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A metabolic network can be broken down into a stoichiometric matrix where the rows represent the compounds of the reactions, while the columns of the matrix correspond to the reactions themselves. Stoichiometry is a quantitative relationship between substrates of a chemical reaction. In order to deduce what the metabolic network suggests, recent research has centered on a few approaches, such as extreme pathways, elementary mode analysis, flux balance analysis, and a number of other constraint-based modeling methods. | 1 | Applied and Interdisciplinary Chemistry |
In the light-dependent reactions, one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron is taken up by a modified form of chlorophyll called pheophytin, which passes the electron to a quinone molecule, starting the flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP to NADPH. In addition, this creates a proton gradient (energy gradient) across the chloroplast membrane, which is used by ATP synthase in the synthesis of ATP. The chlorophyll molecule ultimately regains the electron it lost when a water molecule is split in a process called photolysis, which releases oxygen.
The overall equation for the light-dependent reactions under the conditions of non-cyclic electron flow in green plants is:
Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with absorption peaks in violet-blue and red light. In red algae, the action spectrum is blue-green light, which allows these algae to use the blue end of the spectrum to grow in the deeper waters that filter out the longer wavelengths (red light) used by above-ground green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms. | 0 | Theoretical and Fundamental Chemistry |
Whereas hyperspectral imaging acquires data as many contiguous spectral bands, full spectral imaging acquires data as spectral curves. A significant advantage of FSI over hyperspectral imaging is a significant reduction in data rate and volume. FSI extracts and saves only the information that is in the raw data. The information is contained in the shape of the spectral curves. The rate at which data is produced by an FSI system is proportional to the amount of information in the scene/image. | 0 | Theoretical and Fundamental Chemistry |
Since the industrial revolution, and especially since the end of WWII, human activity has substantially disturbed the global carbon cycle by redistributing massive amounts of carbon from the geosphere. Humans have also continued to shift the natural component functions of the terrestrial biosphere with changes to vegetation and other land use. Man-made (synthetic) carbon compounds have been designed and mass-manufactured that will persist for decades to millennia in air, water, and sediments as pollutants. Climate change is amplifying and forcing further indirect human changes to the carbon cycle as a consequence of various positive and negative feedbacks. | 0 | Theoretical and Fundamental Chemistry |
After World War II he worked in the laboratory of Prof. UG Bijlsma in the area of adrenergic substances and in 1950 both in the field of chemistry and medical doctorate. In 1951, Everhardus Ariëns moved to Nijmegen after there at the Catholic University of the Faculty of Pharmacology was established. From 1954 until his retirement he was employed there as a professor.
Based on his dissertation, he developed together with Jacques van Rossum, a method for quantification of pharmacological effects as a result of ligand-receptor interactions. The thesis developed the concepts of receptor affinity and intrinsic activity. With the help of these terms he could describe the behavior of agonists and antagonists as well as the dual agonist / antagonist behavior of partial agonists. An important accomplishment of Ariëns was the establishment of experiments on isolated organs instead of the living animal (ex vivo), which quickly and reproducibly delivered data on the affinity and intrinsic activity of test substances.
Everhardus Ariëns was also active in the field of structure-activity relationships (SAR), a branch of medicinal chemistry. With the provocative statement that the then commonly used racemates were drugs with 50% contamination. he triggered a debate among pharmacologists and medicinal chemists and alerted the drug regulators. Everhardus Ariëns was thus the crucial precursor for the targeted development of enantiopure drugs. Another, though less noticed controversy he started by expressing his view that drug metabolism is wasted and called for the development of metabolism-resistant drugs. In addition, he followed in the tradition of Dutch pharmacists to combat quackery. | 0 | Theoretical and Fundamental Chemistry |
In formal mathematical presentations of T-symmetry, three different kinds of notation for T need to be carefully distinguished: the T that is an involution, capturing the actual reversal of the time coordinate, the T that is an ordinary finite dimensional matrix, acting on spinors and vectors, and the T that is an operator on an infinite-dimensional Hilbert space.
For a real (not complex) classical (unquantized) scalar field , the time reversal involution can simply be written as
as time reversal leaves the scalar value at a fixed spacetime point unchanged, up to an overall sign . A slightly more formal way to write this is
which has the advantage of emphasizing that is a map, and thus the "mapsto" notation whereas is a factual statement relating the old and new fields to one-another.
Unlike scalar fields, spinor and vector fields might have a non-trivial behavior under time reversal. In this case, one has to write
where is just an ordinary matrix. For complex fields, complex conjugation may be required, for which the mapping can be thought of as a 2x2 matrix. For a Dirac spinor, cannot be written as a 4x4 matrix, because, in fact, complex conjugation is indeed required; however, it can be written as an 8x8 matrix, acting on the 8 real components of a Dirac spinor.
In the general setting, there is no ab initio value to be given for ; its actual form depends on the specific equation or equations which are being examined. In general, one simply states that the equations must be time-reversal invariant, and then solves for the explicit value of that achieves this goal. In some cases, generic arguments can be made. Thus, for example, for spinors in three-dimensional Euclidean space, or four-dimensional Minkowski space, an explicit transformation can be given. It is conventionally given as
where is the y-component of the angular momentum operator and is complex conjugation, as before. This form follows whenever the spinor can be described with a linear differential equation that is first-order in the time derivative, which is generally the case in order for something to be validly called "a spinor".
The formal notation now makes it clear how to extend time-reversal to an arbitrary tensor field In this case,
Covariant tensor indexes will transform as and so on. For quantum fields, there is also a third T, written as which is actually an infinite dimensional operator acting on a Hilbert space. It acts on quantized fields as
This can be thought of as a special case of a tensor with one covariant, and one contravariant index, and thus two 's are required.
All three of these symbols capture the idea of time-reversal; they differ with respect to the specific space that is being acted on: functions, vectors/spinors, or infinite-dimensional operators. The remainder of this article is not cautious to distinguish these three; the T that appears below is meant to be either or or depending on context, left for the reader to infer. | 0 | Theoretical and Fundamental Chemistry |
Vis viva (from the Latin for "living force") is a historical term used to describe a quantity similar to kinetic energy in an early formulation of the principle of conservation of energy. | 0 | Theoretical and Fundamental Chemistry |
Bacteriophage Φ29 DNA polymerase is a high-processivity enzyme that can produce DNA amplicons greater than 70 kilobase pairs. Its high fidelity and 3’–5 proofreading activity reduces the amplification error rate to 1 in 10−10 bases compared to conventional Taq polymerase with a reported error rate of 1 in 9,000. The reaction can be carried out at a moderate isothermal condition of 30 °C and therefore does not require a thermocycler. It has been actively used in cell-free cloning, which is the enzymatic method of amplifying DNA in vitro without cell culturing and DNA extraction. The large fragment of Bst' DNA polymerase is also used in MDA, but Ф29 is generally preferred due to its sufficient product yield and proofreading activity. | 1 | Applied and Interdisciplinary Chemistry |
One should not assume that a carbonate-silicate cycle would appear on all terrestrial planets. To begin, the carbonate-silicate cycle requires the presence of a water cycle. It therefore breaks down at the inner edge of the Solar System's habitable zone. Even if a planet starts out with liquid water on the surface, if it becomes too warm, it will undergo a runaway greenhouse, losing surface water. Without the requisite rainwater, no weathering will occur to produce carbonic acid from gaseous CO. Furthermore, at the outer edge, CO may condense, consequently reducing the greenhouse effect and reducing the surface temperature. As a result, the atmosphere would collapse into polar caps.
Mars is such a planet. Located at the edge of the solar systems habitable zone, its surface is too cold for liquid water to form without a greenhouse effect. With its thin atmosphere, Mars mean surface temperature is . In attempting to explain topographical features resembling fluvial channels, despite seemingly insufficient incoming solar radiation, some have suggested that a cycle similar to Earth's carbonate-silicate cycle could have existed – similar to a retreat from Snowball Earth periods. It has been shown using modeling studies that gaseous CO and HO acting as greenhouse gases could not have kept Mars warm during its early history when the Sun was fainter because CO would condense out into clouds. Even though CO clouds do not reflect in the same way that water clouds do on Earth, it could not have had much of a carbonate-silicate cycle in the past.
By contrast, Venus is located at the inner edge of the habitable zone and has a mean surface temperature of . After losing its water by photodissociation and hydrogen escape, Venus stopped removing carbon dioxide from its atmosphere, and began instead to build it up, and experience a runaway greenhouse effect.
On tidally locked exoplanets, the location of the substellar point will dictate the release of carbon dioxide from the lithosphere. | 0 | Theoretical and Fundamental Chemistry |
The Bromley equation was developed in 1973 by Leroy A. Bromley with the objective of calculating activity coefficients for aqueous electrolyte solutions whose concentrations are above the range of validity of the Debye–Hückel equation. This equation, together with Specific ion interaction theory (SIT) and Pitzer equations is important for the understanding of the behaviour of ions dissolved in natural waters such as rivers, lakes and sea-water. | 0 | Theoretical and Fundamental Chemistry |
Multiple isoforms of the Fas receptor protein are produced by alternative splicing. Two normally occurring isoforms in humans are produced by an exon-skipping mechanism. An mRNA including exon 6 encodes the membrane-bound form of the Fas receptor, which promotes apoptosis, or programmed cell death. Increased expression of Fas receptor in skin cells chronically exposed to the sun, and absence of expression in skin cancer cells, suggests that this mechanism may be important in elimination of pre-cancerous cells in humans. If exon 6 is skipped, the resulting mRNA encodes a soluble Fas protein that does not promote apoptosis. The inclusion or skipping of the exon depends on two antagonistic proteins, TIA-1 and polypyrimidine tract-binding protein (PTB).
* The 5' donor site in the intron downstream from exon 6 in the pre-mRNA has a weak agreement with the consensus sequence, and is not bound usually by the U1 snRNP. If U1 does not bind, the exon is skipped (see "a" in accompanying figure).
* Binding of TIA-1 protein to an intronic splicing enhancer site stabilizes binding of the U1 snRNP. The resulting 5 donor site complex assists in binding of the splicing factor U2AF to the 3 splice site upstream of the exon, through a mechanism that is not yet known (see b).
* Exon 6 contains a pyrimidine-rich exonic splicing silencer, ure6, where PTB can bind. If PTB binds, it inhibits the effect of the 5' donor complex on the binding of U2AF to the acceptor site, resulting in exon skipping (see c).
