text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Plasmas find applications in many fields of research, technology and industry, for example, in industrial and extractive metallurgy, surface treatments such as plasma spraying (coating), etching in microelectronics, metal cutting and welding; as well as in everyday vehicle exhaust cleanup and fluorescent/luminescent lamps, fuel ignition, and even in supersonic combustion engines for aerospace engineering. | 7 | Physical Chemistry |
In a 1987 article in New Scientist, Jack Harris reported that oxide jacking has caused significant damage to many historic structures in the United Kingdom, including St Pauls Cathedral, the British Museum and the Albert Memorial in London, Gloucester Cathedral, St. Margarets Church in King's Lynn, Winchester Cathedral, and Blackburn Cathedral.
Harris also wrote that oxide jacking also damaged the ancient Horses of Saint Mark on the exterior of St. Mark's Basilica in Venice. Expansive rusting of iron and steel bolts and reinforcements affected the structural integrity of the copper horse sculptures, which were relocated indoors and replaced with replicas. Poorly-designed early 20th-century renovations also led to oxide jacking damage to the Acropolis of Athens.
In the United States, rusting of iron pegs inserted into holes in the stone entrance stair in order to support handrails resulted in cracking of the steps at the Basilica of the Sacred Heart in Notre Dame, Indiana.
Oxide jacking damaged the terra cotta cornice on the Land Title Building in Philadelphia, designed in 1897 and expanded in 1902 by pioneer skyscraper architect Daniel Burnham. The Land Title complex, with its two interconnected towers, is on the National Register of Historic Places. By 1922, experts on architectural terra cotta were warning that the rusting of embedded iron fasteners could cause decorative building components to fail. This 1902 cornice is nearly high, projects from the facade of the building and is long. The cornice was stabilized, steel anchors subject to rusting were replaced with new stainless steel anchors, and the cornice was completely renovated. The project was completed in 1991.
Flooding in 2007 damaged the modernist Farnsworth House in Plano, Illinois, designed in 1945 by Ludwig Mies van der Rohe, and now owned by the National Trust for Historic Preservation. Among the damage discovered by an architect inspecting the house in 2007 was oxide jacking at the corners of the house's steel framework. The house flooded again in 2008. | 8 | Metallurgy |
In the context of rheumatoid arthritis (RA), CRP is one of the acute phase reactants, whose assessment is defined as part of the joint 2010 ACR/EULAR classification criteria for RA with abnormal levels accounting for a single point within the criteria Higher levels of CRP are associated with more severe disease and a higher likelihood of radiographic progression. Rheumatoid arthritis associated antibodies together with 14-3-3η YWHAH have been reported to complement CRP in predicting clinical and radiographic outcomes in patients with recent onset inflammatory polyarthritis. Elevated levels of CRP appear to be associated with common comorbidities including cardiovascular disease, metabolic syndrome, diabetes and interstitial lung (pulmonary) disease. Mechanistically, CRP also appears to influence osteoclast activity leading to bone resorption and also stimulates RANKL expression in peripheral blood monocytes.
It has previously been speculated that single-nucleotide polymorphisms in the CRP gene may affect clinical decision-making based on CRP in rheumatoid arthritis, e.g. DAS28 (Disease Activity Score 28 joints). A recent study showed that CRP genotype and haplotype were only marginally associated with serum CRP levels and without any association to the DAS28 score. Thus, that DAS28, which is the core parameter for inflammatory activity in RA, can be used for clinical decision-making without adjustment for CRP gene variants. | 1 | Biochemistry |
Radicals are highly reactive and short-lived, as they have an unpaired electron which makes it extremely unstable. Radicals often react with hydrogens attached carbon molecules, effectively making the carbon a radical while stabilizing the former radical in a process called propagation. The formed product, a carbon radical, can react with non-radical molecule to continue propagation or react with another radical to form a new stable molecule such as a longer carbon chain or an alkyl halide.
The example below of methane chlorination shows a multi-step reaction involving radicals. | 7 | Physical Chemistry |
* Albidiferax (Betaproteobacteria)
* Shewanella (Gammaproteobacteria)
* Geobacter (Deltaproteobacteria)
* Geothrix fermentans (Acidobacteria)
* Deferribacter (Deferribacteres)
* Thermoanaerobacter (Firmicutes) | 1 | Biochemistry |
Semiconductor materials have energy band gaps, and will generate a pair of electron and hole for each absorbed photon if the energy of the photon is higher than the band gap energy of the semiconductor. This property of semiconductor materials has been successfully used to convert solar energy into electrical energy by photovoltaic devices.
In photocatalysis the electron-hole pair is immediately used to drive a redox reaction. However, the electron-hole pairs suffer from fast recombination. In photoelectrocatalysis, a differential potential is applied to diminish the number of recombinations between the electrons and the holes. This allows an increase in the yield of light's conversion into chemical energy. | 5 | Photochemistry |
The largest use of vanillin is as a flavoring, usually in sweet foods. The ice cream and chocolate industries together comprise 75% of the market for vanillin as a flavoring, with smaller amounts being used in confections and baked goods.
Vanillin is also used in the fragrance industry, in perfumes, and to mask unpleasant odors or tastes in medicines, livestock fodder, and cleaning products. It is also used in the flavor industry, as a very important key note for many different flavors, especially creamy profiles such as cream soda.
Additionally, vanillin can be used as a general-purpose stain for visualizing spots on thin-layer chromatography plates. This stain yields a range of colors for these different components.
Vanillin–HCl staining can be used to visualize the localisation of tannins in cells.
Vanillin is becoming a popular choice for the development of bio-based plastics. | 0 | Organic Chemistry |
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
Some examples of facultatively anaerobic bacteria are Staphylococcus spp., Escherichia coli, Salmonella, Listeria spp., Shewanella oneidensis and Yersinia pestis. Certain eukaryotes are also facultative anaerobes, including fungi such as Saccharomyces cerevisiae and many aquatic invertebrates such as nereid polychaetes.
It has been observed that in mutants of Salmonella typhimurium that underwent mutations to be either obligate aerobes or anaerobes, there were varying levels of chromatin-remodeling proteins. The obligate aerobes were later found to have a defective DNA gyrase subunit A gene (gyrA), while obligate anaerobes were defective in topoisomerase I (topI). This indicates that topoisomerase I and its associated relaxation of chromosomal DNA is required for transcription of genes required for aerobic growth, while the opposite is true for DNA gyrase. Additionally, in Escherichia coli K-12 it has been noted that phosphofructokinase (PFK) exists as a dimer under aerobic conditions and as a tetramer under anaerobic conditions. Given PFK’s role in glycolysis, this has implications for the effect of oxygen on the glucose metabolism of E. coli K-12 in relation to the mechanism of the Pasteur effect.
There may exist a core network of transcription factors (TFs) that includes the major oxygen-responsive ArcA and FNR control the adaptation of Escherichia coli to changes in oxygen availability. Activities of these two regulators are indicative of spatial effects that may affect gene expression in the microaerobic range. It has also been observed that these oxygen-sensitive proteins are protected within the cytoplasm by oxygen consumers within the cell membrane, known as terminal oxidases. | 1 | Biochemistry |
Lavello and Grubbs discovered the compound unexpectedly when trying to prepare noncarbonyl, low coordinate, Fe(0) complexes of N-heterocyclic carbenes (NHCs). They found that reactions of Fe(COT) and the NHC, 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIMes), produced tetrametallic, Fe(I)-Fe(0) mixed valent NHC-COT complexes. In an attempt to characterize intermediates of the unusual transformation, they employed the more sterically hindered NHC, 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) (with Dipp substituents).In benzene, the Dipp substituted NHC reacts with Fe(COT) to produce large black rhomboidal crystals of tris(cyclooctatetraene)triiron over 24 h at room temperature. Notably, the reaction was found to occur with catalytic amounts of NHC (10 mol%) yielding 67% of Fe(COT) after 24 h (turn over number=9.5). The synthesis is optimized when the reaction is conducted at 45 °C, yielding 95% conversion to the tris(cyclooctatetraene)triiron cluster. They also highlighted that heating Fe(COT) in benzene without any NHC to 100 °C for 24 h forms trace amounts of Fe(COT), but also large amounts of iron metal. Unsurprisingly, elemental analysis of the cluster affirms a 1:1 Fe:COT ratio.
The formation of Fe(COT) from Fe(COT) has been calculated to be slightly exothermic(15 kcal/mol).
Other NHCs lead to other unique mixed NHC-COT low valent iron complexes. Lavallo and Grubbs rationalize the transformation by emphasizing the capacity of NHCs to catalytically induce the formation of metal-metal bonds, where the steric hinderance of the NHC is essential, in particular, for the lability of the NHC (in coordination and dissociation) in the cycle. The bulky NHC is proposed to prevent reduction of COT by a bimetallic [(L)Fe(COT)] intermediate, where steric constraints block the bonding hapticity required to ligate a reduced form of COT. Another possibility put forward is that reduction of COT occurs only following coordination by a second carbene in the case of SIMes during the catalytic cycle. The sterically hindered NHC prevents such a transformation from occurring. | 7 | Physical Chemistry |
Classification of hydrothermal ore deposits is also achieved by classifying according to the temperature of formation, which roughly also correlates with particular mineralising fluids, mineral associations and structural styles. This scheme, proposed by Waldemar Lindgren (1933) classified hydrothermal deposits as follows:
* Hypothermal — mineral ore deposits formed at great depth under conditions of high temperature.
* Mesothermal — mineral ore deposits formed at moderate temperature and pressure, in and along fissures or other openings in rocks, by deposition at intermediate depths, from hydrothermal fluids.
* Epithermal — mineral ore deposits formed at low temperatures (50–200 °C) near the Earth's surface (<1500 m), that fill veins, breccias, and stockworks.
* Telethermal — mineral ore deposits formed at shallow depth and relatively low temperatures, with little or no wall-rock alteration, presumably far from the source of hydrothermal solutions.
Ore deposits are usually classified by ore formation processes and geological setting. For example, sedimentary exhalative deposits (SEDEX), are a class of ore deposit formed on the sea floor (sedimentary) by exhalation of brines into seawater (exhalative), causing chemical precipitation of ore minerals when the brine cools, mixes with sea water, and loses its metal carrying capacity.
Ore deposits rarely fit neatly into the categories in which geologists wish to place them. Many may be formed by one or more of the basic genesis processes above, creating ambiguous classifications and much argument and conjecture. Often ore deposits are classified after examples of their type, for instance Broken Hill type lead-zinc-silver deposits or Carlin–type gold deposits. | 9 | Geochemistry |
The McCumber relation is confirmed for various media.
In particular, relation (1) makes it possible to approximate two functions of frequency, emission and absorption cross sections, with single fit | 7 | Physical Chemistry |
* [https://www.sciencehistory.org/scientists-you-must-know Scientists You Must Know: Pioneering steroid researcher George Rosenkranzh], Video, from the Scientists You Must Know Film Series, Science History Institute, Philadelphia, PA | 0 | Organic Chemistry |
The syntheses of all aryl hypervalent iodine compounds start from iodobenzene. The compound can be prepared by reaction of iodobenzene with a mixture of trifluoroperacetic acid and trifluoroacetic acid in a method analogous to the synthesis of
It can also be prepared by dissolving diacetoxyiodobenzene (a commercially-available compound) with heating in trifluoroacetic acid: | 0 | Organic Chemistry |
* Important publications in biochemistry (chemistry)
* List of biochemistry topics
* List of biochemists
* List of biomolecules | 1 | Biochemistry |
Nucleosides are typically synthesized through the coupling of a nucleophilic pyrimidine, purine, or other basic heterocycle with a derivative of ribose or deoxyribose that is electrophilic at the anomeric carbon. When an acyl-protected ribose is employed, selective formation of the β-nucleoside (possessing the S configuration at the anomeric carbon) results from neighboring group participation. Stereoselective synthesis of deoxyribonucleosides directly from deoxyribose derivatives is more difficult to achieve because neighboring group participation cannot take place.
