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Homotopic groups in a chemical compound are equivalent groups. Two groups A and B are homotopic if the molecule remains achiral when the groups are interchanged with some other atom (such as bromine) while the remaining parts of the molecule stay fixed. Homotopic atoms are always identical, in any environment. Homotopic NMR-active nuclei have the same chemical shift in an NMR spectrum. For example, the four hydrogen atoms of methane (CH) are homotopic with one another, as are the two hydrogens or the two chlorines in dichloromethane (CHCl). | 0 | Theoretical and Fundamental Chemistry |
Until recently, there were only two known pathways to process Okazaki fragments. However, current investigations have concluded that a new pathway for Okazaki fragmentation and DNA replication exists. This alternate pathway involves the enzymes Pol δ with Pif1 which perform the same flap removal process as Pol δ and FEN1. | 1 | Applied and Interdisciplinary Chemistry |
The International System of Units (SI) unit of radioactive activity is the becquerel (Bq), named in honor of the scientist Henri Becquerel. One Bq is defined as one transformation (or decay or disintegration) per second.
An older unit of radioactivity is the curie, Ci, which was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium (element)". Today, the curie is defined as disintegrations per second, so that 1 curie (Ci) = .
For radiological protection purposes, although the United States Nuclear Regulatory Commission permits the use of the unit curie alongside SI units, the European Union European units of measurement directives required that its use for "public health ... purposes" be phased out by 31 December 1985.
The effects of ionizing radiation are often measured in units of gray for mechanical or sievert for damage to tissue. | 0 | Theoretical and Fundamental Chemistry |
Homologation reactions like the Kowalski ester homologation provide simple examples of insertion process in organic synthesis. In the Arndt-Eistert reaction, a methylene unit is inserted into the carboxyl-carbon bond of carboxylic acid to form the next acid in the homologous series. Organic Syntheses provides the example of t-BOC protected (S)-phenylalanine (2-amino-3-phenylpropanoic acid) being reacted sequentially with triethylamine, ethyl chloroformate, and diazomethane to produce the α-diazoketone, which is then reacted with silver trifluoroacetate / triethylamine in aqueous solution to generate the t-BOC protected form of (S)-3-amino-4-phenylbutanoic acid.
Mechanistically, the α-diazoketone undergoes a Wolff rearrangement to form a ketene in a 1,2-rearrangement. Consequently, the methylene group α- to the carboxyl group in the product is the methylene group from the diazomethane reagent. The 1,2-rearrangement has been shown to conserve the stereochemistry of the chiral centre as the product formed from t-BOC protected (S)-phenylalanine retains the (S) stereochemistry with a reported enantiomeric excess of at least 99%.
A related transformation is the Nierenstein reaction in which a diazomethane methylene group is inserted into the carbon-chlorine bond of an acid chloride to generate an α-chloro ketone. An example, published in 1924, illustrates the reaction in a substituted benzoyl chloride system:
Perhaps surprisingly, α-bromoacetophenone is the minor product when this reaction is carried out with benzoyl bromide, a dimeric dioxane being the major product. Organic azides also provide an example of an insertion reaction in organic synthesis and, like the above examples, the transformations proceed with loss of nitrogen gas. When tosyl azide reacts with norbornadiene, a ring expansion reaction takes place in which a nitrogen atom is inserted into a carbon-carbon bond α- to the bridge head:
The Beckmann rearrangement is another example of a ring expanding reaction in which a heteroatom is inserted into a carbon-carbon bond. The most important application of this reaction is the conversion of cyclohexanone to its oxime, which is then rearranged under acidic conditions to provide ε-caprolactam, the feedstock for the manufacture of Nylon 6. Annual production of caprolactam exceeds 2 billion kilograms.
Carbenes undergo both intermolecular and intramolecular insertion reactions. Cyclopentene moieties can be generated from sufficiently long-chain ketones by reaction with trimethylsilyldiazomethane, (CH)Si–CHN:
Here, the carbene intermediate inserts into a carbon-hydrogen bond to form the carbon-carbon bond needed to close the cyclopentene ring. Carbene insertions into carbon-hydrogen bonds can also occur intermolecularly:
Carbenoids are reactive intermediates that behave similarly to carbenes. One example is the chloroalkyllithium carbenoid reagent prepared in situ from a sulfoxide and t-BuLi which inserts into the carbon-boron bond of a pinacol boronic ester: | 0 | Theoretical and Fundamental Chemistry |
Some ionic liquids have been shown to reduce friction and wear in basic tribological testing, and their polar nature makes them candidate lubricants for tribotronic applications. While the comparatively high cost of ionic liquids currently prevents their use as neat lubricants, adding ionic liquids in concentrations as low as 0.5 wt% may significantly alter the lubricating performance of conventional base oils. Thus, the current focus of research is on using ionic liquids as additives to lubricating oils, often with the motivation to replace widely used, ecologically harmful lubricant additives. However, the claimed ecological advantage of ionic liquids has been questioned repeatedly and is yet to be demonstrated from a lifecycle perspective. | 0 | Theoretical and Fundamental Chemistry |
A bioindicator is any species (an indicator species) or group of species whose function, population, or status can reveal the qualitative status of the environment. The most common indicator species are animals. For example, copepods and other small water crustaceans that are present in many water bodies can be monitored for changes (biochemical, physiological, or behavioural) that may indicate a problem within their ecosystem. Bioindicators can tell us about the cumulative effects of different pollutants in the ecosystem and about how long a problem may have been present, which physical and chemical testing cannot.
A biological monitor or biomonitor is an organism that provides quantitative information on the quality of the environment around it. Therefore, a good biomonitor will indicate the presence of the pollutant and can also be used in an attempt to provide additional information about the amount and intensity of the exposure.
A biological indicator is also the name given to a process for assessing the sterility of an environment through the use of resistant microorganism strains (e.g. Bacillus or Geobacillus). Biological indicators can be described as the introduction of a highly resistant microorganisms to a given environment before sterilization, tests are conducted to measure the effectiveness of the sterilization processes. As biological indicators use highly resistant microorganisms, any sterilization process that renders them inactive will have also killed off more common, weaker pathogens. | 1 | Applied and Interdisciplinary Chemistry |
The National perspective plan envisions about 150-million-acre feet (MAF) (185 billion cubic meters) of water storage along with building inter-links. These storages and the interlinks will add nearly 170 million acre feet of water for beneficial uses in India, enabling irrigation over an additional area of 35 million hectares, generation of 40,000 MW capacity hydro power, flood control and other benefits.
The total surface water available to India is nearly 1440-million-acre feet (1776 billion cubic meters) of which only 220-million-acre feet was being used in the year 1979. The rest is neither utilized nor managed, and it causes disastrous floods year after year. Up to 1979, India had built over 600 storage dams with an aggregate capacity of 171 billion cubic meters. These small storages hardly enable a seventh of the water available in the country to be utilized beneficially to its fullest potential. From India-wide perspective, at least 946 billion cubic meters of water flow annually could be utilized in India, power generation capacity added and perennial inland navigation could be provided. Also some benefits of flood control would be achieved. The project claims that the development of the rivers of the sub-continent, each state of India, as well as its international neighbours stand to gain by way of additional irrigation, hydro power generation, navigation and flood control. The project may also contribute to food security to the anticipated population peak of India.
The Ganga-Brahmaputra-Meghna is a major international drainage basin which carries more than 1,000 million acre feet out of total 1440 million acre feet in India. Water is a scarce commodity and several basins such as Cauvery, Yamuna, Sutlej, Ravi and other smaller inter-State/intra-State rivers are short of water. 99 districts of the country are classified as drought prone, an area of about 40 million hectare is prone to recurring floods. The inter-link project is expected to help reduce the scale of this suffering and associated losses.
The National Perspective Plan comprised, starting 1980s, of two main components:
#Himalayan Rivers Development, and
#Peninsular Rivers Development
An intrastate component was added in 2005. | 1 | Applied and Interdisciplinary Chemistry |
The Geochemical Society was founded in 1955 at a meeting of the Geological Society of America. Its first president was Earl Ingerson and dues started at two dollars per year. In 1990 it was incorporated as a 501(c)(3) nonprofit organization in 1990.
In 1988, the Geochemical society created the Goldschmidt Conferences in honor of the geochemist Victor Goldschmidt (1888–1947), "considered to be the founder of modern geochemistry and crystal chemistry". It was soon joined by the European Association of Geochemistry, and at the 2014 meeting the two organizations signed a Memorandum of Understanding for the governance and trademark protection of the meeting. The conference is one of the worlds largest devoted to geochemistry. The societys board of directors holds its annual meeting during the conference. | 0 | Theoretical and Fundamental Chemistry |
miRNA-324-5p is a relatively new and understudied microRNA. It is an important regulator in several diseases, and its effects span across the body from neuronal dysregulation in seizure to hepatocellular carcinoma and cardiac disease. Because microRNAs have numerous targets, they are capable of regulating multiple pathways and circuits, an ability that may be useful in the treatment of complex disorders like epilepsy in which many subsystems are dysregulated. However, the wide-ranging functions of miRNAs may be limiting as well. microRNA expression modulation could lead to unanticipated physiological effects and not provide adequate specificity. | 1 | Applied and Interdisciplinary Chemistry |
Mediator is a multiprotein complex that functions as a transcriptional coactivator in all eukaryotes. It was discovered in 1990 in the lab of Roger D. Kornberg, recipient of the 2006 Nobel Prize in Chemistry. Mediator complexes interact with transcription factors and RNA polymerase II. The main function of mediator complexes is to transmit signals from the transcription factors to the polymerase.
Mediator complexes are variable at the evolutionary, compositional and conformational levels. The first image shows only one "snapshot" of what a particular mediator complex might be composed of, but it certainly does not accurately depict the conformation of the complex in vivo. During evolution, mediator has become more complex. The yeast Saccharomyces cerevisiae (a simple eukaryote) is thought to have up to 21 subunits in the core mediator (exclusive of the CDK module), while mammals have up to 26.
Individual subunits can be absent or replaced by other subunits under different conditions. Also, there are many intrinsically disordered regions in mediator proteins, which may contribute to the conformational flexibility seen both with and without other bound proteins or protein complexes. A more realistic model of a mediator complex without the CDK module is shown in the second figure.
The mediator complex is required for the successful transcription by RNA polymerase II. Mediator has been shown to make contacts with the polymerase in the transcription preinitiation complex. A recent model showing the association of the polymerase with mediator in the absence of DNA is shown in the figure to the left. In addition to RNA polymerase II, mediator must also associate with transcription factors and DNA. A model of such interactions is shown in the figure to the right. Note that the different morphologies of mediator do not necessarily mean that one of the models is correct; rather those differences may reflect the flexibility of mediator as it interacts with other molecules. For example, after binding the enhancer and core promoter, the mediator complex undergoes a compositional change in which the kinase module dissociates from the complex to allow association with RNA polymerase II and transcriptional activation.
