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ChiRP-Seq (Chromatin Isolation by RNA purification) is a high-throughput sequencing method to discover regions of the genome which are bound by a specific RNA (or by a ribonucleoprotein containing the RNA of interest).
Recent studies have shown that a significant proportion of some genomes (including mouse and human genomes) synthesize RNA that apparently do not code for proteins. The function of most of these non-coding RNA still has to be ascertained. Various genomic methods are being developed to map the functional association of these novel RNA to distinct regions of the genome to gain a better understanding of their function. ChiRP-Seq is one of these new methods which uses the massively parallel sequencing capability of 2nd generation sequencers to catalog the binding sites of these novel RNA molecules on a genome.
Although many have believed that RNAs mainly encode for proteins a very large portion of the eukaryotic genome is composed of RNAs that do not. These RNAs were originally considered junk until new advancements lead to the realization that they may indeed have a biological purpose. Over the last few years lncRNAs have been the least explored and functionally characterized emerging regulatory molecules, especially in comparison to their short counterparts, small ncRNAs. ChiRP-Seq is a new technique that has allowed us to map long RNA occupancy across the genome at a higher resolution than ever before. ChiRP-Seq works via affinity capture of a target complex of lncRNA and chromatin by tiling antisense-oligos. This technique will allow scientists to generate a map of genomic binding sites of several hundred bases very accurately due to high sensitivity and low background. | 1 | Biochemistry |
R-407C is a mixture of hydrofluorocarbons used as a refrigerant. It is a zeotropic blend of difluoromethane (R-32), pentafluoroethane (R-125), and 1,1,1,2-tetrafluoroethane (R-134a). Difluoromethane serves to provide the heat capacity, pentafluoroethane decreases flammability, tetrafluoroethane reduces pressure. R-407C cylinders are colored burnt orange.
This refrigerant is intended as a replacement for R-22. R-22 production will be phased out by 2020 as per the Montreal Protocol. | 2 | Environmental Chemistry |
Iron is an essential bioelement for most forms of life, from bacteria to mammals. Its importance lies in its ability to mediate electron transfer. In the ferrous state (Fe), iron acts as an electron donor, while in the ferric state (Fe) it acts as an acceptor. Thus, iron plays a vital role in the catalysis of enzymatic reactions that involve electron transfer (reduction and oxidation, redox). Proteins can contain iron as part of different cofactors, such as iron–sulfur clusters (Fe-S) and heme groups, both of which are assembled in mitochondria. | 1 | Biochemistry |
Since the Palm Island outbreak, several other species of cyanobacteria have been identified as producing CYN: Anabaena bergii, Anabaena lapponica , Aphanizomenon ovalisporum, Umezakia natans, Raphidiopsis curvata. and Aphanizomenon issatschenkoi. In Australia, three main toxic cyanobacteria exist: Anabaena circinalis, Microcystis species and C. raciborskii. Of these the latter, which produces CYN, has attracted considerable attention, not only due to the Palm Island outbreak, but also as the species is spreading to more temperate areas. Previously, the algae was classed as only tropical, however it has recently been discovered in temperate regions of Australia, Europe, North and South America, and also New Zealand.
In August 1997, three cows and ten calves died from cylindrospermopsin poisoning on a farm in northwest Queensland. A nearby dam containing an algal bloom was tested, and C. raciborskii was identified. Analysis by HPLC/mass spectrometry revealed the presence of CYN in a sample of the biomass. An autopsy of one of the calves reported a swollen liver and gall bladder, along with haemorrhages of the heart and small intestine. Histological examination of the hepatic tissue was consistent with that reported in CYN-affected mice. This was the first report of C. raciborskii causing mortality in animals in Australia.
The effect of a bloom of C. raciborskii on an aquaculture pond in Townsville, Australia was assessed in 1997. The pond contained Redclaw crayfish, along with a population of Lake Eacham Rainbowfish to control the excess food. Analysis revealed that the water contained both extracellular and intracellular CYN, and that the crayfish had accumulated this primarily in the liver but also in the muscle tissue. Examination of the gut contents revealed cyanobacterial cells, indicating that the crayfish had ingested intracellular toxin. An experiment using an extract of the bloom showed that it was also possible to uptake extracellular toxin directly into the tissues. Such bioaccumulation, particularly in the aquaculture industry, was of concern, especially when humans were the end users of the product.
The impact of cyanobacterial blooms has been assessed in economic terms. In December 1991, the world's largest algal bloom occurred in Australia, where 1000 km of the Darling-Barwon River was affected. One million people-days of drinking water were lost, and the direct costs incurred totalled more than A$1.3 million. Moreover, 2000 site-days of recreation were also lost, and the economic cost was estimated at A$10 million, after taking into account indirectly affected industries such as tourism, accommodation and transport. | 0 | Organic Chemistry |
Imidoyl halides are synthesized by combining amides and halogenating agents. The structure of the carboxylic acid amides plays a role in the outcome of the synthesis. Imidoyl chloride can be prepared by treating a monosubstituted carboxylic acid amide with phosgene.
:RC(O)NHR’ + COCl → RC(NR’)Cl + HCl + CO
Thionyl chloride is also used.
Imidoyl chlorides are generally colorless liquids or low-melting solids that are sensitive to both heat and especially moisture. In their IR spectra these compounds exhibit a characteristic ν band near 1650–1689 cm. Although both the syn and anti configurations are possible, most imidoyl chlorides adopt the anti configuration. | 0 | Organic Chemistry |
CyTOF mass cytometry data is recorded in tables that list, for each cell, the signal detected per channel, which is proportional to the number of antibodies tagged with the corresponding channel's isotope bound to that cell. These data are formatted as FCS files, which are compatible with traditional flow cytometry software. Due to the high-dimensional nature of mass cytometry data, novel data analysis tools have been developed as well.
Imaging Mass Cytometry data analysis has its specificity due to different nature of data obtained. In terms of data analysis, both IMC and CyTOF generate large datasets with high dimensionality that require specialized computational methods for analysis. However, data generated by IMC can be more challenging to analyze due to additional data complexity and need for specific tools and pipelines specific for digital image analysis, whereas the data generated by CyTOF is generally analyzed using conventional flow cytometry software. A comprehensive overview of IMC data analysis techniques has been given by Milosevic in. | 3 | Analytical Chemistry |
Slayton Alvin Evans Jr. was born on May 17, 1943, in Chicago, Illinois, to Corine M. Thompson Evans and Slayton A. Evans, Sr. Months later, his father was called to serve in World War II. When Slayton was three years old, the family moved to Meridian, Mississippi, where they lived in a segregated public housing project and his father worked at a J. C. Penney store. Slaytons interest in chemistry began early, when he was given a chemistry set. In addition, a small microscope allowed him to study various plant specimens and insects. Evans and his two younger siblings enrolled at a segregated primary school run by the Roman Catholic Church, and later he attended St. Josephs High School. In 1957, when Evans was in the ninth grade, news of the artificial satellite Sputnik inspired him to learn about rocketry and attempt to build his own. While he was given permission by the nuns at his school to buy chemicals to make rocket fuel, he had to make his own powdered charcoal. He built six rockets, two of them achieving liftoff.
