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Highly malignant tumors rely heavily on anaerobic glycolysis (metabolism of glucose to lactic acid even under ample tissue oxygen; Warburg effect) and thus need to efflux lactic acid via MCTs to the tumor micro-environment to maintain a robust glycolytic flux and to prevent the tumor from being "pickled to death". The MCTs have been successfully targeted in pre-clinical studies using RNAi and a small-molecule inhibitor alpha-cyano-4-hydroxycinnamic acid (ACCA; CHC) to show that inhibiting lactic acid efflux is a very effective therapeutic strategy against highly glycolytic malignant tumors.
In some tumor types, growth and metabolism relies on the exchange of lactate between glycolytic and rapidly respiring cells. This is of particular importance during tumor cell development when cells often undergo anaerobic metabolism, as described by the Warburg effect. Other cells in the same tumor may have access to or recruit sources of oxygen (via angiogenesis), allowing it to undergo aerobic oxidation. The lactate shuttle could occur as the hypoxic cells anaerobically metabolize glucose and shuttle the lactate via MCT to the adjacent cells capable of using the lactate as a substrate for oxidation. Investigation into how MCT-mediated lactate exchange in targeted tumor cells can be inhibited, therefore depriving cells of key energy sources, could lead to promising new chemotherapeutics.
Additionally, lactate has been shown to be a key factor in tumor angiogenesis. Lactate promotes angiogenesis by upregulating HIF-1 in endothelial cells. Thus a promising target of cancer therapy is the inhibition of lactate export, through MCT-1 blockers, depriving developing tumors of an oxygen source. | 1 | Biochemistry |
In 1911, Ernest Rutherford gave a model of the atom in which a central nucleus held most of the atoms mass and a positive charge which, in units of the electrons charge, was to be approximately equal to half of the atoms atomic weight, expressed in numbers of hydrogen atoms. This central charge would thus be approximately half the atomic weight (though it was almost 25% different from the atomic number of gold , ), the single element from which Rutherford made his guess). Nevertheless, in spite of Rutherfords estimation that gold had a central charge of about 100 (but was element on the periodic table), a month after Rutherfords paper appeared, Antonius van den Broek first formally suggested that the central charge and number of electrons in an atom were exactly equal to its place in the periodic table (also known as element number, atomic number, and symbolized Z'). This eventually proved to be the case. | 3 | Analytical Chemistry |
Vectorette PCR is similar to PCR with the difference being that it is capable of obtaining the sequence desired for amplification from an already known primer site. While PCR needs information of already known sequences at both ends, Vectorette PCR only requires previous knowledge of one. This means that is able to apply the method of PCR which needs sequence information from both ends to fragments of DNA that contain the information of the sequence at only one end and not the other. In order to achieve this, there are specific steps that this method must first go through. These steps have been researched for the purpose of discovering the scientific uses of Vectorette PCR and how they can be applied. | 1 | Biochemistry |
The journal was established in 1983 and as submissions increased switched to a biomonthly schedule in 2006. The editor-in-chief is Chengshan Wang (Chinese Academy of Sciences). Baojun Liu (Division of Earth Sciences, Chinese Academy of Sciences) is honorary editor-in-chief. | 9 | Geochemistry |
Polymerization-induced phase separation (PIPS) is the occurrence of phase separation in a multicomponent mixture induced by the polymerization of one or more components. The increase in molecular weight of the reactive component renders one or more components to be mutually immiscible in one another, resulting in spontaneous phase segregation. | 7 | Physical Chemistry |
:Heat removal is done by internal cooling coils. The synthesis gas is bubbled through the waxy products and finely-divided catalyst which is suspended in the liquid medium. This also provides agitation of the contents of the reactor. The catalyst particle size reduces diffusional heat and mass transfer limitations. A lower temperature in the reactor leads to a more viscous product and a higher temperature (> 297 °C, 570 K) gives an undesirable product spectrum. Also, separation of the product from the catalyst is a problem. | 0 | Organic Chemistry |
Electron-rich is jargon that is used in multiple related meanings with either or both kinetic and thermodynamic implications:
* with regards to electron-transfer, electron-rich species have low ionization energy and/or are reducing agents. Tetrakis(dimethylamino)ethylene is an electron-rich alkene because, unlike ethylene, it forms isolable radical cation. In contrast, electron-poor alkene tetracyanoethylene is an electron acceptor, forming isolable anions.
* with regards to acid-base reactions, electron-rich species have high pKa's and react with weak Lewis acids.
* with regards to nucleophilic substitution reactions, electron-rich species are relatively strong nucleophiles, as judged by rates of attack by electrophiles. For example, compared to benzene, pyrrole is more rapidly attacked by electrophiles. Pyrrole is therefore considered to be an electron-rich aromatic ring. Similarly, benzene derivatives with electron-donating groups (EDGs) are attacked by electrophiles faster than in benzene. The electron-donating vs electron-withdrawing influence of various functional groups have been extensively parameterized in linear free energy relationships.
* with regards to Lewis acidity, electron-rich species are strong Lewis bases. | 7 | Physical Chemistry |
The following are examples of sulfotransferases:
* carbohydrate sulfotransferase: CHST1, CHST2, CHST3, CHST4, CHST5, CHST6, CHST7, CHST8, CHST9, CHST10, CHST11, CHST12, CHST13, CHST14
* galactose-3-O-sulfotransferase: GAL3ST1, GAL3ST2, GAL3ST3, GAL3ST4
* heparan sulfate 2-O-sulfotransferase: HS2ST1
* heparan sulfate 3-O-sulfotransferase: HS3ST1, HS3ST2, HS3ST3A1, HS3ST3B1, HS3ST4, HS3ST5, HS3ST6
* heparan sulfate 6-O-sulfotransferase: HS6ST1, HS6ST2, HS6ST3
* N-deacetylase/N-sulfotransferase: NDST1, NDST2, NDST3, NDST4
* tyrosylprotein sulfotransferase: TPST1, TPST2
* uronyl-2-sulfotransferase
* Estrone sulfotransferase
* Chondroitin 4-sulfotransferase
* other: SULT1A1, SULT1A2, SULT1A3, SULT1A4, SULT1B1, SULT1C2, SULT1C3, SULT1C4, SULT1D1P, SULT1E1, SULT2A1, SULT2B1, SULT4A1, SULT6B1 | 1 | Biochemistry |
In fluid mechanics, the Reynolds number is the ratio of inertial forces (vρ) to viscous forces (μ/L). It is one of the most important dimensionless numbers in fluid dynamics and is used, usually along with other dimensionless numbers, to provide a criterion for determining dynamic similitude. As such, the Reynolds number provides the link between modeling results (design) and the full-scale actual conditions. It can also be used to characterize the flow. | 7 | Physical Chemistry |
So-called "butane honey oil" was available briefly in the 1970s. This product was made in Kabul, Afghanistan, and smuggled into the United States by The Brotherhood of Eternal Love. Production is thought to have ceased when the facility was destroyed in an explosion.
Traditional ice water-separated hashish production utilizes water and filter bags to separate plant material from resin, though this method still leaves much residual plant matter and is therefore poorly suited for full vaporization. Gold described the use of alcohol and activated charcoal in honey oil production by 1989, and Michael Starks further detailed procedures and various solvents by 1990.
Large cannabis vaporizers gained popularity in the twentieth century for their ability to vaporize the cannabinoids in cannabis and extracts without burning plant material, using temperature controlled vaporization.
Colorado and Washington began licensing hash oil extraction operations in 2014.
Small portable vape pens saw a dramatic increase in popularity in 2017. | 7 | Physical Chemistry |
* MT-CYB: mtDNA encoded cytochrome b; mutations associated with exercise intolerance
* CYC1: cytochrome c1
* CYCS: cytochrome c
* UQCRFS1: Rieske iron sulfur protein
* UQCRB: Ubiquinone binding protein, mutation linked with mitochondrial complex III deficiency nuclear type 3
* UQCRH: hinge protein
* UQCRC2: Core 2, mutations linked to mitochondrial complex III deficiency, nuclear type 5
* UQCRC1: Core 1
* UQCR: 6.4KD subunit
* UQCR10: 7.2KD subunit
* TTC19: Newly identified subunit, mutations linked to complex III deficiency nuclear type 2. Helps remove the N-terminal fragment of UQCRFS1, which would otherwise interfere with complex III function. | 1 | Biochemistry |
In May, onasemnogene abeparvovec (Zolgensma) was approved by the European Union for the treatment of spinal muscular atrophy in people who either have clinical symptoms of SMA type 1 or who have no more than three copies of the SMN2 gene, irrespective of body weight or age.
In August, Audentes Therapeutics reported that three out of 17 children with X-linked myotubular myopathy participating the clinical trial of a AAV8-based gene therapy treatment AT132 have died. It was suggested that the treatment, whose dosage is based on body weight, exerts a disproportionately toxic effect on heavier patients, since the three patients who died were heavier than the others. The trial has been put on clinical hold.
On 15 October, the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) adopted a positive opinion, recommending the granting of a marketing authorisation for the medicinal product Libmeldy (autologous CD34+ cell enriched population that contains hematopoietic stem and progenitor cells transduced ex vivo using a lentiviral vector encoding the human arylsulfatase A gene), a gene therapy for the treatment of children with the "late infantile" (LI) or "early juvenile" (EJ) forms of metachromatic leukodystrophy (MLD). The active substance of Libmeldy consists of the childs own stem cells which have been modified to contain working copies of the ARSA gene. When the modified cells are injected back into the patient as a one-time infusion, the cells are expected to start producing the ARSA enzyme that breaks down the build-up of sulfatides in the nerve cells and other cells of the patients body. Libmeldy was approved for medical use in the EU in December 2020.
On 15 October, Lysogene, a French biotechnological company, reported the death of a patient in who has received LYS-SAF302, an experimental gene therapy treatment for mucopolysaccharidosis type IIIA (Sanfilippo syndrome type A). | 1 | Biochemistry |
Organic solar cells and polymer solar cells are built from thin films (typically 100 nm) of organic semiconductors including polymers, such as polyphenylene vinylene and small-molecule compounds like copper phthalocyanine (a blue or green organic pigment) and carbon fullerenes and fullerene derivatives such as PCBM.
They can be processed from liquid solution, offering the possibility of a simple roll-to-roll printing process, potentially leading to inexpensive, large-scale production. In addition, these cells could be beneficial for some applications where mechanical flexibility and disposability are important. Current cell efficiencies are, however, very low, and practical devices are essentially non-existent.
Energy conversion efficiencies achieved to date using conductive polymers are very low compared to inorganic materials. However, Konarka Power Plastic reached efficiency of 8.3% and organic tandem cells in 2012 reached 11.1%.
