Myc is found in many cancers. Among many functions, c-Myc negatively regulates microRNAs miR-150 and miR-22. These microRNAs normally repress expression of two genes essential for MMEJ, Lig3 and Parp1, thereby inhibiting this inaccurate, mutagenic DNA repair pathway. Muvarak et al. showed, in leukemias, that constitutive expression of c-Myc, leading to down-regulation of miR-150 and miR-22, allowed increased expression of Lig3 and Parp1. This generates genomic instability through increased inaccurate MMEJ DNA repair, and likely contributes to progression to leukemia.
To show the frequent ability of microRNAs to alter DNA repair expression, Hatano et al. performed a large screening study, in which 810 microRNAs were transfected into cells that were then subjected to ionizing radiation (IR). For 324 of these microRNAs, DNA repair was reduced (cells were killed more efficiently by IR) after transfection. For a further 75 microRNAs, DNA repair was increased, with less cell death after IR. This indicates that alterations in microRNAs may often down-regulate DNA repair, a likely important early step in progression to cancer. | 1 | Biochemistry |
One of the important factors in determining the dentinal bonding is collagen. When dentin is etched, smear layer and minerals from dentinal structure will be removed, hence exposing the collagen fibres. The areas where the minerals are removed are filled with water which functions as plasticizer for collagen and keeps it at expanded soft state. This means that the spaces for resin-dentin bonding are preserved. However, these collagen fibres can collapse in dry condition and if the organic layer of matrix is denatured, this will obstruct the resin to bond with dentin and form a hybrid layer.
Because of this, the presence of moist or wet dentin is required to achieve successful dentin bonding. This is due to presence of water miscible organic solvents like ethanol or acetone in the primers. The acetone trails water and hence improves the penetration of the monomers into the dentin for better micromechanical bonding. Also, water will prevent collagen fibres from collapsing, thus making better penetration and bonding between resin and dentin.
In order to get a moist dentin, it is advisable to not dry dentin with compressed air after rinsing away the etchant. Instead, high volume evacuation suction can be used to remove excess water and then blot the remaining water present on dentin using gauze or cotton. The dentin surface should appear glistening.
If the dentin surface is too wet, water will dilute the resin primer and compete for the sites in collagen network, which will prevent hybrid layer formation.
If the dentin surface is too dry, collapse of collagen fibres and demineralized dentin can occur, leading to low bond strength. | 7 | Physical Chemistry |
The expressome is a supramolecular complex consisting of RNA polymerase and a trailing ribosome linked by a shared mRNA transcript. It is supported by the transcription factors NusG and NusA, which interact with both RNA polymerase and the ribosome to couple the complexes together. When coupled by transcription factor NusG, the ribosome binds newly synthesized mRNA and prevents formation of secondary structures that inhibit transcription. Formation of an expressome complex also aids transcription elongation by the trailing ribosome opposing back-tracking of RNA polymerase. Three-dimensional models of ribosome-RNA polymerase expressome complexes have been determined by cryo-electron microscopy. | 1 | Biochemistry |
Major studies in which knockout of particular amino acids was achieved in the CTD have been carried out. The results indicate that RNA polymerase II CTD truncation mutations affect the ability to induce transcription of a subset of genes in vivo, and the lack of response to induction maps to the upstream activating sequences of these genes. | 1 | Biochemistry |
Coenzymes Q is a coenzyme family that is ubiquitous in animals and many Pseudomonadota, a group of gram-negative bacteria. The fact that the coenzyme is ubiquitous gives the origin of its other name, ubiquinone. In humans, the most common form of coenzymes Q is coenzyme Q, also called CoQ () or ubiquinone-10.
Coenzyme Q is a 1,4-benzoquinone, in which "Q" refers to the quinone chemical group and "10" refers to the number of isoprenyl chemical subunits (shown enclosed in brackets in the diagram) in its tail. In natural ubiquinones, there are from six to ten subunits in the tail, with humans having a tail of 10 isoprene units (50 carbon atoms) connected to its benzoquinone "head".
