text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Bromothymol blue is synthesized by addition of elemental bromine to thymol blue in a solution in glacial acetic acid.
To prepare a solution for use as pH indicator, dissolve 0.10 g in 8.0 cm N/50 (a.k.a. 0.02 Normal) NaOH and dilute with water to 250 cm. To prepare a solution for use as indicator in volumetric work, dissolve 0.1 g in 100 cm of 50% (v/v) ethanol. | 3 | Analytical Chemistry |
Most gilding methods are additive: they deposit gold that was not there before onto the surface of an object. By contrast, depletion gilding is a subtractive process whereby material is removed to increase the purity of gold that is already present on an object's surface.
In depletion gilding, other metals are etched away from the surface of an object composed of a gold alloy by the use of acids or salts, often in combination with heat. Since no gold is added, only an object made of an alloy that already contains gold can be depletion gilded.
Depletion gilding relies on the fact that gold is highly resistant to oxidation or corrosion by most common chemicals, whereas many other metals are not. Depletion gilding is most often used to treat alloys of gold with copper or silver. Unlike gold, both copper and silver readily react with a variety of chemicals. For example, nitric acid is effective as an etching agent for both copper and silver. Under the proper circumstances, even ordinary table salt will react with either metal.
The object to be gilded is coated, immersed, or packed in a suitable acid or salt, and usually heated to speed the process. These chemicals then attack the metallic copper and silver in the objects surface, transforming it to various copper and silver compounds. The resulting copper and silver compounds can be removed from the objects surface by a number of processes. Washing, chemical leaching, heating, or even physical absorption by porous materials such as brick dust have all been used historically. Meanwhile, the relatively inert gold is left unaffected. The result is a thin layer of nearly pure gold on the surface of the original object.
There is no well-defined minimum gold content required to successfully depletion gild an object. However, the less gold that is present, the more other material must be etched away to produce the desired surface appearance. In addition, the removal of the other metals usually leaves the surface covered with microscopic voids and pits. This can make the surface soft and "spongy" with a dull or matte appearance. This effect becomes more pronounced as more base metal is removed. For this reason, most depletion gilded objects are burnished to make their surfaces more durable and give them a more attractive polished finish.
Like other gilding processes, depletion gilding provides a way to produce the appearance of pure gold without its disadvantages: its cost and rarity, and its softness and denseness. By producing a layer of gold over a layer of copper or other metal, objects can be made that are lighter, sturdier, and cheaper while still appearing to be nearly pure gold. | 8 | Metallurgy |
In chemistry, a trigonal pyramid is a molecular geometry with one atom at the apex and three atoms at the corners of a trigonal base, resembling a tetrahedron (not to be confused with the tetrahedral geometry). When all three atoms at the corners are identical, the molecule belongs to point group C. Some molecules and ions with trigonal pyramidal geometry are the pnictogen hydrides (XH), xenon trioxide (XeO), the chlorate ion, , and the sulfite ion, . In organic chemistry, molecules which have a trigonal pyramidal geometry are sometimes described as sp hybridized. The AXE method for VSEPR theory states that the classification is AXE. | 4 | Stereochemistry |
Vapor phase osmometry (VPO), also known as vapor-pressure osmometry, is an experimental technique for the determination of a polymer's number average molecular weight, M. It works by taking advantage of the decrease in vapor pressure that occurs when solutes are added to pure solvent. This technique can be used for polymers with a molecular weight of up to 20,000 though accuracy is best for those below 10,000. Although membrane osmometry is also based on the measurement of colligative properties, it has a lower bound of 25,000 for sample molecular weight that can be measured owing to problems with membrane permeation. | 7 | Physical Chemistry |
Hot-dip galvanizing deposits a thick, robust layer of zinc iron alloys on the surface of a steel item. In the case of automobile bodies, where additional decorative coatings of paint will be applied, a thinner form of galvanizing is applied by electrogalvanizing. The hot-dip process generally does not reduce strength to a measurable degree, with the exception of high-strength steels where hydrogen embrittlement can become a problem.
Thermal diffusion galvanizing, or Sherardizing, provides a zinc diffusion coating on iron- or copper-based materials. | 8 | Metallurgy |
The Mammalian Promoter Database (MPromDb) is a curated database of gene promoters identified from ChIP-seq. The proximal promoter region (upstream of the core-promoter region) contains the cis-regulatory elements of most of the transcription factors (TFs).
Recently, a better approach to annotate active promoters has been demonstrated with a combination of ChIP-seq and computational technique. This technique has been used to find the target genes of TFs in mammalian systems. The MPromDb is based on this technology. Curated promoter sequences for eukaryotic organisms are provided by an EPD database; however, promoter activity information at tissue/ cell centric level is not offered.
The MPromDb data base added active RNAP-II promoters identified after analyzing ten different mouse cell/tissue ChIP-seq experiments performed with RNAP-II antibodies and six different human cell types. The data was acquired by a series of computational methods followed by manual correction to ensure its high level quality. In the newest version of MPromDb, about 507 million uniquely-aligned RNA Pol-II ChIP-seq reads have already been analyzed from 26 different databases, including six human cell-types and 10 distinct mouse cell/tissues. | 1 | Biochemistry |
An overlayer is a layer of adatoms adsorbed onto a surface, for instance onto the surface of a single crystal. | 7 | Physical Chemistry |
Scientists agree that the event that separated myoglobin from hemoglobin occurred after lampreys diverged from jawed vertebrates. This separation of myoglobin and hemoglobin allowed for the different functions of the two molecules to arise and develop: myoglobin has more to do with oxygen storage while hemoglobin is tasked with oxygen transport. The α- and β-like globin genes encode the individual subunits of the protein. The predecessors of these genes arose through another duplication event also after the gnathosome common ancestor derived from jawless fish, approximately 450–500 million years ago. Ancestral reconstruction studies suggest that the preduplication ancestor of the α and β genes was a dimer made up of identical globin subunits, which then evolved to assemble into a tetrameric architecture after the duplication. The development of α and β genes created the potential for hemoglobin to be composed of multiple distinct subunits, a physical composition central to hemoglobins ability to transport oxygen. Having multiple subunits contributes to hemoglobins ability to bind oxygen cooperatively as well as be regulated allosterically. Subsequently, the α gene also underwent a duplication event to form the HBA1 and HBA2 genes. These further duplications and divergences have created a diverse range of α- and β-like globin genes that are regulated so that certain forms occur at different stages of development.
Most ice fish of the family Channichthyidae have lost their hemoglobin genes as an adaptation to cold water. | 7 | Physical Chemistry |
Chloroplast DNAs are circular, and are typically 120,000–170,000 base pairs long. They can have a contour length of around 30–60 micrometers, and have a mass of about 80–130 million daltons.
Most chloroplasts have their entire chloroplast genome combined into a single large ring, though those of dinophyte algae are a notable exception—their genome is broken up into about forty small plasmids, each 2,000–10,000 base pairs long. Each minicircle contains one to three genes, but blank plasmids, with no coding DNA, have also been found.
Chloroplast DNA has long been thought to have a circular structure, but some evidence suggests that chloroplast DNA more commonly takes a linear shape. Over 95% of the chloroplast DNA in corn chloroplasts has been observed to be in branched linear form rather than individual circles. | 5 | Photochemistry |
The replication initiator protein (Rep) plays a key role in initiation of replication in plasmids. In its monomer form, Rep binds an iteron and promotes replication. The protein itself is known to contain two independent N-terminal and C-terminal globular domains that subsequently bind to two domains of the iteron. The dimer version of the protein is generally inactive in iteron binding, however it is known to bind to the repE operator. This operator contains half of the iteron sequence making it able to bind the dimer and promote gene expression.
Plasmids containing iterons are all organized very similarly in structure. The gene for Rep proteins is usually found directly downstream of the origin of replication. This means that the iterons themselves are known to regulate the synthesis of the rep proteins. | 1 | Biochemistry |
In molecular biology, a reporter gene (often simply reporter) is a gene that researchers attach to a regulatory sequence of another gene of interest in bacteria, cell culture, animals or plants. Such genes are called reporters because the characteristics they confer on organisms expressing them are easily identified and measured, or because they are selectable markers. Reporter genes are often used as an indication of whether a certain gene has been taken up by or expressed in the cell or organism population. | 1 | Biochemistry |
In the 1970s, the Chesapeake Bay was found to contain one of the planets first identified marine dead zones, where waters were so depleted of oxygen that they were unable to support life, resulting in massive fish kills. In 2010 the bays dead zones were estimated to kill 75,000 tons of bottom-dwelling clams and worms each year, weakening the base of the estuary's food chain and robbing the blue crab in particular of a primary food source. Crabs are sometimes observed to amass on shore to escape pockets of oxygen-poor water, a behavior known as a "crab jubilee". Hypoxia results in part from large algal blooms, which are nourished by the runoff of residential, farm and industrial waste throughout the watershed. A 2010 report criticized Amish farmers in Pennsylvania for raising cows with inadequate controls on the manure that they generate. Farms in Lancaster County, Pennsylvania generate large quantities of manure that washes into tributaries of the bay.
The pollution entering the bay has multiple components that contribute to algal blooms, principally the nutrients phosphorus and nitrogen. The algae prevents sunlight from reaching the bottom of the bay while alive and deoxygenates the bays water when it dies and rots. Soil erosion and runoff of sediment into the bay, exacerbated by devegetation, construction and the prevalence of pavement in urban and suburban areas, also block vital sunlight. The resulting loss of aquatic vegetation has depleted the habitat for much of the bays animal life. Beds of eelgrass, the dominant variety in the southern Chesapeake Bay, have shrunk by more than half there since the early 1970s. Overharvesting, pollution, sedimentation and disease have turned much of the bay's bottom into a muddy wasteland.
The principal sources of nutrient pollution in the bay are surface runoff from farms, as well as runoff from urban and suburban areas. About half of the nutrient pollutant loads in the bay are generated by manure and poultry litter. Extensive use of lawn fertilizers and air pollution from motor vehicles and power plants are also significant nutrient sources.
One particularly harmful source of toxicity is Pfiesteria piscicida, which can affect both fish and humans. Pfiesteria caused a small regional panic in the late 1990s when a series of large blooms started killing large numbers of fish while giving swimmers mysterious rashes; nutrient runoff from chicken farms was blamed for the growth. | 2 | Environmental Chemistry |
Supercritical water can be used to decompose biomass via Supercritical Water Gasification of biomass. This type of biomass gasification can be used to produce hydrocarbon fuels for use in an efficient combustion device or to produce hydrogen for use in a fuel cell. In the latter case, hydrogen yield can be much higher than the hydrogen content of the biomass due to steam reforming where water is a hydrogen-providing participant in the overall reaction. | 7 | Physical Chemistry |
It is the similar to the bacterial code (translation table 11) but it contains an additional stop codon (TTA) and also has a different set of start codons. | 1 | Biochemistry |
Sulfonyl chlorides react with water to give the corresponding sulfonic acid:
These compounds react readily with many other nucleophiles as well, most notably alcohols and amines (see Hinsberg reaction). If the nucleophile is an alcohol, the product is a sulfonate ester; if it is an amine, the product is a sulfonamide. Using sodium sulfite as the nucleophilic reagent, p-toluenesulfonyl chloride is converted to its sulfinate salt, . Chlorosulfonated alkanes are susceptible to crosslinking via reactions with various nucleophiles.
Sulfonyl chlorides readily undergo Friedel–Crafts reactions with arenes giving sulfones, for example:
The desulfonation of arylsulfonyl chlorides provides a route to aryl chlorides:
1,2,4-Trichlorobenzene is made industrially in this way.