Three general methods have been used to synthesize nucleosides from nucleophilic bases and electrophilic sugars. The fusion method involves heating the base and acetyl-protected 1-acetoxyribose to 155 °C and results in the formation of the nucleoside with a maximum yield of 70%.
The metal salt method involves the combination of a metal salt of the heterocycle with a protected sugar halide. Silver and mercury salts were originally used; however, more recently developed methods use sodium salts.
The silyl-Hilbert-Johnson (SHJ) reaction (or Vorbrüggen reaction), the mildest general method for the formation of nucleosides, is the combination of a silylated heterocycle and protected sugar acetate (such as 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranose) in the presence of a Lewis acid. Problems associated with the insolubility of the heterocyclic bases and their metal salts are avoided; however, site selectivity is sometimes a problem when heterocycles containing multiple basic sites are used, as the reaction is often reversible. | 0 | Organic Chemistry |
The Early Iron Age at Norşuntepe (1150–800 BC) is characterized by a shift away from Hittite material culture, possibly as a result of the influx of immigrants such as the Mushki. The settlement seems to have been restricted to the south terrace and may have had a rural character. During its final occupation phases (800–600 BC), Norşuntepe was part of Urartu. A building with a large, columned hall was located on the mail hill, whereas a second large building, possibly a caravanserai, was excavated on the south terrace. A cemetery located on the hill top included a burial chamber where three horses together with gear and weapons were buried.
The hilltop was again used as a cemetery during the Medieval Period. | 8 | Metallurgy |
Carbon dioxide occupies a different binding site on the hemoglobin. At tissues, where carbon dioxide concentration is higher, carbon dioxide binds to allosteric site of hemoglobin, facilitating unloading of oxygen from hemoglobin and ultimately its removal from the body after the oxygen has been released to tissues undergoing metabolism. This increased affinity for carbon dioxide by the venous blood is known as the Bohr effect. Through the enzyme carbonic anhydrase, carbon dioxide reacts with water to give carbonic acid, which decomposes into bicarbonate and protons:
:CO + HO → HCO → HCO + H
Hence, blood with high carbon dioxide levels is also lower in pH (more acidic). Hemoglobin can bind protons and carbon dioxide, which causes a conformational change in the protein and facilitates the release of oxygen. Protons bind at various places on the protein, while carbon dioxide binds at the α-amino group. Carbon dioxide binds to hemoglobin and forms carbaminohemoglobin. This decrease in hemoglobins affinity for oxygen by the binding of carbon dioxide and acid is known as the Bohr effect. The Bohr effect favors the T state rather than the R state. (shifts the O-saturation curve to the right'). Conversely, when the carbon dioxide levels in the blood decrease (i.e., in the lung capillaries), carbon dioxide and protons are released from hemoglobin, increasing the oxygen affinity of the protein. A reduction in the total binding capacity of hemoglobin to oxygen (i.e. shifting the curve down, not just to the right) due to reduced pH is called the root effect. This is seen in bony fish.
It is necessary for hemoglobin to release the oxygen that it binds; if not, there is no point in binding it. The sigmoidal curve of hemoglobin makes it efficient in binding (taking up O in lungs), and efficient in unloading (unloading O in tissues).
In people acclimated to high altitudes, the concentration of 2,3-Bisphosphoglycerate (2,3-BPG) in the blood is increased, which allows these individuals to deliver a larger amount of oxygen to tissues under conditions of lower oxygen tension. This phenomenon, where molecule Y affects the binding of molecule X to a transport molecule Z, is called a heterotropic allosteric effect. Hemoglobin in organisms at high altitudes has also adapted such that it has less of an affinity for 2,3-BPG and so the protein will be shifted more towards its R state. In its R state, hemoglobin will bind oxygen more readily, thus allowing organisms to perform the necessary metabolic processes when oxygen is present at low partial pressures.
Animals other than humans use different molecules to bind to hemoglobin and change its O affinity under unfavorable conditions. Fish use both ATP and GTP. These bind to a phosphate "pocket" on the fish hemoglobin molecule, which stabilizes the tense state and therefore decreases oxygen affinity. GTP reduces hemoglobin oxygen affinity much more than ATP, which is thought to be due to an extra hydrogen bond formed that further stabilizes the tense state. Under hypoxic conditions, the concentration of both ATP and GTP is reduced in fish red blood cells to increase oxygen affinity.
A variant hemoglobin, called fetal hemoglobin (HbF, αγ), is found in the developing fetus, and binds oxygen with greater affinity than adult hemoglobin. This means that the oxygen binding curve for fetal hemoglobin is left-shifted (i.e., a higher percentage of hemoglobin has oxygen bound to it at lower oxygen tension), in comparison to that of adult hemoglobin. As a result, fetal blood in the placenta is able to take oxygen from maternal blood.
Hemoglobin also carries nitric oxide (NO) in the globin part of the molecule. This improves oxygen delivery in the periphery and contributes to the control of respiration. NO binds reversibly to a specific cysteine residue in globin; the binding depends on the state (R or T) of the hemoglobin. The resulting S-nitrosylated hemoglobin influences various NO-related activities such as the control of vascular resistance, blood pressure and respiration. NO is not released in the cytoplasm of red blood cells but transported out of them by an anion exchanger called AE1. | 7 | Physical Chemistry |
* Soil applied: Herbicides applied to the soil are usually taken up by the root or shoot of the emerging seedlings and are used as preplant or preemergence treatment. Several factors influence the effectiveness of soil-applied herbicides. Weeds absorb herbicides by both passive and active mechanisms. Herbicide adsorption to soil colloids or organic matter often reduces the amount available for weed absorption. Positioning of the herbicide in the correct layer of soil is very important, which can be achieved mechanically and by rainfall. Herbicides on the soil surface are subjected to several processes that reduce their availability. Volatility and photolysis are two common processes that reduce the availability of herbicides. Many soil-applied herbicides are absorbed through plant shoots while they are still underground leading to their death or injury. EPTC and trifluralin are soil-applied herbicides.
* Foliar applied: These are applied to a portion of the plant above the ground and are absorbed by exposed tissues. These are generally postemergence herbicides and can either be translocated (systemic) throughout the plant or remain at a specific site (contact). External barriers of plants like cuticles, waxes, cell walls etc. affect herbicide absorption and action. Glyphosate, 2,4-D, and dicamba are foliar-applied herbicides. | 2 | Environmental Chemistry |
Carbon subsulfide is an organic, sulfur-containing chemical compound with the formula and structure . This deep red liquid is immiscible with water but soluble in organic solvents. It readily polymerizes at room temperature to form a hard black solid. | 0 | Organic Chemistry |
Consider, for one, the familiar example of a marble on the edge of a bowl. If we consider the marble and bowl to be an isolated system, then when the marble drops, the potential energy will be converted to the kinetic energy of motion of the marble. Frictional forces will convert this kinetic energy to heat, and at equilibrium, the marble will be at rest at the bottom of the bowl, and the marble and the bowl will be at a slightly higher temperature. The total energy of the marble-bowl system will be unchanged. What was previously the potential energy of the marble, will now reside in the increased heat energy of the marble-bowl system. This will be an application of the maximum entropy principle as set forth in the principle of minimum potential energy, since due to the heating effects, the entropy has increased to the maximum value possible given the fixed energy of the system.
If, on the other hand, the marble is lowered very slowly to the bottom of the bowl, so slowly that no heating effects occur (i.e. reversibly), then the entropy of the marble and bowl will remain constant, and the potential energy of the marble will be transferred as energy to the surroundings. The surroundings will maximize its entropy given its newly acquired energy, which is equivalent to the energy having been transferred as heat. Since the potential energy of the system is now at a minimum with no increase in the energy due to heat of either the marble or the bowl, the total energy of the system is at a minimum. This is an application of the minimum energy principle.
Alternatively, suppose we have a cylinder containing an ideal gas, with cross sectional area A and a variable height x. Suppose that a weight of mass m has been placed on top of the cylinder. It presses down on the top of the cylinder with a force of mg where g is the acceleration due to gravity.
Suppose that x is smaller than its equilibrium value. The upward force of the gas is greater than the downward force of the weight, and if allowed to freely move, the gas in the cylinder would push the weight upward rapidly, and there would be frictional forces that would convert the energy to heat. If we specify that an external agent presses down on the weight so as to very slowly (reversibly) allow the weight to move upward to its equilibrium position, then there will be no heat generated and the entropy of the system will remain constant while energy is transferred as work to the external agent. The total energy of the system at any value of x is given by the internal energy of the gas plus the potential energy of the weight:
where T is temperature, S is entropy, P is pressure, μ is the chemical potential, N is the number of particles in the gas, and the volume has been written as V=Ax. Since the system is closed, the particle number N is constant and a small change in the energy of the system would be given by:
Since the entropy is constant, we may say that dS=0 at equilibrium and by the principle of minimum energy, we may say that dU=0 at equilibrium, yielding the equilibrium condition:
which simply states that the upward gas pressure force (PA) on the upper face of the cylinder is equal to the downward force of the mass due to gravitation (mg). | 7 | Physical Chemistry |
During thin film growth, there can be a balance between surface energy and internal strain, with surface stress a coupling term combining the two. Instead of growing as a continuous thin film, a morphological instability can occur and the film can start to become very uneven, in many cases due to a breakdown of a balance between elastic and surface energies. The surface stress can lead to comparable wrinkling in nanowires, and also a morphological instability in a thin film. | 7 | Physical Chemistry |
Material is put on a sinter machine in two layers. The bottom layer may vary in thickness from . A 12 to 20 mm sinter fraction is used, also referred to as the hearth layer. The second, covering layer consists of mixed materials, making for a total bed height of . The mixed materials are applied with drum feeders and roll feeders, which distributes the nodules in certain depth throughout the sinterring machine . The upper layer is smoothed using a leveler. The material, also known as a charge, enters the ignition furnace into rows of multi-slit burners. In the case of one plant, the first (ignition) zone has eleven burners. The next (soaking/annealing) zone typically offers 12 burners. Air is sucked from the bottom of the bed of mixed material throughout the sintering machine. Fire penetrates the mixed material gradually, until it reaches the hearth layer. This end point of burning is called burn through point (BTP). The hearth layer, which is nothing but sinter in smaller size, restricts sticking of hot sinter with pallets. BTP is achieved in a certain zone of sinter machine, to optimize the process, by means of several temperature measuring instrument placed throughout the sinter machine. After completion of burning, the mix converts into sinter, which then breaks into smaller size by sinter breaker. After breaking into small sizes, it cools down in cooler (linear or circular) by means of forced air. At discharge of sinter cooler, temperature of sinter is maintained as low, so that the hot sinter can be transported by a conveyor belt made of rubber. Necessary precautions are taken to trace any existence of fire in the belt and necessary extinguishing is done by spraying water. Then this product is being passed through a jaw-crusher, where the size of sinter is further reduced (~ 50 mm) into smaller size. Then the complete mixture is being passed through two screens. Smallest sinter fines (< 5 mm) are stored in proportioning bins and reused for preparing sinter again through mixing and nodulizing drum and fed to sinter machine for burning. A part of the smaller one ( 5 – 20 mm) is used for hearth layer in sinter machine and the rest is taken to the blast furnace along with the biggest sized sinters.
