text stringlengths 105 4.57k | label int64 0 1 | label_text stringclasses 2
values |
|---|---|---|
Above approximately 900 °C a typical low-carbon steel is composed entirely of austenite, a high-temperature phase of iron that has a cubic close-packed crystal structure. On cooling, it tends to transform into a mixture of phases, ferrite and cementite, depending on the exact chemical composition. A steel of eutectoid composition will under equilibrium conditions transform into pearlite – an interleaved mixture of ferrite and cementite (FeC). In addition to the thermodynamic considerations indicated by the phase diagram, the phase transformations in steel are heavily influenced by the chemical kinetics. This is because the diffusion of iron atoms becomes difficult below about 600 °C under typical processing conditions. As a consequence, a complex array of microstructures occurs when the atomic mobility is limited. This leads to the complexity of steel microstructures which are strongly influenced by the cooling rate. This can be illustrated by a continuous cooling transformation (CCT) diagram which plots the time required to form a phase when a sample is cooled at a specific rate thus showing regions in time-temperature space from which the expected phase fractions can be deduced for a given thermal cycle.
If the steel is cooled slowly or isothermally transformed at elevated temperatures, the microstructure obtained will be closer to equilibrium, containing for example of allotriomorphic ferrite, cementite and pearlite. However, the transformation from austenite to pearlite is a time-dependent reconstructive reaction which requires the large scale movement of the iron and carbon atoms. While the interstitial carbon diffuses readily even at moderate temperatures the self-diffusion of iron becomes extremely slow at temperatures below 600 °C until, for all practical purposes, it stops. As a consequence, a rapidly cooled steel may reach a temperature where pearlite can no longer form despite the reaction being incomplete and the remaining austenite being thermodynamically unstable.
Austenite that is cooled sufficiently rapidly to avoid higher temperature transformations, can form martensite, without any diffusion of either iron or carbon, by the deformation of the austenite's face-centred crystal structure into a distorted body-centred tetragonal or body-centred cubic structure. This non-equilibrium phase can only form at low temperatures, where the driving force for the reaction is sufficient to overcome the considerable lattice strain imposed by the transformation. The transformation is essentially time-independent with the phase fraction depending only the degree of cooling below the critical martensite start temperature. Further, it occurs without the diffusion of either substitutional or interstitial atoms and so martensite inherits the composition of the parent austenite.
Bainite occupies a region between these two process in a temperature range where iron self-diffusion is limited but there is insufficient driving force to form martensite. The bainite, like martensite, grows without diffusion but some of the carbon then partitions into any residual austenite, or precipitates as cementite. A further distinction is often made between so-called lower-bainite, which forms at temperatures closer to the martensite start temperature, and upper-bainite which forms at higher temperatures. This distinction arises from the diffusion rates of carbon at the temperature at which the bainite is forming. If the temperature is high then the carbon will diffuse rapidly away from the newly formed ferrite and form carbides in the carbon-enriched residual austenite between the ferritic plates leaving them carbide-free. At low temperatures the carbon will diffuse more sluggishly and may precipitate before it can leave the bainitic ferrite. There is some controversy over the specifics of bainite's transformation mechanism; both theories are represented below. | 1 | Applied and Interdisciplinary Chemistry |
3 kinds of ground state or static electrical influences predominate:
* Resonance (mesomeric) effect
* Inductive effect: electrical influence of a group which is transmitted primarily by polarization of the bonding electrons from one atom to the next
* Direct electrostatic (field) effect: electrical influence of a polar or dipolar substituent which is transmitted primarily to the reactive group through space (including solvent, if any) according to the laws of classical electrostatics
The latter two influences are often treated together as a composite effect, but are treated here separately. Westheimer demonstrated that the electrical effects of π-substituted dipolar groups on the acidities of benzoic and phenylacetic acids can be quantitatively correlated, by assuming only direct electrostatic action of the substituent on the ionizable proton of the carboxyl group. Westheimer's treatment worked well except for those acids with substituents that have unshared electron pairs such as –OH and –OCH3, as these substituents interact strongly with the benzene ring.
Roberts and Moreland studied the reactivities of 4-substituted bicyclo[2.2.2]octane-1-carboxylic acids and esters. In such a molecule, transmission of electrical effects of substituents through the ring by resonance is not possible. Hence, this hints on the role of the π-electrons in the transmission of substituent effects through aromatic systems.
Reactivity of 4-substituted bicyclo[2.2.2]octane-1-carboxylic acids and esters were measured in 3 different processes, each of which had been previously used with the benzoic acid derivatives. A plot of log(k) against log(K) showed a linear relationship. Such linear relationships correspond to linear free energy relationships, which strongly imply that the effect of the substituents are exerted through changes of potential energy and that the steric and entropy terms remain almost constant through the series. The linear relationship fit well in the Hammett Equation. For the 4-substituted bicyclo[2.2.2.]octane-1-carboxylic acid derivatives, the substituent and reaction constants are designated σ’ and ρ’. | 0 | Theoretical and Fundamental Chemistry |
To understand the electronic behavior of a solar cell, it is useful to create a model which is electrically equivalent, and is based on discrete ideal electrical components whose behavior is well defined. An ideal solar cell may be modelled by a current source in parallel with a diode; in practice no solar cell is ideal, so a shunt resistance and a series resistance component are added to the model. The resulting equivalent circuit of a solar cell is shown on the right. Also shown, on the left, is the schematic representation of a solar cell for use in circuit diagrams. There are several electrical models that translate the solar cell's behaviour. The most used one is presented below, but others novel models have been proposed, like the d1MxP | 0 | Theoretical and Fundamental Chemistry |
Using laser light scattering, Bax examined how speech-generated droplets and aerosols may be a dominant SARS-CoV-2 transmission mode that may be mitigated by wearing face coverings or face masks. | 0 | Theoretical and Fundamental Chemistry |
Primary and secondary waves are body waves that travel within the Earth. The motion and behavior of both P and S waves in the Earth are monitored to probe the interior structure of the Earth. Discontinuities in velocity as a function of depth are indicative of changes in phase or composition. Differences in arrival times of waves originating in a seismic event like an earthquake as a result of waves taking different paths allow mapping of the Earth's inner structure. | 1 | Applied and Interdisciplinary Chemistry |
Christoph Weder is the former director of the Adolphe Merkle Institute (AMI) at the University of Fribourg, Switzerland, and a professor of polymer chemistry and materials. He is best known for his work on stimuli-responsive polymers, polymeric materials that change one or more of their properties when exposed to external cues. His research is focused on the development, investigation, and application of functional materials, in particular stimuli-responsive and bio-inspired polymers. | 0 | Theoretical and Fundamental Chemistry |
The non-dispersive infrared analysis (NDIR) method offers the only practical interference-free method for detecting CO in TOC analysis. The principal advantage of using NDIR is that it directly and specifically measures the CO generated by oxidation of the organic carbon in the oxidation reactor, rather than relying on a measurement of a secondary, corrected effect, such as used in conductivity measurements.
A traditional NDIR detector relies upon flow-through-cell technology, where the oxidation product flows into and out of the detector continuously. A region of absorption of infrared light specific to CO, usually around 4.26 µm (2350 cm), is measured over time as the gas flows through the detector. A second reference measurement that is non-specific to CO is also taken concentration in the detector at that moment. As the gas continues to flow into and out of the detector cell the sum of the measurements results in a peak that is integrated and correlated to the total CO concentration in the sample aliquot.
A new advance of NDIR technology is static pressurized concentration (SPC). The exit valve of the NDIR is closed to allow the detector to become pressurized. Once the gases in the detector have reached equilibrium, the concentration of the CO is analyzed. This pressurization of the sample gas stream in the NDIR, a patented technique, allows for increased sensitivity and precision by measuring the entirety of the oxidation products of the sample in one reading, compared to flow-through cell technology. The output signal is proportional to the concentration of CO in the carrier gas, from the oxidation of the sample aliquot. UV/ Persulfate oxidation combined with NDIR detection provides good oxidation of organics, low instrument maintenance, good precision at ppb levels, relatively fast sample analysis time and easily accommodates multiple applications, including purified water (PW), water for injection (WFI), CIP, drinking water and ultra-pure water analyses. | 0 | Theoretical and Fundamental Chemistry |
A well studied biradical is trimethylenemethane (TMM), . In 1966 Paul Dowd determined with electron spin resonance that this compound also has a triplet state. In a crystalline host the 6 hydrogen atoms in TMM are identical. | 0 | Theoretical and Fundamental Chemistry |
Aquatic toxicity testing subjects key indicator species of fish or crustacea to certain concentrations of a substance in their environment to determine the lethality level. Fish are exposed for 96 hours while crustacea are exposed for 48 hours. While GHS does not define toxicity past 100 mg/L, the EPA currently lists aquatic toxicity as "practically non-toxic" in concentrations greater than 100 ppm.
Note: A category 4 is established for chronic exposure, but simply contains any toxic substance which is mostly insoluble, or has no data for acute toxicity. | 1 | Applied and Interdisciplinary Chemistry |
Bulk materials (>100 nm in size) are expected to have constant physical properties (such as thermal and electrical conductivity, stiffness, density, and viscosity) regardless of their size, for nanoparticles, however, this is different: the volume of the surface layer (a few atomic diameters-wide) becomes a significant fraction of the particle's volume; whereas that fraction is insignificant for particles with a diameter of one micrometer or more. In other words, the surface area/volume ratio impacts certain properties of the nanoparticles more prominently than in bulk particles. | 0 | Theoretical and Fundamental Chemistry |
Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air. Industrial biofiltration can be classified as the process of utilizing biological oxidation to remove volatile organic compounds, odors, and hydrocarbons. | 1 | Applied and Interdisciplinary Chemistry |
Benefits of ecosan systems include:
* Minimizing the introduction of pathogens from human excreta into the water cycle (groundwater and surface water) - for example groundwater pollution by pit latrines.
* Conservation of resources through lower water consumption, substitution of mineral fertilizer and minimization of water pollution.
* Less reliance on mined phosphorus and other non-renewable resources for fertilizer production.
* Reduced consumption of energy in fertilizer production: Urea is a major component of urine, yet we produce vast quantities of urea by using fossil fuels. By properly managing urine, treatment costs as well as fertilizer costs can be reduced. | 1 | Applied and Interdisciplinary Chemistry |
BioModels is composed of several branches. The curated branch hosts models that are well curated and annotated. The non-curated-branch provides models that are still not curated, are non-curatable (spatial models, steady-state models etc.), or too huge to be curated. Non-curated models can be later moved into the curated branch. The repository also hosts models which were automatically generated from pathways databases.
