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* Frq – The Frq gene, also known as the Frequency gene, encodes central components of an oscillatory loop within the circadian clock in Neurospora. In the oscillator's feedback loop, frq gives rise to transcripts that encode for two forms of the FRQ protein. Both forms are required for robust rhythmicity throughout the organism. Rhythmic changes in the amount of frq transcript are essential for synchronous activity, and abrupt changes in frq levels reset the clock. | 1 | Biochemistry |
Use of certain chloroalkanes as solvents for large scale application, such as dry cleaning, have been phased out, for example, by the IPPC directive on greenhouse gases in 1994 and by the volatile organic compounds (VOC) directive of the EU in 1997. Permitted chlorofluoroalkane uses are medicinal only.
Bromofluoroalkanes have been largely phased out and the possession of equipment for their use is prohibited in some countries like the Netherlands and Belgium, from 1 January 2004, based on the Montreal Protocol and guidelines of the European Union.
Production of new stocks ceased in most (probably all) countries in 1994. However many countries still require aircraft to be fitted with halon fire suppression systems because no safe and completely satisfactory alternative has been discovered for this application. There are also a few other, highly specialized uses. These programs recycle halon through "halon banks" coordinated by the Halon Recycling Corporation to ensure that discharge to the atmosphere occurs only in a genuine emergency and to conserve remaining stocks.
The interim replacements for CFCs are hydrochlorofluorocarbons (HCFCs), which deplete stratospheric ozone, but to a much lesser extent than CFCs. Ultimately, hydrofluorocarbons (HFCs) will replace HCFCs. Unlike CFCs and HCFCs, HFCs have an ozone depletion potential (ODP) of 0. DuPont began producing hydrofluorocarbons as alternatives to Freon in the 1980s. These included Suva refrigerants and Dymel propellants. Natural refrigerants are climate friendly solutions that are enjoying increasing support from large companies and governments interested in reducing global warming emissions from refrigeration and air conditioning. | 2 | Environmental Chemistry |
Middens are excellent traps for pollen derived from the local and regional surroundings either via the alimentary channel of the animals (excreted in pellets) or via deposition on the middens. The airborne pollen rain is incorporated by (1) collecting on the surface of the midden, (2) being brought in on the fur of the hyraxes, or (3) being ingested as dust on dietary items such as plant leaves or drinking water. The dietary component may also represent the ingestion of flowers, which may result in the occasional over-representation of pollen of certain plant species in the pellet fraction of certain middens. A clear benefit of midden pollen spectra over wetland pollen spectra is that they may more clearly reflect terrestrial vegetation, without the high proportions of hydrophilic elements found in wetland sequences, which is particularly problematic in some dryland pollen records. Furthermore, as the pollen found in hyraceum is not exclusively wind-transported, usually under-represented entomophilous plants are more clearly represented.
Preservation of pollen sealed in hyraceum is usually very good, but the degradation of pollen grains has been occasionally observed in loose pellets or middens semi-exposed to the elements, such as in dolerite shelters in the central grassland region of South Africa, where some Asteraceae pollen have apparently lost their ektexine (L. Scott, unpublished observation). Compared to other available palaeoarchives in the region, such as fluvial sediments or paleosols, and to more widely used pollen records from peat bog and lakes, middens contain high fossil pollen concentrations; usually between 1 and 2 x 10 pollen grains per gram of sample. Pollen concentrations are high even in poorly productive ecosystems such as the Namib Desert margins. Concentrations increase markedly when analysing pollen contents from pellets, reaching 5-30 x 10 pollen grains/gram of sample. | 9 | Geochemistry |
The mobile phase or eluent is a solvent or a mixture of solvents used to move the compounds through the column. It is chosen so that the retention factor value of the compound of interest is roughly around 0.2 - 0.3 in order to minimize the time and the amount of eluent to run the chromatography. The eluent has also been chosen so that the different compounds can be separated effectively. The eluent is optimized in small scale pretests, often using thin layer chromatography (TLC) with the same stationary phase, using solvents of different polarity until a suitable solvent system is found. Common mobile phase solvents, in order of increasing polarity, include hexane, dichloromethane, ethyl acetate, acetone, and methanol. A common solvent system is a mixture of hexane and ethyl acetate, with proportions adjusted until the target compound has a retention factor of 0.2 - 0.3. Contrary to common misconception, methanol alone can be used as an eluent for highly polar compounds, and does not dissolve silica gel.
There is an optimum flow rate for each particular separation. A faster flow rate of the eluent minimizes the time required to run a column and thereby minimizes diffusion, resulting in a better separation. However, the maximum flow rate is limited because a finite time is required for the analyte to equilibrate between the stationary phase and mobile phase, see Van Deemter's equation. A simple laboratory column runs by gravity flow. The flow rate of such a column can be increased by extending the fresh eluent filled column above the top of the stationary phase or decreased by the tap controls. Faster flow rates can be achieved by using a pump or by using compressed gas (e.g. air, nitrogen, or argon) to push the solvent through the column (flash column chromatography).
The particle size of the stationary phase is generally finer in flash column chromatography than in gravity column chromatography. For example, one of the most widely used silica gel grades in the former technique is mesh 230 – 400 (40 – 63 µm), while the latter technique typically requires mesh 70 – 230 (63 – 200 µm) silica gel.
A spreadsheet that assists in the successful development of flash columns has been developed. The spreadsheet estimates the retention volume and band volume of analytes, the fraction numbers expected to contain each analyte, and the resolution between adjacent peaks. This information allows users to select optimal parameters for preparative-scale separations before the flash column itself is attempted. | 3 | Analytical Chemistry |
PAF is a potent activator of platelet aggregation, inflammation, and anaphylaxis. It is similar to the ubiquitous membrane phospholipid phosphatidylcholine except that it contains an acetyl-group in the SN-2 position and the SN-1 position contains an ether-linkage. PAF signals through a dedicated G-protein coupled receptor, PAFR and is inactivated by PAF acetylhydrolase. | 1 | Biochemistry |
Consider the example burning of magnesium ribbon (Mg). When magnesium burns, it combines with oxygen () from the air to form magnesium oxide (MgO) according to the following equation:
Magnesium oxide is an ionic compound containing and ions whereas and are elements with no charges.
The with zero charge gains a +2 charge going from the reactant side to product side, and the with zero charge gains a –2 charge. This is because when becomes , it loses 2 electrons. Since there are 2 Mg on left side, a total of 4 electrons are lost according to the following oxidation half reaction:
On the other hand, was reduced: its oxidation state goes from 0 to -2. Thus, a reduction half reaction can be written for the O2 as it gains 4 electrons:
The overall reaction is the sum of both half reactions:
When chemical reaction, especially, redox reaction takes place, we do not see the electrons as they appear and disappear during the course of the reaction. What we see is the reactants (starting material) and end products. Due to this, electrons appearing on both sides of the equation are canceled. After canceling, the equation is re-written as
Two ions, positive () and negative () exist on product side and they combine immediately to form a compound magnesium oxide (MgO) due to their opposite charges (electrostatic attraction). In any given oxidation-reduction reaction, there are two half reactions—oxidation half reaction and reduction half reaction. The sum of these two half reactions is the oxidation–reduction reaction. | 7 | Physical Chemistry |
In 2008, simultaneous publications described the allylic C-H alkylation of substrates. These reactions were catalyzed by the White catalyst or by an earlier version of the complex bearing benzyl substituents on the sulfoxide in place of phenyl. It was demonstrated that an additional sulfoxide ligand, dimethylsulfoxide (DMSO), was essential for promoting functionalization of the π-allyl intermediate; the bis-sulfoxide ligand alone was unable to complete the catalytic cycle. | 0 | Organic Chemistry |
Many complexes feature coordination bonds between a metal and organic ligands. Complexes where the organic ligands bind the metal through a heteroatom such as oxygen or nitrogen are considered coordination compounds (e.g., heme A and Fe(acac)). However, if any of the ligands form a direct metal-carbon (M-C) bond, then the complex is considered to be organometallic. Although the IUPAC has not formally defined the term, some chemists use the term "metalorganic" to describe any coordination compound containing an organic ligand regardless of the presence of a direct M-C bond.
The status of compounds in which the canonical anion has a negative charge that is shared between (delocalized) a carbon atom and an atom more electronegative than carbon (e.g. enolates) may vary with the nature of the anionic moiety, the metal ion, and possibly the medium. In the absence of direct structural evidence for a carbon–metal bond, such compounds are not considered to be organometallic. For instance, lithium enolates often contain only Li-O bonds and are not organometallic, while zinc enolates (Reformatsky reagents) contain both Zn-O and Zn-C bonds, and are organometallic in nature. | 0 | Organic Chemistry |
The Vinland Map is a document that appears to be a 15th-century mappa mundi and which shows a landmass in the Atlantic Ocean, directly south-west of Greenland, labelled Vinlanda Insula ("Isle of Vinland"). It first came to light in 1957 and was acquired by Yale University in 1964. The map's authenticity would have established the awareness of a part of the American continent by European cartographers, before the voyages of Christopher Columbus. McCrone, already reputed for his expertise in authenticating ancient documents and works of art, was asked by Yale to analyze the map in 1972. In 1974, he published evidence that the ink of the map contained synthetic anatase (a form of titanium dioxide), a substance not used as a pigment until the 1920s. According to McCrone, the anatase is present in the yellow ink that the forger used to simulate the natural discoloration that appears over long periods of time around lines drawn on parchment in medieval iron gall ink.
McCrones work on the Vinland Map led to a protracted controversy, with other researchers continuing to argue for the documents authenticity and discounting the presence of titanium as insignificant. In 2021, Raymond Clemens, the curator of early books and manuscripts at Yale's Beinecke Rare Book & Manuscript Library where the map is housed, declared that it had been conclusively shown to be a fake. That judgment was largely based on the presence of synthetic anatase in the ink, as first identified by McCrone. | 3 | Analytical Chemistry |
Sono-Seq (Sonication of Cross-linked Chromatin Sequencing) is a method in molecular biology used for determining the sequences of those DNA regions in the genome near regions of open chromatin of expressed genes. It is also known as "Input" in the Chip-Seq protocol, since it follows the same steps except it doesn't require immunoprecipitation. | 1 | Biochemistry |
The Puerto Mosquito Bioluminescent Bay (), or Mosquito Bio Bay, is a bay in the island of Vieques famous for its bioluminescence produced by the dinoflagellate Pyrodinium bahamense, which glows blue when agitated. This species of phytoplankton is found in bays in the Virgin Islands, Puerto Rico and The Bahamas. | 1 | Biochemistry |
The ancient record on Earth provides an opportunity to see what geochemical signatures are produced by microbial life and how these signatures are preserved over geologic time. Some related disciplines such as geochemistry, geobiology, and geomicrobiology often use biosignatures to determine if living organisms are or were present in a sample. These possible biosignatures include: (a) microfossils and stromatolites; (b) molecular structures (biomarkers) and isotopic compositions of carbon, nitrogen and hydrogen in organic matter; (c) multiple sulfur and oxygen isotope ratios of minerals; and (d) abundance relationships and isotopic compositions of redox-sensitive metals (e.g., Fe, Mo, Cr, and rare earth elements).
