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The Griess test is an analytical chemistry test which detects the presence of nitrite ion in solution. One of its most important uses is the determination of nitrite in drinking water. The Griess diazotization reaction, on which the Griess reagent relies, was first described in 1858 by Peter Griess. The test has also been widely used for the detection of nitrates (N-oxidation state = 5+), which are a common component of explosives, as they can be reduced to nitrites (N-oxidation state = 3+) and detected with the Griess test. | 3 | Analytical Chemistry |
Corrosion is a major issue with neural electrodes. Corrosion can occur because electrode metals are placed in an electrolytic solution, where the presence of current can either increase the rate of corrosion mechanisms or overcome limiting activation energies. Redox reactions are a mechanism of corrosion that can lead to dissolution of ions from the electrode surface. There is a base level of metal ions in tissue, however, when these levels increase beyond threshold values the ions become toxic and can cause severe health problems. In addition, the fidelity of the electrode system can be compromised. Knowing the impedance of an electrode is important whether the electrode is used for stimulation or recording. When degradation of the electrode surface occurs because of corrosion, the surface area increases with its roughness. Calculating a new electrode impedance to compensate for the change in surface area once implanted it is not easy. This computational flaw can skew data from recording or pose a dangerous obstacle limiting safe stimulation. | 7 | Physical Chemistry |
José Joaquín Barluenga Mur (27 July 1940 – 7 September 2016) was a Spanish chemist known for his research in organometallic chemistry. He was a professor of chemistry at Oviedo University until his retirement in 2014. | 0 | Organic Chemistry |
Energy-dispersive X-ray diffraction (EDXRD) is an analytical technique for characterizing materials. It differs from conventional X-ray diffraction by using polychromatic photons as the source and is usually operated at a fixed angle. With no need for a goniometer, EDXRD is able to collect full diffraction patterns very quickly. EDXRD is almost exclusively used with synchrotron radiation which allows for measurement within real engineering materials. | 3 | Analytical Chemistry |
Cyanobacteria are photosynthetic prokaryotes with highly differentiated membrane systems. Cyanobacteria have an internal system of thylakoid membranes where the fully functional electron transfer chains of photosynthesis and respiration reside. The presence of different membrane systems lends these cells a unique complexity among bacteria. Cyanobacteria must be able to reorganize the membranes, synthesize new membrane lipids, and properly target proteins to the correct membrane system. The outer membrane, plasma membrane, and thylakoid membranes each have specialized roles in the cyanobacterial cell. Understanding the organization, functionality, protein composition, and dynamics of the membrane systems remains a great challenge in cyanobacterial cell biology.
In contrast to the thylakoid network of higher plants, which is differentiated into grana and stroma lamellae, the thylakoids in cyanobacteria are organized into multiple concentric shells that split and fuse to parallel layers forming a highly connected network. This results in a continuous network that encloses a single lumen (as in higher‐plant chloroplasts) and allows water‐soluble and lipid‐soluble molecules to diffuse through the entire membrane network. Moreover, perforations are often observed within the parallel thylakoid sheets. These gaps in the membrane allow for the traffic of particles of different sizes throughout the cell, including ribosomes, glycogen granules, and lipid bodies. The relatively large distance between the thylakoids provides space for the external light-harvesting antennae, the phycobilisomes. This macrostructure, as in the case of higher plants, shows some flexibility during changes in the physicochemical environment. | 5 | Photochemistry |
Mauveine, also known as aniline purple and Perkin's mauve, was one of the first synthetic dyes. It was discovered serendipitously by William Henry Perkin in 1856 while he was attempting to synthesise the phytochemical quinine for the treatment of malaria. It is also among the first chemical dyes to have been mass-produced. | 7 | Physical Chemistry |
Carbohydrates are reactants in many organic reactions. For example:
* Cyanohydrin reaction
* Lobry-de Bruyn-van Ekenstein transformation
* Amadori rearrangement
* Wohl degradation
* Tipson-Cohen reaction
* Ferrier rearrangement
* Ferrier II reaction | 0 | Organic Chemistry |
According to the Journal Citation Reports, the journal had an impact factor of 6.88 for 2021.
It is indexed in the following bibliographic databases:
* Cambridge Structural Database (Cambridge Crystallographic Data Centre)
* Chemical Abstracts Service/SciFinder (ACS)
* ChemWeb (ChemIndustry.com)
* Chimica Database (Elsevier)
* Current Contents: Physical, Chemical & Earth Sciences (Thomson Reuters)
* INSPEC (IET)
* Journal Citation Reports/Science Edition (Thomson Reuters)
* Nature Index (Springer Nature)
* PASCAL Database (INIST/CNRS)
* Science Citation Index (Thomson Reuters)
* Science Citation Index Expanded (Thomson Reuters)
* SCOPUS (Elsevier)
* VINITI (All-Russian Institute of Science & Technological Information)
* Web of Science (Thomson Reuters) | 7 | Physical Chemistry |
Pisum sativum (garden pea) plants communicate stress cues via their roots to allow neighboring unstressed plants to anticipate an abiotic stressor. Pea plants are commonly grown in temperate regions throughout the world. However, this adaptation allows plants to anticipate abiotic stresses such as drought. In 2011, Falik et al. tested the ability of unstressed pea plants to sense and respond to stress cues by inducing osmotic stress on a neighboring plant. Falik et al. subjected the root of an externally-induced plant to mannitol in order to inflict osmotic stress and drought-like conditions. Five unstressed plants neighbored both sides of this stressed plant. On one side, the unstressed plants shared their root system with their neighbors to allow for root communication. On the other side, the unstressed plants did not share root systems with their neighbors.
Falik et al. found that unstressed plants demonstrated the ability to sense and respond to stress cues emitted from the roots of the osmotically stressed plant. Furthermore, the unstressed plants were able to send additional stress cues to other neighboring unstressed plants in order to relay the signal. A cascade effect of stomatal closure was observed in neighboring unstressed plants that shared their rooting system but was not observed in the unstressed plants that did not share their rooting system. Therefore, neighboring plants demonstrate the ability to sense, integrate, and respond to stress cues transmitted through roots. Although Falik et al. did not identify the chemical responsible for perceiving stress cues, research conducted in 2016 by Delory et al. suggests several possibilities. They found that plant roots synthesize and release a wide array of organic compounds including solutes and volatiles (i.e. terpenes). They cited additional research demonstrating that root-emitted molecules have the potential to induce physiological responses in neighboring plants either directly or indirectly by modifying the soil chemistry. Moreover, Kegge et al. demonstrated that plants perceive the presence of neighbors through changes in water/nutrient availability, root exudates, and soil microorganisms.
Although the underlying mechanism behind stress cues emitted by roots remains largely unknown, Falik et al. suggested that the plant hormone abscisic acid (ABA) may be responsible for integrating the observed phenotypic response (stomatal closure). Further research is needed to identify a well-defined mechanism and the potential adaptive implications for priming neighbors in preparation for forthcoming abiotic stresses; however, a literature review by Robbins et al. published in 2014 characterized the root endodermis as a signaling control center in response to abiotic environmental stresses including drought. They found that the plant hormone ABA regulates the root endodermal response under certain environmental conditions. In 2016 Rowe et al. experimentally validated this claim by showing that ABA regulated root growth under osmotic stress conditions. Additionally, changes in cytosolic calcium concentrations act as signals to close stomata in response to drought stress cues. Therefore, the flux of solutes, volatiles, hormones, and ions are likely involved in the integration of the response to stress cues emitted by roots. | 1 | Biochemistry |
To improve its biophysical properties, derivatives of coelenterazine have been synthesized by means of different procedures including multicomponent strategies. | 1 | Biochemistry |
Legumes such as clover provide nitrogen compounds to neighbouring plants such as grasses by fixing nitrogen from the air with symbiotic bacteria in their root nodules. These enable the grasses or other neighbours to produce more protein (with lower inputs of artificial fertiliser) and hence to grow more. | 1 | Biochemistry |
Some materials may merge at the joint by diffusion. This may occur when the molecules of both materials are mobile and soluble in each other. This would be particularly effective with polymer chains where one end of the molecule diffuses into the other material. It is also the mechanism involved in sintering. When metal or ceramic powders are pressed together and heated, atoms diffuse from one particle to the next. This joins the particles into one.
Diffusive forces are somewhat like mechanical tethering at the molecular level. Diffusive bonding occurs when species from one surface penetrate into an adjacent surface while still being bound to the phase of their surface of origin. One instructive example is that of polymer-on-polymer surfaces. Diffusive bonding in polymer-on-polymer surfaces is the result of sections of polymer chains from one surface interdigitating with those of an adjacent surface. The freedom of movement of the polymers has a strong effect on their ability to interdigitate, and hence, on diffusive bonding. For example, cross-linked polymers are less capable of diffusion and interdigitation because they are bonded together at many points of contact, and are not free to twist into the adjacent surface. Uncrosslinked polymers (thermoplastics), on the other hand are freer to wander into the adjacent phase by extending tails and loops across the interface.
Another circumstance under which diffusive bonding occurs is “scission”. Chain scission is the cutting up of polymer chains, resulting in a higher concentration of distal tails. The heightened concentration of these chain ends gives rise to a heightened concentration of polymer tails extending across the interface. Scission is easily achieved by ultraviolet irradiation in the presence of oxygen gas, which suggests that adhesive devices employing diffusive bonding actually benefit from prolonged exposure to heat/light and air. The longer such a device is exposed to these conditions, the more tails are scissed and branch out across the interface.
Once across the interface, the tails and loops form whatever bonds are favorable. In the case of polymer-on-polymer surfaces, this means more van der Waals forces. While these may be brittle, they are quite strong when a large network of these bonds is formed. The outermost layer of each surface plays a crucial role in the adhesive properties of such interfaces, as even a tiny amount of interdigitation – as little as one or two tails of 1.25 angstrom length – can increase the van der Waals bonds by an order of magnitude. | 6 | Supramolecular Chemistry |
Minerals that have the same composition but different structures (polymorphic minerals) may also have epitaxic relations. Examples are pyrite and marcasite, both FeS, and sphalerite and wurtzite, both ZnS. | 3 | Analytical Chemistry |
The compound is typically prepared by heating thin layers of urea, the thin layers facilitating escape of ammonia:
:3 (HN)CO → [HNC(O)NH]CO + 2 NH
It can also prepared by treatment of urea with phosgene:
:2 (HN)CO + COCl → [HNC(O)NH]CO + 2 HCl
A similar synthesis employs urea and dimethyl carbonate with potassium methoxide as a catalyst:
:2 (HN)CO + CO(OCH) → [HNC(O)NH]CO + 2 MeOH
The original synthesis entailed oxidation of uric acid with hydrogen peroxide.