All the models are freely available under the Creative Commons CC0 Public Domain Dedication, and can be easily accessed via the website or [http://www.ebi.ac.uk/biomodels-main/webservices Web Services]. One can also download archives of all the models from the [http://ftp.ebi.ac.uk/pub/databases/biomodels/releases/latest/ EBI FTP server].
BioModels announced its 31st release on June 26, 2017. It now publicly provides 144,710 models. This corresponds to 1,640 models published in the literature and 143,070 models automatically generated from pathway resources.
Deposition of models in BioModels is advocated by many scientific journals, included Molecular Systems Biology, all the journals of the Public Library of Science, all the journals of BioMed Central and all the journals published by the Royal Society of Chemistry. | 1 | Applied and Interdisciplinary Chemistry |
Plasma spraying systems can be categorized by several criteria.
Plasma jet generation:
*direct current (DC plasma), where the energy is transferred to the plasma jet by a direct current, high-power electric arc
*induction plasma or RF plasma, where the energy is transferred by induction from a coil around the plasma jet, through which a radio-frequency current passes. This electrode-free technology allows to produce coatings with high purity and high density.
Plasma-forming medium:
*gas-stabilized plasma (GSP), where the plasma forms from a gas; typically argon, hydrogen, helium or their mixtures
*water-stabilized plasma (WSP), where plasma forms from water (through evaporation, dissociation and ionization) or other suitable liquid
*hybrid plasma – with combined gas and liquid stabilization, typically argon and water
Spraying environment:
*atmospheric plasma spraying (APS), performed in ambient air
*controlled atmosphere plasma spraying (CAPS), usually performed in a closed chamber, either filled with inert gas or evacuated
*variations of CAPS: high-pressure plasma spraying (HPPS), low-pressure plasma spraying (LPPS), the extreme case of which is vacuum plasma spraying (VPS, see below)
*underwater plasma spraying
Another variation consists of having a liquid feedstock instead of a solid powder for melting, this technique is known as Solution precursor plasma spray | 1 | Applied and Interdisciplinary Chemistry |
The summation theorems can be interpreted in various ways. The first is that the influence enzymes have over steady-state fluxes and concentrations is not necessarily concentrated at one location. In the past, control of a pathway was considered to be located at one point only, called the master reaction or rate limiting step. The summation theorem suggests this does not necessarily have to be the case.
The flux summation theorem also suggests that there is a total amount of flux control in a pathway such that if one step gains control another step most lose control.
Although flux control is shared, this doesn't imply that control is evenly distributed. For a large network, the average flux control will, according to the flux summation theorem, be equal to , that is a small number. In order for a biological cell to have any appreciable control over a pathway via changes in gene expression, some concentration of flux control at a small number of sites will be necessary. For example, in mammalian cancer cell lines, it has been shown that flux control is concentrated at four sites: glucose import, hexokinase, phosphofructokinase, and lactate export.
Moreover, Kacser and Burns suggested that since the flux–enzyme relationship is somewhat hyperbolic, and that for most enzymes, the wild-type diploid level of enzyme activity occurs where the curve is reaching a point in the curve where changes have little effect, then since a heterozygote of the wild-type with a null mutant will have half the enzyme activity it will not exhibit a noticeably reduced flux. Therefore, the wild type appears dominant and the mutant recessive because of the system characteristics of a metabolic pathway. Although originally suggested by Sewall Wright, the development of metabolic control analysis put the idea on a more sound theoretical footing. The flux summation theorem in particular is consistent with the flux summation theorem for large systems. Not all dominance properties can be explained in this way but it does offers an explanation for dominance at least at the metabolic level. | 1 | Applied and Interdisciplinary Chemistry |
One force capable of confining the fuel well enough to satisfy the Lawson criterion is gravity. The mass needed, however, is so great that gravitational confinement is only found in stars—the least massive stars capable of sustained fusion are red dwarfs, while brown dwarfs are able to fuse deuterium and lithium if they are of sufficient mass. In stars heavy enough, after the supply of hydrogen is exhausted in their cores, their cores (or a shell around the core) start fusing helium to carbon. In the most massive stars (at least 8–11 solar masses), the process is continued until some of their energy is produced by fusing lighter elements to iron. As iron has one of the highest binding energies, reactions producing heavier elements are generally endothermic. Therefore, significant amounts of heavier elements are not formed during stable periods of massive star evolution, but are formed in supernova explosions. Some lighter stars also form these elements in the outer parts of the stars over long periods of time, by absorbing energy from fusion in the inside of the star, by absorbing neutrons that are emitted from the fusion process.
All of the elements heavier than iron have some potential energy to release, in theory. At the extremely heavy end of element production, these heavier elements can produce energy in the process of being split again back toward the size of iron, in the process of nuclear fission. Nuclear fission thus releases energy that has been stored, sometimes billions of years before, during stellar nucleosynthesis. | 0 | Theoretical and Fundamental Chemistry |
Another method involves the use of oxalyl chloride:
The reaction is catalysed by dimethylformamide (DMF), which reacts with oxalyl chloride to give the Vilsmeier reagent, an iminium intermediate that which reacts with the carboxylic acid to form a mixed imino-anhydride. This structure undergoes an acyl substitution with the liberated chloride, forming the acid anhydride and releasing regenerated molecule of DMF. Relative to thionyl chloride, oxalyl chloride is more expensive but also a milder reagent and therefore more selective. | 0 | Theoretical and Fundamental Chemistry |
Additive nomenclature is generally recommended for organometallic compounds of groups 3-12 (transition metals and zinc, cadmium and mercury). | 0 | Theoretical and Fundamental Chemistry |
A class of substances known as photocages contain “photosensitive groups, also known as ‘photoremovable protecting groups’, from which target substances are released upon exposure to specific wavelengths of light”. The photosensitive groups physically and chemically protect the target from being released until the molecule undergoes photoreaction. Due to these interactions with light, they are commonly used molecules in photopharmacology. More recently, they have played an important role in photoactivated chemotherapy (PACT). In PACT, photocages utilize a photoremovable protecting group that protects cytotoxic drugs until the bond is cleaved via light interaction and the cytotoxic drug is released. Some well-known photocages include “o-nitrobenzyl derivatives, coumarin derivatives, BODIPY, xanthene derivatives, quinone and diarylenes derivatives”. However, there are limitations with using photocages in clinical applications as there are not many PPGs that can be used in vivo. This is due to PPG-payload conjugates needing to have acceptable solubility and biological inertness for biocompatibility and the need for efficient uncaging above 600 nm.
Figure 5. Example of a photocage release system activated by NIR | 1 | Applied and Interdisciplinary Chemistry |
When brickwork is persistently wet, as in foundations, retaining walls, parapets and chimneys, sulfates in bricks and mortar may in time crystallise and expand and cause mortar and renderings to disintegrate. To minimise this effect specialised brickwork with low sulfate levels should be used. Acid sulfates that are located within the subsoil strata has the same effects on the foundations of a building. Adequate protection can exist using a polythene sheeting to encase the foundations or using a sulfate-resistant Portland cement. To identify the pH level of the ground a soil investigation must take place. | 0 | Theoretical and Fundamental Chemistry |
This enzyme transfers the electron from reduced ferredoxin to to complete the reduction to NADPH. FNR may also accept an electron from NADPH by binding to it. | 0 | Theoretical and Fundamental Chemistry |
The Stored Waste Examination Pilot Plant (SWEPP) is a facility at the Idaho National Laboratory for nondestructively examining containers of radioactive waste to determine if they meet criteria to be stored at the Waste Isolation Pilot Plant. SWEPP is part of the Radioactive Waste Management Complex, located southwest of EBR-I. | 0 | Theoretical and Fundamental Chemistry |
The most common method of measuring amino acid hydrophobicity is partitioning between two immiscible liquid phases. Different organic solvents are most widely used to mimic the protein interior. However, organic solvents are slightly miscible with water and the characteristics of both phases change making it difficult to obtain pure hydrophobicity scale. Nozaki and Tanford proposed the first major hydrophobicity scale for nine amino acids. Ethanol and dioxane are used as the organic solvents and the free energy of transfer of each amino acid was calculated. Non liquid phases can also be used with partitioning methods such as micellar phases and vapor phases. Two scales have been developed using micellar phases. Fendler et al. measured the partitioning of 14 radiolabeled amino acids using sodium dodecyl sulfate (SDS) micelles. Also, amino acid side chain affinity for water was measured using vapor phases. Vapor phases represent the simplest non polar phases, because it has no interaction with the solute. The hydration potential and its correlation to the appearance of amino acids on the surface of proteins was studied by Wolfenden. Aqueous and polymer phases were used in the development of a novel partitioning scale. Partitioning methods have many drawbacks. First, it is difficult to mimic the protein interior. In addition, the role of self solvation makes using free amino acids very difficult. Moreover, hydrogen bonds that are lost in the transfer to organic solvents are not reformed but often in the interior of protein. | 0 | Theoretical and Fundamental Chemistry |
The use of η to denote hapticity is systematised. The use of η is not recommended. When the specification of the atoms involved is ambiguous the position of the atoms must be specified. This is illustrated by the examples:
* Cr(η-CH), named as bis(η-benzene)chromium as all of the (contiguous) atoms in the benzene ligands are involved their position does not have to be specified
* [(1,2,5,6-η)-cycloocta-1,3,5,7-tetraene](η-cyclopentadienyl)cobalt in this only two (at positions 1 and 5) of the four double bonds are linked to the central atom. | 0 | Theoretical and Fundamental Chemistry |
Dead zones can be classified by type, and are identified by the length of their occurrence:
* Permanent dead zones are deep water occurrences that rarely exceed 2 milligrams per liter.
* Temporary dead zones are short lived dead zones lasting hours or days.
* Seasonal dead zones are annually occurring, typically in warm months of summer and autumn.
* Diel cycling hypoxia is a specific seasonal dead zone that only becomes hypoxic during the night
The type of dead zone can, in some ways, be categorized by the time required for the water to return to full health. This time frame depends on the intensity of eutrophication and level of oxygen depletion. A water body that sinks to anoxic conditions and experiences extreme reduction in community diversity will have to travel a much longer path to return to full health. A water body that only experiences mild hypoxia and maintains community diversity and maturity will require a much shorter path length to return to full health. | 0 | Theoretical and Fundamental Chemistry |
Ultrasensitive behavior is typically represented by a sigmoidal curve, as small alterations in the stimulus can trigger large changes in the response . One such relation is the Hill equation:
where is the Hill coefficient which quantifies the steepness of the sigmoidal stimulus-response curve and it is therefore a sensitivity parameter. It is often used to assess the cooperativity of a system. A Hill coefficient greater than one is indicative of positive cooperativity and thus, the system exhibits ultrasensitivity.