Treatment of alkanesulfonyl chlorides having α-hydrogens with amine bases can give sulfenes, highly unstable species that can be trapped:
Sulfonamides can be prepared by reaction of sulfonyl chlorides with amines:
A readily available sulfonyl chloride source is tosyl chloride.
Reduction with tetrathiotungstate ions () induces dimerization to the disulfide. | 0 | Organic Chemistry |
Lethal synthesis, or suicide metabolism, is the biosynthesis of a toxin from a precursor which is not itself toxic, such as the synthesis of fluorocitrate from fluoroacetate or the synthesis of methylglyoxal from glycerol.
The term was first publicised by Rudolph Peters in his Croonian Lecture of 1951. | 1 | Biochemistry |
In China, the Ministry of Health and the Ministry of Agriculture have jointly established mechanisms and working procedures relating to maximum residue limit standards, while updating them continuously, according to the food safety law and regulations issued by the State Council. From GB25193-2010 to GB28260-2011, from Maximum Residue Limits for 12 Pesticides to 85 pesticides, they have improved the standards in response to Chinese national needs. | 2 | Environmental Chemistry |
The semiconductor material gallium arsenide (GaAs) is also used for single-crystalline thin film solar cells. Although GaAs cells are very expensive, they hold the world's record in efficiency for a single-junction solar cell at 28.8%. Typically fabricated on crystalline silicon wafer with a 41% fill factor, by moving to porous silicon fill factor can be increased to 56% with potentially reduced cost. Using less active GaAs material by fabricating nanowires is another potential pathway to cost reduction. GaAs is more commonly used in multijunction photovoltaic cells for concentrated photovoltaics (CPV, HCPV) and for solar panels on spacecraft, as the industry favours efficiency over cost for space-based solar power. Based on the previous literature and some theoretical analysis, there are several reasons why GaAs has such high power conversion efficiency. First, GaAs bandgap is 1.43ev which is almost ideal for solar cells. Second, because Gallium is a by-product of the smelting of other metals, GaAs cells are relatively insensitive to heat and it can keep high efficiency when temperature is quite high. Third, GaAs has the wide range of design options. Using GaAs as active layer in solar cell, engineers can have multiple choices of other layers which can better generate electrons and holes in GaAs. | 7 | Physical Chemistry |
The Merrill–Crowe Process is a separation technique for removing gold from the solution obtained by the cyanide leaching of gold ores. It is an improvement of the MacArthur-Forrest process, where an additional vacuum is managed to remove air in the solution (invention of Crowe), and zinc dust is used instead of zinc shavings (improvement of Merrill).
The solution is separated from the ore by methods such as filtration (e.g. vertical leaf type clarifier filters) and counter current decantation (CCD). Afterwards a very clear solution is achieved by using pre-coated filters applying diatomaceous earth. Oxygen is then removed by passing the solution through a vacuum de-aeration column. Zinc dust is added to the clarified, de-aerated solution which precipitates the gold; zinc having a higher affinity for the cyanide ion than gold. Other precious metals, silver, and base metals, like copper, will also precipitate, if present.
Automated membrane filtration offers a cost savings alternative to CCD. Both applications are compared in detail by [http://www.tonsperhour.com/wp-content/uploads/Kent-McGrew_CCD-vs-AFP_Final.pdf K. McGrew, 2016.]
The gold precipitate (mixed with zinc dust) is then filtered out of the solution, and the zinc dust and gold are mixed with sulfuric acid to dissolve the zinc. The solution is filtered, and the remaining solids are smelted to a gold dore bar. These bars are sent to a refinery to remove the copper and silver, the specific process used depending upon the impurities in the gold.
The basic process was discovered and patented by Charles Washington Merrill around 1900, and later refined by Thomas Bennett Crowe, working for the Merrill Company. | 8 | Metallurgy |
The hexapede (Yerik in Navi) are hexapodal deer-like creatures. They are dark blue herbivores with white and yellow stripes. Twin horn structures sheathe a thin, patterned membrane structure. Their small, sloped skull is topped by this light-colored fan structure. This fan has an eye pattern on it similar to those found in actual insects. A skin membrane hangs under the jaw and runs the length of the neck. Twin lines of dark hairlike bristles run down the hexapedes back. The antennae are at the back at the head. As a threat display, the hexapede flares up its twin membrane structure like a satellite dish and retracts both lips. It is scientifically known as Sexcruscervus caeruleus. | 1 | Biochemistry |
4-Nitrophenol (also called p-nitrophenol or 4-hydroxynitrobenzene) is a phenolic compound that has a nitro group at the opposite position of the hydroxyl group on the benzene ring. | 3 | Analytical Chemistry |
An enhancer near the gene GADD45g has been described that may regulate brain growth in chimpanzees and other mammals, but not in humans. The GADD45G regulator in mice and chimps is active in regions of the brain where cells that form the cortex, ventral forebrain, and thalamus are located and may suppress further neurogenesis. Loss of the GADD45G enhancer in humans may contribute to an increase of certain neuronal populations and to forebrain expansion in humans. | 1 | Biochemistry |
* Ligand-gated ion channels such as the nicotinic acetylcholine receptor and GABA receptor are composed of five subunits arranged around a central pore that opens to allow ions to pass through. There are many different subunits available that can come together in a wide variety of combinations to form different subtypes of the ion channel. Sometimes the channel can be made from only one type of subunit, such as the α7 nicotinic receptor, which is made up from five α7 subunits, and so is a [http://en.wiktionary.org/wiki/homomer homomer] rather than a heteromer, but more commonly several different types of subunit will come together to form a heteromeric complex (e.g., the α4β2 nicotinic receptor, which is made up from two α4 subunits and three β2 subunits). Because the different ion channel subtypes are expressed to different extents in different tissues, this allows selective modulation of ion transport and means that a single neurotransmitter can produce varying effects depending on where in the body it is released.
* G protein-coupled receptors are composed of seven membrane-spanning alpha-helical segments that are usually linked together into a single folded chain to form the receptor complex. However, research has demonstrated that a number of GPCRs are also capable of forming heteromers from a combination of two or more individual GPCR subunits under some circumstances, especially where several different GPCRs are densely expressed in the same neuron. Such heteromers may be between receptors from the same family (e.g., adenosine A/A heteromers and dopamine D/D and D/D heteromers) or between entirely unrelated receptors such as CB/A, glutamate mGluR / adenosine A heteromers, cannabinoid CB / dopamine D heteromers, and even CB/A/D heterotrimers where three different receptors have come together to form a heteromer. The ligand binding properties and intracellular trafficking pathways of GPCR heteromers usually show elements from both parent receptors, but may also produce quite unexpected pharmacological effects, making such heteromers an important focus of current research. | 1 | Biochemistry |
Cyanate is an ambidentate ligand which can donate the pair of electrons on the nitrogen atom or the oxygen atom, or both. Structurally the isomers can be distinguished by the geometry of the complex. In N-bonded cyanate complexes the M−NCO unit sometimes has a linear structure, but with O-bonded cyanate the M−O−C unit is bent. Thus, the silver cyanato complex, , has a linear structure as shown by X-ray crystallography. However, the crystal structure of silver cyanate shows zigzag chains of nitrogen atoms and silver atoms. There also exists a structure
NCO
Ni Ni
OCN
in which the Ni-N-C group is bent.
Infrared spectroscopy has been used extensively to distinguish between isomers. Many complexes of divalent metals are N-bonded. O-Bonding has been suggested for complexes of the type , M = Mo(III), Re(IV), and Re(V). The yellow complex and orange complex are linkage isomers and show differences in their infrared spectra which can be used for diagnosis.
The cyanate ion can bridge between two metal atoms by using both its donor atoms. For example, this structure is found in the compound . In this compound both the Ni−N−C unit and Ni−O−C unit are bent, even though in the first case donation is through the nitrogen atom. | 0 | Organic Chemistry |
The Paschen–Back effect is the splitting of atomic energy levels in the presence of a strong magnetic field. This occurs when an external magnetic field is sufficiently strong to disrupt the coupling between orbital () and spin () angular momenta. This effect is the strong-field limit of the Zeeman effect. When , the two effects are equivalent. The effect was named after the German physicists Friedrich Paschen and Ernst E. A. Back.
When the magnetic-field perturbation significantly exceeds the spin–orbit interaction, one can safely assume . This allows the expectation values of and to be easily evaluated for a state . The energies are simply
The above may be read as implying that the LS-coupling is completely broken by the external field. However and are still "good" quantum numbers. Together with the selection rules for an electric dipole transition, i.e., this allows to ignore the spin degree of freedom altogether. As a result, only three spectral lines will be visible, corresponding to the selection rule. The splitting is independent of the unperturbed energies and electronic configurations of the levels being considered.
More precisely, if , each of these three components is actually a group of several transitions due to the residual spin–orbit coupling and relativistic corrections (which are of the same order, known as fine structure). The first-order perturbation theory with these corrections yields the following formula for the hydrogen atom in the Paschen–Back limit: | 7 | Physical Chemistry |
Philippe Gengembre (1764–1838), a student of Lavoisier, first obtained phosphine in 1783 by heating white phosphorus in an aqueous solution of potash (potassium carbonate).
Perhaps because of its strong association with elemental phosphorus, phosphine was once regarded as a gaseous form of the element, but Lavoisier (1789) recognised it as a combination of phosphorus with hydrogen and described it as phosphure dhydrogène' (phosphide of hydrogen).
In 1844, Paul Thénard, son of the French chemist Louis Jacques Thénard, used a cold trap to separate diphosphine from phosphine that had been generated from calcium phosphide, thereby demonstrating that is responsible for spontaneous flammability associated with , and also for the characteristic orange/brown color that can form on surfaces, which is a polymerisation product. He considered diphosphine's formula to be , and thus an intermediate between elemental phosphorus, the higher polymers, and phosphine. Calcium phosphide (nominally ) produces more than other phosphides because of the preponderance of P-P bonds in the starting material.
The name "phosphine" was first used for organophosphorus compounds in 1857, being analogous to organic amines (). The gas was named "phosphine" by 1865 (or earlier). | 0 | Organic Chemistry |
Partially hydrolysed potato starch makes for another non-toxic medium for protein electrophoresis. The gels are slightly more opaque than acrylamide or agarose. Non-denatured proteins can be separated according to charge and size. They are visualised using Napthal Black or Amido Black staining. Typical starch gel concentrations are 5% to 10%. | 1 | Biochemistry |
Single-crystal superalloys (SX or SC superalloys) are formed as a single crystal using a modified version of the directional solidification technique, leaving no grain boundaries. The mechanical properties of most other alloys depend on the presence of grain boundaries, but at high temperatures, they participate in creep and require other mechanisms. In many such alloys, islands of an ordered intermetallic phase sit in a matrix of disordered phase, all with the same crystal lattice. This approximates the dislocation-pinning behavior of grain boundaries, without introducing any amorphous solid into the structure.
Single crystal (SX) superalloys have wide application in the high-pressure turbine section of aero- and industrial gas turbine engines due to the unique combination of properties and performance. Since introduction of single crystal casting technology, SX alloy development has focused on increased temperature capability, and major improvements in alloy performance are associated with rhenium (Re) and ruthenium (Ru).