The active region of an organic device consists of two materials, one electron donor and one electron acceptor. When a photon is converted into an electron hole pair, typically in the donor material, the charges tend to remain bound in the form of an exciton, separating when the exciton diffuses to the donor-acceptor interface, unlike most other solar cell types. The short exciton diffusion lengths of most polymer systems tend to limit the efficiency of such devices. Nanostructured interfaces, sometimes in the form of bulk heterojunctions, can improve performance.
In 2011, MIT and Michigan State researchers developed solar cells with a power efficiency close to 2% with a transparency to the human eye greater than 65%, achieved by selectively absorbing the ultraviolet and near-infrared parts of the spectrum with small-molecule compounds. Researchers at UCLA more recently developed an analogous polymer solar cell, following the same approach, that is 70% transparent and has a 4% power conversion efficiency. These lightweight, flexible cells can be produced in bulk at a low cost and could be used to create power generating windows.
In 2013, researchers announced polymer cells with some 3% efficiency. They used block copolymers, self-assembling organic materials that arrange themselves into distinct layers. The research focused on P3HT-b-PFTBT that separates into bands some 16 nanometers wide. | 7 | Physical Chemistry |
Ellipsometric porosimetry measures the change of the optical properties and thickness of the materials during adsorption and desorption of a volatile species at atmospheric pressure or under reduced pressure depending on the application. The EP technique is unique in its ability to measure porosity of very thin films down to 10 nm, its reproducibility and speed of measurement. Compared to traditional porosimeters, Ellipsometer porosimeters are well suited to very thin film pore size and pore size distribution measurement. Film porosity is a key factor in silicon based technology using low-κ materials, organic industry (encapsulated organic light-emitting diodes) as well as in the coating industry using sol gel techniques. | 7 | Physical Chemistry |
In geophysics the anisotropy in elastic properties is usually weak, in which case . When the exact expressions for the wave velocities above are linearized in these small quantities, they simplify to
where
are the P and S wave velocities in the direction of the axis of symmetry () (in geophysics, this is usually, but not always, the vertical direction). Note that may be further linearized, but this does not lead to further simplification.
The approximate expressions for the wave velocities are simple enough to be physically interpreted, and sufficiently accurate for most geophysical applications. These expressions are also useful in some contexts where the anisotropy is not weak. | 3 | Analytical Chemistry |
Pigments offer great potential in modifying the application properties of a coating. Due to their fine particle size and inherently high surface energy, they often require a surface treatment in order to enhance their ease of dispersion in a liquid medium. A wide variety of surface treatments have been previously used, including the adsorption on the surface of a molecule in the presence of polar groups, monolayers of polymers, and layers of inorganic oxides on the surface of organic pigments.
New surfaces are constantly being created as larger pigment particles get broken down into smaller subparticles. These newly-formed surfaces consequently contribute to larger surface energies, whereby the resulting particles often become cemented together into aggregates. Because particles dispersed in liquid media are in constant thermal or Brownian motion, they exhibit a strong affinity for other pigment particles nearby as they move through the medium and collide. This natural attraction is largely attributed to the powerful short-range van der Waals forces, as an effect of their surface energies.
The chief purpose of pigment dispersion is to break down aggregates and form stable dispersions of optimally sized pigment particles. This process generally involves three distinct stages: wetting, deaggregation, and stabilization. A surface that is easy to wet is desirable when formulating a coating that requires good adhesion and appearance. This also minimizes the risks of surface tension related defects, such as crawling, cratering, and orange peel. This is an essential requirement for pigment dispersions; for wetting to be effective, the surface tension of the pigment's vehicle must be lower than the surface free energy of the pigment. This allows the vehicle to penetrate into the interstices of the pigment aggregates, thus ensuring complete wetting. Finally, the particles are subjected to a repulsive force in order to keep them separated from one another and lowers the likelihood of flocculation.
Dispersions may become stable through two different phenomena: charge repulsion and steric or entropic repulsion. In charge repulsion, particles that possess the same like electrostatic charges repel each other. Alternatively, steric or entropic repulsion is a phenomenon used to describe the repelling effect when adsorbed layers of material (such as polymer molecules swollen with solvent) are present on the surface of the pigment particles in dispersion. Only certain portions (anchors) of the polymer molecules are adsorbed, with their corresponding loops and tails extending out into the solution. As the particles approach each other their adsorbed layers become crowded; this provides an effective steric barrier that prevents flocculation. This crowding effect is accompanied by a decrease in entropy, whereby the number of conformations possible for the polymer molecules is reduced in the adsorbed layer. As a result, energy is increased and often gives rise to repulsive forces that aid in keeping the particles separated from each other. | 7 | Physical Chemistry |
A primitive cell is a unit cell that contains exactly one lattice point. For unit cells generally, lattice points that are shared by cells are counted as of the lattice points contained in each of those cells; so for example a primitive unit cell in three dimensions which has lattice points only at its eight vertices is considered to contain of each of them. An alternative conceptualization is to consistently pick only one of the lattice points to belong to the given unit cell (so the other lattice points belong to adjacent unit cells).
The primitive translation vectors , , span a lattice cell of smallest volume for a particular three-dimensional lattice, and are used to define a crystal translation vector
where , , are integers, translation by which leaves the lattice invariant. That is, for a point in the lattice , the arrangement of points appears the same from as from .
Since the primitive cell is defined by the primitive axes (vectors) , , , the volume of the primitive cell is given by the parallelepiped from the above axes as
Usually, primitive cells in two and three dimensions are chosen to take the shape parallelograms and parallelepipeds, with an atom at each corner of the cell. This choice of primitive cell is not unique, but volume of primitive cells will always be given by the expression above. | 3 | Analytical Chemistry |
The Council of Scientific and Industrial Research awarded Natarajan the Shanti Swarup Bhatnagar Prize, one of the highest Indian science awards, in 1984. He received the Best Teacher Award from the Government of Tamil Nadu the same year. In 1999, he was awarded the Acharya P.C. Ray Memorial Award by the Indian Chemical Society. He held the National Lectureship and the National Fellowship of the University Grants Commission of India during 1986–87 and 1989–91 respectively. Sir M. Visweshwaraiah Chair of the University of Mysore (1999), Pandit Jawaharlal Nehru Chair of the University of Hyderabad (2004), Raja Ramanna Fellowship of the Department of Science and Technology (2006–09) and the senior scientist professorship of the Indian National Science Academy (at the time of his death) were some of the other notable positions he held. He was an elected fellow of the Indian Academy of Sciences, Indian National Science Academy, International Union of Pure and Applied Chemistry, Tamil Nadu Academy of Sciences, Society of Bio-Sciences and Gujarat Academy of Sciences and a member of Sigma Xi: The Scientific Research Society. | 5 | Photochemistry |
For hydrocarbons, the DBE (or IHD) tells us the number of rings and/or extra bonds in a non-saturated structure, which equals the number of hydrogen pairs that are required to make the structure saturated, simply because joining two elements to form a ring or adding one extra bond (e.g., a single bond changed to a double bond) in a structure reduces the need for two Hs. For non-hydrocarbons, the elements in a pair can include any elements in the lithium family and the fluorine family in the periodic table, not necessarily all Hs.
A popular form of the formula is as follows:
where , , and represent the number of carbon, nitrogen, hydrogen and halogen atoms, respectively. Each of the terms on the RHS can be explained, respectively, as follows:
*Except for the terminal carbons, every carbon chained to the structure with two single bonds requires a pair of hydrogen atoms attached to it. The number of carbons in the formula actually represents the number of hydrogen pairs required for that number of carbons to form a saturated structure. (This is also true if a carbon is added to the structure, whether it is inserted into a backbone chain, attached to a terminal to replace a hydrogen, or branched out from a carbon to replace a hydrogen.)
*Each of the two terminal carbons in the backbone chain needs one extra hydrogen – that is why "1" is added to the formula. (A branchs terminal doesnt need an H added in the calculation because the H replaced by the brunch can be counted as the H added to the brunch terminal. This is also true for a branch terminated with any element.)
*Except the terminal nitrogens, each nitrogen in the chain only requires one H attached to it, which is half a pair of hydrogens—that is why is in the formula, which gives a value of 1 for every two nitrogens. (This is also true if nitrogen is added into the structure, whether it is inserted into a backbone chain, attached to a terminal to replace an H, or branched out from a C to replace an H.)
*The represents the number of hydrogen pairs because it gives a value of 1 for every two hydrogen atoms. It is subtracted in the formula to count how many pairs of hydrogen atoms are missing in the unsaturated structure, which tells us the degree of hydrogen deficiency. (No hydrogen pair is missing if , which corresponds to no hydrogen deficiency.)
*The presence of is for a reason similar to .
Adding an oxygen atom to the structure requires no hydrogen added, which is why the number of oxygen atoms does not appear in the formula.
Furthermore, the formula can be generalised to include all elements of Group I (the hydrogen and lithium family), Group IV (the carbon family), Group V (the nitrogen family) and Group VII (the fluorine family) of CAS A group in the periodic table as follows:
Or simply, | 0 | Organic Chemistry |
For density matrices and on a Hilbert space, the quantum relative entropy from to is defined to be
In quantum information science the minimum of over all separable states can also be used as a measure of entanglement in the state . | 7 | Physical Chemistry |
In polyadenylation, a poly-adenosine tail of about 200 adenylate residues is added by a nuclear polymerase post-transcriptionally. This is known as a Poly-A tail and is used for stability and guidance, so that the mRNA can exit the nucleus and find the ribosome. It is added at a polyadenylation site in the 3' untranslated region of the mRNA, cleaving the mRNA in the process. When there are multiple polyadenylation sites on the same mRNA molecule, alternative polyadenylation can occur. See polyadenylation for further details. | 1 | Biochemistry |
Arthur Eichengrün (13 August 1867 – 23 December 1949) was a German Jewish chemist, materials scientist, and inventor. He is known for developing the highly successful anti-gonorrhea drug Protargol, the standard treatment for 50 years until the adoption of antibiotics, and for his pioneering contributions in plastics: co-developing (with Theodore Becker) the first soluble cellulose acetate materials in 1903, called "Cellit", and creating processes for the manufacture of these materials which were influential in the development of injection moulding. During World War I his relatively non-flammable synthetic cellulose acetate lacquers, marketed under the name "Cellon", were important in the aircraft industry. He contributed to photochemistry by inventing the first process for the production and development of cellulose acetate film, which he patented with Becker.
Eichengrün claimed to have directed the initial synthesis of aspirin in 1897, but his claim has been disputed. For many years Bayer credited Felix Hoffmann, Eichengrün's junior, with the invention of aspirin. However, the first attribution of the discovery to Hoffmann appears in 1934, and may have reflected anti-Jewish revisionism.