Evans helped pay for his school tuition by mowing lawns and during eighth grade he was a junior assistant janitor at his elementary school. Later he worked in the high school cafeteria. In his third year of high school, he considered going into the Air Force, but was too tall for flight training. However, he took several competitive examinations and was the recipient of an academic scholarship to Tougaloo College where he also received an athletic scholarship for basketball. He enrolled at Tougaloo in 1961.
By the end of his first year, Evans had top marks in chemistry in his class. He got a summer job working for the pharmaceutical company Abbott Laboratories in Chicago where he was tasked first with creating chemical compounds from raw materials, and later with identifying the stages of chemical reactions. Evans graduated from Tougaloo with a Bachelor of Science in chemistry in 1965. Evans was encouraged to attend graduate school, though he didnt know how to pay for it. He briefly attended the Illinois Institute of Technology before transferring to Case Western Reserve University in Cleveland, Ohio, where he was offered a research assistant position in the chemistry department. In his first year, he received a draft notice to go to the Vietnam War. University officials contacted the draft board and explained that Evans research was crucial to the war effort. He was researching a medicine to treat schistosomiasis, a disease caused by parasitic flatworms that are common in Southeast Asia. He completed his coursework in 1969 and received his Ph.D. in chemistry in early 1970. | 4 | Stereochemistry |
Cyrus Eaton (1883–1979) in 1925 purchased the small Trumbull Steel Company of Warren, Ohio, for $18 million. In the late 1920s he purchased undervalued steel and rubber companies. In 1930, Eaton consolidated his steel holdings into the Republic Steel, based in Cleveland; it became the third-largest steel producer in the U.S., after US Steel and Bethlehem Steel. | 8 | Metallurgy |
Glomalin is a hypothetical glycoprotein produced abundantly on hyphae and spores of arbuscular mycorrhizal (AM) fungi in soil and in roots. Glomalin was proposed in 1996 by Sara F. Wright, a scientist at the USDA Agricultural Research Service, but it was not isolated and described yet. The name comes from Glomerales, an order of fungi. Most AM fungi are of the division Glomeromycota. An elusive substance, it is mostly assumed to have a glue-like effect on soil, but it has not been isolated yet. | 9 | Geochemistry |
Pseudoephedrine is contraindicated in patients with diabetes mellitus, cardiovascular disease, severe or uncontrolled hypertension, severe coronary artery disease, prostatic hypertrophy, hyperthyroidism, closed angle glaucoma, or by pregnant women. The safety and effectiveness of nasal decongestant use in children is unclear. | 4 | Stereochemistry |
The Davies equation is an empirical extension of Debye–Hückel theory which can be used to calculate activity coefficients of electrolyte solutions at relatively high concentrations at 25 °C. The equation, originally published in 1938, was refined by fitting to experimental data. The final form of the equation gives the mean molal activity coefficient of an electrolyte that dissociates into ions having charges and as a function of ionic strength :
The second term, , goes to zero as the ionic strength goes to zero, so the equation reduces to the Debye–Hückel equation at low concentration. However, as concentration increases, the second term becomes increasingly important, so the Davies equation can be used for solutions too concentrated to allow the use of the Debye–Hückel equation. For 1:1 electrolytes the difference between measured values and those calculated with this equation is about 2% of the value for 0.1 M solutions. The calculations become less precise for electrolytes that dissociate into ions with higher charges. Further discrepancies will arise if there is association between the ions, with the formation of ion pairs, such as . | 7 | Physical Chemistry |
Surfactants reduce oil-water interfacial tension, which helps waves break oil into small droplets. A mixture of oil and water is normally unstable, but can be stabilized with the addition of surfactants; these surfactants can prevent coalescence of dispersed oil droplets. The effectiveness of the dispersant depends on the weathering of the oil, sea energy (waves), salinity of the water, temperature and the type of oil. Dispersion is unlikely to occur if the oil spreads into a thin layer, because the dispersant requires a particular thickness to work; otherwise, the dispersant will interact with both the water and the oil. More dispersant may be required if the sea energy is low. The salinity of the water is more important for ionic-surfactant dispersants, as salt screens electrostatic interactions between molecules. The viscosity of the oil is another important factor; viscosity can retard dispersant migration to the oil-water interface and also increase the energy required to shear a drop from the slick. Viscosities below 2,000 centipoise are optimal for dispersants. If the viscosity is above 10,000 centipoise, no dispersion is possible. | 2 | Environmental Chemistry |
In spark plasma sintering (SPS), external pressure and an electric field are applied simultaneously to enhance the densification of the metallic/ceramic powder compacts. However, after commercialization it was determined there is no plasma, so the proper name is spark sintering as coined by Lenel. The electric field driven densification supplements sintering with a form of hot pressing, to enable lower temperatures and taking less time than typical sintering. For a number of years, it was speculated that the existence of sparks or plasma between particles could aid sintering; however, Hulbert and coworkers systematically proved that the electric parameters used during spark plasma sintering make it (highly) unlikely. In light of this, the name "spark plasma sintering" has been rendered obsolete. Terms such as field assisted sintering technique (FAST), electric field assisted sintering (EFAS), and direct current sintering (DCS) have been implemented by the sintering community. Using a direct current (DC) pulse as the electric current, spark plasma, spark impact pressure, joule heating, and an electrical field diffusion effect would be created. By modifying the graphite die design and its assembly, it is possible to perform pressureless sintering in spark plasma sintering facility. This modified die design setup is reported to synergize the advantages of both conventional pressureless sintering and spark plasma sintering techniques. | 8 | Metallurgy |
Early results from Dan Nocera, a researcher at Harvard University, gave insight on how his newly created bionic leaf can be used for fertilizer production. This new bionic leaf uses photovoltaic cells in conjunction with Xanthobacter autotrophicus bacteria to create a plastic called polyhydroxybutyrate (PHB). PHB supplies energy to the bacterias natural enzymes which then converts nitrogen gas from the air into ammonia. The bionic leaf, can perform this process using renewable electricity, allowing for the sustainable production of ammonia and bio-fertilizers. Currently, the main industrial production of ammonia is performed by what is known as the Haber-Bosch Process, which uses natural gas as the main energy source. The bacteria within the bionic leaf also help to remove carbon dioxide from the environment. The bionic leaf must still pass an environmental impact study in order to determine if this bacteria is safe to release into the wild. Although the bionic leaf currently operates at a mere 25% efficiency, research and development is still with the hopes of improving the process. X. autotrophicus cells act as a living bio-fertilizer due to their ability to directly promote plant growth when applied to organic material. A study was conducted by comparing plants treated with no fertilizer to the same treated with increasing amounts of X. autotrophicus' culture. The treated plants root mass and total mass increased by approximately 130% and 100% respectively, compared to that of the untreated control group. | 5 | Photochemistry |
Quasi-crystals are supramolecular aggregates exhibiting both crystalline (solid) properties as well as amorphous, liquid-like properties.