The temperature is typically maintained between in the ignition zone and between 900 and 1000 °C in the soaking zone to prevent sudden quenching of the sintered layer. The top 5 mm from screens goes to the conveyor carrying the sinter for the blast furnace and, along with blast furnace grade sinter, either goes to sinter storage bunkers or to BF bunkers. Blast furnace-grade sinter consists of particles sized 5 to 12 mm as well as 20 mm and above. | 8 | Metallurgy |
Many metal alkoxides thermally decompose in the range ≈100–300 °C. Depending on process conditions, this thermolysis can afford nanosized powders of oxide or metallic phases. This approach is a basis of processes of fabrication of functional materials intended for aircraft, space, electronic fields, and chemical industry: individual oxides, their solid solutions, complex oxides, powders of metals and alloys active towards sintering. Decomposition of mixtures of mono- and heterometallic alkoxide derivatives has also been examined. This method represents a prospective approach possessing an advantage of capability of obtaining functional materials with increased phase and chemical homogeneity and controllable grain size (including the preparation of nanosized materials) at relatively low temperature (less than 500−900 °C) as compared with the conventional techniques. | 0 | Organic Chemistry |
Kodevirions are FSL modified viruses. Several FSL Kode constructs have been used to label viruses to assist in their flow-cytometric visualisation and to track them real time distribution in animal models. They have also been used to modify the surface of viruses with the intention of targeting them to be used to attach tumors (oncolytic). | 1 | Biochemistry |
Health Canada classifies VOCs as organic compounds that have boiling points roughly in the range of . The emphasis is placed on commonly encountered VOCs that would have an effect on air quality. | 0 | Organic Chemistry |
Ferrous iron is a soluble form of iron that is stable at extremely low pHs or under anaerobic conditions. Under aerobic, moderate pH conditions ferrous iron is oxidized spontaneously to the ferric () form and is hydrolyzed abiotically to insoluble ferric hydroxide (). There are three distinct types of ferrous iron-oxidizing microbes. The first are acidophiles, such as the bacteria Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, as well as the archaeon Ferroplasma. These microbes oxidize iron in environments that have a very low pH and are important in acid mine drainage. The second type of microbes oxidize ferrous iron at near-neutral pH. These micro-organisms (for example Gallionella ferruginea, Leptothrix ochracea, or Mariprofundus ferrooxydans) live at the oxic-anoxic interfaces and are microaerophiles. The third type of iron-oxidizing microbes are anaerobic photosynthetic bacteria such as Rhodopseudomonas, which use ferrous iron to produce NADH for autotrophic carbon dioxide fixation. Biochemically, aerobic iron oxidation is a very energetically poor process which therefore requires large amounts of iron to be oxidized by the enzyme rusticyanin to facilitate the formation of proton motive force. Like sulfur oxidation, reverse electron flow must be used to form the NADH used for carbon dioxide fixation via the Calvin cycle. | 1 | Biochemistry |
When either the laser intensity is further increased or a longer wavelength is applied as compared with the regime in which multi-photon ionization takes place, a quasi-stationary approach can be used and results in the distortion of the atomic potential in such a way that only a relatively low and narrow barrier between a bound state and the continuum states remains. Then, the electron can tunnel through or for larger distortions even overcome this barrier. These phenomena are called tunnel ionization and over-the-barrier ionization, respectively. | 7 | Physical Chemistry |
When atoms join into molecules, their inner electrons remain bound to their original nucleus while the outer valence electrons are distributed around the molecule. The charge distribution of these valence electrons determines the electronic energy level of a molecule, and can be described by molecular orbital theory, which closely follows the atomic orbital theory used for single atoms. Assuming that the momenta of the electrons are on the order of ħ/a (where ħ is the reduced Planck's constant and a is the average internuclear distance within a molecule, ~1Å), the magnitude of the energy spacing for electronic states can be estimated at a few electron volts. This is the case for most low-lying molecular energy states, and corresponds to transitions in the visible and ultraviolet regions of the electromagnetic spectrum.
In addition to the electronic energy levels shared with atoms, molecules have additional quantized energy levels corresponding to vibrational and rotational states. Vibrational energy levels refer to motion of the nuclei about their equilibrium positions in the molecule. The approximate energy spacing of these levels can be estimated by treating each nucleus as a quantum harmonic oscillator in the potential produced by the molecule, and comparing its associated frequency to that of an electron experiencing the same potential. The result is an energy spacing about 100x smaller than that for electronic levels. In agreement with this estimate, vibrational spectra show transitions in the near infrared (about 1 - 5 μm). Finally, rotational energy states describe semi-rigid rotation of the entire molecule and produce transition wavelengths in the far infrared and microwave regions (about 100-10,000 μm in wavelength). These are the smallest energy spacings, and their size can be understood by comparing the energy of a diatomic molecule with internuclear spacing ~1Å to the energy of a valence electron (estimated above as ~ħ/a).
Actual molecular spectra also show transitions which simultaneously couple electronic, vibrational, and rotational states. For example, transitions involving both rotational and vibrational states are often referred to as rotational-vibrational or rovibrational transitions. Vibronic transitions combine electronic and vibrational transitions, and rovibronic transitions combine electronic, rotational, and vibrational transitions. Due to the very different frequencies associated with each type of transition, the wavelengths associated with these mixed transitions vary across the electromagnetic spectrum. | 7 | Physical Chemistry |
This involved the development and integration of an automated spotting system to spot multiple single molecules on a slide (like a microarray) for parallel enzymatic processing, automated fluorescence microscopy for image acquisition, image procession vision to handle images, algorithms for optical map construction, cluster computing for processing large amounts of data | 1 | Biochemistry |
Organic compounds such as amino acids, carbohydrates, fatty acids, and phenols are highly enriched in the SML interface. Most of these come from biota in the sub-surface waters, which decay and become transported to the surface, though other sources exist also such as atmospheric deposition, coastal runoff, and anthropogenic nutrification. The relative concentration of these compounds is dependent on the nutrient sources as well as climate conditions such as wind speed and precipitation. These organic compounds on the surface create a "film," referred to as a "slick" when visible, which affects the physical and optical properties of the interface. These films occur because of the hydrophobic tendencies of many organic compounds, which causes them to protrude into the air-interface. The existence of organic surfactants on the ocean surface impedes wave formation for low wind speeds. For increasing concentrations of surfactant there is an increasing critical wind speed necessary to create ocean waves. Increased levels of organic compounds at the surface also hinders air-sea gas exchange at low wind speeds. One way in which particulates and organic compounds on the surface are transported into the atmosphere is the process called "bubble bursting". Bubbles generate the major portion of marine aerosols. They can be dispersed to heights of several meters, picking up whatever particles latch on to their surface. However, the major supplier of materials comes from the SML. | 7 | Physical Chemistry |
Vitamin A is a fat-soluble vitamin, a category that also includes vitamins D, E and K. The vitamin encompasses several chemically related naturally occurring compounds or metabolites, i.e., vitamers, that all contain a β-ionone ring. The primary dietary form is retinol, which may have a fatty acid molecule attached, creating a retinyl ester, when stored in the liver. Retinol the transport and storage form of vitamin A is interconvertible with retinal, catalyzed to retinal by retinol dehydrogenases and back to retinol by retinaldehyde reductases.
:retinal + NADPH + H retinol + NADP
:retinol + NAD retinal + NADH + H
Retinal, (also known as retinaldehyde) can be irreversibly converted to all-trans-retinoic acid by the action of retinal dehydrogenase
:retinal + NAD + HO → retinoic acid + NADH + H
Retinoic acid diffuses into the cell nucleus where it regulates more than 500 genes by binding directly to gene targets via retinoic acid receptors.
In addition to retinol, retinal and retinoic acid, there are plant-, fungi- or bacteria-sourced carotenoids which can be metabolized to retinol, and are thus vitamin A vitamers.
There are also what are referred to as 2nd, 3rd and 4th generation retinoids which are not considered vitamin A vitamers because they cannot be converted to retinol, retinal or all-trans-retinoic acid. Some are prescription drugs, oral or topical, for various indications. Examples are etretinate, acitretin, adapalene, bexarotene, tazarotene and trifarotene. | 1 | Biochemistry |
Substrate transformation involves the transformation of a specific compound into another, such as in the case of phenylacetylcarbinol, and steroid biotransformation, or the transformation of a raw material into a finished product, in the case of food fermentations and sewage treatment. | 1 | Biochemistry |
In order for long-term potentiation (LTP) to occur, there must be stimulation of NMDA receptors, which causes AMPA receptors to be inserted postsynaptically. PI3K binds to AMPA receptors in a conserved region to orient the receptors in the membrane, specifically at the GluR subunit. PI3K activity increases in response to calcium ions and CaM. Additionally, AKT localizes PtdIns-3Ps in the post synapse, which recruits docking proteins such as tSNARE and Vam7. This directly leads to the docking of AMPA in the post synapse. mTOR activated p70S6K and inactivated 4EBP1 which changes gene expression to allow LTP to occur. Long-term fear conditioning training was affected in rats but there was no effect in short term conditioning. Specifically, amygdala fear conditioning was lost. This is a type of trace conditioning which is a form of learning that requires association of a conditioned stimulus with an unconditioned stimulus. This effect was lost in PI3K knockdowns and increased in PI3K overexpressions. | 1 | Biochemistry |
Sunset yellow FCF (also known as orange yellow S, or C.I. 15985) is a petroleum-derived orange azo dye with a pH dependent maximum absorption at about 480 nm at pH 1 and 443 nm at pH 13 with a shoulder at 500 nm. When added to foods sold in the United States it is known as FD&C Yellow 6; when sold in Europe, it is denoted by E Number E110. | 3 | Analytical Chemistry |
The drinking bird has been used in many fictional contexts to automatically press buttons. In The Simpsons episode "King-Size Homer", Homer used one to repeatedly press a key on a computer keyboard. Herb Powell also showed one to Homer as part of a demonstration regarding inventions in the episode "Brother, Can You Spare Two Dimes?". Two of them were used in the 1990 film Darkman to set off explosions. Drinking birds have appeared as part of a Rube Goldberg machine in the film Pee-wees Big Adventure and the Family Guy episode "8 Simple Rules for Buying My Teenage Daughter". In Bojack Horseman' an Alcoholics Anonymous attendee resembles a Drinking Bird.
Drinking birds have been featured as plot elements in the 1951 Merrie Melodies cartoon Putty Tat Trouble and the 1968 science fiction thriller The Power. They have also had minor appearances in several movies and TV shows, including mission briefings in two episodes of TVs original Mission: Impossible, the Woody Allen movie Sleeper, the 1979 science fiction film Alien (also referenced in Alien 3 and Alien: Covenant), the 1989 comedy When Harry Met Sally..., the 2005 film Robots, the 2008 film Max Payne, the 2010 film Megamind, the 2021 film Fortress',
and episodes of the American TV shows The Simpsons, Mad Men and Ed, Edd n Eddy. Episode 508 of Mystery Science Theater 3000 features a spoof of the drinking bird called the Bobbing Buzzard, which runs on carrion instead of water. In S4E11 of the comedy series Arrested Development, a delusional character hears the voice of God speaking through a drinking bird. In Episode 7 of Season 2, Headspace, of Ted Lasso on AppleTV, a non-functioning drinking bird is prominently displayed on the desk of the team psychologist.
Among video games, the drinking bird appeared as the "dunkin dragon" in the Sierra game Quest for Glory (1989) and in the Gremlin Interactive game Normality (1996). Porygon2, a Pokémon introduced in Generation II (Pokémon Gold and Silver), resembles a drinking bird, and in 3D Pokémon games, it moves its head in a "dipping" motion. More recently, in the game Quantum Conundrum (2012), one of the main gameplay mechanics is a drinking bird that is used as a timer to press buttons. In the 2014 Creative Assembly video game Alien: Isolation, drinking birds are frequently seen on desks across the games main setting, Sevastopol Station.