This mechanism is an example of exon definition in splicing. A spliceosome assembles on an intron, and the snRNP subunits fold the RNA so that the 5 and 3 ends of the intron are joined. However, recently studied examples such as this one show that there are also interactions between the ends of the exon. In this particular case, these exon definition interactions are necessary to allow the binding of core splicing factors prior to assembly of the spliceosomes on the two flanking introns. | 1 | Applied and Interdisciplinary Chemistry |
The most intense sources of gamma rays, are also the most intense sources of any type of electromagnetic radiation presently known. They are the "long duration burst" sources of gamma rays in astronomy ("long" in this context, meaning a few tens of seconds), and they are rare compared with the sources discussed above. By contrast, "short" gamma-ray bursts of two seconds or less, which are not associated with supernovae, are thought to produce gamma rays during the collision of pairs of neutron stars, or a neutron star and a black hole.
The so-called long-duration gamma-ray bursts produce a total energy output of about 10 joules (as much energy as the Sun will produce in its entire life-time) but in a period of only 20 to 40 seconds. Gamma rays are approximately 50% of the total energy output. The leading hypotheses for the mechanism of production of these highest-known intensity beams of radiation, are inverse Compton scattering and synchrotron radiation from high-energy charged particles. These processes occur as relativistic charged particles leave the region of the event horizon of a newly formed black hole created during supernova explosion. The beam of particles moving at relativistic speeds are focused for a few tens of seconds by the magnetic field of the exploding hypernova. The fusion explosion of the hypernova drives the energetics of the process. If the narrowly directed beam happens to be pointed toward the Earth, it shines at gamma ray frequencies with such intensity, that it can be detected even at distances of up to 10 billion light years, which is close to the edge of the visible universe. | 0 | Theoretical and Fundamental Chemistry |
The magazine was established in 1923, and has been on the internet since 1998.
The editor-in-chief is Nick Ishmael-Perkins. | 1 | Applied and Interdisciplinary Chemistry |
The four most common Maxwell's relations are:
More relations include the following.
Other differential equations are: | 0 | Theoretical and Fundamental Chemistry |
Paramural bodies are membranous or vesicular structures located between the cell walls and cell membranes of plant and fungal cells. When these are continuous with the cell wall, they are termed lomasomes, while they are referred to as plasmalemmasomes if associated with the plasmalemma. | 1 | Applied and Interdisciplinary Chemistry |
Temperature measurement (also known as thermometry) describes the process of measuring a current temperature for immediate or later evaluation. Datasets consisting of repeated standardized measurements can be used to assess temperature trends. | 0 | Theoretical and Fundamental Chemistry |
Electrophoretic mobility is proportional to electrophoretic velocity, which is the measurable parameter. There are several theories that link electrophoretic mobility with zeta potential. They are briefly described in the article on electrophoresis and in details in many books on colloid and interface science.
There is an IUPAC Technical Report prepared by a group of world experts on the electrokinetic phenomena.
From the instrumental viewpoint, there are three different experimental techniques: microelectrophoresis, electrophoretic light scattering, and tunable resistive pulse sensing. Microelectrophoresis has the advantage of yielding an image of the moving particles. On the other hand, it is complicated by electro-osmosis at the walls of the sample cell. Electrophoretic light scattering is based on dynamic light scattering. It allows measurement in an open cell which eliminates the problem of electro-osmotic flow except for the case of a capillary cell. And, it can be used to characterize very small particles, but at the price of the lost ability to display images of moving particles. Tunable resistive pulse sensing (TRPS) is an impedance-based measurement technique that measures the zeta potential of individual particles based on the duration of the resistive pulse signal. The translocation duration of nanoparticles is measured as a function of voltage and applied pressure. From the inverse translocation time versus voltage-dependent electrophoretic mobility, and thus zeta potentials are calculated. The main advantage of the TRPS method is that it allows for simultaneous size and surface charge measurements on a particle-by-particle basis, enabling the analysis of a wide spectrum of synthetic and biological nano/microparticles and their mixtures.
All these measuring techniques may require dilution of the sample. Sometimes this dilution might affect properties of the sample and change zeta potential. There is only one justified way to perform this dilution – by using equilibrium supernatant. In this case, the interfacial equilibrium between the surface and the bulk liquid would be maintained and zeta potential would be the same for all volume fractions of particles in the suspension. When the diluent is known (as is the case for a chemical formulation), additional diluent can be prepared. If the diluent is unknown, equilibrium supernatant is readily obtained by centrifugation. | 0 | Theoretical and Fundamental Chemistry |
Eoxin D4, also known as 14,15-leukotriene D4, is an eoxin. Cells make eoxins by metabolizing arachidonic acid with a 15-lipoxygenase enzyme to form 15(S)-hydroperoxyeicosapentaenoic acid (i.e. 15(S)-HpETE). This product is then converted serially to eoxin A4 (i.e. EXA4), EXC4, EXD4, and EXE4 by LTC4 synthase, an unidentified gamma-glutamyltransferase, and an unidentified dipeptidase, respectively, in a pathway which appears similar if not identical to the pathway which forms leukotreines, i.e. LTA4, LTC4, LTD4, and LTE4. This pathway is schematically shown as follows:
EXA is viewed as an intracellular-bound, short-lived intermediate which is rapidly metabolized to the down-stream eoxins. The eoxins down stream of EXA4 are secreted from their parent cells and, it is proposed but not yet proven, serve to regulate allergic responses and the development of certain cancers (see Eoxins). | 1 | Applied and Interdisciplinary Chemistry |
When comparing relative stability, 6- and 7-atom interactions can be used to approximate differences in enthalpy between conformations. Each 6-atom interaction is worth and each 7-atom interaction is worth . | 0 | Theoretical and Fundamental Chemistry |
Caustic ingestion occurs when someone accidentally or deliberately ingests a caustic or corrosive substance. Depending on the nature of the substance, the duration of exposure and other factors it can lead to varying degrees of damage to the oral mucosa, the esophagus, and the lining of the stomach.
The severity of the injury can be determined by endoscopy of the upper digestive tract, although CT scanning may be more useful to determine whether surgery may be required.
During the healing process, strictures of the oesophagus may form, which may require therapeutic dilatation and insertion of a stent. | 1 | Applied and Interdisciplinary Chemistry |
In the early modern period, Aristotelian hylomorphism fell out of favor with the rise of the "mechanical philosophy" of thinkers like Descartes and John Locke, who were more sympathetic to the ancient Greek atomism of Democritus than to the natural minima of Aristotle. However, the concept of minima naturalia continued to shape philosophical thinking even among these mechanistic philosophers in the transitional centuries between the Aristotelianism of the medieval Scholastics and the worked-out atomic theory of modern scientists like Dalton.
The mechanist Pierre Gassendi discussed minima naturalia in the course of expounding his opposition to Scholastic Aristotelianism, and his own attempted reconciliation between the atomism of Epicurus and the Catholic faith. Aristotles mininima naturalia became "corpuscles" in the alchemical works of Geber and Daniel Sennert, who in turn influenced the corpuscularian alchemist Robert Boyle, one of the founders of modern chemistry. Boyle occasionally referred to his postulated corpuscles as minima naturalia'. | 1 | Applied and Interdisciplinary Chemistry |
Many other deoxyribozymes have since been developed that catalyze DNA phosphorylation, DNA adenylation, DNA deglycosylation, porphyrin metalation, thymine dimer photoreversion
and DNA cleavage. | 0 | Theoretical and Fundamental Chemistry |
The largest use of bitumen is for making asphalt concrete for road surfaces; this accounts for approximately 85% of the bitumen consumed in the United States. There are about 4,000 asphalt concrete mixing plants in the US, and a similar number in Europe.
Asphalt concrete pavement mixes are typically composed of 5% bitumen (known as asphalt cement in the US) and 95% aggregates (stone, sand, and gravel). Due to its highly viscous nature, bitumen must be heated so it can be mixed with the aggregates at the asphalt mixing facility. The temperature required varies depending upon characteristics of the bitumen and the aggregates, but warm-mix asphalt technologies allow producers to reduce the temperature required.
The weight of an asphalt pavement depends upon the aggregate type, the bitumen, and the air void content. An average example in the United States is about 112 pounds per square yard, per inch of pavement thickness.
When maintenance is performed on asphalt pavements, such as milling to remove a worn or damaged surface, the removed material can be returned to a facility for processing into new pavement mixtures. The bitumen in the removed material can be reactivated and put back to use in new pavement mixes. With some 95% of paved roads being constructed of or surfaced with asphalt, a substantial amount of asphalt pavement material is reclaimed each year. According to industry surveys conducted annually by the Federal Highway Administration and the National Asphalt Pavement Association, more than 99% of the bitumen removed each year from road surfaces during widening and resurfacing projects is reused as part of new pavements, roadbeds, shoulders and embankments or stockpiled for future use.
Asphalt concrete paving is widely used in airports around the world. Due to the sturdiness and ability to be repaired quickly, it is widely used for runways. | 0 | Theoretical and Fundamental Chemistry |
The electrochemical promotion of catalysis (EPOC) effect in the realm of chemistry refers to the pronounced enhancement of catalytic reactions or significant changes in the catalytic properties of a conductive catalyst in the presence of electrical currents or interfacial potentials. Also known as Non-faradaic electrochemical modification of catalytic activity (the NEMCA effect), it can increase in catalytic activity (up to 90-fold) and selectivity of a gas exposed electrode on a solid electrolyte cell upon application of a potential. This phenomenon is well documented and has been observed on various surfaces (Ni, Au, Pt, Pd, IrO2, RuO2) supported by O, Na and proton conducting solid electrolytes.
The EPOC effect can also be utilized in a reverse manner in order to influence the selectivity of versatile heterogeneous catalytic reactions. In most cases, the electronically conductive catalyst is in metallic or metal oxide states in the form of a porous film deposited on a solid electrolyte (O or mixed O electronic conductor). The EPOC effect was firstly discovered by M. Stoukides and C. Vayenas in the early 1980s and have been widely studied by various research groups for more than 100 heterogeneous catalytic reactions of mostly gaseous molecules. The EPOC effect has been evaluated as an important phenomenon which can closely link electrocatalysis and thermal catalysis. | 0 | Theoretical and Fundamental Chemistry |
According to some studies, up to 22.1% of teenagers abused substances during their most recent sexual experience.