The creep deformation behavior of superalloy single crystal is strongly temperature-, stress-, orientation- and alloy-dependent. For a single-crystal superalloy, three modes of creep deformation occur under regimes of different temperature and stress: rafting, tertiary, and primary. At low temperature (~750 °C), SX alloys exhibits mostly primary creep behavior. Matan et al. concluded that the extent of primary creep deformation depends strongly on the angle between the tensile axis and the <001>/<011> symmetry boundary. At temperatures above 850 °C, tertiary creep dominates and promotes strain softening behavior. When temperature exceeds 1000 °C, the rafting effect is prevalent where cubic particles transform into flat shapes under tensile stress. The rafts form perpendicular to the tensile axis, since γ phase is transported out of the vertical channels and into the horizontal ones. Reed et al. studied unaxial creep deformation of <001> oriented CMSX-4 single crystal superalloy at 1105 °C and 100 MPa. They reported that rafting is beneficial to creep life since it delays evolution of creep strain. In addition, rafting occurs quickly and suppresses the accumulation of creep strain until a critical strain is reached. | 8 | Metallurgy |
There is a fairly large variation in the types of inorganic substrates that these microorganisms can use to produce energy. Sulfur is one of many inorganic substrates that can be used in different reduced forms depending on the specific biochemical process that a lithotroph uses. The chemolithotrophs that are best documented are aerobic respirers, meaning that they use oxygen in their metabolic process. The list of these microorganisms that employ anaerobic respiration though is growing. At the heart of this metabolic process is an electron transport system that is similar to that of chemoorganotrophs. The major difference between these two microorganisms is that chemolithotrophs directly provide electrons to the electron transport chain, while chemoorganotrophs must generate their own cellular reducing power by oxidizing reduced organic compounds. Chemolithotrophs bypass this by obtaining their reducing power directly from the inorganic substrate or by the reverse electron transport reaction. Certain specialized chemolithotrophic bacteria use different derivatives of the Sox system; a central pathway specific to sulfur oxidation. This ancient and unique pathway illustrates the power that chemolithotrophs have evolved to use from inorganic substrates, such as sulfur.
In chemolithotrophs, the compounds - the electron donors - are oxidized in the cell, and the electrons are channeled into respiratory chains, ultimately producing ATP. The electron acceptor can be oxygen (in aerobic bacteria), but a variety of other electron acceptors, organic and inorganic, are also used by various species. Aerobic bacteria such as the nitrifying bacteria, Nitrobacter, use oxygen to oxidize nitrite to nitrate. Some lithotrophs produce organic compounds from carbon dioxide in a process called chemosynthesis, much as plants do in photosynthesis. Plants use energy from sunlight to drive carbon dioxide fixation, but chemosynthesis can take place in the absence of sunlight (e.g., around a hydrothermal vent). Ecosystems establish in and around hydrothermal vents as the abundance of inorganic substances, namely hydrogen, are constantly being supplied via magma in pockets below the sea floor. Other lithotrophs are able to directly use inorganic substances, e.g., ferrous iron, hydrogen sulfide, elemental sulfur, thiosulfate, or ammonia, for some or all of their energy needs.
Here are a few examples of chemolithotrophic pathways, any of which may use oxygen or nitrate as electron acceptors: | 1 | Biochemistry |
In the determination of hypochlorite (for example in commercial bleach formulations), a direct titration with thiosulfate can be employed without recourse to an iodometric finish.
: ClO + HO + 2e ↔ Cl + 2OH
: O ↔ SO + 2e </u>
: 2SO +ClO +HO ↔ SO +Cl +2OH
Thermometric iodometric titrations employing thiosulfate as a titrant are also practical, for example in the determination of Cu(II). In this instance, it has been found advantageous to incorporate the potassium iodide reagent with the thiosulfate titrant in such proportions that iodine is released into solution just prior to its reduction by thiosulfate. This minimizes iodine losses during the course of the titration. | 3 | Analytical Chemistry |
The Society for Cryobiology is an international scientific society that was founded in 1964. Its objectives are to promote research in low temperature biology, to improve scientific understanding in this field, and to disseminate and aid in the application of this knowledge. The Society also publishes a journal called Cryobiology.
The society has hosted 60 annual meetings to date, with the 2024 annual meeting being held in Washington. The three-day event will host over 350 delegates from more than 35 countries. | 1 | Biochemistry |
Between 1920 and 1930 fundamental concepts of quantum mechanics were developed by Pauli, Heisenberg, Schrödinger, and Dirac. Understanding of the spin and exclusion principle allowed conceiving how electron shells of atoms are filled with the increasing atomic number. | 7 | Physical Chemistry |
Unlike a du Noüy ring, no correction factors are required when calculating surface tensions. Due to its small size the rod can be used in high throughput instruments that use a 96-well plate to determine the surface tension. The small diameter of the rod allows its use in a small volume of liquid with 50 l samples being used in some devices.
In addition, the rod also allows use for the Wilhelmy method because the rod is not completely removed during measurements. For this the dynamic surface tension can be used for accurate determination of surface kinetics on a wide range of timescales.
The Padday technique also offers low operator variance and does not need an anti-vibration table. This advantage over other devices allows the Padday devices to be used in the field easily. The rod when made of composite material is also less likely to bend and therefore cheaper than the more costly platinum rod offered in the du Noüy method.
In a typical experiment, the rod is lowered using a manual or automatic device to the surface being analyzed until a meniscus is formed, and then raised so that the bottom edge of the rod lies on the plane of the undisturbed surface. One disadvantage of this technique is that it can not bury the rod into the surface to measure interfacial tension between two liquids. | 7 | Physical Chemistry |
Drospirenone is an antagonist of the AR, the biological target of androgens like testosterone and dihydrotestosterone (DHT). It has about 1 to 65% of the affinity of the synthetic anabolic steroid metribolone for the AR. The medication is more potent as an antiandrogen than spironolactone, but is less potent than cyproterone acetate, with about 30% of its antiandrogenic activity in animals. Progesterone displays antiandrogenic activity in some assays similarly to drospirenone, although this issue is controversial and many researchers regard progesterone as having no significant antiandrogenic activity.
Drospirenone shows antiandrogenic effects on the serum lipid profile, including higher HDL cholesterol and triglyceride levels and lower LDL cholesterol levels, at a dose of 3 mg/day in women. The medication does not inhibit the effects of ethinylestradiol on sex hormone-binding globulin (SHBG) and serum lipids, in contrast to androgenic progestins like levonorgestrel but similarly to other antiandrogenic progestins like cyproterone acetate. SHBG levels are significantly higher with ethinylestradiol and cyproterone acetate than with ethinylestradiol and drospirenone, owing to the more potent antiandrogenic activity of cyproterone acetate relative to drospirenone. Androgenic progestins like levonorgestrel have been found to inhibit the procoagulatory effects of estrogens like ethinylestradiol on hepatic synthesis of coagulation factors, whereas this may occur less or not at all with weakly androgenic progestins like desogestrel and antiandrogenic progestins like drospirenone. | 4 | Stereochemistry |
The nonlinear nature of ferroelectric materials can be used to make capacitors with adjustable capacitance. Typically, a ferroelectric capacitor simply consists of a pair of electrodes sandwiching a layer of ferroelectric material. The permittivity of ferroelectrics is not only adjustable but commonly also very high, especially when close to the phase transition temperature. Because of this, ferroelectric capacitors are small in physical size compared to dielectric (non-tunable) capacitors of similar capacitance.
The spontaneous polarization of ferroelectric materials implies a hysteresis effect which can be used as a memory function, and ferroelectric capacitors are indeed used to make ferroelectric RAM for computers and RFID cards. In these applications thin films of ferroelectric materials are typically used, as this allows the field required to switch the polarization to be achieved with a moderate voltage. However, when using thin films a great deal of attention needs to be paid to the interfaces, electrodes and sample quality for devices to work reliably.
Ferroelectric materials are required by symmetry considerations to be also piezoelectric and pyroelectric. The combined properties of memory, piezoelectricity, and pyroelectricity make ferroelectric capacitors very useful, e.g. for sensor applications. Ferroelectric capacitors are used in medical ultrasound machines (the capacitors generate and then listen for the ultrasound ping used to image the internal organs of a body), high quality infrared cameras (the infrared image is projected onto a two dimensional array of ferroelectric capacitors capable of detecting temperature differences as small as millionths of a degree Celsius), fire sensors, sonar, vibration sensors, and even fuel injectors on diesel engines.
Another idea of recent interest is the ferroelectric tunnel junction (FTJ) in which a contact is made up by nanometer-thick ferroelectric film placed between metal electrodes. The thickness of the ferroelectric layer is small enough to allow tunneling of electrons. The piezoelectric and interface effects as well as the depolarization field may lead to a giant electroresistance (GER) switching effect.
Yet another burgeoning application is multiferroics, where researchers are looking for ways to couple magnetic and ferroelectric ordering within a material or heterostructure; there are several recent reviews on this topic.
Catalytic properties of ferroelectrics have been studied since 1952 when Parravano observed anomalies in CO oxidation rates over ferroelectric sodium and potassium niobates near the Curie temperature of these materials. Surface-perpendicular component of the ferroelectric polarization can dope polarization-dependent charges on surfaces of ferroelectric materials, changing their chemistry. This opens the possibility of performing catalysis beyond the limits of the Sabatier principle. Sabatier principle states that the surface-adsorbates interaction has to be an optimal amount: not too weak to be inert toward the reactants and not too strong to poison the surface and avoid desorption of the products: a compromise situation. This set of optimum interactions is usually referred to as "top of the volcano" in activity volcano plots. On the other hand, ferroelectric polarization-dependent chemistry can offer the possibility of switching the surface—adsorbates interaction from strong adsorption to strong desorption, thus a compromise between desorption and adsorption is no longer needed. Ferroelectric polarization can also act as an energy harvester. Polarization can help the separation of photo-generated electron-hole pairs, leading to enhanced photocatalysis. Also, due to pyroelectric and piezoelectric effects under varying temperature (heating/cooling cycles) or varying strain (vibrations) conditions extra charges can appear on the surface and drive various (electro)chemical reactions forward.
Photoferroelectric imaging is a technique to record optical information on pieces of ferroelectric material. The images are nonvolatile and selectively erasable. | 7 | Physical Chemistry |
In 1984, a retrovirus vector system was designed that could efficiently insert foreign genes into mammalian chromosomes. | 1 | Biochemistry |
In ene-yne activation, the least common of the five modes, a single metal species coordinates with the enol alkene and the tethered alkyne, simultaneously activating both moieties for reaction. Nickel, cobalt, and rhenium complexes have all been employed in this manner. A representative example was reported by Malacria et al. in 1994, in which an alkynyl substituted β-ketoester was treated with cyclopentadienyl cobalt complex and irradiation to give disubstituted methylene cyclopentane. | 0 | Organic Chemistry |
Nitrification is the process by which ammonia () is converted to nitrate (). Nitrification is actually the net result of two distinct processes: oxidation of ammonia to nitrite () by nitrosifying bacteria (e.g. Nitrosomonas) and oxidation of nitrite to nitrate by the nitrite-oxidizing bacteria (e.g. Nitrobacter). Both of these processes are extremely energetically poor leading to very slow growth rates for both types of organisms. Biochemically, ammonia oxidation occurs by the stepwise oxidation of ammonia to hydroxylamine () by the enzyme ammonia monooxygenase in the cytoplasm, followed by the oxidation of hydroxylamine to nitrite by the enzyme hydroxylamine oxidoreductase in the periplasm.
Electron and proton cycling are very complex but as a net result only one proton is translocated across the membrane per molecule of ammonia oxidized. Nitrite oxidation is much simpler, with nitrite being oxidized by the enzyme nitrite oxidoreductase coupled to proton translocation by a very short electron transport chain, again leading to very low growth rates for these organisms. Oxygen is required in both ammonia and nitrite oxidation, meaning that both nitrosifying and nitrite-oxidizing bacteria are aerobes. As in sulfur and iron oxidation, NADH for carbon dioxide fixation using the Calvin cycle is generated by reverse electron flow, thereby placing a further metabolic burden on an already energy-poor process.