In Australian contemporary playwright John Romerils play The Floating World, drinking birds are a symbolic prop which represent the progression of Les insanity. They are referred to as "dippy birds" and are perhaps used to symbolize insanity due to Romeril's opinion that they are insane for their uselessness and repeatability. | 7 | Physical Chemistry |
Alkene carboamination is the simultaneous formation of C–N and C–C bonds across an alkene. This method represents a powerful strategy to build molecular complexity with up to two stereocenters in a single operation. Generally, there are four categories of reaction modes for alkene carboamination. The first class is cyclization reactions, which will form a N-heterocycle as a result. The second class has been well established in the last decade. Alkene substrates with a tethered nitrogen nucleophile have been used in these transformations to promote intramolecular aminocyclization. While intermolecular carboamination is extremely hard, people have developed a strategy to combine the nitrogen and carbon part, which is known as the third class. The most general carboamination, which takes three individual parts and couples them together is still underdeveloped. | 0 | Organic Chemistry |
Hyperbilirubinemia is a higher-than-normal level of bilirubin in the blood. Hyperbilirubinemia may refer to increased levels of conjugated, unconjugated or both conjugated and unconjugated bilirubin. The causes of hyperbilirubinemia can also be classified into prehepatic, intrahepatic, and posthepatic.
Prehepatic causes are associated mostly with an increase of unconjugated (indirect) bilirubin. They include:
* Hemolysis or increased breakdown of red blood cells (for example hematoma resorption)
Intrahepatic causes can be associated with elevated levels of conjugated bilirubin, unconjugated bilirubin or both. They include:
* Neonatal hyperbilirubinemia, where the newborn's liver is not able to properly process the bilirubin causing jaundice
* Hepatocellular disease
** Viral infections (hepatitis A, B, and C)
** Chronic alcohol use
** Autoimmune disorders
* Genetic syndromes:
** Gilbert's syndrome – a genetic disorder of bilirubin metabolism that can result in mild jaundice, found in about 5% of the population
** Rotor syndrome: non-itching jaundice, with rise of bilirubin in the patient's serum, mainly of the conjugated type
** Dubin–Johnson syndrome
** Crigler–Najjar syndrome
* Pharmaceutical drugs (especially antipsychotic, some sex hormones, and a wide range of other drugs)
** Sulfonamides are contraindicated in infants less than 2 months old (exception when used with pyrimethamine in treating toxoplasmosis) as they increase unconjugated bilirubin leading to kernicterus.
** Drugs such as protease inhibitors like Indinavir can also cause disorders of bilirubin metabolism by competitively inhibiting the UGT1A1 enzyme.
Post-hepatic causes are associated with elevated levels of conjugated bilirubin. These include:
* Unusually large bile duct obstruction, e.g. gallstone in common bile duct (which is the most common post-hepatic cause)
* Biliary stricture (benign or malignant)
* Cholangitis
* Severe liver failure with cirrhosis (e.g. primary biliary cirrhosis)
* Pancreatitis
Cirrhosis may cause normal, moderately high or high levels of bilirubin, depending on exact features of the cirrhosis.
To further elucidate the causes of jaundice or increased bilirubin, it is usually simpler to look at other liver function tests (especially the enzymes alanine transaminase, aspartate transaminase, gamma-glutamyl transpeptidase, alkaline phosphatase), blood film examination (hemolysis, etc.) or evidence of infective hepatitis (e.g., hepatitis A, B, C, delta, E, etc.). | 1 | Biochemistry |
Over time, many parts of the chloroplast genome were transferred to the nuclear genome of the host, a process called endosymbiotic gene transfer. As a result, the chloroplast genome is heavily reduced compared to that of free-living cyanobacteria. Chloroplasts may contain 60–100 genes whereas cyanobacteria often have more than 1500 genes in their genome. Recently, a plastid without a genome was found, demonstrating chloroplasts can lose their genome during endosymbiotic the gene transfer process.
Endosymbiotic gene transfer is how we know about the lost chloroplasts in many CASH lineages. Even if a chloroplast is eventually lost, the genes it donated to the former hosts nucleus persist, providing evidence for the lost chloroplasts existence. For example, while diatoms (a heterokontophyte) now have a red algal derived chloroplast, the presence of many green algal genes in the diatom nucleus provide evidence that the diatom ancestor had a green algal derived chloroplast at some point, which was subsequently replaced by the red chloroplast.
In land plants, some 11–14% of the DNA in their nuclei can be traced back to the chloroplast, up to 18% in Arabidopsis, corresponding to about 4,500 protein-coding genes. There have been a few recent transfers of genes from the chloroplast DNA to the nuclear genome in land plants.
Of the approximately 3000 proteins found in chloroplasts, some 95% of them are encoded by nuclear genes. Many of the chloroplasts protein complexes consist of subunits from both the chloroplast genome and the hosts nuclear genome. As a result, protein synthesis must be coordinated between the chloroplast and the nucleus. The chloroplast is mostly under nuclear control, though chloroplasts can also give out signals regulating gene expression in the nucleus, called retrograde signaling. Recent research indicates that parts of the retrograde signaling network once considered characteristic for land plants emerged already in an algal progenitor, integrating into co-expressed cohorts of genes in the closest algal relatives of land plants. | 5 | Photochemistry |
Precious metal refining is the separation of precious metals from noble-metalliferous materials. Examples of these materials include used catalysts, electronic assemblies, ores or metal alloys. | 8 | Metallurgy |
A nested intronic gene lies within the non-coding intronic region of a larger gene, and occurs relatively frequently, especially in the introns of metazoans and higher eukaryotes. Because only eukaryotic DNA contains intronic regions, this type of gene does not occur in bacteria or archaea.
The human genome contains a relatively high proportion of nested intronic genes. It is predicted to contain at least 158 functional intronic nested genes, with an additional 212 pseudogenes and three snoRNA genes nested in intronic regions. These genes seem to be distributed randomly across all chromosomes, and the majority code for proteins that are functionally unrelated to their host genes. | 1 | Biochemistry |
*Bisulfite sequencing
*DNA sequencing
*Expression cloning
*Fluorescence in situ hybridization
*Lab-on-a-chip
*Comparison of nucleic acid simulation software
*Northern blot
*Nuclear run-on assay
*Radioactivity in the life sciences
*Southern blot
*Differential centrifugation (sucrose gradient)
*Toeprinting assay
*Several bioinformatics methods, as seen in list of RNA structure prediction software | 1 | Biochemistry |
The acetonides of small di- and triols, as well as many sugars and sugar alcohols, are common. The hexaol mannitol reacts with 2,2-dimethoxypropane to give the bis-acetonide, which oxidizes to give the acetonide of glyceraldehyde:
:(CHOHCHOHCHOH) + 2 (MeO)CMe → (CHOHCHCHOCMe) + 4 MeOH
:(CHOHCHOCHOCMe) + [O] → 2 OCHCHCHOCMe + HO
An example of its use as a protecting group in a complex organic synthesis is the Nicolaou Taxol total synthesis. It is a common protecting group for sugars and sugar alcohols, a simple example being solketal.
The acetonides of corticosteroid are used in dermatology, because their increased lipophilicity leads to better penetration into the skin.
* Fluclorolone acetonide
* Fluocinolone acetonide
* Triamcinolone acetonide | 0 | Organic Chemistry |
Tetsuo Nozoe was married to Kyoko Horiuchi and had four children – one son and three daughters. Tetsuo died of cancer on 4 April 1996.
He was collecting autographs and tributes from famous chemists all over the world, including at least 32 Nobel laureates, and had collected more than 4,000 signatures and comments in his note books. Tetsuo's autograph books, of 1,179 pages, are kept in the archives in Tohoku University.
His son Shigeo, daughter Yoko, grandson and granddaughters also studied chemistry. Shigeo Nozoe was also a professor of chemistry at Tokohu University. | 0 | Organic Chemistry |
Arsenic poisoning is caused by incidental ingestion or inhalation of arsenic, typically from drinking contaminated well water, eating food cooked in contaminated water, or being exposed to arsenic-containing pesticides, folk medicines, or industrial chemicals. The World Health Organization considers arsenic levels above 10 parts per billion (10 micrograms per liter) to be unsafe. | 1 | Biochemistry |
In molecular clouds, simple carbon molecules are formed, including carbon monoxide and dicarbon. Reactions with the trihydrogen cation of the simple carbon molecules yield carbon containing ions that readily react to form larger organic molecules. Carbon compounds that exist as ions, or isolated gas molecules in the interstellar medium, can condense onto dust grains. Carbonaceous dust grains consist mostly of carbon. Grains can stick together to form larger aggregates. | 9 | Geochemistry |
Phosphaalkynes with small substituents (H, F, Me, Ph, etc.) undergo decomposition at or below room temperature by way of polymerization/oligimerization to yield mixtures of products which are challenging to characterize. The same is largely true of kinetically stable phosphaalkynes, which undergo oligomerization reactions at elevated temperature. In spite of the challenges associated with isolating and identifying the products of these oligimerizations, however, cuboidal tetramers of tert-butylphosphaalkyne and tert-pentylphosphaalkyne have been isolated (albeit in low yield) and identified following heating of the respective phosphaalkyne.
Computational chemistry has proved a valuable tool for studying these synthetically complex reactions, and it has been shown that while the formation of phosphaalkyne dimers is thermodynamically favorable, the formation of trimers, tetramers, and higher order oligomeric species tends to be more favorable, accounting for the generation of intractable mixtures upon inducing oligomerization of phosphaalkynes experimentally. | 0 | Organic Chemistry |
Plaster casting is similar to sand casting except that plaster of paris is used instead of sand as a mold material. Generally, the form takes less than a week to prepare, after which a production rate of 1–10 units/hr-mold is achieved, with items as massive as and as small as with very good surface finish and close tolerances. Plaster casting is an inexpensive alternative to other molding processes for complex parts due to the low cost of the plaster and its ability to produce near net shape castings. The biggest disadvantage is that it can only be used with low melting point non-ferrous materials, such as aluminium, copper, magnesium, and zinc. | 8 | Metallurgy |
Lutathera is a peptide receptor radioligand/radionuclide therapy (approved by the FDA in 2018) specifically for patients with gastroenteropancreatic neuroendocrine tumors (GEP-NETs) that have somatostatin hormone receptors (SSTR). The radioisotope is Lu-177 and the ligand is a SSTR on the surface of tumor cells.
Lu-177 is produced by bombarding the stable isotope Yb-176 (which is found in monazite sand as well as the ores euxenite and xenotime) with neutrons. Yb-176 turns into Yb-177 which is unstable and has a half life of 1.9 hours so it quickly decays into the medical isotope Lu-177. For mass production, it is better to produce Yb-176 through fission reactors. This is the indirect production method and requires elaborate radiochemical separation, purification, and results in large amounts of radioactive waste. The direct method of producing Lu-177 is by performing neutron irradiation on Lu-176 to Lu-177. This is an inexpensive and effective method to produce Lu-177. In the United States, the main place that Lu-177 is produced is the University of Missouri Research Reactor.
Once produced, Lu-177 is stable for 72 hours if stored below room temperature. Freeze dried kits of Lutathera do show reduced effectiveness in radiation therapy but they maintain radiochemical purity. Lu-177 requires radiation shielding for handling. Lu-177 is stored and transported in a vial with lead/plexiglass shielding ready-to-use. Repeated production, timely delivery, and quick administration are important so that the therapy remains effective.
Once transported to the hospital or cancer treatment / oncology center, the patient is prepped, all necessary tests are done, and the patient requires two separate IV sites for infusion. One site for radioactive Lu-177 infusion and one site for amino acid infusion. Amino acid infusion is needed to reduce radiation toxicity to the organs - specifically the kidneys. The sites are separate to prevent radioactive contamination after therapy. The patient receives therapy by automated syringe, infusion pump, or gravity using long/short needles, tubing, and sodium chloride solution. Antiemetic (anti-nausea) medications or short/long acting octreotide (cancer growth control) can be used post-therapy for symptom management.