Self-organized structures termed "quasi-crystals" were originally described in 1978 by the Israeli scientist Valeri A. Krongauz of the Weizmann Institute of Science, in the Nature paper, Quasi-crystals from irradiated photochromic dyes in an applied electric field.
In his 1978 paper Krongauz coined the term “Quasi-Crystals” for the new self-organized colloidal particles . The Quasi-crystals are supramolecular aggregates manifesting both crystalline properties e.g. Bragg scattering, as well as amorphous, liquid-like properties i.e. drop-like shapes, fluidity, extensibility and elasticity in electric field. The supramolecular Quasi-crystals are produced in photochemical reaction by exposing solutions of photochromic spiropyran molecules to UV radiation. The ultraviolet light induces the conversion of the spiropyrans to merocyanine molecules that manifest electric dipole moments. (see Scheme 1). The quasi-crystals have external shape of submicron globules and their internal structure consists of crystals enveloped by an amorphous matter (see Fig. 1). The crystals are formed by self-assembled stacks of the merocyanine molecular dipoles aligning themselves in a parallel manner, while amorphous envelopes consist of the same merocyanine dipoles aligned in an anti-parallel manner (Fig. 1, Scheme 2). In an applied electrostatic field, quasi-crystals form macroscopic threads that show linear optical dichroism.
Later Krongauz described unusual phase transitions of molecules composed of mesogenic and spiropyran moieties, which he named "quasi-liquid crystals." A micrograph of their mesophase appeared on the cover of Nature in a 1984 paper, “Quasi-Liquid Crystals.” The investigation of spiropyran-merocyanine self-organized systems, including macromolecules (see, for example, Fig. 2), has continued over the years.
These studies have resulted in discoveries of unusual and practically significant phenomena. Thus, in the electrostatic field, quasi-crystals and quasi-liquid crystals have exhibited 2nd order non-linear optical properties.
Potential applications of these fascinating materials have been described and patented.
Work on spiropyran-merocyanine self-assemblies currently continues in several laboratories. | 6 | Supramolecular Chemistry |
A glycosyl donor is a carbohydrate mono- or oligosaccharide that will react with a suitable glycosyl acceptor to form a new glycosidic bond. By convention, the donor is the member of this pair that contains the resulting anomeric carbon of the new glycosidic bond. The resulting reaction is referred to as a glycosylation or chemical glycosylation.
In a glycosyl donor, a leaving group is required at the anomeric position. The simplest leaving group is the OH group that is naturally present in monosaccharides, but it requires activation by acid catalysis in order to function as leaving group (in the Fischer glycosylation). More effective leaving groups are in general used in the glycosyl donors employed in chemical synthesis of glycosides. Typical leaving groups are halides, thioalkyl groups, or imidates, but acetate, phosphate, and O-pentenyl groups are also employed. Natural glycosyl donors contain phosphates as leaving groups.
The so-called “armed-disarmed” principle
The concept of armed and disarmed glycosyl donors refers to the increased reactivity of benzylated over benzoylated glycosyl donors, a phenomenon observed very early, and which originates from the greater electron-withdrawing capability of ester blocking groups over ether blocking groups. However, it was Bertram Fraser-Reid who realised that benzylated glycosyl donors can be activated when benzoylated donors are not, and invented the terms armed glycosyl donor for the former, and disarmed glycosyl donor for the latter. He and his group showed that armed glycosyl donors could be coupled to a glycosyl acceptor, that was at the same time a disarmed glycosyl donor, without self-coupling of the disarmed donor/acceptor. This approach allowed him to carry out a one-pot synthesis of a trisaccharide by the n-pentenyl glycoside method.
The concept has been extended to superarmed glycosyl donor by Mikael Bols and his collaborators. He realised that the hydroxy groups of carbohydrates are less electron-withdrawing towards the anomeric center when they are axial than when they are equatorial, which means that glycosyl donor conformers with more axial oxy functions are more reactive. Protection of a glycosyl donor with bulky silyl groups (tert-butyldimethylsilyl or triisopropyl) cause it to change conformation to a more axial-rich conformation that, as a consequence, is more reactive, which Bols and his group called superarmed. They showed that a superarmed donor can be coupled to an armed glycosyl donor/acceptor. | 0 | Organic Chemistry |
The simplest test to evaluate whether a coal is suitable for production of coke is the free swelling index test. This involves heating a small sample of coal in a standardised crucible to around 800 degrees Celsius (1500 °F).<br>
After heating for a specified time, or until all volatiles are driven off, a small coke button remains in the crucible. The cross sectional profile of this coke button compared to a set of standardised profiles determines the Free Swelling Index. | 3 | Analytical Chemistry |
Ouabain is no longer approved for use in the USA. In France and Germany, however, intravenous ouabain has a long history in the treatment of heart failure, and some continue to advocate its use intravenously and orally in angina pectoris and myocardial infarction despite its poor and variable absorption. The positive properties of ouabain regarding the prophylaxis and treatment of these two indications are documented by several studies. | 0 | Organic Chemistry |
The measurement of the angles can be used to determine crystal structure, see x-ray crystallography for more details. As a simple example, Bragg's law, as stated above, can be used to obtain the lattice spacing of a particular cubic system through the following relation:
where is the lattice spacing of the cubic crystal, and , , and are the Miller indices of the Bragg plane. Combining this relation with Bragg's law gives:
One can derive selection rules for the Miller indices for different cubic Bravais lattices as well as many others, a few of the selection rules are given in the table below.
These selection rules can be used for any crystal with the given crystal structure. KCl has a face-centered cubic Bravais lattice. However, the K and the Cl ion have the same number of electrons and are quite close in size, so that the diffraction pattern becomes essentially the same as for a simple cubic structure with half the lattice parameter. Selection rules for other structures can be referenced elsewhere, or derived. Lattice spacing for the other crystal systems can be found here. | 3 | Analytical Chemistry |
Transactivation can be triggered either by endogenous cellular or viral proteins, also called transactivators. These protein factors act in trans (i.e., intermolecularly). HIV and HTLV are just two of the many viruses that encode transactivators to enhance viral gene expression. These transactivators can also be linked to cancer if they start interacting with, and increasing expression of, a cellular proto-oncogene. HTLV, for instance, has been associated with causing leukemia primarily through this process. Its transactivator, Tax, can interact with p40, inducing overexpression of interleukin 2, interleukin receptors, GM-CSF and the transcription factor c-Fos. HTLV infects T-cells and via the increased expression of these stimulatory cytokines and transcription factors, leads to uncontrolled proliferation of T-cells and hence lymphoma. | 1 | Biochemistry |
TFA is the precursor to many other fluorinated compounds such as trifluoroacetic anhydride, trifluoroperacetic acid, and 2,2,2-trifluoroethanol. It is a reagent used in organic synthesis because of a combination of convenient properties: volatility, solubility in organic solvents, and its strength as an acid. TFA is also less oxidizing than sulfuric acid but more readily available in anhydrous form than many other acids. One complication to its use is that TFA forms an azeotrope with water (b. p. 105 °C).