The Mediator complex is located within the cell nucleus. It is required for the successful transcription of nearly all class II gene promoters in yeast. It works in the same manner in mammals. The mediator functions as a coactivator and binds to the C-terminal domain of RNA polymerase II holoenzyme, acting as a bridge between this enzyme and transcription factors. | 1 | Applied and Interdisciplinary Chemistry |
Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of CaC. Its main use industrially is in the production of acetylene and calcium cyanamide.
The pure material is colorless, while pieces of technical-grade calcium carbide are grey or brown and consist of about 80–85% of CaC (the rest is CaO (calcium oxide), CaP (calcium phosphide), CaS (calcium sulfide), CaN (calcium nitride), SiC (silicon carbide), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic.
Applications of calcium carbide include manufacture of acetylene gas, generation of acetylene in carbide lamps, manufacture of chemicals for fertilizer, and steelmaking. | 1 | Applied and Interdisciplinary Chemistry |
The Ginzburg–Landau equation, named after Vitaly Ginzburg and Lev Landau, describes the nonlinear evolution of small disturbances near a finite wavelength bifurcation from a stable to an unstable state of a system. At the onset of finite wavelength bifurcation, the system becomes unstable for a critical wavenumber which is non-zero. In the neighbourhood of this bifurcation, the evolution of disturbances is characterised by the particular Fourier mode for with slowly varying amplitude (more precisely the real part of ). The Ginzburg–Landau equation is the governing equation for . The unstable modes can either be non-oscillatory (stationary) or oscillatory.
For non-oscillatory bifurcation, satisfies the real Ginzburg–Landau equation
which was first derived by Alan C. Newell and John A. Whitehead and by Lee Segel in 1969. For oscillatory bifurcation, satisfies the complex Ginzburg–Landau equation
which was first derived by Keith Stewartson and John Trevor Stuart in 1971.
When the problem is homogeneous, i.e., when is independent of the spatial coordinates, the Ginzburg–Landau equation reduces to Stuart–Landau equation. | 1 | Applied and Interdisciplinary Chemistry |
In coordination chemistry, a coordinate covalent bond, also known as a dative bond, dipolar bond, or coordinate bond is a kind of two-center, two-electron covalent bond in which the two electrons derive from the same atom. The bonding of metal ions to ligands involves this kind of interaction. This type of interaction is central to Lewis acid–base theory.
Coordinate bonds are commonly found in coordination compounds.
__TOC__ | 0 | Theoretical and Fundamental Chemistry |
The discoverers were reluctant to assert an oxidation state of the iron centers in the compound, instead deferring the details of the electronic structure to computational studies.
The crystal structure reveals that the three iron centers arrange in an equilateral triangle (nearly ideal; Fe1 = 59.67°, Fe2 = 60.15°, and Fe3 = 60.18°) The corresponding bond lengths are similar to one another, (Fe1–Fe2 = 2.829 Å, Fe1–Fe3 = 2.815 Å, and Fe2–Fe3 = 2.830 Å), and reflective of Fe-Fe single bonds. As a trinuclear cluster, it would be thought to have a stable 48-electron closed-shell configuration (24 electrons from the three iron atoms and 24 electrons from the three COT rings).
In the original depiction, each COT ligand acts as an η and η donor, and thus, some degree of π-allylic and pentadienyl bonding modes can be inferred – though the degree of metal-to-ligand electron transfer is uncertain. Computational models suggest the binding mode to lie between η and η, as small shifts in geometry make each mode effectively equivalent (see section on fluxional behavior). Furthermore, DFT calculations with the BLYP functional using a TZP basis set for iron and DZP for carbon and hydrogen estimate a Hirshfeld charge of 0.08 on the iron centers (and Voronoi deformation density of 0.00). Interestingly, all of the bond orders of the C-C ring lie between 1.26 and 1.33, sharply contrasting the discrete single and double bonds of free cyclooctatetraene, or COT complexes with non-bound olefins.
Doubly reduced COT (dianion) is known to adopt a planar (aromatic) comformation to metal centers, which is not observed in Fe(COT). However, arguments also exist that such comformations are more related to binding efficiency than aromaticity.
In computational studies (BP86), when Fe(CH) is optimized as a singlet (gas phase), the iron centers are arranged in an ideal equilateral triangle, as experimentally observed in the crystal structure. In such an electronic configuration, each iron atom achieves an 18-electron configuration through pseudo η and η coordination to alternating COT ligands. However, if the compound is optimized as a triplet structure, the iron centers instead are a scalene triangle, featuring significant Jahn-Teller distortions.
Additional NBO analysis of the singlet structure reveals Wiberg Bond Indices of 0.22 for the Fe-Fe bonds, closely reminiscent of that of D Fe(CO) (0.18). | 0 | Theoretical and Fundamental Chemistry |
In PET imaging, [F]FDG is primarily used for imaging tumors in oncology, where a static [F]FDG PET scan is performed and the tumor [F]FDG uptake is analyzed in terms of Standardized Uptake Value (SUV). FDG PET/CT can be used for the assessment of glucose metabolism in the heart and the brain. [F]FDG is taken up by cells, and subsequently phosphorylated by hexokinase (whose mitochondrial form is greatly elevated in rapidly growing malignant tumours). Phosphorylated [F]FDG cannot be further metabolised and is thus retained by tissues with high metabolic activity, such as most types of malignant tumours. As a result, FDG-PET can be used for diagnosis, staging, and monitoring treatment of cancers, particularly in Hodgkins disease, non-Hodgkin lymphoma, colorectal cancer, breast cancer, melanoma, and lung cancer. It has also been approved for use in diagnosing Alzheimers disease.
In body-scanning applications in searching for tumor or metastatic disease, a dose of [F]-FDG in solution (typically 5 to 10 millicuries or 200 to 400 MBq) is typically injected rapidly into a saline drip running into a vein, in a patient who has been fasting for at least six hours, and who has a suitably low blood sugar. (This is a problem for some diabetics; usually PET scanning centers will not administer the isotope to patients with blood glucose levels over about 180 mg/dL = 10 mmol/L, and such patients must be rescheduled). The patient must then wait about an hour for the sugar to distribute and be taken up into organs which use glucose – a time during which physical activity must be kept to a minimum, in order to minimize uptake of the radioactive sugar into muscles (this causes unwanted artifacts in the scan, interfering with reading especially when the organs of interest are inside the body vs. inside the skull). Then, the patient is placed in the PET scanner for a series of one or more scans which may take from 20 minutes to as long as an hour (often, only about one-quarter of the body length may be imaged at a time). | 1 | Applied and Interdisciplinary Chemistry |
* Orbifold signature:
* Coxeter notation: [∞,2,∞] or [∞,2,∞]
* Lattice: rhombic
* Point group: D
* The group cm contains no rotations. It has reflection axes, all parallel. There is at least one glide reflection whose axis is not a reflection axis; it is halfway between two adjacent parallel reflection axes.
*This group applies for symmetrically staggered rows (i.e. there is a shift per row of half the translation distance inside the rows) of identical objects, which have a symmetry axis perpendicular to the rows.
;Examples of group cm | 0 | Theoretical and Fundamental Chemistry |
Like the ALR genes, the MRS2 gene was cloned and sequenced before it was identified as a Mg transporter. The MRS2 gene was identified in the nuclear genome of yeast in a screen for suppressors of a mitochondrial gene RNA splicing mutation, and was cloned and sequenced by Wiesenberger et al. (1992). Mrs2p was not identified as a putative Mg transporter until Bui et al. (1999). Gregan et al. (2001a) identified LPE10 by homology to MRS2 and showed that both LPE10 and MRS2 mutants altered the Mg content of yeast mitochondria and affected RNA splicing activity in the organelle. Mg transport has been shown to be directly mediated by Mrs2p, but not for Lpe10p.
The Mrs2p and Lpe10p proteins are 470 and 413 amino acid residues in size, respectively, and a 250–300 amino acid region in the middle of the proteins shows a weak similarity to the full CorA protein. The TM topologies of the Mrs2p and Lpe10p proteins have been assessed using a protease protection assay and are shown in the figure. TM 1 and 2 correspond to TM 2 and 3 in the CorA protein. The conserved GMN motif is at the outside end of the first TM domain, and when the glycine (G) in this motif was mutated to a cysteine (C) in Mrs2p, Mg transport was strongly reduced.
The figure shows the experimentally determined topology of Mrs2p and Lpe10p as adapted from Bui et al. (1999) and Gregan et al. (2001a). The GMN motif location is indicated in red and the TM domains in light blue. The orientation in the membrane and the positions of the N- and C-termini are indicated. The various sizes of the soluble domains are given in amino acids (AA), TM domains are numbered, and the figure is not drawn to scale.
Mrs2p has been localised to the mitochondrial inner membrane by subcellular fractionation and immunodetection and Lpe10p to the mitochondria. Mitochondria lacking Mrs2p do not show a fast Mg uptake, only a slow ‘leak’, and overaccumulation of Mrs2p leads to an increase in the initial rate of uptake. Additionally, CorA, when fused to the mitochondrial leader sequence of Mrs2p, can partially complement the mitochondrial defect conferred by the loss of either Mrs2p or Lpe10p. Hence, Mrs2p and/or Lpe10p may be the major Mg uptake system for mitochondria. A possibility is that the proteins form heterodimers, as neither protein (when overexpressed) can fully complement the loss of the other.
The characteristics of Mg uptake in isolated mitochondria by Mrs2p were quantified using mag-fura 2. The uptake of Mg by Mrs2p shared a number of attributes with CorA. First, Mg uptake was directly dependent on the electric potential (ΔΨ) across the boundary membrane. Second, the uptake is saturated far below that which the ΔΨ theoretically permits, so the transport of Mg by Mrs2p is likely to be regulated in a similar manner to CorA, possibly by the inactivation of the protein. Third, Mg efflux was observed via Mrs2p upon the artificial depolarisation of the mitochondrial membrane by valinomycin. Finally, the Mg fluxes through Mrs2p are inhibited by cobalt (III) hexaammine.