Triuret is a complicating by-product in the industrial synthesis of melamine from urea. | 0 | Organic Chemistry |
Endiandric acid C, isolated from the tree Endiandra introrsa, is a well characterized chemical compound. Endiadric acid C is reported to have better antibiotic activity than ampicillin.
This genus of trees is in the family Lauraceae. These trees are found in the north-eastern Australian rainforests and other tropical and subtropical regions. However, they are also found in southern Canada and in Chile. Endiandric acid C is also isolated from the species E. xanthocarpa. Endiandric acids are also found in Beilschmiedia trees, which were categorized under the genus Endiandra, but moved to their own genus as they found in cold, high latitude areas, and even in New Zealand. Other endiandric acids are found in B. oligandra and B. anacardioides, which are found in the Western Province of Cameroon. | 0 | Organic Chemistry |
During the 1940s and 1950s, chemists had trouble explaining why even slight changes in the reactants caused significant differences in the rate and product distributions of a reaction. In 1955 George Hammond, a young professor at Iowa State University, postulated that transition-state theory could be used to qualitatively explain the observed structure-reactivity relationships. Notably, John E. Leffler of Florida State University proposed a similar idea in 1953. However, Hammonds version has received more attention since its qualitative nature was easier to understand and employ than Lefflers complex mathematical equations. Hammond's postulate is sometimes called the Hammond–Leffler postulate to give credit to both scientists. | 7 | Physical Chemistry |
In organic chemistry, a coupling reaction is a type of reaction in which two reactant molecules are bonded together. Such reactions often require the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (where R = organic group, M = main group centre metal atom) reacts with an organic halide of the type R-X with formation of a new carbon-carbon bond in the product R-R. The most common type of coupling reaction is the cross coupling reaction.
Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki were awarded the 2010 Nobel Prize in Chemistry for developing palladium-catalyzed cross coupling reactions.
Broadly speaking, two types of coupling reactions are recognized:
*Homocouplings joining two identical partners. The product is symmetrical
*Heterocouplings joining two different partners. These reactions are also called cross-coupling reactions. The product is unsymmetrical, . | 0 | Organic Chemistry |
Thermocouples of platinum/molybdenum-alloy (95%Pt/5%Mo–99.9%Pt/0.1%Mo, by weight) are sometimes used in nuclear reactors, since they show a low drift from nuclear transmutation induced by neutron irradiation, compared to the platinum/rhodium-alloy types. | 8 | Metallurgy |
In the ara operon (also known as the ara or araBAD operon), arabinose acts as both an inducer and a repressor. When arabinose is present, it allosterically binds to the regulatory protein AraC, which then helps to recruit RNA polymerase for transcription. | 0 | Organic Chemistry |
2-Amino-4-hydroxy-6-pyrophosphoryl-methylpteridine (7,8-Dihydropterin pyrophosphate, dihydropterin-CH2OH-diphosphate) is a pteridine; a precursor to dihydrofolic acid. | 1 | Biochemistry |
Atomic-force microscopy is used to study the local roughness and mechanical properties of a surface. AFM is also used to characterize adhesion and friction properties for micro- and nano-patterned superhydrophobic surfaces. Results can be used to fit a curve to the surface topography and determine the radius of curvature of nanostructures. | 7 | Physical Chemistry |
with:
*σ is surface tension of the mixture
*σ is surface tension of pure water
*a is component specific constant (see table below)
*x is mole fraction of the solvated component
The equation can be rearranged to be explicit in a:
This allows the direct calculation of that component specific parameter a from experimental data.
The equation can also be written as:
with:
*γ is surface tension of the mixture
*γ is surface tension of pure water
*R is ideal gas constant 8.31 J/(mol*K)
*T is temperature in K
*ω is cross-sectional area of the surfactant molecules at the surface
The surface tension of pure water is dependent on temperature. At room temperature (298 K), it is equal to 71.97 mN/m | 7 | Physical Chemistry |
Bionic leaves have been considered as an alternative to vertical greenery systems (VGS), also known as green facades. Like VGS, bionic facades can be implemented in buildings to reduce energy consumption from cooling, absorb solar radiation, and reduce CO emissions. Unlike their natural counterpart, bionic facades require less costly maintenance (irrigation, fertilization, pest-control) and can be potentially adjusted to external conditions like the changing of seasons. The general structure of the bionic leaves used for these experiments can be characterized as a photovoltaic (PV) cell or plate resistive heater backed with a ceramic evaporative matrix. An experiment comparing the performance of a PV panel alone versus the bionic leaf panel showed increased electricity production of up to 6.6% due to the evaporative cooling from the matrix. The bionic facade also had a comparable effect on lowering the ambient temperature at the building-to-air interface as a green facade planted with ivy. The cooling effect paired with the electricity output of the bionic facade showed a CO emissions reduction that was 25 times greater than the daily average CO consumption of the ivy wall. | 5 | Photochemistry |
The basis for determination of the absolute electrode potential under the Trasatti definition is given by the equation:
where:
: is the absolute potential of the electrode made of metal M
: is the electron work function of metal M
: is the contact (Volta) potential difference at the metal(M)–solution(S) interface.
For practical purposes, the value of the absolute electrode potential of the standard hydrogen electrode is best determined with the utility of data for an ideally-polarizable mercury (Hg) electrode:
where:
: is the absolute standard potential of the hydrogen electrode
: denotes the condition of the point of zero charge at the interface.
The types of physical measurements required under the Rockwood definition are similar to those required under the Trasatti definition, but they are used in a different way, e.g. in Rockwood's approach they are used to calculate the equilibrium vapour pressure of the electron gas. The numerical value for the absolute potential of the standard hydrogen electrode one would calculate under the Rockwood definition is sometimes fortuitously close to the value one would obtain under the Trasatti definition. This near-agreement in the numerical value depends on the choice of ambient temperature and standard states, and is the result of the near-cancellation of certain terms in the expressions. For example, if a standard state of one atmosphere ideal gas is chosen for the electron gas then the cancellation of terms occurs at a temperature of 296 K, and the two definitions give an equal numerical result. At 298.15 K a near-cancellation of terms would apply and the two approaches would produce nearly the same numerical values. However, there is no fundamental significance to this near agreement because it depends on arbitrary choices, such as temperature and definitions of standard states. | 7 | Physical Chemistry |
Values for log K typically range between -3 (very hydrophilic) and +10 (extremely lipophilic/hydrophobic).
The values listed here are sorted by the partition coefficient. Acetamide is hydrophilic, and 2,2′,4,4′,5-Pentachlorobiphenyl is lipophilic. | 7 | Physical Chemistry |
Several gene families are involved in the processes of hyperaccumulation including upregulation of absorption and sequestration of heavy metal metals. These hyperaccumulation genes (HA genes) are found in over 450 plant species, including the model organisms Arabidopsis and Brassicaceae. The expression of such genes is used to determine whether a species is capable of hyperaccumulation. Expression of HA genes provides the plant with capacity to uptake and sequester metals such as As, Co, Fe, Cu, Cd, Pb, Hg, Se, Mn, Zn, Mo and Ni in 100–1000x the concentration found in sister species or populations.
The ability to hyperaccumulate is determined by two major factors: environmental exposure and the expression of ZIP gene family.
Although experiments have shown that the hyperaccumulation is partially dependent on environmental exposure (i.e. only plants exposed to metal are observed with high concentrations of that metal), hyperaccumulation is ultimately dependent on the presence and upregulation of genes involved with that process. It has been shown that hyperaccumulation capacities can be inherited in Thlaspi caerulescens (Brassicaceae) and others. As there is a wide variety among hyperaccumulating species that span across different plant families, it is likely that HA genes were eco typically selected for.
In most hyperaccumulating plants, the main mechanism for metal transport are the proteins coded by genes in the ZIP family, however other families such as the HMA, MATE, YSL and MTP families have also been observed to be involved. The ZIP gene family is a novel, plant-specific gene family that encodes Cd, Mn, Fe and Zn transporters. The ZIP family plays a role in supplying Zn to metalloproteins.
In one study on Arabidopsis, it was found that the metallophyte Arabidopsis halleri expressed a member of the ZIP family that was not expressed in a non-metallophyte sister species. This gene was an iron regulated transporter (IRT-protein) that encoded several primary transporters involved with cellular uptake of cations above the concentration gradient. When this gene was transformed into yeast, hyperaccumulation was observed. This suggests that overexpression of ZIP family genes that encode cation transporters is a characteristic genetic feature of hyperaccumulation.
Another gene family that has been observed ubiquitously in hyperaccumulators are the ZTP and ZNT families. A study on T. caerulescens identified the ZTP family as a plant specific family with high sequence similarity to other zinc transporter4. Both the ZTP and ZNT families, like the ZIP family, are zinc transporters. It has been observed in hyperaccumulating species, that these genes, specifically ZNT1 and ZNT2 alleles are chronically overexpressed.
While the precise mechanism by which these genes facilitate hyperaccumulation is unknown, expression patterns strongly correlate with individual hyperaccumulation capacity and metal exposure, implying that these gene families play a regulatory role. Because the presence and expression of zinc transporter gene families are highly prevalent in hyperaccumulators, the ability to accumulate a diverse range of heavy metals is most likely due to the zinc transporters inability to discriminate against specific metal ions. The response of the plants to hyperaccumulation of any metal also supports this theory as it has been observed that AhHMHA3 is expressed in hyperaccumulating individuals. AhHMHA3 has been identified to be expressed in response to and aid of Zn detoxification. In another study, using metallophytic and non-metallophytic Arabidopsis' populations, back crosses indicated pleiotropy between Cd and Zn tolerances. This response suggests that plants are unable to detect specific metals, and that hyperaccumulation is likely a result of an overexpressed Zn transportation system.
The overall effect of these expression patterns has been hypothesized to assist in plant defense systems. In one hypothesis, "the elemental defense hypothesis", provided by Poschenrieder, it is suggested that the expression of these genes assist in antiherbivory or pathogen defenses by making tissues toxic to organisms attempting to feed on that plant. Another hypothesis, "the joint hypothesis", provided by Boyd, suggests that expression of these genes assists in systemic defense. | 2 | Environmental Chemistry |
In Europe since early 1980s, cars must be equipped with one or two red rear fog lamps. A single rear fog lamp must be located between the vehicles longitudinal centreline and the outer extent of the drivers side of the vehicle. | 4 | Stereochemistry |
Dialkylphosphinic acids have the formula RPOH, where R is an alkyl or aryl group. The phosphorus(V) center has tetrahedral molecular geometry. Under the brand names Aerophine and Cyanex, dialkylphosphinic acids are used in extraction and separation of metals as one of the techniques of hydrometallurgy Characteristically the organic substituents are branched to confer solubility and preclude crystallization.