This family of fat-soluble substances is present in all respiring eukaryotic cells, primarily in the mitochondria. Ninety-five percent of the human body's energy is generated this way. Organs with the highest energy requirements—such as the heart, liver, and kidney—have the highest CoQ concentrations.
There are three redox states of CoQ: fully oxidized (ubiquinone), semiquinone (ubisemiquinone), and fully reduced (ubiquinol). The capacity of this molecule to act as a two-electron carrier (moving between the quinone and quinol form) and a one-electron carrier (moving between the semiquinone and one of these other forms) is central to its role in the electron transport chain due to the iron–sulfur clusters that can only accept one electron at a time, and as a free radical–scavenging antioxidant. | 1 | Biochemistry |
The dehydration theory explains why mucoadhesion can arise rapidly. When two gels capable of rapid gelation in an aqueous environment are brought into contact, movement occurs between the two gels until a state of equilibrium is reached. Gels associated with a strong affinity for water will have high osmotic pressures and large swelling forces. The difference in osmotic pressure when these gels contact mucus gels will draw water into the formulation and quickly dehydrate the mucus gel, forcing intermixing and consolidation until equilibrium results.
This mixture of formulation and mucus can increase contact time with the mucous membrane, leading to the consolidation of the adhesive bond. However, the dehydration theory does not apply to solid formulations or highly hydrated forms. | 1 | Biochemistry |
In coordination chemistry, a stability constant (also called formation constant or binding constant) is an equilibrium constant for the formation of a complex in solution. It is a measure of the strength of the interaction between the reagents that come together to form the complex. There are two main kinds of complex: compounds formed by the interaction of a metal ion with a ligand and supramolecular complexes, such as host–guest complexes and complexes of anions. The stability constant(s) provide(s) the information required to calculate the concentration(s) of the complex(es) in solution. There are many areas of application in chemistry, biology and medicine. | 7 | Physical Chemistry |
Selegiline has an oral bioavailability of about 10%, which increases when ingested together with a fatty meal, as the molecule is fat soluble. Selegiline and its metabolites bind extensively to plasma proteins (at a rate of 94%). They cross the blood–brain barrier and enter the brain, where they most concentrated at the thalamus, basal ganglia, midbrain, and cingulate gyrus.
Selegiline is mostly metabolized in the intestines and liver; it and its metabolites are excreted in the urine.
Buccal administration of selegiline results in 5-fold higher bioavailability, more reproducible blood concentration, and produces fewer amphetamine metabolites than the oral tablet form. | 4 | Stereochemistry |
Diazo compounds were first produced by Peter Griess who had discovered a versatile new chemical reaction, as detailed in his 1858 paper "Preliminary notice on the influence of nitrous acid on aminonitro- and aminodinitrophenol." | 0 | Organic Chemistry |
Proline-, glutamic acid- and leucine-rich protein 1 (PELP1) also known as modulator of non-genomic activity of estrogen receptor (MNAR) and transcription factor HMX3 is a protein that in humans is encoded by the PELP1 gene. is a transcriptional corepressor for nuclear receptors such as glucocorticoid receptors and a coactivator for estrogen receptors.
Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) is transcription coregulator and modulates functions of several hormonal receptors and transcription factors. PELP1 plays essential roles in hormonal signaling, cell cycle progression, and ribosomal biogenesis. PELP1 expression is upregulated in several cancers; its deregulation contributes to hormonal therapy resistance and metastasis; therefore, PELP1 represents a novel therapeutic target for many cancers. | 1 | Biochemistry |
Chayen is best known for her invention of novel protein crystallization methods. In 1990, she first published a method of suspending droplets of protein solution and precipitant solutions in low-density paraffin oil to prevent evaporation during the microbatch crystallization process. The microbatch process can be suitable for membrane proteins, which are ordinarily difficult to crystallize. Chayen's method has since been applied towards the analysis of many biomolecules that are relevant to human diseases such as cancer, HIV, diabetes, and heart disease.