For example, the particular fatty acids measured in a sample can indicate which types of bacteria and archaea live in that environment. Another example is the long-chain fatty alcohols with more than 23 atoms that are produced by planktonic bacteria. When used in this sense, geochemists often prefer the term biomarker. Another example is the presence of straight-chain lipids in the form of alkanes, alcohols, and fatty acids with 20–36 carbon atoms in soils or sediments. Peat deposits are an indication of originating from the epicuticular wax of higher plants.
Life processes may produce a range of biosignatures such as nucleic acids, lipids, proteins, amino acids, kerogen-like material and various morphological features that are detectable in rocks and sediments. Microbes often interact with geochemical processes, leaving features in the rock record indicative of biosignatures. For example, bacterial micrometer-sized pores in carbonate rocks resemble inclusions under transmitted light, but have distinct sizes, shapes, and patterns (swirling or dendritic) and are distributed differently from common fluid inclusions. A potential biosignature is a phenomenon that may have been produced by life, but for which alternate abiotic origins may also be possible. | 2 | Environmental Chemistry |
Flow-FISH was first published in 1998 by Rufer et al. as a modification of another technique for analyzing telomere length, Q-FISH, that employs peptide nucleic acid probes of a 3-CCCTAACCCTAACCCTAA-5 sequence labeled with a fluorescin fluorophore to stain telomeric repeats on prepared metaphase spreads of cells that have been treated with colcemid, hypotonic shock, and fixation to slides via methanol/acetic acid treatment Images of the resultant fluorescent spots could then be analyzed via a specialized computer program to yield quantitative fluorescence values that can then be used to estimate actual telomere length. The fluorescence yielded by probe staining is considered to be quantitative because PNA binds preferentially to DNA at low ionic salt concentrations and in the presence of formamide, thus the DNA duplex may not reform once it has been melted and annealed to PNA probe, allowing the probe to saturate its target repeat sequence (as it is not displaced from the target DNA by competing anti sense DNA on the complementary strand), thus yielding a reliable and quantifiable readout of the frequency of PNA probe target at a given chromosomal site after washing away of unbound probe. | 1 | Biochemistry |
Some cyanobacteria can fix atmospheric nitrogen in anaerobic conditions by means of specialized cells called heterocysts. Heterocysts may also form under the appropriate environmental conditions (anoxic) when fixed nitrogen is scarce. Heterocyst-forming species are specialized for nitrogen fixation and are able to fix nitrogen gas into ammonia (), nitrites () or nitrates (), which can be absorbed by plants and converted to protein and nucleic acids (atmospheric nitrogen is not bioavailable to plants, except for those having endosymbiotic nitrogen-fixing bacteria, especially the family Fabaceae, among
others).
Free-living cyanobacteria are present in the water of rice paddies, and cyanobacteria can be found growing as epiphytes on the surfaces of the green alga, Chara, where they may fix nitrogen. Cyanobacteria such as Anabaena (a symbiont of the aquatic fern Azolla) can provide rice plantations with biofertilizer. | 5 | Photochemistry |
In the early 1830s, Michael Faraday laid the foundations of electrochemistry and solid-state ionics by discovering the motion of ions in liquid and solid electrolytes. Earlier, around 1800, Alessandro Volta used a liquid electrolyte in his voltaic pile, the first electrochemical battery, but failed to realize that ions are involved in the process. Meanwhile, in his work on decomposition of solutions by electric current, Faraday used not only the ideas of ion, cation, anion, electrode, anode, cathode, electrolyte and electrolysis, but even the present-day terms for them. Faraday associated electric current in an electrolyte with the motion of ions, and discovered that ions can exchange their charges with an electrode while they were transformed into elements by electrolysis. He quantified those processes by two laws of electrolysis. The first law (1832) stated that the mass of a product at the electrode, Δm, increases linearly with the amount of charge passed through the electrolyte, Δq. The second law (1833) established the proportionality between Δm and the “electrochemical equivalent” and defined the Faraday constant F as F = (Δq/Δm)(M/z), where M is the molar mass and z is the charge of the ion.
In 1834, Faraday discovered ionic conductivity in heated solid electrolytes AgS and PbF. In PbF, the conductivity increase upon heating was not sudden, but spread over a hundred degrees Celsius. Such behavior, called Faraday transition, is observed in the cation conductors NaS and LiSiO and anion conductors PbF, CaF, SrF, SrCl and LaF.
Later in 1891, Johann Wilhelm Hittorf reported on the ion transport numbers in electrochemical cells, and in the early 20th century those numbers were determined for solid electrolytes. | 7 | Physical Chemistry |
Ethenium has been observed in rarefied gases subjected to radiation. Another preparation method is to react certain proton donors such as trihydrogen cation|, helium hydride ion|, diazenylium|, and with ethane at ambient temperature and pressures below 1 mmHg. (Other donors such as methanium| and form ethanium preferably to ethenium.)
At room temperature and in a rarefied methane atmosphere, ethanium slowly dissociates to ethenium and . The reaction is much faster at 90 °C. | 7 | Physical Chemistry |
A more specific term than bioadhesion is mucoadhesion. Most mucosal surfaces such as in the gut or nose are covered by a layer of mucus. Adhesion of a matter to this layer is hence called mucoadhesion. Mucoadhesive agents are usually polymers containing hydrogen bonding groups that can be used in wet formulations or in dry powders for drug delivery purposes. The mechanisms behind mucoadhesion have not yet been fully elucidated, but a generally accepted theory is that close contact must first be established between the mucoadhesive agent and the mucus, followed by interpenetration of the mucoadhesive polymer and the mucin and finishing with the formation of entanglements and chemical bonds between the macromolecules. In the case of a dry polymer powder, the initial adhesion is most likely achieved by water movement from the mucosa into the formulation, which has also been shown to lead to dehydration and strengthening of the mucus layer. The subsequent formation of van der Waals, hydrogen and, in the case of a positively charged polymer, electrostatic bonds between the mucins and the hydrated polymer promotes prolonged adhesion. | 1 | Biochemistry |
The eluent or eluant is the "carrier" portion of the mobile phase. It moves the analytes through the chromatograph. In liquid chromatography, the eluent is the liquid solvent; in gas chromatography, it is the carrier gas. | 3 | Analytical Chemistry |
Two modes can be used for this measurement. One is the isochromat mode, which scans the incident electron energy and keeps the detected photon energy constant. The other is the tunable photon energy mode, or spectrograph mode, which keeps the incident electron energy constant and measures the distribution of the detected photon energy. The latter can also measure the resonant inverse photoemission spectroscopy. | 7 | Physical Chemistry |
Engineers have studied the various heat-engine cycles to improve the amount of usable work they could extract from a given power source. The Carnot cycle limit cannot be reached with any gas-based cycle, but engineers have found at least two ways to bypass that limit and one way to get better efficiency without bending any rules:
#Increase the temperature difference in the heat engine. The simplest way to do this is to increase the hot side temperature, which is the approach used in modern combined-cycle gas turbines. Unfortunately, physical limits (such as the melting point of the materials used to build the engine) and environmental concerns regarding NO production (if the heat source is combustion with ambient air) restrict the maximum temperature on workable heat-engines. Modern gas turbines run at temperatures as high as possible within the range of temperatures necessary to maintain acceptable NO output . Another way of increasing efficiency is to lower the output temperature. One new method of doing so is to use mixed chemical working fluids, then exploit the changing behavior of the mixtures. One of the most famous is the so-called Kalina cycle, which uses a 70/30 mix of ammonia and water as its working fluid. This mixture allows the cycle to generate useful power at considerably lower temperatures than most other processes.
#Exploit the physical properties of the working fluid. The most common such exploitation is the use of water above the critical point (supercritical water). The behavior of fluids above their critical point changes radically, and with materials such as water and carbon dioxide it is possible to exploit those changes in behavior to extract greater thermodynamic efficiency from the heat engine, even if it is using a fairly conventional Brayton or Rankine cycle. A newer and very promising material for such applications is supercritical CO. SO and xenon have also been considered for such applications. Downsides include issues of corrosion and erosion, the different chemical behavior above and below the critical point, the needed high pressures and – in the case of sulfur dioxide and to a lesser extent carbon dioxide – toxicity. Among the mentioned compounds xenon is least suitable for use in a nuclear reactor due to the high neutron absorption cross section of almost all isotopes of xenon, whereas carbon dioxide and water can also double as a neutron moderator for a thermal spectrum reactor.
#Exploit the chemical properties of the working fluid. A fairly new and novel exploit is to use exotic working fluids with advantageous chemical properties. One such is nitrogen dioxide (NO), a toxic component of smog, which has a natural dimer as di-nitrogen tetraoxide (NO). At low temperature, the NO is compressed and then heated. The increasing temperature causes each NO to break apart into two NO molecules. This lowers the molecular weight of the working fluid, which drastically increases the efficiency of the cycle. Once the NO has expanded through the turbine, it is cooled by the heat sink, which makes it recombine into NO. This is then fed back by the compressor for another cycle. Such species as aluminium bromide (AlBr), NOCl, and GaI have all been investigated for such uses. To date, their drawbacks have not warranted their use, despite the efficiency gains that can be realized. | 7 | Physical Chemistry |
SIN3A has been shown to interact with:
* CABIN1
* HBP1,
* HDAC1,
* HDAC9,
* Histone deacetylase 2,
* Host cell factor C1,
* IKZF1,
* ING1,
* KLF11,
* MNT,
* MXD1,
* Methyl-CpG-binding domain protein 2,
* Nuclear receptor co-repressor 2,
* OGT,
* PHF12,
* Promyelocytic leukemia protein,
* RBBP4,
* RBBP7,
* SAP130,
* SAP30,
* SMARCA2,
* SMARCA4,
* SMARCC1,
* SUDS3,
* TAL1, and
* Zinc finger and BTB domain-containing protein 16. | 1 | Biochemistry |
Mitochondrial disorders may be caused by mutations (acquired or inherited), in mitochondrial DNA (mtDNA), or in nuclear genes that code for mitochondrial components. They may also be the result of acquired mitochondrial dysfunction due to adverse effects of drugs, infections, or other environmental causes.
Nuclear DNA has two copies per cell (except for sperm and egg cells), one copy being inherited from the father and the other from the mother. Mitochondrial DNA, however, is inherited from the mother only (with some exceptions) and each mitochondrion typically contains between 2 and 10 mtDNA copies. During cell division the mitochondria segregate randomly between the two new cells. Those mitochondria make more copies, normally reaching 500 mitochondria per cell. As mtDNA is copied when mitochondria proliferate, they can accumulate random mutations, a phenomenon called heteroplasmy. If only a few of the mtDNA copies inherited from the mother are defective, mitochondrial division may cause most of the defective copies to end up in just one of the new mitochondria (for more detailed inheritance patterns, see human mitochondrial genetics). Mitochondrial disease may become clinically apparent once the number of affected mitochondria reaches a certain level; this phenomenon is called "threshold expression".