TFA is popularly used as a strong acid to remove protecting groups such as Boc used in organic chemistry and peptide synthesis.
At a low concentration, TFA is used as an ion pairing agent in liquid chromatography (HPLC) of organic compounds, particularly peptides and small proteins. TFA is a versatile solvent for NMR spectroscopy (for materials stable in acid). It is also used as a calibrant in mass spectrometry.
TFA is used to produce trifluoroacetate salts. | 0 | Organic Chemistry |
In biochemistry, mixed acid fermentation is the metabolic process by which a six-carbon sugar (e.g. glucose, ) is converted into a complex and variable mixture of acids. It is an anaerobic (non-oxygen-requiring) fermentation reaction that is common in bacteria. It is characteristic for members of the Enterobacteriaceae, a large family of Gram-negative bacteria that includes E. coli.
The mixture of end products produced by mixed acid fermentation includes lactate, acetate, succinate, formate, ethanol and the gases and . The formation of these end products depends on the presence of certain key enzymes in the bacterium. The proportion in which they are formed varies between different bacterial species. The mixed acid fermentation pathway differs from other fermentation pathways, which produce fewer end products in fixed amounts. The end products of mixed acid fermentation can have many useful applications in biotechnology and industry. For instance, ethanol is widely used as a biofuel. Therefore, multiple bacterial strains have been metabolically engineered in the laboratory to increase the individual yields of certain end products. This research has been carried out primarily in E. coli and is ongoing. Variations of mixed acid fermentation occur in a number of bacterial species, including bacterial pathogens such as Haemophilus influenzae where mostly acetate and succinate are produced and lactate can serve as a growth substrate. | 1 | Biochemistry |
Some polymer solutions have an LCST at temperatures higher than the UCST. As shown in the diagram, this means that there is a temperature interval of complete miscibility, with partial miscibility at both higher and lower temperatures.
In the case of polymer solutions, the LCST also depends on polymer degree of polymerization, polydispersity and branching as well as on the polymer's composition and architecture. One of the most studied polymers whose aqueous solutions exhibit LCST is poly(N-isopropylacrylamide). Although it is widely believed that this phase transition occurs at , the actual temperatures may differ 5 to 10 °C (or even more) depending on the polymer concentration, molar mass of polymer chains, polymer dispersity as well as terminal moieties. Furthermore, other molecules in the polymer solution, such as salts or proteins, can alter the cloud point temperature. Another monomer whose homo- and co-polymers exhibit LCST behavior in solution is 2-(dimethylamino)ethyl methacrylate.
The LCST depends on the polymer preparation and in the case of copolymers, the monomer ratios, as well as the hydrophobic or hydrophilic nature of the polymer.
To date, over 70 examples of non-ionic polymers with an LCST in aqueous solution have been found. | 7 | Physical Chemistry |
A correlation with drug-lipid-complexes were correlated with high-throughput surface tension device to predict phospholipidosis in particular cationic drugs. | 7 | Physical Chemistry |
A further dynamic method to assemble such structures was introduced by Lee et al. Here, polymeric beads are placed together with a fluid of higher density inside a rotating lathe.
When the lathe is static, the beads float on top of the liquid. With increasing rotational speed, the centripetal force then pushes the fluid outwards and the beads toward the central axis. Hence, the beads are essentially confined by a potential given by the rotational energywhere is the mass of the beads, the distance from the central axis, and the rotational speed. Due to the proportionality, the confining potential resembles that of a cylindrical harmonic oscillator.
Depending on number of spheres and rotational speed, a variety of ordered structures that are comparable to the dense sphere packings were discovered.
A comprehensive theory to this experiment was developed by Winkelmann et al. It is based on analytic energy calculations using a generic sphere model and predicts peritectoid structure transitions. | 3 | Analytical Chemistry |
In general, many questions exist about the health and environmental effects of many herbicides because of the large number of herbicides and the myriad potential targets, mostly unintended. For example, a 1995 panel of 13 scientists reviewing studies on the carcinogenicity of 2,4-D had divided opinions on the likelihood 2,4-D causes cancer in humans. , studies on phenoxy herbicides were too few to accurately assess the risk of many types of cancer from these herbicides, even although evidence was stronger that exposure to these herbicides is associated with increased risk of soft tissue sarcoma and non-Hodgkin lymphoma.
Herbicides have widely variable toxicity in addition to acute toxicity arising from ingestion of a significant quantity rapidly, and chronic toxicity arising from environmental and occupational exposure over long periods. Much public suspicion of herbicides revolves around a confusion between valid statements of acute toxicity as opposed to equally valid statements of lack of chronic toxicity at the recommended levels of usage. For instance, while glyphosate formulations with tallowamine adjuvants are acutely toxic, their use was found to be uncorrelated with any health issues like cancer in a massive US Department of Health study on 90,000 members of farmer families for over a period of 23 years. That is, the study shows lack of chronic toxicity, but cannot question the herbicide's acute toxicity.
Some herbicides cause a range of health effects ranging from skin rashes to death. The pathway of attack can arise from intentional or unintentional direct consumption, improper application resulting in the herbicide coming into direct contact with people or wildlife, inhalation of aerial sprays, or food consumption prior to the labelled preharvest interval. Under some conditions, certain herbicides can be transported via leaching or surface runoff to contaminate groundwater or distant surface water sources. Generally, the conditions that promote herbicide transport include intense storm events (particularly shortly after application) and soils with limited capacity to adsorb or retain the herbicides. Herbicide properties that increase likelihood of transport include persistence (resistance to degradation) and high water solubility.
Cases have been reported where Phenoxy herbicides are contaminated with dioxins such as TCDD; research has suggested such contamination results in a small rise in cancer risk after occupational exposure to these herbicides. Triazine exposure has been implicated in a likely relationship to increased risk of breast cancer, although a causal relationship remains unclear.
Herbicide manufacturers have at times made false or misleading claims about the safety of their products. Chemical manufacturer Monsanto Company agreed to change its advertising after pressure from New York attorney general Dennis Vacco; Vacco complained about misleading claims that its spray-on glyphosate-based herbicides, including Roundup, were safer than table salt and "practically non-toxic" to mammals, birds, and fish (though proof that this was ever said is hard to find). Roundup is toxic and has resulted in death after being ingested in quantities ranging from 85 to 200 ml, although it has also been ingested in quantities as large as 500 ml with only mild or moderate symptoms. The manufacturer of Tordon 101 (Dow AgroSciences, owned by the Dow Chemical Company) has claimed Tordon 101 has no effects on animals and insects, in spite of evidence of strong carcinogenic activity of the active ingredient, picloram, in studies on rats. | 2 | Environmental Chemistry |
Optodes can apply various optical measurement schemes such as reflection, absorption, evanescent wave, luminescence (fluorescence and phosphorescences), chemiluminescence, surface plasmon resonance. By far the most popular methodology is luminescence.