Systems with a Hill coefficient of 1 are noncooperative and follow the classical Michaelis-Menten kinetics. Enzymes exhibiting noncooperative activity are represented by hyperbolic stimulus/response curves, compared to sigmoidal curves for cooperative (ultrasensitive) enzymes.
In mitogen-activated protein kinase (MAPK) signaling (see example below), the ultrasensitivity of the signaling is supported by the sigmoidal stimulus/response curve that is comparable to an enzyme with a Hill coefficient of 4.0-5.0. This is even more ultrasensitive to the cooperative binding activity of hemoglobin, which has a Hill coefficient of 2.8. | 1 | Applied and Interdisciplinary Chemistry |
Zearalanone (ZAN) is a mycoestrogen that is a derivative of zearalenone (ZEN). Zearalanone can be extracted from medical herbs and edible herbs along with aflatoxins in the same time by a specific immunoaffinity column. | 1 | Applied and Interdisciplinary Chemistry |
Glyceroneogenesis can be regulated at two reaction pathways. First, it can be held at the decarboxylation of oxaloacetate to phosphoenolpyruvate. Secondly, the TCA cycle can affect glyceroneogenesis when the glutamate or substrates in the TCA cycle are being used as a precursor.
Decarboxylation of oxaloacetate to phosphoenolpyruvate is catalyzed by PEPC-K, the essential enzyme which regulates glyceroneogenesis. Increases in PEPC-K levels or overexpression of the gene that codes for PEPC-K will increase glyceroneogenesis. Also, oxaloacetate can be decarboxylated to phosphoenolpyruvate when more PEPC-K can catalyze the reaction.
Gene expression of PEPC-K can be suppressed by norepinephrine, glucocorticoids, and insulin. Norepinephrine is a neurotransmitter which decreases the activity of PEPC-K when the cell is in a cold environment. Glucocorticoids are steroid hormones involved in the reciprocal regulation of glyceroneogenesis in the liver and adipose tissues. Through a poorly-understood mechanism, they induce transcription of PEPC-K in the liver while decreasing transcription in adipose tissues. Insulin is a peptide hormone that causes cells to take in glucose. Through glyceroneogenesis, insulin down-regulates the expression of PEPC-K in both liver and adipose tissues. | 1 | Applied and Interdisciplinary Chemistry |
The matrix consists of crystallized molecules, of which the three most commonly used are sinapinic acid, α-cyano-4-hydroxycinnamic acid (α-CHCA, alpha-cyano or alpha-matrix) and 2,5-dihydroxybenzoic acid (DHB). A solution of one of these molecules is made, often in a mixture of highly purified water and an organic solvent such as acetonitrile (ACN) or ethanol. A counter ion source such as trifluoroacetic acid (TFA) is usually added to generate the [M+H] ions. A good example of a matrix-solution would be 20 mg/mL sinapinic acid in ACN:water:TFA (50:50:0.1).
The identification of suitable matrix compounds is determined to some extent by trial and error, but they are based on some specific molecular design considerations. They are of a fairly low molecular weight (to allow easy vaporization), but are large enough (with a low enough vapor pressure) not to evaporate during sample preparation or while standing in the mass spectrometer. They are often acidic, therefore act as a proton source to encourage ionization of the analyte. Basic matrices have also been reported. They have a strong optical absorption in either the UV or IR range, so that they rapidly and efficiently absorb the laser irradiation. This efficiency is commonly associated with chemical structures incorporating several conjugated double bonds, as seen in the structure of cinnamic acid. They are functionalized with polar groups, allowing their use in aqueous solutions. They typically contain a chromophore.
The matrix solution is mixed with the analyte (e.g. protein-sample). A mixture of water and organic solvent allows both hydrophobic and water-soluble (hydrophilic) molecules to dissolve into the solution. This solution is spotted onto a MALDI plate (usually a metal plate designed for this purpose). The solvents vaporize, leaving only the recrystallized matrix, but now with analyte molecules embedded into MALDI crystals. The matrix and the analyte are said to be co-crystallized. Co-crystallization is a key issue in selecting a proper matrix to obtain a good quality mass spectrum of the analyte of interest.
In analysis of biological systems, inorganic salts, which are also part of protein extracts, interfere with the ionization process. The salts can be removed by solid phase extraction or by washing the dried-droplet MALDI spots with cold water. Both methods can also remove other substances from the sample. The matrix-protein mixture is not homogeneous because the polarity difference leads to a separation of the two substances during co-crystallization. The spot diameter of the target is much larger than that of the laser, which makes it necessary to make many laser shots at different places of the target, to get the statistical average of the substance concentration within the target spot.
The matrix can be used to tune the instrument to ionize the sample in different ways. As mentioned above, acid-base like reactions are often utilized to ionize the sample, however, molecules with conjugated pi systems, such as naphthalene like compounds, can also serve as an electron acceptor and thus a matrix for MALDI/TOF. This is particularly useful in studying molecules that also possess conjugated pi systems. The most widely used application for these matrices is studying porphyrin-like compounds such as chlorophyll. These matrices have been shown to have better ionization patterns that do not result in odd fragmentation patterns or complete loss of side chains. It has also been suggested that conjugated porphyrin like molecules can serve as a matrix and cleave themselves eliminating the need for a separate matrix compound. | 1 | Applied and Interdisciplinary Chemistry |
The transposed Paternò−Büchi reaction involves a ππ* excited state of alkene reacting with a ground state carbonyl functionality. This is reversal of the traditional Paternò−Büchi reaction where an excited carbonyl group reacts with a ground state alkene. This strategy was first reported by Sivaguru and co-workers with reaction of enamides.
<br /> | 0 | Theoretical and Fundamental Chemistry |
Nitrite consumption is primarily determined by the amount of processed meats eaten, and the concentration of nitrates in these meats. Although nitrites are the nitrogen compound chiefly used in meat curing, nitrates are used as well. Nitrates lead to the formation of nitrosamines. The production of carcinogenic nitrosamines may be inhibited by the use of the antioxidants vitamin C and the alpha-tocopherol form of vitamin E during curing.
Many meat processors claim their meats (e.g. bacon) is "uncured" - which is a marketing claim with no factual basis: there is no such thing as "uncured" bacon (as that would be, essentially, raw sliced pork belly). "Uncured" meat is in fact actually cured with nitrites with virtually no distinction in process -- the only difference being the USDA labeling requirement between nitrite of vegetable origin (such as from celery) vs. synthetic sodium nitrite. (An analogy would be purified "sea salt" vs. sodium chloride - both being the exact same chemical with the only essential difference being the origin.)
Anti-hypertensive diets, such as the DASH diet, typically contain high levels of nitrates, which are first reduced to nitrite in the saliva, as detected in saliva testing, prior to forming nitric oxide. | 0 | Theoretical and Fundamental Chemistry |
Based on the simplifying assumption that the signal can be attributed to temperature change alone, with the effects of salinity and ice volume change ignored, Epstein et al. (1953) estimated that
a increase of 0.22‰ is equivalent to a cooling of 1 °C (or 1.8 °F).
More precisely, Epstein et al. (1953) give a quadratic extrapolation for the temperature, as
where T is the temperature in °C (based on a least-squares fit for a range of temperature values between 9 °C and 29 °C, with a standard deviation of ±0.6 °C, and δ is δO for a calcium carbonate sample). | 0 | Theoretical and Fundamental Chemistry |
The Lewis basic lone pairs on sulfur dominate the sulfides' reactivity. Sulfides readily alkylate to stable sulfonium salts, such as trimethylsulfonium iodide:
Sulfides also oxidize easily to sulfoxides (), which can themselves be further oxidized to sulfones (). Hydrogen peroxide is a typical oxidant—for example, with dimethyl sulfide ():
In analogy to their easy alkylation, sulfides bind to metals to form thioether complexes. Consequently Lewis acids do not decompose thioethers as they do ethers. Sulfides are soft ligands, but their affinity for metals is lower than typical phosphines. Chelating thioethers are known, such as 1,4,7-trithiacyclononane.
Sulfides undergo hydrogenolysis in the presence of certain metals:
Raney nickel is useful for stoichiometric reactions in organic synthesis whereas molybdenum-based catalysts are used to "sweeten" petroleum fractions, in the process called hydrodesulfurization.
Unlike ethers, thioethers are stable in the presence of Grignard reagents. The protons adjacent to the sulfur atom are labile, and can be deprotonated with strong bases. | 0 | Theoretical and Fundamental Chemistry |
* Advantages
** At large, protocells are advantageous because they can store more drugs, be loaded faster than other nanomedicine delivery systems, and are more stable than liposomes. By keeping more drugs, researchers can reduce the quantity of medications needed to be administered, potentially reducing side effects and toxicity. In like manner, controlling the direction and movement of a drug also reduces the amount of medication needed, increases the speed of delivery, and allows for the controlled release of high-concentration multicomponent cargo within cancer cells. Finally, the stability of protocells is vital because it ensures that the drugs remain effective and do not degrade before reaching their target. Overall, the development of protocells as a drug delivery system, coupled with chemotactic properties, holds great promise for targeted drug delivery.
* Limitations
** One fundamental limitation of protocells is their modularity and versatility, which must be accounted for when assessing clinical applications. Modularity and versatility are essential considerations for targeted drug delivery because they enable the customization and adaptation of drug delivery systems to meet specific clinical needs. In fact, without modularity and versatility, it will be hard to tailor protocells to different therapeutic applications and particular populations. Another critical challenge, especially when using enzymes to maneuver the protocell, is that the motility reduces when the enzymes become oversaturated with the chemical stimuli. Reducing motility becomes a problem because this is essential for targeted drug delivery efficiency, limiting the system's effectiveness and increasing the risk of off-target effects. Therefore, further research is still needed to improve our understanding of protocells and their potential clinical applications. | 1 | Applied and Interdisciplinary Chemistry |
Raman spectroscopy is one of the easiest methods to integrate into a heterogeneous operando experiment, as these reactions typically occur in the gas phase, so there is very low litter interference and good data can be obtained for the species on the catalytic surface. In order to use Raman, all that is required is to insert a small probe containing two optical fibers for excitation and detection. Pressure and heat complications are essentially negligible, due to the nature of the probe. Operando confocal Raman micro-spectroscopy has been applied to the study of fuel cell catalytic layers with flowing reactant streams and controlled temperature. | 0 | Theoretical and Fundamental Chemistry |
Phenol in the Berthelot reagent can be replaced by a variety of phenolic reagents, the most common being sodium salicylate, which is significantly less toxic. This has been used for blood urea nitrogen (BUN) determinations and commonly is used to determine water and soil total and ammonia-N. Replacement of phenol by 2-phenylphenol reduces interferences by a variety of soil and water constituents and improves color stability at slightly lower pH. | 0 | Theoretical and Fundamental Chemistry |
Brevetoxins share the common backbone structure of polyketides, but there are several methyl and oxygen groups that are not typical of a traditional polyketide synthesis. Labelling studies identifying the origin of the various carbon atoms have shown that the biosynthesis of brevetoxins greatly deviates from the polyketide synthetic pathway.