During World War II, Eichengrün was imprisoned in the Theresienstadt concentration camp. | 5 | Photochemistry |
Besides trying to re-activate the tumor suppressive function of pRb, one other distinct approach to treat dysregulated pRb pathway cancers is to take advantage of certain cellular consequences induced by pRb loss. It has been shown that E2F stimulates expression of pro-apoptotic genes in addition to G1/S transition genes, however, cancer cells have developed defensive signaling pathways that protect themselves from death by deregulated E2F activity. Development of inhibitors of these protective pathways could thus be a synthetically lethal method to kill cancer cells with overactive E2F.
In addition, it has been shown that the pro-apoptotic activity of p53 is restrained by the pRb pathway, such that pRb deficient tumor cells become sensitive to p53 mediated cell death. This opens the door to research of compounds that could activate p53 activity in these cancer cells and induce apoptosis and reduce cell proliferation. | 1 | Biochemistry |
Dentistry is one field in which free radical photopolymers have found wide usage as adhesives, sealant composites, and protective coatings. These dental composites are based on a camphorquinone photoinitiator and a matrix containing methacrylate oligomers with inorganic fillers such as silicon dioxide. Resin cements are utilized in luting cast ceramic, full porcelain, and veneer restorations that are thin or translucent, which permits visible light penetration in order to polymerize the cement. Light-activated cements may be radiolucent and are usually provided in various shades since they are utilized in esthetically demanding situations.
Conventional halogen bulbs, argon lasers and xenon arc lights are currently used in clinical practice. A new technological approach for curing light-activated oral biomaterials using a light curing unit (LCU) is based on blue light-emitting diodes (LED). The main benefits of LED LCU technology are the long lifetime of LED LCUs (several thousand hours), no need for filters or a cooling fan, and virtually no decrease of light output over the lifetime of the unit, resulting in consistent and high quality curing. Simple depth of cure experiments on dental composites cured with LED technology show promising results. | 5 | Photochemistry |
PHBV, being biodegradable, biocompatible and renewable, is a good alternative for synthetic nonbiodegradable polymers made from petroleum. But it has the following drawbacks,
* Expensive
* Low thermal stability
* Brittle
* Primitive mechanical properties
* Processing difficulty | 1 | Biochemistry |
For any substance, the number density can be expressed in terms of its amount concentration c (in mol/m) as
where is the Avogadro constant. This is still true if the spatial dimension unit, metre, in both n and c is consistently replaced by any other spatial dimension unit, e.g. if n is in cm and c is in mol/cm, or if n is in L and c is in mol/L, etc. | 3 | Analytical Chemistry |
The effects of anaerobic corrosion are evident when evaluating the safety of chemical waste disposal. Currently, the permanent disposal of nuclear waste is commonly in deep geological repositories (DGR) that use copper coating to prevent metal corrosion. In the DGR, four major types of corrosion are expected to occur, including oxygen-driven, radiation-influenced, anaerobic, and microbiologically-influenced corrosion. Of these, the most notable process is the microbiologically-influenced corrosion in terms of the magnitude of corrosion. The ability of microorganisms such as SRB to survive in a wide range of environments also lends to their relevance when considering the threat of corrosion to permanent chemical waste disposal. | 8 | Metallurgy |
Gas molecules in soil are in continuous thermal motion according to the kinetic theory of gases, and there is also collision between molecules – a random walk process. In soil, a concentration gradient causes net movement of molecules from high concentration to low concentration, which gives the movement of gas by diffusion. Numerically, it is explained by the Fick's law of diffusion. Soil gas migration, specifically that of hydrocarbon species with one to five carbons, can also be caused by microseepage.
The soil atmosphere's variable composition and constant motion can be attributed to chemical processes such as diffusion, decomposition, and, in some regions of the world, thawing, among other processes. Diffusion of soil air with the atmosphere causes the preferential replacement of soil gases with atmospheric air. More significantly, moreover, variation in soil gas composition due to seasonal, or even daily, temperature and/or moisture change can influence the rate of soil respiration.
According to the USDA, soil respiration refers to the quantity of carbon dioxide released from soil. This excess carbon dioxide is created by the decomposition of organic material by microbial organisms, in the presence of oxygen. Given the importance of both soil gases to soil life, significant fluctuation of carbon dioxide and oxygen can result in changes in rate of decay, while changes in microbial abundance can inversely influence soil gas composition.
In regions of the world where freezing of soils or drought is common, soil thawing and rewetting due to seasonal or meteorological changes influences soil gas flux. Both processes hydrate the soil and increase nutrient availability leading to an increase in microbial activity. This results in greater soil respiration and influences the composition of soil gases. | 9 | Geochemistry |
Upon illumination of a dark-adapted leaf, there is a rapid rise in fluorescence from Photosystem II (PSII), followed by a slow decline. First observed by Kautsky et al., 1932, this is called the Kautsky Effect. This variable rise in chlorophyll fluorescence is due to photosystem II. Fluorescence from photosystem I is not variable, but constant.
The increase in fluorescence is due to PSII reaction centers being in a "closed" or chemically reduced state. Reaction centers are "closed" when unable to accept further electrons. This occurs when electron acceptors downstream of PSII have not yet passed their electrons to a subsequent electron carrier, so are unable to accept another electron. Closed reaction centres reduce the overall photochemical efficiency, and so increases the level of fluorescence. Transferring a leaf from dark into light increases the proportion of closed PSII reaction centres, so fluorescence levels increase for 1–2 seconds. Subsequently, fluorescence decreases over a few minutes. This is due to; 1. more "photochemical quenching" in which electrons are transported away from PSII due to enzymes involved in carbon fixation; and 2. more "non-photochemical quenching" in which more energy is converted to heat. | 5 | Photochemistry |
The classical examples of the two nearly ideal types of electrodes, polarizable and non-polarizable, are the mercury droplet electrode in contact with an oxygen-free KCl solution and the silver/silver chloride electrode, respectively. | 7 | Physical Chemistry |
This experiment provides correlations between a carbon and its attached protons. The constant time (CT) version of H—C HSQC is normally used as it circumvents the issue of splitting of signal due to homonuclear C—C J couplings which reduces spectral resolution. The "constant time" refers to the entire evolution period between the two INEPT steps which is kept constant in this experiment. If this evolution period is set to be the inverse of the J-coupling constant, then the sign of the magnetization of those carbons with an odd number of aliphatic carbon attached will be opposite to those with an even number. For example, if the C of leucine appears as a positive peak (2 aliphatic carbons attached), then the C (3 aliphatic carbons attached) and C (1 aliphatic carbons attached) would appear negative. | 7 | Physical Chemistry |
Redox conditions are measured according to the redox potential (E) in volts, which represents the tendency for electrons to transfer from an electron donor to an electron acceptor. E can be calculated using half reactions and the Nernst equation. An E of zero represents the redox couple of the standard hydrogen electrode H/H a positive E indicates an oxidizing environment (electrons will be accepted), and a negative E indicates a reducing environment (electrons will be donated). In a redox gradient, the most energetically favorable chemical reaction occurs at the “top” of the redox ladder and the least energetically favorable reaction occurs at the “bottom” of the ladder.
E can be measured by collecting samples in the field and performing analyses in the lab, or by inserting an electrode into the environment to collect in situ measurements. Typical environments to measure redox potential are in bodies of water, soils, and sediments, all of which can exhibit high levels of heterogeneity. Collecting a high number of samples can produce high spatial resolution, but at the cost of low temporal resolution since samples only reflect a singular a snapshot in time. In situ monitoring can provide high temporal resolution by collecting continuous real-time measurements, but low spatial resolution since the electrode is in a fixed location.
Redox properties can also be tracked with high spatial and temporal resolution through the use of induced-polarization imaging, however, further research is needed to fully understand contributions of redox species to polarization. | 7 | Physical Chemistry |
* Studied and identified chromophores and a variety of dyes commonly used as biomolecule labels like: tryptophan, DAPI, fluorescein, thiazole orange, and BEBO.
* Explained DNA strand exchange in homologous recombination.
* Applying Widlund experiment, identified specific nucleosome positioning sequences.
* Uncovered mechanism of oncogene activation involving the formation of internal G-quadruplexes.
* Designed a probe that exhibit luminescence upon binding to specific nucleic acids.
* Techniques for gene expression at the level of individual cells and subcellular compartments.
* The occurrence of horizontal transfer of mitochondria within living organisms. | 1 | Biochemistry |
A single-stranded non-circular DNA molecule has two non-identical ends, the 3 end and the 5 end (usually pronounced "three prime end" and "five prime end"). The numbers refer to the numbering of carbon atoms in the deoxyribose, which is a sugar forming an important part of the backbone of the DNA molecule. In the backbone of DNA the 5 carbon of one deoxyribose is linked to the 3 carbon of another by a phosphodiester bond linkage. The 5 carbon of this deoxyribose is again linked to the 3 carbon of the next, and so forth. | 1 | Biochemistry |
Phosphonate esters are generally susceptible to hydrolysis under both acidic and basic conditions. Cleavage of the P-C bond is harder but can be achieved under aggressive conditions.
:O=PC(OR) + 2 HO → O=PC(OH) + 2 ROH | 0 | Organic Chemistry |
Bouguer-Lambert law: This law is based on observations made by Pierre Bouguer before 1729. It is often attributed to Johann Heinrich Lambert, who cited Bouguers (Claude Jombert, Paris, 1729) – and even quoted from it – in his Photometria' in 1760. Lambert expressed the law, which states that the loss of light intensity when it propagates in a medium is directly proportional to intensity and path length, in the mathematical form used today.
Lambert began by assuming that the intensity of light traveling into an absorbing body would be given by the differential equation: which is compatible with Bouguer's observations. The constant of proportionality was often termed the "optical density" of the body. Integrating to find the intensity at a distance into the body, one obtains: For a homogeneous medium, this reduces to: from which follows the exponential attenuation law:
Beers law: Much later, in 1852, the German scientist August Beer studied another attenuation relation. In the introduction to his classic paper, he wrote: "The absorption of light during the irradiation of a colored substance has often been the object of experiment; but attention has always been directed to the relative diminution of the various colors or, in the case of crystalline bodies, the relation between the absorption and the direction of polarization. Concerning the absolute magnitude of the absorption that a particular ray of light suffers during its propagation through an absorbing medium, there is no information available." By studying absorption of red light in colored aqueous solutions of various salts, he concluded that "the transmittance of a concentrated solution can be derived from a measurement of the transmittance of a dilute solution". It is clear that he understood the exponential relationship, as he wrote: "If is the coefficient (fraction) of diminution, then this coefficient (fraction) will have the value for double this thickness." Furthermore Beer stated: "We shall take the absorption coefficient to be the coefficient giving the diminution in amplitude suffered by a light ray as it passes through a unit length of an absorbing material. We then have, according to theory, and as I have found verified by experiment, where is the absorption coefficient and D the length of the absorbing material traversed in the experiment." This is the relationship that might properly be called Beers law. There is no evidence that Beer saw concentration and path length as symmetrical variables in an equation in the manner of the Beer-Lambert law.