Formaldehyde and HPO react to give (HOCH)POH. | 0 | Organic Chemistry |
Laser snow is the precipitation through a chemical reaction, condensation and coagulation process, of clustered atoms or molecules, induced by passing a laser beam through certain gasses. It was first observed by Tam, Moe and Happer in 1975, and has since been noted in a number of gases. | 7 | Physical Chemistry |
While most mining companies have shifted from a previously accepted sprinkler method to the percolation of slowly dripping choice chemicals including cyanide or sulfuric acid closer to the actual ore bed, heap leach pads have not changed too much throughout the years. There are still four main categories of pads: conventional, dump leach, valley fills, and on/off pads. Typically, each pad only has a single, geomembrane liner for each pad, with a minimum thickness of 1.5mm, usually thicker.
The conventional pads simplest in design are used for mostly flat or gentle areas and hold thinner layers of crushed ore. Dump leach pads hold more ore and can usually handle a less flat terrain. Valley fills are pads situated at valley bottoms or levels that can hold everything falling into it. On/off pads involve putting significantly larger loads on the pads and removing and reloading it after every cycle.
Many of these mines which previously had digging depths of about 15 meters are digging deeper than ever before to mine materials, approximately 50 meters, sometimes more, which means that, in order to accommodate all of the ground being displaced, pads will have to hold higher weights from more crushed ore being contained in a smaller area (Lupo 2010). With that increase in build up comes in potential for decrease in yield or ore quality, as well as potential either weak spots in the lining or areas of increased pressure buildup. This build up still has the potential to lead to punctures in the liner. As of 2004 cushion fabrics, which could reduce potential punctures and their leaking, were still being debated due to their tendency to increase risks if too much weight on too large a surface was placed on the cushioning (Thiel and Smith 2004). In addition, some liners, depending on their composition, may react with salts in the soil as well as acid from the chemical leaching to affect the successfulness of the liner. This can be amplified over time. | 8 | Metallurgy |
From a 2010 study by the University of Maryland, photosynthesizing cyanobacteria have been shown to be a significant species in the global carbon cycle, accounting for 20–30% of Earth's photosynthetic productivity and convert solar energy into biomass-stored chemical energy at the rate of ~450 TW.
Some pigments such as B-phycoerythrin that are mostly found in red algae and cyanobacteria has much higher light-harvesting efficiency compared to that of other plants. Such organisms are potentially candidates for biomimicry technology to improve solar panels design. | 5 | Photochemistry |
In an isolated system, thermodynamic equilibrium by definition persists over an indefinitely long time. In classical physics it is often convenient to ignore the effects of measurement and this is assumed in the present account.
To consider the notion of fluctuations in an isolated thermodynamic system, a convenient example is a system specified by its extensive state variables, internal energy, volume, and mass composition. By definition they are time-invariant. By definition, they combine with time-invariant nominal values of their conjugate intensive functions of state, inverse temperature, pressure divided by temperature, and the chemical potentials divided by temperature, so as to exactly obey the laws of thermodynamics. But the laws of thermodynamics, combined with the values of the specifying extensive variables of state, are not sufficient to provide knowledge of those nominal values. Further information is needed, namely, of the constitutive properties of the system.
It may be admitted that on repeated measurement of those conjugate intensive functions of state, they are found to have slightly different values from time to time. Such variability is regarded as due to internal fluctuations. The different measured values average to their nominal values.
If the system is truly macroscopic as postulated by classical thermodynamics, then the fluctuations are too small to detect macroscopically. This is called the thermodynamic limit. In effect, the molecular nature of matter and the quantal nature of momentum transfer have vanished from sight, too small to see. According to Buchdahl: "... there is no place within the strictly phenomenological theory for the idea of fluctuations about equilibrium (see, however, Section 76)."
If the system is repeatedly subdivided, eventually a system is produced that is small enough to exhibit obvious fluctuations. This is a mesoscopic level of investigation. The fluctuations are then directly dependent on the natures of the various walls of the system. The precise choice of independent state variables is then important. At this stage, statistical features of the laws of thermodynamics become apparent.
If the mesoscopic system is further repeatedly divided, eventually a microscopic system is produced. Then the molecular character of matter and the quantal nature of momentum transfer become important in the processes of fluctuation. One has left the realm of classical or macroscopic thermodynamics, and one needs quantum statistical mechanics. The fluctuations can become relatively dominant, and questions of measurement become important.
The statement that the system is its own internal thermodynamic equilibrium may be taken to mean that indefinitely many such measurements have been taken from time to time, with no trend in time in the various measured values. Thus the statement, that a system is in its own internal thermodynamic equilibrium, with stated nominal values of its functions of state conjugate to its specifying state variables, is far far more informative than a statement that a set of single simultaneous measurements of those functions of state have those same values. This is because the single measurements might have been made during a slight fluctuation, away from another set of nominal values of those conjugate intensive functions of state, that is due to unknown and different constitutive properties. A single measurement cannot tell whether that might be so, unless there is also knowledge of the nominal values that belong to the equilibrium state. | 7 | Physical Chemistry |
* 1997 Alexander von Humboldt Fellowship
* 1999 National Laboratory Visiting Fellow (NSERC)
* 2004 Fred Beamish Award (CSC)
* 2008 JSPS Invitation Fellow
* 2011 W. Lash Miller Award (ECS Canadian Section)
* 2012 Tajima Prize (ISE)
* 2015 W.A.E. McBryde Medal (CSC)
* 2021 Fellow, Royal Society of Chemistry | 3 | Analytical Chemistry |
Although much of the literature on the subject is concerned with just one mechanism, there are actually several different mechanisms that produce the photoacoustic effect. The primary universal mechanism is photothermal, based on the heating effect of the light and the consequent expansion of the light-absorbing material. In detail, the photothermal mechanism consists of the following stages:
# conversion of the absorbed pulsed or modulated radiation into heat energy.
# temporal changes of the temperatures at the loci where radiation is absorbed – rising as radiation is absorbed and falling when radiation stops and the system cools.
# expansion and contraction following these temperature changes, which are "translated" to pressure changes. The pressure changes, which occur in the region where light was absorbed, propagate within the sample body and can be sensed by a sensor coupled directly to it. Commonly, for the case of a condensed phase sample (liquid, solid), pressure changes are rather measured in the surrounding gaseous phase (commonly air), formed there by the diffusion of the thermal pulsations.
The main physical picture, in this case, envisions the original temperature pulsations as origins of propagating temperature waves ("thermal waves"), which travel in the condensed phase, ultimately reaching the surrounding gaseous phase. The resulting temperature pulsations in the gaseous phase are the prime cause of the pressure changes there. The amplitude of the traveling thermal wave decreases strongly (exponentially) along its propagation direction, but if its propagation distance in the condensed phase is not too long, its amplitude near the gaseous phase is sufficient to create detectable pressure changes. This property of the thermal wave confers unique features to the detection of light absorption by the photoacoustic method. The temperature and pressure changes involved are minute, compared to everyday scale – typical order of magnitude for the temperature changes, using ordinary light intensities, is about micro- to millidegrees and for the resulting pressure changes is about nano- to microbars.
The photothermal mechanism manifests itself, besides the photoacoustic effect, also by other physical changes, notably emission of infra-red radiation and changes in the refraction index. Correspondingly, it may be detected by various other means, described by terms such as "photothermal radiometry", "thermal lens" and "thermal beam deflection" (popularly also known as "mirage" effect, see Photothermal spectroscopy). These methods parallel the photoacoustic detection. However, each method has its special range of application. | 7 | Physical Chemistry |
The Manhès–David process is a refining process of the copper mattes, invented in 1880 by the French industrialist Pierre Manhès and his engineer . Inspired by the Bessemer process, it consists of the use of a converter to oxidise with air the undesirable chemical elements (mainly iron and sulfur) contained in the matte, to transform it into copper.
The quantity of the elements to be oxidized, as well as the low heat produced by the chemical reactions, lead to drastics modifications of the converter. Manhès and David designed it as a horizontal cylinder, with nozzles aligned from one end to the other. A few years later, the Americans engineers William H. Peirce and Elias Anton Cappelen Smith lined it with basic refractory materials, much more durable than that used by the French inventors. While this improvement does not alter the principles of the process, it eases its widespread use, accelerating the switchover of copper production from Britain to the United States.
At the beginning of the 21st century, the refine 90% of the copper mattes and is used in 60% of the nickel extracted. This converter, like the addition of pure oxygen, the automation of the running, the treatment of smoke and the increasing size of the tools, ensured the durability of the Manhès–David process, even if modern tools have little relationship with their ancestors. | 8 | Metallurgy |
The potentially hazardous effects of methylglyoxal require regulation of the reactions with this substrate. Synthesis of methylglyoxal is regulated by levels of DHAP and phosphate concentrations. High concentrations of DHAP encourage methylglyoxal synthase to produce methylglyoxal, while high phosphate concentrations inhibit the enzyme, and therefore the production of more methylglyoxal. The enzyme triose phosphate isomerase affects the levels of DHAP by converting glyceraldehyde 3-phosphate (GAP) into DHAP. The usual pathway converting GAP to pyruvate starts with the enzyme glyceraldehyde 3-phosphate dehydrogenase ([http://mic.sgmjournals.org/cgi/reprint/151/3/707 Weber] 711–13). Low phosphate levels inhibit GAP dehydrogenase; GAP is instead converted into DHAP by triosephosphate isomerase. Again, increased levels of DHAP activate methylglyoxal synthase and methylglyoxal production ([http://mic.sgmjournals.org/cgi/reprint/151/3/707 Weber] 711–13). | 1 | Biochemistry |
In particle physics and astrophysics, the term strange matter is used in two different contexts, one broader and the other more specific and hypothetical:
# In the broader context, our current understanding of the laws of nature predicts that strange matter could be created when nuclear matter (made of protons and neutrons) is compressed beyond a critical density. At this critical pressure and density, the protons and neutrons dissociate into quarks, yielding quark matter and potentially strange matter.
# A more specific hypothesis is that quark matter is the true ground state of all matter, and thus more stable than ordinary nuclear matter. This idea is known as the "strange matter hypothesis", or the Bodmer–Witten assumption. Under this hypothesis, the nuclei of the atoms we see around us are only metastable, even when the external critical pressure is zero, and given enough time (or the right stimulus) the nuclei would decay into stable droplets of strange matter. Droplets of strange matter are also referred to as strangelets. | 7 | Physical Chemistry |
A membrane brings many new elements for the separation. Amino acids has been separated by perstraction. Membranes did not only separate extractants and the primary solution but also were selective for amino acids. Charged membranes were used. So they selected amino acids by pKa. Besides the selectivity of a membrane is affected by its thickness, pore diameter and charge potential. The bigger pore is, the better amino acids permeate the membrane. The higher charge potential is, the bigger electrostatic rejection effects are. The thinner membrane, the less it is selective. | 3 | Analytical Chemistry |
One of the most important results of Wnt signaling and the elevated level of β-catenin in certain cell types is the maintenance of pluripotency. The rate of stem cells in the colon is for instance ensured by such accumulation of β-catenin, which can be stimulated by the Wnt pathway. High frequency peristaltic mechanical strains of the colon are also involved in the β-catenin dependent maintenance of homeostatic levels of colonic stem cells through processes of mechanotransduction. This feature is pathologically enhanced towards tumorigenic hyperproliferation in healthy cells compressed by pressure due genetically altered hyperproliferative tumorous cells.