In 2015, two groups independently showed the microbial genus Nitrospira is capable of complete nitrification (Comammox). | 1 | Biochemistry |
These are liquid solutions of one or more organic scintillators in an organic solvent. The typical solutes are fluors such as p-terphenyl (), PBD (), butyl PBD (), PPO (), and wavelength shifter such as POPOP (). The most widely used solvents are toluene, xylene, benzene, phenylcyclohexane, triethylbenzene, and decalin. Liquid scintillators are easily loaded with other additives such as wavelength shifters to match the spectral sensitivity range of a particular PMT, or B to increase the neutron detection efficiency of the scintillation counter itself (since B has a high interaction cross section with thermal neutrons). Newer approaches combine several solvents or load different metals to achieve identification of incident particles. For many liquids, dissolved oxygen can act as a quenching agent and lead to reduced light output, hence the necessity to seal the solution in an oxygen-free, airtight enclosure. | 5 | Photochemistry |
Pheromone traps are very sensitive, meaning they attract insects present at very low densities. They are often used to detect presence of exotic pests, or for sampling, monitoring, or to determine the first appearance of a pest in an area. They can be used for legal control, and are used to monitor the success of the Boll Weevil Eradication Program and the spread of the spongy moth. The high species-specificity of pheromone traps can also be an advantage, and they tend to be inexpensive and easy to implement. This sensitivity is especially suited to some investigations of invasive species: Flying males are easily blown off course by winds. Rather than introducing noise, Frank et al 2013 find this can actually help detect isolated nests or populations and determine the length of time necessary between introduction and establishment. (Although any trap can answer the same questions, high sensitivity such as provided by pheromone traps does so more accurately.)
However, it is impractical in most cases to completely remove or "trap out" pests using a pheromone trap. Some pheromone-based pest control methods have been successful, usually those designed to protect enclosed areas such as households or storage facilities. There has also been some success in mating disruption. In one form of mating disruption, males are attracted to a powder containing female attractant pheromones. The pheromones stick to the males' bodies, and when they fly off, the pheromones make them attractive to other males. It is hoped that if enough males chase other males instead of females, egg-laying will be severely impeded.
Some difficulties surrounding pheromone traps include sensitivity to bad weather, their ability to attract pests from neighboring areas, and that they generally only attract adults, although it is the juveniles in many species that are pests. They are also generally limited to one sex. | 1 | Biochemistry |
There are two types. One uses semiconductor, or less efficient metal, i.e. thermocouples, working on the principles of the Peltier-Seebeck effect. The other relies on vacuum tubes and the principles of thermionic emission. | 7 | Physical Chemistry |
Partition equilibrium is a special case of chemical equilibrium wherein one or more solutes are in equilibrium between two immiscible solvents. The most common chemical equilibrium systems involve reactants and products in the same phase - either all gases or all solutions. However, it is also possible to get equilibria between substances in different phases, such a liquid and gas that do not mix (are immiscible). One example is gas-liquid partition equilibrium chromatography, where an analyte equilibrates between a gas and liquid phase. Partition equilibria are described by Nernst's distribution law. Partition equilibrium are most commonly seen and used for Liquid–liquid extraction.
The time until a partition equilibrium emerges is influenced by many factors, such as: temperature, relative concentrations, surface area of interface, degree of stirring, and the nature of the solvents and solute. | 7 | Physical Chemistry |
A large-scale application of carbenes is the industrial production of tetrafluoroethylene, the precursor to Teflon. Tetrafluoroethylene is generated via the intermediacy of difluorocarbene:
: CHClF → CF + HCl
:2 CF → FC=CF
The insertion of carbenes into C–H bonds has been exploited widely, e.g. the functionalization of polymeric materials and electro-curing of adhesives. Many applications rely on synthetic 3-aryl-3-trifluoromethyldiazirines (a carbene precursor that can be activated by heat, light, or voltage) but there is a whole family of carbene dyes. | 0 | Organic Chemistry |
Because of the risk of small-bowel lesions, the US FDA requires some potassium salts (for example potassium chloride) containing more than 99 mg (about 1.3 mEq) to be labeled with a warning. | 1 | Biochemistry |
Stainless steel is one of the most commonly used metals in many industries. Solid solution strengthening of steel is one of the mechanisms used to enhance the properties of the alloy. Austenitic steels mainly contain chromium, nickel, molybdenum, and manganese. It is being used mostly for cookware, kitchen equipment, and in marine applications for its good corrosion properties in saline environments. | 8 | Metallurgy |
The following derivation is adapted from Foundations of Chemical Kinetics.
This derivation assumes the reaction . Consider a sphere of radius , centered at a spherical molecule A, with reactant B flowing in and out of it. A reaction is considered to occur if molecules A and B touch, that is, when the distance between the two molecules is apart.
If we assume a local steady state, then the rate at which B reaches is the limiting factor and balances the reaction.
Therefore, the steady state condition becomes
where
is the flux of B, as given by Fick's law of diffusion,
where is the diffusion coefficient and can be obtained by the Stokes-Einstein equation, and the second term is the gradient of the chemical potential with respect to position. Note that [B] refers to the average concentration of B in the solution, while [B](r) is the "local concentration" of B at position r.
Inserting 2 into 1 results in
It is convenient at this point to use the identity
allowing us to rewrite 3 as
Rearranging 4 allows us to write
Using the boundary conditions that , ie the local concentration of B approaches that of the solution at large distances, and consequently , as , we can solve 5 by separation of variables, we get
or
7. <math> \frac{k[B]}{4\pi D_{AB}\beta }=
[B]-[B](R_{AB})\exp(U(R_{AB})/k_{B}T ) )
For the reaction between A and B, there is an inherent reaction constant , so . Substituting this into 7 and rearranging yields | 7 | Physical Chemistry |
There may be leftover embryos or eggs from IVF procedures if the person for whom they were originally created has successfully carried one or more pregnancies to term, and no longer wishes to use them. With the patient's permission, these may be donated to help others conceive by means of third party reproduction.
In embryo donation, these extra embryos are given to others for transfer, with the goal of producing a successful pregnancy. Embryo recipients have genetic issues or poor-quality embryos or eggs of their own. The resulting child is considered the child of whoever birthed them, and not the child of the donor, the same as occurs with egg donation or sperm donation. As per The National Infertility Association, typically, genetic parents donate the eggs or embryos to a fertility clinic where they are preserved by oocyte cryopreservation or embryo cryopreservation until a carrier is found for them. The process of matching the donation with the prospective parents is conducted by the agency itself, at which time the clinic transfers ownership of the embryos to the prospective parent(s).
Alternatives to donating unused embryos are destroying them (or having them transferred at a time when pregnancy is very unlikely), keeping them frozen indefinitely, or donating them for use in research (rendering them non-viable). Individual moral views on disposing of leftover embryos may depend on personal views on the beginning of human personhood and the definition and/or value of potential future persons, and on the value that is given to fundamental research questions. Some people believe donation of leftover embryos for research is a good alternative to discarding the embryos when patients receive proper, honest and clear information about the research project, the procedures and the scientific values.
During the embryo selection and transfer phases, many embryos may be discarded in favour of others. This selection may be based on criteria such as genetic disorders or the sex. One of the earliest cases of special gene selection through IVF was the case of the Collins family in the 1990s, who selected the sex of their child.
The ethic issues remain unresolved as no worldwide consensus exists in science, religion, and philosophy on when a human embryo should be recognised as a person. For those who believe that this is at the moment of conception, IVF becomes a moral question when multiple eggs are fertilised, begin development, and only a few are chosen for uterus transfer.
If IVF were to involve the fertilisation of only a single egg, or at least only the number that will be transferred, then this would not be an issue. However, this has the chance of increasing costs dramatically as only a few eggs can be attempted at a time. As a result, the couple must decide what to do with these extra embryos. Depending on their view of the embryo's humanity or the chance the couple will want to try to have another child, the couple has multiple options for dealing with these extra embryos. Couples can choose to keep them frozen, donate them to other infertile couples, thaw them, or donate them to medical research. Keeping them frozen costs money, donating them does not ensure they will survive, thawing them renders them immediately unviable, and medical research results in their termination. In the realm of medical research, the couple is not necessarily told what the embryos will be used for, and as a result, some can be used in stem cell research.
In February 2024, the Alabama Supreme Court ruled in LePage v. Center for Reproductive Medicine that cryopreserved embryos were "persons" or "extrauterine children". After Dobbs v. Jackson Women's Health Organization (2022), some antiabortionists had hoped to get a judgement that fetuses and embryos were "person[s]". | 1 | Biochemistry |
Most of the calculations above are exact at zero temperature, yet remain as good approximations for temperatures lower than the Fermi temperature. For other thermodynamics variables it is necessary to write a thermodynamic potential. For an ensemble of identical fermions, the best way to derive a potential is from the grand canonical ensemble with fixed temperature, volume and chemical potential µ. The reason is due to Pauli exclusion principle, as the occupation numbers of each quantum state are given by either 1 or 0 (either there is an electron occupying the state or not), so the (grand) partition function can be written as
where , indexes the ensembles of all possible microstates that give the same total energy and number of particles , is the single particle energy of the state (it counts twice if the energy of the state is degenerate) and , its occupancy. Thus the grand potential is written as
The same result can be obtained in the canonical and microcanonical ensemble, as the result of every ensemble must give the same value at thermodynamic limit . The grand canonical ensemble is recommended here as it avoids the use of combinatorics and factorials.
As explored in previous sections, in the macroscopic limit we may use a continuous approximation (Thomas–Fermi approximation) to convert this sum to an integral:
where is the total density of states. | 7 | Physical Chemistry |
When stored in air, it forms a yellow potassium superoxide coating and may ignite. This superoxide reacts explosively with water and organics. NaK is not dense enough to sink in most hydrocarbons, but will sink in lighter mineral oil. It is unsafe to store in this manner if the superoxide has formed. A large explosion took place at the Oak Ridge Y-12 facility on December 8, 1999, when NaK cleaned up after an accidental spill and inappropriately treated with mineral oil was scratched with a metal tool. The liquid alloy also attacks PTFE ("Teflon"). | 8 | Metallurgy |
Ion interaction chromatography (ion-pair chromatography) is a laboratory technique for separating ions with chromatography. In this technique ions are mixed with ion pairing reagents (IPR). The analyte combines with its reciprocal ion in the IPR, this corresponds to retention time. Often organic salts are selected to pair with solute(s). The formation of this pair affects the interaction of the pair with the mobile phase and the stationary phase. | 3 | Analytical Chemistry |
This section lists only historical data. For recent data, see Abundance of elements in Earth's crust.
Technical definition of "clarke", "Earth's crust" and "lithosphere" differ among authors, and the actual numbers vary accordingly, sometimes by several times. Even the same author presents multiple versions, with various estimation parameters or knowledge refinements. Yet they are often quoted without source, rendering the data unverifiable.
Clarke & Washington presented estimations of the average composition of outer part of Earth with four variants:
# 10-mile crust, hydrosphere and atmosphere.
# 20-mile crust, hydrosphere and atmosphere.
# 10-mile crust, only igneous rocks and sedimentary rocks. (i.e. exclude hydrosphere and atmosphere)
# 10-mile crust, only igneous rocks. (i.e. exclude hydrosphere and atmosphere)
"The earth's crust" in Clarke and Washington works can mean two different things: (a) The whole outer part of Earth, ie. lithosphere, hydrosphere and atmosphere; (b) Only the lithosphere, which in their works just meant "the rocky crust of the earth". "Crust" here means (b).