Luminescence in solution obeys the linear Stern–Volmer relationship. Fluorescence of a molecule is quenched by specific analytes, e.g., ruthenium complexes are quenched by oxygen. When a fluorophore is immobilised within a polymer matrix myriad micro-environments are created. The micro-environments reflect varying diffusion co-efficients for the analyte. This leads to a non-linear relationship between the fluorescence and the quencher (analyte). This relationship is modelled in various ways, the most popular model is the two site model created by James Demas (University of Virginia).
The signal (fluorescence) to oxygen ratio is not linear, and an optode is most sensitive at low oxygen concentration, i.e., the sensitivity decreases as oxygen concentration increases. The optode sensors can however work in the whole region 0–100% oxygen saturation in water, and the calibration is done the same way as with the Clark type sensor. No oxygen is consumed and hence the sensor is stirring insensitive, but the signal will stabilize more quickly if the sensor is stirred after being put into the sample. | 7 | Physical Chemistry |
There have been several enantioselective versions of this reaction developed, and even employed in synthesis of complex molecules. Hoyvedas synthesis of (R')-(-)-sporochnol included an asymmetric copper-catalyzed allylic substitution with an organozinc nucleophile and peptide ligand.
A TaniaPHOS ligand, a ferrocenylphosphine, is used with a methyl Grignard nucleophile to form an allylic stereocenter towards the total synthesis of (S)-(-)-Zearalenone
Allylic substitutions are one class of the several types of reactions carried out by organocuprate reagents. | 0 | Organic Chemistry |
The eastern blotting technique is used to detect post-translational modification of proteins. Proteins blotted on to the PVDF or nitrocellulose membrane are probed for modifications using specific substrates. | 1 | Biochemistry |
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S or a compound containing one or more S ions. Solutions of sulfide salts are corrosive. Sulfide also refers to large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (HS) and bisulfide (SH) are the conjugate acids of sulfide. | 0 | Organic Chemistry |
SK channels (small conductance calcium-activated potassium channels) are a subfamily of calcium-activated potassium channels. They are so called because of their small single channel conductance in the order of 10 pS. SK channels are a type of ion channel allowing potassium cations to cross the cell membrane and are activated (opened) by an increase in the concentration of intracellular calcium through N-type calcium channels. Their activation limits the firing frequency of action potentials and is important for regulating afterhyperpolarization in the neurons of the central nervous system as well as many other types of electrically excitable cells. This is accomplished through the hyperpolarizing leak of positively charged potassium ions along their concentration gradient into the extracellular space. This hyperpolarization causes the membrane potential to become more negative. SK channels are thought to be involved in synaptic plasticity and therefore play important roles in learning and memory. | 1 | Biochemistry |
Titanium tetrachloride is the inorganic compound with the formula . It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide () and hydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4", as a phonetic representation of the symbols of its molecular formula (). | 0 | Organic Chemistry |
Adsorption of molecules onto polymer surfaces is central to a number of applications, including development of non-stick coatings and in various biomedical devices. Polymers may also be adsorbed to surfaces through polyelectrolyte adsorption. | 7 | Physical Chemistry |
There are three modes of formation of twinned crystals.
* Growth twins are the result of an interruption or change in the lattice during formation or growth due to a possible deformation from a larger substituting ion. Parallel growth describes a form of crystal growth that produces the appearance of a cluster of aligned crystals. Close examination reveals that the cluster is actually a single crystal. This is not twinning, since the crystal lattice is continuous throughout the cluster. Parallel growth likely takes place because it reduces system energy.
* Annealing or transformation twins are the result of a change in crystal system during cooling as one form becomes unstable and the crystal structure must re-organize or transform into another more stable form.
* Deformation or gliding twins are the result of stress on the crystal after the crystal has formed. Because growth twins are formed during the initial growth of the crystal, they are described as primary, whereas transformation or deformation twins are formed in an existing crystal and are described as secondary. | 3 | Analytical Chemistry |
Mitochondrial disease is a group of disorders caused by mitochondrial dysfunction. Mitochondria are the organelles that generate energy for the cell and are found in every cell of the human body except red blood cells. They convert the energy of food molecules into the ATP that powers most cell functions.
Mitochondrial diseases take on unique characteristics both because of the way the diseases are often inherited and because mitochondria are so critical to cell function. A subclass of these diseases that have neuromuscular symptoms are known as mitochondrial myopathies. | 1 | Biochemistry |
SVA elements are present at lower levels than SINES and LINEs in humans. The starts of SVA and Alu elements are similar, followed by repeats and an end similar to endogenous retrovirus. LINEs bind to sites flanking SVA elements to transpose them. SVA are one of the youngest transposons in great apes genome and among the most active and polymorphic in the human population. SVA was created by a fusion between an Alu element, a VNTR (variable number tandem repeat), and an LTR fragment. | 1 | Biochemistry |
Dark pigments in the substantia nigra were first described in 1838 by Purkyně, and the term neuromelanin was proposed in 1957 by Lillie, though it has been thought to serve no function until recently. It is now believed to play a vital role in preventing cell death in certain parts of the brain. It has been linked to Parkinson's disease and because of this possible connection, neuromelanin has been heavily researched in the last decade. | 1 | Biochemistry |
Children with acute otitis media who are younger than six months of age are generally treated with amoxicillin or other antibiotics. Although most children with acute otitis media who are older than two years old do not benefit from treatment with amoxicillin or other antibiotics, such treatment may be helpful in children younger than two years old with acute otitis media that is bilateral or accompanied by ear drainage. In the past, amoxicillin was dosed three times daily when used to treat acute otitis media, which resulted in missed doses in routine ambulatory practice. There is now evidence that two times daily dosing or once daily dosing has similar effectiveness. | 4 | Stereochemistry |
For Regime I, the growth rate on the front laterally, referred to as g, is the rate-determining step (RDS) and exceeds the secondary nucleation rate, i. In this instance of g >> i, monolayers are formed one at a time so that if the substrate has a length of L and thickness, b, the overall linear growth can be described through the equation
and the rate of nucleation in specific can further be described by
with K equal to
where
This shows that in Region I, lateral nucleation along the front successfully dominates at temperatures close to the melting temperature, however at more extreme temperatures other forces such as diffusion can impact nucleation rates.