Likewise, studies have shown adolescents who regularly abuse substances are more likely to initiate sexual activity at an earlier age, have a more significant number of sexual partners, and engage in unprotected sex more often.
Additionally, substance abuse has been linked to an increased risk of sexually transmitted infection (STI). | 1 | Applied and Interdisciplinary Chemistry |
IHC staining has been shown to be a useful diagnostic tool for prioritizing patients for SDH mutation testing in early stages of cancer. The absence of SDHB in IHC staining would be linked to the presence of SDH oncogene mutations. The already commercialized drug decitabine (Dacogen®) could be an effective therapy to repress the migration capacities of SDHB-mutant cells, | 1 | Applied and Interdisciplinary Chemistry |
Post Irradiation Examination (PIE) is the study of used nuclear materials such as nuclear fuel. It has several purposes. It is known that by examination of used fuel that the failure modes which occur during normal use (and the manner in which the fuel will behave during an accident) can be studied. In addition information is gained which enables the users of fuel to assure themselves of its quality and it also assists in the development of new fuels. After major accidents the core (or what is left of it) is normally subject to PIE in order to find out what happened. One site where PIE is done is the ITU which is the EU centre for the study of highly radioactive materials.
Materials in a high radiation environment (such as a reactor) can undergo unique behaviors such as swelling and non-thermal creep. If there are nuclear reactions within the material (such as what happens in the fuel), the stoichiometry will also change slowly over time. These behaviors can lead to new material properties, cracking, and fission gas release: | 0 | Theoretical and Fundamental Chemistry |
The Weber number (We) is a dimensionless number in fluid mechanics that is often useful in analysing fluid flows where there is an interface between two different fluids, especially for multiphase flows with strongly curved surfaces. It is named after Moritz Weber (1871–1951). It can be thought of as a measure of the relative importance of the fluid's inertia compared to its surface tension. The quantity is useful in analyzing thin film flows and the formation of droplets and bubbles. | 1 | Applied and Interdisciplinary Chemistry |
Messenger RNA is the bridge between the genetic code and the resulting proteins, as it is what carries the necessary information that gets translated into proteins. Modifications to the actual, physical genetic code are likely to be deleterious; therefore, minor modifications, such as methylation, done to mRNA are preferable (nevertheless, modifications are still seen throughout the genome). The four major types of modifications done to mRNA are N7-methylguanine (at the 5′ cap), N-methyladenosine, 5-methylcytosine, and 2′-O-methylation. The modification seen at the 5 cap perfectly demonstrates how modifications to mRNA can impact its function, as the 5 cap is necessary to initiate translation. Therefore, modifications, such as N7-methylguanine during RNA processing, to the 5' cap may effect the ability of the ribosome to initiate translation. It is important to note that not all modifications happening to the mRNA are epigenetic, some, like the N7-methylguanosine cap, are RNA editing.
mRNA molecules demonstrate something known as "modification stoichiometry". Modification stoichiometry is when only a portion of transcripts have a specific modification at a particular modification site. Typically, under normal cell conditions, the modification stoichiometry is very low, there are a very few number of transcripts that have specific modifications. However, as cell conditions change, the fraction of modified transcripts can change as well. As with other types of RNA, modifications impact the overall structure of the mRNA. Altering its structure may cause the mRNA to take different paths. For example, a normal transcript might be fated to be translated; however, the introduction of a modified base can disrupt its structure and send it down a different path, and that particular transcript may now be targeted for degradation. | 1 | Applied and Interdisciplinary Chemistry |
This classification, based on the effects on behavior, remains artificial. Pheromones fill many additional functions.
* Nasonov pheromones (worker bees)
* Royal pheromones (bees)
* Calming (appeasement) pheromones (mammals)
* Necromones, given off by a deceased and decomposing organism; consisting of oleic and linoleic acids, they allow crustaceans and hexapods to identify the presence of dead conspecifics.
* Suckling: TAA is present in rabbit milk and seems to play a role of pheromone inducing suckling in the newborn rabbit. | 1 | Applied and Interdisciplinary Chemistry |
Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the gut, muscles, and heart.
Neuropeptides are synthesized from large precursor proteins which are cleaved and post-translationally processed then packaged into dense core vesicles. Neuropeptides are often co-released with other neuropeptides and neurotransmitters in a single neuron, yielding a multitude of effects. Once released, neuropeptides can diffuse widely to affect a broad range of targets. | 1 | Applied and Interdisciplinary Chemistry |
* United States: California, Minnesota, Delaware, Washington DC and Wisconsin restrict use of less than lethal projectiles and devices using them.
* United Kingdom: Citizens may not use PAVA, under Section 5 of the Firearms Act 1968; however, police, prison officers and other officials are allowed to use PAVA to uphold the law. | 1 | Applied and Interdisciplinary Chemistry |
Secondary ion mass spectrometry (SIMS) is a technique similar to DESI, but while DESI is an ambient ionization technique, SIMS happens in vacuum. The solid sample surface is bombarded by a highly focused beam of primary ions. As they hit the surface, molecules are emitted from the surface and ionized. The choice of primary ions determines the size of the beam and also the extent of ionization and fragmentation. Pareek et al. performed metabolomics to trace how purines are synthesized within purinosomes and used isotope labeling and SIMS imaging to directly observe hotspots of metabolic activity within frozen HeLa cells. | 1 | Applied and Interdisciplinary Chemistry |
Melanopsin is a visual opsin present in Intrinsically photosensitive retinal ganglion cell (ipRGC) also with a retinal chromaphore. However, unlike the rod and cone pigments, melanopsin has the ability to act as both the excitable photopigment and as a photoisomerase. Melanopsin is therefore able to isomerize all-trans-retinal into 11-cis-retinal itself when stimulated with another photon. An ipRGC therefore does not rely on Müller cells and/or retinal pigment epithelium cells for this conversion. | 1 | Applied and Interdisciplinary Chemistry |
Adenylate kinase (EC [http://enzyme.expasy.org/EC/2.7.4.3 2.7.4.3]) (also known as ADK or myokinase) is a phosphotransferase enzyme that catalyzes the interconversion of the various adenosine phosphates (ATP, ADP, and AMP). By constantly monitoring phosphate nucleotide levels inside the cell, ADK plays an important role in cellular energy homeostasis. | 1 | Applied and Interdisciplinary Chemistry |
Recrystallization is defined as the process in which grains of a crystal structure come in a new structure or new crystal shape.
A precise definition of recrystallization is difficult to state as the process is strongly related to several other processes, most notably recovery and grain growth. In some cases it is difficult to precisely define the point at which one process begins and another ends. Doherty et al. defined recrystallization as:
Thus the process can be differentiated from recovery (where high angle grain boundaries do not migrate) and grain growth (where the driving force is only due to the reduction in boundary area).
Recrystallization may occur during or after deformation (during cooling or subsequent heat treatment, for example). The former is termed dynamic while the latter is termed static. In addition, recrystallization may occur in a discontinuous manner, where distinct new grains form and grow, or a continuous manner, where the microstructure gradually evolves into a recrystallized microstructure. The different mechanisms by which recrystallization and recovery occur are complex and in many cases remain controversial. The following description is primarily applicable to static discontinuous recrystallization, which is the most classical variety and probably the most understood. Additional mechanisms include (geometric) dynamic recrystallization and strain induced boundary migration.
Secondary recrystallization occurs when a certain very small number of {110}<001> (Goss) grains grow selectively, about one in 106 primary grains, at the expense of many other primary recrystallized grains. This results in abnormal grain growth, which may be beneficial or detrimental for product material properties. The mechanism of secondary recrystallization is a small and uniform primary grain size, achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. Goss grains are named in honor of Norman P. Goss, the inventor of grain-oriented electrical steel circa 1934. | 1 | Applied and Interdisciplinary Chemistry |
Planktonic foraminiferal species diversity depends on available niches, which are in turn related to ocean circulation. By correlation with stable isotope records, maximum diversity has been found to occur after the initiation of a glaciation period. | 0 | Theoretical and Fundamental Chemistry |
Thiolated polymers designated thiomers are functional polymers used in biotechnology product development with the intention to prolong mucosal drug residence time and to enhance absorption of drugs. The name thiomer was coined by Andreas Bernkop-Schnürch in 2000. Thiomers have thiol bearing side chains. Sulfhydryl ligands of low molecular mass are covalently bound to a polymeric backbone consisting of mainly biodegradable polymers, such as chitosan, hyaluronic acid, cellulose derivatives, pullulan, starch, gelatin, polyacrylates, cyclodextrins, or silicones.
Thiomers exhibit properties potentially useful for non-invasive drug delivery via oral, ocular, nasal, vesical, buccal and vaginal routes. Thiomers show also potential in the field of tissue engineering and regenerative medicine. Various thiomers such as thiolated chitosan and thiolated hyaluronic acid are commercialy available as scaffold materials. Thiomers can be directly compressed to tablets or given as solutions. In 2012, a second generation of thiomers – called "preactivated" or "S-protected" thiomers – were introduced.
In contrast to thiomers of the first generation, preactivated thiomers are stable towards oxidation and display comparatively higher mucoadhesive and permeation enhancing properties. Approved thiomer products for human use are for example eyedrops for treatment of dry eye syndrome or adhesive gels for treatment of nickel allergy. | 0 | Theoretical and Fundamental Chemistry |
Sonogashira couplings are employed in a wide array of synthetic reactions, primarily due to their success in facilitating the following challenging transformations: | 0 | Theoretical and Fundamental Chemistry |
Compared to other heteroallenes, carbodiimides are very weak electrophiles and only react with nucleophiles in the presence of catalysts, such as acids. In this way, guanidines can be prepared. As weak bases, carbodiimides bind to Lewis acids to give adducts. | 0 | Theoretical and Fundamental Chemistry |
First published synthesis and report of properties of fluorine-18 were in 1937 by Arthur H. Snell, produced by the nuclear reaction of Ne(d,α)F in the cyclotron laboratories of Ernest O. Lawrence. | 1 | Applied and Interdisciplinary Chemistry |
Yttrium in the Solar System was created through stellar nucleosynthesis, mostly by the s-process (≈72%), but also by the r-process (≈28%). The r-process consists of rapid neutron capture by lighter elements during supernova explosions. The s-process is a slow neutron capture of lighter elements inside pulsating red giant stars.