From the labelling experiments of Brevetoxin-B (BTX-B), a 50-carbon molecule, 16 carbon signals were enhanced by [1-C13] acetate, 30 signals were enhanced by [2-C13] acetate, and 4 carbon signals were enhanced by [methyl-C13] methionine. Furthermore, 14 intact acetate units were identified with a fifteenth two carbon unit with a weak possibility of being an acetate unit. It is clear based on the oxygen locations of BTX-B that this molecule could not be produced using a traditional polyketide synthetic pathway. Attention was turned to the citric acid cycle to solve the problem. Acetate can be used in the polyketide synthetic pathway or modified by the citric acid cycle. Intermediate products of this cycle can then be reintroduced to the polyketide synthetic pathway, resulting in the addition of atypical carbon units. Previous studies of the citric acid pathway revealed three and four carbon units that can potentially explain the atypical condensation and oxidation pattern seen in BTX-B. That being said, there is currently no explanation as to why this particular pattern is favored.
All these things considered, a proposed biosynthetic pathway for brevetoxin class compounds begins with a traditional polyketide synthesis that has the potential to incorporate larger carbon units originating from acetate modified by the citric acid cycle. After the carbon backbone is synthesized, oxidation produces the necessary epoxides that lead to the closure of the multi-ring system. It is unclear if methyl groups as seen in BTX-B are added after cyclization or during the modification of the polyketide metabolites, but it is clear that methyl groups can originate from sources outside of acetate such as S-adenosylmethionine. | 0 | Theoretical and Fundamental Chemistry |
Golden Gate Cloning or Golden Gate assembly is a molecular cloning method that allows a researcher to simultaneously and directionally assemble multiple DNA fragments into a single piece using Type IIS restriction enzymes and T4 DNA ligase. This assembly is performed in vitro. Most commonly used Type IIS enzymes include BsaI, BsmBI, and BbsI.
Unlike standard Type II restriction enzymes like EcoRI and BamHI, these enzymes cut DNA outside of their recognition sites and, therefore, can create non-palindromic overhangs. Since 256 potential overhang sequences are possible, multiple fragments of DNA can be assembled by using combinations of overhang sequences. In practice, this means that Golden Gate Cloning is typically scarless. Additionally, because the final product does not have a Type IIS restriction enzyme recognition site, the correctly-ligated product cannot be cut again by the restriction enzyme, meaning the reaction is essentially irreversible. This has multiple benefits, the first is that it is possible to do digestion and ligation of the DNA fragments in a single reaction, in contrast to conventional cloning methods where these reactions are separate. The second is higher efficiency because the end product cannot be cut again by the restriction enzyme.
A typical thermal cycler protocol oscillates between 37 °C (optimal for restriction enzymes) and 16 °C (optimal for ligases) many times. While this technique can be used for a single insert, researchers have used Golden Gate Cloning to assemble many pieces of DNA simultaneously. | 1 | Applied and Interdisciplinary Chemistry |
Since cyclic AMP is a second messenger and plays vital role in cell signalling, it has been implicated in various disorders but not restricted to the roles given below: | 1 | Applied and Interdisciplinary Chemistry |
After the left-wing uprising in 1944, the newly established far-left authorities in Bulgaria labeled Karamichailova as "unreliable" due to her anti-communist views and prohibited her from going abroad. She continued her work in the field of radioactivity in Bulgaria, initially at Sofia University and later, at the Bulgarian Academy of Sciences, where she received the title of "professor". Karamichailova died of cancer in 1968, most likely from long-term radiation exposure. | 0 | Theoretical and Fundamental Chemistry |
A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, molecule, or phenomenon – that provides scientific evidence of past or present life on a planet. Measurable attributes of life include its complex physical or chemical structures, its use of free energy, and the production of biomass and wastes.
The field of astrobiology uses biosignatures as evidence in the search for past or present extraterrestrial life. | 1 | Applied and Interdisciplinary Chemistry |
The Reynolds number for an object moving in a fluid, called the particle Reynolds number and often denoted , characterizes the nature of the surrounding flow and its fall velocity. | 1 | Applied and Interdisciplinary Chemistry |
The particle size of a spherical object can be unambiguously and quantitatively defined by its diameter. However, a typical material object is likely to be irregular in shape and non-spherical. The above quantitative definition of particle size cannot be applied to non-spherical particles. There are several ways of extending the above quantitative definition to apply to non-spherical particles. Existing definitions are based on replacing a given particle with an imaginary sphere that has one of the properties identical with the particle.
;Volume-based particle size: Volume-based particle size equals the diameter of the sphere that has the same volume as a given particle. Typically used in sieve analysis, as shape hypothesis (sieve's mesh size as the sphere diameter).
:where
::: diameter of representative sphere
::: volume of particle
;Area-based particle size: Area-based particle size equals the diameter of the sphere that has the same surface area as a given particle. Typically used in optical granulometry techniques.
:where
::: diameter of representative sphere
::: surface area of particle | 0 | Theoretical and Fundamental Chemistry |
In an isotopic/achiral environment, enantiomers exhibit identical physicochemical properties, and therefore are indistinguishable under these conditions. For the separation of chiral molecules the challenge is to construct the right chiral environment. In a chromatographic system there are three variables namely, the chiral analyte (CA), mobile phase and stationary phase, that can be manipulated to provide the crucial chiral environment. The strategy is to make these variables to interact with a chiral auxiliary (chiral selector, CS) whereby it forms a diastereomeric complex which has different physicochemical properties and makes it possible to separate the enantiomers. Based on the nature of the diastereomeric complex formed between the CS-CA species, enantiomer separation mythologies are categorized as indirect and direct enantiomer separation mode | 0 | Theoretical and Fundamental Chemistry |
Hammond's postulate is especially important when looking at the rate-limiting step of a reaction. However, one must be cautious when examining a multistep reaction or one with the possibility of rearrangements during an intermediate stage. In some cases, the final products appear in skewed ratios in favor of a more unstable product (called the kinetic product) rather than the more stable product (the thermodynamic product). In this case one must examine the rate-limiting step and the intermediates. Often, the rate-limiting step is the initial formation of an unstable species such as a carbocation. Then, once the carbocation is formed, subsequent rearrangements can occur. In these kinds of reactions, especially when run at lower temperatures, the reactants simply react before the rearrangements necessary to form a more stable intermediate have time to occur. At higher temperatures when microscopic reversal is easier, the more stable thermodynamic product is favored because these intermediates have time to rearrange. Whether run at high or low temperatures, the mixture of the kinetic and thermodynamic products eventually reach the same ratio, one in favor of the more stable thermodynamic product, when given time to equilibrate due to microreversal. | 0 | Theoretical and Fundamental Chemistry |
Both TLR3 and TLR4 use the TRIF-dependent pathway, which is triggered by dsRNA and LPS, respectively. For TLR3, dsRNA leads to activation of the receptor, recruiting the adaptor TRIF. TRIF activates the kinases TBK1 and RIPK1, which creates a branch in the signaling pathway. The TRIF/TBK1 signaling complex phosphorylates IRF3 allowing its translocation into the nucleus and production of Interferon type I. Meanwhile, activation of RIPK1 causes the polyubiquitination and activation of TAK1 and NFκB transcription in the same manner as the MyD88-dependent pathway.
TLR signaling ultimately leads to the induction or suppression of genes that orchestrate the inflammatory response. In all, thousands of genes are activated by TLR signaling, and collectively, the TLRs constitute one of the most pleiotropic yet tightly regulated gateways for gene modulation.
TLR4 is the only TLR that uses all four adaptors. Complex consisting of TLR4, MD2 and LPS recruits TIR domain-containing adaptors TIRAP and MyD88 and thus initiates activation of NFκB (early phase) and MAPK. TLR4-MD2-LPS complex then undergoes endocytosis and in endosome it forms a signalling complex with TRAM and TRIF adaptors. This TRIF-dependent pathway again leads to IRF3 activation and production of type I interferons, but it also activates late-phase NFκB activation. Both late and early phase activation of NFκB is required for production of inflammatory cytokines. | 1 | Applied and Interdisciplinary Chemistry |
The function of the C-terminal domain has been experimentally determined as being important for cytoplasmic localisation. The residues are scattered along the C-terminal domain sequence however once the protein folds, they position themselves closely together. | 1 | Applied and Interdisciplinary Chemistry |
The first ORF of L1 encodes a 500-amino acid, 40-kDa protein that lacks homology with any protein of known function. In vertebrates, it contains a conserved C-terminus domain and a highly variable coiled-coil N-terminus that mediates the formation of ORF1 trimeric complexes. ORF1 trimers have RNA-binding and nucleic acid chaperone activity that are necessary for retrotransposition. | 1 | Applied and Interdisciplinary Chemistry |
At least partly because TNFR2 has no intracellular death domain, TNFR2 is neuroprotective.
Patients with schizophrenia have increased levels of soluble tumor necrosis factor receptor 2 (sTNFR2). | 1 | Applied and Interdisciplinary Chemistry |
The concentration of ATP must be kept above equilibrium level so that the rates of ATP-dependent biochemical reactions meet metabolic demands. A decrease in ATP will result in a decreased saturation of enzymes that use ATP as substrate, and thus a decreased reaction rate. The concentration of ATP is also kept higher than that of AMP, and a decrease in the ATP/AMP ratio triggers AMPK to activate cellular processes that will return ATP and AMP concentrations to steady state.