The kinetics of Mg uptake by Mrs2p were determined in the Froschauer et al. (2004) paper on CorA in bacteria. The initial change in free Mg concentration was 150 μM s-1 for wild type and 750 μM s-1 for mitochondria from yeast overexpressing MRS2. No attempt was made to scale the observed transport to the amount of transporter present. | 1 | Applied and Interdisciplinary Chemistry |
BTO draws upon the comprehensive enzyme specific data of the BRENDA enzyme information system. Presently (October 2019) 112,200 enzyme-organism-tissue specific data from more than 11,000 proteins are stored in BRENDA. These entries were manually annotated from more than 150,000 different literature references. All terms in BTO are evaluated and classified according to the OBO-format, and are connected by specific relationships. Each term is a distinct entry within the ontology and is automatically assigned to a unique BTO-identifier (BTO-ID). The BTO-IDs serve as stable accession numbers in order to create cross-references to further external biochemical databases. Further tissue und cell-type specific terms from external databases (i.e. UniProt) are integrated into BTO.
The terms are classified in 4 main categories (subgraphs):
* animal
* plant
* fungus
* other sources
Further levels are defined below the main categories (=nodes), classifying the “parent”, “child”, and “grandchild” all connected via specific relationships (=edges)
* is_a (e.g. skeletal muscle fibre is_a muscle fibre)
* part_of (e.g. muscle fibre part_of muscle)
* develops/derives_from (e.g.myoma cell develops/derives_from muscle fibre)
* related_to (description of more general relationships between terms which are not covered by the other ones)
Most of the terms are clearly associated with specific organisms, organs, tissues, or cell types. There are several identical designations for tissues both in plants and animals, e.g. “epidermis”. To distinguish between those tissue terms and to classify them correctly into BTO for plant tissues the prefix “plant” is placed before the term, e.g. “plant epidermis”.
More than 80% of the tissue terms have definitions that describe the meaning and context. These definitions are obtained from i.e. medical dictionaries and cell line databases (Webster's Dictionary, DSMZ). | 1 | Applied and Interdisciplinary Chemistry |
Recently, the Woodward–Hoffmann rules have been reinterpreted using conceptual density functional theory (DFT). The key to the analysis is the dual descriptor function, proposed by Christophe Morell, André Grand and Alejandro Toro-Labbé , the second derivative of the electron density with respect to the number of electrons . This response function is important as the reaction of two components A and B involving a transfer of electrons will depend on the responsiveness of the electron density to electron donation or acceptance, i.e. the derivative of the Fukui function . In fact, from a simplistic viewpoint, the dual descriptor function gives a readout on the electrophilicity or nucleophilicity of the various regions of the molecule. For , the region is electrophilic, and for , the region is nucleophilic. Using the frontier molecular orbital assumption and a finite difference approximation of the Fukui function, one may write the dual descriptor as
This makes intuitive sense as if a region is better at accepting electrons than donating, then the LUMO must dominate and dual descriptor function will be positive. Conversely, if a region is better at donating electrons then the HOMO term will dominate and the descriptor will be negative. Notice that although the concept of phase and orbitals are replaced simply by the notion of electron density, this function still takes both positive and negative values.
The Woodward–Hoffmann rules are reinterpreted using this formulation by matching favorable interactions between regions of electron density for which the dual descriptor has opposite signs. This is equivalent to maximizing predicted favorable interactions and minimizing repulsive interactions. For the case of a [4+2] cycloaddition, a simplified schematic of the reactants with the dual descriptor function colored (red=positive, blue=negative) is shown in the optimal supra/supra configuration to the left. This method correctly predicts the WH rules for the major classes of pericyclic reactions. | 0 | Theoretical and Fundamental Chemistry |
A heterogeneous mixture (e. g. liquid and solid) can be separated by mechanical separation processes like filtration or centrifugation. Homogeneous mixtures can be separated by molecular separation processes; these are either equilibrium-based or rate-controlled. Equilibrium-based processes are operating by the formation of two immiscible phases with different compositions at equilibrium, an example is distillation (in distillation the vapor has another composition than the liquid). Rate-controlled processes are based on different transport rates of compounds through a medium, examples are adsorption, ion exchange or crystallization.
Separation of a mixture into two phases can be done by an energy separating agent, a mass separating agent, a barrier or external fields. Energy-separating agents are used for creating a second phase (immiscible of different composition than the first phase), they are the most common techniques used in industry. For example, leads the addition of heat (the separating agent) to a liquid (first phase) to the formation of vapor (second phase). Mass-separating agents are other chemicals. They selectively dissolve or absorb one of the products; they are either a liquid (for sorption, extractive distillation or extraction) or a solid (for adsorption or ion exchange). The use of a barrier which restricts the movement of one compound but not of the other one (semipermeable membranes) is less common; external fields are used just in special applications. | 0 | Theoretical and Fundamental Chemistry |
Margaret was an only child, born in Berkeley, California to mother Margaret Orchard and father John Melhase, who worked as a geologist.
During her time at UC Berkeley, Melhase was a member of the Berkeley Folk Dancers and edited the group's newsletter. She met mathematics professor Robert A. Fuchs at a folk dance, and the two married in 1945 and had three children. She and her husband moved to Los Angeles. She was a supporter of social causes, organizing marches for agricultural workers and housing and aiding immigrant Laotian families in Los Angeles. | 0 | Theoretical and Fundamental Chemistry |
TopFIND is a resource for comprehensive coverage of protein N- and C-termini discovered by all available in silico, in vitro as well as in vivo methodologies. It makes use of existing knowledge by seamless integration of data from UniProt and MEROPS and provides access to new data from community submission and manual literature curating. It renders modifications of protein termini, such as acetylation and citrullination, easily accessible and searchable and provides the means to identify and analyse extend and distribution of terminal modifications across a protein. Since its inception TopFIND has been expanded to further species. | 1 | Applied and Interdisciplinary Chemistry |
The coffee-ring pattern originates from the capillary flow induced by the evaporation of the drop: liquid evaporating from the edge is replenished by liquid from the interior. The resulting current can carry nearly all the dispersed material to the edge. As a function of time, this process exhibits a "rush-hour" effect, that is, a rapid acceleration of the flow towards the edge at the final stage of the drying process.
Evaporation induces a Marangoni flow inside a droplet. The flow, if strong, redistributes particles back to the center of the droplet. Thus, for particles to accumulate at the edges, the liquid must have a weak Marangoni flow, or something must occur to disrupt the flow. For example, surfactants can be added to reduce the liquid's surface tension gradient, disrupting the induced flow. Water has a weak Marangoni flow to begin with, which is then reduced significantly by natural surfactants.
Interaction of the particles suspended in a droplet with the free surface of the droplet is important in creating a coffee ring. "When the drop evaporates, the free surface collapses and traps the suspended particles ... eventually all the particles are captured by the free surface and stay there for the rest of their trip towards the edge of the drop." This result means that surfactants can be used to manipulate the motion of the solute particles by changing the surface tension of the drop, rather than trying to control the bulk flow inside the drop. A number of interesting morphologies of the deposited particles can result. For example, an enantiopure poly (isocyanate) derivative has been shown to form ordered arrays of squashed donut structures. | 0 | Theoretical and Fundamental Chemistry |
Both HHV and LHV can be expressed in terms of AR (all moisture counted), MF and MAF (only water from combustion of hydrogen). AR, MF, and MAF are commonly used for indicating the heating values of coal:
* AR (as received) indicates that the fuel heating value has been measured with all moisture- and ash-forming minerals present.
* MF (moisture-free) or dry indicates that the fuel heating value has been measured after the fuel has been dried of all inherent moisture but still retaining its ash-forming minerals.
* MAF (moisture- and ash-free) or DAF (dry and ash-free) indicates that the fuel heating value has been measured in the absence of inherent moisture- and ash-forming minerals. | 0 | Theoretical and Fundamental Chemistry |
Once the soluble compounds from the creosote preservative leach into the water, the compounds begin reacting with the external environment or are consumed by organisms. The reactions vary depending on the concentration of each compound that is released from the creosote, but major reactions are outlined below: | 0 | Theoretical and Fundamental Chemistry |
It has been shown that the activity of the sorbent reduces quite markedly in laboratory, bench-scale and pilot plant tests. This degradation has been attributed to three main mechanisms, as shown below. | 1 | Applied and Interdisciplinary Chemistry |
During a meeting of the New York Academy of Sciences Section of Geology and Mineralogy in 1903, geologist Amadeus William Grabau proposed a new rock classification system in his paper Discussion of and Suggestions Regarding a New Classification of Rocks'. Within the primary subdivision of "Endogenetic rocks" – rocks formed through chemical processes – was a category termed "Biogenic rocks", which was used synonymously with "Organic rocks". Other secondary categories were "Igneous" and "Hydrogenic" rocks.
In the 1930s German chemist Alfred E. Treibs first detected biogenic substances in petroleum as part of his studies of porphyrins. Based on this research, there was a later increase in the 1970s in the investigation of biogenic substances in sedimentary rocks as part of the study of geology. This was facilitated by the development of more advanced analytical methods, and led to greater collaboration between geologists and organic chemists in order to research the biogenic compounds in sediments.
Researchers additionally began to investigate the production of compounds by microorganisms in the marine environment during the early 1960s. By 1975, different research areas had developed in the study of marine biochemistry. These were "marine toxins, marine bioproducts and marine chemical ecology". Following this in 1994, Teuscher and Lindequist defined biogenic substances as "chemical compounds which are synthesised by living organisms and which, if they exceed certain concentrations, cause temporary or permanent damage or even death of other organisms by chemical or physicochemical effects" in their book, Biogene Gifte. This emphasis in research and classification on the toxicity of biogenic substances was partly due to the cytotoxicity-directed screening assays that were used to detect the biologically active compounds. The diversity of biogenic products has since been expanded from cytotoxic substances through the use of alternative pharmaceutical and industrial assays. | 0 | Theoretical and Fundamental Chemistry |
It is possible to do these simple calculations on paper or to use software. A program which does it can be obtained free of charge. In 2020 David Brown published a nearly comprehensive set of bond valence parameters on the IuCr web site. | 0 | Theoretical and Fundamental Chemistry |
The mammalian target of rapamycin (mTOR), also referred to as the mechanistic target of rapamycin, and sometimes called FK506-binding protein 12-rapamycin-associated protein 1 (FRAP1), is a kinase that in humans is encoded by the MTOR gene. mTOR is a member of the phosphatidylinositol 3-kinase-related kinase family of protein kinases.
mTOR links with other proteins and serves as a core component of two distinct protein complexes, mTOR complex 1 and mTOR complex 2, which regulate different cellular processes. In particular, as a core component of both complexes, mTOR functions as a serine/threonine protein kinase that regulates cell growth, cell proliferation, cell motility, cell survival, protein synthesis, autophagy, and transcription. As a core component of mTORC2, mTOR also functions as a tyrosine protein kinase that promotes the activation of insulin receptors and insulin-like growth factor 1 receptors. mTORC2 has also been implicated in the control and maintenance of the actin cytoskeleton. | 1 | Applied and Interdisciplinary Chemistry |
In this group of mechanisms, the strain is accommodated by migration of vacancies in crystallographic lattice. This results in a change in crystal shape involving the transfer of mass by diffusion. These migrations are oriented towards sites of maximum stress and are limited by the grain boundaries; which conditions a crystallographic shape fabric or strain. The result is a more perfect crystal. This process is grain-size sensitive and occurs at low strain rates or very high temperatures, and is accommodated by migration of lattice defects from areas of low to those of high compressive stress. The main mechanisms of diffusive mass transfer are Nabarro-Herring creep, Coble creep, and pressure solution.