Yttrium isotopes are among the most common products of the nuclear fission of uranium in nuclear explosions and nuclear reactors. In the context of nuclear waste management, the most important isotopes of yttrium are Y and Y, with half-lives of 58.51 days and 64 hours, respectively. Though Y has a short half-life, it exists in secular equilibrium with its long-lived parent isotope, strontium-90 (Sr) with a half-life of 29 years.
All group 3 elements have an odd atomic number, and therefore few stable isotopes. Scandium has one stable isotope, and yttrium itself has only one stable isotope, Y, which is also the only isotope that occurs naturally. However, the lanthanide rare earths contain elements of even atomic number and many stable isotopes. Yttrium-89 is thought to be more abundant than it otherwise would be, due in part to the s-process, which allows enough time for isotopes created by other processes to decay by electron emission (neutron → proton). Such a slow process tends to favor isotopes with atomic mass numbers (A = protons + neutrons) around 90, 138 and 208, which have unusually stable atomic nuclei with 50, 82, and 126 neutrons, respectively. This stability is thought to result from their very low neutron-capture cross-section. Electron emission of isotopes with those mass numbers is simply less prevalent due to this stability, resulting in them having a higher abundance. Y has a mass number close to 90 and has 50 neutrons in its nucleus.
At least 32 synthetic isotopes of yttrium have been observed, and these range in atomic mass number from 76 to 108. The least stable of these is Y with a half-life of >150 ns (Y has a half-life of >200 ns) and the most stable is Y with a half-life of 106.626 days. Apart from the isotopes Y, Y, and Y, with half-lives of 58.51 days, 79.8 hours, and 64 hours, respectively, all the other isotopes have half-lives of less than a day and most of less than an hour.
Yttrium isotopes with mass numbers at or below 88 decay primarily by positron emission (proton → neutron) to form strontium (Z = 38) isotopes. Yttrium isotopes with mass numbers at or above 90 decay primarily by electron emission (neutron → proton) to form zirconium (Z = 40) isotopes. Isotopes with mass numbers at or above 97 are also known to have minor decay paths of β delayed neutron emission.
Yttrium has at least 20 metastable ("excited") isomers ranging in mass number from 78 to 102. Multiple excitation states have been observed for Y and Y. While most of yttrium's isomers are expected to be less stable than their ground state, Y, Y, Y, Y, Y, Y, and Y have longer half-lives than their ground states, as these isomers decay by beta decay rather than isomeric transition. | 1 | Applied and Interdisciplinary Chemistry |
kainic acid receptor - kallidin - kappa opioid receptor - kappa-chain immunoglobulin - karyoplasm - karyotype - kelvin - keratin - kinase - kinesin - kinetic energy - kinetic exclusion assay - kinetics - knock-out mouse - Krebs cycle | 1 | Applied and Interdisciplinary Chemistry |
At the mouth of a river, the change in flow conditions can cause the river to drop any sediment it is carrying. This sediment deposition can generate a variety of landforms, such as deltas, sand bars, spits, and tie channels. Landforms at the river mouth drastically alter the geomorphology and ecosystem. Along coasts, sand bars and similar landforms act as barriers, sheltering sensitive ecosystems that are enriched by nutrients deposited from the river. However, the damming of rivers can starve the river of sand and nutrients, creating a deficit at the river's mouth. | 1 | Applied and Interdisciplinary Chemistry |
Design equations are equations relating the space time to the fractional conversion and other properties of the reactor. Different design equations have been derived for different types of the reactor and depending on the reactor the equation more or less resemble that describing the average residence time. Often design equations are used to minimize the reactor volume or volumetric flow rate required to operate a reactor. | 0 | Theoretical and Fundamental Chemistry |
Bismuth-containing solid-state compounds pose an interest to both the physical inorganic chemists as well as condensed matter physicists due to the element's massive spin-orbit coupling, stabilization of lower oxidation states, and the inert pair effect. Additionally, the stabilization of the Bi in the +1 oxidation state gives rise to a plethora of subhalide compounds with interesting electronics and 3D structures. | 0 | Theoretical and Fundamental Chemistry |
The main function of glycolipids in the body is to serve as recognition sites for cell–cell interactions. The saccharide of the glycolipid will bind to a specific complementary carbohydrate or to a lectin (carbohydrate-binding protein), of a neighboring cell. The interaction of these cell surface markers is the basis of cell recognitions, and initiates cellular responses that contribute to activities such as regulation, growth, and apoptosis. | 0 | Theoretical and Fundamental Chemistry |
Over 6 kilometers of new fish spawning and rearing habitats were installed in upper to middle Hazeltine Creek. The successful spawning of Rainbow Trout was later observed in 2018 and 2019 in upper Hazeltine Creek. | 1 | Applied and Interdisciplinary Chemistry |
In 1955, biologists Britton Chance and G. R. Williams were the first to propose the idea that respiratory enzymes assemble into larger complexes, although the fluid state model remained the standard. However, as early as 1985, researchers had begun isolating complex III/complex IV supercomplexes from bacteria and yeast. Finally, in 2000 Hermann Schägger and Kathy Pfeiffer used Blue Native PAGE to isolate bovine mitochondrial membrane proteins, showing Complex I, III, and IV arranged in supercomplexes. | 1 | Applied and Interdisciplinary Chemistry |
Crack growth is reported to be very slow by Luxfer, a major manufacturer of aluminium high-pressure cylinders. Cracks are reported to develop over periods in the order of 8 or more years before reaching a stage where the cylinder is likely to leak, which allows timely detection by properly trained inspectors using eddy-current crack-detection equipment.
SLC cracks have been detected in cylinders produced by several manufacturers, including Luxfer, Walter Kidde, and CIG gas cylinders.
Most of the cracking has been observed in the neck and shoulder areas of cylinders, though some cracks in the cylindrical part have also been reported. | 1 | Applied and Interdisciplinary Chemistry |
Copy number alteration (CNA) analyses are commonly used in cancer studies. Gain and loss of the genes have signalling pathway implications and are a key biomarker of molecular dysfunction in oncology. Calling the CNA information from RNA-Seq data is not straightforward because of the differences in gene expression, which lead to the read depth variance of different magnitudes across genes. Due to these difficulties, most of these analyses are usually done using whole-genome sequencing / whole-exome sequencing (WGS/WES). But advanced bioinformatics tools can call CNA from RNA-Seq. | 1 | Applied and Interdisciplinary Chemistry |
* For a completely isolated system, S is maximum at thermodynamic equilibrium.
* For a closed system at controlled constant temperature and volume, A is minimum at thermodynamic equilibrium.
* For a closed system at controlled constant temperature and pressure without an applied voltage, G is minimum at thermodynamic equilibrium.
The various types of equilibriums are achieved as follows:
* Two systems are in thermal equilibrium when their temperatures are the same.
* Two systems are in mechanical equilibrium when their pressures are the same.
* Two systems are in diffusive equilibrium when their chemical potentials are the same.
* All forces are balanced and there is no significant external driving force. | 0 | Theoretical and Fundamental Chemistry |
Evolution in bacteria was previously viewed as a result of mutation or genetic drift. Today, genetic exchange, or gene transfer is viewed as a major driving force in the evolution of prokaryotes. This driving force has been widely studied in organisms like E. coli. Bacteria reproduces asexually, where daughter cells are clones of the parent. This clonal nature leads to random mutations that occur during DNA replication that potentially helps bacteria evolve. It was originally thought that only accumulated mutations helped bacteria evolve. In contrast, bacteria also import genes in a process called homologous recombination, first discovered by the observation of mosaic genes at loci encoding antibiotic resistance. The discovery of homologous recombination has made an impact on the understanding of bacterial evolution. The importance of evolution in bacterial recombination is its adaptivity. For example, bacterial recombination has been shown to promote the transfer of multi drug resistance genes via homologous recombination that goes beyond levels purely obtained by mutation. | 1 | Applied and Interdisciplinary Chemistry |
Woollins reagent is an organic compound containing phosphorus and selenium. Analogous to Lawessons reagent, it is used mainly as a selenation reagent. It is named after John Derek Woollins. | 0 | Theoretical and Fundamental Chemistry |
Many hypotheses about how scaffolds coordinate positive and negative feedback come from engineered scaffolds and mathematical modeling. In three-kinase signaling cascades, scaffolds bind all three kinases, enhancing kinase specificity and restricting signal amplification by limiting kinase phosphorylation to only one downstream target. These abilities may be related to stability of the interaction between the scaffold and the kinases, the basal phosphatase activity in the cell, scaffold location, and expression levels of the signaling components. | 1 | Applied and Interdisciplinary Chemistry |
Geometrical constraints in a molecule can cause a severe distortion of idealized tetrahedral geometry. In compounds featuring "inverted" tetrahedral geometry at a carbon atom, all four groups attached to this carbon are on one side of a plane. The carbon atom lies at or near the apex of a square pyramid with the other four groups at the corners.
The simplest examples of organic molecules displaying inverted tetrahedral geometry are the smallest propellanes, such as [[1.1.1-Propellane|[1.1.1]propellane]]; or more generally the paddlanes, and pyramidane ([3.3.3.3]fenestrane). Such molecules are typically strained, resulting in increased reactivity. | 0 | Theoretical and Fundamental Chemistry |
Bacteria can use several different electron donors. When organic matter is the electron source, the donor may be NADH or succinate, in which case electrons enter the electron transport chain via NADH dehydrogenase (similar to Complex I in mitochondria) or succinate dehydrogenase (similar to Complex II). Other dehydrogenases may be used to process different energy sources: formate dehydrogenase, lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, H dehydrogenase (hydrogenase), electron transport chain. Some dehydrogenases are also proton pumps, while others funnel electrons into the quinone pool. Most dehydrogenases show induced expression in the bacterial cell in response to metabolic needs triggered by the environment in which the cells grow. In the case of lactate dehydrogenase in E. coli, the enzyme is used aerobically and in combination with other dehydrogenases. It is inducible and is expressed when the concentration of DL-lactate in the cell is high. | 1 | Applied and Interdisciplinary Chemistry |
Even though photoemission can occur from any material, it is most readily observed from metals and other conductors. This is because the process produces a charge imbalance which, if not neutralized by current flow, results in the increasing potential barrier until the emission completely ceases. The energy barrier to photoemission is usually increased by nonconductive oxide layers on metal surfaces, so most practical experiments and devices based on the photoelectric effect use clean metal surfaces in evacuated tubes. Vacuum also helps observing the electrons since it prevents gases from impeding their flow between the electrodes.