Beer-Lambert law: The modern formulation of the Beer–Lambert law combines the observations of Bouguer and Beer into the mathematical form of Lambert. It correlates the absorbance, most often expressed as the negative decadic logarithm of the transmittance, to both the concentrations of the attenuating species and the thickness of the material sample. An early, possibly the first, modern formulation was given by Robert Luther and Andreas Nikolopulos in 1913. | 7 | Physical Chemistry |
Saloximes are used in the extraction and separation of metals from their ores. In one application of hydrometallurgy, Cu is extracted into organic solvents as its saloxime complex. | 3 | Analytical Chemistry |
More accurately, a single formula that describes the titration of a weak acid with a strong base from start to finish is given below:
where
" φ = fraction of completion of the titration (φ < 1 is before the equivalence point, φ = 1 is the equivalence point, and φ > 1 is after the equivalence point)
: = the concentrations of the acid and base respectively
: = the volumes of the acid and base respectively | 3 | Analytical Chemistry |
In organic chemistry, annulation (; occasionally annelation) is a chemical reaction in which a new ring is constructed on a molecule.
Examples are the Robinson annulation, Danheiser annulation and certain cycloadditions. Annular molecules are constructed from side-on condensed cyclic segments, for example helicenes and acenes. In transannulation a bicyclic molecule is created by intramolecular carbon-carbon bond formation in a large monocyclic ring. An example is the samarium(II) iodide induced ketone - alkene cyclization of 5-methylenecyclooctanone which proceeds through a ketyl intermediate: | 0 | Organic Chemistry |
The amount of carbon dioxide varies naturally in a dynamic equilibrium with photosynthesis of land plants. The natural carbon sinks are:
*Soil is a carbon store and active carbon sink.
* Photosynthesis by terrestrial plants with grass and trees allows them to serve as carbon sinks during growing seasons.
* Absorption of carbon dioxide by the oceans via solubility and biological pumps.
Artificial carbon sinks are those that store carbon in building materials or deep underground (geologic carbon sequestration). No major artificial systems remove carbon from the atmosphere on a large scale yet.
Public awareness of the significance of sinks has grown since passage of the 1997 Kyoto Protocol, which promotes their use as a form of carbon offset. | 5 | Photochemistry |
Instead of cloning, adaptors containing the endonuclease sequence are ligated to the ends of fragmented genomic DNA or cDNA. The molecules are then self-circularized and digested with endonuclease, releasing the PET. Before sequencing, these PETs are ligated to adaptors to which PCR primers anneal for amplification.
The advantage of cloning based construction of the library is that it maintains the fragments or cDNA intact for future use. However, the construction process is much longer than the cloning-free method. Variations on library construction have been produced by next-generation sequencing companies to suit their respective technologies. | 1 | Biochemistry |
In general, the Gouy-Stodola theorem is used to quantify irreversibilities in a system and to perform exergy analysis. That is, it allows one to take a thermodynamic system and better understand how inefficient it is (energy-wise), how much work is lost, how much room there is for improvement and where. The second law of thermodynamics states, in essence, that the entropy of a system only increases. Over time, thermodynamic systems tend to gain entropy and lose energy (in approaching equilibrium): thus, the entropy is "somehow" related to how much exergy or potential for useful work a system has. The Gouy-Stodola theorem provides a concrete link. For the most part, this is how the theorem is used - to find and quantify inefficiencies in a system. | 7 | Physical Chemistry |
The concentration of ferritin has been shown to increase in response to stresses such as anoxia, which implies that it is an acute phase protein. | 1 | Biochemistry |
Although inorganic phosphate is primarily used in the Pho regulon system, there are several species of bacteria that can utilize varying forms of phosphate. One example is seen in E. coli which can use both inorganic and organic phosphate, as well as naturally occurring or synthetic phosphates (Phn). Several enzymes breakdown the compounds of the alternative phosphates, allowing the organism to use the phosphate via the C-P lyase pathway. Other species of bacteria like Pseudomonas aeruginosa and Salmonella typhimurium use a different pathway called the phosphonatase pathway, whereas the bacterium Enterobacter aerogenes can use either one of the pathways to cleave the C-P bond found in the alternative phosphates. | 1 | Biochemistry |
Although N-terminus arginylation was originally thought to be the only site for targeting by ATE1 enzymes, it has recently been discovered that arginylation may also occur in the middle of the peptide chain of a protein. The first discovery of this unprecedented modification occurred when neurotensin, a biological peptide found in the central nervous system, was isolated from cells and it was discovered that arginine was attached to a mid-chain glutamine residue. This discovery changed the view of how arginylation occurs, as this meant that there may be ways to modify and arginylate intact proteins.
In an effort to determine the prevalence of mid-chain arginylation, a mass spectrometry screen of various peptides was performed. The results from this experiment revealed a plethora of various proteins which contained modified asparagine and glutamine residues present in the middle of their peptide chain, and further studies determined that ATE1 could also be mediating this reaction. Indeed, this discovery changed the biological scope of arginylation by suggesting that arginylation can also occur on fully intact proteins, not just on the N-terminus of protein fragments or pre-processed proteins. | 1 | Biochemistry |
IUBMB organizes a triennial Congress of Biochemistry and Molecular Biology and sponsors three annual focussed meetings. In addition, it supports symposia, educational activities (including the Tang Fellowships), award lectures (including Jubilee Lectures), and travel grants for students around the world. | 1 | Biochemistry |
The benzene dimer is the prototypical system for the study of pi stacking, and is experimentally bound by 8–12 kJ/mol (2–3 kcal/mol) in the gas phase with a separation of 4.96 Å between the centers of mass for the T-shaped dimer. The small binding energy makes the benzene dimer difficult to study experimentally, and the dimer itself is only stable at low temperatures and is prone to cluster.
Other evidence against pi stacking comes from X-ray crystal structure determination. Perpendicular and offset parallel configurations can be observed in the crystal structures of many simple aromatic compounds. Similar offset parallel or perpendicular geometries were observed in a survey of high-resolution x-ray protein crystal structures in the Protein Data Bank. Analysis of the aromatic amino acids phenylalanine, tyrosine, histidine, and tryptophan indicates that dimers of these side chains have many possible stabilizing interactions at distances larger than the average van der Waals radii. | 6 | Supramolecular Chemistry |
In molecular biology, fibrous proteins or scleroproteins are one of the three main classifications of protein structure (alongside globular and membrane proteins). Fibrous proteins are made up of elongated or fibrous polypeptide chains which form filamentous and sheet-like structures. These kind of protein can be distinguished from globular protein by its low solubility in water. Such proteins serve protective and structural roles by forming connective tissue, tendons, bone matrices, and muscle fiber.
Fibrous proteins consist of many superfamilies including keratin, collagen, elastin, and fibrin. Collagen is the most abundant of these proteins which exists in vertebrate connective tissue including tendon, cartilage, and bone. | 1 | Biochemistry |
A notable feature of eukaryotic nuclear pre-mRNA introns is the relatively high level of conservation of the primary sequences of 5 and 3 splice sites over a great range of organisms.
Between 1989 and 1991, several groups reported four independent examples of introns with a splice site that differed from the common intron:
*Cartilage matrix protein (CMP/MATN1) gene in humans and chickens
*Proliferating cell nucleolar protein P120 (NOL1) gene in humans
*Mouse Rep3 gene, presumably involved in DNA repair
*Drosophila prospero gene that encodes for a homeobox protein
In 1991 by comparing the intron sequences of P120 and CMP genes, IJ Jackson reported the existence of ATATCC (5) and YYCAC (3) splice sites in these introns. The finding indicated a possible novel splicing mechanism.
In 1994, S.L. Hall and R.A. Padgett compared the primary sequence of all reports on the four genes mentioned above. The results suggested a new type of introns with ATATCCTT 5 splice sites and YCCAC 3 splice sites and an almost invariant TCCTTAAC sequence near the 3 end of the introns (so called 3 upstream element). A search for small nuclear RNA sequences that are complementary to these splice sites suggested U12 snRNA (matches the 3 sequence) and U11 snRNA (matches the 5 sequence) as being putative factors involved in splicing of this new type of introns.
In all these four genes, the pre-mRNA contains other introns whose sequences conform to those of major class introns. Neither the size nor the position of the AT–AC intron within the host gene is conserved.
In 1996, Woan-Yuh Tarn and Joan A. Steitz described an in vitro system that splices a pre-mRNA substrate containing an AT–AC intron derived from the human P120 gene. Psoralen cross-linking confirms the base-pairing interaction predicted by Hall and Padgett between the branch site of the pre-mRNA substrate and U12 RNA. Native gel electrophoresis reveals that U11, U12, and U5 snRNPs assemble onto the P120 pre-mRNA to form splicing complexes. | 1 | Biochemistry |
The location of substrate attachment to the complex has yet to be elucidated. It is believed that the Fe atoms closest to the interstitial carbon participate in substrate activation, but the terminal molybdenum is also a candidate for nitrogen fixation. X-ray crystallographic studies utilizing MoFe-protein and carbon monoxide (CO), which is isoelectronic to dinitrogen, demonstrated that carbon monoxide is binding to the Fe2-Fe6-edge of FeMoco. Additional studies showed simultaneous binding of two CO-molecules to FeMoco, providing a structural basis for biological Fischer-Tropsch-type chemistry. Se-incorporation studies in combination with time-resolved X-ray crystallography evidenced major structural rearrangements in the FeMoco-structure upon substrate binding events. | 7 | Physical Chemistry |
The first substrate-level phosphorylation occurs after the conversion of 3-phosphoglyceraldehyde and Pi and NAD+ to 1,3-bisphosphoglycerate via glyceraldehyde 3-phosphate dehydrogenase. 1,3-bisphosphoglycerate is then dephosphorylated via phosphoglycerate kinase, producing 3-phosphoglycerate and ATP through a substrate-level phosphorylation.
The second substrate-level phosphorylation occurs by dephosphorylating phosphoenolpyruvate, catalyzed by pyruvate kinase, producing pyruvate and ATP.