In addition to her work on microbatch methods, Chayen invented a novel gel-glass nucleant now known as "Naomis Nucleant." Naomis Nucleant has been used to crystallize more than 20 proteins, the most of any single nucleant. In 2015, she collaborated with Subrayal Reddy at University of Central Lancashire to develop the first non-protein nucleant, a semi-liquid molecularly imprinted polymer designed for high-throughput screening. The nucleant was commercialized as "Chayen Reddy MIP."
Chayen's current research interests include protein crystallization, structural biology, and structural genomics and proteomics. | 1 | Biochemistry |
Atmospheric optics ray tracing codes - this article list codes for light scattering using ray-tracing technique to study atmospheric optics phenomena such as rainbows and halos. Such particles can be large raindrops or hexagonal ice crystals. Such codes are one of many approaches to calculations of light scattering by particles. | 7 | Physical Chemistry |
Hazardous materials are often carried in pipelines and thus their structural integrity is of paramount importance. Corrosion of a pipeline can thus have grave consequences. One of the methods used to control pipeline corrosion is by the use of Fusion bonded epoxy coatings. DCVG is used to monitor it. Impressed current cathodic protection is also used. | 8 | Metallurgy |
The plot reveals whether hydrophobic amino acids are concentrated on one side of the helix, usually with polar or hydrophilic amino acids on the other. This arrangement is common in alpha helices within globular proteins, where one face of the helix is oriented toward the hydrophobic core and one face is oriented toward the solvent-exposed surface. Specific patterns characteristic of protein folds and protein docking motifs are also revealed, as in the identification of leucine zipper dimerization regions and coiled coils. This projection diagram is often called and "Edmundson wheel" after its inventor. | 1 | Biochemistry |
Lysophosphatidylinositol (LPI, lysoPI), or -α-lysophosphatidylinositol, is an endogenous lysophospholipid and endocannabinoid neurotransmitter. LPI, along with its 2-arachidonoyl- derivative, 2-arachidonoyl lysophosphatidylinositol (2-ALPI), have been proposed as the endogenous ligands of GPR55. | 1 | Biochemistry |
Although most experiments use cellular response as a measure of the effect, the effect is, in essence, a result of the binding kinetics; so, in order to illustrate the mechanism, ligand binding is used. A ligand A will bind to a receptor R according to an equilibrium constant :
Although the equilibrium constant is more meaningful, texts often mention its inverse, the affinity constant (K = k/k): A better binding means an increase of binding affinity.
The equation for simple ligand binding to a single homogeneous receptor is
This is the Hill-Langmuir equation, which is practically the Hill equation described for the agonist binding. In chemistry, this relationship is called the Langmuir equation, which describes the adsorption of molecules onto sites of a surface (see adsorption).
is the total number of binding sites, and when the equation is plotted it is the horizontal asymptote to which the plot tends; more binding sites will be occupied as the ligand concentration increases, but there will never be 100% occupancy. The binding affinity is the concentration needed to occupy 50% of the sites; the lower this value is the easier it is for the ligand to occupy the binding site.
The binding of the ligand to the receptor at equilibrium follows the same kinetics as an enzyme at steady-state (Michaelis–Menten equation) without the conversion of the bound substrate to product.
Agonists and antagonists can have various effects on ligand binding. They can change the maximum number of binding sites, the affinity of the ligand to the receptor, both effects together or even more bizarre effects when the system being studied is more intact, such as in tissue samples. (Tissue absorption, desensitization, and other non equilibrium steady-state can be a problem.)