As sunlight, due to atmosphere's absorption, does not provide much ultraviolet light, the light rich in ultraviolet rays used to be obtained by burning magnesium or from an arc lamp. At the present time, mercury-vapor lamps, noble-gas discharge UV lamps and radio-frequency plasma sources, ultraviolet lasers, and synchrotron insertion device light sources prevail.
The classical setup to observe the photoelectric effect includes a light source, a set of filters to monochromatize the light, a vacuum tube transparent to ultraviolet light, an emitting electrode (E) exposed to the light, and a collector (C) whose voltage V can be externally controlled.
A positive external voltage is used to direct the photoemitted electrons onto the collector. If the frequency and the intensity of the incident radiation are fixed, the photoelectric current I increases with an increase in the positive voltage, as more and more electrons are directed onto the electrode. When no additional photoelectrons can be collected, the photoelectric current attains a saturation value. This current can only increase with the increase of the intensity of light.
An increasing negative voltage prevents all but the highest-energy electrons from reaching the collector. When no current is observed through the tube, the negative voltage has reached the value that is high enough to slow down and stop the most energetic photoelectrons of kinetic energy K. This value of the retarding voltage is called the stopping potential or cut off potential V. Since the work done by the retarding potential in stopping the electron of charge e is eV, the following must hold eV = K
The current-voltage curve is sigmoidal, but its exact shape depends on the experimental geometry and the electrode material properties.
For a given metal surface, there exists a certain minimum frequency of incident radiation below which no photoelectrons are emitted. This frequency is called the threshold frequency. Increasing the frequency of the incident beam increases the maximum kinetic energy of the emitted photoelectrons, and the stopping voltage has to increase. The number of emitted electrons may also change because the probability that each photon results in an emitted electron is a function of photon energy.
An increase in the intensity of the same monochromatic light (so long as the intensity is not too high), which is proportional to the number of photons impinging on the surface in a given time, increases the rate at which electrons are ejected—the photoelectric current I—but the kinetic energy of the photoelectrons and the stopping voltage remain the same. For a given metal and frequency of incident radiation, the rate at which photoelectrons are ejected is directly proportional to the intensity of the incident light.
The time lag between the incidence of radiation and the emission of a photoelectron is very small, less than 10 second. Angular distribution of the photoelectrons is highly dependent on polarization (the direction of the electric field) of the incident light, as well as the emitting materials quantum properties such as atomic and molecular orbital symmetries and the electronic band structure of crystalline solids. In materials without macroscopic order, the distribution of electrons tends to peak in the direction of polarization of linearly polarized light. The experimental technique that can measure these distributions to infer the materials properties is angle-resolved photoemission spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
In some spoil tips, the waste resulting from industries such as coal or oil shale production can contain a relatively high proportion of hydrocarbons or coal dust. Spontaneous subterranean combustion may result, which can be followed by surface fires. In some coal mining districts, such fires were considered normal and no attempt was made to extinguish them.
Such fires can follow slow combustion of residual hydrocarbons. Their extinction can require complete encasement, which can prove impossible for technical and financial reasons. Sprinkling is generally ineffective and injecting water under pressure counter-productive, because it carries oxygen, bringing the risk of explosion.
The perceived weak environmental and public health effects of these fires leads generally to waiting for their natural extinction, which can take a number of decades. | 1 | Applied and Interdisciplinary Chemistry |
Researchers successfully treated a boy with epidermolysis bullosa using skin grafts grown from his own skin cells, genetically altered to repair the mutation that caused his disease.
In November, researchers announced that they had treated a baby girl, Layla Richards, with an experimental treatment using donor T cells genetically engineered using TALEN to attack cancer cells. One year after the treatment she was still free of her cancer (a highly aggressive form of acute lymphoblastic leukaemia [ALL]). Children with highly aggressive ALL normally have a very poor prognosis and Layla's disease had been regarded as terminal before the treatment. | 1 | Applied and Interdisciplinary Chemistry |
There are two classes of receptors for neurotrophins: p75 and the "Trk" family of Tyrosine kinases receptors. | 1 | Applied and Interdisciplinary Chemistry |
As the neutron stars undergo accretion, the density in the crust increases, passing the electron capture threshold. As the electron capture threshold ( g cm) is exceeded, it allows for the formation of light nuclei from the process of double electron capture (), forming the light neon nuclei and free neutrons, which further increases the density of the crust. As the density increases, the crystal lattices of neutron-rich nuclei are forced closer together due to gravitational collapse of accreting material, and at a point where the nuclei are pushed so close together that their zero-point oscillations allow them to break through the Coulomb barrier, fusion occurs. While the main site of pycnonuclear fusion within neutron stars is the inner crust, pycnonuclear reactions between light nuclei can occur even in the plasma ocean. Since the core of neutron stars was approximated to be g cm, at such extreme densities, pycnonuclear reactions play a large role as demonstrated by Haensel & Zdunik, who showed that at densities of g cm, they serve as a major heat source. In the fusion processes of the inner crust, the burning of neutron-rich nuclei () releases a lot of heat, allowing pycnonuclear fusion to perform as a major energy source, possibly even acting as an energy basin for gamma-ray bursts.
Further studies have established that most magnetars are found at densities of g cm, indicating that pycnonuclear reactions along with subsequent electron capture reactions could serve as major heat sources. | 0 | Theoretical and Fundamental Chemistry |
Carbon-14 has a long half-life of . Its maximum specific activity is . It is used in applications such as radiometric dating or drug tests. Carbon-14 labeling is common in drug development to do ADME (absorption, distribution, metabolism and excretion) studies in animal models and in human toxicology and clinical trials. Since tritium exchange may occur in some radiolabeled compounds, this does not happen with carbon-14 and may thus be preferred. | 0 | Theoretical and Fundamental Chemistry |
First combine template RNA, primer, dNTP mix, and nuclease-free water in a PCR tube. Then, add an RNase inhibitor and reverse transcriptase to the PCR tube. Next, place the PCR tube into a thermal cycler for one cycle wherein annealing, extending, and inactivating of reverse transcriptase occurs. Finally, proceed directly to step two which is PCR or store product on ice until PCR can be performed. | 1 | Applied and Interdisciplinary Chemistry |
Hyperpolarization-activated and cyclic nucleotide–gated (HCN) channels belong to the superfamily of voltage-gated K (Kv) and cyclic nucleotide–gated (CNG) channels. HCN channels are thought to consist of four either identical or non-identical subunits that are integrally embedded in the cell membrane to create an ion-conducting pore. Each subunit comprises six membrane-spanning (S1–6) domains which include a putative voltage sensor (S4) and a pore region between S5 and S6 carrying the GYG triplet signature of K-permeable channels, and a cyclic nucleotide-binding domain (CNBD) in the C-terminus. HCN isoforms are highly conserved in their core transmembrane regions and cyclic nucleotide binding domain (80–90% identical), but diverge in their amino- and carboxy-terminal cytoplasmic regions.
HCN channels are regulated by both intracellular and extracellular molecules, but most importantly, by cyclic nucleotides (cAMP, cGMP, cCMP). Binding of cyclic nucleotides lowers the threshold potential of HCN channels, thus activating them. cAMP is a primary agonist of HCN2 while cGMP and cCMP may also bind to it. All three, however, are potent agonists. | 1 | Applied and Interdisciplinary Chemistry |
Arketamine (developmental code names PCN-101, HR-071603), also known as (R)-ketamine or (R)-(−)-ketamine, is the (R)-(−) enantiomer of ketamine. Similarly to racemic ketamine and esketamine, the S(+) enantiomer of ketamine, arketamine is biologically active; however, it is less potent as an NMDA receptor antagonist and anesthetic and thus has never been approved or marketed for clinical use as an enantiopure drug. Arketamine is currently in clinical development as a novel antidepressant.
Relative to esketamine, arketamine possesses 4 to 5 times lower affinity for the PCP site of the NMDA receptor. In accordance, arketamine is significantly less potent than racemic ketamine and especially esketamine in terms of anesthetic, analgesic, and sedative-hypnotic effects. Racemic ketamine has weak affinity for the sigma receptor, where it acts as an agonist, whereas esketamine binds negligibly to this receptor, and so the sigma receptor activity of racemic ketamine lies in arketamine. It was suggested that this action of arketamine may play a role in the hallucinogenic effects of racemic ketamine and that it may be responsible for the lowering of the seizure threshold seen with racemic ketamine. However several subsequent studies have indicated that esketamine is more likely to induce dissociative events, while studies in patients undergoing electroconvulsive therapy suggested that esketamine is a potent inducer of seizures. Esketamine inhibits the dopamine transporter about 8-fold more potently than does arketamine, and so is about 8 times more potent as a dopamine reuptake inhibitor. Arketamine and esketamine possess similar potency for interaction with the muscarinic acetylcholine receptors. | 0 | Theoretical and Fundamental Chemistry |
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or "decays" into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. It has a charge of and a mass of . For example, uranium-238 decays to form thorium-234.
While alpha particles have a charge , this is not usually shown because a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms.
Alpha decay typically occurs in the heaviest nuclides. Theoretically, it can occur only in nuclei somewhat heavier than nickel (element 28), where the overall binding energy per nucleon is no longer a maximum and the nuclides are therefore unstable toward spontaneous fission-type processes. In practice, this mode of decay has only been observed in nuclides considerably heavier than nickel, with the lightest known alpha emitter being the second lightest isotope of antimony, Sb. Exceptionally, however, beryllium-8 decays to two alpha particles.
Alpha decay is by far the most common form of cluster decay, where the parent atom ejects a defined daughter collection of nucleons, leaving another defined product behind. It is the most common form because of the combined extremely high nuclear binding energy and relatively small mass of the alpha particle. Like other cluster decays, alpha decay is fundamentally a quantum tunneling process. Unlike beta decay, it is governed by the interplay between both the strong nuclear force and the electromagnetic force.
Alpha particles have a typical kinetic energy of 5 MeV (or ≈ 0.13% of their total energy, 110 TJ/kg) and have a speed of about 15,000,000 m/s, or 5% of the speed of light. There is surprisingly small variation around this energy, due to the strong dependence of the half-life of this process on the energy produced. Because of their relatively large mass, the electric charge of and relatively low velocity, alpha particles are very likely to interact with other atoms and lose their energy, and their forward motion can be stopped by a few centimeters of air.