Mitochondria possess many of the same DNA repair pathways as nuclei do—but not all of them; therefore, mutations occur more frequently in mitochondrial DNA than in nuclear DNA (see Mutation rate). This means that mitochondrial DNA disorders may occur spontaneously and relatively often. Defects in enzymes that control mitochondrial DNA replication (all of which are encoded for by genes in the nuclear DNA) may also cause mitochondrial DNA mutations.
Most mitochondrial function and biogenesis is controlled by nuclear DNA. Human mitochondrial DNA encodes 13 proteins of the respiratory chain, while most of the estimated 1,500 proteins and components targeted to mitochondria are nuclear-encoded. Defects in nuclear-encoded mitochondrial genes are associated with hundreds of clinical disease phenotypes including anemia, dementia, hypertension, lymphoma, retinopathy, seizures, and neurodevelopmental disorders.
A study by Yale University researchers (published in the February 12, 2004, issue of the New England Journal of Medicine) explored the role of mitochondria in insulin resistance among the offspring of patients with type 2 diabetes.
Other studies have shown that the mechanism may involve the interruption of the mitochondrial signaling process in body cells (intramyocellular lipids). A study conducted at the Pennington Biomedical Research Center in Baton Rouge, Louisiana showed that this, in turn, partially disables the genes that produce mitochondria. | 1 | Biochemistry |
Opportunity Rover found meteorites just sitting on the plains. The first one analyzed with Opportunitys instruments was called "Heatshield Rock," as it was found near where Opportunitys heatshield landed. Examination with the Miniature Thermal Emission Spectrometer (Mini-TES), Mossbauer spectrometer, and APXS lead researchers to, classify it as an IAB meteorite. The APXS determined it was composed of 93% iron and 7% nickel. The cobble named "Fig Tree Barberton" is thought to be a stony or stony-iron meteorite (mesosiderite silicate), while "Allan Hills," and "Zhong Shan" may be iron meteorites. | 9 | Geochemistry |
Many former British colonies in the region have always been LHT, including Australia, New Zealand, Fiji, Kiribati, Solomon Islands, Tonga, and Tuvalu; and nations that were previously administered by Australia: Nauru and Papua New Guinea. | 4 | Stereochemistry |
Since mesoionic carbene ligands are very strong σ-donors and make it easier for a metal center to undergo oxidative addition, MIC ligands have the potential to be useful in catalysis. MIC transition metal complexes have been tested as catalysts in olefin metathesis, ring closure metathesis, and ring opening polymerization metathesis. The MIC complexes work very well, and in many cases, they outperform their NHC counterparts. MIC complexes have been successful as catalysts for Suzuki-Miyaura and Heck-Mizoroki cross-coupling reactions. Again, in many cases, MIC catalysts are superior to their NHC counterparts. For example, in olefin metathesis, MIC catalysts are active at room temperature after simply addition of a Brønsted acid, such as hydrochloric acid or trifluoroacetic acid, compared to the large amount of thermal activation required for NHC catalysts. MIC complexes have found use as catalysts in olefin hydrogenation. They have been shown to hydrogenate terminal and cis-alkenes. They work better than their NHC counterparts due to the MIC ligand’s stronger electron-donating properties. They are better able to provide electron density to promote hydrogen gas oxidative addition to the metal. MIC complexes have been used in transfer hydrogenation reactions. For example, they have been used to hydrogenate a diaryl ketone using isopropanol as a hydrogen source., MIC complexes are being considered as green chemistry catalysts. They act as catalysts for base- and oxidant-free oxidation of alcohols and amines. Some complexes have also been shown to synthesize certain aryl amides. Other MIC complexes have been used in hydroarylation, involving the addition of an electron-rich aryl group and a hydrogen across a multiple bond. The reactions that mesoionic carbene complexes catalyze will continue to expand as more research is done. | 0 | Organic Chemistry |
Many grow lights often missing an integrating sphere test report which means that values like photosynthetic photon flux (PPF) are guessed by the manufacturer. Also, false advertising of photosynthetic photon efficacy (PPE) (photosynthetic photon flux (PPF) μmol/W) values from grow light manufacturers can be avoided by simply control calculate the value. Furthermore, some manufacturers state the photosynthetic photon flux density (PPFD) value of the center light-emitting diode (LED) instead of the PPF in the area of one square meter. | 5 | Photochemistry |
The process of pseudorotation occurs when the two axial ligands close like a pair of scissors pushing their way in between two of the equatorial groups which scissor out to accommodate them. Both the axial and equatorial constituents move at the same rate of increasing the angle between the other axial or equatorial constituent. This forms a square based pyramid where the base is the four interchanging ligands and the tip is the pivot ligand, which has not moved. The two originally equatorial ligands then open out until they are 180 degrees apart, becoming axial groups perpendicular to where the axial groups were before the pseudorotation. This requires about 3.6 kcal/mol in PF.
This rapid exchange of axial and equatorial ligands renders complexes with this geometry unresolvable (unlike carbon atoms with four distinct substituents), except at low temperatures or when one or more of the ligands is bi- or poly-dentate. | 4 | Stereochemistry |
Ruderfer et al. analyzed the ancestry of natural S. cerevisiae strains and concluded that matings involving out-crossing occur only about once every 50,000 cell divisions. Thus it appears that, in nature, mating is most often between closely related yeast cells. Mating occurs when haploid cells of opposite mating type MATa and MATα come into contact. Ruderfer et al. pointed out that such contacts are frequent between closely related yeast cells for two reasons. The first is that cells of opposite mating type are present together in the same ascus, the sac that contains the cells directly produced by a single meiosis, and these cells can mate with each other. The second reason is that haploid cells of one mating type, upon cell division, often produce cells of the opposite mating type with which they can mate (see section "Mating type switching", above). The relative rarity in nature of meiotic events that result from out-crossing appears to be inconsistent with the idea that production of genetic variation is the primary selective force maintaining mating capability in this organism. However this finding is consistent with the alternative idea that the primary selective force maintaining mating capability is enhanced recombinational repair of DNA damage during meiosis, since this benefit is realized during each meiosis subsequent to a mating, whether or not out-crossing occurs. | 1 | Biochemistry |
Realtime spectrum analyzers are able to see signals hidden behind other signals. This is possible because no information is missed and the display to the user is the output of FFT calculations. An example of this can be seen on the right. | 7 | Physical Chemistry |
Wrought iron is no longer made. The particles of slag present in the iron after preparation by puddling were drawn into long fibres during the forging or rolling process. The proportion of slag was intended to be about 3%, but the process was difficult to control and examples with up to 10% slag were produced. | 8 | Metallurgy |
The foundations of the compensation effect are still not fully understood though many theories have been brought forward. Compensation of Arrhenius processes in solid-state materials and devices can be explained quite generally from the statistical physics of aggregating fundamental excitations from the thermal bath to surmount a barrier whose activation energy is significantly larger than the characteristic energy of the excitations used (e.g., optical phonons). To rationalize the occurrences of enthalpy-entropy compensation in protein folding and enzymatic reactions, a Carnot-cycle model in which a micro-phase transition plays a crucial role was proposed. In drug receptor binding, it has been suggested that enthalpy-entropy compensation arises due to an intrinsic property of hydrogen bonds. A mechanical basis for solvent-induced enthalpy-entropy compensation has been put forward and tested at the dilute gas limit. There is some evidence of enthalpy-entropy compensation in biochemical or metabolic networks particularly in the context of intermediate-free coupled reactions or processes. However, a single general statistical mechanical explanation applicable to all compensated processes has not yet been developed. | 7 | Physical Chemistry |
Cegelski has authored or co-authored multiple publications that have been cited 100 or more times. As of January 2021, these include:
* "The biology and future prospects of antivirulence therapies," Nature Reviews Microbiology.
* "Morphological plasticity as a bacterial survival strategy," Nature Reviews Microbiology.
* "Small-molecule inhibitors target Escherichia coli amyloid biogenesis and biofilm formation," Nature Chemical Biology.
* "Conformation of microtubule-bound paclitaxel determined by fluorescence spectroscopy and REDOR NMR," Biochemistry.
* "Oritavancin exhibits dual mode of action to inhibit cell-wall biosynthesis in Staphylococcus aureus," Journal of Molecular Biology.
* "Mechanochemical unzipping of insulating polyladderene to semiconducting polyacetylene," Science.
* "Phosphoethanolamine cellulose: a naturally produced chemically modified cellulose," Science. | 7 | Physical Chemistry |
Depending on whether an assay just looks at a single time point or timed readings taken at multiple time points, an assay may be:
#An end point assay, in which a single measurement is performed after a fixed incubation period; or
#A kinetic assay, in which measurements are performed multiple times over a fixed time interval. Kinetic assay results may be visualized numerically (for example, as a slope parameter representing the rate of signal change over time), or graphically (for example, as a plot of the signal measured at each time point). For kinetic assays, both the magnitude and shape of the measured response over time provide important information.
#A high throughput assay can be either an endpoint or a kinetic assay usually done on an automated platform in 96-, 384- or 1536-well microplate formats (High Throughput Screening). Such assays are able to test large number of compounds or analytes or make functional biological readouts in response to a stimuli and/or compounds being tested. | 1 | Biochemistry |
Telomerization is a reaction that produces a particular kind of oligomer with two distinct end groups. The oligomer is called a telomer. Some telomerizations proceed by radical pathways, many do not. A generic equation is:
where M is the monomer, and A and B are the end groups, and n is the degree of polymerization.
One example is the coupled dimerization and hydroesterification of 1,3-butadiene. This step produces a doubly unsaturated C9-ester:
:2CH=CH-CH=CH + CO + CHOH → CH=CH(CH)CH=CHCHCOCH
The monomer in this reaction is butadiene, the degree of polymerization is 2, and the end groups are vinyl and the carboxy methyl (COCH). This and several related reactions proceed with palladium catalysts. Many telomerizations are used in industrial chemistry. | 7 | Physical Chemistry |
Alkyne activation with π–acidic metals such as Au or Pt is a conventional method in complex organic manifold synthesis, however how this activation exacts reactivity is not fully understood and thus mechanism is largely proposed on the basis of reaction outcome and theoretical calculations. Cationic Au(I) and Pt(II) catalyst are attractive choices as they display strong Lewis acid character and the ability to stabilize cationic intermediates while being bench stable.
A versatile function of Au(I) catalyzed enyne cycloisomerization is the construction of asymmetric medium–sized rings, which is a challenge in the synthesis of ornamented molecular design. Convenient access to asymmetric 7– and 8–membered carbocycles is possible using chiral BINAP Au(I) gold catalyst, giving a wide variety of products.
It is proposed that intramolecular cyclopropanation occurs via a 1,2–shift of the propargyl ester mediated by Au to give a syn–Au vinyl carbenoid species (29). Computational studies show that the syn–intermediate, 29, is formed under kinetic control and it is suggested that it is in equilibrium with the thermodynamically favorable cis–intermediate which may be intercepted by a nucleophile leading to vinyl cyclopropane diene products, however this is beyond the scope of this article.