In other cell types and developmental stages, β-catenin may promote differentiation, especially towards mesodermal cell lineages. | 1 | Biochemistry |
For an extreme example, in a tensile test a bar of steel is strained to just before the length at which it usually fractures. The load is released smoothly and the material relieves some of its strain by decreasing in length. The decrease in length is called the elastic recovery, and the result is a work-hardened steel bar. The fraction of length recovered (length recovered/original length) is equal to the yield-stress divided by the modulus of elasticity. (Here we discuss true stress in order to account for the drastic decrease in diameter in this tensile test.) The length recovered after removing a load from a material just before it breaks is equal to the length recovered after removing a load just before it enters plastic deformation.
The work-hardened steel bar has a large enough number of dislocations that the strain field interaction prevents all plastic deformation. Subsequent deformation requires a stress that varies linearly with the strain observed, the slope of the graph of stress vs. strain is the modulus of elasticity, as usual.
The work-hardened steel bar fractures when the applied stress exceeds the usual fracture stress and the strain exceeds usual fracture strain. This may be considered to be the elastic limit and the yield stress is now equal to the fracture toughness, which is much higher than a non-work-hardened steel yield stress.
The amount of plastic deformation possible is zero, which is less than the amount of plastic deformation possible for a non-work-hardened material. Thus, the ductility of the cold-worked bar is reduced.
Substantial and prolonged cavitation can also produce strain hardening. | 8 | Metallurgy |
Fish scales are calcium phosphate composites coated with a mucus layer. Fish scale properties have been mimicked by polyacrylamide hydrogels, which are both hydrophilic and mimic the mucus’ retention of water. Additionally, fish scales have been used as a template for a casting technique, and as a model for a lithography and chemical etching techniques on silicon wafers that exhibited oleophobic contact angles of oil in water of 163° and 175°, respectively. | 7 | Physical Chemistry |
The halomethanes are produced on an industrial scale from abundant precursors such as natural gas or methanol, and from halogens or halides. They are usually prepared by one of three methods.
*Free radical chlorination of methane (under ultraviolet light):
This method is useful for the production of (n = 1, 2, 3, or 4). The main problems with this method are that it cogenerates HCl and it produces mixtures of different products. Using in large excess generates primarily and using in large excess generates primarily , but mixtures of other products will still be present.
*Halogenation of methanol. This method is used for the production of the mono-chloride, -bromide, and -iodide.
*Halogen exchange. The method is mainly used to produce fluorinated derivatives from the chlorides.
*Reaction of methane with hypochlorous acid, producing water.
*Reaction of methanol with hypochlorous acid, producing hydrogen peroxide.
Traces of halomethanes in the atmosphere arise through the introduction of other non-natural, industrial materials. | 2 | Environmental Chemistry |
Although anti-Jo-1 antibodies are often included with ANAs, they are actually antibodies to the cytoplasmic protein, Histidyl-tRNA synthetase – an aminoacyl-tRNA synthetase essential for the synthesis of histidine loaded tRNA. They are highly associated with polymyositis and dermatomyositis, and are rarely found in other connective tissue diseases. Around 20–40% of polymyositis is positive for Jo-1 antibodies and most will have interstitial lung disease, HLA-DR3 and HLA-DRw52 human leukocyte antigen (HLA) markers; collectively known as Jo-1 syndrome. | 1 | Biochemistry |
Photoluminescence (PL) is a phenomenon related to the ability of some compounds that, after absorbing specific electromagnetic radiation, relax to a lower energy state through emission of photons. This spectroelectrochemical technique is limited to those compounds with fluorescent or luminescent properties. The experiments are strongly interfered by ambient light. This technique provides structural information and quantitative information with great detection limits. | 7 | Physical Chemistry |
As a pseudohalide, azide generally displaces many leaving group, e.g. , , , sulfonate, and others to give the azido compound. The azide source is most often sodium azide (), although lithium azide () has been demonstrated. | 0 | Organic Chemistry |
There are a number of natural products with neurotrophic activity, which results from several mechanisms including enhancing BDNF gene transcription, upregulating the expression of BDNF and TrkB, and extracellular signal-regulated kinase (ERK) and CREB signalling.
The first discovered non-protein neurotrophic natural product was lactacystin, isolated from a culture broth of Streptomyces sp. Magnolol and honokiol, the main constituents of Magnolia officinalis and Magnolia obovata stem bark, have been reported to have neurotrophic activity in primary cultured rat cortical by enhancing the BDNF expression. Merrilactone A, jiadifenin, jiadifenolide, (1R,10S)-2-oxo-3,4-dehydroxyneomajucin, jiadifenoxolane A, (2R)-hydroxynorneomajucin, 11-O-debenzoyltashironin,tricycloillicinone, and bicycloillicinone, natural products of the Illicium family have been shown to promote neurite outgrowth in primary cultures of cortical neurons of fetal rats. Neurotrophic properties are also possessed by several members of the Lycopodium alkaloids (huperzine A, lyconadins, complanadine A and B, and nankakurine A and B). Studies have shown that huperazine A can elevate the levels of NGF and BDNF. Synthesis of NGF can be upregulated by administration of cyathanediterpenoids specifically erinacines, scabronines and cyrneines.
Some flavonoids, Isoflavonoids and neoflavonoids were found to have neuroprotective activity. Among the effective flavonoids, luteolin from Lonicera japonica sp., isorhamnetin from Opuntia ficus-indica, genistein from Genista tinctoria, and calycosin from Astragalus membranaceus showed the most promising effects by increasing the mRNA expression and protein secretion of NGF, GDNF, and BDNF. Paecilomycine A and spirotenuipesines A and B, members of the trichothecenes, isolated from the fruiting bodies of Paecilomycestenuipes, have significant neurotrophic profiles especially paecilomycine A which can stimulate the synthesis of neurotrophic factors. Polyprenylatedacylphloroglucinols (PPAPs) represented by hyperforin, hypericin and garsubellin A, have neurotrophic like properties. Hyperforin, isolated from the herb St. Johns wort (Hypericum perforatum'), can stimulate the upregulation of the TrkB receptor.
Beside natural products, there are some small molecules of natural origin that exert neurotrophic activities such as: Panaxytriol (promotes NGF-induced neurite outgrowth in PC-12 cells); 7,8-dihydroxyflavone (TrkB activator); Deoxygedunin (BDNF mimetic); Kansuinin E (promotes neurotrophic activity, most likely through TrkA activation); Tripchlorolide (stimulates expression of BDNF mRNA); Fucoxanthin (increases BDNF production and activates PKA/CREB pathway); Silibinin (Activate hippocampal ROS-BDNF-TrkB patway). | 1 | Biochemistry |
CCPs can be a valuable resource of genetic material. They can be used to preserve valuable genetic diversity for future use, or as base for new breeding programs. Promising plants can be selected and multiplied, generating new varieties. | 1 | Biochemistry |
Partial molar properties satisfy relations analogous to those of the extensive properties. For the internal energy U, enthalpy H, Helmholtz free energy A, and Gibbs free energy G, the following hold:
where is the pressure, the volume, the temperature, and the entropy. | 7 | Physical Chemistry |
Source:
* Kern Prize of the ETH Zurich (1949)
* Werner Prize of the Swiss Chemical Society (1956)
* Ruzicka Prize of the ETH Zurich (1958)
* Ernest Guenther Award (1966)
* Austrian Cross of Honour for Science and Art (1974)
* Welch Award (1974)
* Kirkwood Medal, Yale University (1976)
* Davy Medal (1978)
* Tetrahedron Prize for Creativity in Organic Chemistry (1981)
* Arthur C. Cope Award (1984)
* Wolf Prize in Chemistry of the Wolf Foundation, Tel Aviv, Israel (1986)
* Cothenius Medal (1991)
* Nakanishi Prize (1998)
* Oparin Medal (2002)
* Frank H. Westheimer Medal (Harvard University (2004)
* F.A. Cotton Medal for Excellence in Chemical Research of the American Chemical Society (2004)
* Paul Karrer Gold Medal (University of Zurich, 2008)
* Benjamin Franklin Medal in Chemistry from the Franklin Institute in Philadelphia, Pennsylvania (2008) | 0 | Organic Chemistry |
The inverse sixth-power distance dependence of Förster resonance energy transfer was experimentally confirmed by Wilchek, Edelhoch and Brand using tryptophyl peptides. Stryer, Haugland and Yguerabide also experimentally demonstrated the theoretical dependence of Förster resonance energy transfer on the overlap integral by using a fused indolosteroid as a donor and a ketone as an acceptor. Calculations on FRET distances of some example dye-pairs can be found here.
However, a lot of contradictions of special experiments with the theory was observed under complicated environment when the orientations and quantum yields of the molecules are difficult to estimate. | 1 | Biochemistry |
Many gas-fed heating appliances such as ovens and water heaters make use of a pilot flame to ignite the main gas burner when required. If the pilot flame goes out, unburned gas may be released, which is an explosion risk and a health hazard. To prevent this, some appliances use a thermocouple in a fail-safe circuit to sense when the pilot light is burning. The tip of the thermocouple is placed in the pilot flame, generating a voltage which operates the supply valve which feeds gas to the pilot. So long as the pilot flame remains lit, the thermocouple remains hot, and the pilot gas valve is held open. If the pilot light goes out, the thermocouple temperature falls, causing the voltage across the thermocouple to drop and the valve to close.
Where the probe may be easily placed above the flame, a rectifying sensor may often be used instead. With part ceramic construction, they may also be known as flame rods, flame sensors or flame detection electrodes.
Some combined main burner and pilot gas valves (mainly by Honeywell) reduce the power demand to within the range of a single universal thermocouple heated by a pilot (25 mV open circuit falling by half with the coil connected to a 10–12 mV, 0.2–0.25 A source, typically) by sizing the coil to be able to hold the valve open against a light spring, but only after the initial turning-on force is provided by the user pressing and holding a knob to compress the spring during lighting of the pilot. These systems are identifiable by the "press and hold for x minutes" in the pilot lighting instructions. (The holding current requirement of such a valve is much less than a bigger solenoid designed for pulling the valve in from a closed position would require.) Special test sets are made to confirm the valve let-go and holding currents, because an ordinary milliammeter cannot be used as it introduces more resistance than the gas valve coil. Apart from testing the open circuit voltage of the thermocouple, and the near short-circuit DC continuity through the thermocouple gas valve coil, the easiest non-specialist test is substitution of a known good gas valve.