A surmountable drug changes the binding affinity:
* competitive ligand:
* cooperative allosteric ligand:
A nonsurmountable drug changes the maximum binding:
* noncompetitive binding:
* irreversible binding
The Schild regression also can reveal if there are more than one type of receptor and it can show if the experiment was done wrong as the system has not reached equilibrium. <br/> | 1 | Biochemistry |
Chirality is not limited to carbon atoms, though carbon atoms are often centers of chirality due to their ubiquity in organic chemistry. Nitrogen and phosphorus atoms can also form bonds in a tetrahedral configuration. A nitrogen in an amine may be a stereocenter if all three groups attached are different because the electron pair of the amine functions as a fourth group. However, nitrogen inversion, a form of pyramidal inversion, causes racemization which means that both epimers at that nitrogen are present under normal circumstances. Racemization by nitrogen inversion may be restricted (such as quaternary ammonium or phosphonium cations), or slow, which allows the existence of chirality.
Metal atoms with tetrahedral or octahedral geometries may also be chiral due to having different ligands. For the octahedral case, several chiralities are possible. Having three ligands of two types, the ligands may be lined up along the meridian, giving the mer-isomer, or forming a face—the fac isomer. Having three bidentate ligands of only one type gives a propeller-type structure, with two different enantiomers denoted Λ and Δ. | 4 | Stereochemistry |
One example of imbibition in nature is the absorption of water by hydrophilic colloids. Matrix potential contributes significantly to water in such substances. Dry seeds germinate in part by imbibition. Imbibition can also control circadian rhythms in Arabidopsis thaliana and (probably) other plants. The Amott test employs imbibition.
Proteins have high imbibition capacities, so proteinaceous pea seeds swell more than starchy wheat seeds.
Imbibition of water increases imbibant volume, which results in imbibitional pressure (IP). The magnitude of such pressure can be demonstrated by the splitting of rocks by inserting dry wooden stalks in their crevices and soaking them in water, a technique used by early Egyptians to cleave stone blocks.
Skin grafts (split thickness and full thickness) receive oxygenation and nutrition via imbibition, maintaining cellular viability until the processes of inosculation and revascularisation have re-established a new blood supply within these tissues. | 7 | Physical Chemistry |
Force spectroscopy is used in biophysics to measure the mechanical properties of living material (such as tissue or cells) or detect structures of different stiffness buried into the bulk of the sample using the stiffness tomography. Another application was to measure the interaction forces between from one hand a material stuck on the tip of the cantilever, and from another hand the surface of particles either free or occupied by the same material. From the adhesion force distribution curve, a mean value of the forces has been derived. It allowed to make a cartography of the surface of the particles, covered or not by the material. AFM has also been used for mechanically unfolding proteins. In such experiments, the analyzes of the mean unfolding forces with the appropriate model leads to the obtainment of the information about the unfolding rate and free energy profile parameters of the protein. | 6 | Supramolecular Chemistry |
The rate of substrate utilization is related to the specific growth rate as
where
: X is the total biomass (since the specific growth rate μ is normalized to the total biomass),
: Y is the yield coefficient.
r is negative by convention.
In some applications, several terms of the form [S] / (K + [S]) are multiplied together where more than one nutrient or growth factor has the potential to be limiting (e.g. organic matter and oxygen are both necessary to heterotrophic bacteria). When the yield coefficient, being the ratio of mass of microorganisms to mass of substrate utilized, becomes very large, this signifies that there is deficiency of substrate available for utilization. | 7 | Physical Chemistry |
The flow cells are connected to a display and/or recorder. On older systems this was a simple chart recorder, on modern systems a computer with hardware interface and display is used. This permits the experimenter to identify when peaks in protein concentration occur, indicating that specific components of the mixture are being eluted. | 3 | Analytical Chemistry |
Although there were some studies that showed an inverse correlation between serum bilirubin level and prevalences of ischemic coronary artery disease, cancer mortality, or colorectal cancer in general population, the potential benefits of the chemopreventive function of bilirubin and their causative relations haven't been proved. | 1 | Biochemistry |
Polymer melts exhibit different deformation mechanisms when subjected to shear or tensile stresses. For example, a polymer melt’s ductility can increase when a stimulus, such as light, causes fragmentation of the polymer chains through bond breaking. This process is known as chain scission. In the low temperature regime of a polymer melt (T < Tg), crazing or shear banding can occur. The former mechanism resembles crack formation, but this deformation mechanism actually involves the formation of fibrils separated by porous domains or voids. The latter mechanism (shear banding) involves the formation of localized regions of plastic deformation, which typically arise near the position of the maximal shear point in a polymer melt. It is important to note that crazing and shear banding are deformation mechanisms observed in glassy polymers.