In one step of the glycolysis pathway catalyzed by PFK-1, the equilibrium constant of reaction is approximately 1000, but the steady state concentration of products (fructose-1,6-bisphosphate and ADP) over reactants (fructose-6-phosphate and ATP) is only 0.1, indicating that the ratio of ATP to AMP remains in a steady state significantly above equilibrium concentration. Regulation of PFK-1 maintains ATP levels above equilibrium.
In the cytoplasm of hepatocytes, the steady state ratio of NADP to NADPH is approximately 0.1 while that of NAD to NADH is approximately 1000, favoring NADPH as the main reducing agent and NAD as the main oxidizing agent in chemical reactions. | 0 | Theoretical and Fundamental Chemistry |
Matthew John Fuchter is a British chemist who is a Professor of Chemistry at Imperial College London. His research focuses on the development and application of novel functional molecular systems to a broad range of areas; from materials to medicine. He has been awarded both the Harrison-Meldola Memorial Prize (2014) and the Corday–Morgan Prizes (2021) of the Royal Society of Chemistry. In 2020 he was a finalist for the Blavatnik Awards for Young Scientists. | 1 | Applied and Interdisciplinary Chemistry |
Current Topics in Medicinal Chemistry is a biweekly peer-reviewed medical journal published by Bentham Science Publishers. It includes review articles on all aspects of medicinal chemistry, including drug design. The current editor-in-chief is Jia Zhou (University of Texas, Medical Branch). | 1 | Applied and Interdisciplinary Chemistry |
The Russell Varian Prize was an international scientific prize awarded for a single, high-impact and innovative contribution in the field of nuclear magnetic resonance (NMR), that laid the foundation for the development of new technologies in the field. It honored the memory of Russell Varian, the pioneer behind the creation of the first commercial NMR spectrometer and the co-founder, in 1948, of Varian Associates, one of the first high-tech companies in Silicon Valley. The prize carried a monetary award of €15,000 and it was awarded annually between the years 2002 and 2015 (except for 2003) by a committee of experts in the field. The award ceremony alternated between the European Magnetic Resonance (EUROMAR) Conference and the International Council on Magnetic Resonance in Biological Systems (ICMRBS) Conference. Originally, the prize was sponsored by Varian, Inc. and later by Agilent Technologies, after the latter acquired Varian, Inc. in 2010. The prize was discontinued in 2016 after Agilent Technologies closed its NMR division. | 0 | Theoretical and Fundamental Chemistry |
The NRC and approved state agencies regulate the use of injected radionuclides in hydraulic fracturing in the United States.
The US EPA sets radioactivity standards for drinking water. Federal and state regulators do not require sewage treatment plants that accept gas well wastewater to test for radioactivity. In Pennsylvania, where the hydraulic fracturing drilling boom began in 2008, most drinking-water intake plants downstream from those sewage treatment plants have not tested for radioactivity since before 2006. The EPA has asked the Pennsylvania Department of Environmental Protection to require community water systems in certain locations, and centralized wastewater treatment facilities to conduct testing for radionuclides. | 0 | Theoretical and Fundamental Chemistry |
Sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) produce hydrogen sulfide () and sulfuric acid () respectively. When the sulfur cycle is active in sewers and emanations from the effluent waters are oxidized in by atmospheric oxygen at the moist surface of tunnel walls, sulfuric acid can attack the hydrated Portland cement paste of cementitious materials, especially in the non-totally immersed sections of sewers (non-completely water-filled vadose zone). It causes extensive damages to masonry mortar and concrete in older sewage infrastructures. Sulfur concrete, if proven resistant to long-term chemical and bacterial attacks, could provide an effective and long-lasting solution to this problem. However, since elemental sulfur itself participates in redox reactions used by some autotrophic bacteria to produce the energy they need from the sulfur cycle, elemental sulfur could contribute directly fueling the bacterial activity. Biofilms adhering to the surface of sewer walls could harbor autotrophic microbial colonies that can degrade sulfur concrete if they are able to use elemental sulfur directly as an electron donor to reduce nitrate (autotrophic denitrification process), or sulfate, present in wastewater. Studies and real life tests have shown that only bio sulfur is accessible to these bacteria.
The very long-term durability of sulfur concrete also depends on physicochemical factors such as those controlling, among other things, the diffusion of modifying agents (if not completely chemically fixed) out of the elemental sulfur matrix and their leaching by water. The resulting changes in the physical properties of the material will determine its long-term mechanical strength and chemical behavior. The biodegradability of the organic admixtures (sulfur modifiers), or their resistance to microbial activity, and their possible biocidal properties (which may protect the sulfur concrete from microbial attack) are important aspects in assessing the durability of the material. This could also depend on the progressive recrystallization of elemental sulfur over time, or on the rate of plastic deformation of its structure modified by the different types of organic admixtures. | 1 | Applied and Interdisciplinary Chemistry |
In veterinary medicine, selegiline is sold under the brand name Anipryl (manufactured by Zoetis). It is used in dogs to treat canine cognitive dysfunction and, at higher doses, pituitary-dependent hyperadrenocorticism (PDH). Canine cognitive dysfunction is a form of dementia that mimics Alzheimer's disease in humans. Geriatric dogs treated with selegiline show improvements in sleeping pattern, reduced incontinence, and increased activity level; most show improvements by one month. Though it is labeled for dog use only, selegiline has been used off-label for geriatric cats with cognitive dysfunction.
Selegiline's efficacy in treating pituitary-dependent hyperadrenocorticism has been disputed. Theoretically, it works by increasing dopamine levels, which downregulates the release of ACTH, eventually leading to reduced levels of cortisol. Some claim that selegiline is only effective at treating PDH caused by lesions in the anterior pituitary (which comprise most canine cases). The greatest sign of improvement is lessening of abdominal distention.
Side effects in dogs are uncommon, but they include vomiting, diarrhea, diminished hearing, salivation, decreased weight and behavioral changes such as hyperactivity, listlessness, disorientation, and repetitive motions.
Selegiline does not appear to have a clinical effect on horses. | 0 | Theoretical and Fundamental Chemistry |
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI) | 1 | Applied and Interdisciplinary Chemistry |
Cone meters are a newer differential pressure metering device first launched in 1985 by McCrometer in Hemet, CA. The cone meter is a generic yet robust differential pressure (DP) meter that has shown to be resistant to effects of asymmetric and swirling flow. While working with the same basic principles as Venturi and orifice type DP meters, cone meters don't require the same upstream and downstream piping. The cone acts as a conditioning device as well as a differential pressure producer. Upstream requirements are between 0–5 diameters compared to up to 44 diameters for an orifice plate or 22 diameters for a Venturi. Because cone meters are generally of welded construction, it is recommended they are always calibrated prior to service. Inevitably heat effects of welding cause distortions and other effects that prevent tabular data on discharge coefficients with respect to line size, beta ratio and operating Reynolds numbers from being collected and published. Calibrated cone meters have an uncertainty up to ±0.5%. Un-calibrated cone meters have an uncertainty of ±5.0% | 1 | Applied and Interdisciplinary Chemistry |
By 1928, James was terminally ill. He died on 10 December 1928.
There is a legend, captured by John Greenleaf Whittier in the poem, "Telling the bees," which explains that someone must tell the bees of their master's death or they will fly away.
James died in the winter, so he could not be buried in the intended cemetery plot until the spring. He was then buried in the desired plot. A day or two later a swarm of bees appeared at the grave.
The bees belonged to Jesse Hepler, who lived two miles away. They had been given to him by James.
No one told the James-Hepler bees of James' death, and, as in the legend, they flew away. Miraculously they flew to the grave of their former master, two miles away. | 1 | Applied and Interdisciplinary Chemistry |
When a photoemission event takes place, the following energy conservation rule holds:
where is the photon energy, is the electron BE (binding energy with respect to the vacuum level) prior to ionization, and is the kinetic energy of the photoelectron. If reference is taken with respect to the Fermi level (as it is typically done in photoelectron spectroscopy) must be replaced by the sum of the binding energy (BE) relative to the Fermi level, , and the sample work function, .
From the theoretical point of view, the photoemission process from a solid can be described with a semiclassical approach, where the electromagnetic field is still treated classically, while a quantum-mechanical description is used for matter.
The one—particle Hamiltonian for an electron subjected to an electromagnetic field is given by:
where is the electron wave function, is the vector potential of the electromagnetic field and is the unperturbed potential of the solid.
In the Coulomb gauge (), the vector potential commutes with the momentum operator
(), so that the expression in brackets in the Hamiltonian simplifies to:
Actually, neglecting the term in the Hamiltonian, we are disregarding possible photocurrent contributions. Such effects are generally negligible in the bulk, but may become important at the surface.
The quadratic term in can be instead safely neglected, since its contribution in a typical photoemission experiment is about one order of magnitude smaller than that of the first term .
In first-order perturbation approach, the one-electron Hamiltonian can be split into two terms, an unperturbed Hamiltonian , plus an interaction Hamiltonian , which describes the effects of the electromagnetic field:
In time-dependent perturbation theory, for an harmonic or constant perturbation, the transition rate between the initial state and the final state is expressed by Fermi's Golden Rule:
where and are the eigenvalues of the unperturbed Hamiltonian in the initial and final state, respectively, and is the photon energy. Fermi's Golden Rule uses the approximation that the perturbation acts on the system for an infinite time. This approximation is valid when the time that the perturbation acts on the system is much larger than the time needed for the transition. It should be understood that this equation needs to be integrated with the density of states which gives:
In a real photoemission experiment the ground state core electron BE cannot be directly probed, because the measured BE
incorporates both initial state and final state effects, and the spectral linewidth is broadened owing to the finite core-hole lifetime ().
Assuming an exponential decay probability for the core hole in the time domain (), the spectral function will have a Lorentzian shape, with a FWHM (Full Width at Half Maximum) given by:
From the theory of Fourier transforms, and are linked by the indeterminacy relation:
The photoemission event leaves the atom in a highly excited core ionized state, from which it can decay radiatively (fluorescence) or non-radiatively (typically by Auger decay).
Besides Lorentzian broadening, photoemission spectra are also affected by a Gaussian broadening, whose contribution can be expressed by
Three main factors enter the Gaussian broadening of the spectra: the experimental energy resolution, vibrational and inhomogeneous broadening.
The first effect is caused by the non perfect monochromaticity of the photon beam -which results in a finite bandwidth- and by the limited resolving power of the analyzer. The vibrational component is produced by the excitation of low energy vibrational modes both in the initial and in the final state. Finally, inhomogeneous broadening can originate from the presence of unresolved core level components in the spectrum. | 0 | Theoretical and Fundamental Chemistry |
The rough timeline of events during the putrefaction stage is as follows:
*1–2 days: Pallor mortis, algor mortis, rigor mortis, and livor mortis are the first steps in the process of decomposition before the process of putrefaction.