The most common side effects include decreased blood cell counts, increased liver enzymes, vomiting, nausea, increased blood glucose, and decreased blood potassium levels. Lutathera is not given to pregnant or breastfeeding individuals. The therapy shrinks tumors by an average of 30%, reduces disease progression by 72%, and delays the growth of tumors. | 1 | Biochemistry |
CSMBLM cooperates with professional and scientific organizations of medical biochemistry in other countries. it has been a full member of the International Federation of Clinical Chemistry (IFCC) since 1972, first as part of the Yugoslav Society of Medical Biochemists and since 1992 as an independent party. In 1993, CSMBLM became a member of the Forum of the European Societies of Clinical Chemistry, nowadays the European Federation of Clinical Chemistry and Laboratory Medicine ([http://www.efcclm.org/ EFLM]). | 1 | Biochemistry |
In this case, the aglycone contains a cyanohydrin group. Plants that make cyanogenic glycosides store them in the vacuole, but, if the plant is attacked, they are released and become activated by enzymes in the cytoplasm. These remove the sugar part of the molecule, allowing the cyanohydrin structure to collapse and release toxic hydrogen cyanide. Storing them in inactive forms in the vacuole prevents them from damaging the plant under normal conditions.
Along with playing a role in deterring herbivores, in some plants they control germination, bud formation, carbon and nitrogen transport, and possibly act as antioxidants. The production of cyanogenic glycosides is an evolutionarily conserved function, appearing in species as old as ferns and as recent as angiosperms. These compounds are made by around 3,000 species. In screens they are found in about 11% of cultivated plants but only 5% of plants overall; humans seem to have selected for them.
Examples include amygdalin and prunasin which are made by the bitter almond tree; other species that produce cyanogenic glycosides are sorghum (from which dhurrin, the first cyanogenic glycoside to be identified, was first isolated), barley, flax, white clover, and cassava, which produces linamarin and lotaustralin.
Amygdalin and a synthetic derivative, laetrile, were investigated as potential drugs to treat cancer and were heavily promoted as alternative medicine; they are ineffective and dangerous.
Some butterfly species, such as the Dryas iulia and Parnassius smintheus, have evolved to use the cyanogenic glycosides found in their host plants as a form of protection against predators through their unpalatability. | 0 | Organic Chemistry |
In chemistry, an imidic acid is any molecule that contains the -C(=NH)-OH functional group. It is the tautomer of an amide and the isomer of an oxime.
The term "imino acid" is an obsolete term for this group that should not be used in this context because it has a different molecular structure.
Imidic acids can be formed by metal-catalyzed dehydrogenation of geminal amino alcohols. For example, methanolamine, the parent compound of the amino alcohols, can be dehydrogenated to methanimidic acid, the parent compound of the imidic acids.
:HNCHOH → HNCHOH + H (tautomer of formamide)
Geminal amino alcohols with side chains similarly form imidic acids with the same side chains:
:HNCHROH → HNCROH + H
Another way to form imidic acids is the reaction of carboxylic acids with azanone. For example, the reaction for carbamic acid:
:HNCOOH + HNO → HNCNHOH + O (tautomer of urea)
And the general reaction for substituted imidic acids:
:RCOOH + RNO → RCNROH + O
Another mechanism is the reaction of carboxylic acids with diazene or other azo compounds, forming azanone.
:RCOOH + HNNH → RCNHOH + HNO
Imidic acids tautomerize to amides by a hydrogen shift from the oxygen to the nitrogen atom. Amides are more stable in an environment with oxygen or water, whereas imidic acids dominate the equilibrium in solution with ammonia or methane.
:HNCHOH ⇌ HCONH
:RNCROH ⇌ RCONHR | 0 | Organic Chemistry |
Supercritical fluids act as a new medium for the generation of novel crystalline forms of APIs (Active Pharmaceutical Ingredients) named as pharmaceutical cocrystals. Supercritical fluid technology offers a new platform that allows a single-step generation of particles that are difficult or even impossible to obtain by traditional techniques. The generation of pure and dried new cocrystals (crystalline molecular complexes comprising the API and one or more conformers in the crystal lattice) can be achieved due to unique properties of SCFs by using different supercritical fluid properties: supercritical CO solvent power, anti-solvent effect and its atomization enhancement. | 7 | Physical Chemistry |
In signal processing, the power spectrum of a continuous time signal describes the distribution of power into frequency components composing that signal. According to Fourier analysis, any physical signal can be decomposed into a number of discrete frequencies, or a spectrum of frequencies over a continuous range. The statistical average of any sort of signal (including noise) as analyzed in terms of its frequency content, is called its spectrum.
When the energy of the signal is concentrated around a finite time interval, especially if its total energy is finite, one may compute the energy spectral density. More commonly used is the power spectral density (or simply power spectrum), which applies to signals existing over all time, or over a time period large enough (especially in relation to the duration of a measurement) that it could as well have been over an infinite time interval. The power spectral density (PSD) then refers to the spectral energy distribution that would be found per unit time, since the total energy of such a signal over all time would generally be infinite. Summation or integration of the spectral components yields the total power (for a physical process) or variance (in a statistical process), identical to what would be obtained by integrating over the time domain, as dictated by Parseval's theorem.
The spectrum of a physical process often contains essential information about the nature of . For instance, the pitch and timbre of a musical instrument are immediately determined from a spectral analysis. The color of a light source is determined by the spectrum of the electromagnetic wave's electric field as it fluctuates at an extremely high frequency. Obtaining a spectrum from time series such as these involves the Fourier transform, and generalizations based on Fourier analysis. In many cases the time domain is not specifically employed in practice, such as when a dispersive prism is used to obtain a spectrum of light in a spectrograph, or when a sound is perceived through its effect on the auditory receptors of the inner ear, each of which is sensitive to a particular frequency.
However this article concentrates on situations in which the time series is known (at least in a statistical sense) or directly measured (such as by a microphone sampled by a computer). The power spectrum is important in statistical signal processing and in the statistical study of stochastic processes, as well as in many other branches of physics and engineering. Typically the process is a function of time, but one can similarly discuss data in the spatial domain being decomposed in terms of spatial frequency. | 7 | Physical Chemistry |
Photolysis or thermolysis of mononuclear carbonyls generates di- and polymetallic carbonyls such as diiron nonacarbonyl (Fe(CO)). On further heating, the products decompose eventually into the metal and carbon monoxide.
:2 Fe(CO) → Fe(CO) + CO
The thermal decomposition of triosmium dodecacarbonyl (Os(CO)) provides higher-nuclear osmium carbonyl clusters such as Os(CO), Os(CO) up to Os(CO).
Mixed ligand carbonyls of ruthenium, osmium, rhodium, and iridium are often generated by abstraction of CO from solvents such as dimethylformamide (DMF) and 2-methoxyethanol. Typical is the synthesis of IrCl(CO)(PPh) from the reaction of iridium(III) chloride and triphenylphosphine in boiling DMF solution. | 0 | Organic Chemistry |
Levomethorphan (LVM) (INN, BAN) is an opioid analgesic of the morphinan family that has never been marketed. It is the -stereoisomer of racemethorphan (methorphan). The effects of the two isomers of racemethorphan are quite different, with dextromethorphan (DXM) being an antitussive at low doses and a dissociative hallucinogen at much higher doses. Levomethorphan is about five times stronger than morphine.
Levomethorphan is a prodrug to levorphanol, analogously to DXM acting as a prodrug to dextrorphan or codeine behaving as a prodrug to morphine. As such, levomethorphan has similar effects to levorphanol but is less potent as it must be demethylated to the active form by liver enzymes before being able to produce its effects. As a prodrug of levorphanol, levomethorphan functions as a potent agonist of all three of the opioid receptors, μ, κ (κ and κ but notably not κ), and δ, as an NMDA receptor antagonist, and as a serotonin-norepinephrine reuptake inhibitor. Via activation of the κ-opioid receptor, levomethorphan can produce dysphoria and psychotomimetic effects such as dissociation and hallucinations.
Levomethorphan is listed under the Single Convention on Narcotic Drugs 1961 and is regulated like morphine in most countries. In the United States it is a Schedule II Narcotic controlled substance with a DEA ACSCN of 9210 and a 2014 annual aggregate manufacturing quota of 195 grams, up from 6 grams the year before. The salts in use are the tartrate (free base conversion ratio 0.644) and hydrobromide (0.958). At the current time, no levomethorphan pharmaceuticals are marketed in the United States. | 4 | Stereochemistry |
Trifluoromethanesulfonic acid was first synthesized in 1954 by Robert Haszeldine and Kidd by the following reaction: | 0 | Organic Chemistry |
To perform spectral analysis of a source, monochromatic light at every wavelength would be needed to create a spectrum response of the illuminant. A monochromator is used to sample wavelengths from the source and essentially produce a monochromatic signal. It is essentially a variable filter, selectively separating and transmitting a specific wavelength or band of wavelengths from the full spectrum of measured light and excluding any light that falls outside that region.
A typical monochromator achieves this through the use of entrance and exit slits, collimating and focus optics, and a wavelength-dispersing element such as a diffraction grating or prism. Modern monochromators are manufactured with diffraction gratings, and diffraction gratings are used almost exclusively in spectroradiometric applications. Diffraction gratings are preferable due to their versatility, low attenuation, extensive wavelength range, lower cost, and more constant dispersion. Single or double monochromators can be used depending on application, with double monochromators generally providing more precision due to the additional dispersion and baffling between gratings. | 7 | Physical Chemistry |
The biosynthesis of the Fe–S clusters has been well studied.
The biogenesis of iron sulfur clusters has been studied most extensively in the bacteria E. coli and A. vinelandii and yeast S. cerevisiae. At least three different biosynthetic systems have been identified so far, namely nif, suf, and isc systems, which were first identified in bacteria. The nif system is responsible for the clusters in the enzyme nitrogenase. The suf and isc systems are more general.
The yeast isc system is the best described. Several proteins constitute the biosynthetic machinery via the isc pathway. The process occurs in two major steps:
(1) the Fe/S cluster is assembled on a scaffold protein followed by (2) transfer of the preformed cluster to the recipient proteins.
The first step of this process occurs in the cytoplasm of prokaryotic organisms or in the mitochondria of eukaryotic organisms. In the higher organisms the clusters are therefore transported out of the mitochondrion to be incorporated into the extramitochondrial enzymes. These organisms also possess a set of proteins involved in the Fe/S clusters transport and incorporation processes that are not homologous to proteins found in prokaryotic systems. | 7 | Physical Chemistry |
"The Gaia Hypothesis" is the title of the award-winning collection of short stories A Hipótese de Gaia by Jorge Reis-Sá, published in Portuguese in 2022. | 9 | Geochemistry |
The other possible case would be that the second step is slow and rate-determining, meaning that it is slower than the first step in the reverse direction: r ≪ r. In this hypothesis, r − r ≈ 0, so that the first step is (almost) at equilibrium. The overall rate is determined by the second step: r = r ≪ r, as very few molecules that react at the first step continue to the second step, which is much slower. Such a situation in which an intermediate (here ) forms an equilibrium with reactants prior to the rate-determining step is described as a pre-equilibrium For the reaction of and CO, this hypothesis can be rejected, since it implies a rate equation that disagrees with experiment.