During the preparatory phase, each 6-carbon glucose molecule is broken into two 3-carbon molecules. Thus, in glycolysis dephosphorylation results in the production of 4 ATP. However, the prior preparatory phase consumes 2 ATP, so the net yield in glycolysis is 2 ATP. 2 molecules of NADH are also produced and can be used in oxidative phosphorylation to generate more ATP. | 1 | Biochemistry |
The hash oils made in the 19th century were made from hand collected hashish called charas and kief. The term hash oil was hashish that had been dissolved or infused into a vegetable oil for use in preparing foods for oral administration. Efforts to isolate the active ingredient in cannabis were well documented in the 19th century, and cannabis extracts and tinctures of cannabis were included in the British Pharmacopoeia and the United States Pharmacopoeia. These solvent extracts were termed cannabin (1845), cannabindon, cannabinine, crude cannabinol and cannabinol. | 7 | Physical Chemistry |
Secondary structures in the DNA can result in folding or knotting of DNA template or primers, leading to decreased product yield or failure of the reaction. Hairpins, which consist of internal folds caused by base-pairing between nucleotides in inverted repeats within single-stranded DNA, are common secondary structures and may result in failed PCRs.
Typically, primer design that includes a check for potential secondary structures in the primers, or addition of DMSO or glycerol to the PCR to minimize secondary structures in the DNA template, are used in the optimization of PCRs that have a history of failure due to suspected DNA hairpins. | 1 | Biochemistry |
A chloridometer is a measuring instrument used to determine the concentration of chloride ions (Cl) in a solution. It uses a process known as coulometric titration or amperostatic coulometry, the accepted electrochemistry reference method to determine the concentration of chloride in biological fluids, including blood serum, blood plasma, urine, sweat, and cerebrospinal fluid. The coulometry process generates silver ions, which react with the chloride to form silver chloride (AgCl).
The first chloridometer was designed by a team led by Ernest Cotlove in 1958.
Other methods to determine chloride concentration include photometric titration and isotope dilution mass spectrometry. | 3 | Analytical Chemistry |
The reaction was discovered in the 1970s as part of a synthetic route to certain prostanoids. The reaction required tin tetrachloride and a stoichiometric amount of Wilkinson's catalyst:
An equal amount of a cyclopropane was formed as the result of decarbonylation.
The first catalytic application involved cyclization of 4-pentenal to cyclopentanone using (again) Wilkinson's catalyst. In this reaction the solvent was saturated with ethylene.
:CH=CHCHCHCHO → (CH)CO | 0 | Organic Chemistry |
In general, a geometric lattice is an infinite, regular array of vertices (points) in space, which can be modelled vectorially as a Bravais lattice. Some lattices may be skew, which means that their primary lines may not necessarily be at right angles. In reciprocal space, a reciprocal lattice is defined as the set of wavevectors of plane waves in the Fourier series of any function whose periodicity is compatible with that of an initial direct lattice in real space. Equivalently, a wavevector is a vertex of the reciprocal lattice if it corresponds to a plane wave in real space whose phase at any given time is the same (actually differs by with an integer ) at every direct lattice vertex.
One heuristic approach to constructing the reciprocal lattice in three dimensions is to write the position vector of a vertex of the direct lattice as , where the are integers defining the vertex and the are linearly independent primitive translation vectors (or shortly called primitive vectors) that are characteristic of the lattice. There is then a unique plane wave (up to a factor of negative one), whose wavefront through the origin contains the direct lattice points at and , and with its adjacent wavefront (whose phase differs by or from the former wavefront passing the origin) passing through . Its angular wavevector takes the form , where is the unit vector perpendicular to these two adjacent wavefronts and the wavelength must satisfy , means that is equal to the distance between the two wavefronts. Hence by construction and .
Cycling through the indices in turn, the same method yields three wavevectors with , where the Kronecker delta equals one when and is zero otherwise. The comprise a set of three primitive wavevectors or three primitive translation vectors for the reciprocal lattice, each of whose vertices takes the form , where the are integers. The reciprocal lattice is also a Bravais lattice as it is formed by integer combinations of the primitive vectors, that are , , and in this case. Simple algebra then shows that, for any plane wave with a wavevector on the reciprocal lattice, the total phase shift between the origin and any point on the direct lattice is a multiple of (that can be possibly zero if the multiplier is zero), so the phase of the plane wave with will essentially be equal for every direct lattice vertex, in conformity with the reciprocal lattice definition above. (Although any wavevector on the reciprocal lattice does always take this form, this derivation is motivational, rather than rigorous, because it has omitted the proof that no other possibilities exist.)
The Brillouin zone is a primitive cell (more specifically a Wigner–Seitz cell) of the reciprocal lattice, which plays an important role in solid state physics due to Bloch's theorem. In pure mathematics, the dual space of linear forms and the dual lattice provide more abstract generalizations of reciprocal space and the reciprocal lattice. | 3 | Analytical Chemistry |
Metals typically are strong, dense, and good conductors of both electricity and heat.
The bulk of the elements in the periodic table, those to the left of a diagonal line drawn from boron to polonium, are metals.
Mixtures of two or more elements in which the major component is a metal are known as alloys.
People have been using metals for a variety of purposes since prehistoric times.
The strength and reliability of metals has led to their widespread use in construction of buildings and other structures, as well as in most vehicles, many appliances and tools, pipes, road signs and railroad tracks. Iron and aluminium are the two most commonly used structural metals. They are also the most abundant metals in the Earth's crust. Iron is most commonly used in the form of an alloy, steel, which contains up to 2.1% carbon, making it much harder than pure iron.
Because metals are good conductors of electricity, they are valuable in electrical appliances and for carrying an electric current over long distances with little energy loss or dissipation. Thus, electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for example, are wired with copper for its good conducting properties and easy machinability. The high thermal conductivity of most metals also makes them useful for stovetop cooking utensils.
The study of metallic elements and their alloys makes up a significant portion of the fields of solid-state chemistry, physics, materials science and engineering.
Metallic solids are held together by a high density of shared, delocalized electrons, known as "metallic bonding". In a metal, atoms readily lose their outermost ("valence") electrons, forming positive ions. The free electrons are spread over the entire solid, which is held together firmly by electrostatic interactions between the ions and the electron cloud. The large number of free electrons gives metals their high values of electrical and thermal conductivity. The free electrons also prevent transmission of visible light, making metals opaque, shiny and lustrous.
More advanced models of metal properties consider the effect of the positive ions cores on the delocalised electrons. As most metals have crystalline structure, those ions are usually arranged into a periodic lattice. Mathematically, the potential of the ion cores can be treated by various models, the simplest being the nearly free electron model. | 7 | Physical Chemistry |
* RdRps can be used as drug targets for viral pathogens as their function is not necessary for eukaryotic survival. By inhibiting RNA-dependent RNA polymerase function, new RNAs cannot be replicated from an RNA template strand, however, DNA-dependent RNA polymerase will remain functional.
* There are currently antiviral drugs against Hepatitis C and COVID-19 that specifically target RdRp. These include Sofosbuvir and Ribavirin against Hepatitis C and Remdesivir, the only FDA approved drug against COVID-19.
* GS-441524 triphosphate, is a substrate for RdRp, but not mammalian polymerases. It results in premature chain termination and inhibition of viral replication. GS-441524 triphosphate is the biologically active form of the phosphate pro-drug, Remdesivir. Remdesivir is classified as a nucleotide analog in which it works to inhibit the function of RdRp by covalently binding to and interrupting termination of the nascent RNA through early or delayed termination or preventing further elongation of the RNA polynucleotide. This early termination leads to nonfunctional RNA that will be degraded through normal cellular processes. | 1 | Biochemistry |
The treatment of this type of data is similar to the treatment of absorbance data. In fact the equation defining the relation between fluorescent intensity and species' concentrations is very similar.
where is the fluorescent intensity of the ith species at unit concentration. | 6 | Supramolecular Chemistry |
Arrow pushing or electron pushing is a technique used to describe the progression of organic chemistry reaction mechanisms. It was first developed by Sir Robert Robinson. In using arrow pushing, "curved arrows" or "curly arrows" are drawn on the structural formulae of reactants in a chemical equation to show the reaction mechanism. The arrows illustrate the movement of electrons as bonds between atoms are broken and formed. It is important to note that arrow pushing never directly show the movement of atoms; it is used to show the movement of electron density, which indirectly shows the movement of atoms themselves. Arrow pushing is also used to describe how positive and negative charges are distributed around organic molecules through resonance. It is important to remember, however, that arrow pushing is a formalism and electrons (or rather, electron density) do not move around so neatly and discretely in reality.
Arrow pushing has been extended to inorganic chemistry, especially to the chemistry of s- and p-block elements. It has been shown to work well for hypervalent compounds. | 0 | Organic Chemistry |
The chemical potential of species in solution depends on the activity a using the following equation:
where is the chemical potential of the -th component, is the chemical potential of the -th component at a reference state, is the gas constant, is the temperature, and is the activity of the -th component.
Differentiation of the chemical potential equation results in:
where is the activity coefficient of component , and is the concentration of species in the bulk phase.
If the solutions in the and phases are dilute (rich in one particular component ) then activity coefficient of the component approaches unity and the Gibbs isotherm becomes:
The above equation assumes the interface to be bidimensional, which is not always true. Further models, such as Guggenheim's, correct this flaw. | 7 | Physical Chemistry |
At pressures above approximately 10-13 GPa and temperatures up to around 700 K, α-iron changes into a hexagonal close-packed (hcp) structure, which is also known as ε-iron or hexaferrum; the higher-temperature γ-phase also changes into ε-iron, but generally requires far higher pressures as temperature increases. The triple point of hexaferrum, ferrite, and austenite is 10.5 GPa at 750 K. Antiferromagnetism in alloys of epsilon-Fe with Mn, Os and Ru has been observed. | 8 | Metallurgy |
LA-ICP-MS can determine major and trace elements, however, with LA-ICPMS, the melt inclusion and any accompanying materials within the melt inclusion are ionized, thus destroying the melt inclusion, and then analyzed with a mass spectrometer. | 9 | Geochemistry |
The folding funnel hypothesis is a specific version of the energy landscape theory of protein folding, which assumes that a protein's native state corresponds to its free energy minimum under the solution conditions usually encountered in cells. Although energy landscapes may be "rough", with many non-native local minima in which partially folded proteins can become trapped, the folding funnel hypothesis assumes that the native state is a deep free energy minimum with steep walls, corresponding to a single well-defined tertiary structure. The term was introduced by Ken A. Dill in a 1987 article discussing the stabilities of globular proteins.
The folding funnel hypothesis is closely related to the hydrophobic collapse hypothesis, under which the driving force for protein folding is the stabilization associated with the sequestration of hydrophobic amino acid side chains in the interior of the folded protein. This allows the water solvent to maximize its entropy, lowering the total free energy. On the side of the protein, free energy is further lowered by favorable energetic contacts: isolation of electrostatically charged side chains on the solvent-accessible protein surface and neutralization of salt bridges within the protein's core. The molten globule state predicted by the folding funnel theory as an ensemble of folding intermediates thus corresponds to a protein in which hydrophobic collapse has occurred but many native contacts, or close residue-residue interactions represented in the native state, have yet to form.