Nabarro–herring creep, or volume diffusion, acts at high homologous temperatures and is grain size dependent with the strain-rate inversely proportional to the square of the grain size (creep rate decreases as the grain size increases). During Nabarro-Herring creep, the diffusion of vacancies occurs through the crystal lattice (microtectonics), which causes grains to elongate along the stress axis. Nabarro-Herring creep has a weak stress dependence.
Coble creep, or grain-boundary diffusion, is the diffusion of vacancies occurs along grain-boundaries to elongate the grains along the stress axis. Coble creep has a stronger grain-size dependence than Nabarro–Herring creep, and occurs at lower temperatures while remaining temperature dependent. It play a more important role than Nabarro–Herring creep and is more important in the deformation of the plastic crust. | 1 | Applied and Interdisciplinary Chemistry |
Some alternatives to IVF are:
*Artificial insemination, including intracervical insemination and intrauterine insemination of semen. It requires that a woman ovulates, but is a relatively simple procedure, and can be used in the home for self-insemination without medical practitioner assistance. The beneficiaries of artificial insemination are people who desire to give birth to their own child who may be single, people who are in a lesbian relationship or females who are in a heterosexual relationship but with a male partner who is infertile or who has a physical impairment which prevents full intercourse from taking place.
*Ovulation induction (in the sense of medical treatment aiming for the development of one or two ovulatory follicles) is an alternative for people with anovulation or oligoovulation, since it is less expensive and more easy to control. It generally involves antiestrogens such as clomifene citrate or letrozole, and is followed by natural or artificial insemination.
*Surrogacy, the process in which a surrogate agrees to bear a child for another person or persons, who will become the child's parent(s) after birth. People may seek a surrogacy arrangement when pregnancy is medically impossible, when pregnancy risks are too dangerous for the intended gestational carrier, or when a single man or a male couple wish to have a child.
*Adoption whereby a person assumes the parenting of another, usually a child, from that person's biological or legal parent or parents. | 1 | Applied and Interdisciplinary Chemistry |
Sacrificial writing into function tissue (SWIFT) is a method of organ printing where living cells are packed tightly to mimic the density that occurs in the human body. While packing, tunnels are carved to mimic blood vessels and oxygen and essential nutrients are delivered via these tunnels. This technique pieces together other methods that only packed cells or created vasculature. SWIFT combines both and is an improvement that brings researchers closer to creating functional artificial organs. | 1 | Applied and Interdisciplinary Chemistry |
Reagent grade detergents are employed for the isolation and purification of integral membrane proteins found in biological cells. Solubilization of cell membrane bilayers requires a detergent that can enter the inner membrane monolayer. Advancements in the purity and sophistication of detergents have facilitated structural and biophysical characterization of important membrane proteins such as ion channels also the disrupt membrane by binding lipopolysaccharide, transporters, signaling receptors, and photosystem II. | 0 | Theoretical and Fundamental Chemistry |
Aminosulfuranes compare favorably with many of the other fluorination methods available. They are easier to handle than sulfur tetrafluoride; however SF does not promote cationic rearrangements. With respect to carboxylic acids, aminosulfuranes and SF are complementary: the former gives acid fluorides, while the latter gives trifluoromethyl compounds.
Perfluorinated alkylamines, such as Ishikawas reagent (N,N'-diethyl-1,1,2,3,3,3-hexafluoropropylamine WRONG MOLECULE IN SCHEME BELOW), are highly selective for hydroxyl groups and do not react with aldehydes and ketones. The amide byproducts of these reagents, however, are harder to separate from the desired products than aminosulfurane byproducts.
Alkali and tetraalkylammonium fluorides can be used to displace sulfonate esters; however, these reactions require higher temperatures than aminosulfurane fluorination of the corresponding free alcohols. | 0 | Theoretical and Fundamental Chemistry |
Polypropylene is suitable for use with foodstuffs, potable and ultra pure waters, as well as within the pharmaceutical and chemical industries.
PP is a thermoplastic polymer made from polypropylene. It was first invented in the 1950s and has been used for pipes since the 1970s. Due to the high impact resistance combined with good stiffness and high chemical resistance makes this material suitable for sewer applications. A good performance at operating temperature range from up to (continuous) makes this material suitable for in-house discharge systems for soil & waste. A special PP grade with high temperature behaviour up to (short-term) makes that material a good choice for in-house warm water supply. | 1 | Applied and Interdisciplinary Chemistry |
Archaeometallurgical experimentation typically takes place in controlled laboratories or tries to remain as authentic as possible by being conducted using only the materials and facilities that were available to the subjects whose technology is trying to be reconstructed. Regardless of location though, the experimentation is always conducted under a different mindset outside the context of what was originally intended. A constant problem in any type of experimental archaeology is the cultural distance between the archaeologist and the individual who originally was involved with the metallurgy. This difference in mindset may lead to misunderstandings in the processes behind the metallurgy. Second to this, not all experiments are successful and it is hard to determine if this is the fault of the techniques used or the individual conducting the experiment. | 1 | Applied and Interdisciplinary Chemistry |
Although black lights produce light in the UV range, their spectrum is mostly confined to the longwave UVA region, that is, UV radiation nearest in wavelength to visible light, with low frequency and therefore relatively low energy. While low, there is still some power of a conventional black light in the UVB range. UVA is the safest of the three spectra of UV light, although high exposure to UVA has been linked to the development of skin cancer in humans. The relatively low energy of UVA light does not cause sunburn. UVA is capable of causing damage to collagen fibers, however, so it does have the potential to accelerate skin aging and cause wrinkles. UVA can also destroy vitamin A in the skin.
UVA light has been shown to cause DNA damage, but not directly, like UVB and UVC. Due to its longer wavelength, it is absorbed less and reaches deeper into skin layers, where it produces reactive chemical intermediates such as hydroxyl and oxygen radicals, which in turn can damage DNA and result in a risk of melanoma. The weak output of black lights, however, is not considered sufficient to cause DNA damage or cellular mutations in the way that direct summer sunlight can, although there are reports that overexposure to the type of UV radiation used for creating artificial suntans on sunbeds can cause DNA damage, photoaging (damage to the skin from prolonged exposure to sunlight), toughening of the skin, suppression of the immune system, cataract formation and skin cancer.
UV-A can have negative effects on eyes in both the short-term and long-term. | 0 | Theoretical and Fundamental Chemistry |
Manganese is found in leafy green vegetables, fruits, nuts, cinnamon and whole grains. The nutritious kernel, called wheat germ, which contains the most minerals and vitamins of the grain, has been removed from most processed grains (such as white bread). The wheat germ is often sold as livestock feed. Many common vitamin and mineral supplement products fail to include manganese in their compositions. Relatively high dietary intake of other minerals such as iron, magnesium, and calcium may inhibit the proper intake of manganese. | 1 | Applied and Interdisciplinary Chemistry |
In the Middle Bronze (MB) Age (end of 3rd–middle of 2nd millennium BCE) hundreds of metal objects were found. The development of more complex weapons (longer daggers, swords, complex battle axes, etc.) was possible by alloying the copper with arsenic or with tin. All the MBII weapons that were analyzed were made of copper alloyed either with tin (14%–2% Sn) or with arsenic (4.3%–0.5% As), sometimes with a mixture of both usually in low concentrations. These changes in the metal properties of weapons are also reflected in the composition of small objects, like toggle pins that were probably made mainly from re-melting of scrap. Lead (Pb) started to play a greater role as a major alloy for thick casts of copper-based objects, mainly of battle axes during this period.
Although two definite major alloying compositions for the production of MBII copper-based artifacts, (1)copper with arsenic and (2) copper with tin, are detected, to date no visible connection of specific alloy with specific type of object or different periods has been seen: both alloys appear in similar objects and in burials dated to the beginning as well as to later parts of the ca. 400 years of the MBII age. Currently, there is no visible correlation between any specific alloying tradition and the spatial distribution of finds, as well. Similar objects made of arsenical coppers and of tin bronze were found in the same geographic region and identical objects with similar metal composition were found in distant areas like Palestine and Upper Egypt. The difference in the overall alloying pattern curve in Jericho and in Tell El-Dab'a shown by Philip (1995) does not necessarily have to be related to two different production centers, but could as well be the result of comparing different groups of objects (i.e., more prestigious weapons of control alloying either with tin or with arsenic) at Tell El Dab’a and similar objects mixed with simpler copper-based ones (like simple daggers, knives, toggle pins, etc.) in Jericho and/or types like the spearheads that have more mixed, low levels of both alloys.
The examination of metal composition in the formation of different types does add knowledge concerning production modes. The thicker the object is, the more lead was
deliberately added to the cast. The highest amounts of lead were measured in the duckbill axes, less in the flat socketed axes, and much less in thinner blades like spears and daggers, which were much more worked and annealed after being cast. This observation corresponds well with the controlled alloying of the duckbill axes and ribbed daggers (with much less lead in the latter) from the MBIIa, but does not correspond with the spears. Although they are derived mainly from MBIIa contexts, their composition is less controlled and more varied. There might be a connection between the level of allowing control and the investment in the cast — the more complex types, like duckbill and flat socketed axes and ribbed daggers, are usually cast in steatite, two-piece closed and well-carved moulds.
On the other hand, some of the less controlled alloyed types, like spearheads and knives as well as more simple tools such as chisel points, were mainly cast into open, relatively roughly carved limestone moulds. | 1 | Applied and Interdisciplinary Chemistry |
All crystal structures belong to one of thirty-two crystal classes based on the number of rotational axes and reflection planes they possess that leave the crystal structure unchanged (point groups). Of the thirty-two crystal classes, twenty-one are non-centrosymmetric (not having a centre of symmetry). Of these twenty-one, twenty exhibit direct piezoelectricity, the remaining one being the cubic class 432. Ten of these twenty piezoelectric classes are polar, i.e., they possess a spontaneous polarization, having a dipole in their unit cell, and exhibit pyroelectricity. If this dipole can be reversed by the application of an electric field, the material is said to be ferroelectric. Any dielectric material develops a dielectric polarization (electrostatics) when an electric field is applied, but a substance which has such a natural charge separation even in the absence of a field is called a polar material. Whether or not a material is polar is determined solely by its crystal structure. Only 10 of the 32 point groups are polar. All polar crystals are pyroelectric, so the ten polar crystal classes are sometimes referred to as the pyroelectric classes.