# + → NO + (fast step)
# + CO → + (slow step, rate-determining)
If the first step were at equilibrium, then its equilibrium constant expression permits calculation of the concentration of the intermediate in terms of more stable (and more easily measured) reactant and product species:
The overall reaction rate would then be
which disagrees with the experimental rate law given above, and so disproves the hypothesis that the second step is rate-determining for this reaction. However, some other reactions are believed to involve rapid pre-equilibria prior to the rate-determining step, as shown below. | 7 | Physical Chemistry |
Another use of methylene blue is to treat ifosfamide neurotoxicity. Methylene blue was first reported for treatment and prophylaxis of ifosfamide neuropsychiatric toxicity in 1994. A toxic metabolite of ifosfamide, chloroacetaldehyde (CAA), disrupts the mitochondrial respiratory chain, leading to an accumulation of nicotinamide adenine dinucleotide hydrogen (NADH). Methylene blue acts as an alternative electron acceptor, and reverses the NADH inhibition of hepatic gluconeogenesis while also inhibiting the transformation of chloroethylamine into chloroacetaldehyde, and inhibits multiple amine oxidase activities, preventing the formation of CAA. The dosing of methylene blue for treatment of ifosfamide neurotoxicity varies, depending upon its use simultaneously as an adjuvant in ifosfamide infusion, versus its use to reverse psychiatric symptoms that manifest after completion of an ifosfamide infusion. Reports suggest that methylene blue up to six doses a day have resulted in improvement of symptoms within 10 minutes to several days. Alternatively, it has been suggested that intravenous methylene blue every six hours for prophylaxis during ifosfamide treatment in people with history of ifosfamide neuropsychiatric toxicity. Prophylactic administration of methylene blue the day before initiation of ifosfamide, and three times daily during ifosfamide chemotherapy has been recommended to lower the occurrence of ifosfamide neurotoxicity. | 3 | Analytical Chemistry |
Fluorescent chloride sensors are used for chemical analysis. The discoveries of chloride (Cl) participations in physiological processes stimulates the measurements of intracellular Cl in live cells and the development of fluorescent tools referred below. | 3 | Analytical Chemistry |
The formation of electron quadruplets or charge-4e superconductivity is a proposed state of matter in which Cooper pairs do not exhibit long-range order, but electron quadruplets do. This "quartic metal" phase is related to but distinct from those superconductors explained by the standard BCS theory; rather than expelling magnetic field lines as in the Meissner effect, it generates them, a spontaneous Nernst effect that indicates the breaking of time-reversal symmetry. After the theoretical possibility was raised, observations consistent with electron quadrupling were published using hole-doped BaKFeAs in 2021. | 7 | Physical Chemistry |
A number of factors can affect the migration of nucleic acids: the dimension of the gel pores (gel concentration), size of DNA being electrophoresed, the voltage used, the ionic strength of the buffer, and the concentration of intercalating dye such as ethidium bromide if used during electrophoresis.
Smaller molecules travel faster than larger molecules in gel, and double-stranded DNA moves at a rate that is inversely proportional to the logarithm of the number of base pairs. This relationship however breaks down with very large DNA fragments, and separation of very large DNA fragments requires the use of pulsed field gel electrophoresis (PFGE), which applies alternating current from different directions and the large DNA fragments are separated as they reorient themselves with the changing field.
For standard agarose gel electrophoresis, larger molecules are resolved better using a low concentration gel while smaller molecules separate better at high concentration gel. Higher concentration gels, however, require longer run times (sometimes days).
The movement of the DNA may be affected by the conformation of the DNA molecule, for example, supercoiled DNA usually moves faster than relaxed DNA because it is tightly coiled and hence more compact. In a normal plasmid DNA preparation, multiple forms of DNA may be present. Gel electrophoresis of the plasmids would normally show the negatively supercoiled form as the main band, while nicked DNA (open circular form) and the relaxed closed circular form appears as minor bands. The rate at which the various forms move however can change using different electrophoresis conditions, and the mobility of larger circular DNA may be more strongly affected than linear DNA by the pore size of the gel.
Ethidium bromide which intercalates into circular DNA can change the charge, length, as well as the superhelicity of the DNA molecule, therefore its presence in gel during electrophoresis can affect its movement. For example, the positive charge of ethidium bromide can reduce the DNA movement by 15%. Agarose gel electrophoresis can be used to resolve circular DNA with different supercoiling topology.
DNA damage due to increased cross-linking will also reduce electrophoretic DNA migration in a dose-dependent way.
The rate of migration of the DNA is proportional to the voltage applied, i.e. the higher the voltage, the faster the DNA moves. The resolution of large DNA fragments however is lower at high voltage. The mobility of DNA may also change in an unsteady field – in a field that is periodically reversed, the mobility of DNA of a particular size may drop significantly at a particular cycling frequency. This phenomenon can result in band inversion in field inversion gel electrophoresis (FIGE), whereby larger DNA fragments move faster than smaller ones. | 1 | Biochemistry |
Three patients' deaths have been reported in gene therapy trials, putting the field under close scrutiny. The first was that of Jesse Gelsinger, who died in 1999, because of immune rejection response. One X-SCID patient died of leukemia in 2003. In 2007, a rheumatoid arthritis patient died from an infection; the subsequent investigation concluded that the death was not related to gene therapy. | 1 | Biochemistry |
Ribosomal pause refers to the queueing or stacking of ribosomes during translation of the nucleotide sequence of mRNA transcripts. These transcripts are decoded and converted into an amino acid sequence during protein synthesis by ribosomes. Due to the pause sites of some mRNA's, there is a disturbance caused in translation. Ribosomal pausing occurs in both eukaryotes and prokaryotes. A more severe pause is known as a ribosomal stall.
Its been known since the 1980s that different mRNAs are translated at different rates. The main reason for these differences was thought to be the concentration of varieties of rare tRNAs limiting the rate at which some transcripts could be decoded. However, with research techniques such as ribosome profiling, it was found that at certain sites there were higher concentrations of ribosomes than average, and these pause sites were tested with specific codons. No link was found between the occupancy of specific codons and amount of their tRNAs. Thus, the early findings about rare tRNAs causing pause sites doesnt seem plausible.
Two techniques can localize the ribosomal pause site in vivo; a micrococcal nuclease protection assay and isolation of polysomal transcript. Isolation of polysomal transcripts occurs by centrifuging tissue extracts through a sucrose cushion with translation elongation inhibitors, for example cycloheximide.
Ribosome pausing can be detected during preprolactin synthesis on free polysomes, when the ribosome is paused the other ribosomes are tightly stacked together. When the ribosome pauses, during translation, the fragments that started to translate before the pause took place are overrepresented. However, along with the mRNA if the ribosome pauses then specific bands will be improved in the trailing edge of the ribosome.
Some of the elongation inhibitors, such as: cycloheximide (in eukaryotes) or chloramphenicol, cause the ribosomes to pause and to accumulate in the start codons. Elongation Factor P regulates the ribosomal pause at polyproline in bacteria, and when there is no EFP the density of ribosomes decreases from the polyproline motifs. If there are multiple ribosome pauses, then the EFP won't resolve it. | 1 | Biochemistry |
Optical rotation is measured with an instrument called a polarimeter. There is a linear relationship between the observed rotation and the concentration of optically active compound in the sample. There is a nonlinear relationship between the observed rotation and the wavelength of light used. Specific rotation is calculated using either of two equations, depending on whether the sample is a pure chemical to be tested or that chemical dissolved in solution. | 4 | Stereochemistry |
is a traditional Japanese chemical compound used in the niiro process for artificially inducing patination in decorative non-ferrous metals, especially several copper alloys, with the results being metals of the irogane class. These "colour metals," virtually unknown outside Japan until the late 19th century, have achieved some popularity in craft circles in other parts of the world since then. | 8 | Metallurgy |
A variety of supramolecular polymers can be synthesized by using monomers with host-guest complementary binding motifs, such as crown ethers/ammonium ions, cucurbiturils/viologens, calixarene/viologens, cyclodextrins/adamantane derivatives, and pillar arene/imidazolium derivatives [30–33]. When the monomers are "heteroditopic", supramolecular copolymers results, provided the monomers does not homopolymerize. Akira Harada was one of the firstwhorecognize the importance of combining polymers and cyclodextrins. Feihe Huang showed an example of supramolecular alternating copolymer from two heteroditopic monomers carrying both crown ether and ammonium ion termini. Takeharo Haino demonstrated an extreme example of sequence control in supramolecular copolymer, where three heteroditopic monomers are arranged in an ABC sequence along the copolymer chain. The design strategy utilizing three distinct binding interactions; ball-and-socket (calix[5]arene/C60), donor-acceptor (bisporphyrin/trinitrofluorenone), and Hamilton's H-bonding interactions is the key to attain a high orthogonality to form an ABC supramolecular terpolymer. | 6 | Supramolecular Chemistry |
Because solids have thermal energy, their atoms vibrate about fixed mean positions within the ordered (or disordered) lattice. The spectrum of lattice vibrations in a crystalline or glassy network provides the foundation for the kinetic theory of solids. This motion occurs at the atomic level, and thus cannot be observed or detected without highly specialized equipment, such as that used in spectroscopy.
Thermal properties of solids include thermal conductivity, which is the property of a material that indicates its ability to conduct heat. Solids also have a specific heat capacity, which is the capacity of a material to store energy in the form of heat (or thermal lattice vibrations). | 7 | Physical Chemistry |
Al-Youbi received his bachelor’s and master’s degree in chemistry from King Abdulaziz University. He attended the University of Essex on a scholarship, where he received his PhD in physical chemistry in 1986.
Before being appointed as president of King Abdulaziz University in 2016, he served as vice president. He was a consultant at the Ministry of Higher Education, and was dean and vice-dean of the faculty of science, King Abdulaziz University. | 7 | Physical Chemistry |
The ground state of methylene has an ionisation energy of 10.396 eV. It has a bent configuration, with H-C-H angle of 133.84°, and is thus paramagnetic. (The correct prediction of this angle was an early success of ab initio quantum chemistry.) However conversion to a linear configuration requires only 5.5 kcal/mol.
The singlet state has a slightly higher energy (by about 9 kcal/mol) than the triplet state, and its H-C-H angle is smaller, about 102°. In dilute mixtures with an inert gas, the two states will convert to each other until reaching an equilibrium. | 0 | Organic Chemistry |
Current Opinion in Colloid & Interface Science is a bimonthly peer-reviewed scientific journal published by Elsevier. It covers the field of physical chemistry, especially research on colloids and interfaces. The journal was established in 1996 and the editors-in-chiefs are Dganit Danino and Marie Pierre Krafft. According to the Journal Citation Reports, the journal has a 2021 impact factor of 8.209. | 7 | Physical Chemistry |
The modified gene therapy strategy of antisense IGF-I RNA (NIH n˚ 1602) using antisense / triple helix anti-IGF-I approach was registered in 2002, by Wiley gene therapy clinical trial - n˚ 635 and 636. The approach has shown promising results in the treatment of six different malignant tumors: glioblastoma, cancers of liver, colon, prostate, uterus, and ovary (Collaborative NATO Science Programme on Gene Therapy USA, France, Poland n˚ LST 980517 conducted by J. Trojan) (Trojan et al., 2012). This anti-gene antisense/triple helix therapy has proven to be efficient, due to the mechanism stopping simultaneously IGF-I expression on translation and transcription levels, strengthening anti-tumor immune and apoptotic phenomena. | 1 | Biochemistry |
White-beam topography uses the full bandwidth of X-ray wavelengths in the incoming beam, without any wavelength filtering (no monochromator). The technique is particularly useful in combination with synchrotron radiation sources, due to their wide and continuous wavelength spectrum. In contrast to the monochromatic case, in which accurate sample adjustment is often necessary in order to reach diffraction conditions, the Bragg equation is always and automatically fulfilled in the case of a white X-ray beam: Whatever the angle at which the beam hits a specific lattice plane, there is always one wavelength in the incident spectrum for which the Bragg angle is fulfilled just at this precise angle (on condition that the spectrum is wide enough). White-beam topography is therefore a very simple and fast technique. Disadvantages include the high X-ray dose, possibly leading to radiation damage to the sample, and the necessity to carefully shield the experiment.