In the canonical depiction of the folding funnel, the depth of the well represents the energetic stabilization of the native state versus the denatured state, and the width of the well represents the conformational entropy of the system. The surface outside the well is shown as relatively flat to represent the heterogeneity of the random coil state. The theory's name derives from an analogy between the shape of the well and a physical funnel, in which dispersed liquid is concentrated into a single narrow area. | 1 | Biochemistry |
The Ritchie equation, derived in 1972, is another free-energy relationship:
where N is the nucleophile dependent parameter and k the reaction rate constant for water. In this equation, a substrate-dependent parameter like s in the Swain–Scott equation is absent. The equation states that two nucleophiles react with the same relative reactivity regardless of the nature of the electrophile, which is in violation of the reactivity–selectivity principle. For this reason, this equation is also called the constant selectivity relationship.
In the original publication the data were obtained by reactions of selected nucleophiles with selected electrophilic carbocations such as tropylium or diazonium cations:
or (not displayed) ions based on malachite green. Many other reaction types have since been described.
Typical Ritchie N values (in methanol) are: 0.5 for methanol, 5.9 for the cyanide anion, 7.5 for the methoxide anion, 8.5 for the azide anion, and 10.7 for the thiophenol anion. The values for the relative cation reactivities are −0.4 for the malachite green cation, +2.6 for the benzenediazonium cation, and +4.5 for the tropylium cation. | 7 | Physical Chemistry |
Typically, to understand how a given physical law applies to the system under consideration, one first begins by considering how it applies to a small, control volume, or "representative volume". There is nothing special about a particular control volume, it simply represents a small part of the system to which physical laws can be easily applied. This gives rise to what is termed a volumetric, or volume-wise formulation of the mathematical model.
One can then argue that since the physical laws behave in a certain way on a particular control volume, they behave the same way on all such volumes, since that particular control volume was not special in any way. In this way, the corresponding point-wise formulation of the mathematical model can be developed so it can describe the physical behaviour of an entire (and maybe more complex) system.
In continuum mechanics the conservation equations (for instance, the Navier-Stokes equations) are in integral form. They therefore apply on volumes. Finding forms of the equation that are independent of the control volumes allows simplification of the integral signs. The control volumes can be stationary or they can move with an arbitrary velocity. | 7 | Physical Chemistry |
Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is used intravenously (injection into a vein) as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infections, and meningitis caused by methicillin-resistant Staphylococcus aureus. Blood levels may be measured to determine the correct dose. Vancomycin is also taken orally (by mouth) as a treatment for severe Clostridium difficile colitis. When taken orally it is poorly absorbed.
Common side effects include pain in the area of injection and allergic reactions. Occasionally, hearing loss, low blood pressure, or bone marrow suppression occur. Safety in pregnancy is not clear, but no evidence of harm has been found, and it is likely safe for use when breastfeeding. It is a type of glycopeptide antibiotic and works by blocking the construction of a cell wall.
Vancomycin was approved for medical use in the United States in 1958. It is on the World Health Organizations List of Essential Medicines. The World Health Organization classifies vancomycin as critically important for human medicine. It is available as a generic medication. Vancomycin is made by the soil bacterium Amycolatopsis orientalis'. | 0 | Organic Chemistry |
The experimental setup to perform Raman spectroelectrochemistry consists of a light source, a spectrometer, a potentiostat, a spectroelectrochemical cell, a three-electrode system, radiation beam conducting devices, data collection and analysis devices. Nowadays, there are commercial instruments that integrate all these elements in a single instrument, significantly simplifying the performance of spectroelectrochemical experiments.
* Light source. It provides the monochromatic electromagnetic radiation that interacts with the sample during the electrochemical process. In Raman-SEC, the light source is usually a laser corresponding to the VIS or NIR regions, which commonly emits at 532, 633, 785 or 1064 nm, although there is the possibility of using many other lasers, including UV-lasers.
* Spectrometer. It records the scattered radiation and provides the Raman spectra of the molecules. In Raman-SEC, spectrometers are usually combined with confocal microscopes (micro-Raman) to remove the information out of the focus, obtaining an excellent spectral resolution. However, it is possible to work with low resolution Raman spectrometers obtaining very good results.
* Potentiostat/Galvanostat. It is the electronic device that allows controlling the potential of the working electrode respect to the reference electrode, or controlling the current that passes respect to the auxiliary electrode.
* Three-electrode system. It contains a working electrode, a reference electrode and an auxiliary electrode. This system can be simplified by using screen-printed electrodes that include all three electrodes in a single holder.
* Spectroelectrochemical cell (SEC cell). It is the device that includes the three-electrode system and allows the simultaneous recording of the Raman spectra of the species and the electrochemical signal. It is the link between optical and electrochemical techniques.
* Devices for conducting the radiation beam: lenses, mirrors and/or optical fibres. The last ones conduct the electromagnetic radiation over long distances with hardly any losses. In addition, they simplify the optical configurations since they allow working with a small amount of solution; in this way, it is easier to conduct and collect the light in the nearness of the electrode.
* Data collection and analysis devices. It consists of a computer to collect simultaneously the signals provided by the spectrometer and the electrochemical instrument. Using an appropriate software, the generated signals can be acquired, transformed, analyzed and interpreted. | 7 | Physical Chemistry |
Manganese is a component of some enzymes and stimulates the development and activity of other enzymes. Manganese superoxide dismutase (MnSOD) is the principal antioxidant in mitochondria. Several enzymes activated by manganese contribute to the metabolism of carbohydrates, amino acids, and cholesterol.
A deficiency of manganese causes skeletal deformation in animals and inhibits the production of collagen in wound healing. | 1 | Biochemistry |
Typical stages in a U6 snRNA (also termed class III) gene initiation (documented in vertebrates only):
*SNAPc (SNRNA Activating Protein complex; subunits: 1, 2, 3, 4, 5) (also termed PBP and PTF) binds to the PSE (Proximal Sequence Element) centered approximately 55 base pairs upstream of the start site of transcription. This assembly is greatly stimulated by the Pol II transcription factors Oct1 and STAF that bind to an enhancer-like DSE (Distal Sequence Element) at least 200 base pairs upstream of the start site of transcription. These factors and promoter elements are shared between Pol II and Pol III transcription of snRNA genes.
*SNAPc acts to assemble TFIIIB at a TATA box centered 26 base pairs upstream of the start site of transcription. It is the presence of a TATA box that specifies that the snRNA gene is transcribed by Pol III rather than Pol II.
*The TFIIIB for U6 snRNA transcription contains a smaller Brf1 paralogue, Brf2.
*TFIIIB is the transcription factor that assembles Pol III at the start site of transcription. Sequence conservation predicts that TFIIIB containing Brf2 also plays a role in promoter opening. | 1 | Biochemistry |
The process starts when light is absorbed by two BChl molecules that lie near the periplasmic side of the membrane. This pair of chlorophyll molecules, often called the "special pair", absorbs photons at 870 nm or 960 nm, depending on the species and, thus, is called P870 (for Rhodobacter sphaeroides) or P960 (for Blastochloris viridis), with P standing for "pigment"). Once P absorbs a photon, it ejects an electron, which is transferred through another molecule of Bchl to the BPh in the L subunit. This initial charge separation yields a positive charge on P and a negative charge on the BPh. This process takes place in 10 picoseconds (10 seconds).
The charges on the P and the BPh could undergo charge recombination in this state, which would waste the energy and convert it into heat. Several factors of the reaction center structure serve to prevent this. First, the transfer of an electron from BPh to P960 is relatively slow compared to two other redox reactions in the reaction center. The faster reactions involve the transfer of an electron from BPh (BPh is oxidized to BPh) to the electron acceptor quinone (Q), and the transfer of an electron to P960 (P960 is reduced to P960) from a heme in the cytochrome subunit above the reaction center.
The high-energy electron that resides on the tightly bound quinone molecule Q is transferred to an exchangeable quinone molecule Q. This molecule is loosely associated with the protein and is fairly easy to detach. Two electrons are required to fully reduce Q to QH, taking up two protons from the cytoplasm in the process. The reduced quinone QH diffuses through the membrane to another protein complex (cytochrome bc-complex) where it is oxidized. In the process the reducing power of the QH is used to pump protons across the membrane to the periplasmic space. The electrons from the cytochrome bc-complex are then transferred through a soluble cytochrome c intermediate, called cytochrome c, in the periplasm to the cytochrome subunit. | 5 | Photochemistry |
Nitrogen use efficiency (NUE) is the proportion of nitrogen present that a plant absorbs and uses. Improving nitrogen use efficiency and thus fertilizer efficiency is important to make agriculture more sustainable, by reducing pollution (fertilizer runoff) and production cost and increasing yield. Worldwide, crops generally have less than 50% NUE. Better fertilizers, improved crop management, selective breeding, and genetic engineering can increase NUE.
Nitrogen use efficiency can be measured at various levels: the crop plant, the soil, by fertilizer input, by ecosystem productivity, etc. At the level of photosynthesis in leaves, it is termed photosynthetic nitrogen use efficiency (PNUE). | 1 | Biochemistry |
Among the theoretical criteria for melting, the Lindemann and Born criteria are those most frequently used as a basis to analyse the melting conditions.
The Lindemann criterion states that melting occurs because of "vibrational instability", e.g. crystals melt; when the average amplitude of thermal vibrations of atoms is relatively high compared with interatomic distances, e.g. > > δR, where δu is the atomic displacement, the Lindemann parameter δ ≈ 0.20...0.25 and R is one-half of the inter-atomic distance. The "Lindemann melting criterion" is supported by experimental data both for crystalline materials and for glass-liquid transitions in amorphous materials.
The Born criterion is based on a rigidity catastrophe caused by the vanishing elastic shear modulus, i.e. when the crystal no longer has sufficient rigidity to mechanically withstand the load, it becomes liquid. | 7 | Physical Chemistry |
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events.
Chain reactions are one way that systems which are not in thermodynamic equilibrium can release energy or increase entropy in order to reach a state of higher entropy. For example, a system may not be able to reach a lower energy state by releasing energy into the environment, because it is hindered or prevented in some way from taking the path that will result in the energy release. If a reaction results in a small energy release making way for more energy releases in an expanding chain, then the system will typically collapse explosively until much or all of the stored energy has been released.