In Regime II, the lateral growth rate is either comparable or smaller than the nucleation rate g ≤ i, which causes secondary (or more) layers to form before the initial layer has been covered. This allows the linear growth rate to be modeled by
Using the assumption that g and i are independent of time, the rate at which new layers are formed can be approximated and the rate of nucleation in regime II can be expressed as
with K equal to about 1/2 of the K from Regime I,
Lastly, Regime III in the L-H model depicts the scenario where lateral growth is inconsequential to the overall rate, since the nucleation of multiple sites causes i >> g. This means that the growth rate can be modeled by the same equation as Regime I,
where G is the prefactor for Regime III and can be experimentally determined through applying the Lauritzen–Hoffman Plot. | 7 | Physical Chemistry |
It has been shown by Fulda et al. that the naturally occurring compound resveratrol (a polyphenol found in grapes and red wine) can be used as a sensitizer for anticancer drug-induced apoptosis by the action of causing cell cycle arrest. This cell cycle arrest causes a dramatic decline in survivin levels in the cells, as it is known from the literature that survivin expression is highly linked with the cell cycle phase state. Thus, the decrease in survivin, which is a contributing factor to chemotherapy resistance and apoptosis induction therapies, would render the cancer cells more prone to such cancer treatments. Fulda et al. have demonstrated the benefits of resveratrol through a series of experiments. First, the authors of the paper tested the intrinsic cytotoxic effects of resveratrol. They found that it induced moderate apoptosis levels only in SHEP neuroblastoma cells. After, they tested resveratrol in combination with several different known anticancer agents. They found a consistent increase in the level of apoptosis induced by the drugs when resveratrol was also present. Moreover, they varied the order with which either the drugs or resveratrol was introduced to the cancer cells to determine whether the sequence of treatment had any important effect. It was found that the highest levels of apoptosis induction were observed when resveratrol was added prior to anticancer drug treatment. Next, the authors tested for any differential sensitivity to apoptosis linked to the phase of the cell cycle the cells were in. Analysis by flow cytometry revealed an accumulation of cells in S phase upon treatment with resveratrol. The cells were also halted in different phases of the cell cycle using special compounds and then treated with the anticancer drugs. They found that cells halted in S phase were significantly more sensitive to the cytotoxic effects of the drugs.
To determine the involvement of survivin in resveratrol-mediated sensitization, the authors decided to test whether downregulation of the specific survivin protein expression would confer a similar effect on the phenotype of resveratrol-treated cells. In terms of seeing at which level resveratrol worked, they did a northern blot and found that resveratrol treatment resulted in a decrease in survivin mRNA levels, thus implying resveratrol's inhibitory action at the transcriptional level. To further see whether survivin played a key role in sensitization of the cancer cells to cytotoxic drugs, survivin antisense oligonucleotides were used to knock down any survivin mRNA, and, thus, its possibility to be translated is also eliminated. siRNAs for survivin are complements in sequence to the mRNA sequence encoding survivin. When these siRNAs for survivin are introduced into cells, they will bind to the respective complementary mRNA and, thus, prevent its translation since the mRNA is now impeded from proper physical interaction with the translational machinery. In this way, the siRNAs for survivin effectively downregulates survivin expression level in the cell. Cells treated with antisense oligonucleotides for survivin showed similar sensitization to cytotoxic drugs as cells treated with resveratrol, which offers support for the mechanism of action of resveratrol. | 1 | Biochemistry |
Among the TrkA agonists, the small molecule gambogic amide exerts a potent neurotrophic activity decreasing apoptosis in primary hippocampal neurons. The non-peptidic TrkA agonist MT2 protects neurons from Aβ amyloid-mediated death in NGF-deficient neurons and talaumidin and its derivatives show neuroprotective effects, promoting neurite outgrowth in PC12 cells. Furthermore, the peptidomimetic cerebrolysin is known for its protective role in Alzheimer’s disease (AD). It was shown to improve the activities of daily living and the psychiatric symptoms in patients with mild to severe form of AD, after intravenous administration in a double-blind trial. In addition, the cyclic peptide tavilermide (MIM-D3), acting as a partial TrkA receptor agonist, showed a relevant improvement of cognitive capacities of treated aged rats, leading to a selective survival of the cholinergic neurons.
A phase 3 clinical trial of 5% and 1% tavilermide ophthalmic solutions for the treatment of dry eye was completed in 2020 (NCT03925727), with positive results concerning safety and efficacy. Recent studies demonstrated the neurotrophic activity of carvacrol by inducing neurite outgrowth and phosphorylation of TrkA in cells deprived of NGF. The same research group investigated the neurotrophic effect of the well-known antibiotic doxycycline and they found that it prevents amyloid toxicity in a Drosophila model of AD both in vitro and in vivo and induces neuritogenesis by activation of TrkA.
Additionally, some novel DHEA derivatives were shown to be TrkA agonists. In particular, the C17-spiroepoxy derivative, BNN-27, induces phosphorylation of TrkA in neuronal and glial cells in culture and it exerts antiapoptotic effect without inducing hyperalgesia. Moreover, it improved memorizing abilities in rats after i.p. administration and restored the myelin loss in cuprizone-induced demyelination in vivo. Moreover, the C17-spirocyclopryl DHEA derivatives, ENT-A010 and ENT-A013, were shown to be potent TrkA agonists. In particular, ENT-A010 acts as dual TrkA and TrkB agonist while, ENT-A013 acts as a selective TrkA agonist. Both induce phosphorylation of TrkA and its downstream signaling pathways, and promote cell survival of PC12 cells from serum deprivation. In addition, they exhibit potent neuroprotective effects in dorsal root ganglia and anti-amyloid activity in hippocampal neurons. | 1 | Biochemistry |
The breakdown of phytoplankton in the environment depends on the presence of oxygen, and once oxygen is no longer in the bodies of water, ligninperoxidases cannot continue to break down the lignin. When oxygen is not present in the water, the time required for breakdown of phytoplankton changes from 10.7 days to a total of 160 days.
The rate of phytoplankton breakdown can be represented using this equation:
In this equation, G(t) is the amount of particulate organic carbon (POC) overall at a given time, t. G(0) is the concentration of POC before breakdown takes place. k is a rate constant in year-1, and t is time in years. For most POC of phytoplankton, the k is around 12.8 years-1, or about 28 days for nearly 96% of carbon to be broken down in these systems. Whereas for anoxic systems, POC breakdown takes 125 days, over four times longer. It takes approximately 1 mg of oxygen to break down 1 mg of POC in the environment, and therefore, hypoxia takes place quickly as oxygen is used up quickly to digest POC. About 9% of POC in phytoplankton can be broken down in a single day at 18 °C. Therefore, it takes about eleven days to completely break down phytoplankton.
After POC is broken down, this particulate matter can be turned into other dissolved carbon, such as carbon dioxide, bicarbonate ions, and carbonate. As much as 30% of phytoplankton can be broken down into dissolved carbon. When this particulate organic carbon interacts with 350 nm ultraviolet light, dissolved inorganic carbon is formed, removing even more oxygen from the environment in the forms of carbon dioxide, bicarbonate ions, and carbonate. Dissolved inorganic carbon is made at a rate of 2.3–6.5 mg/(m⋅day).