Piezoelectric crystal classes: 1, 2, m, 222, mm2, 4, -4, 422, 4mm, -42m, 3, 32, 3m, 6, -6, 622, 6mm, -62m, 23, -43m
Pyroelectric: 1, 2, m, mm2, 3, 3m, 4, 4mm, 6, 6mm | 0 | Theoretical and Fundamental Chemistry |
Mediator is a crucial component for transcription initiation. Mediator interacts with the pre-initiation complex, composed of RNA Polymerase II and general transcription factors TFIIB, TFIID, TFIIE, TFIIF, and TFIIH to stabilize and initiate transcription. Studies of Mediator-RNA Pol II contacts in budding yeast have emphasized the importance of TFIIB-Mediator contacts in the formation of the complex. Interactions of Mediator with TFIID in the initiation complex has been shown.
The Structure of a core Mediator (cMed) that's associated with a core pre-initiation complex was elucidated. | 1 | Applied and Interdisciplinary Chemistry |
Copper can exist in non-ionic form (as Cu) or in one of two redox states: Cu (reduced) or Cu (oxidized). Each form of Cu has a specific distribution of electrons (i.e., electron configuration), tabulated below:
The electronic configurations of Cu control the number and types of bonds Cu can form with other atoms (e.g., see Copper Biology section). These diverse coordination chemistries are what enable Cu to participate in many different biological and chemical reactions.
Finally, due to its full d-orbital, Cu has diamagnetic resonance. In contrast, Cu has one unpaired electron in its d-orbital, giving it paramagnetic resonance. The different resonances of the Cu ions enable determination of Cu's redox state by techniques such as electron paramagnetic resonance (epr) spectroscopy, which can identify atoms with unpaired electrons by exciting electron spins. | 0 | Theoretical and Fundamental Chemistry |
In chemistry and fluid mechanics, the volume fraction is defined as the volume of a constituent V divided by the volume of all constituents of the mixture V prior to mixing:
Being dimensionless, its unit is 1; it is expressed as a number, e.g., 0.18. It is the same concept as volume percent (vol%) except that the latter is expressed with a denominator of 100, e.g., 18%.
The volume fraction coincides with the volume concentration in ideal solutions where the volumes of the constituents are additive (the volume of the solution is equal to the sum of the volumes of its ingredients).
The sum of all volume fractions of a mixture is equal to 1:
The volume fraction (percentage by volume, vol%) is one way of expressing the composition of a mixture with a dimensionless quantity; mass fraction (percentage by weight, wt%) and mole fraction (percentage by moles, mol%) are others. | 0 | Theoretical and Fundamental Chemistry |
The strength and directionality of halogen bonds are a key tool in the discipline of crystal engineering, which attempts to shape crystal structures through close control of intermolecular interactions. Halogen bonds can stabilize copolymers or induce mesomorphism in otherwise isotropic liquids. Indeed, halogen bond-induced liquid crystalline phases are known in both alkoxystilbazoles and silsesquioxanes (pictured). Alternatively, the steric sensitivity of halogen bonds can cause bulky molecules to crystallize into porous structures; in one notable case, halogen bonds between iodine and aromatic π-orbitals caused molecules to crystallize into a pattern that was nearly 40% void. | 0 | Theoretical and Fundamental Chemistry |
Consider a planar disk of infinite radius rotating at a constant angular velocity in fluid which is initially at rest everywhere. Near to the surface, the fluid is being turned by the disk, due to friction, which then causes centrifugal forces which move the fluid outwards. This outward radial motion of the fluid near the disk must be accompanied by an inward axial motion of the fluid towards the disk to conserve mass. Theodore von Kármán noticed that the governing equations and the boundary conditions allow a solution such that and are functions of only, where are the velocity components in cylindrical coordinate with being the axis of rotation and represents the plane disk. Due to symmetry, pressure of the fluid can depend only on radial and axial coordinate .
Then the continuity equation and the incompressible Navier–Stokes equations reduce to
where is the kinematic viscosity. | 1 | Applied and Interdisciplinary Chemistry |
In vertebrates, ferritin is usually found within cells, although it is also present in smaller quantities in the plasma. | 1 | Applied and Interdisciplinary Chemistry |
In Japan, with the passage of the 2003 Soil Contamination Countermeasures Law, there is a strong movement to conduct Phase I studies more routinely. At least one jurisdiction in Canada (Ontario) now requires the completion of a Phase I prior to the transfer of some types of industrial properties. Some parts of Europe began to conduct Phase I studies on selected properties in the 1990s, but still lack the comprehensive attention given to virtually all major real estate transactions in the USA.
In the United Kingdom contaminated land regulation is outlined in the Environment Act 1995. The Environment Agency of England and Wales have produced a set of guidance; CLEA a standardized approach to the assessment of land contamination. A Phase 1 Desktop Study is often required in support of a planning application. These reports must be assembled by a "competent person". | 1 | Applied and Interdisciplinary Chemistry |
The standard pressure, , is used to define the reference state for the Van 't Hoff equation, which is
where denotes the natural logarithm, is the thermodynamic equilibrium constant, and is the ideal gas constant. This equation is exact at any one temperature and all pressures, derived from the requirement that the Gibbs free energy of reaction be stationary in a state of chemical equilibrium.
In practice, the equation is often integrated between two temperatures under the assumption that the standard reaction enthalpy is constant (and furthermore, this is also often assumed to be equal to its value at standard temperature). Since in reality and the standard reaction entropy do vary with temperature for most processes, the integrated equation is only approximate. Approximations are also made in practice to the activity coefficients within the equilibrium constant.
A major use of the integrated equation is to estimate a new equilibrium constant at a new absolute temperature assuming a constant standard enthalpy change over the temperature range. To obtain the integrated equation, it is convenient to first rewrite the Van 't Hoff equation as
The definite integral between temperatures and is then
In this equation is the equilibrium constant at absolute temperature , and is the equilibrium constant at absolute temperature . | 0 | Theoretical and Fundamental Chemistry |
Cyanate esters can be cured and postcured by heating, either alone at elevated temperatures or at lower temperatures in presence of a suitable catalyst. The most common catalysts are transition metal complexes of cobalt, copper, manganese and zinc. The result is a thermoset material with a very high glass-transition temperature (T) of up to 400 °C, and a very low dielectric constant, providing excellent long term thermal stability at elevated end use temperatures, very good fire, smoke and toxicity performance and specific suitability for printed circuit boards installed in critical electrical devices. This is also due to its low moisture uptake.
This property, together with a higher toughness compared to epoxies, also makes it a valuable material in aerospace applications. For example, the Lynx Mark II spaceplane is primarily made of carbon/cyanate ester.
The chemistry of the cure reaction is a trimerization of three CN groups to a triazine ring. When the monomer contains two cyanate groups the resulting structure is a 3D polymer network. Thermoset polymer matrix properties can be fine tuned by the choice of substituents in the bisphenolic compound. Bisphenol A and novolac based cyanate esters are the major products; bisphenol F and bisphenol E are also used. The aromatic ring of the bisphenol can be substituted with an allylic group for improved toughness of the material. Cyanate esters can also be mixed with bismaleimides to form BT-resins or with epoxy resins to optimize the end use properties. | 0 | Theoretical and Fundamental Chemistry |
* Soil applied: Herbicides applied to the soil are usually taken up by the root or shoot of the emerging seedlings and are used as preplant or preemergence treatment. Several factors influence the effectiveness of soil-applied herbicides. Weeds absorb herbicides by both passive and active mechanisms. Herbicide adsorption to soil colloids or organic matter often reduces the amount available for weed absorption. Positioning of the herbicide in the correct layer of soil is very important, which can be achieved mechanically and by rainfall. Herbicides on the soil surface are subjected to several processes that reduce their availability. Volatility and photolysis are two common processes that reduce the availability of herbicides. Many soil-applied herbicides are absorbed through plant shoots while they are still underground leading to their death or injury. EPTC and trifluralin are soil-applied herbicides.
* Foliar applied: These are applied to a portion of the plant above the ground and are absorbed by exposed tissues. These are generally postemergence herbicides and can either be translocated (systemic) throughout the plant or remain at a specific site (contact). External barriers of plants like cuticles, waxes, cell walls etc. affect herbicide absorption and action. Glyphosate, 2,4-D, and dicamba are foliar-applied herbicides. | 1 | Applied and Interdisciplinary Chemistry |
In this technique the cells are lysed in alkaline conditions. The DNA in the mixture is denatured (strands separated) by disrupting the hydrogen bonds between the two strands. The large genomic DNA is subject to tangling and staying denatured when the pH is lowered during the neutralization. In other words, the strands come back together in a disordered fashion, basepairing randomly. The circular supercoiled plasmids' strands will stay relatively closely aligned and will renature correctly. Therefore, the genomic DNA will form an insoluble aggregate and the supercoiled plasmids will be left in solution. This can be followed by phenol extraction to remove proteins and other molecules. Then the DNA can be subjected to ethanol precipitation to concentrate the sample. | 1 | Applied and Interdisciplinary Chemistry |
Ruthenium forms highly active catalysts. Allowing milder operating pressures and temperatures, Ru-based materials are referred to as second-generation catalysts. Such catalysts are prepared by the decomposition of triruthenium dodecacarbonyl on graphite. A drawback of activated-carbon-supported ruthenium-based catalysts is the methanation of the support in the presence of hydrogen. Their activity is strongly dependent on the catalyst carrier and the promoters. A wide range of substances can be used as carriers, including carbon, magnesium oxide, aluminium oxide, zeolites, spinels, and boron nitride.
Ruthenium-activated carbon-based catalysts have been used industrially in the KBR Advanced Ammonia Process (KAAP) since 1992. The carbon carrier is partially degraded to methane; however, this can be mitigated by a special treatment of the carbon at 1500 °C, thus prolonging the catalyst lifetime. In addition, the finely dispersed carbon poses a risk of explosion. For these reasons and due to its low acidity, magnesium oxide has proven to be a good choice of carrier. Carriers with acidic properties extract electrons from ruthenium, make it less reactive, and have the undesirable effect of binding ammonia to the surface. | 0 | Theoretical and Fundamental Chemistry |
In fluid dynamics, inviscid flow is the flow of an inviscid fluid which is a fluid with zero viscosity.