For crystalline polymers, the deformation mechanism is best described by a stress-strain curve for a crystalline polymer, such as nylon. The stress-strain behavior exhibits four characteristic regions. The first region is the linear-elastic regime, where the stress-strain behavior is elastic with no plastic deformation. The characteristic deformation mechanism in the second region is yielding, where plastic deformation can occur in the form phenomena such as twinning. The third region shows the formation of a neck, and the fourth region is characterized as a steep increase in stress due to viscous flow. Additionally, region four corresponds to alignment and elongation of the polymer backbone from its coiled or folded state—eventually leading to fracture. | 8 | Metallurgy |
The nature of chemical reactions and their description is one of the most fundamental problems in chemistry. The concepts of covalent and ionic bonds which emerged in the beginning of the 20th century specify the profound differences between their electronic structures. These differences, in turn, lead to dramatically different behavior of covalent and ionic compounds both in the solution and solid phase. In the solid phase, ionic compounds, e.g. salts, are prone to formation of crystal lattices; in polar solvents, they dissociate into ions surrounded by solvate shells, thus rendering the solution highly ionic conductive. In contrast to covalent bonds, ionic interactions demonstrate flexible, dynamic behavior, which allows tuning ionic compounds to obtain desired properties. | 1 | Biochemistry |
The primary commercial use of dimethyl methylphosphonate is as a flame retardant. Other commercial uses are a preignition additive for gasoline, anti-foaming agent, plasticizer, stabilizer, textile conditioner, antistatic agent, and an additive for solvents and low-temperature hydraulic fluids. It can be used as a catalyst and a reagent in organic synthesis, as it can generate a highly reactive ylide. The yearly production in the United States varies between .
About 190 liters of dimethyl methylphosphonate, together with other chemicals, were released during the crash of El Al Flight 1862 at Bijlmer in Amsterdam in 1992. | 1 | Biochemistry |
Generally this topic is discussed when covering tandem mass spectrometry fragmentation and occurs generally by the same mechanisms.
For example, of a mechanism of alpha-cleavage, an electron is knocked off an atom (usually by electron collision) to form a radical cation. Electron removal generally happens in the following order: 1) lone pair electrons, 2) pi bond electrons, 3) sigma bond electrons.
One of the lone pair electrons moves down to form a pi bond with an electron from an adjacent (alpha) bond. The other electron from the bond moves to an adjacent atom (not one adjacent to the lone pair atom) creating a radical. This creates a double bond adjacent to the lone pair atom (oxygen is a good example) and breaks/cleaves the bond from which the two electrons were removed.
In molecules containing carbonyl groups, alpha-cleavage often competes with McLafferty rearrangement. | 0 | Organic Chemistry |
Biuret is also used as a non-protein nitrogen source in ruminant feed, where it is converted into protein by gut microorganisms. It is less favored than urea, due to its higher cost and lower digestibility but the latter characteristic also slows down its digestion and so decreases the risk of ammonia toxicity. | 0 | Organic Chemistry |
The funeral was large. The newspapers carried tributes and subsequently lengthier obituaries from learned societies were published, such as that in the Australian Medical Journal and elsewhere. The Melbourne Leader described the funeral: "The coffin was drawn by four horses. Four mourning coaches contained the chief mourners and the more intimate friends of the deceased gentleman. A large procession followed, in which were several members of Parliament, the members of the Royal Society, the Chief Justice; the Mayor and corporation of the city of Melbourne. A number of private carriages and the public wound up the procession....At the University, the chancellor, the vice-chancellor, and a number of the students, all in their academic robes, met the funeral cortege, and proceeded the remainder of the distance". The chief mourner was his youngest brother, George Robert Macadam (1837-1918). John Macadam's grave, surmounted by a marble obelisk, is in Melbourne General Cemetery. | 3 | Analytical Chemistry |
Convection (or convective heat transfer) is the transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes of conduction (heat diffusion) and advection (heat transfer by bulk fluid flow). Convection is usually the dominant form of heat transfer in liquids and gases.