Some systems, known as millivolt control systems, extend the thermocouple concept to both open and close the main gas valve as well. Not only does the voltage created by the pilot thermocouple activate the pilot gas valve, it is also routed through a thermostat to power the main gas valve as well. Here, a larger voltage is needed than in a pilot flame safety system described above, and a thermopile is used rather than a single thermocouple. Such a system requires no external source of electricity for its operation and thus can operate during a power failure, provided that all the other related system components allow for this. This excludes common forced air furnaces because external electrical power is required to operate the blower motor, but this feature is especially useful for un-powered convection heaters. A similar gas shut-off safety mechanism using a thermocouple is sometimes employed to ensure that the main burner ignites within a certain time period, shutting off the main burner gas supply valve should that not happen.
Out of concern about energy wasted by the standing pilot flame, designers of many newer appliances have switched to an electronically controlled pilot-less ignition, also called intermittent ignition. With no standing pilot flame, there is no risk of gas buildup should the flame go out, so these appliances do not need thermocouple-based pilot safety switches. As these designs lose the benefit of operation without a continuous source of electricity, standing pilots are still used in some appliances. The exception is later model instantaneous (aka "tankless") water heaters that use the flow of water to generate the current required to ignite the gas burner; these designs also use a thermocouple as a safety cut-off device in the event the gas fails to ignite, or if the flame is extinguished. | 8 | Metallurgy |
Nesmeyanov, together with N.K. Kochetkov and M.I. Rybinskaya, developed a method for the synthesis of various five- and six-membered heterocycles, which is based on the high activity of carbonyl groups and the mobility of the β-substituent in compounds of the type RCOCH=CHX. The same group of scientists developed the method of "β-ketovinylation", which consists in introducing an RCOCH=CH group into the molecule. The reaction of β-substituted vinyl ketones with an azide ion made it possible to study the stereochemistry and propose a mechanism for nucleophilic substitution at the activated double bond.
In collaboration with other scientists, Nesmeyanov carried out a number of works in the field of radical telomerization and rearrangement radicals. In addition to studies of already known reactions, thermal telomerization of ethylene and propylene with silicon hydrides has been developed and other new telomerization reactions. Also, new routes for the synthesis of compounds containing groups such as CCl, CClCHCl, CClC=CH, CCl=CHX and others. The study of compounds containing the CCl-C=CCBr=CH to CCl=CClCHBr under ultraviolet illumination.
In continuation of the work related to the previously created diazo method, Nesmeyanov and L. G. Makarova investigated the mechanism of decomposition of aryldiazonium and diaryliodonium salts. This made it possible to synthesize new types of onium compounds - diphenylbromonium, diphenylchloronium and triphenyloxonium salts. Together with T. P. Tolstaya and other scientists, Nesmeyanov showed that double salts of diphenylbromonium and diphenylchloronium halides with heavy metal halides are decomposed by powders of the corresponding metals with the formation of organometallic compounds. Thus, the diazo method began to be used to obtain σ-aryl complexes of transition metals and other organometallic compounds. | 0 | Organic Chemistry |
SUMO enzymatic cascade catalyzes the dynamic posttranslational modification process of sumoylation (i.e. transfer of SUMO protein to other proteins). The Small Ubiquitin-related Modifier, SUMO-1, is a ubiquitin-like family member that is conjugated to its substrates through three discrete enzymatic steps (see the figure on the right): activation, involving the E1 enzyme (SAE1/SAE2); conjugation, involving the E2 enzyme (UBE2I); substrate modification, through the cooperation of the E2 and E3 protein ligases.
SUMO pathway modifies hundreds of proteins that participate in diverse cellular processes. SUMO pathway is the most studied ubiquitin-like pathway that regulates a wide range of cellular events, evidenced by a large number of sumoylated proteins identified in more than ten large-scale studies. | 1 | Biochemistry |
Hydrolysis constants (log values) in critical compilations at infinite dilution, T = 298.15 K and I = 3 M NaClO () or 0.1 M Na medium, Data at I = 0 are not available (): | 7 | Physical Chemistry |
The empirical Monod equation is
where:
: μ is the growth rate of a considered microorganism,
: μ is the maximum growth rate of this microorganism,
: [S] is the concentration of the limiting substrate S for growth,
: K is the "half-velocity constant"—the value of [S] when μ/μ = 0.5.
μ and K are empirical (experimental) coefficients to the Monod equation. They will differ between microorganism species and will also depend on the ambient environmental conditions, e.g., on the temperature, on the pH of the solution, and on the composition of the culture medium. | 7 | Physical Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V). | 1 | Biochemistry |
Various analytical methods approved by the United States Environmental Protection Agency (EPA) for measuring mercury in wastewater are in common use. EPA Methods 245.7 and 1631 are commonly used for measurement of industrial wastewater using CVAFS. | 7 | Physical Chemistry |
The geology that underlies a river or lake has a major impact on its chemistry. A river flowing across very ancient precambrian schists is likely to have dissolved very little from the rocks and maybe similar to de-ionised water at least in the headwaters. Conversely a river flowing through chalk hills, and especially if its source is in the chalk, will have a high concentration of carbonates and bicarbonates of Calcium and possibly Magnesium.
As a river progresses along its course it may pass through a variety of geological types and it may have inputs from aquifers that do not appear on the surface anywhere in the locality. | 2 | Environmental Chemistry |
Spectrochemistry is the application of spectroscopy in several fields of chemistry. It includes analysis of [https://imagine.gsfc.nasa.gov/science/toolbox/spectra1.html ] in chemical terms, and use of spectra to derive the structure of chemical compounds, and also to qualitatively and quantitively analyze their presence in the sample. It is a method of chemical analysis that relies on the measurement of [https://www.qrg.northwestern.edu/projects/vss/docs/communications/1-what-is-wavelength.html ] and intensity of . | 7 | Physical Chemistry |
Photo-reactive amino acid analogs are artificial analogs of natural amino acids that can be used for crosslinking of protein complexes. Photo-reactive amino acid analogs may be incorporated into proteins and peptides in vivo or in vitro. Photo-reactive amino acid analogs in common use are photoreactive diazirine analogs to leucine and methionine, and para-benzoylphenylalanine. Upon exposure to ultraviolet light, they are activated and covalently bind to interacting proteins that are within a few angstroms of the photo-reactive amino acid analog.
-Photo-leucine and -photo-methionine are analogs of the naturally occurring -leucine and -methionine amino acids that are endogenously incorporated into the primary sequence of proteins during synthesis using the normal translation machinery. They are then ultraviolet light (UV)-activated to covalently crosslink proteins within protein–protein interaction domains in their native in-vivo environment. The method enables the determination and characterization of both stable and transient protein interactions in cells without the addition of chemical crosslinkers and associated solvents that can adversely affect the cell biology being studied in the experiment.
When used in combination with limiting media that is devoid of leucine and methionine, the photo-activatable derivatives are treated like naturally occurring amino acids by the cellular protein synthesis machinery. As a result, they can be substituted for leucine or methionine in the primary structure of proteins. Photo-leucine and photo-methionine derivatives contain diazirine rings that are activated when exposed to UV light to become reactive intermediates that form covalent bonds with nearby protein side chains and backbones. Naturally interacting proteins within the cell can be instantly trapped by photoactivation of the diazirine-containing proteins in the cultured cells. Crosslinked protein complexes can be detected by decreased mobility on SDS-PAGE followed by Western blotting, size exclusion chromatography, sucrose density gradient sedimentation or mass spectrometry. | 1 | Biochemistry |
CellCognition has been used in RNAi-based screening, applied in basic cell cycle study, and extended to unsupervised modeling. | 1 | Biochemistry |
Sucrose esters are off-white powders. Though produced from sucrose, sucrose esters do not have a sweet taste, but are bland or bitter. | 0 | Organic Chemistry |
TNF receptor associated factors (TRAFs) are a family of proteins primarily involved in the regulation of inflammation, antiviral responses and apoptosis.
Currently, seven TRAF proteins have been characterized in mammals: TRAF1, TRAF2, TRAF3, TRAF4, TRAF5, TRAF6 and TRAF7.
Except for TRAF7, these proteins share a relatively conserved secondary structure, including a namesake C-terminal TRAF domain that mediates interactions with other signaling components such as the transmembrane TNF receptors and CD40. | 1 | Biochemistry |
The oligodynamic effect (from Greek oligos, "few", and dynamis, "force") is a biocidal effect of metals, especially heavy metals, that occurs even in low concentrations. This effect is attributed to the antibacterial behavior of metal ions, which are absorbed by bacteria upon contact and damage their cell membranes.
In modern times, the effect was observed by Carl Nägeli, although he did not identify the cause. Brass doorknobs and silverware both exhibit this effect to an extent. | 1 | Biochemistry |
An important technique for characterizing metal carbonyls is infrared spectroscopy. The C–O vibration, typically denoted ν, occurs at 2143 cm for carbon monoxide gas. The energies of the ν band for the metal carbonyls correlates with the strength of the carbon–oxygen bond, and inversely correlated with the strength of the π-backbonding between the metal and the carbon. The π-basicity of the metal center depends on a lot of factors; in the isoelectronic series (titanium to iron) at the bottom of this section, the hexacarbonyls show decreasing π-backbonding as one increases (makes more positive) the charge on the metal. π-Basic ligands increase π-electron density at the metal, and improved backbonding reduces ν. The Tolman electronic parameter uses the Ni(CO) fragment to order ligands by their π-donating abilities.
The number of vibrational modes of a metal carbonyl complex can be determined by group theory. Only vibrational modes that transform as the electric dipole operator will have nonzero direct products and are observed. The number of observable IR transitions (but not their energies) can thus be predicted. For example, the CO ligands of octahedral complexes, such as Cr(CO), transform as a, e, and t, but only the t mode (antisymmetric stretch of the apical carbonyl ligands) is IR-allowed. Thus, only a single ν band is observed in the IR spectra of the octahedral metal hexacarbonyls. Spectra for complexes of lower symmetry are more complex. For example, the IR spectrum of Fe(CO) displays CO bands at 2082, 2019 and 1829 cm. The number of IR-observable vibrational modes for some metal carbonyls are shown in the table. Exhaustive tabulations are available. These rules apply to metal carbonyls in solution or the gas phase. Low-polarity solvents are ideal for high resolution. For measurements on solid samples of metal carbonyls, the number of bands can increase owing in part to site symmetry. | 0 | Organic Chemistry |
According to some definitions, covalent hydrides cover all other compounds containing hydrogen. Some definitions limit hydrides to hydrogen centres that formally react as hydrides, i.e. are nucleophilic, and hydrogen atoms bound to metal centers. These hydrides are formed by all the true non-metals (except zero group elements) and the elements like Al, Ga, Sn, Pb, Bi, Po, etc., which are normally metallic in nature, i.e., this class includes the hydrides of p-block elements. In these substances the hydride bond is formally a covalent bond much like the bond made by a proton in a weak acid. This category includes hydrides that exist as discrete molecules, polymers or oligomers, and hydrogen that has been chem-adsorbed to a surface. A particularly important segment of covalent hydrides are complex metal hydrides, powerful soluble hydrides commonly used in synthetic procedures.