As phytoplankton breakdown, free phosphorus and nitrogen become available in the environment, which also fosters hypoxic conditions. As the breakdown of this phytoplankton takes place, the more phosphorus turns into phosphates, and nitrogens turn into nitrates. This depletes the oxygen even more so in the environment, further creating hypoxic zones in higher quantities. As more minerals such as phosphorus and nitrogen are displaced into these aquatic systems, the growth of phytoplankton greatly increases, and after their death, hypoxic zones are formed. | 9 | Geochemistry |
Gene targeting (GT), or homology-directed repair (HDR), is used routinely in plant genome engineering to insert specific sequences, with the first published example of GT in plants in the 1980s. However, gene targeting is particularly challenging in higher plants due to the low rates of Homologous Recombination, or Homology Directed Repair, in higher plants and the low rate of transformation (DNA uptake) by many plant species. However, there has been much effort to increase the frequencies of gene targeting in plants in the past decades, as it is very useful to be able to introduce specific sequences in the plant genome for plant genome engineering. The most significant improvement to gene targeting frequencies in plants was the induction of double-strand-breaks through site specific nucleases such as CRISPR, as described above. Other strategies include in planta gene targeting, whereby the homology repair template is embedded within the plant genome and then liberated using CRISPR cutting; upregulation of genes involved in the homologous recombination pathway; downregulation of the competing Non-Homologous-End-Joining pathway; increasing copy numbers of the homologous repair template; and engineering Cas variants to be optimised for plant tissue culture. Some of these approaches have also been used to improve gene targeting efficiencies in mammalian cells.
Plants that have been gene-targeted include Arabidopsis thaliana (the most commonly used model plant), rice, tomato, maize, tobacco and wheat. | 1 | Biochemistry |
Paste tailings is a modification to the conventional methods of disposal of tailings (pond storage). Conventional tailings slurries are composed of a low percent of solids and relatively high water content (normally ranging from 20% to 60% solids for most hard rock mining) and when deposited into the tailings pond the solids and liquids separate. In paste tailings the percent of solids in the tailings slurry is increased through the use of paste thickeners to produce a product where the minimal separation of water and solids occurs and the material is deposited into a storage area as a paste (with a consistency somewhat like toothpaste). Paste tailings has the advantage that more water is recycled in the processing plant and therefore the process is more water efficient than conventional tailings and there is a lower potential for seepage. However the cost of the thickening is generally higher than for conventional tailings and the pumping costs for the paste are also normally higher than for conventional tailings as positive displacement pumps are normally required to transport the tailings from the processing plant to the storage area. Paste tailings are used in several locations around the world including Sunrise Dam in Western Australia and Bulyanhulu Gold Mine in Tanzania. | 8 | Metallurgy |
Empowering Women in Organic Chemistry (EWOC) is a scientific conference designed to bring the research and career interests of women in organic chemistry to the forefront and seeks to empower all marginalized individuals by promoting equity, justice, diversity, and inclusion across all chemistry fields. EWOC is the world's largest gathering of women in organic chemistry, and hosts an annual meeting of women (students, post-docs, faculty and professionals) who work or plan to work in the field of Organic Chemistry, broadly defined, from all types of institutions (academic, industry, biotech, non-profit and government).
The meeting goals are to
*Establish a peer group network for collaborating and recruiting diverse talent
* Afford a novel mechanism to provide advice and counsel for women organic chemists
* Share stories from different perspectives about career development and challenges faced – and overcome – along the way
* Establish an inclusive community, with an emphasis on Diversity, Inclusion and Belonging, to engage, network and support each other in the field of Organic Chemistry
* Provide support and guidance to graduate students and post-docs making career decisions
* Provide community support to enhance retention of women in chemistry. | 0 | Organic Chemistry |
The magnitude and composition of the starvation response (i.e. metabolic adaptation) was estimated in a study of 8 individuals living in isolation in Biosphere 2 for two years. During their isolation, they gradually lost an average of 15% (range: 9–24%) of their body weight due to harsh conditions. On emerging from isolation, the eight isolated individuals were compared with a 152-person control group that initially had similar physical characteristics. On average, the starvation response of the individuals after isolation was a reduction in daily total energy expenditure. of the starvation response was explained by a reduction in fat-free mass and fat mass. An additional was explained by a reduction in fidgeting. The remaining was statistically insignificant. | 1 | Biochemistry |
Cell–cell fusogens are proteins that promote plasma membrane fusion among different cells. To be considered a fusogen, it must be required for fusion, fuse unfamiliar membranes, and be present on the fusing membrane when need be. These cells include but are not limited too: gametes, trophoblasts, epithelial, and other developmental cells. These fusogens mediate cell-cell fusion and can perform neuron repairs, auto-fusion, and sealing of the phagosomes. Although these proteins promote similar functions among cells, they have individual mechanisms. These are called unilateral (one fusing membrane needed to be present) and bilateral (same or different fusogens present at both membranes) mechanisms. Most fusogen mechanisms begin with hemifusion, but the mechanism for cell-cell fusogens consists of four separate steps. | 1 | Biochemistry |
Lead(II) fluoride can be prepared by treating lead(II) hydroxide or lead(II) carbonate with hydrofluoric acid:
: Pb(OH) + 2 HF → PbF + 2 HO
Alternatively, it is precipitated by adding hydrofluoric acid to a lead(II) salt solution, or by adding a fluoride salt to a lead salt, such as potassium fluoride to a lead(II) nitrate solution,
: 2 KF + Pb(NO) → PbF + 2 KNO
or sodium fluoride to a lead(II) acetate solution.
: 2 NaF + Pb(CHCOO) → PbF + 2 NaCHCOO
It appears as the very rare mineral fluorocronite. | 0 | Organic Chemistry |
The first definitive description of a chloroplast (Chlorophyllkörnen, "grain of chlorophyll") was given by Hugo von Mohl in 1837 as discrete bodies within the green plant cell. In 1883, Andreas Franz Wilhelm Schimper named these bodies as "chloroplastids" (Chloroplastiden). In 1884, Eduard Strasburger adopted the term "chloroplasts" (Chloroplasten). | 5 | Photochemistry |
Epinephrine and glucagon affect the activity of protein kinase A by changing the levels of cAMP in a cell via the G-protein mechanism, using adenylate cyclase. Protein kinase A acts to phosphorylate many enzymes important in metabolism. For example, protein kinase A phosphorylates acetyl-CoA carboxylase and pyruvate dehydrogenase. Such covalent modification has an inhibitory effect on these enzymes, thus inhibiting lipogenesis and promoting net gluconeogenesis. Insulin, on the other hand, decreases the level of phosphorylation of these enzymes, which instead promotes lipogenesis. Recall that gluconeogenesis does not occur in myocytes. | 1 | Biochemistry |
Lawrence Stamper Darken has shown that the Gibbs-Duhem equation can be applied to the determination of chemical potentials of components from a multicomponent system from experimental data regarding the chemical potential of only one component (here component 2) at all compositions. He has deduced the following relation
x, amount (mole) fractions of components.