*2–3 days: Discoloration appears on the skin of the abdomen. The abdomen begins to swell due to gas formation.
*3–4 days: The discoloration spreads and discolored veins become visible.
*5–6 days: The abdomen swells noticeably and the skin blisters.
*10–20 days: Black putrefaction occurs, which is when noxious odors are released from the body and the parts of the body undergo a black discoloration.
*2 weeks: The abdomen is bloated; internal gas pressure nears maximum capacity.
*3 weeks: Tissues have softened. Organs and cavities are bursting. The nails and hair fall off.
*4 weeks: Soft tissues such as the internal organs begin to liquefy and the face becomes unrecognizable. The skin, muscles, tendons and ligaments degrade exposing the skeleton.
Order of organs' decomposition in the body:
#Larynx and trachea
#Infant brain
#Stomach
#Intestines
#Spleen
#Omentum and mesentery
#Liver
#Adult brain
#Heart
#Lungs
#Kidneys
#Bladder
#Esophagus
#Pancreas
#Diaphragm
#Blood vessels
#Uterus
The rate of putrefaction is greatest in air, followed by water, soil, and earth. The exact rate of putrefaction is dependent upon many factors such as weather, exposure and location. Thus, refrigeration at a morgue or funeral home can retard the process, allowing for burial in three days or so following death without embalming. The rate increases dramatically in tropical climates. The first external sign of putrefaction in a body lying in air is usually a greenish discoloration of the skin over the region of the cecum, which appears in 12–24 hours. The first internal sign is usually a greenish discoloration on the undersurface of the liver. | 1 | Applied and Interdisciplinary Chemistry |
Biomedical spectroscopy is a multidisciplinary research field involving spectroscopic tools for applications in the field of biomedical science. Vibrational spectroscopy such as Raman or infrared spectroscopy is used to determine the chemical composition of a material based on detection of vibrational modes of constituent molecules. Some spectroscopic methods are routinely used in clinical settings for diagnosis of disease; an example is Magnetic resonance imaging (MRI). Fourier transform infrared (FTIR) spectroscopic imaging is a form of chemical imaging for which the contrast is provided by composition of the material. | 0 | Theoretical and Fundamental Chemistry |
Currently orbiting satellites detect an average of about one gamma-ray burst per day. Because gamma-ray bursts are visible to distances encompassing most of the observable universe, a volume encompassing many billions of galaxies, this suggests that gamma-ray bursts must be exceedingly rare events per galaxy.
Measuring the exact rate of gamma-ray bursts is difficult, but for a galaxy of approximately the same size as the Milky Way, the expected rate (for long GRBs) is about one burst every 100,000 to 1,000,000 years. Only a few percent of these would be beamed toward Earth. Estimates of rates of short GRBs are even more uncertain because of the unknown beaming fraction, but are probably comparable.
A gamma-ray burst in the Milky Way, if close enough to Earth and beamed toward it, could have significant effects on the biosphere. The absorption of radiation in the atmosphere would cause photodissociation of nitrogen, generating nitric oxide that would act as a catalyst to destroy ozone.
The atmospheric photodissociation
would yield
* NO (consumes up to 400 ozone molecules)
* CH (nominal)
* CH (nominal)
* CO
(incomplete)
According to a 2004 study, a GRB at a distance of about a kiloparsec could destroy up to half of Earth's ozone layer; the direct UV irradiation from the burst combined with additional solar UV radiation passing through the diminished ozone layer could then have potentially significant impacts on the food chain and potentially trigger a mass extinction. The authors estimate that one such burst is expected per billion years, and hypothesize that the Ordovician-Silurian extinction event could have been the result of such a burst.
There are strong indications that long gamma-ray bursts preferentially or exclusively occur in regions of low metallicity. Because the Milky Way has been metal-rich since before the Earth formed, this effect may diminish or even eliminate the possibility that a long gamma-ray burst has occurred within the Milky Way within the past billion years. No such metallicity biases are known for short gamma-ray bursts. Thus, depending on their local rate and beaming properties, the possibility for a nearby event to have had a large impact on Earth at some point in geological time may still be significant. | 0 | Theoretical and Fundamental Chemistry |
In cases where an enolization is occurring around an allylic group (usually as part of a cyclic system), A strain can cause the reaction to be nearly impossible. In these situations, acid treatment would normally cause the alkene to become protonated, moving the double bond to the carboxylic group, changing it to a hydroxy group. The resulting allylic strain between the alcohol and the other group involved in the allylic system is so great that the reaction can not occur under normal thermodynamic conditions. This same enolization occurs much more rapidly under basic conditions, as the carboxylic group is retained in the transition state and allows the molecule to adopt a conformation that does not cause allylic strain. | 0 | Theoretical and Fundamental Chemistry |
The Raschig ring is a piece of tube, invented circa 1914, that is used in large numbers in a packing column. Raschig rings are usually made of ceramic or metals, and they provide a large surface area within the column, allowing for interaction between liquid and gas vapors. | 1 | Applied and Interdisciplinary Chemistry |
Resazurin is effectively reduced in mitochondria, making it useful also to assess mitochondrial metabolic activity.
Usually, in the presence of NADPH dehydrogenase or NADH dehydrogenase as the enzyme, NADPH or NADH is the reductant that converts resazurin to resorufin. Hence the resazurin/diaphorase/NADPH system can be used to detect NADH, NADPH, or diaphorase level, and any biochemical or enzyme activity that is involved in a biochemical reaction generating NADH or NADPH.
Resazurin can be used to assay L-Glutamate, achieving a sensitivity of 2.0 pmol per well in a 96 well plate.
Resazurin can also be used to measure the aerobic biodegradation of organic matter found in effluents.
Resazurin is used to measure the amount of aerobic respiration in streams. Since most aerobic respiration occurs in the stream bed, the conversion of resazurin to resorufin is also a measure of the amount of exchange between the water column and the stream bed. | 0 | Theoretical and Fundamental Chemistry |
In order to provide access to relevant data to users ChemSeer provides new features that are not available in traditional search engines or digital libraries.
# Chemical Entity Search: A tool capable of identifying Chemical formulae and chemical names, and extracting and disambiguating them from general terms within documents. Those disambiguated terms are used for performing searches.
# TableSeer: In scholarly articles Tables are used to present, list, summarize, and structure important data. TableSeer automatically identifies tables in digital documents, extracts the table Metadata as well as the cells content, and stores them in such a way that allows users to either query the table content or search for tables in a large set of documents.
# Dataset search: ChemSeer provides tools to incorporate datasets from different experiments sources. The system is able to manipulate results from multiple formats such as XML, Microsoft Excel, Gaussian, and CHARMM, create databases, to allow direct queries over the data, create Metadata, using an annotation tool, which will allow users to search over the datasets, as well as a way to create links among datasets and/or between datasets and documents.
In addition to these tools, ChemSeer will integrate the advances made by its sister project CiteSeer to provide:
* Full text search
* Author, affiliation, title and venue search
* Citation and acknowledgement search
* Citation linking and statistics | 1 | Applied and Interdisciplinary Chemistry |
The ancient record on Earth provides an opportunity to see what geochemical signatures are produced by microbial life and how these signatures are preserved over geologic time. Some related disciplines such as geochemistry, geobiology, and geomicrobiology often use biosignatures to determine if living organisms are or were present in a sample. These possible biosignatures include: (a) microfossils and stromatolites; (b) molecular structures (biomarkers) and isotopic compositions of carbon, nitrogen and hydrogen in organic matter; (c) multiple sulfur and oxygen isotope ratios of minerals; and (d) abundance relationships and isotopic compositions of redox-sensitive metals (e.g., Fe, Mo, Cr, and rare earth elements).
For example, the particular fatty acids measured in a sample can indicate which types of bacteria and archaea live in that environment. Another example is the long-chain fatty alcohols with more than 23 atoms that are produced by planktonic bacteria. When used in this sense, geochemists often prefer the term biomarker. Another example is the presence of straight-chain lipids in the form of alkanes, alcohols, and fatty acids with 20–36 carbon atoms in soils or sediments. Peat deposits are an indication of originating from the epicuticular wax of higher plants.
Life processes may produce a range of biosignatures such as nucleic acids, lipids, proteins, amino acids, kerogen-like material and various morphological features that are detectable in rocks and sediments. Microbes often interact with geochemical processes, leaving features in the rock record indicative of biosignatures. For example, bacterial micrometer-sized pores in carbonate rocks resemble inclusions under transmitted light, but have distinct sizes, shapes, and patterns (swirling or dendritic) and are distributed differently from common fluid inclusions. A potential biosignature is a phenomenon that may have been produced by life, but for which alternate abiotic origins may also be possible. | 1 | Applied and Interdisciplinary Chemistry |
The methods for sequence analysis of synthetic polymers differ from the sequence analysis of biopolymers (e. g. DNA or proteins). Synthetic polymers are produced by chain-growth or step-growth polymerization and show thereby polydispersity, whereas biopolymers are synthesized by complex template-based mechanisms and are sequence-defined and monodisperse. Synthetic polymers are a mixture of macromolecules of different length and sequence and are analysed via statistical measures (e. g. the degree of polymerization, comonomer composition or dyad and triad fractions). | 0 | Theoretical and Fundamental Chemistry |
SoRI-20041 is an "antagonist-like" allosteric modulator of amphetamine-induced dopamine release (in contrast to the related research chemicals SoRI-9804 and SoRI-20040, which are "agonist-like"). SoRI-20041 is believed to be the first example of a drug that separately modulates uptake versus release in the dopamine transporter (possibly showing how inward and outward transport represent distinct operational modes of DAT); it produces the same effects as SoRI-20040 and SoRI-9804 in uptake assays and binding assays, inhibiting the re-uptake of dopamine, but does not modulate d-amphetamine-induced DA release by inhibiting that as well, like agonists of the series do.