Vinylcycloalkenes is another functional class of products accessible through alkyne activation of enynes with π–acidic metals. PtCl has been shown to catalyze the formation of a variety of exotic vinylcycloalkenes from readily accessible starting materials (figure 10).
Notably, a ring expansion is observed for enynes with cyclic alkene motifs. This is rationalized by a formal insertion of the methylene group of the olefin between the two carbons of the alkyne; a mechanistic reasoning for this ring expansion has also been proposed. The formation of these vinycloalkenes in concert with its ability to undergo a ring expansion was exploited to construct intermediate 36 en route to streptorubin B. A similar transformation is possible using cationic Au(I) complexes, however here one can select for vinycycloalkene products through a mechanism proceeding via an initial 5–exo–dig or bicyclopropanes can be produced via an initial 6–endo–dig. It is suggested through DFT calculations that the 5–exo–dig cyclization is favored for Au(I) complexes as it has a lower activation barrier relative to the 6–endo–dig and indeed numerous examples of vinylcycloalkenes products produced via an initial 5–exo–dig are given (figure 11).
The reactivity can be reversed by careful selection of reaction conditions, catalyst selection and substrate. The divergent reactivity of these transition metal catalyzed cycloisomerizations further demonstrates their synthetic utility in building unique molecular skeletons. | 0 | Organic Chemistry |
By chemical modifications certain properties of polysaccharides can be improved. Various ligands can be covalently attached to their hydroxyl groups. Due to the covalent attachment of methyl-, hydroxyethyl- or carboxymethyl- groups on cellulose, for instance, high swelling properties in aqueous media can be introduced. Another example are thiolated polysaccharides ( see thiomers). Thiol groups are covalently attached to polysaccharides such as hyaluronic acid or chitosan. As thiolated polysaccharides can crosslink via disulfide bond formation, they form stable three-dimensional networks. Furthermore, they can bind to cysteine subunits of proteins via disulfide bonds. Because of these bonds polysaccharides can be covalently attached to endogenous proteins such as mucins or keratins. | 0 | Organic Chemistry |
Early in embryonic development, the embryo has three germ layers and abuts a yolk sac. During the second week of development, the embryo grows and begins to surround and envelop portions of this sac. The enveloped portions form the basis for the adult gastrointestinal tract. Sections of this foregut begin to differentiate into the organs of the gastrointestinal tract, such as the esophagus, stomach, and intestines.
During the fourth week of development, the stomach rotates. The stomach, originally lying in the midline of the embryo, rotates so that its body is on the left. This rotation also affects the part of the gastrointestinal tube immediately below the stomach, which will go on to become the duodenum. By the end of the fourth week, the developing duodenum begins to spout a small outpouching on its right side, the hepatic diverticulum, which will go on to become the biliary tree. Just below this is a second outpouching, known as the cystic diverticulum, that will eventually develop into the gallbladder. | 1 | Biochemistry |
Prototropy is the most common form of tautomerism and refers to the relocation of a hydrogen atom. Prototropic tautomerism may be considered a subset of acid-base behavior. Prototropic tautomers are sets of isomeric protonation states with the same empirical formula and total charge. Tautomerizations are catalyzed by:
* bases, involving a series of steps: deprotonation, formation of a delocalized anion (e.g., an enolate), and protonation at a different position of the anion; and
* acids, involving a series of steps: protonation, formation of a delocalized cation, and deprotonation at a different position adjacent to the cation).
Two specific further subcategories of tautomerizations:
*Annular tautomerism is a type of prototropic tautomerism wherein a proton can occupy two or more positions of the heterocyclic systems found in many drugs, for example, 1H- and 3H-imidazole; 1H-, 2H- and 4H- 1,2,4-triazole; 1H- and 2H- isoindole.
*Ring–chain tautomers occur when the movement of the proton is accompanied by a change from an open structure to a ring, such as the open chain and cyclic hemiacetal (typically pyranose or furanose forms) of many sugars. (See .) The tautomeric shift can be described as H−O ⋅ C=O ⇌ O−C−O−H, where the "⋅" indicates the initial absence of a bond. | 4 | Stereochemistry |
Chaotic scattering is a branch of chaos theory dealing with scattering systems displaying a strong sensitivity to initial conditions. In a classical scattering system there will be one or more impact parameters, b, in which a particle is sent into the scatterer. This gives rise to one or more exit parameters, y, as the particle exits towards infinity. While the particle is traversing the system, there may also be a delay time, T—the time it takes for the particle to exit the system—in addition to the distance travelled, s. In certain systems (e.g. "billiard-like" systems in which the particle undergoes lossless collisions with hard, fixed objects) the two will be equivalent—see below. In a chaotic scattering system, a minute change in the impact parameter, may give rise to a very large change in the exit parameters. | 7 | Physical Chemistry |
The upper critical magnetic field H of the superconducting state of CeCoIn is anisotropic, in accordance with the crystal structure and other physical properties. For magnetic fields applied along the [100] direction, H amounts to approximately 11.6 T, and H for fields along the [001] directions to 4.95 T.
The superconducting order parameter has d-wave symmetry, as established by several experiments, such as scanning tunneling microscopy (STM) and spectroscopy (STS).
Detailed studies close to the critical field have been performed on CeCoIn, and indications were found that certain regimes in the phase diagram of this material should be interpreted in terms of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase.
Subsequently, the neutron-diffraction experiments showed that this regime features a more complex phase that also exhibits incommensurate antiferromagnetic order, a so-called Q phase.
Evidence for a delocalization quantum phase transition without symmetry breaking is presented. | 8 | Metallurgy |
Atomic coherence is the induced coherence between levels of a multi-level atomic system.
The internal state of an atom is characterized by a superposition of excited states and their associated energy levels. In the presence of external electromagnetic fields, the atoms energy levels acquire perturbations to the excited states that describe the atoms internal state. When the acquired phase is the same over the range of internal states, the atom is coherent. Atomic coherence is characterized by the length of time over which the internal state of the atom can be reliably manipulated. | 7 | Physical Chemistry |
The amide tail synthesis (scheme 7) was based on an asymmetric Aldol reaction. The starting compound is the commercially available Benzyloxyacetic acid 53 which was converted to the thio ester 55 (Ethanethiol) through the acid chloride 54 (thionyl chloride, pyridine). This formed the silyl enol ether 55 (n-butyllithium, trimethylsilyl chloride, Diisopropylamine) which reacted with chiral amine catalyst 58, tin triflate and nBu(OAc) in a Mukaiyama aldol addition with benzaldehyde to alcohol 59 with 99% anti selectivity and 96% ee. The next step converting the alcohol group to an amine in 60 was a Mitsunobu reaction (hydrogen azide, diethyl azodicarboxylate, triphenylphosphine with azide reduction to amine by PhP). The amine group was benzoylated with benzoyl chloride (61) and hydrolysis removes the thioether group in 62. | 0 | Organic Chemistry |
Alkenes engage in an acid catalyzed hydration reaction using concentrated sulfuric acid as a catalyst that gives usually secondary or tertiary alcohols. Formation of a secondary alcohol via alkene reduction and hydration is shown on the right:
The hydroboration-oxidation and oxymercuration-reduction of alkenes are more reliable in organic synthesis. Alkenes react with N-bromosuccinimide and water in halohydrin formation reaction. Amines can be converted to diazonium salts, which are then hydrolyzed. | 0 | Organic Chemistry |
X-ray absorption fine-structure spectroscopy is an atomic scale probe making it useful for studying materials lacking in long range order. Spectra obtained using this method provide information on the oxidation state, coordination number, and species surrounding the atom in question as well as the distances at which they are found. | 7 | Physical Chemistry |
Prisms have higher dispersion in the UV region. Prism monochromators are favored in some instruments that are principally designed to work in the far UV region. Most monochromators use gratings, however. Some monochromators have several gratings that can be selected for use in different spectral regions. A double monochromator made by placing a prism and a grating monochromator in series typically does not need additional bandpass filters to isolate a single grating order. | 7 | Physical Chemistry |
The isohydric principle is the phenomenon whereby multiple acid/base pairs in solution will be in equilibrium with one another, tied together by their common reagent: the hydrogen ion and hence, the pH of solution. That is, when several buffers are present together in the same solution, they are all exposed to the same hydrogen ion activity. Hence, the pK of each buffer will dictate the ratio of the concentrations of its base and weak acid forms at the given pH, in accordance with the Henderson-Hasselbalch equation.
Any condition that changes the balance of one of the buffer systems, also changes the balance of all the others because the buffer systems actually buffer one another by shifting hydrogen ions back and forth from one to the other.
The isohydric principle has special relevance to in vivo biochemistry where multiple acid/ base pairs are in solution. The simplifying isohydric principle gives two important concepts. First, all of the buffers in a multiple-buffered system contribute to pH of the system. Secondly, the pH (at equilibrium) can be calculated from an individual buffer system regardless of other buffers present. That is, in vivo, knowing the concentration of pCO (weak acid) and bicarbonate (conjugate base) and the pKa of that buffer system, the pH can be calculated regardless of the presence of other contributing buffers. The clinical relevance is that arterial blood gas often directly measures the levels and the pH, but the bicarbonate levels are then calculated from that information—without regard to other buffers present | 7 | Physical Chemistry |
Electron magnetic circular dichroism (EMCD) (also known as electron energy-loss magnetic chiral dichroism) is the EELS equivalent of XMCD.
The effect was first proposed in 2003 and experimentally confirmed in 2006 by the group of Prof. Peter Schattschneider at the Vienna University of Technology.
Similarly to XMCD, EMCD is a difference spectrum of two EELS spectra taken in a magnetic field with opposite helicities. Under appropriate scattering conditions virtual photons with specific circular polarizations can be absorbed, giving rise to spectral differences. The largest difference is expected between the case where one virtual photon with left circular polarization and one with right circular polarization are absorbed. By closely analyzing the difference in the EMCD spectrum, information can be obtained on the magnetic properties of the atom, such as its spin and orbital magnetic moment.
In the case of transition metals such as iron, cobalt, and nickel, the absorption spectra for EMCD are usually measured at the L-edge. This corresponds to the excitation of a 2p electron to a 3d state by the absorption of a virtual photon providing the ionisation energy. The absorption is visible as a spectral feature in the electron energy loss spectrum (EELS). Because the 3d electron states are the origin of the magnetic properties of the elements, the spectra contain information on the magnetic properties. Moreover, since the energy of each transition depends on the atomic number, the information obtained is element specific, that is, it is possible to distinguish the magnetic properties of a given element by examining the EMCD spectrum at its characteristic energy (708 eV for iron).
Since in both EMCD and XMCD the same electronic transitions are probed, the information obtained is the same. However EMCD has a higher spatial resolution and depth sensitivity than its X-ray counterpart. Moreover, EMCD can be measured on any TEM equipped with an EELS detector, whereas XMCD is normally measured only on dedicated synchrotron beamlines.