White-beam topography produces a pattern of several diffraction spots, each spot being related to one specific lattice plane in the crystal. This pattern, typically recorded on X-ray film, corresponds to a Laue pattern and shows the symmetry of the crystal lattice. The fine structure of each single spot (topograph) is related to defects and distortions in the sample. The distance between spots, and the details of contrast within one single spot, depend on the distance between sample and film; this distance is therefore an important degree of freedom for white-beam topography experiments.
Deformation of the crystal will cause variation in the size of the diffraction spot. For a cylindrically bent crystal the Bragg planes in the crystal lattice will lie on Archimedean spirals (with the exception of those orientated tangentially and radially to the curvature of the bend, which are respectively cylindrical and planar), and the degree of curvature can be determined in a predictable way from the length of the spots and the geometry of the set-up.
White-beam topographs are useful for fast and comprehensive visualization of crystal defect and distortions. They are, however, rather difficult to analyze in any quantitative way, and even a qualitative interpretation often requires considerable experience and time. | 3 | Analytical Chemistry |
The two N-terminal cysteines of CXC chemokines (or α-chemokines) are separated by one amino acid, represented in this name with an "X". There have been 17 different CXC chemokines described in mammals, that are subdivided into two categories, those with a specific amino acid sequence (or motif) of glutamic acid-leucine-arginine (or ELR for short) immediately before the first cysteine of the CXC motif (ELR-positive), and those without an ELR motif (ELR-negative). ELR-positive CXC chemokines specifically induce the migration of neutrophils, and interact with chemokine receptors CXCR1 and CXCR2. An example of an ELR-positive CXC chemokine is interleukin-8 (IL-8), which induces neutrophils to leave the bloodstream and enter into the surrounding tissue. Other CXC chemokines that lack the ELR motif, such as CXCL13, tend to be chemoattractant for lymphocytes. CXC chemokines bind to CXC chemokine receptors, of which seven have been discovered to date, designated CXCR1-7. | 1 | Biochemistry |
Residue storage methods have changed substantially since the original plants were built. The practice in early years was to pump the slurry, at a concentration of about 20% solids, into lagoons or ponds sometimes created in former bauxite mines or depleted quarries. In other cases, impoundments were constructed with dams or levees, while for some operations valleys were dammed and the residue deposited in these holding areas.
It was once common practice for the red mud to be discharged into rivers, estuaries, or the sea via pipelines or barges; in other instances the residue was shipped out to sea and disposed of in deep ocean trenches many kilometres offshore. From 2016, all disposal into the sea, estuaries and rivers was stopped.
As residue storage space ran out and concern increased over wet storage, since the mid-1980s dry stacking has been increasingly adopted. In this method, residues are thickened to a high density slurry (48–55% solids or higher), and then deposited in a way that it consolidates and dries.
An increasingly popular treatment process is filtration whereby a filter cake (typically resulting in 23–27% moisture) is produced. This cake can be washed with either water or steam to reduce alkalinity before being transported and stored as a semi-dried material. Residue produced in this form is ideal for reuse as it has lower alkalinity, is cheaper to transport, and is easier to handle and process. Another option for ensuring safe storage is to use amphirols to dewater the material once deposited and then conditioned using farming equipment such as harrows to accelerate carbonation and thereby reduce the alkalinity. Bauxite residue produced after press filtration and 'conditioning as described above are classified as non-hazardous under the EU Waste Framework Directive.
In 2013 Vedanta Aluminium, Ltd. commissioned a red mud powder-producing unit at its Lanjigarh refinery in Odisha, India, describing it as the first of its kind in the alumina industry, tackling major environmental hazards. | 2 | Environmental Chemistry |
The thylakoids are the site of the light-dependent reactions of photosynthesis. These include light-driven water oxidation and oxygen evolution, the pumping of protons across the thylakoid membranes coupled with the electron transport chain of the photosystems and cytochrome complex, and ATP synthesis by the ATP synthase utilizing the generated proton gradient. | 5 | Photochemistry |
Upon deprotonation, the corrinoid ring is capable of binding cobalt. In vitamin B, the resulting complex also features a benzimidazole-derived ligand, and the sixth site on the octahedron serves as the catalytic center.
The corrin ring resembles the porphyrin ring. Both feature four pyrrole-like subunits organized into rings. Corrins have a central 15-membered ring whereas porphryins have an interior 16-membered ring. All four nitrogen centers are linked by conjugation structure, with alternating double and single bonds. In contrast to porphyrins, corrins lack one of the carbon groups that link the pyrrole-like units into a fully conjugated structure. With a conjugated system that extends only 3/4 of the way around the ring, and does not include any of the outer edge carbons, corrins have a number of non-conjugated sp carbons, making them more flexible than porphyrins and not as flat. A third closely related biological structure, the chlorin ring system found in chlorophyll, is intermediate between porphyrin and corrin, having 20 carbons like the porphyrins and a conjugated structure extending all the way around the central atom, but with only 6 of the 8 edge carbons participating.
Corroles (octadehydrocorrins) are fully aromatic derivatives of corrins. | 1 | Biochemistry |
V̇O max (also maximal oxygen consumption, maximal oxygen uptake or maximal aerobic capacity) is the maximum rate of oxygen consumption attainable during physical exertion. The name is derived from three abbreviations: "V̇" for volume (the dot over the V indicates "per unit of time" in Newton's notation), "O" for oxygen, and "max" for maximum and usually normalized per kilogram of body mass. A similar measure is V̇O peak (peak oxygen consumption), which is the measurable value from a session of physical exercise, be it incremental or otherwise. It could match or underestimate the actual V̇O max. Confusion between the values in older and popular fitness literature is common. The capacity of the lung to exchange oxygen and carbon dioxide is constrained by the rate of blood oxygen transport to active tissue.
The measurement of V̇O max in the laboratory provides a quantitative value of endurance fitness for comparison of individual training effects and between people in endurance training. Maximal oxygen consumption reflects cardiorespiratory fitness and endurance capacity in exercise performance. Elite athletes, such as competitive distance runners, racing cyclists or Olympic cross-country skiers, can achieve V̇O max values exceeding 90 mL/(kg·min), while some endurance animals, such as Alaskan huskies, have V̇O max values exceeding 200 mL/(kg·min).
In physical training, especially in its academic literature, V̇O max is often used as a reference level to quantify exertion levels, such as 65% V̇O max as a threshold for sustainable exercise, which is generally regarded as more rigorous than heart rate, but is more elaborate to measure. | 1 | Biochemistry |
Mitochondria contain their own genome. The human mitochondrial genome is a circular double-stranded DNA molecule of about 16 kilobases. It encodes 37 genes: 13 for subunits of respiratory complexes I, III, IV and V, 22 for mitochondrial tRNA (for the 20 standard amino acids, plus an extra gene for leucine and serine), and 2 for rRNA (12S and 16S rRNA). One mitochondrion can contain two to ten copies of its DNA. One of the two mitochondrial DNA (mtDNA) strands has a disproportionately higher ratio of the heavier nucleotides adenine and guanine, and this is termed the heavy strand (or H strand), whereas the other strand is termed the light strand (or L strand). The weight difference allows the two strands to be separated by centrifugation. mtDNA has one long non-coding stretch known as the non-coding region (NCR), which contains the heavy strand promoter (HSP) and light strand promoter (LSP) for RNA transcription, the origin of replication for the H strand (OriH) localized on the L strand, three conserved sequence boxes (CSBs 1–3), and a termination-associated sequence (TAS). The origin of replication for the L strand (OriL) is localized on the H strand 11,000 bp downstream of OriH, located within a cluster of genes coding for tRNA.
As in prokaryotes, there is a very high proportion of coding DNA and an absence of repeats. Mitochondrial genes are transcribed as multigenic transcripts, which are cleaved and polyadenylated to yield mature mRNAs. Most proteins necessary for mitochondrial function are encoded by genes in the cell nucleus and the corresponding proteins are imported into the mitochondrion. The exact number of genes encoded by the nucleus and the mitochondrial genome differs between species. Most mitochondrial genomes are circular. In general, mitochondrial DNA lacks introns, as is the case in the human mitochondrial genome; however, introns have been observed in some eukaryotic mitochondrial DNA, such as that of yeast and protists, including Dictyostelium discoideum. Between protein-coding regions, tRNAs are present. Mitochondrial tRNA genes have different sequences from the nuclear tRNAs, but lookalikes of mitochondrial tRNAs have been found in the nuclear chromosomes with high sequence similarity.
In animals, the mitochondrial genome is typically a single circular chromosome that is approximately 16 kb long and has 37 genes. The genes, while highly conserved, may vary in location. Curiously, this pattern is not found in the human body louse (Pediculus humanus). Instead, this mitochondrial genome is arranged in 18 minicircular chromosomes, each of which is 3–4 kb long and has one to three genes. This pattern is also found in other sucking lice, but not in chewing lice. Recombination has been shown to occur between the minichromosomes. | 1 | Biochemistry |
Originally developed by the Dow Chemical Company, sulfuryl fluoride is in widespread use as a structural fumigant insecticide to control drywood termites, particularly in warm-weather portions of the southwestern and southeastern United States and in Hawaii. Less commonly, it can also be used to control rodents, powderpost beetles, deathwatch beetles, bark beetles, and bedbugs. Its use has increased as a replacement for methyl bromide, which was phased out because of harm to the ozone layer. It is an alternative to the use of phosphine, which is acutely toxic. | 2 | Environmental Chemistry |
ITCH is a HECT domain–containing E3 ubiquitin ligase that is ablated in non-agouti-lethal 18H (aka Itchy) mice. Itchy mice develop a severe immunological phenotype after birth that includes hyperplasia of lymphoid and hematopoietic cells, and stomach and lung inflammation. In humans ITCH deficiency causes altered physical growth, craniofacial morphology defects, defective muscle development, and aberrant immune system function. The ITCH gene is located on chromosome 20 in humans. ITCH contains a C2 domain, proline-rich region, WW domains, HECT domain, and multiple amino acids that are phosphorylated and ubiquitinated. | 1 | Biochemistry |
Peptidomimetic foldamers often break the previously mentioned definition of foldamers as they often adopt helical structures. They represent a major landmark of foldamer research due to their design and capabilities. The largest groups of peptidomimetic consist of β-peptides, γ-peptides and δ-peptides, and the possible monomeric combinations. The amino acids of these peptides only differ by one (β), two (γ), or three (δ) methylene carbons, yet the structural changes were profound. These peptide sequences are highly studied as sequence control leads to reliable folding prediction. Additionally, with multiple methylene carbons between the carboxyl and amino termini of the flanking peptide bonds, varying R-group side chains can be designed. One example of the novelty of β-peptides can be seen in the findings of Reiser and coworkers. Using a heteroligopeptide consisting of α-amino acids and cis-β-aminocyclopropanecarboxulic acids (cis-β-ACCs), they found the formation of helical sequences in oligomers as short as seven residues and defined conformation in five residues, a quality unique to peptides containing cyclic β-amino acids. | 6 | Supramolecular Chemistry |
There is no antidote for palytoxin. Only the symptoms can be alleviated.
Animal studies have shown that vasodilators, such as papaverine and isosorbide dinitrate, can be used as antidotes. The animal experiments only showed benefit if the antidotes were injected into the heart immediately following exposure. | 0 | Organic Chemistry |
Intermolecular forces observed between atoms and molecules can be described phenomenologically as occurring between permanent and instantaneous dipoles, as outlined above. Alternatively, one may seek a fundamental, unifying theory that is able to explain the various types of interactions such as hydrogen bonding, van der Waals force and dipole–dipole interactions. Typically, this is done by applying the ideas of quantum mechanics to molecules, and Rayleigh–Schrödinger perturbation theory has been especially effective in this regard. When applied to existing quantum chemistry methods, such a quantum mechanical explanation of intermolecular interactions provides an array of approximate methods that can be used to analyze intermolecular interactions. One of the most helpful methods to visualize this kind of intermolecular interactions, that we can find in quantum chemistry, is the non-covalent interaction index, which is based on the electron density of the system. London dispersion forces play a big role with this.