The Reynolds number of inviscid flow approaches infinity as the viscosity approaches zero. When viscous forces are neglected, such as the case of inviscid flow, the Navier–Stokes equation can be simplified to a form known as the Euler equation. This simplified equation is applicable to inviscid flow as well as flow with low viscosity and a Reynolds number much greater than one. Using the Euler equation, many fluid dynamics problems involving low viscosity are easily solved, however, the assumed negligible viscosity is no longer valid in the region of fluid near a solid boundary (the boundary layer) or, more generally in regions with large velocity gradients which are evidently accompanied by viscous forces.
The flow of a superfluid is inviscid.
Inviscid flows are broadly classified into potential flows (or, irrotational flows) and rotational inviscid flows. | 1 | Applied and Interdisciplinary Chemistry |
Thiourea is employed as a source of sulfide, such as for converting alkyl halides to thiols. The reaction capitalizes on the high nucleophilicity of the sulfur center and easy hydrolysis of the intermediate isothiouronium salt:
In this example, ethane-1,2-dithiol is prepared from 1,2-dibromoethane:
Like other thioamides, thiourea can serve as a source of sulfide upon reaction with metal ions. For example, mercury sulfide forms when mercuric salts in aqueous solution are treated with thiourea:
These sulfiding reactions, which have been applied to the synthesis of many metal sulfides, require water and typically some heating. | 0 | Theoretical and Fundamental Chemistry |
The p3 protein is anchored to one end of the virion by the C-terminal domain of p3. Infection of host bacteria involves interaction of two different N-terminal regions of p3 with two different sites of the host bacteria. First, the N2 domain of p3 attaches to the outer tip of the F-pilus, and the pilus retracts into the cell. This retraction may involve depolymerization of the pilus subunit assembly into the cell membrane at the base of the pilus by a reversal of the pilus growth and polymerization process. As the tip of the pilus bearing p3 approaches the cell wall, the N1 domain of p3 interacts with the bacterial TolQRA protein to complete infection and release the genome into the cytoplasm of the host. | 1 | Applied and Interdisciplinary Chemistry |
The starting material for calcium looping is limestone, which is environmentally benign and widely available, accounting for over 10% (by volume) of all sedimentary rock. Limestone is already mined and cheaply obtainable. The mining process has no major known adverse environmental effects, beyond the unavoidable intrusiveness of any mining operation. However, as the following calculation shows, despite integration with cement industry, waste from Ca-looping can still be a problem.
From the environmental and health standpoint, Ca-looping compares favorably with amine scrubbing. Amine scrubbing is known to generate air pollutants, including amines and ammonia, which can react to form carcinogenic nitrosamines. Calcium looping, on the other hand, does not produce harmful pollutants. In addition, not only does it capture CO, but it also removes the pollutant SO from the flue gas. This is both an advantage and disadvantage, as the air quality improves, but the captured SO has a detrimental effect on the cement that is generated from the calcium looping wastes. | 1 | Applied and Interdisciplinary Chemistry |
This is a highly competitive area and a number of people claim patents in the field, most notably Alere (formerly Inverness Medical Innovations, now owned by Abbott) who own patents originally filed by Unipath. The US 6,485,982 patent, that has been litigated, expired in 2019. A number of other companies also hold patents in this arena. A group of competitors are challenging the validity of the patents. The original patent is apparently from 1988. | 1 | Applied and Interdisciplinary Chemistry |
In the U.S., a push for revisions of the FD&C Act emerged from Congressional hearings led by Senator Estes Kefauver of Tennessee in 1959. The hearings covered a wide range of policy issues, including advertising abuses, questionable efficacy of drugs, and the need for greater regulation of the industry. While momentum for new legislation temporarily flagged under extended debate, a new tragedy emerged that underscored the need for more comprehensive regulation and provided the driving force for the passage of new laws.
On 12 September 1960, an American licensee, the William S. Merrell Company of Cincinnati, submitted a new drug application for Kevadon (thalidomide), a sedative that had been marketed in Europe since 1956. The FDA medical officer in charge of reviewing the compound, Frances Kelsey, believed that the data supporting the safety of thalidomide was incomplete. The firm continued to pressure Kelsey and the FDA to approve the application until November 1961, when the drug was pulled off the German market because of its association with grave congenital abnormalities. Several thousand newborns in Europe and elsewhere suffered the teratogenic effects of thalidomide. Without approval from the FDA, the firm distributed Kevadon to over 1,000 physicians there under the guise of investigational use. Over 20,000 Americans received thalidomide in this "study," including 624 pregnant patients, and about 17 known newborns suffered the effects of the drug.
The thalidomide tragedy resurrected Kefauver's bill to enhance drug regulation that had stalled in Congress, and the Kefauver-Harris Amendment became law on 10 October 1962. Manufacturers henceforth had to prove to FDA that their drugs were effective as well as safe before they could go on the US market. The FDA received authority to regulate advertising of prescription drugs and to establish good manufacturing practices. The law required that all drugs introduced between 1938 and 1962 had to be effective. An FDA - National Academy of Sciences collaborative study showed that nearly 40 percent of these products were not effective. A similarly comprehensive study of over-the-counter products began ten years later. | 1 | Applied and Interdisciplinary Chemistry |
Alkenes are named for their parent alkane chain with the suffix "-ene" and a numerical root indicating the position of the carbon with the lower number for each double bond in the chain: is but-1-ene.
Multiple double bonds take the form -diene, -triene, etc., with the size prefix of the chain taking an extra "a": is buta-1,3-diene. Simple cis and trans isomers may be indicated with a prefixed cis- or trans-: cis-but-2-ene, trans-but-2-ene. However, cis- and trans- are relative descriptors. It is IUPAC convention to describe all alkenes using absolute descriptors of Z- (same side) and E- (opposite) with the Cahn–Ingold–Prelog priority rules (see alse E–Z notation). | 0 | Theoretical and Fundamental Chemistry |
A different, but related, mechanism is Dexter electron transfer.
An alternative method to detecting protein–protein proximity is the bimolecular fluorescence complementation (BiFC), where two parts of a fluorescent protein are each fused to other proteins. When these two parts meet, they form a fluorophore on a timescale of minutes or hours. | 1 | Applied and Interdisciplinary Chemistry |
Although nearly 100% sulfuric acid solutions can be made, the subsequent loss of sulfur trioxide| at the boiling point brings the concentration to 98.3% acid. The 98.3% grade, which is more stable in storage, is the usual form of what is described as "concentrated sulfuric acid". Other concentrations are used for different purposes. Some common concentrations are:
"Chamber acid" and "tower acid" were the two concentrations of sulfuric acid produced by the lead chamber process, chamber acid being the acid produced in the lead chamber itself (<70% to avoid contamination with nitrosylsulfuric acid) and tower acid being the acid recovered from the bottom of the Glover tower. They are now obsolete as commercial concentrations of sulfuric acid, although they may be prepared in the laboratory from concentrated sulfuric acid if needed. In particular, "10 M" sulfuric acid (the modern equivalent of chamber acid, used in many titrations), is prepared by slowly adding 98% sulfuric acid to an equal volume of water, with good stirring: the temperature of the mixture can rise to 80 °C (176 °F) or higher. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, a methylene bridge, methylene spacer, or methanediyl group is any part of a molecule with formula ; namely, a carbon atom bound to two hydrogen atoms and connected by single bonds to two other distinct atoms in the rest of the molecule. It is the repeating unit in the skeleton of the unbranched alkanes.
A methylene bridge can also act as a bidentate ligand joining two metals in a coordination compound, such as titanium and aluminum in Tebbe's reagent.
A methylene bridge is often called a methylene group or simply methylene, as in "methylene chloride" (dichloromethane ). As a bridge in other compounds, for example in cyclic compounds, it is given the name methano. However, the term methylidene group (not to be confused with the term methylene group, nor the carbene methylidene) properly applies to the group when it is connected to the rest of the molecule by a double bond (), giving it chemical properties very distinct from those of a bridging group. | 0 | Theoretical and Fundamental Chemistry |
Nesslers reagent, named after Julius Neßler (Nessler), is a 0.09 mol/L solution of potassium tetraiodomercurate(II) in 2.5 mol/L potassium hydroxide. This pale solution becomes deeper yellow in the presence of ammonia (). At higher concentrations, a brown precipitate derivative of Millons base () may form. The sensitivity as a spot test is about 0.3 μg Ammonia| in 2 μL.
The brown precipitate is not fully characterized and may vary from to . | 0 | Theoretical and Fundamental Chemistry |
Vacuum ceramic filters are to be found in the following industries:
* paper making
* metallurgy
* water treatment
* chemical
* ore beneficiation process in mining (iron, gold, nickel, copper and quartz).
The process is used during a large continuous process of separating free filtering suspensions where washing is not required. Basically the filter works to separates solid-liquid mixtures by removing the water from mineral concentrates and moulding the feed slurries into pellets. This is accomplished by capillary action under low vacuum pressure. The pelletizing of the slurries is done by adding some solid matter to the sewage sludge so that water can be easily removed from the mixture. Eventually, the final cake products contain very little moisture and can be deposited as sewage. This process is commonly followed by bleaching and heating the cake. The end product of this filtration is a dry cake and filtrate containing no solid product. | 0 | Theoretical and Fundamental Chemistry |
Pyruvate decarboxylation or pyruvate oxidation, also known as the link reaction (or oxidative decarboxylation of pyruvate), is the conversion of pyruvate into acetyl-CoA by the enzyme complex pyruvate dehydrogenase complex.
The reaction may be simplified as:
:Pyruvate + NAD + CoA → Acetyl-CoA + NADH + CO
Pyruvate oxidation is the step that connects glycolysis and the Krebs cycle. In glycolysis, a single glucose molecule (6 carbons) is split into 2 pyruvates (3 carbons each). Because of this, the link reaction occurs twice for each glucose molecule to produce a total of 2 acetyl-CoA molecules, which can then enter the Krebs cycle.
Energy-generating ions and molecules, such as amino acids and carbohydrates, enter the Krebs cycle as acetyl coenzyme A and oxidize in the cycle. The pyruvate dehydrogenase complex (PDC) catalyzes the decarboxylation of pyruvate, resulting in the synthesis of acetyl-CoA, CO, and NADH. In eukaryotes, this enzyme complex regulates pyruvate metabolism, and ensures homeostasis of glucose during absorptive and post-absorptive state metabolism. As the Krebs cycle occurs in the mitochondrial matrix, the pyruvate generated during glycolysis in the cytosol is transported across the inner mitochondrial membrane by a pyruvate carrier under aerobic conditions. | 1 | Applied and Interdisciplinary Chemistry |
After phase II reactions, the xenobiotic conjugates may be further metabolized. A common example is the processing of glutathione conjugates to acetylcysteine (mercapturic acid) conjugates. Here, the γ-glutamate and glycine residues in the glutathione molecule are removed by gamma-glutamyl transpeptidase and dipeptidases. In the final step, the cysteine residue in the conjugate is acetylated.