A macroscopic metaphor for chain reactions is thus a snowball causing a larger snowball until finally an avalanche results ("snowball effect"). This is a result of stored gravitational potential energy seeking a path of release over friction. Chemically, the equivalent to a snow avalanche is a spark causing a forest fire. In nuclear physics, a single stray neutron can result in a prompt critical event, which may finally be energetic enough for a nuclear reactor meltdown or (in a bomb) a nuclear explosion.
Numerous chain reactions can be represented by a mathematical model based on Markov chains. | 7 | Physical Chemistry |
* Diffusion constant, relates the flux of particles with the negative gradient of the concentration (see Fick's laws of diffusion)
* Thermal conductivity (see Fourier's law)
* Ionic conductivity
* Mass transport coefficient
* Shear viscosity , where is the viscous stress tensor (see Newtonian fluid)
* Electrical conductivity | 7 | Physical Chemistry |
Ochir has been a professor at the Mongolian University of Science and Technology since 1965. She held the positions of assistant professor, associate professor and professor, teaching courses in petrology and petrography. She served as the head of the universitys Department of Geology and Mineralogy from 1978 to 2009. She has also served as Director of the universitys Geoscience Center since 2001.
Ochir has carried out field and basic research work through joint expeditions of the Russian and Mongolian Academies of Sciences. She is the author of over 350 scientific publications and was the lead editor of the book Mineral Resources of Mongolia.
Ochir served as vice president of the International Union of Geological Sciences for four years. She is an adjunct professor at the Institute of Mineral Resources of the Chinese Academy of Geological Sciences and a foreign member of the Russian Academy of Natural Sciences.
Ochir is an Honoured Scientist of Mongolia. She was presented with the Jan Masaryk Medal by the Czech Ambassador in 2021. | 9 | Geochemistry |
Bauxite tailings is a waste product generated in the industrial production of aluminium. Making provision for the approximately 77 million tons that is produced annually is one of the most significant problems for the aluminium mining industry. | 8 | Metallurgy |
Total pesticides use in agriculture in 2021 was 3.54 million tonnes of active ingredients (Mt), a 4 percent increase with respect to 2020, a 11 percent increase in a decade, and a doubling since 1990. Pesticides use per area of cropland in 2021 was 2.26 kg per hectare (kg/ha), an increase of 4 percent with respect to 2020; use per value of agricultural production was 0.86 kg per thousand international dollar (kg/1000 I$) (+2%); and use per person was 0.45 kg per capita (kg/cap) (+3%). Between 1990 and 2021, these indicators increased by 85 percent, 3 percent, and 33 percent, respectively. Brazil was the world's largest user of pesticides in 2021, with 720 kt of pesticides applications for agricultural use, while USA (457 kt) was the second largest user.
Applications per cropland area in 2021 varied widely, from 10.9 kg/hectare in Brazil to 0.8 kg/ha in the Russian Federation. The level in Brazil was about twice as high as in Argentina (5.6 kg/ha) and Indonesia (5.3 kg/ha). Insecticide use in the US has declined by more than half since 1980 (0.6%/yr), mostly due to the near phase-out of organophosphates. In corn fields, the decline was even steeper, due to the switchover to transgenic Bt corn. | 2 | Environmental Chemistry |
An alternative, catalyst-free method for transesterification uses supercritical methanol at high temperatures and pressures in a continuous process. In the supercritical state, the oil and methanol are in a single phase, and reaction occurs spontaneously and rapidly. The process can tolerate water in the feedstock, free fatty acids are converted to methyl esters instead of soap, so a wide variety of feedstocks can be used. Also the catalyst removal step is eliminated.
High temperatures and pressures are required, but energy costs of production are similar or less than catalytic production routes. | 0 | Organic Chemistry |
Paired receptors are membrane proteins with extracellular domains that interact with extracellular ligands. The extracellular region may contain multiple repeating protein domains and may be members of either the immunoglobulin or C-type lectin families. The extracellular domains of homologous paired receptors are typically very similar in sequence but have different binding affinity for their shared ligands, with the inhibitory member of the pair binding more tightly.
Homologous paired receptors have characteristic differences in their transmembrane and cytoplasmic regions that distinguish the activating and inhibiting members of the pair. Inhibitory receptors have a cytoplasmic sequence typically containing at least one immunoreceptor tyrosine-based inhibitory motif (ITIM). Activating receptors have a truncated cytoplasmic sequence compared to their corresponding inhibitory receptor and feature a positively charged amino acid residue in their transmembrane domain, enabling protein-protein interaction with an adaptor protein that possesses a immunoreceptor tyrosine-based activation motif (ITAM). | 1 | Biochemistry |
In Laser ablation electrospray ionization (LAESI) a laser is used to ablate the surface of the sample and the emitted molecules are ionized in the gas phase by charged droplets from electrospray. Similar to DESI the ionization happens in ambient conditions. Anderton et al. used this ionization technique coupled to a Fourier transform mass spectrometer to analyzed 200 single cells of Allium cepa (red onion) in high spatial resolution. | 1 | Biochemistry |
Absorbance is a number that measures the attenuation of the transmitted radiant power in a material. Attenuation can be caused by the physical process of "absorption", but also reflection, scattering, and other physical processes. Absorbance of a material is approximately equal to its attenuance when both the absorbance is much less than 1 and the emittance of that material (not to be confused with radiant exitance or emissivity) is much less than the absorbance. Indeed,
where
* is the radiant power transmitted by that material,
* is the radiant power attenuated by that material,
* is the radiant power received by that material, and
* is the radiant power emitted by that material.
This is equivalent to
where
* is the transmittance of that material,
* is the of that material,
* is the emittance of that material.
According to the Beer–Lambert law, , so
and finally | 7 | Physical Chemistry |
The second ORF of L1 encodes a protein that has endonuclease and reverse transcriptase activity. The encoded protein has a molecular weight of 150 kDa. The structure of the ORF2 protein was solved in 2023. Its protein core contains three domains of unknown functions, termed "tower/EN-linker" and "wrist/RNA-binding domain" that bind Alu RNA's polyA tail and C-terminal domain that binds Alu RNA stem loop.
The nicking and reverse transcriptase activities of L1 ORF2p are boosted by single-stranded DNA structures likely present on the active replication forks. Unlike viral RTs, L1 ORF2p can be primed by RNA, including RNA hairpin primers produced by the Alu element. | 1 | Biochemistry |
Wetlands are frequently applied to solve the issue of eutrophication. Nitrate is transformed in wetlands to free nitrogen and discharged to the air. Phosphorus is adsorbed by wetland soils which are taken up by the plants. Therefore, wetlands could help to reduce the concentration of nitrogen and phosphorus to remit and solve the eutrophication. However, wetland soils can only hold a limited amount of phosphorus. To remove phosphorus continually, it is necessary to add more new soils within the wetland from remnant plant stems, leaves, root debris, and undecomposable parts of dead algae, bacteria, fungi, and invertebrates. | 9 | Geochemistry |
Levonorgestrel can be taken by mouth as a form of emergency birth control. The typical dosage is either 1.5 mg taken once or 0.75 mg taken 12–24 hours apart. The effectiveness in both methods is similar. The most widely used form of oral emergency contraception is the progestin-only pill, which contains a 1.5 mg dosage of levonorgestrel. Levonorgestrel-only emergency contraceptive pills are reported to have an 89% effectiveness rate if taken within the recommended 72 hours after sex. The efficacy of the drug decreases by 50% for each 12-hour delay in taking the dose after the emergency contraceptive regimen has been started. | 4 | Stereochemistry |
Organic ladder polymers are interesting because they can exhibit exceptional thermal stabilities and the conformation of the subunits is constrained. Because they are less flexible, their processing can be challenging. An early example was derived from condensation of the 1,2,4,5-tetraaminobenzene with naphthalenetetracarboxylic dianhydride. | 7 | Physical Chemistry |
The canonical partition function Z of an ideal gas consisting of N = nN identical (non-interacting) particles, is:
where is the thermal de Broglie wavelength:
with the usual definitions: h is the Planck constant, m the mass of a particle, k the Boltzmann constant and T the absolute temperature. In an ideal gas z is the partition function of a single particle in a container of volume V. In order to derive the Van der Waals equation we assume now that each particle moves independently in an average potential field offered by the other particles. The averaging over the particles is easy because we will assume that the particle density of the Van der Waals fluid is homogeneous.
The interaction between a pair of particles, which are hard spheres, is taken to be:
r is the distance between the centers of the spheres and d is the distance where the hard spheres touch each other (twice the Van der Waals radius). The depth of the Van der Waals well is .
Because the particles are not coupled under the mean field Hamiltonian, the mean field approximation of the total partition function still factorizes:
but the intermolecular potential necessitates two modifications to z. First, because of the finite size of the particles, not all of V is available, but only V − Nb′, where (just as in the conventional derivation above):
Second, we insert a Boltzmann factor
exp[−Φ/2kT] to take care of the average intermolecular potential. We divide here the potential by two because this interaction energy is shared between two particles. Thus:
The total attraction felt by a single particle is:
where we assumed that in a shell of thickness dr there are particles. This is a mean field approximation; the position of the particles is averaged. In reality the density close to the particle is different than far away as can be described by a pair correlation function. Furthermore, it is neglected that the fluid is enclosed between walls. Performing the integral we get:
Hence, we obtain:
From statistical thermodynamics we know that:
so that we only have to differentiate the terms containing . We get: | 7 | Physical Chemistry |
To generate a nonthermal plasma at atmospheric pressure, a working gas (molecular or inert gas, e.g. air, nitrogen, argon, helium) is passed through an electric field. Electrons originating from ionization processes can be accelerated in this field to trigger impact ionization processes. If more free electrons are produced during this process than are lost, a discharge can build up. The degree of ionization in technically used plasmas is usually very low, typically a few per mille or less. The electrical conductivity generated by these free charge carriers is used to couple in electrical power. When colliding with other gas atoms or molecules, the free electrons can transfer their energy to them and thus generate highly reactive species that act on the material to be treated (gaseous, liquid, solid). The electron energy is sufficient to split covalent bonds in organic molecules. The energy required to split single bonds is in the range of about 1.5 - 6.2 eV, for double bonds in the range of about 4.4 - 7.4 eV and for triple bonds in the range of 8.5 - 11.2 eV . For gases that can also be used as process gases, dissociation energies are e.g. 5.7 eV (O2) and 9.8 eV (N2) | 7 | Physical Chemistry |
V̇O max/peak is widely used as an indicator of cardiorespiratory fitness (CRF) in select groups of athletes or, rarely, in people under assessment for disease risk. In 2016, the American Heart Association (AHA) published a scientific statement recommending that CRF quantifiable as V̇O max/peak be regularly assessed and used as a clinical vital sign; ergometry (exercise wattage measurement) may be used if VO is unavailable. This statement was based on evidence that lower fitness levels are associated with a higher risk of cardiovascular disease, all-cause mortality, and mortality rates. In addition to risk assessment, the AHA recommendation cited the value for measuring fitness to validate exercise prescriptions, physical activity counseling, and improve both management and health of people being assessed.