Approximately 99% of the helium produced on Earth is the result of the alpha decay of underground deposits of minerals containing uranium or thorium. The helium is brought to the surface as a by-product of natural gas production. | 0 | Theoretical and Fundamental Chemistry |
Sagan and Khare note the presence of tholins through multiple locations: "as a constituent of the Earth's primitive oceans and therefore relevant to the origin of life; as a component of red aerosols in the atmospheres of the outer planets and Titan; present in comets, carbonaceous chondrites asteroids, and pre-planetary solar nebulae; and as a major constituent of the interstellar medium." The surfaces of comets, centaurs, and many icy moons and Kuiper-belt objects in the outer Solar System are rich in deposits of tholins. | 0 | Theoretical and Fundamental Chemistry |
A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. It forms a weak complex with the ions present in the solution, which has a significantly different color from the form existing outside the complex.
Complexometric indicators are also known as pM indicators. | 0 | Theoretical and Fundamental Chemistry |
Solubility is sensitive to changes in temperature. For example, sugar is more soluble in hot water than cool water. It occurs because solubility products, like other types of equilibrium constants, are functions of temperature. In accordance with Le Chatelier's Principle, when the dissolution process is endothermic (heat is absorbed), solubility increases with rising temperature. This effect is the basis for the process of recrystallization, which can be used to purify a chemical compound. When dissolution is exothermic (heat is released) solubility decreases with rising temperature.
Sodium sulfate shows increasing solubility with temperature below about 32.4 °C, but a decreasing solubility at higher temperature. This is because the solid phase is the decahydrate () below the transition temperature, but a different hydrate above that temperature.
The dependence on temperature of solubility for an ideal solution (achieved for low solubility substances) is given by the following expression containing the enthalpy of melting, ΔH, and the mole fraction of the solute at saturation:
where is the partial molar enthalpy of the solute at infinite dilution and the enthalpy per mole of the pure crystal.
This differential expression for a non-electrolyte can be integrated on a temperature interval to give:
For nonideal solutions activity of the solute at saturation appears instead of mole fraction solubility in the derivative with respect to temperature: | 0 | Theoretical and Fundamental Chemistry |
Congo red is an organic compound, the sodium salt of 3,3′-([1,1′-biphenyl]-4,4′-diyl)bis(4-aminonaphthalene-1-sulfonic acid). It is an azo dye. Congo red is water-soluble, yielding a red colloidal solution; its solubility is greater in organic solvents. The use of Congo red in the textile industry has long been abandoned, primarily because of its carcinogenic properties, but it is still used for histological staining. | 0 | Theoretical and Fundamental Chemistry |
Pre-treatment is recommended to remove pollutants such as trash, debris, and larger sediments. Incorporation of a pretreatment system, such as a hydrodynamic separator, can prolong the longevity of the entire system by preventing the primary treatment practice from becoming prematurely clogged. | 1 | Applied and Interdisciplinary Chemistry |
The first Watt engines were atmospheric pressure engines, like the Newcomen engine but with the condensation taking place separate from the cylinder. Driving the engines using both low pressure steam and a partial vacuum raised the possibility of reciprocating engine development. An arrangement of valves could alternately admit low pressure steam to the cylinder and then connect with the condenser. Consequently, the direction of the power stroke might be reversed, making it easier to obtain rotary motion. Additional benefits of the double acting engine were increased efficiency, higher speed (greater power) and more regular motion.
Before the development of the double acting piston, the linkage to the beam and the piston rod had been by means of a chain, which meant that power could only be applied in one direction, by pulling. This was effective in engines that were used for pumping water, but the double action of the piston meant that it could push as well as pull. This was not possible as long as the beam and the rod were connected by a chain. Furthermore, it was not possible to connect the piston rod of the sealed cylinder directly to the beam, because while the rod moved vertically in a straight line, the beam was pivoted at its centre, with each side inscribing an arc. To bridge the conflicting actions of the beam and the piston, Watt developed his parallel motion. This device used a four bar linkage coupled with a pantograph to produce the required straight line motion much more cheaply than if he had used a slider type of linkage. He was very proud of his solution.
Having the beam connected to the piston shaft by a means that applied force alternately in both directions also meant that it was possible to use the motion of the beam to turn a wheel. The simplest solution to transforming the action of the beam into a rotating motion was to connect the beam to a wheel by a crank, but because another party had patent rights on the use of the crank, Watt was obliged to come up with another solution. He adopted the epicyclic sun and planet gear system suggested by an employee William Murdoch, only later reverting, once the patent rights had expired, to the more familiar crank seen on most engines today. The main wheel attached to the crank was large and heavy, serving as a flywheel which, once set in motion, by its momentum maintained a constant power and smoothed the action of the alternating strokes. To its rotating central shaft, belts and gears could be attached to drive a great variety of machinery.
Because factory machinery needed to operate at a constant speed, Watt linked a steam regulator valve to a centrifugal governor which he adapted from those used to automatically control the speed of windmills. The centrifugal was not a true speed controller because it could not hold a set speed in response to a change in load.
These improvements allowed the steam engine to replace the water wheel and horses as the main sources of power for British industry, thereby freeing it from geographical constraints and becoming one of the main drivers in the Industrial Revolution.
Watt was also concerned with fundamental research on the functioning of the steam engine. His most notable measuring device, still in use today, is the Watt indicator incorporating a manometer to measure steam pressure within the cylinder according to the position of the piston, enabling a diagram to be produced representing the pressure of the steam as a function of its volume throughout the cycle. | 0 | Theoretical and Fundamental Chemistry |
LAGP is one of the most studied solid-state electrolytes for lithium-ion batteries. The use of a solid-state electrolyte improves the battery safety eliminating liquid-based electrolytes, which are flammable and usually unstable above 4.3 V. In addition, it physically separates the anode from the cathode, reducing the risk of short-circuit, and strongly inhibits lithium dendrite growth. Finally, solid-state electrolytes can operate in a wide range of temperatures, with minimum conductivity loss and decomposition issues. Nevertheless, the ionic conductivity of solid-state electrolytes is some orders of magnitude lower than the one of conventional liquid-based electrolytes, therefore a thin electrolyte layer is preferred to reduce the overall internal impedance and to achieve a shorter diffusion path and larger energy densities. Therefore, LAGP is a suitable candidate for all-solid-state thin-film lithium-ion batteries, in which the electrolyte thickness ranges from 1 to some hundreds of micrometres. The good mechanical strength of LAGP effectively suppress lithium dendrites during lithium stripping and plating, reducing the risk of internal short-circuit and battery failure.
LAGP is applied as a solid-state electrolyte both as a pure material and as a component in organic-inorganic composite electrolytes. For example, LAGP can be composited with polymeric materials, like polypropylene (PP) or polyethylene oxide (PEO), to improve the ionic conductivity and to tune the electrochemical stability. Moreover, since LAGP is not fully stable against metallic lithium because of the electrochemical reactivity of Ge cations, additional interlayers can be introduced between the lithium anode and the solid electrolyte to improve the interfacial stability. The addition of a thin layer of metallic germanium inhibits the electrochemical reduction by lithium metal at very negative potentials and promotes the interfacial contact between the anode and the electrolyte, resulting in improved cycling performance and battery stability. The use of polymer-ceramic composite interlayers or the excess of LiO are alternative strategies to improve the electrochemical stability of LAGP at negative potentials.
LAGP has been also tested not only as a solid electrolyte, but also as an anode material in lithium-ion battery, showing high electrochemical stability and good cycling performance. | 0 | Theoretical and Fundamental Chemistry |
On July 1, 1992, the National Foundation for History of Chemistry changed its name to the Chemical Heritage Foundation, in recognition of the international nature of chemical history. By 1994, the organization was searching for a permanent home for the Beckman Center and Othmer Library. One candidate was the First National Bank building at 315 Chestnut Street, an 1866 masonry-and-brick structure with a two-story Palazzo facade. The institution bought the bank building and nearby property in 1995, in part with a matching grant from Donald Othmer. Soon afterward, its endowment was expanded by a bequest from Othmer's estate. The Chemical Heritage Foundation moved to 315 Chestnut Street on February 1, 1996. The buildings were renovated by Richard Conway Meyer over the next few years. Phase 1, providing temporary office space and book storage, was completed in 1998. Phase 2, a move to more permanent facilities, was completed in 2000. Phase 3, construction of the adjoining Ullyot conference space for meetings and events, began soon after. | 1 | Applied and Interdisciplinary Chemistry |
Aluminium is produced by electrolytic reduction of aluminium oxide dissolved in molten cryolite.
At the same time the carbon electrode is oxidised, initially to carbon monoxide
Although the formation of carbon monoxide (CO) is thermodynamically favoured at the reaction temperature, the presence of considerable overvoltage (difference between reversible and polarization potentials) changes the thermodynamic equilibrium and a mixture of CO and is produced. Thus the idealised overall reactions may be written as
By increasing the current density up to 1 A/cm, the proportion of increases and carbon consumption decreases.
As three electrons are needed to produce each atom of aluminium, the process consumes a large amount of electricity. For this reason aluminium smelters are sited close to sources of inexpensive electricity, such as hydroelectric. | 1 | Applied and Interdisciplinary Chemistry |
While EPIC-seq offers significant potential in various biomedical applications, it also has limitations that warrant consideration in its implementation and interpretation. | 1 | Applied and Interdisciplinary Chemistry |
Progesterone also appears to be involved in the pathophysiology of breast cancer, though its role, and whether it is a promoter or inhibitor of breast cancer risk, has not been fully elucidated. Most progestins, or synthetic progestogens, like medroxyprogesterone acetate, have been found to increase the risk of breast cancer in postmenopausal women in combination with estrogen as a component of menopausal hormone therapy. The combination of natural oral progesterone or the atypical progestin dydrogesterone with estrogen has been associated with less risk of breast cancer than progestins plus estrogen. However, this may simply be an artifact of the low progesterone levels produced with oral progesterone. More research is needed on the role of progesterone in breast cancer. | 0 | Theoretical and Fundamental Chemistry |
Gestational trophoblastic disease like hydatidiform moles ("molar pregnancy") or choriocarcinoma may produce high levels of βhCG due to the presence of syncytiotrophoblasts, part of the villi that make up the placenta, and despite the absence of an embryo. This, as well as several other conditions, can lead to elevated hCG readings in the absence of pregnancy.
hCG levels are also a component of the triple test, a screening test for certain fetal chromosomal abnormalities/birth defects. High hCG levels in the maternal serum could suggest Down syndrome, potentially due to continued hCG production by the placenta beyond the first trimester.