Conjugates and their metabolites can be excreted from cells in phase III of their metabolism, with the anionic groups acting as affinity tags for a variety of membrane transporters of the multidrug resistance protein (MRP) family. These proteins are members of the family of ATP-binding cassette transporters and can catalyse the ATP-dependent transport of a huge variety of hydrophobic anions, and thus act to remove phase II products to the extracellular medium, where they may be further metabolized or excreted. | 1 | Applied and Interdisciplinary Chemistry |
Reaction (a) is the sum of reactions (b) and (c), for which the total ΔH = −393.5 kJ/mol, which is equal to ΔH in (a).
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In 1999, Meléndez et al claimed that the structure of glycogen is optimal under a particular metabolic constraint model, where the structure was suggested to be "fractal" in nature. However, research by Besford et al used small angle X-ray scattering experiments accompanied by branching theory models to show that glycogen is a randomly hyperbranched polymer nanoparticle. Glycogen is not fractal in nature. This has been subsequently verified by others who have performed Monte Carlo simulations of glycogen particle growth, and shown that the molecular density reaches a maximum near the centre of the nanoparticle structure, not at the periphery (contradicting a fractal structure that would have greater density at the periphery). | 1 | Applied and Interdisciplinary Chemistry |
Rabi resonance method is a technique developed by Isidor Isaac Rabi for measuring the nuclear spin. The atom is placed in a static magnetic field and a perpendicular rotating magnetic field.
We present a classical treatment in here. | 0 | Theoretical and Fundamental Chemistry |
The term wetware is used to describe the protocols and molecular devices used in molecular biology and synthetic biology.
Where biological components and systems are treated in a similar manner to software, and similar development models and methodologies are applied, the term wetware can be used to imply an approach to their problems as bugs and their beneficial aspects as features. In this manner, genetic code can be subjected to Version Control Systems such as Git, for the development of improvements and new gene edits, therapeutic components and therapies. | 1 | Applied and Interdisciplinary Chemistry |
Sumerian cuneiform tablets record prescriptions for medicine.
Ancient Egyptian pharmacological knowledge was recorded in various papyri, such as the Ebers Papyrus of 1550 BC and the Edwin Smith Papyrus of the 16th century BC.
The very beginnings of pharmaceutical texts were written on clay tablets by Mesopotamians. Some texts included formulas, instructions via pulverization, infusion, boiling, filtering and spreading; herbs were mentioned as well. Babylon, a state within Mesopotamia, provided the earliest known practice of running an apothecary i.e. pharmacy. Alongside the ill person included a priest, physician, and a pharmacist to tend to their needs. | 1 | Applied and Interdisciplinary Chemistry |
In contrast to antiporters, symporters move ions or molecules in the same direction. In this case both ions being transported will be moved either from the exoplasmic space into the cytoplasmic space or from the cytoplasmic space into the exoplasmic space. An example of a symporter is the sodium-glucose linked transporter or SGLT. The SGLT functions to couple the transport of sodium in the exoplasmic space down its concentration gradient (again, established by the active transport of sodium out of the cell by the sodium-potassium pump) into the cytoplasmic space to the transport of glucose in the exoplasmic space against its concentration gradient into the cytoplasmic space. The SGLT couples the movement of 1 glucose ion with the movement of 2 sodium ions. | 1 | Applied and Interdisciplinary Chemistry |
Elemental iodine is an oxidizing irritant, and direct contact with skin can cause lesions, so iodine crystals should be handled with care. Solutions with high elemental iodine concentration such as tincture of iodine are capable of causing tissue damage if use for cleaning and antisepsis is prolonged. Although elemental iodine is used in the formulation of Lugols solution, a common medical disinfectant, it becomes triiodide upon reacting with the potassium iodide used in the solution and is therefore non-toxic. Only a small amount of elemental iodine will dissolve in water, but triiodides are highly soluble; potassium iodide thus serves as a phase transfer catalyst in the tincture. This allows Lugols iodine to be produced in strengths varying from 2% to 15% iodine.
Elemental iodine (I) is poisonous if taken orally in large amounts; 2–3 grams is a lethal dose for an adult human.
Iodine vapor is very irritating to the eye, to mucous membranes, and in the respiratory tract. Concentration of iodine in the air should not exceed 1 mg/m (eight-hour time-weighted average).
When mixed with ammonia and water, elemental iodine forms nitrogen triiodide, which is extremely shock-sensitive and can explode unexpectedly. | 1 | Applied and Interdisciplinary Chemistry |
A monovalent ion requires 1 electron for discharge, a divalent ion requires 2 electrons for discharge and so on. Thus, if electrons flow, atoms are discharged.
Thus, the mass discharged is
where
* is the Avogadro constant;
* is the total charge, equal to the number of electrons () times the elementary charge ;
* is the Faraday constant. | 0 | Theoretical and Fundamental Chemistry |
Olfactory processing of chemical signals like pheromones exists in all animal phyla and is thus the oldest of the senses. It has been suggested that it serves survival by generating appropriate behavioral responses to the signals of threat, sex and dominance status among members of the same species.
Furthermore, it has been suggested that in the evolution of unicellular prokaryotes to multicellular eukaryotes, primordial pheromone signaling between individuals may have evolved to paracrine and endocrine signaling within individual organisms.
Some authors assume that approach-avoidance reactions in animals, elicited by chemical cues, form the phylogenetic basis for the experience of emotions in humans. | 1 | Applied and Interdisciplinary Chemistry |
Under the evidence of Jean Baptiste Perrins experiments on Brownian motion that confirmed Albert Einsteins theory, Ostwald renounced to energeticism as physical theory in his fourth edition of Outline of General Chemistry in 1908, embracing atomic theory. However he modified energeticism into an ontological philosophy, supported by the recently discovered Einstein's mass–energy equivalence . | 1 | Applied and Interdisciplinary Chemistry |
Terphthalaldehyde is used in the preparation of imines, which are also commonly referred to as Schiff bases, following a condensation reaction with amines. During this reaction, water is also formed. This reaction is also reversible. However, due to aromatic conjugation with the benzene ring, the imines are relatively stable and will not easily hydrolyse back to the aldehyde. When in an acidic aqueous environment, the imines will start to hydrolyse more easily. Typically, an equilibrium between the imine and aldehyde is formed, which is dependent on the concentration of the relevant compounds and the pH of the solution.
Imines from terephthalaldehyde find use in the preparation of metal-organic coordination complexes. In addition, terepthaldehyde is a commonly used monomer in the production of imine polymers (polyimines), covalent organic frameworks (COFs), and molecular cages. Terephthalaldehyde is also used as an intermediate for the preparation of dyes and fluorescent whitening agents. | 0 | Theoretical and Fundamental Chemistry |
The existence of two or more binding domains increases the difficulty of synthesis for chimeric molecules. Each component must be discovered, optimized, and synthesized in such a way that they can be linked together, driving up cost relative to single-domain inhibitors. The large size of chimeric molecules (typically 700-1100 Da) makes effective delivery difficult and increases complexity in pharmacokinetic design. Care must be taken to ensure that the molecule is capable of passing through the cell membrane and subsisting long enough to have therapeutic effect. Additionally, protein-protein ternary complexes are generally unstable, adding to the difficulty of chimeric drug design | 1 | Applied and Interdisciplinary Chemistry |
Most detection mechanisms involved in small molecule sensors comprise some modulation in the fluorescent behavior of the sensing molecule upon binding the target metal. When a metal coordinates to such a sensor, it may either enhance or reduce the original fluorescent emission. The former is known as the Chelation Enhancement Fluorescence effect (CHEF), while the latter is called the Chelation Enhancement Quenching effect (CHEQ). By changing the intensity of emission at different wavelengths, the resulting fluorescent spectrum may attenuate, amplify, or shift upon the binding and dissociation of a metal. This shift in spectra can be monitored using a detector such as a microscope or a photodiode.
Listed below are some examples of mechanisms by which emission is modulated. Their participation in CHEQ or CHEF is dependent on the metal and small molecule sensor in question. | 0 | Theoretical and Fundamental Chemistry |
When water flows through cracks present in concrete, water may dissolve various minerals present in the hardened cement paste or in the aggregates, if the solution is unsaturated with respect to them. Dissolved ions, such as calcium (Ca), are leached out and transported in solution some distance. If the physico-chemical conditions prevailing in the seeping water evolve with distance along the water path and water becomes supersaturated with respect to certain minerals, they can further precipitate, making calthemite deposits (predominately calcium carbonate) inside the cracks, or at the concrete outer surface. This process can cause the self-healing of fractures in particular conditions.
Fagerlund (2000) determined that, “About 15% of the lime has to be dissolved before strength is affected. This corresponds to about 10% of the cement weight, or almost all of the initially formed Ca(OH).” Therefore, a large amount of "calcium hydroxide" (Ca(OH)) must be leached from the concrete before structural integrity is affected. The other issue however is that leaching away Ca(OH) may allow the corrosion of reinforcing steel to affect structural integrity. | 1 | Applied and Interdisciplinary Chemistry |
In Japan, drugs and medical devices are given the designation as an orphan drug or device based on the Act of Securing Quality, Efficacy, Safety of Pharmaceuticals, Medical Devices, Regenerative or Cellular Therapy Products, Gene Therapy Products, and Cosmetics if they are intended for use in less than 50,000 patients in Japan for which there is a high medical need. | 1 | Applied and Interdisciplinary Chemistry |
Drugs receive regulatory approval and are granted patents for only a single polymorph.
In a classic patent dispute, the GlaxoSmithKline defended its patent for the Type II polymorph of the active ingredient in Zantac against competitors while that of the Type I polymorph had already expired.
Polymorphism in drugs can also have direct medical implications since dissolution rates depend on the polymorph. Polymorphic purity of drug samples can be checked using techniques such as powder X-ray diffraction, IR/Raman
spectroscopy, and utilizing the differences in their optical properties in some cases. | 0 | Theoretical and Fundamental Chemistry |
Deflagrations are often used in engineering applications when the force of the expanding gas is used to move an object such as a projectile down a barrel, or a piston in an internal combustion engine. Deflagration systems and products can also be used in mining, demolition and stone quarrying via gas pressure blasting as a beneficial alternative to high explosives. | 0 | Theoretical and Fundamental Chemistry |
Immediate manifestations of caustic substance ingestions include erosions of mucosal surfaces of the gastrointestinal tract or airway (which can cause bleeding if the erosions extend to a blood vessel), mouth and tongue swelling, drooling or hypersalivation, nausea, vomiting, dyspnea, dysphonia/aphonia irritation of the eyes and skin. Perforation of the esophagus can lead to mediastinitis or perforation of the stomach or bowel can lead to peritonitis Swelling of the airway or laryngospasm can occur leading to compromised breathing. Injuries affecting the respiratory system include aspiration pneumonia and laryngeal sores. Signs of respiratory compromise include stridor and a change in a person's voice.