A disadvantage of EMCD in its original incarnation is its requirement of crystalline materials with a thickness and orientation that just precisely gives the correct 90 degree phase shift needed for EMCD. However, a new method has recently demonstrated that electron vortex beams can also be used to measure EMCD without the geometrical constraints of the original procedure. | 7 | Physical Chemistry |
When combining a passive daytime radiative cooling system with thermal insulation and evaporative cooling, one study found a 300% increase in ambient cooling power when compared to a stand-alone radiative cooling surface, which could extend the shelf life of food by 40% in humid climates and 200% in desert climates without refrigeration. The system's evaporative cooling layer would require water "re-charges" every 10 days to a month in humid areas and every 4 days in hot and dry areas. | 7 | Physical Chemistry |
Capillary electrochromatography (CEC) combines the principles used in HPLC and CE. The mobile phase is driven across the chromatographic bed using electroosmosis instead of pressure (as in HPLC). Electroosmosis is the motion of liquid induced by an applied potential across a porous material, capillary tube, membrane or any other fluid conduit. Electroosmotic flow is caused by the Coulomb force induced by an electric field on net mobile electric charge in a solution. Under alkaline conditions, the surface silanol groups of the fused silica will become ionised leading to a negatively charged surface. This surface will have a layer of positively charged ions in close proximity which are relatively immobilised. This layer of ions is called the Stern layer. The thickness of the double layer is given by the formula:
where ε is the relative permittivity of the medium, ε is the permittivity of vacuum, R is the universal gas constant, T is the absolute temperature, c is the molar concentration, and F is the Faraday constant
When an electric field is applied to the fluid (usually via electrodes placed at inlets and outlets), the net charge in the electrical double layer is induced to move by the resulting Coulomb force. The resulting flow is termed electroosmotic flow. In CEC positive ions of the electrolyte added along with the analyte accumulate in the electrical double layer of the particles of the column packing on application of an electric field they move towards the cathode and drag the liquid mobile phase with them.
The relationship between the linear velocity u of the liquid in the capillary and the applied electric field is given by the Smoluchowski equation as
where ζ is the potential across the Stern layer (zeta potential), E is the electric field strength, and η is the viscosity of the solvent.
Separation of components in CEC is based on interactions between the stationary phase and differential electrophoretic migration of solutes. | 1 | Biochemistry |
The underlying principle corresponds to that of the Fabry-Pérot interferometer, which is also the underlying principle for the white-light interferometry. | 7 | Physical Chemistry |
The sigma (σ) phase is an intermetallic compound known as the one without definite stoichiometric composition and formed at the electron/atom ratio range of 6.2 to 7. It has a primitive tetragonal unit cell with 30 atoms. CrFe is a typical alloy crystallizing in the σ phase at the equiatomic composition. With physical properties adjustable based on its structural components, or its chemical composition provided a given structure.
The μ phase has an ideal AB stoichiometry, with its prototype WFe, containing rhombohedral cell with 13 atoms. While many other Frank-Kasper alloy types have been identified, more continue to be found. The alloy NbNiAl is the prototype for the M phase. It has orthorhombic space group with 52 atoms per unit cell. The alloy CrMoNi is the prototype for the P-phase. It has a primitive orthorhombic cell with 56 atoms. The alloy CoCrMo is the prototype for the R-phase which belongs to the rhombohedral space group with 53 atoms per cell. | 8 | Metallurgy |
A stream of airborne microorganisms, including marine viruses, bacteria and protists, circles the planet above weather systems but below commercial air lanes. Some peripatetic microorganisms are swept up from terrestrial dust storms, but most originate from marine microorganisms in sea spray. In 2018, scientists reported that hundreds of millions of these viruses and tens of millions of bacteria are deposited daily on every square meter around the planet.
Compared to the sub-surface waters, the sea surface microlayer contains elevated concentration of bacteria and viruses, as well as toxic metals and organic pollutants. These materials can be transferred from the sea-surface to the atmosphere in the form of wind-generated aqueous aerosols due to their high vapor tension and a process known as volatilisation. When airborne, these microbes can be transported long distances to coastal regions. If they hit land they can have detrimental effects on animals, vegetation and human health. Marine aerosols that contain viruses can travel hundreds of kilometers from their source and remain in liquid form as long as the humidity is high enough (over 70%). These aerosols are able to remain suspended in the atmosphere for about 31 days. Evidence suggests that bacteria can remain viable after being transported inland through aerosols. Some reached as far as 200 meters at 30 meters above sea level. It was also noted that the process which transfers this material to the atmosphere causes further enrichment in both bacteria and viruses in comparison to either the SML or sub-surface waters (up to three orders of magnitude in some locations). | 7 | Physical Chemistry |
Chiral amide bases may be used in catalytic amounts to isomerize meso epoxides to chiral allylic alcohols with high enantioselectivity. | 0 | Organic Chemistry |
The society was founded in 1911 by Benjamin Moore, W.D. Halliburton and others, under the name of the Biochemical Club. It acquired the existing Biochemical Journal in 1912.
The society name changed to the Biochemical Society in 1913.
In 2005, the headquarters of the society moved from Portland Place to purpose-built offices in Holborn.
In 2009, the headquarters moved again to Charles Darwin House, near Gray's Inn Road.
Past presidents include Professor Ron Laskey, Sir Philip Cohen, and Sir Tom Blundell. | 1 | Biochemistry |
Even for interacting particles, at high scattering vector the structure factor goes to 1. This result follows from Equation (), since is the Fourier transform of the "regular" function and thus goes to zero for high values of the argument . This reasoning does not hold for a perfect crystal, where the distribution function exhibits infinitely sharp peaks. | 3 | Analytical Chemistry |
The parallel configuration or long optical path-length arrangement only provides information about the spectral changes that occur in the solution adjacent to the working electrode surface, improving the sensitivity to soluble compounds because the length of the optical pathway can be as longer as the length of the electrode.
The light beam travels parallel to the working electrode surface, sampling the first micrometers of the solution adjacent to the working electrode surface, and collecting the information on the spectrometer.
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Usually, aligning light beams has been a difficult task. However, simple alternatives have been developed to perform measurements in parallel configuration. There are several advantages in this configuration respect to the normal one: better sensitivity, lower detection limits; optically transparent electrodes are not required; and the spectral changes are related only to the diffusion layer. | 7 | Physical Chemistry |
Many organisms have a ribonucleoprotein enzyme called telomerase, which carries out the task of adding repetitive nucleotide sequences to the ends of the DNA. Telomerase "replenishes" the telomere "cap" and requires no ATP In most multicellular eukaryotic organisms, telomerase is active only in germ cells, some types of stem cells such as embryonic stem cells, and certain white blood cells. Telomerase can be reactivated and telomeres reset back to an embryonic state by somatic cell nuclear transfer. The steady shortening of telomeres with each replication in somatic (body) cells may have a role in senescence and in the prevention of cancer. This is because the telomeres act as a sort of time-delay "fuse", eventually running out after a certain number of cell divisions and resulting in the eventual loss of vital genetic information from the cell's chromosome with future divisions. | 1 | Biochemistry |
The reaction between a ketone and ammonia results in an imine and byproduct water. This reaction is water sensitive and thus drying agents such as aluminum chloride or a Dean–Stark apparatus must be employed to remove water. The resulting imine will react and decompose back into the ketone and the ammonia when in the presence of water. This is due to the fact that this reaction is reversible: | 1 | Biochemistry |
A free radical is formed from the carboxylic acid in an oxidative decarboxylation with silver salts and an oxidizing agent. The oxidizing agent (ammonium persulfate) oxidizes the Ag(+) to Ag(2+) under the acidic reaction conditions. This induces a hydrogen atom abstraction by the silver, followed by radical decarboxylation. The carbon-centered radical then reacts with the pyridinium aromatic compound. The ultimate product is formed by rearomatization. The acylated product is formed from the acyl radical. | 0 | Organic Chemistry |
Ammonia-Oxidizing Bacteria (AOB) are typically Gram-negative bacteria and belong to Betaproteobacteria and Gammaproteobacteria including the commonly studied genera including Nitrosomonas and Nitrococcus. They are known for their ability to utilize ammonia as an energy source and are prevalent in a wide range of environments, such as soils, aquatic systems, and wastewater treatment plants.
AOB possess enzymes called ammonia monooxygenases (AMOs), which are responsible for catalyzing the conversion of ammonia to hydroxylamine (NHOH), a crucial intermediate in the process of nitrification. This enzymatic activity is sensitive to environmental factors, such as pH, temperature, and oxygen availability.
AOB play a vital role in soil nitrification, making them key players in nutrient cycling. They contribute to the transformation of ammonia derived from organic matter decomposition or fertilizers into nitrite, which subsequently serves as a substrate for nitrite-oxidizing bacteria (NOB). | 1 | Biochemistry |
Alpha spectrometry (also known as alpha(-particle) spectroscopy) is the quantitative study of the energy of alpha particles emitted by a radioactive nuclide that is an alpha emitter.
As emitted alpha particles are mono-energetic (i.e. not emitted with a spectrum of energies, such as beta decay) with energies often distinct to the decay they can be used to identify which radionuclide they originated from. | 7 | Physical Chemistry |
A diose is a monosaccharide containing two carbon atoms. Because the general chemical formula of an unmodified monosaccharide is (C·HO), where n is three or greater, it does not meet the formal definition of a monosaccharide. However, since it does fit the formula (C·HO), it is sometimes thought of as the most basic sugar.
There is only one possible diose, glycolaldehyde (2-hydroxyethanal), which is an aldodiose (a ketodiose is not possible since there are only two carbons). | 1 | Biochemistry |
Cleavage stimulatory factor or cleavage stimulation factor (CstF or CStF) is a heterotrimeric protein, made up of the proteins CSTF1 (55kDa), CSTF2 (64kDa) and CSTF3 (77kDa), totalling about 200 kDa. It is involved in the cleavage of the 3 signaling region from a newly synthesized pre-messenger RNA (mRNA) molecule. CstF is recruited by cleavage and polyadenylation specificity factor (CPSF) and assembles into a protein complex on the 3 end to promote the synthesis of a functional polyadenine tail, which results in a mature mRNA molecule ready to be exported from the cell nucleus to the cytosol for translation.
The amount of CstF in a cell is dependent on the phase of the cell cycle, increasing significantly during the transition from G0 phase to S phase in mouse fibroblast and human splenic B cells. | 1 | Biochemistry |
In humans, pyrimidine rings (C, T, U) can be degraded completely to CO and NH (urea excretion). That having been said, purine rings (G, A) cannot. Instead, they are degraded to the metabolically inert uric acid which is then excreted from the body. Uric acid is formed when GMP is split into the base guanine and ribose. Guanine is deaminated to xanthine which in turn is oxidized to uric acid. This last reaction is irreversible. Similarly, uric acid can be formed when AMP is deaminated to IMP from which the ribose unit is removed to form hypoxanthine. Hypoxanthine is oxidized to xanthine and finally to uric acid. Instead of uric acid secretion, guanine and IMP can be used for recycling purposes and nucleic acid synthesis in the presence of PRPP and aspartate (NH donor). | 1 | Biochemistry |
Biebrich scarlet (C.I. 26905) is a molecule used in Lillie's trichrome.