Molecular hydrides often involve additional ligands; for example, diisobutylaluminium hydride (DIBAL) consists of two aluminum centers bridged by hydride ligands. Hydrides that are soluble in common solvents are widely used in organic synthesis. Particularly common are sodium borohydride () and lithium aluminium hydride and hindered reagents such as DIBAL. | 0 | Organic Chemistry |
Transposons have coexisted with eukaryotes for thousands of years and through their coexistence have become integrated in many organisms genomes. Colloquially known as jumping genes', transposons can move within and between genomes allowing for this integration.
While there are many positive effects of transposons in their host eukaryotic genomes, there are some instances of mutagenic effects that TEs have on genomes leading to disease and malignant genetic alterations. | 1 | Biochemistry |
Consider the series of delta functions given by
The Patterson function is given by the following series of delta functions and unit step functions | 3 | Analytical Chemistry |
In the built environment, evaporation limited capillary penetration is responsible for the phenomenon of rising damp in concrete and masonry, while in industry and diagnostic medicine this phenomenon is increasingly being harnessed in the field of paper-based microfluidics.
In physiology, capillary action is essential for the drainage of continuously produced tear fluid from the eye. Two canaliculi of tiny diameter are present in the inner corner of the eyelid, also called the lacrimal ducts; their openings can be seen with the naked eye within the lacrymal sacs when the eyelids are everted.
Wicking is the absorption of a liquid by a material in the manner of a candle wick.
Paper towels absorb liquid through capillary action, allowing a fluid to be transferred from a surface to the towel. The small pores of a sponge act as small capillaries, causing it to absorb a large amount of fluid. Some textile fabrics are said to use capillary action to "wick" sweat away from the skin. These are often referred to as wicking fabrics, after the capillary properties of candle and lamp wicks.
Capillary action is observed in thin layer chromatography, in which a solvent moves vertically up a plate via capillary action. In this case the pores are gaps between very small particles.
Capillary action draws ink to the tips of fountain pen nibs from a reservoir or cartridge inside the pen.
With some pairs of materials, such as mercury and glass, the intermolecular forces within the liquid exceed those between the solid and the liquid, so a convex meniscus forms and capillary action works in reverse.
In hydrology, capillary action describes the attraction of water molecules to soil particles. Capillary action is responsible for moving groundwater from wet areas of the soil to dry areas. Differences in soil potential () drive capillary action in soil.
A practical application of capillary action is the capillary action siphon. Instead of utilizing a hollow tube (as in most siphons), this device consists of a length of cord made of a fibrous material (cotton cord or string works well). After saturating the cord with water, one (weighted) end is placed in a reservoir full of water, and the other end placed in a receiving vessel. The reservoir must be higher than the receiving vessel. A related but simplified capillary siphon only consists of two hook-shaped stainless-steel rods, whose surface is hydrophilic, allowing water to wet the narrow grooves between them. Due to capillary action and gravity, water will slowly transfer from the reservoir to the receiving vessel. This simple device can be used to water houseplants when nobody is home. This property is also made use of in the lubrication of steam locomotives: wicks of worsted wool are used to draw oil from reservoirs into delivery pipes leading to the bearings. | 7 | Physical Chemistry |
A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains.
Bacillite is a type of crystallite. It is rodlike with parallel longulites. | 8 | Metallurgy |
The asymmetric Darzens reaction between aldehydes and (alpha)-haloesters is an effective method for the synthesis of glycidic esters. Chiral auxiliaries, chiral boron enolates, and asymmetric phase transfer catalysis have been used successfully to effect asymmetric induction in the Darzens reaction.
Diastereoselective epoxidations of chiral, non-racemic alkenes suffer from the limitation that removal of the auxiliary without disturbing the epoxide is often difficult. Nonetheless, diastereoselectivity is high in some cases.
Oxidation of epoxy alcohols generated via Sharpless epoxidation is a third method for the enantioselective synthesis of chiral α,β-epoxy carbonyl compounds. Swern and Parikh-Doering conditions are most commonly applied to accomplish these oxidations. | 0 | Organic Chemistry |
Grating monochromators disperse ultraviolet, visible, and infrared radiation typically using replica gratings, which are manufactured from a master grating. A master grating consists of a hard, optically flat, surface that has a large number of parallel and closely spaced grooves. The construction of a master grating is a long, expensive process because the grooves must be of identical size, exactly parallel, and equally spaced over the length of the grating (3–10 cm). A grating for the ultraviolet and visible region typically has 300–2000 grooves/mm, however 1200–1400 grooves/mm is most common. For the infrared region, gratings usually have 10–200 grooves/mm. When a diffraction grating is used, care must be taken in the design of broadband monochromators because the diffraction pattern has overlapping orders. Sometimes broadband preselector filters are inserted in the optical path to limit the width of the diffraction orders so they do not overlap. Sometimes this is done by using a prism as one of the monochromators of a dual monochromator design.
The original high-resolution diffraction gratings were ruled. The construction of high-quality ruling engines was a large undertaking (as well as exceedingly difficult, in past decades), and good gratings were very expensive. The slope of the triangular groove in a ruled grating is typically adjusted to enhance the brightness of a particular diffraction order. This is called blazing a grating. Ruled gratings have imperfections that produce faint "ghost" diffraction orders that may raise the stray light level of a monochromator. A later photolithographic technique allows gratings to be created from a holographic interference pattern. Holographic gratings have sinusoidal grooves and so are not as bright, but have lower scattered light levels than blazed gratings. Almost all the gratings actually used in monochromators are carefully made replicas of ruled or holographic master gratings. | 7 | Physical Chemistry |
Stainless steel alloys remain a research target because of lower production costs, as well as the need for an austenitic stainless steel with high-temperature corrosion resistance in environments with water vapor. Research focuses on increasing high-temperature tensile strength, toughness, and creep resistance to compete with Ni-based superalloys.
Oak Ridge National Laboratory is researching austenitic alloys, achieving similar creep and corrosion resistance at 800 °C to that of other austenitic alloys, including Ni-based superalloys. | 8 | Metallurgy |
The iron-tin intermetallic forms at around and naturally assumes a kagome structure. Quenching in an ice bath then cools the material to room temperature without disrupting the atomic structure. | 8 | Metallurgy |
Camille Alphonse Faure (21 May 1840, Vizille – 14 September 1898) was a French chemical engineer who in 1881 significantly improved the design of the lead-acid battery, which had been invented by Gaston Planté in 1859. Faure's improvements greatly increased the capacity of such batteries and led directly to their manufacture on an industrial scale. The patents were assigned to the Société La Force et la Lumière. The right to use these patents in the British Isles were sold to the Faure Electric Accumulator Company on 29 March 1881. Faure was a consultant engineer with William Edward Ayrton for this company. | 7 | Physical Chemistry |
The epoxidation of ethylene involves its reaction with oxygen. According to a reaction mechanism suggested in 1974 at least one ethylene molecule is totally oxidized for every six that are converted to ethylene oxide:
The direct reaction of oxygen with alkenes is useful only for this epoxide. Modified heterogeneous silver catalysts are typically employed. Other alkenes fail to react usefully, even propylene, though TS-1 supported Au catalysts can perform propylene epoxidation selectively. | 0 | Organic Chemistry |
In humans, transferrin consists of a polypeptide chain containing 679 amino acids and two carbohydrate chains. The protein is composed of alpha helices and beta sheets that form two domains. The N- and C- terminal sequences are represented by globular lobes and between the two lobes is an iron-binding site.
The amino acids which bind the iron ion to the transferrin are identical for both lobes; two tyrosines, one histidine, and one aspartic acid. For the iron ion to bind, an anion is required, preferably carbonate ().
Transferrin also has a transferrin iron-bound receptor; it is a disulfide-linked homodimer. In humans, each monomer consists of 760 amino acids. It enables ligand bonding to the transferrin, as each monomer can bind to one or two atoms of iron. Each monomer consists of three domains: the protease, the helical, and the apical domains. The shape of a transferrin receptor resembles a butterfly based on the intersection of three clearly shaped domains. Two main transferrin receptors found in humans denoted as transferrin receptor 1 (TfR1) and transferrin receptor 2 (TfR2). Although both are similar in structure, TfR1 can only bind specifically to human TF where TfR2 also has the capability to interact with bovine TF. | 1 | Biochemistry |
ASPicDB is a database of human protein variants generated by alternative splicing, a process by which the exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing. | 1 | Biochemistry |
Methanol economy advantages compared to a hydrogen economy:
* Efficient energy storage by volume, as compared with compressed hydrogen. When hydrogen pressure-confinement vessel is taken into account, an advantage in energy storage by weight can also be realized. The volumetric energy density of methanol is considerably higher than liquid hydrogen, in part because of the low density of liquid hydrogen of 71 grams/litre. Hence there is actually more hydrogen in a litre of methanol (99 grams/litre) than in a litre of liquid hydrogen, and methanol needs no cryogenic container maintained at a temperature of -253 °C .
* A liquid hydrogen infrastructure would be prohibitively expensive. Methanol can use existing gasoline infrastructure with only limited modifications.
* Can be blended with gasoline (for example in M85, a mixture containing 85% methanol and 15% gasoline).
* User friendly. Hydrogen is volatile, and its confinements uses high pressure or cryogenic systems.
* Less losses : Hydrogen leaks more easily than methanol. Heat will evaporate liquid hydrogen, giving expected losses up to 0.3% per day in storage tanks. (see [http://www.chart-ferox.com/getattachment/37f20eca-f9ee-4eaa-88c7-0f373e93f8ca/VT_FULL_EN.aspx Chart Ferox storage tanks Liquid oxygen]). | 2 | Environmental Chemistry |
The Pathway Interaction Database (PID) is a free biomedical database of human cellular signaling pathways. The database contains information about the molecular interactions and reactions that take place in cells, with a particular focus on processes that might be relevant to cancer research and treatment. The database was established as collaboration between the U.S. National Cancer Institute, NIH and Nature Publishing Group in 2005 and was launched in November 2006. In September 2012, active curation was stopped and the PID data are now available in the [http://www.ndexbio.org/#/user/301a91c6-a37b-11e4-bda0-000c29202374 Network Data Exchange, NDEx]. | 1 | Biochemistry |
When tested by commercial laboratories, alguronic acid showed significant results in several skin benefit and anti-aging parameters, both independently and compared to other well-known anti-aging ingredients. The funding for these third party laboratories is not disclosed. The acid, an heterogeneous mix of polysaccharides, will vary in composition depending on the growth conditions of the mixed algae cultures; the individual structures of the components of this mix has not been established.