Note that this definition of convection is only applicable in Heat transfer and thermodynamic contexts. It should not be confused with the dynamic fluid phenomenon of convection, which is typically referred to as Natural Convection in thermodynamic contexts in order to distinguish the two. | 7 | Physical Chemistry |
The mechanistic study of the palladium-catalyzed meta-selective C–H bond activation with a nitrile-containing template was done by Yu, Wu, Houk and their co-workers. The DFT calculations suggest that the regioselectivity is achieved in the C–H activation step, which is the rate-determining step. It proceeds via a concerted metalation-deprotonation (CMD) pathway, which means that palladation and deprotonation of the C–H bond happen at the same time. Surprisingly, calculations reveal that the Pd–Ag heterodimeric transition state leads to meta-selectivity while the Pd monomeric transition state leads to ortho-selectivity.
The role of mono-N-protected amino acid is proposed as a dianionic ligand which participates in the CMD step assisting the deprotonation of the C–H bond in the rate- and regio-determining step. | 0 | Organic Chemistry |
Anion (−) and cation (+) indicate the net electric charge on an ion. An ion that has more electrons than protons, giving it a net negative charge, is named an anion, and a minus indication "Anion (−)" indicates the negative charge. With a cation it is just the opposite: it has fewer electrons than protons, giving it a net positive charge, hence the indication "Cation (+)".
Since the electric charge on a proton is equal in magnitude to the charge on an electron, the net electric charge on an ion is equal to the number of protons in the ion minus the number of electrons.
An (−) ( , from the Greek word ἄνω (ánō), meaning "up") is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged).
A (+) ( , from the Greek word κάτω (káto), meaning "down") is an ion with fewer electrons than protons, giving it a positive charge.
There are additional names used for ions with multiple charges. For example, an ion with a −2 charge is known as a dianion and an ion with a +2 charge is known as a dication. A zwitterion is a neutral molecule with positive and negative charges at different locations within that molecule.
Cations and anions are measured by their ionic radius and they differ in relative size: "Cations are small, most of them less than 10 m (10 cm) in radius. But most anions are large, as is the most common Earth anion, oxygen. From this fact it is apparent that most of the space of a crystal is occupied by the anion and that the cations fit into the spaces between them."
The terms anion and cation (for ions that respectively travel to the anode and cathode during electrolysis) were introduced by Michael Faraday in 1834 following his consultation with William Whewell. | 7 | Physical Chemistry |
Nitric acid has been used in various forms as the oxidizer in liquid-fueled rockets. These forms include red fuming nitric acid, white fuming nitric acid, mixtures with sulfuric acid, and these forms with HF inhibitor. IRFNA (inhibited red fuming nitric acid) was one of three liquid fuel components for the BOMARC missile. | 3 | Analytical Chemistry |
The addition of certain alloying elements, such as manganese and nickel, can stabilize the austenitic structure, facilitating heat-treatment of low-alloy steels. In the extreme case of austenitic stainless steel, much higher alloy content makes this structure stable even at room temperature.
On the other hand, such elements as silicon, molybdenum, and chromium tend to de-stabilize austenite, raising the eutectoid temperature. | 8 | Metallurgy |
Subsets and Splits