Concerning electron density topology, recent methods based on electron density gradient methods have emerged recently, notably with the development of IBSI (Intrinsic Bond Strength Index), relying on the IGM (Independent Gradient Model) methodology. | 6 | Supramolecular Chemistry |
In industrial water treatment terminology, water quality with high RSC index is synonymous with the soft water but is chemically very different from naturally soft water which has a very low ionic concentration. When calcium and magnesium salts are present in dissolved form in water, these salts precipitate on the heat transfer surfaces forming insulating hard scaling / coating which reduces the heat transfer efficiency of the heat exchangers. To avoid scaling in water cooled heat exchangers, water is treated by lime and or soda ash to remove the water hardness.
The following chemical reactions take place in lime soda softening process which precipitates the calcium and magnesium salts as calcium carbonate and magnesium hydroxide which have very low solubility in water.
* CaSO + NaCO ---> CaCO↓ + NaSO
* CaCl + NaCO ---> CaCO↓ + 2NaCl
* MgSO + Ca(OH) + NaCO ---> Mg(OH)↓ + CaCO↓ + NaSO
* MgCl + Ca(OH) + NaCO ---> Mg(OH)↓ + CaCO↓ + 2NaCl
* 2NaHCO + Ca(OH) ---> CaCO↓ + NaCO + 2HO
* NaCO + Ca(OH) ---> CaCO↓ + 2NaOH
* Ca(HCO) + Ca(OH) ---> 2CaCO↓ + 2HO
* Mg(HCO) + 2Ca(OH) ---> Mg(OH)↓ + 2CaCO↓ + 2HO
* MgCO + Ca(OH) ---> Mg(OH)↓ + CaCO↓
The excess soda ash after precipitating the calcium and magnesium salts is in carbonates & bicarbonates of sodium which imparts high pH or alkalinity to soil water. | 9 | Geochemistry |
Ro-vibrational spectroscopy concerns molecules in the gas phase. There are sequences of quantized rotational levels associated with both the ground and excited vibrational states. The spectra are often resolved into lines due to transitions from one rotational level in the ground vibrational state to one rotational level in the vibrationally excited state. The lines corresponding to a given vibrational transition form a band.
In the simplest cases the part of the infrared spectrum involving vibrational transitions with the same rotational quantum number (ΔJ = 0) in ground and excited states is called the Q-branch. On the high frequency side of the Q-branch the energy of rotational transitions is added to the energy of the vibrational transition. This is known as the R-branch of the spectrum for ΔJ = +1. The P-branch for ΔJ = −1 lies on the low wavenumber side of the Q branch. The appearance of the R-branch is very similar to the appearance of the pure rotation spectrum (but shifted to much higher wavenumbers), and the P-branch appears as a nearly mirror image of the R-branch. The Q branch is sometimes missing because of transitions with no change in J being forbidden.
The appearance of rotational fine structure is determined by the symmetry of the molecular rotors which are classified, in the same way as for pure rotational spectroscopy, into linear molecules, spherical-, symmetric- and asymmetric- rotor classes. The quantum mechanical treatment of rotational fine structure is the same as for pure rotation.
The strength of an absorption line is related to the number of molecules with the initial values of the vibrational quantum number ν and the rotational quantum number , and depends on temperature. Since there are actually states with rotational quantum number , the population with value increases with initially, and then decays at higher . This gives the characteristic shape of the P and R branches.
A general convention is to label quantities that refer to the vibrational ground and excited states of a transition with double prime and single prime, respectively. For example, the rotational constant for the ground state is written as and that of the excited state as
Also, these constants are expressed in the molecular spectroscopist's units of cm. so that in this article corresponds to in the definition of rotational constant at Rigid rotor. | 7 | Physical Chemistry |
Pyrethrin I is one of the two pyrethrins, natural organic compounds with potent insecticidal activity. It is an ester of (+)-trans-chrysanthemic acid with (S)-(Z)-pyrethrolone. | 0 | Organic Chemistry |
Mefloquine is useful for the prevention of malaria in all areas except for those where parasites may have resistance to multiple medications, and is one of several anti-malarial medications recommended by the United States Centers for Disease Control and Prevention for this purpose. It is also recommended by the Infectious Disease Society of America for malaria prophylaxis as a first or second-line agent, depending on resistance patterns in the malaria found in the geographic region visited. It is typically taken for one to two weeks before entering an area with malaria. Doxycycline and atovaquone/proguanil provide protection within one to two days and may be better tolerated. If a person becomes ill with malaria despite prophylaxis with mefloquine, the use of halofantrine and quinine for treatment may be ineffective. | 4 | Stereochemistry |
Bis(trifluoromethanesulfonyl)aniline is a source of the triflyl () group.
The disulfonimides are of the type with two sulfonyl groups flanking an amine. As with sulfinamides, this class of compounds is used as catalysts in enantioselective synthesis. | 0 | Organic Chemistry |
Acylhydrazines are derivatives of carboxylic acids, although they are typically prepared by the reaction of esters with hydrazine: | 0 | Organic Chemistry |
The structure of a transcription factory appears to be determined by cell type, transcriptional activity of the cell and also the method of technique used to visualise the structure. The generalised view of a transcription factory would feature between 4 – 30 RNA polymerase molecules and it is thought that the more transcriptionally active a cell is, the more polymerases that will be present in a factory in order to meet the demands of transcription. The core of the factory is porous and protein rich, with the hyperphosphorylated, elongating form polymerases on the perimeter. The type of proteins present include: ribonucleoproteins, co-activators, transcription factors, RNA helicase and splicing and processing enzymes. A factory only contains one type of RNA polymerase and the diameter of the factory varies depending on the RNA polymerase featured; RNA polymerase I factories are roughly 500 nm in width whereas RNA polymerase II and III factories a magnitude smaller at 50 nm. It has been experimentally shown that the transcription factory is immobilised to a structure and it is postulated that this immobilisation is because of a tethering to the nuclear matrix; this is because it has been shown it is tied to a structure that is unaffected by restriction enzymes. Proteins that have been thought to be involved in the tethering includes spectrin, actin and lamins. | 1 | Biochemistry |
Nüchter et al. (2001) have shown a new approach to Fischer glycosidation. Employing a microwave oven equipped with refluxing apparatus in a rotor reactor with pressure bombs, Nüchter et al. (2001) were able to achieve 100% yield of α- and β-D-glucosides. This method can be performed on a multi-kilogram scale. | 0 | Organic Chemistry |
The notation common with mass density underlines the connection between the two quantities (the mass concentration being the mass density of a component in the solution), but it can be a source of confusion especially when they appear in the same formula undifferentiated by an additional symbol (like a star superscript, a bolded symbol or varrho). | 3 | Analytical Chemistry |
mRNA binding allows repression of protein translation through direct blocking, degradation or cleavage of mRNA. Certain mRNA binding mechanisms have high specificity, which can act as a form of the intrinsic immune response during certain viral infections. Certain segmented RNA viruses can also regulate viral gene expression through RNA binding of another genome segment, however, the details of this mechanism are still unclear.
Specific examples include:
* RNA binding protein
* siRNA
* miRNA
* piRNA | 1 | Biochemistry |
Lattice models in biophysics represent a class of statistical-mechanical models which consider a biological macromacromolecule (such as DNA, protein, actin, etc.) as a lattice of units, each unit being in different states or conformations.
For example, DNA in chromatin can be represented as a one-dimensional lattice, whose elementary units are the nucleotide, base pair or nucleosome. Different states of the unit can be realized either by chemical modifications (e.g. DNA methylation or modifications of DNA-bound histones), or due to quantized internal degrees of freedom (e.g. different angles of the bond joining two neighboring units), or due to binding events involving a given unit (e.g. reversible binding of small ligands or proteins to DNA, or binding/unbinding of two complementary nucleotides in the DNA base pair). | 1 | Biochemistry |
One model of Z-ring formation permits its formation only after a certain spatial signal that tells the cell that it is big enough to divide.
The MinCDE system prevents FtsZ polymerization near certain parts of the plasma membrane. MinD localizes to the membrane only at cell poles and contains an ATPase and an ATP-binding domain. MinD is only able to bind to the membrane when in its ATP-bound conformation. Once anchored, the protein polymerizes, resulting in clusters of MinD. These clusters bind and then activate another protein called MinC, which has activity only when bound by MinD.
MinC serves as a FtsZ inhibitor that prevents FtsZ polymerization. The high concentration of a FtsZ polymerization inhibitor at the poles prevents FtsZ from initiating division at anywhere but the mid-cell.
MinE is involved in preventing the formation of MinCD complexes in the middle of the cell. MinE forms a ring near each cell pole. This ring is not like the Z-ring. Instead, it catalyzes the release of MinD from the membrane by activating MinDs ATPase. This hydrolyzes the MinDs bound ATP, preventing it from anchoring itself to the membrane.
MinE prevents the MinD/C complex from forming in the center but allows it to stay at the poles. Once the MinD/C complex is released, MinC becomes inactivated. This prevents MinC from deactivating FtsZ. As a consequence, this activity imparts regional specificity to Min localization.
Thus, FtsZ can form only in the center, where the concentration of the inhibitor MinC is minimal. Mutations that prevent the formation of MinE rings result in the MinCD zone extending well beyond the polar zones, preventing FtsZ to polymerize and to perform cell division.
MinD requires a nucleotide exchange step to re-bind to ATP so that it can re-associate with the membrane after MinE release. The time lapse results in a periodicity of Min association that may yield clues to a temporal signal linked to a spatial signal.
In vivo observations show that the oscillation of Min proteins between cell poles occurs approximately every 50 seconds.
Oscillation of Min proteins, however, is not necessary for all bacterial cell division systems. Bacillus subtilis has been shown to have static concentrations of MinC and MinD at the cell poles.
This system still links cell size to the ability to form a septum via FtsZ and divide. | 1 | Biochemistry |
PCBs undergo xenobiotic biotransformation, a mechanism used to make lipophilic toxins more polar and more easily excreted from the body. The biotransformation is dependent on the number of chlorine atoms present, along with their position on the rings. Phase I reactions occur by adding an oxygen to either of the benzene rings by Cytochrome P450. The type of P450 present also determines where the oxygen will be added; phenobarbital (PB)-induced P450s catalyze oxygenation to the meta-para positions of PCBs while 3-methylcholanthrene (3MC)-induced P450s add oxygens to the ortho–meta positions. PCBs containing ortho–meta and meta–para protons can be metabolized by either enzyme, making them the most likely to leave the organism. However, some metabolites of PCBs containing ortho–meta protons have increased steric hindrance from the oxygen, causing increased stability and an increased chance of accumulation. | 2 | Environmental Chemistry |
RuCl(PPh) is the product of the reaction of ruthenium trichloride trihydrate with a methanolic solution of triphenylphosphine.
:2 RuCl(HO) + 7 PPh → 2 RuCl(PPh) + 2 HCl + 5 HO + OPPh
The coordination sphere of RuCl(PPh) can be viewed as either five-coordinate or octahedral. One coordination site is occupied by one of the hydrogen atoms of a phenyl group. This Ru---H agostic interaction is long (2.59 Å) and weak. The low symmetry of the compound is reflected by the differing lengths of the Ru-P bonds: 2.374, 2.412, and 2.230 Å. The Ru-Cl bond lengths are both 2.387 Å. | 0 | Organic Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.