This suggests the possibility of simultaneous action and increase of indirect-agonism through the dual action of DRA and DRI efficacy existing together. This increases the inhibition of re-uptake at synaptic dopamine concentrations without interfering in the flow of release of dopamine from amphetaminergic phosphorylation at the affected transporter. This overcomes the obstacle of a compromised binding site that would be rendered unusable through the action of amphetamine. Conventional dopamine re-uptake inhibitors (such as cocaine or methylphenidate) would otherwise ineffectively target such a site on each specific transporter so affected by amphetamine, making this an example of a DRI that does not have a mutually exclusive functionality against DRA action at individual instances of DAT. | 1 | Applied and Interdisciplinary Chemistry |
Carbon dioxide is not a typical feedstock for FT catalysis. Hydrogen and carbon dioxide react over a cobalt-based catalyst, producing methane. With iron-based catalysts unsaturated short-chain hydrocarbons are also produced. Upon introduction to the catalyst's support, ceria functions as a reverse water-gas shift catalyst, further increasing the yield of the reaction. The short-chain hydrocarbons were upgraded to liquid fuels over solid acid catalysts, such as zeolites. | 0 | Theoretical and Fundamental Chemistry |
The notions that not all enhancers are transcribed at the same time and that eRNA transcription correlates with enhancer-specific activity support the idea that individual eRNAs carry distinct and relevant biological functions. However, there is still no consensus on the functional significance of eRNAs. Furthermore, eRNAs can easily be degraded through exosomes and nonsense-mediated decay, which limits their potential as important transcriptional regulators. To date, four main models of eRNA function have been proposed, each supported by different lines of experimental evidence. | 1 | Applied and Interdisciplinary Chemistry |
The tides received relatively little attention in the civilizations around the Mediterranean Sea, as the tides there are relatively small, and the areas that experience tides do so unreliably. A number of theories were advanced, however, from comparing the movements to breathing or blood flow to theories involving whirlpools or river cycles. A similar "breathing earth" idea was considered by some Asian thinkers. Plato reportedly believed that the tides were caused by water flowing in and out of undersea caverns. Crates of Mallus attributed the tides to "the counter-movement (ἀντισπασμός) of the sea” and Apollodorus of Corcyra to "the refluxes from the Ocean". An ancient Indian Purana text dated to 400-300 BC refers to the ocean rising and falling because of heat expansion from the light of the Moon.
Ultimately the link between the Moon (and Sun) and the tides became known to the Greeks, although the exact date of discovery is unclear; references to it are made in sources such as Pytheas of Massilia in 325 BC and Pliny the Elders Natural History in 77 AD. Although the schedule of the tides and the link to lunar and solar movements was known, the exact mechanism that connected them was unclear. Classicists Thomas Little Heath claimed that both Pytheas and Posidonius connected the tides with the moon, "the former directly, the latter through the setting up of winds". Seneca mentions in De Providentia the periodic motion of the tides controlled by the lunar sphere. Eratosthenes (3rd century BC) and Posidonius (1st century BC) both produced detailed descriptions of the tides and their relationship to the phases of the Moon, Posidonius in particular making lengthy observations of the sea on the Spanish coast, although little of their work survived. The influence of the Moon on tides was mentioned in Ptolemys Tetrabiblos as evidence of the reality of astrology. Seleucus of Seleucia is thought to have theorized around 150 BC that tides were caused by the Moon as part of his heliocentric model.
Aristotle, judging from discussions of his beliefs in other sources, is thought to have believed the tides were caused by winds driven by the Suns heat, and he rejected the theory that the Moon caused the tides. An apocryphal legend claims that he committed suicide in frustration with his failure to fully understand the tides. Heraclides also held "the sun sets up winds, and that these winds, when they blow, cause the high tide and, when they cease, the low tide". Dicaearchus also "put the tides down to the direct action of the sun according to its position". Philostratus discusses tides in Book Five of Life of Apollonius of Tyana' (circa 217-238 AD); he was vaguely aware of a correlation of the tides with the phases of the Moon but attributed them to spirits moving water in and out of caverns, which he connected with the legend that spirits of the dead cannot move on at certain phases of the Moon. | 1 | Applied and Interdisciplinary Chemistry |
The success of DNA nanotechnology in constructing artificially designed nanostructures out of nucleic acids such as DNA, combined with the demonstration of systems for DNA computing, has led to speculation that artificial nucleic acid nanodevices can be used to target drug delivery based upon directly sensing its environment. These methods make use of DNA solely as a structural material and a chemical, and do not make use of its biological role as the carrier of genetic information. Nucleic acid logic circuits that could potentially be used as the core of a system that releases a drug only in response to a stimulus such as a specific mRNA have been demonstrated. In addition, a DNA "box" with a controllable lid has been synthesized using the DNA origami method. This structure could encapsulate a drug in its closed state, and open to release it only in response to a desired stimulus. | 1 | Applied and Interdisciplinary Chemistry |
In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy — and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy).
A notable effect of the absorption of electromagnetic radiation is attenuation of the radiation; attenuation is the gradual reduction of the intensity of light waves as they propagate through the medium.
Although the absorption of waves does not usually depend on their intensity (linear absorption), in certain conditions (optics) the medium's transparency changes by a factor that varies as a function of wave intensity, and saturable absorption (or nonlinear absorption) occurs. | 0 | Theoretical and Fundamental Chemistry |
Gene nomenclature is the scientific naming of genes, the units of heredity in living organisms. It is also closely associated with protein nomenclature, as genes and the proteins they code for usually have similar nomenclature. An international committee published recommendations for genetic symbols and nomenclature in 1957. The need to develop formal guidelines for human gene names and symbols was recognized in the 1960s and full guidelines were issued in 1979 (Edinburgh Human Genome Meeting). Several other genus-specific research communities (e.g., Drosophila fruit flies, Mus mice) have adopted nomenclature standards, as well, and have published them on the relevant model organism websites and in scientific journals, including the Trends in Genetics Genetic Nomenclature Guide. Scientists familiar with a particular gene family may work together to revise the nomenclature for the entire set of genes when new information becomes available. For many genes and their corresponding proteins, an assortment of alternate names is in use across the scientific literature and public biological databases, posing a challenge to effective organization and exchange of biological information. Standardization of nomenclature thus tries to achieve the benefits of vocabulary control and bibliographic control, although adherence is voluntary. The advent of the information age has brought gene ontology, which in some ways is a next step of gene nomenclature, because it aims to unify the representation of gene and gene product attributes across all species. | 1 | Applied and Interdisciplinary Chemistry |
The Kröhnke pyridine synthesis provides a fairly general method for generating substituted pyridines using pyridine itself as a reagent which does not become incorporated into the final product. The reaction of pyridine with bromomethyl ketones gives the related pyridinium salt, wherein the methylene group is highly acidic. This species undergoes a Michael-like addition to α,β-unsaturated carbonyls in the presence of ammonium acetate to undergo ring closure and formation of the targeted substituted pyridine as well as pyridinium bromide.
The Ciamician–Dennstedt rearrangement entails the ring-expansion of pyrrole with dichlorocarbene to 3-chloropyridine.
In the Gattermann–Skita synthesis, a malonate ester salt reacts with dichloromethylamine.
Other methods include the Boger pyridine synthesis and Diels–Alder reaction of an alkene and an oxazole. | 0 | Theoretical and Fundamental Chemistry |
This pathway is also called the “Xylose Reductase-Xylitol Dehydrogenase” or XR-XDH pathway. Xylose reductase (XR) and xylitol dehydrogenase (XDH) are the first two enzymes in this pathway. XR is reducing D-xylose to xylitol using NADH or NADPH. Xylitol is then oxidized to D-xylulose by XDH, using the cofactor NAD. In the last step D-xylulose is phosphorylated by an ATP utilising kinase, XK, to result in D-xylulose-5-phosphate which is an intermediate of the pentose phosphate pathway. | 1 | Applied and Interdisciplinary Chemistry |
There are two distinct types of palladacycle: four-electron donor (CY) and six-electron donor (YCY) complexes. | 0 | Theoretical and Fundamental Chemistry |
The first standardization of cast iron water pipes in Britain occurred in 1917 with the publishing of BS 78. This standard specified a dimensionless nominal size, which approximately corresponded with the internal diameter in inches of the pipe, and four pressure classes, Class A, Class B, Class C and Class D, each with a specified wall thickness and outer diameter. It is noted that the outer diameter is identical between classes with the exception of sizes 12 to 27, where Classes A and B share one diameter and Classes C and D have another, larger diameter.
BS 78 was finally superseded when the UK harmonised with incompatible European standards, however, the specified outer dimensions continue to remain in effect (albeit in metric form) as the standard pipe outer diameter for ductile iron pipe in Australia and New Zealand through the descendant specification, AS/NZS 2280. | 1 | Applied and Interdisciplinary Chemistry |
The nines are a count of the leftmost digits 9 that appear in a proportion. For example, 90% would be described as "one nine"; 99% as "two nines"; 99.9% as "three nines"; and so forth.
However, there are different conventions for representing inexact multiples of 9. For example, a percentage of 99.5% could be expressed as "two nines five" (2N5, or N2.5) or as 2.3 nines, following from the logarithm definition.
A percentage of 100% would, in theory, have an infinite number of nines – though, in the context of purity of materials, 100% is virtually unachievable.
The number of nines of a proportion is: | 1 | Applied and Interdisciplinary Chemistry |
The gradation of soils, or soil texture, affects water and nutrient holding and drainage capabilities. For sand-based soils, particle size can be the dominant characteristic affecting soil performances and hence crop. Sieving has long been the technique of choice for soil texture analysis, although laser diffraction instruments are increasingly used as they considerably speed up the analytical process, and provide highly reproducible results.
Particle size analysis in the agriculture industry is paramount because unwanted materials will contaminate products if they are not detected. By having an automated particle size analyzer, companies can closely monitor their processes. | 0 | Theoretical and Fundamental Chemistry |
Two RNA genomes are packaged into each retrovirus particle, but, after an infection, each virus generates only one provirus. After infection, reverse transcription occurs and this process is accompanied by recombination. Recombination involves template strand switching between the two genome copies (copy choice recombination) during reverse transcription. From 5 to 14 recombination events per genome occur at each replication cycle. Genetic recombination appears to be necessary for maintaining genome integrity and as a repair mechanism for salvaging damaged genomes. | 1 | Applied and Interdisciplinary Chemistry |
In 2022, Japanese Tiger Corporation was working on an automated coffee-maker based on the vacuum coffee maker principle, the Siphonysta. The Siphonysta's heating is electrical. The chambers are made of plastic ("resin"). | 1 | Applied and Interdisciplinary Chemistry |
In stereochemistry, a chiral auxiliary is a stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis. The chirality present in the auxiliary can bias the stereoselectivity of one or more subsequent reactions. The auxiliary can then be typically recovered for future use.
<br>
Most biological molecules and pharmaceutical targets exist as one of two possible enantiomers; consequently, chemical syntheses of natural products and pharmaceutical agents are frequently designed to obtain the target in enantiomerically pure form. Chiral auxiliaries are one of many strategies available to synthetic chemists to selectively produce the desired stereoisomer of a given compound.