The dye was created in 1878 by the German chemist Rudolf Nietzki.
Biebrich scarlet dyes are used to color hydrophobic materials like fats and oils. The dye is an illegal dye for food additives because of its carcinogenic properties. Biebrich scarlet can have harmful effects on living and non-living organisms in natural water, therefore the pollutant must be removed. Removal of the pollutant involves absorption, membrane filtration, precipitation, ozonation, fungal detachment, and electrochemical separation. Hydrogel absorbents have active sites to which the dye is held using electrostatic interactions. Photocatalysis allows for almost total degradation of Biebrich scarlet azo dye bonds in less than 10 hours. Degradation of Biebrich scarlet is also observed using lignin peroxidase enzyme from wood rotting fungus in the presence of mediators like 2-chloro-1,4-dimethoxybenzene. | 1 | Biochemistry |
Sevoflurane has an excellent safety record, but is under review for potential hepatotoxicity, and may accelerate Alzheimer's. There were rare reports involving adults with symptoms similar to halothane hepatotoxicity. Sevoflurane is the preferred agent for mask induction due to its lesser irritation to mucous membranes.
Sevoflurane is an inhaled anaesthetic that is often used to induction and maintenance of anaesthesia in children for surgery. During the process of awakening from the medication, it has been associated with a high incidence (>30%) of agitation and delirium in preschool children undergoing minor noninvasive surgery. It is not clear if this can be prevented.
Studies examining a current significant health concern, anesthetic-induced neurotoxicity (including with sevoflurane, and especially with children and infants) are "fraught with confounders, and many are underpowered statistically", and so are argued to need "further data... to either support or refute the potential connection".
Concern regarding the safety of anaesthesia is especially acute with regard to children and infants, where preclinical evidence from relevant animal models suggest that common clinically important agents, including sevoflurane, may be neurotoxic to the developing brain, and so cause neurobehavioural abnormalities in the long term; two large-scale clinical studies (PANDA and GAS) were ongoing as of 2010, in hope of supplying "significant [further] information" on neurodevelopmental effects of general anaesthesia in infants and young children, including where sevoflurane is used.
In 2021, researchers at Massachusetts General Hospital published in Communications Biology research that sevoflurane may accelerate existing Alzheimer's or existing tau protein to spread: "These data demonstrate anesthesia-associated tau spreading and its consequences. [...] This tau spreading could be prevented by inhibitors of tau phosphorylation or extracellular vesicle generation." According to Neuroscience News, "Their previous work showed that sevoflurane can cause a change (specifically, phosphorylation, or the addition of phosphate) to tau that leads to cognitive impairment in mice. Other researchers have also found that sevoflurane and certain other anesthetics may affect cognitive function."
Additionally, there has been some investigation into potential correlation of sevoflurane use and renal damage (nephrotoxicity). However, this should be subject to further investigation, as a recent study shows no correlation between sevoflurane use and renal damage as compared to other control anesthetic agents. | 2 | Environmental Chemistry |
It is uncertain whether the oxhide ingots served as a form of currency. Ingots found in excavations at Mycenae are now part of the exhibits of the Numismatic Museum of Athens. Cemal Pulak argues that the weights of the Uluburun ingots are similar enough to have allowed "a rough but quick reckoning of a given quantity of raw metal prior to weighing". But George Bass proposes, via the Gelidonya ingots, whose weights are approximately the same if somewhat lower than the Uluburun ingot weights, that the weights were not standard and thus the ingots were not a currency. Another theory is that the oxhide shape, as well as the bun shape that some ingots took, was a visual statement that the ingot at hand is part of a legitimate trade. In Sardinia, oxhide ingot fragments have been found in hoards with bun ingots and scrap metal and, in some cases, in a metallurgical workshop. Citing this evidence, Vasiliki Kassianidou argues that the oxhide ingots "were meant to be used rather than to be kept as prestige goods". | 8 | Metallurgy |
Given a thermodynamic system at an absolute temperature , the average thermal energy carried by each microscopic degree of freedom in the system is (i.e., about , or , at room temperature). This is generally true only for classical systems with a large number of particles, and in which quantum effects are negligible.
In classical statistical mechanics, this average is predicted to hold exactly for homogeneous ideal gases. Monatomic ideal gases (the six noble gases) possess three degrees of freedom per atom, corresponding to the three spatial directions. According to the equipartition of energy this means that there is a thermal energy of per atom. This corresponds very well with experimental data. The thermal energy can be used to calculate the root-mean-square speed of the atoms, which turns out to be inversely proportional to the square root of the atomic mass. The root mean square speeds found at room temperature accurately reflect this, ranging from for helium, down to for xenon.
Kinetic theory gives the average pressure for an ideal gas as
Combination with the ideal gas law
shows that the average translational kinetic energy is
Considering that the translational motion velocity vector has three degrees of freedom (one for each dimension) gives the average energy per degree of freedom equal to one third of that, i.e. .
The ideal gas equation is also obeyed closely by molecular gases; but the form for the heat capacity is more complicated, because the molecules possess additional internal degrees of freedom, as well as the three degrees of freedom for movement of the molecule as a whole. Diatomic gases, for example, possess a total of six degrees of simple freedom per molecule that are related to atomic motion (three translational, two rotational, and one vibrational). At lower temperatures, not all these degrees of freedom may fully participate in the gas heat capacity, due to quantum mechanical limits on the availability of excited states at the relevant thermal energy per molecule. | 7 | Physical Chemistry |
DABCO is used as a nucleophilic catalyst for:
*formation of polyurethane from alcohol and isocyanate functionalized monomers and pre-polymers.
*Baylis–Hillman reactions of aldehydes and unsaturated ketones and aldehydes. | 0 | Organic Chemistry |
The FCC lattice is a Bravais lattice, and its Fourier transform is a body-centered cubic lattice. However to obtain without this shortcut, consider an FCC crystal with one atom at each lattice point as a primitive or simple cubic with a basis of 4 atoms, at the origin and at the three adjacent face centers, , and . Equation () becomes
with the result
The most intense diffraction peak from a material that crystallizes in the FCC structure is typically the (111). Films of FCC materials like gold tend to grow in a (111) orientation with a triangular surface symmetry. A zero diffracted intensity for a group of diffracted beams (here, of mixed parity) is called a systematic absence. | 3 | Analytical Chemistry |
A DNA microarray (also commonly known as DNA chip or biochip) is a collection of microscopic DNA spots attached to a solid surface. Scientists use DNA microarrays to measure the expression levels of large numbers of genes simultaneously or to genotype multiple regions of a genome. Each DNA spot contains picomoles (10 moles) of a specific DNA sequence, known as probes (or reporters or oligos). These can be a short section of a gene or other DNA element that are used to hybridize a cDNA or cRNA (also called anti-sense RNA) sample (called target) under high-stringency conditions. Probe-target hybridization is usually detected and quantified by detection of fluorophore-, silver-, or chemiluminescence-labeled targets to determine relative abundance of nucleic acid sequences in the target. The original nucleic acid arrays were macro arrays approximately 9 cm × 12 cm and the first computerized image based analysis was published in 1981. It was invented by Patrick O. Brown. An example of its application is in SNPs arrays for polymorphisms in cardiovascular diseases, cancer, pathogens and GWAS analysis. It is also used for the identification of structural variations and the measurement of gene expression. | 1 | Biochemistry |
Plants can absorb nitrate or ammonium from the soil by their root hairs. If nitrate is absorbed, it is first reduced to nitrite ions and then ammonium ions for incorporation into amino acids, nucleic acids, and chlorophyll. In plants that have a symbiotic relationship with rhizobia, some nitrogen is assimilated in the form of ammonium ions directly from the nodules. It is now known that there is a more complex cycling of amino acids between Rhizobia bacteroids and plants. The plant provides amino acids to the bacteroids so ammonia assimilation is not required and the bacteroids pass amino acids (with the newly fixed nitrogen) back to the plant, thus forming an interdependent relationship. While many animals, fungi, and other heterotrophic organisms obtain nitrogen by ingestion of amino acids, nucleotides, and other small organic molecules, other heterotrophs (including many bacteria) are able to utilize inorganic compounds, such as ammonium as sole N sources. Utilization of various N sources is carefully regulated in all organisms. | 1 | Biochemistry |
The FLC operon is a conserved eukaryotic locus that is negatively associated with flowering via repression of genes needed for the development of the meristem to switch to a floral state in the plant species Arabidopsis thaliana. FLC expression has been shown be regulated by the presence of [https://www.uniprot.org/uniprot/P0DH90 FRIGIDA], and negatively correlates with decreases in temperature resulting in the prevention of vernalization. The degree to which expression decreases depends on the temperature and exposure time as seasons progress. After the downregulation of FLC expression, the potential for flowering is enabled. The regulation of FLC expression involves both genetic and epigenetic factors such as histone methylation and DNA methylation. Furthermore, a number of genes are cofactors act as negative transcription factors for FLC genes. FLC genes also have a large number of homologues across species that allow for specific adaptations in a range of climates. | 1 | Biochemistry |
On a daily scale, GPP rates are most affected by the diel cycle of photosynthetically active radiation while ER is largely affected by changes in water temperature. Additionally, ER rates are also tied to the quantity or quality of the organic substrate and relative contributions of autotrophic and heterotrophic respiration, as indicated by studies of the patterns of night-time respiration (e.g. Sadro et al. 2014). For example, bacterioplankton respiration can be higher during the day and in the first hours of the night, due to the higher availability of labile dissolved organic matter produced by phytoplankton. As the sun rises, there is a rapid increase in primary production in the lake, often making it autotrophic (NEP > 0) and reducing dissolved that was produced from carbon mineralization that occurred during the night. This behavior continues until reaching a peak in NEP, typically around the maximum light availability. Then there is a tendency for the NEP to fall steadily between the hours of maximum light availability until the next day's sunrise.
Day-to-day differences in incoming light and temperature, due to differences in the weather, such as cloud cover and storms, affect rates of primary production and, to a lesser extent, respiration. These weather variations also cause short-term variability in mixed layer depth, which in turn affects nutrients, organic matter, and light availability, as well as vertical and horizontal gas exchanges. Deep mixing reduces light availability but also increases nutrients and organic matter availability in the upper layers. Thus the effects of short-term variability in mixed layer depth on gross primary production (GPP) will depend on which are the limiting factors on each lake at a given period. Thus a deeper mixing layer could either increase or decrease GPP rates depending on the balance between nutrient and light limitation of photosynthesis ().