A 2023 meta-analysis of observational cohort studies showed an inverse and independent association between V̇O max and all-cause mortality risk. Every one metabolic equivalent increase in estimated cardiorespiratory fitness was associated with an 11% reduction in mortality. The top third of V̇O max scores represented a 45% lower mortality in people compared with the lowest third.
As of 2023, V̇O max is rarely employed in routine clinical practice to assess cardiorespiratory fitness or mortality due to its considerable demand for resources and costs. | 1 | Biochemistry |
Due to reclassification as UN0508, a class 1.3C explosive, hydroxybenzotriazole and its monohydrate crystal are no longer allowed to be transported by sea or air as per 49CFR (USDOT hazardous materials regulations). However, UNECE draft proposal ECE/TRANS/WP.15/AC.1/HAR/2009/1 has been circulated to UN delegates and, if implemented, would amend current regulations thus allowing for the monohydrate crystal to be shipped under the less-stringent code of UN3474 as a class 4.1 desensitized explosive. | 1 | Biochemistry |
Although not well understood at the time, the Fürst-Plattner rule played a critical role during R. B. Woodward's synthesis of Reserpine. The problematic stereocenter is highlighted in red, below.
Woodward's synthetic strategy used a Bischler-Napieralski reaction to form the tetrahydrocarbazole portion of Reserpine. The subsequent imine intermediate was treated with sodium borohydride, affording the wrong stereoisomer due to the Fürst-Plattner effect.
Examining the intermediate structure shows that the hydride preferentially added to the 3-carbon via the top face of the imine to avoid an unfavorable twist-boat intermediate. Unfortunately, this outcome required Woodward to perform several additional steps to complete the total synthesis of reserpine with the proper stereochemistry. | 4 | Stereochemistry |
Atta-ur-Rahman has been selected as one of the 500 most influential personalities of the Islamic World. Institutions have been named after Rahman in China, the Atta-ur-Rahman Institute for Natural Product Discovery (AuRIns) in Malaysia and the Academician Professor Atta-ur-Rahman One Belt and One Road TCM Research Center were named after Rahman, as well as the Atta-ur-Rahman School of Applied Biosciences at the National University of Sciences & Technology (Islamabad, Pakistan) and the Atta-ur-Rahman Laboratories, International Center for Chemical and Biological Sciences at the University of Karachi (Karachi, Pakistan). The US Publisher ARKAT USA has published a special issue of the journal Arkivoc, Vol 2007, in honour of Atta-ur-Rahman FRS which had contributions from top scientists in the field of natural product chemistry. Similarly, the international journal Molecules published by the Swiss publisher MDPI published a special issue of the journal in honour of Atta-ur-Rahman. The World Academy of Science, Italy has introduced a special Prize in his honour (TWAS-Atta-ur-Rahman Award in Chemistry) for young scientists which is awarded once every two years. In recognition of his eminent contributions, Prof. Atta-ur-Rahman has received honorary doctorate degrees from many universities including the University of Cambridge (UK), Coventry University (UK), Bradford University (UK), Universiti Teknologi Mara (Malaysia), Asian Institute of Teknologi (Thailand), University of Karachi (Pakistan), Gomal University (Pakistan), and several other universities | 0 | Organic Chemistry |
Possible biomedical-oriented applications of this technique are related to the study of the myelin and myelopathies. Myelin is a highly ordered structure, in which many lipid-
enriched, densely compacted phospholipid bilayers are spirally rolled up around the
cylindrical axons. The linear acyl chains of the phospholipid molecules present a
perpendicular orientation with respect to the myelin surface. Therefore, in a myelinated nerve
fiber, a large number of molecular bonds are ordered around a radial axis of symmetry. Such a
strong molecular anisotropy and azimuthal symmetry make RP-CARS a suitable tool to investigate
neural white matter. | 3 | Analytical Chemistry |
James N. Pitts Jr. (January 10, 1921 – June 19, 2014) was an American chemist and researcher known for his work in the fields of photochemistry and atmospheric chemistry. Pitts was a pioneer in the study of smog and air pollution, especially in Los Angeles County. Pitts co-founded the Statewide Air Pollution Research Center at the University of California, Riverside in 1961 and served as the center's director from 1970 to 1988. He authored more than 400 scientific publications and four books on the subjects, especially smog.
Pitts research formed the basis for Californias air quality laws. According to the chair of the Air Resources Board, Mary Nichols, "Jim Pitts was probably the single person most responsible for the understanding of what strategies we need to clean up Southern California's air...He was able to explain all of this in English to policymakers so that they would be able to accept that it was going to take extensive and difficult actions to control emissions." He often invited state and federal officials to his smog chamber at UC Irvine, including Jerry Brown and Ronald Reagan, to demonstrate the effects of smog and air pollution. In a common demonstration, Pitts would fill an Erlenmeyer flask with ozone and then twist a slice of lemon onto the flask. The ensuing chemical reaction, which quickly produced a fog, demonstrated the formation of smog in the atmosphere.
Pitts refused funding from industry groups, which increased his center's credibility. He was the recipient of numerous awards and recognitions from the California State Assembly, the United States Congress, the Coalition for Clean Air, the South Coast Air Quality Management District, and the California state air board.
Pitts was born on January 10, 1921, in Salt Lake City, Utah, to Esther (née Bengtson) and James N. Pitts. The family moved to West Los Angeles when he was just six months old. A high school teacher sparked his interest in chemistry during his junior year.
Pitts enrolled as a chemistry student at University of California, Los Angeles (UCLA) in 1939. He left during World War II, joining a group of young scientists who conducted classified chemical warfare field tests. Their work led to the development of more effective gas mask for Allied forces during the war. He returned to UCLA, where he received a bachelor's degree in chemistry in 1945 and a doctorate in 1949. Pitts initially worked as a faculty member of Northwestern University. He was at the time married to a woman by the name of Nancy Ann Quirt. James and Nancy had three daughters Linda, Christie and Beckie.
Pitts was hired as a founding professor at UC Riverside in 1954.
Pitts married his second wife, UC Irvine chemist and professor Barbara Finlayson-Pitts in 1970. He followed her to the University of California, Irvine in 1994, where the two collaborated of research and co-authored books and other publications.
James Pitts died of natural causes at his home in Irvine, California, on June 19, 2014, at the age of 93. He was survived by his wife, Barbara Finlayson-Pitts, and three daughters, Linda Lee, Christie Hoffman and Beckie St. George. He was also survived by five grandchildren Kristin Cohn, Brianna Hoffman, Trevin Hoffman, Mallory St George and Ryan Giordano. His great-grandchildren include Brandon, Kyle, Austin and Riley. | 5 | Photochemistry |
Tin pest is an autocatalytic, allotropic transformation of the element tin, which causes deterioration of tin objects at low temperatures. Tin pest has also been called tin disease, tin blight or tin leprosy (lèpre détain').
It was observed in medieval Europe that the pipes of pipe organs were affected in cool climates. As soon as the tin began decomposing, the process accelerated.
With the adoption of the Restriction of Hazardous Substances Directive (RoHS) regulations in Europe, and similar regulations elsewhere, traditional lead/tin solder alloys in electronic devices have been replaced by nearly pure tin, introducing tin pest and related problems such as tin whiskers. | 8 | Metallurgy |
Molecular breeding is the application of molecular biology tools, often in plant breeding and animal breeding. In the broad sense, molecular breeding can be defined as the use of genetic manipulation performed at the level of DNA to improve traits of interest in plants and animals, and it may also include genetic engineering or gene manipulation, molecular marker-assisted selection, and genomic selection. More often, however, molecular breeding implies molecular marker-assisted breeding (MAB) and is defined as the application of molecular biotechnologies, specifically molecular markers, in combination with linkage maps and genomics, to alter and improve plant or animal traits on the basis of genotypic assays.
The areas of molecular breeding include:
* QTL mapping or gene discovery
* Marker assisted selection and genomic selection
* Genetic engineering
* Genetic transformation | 1 | Biochemistry |
In addition to serving as building blocks in total synthesis, the chiral pool is tapped to produce asymmetric catalysts, chiral protecting groups, and resolving agents. | 0 | Organic Chemistry |
Sporopollenin is a biological polymer found as a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable (one of the most inert among biopolymers) and is usually well preserved in soils and sediments. The exine layer is often intricately sculptured in species-specific patterns, allowing material recovered from (for example) lake sediments to provide useful information to palynologists about plant and fungal populations in the past. Sporopollenin has found uses in the field of paleoclimatology as well. Sporopollenin is also found in the cell walls of several taxa of green alga, including Phycopeltis (an ulvophycean) and Chlorella.
Spores are dispersed by many different environmental factors, such as wind, water or animals. In suitable conditions, the sporopollenin-rich walls of pollen grains and spores can persist in the fossil record for hundreds of millions of years, since sporopollenin is resistant to chemical degradation by organic and inorganic chemicals. | 1 | Biochemistry |
Determining chirality based on Fischer Projections is effectively the same as the standard method. The primary difference is the benefit that Fischer Projections provide in depicting the orientation of substituents with the vertical and horizontal lines. Considering that orientation of these molecules is already known, it may be properly depicted with wedges and dashes if needed. After this, the priority of each of the groups bonded to the carbon are ranked and the chirality is determined in the standard fashion. While there is no significant difference in the actual process of determining chirality, Fischer Projections allow one to better visualize where substituents are in space making it convenient to assign S or R chirality based on this model. In certain cases, it can be helpful to draw a Fischer Projection from a larger molecule to visualize and determine the chirality of a specific carbon. | 4 | Stereochemistry |
*Paramagnetic Fluorescence Quenching, the allowance of new electronic states upon binding a paramagnetic metal atom
*Photoinduced Electron Transfer (PET), the blocking of a lower energy state due to the binding of a metal atom.
*Photoinduced Charge Transfer (PCT), the modulation of energy levels in a complex by charge transfer within a conjugated pi system.
*[http://chemwiki.ucdavis.edu/Theoretical_Chemistry/Fundamentals/Fluorescence_Resonance_Energy_Transfer Fluorescence Resonance Energy Transfer (FRET)], the transfer of an exciton from a donor to an acceptor, modulating the emission spectrum.
*Excimer/Exciplex formation, the formation of a state that is a hybrid of the ground and excited states. This has novel fluorescent properties.
*Chemodosimeters, complexes that undergo irreversible reactions with other species upon binding a metal to form new compounds with novel fluorescent spectra. | 5 | Photochemistry |
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