A study of 32 normal pregnancies came to the result that a gestational sac of 1–3 mm was detected at a mean hCG level of 1150 IU/L (range 800–1500), a yolk sac was detected at a mean level of 6000 IU/L (range 4500–7500) and fetal heartbeat was visible at a mean hCG level of 10,000 IU/L (range 8650–12,200). | 1 | Applied and Interdisciplinary Chemistry |
Fazlul Halim Chowdhury (1 August 19309 April 1996) was a fellow of the Bangladesh Academy of Sciences and one of the longest-serving Vice-Chancellors of the University of Dhaka. He made pioneering contributions to the development of physical chemistry in Bangladesh, publishing more than 20 articles. He focused on cellulose fibers (especially jute), polyelectrolytes, and proteins. | 0 | Theoretical and Fundamental Chemistry |
Methylation of adenosine does not affect its ability to base-pair with thymidine or uracil, so N-methyladenosine (mA) cannot be detected using standard sequencing or hybridization methods. This modification is marked by the methylation of the adenosine base at the nitrogen-6 position. It is abundantly found in polyA+ mRNA; also found in tRNA, rRNA, snRNA, and long ncRNA. | 1 | Applied and Interdisciplinary Chemistry |
With the discovery of protactinium, most of the decay chains of uranium had been mapped. When Hahn returned to his work after the war, he looked back over his 1914 results, and considered some anomalies that had been dismissed or overlooked. He dissolved uranium salts in a hydrofluoric acid solution with tantalic acid. First the tantalum in the ore was precipitated, then the protactinium. In addition to the uranium X1 (thorium-234) and uranium X2 (protactinium-234), Hahn detected traces of a radioactive substance with a half life of between 6 and 7 hours. There was one isotope known to have a half life of 6.2 hours, mesothorium II (actinium-228). This was not in any probable decay chain, but it could have been contamination, as the Kaiser Wilhelm Institute for Chemistry had experimented with it. Hahn and Meitner demonstrated in 1919 that when actinium is treated with hydrofluoric acid, it remains in the insoluble residue. Since mesothorium II was an isotope of actinium, the substance was not mesothorium II; it was protactinium.
Hahn was now confident enough that he had found something that he named his new isotope "uranium Z", and in February 1921, he published the first report on his discovery.
Hahn determined that uranium Z had a half life of around 6.7 hours (with a two per cent margin of error) and that when uranium X1 decayed, it became uranium X2 about 99.75 per cent of the time, and uranium Z around 0.25 per cent of the time. He found that the proportion of uranium X to uranium Z extracted from several kilograms of uranyl nitrate remained constant over time, strongly indicating that uranium X was the mother of uranium Z. To prove this, Hahn obtained a hundred kilograms of uranyl nitrate; separating the uranium X from it took weeks. He found that the half life of the parent of uranium Z differed from the known 24 day half life of uranium X1 by no more than two or three days, but was unable to get a more accurate value. Hahn concluded that uranium Z and uranium X2 were both the same isotope of protactinium (protactinium-234), and they both decayed into uranium II (uranium-234), but with different half lives.
Uranium Z was the first example of nuclear isomerism. Walther Gerlach later remarked that this was "a discovery that was not understood at the time but later became highly significant for nuclear physics". Not until 1936 was Carl Friedrich von Weizsäcker able to provide a theoretical explanation of the phenomenon. For this discovery, whose full significance was recognised by very few, Hahn was again proposed for the Nobel Prize in Chemistry by Bernhard Naunyn, Goldschmidt and Planck. | 0 | Theoretical and Fundamental Chemistry |
Selenenic acids derived from selenocysteine are involved in cell signaling and certain enzymatic processes. The best known selenoenzyme, glutathione peroxidase (GPx), catalyzes the reduction of peroxides by glutathione (GSH). The selenenic acid intermediate (E-SeOH) is formed upon oxidation of the catalytically active selenol (E-SeH) by hydrogen peroxide. This selenenic acid derivative of the peroxidase then reacts with a thiol-containing cofactor (GSH) to generate the key intermediate selenenyl sulfide (E-SeSG). This intermediate is subsequently attacked by a second GSH to regenerate the selenol and the glutathione cofactor is released in its oxidized form, GSSG. The catalytic mechanism of GPx, involves selenol (R-SeH), selenenyl sulfide (R1-SeS-R2), and selenenic acid intermediates.
:RSeH + HO → RSeOH + HO
:RSeOH + GSH → GS-SeR + HO
:GS-SeR + GSH → GS-SG + RSeH
In the absence of thiols, selenols tend to overoxidize to produce seleninic acids. Many organoselenium compounds (selenenamides, diaryl diselenides) contain "interesting" biological activities. Their activity is attributed to their mimicry of glutathione peroxidase activity. They reduce hydroperoxides that otherwise convert to toxic byproducts and/or reactive oxygen species that can cause further damage to the cell. | 0 | Theoretical and Fundamental Chemistry |
Carboximidates can act as protecting group for alcohols. For example, the base catalyzed reaction of benzyl alcohol upon trichloroacetonitrile yields a trichloroacetimidate. This species has orthogonal stability to acetate and TBS protections and may be cleaved by acid hydrolysis. | 0 | Theoretical and Fundamental Chemistry |
The resorcinarene hexamer has been described as a yoctolitre reaction vessel. Within the confines of the container, terpene cyclizations and iminium catalyzed reactions have been observed. | 0 | Theoretical and Fundamental Chemistry |
In general, ultraviolet detectors use either a solid-state device, such as one based on silicon carbide or aluminium nitride, or a gas-filled tube as the sensing element. UV detectors that are sensitive to UV in any part of the spectrum respond to irradiation by sunlight and artificial light. A burning hydrogen flame, for instance, radiates strongly in the 185- to 260-nanometer range and only very weakly in the IR region, whereas a coal fire emits very weakly in the UV band yet very strongly at IR wavelengths; thus, a fire detector that operates using both UV and IR detectors is more reliable than one with a UV detector alone. Virtually all fires emit some radiation in the UVC band, whereas the Suns radiation at this band is absorbed by the Earths atmosphere. The result is that the UV detector is "solar blind", meaning it will not cause an alarm in response to radiation from the Sun, so it can easily be used both indoors and outdoors.
UV detectors are sensitive to most fires, including hydrocarbons, metals, sulfur, hydrogen, hydrazine, and ammonia. Arc welding, electrical arcs, lightning, X-rays used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect. | 0 | Theoretical and Fundamental Chemistry |
In the case of oxide copper ore, a heap leaching pad will dissolve a dilute copper sulfate solution in a weak sulfuric acid solution. This pregnant leach solution (PLS) is pumped to an extraction mixer settler where it is mixed with the organic phase (a kerosene hosted extractant). The copper transfers to the organic phase, and the aqueous phase (now called raffinate) is pumped back to the heap to recover more copper.
In a high-chloride environment typical of Chilean copper mines, a wash stage will rinse any residual pregnant solution entrained in the organic with clean water.
The copper is then stripped from organic phase in the strip stage into a strong sulfuric acid solution suitable for electrowinning. This strong acid solution is called barren electrolyte when it enters the cell, and strong electrolyte when it is copper bearing after reacting in the cell. | 0 | Theoretical and Fundamental Chemistry |
"Ternatin" is a term used for two unrelated categories of biochemical compounds:
* The ternatin heptapeptide derived from the mushroom Coriolus versicolor
* Delphinidin ternatins derivatives of delphinidin, an anthocyanidin | 1 | Applied and Interdisciplinary Chemistry |
The geometry of a base, or base pair step can be characterized by 6 coordinates: shift, slide, rise, tilt, roll, and twist. These values precisely define the location and orientation in space of every base or base pair in a nucleic acid molecule relative to its predecessor along the axis of the helix. Together, they characterize the helical structure of the molecule. In regions of DNA or RNA where the normal structure is disrupted, the change in these values can be used to describe such disruption.
For each base pair, considered relative to its predecessor, there are the following base pair geometries to consider:
* Shear
* Stretch
* Stagger
* Buckle
* Propeller: rotation of one base with respect to the other in the same base pair.
* Opening
* Shift: displacement along an axis in the base-pair plane perpendicular to the first, directed from the minor to the major groove.
* Slide: displacement along an axis in the plane of the base pair directed from one strand to the other.
* Rise: displacement along the helix axis.
* Tilt: rotation around the shift axis.
* Roll: rotation around the slide axis.
* Twist: rotation around the rise axis.
* x-displacement
* y-displacement
* inclination
* tip
* pitch: the height per complete turn of the helix.
Rise and twist determine the handedness and pitch of the helix. The other coordinates, by contrast, can be zero. Slide and shift are typically small in B-DNA, but are substantial in A- and Z-DNA. Roll and tilt make successive base pairs less parallel, and are typically small.
"Tilt" has often been used differently in the scientific literature, referring to the deviation of the first, inter-strand base-pair axis from perpendicularity to the helix axis. This corresponds to slide between a succession of base pairs, and in helix-based coordinates is properly termed "inclination". | 0 | Theoretical and Fundamental Chemistry |
By determination of the interaction partners of unknown proteins, the possible functions of these new proteins may be inferred. This can be done using a single known protein against a library of unknown proteins or conversely, by selecting from a library of known proteins using a single protein of unknown function. | 1 | Applied and Interdisciplinary Chemistry |
An MC-ICP-MS instrument is a multiple collector mass spectrometer with a plasma source. MC-ICP-MS was developed to improve the precision achievable by ICP-MS during isotope-ratio measurements. Conventional ICP-MS analysis uses a quadrupole analyser, which only allows single-collector analysis. Due to the inherent instability of the plasma, this limits the precision of ICP-MS with a quadrupole analyzer to around 1%, which is insufficient for most radiogenic isotope systems.
Isotope-ratio analysis for radiometric dating has normally been determined by TIMS. However, some systems (e.g. Hf-W and Lu-Hf) are difficult or impossible to analyse by TIMS, due to the high ionization potential of the elements involved. Therefore, these methods can now be analysed using MC-ICP-MS.
The Ar-ICP produces an ion-beam with a large inherent kinetic energy distribution, which makes the design of the mass-spectrometer somewhat more complex than it is the case for conventional TIMS instruments. First, different from Quadrupole ICP-MS systems, magnetic sector instruments have to operate with a higher acceleration potential (several 1000 V) in order to minimize the energy distribution of the ion beam. Modern instruments operate at 6-10kV.