Responses in metabolic rates are as dynamic as the physical and chemical processes occurring in the lake, but changes in algal biomass are less variable, involving growth and loss over longer periods. High light and nutrients availability are associated with the formation of algal blooms in lakes; during these blooms GPP rates are very high, and ER rates usually increase almost as much as GPP rates, and the balance of GPP and ER is close to 1. Right after the bloom, GPP rates start to decrease but ER rates continue higher due to the high availability of labile organic matter, which can lead to a fast depletion of dissolved oxygen concentration in the water column, resulting in fish kills. | 1 | Biochemistry |
The absorption of methyl orange on the UV/vis spectrum is between 350-550 nm, with its peak at 464 nm. This is in the green-purple visible light range and explains why methyl orange is, in fact, orange. | 3 | Analytical Chemistry |
The standard enthalpy of a reaction is defined so as to depend simply upon the standard conditions that are specified for it, not simply on the conditions under which the reactions actually occur. There are two general conditions under which thermochemical measurements are actually made.
: (a) Constant volume and temperature: heat , where (sometimes written as ) is the internal energy of the system
: (b) Constant pressure and temperature: heat , where is the enthalpy of the system
The magnitudes of the heat effects in these two conditions are different. In the first case the volume of the system is kept constant during the course of the measurement by carrying out the reaction in a closed and rigid container, and as there is no change in the volume no work is involved. From the first law of thermodynamics, , where W is the work done by the system. When only expansion work is possible for a process we have ; this implies that the heat of reaction at constant volume is equal to the change in the internal energy of the reacting system.
The thermal change that occurs in a chemical reaction is only due to the difference between the sum of internal energy of the products and the sum of the internal energy of reactants. We have
This also signifies that the amount of heat absorbed at constant volume could be identified with the change in the thermodynamic quantity internal energy.
At constant pressure on the other hand, the system is either kept open to the atmosphere or confined within a container on which a constant external pressure is exerted and under these conditions the volume of the system changes.
The thermal change at a constant pressure not only involves the change in the internal energy of the system but also the work performed either in expansion or contraction of the system. In general the first law requires that
: (work)
If is only pressure–volume work, then at constant pressure
Assuming that the change in state variables is due solely to a chemical reaction, we have
As enthalpy or heat content is defined by , we have
By convention, the enthalpy of each element in its standard state is assigned a value of zero. If pure preparations of compounds or ions are not possible, then special further conventions are defined. Regardless, if each reactant and product can be prepared in its respective standard state, then the contribution of each species is equal to its molar enthalpy of formation multiplied by its stoichiometric coefficient in the reaction, and the enthalpy of reaction at constant (standard) pressure and constant temperature (usually 298 K) may be written as
As shown above, at constant pressure the heat of the reaction is exactly equal to the enthalpy change, , of the reacting system. | 7 | Physical Chemistry |
See: Partition chromatography, Gas chromatography
Partition equilibrium chromatography is a type of chromatography that is typically used in gas chromatography (GC) and high performance liquid chromatography (HPLC). The stationary phase in GC is a high boiling liquid bonded to solid surface and the mobile phase is a gas. In gas-liquid chromatography, analyte from the mobile gas phase equilibrates with the liquid phase. Molecules more soluble in the liquid phase will remain longer in the column, allowing for separation using partition equilibriums. | 7 | Physical Chemistry |
There is great variability in the use of the lost-wax method in East Asia. The casting method to make bronzes till the early phase of Eastern Zhou (770-256 ) was almost invariably section-mold process. Starting from around 600 , there was an unmistakable rise of lost-wax casting in the central plains of China, first witnessed in the Chu cultural sphere.
Further investigations have revealed this not to be the case as it is clear that the piece-mould casting method was the principal technique used to manufacture bronze vessels in China. The lost-wax technique did not appear in northern China until the 6th century BC. Lost-wax casting is known as rōgata in Japanese, and dates back to the Yayoi period, . The most famous piece made by cire perdue is the bronze image of Buddha in the temple of the Todaiji monastery at Nara. It was made in sections between 743 and 749, allegedly using seven tons of wax. | 8 | Metallurgy |
Homologous series are not unique to organic chemistry. Titanium, vanadium, and molybdenum oxides all form homologous series (e.g. VO for 2 H (with n up to 8) that are analogous to the alkanes, CH. | 0 | Organic Chemistry |
One hypothesis for mitochondrial diseases is that mitochondrial damage and dysfunction play an important role in aging. Protofection is being researched as a possibly viable laboratory technique for constructing gene therapies for inherited mitochondrial diseases, such as Leber's hereditary optic neuropathy. Studies have shown that protofection can lead to improved mitochondrial function in targeted cells.
Protofection could be applied to modified or artificial mitochondria. Mitochondria could be modified to produce few or no free radicals without compromising energy production. Recent studies have demonstrated that mitochondrial transplants may be useful to rejuvenate dead or dying tissue, such as in heart attacks, for which the mitochondria is the first part of the cell that dies. | 1 | Biochemistry |
Because surface tension manifests itself in various effects, it offers a number of paths to its measurement. Which method is optimal depends upon the nature of the liquid being measured, the conditions under which its tension is to be measured, and the stability of its surface when it is deformed. An instrument that measures surface tension is called tensiometer.
* Du Noüy ring method: The traditional method used to measure surface or interfacial tension. Wetting properties of the surface or interface have little influence on this measuring technique. Maximum pull exerted on the ring by the surface is measured.
*Wilhelmy plate method: A universal method especially suited to check surface tension over long time intervals. A vertical plate of known perimeter is attached to a balance, and the force due to wetting is measured.
* Spinning drop method: This technique is ideal for measuring low interfacial tensions. The diameter of a drop within a heavy phase is measured while both are rotated.
* Pendant drop method: Surface and interfacial tension can be measured by this technique, even at elevated temperatures and pressures. Geometry of a drop is analyzed optically. For pendant drops the maximum diameter and the ratio between this parameter and the diameter at the distance of the maximum diameter from the drop apex has been used to evaluate the size and shape parameters in order to determine surface tension.
* Bubble pressure method (Jaeger's method): A measurement technique for determining surface tension at short surface ages. Maximum pressure of each bubble is measured.
* Drop volume method: A method for determining interfacial tension as a function of interface age. Liquid of one density is pumped into a second liquid of a different density and time between drops produced is measured.
* Capillary rise method: The end of a capillary is immersed into the solution. The height at which the solution reaches inside the capillary is related to the surface tension by the equation discussed above.
* Stalagmometric method: A method of weighting and reading a drop of liquid.
* Sessile drop method: A method for determining surface tension and density by placing a drop on a substrate and measuring the contact angle (see Sessile drop technique).
*Du Noüy–Padday method: A minimized version of Du Noüy method uses a small diameter metal needle instead of a ring, in combination with a high sensitivity microbalance to record maximum pull. The advantage of this method is that very small sample volumes (down to few tens of microliters) can be measured with very high precision, without the need to correct for buoyancy (for a needle or rather, rod, with proper geometry). Further, the measurement can be performed very quickly, minimally in about 20 seconds.
* Vibrational frequency of levitated drops: The natural frequency of vibrational oscillations of magnetically levitated drops has been used to measure the surface tension of superfluid He. This value is estimated to be 0.375 dyn/cm at = 0 K.
* Resonant oscillations of spherical and hemispherical liquid drop: The technique is based on measuring the resonant frequency of spherical and hemispherical pendant droplets driven in oscillations by a modulated electric field. The surface tension and viscosity can be evaluated from the obtained resonant curves.
* Drop-bounce method: This method is based on aerodynamic levitation with a split-able nozzle design. After dropping a stably levitated droplet onto a platform, the sample deforms and bounces back, oscillating in mid-air as it tries to minimize its surface area. Through this oscillation behavior, the liquid's surface tension and viscosity can be measured. | 6 | Supramolecular Chemistry |
In biological oceanography, new production is supported by nutrient inputs from outside the euphotic zone, especially upwelling of nutrients from deep water, but also from terrestrial and atmosphere sources (as opposite to regenerated production, which is supported by recycling of nutrients in the euphotic zone). New production depends on mixing and vertical advective processes associated with the circulation. | 9 | Geochemistry |
The detection of -2-hydroxyglutarate in glioma patients using proton magnetic resonance spectroscopy (MRS) has been shown to be a noninvasive procedure. The presence of IDH1 or IDH2 mutations was linked to the detection of this oncometabolite 100 percent of the time. IDH2/R140Q is a specific mutation that has shown promising results after its inhibition by the small molecule AGI-6780. Therefore, limiting the supply of -2-hydroxyglutarate by inhibiting the detected mutant IDH enzymes could be a good therapeutical approach to IDH-mutant cancers. | 1 | Biochemistry |
The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula, including parts of the Eastern Shore of Maryland, the Eastern Shore of Virginia, and the state of Delaware. The mouth of the Bay at its southern point is located between Cape Henry and Cape Charles. With its northern portion in Maryland and the southern part in Virginia, the Chesapeake Bay is a very important feature for the ecology and economy of those two states, as well as others surrounding within its watershed. More than 150 major rivers and streams flow into the Bay's drainage basin, which covers parts of six states, New York, Pennsylvania, Delaware, Maryland, Virginia, and West Virginia, and all of Washington, D.C.
The Bay is approximately long from its northern headwaters in the Susquehanna River to its outlet in the Atlantic Ocean. It is wide at its narrowest (between Kent County's Plum Point near Newtown in the east and the Harford County western shore near Romney Creek) and at its widest (just south of the mouth of the Potomac River which divides Maryland from Virginia). Total shoreline including tributaries is , circumnavigating a surface area of . Average depth is , reaching a maximum of . The Bay is spanned twice, in Maryland by the Chesapeake Bay Bridge from Sandy Point (near Annapolis) to Kent Island and in Virginia by the Chesapeake Bay Bridge–Tunnel connecting Virginia Beach to Cape Charles.