* Following tables do not cover all elements. Some elements not on the table may have larger abundance. Some minor elements are listed here to aid identifying the origin of unsourced documents.
* Some entries contain data for the disputed element 43 masurium.
* Precision (number of digits) may be adjusted to improve legibility. | 9 | Geochemistry |
Activity coefficients may be determined experimentally by making measurements on non-ideal mixtures. Use may be made of Raoults law or Henrys law to provide a value for an ideal mixture against which the experimental value may be compared to obtain the activity coefficient. Other colligative properties, such as osmotic pressure may also be used. | 7 | Physical Chemistry |
Site-specific recombination makes use of phage integrases instead of restriction enzymes, eliminating the need for having restriction sites in the DNA fragments. Instead, integrases make use of unique attachment (att) sites, and catalyse DNA rearrangement between the target fragment and the destination vector. The Invitrogen Gateway cloning system was invented in the late 1990s and uses two proprietary enzyme mixtures, BP clonase and LR clonase. The BP clonase mix catalyses the recombination between attB and attP sites, generating hybrid attL and attR sites, while the LR clonase mix catalyse the recombination of attL and attR sites to give attB and attP sites. As each enzyme mix recognises only specific att sites, recombination is highly specific and the fragments can be assembled in the desired sequence.
Vector design and assembly
Because Gateway cloning is a proprietary technology, all Gateway reactions must be carried out with the Gateway kit that is provided by the manufacturer. The reaction can be summarised into two steps. The first step involves assembling the entry clones containing the DNA fragment of interest, while the second step involves inserting this fragment of interest into the destination clone.
# Entry clones must be made using the supplied "Donor" vectors containing a Gateway cassette flanked by attP sites. The Gateway cassette contains a bacterial suicide gene (e.g. ccdB) that will allow for survival and selection of successfully recombined entry clones. A pair of attB sites are added to flank the DNA fragment of interest, and this will allow recombination with the attP sites when the BP clonase mix is added. Entry clones are produced, and the fragment of interest is flanked by attL sites.
# The destination vector also comes with a Gateway cassette, but is instead flanked by a pair of attR sites. Mixing this destination plasmid with the entry clones and the LR clonase mix will allow for recombination to occur between the attR and attL sites. A destination clone is produced, with the fragment of interest successfully inserted. The lethal gene is inserted into the original vector, and bacteria transformed with this plasmid will die. The desired vector can thus be easily selected.
The earliest iterations of the Gateway cloning method only allowed for only one entry clone to be used for each destination clone produced. However, further research revealed that four more orthogonal att sequences could be generated, allowing for the assembly of up to four different DNA fragments, and this process is now known as the Multisite Gateway technology.
Besides Gateway cloning, non-commercial methods using other integrases have also been developed. For example, the Serine Integrase Recombinational Assembly (SIRA) method uses the ϕC31 integrase, while the Site-Specific Recombination-based Tandem Assembly (SSRTA) method uses the Streptomyces phage φBT1 integrase. Other methods, like the HomeRun Vector Assembly System (HVAS), build on the Gateway cloning system and further incorporate homing endonucleases to design a protocol that could potentially support the industrial synthesis of synthetic DNA constructs. | 1 | Biochemistry |
The relationship between cellular proliferation and mitochondria has been investigated. Tumor cells require ample ATP to synthesize bioactive compounds such as lipids, proteins, and nucleotides for rapid proliferation. The majority of ATP in tumor cells is generated via the oxidative phosphorylation pathway (OxPhos). Interference with OxPhos cause cell cycle arrest suggesting that mitochondria play a role in cell proliferation. Mitochondrial ATP production is also vital for cell division and differentiation in infection in addition to basic functions in the cell including the regulation of cell volume, solute concentration, and cellular architecture. ATP levels differ at various stages of the cell cycle suggesting that there is a relationship between the abundance of ATP and the cells ability to enter a new cell cycle. ATPs role in the basic functions of the cell make the cell cycle sensitive to changes in the availability of mitochondrial derived ATP. The variation in ATP levels at different stages of the cell cycle support the hypothesis that mitochondria play an important role in cell cycle regulation. Although the specific mechanisms between mitochondria and the cell cycle regulation is not well understood, studies have shown that low energy cell cycle checkpoints monitor the energy capability before committing to another round of cell division. | 1 | Biochemistry |
It accumulates in pipecolic acidemia. Elevation of pipecolic acid can be associated with some forms of epilepsy, such as pyridoxine-dependent epilepsy. | 1 | Biochemistry |
The core principle behind microarrays is hybridization between two DNA strands, the property of complementary nucleic acid sequences to specifically pair with each other by forming hydrogen bonds between complementary nucleotide base pairs. A high number of complementary base pairs in a nucleotide sequence means tighter non-covalent bonding between the two strands. After washing off non-specific bonding sequences, only strongly paired strands will remain hybridized. Fluorescently labeled target sequences that bind to a probe sequence generate a signal that depends on the hybridization conditions (such as temperature), and washing after hybridization. Total strength of the signal, from a spot (feature), depends upon the amount of target sample binding to the probes present on that spot. Microarrays use relative quantitation in which the intensity of a feature is compared to the intensity of the same feature under a different condition, and the identity of the feature is known by its position. | 1 | Biochemistry |
Numerous methods exist to synthesize phenylboronic acid. One of the most common synthesis uses phenylmagnesium bromide and trimethyl borate to form the ester PhB(OMe), which is then hydrolyzed to the product.
:PhMgBr + B(OMe) → PhB(OMe) + MeOMgBr
:PhB(OMe) + HO → PhB(OH) + MeOH
Other routes to phenylboronic acid involve electrophilic borates to trap phenylmetal intermediates from phenyl halides or from directed ortho-metalation. Phenylsilanes and phenylstannanes transmetalate with BBr, followed by hydrolysis form phenylboronic acid. Aryl halides or triflates can be coupled with diboronyl reagents using transition metal catalysts. Aromatic C-H functionalization can also be done using transition metal catalysts. | 0 | Organic Chemistry |
It has been hypothesized that blockage of the PI3K/AKT/mTOR pathway can lead to increased antitumor activity in TNBC. Preclinical data have shown that the combination of compounds targeting different cognate molecules in the PI3K/AKT/mTOR pathway leads to synergistic activity. On the basis of these findings, new compounds targeting different components of the PI3K/AKT/mTOR pathway simultaneously continue to be developed. For example, gedatolisib inhibits mutant forms of PI3K-α with elevated kinase activity at concentrations equivalent to the IC50 for wild-type PI3K-α. PI3K-β, -δ and -γ isoforms were inhibited by gedatolisib at concentrations approximately 10-fold higher than those observed for PI3K-α. Another advantage of simultaneously targeting PI3K and mTOR is the ensuing more robust inhibition of receptor tyrosine kinase-positive feedback loops seen with isolated PI3K inhibition. Gedatolisib is currently under development for the treatment of TNBC, in combination with PTK7 antibody–drug conjugate. Apitolisib (GDC-0980) is a PI3K inhibitor (subunits α, δ, and γ) that also targets mTORC | 1 | Biochemistry |
Corepressors are known to regulate transcription through different activation and inactivation states.
NCoR and SMRT act as a corepressor complex to regulate transcription by becoming activated once the ligand is bound. Knockouts of NCoR resulted in embryo death, indicating its importance in erythrocytic, thymic, and neural system development.
Mutations in certain corepressors can result in deregulation of signals. SMRT contributes to cardiac muscle development, with knockouts of the complex resulting in less developed muscle and improper development.
NCoR has also been found to be an important checkpoint in processes such as inflammation and macrophage activation.
Recent evidence also suggests the role of corepressor RIP140 in metabolic regulation of energy homeostasis. | 1 | Biochemistry |
William Frohring was born in Cleveland, Ohio, the son of William Erhardt Frohring, a railroad engineer, and Martha Louise Bliss. He graduated from East Technical High School in Cleveland. After graduation, he worked as a motorcycle mechanic at the Luna Park, Cleveland Motordrome. In 1911, he received a two-year scholarship to Ohio State Agricultural College, where he majored in bacteriology and dairy technology. He graduated in 1915. | 7 | Physical Chemistry |
Alpha hydroxy acids can be converted into amino acids directly using aqueous ammonia solution, hydrogen gas and a heterogeneous metallic ruthenium catalyst. | 0 | Organic Chemistry |
DNA sequencing is the process of determining the nucleotide order of a given DNA fragment. So far, most DNA sequencing has been performed using the chain termination method developed by Frederick Sanger. This technique uses sequence-specific termination of a DNA synthesis reaction using modified nucleotide substrates. However, new sequencing technologies such as pyrosequencing are gaining an increasing share of the sequencing market. More genome data are now being produced by pyrosequencing than Sanger DNA sequencing. Pyrosequencing has enabled rapid genome sequencing. Bacterial genomes can be sequenced in a single run with several times coverage with this technique. This technique was also used to sequence the genome of James Watson recently.
The sequence of DNA encodes the necessary information for living things to survive and reproduce. Determining the sequence is therefore useful in fundamental research into why and how organisms live, as well as in applied subjects. Because of the key importance DNA has to living things, knowledge of DNA sequences is useful in practically any area of biological research. For example, in medicine it can be used to identify, diagnose, and potentially develop treatments for genetic diseases. Similarly, research into pathogens may lead to treatments for contagious diseases. Biotechnology is a burgeoning discipline, with the potential for many useful products and services.
The Carlson curve is a term coined by The Economist to describe the biotechnological equivalent of Moores law, and is named after author Rob Carlson. Carlson accurately predicted the doubling time of DNA sequencing technologies (measured by cost and performance) would be at least as fast as Moores law. Carlson curves illustrate the rapid (in some cases hyperexponential) decreases in cost, and increases in performance, of a variety of technologies, including DNA sequencing, DNA synthesis, and a range of physical and computational tools used in protein expression and in determining protein structures. | 1 | Biochemistry |
Gadolinium-based pharmaceuticals alter the relaxation time, and hence spectral line shape, of those protons that are in water molecules that are transiently attached to the paramagnetic atoms, resulting contrast enhancement of the MRI image. This allows better visualisation of some brain tumours. | 7 | Physical Chemistry |
A knowledge of environmental soil chemistry is paramount to predicting the fate of contaminants, as well as the processes by which they are initially released into the soil. Once a chemical is exposed to the soil environment, myriad chemical reactions can occur that may increase or decrease contaminant toxicity. These reactions include adsorption/desorption, precipitation, polymerization, dissolution, hydrolysis, hydration, complexation and oxidation/reduction. These reactions are often disregarded by scientists and engineers involved with environmental remediation. Understanding these processes enable us to better predict the fate and toxicity of contaminants and provide the knowledge to develop scientifically correct, and cost-effective remediation strategies. | 9 | Geochemistry |
The sources of the energy required for the formation of magma oceans in the early Solar System were the radioactive decay of aluminium-26, accretionary impacts, and core formation. The abundance and short half life of aluminium-26 allowed it to function as one of the sources of heat for the melting of planetesimals. With aluminium-26 as a heat source, planetesimals that had accreted within 2 Ma after the formation of the first solids in the Solar System could melt. Melting in the planetesimals began in the interior and the interior magma ocean transported heat via convection. Planetesimals larger than 20 km in radius that accreted within 2 Ma are expected to have melted, although not completely.