Later manifestations of caustic substance ingestions include esophageal strictures or stenosis; which can result in chronic pain and malnutrition. Esophageal strictures more commonly occur after more severe mucosal injury, occurring in to 71% and 100% of grade 2b and 3 mucosal lesions respectively. Remote manifestations of caustic ingestions include esophageal cancer. People who have a history of caustic substance ingestion are 1000-3000 times more likely to develop esophageal cancer with most cases occurring 10–30 years after the ingestion. | 1 | Applied and Interdisciplinary Chemistry |
fMRS has several advantages over other functional neuroimaging and brain biochemistry detection techniques.
Unlike push-pull cannula, microdialysis and in vivo voltammetry, fMRS is a non-invasive method for studying dynamics of biochemistry in an activated brain. It is done without exposing subjects to ionizing radiation like it is done in positron emission tomography (PET) or single-photon emission computed tomography (SPECT) studies. fMRS gives a more direct measurement of cellular events occurring during brain activation than BOLD fMRI or PET which rely on hemodynamic responses and show only global neuronal energy uptake during brain activation while fMRS gives also information about underlying metabolic processes that support the working brain.
However, fMRS requires very sophisticated data acquisition, quantification methods and interpretation of results. This is one of the main reasons why in the past it received less attention than other MR techniques, but the availability of stronger magnets and improvements in data acquisition and quantification methods are making fMRS more popular.
Main limitations of fMRS are related to signal sensitivity and the fact that many metabolites of potential interest can not be detected with current fMRS techniques.
Because of limited spatial and temporal resolution fMRS can not provide information about metabolites in different cell types, for example, whether lactate is used by neurons or by astrocytes during brain activation. The smallest volume that can currently be characterized with fMRS is 1 cm, which is too big to measure metabolites in different cell types. To overcome this limitation, mathematical and kinetic modeling is used.
Many brain areas are not suitable for fMRS studies because they are too small (like small nuclei in brainstem) or too close to bone tissue, CSF or extracranial lipids, which could cause inhomogeneity in the voxel and contaminate the spectra. To avoid these difficulties, in most fMRS studies the volume of interest is chosen from the visual cortex – because it is easily stimulated, has high energy metabolisms, and yields good MRS signals. | 0 | Theoretical and Fundamental Chemistry |
As of November 2019, arketamine is under development for the treatment of depression under the developmental code names PCN-101 by Perception Neuroscience in the United States and HR-071603 by Jiangsu Hengrui Medicine in China. | 0 | Theoretical and Fundamental Chemistry |
In the aldol reaction, the diastereoselectivity of the product is often dictated by the geometry of the enolate. The Zimmerman–Traxler model predicts that the Z enolate will give syn products, and that E enolates will give anti products. Reactions catalyzed by tin-based CLAs allow products to deviate from this pattern.
The transition structures for reactions with both the R and S catalyst enantiomers are: | 0 | Theoretical and Fundamental Chemistry |
Taking advantage of the unique tip geometry of the NFP nanomaterials are directly injected into live cells with minimal invasiveness. This enables unique studies of nanoparticle-mediated delivery, as well as cellular pathways and toxicity. Whereas typical in vitro studies are limited to cell populations, these broadly-applicable tools enable multifaceted interrogation at a truly single cell level. | 1 | Applied and Interdisciplinary Chemistry |
Nanocars are a new class of molecular machines that can roll across solid surfaces with structurally defined direction. They are molecules essentially composed of a few tens or hundreds of hydrogen and carbon atoms and are measuring one to three nanometers.
The nanocar is propelled step by step by electrical impulses and electron transfer from the tip of the STM. The resulting tunnel current flows through the nanocar between the tip of the microscope and the common metal track. There is no direct mechanical contact with the tip. The nanocar is therefore neither pushed nor deformed by the tip of the microscope during the race. Some of the electrons that pass through the nanocar release energy as small intramolecular vibrations that activate the nanocar's motor. | 0 | Theoretical and Fundamental Chemistry |
Some authors define stereographic projection from the north pole (0, 0, 1) onto the plane , which is tangent to the unit sphere at the south pole (0, 0, −1). This can be described as a composition of a projection onto the equatorial plane described above, and a homothety from it to the polar plane. The homothety scales the image by a factor of 2 (a ratio of a diameter to a radius of the sphere), hence the values and produced by this projection are exactly twice those produced by the equatorial projection described in the preceding section. For example, this projection sends the equator to the circle of radius 2 centered at the origin. While the equatorial projection produces no infinitesimal area distortion along the equator, this pole-tangent projection instead produces no infinitesimal area distortion at the south pole.
Other authors use a sphere of radius and the plane . In this case the formulae become
In general, one can define a stereographic projection from any point on the sphere onto any plane such that
* is perpendicular to the diameter through , and
* does not contain .
As long as meets these conditions, then for any point other than the line through and meets in exactly one point , which is defined to be the stereographic projection of P onto E. | 0 | Theoretical and Fundamental Chemistry |
After receiving his doctorate in 1952, he remained at TU. He continued his research on the organometallic chemistry of the transition metal. He almost immediately challenged the structure for ferrocene as postulated by Pauson and Keally. Shortly thereafter, he published the structural data of ferrocene and the new complexes nickelocene and cobaltocene. Near the same time, he focused also on the then baffling chemistry resulting from Hein's reactions of chromium(III) chloride with phenylmagnesium bromide. This effort resulted in his isolation of bis(benzene)chromium, foretelling an entirely new class of sandwich complexes. | 0 | Theoretical and Fundamental Chemistry |
NIM811 is a mitochondrial permeability transition inhibitor. Also known as N-methyl-4-isoleucine cyclosporin, it is a four-substituted cyclosporine analogue that binds to cyclophilin, however this binary complex cannot bind to calcineurin, and therefore lacks immunosuppressive activity.
NIM811 is a form of treatment for patients with the hepatitis C virus (HCV). Studies indicate a strong relationship between a treatments cyclophilin binding affinity and suppression of HCV activity. NIM811 is also being studied as a potential treatment to genetic muscular diseases such as Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM) disease, diseases altering the genes for collagen VI production. | 1 | Applied and Interdisciplinary Chemistry |
A bimetallic strip is a strip that consists of two strips of different metals which expand at different rates as they are heated. They are used to convert a temperature change into mechanical displacement. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its initial temperature. The metal with the higher coefficient of thermal expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled.
The invention of the bimetallic strip is generally credited to John Harrison, an eighteenth-century clockmaker who made it for his third marine chronometer (H3) of 1759 to compensate for temperature-induced changes in the balance spring. Harrison's invention is recognized in the memorial to him in Westminster Abbey, England. | 1 | Applied and Interdisciplinary Chemistry |
PAMORAs act by inhibiting the binding of opioids agonist to the μ-opioid receptor (MOR). The objective of PAMORAs treatment is to restore the enteric nervous system function (ENS). The MOR is found in several places in the body and PAMORAs is a competitive antagonist for binding to the receptor. The MORs in the gastrointestinal tract are the main receptors that PAMORAs are intended to block and prevent the binding of opioid agonists. PAMORAs are used in the treatment of opioid-induced bowel dysfunction (OIBD), a potential adverse effect caused by chronic opioid use. PAMORAs act on the three pathophysiological mechanisms of this adverse effect. They act on gut motility, gut secretion and sphincter function.
PAMORAs effect on gut motility is that it can increase the resting tone in the circular muscle layer. The antagonist enhances the effect on tonic inhibition of the muscle tone. This will normalize the tone in the circular muscle layer and therefore prevent opioid-induced rhythmic contractions. When these two factors are combined, it results in decreased transit time. Impliedly these effects will decrease the passive absorption of fluids which helps with decreasing OIBD symptoms such as constipation, gut spasm and abdominal cramp.
PAMORAs effect on gut secretion will help reverse the decreased cAMP formation that opioid agonists induce. Also, the antagonist will establish a normal secretion of chloride. Opioids agonists can also reduce the secretion of peptides by increasing the sympathetic nervous system through the μ-receptors in the ENS, which can lead to drier and harder stool. PAMORAs work against it so the stool becomes softer and less dry.
PAMORAs effect on the function of the sphincter is in theory to regulate the movement coordination. The antagonist can prevent sphincter of Oddi dysfunction that is caused by opioids. Antagonists can also reduce opioid-induced anal sphincter dysfunction. The dysfunction is tied to straining, hemorrhoids and incomplete emptying. | 1 | Applied and Interdisciplinary Chemistry |
Choi Yang-do was born in Seoul, South Korea. He studied agricultural chemistry at Seoul National University (1972-1976) and graduated with a BS degree. From 1976 to 1978 he received a MS degree in biological science from Korea Advanced Institute of Science and Technology (KAIST) and earned
his Ph.D. in biochemistry, molecular biology and cell biology from 1981 to 1985 at Northwestern University in Evanston. | 1 | Applied and Interdisciplinary Chemistry |
Traces of many aldehydes are found in essential oils and often contribute to their favorable odours, e.g. cinnamaldehyde, cilantro, and vanillin. Possibly because of the high reactivity of the formyl group, aldehydes are not common in several of the natural building blocks: amino acids, nucleic acids, lipids. Most sugars, however, are derivatives of aldehydes. These aldoses exist as hemiacetals, a sort of masked form of the parent aldehyde. For example, in aqueous solution only a tiny fraction of glucose exists as the aldehyde. | 0 | Theoretical and Fundamental Chemistry |
A direct repeat occurs when a sequence is repeated with the same pattern downstream. There is no inversion and no reverse complement associated with a direct repeat. The nucleotide sequence written in bold characters signifies the repeated sequence. It may or may not have intervening nucleotides.
Linguistically, a typical direct repeat is comparable to rhyming, as in "time on a dime". | 1 | Applied and Interdisciplinary Chemistry |
The Blepharisma nuclear code (translation table 15) is a genetic code found in the nuclei of Blepharisma. | 1 | Applied and Interdisciplinary Chemistry |
The auxiliary can be removed from the desired amine by treatment with hydrochloric acid in protic solvents.
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After Alexis Moussalli died in 1955, his heirs dismissed SECOR administrators, but the company faced increasing competition and lost market shares.
In 1962, the company was sold to Lafarge laboratories, which were in turn purchased by Sanofi in 1976. Lafarge closed the Vichy factory in 1965 and relocated to Châteauroux. With declining sales, the Tho-Radia brand was finally abandoned in 1968. | 0 | Theoretical and Fundamental Chemistry |
Subsets and Splits