Known for both its beauty and bounty, the Bay has become "emptier", with fewer crabs, oysters and watermen (fishermen) since the mid-20th century. Nutrient pollution and urban runoff have been identified as major components of impaired water quality in the bay stressing ecosystems and compounding the decline of shellfish due to overharvesting. Restoration efforts that began in the 1990s have continued into the 21st century and show potential for growth of the native oyster population. The health of the Chesapeake Bay improved in 2015, marking three years of gains over a four-year period. Slight improvements in water quality were observed in 2021, compared to indicators measured in 2020. The bay is experiencing other environmental concerns, including climate change which is causing sea level rise that erodes coastal areas and infrastructure and changes to the marine ecosystem. | 2 | Environmental Chemistry |
The interfacing mechanism is contained inside a common EI source, like that found in any GC-MS system. The liquid phase from a nano HPLC column is admitted from the capillary column port, where the connection tubing and the nebulizer are first introduced and sealed to prevent vacuum loss. The mechanism is based on the formation of an aerosol in high-vacuum conditions, followed by a quick droplet desolvation and final vaporization of the solute prior to the ionization. The completion of the process is quick and complete and reduces chances of thermal decomposition as reported in the Figure, where a scheme of the interface is shown. The core of the interface is represented by the micro-nebulizer. The nebulizer tip protrudes into the ion source so that the spray expansion is completely contained inside the ion volume. The eluate emerges as liquid phase at a flow rate of 300-500 nL/min, and any premature in-tube solvent evaporation is prevented by a convenient thermal insulation of the nebulizer and the connecting tubing from the surrounding source heat. The high temperature of the ion source, between 300 and 400°C, has a double function: to compensate for the latent heat of vaporization during the droplet desolvation, and to convert the solute into the gas phase. If all components of this simple interface are correctly placed and sized, then each substance separated by the nano-column is smoothly converted into the gas phase, the peak profile is nicely reproduced, and high quality mass spectra are generated. Major advantages of this technical solution are the following: 1) It delivers high-quality, fully library matchable mass spectra of most sub-1 kDa molecules amenable by HPLC, 2) It is a chemical ionization free interface (unless operated intentionally) with accurate reproduction of the expected isotope ion abundances, 3) Response is never influenced by matrix components in the sample or in the mobile phase, 4) It can be considered a universal detector for small molecules because response is not related to compound polarity. | 3 | Analytical Chemistry |
The Phillips catalyst is prepared by impregnating high surface area silica gel with chromium trioxide or related chromium compounds. The solid precatalyst is then calcined in air to give the active catalyst. Only a fraction of the chromium is catalytically active, a fact that interferes with elucidation of the catalytic mechanism. The active catalyst is often depicted as a chromate ester bound to the silica surface. The mechanism for the polymerization process is the subject of much research, the central question being the structure of the active species, which is assumed to be an organochromium compound. Robert L. Banks and J. Paul Hogan, both at Phillips Petroleum, filed the first patents on the Phillips catalyst in 1953. Four years later, the process was commercialized. | 7 | Physical Chemistry |
A 2015 study, reported in the journal Ergonomics, showed that, for twenty healthy subjects, exposure to blue-enriched light during the post-lunch dip period significantly reduced the EEG alpha activity, and increased task performance. | 1 | Biochemistry |
The discovery of histone acetylation causing changes in transcription activity can be traced back to the work of Vicent Allfrey and colleagues in 1964. The group hypothesized that histone proteins modified by acetyl groups added negative charges to the positive lysines, and thus, reduced the interaction between DNA and histones. Histone modification is now considered a major regulatory mechanism that is involved in many different stages of genetic functions. Our current understanding is that acetylated lysine residues on histone tails is associated with transcriptional activation. In turn, deacetylated histones are associated with transcriptional repression. In addition, negative correlations have been found between several histone acetylation marks.
The regulatory mechanism is thought to be twofold. Lysine is an amino acid with a positive charge when unmodified. Lysines on the amino terminal tails of histones have a tendency to weaken the chromatin's overall structure. Addition of an acetyl group, which carries a negative charge, effectively removes the positive charge and hence, reduces the interaction between the histone tail and the nucleosome. This opens up the usually tightly packed nucleosome and allows transcription machinery to come into contact with the DNA template, leading to gene transcription. Repression of gene transcription is achieved by the reverse of this mechanism. The acetyl group is removed by one of the HDAC enzymes during deacetylation, allowing histones to interact with DNA more tightly to form compacted nucleosome assembly. This increase in the rigid structure prevents the incorporation of transcriptional machinery, effectively silencing gene transcription.
Another implication of histone acetylation is to provide a platform for protein binding. As a posttranslational modification, the acetylation of histones can attract proteins to elongated chromatin that has been marked by acetyl groups. It has been hypothesized that the histone tails offer recognition sites that attract proteins responsible for transcriptional activation. Unlike histone core proteins, histone tails are not part of the nucleosome core and are exposed to protein interaction. A model proposed that the acetylation of H3 histones activates gene transcription by attracting other transcription related complexes. Therefore, the acetyl mark provides a site for protein recognition where transcription factors interact with the acetylated histone tails via their bromodomain. | 0 | Organic Chemistry |
The gem-diol intermediate cleaves at the C2-C3 bond to form one molecule of glycerate-3-phosphate and a negatively charged carboxylate. Stereo specific protonation of C2 of this carbanion results in another molecule of glycerate-3-phosphate. This step is thought to be facilitated by Lys175 or potentially the carbamylated Lys210. | 5 | Photochemistry |
Several hnRNPs interact with telomeres, which protect the ends of chromosomes from deterioration and are often associated with cell longevity. hnRNP D associates with the G-rich repeat region of the telomeres, possibly stabilizing the region from secondary structures which would inhibit telomere replication.
hnRNP has also been shown to interact with telomerase, the protein responsible for elongating telomeres and prevent their degradation. hnRNPs C1 and C2 associate with the RNA component of telomerase, which improves its ability to access the telomere. | 1 | Biochemistry |
Diffuse reflectance spectroscopy, or diffuse reflection spectroscopy, is a subset of absorption spectroscopy. It is sometimes called remission spectroscopy. Remission is the reflection or back-scattering of light by a material, while transmission is the passage of light through a material. The word remission implies a direction of scatter, independent of the scattering process. Remission includes both specular and diffusely back-scattered light. The word reflection often implies a particular physical process, such as specular reflection.
The use of the term remission spectroscopy is relatively recent, and found first use in applications related to medicine and biochemistry. While the term is becoming more common in certain areas of absorption spectroscopy, the term diffuse reflectance is firmly entrenched, as in diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and diffuse-reflectance ultraviolet–visible spectroscopy. | 7 | Physical Chemistry |
The Riemschneider thiocarbamate synthesis converts alkyl or aryl thiocyanates to thiocarbamates under acidic conditions, followed by hydrolysis with ice water. The reaction was discovered by the German chemist in 1951 as a more efficient method to produce thiocarbamates. Some references spell the name Riemenschneider.
The Riemschneider reaction can also be used to create the corresponding N-substituted thiocarbamate from an alcohol or alkene. | 0 | Organic Chemistry |
Besides the individual toxic effects of each metal, a wide range of metals are nephrotoxic in humans and/or in animals. Some metals and their compounds are carcinogenic to humans. A few metals, such as lead and mercury, can cross the placental barrier and adversely affect fetal development. Several (cadmium, zinc, copper, and mercury) can induce special protein complexes called metallothioneins. | 1 | Biochemistry |
There are two distinct types of palladacycle: four-electron donor (CY) and six-electron donor (YCY) complexes. | 0 | Organic Chemistry |
Demethylation is the chemical process resulting in the removal of a methyl group (CH) from a molecule. A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen atoms.
The counterpart of demethylation is methylation. | 0 | Organic Chemistry |
* Saturated vapor pressures
* Saturated densities
* Viscosities
* Thermal conductivities
* Critical data (T, P, V)
* Triple points
* Melting points
* Heat capacities
* Heats of fusion, sublimation and vaporization
* Heats of formation and combustion
* Heats and temperatures of transitions for solids
* Speed of sound
* P-v-T data including virial coefficients
* Energy functions
* Enthalpies and entropies
* Surface tensions
The pure component properties data bank contains () approx. 157,000 data sets with 1,080,000 data points for 16,700 different components. | 7 | Physical Chemistry |
Tailings deposits tend to be located in rural areas or near marginalized communities, such as indigenous communities. The Global Industry Standard on Tailings Management recommends that "a human rights due diligence process is required to identify and address those that are most at risk from a tailings facility or its potential failure." | 8 | Metallurgy |
In the environmental context, reactive nitrogen compounds include the following classes:
*oxide gases: nitric oxide, nitrogen dioxide, nitrous oxide. Containing oxidized nitrogen, mainly the result of industrial processes and internal combustion engines.
*anions: nitrate, nitrite. Nitrate is a common component of fertilizers, e.g. ammonium nitrate.
*amine derivatives: ammonia and ammonium salts, urea. Containing reduced nitrogen, these compounds are components of fertilizers.
All of these compounds enter into the nitrogen cycle.
As a consequence, an excess of Nr can affect the environment relatively quickly. This also means that nitrogen-related problems need to be looked at in an integrated manner. | 1 | Biochemistry |
C and C plants have different signatures, allowing the abundance of C grasses to be detected through time in the δC record. Whereas plants have a δC of −16 to −10‰, plants have a δC of −33 to −24‰.
Mass extinctions are often marked by a negative δC anomaly thought to represent a decrease in primary productivity and release of plant-based carbon.
Positive δC excursions are interpreted as an increase in burial of organic carbon in sedimentary rocks following either a spike in primary productivity, a drop in decomposition under anoxic ocean conditions or both.
The evolution of large land plants in the late Devonian led to increased organic carbon burial and consequently a rise in δC.
Other important applications of δC involves understanding its signatures from soft sediments especially in lacustrine environments. This depends on the system from which it is extracted (open system, closed system, etc.). Temporal variations in δ13C in organic matter are influenced by diverse internal and external processes:
# Changes in the Dominant Source of Dissolved Inorganic Carbon: In stratified lakes, the accumulation of 13C-depleted carbon in deep water is common as sinking and degrading phytoplankton cells contribute to this pool. Recirculating this water to the surface can lead to a significant decrease in δ13C. Prolonged stratification enriches the dissolved inorganic carbon (DIC) pool in the epilimnion with 13C. Long-term variations in factors affecting upwelling intensity or depth, such as windiness, water temperature, or salinity-related stratification, manifest as shifts between more negative and positive δ13C values.
# Changes in Productivity/Eutrophication: Increased productivity accelerates the transfer of organic matter with negative δ13C values to the hypolimnion, affecting the δ13C of residual epilimnetic DIC. This impact, combined with mixing effects, results in variations in the δ13C signal.
# Changes in Metabolic Pathways for Carbon Fixation: Major changes in lake alkalinity influence benthic and planktonic primary production. Shifts in the dominant source of DIC for photosynthesis, driven by pH changes, can lead to trends toward more positive δ13C, particularly in lakes dominated by autochthonous organic matter and exhibiting evidence of high alkalinity.
# Changes in Availability of Dissolved CO2: Cool water can dissolve higher concentrations of CO2 than warmer water, affecting δ13C in organic matter during cooling events. Changes in atmospheric CO2 concentrations also influence δ13C, with lower pCO2 during glacial periods causing isotopic discrimination in plants using dissolved CO2.
# Changes in Dominant Vegetation Within the Watershed: Shifts in watershed vegetation, especially transitions between C3 and C4 photosynthetic pathways, significantly alter the carbon isotopic composition in lake sediments. These changes can be indicative of broader paleoclimatic shifts.
# Diagenetic Trends: Diagenetic processes, such as the loss of reactive components like amino acids, result in sustained shifts in δ13C in organic matter. Marsh sediments, rich in carbon, exhibit shifts towards more negative bulk organic matter. These diagenetic trends should be considered when interpreting isotopic changes accompanying major Total Organic Carbon (TOC) changes or methanogenesis.
Understanding these processes is crucial for interpreting δ13C variations in lake sediments and reconstructing paleoenvironmental conditions. | 9 | Geochemistry |
Members of the HNF1 subfamily contain a POU-homeodomain and bind to DNA as homodimers.
* HNF1α/TCF1/MODY3 (related disease: MODY 3)
* HNF1β/TCF2/MODY5 (related disease: MODY 5) | 1 | Biochemistry |
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