The kinetic energy provided by accretionary impacts and the loss of potential energy from a planet during core formation are also large heat sources for planet melting. Core formation, also referred to as metal-silicate differentiation, is the separation of metallic components from silicate in the magma that sink to form a planetary core. Accretionary impacts that produce heat for the melting of planet embryos and large terrestrial planets have an estimated timescale of tens to hundreds of millions of years. A prime example would be the Moon-forming impact on Earth, that is thought to have formed a magma ocean with a depth of up to 2000 km. The energy of accretionary impacts foremost melt the exterior of the planetary body, and the potential energy provided by core differentiation and the sinking of metals melts the interior. | 9 | Geochemistry |
In organic chemistry, phosphonites are organophosphorus compounds with the formula P(OR)R. They are found in some pesticides and are used as ligands. | 0 | Organic Chemistry |
A histone fold is a structurally conserved motif found near the C-terminus in every core histone sequence in a histone octamer responsible for the binding of histones into heterodimers.
The histone fold averages about 70 amino acids and consists of three alpha helices connected by two short, unstructured loops. When not in the presence of DNA, the core histones assemble into head-to-tail intermediates (H3 and H4 first assemble into heterodimers then fuse two heterodimers to form a tetramer, while H2A and H2B form heterodimers) via extensive hydrophobic interactions between each histone fold domain in a "handshake motif". Also the histone fold was first found in TATA box-binding protein-associated factors, which is a main component in transcription.
The histone fold's evolution can be found by different combinations of ancestral sets of peptides that make up helix-strand-helix motif that come from the three folds from the ancestral fragments. These peptide chains can be found in the archaeal histones, which could have come from eukaryotic H3-H4 tetramer. The archaeal single-chain histones are also found in the bacterium Aquifex aeolicus. Which helps the diverse bacteria phylogeny coming from the ancestry of eukaryotes and archaea with lateral gene transfers to get to the bacteria. These lead into the octamer articulated protein endoskeleton for DNA compaction. From this endoskeleton it has a central segment that folds for the histone dimerization. This then leads into the end segments of the fold to make properties of dimer-dimer contacts that also cap the protein super helix at the octamer.
One species that looked at is Drosophila, and in the subunits of the Drosophila transcription initiation factor has specific amino acid sequences that have different characteristics of the histone folds that make up the two proteins make up the subunits. When just looking at the histone fold motif in the Drosophila the protein-protein and the protein DNA interaction of the core histone proteins can be found by looking at the non-histone proteins. This can then be used in “Structural studies on the TAFII42/TAFII62 complex from Drosophila and HMfB from Methanococcus fervidus, proteins identified as containing the histone fold in the aforementioned searches, confirmed that a histone-like substructure exists in these proteins, with the individual proteins folding into the canonical histone fold motif”. The evolutionary structure and range of the histone protein-protein and DNA-protein interactions of the histone fold proteins has a very wide range of evolutionary traits that form the structures and other proteins.
Histone folds play a role in the nucleosomal core particle by conserving histone interactions when looking at interface surfaces. These contain more than one histone fold. The structure of the nucleosome core particle has two modes that have the largest interaction surfaces with are in groups H3-H4 and H2A-H2B heterotypic dimer interactions. When looking at the H2A-H2A structure it has a modification of the loop at the interface that excludes it from clustering with the same interface of other structures. Which makes it have a different function in the transcriptional activation. Also the two modes are distinct due to having the longest helix chains. These use the handshake interactions between the two histone folds, while they also use it to make themselves unique comparted to the rest of the modes. Similarly modes 5 and 7 of the core nucleosome particle use two types of histone fold dimers which show that all histone domains share a similar structural motif to be able to be able to interact with one another and to interact in different ways. Showing how flexible and adaptive the structure of histones are.
H4 and H2A can form an internucleosomal contacts that can be acetylated to be able to perform ionic interactions between two peptides, which in turn could change the surrounding internucleosomal contacts that can make a way to opening the chromatin. | 1 | Biochemistry |
Dialkyl peroxides, e.g., dicumyl peroxide, are synthesized by addition of hydrogen peroxide to alkenes or by O-alkylation of hydroperoxides.
Diacyl peroxides are typically prepared by treating hydrogen peroxide with acid chlorides or acid anhydrides in the presence of base:
The reaction competes with hydrolysis of the acylating agent but the hydroperoxide anion is a superior nucleophile relative to hydroxide. Unsymmetrical diacyl peroxides can be produced by treating acyl chlorides with the peroxy acid.
Peresters, an example being tert-Butyl peroxybenzoate, are produced by treating acid anhydrides or acid chlorides with hydroperoxides. | 0 | Organic Chemistry |
Thermal spraying involves heating a feedstock of precursor material and spraying it on a surface. Specific techniques depend on desired particle size, coat thickness, spray speed, desired area, etc. Thermal spraying relies on adhesion to the surface. As a result, the surface of the superalloy must be cleaned and prepared, and usually polished, before application. | 8 | Metallurgy |
Diazonium salts can be converted to thiols in a two-step procedure. Treatment of benzenediazonium chloride with potassium ethylxanthate followed by hydrolysis of the intermediate xanthate ester gives thiophenol: | 0 | Organic Chemistry |
The isomerization of unsubstituted azulene to naphthalene was the first reported thermal transformation of an aromatic hydrocarbon, and has consequently been the most widely studied rearrangement. However, the following mechanisms are generalized to all thermal isomerizations of aromatic hydrocarbons. Many mechanisms have been suggested for this isomerization, yet none have been unequivocally determined as the only correct mechanism. Five mechanisms were originally considered: a reversible ring-closure mechanism, which is shown above, a norcaradiene-vinylidene mechanism, a diradical mechanism, a methylene walk mechanism, and a spiran mechanism. It was quickly determined that the reversible ring-closure mechanism was inaccurate, and it was later decided that there must be multiple reaction pathways occurring simultaneously. This was widely accepted, as at such high temperatures, one mechanism would have to be substantially energetically favored over the others to be occurring alone. Energetic studies displayed similar activation energies for all possible mechanisms.
Four mechanisms for thermal isomerizations have been proposed: a dyotropic mechanism, a diradical mechanism, and two benzene ring contraction mechanisms; a 1,2-carbon shift to a carbene preceding a 1,2-hydrogen shift, and a 1-2-hydrogen shift to a carbene followed by a 1,2-carbon shift. The dyotropic mechanism involves concerted 1,2-shifts as displayed below. Electronic studies show this mechanism to be unlikely, but it must still be considered a viable mechanism as it has not yet been disproven.
The diradical mechanism has been supported by kinetic studies performed on the reaction, which have revealed that the reaction is not truly unimolecular, as it is most likely initiated by hydrogen addition from another gas-phase species. However, the reaction still obeys first-order kinetics, which is a classical characteristic of radical chain reactions. A mechanistic rational for the thermal rearrangement of azulene to naphthalene is included below. Homolysis of the weakest bond in azulene occurs, followed by a hydrogen shift and ring closure so as to retain the aromaticity of the molecule.
Benzene ring contractions are the last two mechanisms that have been suggested, and they are currently the preferred mechanisms. These reaction mechanisms proceed through the lowest free energy transition states compared to the diradical and dyotropic mechanisms. The difference between the two ring contractions is minute however, so it has not been determined which is favored over the other. Both mechanisms are shown as follows for the ring contraction of biphenylene:
The first involves a 1,2-hydrogen shift to a carbene followed by a 1,2-carbon shift on the same C-C bond but in opposite directions. The second differs from the first only by the order of the 1,2-shifts, with the 1,2-carbon shift preceding the 1,2-hydrogen shift.
The four described mechanisms would all result in the isomerization from azulene to naphthalene. Kinetic data and C-labeling have been used to elucidate the correct mechanism, and have led organic chemists to believe that one of the benzene ring contractions is the most likely mechanism through which these isomerizations of aromatic hydrocarbons occur. | 5 | Photochemistry |
The exact compounds an organism is exposed to will be largely unpredictable, and may differ widely over time; these are major characteristics of xenobiotic toxic stress. The major challenge faced by xenobiotic detoxification systems is that they must be able to remove the almost-limitless number of xenobiotic compounds from the complex mixture of chemicals involved in normal metabolism. The solution that has evolved to address this problem is an elegant combination of physical barriers and low-specificity enzymatic systems.
All organisms use cell membranes as hydrophobic permeability barriers to control access to their internal environment. Polar compounds cannot diffuse across these cell membranes, and the uptake of useful molecules is mediated through transport proteins that specifically select substrates from the extracellular mixture. This selective uptake means that most hydrophilic molecules cannot enter cells, since they are not recognised by any specific transporters. In contrast, the diffusion of hydrophobic compounds across these barriers cannot be controlled, and organisms, therefore, cannot exclude lipid-soluble xenobiotics using membrane barriers.
However, the existence of a permeability barrier means that organisms were able to evolve detoxification systems that exploit the hydrophobicity common to membrane-permeable xenobiotics. These systems therefore solve the specificity problem by possessing such broad substrate specificities that they metabolise almost any non-polar compound. Useful metabolites are excluded since they are polar, and in general contain one or more charged groups.
The detoxification of the reactive by-products of normal metabolism cannot be achieved by the systems outlined above, because these species are derived from normal cellular constituents and usually share their polar characteristics. However, since these compounds are few in number, specific enzymes can recognize and remove them. Examples of these specific detoxification systems are the glyoxalase system, which removes the reactive aldehyde methylglyoxal, and the various antioxidant systems that eliminate reactive oxygen species. | 1 | Biochemistry |
Auto Ejection Melt Spinning (AEMS) describes a type of melt spinning where ejection of the melt occurs as soon as it has liquefied, eliminating the need for a technician to manually control the flow rate, temperature, and/or release timing of the melt stream.
This modification allows for a much higher ribbon consistency between runs, and a greater level of automation in the process. | 8 | Metallurgy |
The term host cell reactivation or HCR was first used to describe the survival of UV-irradiated bacteriophages, that were transfected to UV-pretreated cells. This phenomenon was first thought to be the result of homologous recombination between both bacteria and phage, but later recognized as enzymatic repair. Modifications of the assay were later developed, using transient expression plasmid DNA vectors on immortalized fibroblasts, and lately on human lymphocytes.
The HCR assay known also as plasmid reactivation assay, indirectly monitors cellular transcriptional repair system, that is activated by the transcriptional-inhibited damage inflicted by UV-Radiation into the plasmid. Given that UV-induced DNA damage is used as mutagen, the cell uses nucleotide excision repair NER pathway, that is activated by distortion in the DNA helix.
The Host-Cell Reactivation Assay or HCR is a technique used to measure the DNA repair capacity of cell of a particular DNA alteration. In the HCR assay the ability of an intact cell to repair exogenous DNA is measured The host cell is transfected with a damaged plasmid containing a reporter gene, usually luciferase, which has been deactivated due to the damage. The ability of the cell to repair the damage in the plasmid, after it has been introduced to the cell, allows the reporter gene to be reactivated. Earlier versions of this assay were based on the chloramphenicol acetyltransferase [http://www.wikigenes.org/e/gene/e/2847485.html (CAT)] gene, but the version of the assay using luciferase as reporter gene is as much as 100-fold more sensitive. | 1 | Biochemistry |
An improper rotation involves two operation steps: a proper rotation followed by reflection through a plane perpendicular to the rotation axis. The improper rotation is represented by the symbol where is the order. Since the improper rotation is the combination of a proper rotation and a reflection, will always exist whenever and a perpendicular plane exist separately. is usually denoted as , a reflection operation about a mirror plane. is usually denoted as , an inversion operation about an inversion center. When is an even number but when is odd
Rotation axes, mirror planes and inversion centres are symmetry elements, not symmetry operations. The rotation axis of the highest order is known as the principal rotation axis. It is conventional to set the Cartesian -axis of the molecule to contain the principal rotation axis. | 7 | Physical Chemistry |
Deuterium is used in heavy water moderated fission reactors, usually as liquid HO, to slow neutrons without the high neutron absorption of ordinary hydrogen. This is a common commercial use for larger amounts of deuterium.