Alguronic acid is not naturally present in human skin, should not be affected by skin enzymes, and is unlikely to be used by the skin. Conversely, hyaluronic acid is distributed throughout the body, is naturally produced in the skin, and, based on its ability to retain moisture, plays a major role in tissue structure and repair. In testing done by commercial laboratories, alguronic acid was found to inhibit production of hyaluronic-acid-degrading enzymes by up to 67%. The relevance of this inhibition in vitro to skin physiology is unknown. | 0 | Organic Chemistry |
Heating polymers to a sufficiently high temperature can cause damaging chemical changes, even in the absence of oxygen. This usually starts with chain scission, generating free radicals, which primarily engage in disproportionation and crosslinking.
PVC is the most thermally sensitive common polymer, with major degradation occurring from ~ onwards; other polymers degrade at higher temperatures. | 7 | Physical Chemistry |
There are few examples of seven-carbon sugars in nature, among which are:
* sedoheptulose or -altro-heptulose (a ketose), an intermediate in the Calvin cycle and in lipid A biosynthesis
* mannoheptulose (a ketose), found in avocadoes
* -glycero--manno-heptose (an aldose), a late intermediate in lipid A biosynthesis. | 1 | Biochemistry |
The carboxy-terminal domain is also the binding site of the cap-synthesizing and cap-binding complex. In eukaryotes, after transcription of the 5 end of an RNA transcript, the cap-synthesizing complex on the CTD will remove the gamma-phosphate from the 5-phosphate and attach a GMP, forming a 5,5-triphosphate linkage. The synthesizing complex falls off and the cap then binds to the cap-binding complex (CBC), which is bound to the CTD.
The 5'cap of eukaryotic RNA transcripts is important for binding of the mRNA transcript to the ribosome during translation, to the CTD of RNAP, and prevents RNA degradation. | 1 | Biochemistry |
Methionine synthase regenerates methionine (Met) from homocysteine (Hcy). The overall reaction transforms 5-methyltetrahydrofolate (N-MeTHF) into tetrahydrofolate (THF) while transferring a methyl group to Hcy to form Met. Methionine Syntheses can be cobalamin-dependent and cobalamin-independent: Plants have both, animals depend on the methylcobalamin-dependent form.
In methylcobalamin-dependent forms of the enzyme, the reaction proceeds by two steps in a ping-pong reaction. The enzyme is initially primed into a reactive state by the transfer of a methyl group from N-MeTHF to Co(I) in enzyme-bound cobalamin (Cob), forming methyl-cobalamin(Me-Cob) that now contains Me-Co(III) and activating the enzyme. Then, a Hcy that has coordinated to an enzyme-bound zinc to form a reactive thiolate reacts with the Me-Cob. The activated methyl group is transferred from Me-Cob to the Hcy thiolate, which regenerates Co(I) in Cob, and Met is released from the enzyme. | 0 | Organic Chemistry |
A half-cell contains a metal in two oxidation states. Inside an isolated half-cell, there is an oxidation-reduction (redox) reaction that is in chemical equilibrium, a condition written symbolically as follows (here, "M" represents a metal cation, an atom that has a charge imbalance due to the loss of "n" electrons):
: M (oxidized species) + ne M (reduced species)
A galvanic cell consists of two half-cells, such that the electrode of one half-cell is composed of metal A, and the electrode of the other half-cell is composed of metal B; the redox reactions for the two separate half-cells are thus:
: A + ne A
: B + me B
The overall balanced reaction is:
: m A + n B n B + m A
In other words, the metal atoms of one half-cell are oxidized while the metal cations of the other half-cell are reduced. By separating the metals in two half-cells, their reaction can be controlled in a way that forces transfer of electrons through the external circuit where they can do useful work.
* The electrodes are connected with a metal wire in order to conduct the electrons that participate in the reaction.
: In one half-cell, dissolved metal-B cations combine with the free electrons that are available at the interface between the solution and the metal-B electrode; these cations are thereby neutralized, causing them to precipitate from solution as deposits on the metal-B electrode, a process known as plating.
: This reduction reaction causes the free electrons throughout the metal-B electrode, the wire, and the metal-A electrode to be pulled into the metal-B electrode. Consequently, electrons are wrestled away from some of the atoms of the metal-A electrode, as though the metal-B cations were reacting directly with them; those metal-A atoms become cations that dissolve into the surrounding solution.
: As this reaction continues, the half-cell with the metal-A electrode develops a positively charged solution (because the metal-A cations dissolve into it), while the other half-cell develops a negatively charged solution (because the metal-B cations precipitate out of it, leaving behind the anions); unabated, this imbalance in charge would stop the reaction. The solutions of the half-cells are connected by a salt bridge or a porous plate that allows ions to pass from one solution to the other, which balances the charges of the solutions and allows the reaction to continue.
By definition:
* The anode is the electrode where oxidation (loss of electrons) takes place (metal-A electrode); in a galvanic cell, it is the negative electrode, because when oxidation occurs, electrons are left behind on the electrode. These electrons then flow through the external circuit to the cathode (positive electrode) (while in electrolysis, an electric current drives electron flow in the opposite direction and the anode is the positive electrode).
* The cathode is the electrode where reduction (gain of electrons) takes place (metal-B electrode); in a galvanic cell, it is the positive electrode, as ions get reduced by taking up electrons from the electrode and plate out (while in electrolysis, the cathode is the negative terminal and attracts positive ions from the solution). In both cases, the statement the hode attracts ions is true.
Galvanic cells, by their nature, produce direct current. The Weston cell has an anode composed of cadmium mercury amalgam, and a cathode composed of pure mercury. The electrolyte is a (saturated) solution of cadmium sulfate. The depolarizer is a paste of mercurous sulfate. When the electrolyte solution is saturated, the voltage of the cell is very reproducible; hence, in 1911, it was adopted as an international standard for voltage.
A battery is a set of galvanic cells that are connected together to form a single source of voltage. For instance, a typical 12V lead–acid battery has six galvanic cells connected in series with the anodes composed of lead and cathodes composed of lead dioxide, both immersed in sulfuric acid. Large battery rooms, for instance in a telephone exchange providing central office power to user's telephones, may have cells connected in both series and parallel. | 8 | Metallurgy |
The glycoprotein consists of a homodimer of 180 kDA stabilized by intermolecular disulfide bonds. It has a large extracellular domain of about 561 amino acids, a hydrophobic transmembrane domain and a short cytoplasmic tail domain composed of 45 amino acids. The 260 amino acid region closest to the extracellular membrane is referred to as the ZP domain (or, more correctly, ZP module). The outermost extracellular region is termed as the orphan domain (or, more correctly, orphan region (OR)) and it is the part that binds ligands such as BMP-9.
There are two isoforms of endoglin created by alternative splicing: the long isoform (L-endoglin) and the short isoform (S-endoglin). However, the L-isoform is expressed to a greater extent than the S-isoform. A soluble form of endoglin can be produced by the proteolytic cleaving action of metalloproteinase MMP-14 in the extracellular domain near the membrane.
It has been found on endothelial cells in all tissues, activated macrophages, activated monocytes, lymphoblasts fibroblasts, and smooth muscle cells. Endoglin was first identified using monoclonal antibody (mAb) 44G4 but more mAbs against endoglin have been discovered, giving more ways to identify it in tissues.
It is suggested that endoglin has 5 potential N-linked glycosylation sites in the N-terminal domain (of which N102 was experimentally observed in the crystal structure of the orphan region ()) and an O-glycan domain near the membrane domain that is rich in Serine and Threonine. The cytoplasmic tail contains a PDZ-binding motif that allows it to bind to PDZ containing proteins and interact with them. It contains an Arginine-Glycine-Aspartic Acid (RGD) tripeptide sequence that enables cellular adhesion, through the binding of integrins or other RGD binding receptors that are present in the extracellular matrix (ECM). This RGD sequence on endoglin is the first RGD sequence identified on endothelial tissue.
X-ray crystallographic structures of human endoglin () and its complex with ligand BMP-9 () revealed that the orphan region of the protein (residues E26-S337) consists of two domains (OR1 and OR2, corresponding to residues E36-T46 + T200-C330 and residues S47-R199, respectively) with a new fold resulting from gene duplication and circular permutation. The ZP module (residues P338-G581), whose ZP-N and ZP-C moieties (residues T349-L443 and N444-S576, respectively) are closely packed against each other, mediates the homodimerization of endoglin by forming an intermolecular disulfide bond that involves cysteine 516. Together with a second intermolecular disulfide, involving cysteine 582, this generates a molecular clamp that secures the ligand via interaction of two copies of OR1 with the knuckle regions of homodimeric BMP-9. In addition to rationalizing a large number of HHT1 mutations, the crystal structure of endoglin shows that the epitope of anti-ENG monoclonal antibody TRC105 overlaps with the binding site for BMP-9. | 1 | Biochemistry |
The name "photo-reflectance" or "photoreflectance" is shortened from the term "photo-modulated reflectance," which describes the use of an intensity modulated light beam to perturb the reflectance of a sample. The technique has also been referred to as "modulated photo-reflectance," "modulated optical reflectance," and "photo-modulated optical reflectance." It has been known at least since 1967. | 7 | Physical Chemistry |
An androgen conjugate is a conjugate of an androgen, such as testosterone. They occur naturally in the body as metabolites of androgens. Androgen conjugates include sulfate esters and glucuronide conjugates and are formed by sulfotransferase and glucuronosyltransferase enzymes, respectively. In contrast to androgens, conjugates of androgens do not bind to the androgen receptor and are hormonally inactive. However, androgen conjugates can be converted back into active androgens through enzymes like steroid sulfatase.
Examples of androgen conjugates include the sulfates testosterone sulfate, dehydroepiandrosterone sulfate, androstenediol sulfate, dihydrotestosterone sulfate, and androsterone sulfate, and the glucuronides testosterone glucuronide, dihydrotestosterone glucuronide, androsterone glucuronide, and androstanediol glucuronide.
Androgen conjugates are conjugated at the C3 and/or C17β positions, where hydroxyl groups are available. | 1 | Biochemistry |
Enantioselective intermolecular cyclopropanation has been applied to the synthesis of the chiral cyclopropane antibiotics cilastatin.