The radius of deflection of an ion within a magnetic field depends on the kinetic energy and the mass/charge ratio of the ion (strictly, the magnet is a momentum analyzer not just a mass analyzer). Because of the large energy distribution, ions with similar mass/charge ratio can have very different kinetic energies and will thus experience different deflection for the same magnetic field. In practical terms one would see that ions with the same mass/charge ratio focus at different points in space. However, in a mass-spectrometer one wants ions with the same mass/charge ratio to focus at the same point, e.g. where the detector is located. In order to overcome these limitations, commercial MC-ICP-MS are double-focusing instruments. In a double-focusing mass-spectrometer ions are focused due to kinetic energy by the ESA (electro-static-analyzer) and kinetic energy + mass/charge (momentum) in the magnetic field. Magnet and ESA are carefully chosen to match the energy focusing properties of one another and are arranged so that the direction of energy focusing is in opposite directions. To simplify, two components have an energy focus term, when arranged properly, the energy term cancels out and ions with the same mass/charge ratio focus at the same point in space. It is important to note, double-focusing does not reduce the kinetic energy distribution and different kinetic energies are not filtered or homogenized. Double-focusing works for single as well as multi-collector instruments. In single collector instruments ESA and magnet can be arranged in either forward geometry (first ESA then magnet) or reversed geometry (magnet first then ESA), as only point-to-point focusing is required. In multi-collector instruments, only forward geometry (ESA then magnet) is possible due to the array of detectors and the requirements of a focal plane rather than a focal point. | 0 | Theoretical and Fundamental Chemistry |
Schrock entered the olefin metathesis field in 1979 as an extension of work on tantalum alkylidenes. The initial result was disappointing as reaction of with ethylene yielded only a metallacyclopentane, not metathesis products:
But by tweaking this structure to a (replacing chloride by t-butoxide and a cyclopentadienyl by an organophosphine, metathesis was established with cis-2-pentene. In another development, certain tungsten oxo complexes of the type were also found to be effective.
Schrock alkylidenes for olefin metathesis of the type were commercialized starting in 1990.
The first asymmetric catalyst followed in 1993
With a Schrock catalyst modified with a BINOL ligand in a norbornadiene ROMP leading to highly stereoregular cis, isotactic polymer. | 0 | Theoretical and Fundamental Chemistry |
Paper-based microfluidic devices fill a growing niche for portable, cheap, and user-friendly medical diagnostic systems.
Paper based microfluidics rely on the phenomenon of capillary penetration in porous media. To tune fluid penetration in porous substrates such as paper in two and three dimensions, the pore structure, wettability and geometry of the microfluidic devices can be controlled while the viscosity and evaporation rate of the liquid play a further significant role. Many such devices feature hydrophobic barriers on hydrophilic paper that passively transport aqueous solutions to outlets where biological reactions take place. Paper-based microfluidics are considered as portable point-of-care biosensors used in a remote setting where advanced medical diagnostic tools are not accessible. Current applications include portable glucose detection and environmental testing, with hopes of reaching areas that lack advanced medical diagnostic tools. | 1 | Applied and Interdisciplinary Chemistry |
In characteristic manner, TsCl converts alcohols (abbreviated ROH) into the corresponding toluenesulfonate esters, or tosyl derivatives ("tosylates"):
: CHCHSOCl + ROH → CHCHSOOR + HCl
Tosylates can be cleaved with lithium aluminium hydride:
: 4 CHCHSOOR + LiAlH → LiAl(OSCHCH) + 4 RH
Thus, tosylation followed by reduction allows for removal of a hydroxyl group.
Likewise, TsCl is used to prepare sulfonamides from amines:
:CHCHSOCl + RNH → CHCHSONR + HCl
The resulting sulfonamides are non-basic and, when derived from primary amines, are even acidic.
TsCl reacts with hydrazine to give p-toluenesulfonyl hydrazide.
The preparation of tosyl esters and amides are conducted in the presence of a base, which absorbs hydrogen chloride. The selection of the base is often crucial to the efficiency of tosylation. Typical bases include pyridine and triethylamine. Unusual bases are also used; for example, catalytic amounts of trimethylammonium chloride in the presence of triethylamine is highly effective by virtue of the trimethylamine. | 0 | Theoretical and Fundamental Chemistry |
The Scatchard equation is an equation used in molecular biology to calculate the affinity and number of binding sites of a receptor for a ligand. It is named after the American chemist George Scatchard. | 1 | Applied and Interdisciplinary Chemistry |
Some ion channels are classified by the duration of their response to stimuli:
*Transient receptor potential channels: This group of channels, normally referred to simply as TRP channels, is named after their role in Drosophila visual phototransduction. This family, containing at least 28 members, is diverse in its mechanisms of activation. Some TRP channels remain constitutively open, while others are gated by voltage, intracellular Ca, pH, redox state, osmolarity, and mechanical stretch. These channels also vary according to the ion(s) they pass, some being selective for Ca while others are less selective cation channels. This family is subdivided into 6 subfamilies based on homology: canonical TRP (TRPC), vanilloid receptors (TRPV), melastatin (TRPM), polycystins (TRPP), mucolipins (TRPML), and ankyrin transmembrane protein 1 (TRPA). | 1 | Applied and Interdisciplinary Chemistry |
Ketosis is a metabolic state characterized by elevated levels of ketone bodies in the blood or urine. Physiological ketosis is a normal response to low glucose availability, such as low-carbohydrate diets or fasting, that provides an additional energy source for the brain in the form of ketones. In physiological ketosis, ketones in the blood are elevated above baseline levels, but the body's acid–base homeostasis is maintained. This contrasts with ketoacidosis, an uncontrolled production of ketones that occurs in pathologic states and causes a metabolic acidosis, which is a medical emergency. Ketoacidosis is most commonly the result of complete insulin deficiency in type 1 diabetes or late-stage type 2 diabetes. Ketone levels can be measured in blood, urine or breath and are generally between 0.5 and 3.0 millimolar (mM) in physiological ketosis, while ketoacidosis may cause blood concentrations greater than 10 mM.
Trace levels of ketones are always present in the blood and increase when blood glucose reserves are low and the liver shifts from primarily metabolizing carbohydrates to metabolizing fatty acids. This occurs during states of increased fatty acid oxidation such as fasting, starvation, carbohydrate restriction, or prolonged exercise. When the liver rapidly metabolizes fatty acids into acetyl-CoA, some acetyl-CoA molecules can then be converted into ketone bodies: pyruvate, acetoacetate, beta-hydroxybutyrate, and acetone. These ketone bodies can function as an energy source as well as signalling molecules. The liver itself cannot utilize these molecules for energy, so the ketone bodies are released into the blood for use by peripheral tissues including the brain.
When ketosis is induced by carbohydrate restriction, it is sometimes referred to as nutritional ketosis. A low-carbohydrate, moderate protein diet that can lead to ketosis is called a ketogenic diet. Ketosis is well-established as a treatment for epilepsy and is also effective in treating type 2 diabetes. | 1 | Applied and Interdisciplinary Chemistry |
There is evidence that immunological mechanisms may injure hypothermically perfused kidneys after reimplantation if the perfusate contained specific antibody. Cross described two pairs of human cadaver kidneys that were perfused simultaneously with cryoprecipitated plasma containing type specific HLA antibody to one of the pairs. Both these kidneys suffered early arterial thrombosis. Light described similar hyperacute rejection following perfusion storage and showed that the cryoprecipitated plasma used contained cytotoxic IgM antibody. This potential danger of using cryoprecipitated plasma was demonstrated experimentally by Filo who perfused dog kidneys for 24 hours with specifically sensitised cryoprecipitated dog plasma and found that he could induce glomerular and vascular lesions with capillary engorgement, endothelial swelling, infiltration by polymorphonuclear leucocytes and arterial thrombosis. Immunofluorescent microscopy demonstrated specific binding of IgG along endothelial surfaces, in glomeruli, and also in vessels. After reimplantation, complement fixation and tissue damage occurred in a similar pattern. There was some correlation between the severity of the histological damage and subsequent function of the kidneys.
Many workers have attempted to prevent kidneys rewarming during reimplantation but only Cohen has described using a system of active cooling. Measurements of lysosomal enzyme release from kidneys subjected to sham anastomoses, when either in or out of the cooling system, demonstrated how sensitive kidneys were to rewarming after a period of cold storage, and confirmed the effectiveness of the cooling system in preventing enzyme release. A further factor in minimising injury at the reimplantation operations may have been that the kidneys were kept at 7 °C within the cooling coil, which was within a degree of the temperature used during perfusion storage, so that the kidneys were not subjected to the greater changes in temperature that would have occurred if ice cooling had been used.
Dempster described using slow release of the vascular clamps at the end of kidney reimplantation operations to avoid injuring the kidney, but other workers have not mentioned whether or not they used this manoeuvre. After Cohen found vascular injury with intra renal bleeding after 3 days of perfusion storage, a technique of slow revascularisation was used for all subsequent experiments, with the aim of giving the intra- renal vessels time to recover their tone sufficiently to prevent full systolic pressure being applied to the fragile glomerular vessels. The absence of gross vascular injury in his later perfusions may be attributable to the use of this manoeuvre. | 1 | Applied and Interdisciplinary Chemistry |
Live copepods are used in the saltwater aquarium hobby as a food source and are generally considered beneficial in most reef tanks. They are scavengers and also may feed on algae, including coralline algae. Live copepods are popular among hobbyists who are attempting to keep particularly difficult species such as the mandarin dragonet or scooter blenny. They are also popular to hobbyists who want to breed marine species in captivity. In a saltwater aquarium, copepods are typically stocked in the refugium. | 1 | Applied and Interdisciplinary Chemistry |
Hattori's research interest has also extended to porphyry-type deposits, which supply critical metals such as copper, molybdenum, and gold. Through her research, she presented evidence supporting the notion that sulfur and metals have their origin in the mantle, and proposed that they were extracted and transported by mafic magmas from the mantle to shallow crustal levels. This proposal was based on her earlier work on Pinatubo eruption products, where metals and sulphur are released from mafic magmas during their ascent and incorporated into overlying erupted felsic magmas. Furthermore, Cees-Jan DeHoog, her post-doctoral research fellow, provided evidence that oxidized magmas are capable to transport metals and sulphur from deep in the mantle to shallow levels of crust. | 0 | Theoretical and Fundamental Chemistry |
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