In research reactors, liquid H is used in cold sources to moderate neutrons to very low energies and wavelengths appropriate for scattering experiments.
Experimentally, deuterium is the most common nuclide used in fusion reactor designs, especially in combination with tritium, because of the large reaction rate (or nuclear cross section) and high energy yield of the deuterium–tritium (DT) reaction. There is an even higher-yield H–He fusion reaction, though the breakeven point of H–He is higher than that of most other fusion reactions; together with the scarcity of He, this makes it implausible as a practical power source, at least until DT and deuterium–deuterium (DD) fusion have been performed on a commercial scale. Commercial nuclear fusion is not yet an accomplished technology. | 9 | Geochemistry |
Photosynthesis is the only process that allows the conversion of atmospheric carbon (CO2) to organic (solid) carbon, and this process plays an essential role in climate models. This lead researchers to study the sun-induced chlorophyll fluorescence (i.e., chlorophyll fluorescence that uses the Sun as illumination source; the glow of a plant) as an indicator of photosynthetic efficiency of a region. This is interesting for scientists since its shows them things like the CO2 absorption of a forests, or the productivity of an agricultural region. The FLEX (satellite) is the upcoming satellite program by the European Space Agency designated to this type of measurements. | 5 | Photochemistry |
Chain reaction in chemistry and physics is a process that produces products capable of initiating subsequent processes of a similar nature. It is a self-sustaining sequence in which the resulting products continue to propagate further reactions. Examples of chain reactions in living organisms are lipid peroxidation in cell membranes and propagation of excitation of neurons in epilepsy. | 1 | Biochemistry |
At non-relativistic energies, single particles generally produce effects too small to enable their direct detection. The microchannel plate functions as a particle amplifier, turning a single impinging particle into a cloud of electrons. By applying a strong electric field across the MCP, each individual microchannel becomes a continuous-dynode electron multiplier.
A particle or photon that enters one of the channels through a small orifice is guaranteed to hit the wall of the channel, due to the channel being at an angle to the plate. The impact starts a cascade of electrons that propagates through the channel, amplifying the original signal by several orders of magnitude, depending on the electric field strength and the geometry of the microchannel plate. After the cascade, the microchannel takes time to recover (or recharge) before it can detect another signal.
The electrons exit the channels on the opposite side of the plate, where they are collected on an anode. Some anodes are designed to allow spatially resolved ion collection, producing an image of the particles or photons incident on the plate.
Although in many cases the collecting anode functions as the detecting element, the MCP itself can also be used as a detector. The discharging and recharging of the plate produced by the electron cascade, can be decoupled from the high voltage applied to the plate and measured, to directly produce a signal corresponding to a single particle or photon.
The gain of an MCP is very noisy, meaning that two identical particles detected in succession will often produce wildly different signal magnitudes. The temporal jitter resulting from the peak height variation can be removed by using a constant fraction discriminator. Thusly employed, MCPs are capable of measuring particle arrival times with high resolution, making them ideal detectors for mass spectrometers. | 7 | Physical Chemistry |
The parent metallacyclobutane has the formula LM(CH) where L is a ligand attached to M. A stable example is (PPh)Pt(CH). The first example was prepared by oxidative addition of cyclopropane to platinum.
Metallacyclobutane intermediates are involved in the alkene metathesis and in the oligomerization and dimerization of ethylene. In alkene metathesis, the Chauvin mechanism invokes the attack of an alkene at an electrophilic metal carbene catalyst. This work helped to validate the Chauvin mechanism for olefin metathesis. | 0 | Organic Chemistry |
Between 1975 and 1980 Brian Evans Conway conducted extensive fundamental and development work on ruthenium oxide electrochemical capacitors. In 1991 he described the difference between Supercapacitor and Battery behavior in electrochemical energy storage. In 1999 he coined the term supercapacitor to explain the increased capacitance by surface redox reactions with faradaic charge transfer between electrodes and ions.
His "supercapacitor" stored electrical charge partially in the Helmholtz double-layer and partially as the result of faradaic reactions with "pseudocapacitance" charge transfer of electrons and protons between electrode and electrolyte. The working mechanisms of pseudocapacitors are redox reactions, intercalation and electrosorption. | 7 | Physical Chemistry |
For many years, the strong oxidizing agent potassium permanganate (KMnO) was used for measuring chemical oxygen demand. Measurements were called oxygen consumed from permanganate, rather than the oxygen demand of organic substances. Potassium permanganate's effectiveness at oxidizing organic compounds varied widely, and in many cases biochemical oxygen demand (BOD) measurements were often much greater than results from COD measurements. This indicated that potassium permanganate was not able to effectively oxidize all organic compounds in water, rendering it a relatively poor oxidizing agent for determining COD.
Since then, other oxidizing agents such as ceric sulphate, potassium iodate, and potassium dichromate have been used to determine COD. Of these, potassium dichromate (KCrO) has been shown to be the most effective: it is relatively cheap, easy to purify, and is able to nearly completely oxidize almost all organic compounds.
In these methods, a fixed volume with a known excess amount of the oxidant is added to a sample of the solution being analyzed. After a refluxing digestion step, the initial concentration of organic substances in the sample is calculated from a titrimetric or spectrophotometric determination of the oxidant still remaining in the sample. As with all colorimetric methods blanks are used to control for contamination by outside material. | 9 | Geochemistry |
* The mineral components of the soil are derived from the parental rocks or regolith. The minerals present about 90% of the total weight of the soil. Some important elements, which are found in compound state, are oxygen, iron, silicon, aluminium, nitrogen, phosphorus, potassium, calcium, magnesium, carbon, hydrogen, etc.
* The formation of primary and secondary minerals can better define what minerals are in the rock composition | 9 | Geochemistry |
A range of bacteria can grow on sulfoquinovose or its glycosides as sole carbon source. E. coli can grow on sulfoquinovose, methyl α-sulfoquinovoside and α-sulfoquinovosyl glycerol. Growth on sulfoquinovosyl glycerol is both faster and leads to higher cell density than for growth on sulfoquinovose. Pseudomonas aeruginosa strain SQ1, Klebsiella sp. strain ABR11, Klebsiella oxytoca TauN1, Agrobacterium sp. strain ABR2, and Bacillus aryabhattai can grow on sulfoquinovose as sole carbon source. A strain of Flavobacterium was identified that could grow on methyl α-sulfoquinovoside. | 1 | Biochemistry |
Soluble fluorides are moderately toxic. For sodium fluoride, the lethal dose for adults is 5–10 g, which is equivalent to 32–64 mg of elemental fluoride per kilogram of body weight. The dose that may lead to adverse health effects is about one fifth of the lethal dose. Chronic excess fluoride consumption can lead to skeletal fluorosis, a disease of the bones that affects millions in Asia and Africa.
The fluoride ion is readily absorbed by the stomach and intestines. Ingested fluoride forms hydrofluoric acid in the stomach. In this form, fluoride crosses cell membranes and then binds with calcium and interferes with various enzymes. Fluoride is excreted through urine. Fluoride exposure limits are based on urine testing, which is used to determine the human body's capacity for ridding itself of fluoride.
Historically, most cases of fluoride poisoning have been caused by accidental ingestion of insecticides containing inorganic fluoride. Most calls to poison control centers for possible fluoride poisoning come from the ingestion of fluoride-containing toothpaste. Malfunction of water fluoridation equipment has occurred several times, including an Alaskan incident that sickened nearly 300 people and killed one. | 1 | Biochemistry |
P. aeruginosa is an opportunistic human pathogen associated with cystic fibrosis. In P. aeruginosa infections, quorum sensing is critical for biofilm formation and pathogenicity. P. aeruginosa contains two pairs of LuxI/LuxR homologs, LasI/LasR and RhlI, RhlR. LasI and RhlI are synthase enzymes that catalyze the synthesis of N-(3-oxododecanoyl)-homoserine lactone and N-(butyryl)-homoserine lactone, respectively. The LasI/LasR and the RhlI/RhlR circuits function in tandem to regulate the expression of a number of virulence genes. At a threshold concentration, LasR binds N-(3-oxododecanoyl)-homoserine lactone. Together this bound complex promotes the expression of virulence factors that are responsible for early stages of the infection process.
LasR bound by its autoinducer also activates the expression of the RhlI/RhlR system in P. aeruginosa. This causes the expression of RhlR which then binds its autoinducer, N-(butryl)-homoserine lactone. In turn, autoinducer-bound RhlR activates a second class of genes involved in later stages of infection, including genes needed for antibiotic production. Presumably, antibiotic production by P. aeruginosa is used to prevent opportunistic infections by other bacterial species. N-(3-oxododecanoyl)-homoserine lactone prevents binding between N-(butryl)-homoserine lactone and its cognate regulator, RhlR. It is believed that this control mechanism allows P. aeruginosa to initiate the quorum-sensing cascades sequentially and in the appropriate order so that a proper infection cycle can ensue. | 1 | Biochemistry |
A lone pair of electrons resides on the sulfur atom, giving it tetrahedral electron-pair geometry and trigonal pyramidal shape (steric number 4 with one lone pair; see VSEPR theory). When the two organic residues are dissimilar, the sulfur atom is a chiral center, for example, in methyl phenyl sulfoxide. The energy barrier required to invert this stereocenter is sufficiently high that sulfoxides are optically stable near room temperature. That is, the rate of racemization is slow at room temperature. The enthalpy of activation for racemization is in the range 35 - 42 kcal/mol and the corresponding entropy of activation is -8 - +4 cal/mol-K. The barriers are lower for allylic and benzylic substituents. | 0 | Organic Chemistry |
Unlike NAPPA, PISA completely bypasses DNA immobilization as the DNA template is added as a free molecule in the reaction mixture. In 2006, another group refined and miniaturized this method by using multiple spotting technique to spot the DNA template and cell-free transcription and translation mixture on a high-density protein microarray with up to 13,000 spots. This was made possible by the automated system used to accurately and sequentially supply the reagents for the transcription/translation reaction occurs in a small, sub-nanolitre droplet. | 1 | Biochemistry |
The outron is an intron-like sequence possessing similar characteristics such as the G+C content and a splice acceptor site that is the signal for trans-splicing. Such a trans-splice site is essentially defined as an acceptor (3) splice site without an upstream donor (5) splice site.
In eukaryotes such as euglenozoans, dinoflagellates, sponges, nematodes, cnidarians, ctenophores, flatworms, crustaceans, chaetognaths, rotifers, and tunicates, the length of spliced leader (SL) outrons range from 30 to 102 nucleotides (nt), with the SL exon length ranging from 16 to 51 nt, and the full SL RNA length ranging from 46 to 141 nt. | 1 | Biochemistry |
The absorbance of a material, denoted , is given by
where
* is the radiant flux by that material,
* is the radiant flux by that material, and
* is the transmittance of that material.
Absorbance is a dimensionless quantity. Nevertheless, the absorbance unit or AU is commonly used in ultraviolet–visible spectroscopy and its high-performance liquid chromatography applications, often in derived units such as the milli-absorbance unit (mAU) or milli-absorbance unit-minutes (mAU×min), a unit of absorbance integrated over time.