Tandem cyclopropanation/fragmentation is a key step in the synthesis of 12-hydroxyeicosatetraenoic acid. | 0 | Organic Chemistry |
The versatility of spectroelectrochemistry is increasing due to the possibility of using several electrochemical techniques in different spectral regions depending on the purpose of the study and the information of interest.
The main advantages of spectroelectrochemical techniques are:
*The simultaneous information is obtained by different techniques in a single experiment, increasing the selectivity and the sensitivity.
*Both qualitative and quantitative information can be obtained.
*The possibility of working with a small amount of sample, saving it for future analysis.
Due to the high versatility of the technique, the field of applications is considerably wide.
*Study of reaction mechanisms, where the oxidation and reduction of the species involved in the reaction can be observed, as well as the generation of reaction intermediates.
*Characterization of organic and inorganic materials, that allow to understand the structure and properties of the material when is perturbed by a signal (electric, light, etc.).
*Development of spectroelectrochemical sensors, which are based on optical and electrical responses, capable of providing two independent signals about the same sample and offering a self-validated determination.
*Study of catalysts, obtaining relationships between the electrochemical and spectroscopic properties and their photochemical and photophysical behaviour.
*Study different processes and molecules in biotechnology, biochemistry or medicine.
*Determine specific properties and characteristics of new materials in fields such as energy or nanotechnology. | 7 | Physical Chemistry |
Magnetofection is a transfection method that uses magnetic fields to concentrate particles containing vectors to target cells in the body. Magnetofection has been adapted to a variety of vectors, including nucleic acids, non-viral transfection systems, and viruses. This method offers advantages such as high transfection efficiency and biocompatibility which are balanced with limitations. | 1 | Biochemistry |
Grignard was the son of a sailmaker. He was described as having a humble and friendly attitude. After attempting to major in mathematics, Grignard failed his entrance exams before being drafted into the army in 1892. After one year of service, he went back to pursue mathematics at the University of Lyon and finally obtained his degree Licencié ès Sciences Mathématiques in 1894. In December of the same year, he transferred to chemistry and began working with Professors Philippe Barbier (1848–1922) and Louis Bouveault (1864–1909). After working with stereochemistry and enines, Grignard was not impressed with the subject matter and asked Barbier about a new direction for his doctoral research. Barbier advised that Grignard study how a failed Saytzeff reaction using zinc, was successful, in low yields, after substitution of magnesium. They sought to synthesize alcohols from alkyl halides, aldehydes, ketones, and alkenes. Grignard hypothesized that the aldehyde or ketone prevented the magnesium from reacting with the alkyl halide, accounting for the low yields. He tested his hypothesis by first adding an alkyl halide and magnesium filings to a solution of anhydrous ether and then adding the aldehyde or ketone. This resulted in a drastic increase in the yield of the reaction.
A couple of years later, Grignard was able to isolate the intermediate. He had heated a mixture of magnesium turnings and isobutyl iodide and added dry ethyl ether to the mixture, observing the reaction. The product is known as a Grignard reagent. Named after him, this organo-magnesium compound (R-MgX) (R = alkyl ; X = Halogen) readily reacts with ketones, aldehydes, and alkenes to produce their respective alcohols in impressive yields. Grignard had discovered the synthetic reaction that now bears his name (the Grignard reaction) in 1900. In 1901, he published his doctoral thesis titled "Thèses sur les combinaisons organomagnesiennes mixtes et leur application à des synthèses d‘acides, d‘alcools et d‘hydrocarbures". He became a lecturer in organic chemistry at the University of Nancy in 1909, and was promoted to full professor in 1910. In 1912 he and Paul Sabatier (1854–1941) were awarded the Nobel Prize in Chemistry. During World War I he studied chemical warfare agents with Georges Urbain at Sorbonne University, particularly the manufacture of phosgene and the detection of mustard gas. In 1918, Grignard discovered that sodium iodide could be used as a battlefield test for mustard gas. Sodium iodide converts mustard gas to diiododiethyl sulfide, which crystallizes more easily than mustard gas. This test could detect as little as 0.01 gram of mustard gas in one cubic meter of air and was successfully used on the battlefield. His counterpart on the German side was another Nobel Prize–winning chemist, Fritz Haber.
Grignard died on 13 December 1935, in Lyon at the age of 64. | 0 | Organic Chemistry |
In bioinformatics, the BLOSUM (BLOcks SUbstitution Matrix) matrix is a substitution matrix used for sequence alignment of proteins. BLOSUM matrices are used to score alignments between evolutionarily divergent protein sequences. They are based on local alignments. BLOSUM matrices were first introduced in a paper by Steven Henikoff and Jorja Henikoff. They scanned the BLOCKS database for very conserved regions of protein families (that do not have gaps in the sequence alignment) and then counted the relative frequencies of amino acids and their substitution probabilities. Then, they calculated a log-odds score for each of the 210 possible substitution pairs of the 20 standard amino acids. All BLOSUM matrices are based on observed alignments; they are not extrapolated from comparisons of closely related proteins like the PAM Matrices. | 1 | Biochemistry |
Piobert's law applies to the reaction of solid propellant grains to generate hot gas. It is stated: "Burning takes place by parallel layers where the surface of the grain regresses, layer by layer, normal to the surface at every point." | 7 | Physical Chemistry |
The second pair of cephalic appendages in free-living copepods is usually the main time-averaged source of propulsion, beating like oars to pull the animal through the water. However, different groups have different modes of feeding and locomotion, ranging from almost immotile for several minutes (e.g. some harpacticoid copepods) to intermittent motion (e.g., some cyclopoid copepods) and continuous displacements with some escape reactions (e.g. most calanoid copepods).
Some copepods have extremely fast escape responses when a predator is sensed, and can jump with high speed over a few millimetres. Many species have neurons surrounded by myelin (for increased conduction speed), which is very rare among invertebrates (other examples are some annelids and malacostracan crustaceans like palaemonid shrimp and penaeids). Even rarer, the myelin is highly organized, resembling the well-organized wrapping found in vertebrates (Gnathostomata). Despite their fast escape response, copepods are successfully hunted by slow-swimming seahorses, which approach their prey so gradually, it senses no turbulence, then suck the copepod into their snout too suddenly for the copepod to escape.
Several species are bioluminescent and able to produce light. It is assumed this is an antipredatory defense mechanism.
Finding a mate in the three-dimensional space of open water is challenging. Some copepod females solve the problem by emitting pheromones, which leave a trail in the water that the male can follow. Copepods experience a low Reynolds number and therefore a high relative viscosity. One foraging strategy involves chemical detection of sinking marine snow aggregates and taking advantage of nearby low-pressure gradients to swim quickly towards food sources. | 2 | Environmental Chemistry |
A cooling curve is a line graph that represents the change of phase of matter, typically from a gas to a solid or a liquid to a solid. The independent variable (X-axis) is time and the dependent variable (Y-axis) is temperature. Below is an example of a cooling curve used in castings.
The initial point of the graph is the starting temperature of the matter, here noted as the "pouring temperature". When the phase change occurs, there is a "thermal arrest"; that is, the temperature stays constant. This is because the matter has more internal energy as a liquid or gas than in the state that it is cooling to. The amount of energy required for a phase change is known as latent heat. The "cooling rate" is the slope of the cooling curve at any point.
Alloy have range of melting point. It solidifies as above. First, molten alloy reaches to liquidus temperature and then freezing range starts. At solidus temperature, molten alloys becomes solid. | 7 | Physical Chemistry |
The D-gun atomises the powder feedstock into extremely small particles (80–95% of particles by total number are of size <100 nm). This means proper extraction facilities are required for inhalation safety purposes. Also isolation of the D-gun is recommended to avoid operators breathing in the dangerous dust and fumes. If operators are to enter the room they should wear appropriate dust masks or respirators. Many of the compounds used as the feedstock in detonation spraying are detrimental to human health if ingested or inhaled. Airborne metals from the detonation gun in particular are harmful to the lungs. Exposure to cadmium for example can cause harm to the kidneys and lungs, vomiting, loss of consciousness and even reduced fertility. Also heavy metals have been shown in recent studies to be carcinogenic such as lead, nickel, chromium, and cadmium. Some serious lung conditions caused by metal dust inhalation include:
* Silicosis - a lung disease cause by inhaling silica present in the feedstock compounds.
* Siderosis - (silver polishers lung or welders lung), a lung disease cause by inhaling iron present in the feedstock compounds.
* Alzheimer's - a memory loss disease more common among the elderly has been shown by some studies to be caused by high levels of exposure to aluminum (among many other causes). However, it must be noted that these studies were not conclusive, and others have proven otherwise.
* Metal fume fever - this can occur in some individuals following exposure certain metal compounds (such as copper, zinc, magnesium and aluminum alloys or oxides) that have a particularly unpleasant odour. The fumes are caused as a byproduct when the metals are heated and can trigger a fever-like reaction that may need medical attention. | 8 | Metallurgy |
The following is a sample recipe for TBST:
*20 mM Tris
*150 mM NaCl
*0.1% Tween 20
Adjust pH with HCl to pH 7.4–7.6
The simplest way to prepare a TBS-Tween solution is to use TBS-T tablets. They are formulated to give a ready to use TBST solution upon dissolution in 500 ml of deionized water. | 1 | Biochemistry |
Gas-diffusion electrocrystallization is a process electrochemically driven at porous gas-diffusion electrodes, in which a triple phase boundary is established between a liquid solution, an oxidizing gas, and an electrically conducting electrode. The liquid solution containing dissolved metal ions (e.g., CuCl, ZnCl) flows through an electrochemical cell equipped with a gas diffusion electrode, making contact with its electrically conducting part (typially a porous layer). The oxidizing gas (e.g., pure O, O in air, CO, etc.) percolates through a hydrophobic layer on the gas diffusion electrode, acting as a cathode. After the gas diffuses to the electrically conducting layer acting as an electrocatalyst (e.g., hydrophilic activated carbon), the gas is electrochemically reduced. For instance, by imposing specific cathodic polarization conditions (e.g., −0.145 VSHE O is reduced, to HO in a 2 electron (2 e) transfer process and HO in a 4 electron (4 e) transfer process. OH are also produced in the process. As this happens, abrupt local pH and local electrolyte redox potential changes arise within the cathode porosity. As the hydroxyl ions spread to the bulk electrolyte, systematic pH increases become consistently manifest in the electrolyte bulk. In due course, low amounts of HO are generated. In steady state, a reaction front is fully developed throughout the hydrodynamic boundary layer. This creates local saturation conditions at the electrochemical interface, where metal ions precipitate in metastable or stable phases depending on the operational variables. When oxygen is the oxidizing gas, the mechanism for gas-diffusion electrocrystallization has been explained as an oxidation-assisted alkaline precipitation using gas-diffusion electrodes. | 7 | Physical Chemistry |
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