Chiral auxiliaries were introduced by Elias James Corey in 1975 with chiral 8-phenylmenthol and by Barry Trost in 1980 with chiral mandelic acid. The menthol compound is difficult to prepare and as an alternative trans-2-phenyl-1-cyclohexanol was introduced by J. K. Whitesell in 1985. | 0 | Theoretical and Fundamental Chemistry |
RNA polymerase II holoenzyme is a form of eukaryotic RNA polymerase II that is recruited to the promoters of protein-coding genes in living cells. It consists of RNA polymerase II, a subset of general transcription factors, and regulatory proteins known as . | 1 | Applied and Interdisciplinary Chemistry |
In the sense that DNA replication must occur if genetic material is to be provided for the progeny of any cell, whether somatic or reproductive, the copying from DNA to DNA arguably is the fundamental step in information transfer. A complex group of proteins called the replisome performs the replication of the information from the parent strand to the complementary daughter strand. | 1 | Applied and Interdisciplinary Chemistry |
Mollapour completed his postdoctoral research at the University of Sheffield and in 2006 he received the Federation of European Societies (FEBS) fellowship.
He joined the laboratory of Dr Len Neckers in Urological Oncology Branch, (Chief Dr. W. Marston Linehan), at the National Cancer Institute as a research fellow in 2007.
In 2013 he joined the Department of Urology at the Upstate Medical University as an Assistant Professor. He became the Director of the Kidney Cancer Program within the same department in 2015.
In 2018 he became the Professor of Urology and Adjunct Professor of Biochemistry and Molecular Biology at SUNY Upstate Medical University. He was also named the Vice Chair for Translational Research for the Department of Urology in the same year. In 2023, Mollapour was elected the president-elect for the Cell Stress Society International; his term at president will begin in 2025. Mollapour’s h-index is 45, based on 7,751 citations. | 1 | Applied and Interdisciplinary Chemistry |
The data feeds several key products, primarily abundance profiles. These profiles summarize and reorganize the information found in the similarity files in a more easily digestible format. | 1 | Applied and Interdisciplinary Chemistry |
Zero-order ultrasensitivity takes place under saturating conditions. For example, consider an enzymatic step with a kinase, phosphatase, and substrate. Steady state levels of the phosphorylated substrate have an ultrasensitive response when there is enough substrate to saturate all available kinases and phosphatases. Under these conditions, small changes in the ratio of kinase to phosphatase activity can dramatically change the number of phosphorylated substrate (For a graph illustrating this behavior, see ). This enhancement in sensitivity of steady state phosphorylated substrate to Km, or the ratio of kinase to phosphatase activity, is termed zero-order to distinguish it from the first order behavior described by Michaelis-Menten dynamics, wherein the steady state concentration responds in a more gradual fashion than the switch-like behavior exhibited in ultrasensitivity.
Using the notation from Goldbeter & Koshland, let W be a certain substrate protein and let W be a covalently modified version of W. The conversion of W to W is catalyzed by some enzyme and the reverse conversion of W' to W is catalyzed by a second enzyme according to following equations:
The concentrations of all necessary components (such as ATP) are assumed to be constant and represented in the kinetic constants.
Using the chemical equations above, the reaction rate equations for each component are:
The total concentration of each component is given by:
The zero order mechanism assumes that the or . In other words, the system is in a Michaelis-Menten steady state, which means, to a good approximation, and are constant.
From these kinetic expressions one can solve for at steady state defining and
where and
When the is plotted against the molar ratio and it can be seen that the W to W conversion occurs over a much smaller change in the ratio than it would under first order (non-saturating) conditions, which is the telltale sign of ultrasensitivity. | 1 | Applied and Interdisciplinary Chemistry |
Bond stretch isomerism is confirmed for complexes subject to spin crossover transitions. In some octahedral complexes of d configuration, the depopulation of e orbitals causes significant contractions of the metal-ligand bond distances. The phenomenon is mainly manifested in the solid forms of the compounds.
Although no example of bond stretch isomerism has been established in solution, two isomers have been crystallized for pentamethylcyclopentadienyl ruthenium dichloride dimer ([Cp*RuCl]). One has an Ru-Ru bond (2.93 Å) and the other has a long intermetallic distance of 3.75 Å. The former isomer is thought to be diamagnetic, and the latter is magnetic. | 0 | Theoretical and Fundamental Chemistry |
Atomic force microscopy (AFM) is commonly used to directly measure the magnitude of depletion forces. This method uses the deflection of a very small cantilever contacting a sample which is measured by a laser. The force required to cause a certain amount of beam deflection can be determined from the change in angle of the laser. The small scale of AFM allows for dispersion particles to be measured directly yielding a relatively accurate measurement of depletion forces. | 0 | Theoretical and Fundamental Chemistry |
There are many publications dedicated to numerical modeling of volume viscosity. A detailed review of these studies can be found in Sharma (2019) and Cramer. In the latter study, a number of common fluids were found to have bulk viscosities which were hundreds to thousands of times larger than their shear viscosities. | 1 | Applied and Interdisciplinary Chemistry |
The works of the present direction were a direct consequence of the previous section, on the basis of which V.G. Khlopin came to the concept of continuous gas exchange between inner and outer gas atmospheres, about the role of natural waters, in a particular case - in the exchange of noble gases (excluding helium) between outer air and underground atmospheres. In accordance with these ideas in underground gas atmospheres there is a gradual enrichment of argon, krypton and xenon, - depletion of neon in relation to their content in the air. Relation </div>
in underground atmospheres is greater than in air. It has been found that gases dissolved in the lower layers of deep natural reservoirs are sharply enriched with heavy noble gases. | 0 | Theoretical and Fundamental Chemistry |
Fermentation begins once the growth medium is inoculated with the organism of interest. Growth of the inoculum does not occur immediately. This is the period of adaptation, called the lag phase. Following the lag phase, the rate of growth of the organism steadily increases, for a certain period—this period is the log or exponential phase.
After a phase of exponential growth, the rate of growth slows down, due to the continuously falling concentrations of nutrients and/or a continuously increasing (accumulating) concentrations of toxic substances. This phase, where the increase of the rate of growth is checked, is the deceleration phase. After the deceleration phase, growth ceases and the culture enters a stationary phase or a steady state. The biomass remains constant, except when certain accumulated chemicals in the culture chemically break down the cells in a process called chemolysis. Unless other microorganisms contaminate the culture, the chemical constitution remains unchanged. If all of the nutrients in the medium are consumed, or if the concentration of toxins is too great, the cells may become senescent and begin to die off. The total amount of biomass may not decrease, but the number of viable organisms will decrease. | 1 | Applied and Interdisciplinary Chemistry |
-Photo-leucine acquires its function after being exposed to UV light. This causes diazirine ring of -photo-leucine to lose its nitrogen atoms in form of nitrogen gas, leaving its carbon atom as a reactive free radical. The bonds established between this carbon, belonging to one protein (A), and atoms belonging to another protein (B) are responsible for the cross-linking properties of -photo-leucine, which allow it to attach these two peptide chains into a single complex (AB).
The appropriate wavelength to activate the -photo-leucine molecule ranges from 320 to 370 nanometers. Lamps with higher power are more effective in accomplishing this objective and do so in less time. The ideal wavelength for the activation of the photo-leucine amino acid is of 345 nm.
To increase efficiency, a shallow and uncovered plate must be used. Also, rotation of the samples located under the UV right may be necessary to make sure they receive even UV irradiation, and thus to, yet again, improve the cross-linking efficiency. If the cross-linking is done in vivo, within living cells, these must be exposed to the UV radiation during a period of 15 minutes or less. | 0 | Theoretical and Fundamental Chemistry |
Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp hybridized carbon atom. Although this sp center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds. This formal discontinuity is apparently bridged by p-orbital overlap, maintaining a contiguous cycle of π electrons that is responsible for this preserved chemical stability.
The concept of homoaromaticity was pioneered by Saul Winstein in 1959, prompted by his studies of the “tris-homocyclopropenyl” cation. Since the publication of Winsteins paper, much research has been devoted to understanding and classifying these molecules, which represent an additional class of aromatic molecules included under the continuously broadening definition of aromaticity. To date, homoaromatic compounds are known to exist as cationic and anionic species, and some studies support the existence of neutral homoaromatic molecules, though these are less common. The homotropylium' cation (CH) is perhaps the best studied example of a homoaromatic compound. | 0 | Theoretical and Fundamental Chemistry |
Suppose an alloy at an equilibrium temperature T consists of mass fraction of element B. Suppose also that at temperature T the alloy consists of two phases, α and β, for which the α consists of , and β consists of . Let the mass of the α phase in the alloy be so that the mass of the β phase is , where is the total mass of the alloy.
By definition, then, the mass of element B in the α phase is , while the mass of element B in the β phase is . Together these two quantities sum to the total mass of element B in the alloy, which is given by . Therefore,
By rearranging, one finds that
This final fraction is the mass fraction of the α phase in the alloy. | 1 | Applied and Interdisciplinary Chemistry |
Rotations, denoted by R, where c is a point in the plane (the centre of rotation), and θ is the angle of rotation. In terms of coordinates, rotations are most easily expressed by breaking them up into two operations. First, a rotation around the origin is given by
These matrices are the orthogonal matrices (i.e. each is a square matrix whose transpose is its inverse, i.e. ), with determinant 1 (the other possibility for orthogonal matrices is −1, which gives a mirror image, see below). They form the special orthogonal group SO(2).
A rotation around c can be accomplished by first translating c to the origin, then performing the rotation around the origin, and finally translating the origin back to c. That is,
or in other words,
Alternatively, a rotation around the origin is performed, followed by a translation:
A rotation can be seen as a composite of two non-parallel reflections. | 0 | Theoretical and Fundamental Chemistry |
The most common disease in which glycogen metabolism becomes abnormal is diabetes, in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted. Restoration of normal glucose metabolism usually normalizes glycogen metabolism, as well.
In hypoglycemia caused by excessive insulin, liver glycogen levels are high, but the high insulin levels prevent the glycogenolysis necessary to maintain normal blood sugar levels. Glucagon is a common treatment for this type of hypoglycemia.
Various inborn errors of carbohydrate metabolism are caused by deficiencies of enzymes or transport proteins necessary for glycogen synthesis or breakdown. These are collectively referred to as glycogen storage diseases. | 1 | Applied and Interdisciplinary Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.