Absorbance is related to optical depth by
where is the optical depth. | 7 | Physical Chemistry |
Many methods for encoding data in DNA are possible. The optimal methods are those that make economical use of DNA and protect against errors. If the message DNA is intended to be stored for a long period of time, for example, 1,000 years, it is also helpful if the sequence is obviously artificial and the reading frame is easy to identify. | 1 | Biochemistry |
Corrosion engineering involves good design. Using a rounded edge rather than an acute edge reduces corrosion. Also not coupling by welding or other joining method, two dissimilar metals to avoid galvanic corrosion is best practice. Avoiding having a small anode (or anodic material) next to a large cathode (or cathodic material) is good practice. As an example, weld material should always be more noble than the surrounding material. Corrosion in ballast tanks on marine vessels can be an issue if good design is not undertaken. Other examples include simple design such as material thickness. In a known corrosion situation the material can just be made thicker so it will take much longer to corrode. | 8 | Metallurgy |
The microscopic "reversing of time" turns at the kinetic level into the "reversing of arrows": the elementary processes transform into their reverse processes. For example, the reaction
: transforms into
and conversely. (Here, are symbols of components or states, are coefficients). The equilibrium ensemble should be invariant with respect to this transformation because of microreversibility and the uniqueness of thermodynamic equilibrium. This leads us immediately to the concept of detailed balance: each process is equilibrated by its reverse process.
This reasoning is based on three assumptions:
# does not change under time reversal;
# Equilibrium is invariant under time reversal;
# The macroscopic elementary processes are microscopically distinguishable. That is, they represent disjoint sets of microscopic events.
Any of these assumptions may be violated. For example, Boltzmanns collision can be represented as where is a particle with velocity v. Under time reversal transforms into . Therefore, the collision is transformed into the reverse collision by the PT transformation, where P is the space inversion and T is the time reversal. Detailed balance for Boltzmanns equation requires PT-invariance of collisions dynamics, not just T'-invariance. Indeed, after the time reversal the collision transforms into For the detailed balance we need transformation into
For this purpose, we need to apply additionally the space reversal P. Therefore, for the detailed balance in Boltzmanns equation not T-invariance but PT'-invariance is needed.
Equilibrium may be not T- or PT-invariant even if the laws of motion are invariant. This non-invariance may be caused by the spontaneous symmetry breaking. There exist nonreciprocal media (for example, some bi-isotropic materials) without T and PT invariance.
If different macroscopic processes are sampled from the same elementary microscopic events then macroscopic detailed balance may be violated even when microscopic detailed balance holds.
Now, after almost 150 years of development, the scope of validity and the violations of detailed balance in kinetics seem to be clear. | 7 | Physical Chemistry |
Secchi depth is the depth at which a disk is no longer visible to the human eye. This measurement was created in 1865 and represents one of the oldest oceanographic methods. To measure Secchi depth, a white or black-and-white disk is mounted on a pole or line and lowered slowly down in the water. The depth at which the disk is no longer visible is taken as a measure of the transparency of the water. Secchi depth is most useful as a measure of transparency or underwater visibility. | 3 | Analytical Chemistry |
Cannabinoid receptors are G-protein coupled receptors located on the pre-synaptic membrane. While there have been some papers that have linked concurrent stimulation of dopamine and CB receptors to an acute rise in cyclic adenosine monophosphate (cAMP) production, it is generally accepted that CB activation via cannabinoids causes a decrease in cAMP concentration by inhibition of adenylyl cyclase and a rise in the concentration of mitogen-activated protein kinase (MAP kinase). The relative potency of different cannabinoids in inhibition of adenylyl cyclase correlates with their varying efficacy in behavioral assays. This inhibition of cAMP is followed by phosphorylation and subsequent activation of not only a suite of MAP kinases (p38/p42/p44), but also the PI3/PKB and MEK/ERK pathway. Results from rat hippocampal gene chip data after acute administration of tetrahydrocannabinol (THC) showed an increase in the expression of transcripts encoding myelin basic protein, endoplasmic proteins, cytochrome oxidase, and two cell adhesion molecules: NCAM, and SC1; decreases in expression were seen in both calmodulin and ribosomal RNAs. In addition, CB1 activation has been demonstrated to increase the activity of transcription factors like c-Fos and Krox-24. | 1 | Biochemistry |
* Beno, M. A.; Soderholm, L.; Capone, D. W., II; Hinks, D. G.; Jorgensen, J. D.; Grace, J. D.; Schuller, I. K.; Segre, C. U.; Zhang, K., Structure of the single-phase high-temperature superconductor yttrium barium copper oxide (YBaCuO). Appl. Phys. Lett. 1987, 51 (1), 57–9.
* Soderholm, L.; Zhang, K.; Hinks, D. G.; Beno, M. A.; Jorgensen, J. D.; Segre, C. U.; Schuller, I. K., Incorporation of praseodymium in YBaCuO: electronic effects on superconductivity. Nature (London) 1987, 328 (6131), 604–5.
* Antonio, M. R.; Williams, C. W.; Soderholm, L., Berkelium redox speciation. Radiochim. Acta 2002, 90 (12), 851–856.
* Soderholm, L.; Skanthakumar, S.; Neuefeind, J., Determination of actinide speciation in solution using high-energy X-ray scattering. Anal. Bioanal. Chem. 2005, 383 (1), 48–55.
* Forbes, T. Z.; Burns, P. C.; Skanthakumar, S.; Soderholm, L., Synthesis, structure, and magnetism of NpO. J. Am. Chem. Soc. 2007, 129 (10), 2760–2761.
* Soderholm, L.; Almond, P. M.; Skanthakumar, S.; Wilson, R. E.; Burns, P. C., The structure of the plutonium oxide nanocluster [PuOCl(HO)]. Angew. Chem., Int. Ed. 2008, 47 (2), 298–302.
* Jensen, M. P.; Gorman-Lewis, D.; Aryal, B.; Paunesku, T.; Vogt, S.; Rickert, P. G.; Seifert, S.; Lai, B.; Woloschak, G. E.; Soderholm, L., An iron-dependent and transferrin-mediated cellular uptake pathway for plutonium. Nat. Chem. Biol. 2011, 7 (8), 560–565.
* Wilson, R. E.; Skanthakumar, S.; Soderholm, L., Separation of Plutonium Oxide Nanoparticles and Colloids. Angew. Chem., Int. Ed. 2011, 50 (47), 11234–11237.
* Knope, K. E.; Soderholm, L., Solution and solid-state structural chemistry of actinide hydrates and their hydrolysis and condensation products. Chem. Rev. 2013, 113 (2), 944–994.
* Luo, G.; Bu, W.; Mihaylov, M.; Kuzmenko, I.; Schlossman, M. L.; Soderholm, L., X-ray reflectivity reveals a nonmonotonic ion-density profile perpendicular to the surface of ErCl aqueous solutions. J. Phys. Chem. C 2013, 117 (37), 19082–19090.
* Jin, G. B.; Lin, J.; Estes, S. L.; Skanthakumar, S.; Soderholm, L., Influence of countercation hydration enthalpies on the formation of molecular complexes: A thorium-nitrate example. J. Am. Chem. Soc. 2017, 139 (49), 18003–18008. | 7 | Physical Chemistry |
Continuous assays are most convenient, with one assay giving the rate of reaction with no further work necessary. There are many different types of continuous assays. | 1 | Biochemistry |
At the time of discovery, it was the only homoleptic trimetallic non-carbonyl cluster featuring hydrocarbon ligands. An isolobal analogy can be made with the related Fe(CO) (μ-CO) cluster first prepared by Jones and Dewar.
Alternatively, the compound could be compared to ferrocene. In this interpretation, each iron fragment bears an η allyl and η pentadienyl ligand as depicted. Under Green and Parkin's covalent bond classification method, this would yield LX and LX respectively. Then additionally, the iron centers donate a pair of electrons into an adjacent empty iron orbital as an adduct (donor-acceptor pairs L and Z type), to overall yield MLX (18 electrons). In fact, the bond orders in ferrocene and Fe3(COT)3 are reported to be very similar.
In fact, Fe(CO) and the group 5 analogues, Ru(CO) and Os(CO) are also known to feature highly fluxional CO ligands in solution (and even in the solid state).
Hypoelectronic derivatives (M=Ti, Cr, V, Mn) of Fe(CH) would be predicted to have metal multiple bonds. Some somewhat related compounds, notably, Ti(CH) and Cr(CH) have been experimentally isolated. | 7 | Physical Chemistry |
An acid test is a qualitative chemical or metallurgical assay utilizing acid. Historically, it often involved the use of a robust acid to distinguish gold from base metals. Figuratively, the term represents any definitive test for attributes, such as gauging a persons character or evaluating a products performance. | 3 | Analytical Chemistry |
Microarrays can be fabricated using a variety of technologies, including printing with fine-pointed pins onto glass slides, photolithography using pre-made masks, photolithography using dynamic micromirror devices, ink-jet printing, or electrochemistry on microelectrode arrays.
In spotted microarrays, the probes are oligonucleotides, cDNA or small fragments of PCR products that correspond to mRNAs. The probes are synthesized prior to deposition on the array surface and are then "spotted" onto glass. A common approach utilizes an array of fine pins or needles controlled by a robotic arm that is dipped into wells containing DNA probes and then depositing each probe at designated locations on the array surface. The resulting "grid" of probes represents the nucleic acid profiles of the prepared probes and is ready to receive complementary cDNA or cRNA "targets" derived from experimental or clinical samples.
This technique is used by research scientists around the world to produce "in-house" printed microarrays in their own labs. These arrays may be easily customized for each experiment, because researchers can choose the probes and printing locations on the arrays, synthesize the probes in their own lab (or collaborating facility), and spot the arrays. They can then generate their own labeled samples for hybridization, hybridize the samples to the array, and finally scan the arrays with their own equipment. This provides a relatively low-cost microarray that may be customized for each study, and avoids the costs of purchasing often more expensive commercial arrays that may represent vast numbers of genes that are not of interest to the investigator.
Publications exist which indicate in-house spotted microarrays may not provide the same level of sensitivity compared to commercial oligonucleotide arrays, possibly owing to the small batch sizes and reduced printing efficiencies when compared to industrial manufactures of oligo arrays.
In oligonucleotide microarrays, the probes are short sequences designed to match parts of the sequence of known or predicted open reading frames. Although oligonucleotide probes are often used in "spotted" microarrays, the term "oligonucleotide array" most often refers to a specific technique of manufacturing. Oligonucleotide arrays are produced by printing short oligonucleotide sequences designed to represent a single gene or family of gene splice-variants by synthesizing this sequence directly onto the array surface instead of depositing intact sequences. Sequences may be longer (60-mer probes such as the Agilent design) or shorter (25-mer probes produced by Affymetrix) depending on the desired purpose; longer probes are more specific to individual target genes, shorter probes may be spotted in higher density across the array and are cheaper to manufacture.
One technique used to produce oligonucleotide arrays include photolithographic synthesis (Affymetrix) on a silica substrate where light and light-sensitive masking agents are used to "build" a sequence one nucleotide at a time across the entire array. Each applicable probe is selectively "unmasked" prior to bathing the array in a solution of a single nucleotide, then a masking reaction takes place and the next set of probes are unmasked in preparation for a different nucleotide exposure. After many repetitions, the sequences of every probe become fully constructed. More recently, Maskless Array Synthesis from NimbleGen Systems has combined flexibility with large numbers of probes. | 1 | Biochemistry |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.