Making some rearrangements and dividing by (1 – x) gives:
or
or
: as formatting variant
The derivative with respect to one mole fraction x is taken at constant ratios of amounts (and therefore of mole fractions) of the other components of the solution representable in a diagram like ternary plot.
The last equality can be integrated from to gives:
Applying LHopital's rule gives:
This becomes further:
Express the mole fractions of component 1 and 3 as functions of component 2 mole fraction and binary mole ratios:
and the sum of partial molar quantities
gives
and are constants which can be determined from the binary systems 1_2 and 2_3. These constants can be obtained from the previous equality by putting the complementary mole fraction x = 0 for x and vice versa.
Thus
and
The final expression is given by substitution of these constants into the previous equation: | 7 | Physical Chemistry |
Fine chemicals are used as starting materials for specialty chemicals. The latter are obtained either by direct formulation or after chemical/biochemical transformation of intermediates to active substances. Life sciences, primarily pharmaceutical, agrochemical and food and feed industries are the main consumers of fine chemicals. | 0 | Organic Chemistry |
* Cross-coupling reactions
** Castro-Stephens coupling
** Heck reaction
** Stille reaction
** Suzuki reaction
** Negishi coupling
** Kumada coupling
* Transmetalation | 0 | Organic Chemistry |
FMR arises from the precessional motion of the (usually quite large) magnetization of a ferromagnetic material in an external magnetic field . The magnetic field exerts a torque on the sample magnetization which causes the magnetic moments in the sample to precess. The precession frequency of the magnetization depends on the orientation of the material, the strength of the magnetic field, as well as the macroscopic magnetization of the sample; the effective precession frequency of the ferromagnet is much lower in value from the precession frequency observed for free electrons in EPR. Moreover, linewidths of absorption peaks can be greatly affected both by dipolar-narrowing and exchange-broadening (quantum) effects. Furthermore, not all absorption peaks observed in FMR are caused by the precession of the magnetic moments of electrons in the ferromagnet. Thus, the theoretical analysis of FMR spectra is far more complex than that of EPR or NMR spectra.
The basic setup for an FMR experiment is a microwave resonant cavity with an electromagnet. The resonant cavity is fixed at a frequency in the super high frequency band. A detector is placed at the end of the cavity to detect the microwaves. The magnetic sample is placed between the poles of the electromagnet and the magnetic field is swept while the resonant absorption intensity of the microwaves is detected. When the magnetization precession frequency and the resonant cavity frequency are the same, absorption increases sharply which is indicated by a decrease in the intensity at the detector.
Furthermore, the resonant absorption of microwave energy causes local heating of the ferromagnet. In samples with local magnetic parameters varying on the nanometer scale this effect is used for spatial dependent spectroscopy investigations.
The resonant frequency of a film with parallel applied external field is given by the Kittel formula:
where is the magnetization of the ferromagnet and is the gyromagnetic ratio. | 7 | Physical Chemistry |
*1.[https://web.archive.org/web/20060118094514/http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=5039 Nanotechnology: Molecular Speculations on Global Abundance]
*2.[https://www.amazon.com/gp/product/354067215X Functional MRI] | 1 | Biochemistry |
The first refinements of copper alloys by a converter took place in Ducktown, Tennessee where A. Raht worked on a partial refinement of the matte from 1866 to 1875. In 1867, the Russians Jossa and Latelin tried to experimentally verify the studies of Semenikow. In 1870, they stopped their experiments after only having succeeded to increase the copper content from 31% to 72-80%.
In England, John Hollway continued these trials until 1878. Like his predecessors, he observed that if blowing began in a satisfactory manner, it became more and more intermittent as the refinement progressed. The obstacles he encountered were numerous:
* The weight of produced slag was equal to that of copper and its volume was much greater than that in the converter. It was thus necessary to drain the retort regularly.
* The density of the molten metal changed greatly (with copper having a density three times as great as the pyrite from which it is made).
* The duration of the air blowing, which can reach two hours, involved large thermal losses.
* The siliceous refractory material was absorbed by the slag, in which it acted as flux.
All of the encountered difficulties could not be easily resolved: the thermal heat balance of the refinement reaction in air of copper was not as favorable as for iron, and the matte solidified in the tuyeres before being refined. Even when modified, a Bessemer converter was capable at best of removing iron and a portion of sulfur. Hollway failed, but by publishing all of the details of his experiments, he identified the essential problems. | 8 | Metallurgy |
Some amino acids are more likely to be replaced. One of the factors that influences this tendency is physicochemical distance. Example of a measure of amino acid can be Graurs Stability Index. The assumption of this measure is that the amino acid replacement rate and proteins evolution is dependent on the amino acid composition of protein. Stability index S of an amino acid is calculated based on physicochemical distances of this amino acid and its alternatives than can mutate through single nucleotide substitution and probabilities to replace into these amino acids. Based on Grantham's distance the most immutable amino acid is cysteine, and the most prone to undergo exchange is methionine. | 1 | Biochemistry |
Modified Lak wettability index exists which is based on the areas below water and oil relative permeability curves.
where
: : modified Lak wettability index (index values near -1 and 1 represent strongly oil-wet and strongly water-wet rocks, respectively)
: : Area under the oil relative permeability curve
: : Area under the water relative permeability curve | 7 | Physical Chemistry |
SABIO-RK (System for the Analysis of Biochemical Pathways - Reaction Kinetics) is a web-accessible database storing information about biochemical reactions and their kinetic properties.
SABIO-RK comprises a reaction-oriented representation of quantitative information on reaction dynamics based on a given selected publication.
This comprises all available kinetic parameters together with their corresponding rate equations,
as well as kinetic law and parameter types and experimental and environmental conditions under which the kinetic data were determined.
Additionally, SABIO-RK contains information about the underlying biochemical reactions and pathways including their reaction participants,
cellular location and detailed information about the enzymes catalysing the reactions. | 1 | Biochemistry |
Trandolapril is teratogenic (US: pregnancy category D) and can cause birth defects and even death of the developing fetus. The highest risk to the fetus is during the second and third trimesters. When pregnancy is detected, trandolapril should be discontinued as soon as possible. Trandolapril should not be administered to nursing mothers. | 4 | Stereochemistry |
A ribonucleotide tri-phosphate (rNTP) is composed of a ribose sugar, 3 phosphate groups attached via diester bonds to the 5 oxygen on the ribose and a nitrogenous base attached to the 1 carbon on the ribose. rNTP's are also referred to as NTPs while the deoxyribose version is referred to as dNTPs. The nitrogenous base can either be a purine such as a Adenine or Guanine or a pyrimidine such as a Uracil or Cytosine. rNTPs have significant biological uses, they can serve as building blocks of RNA synthesis, primers in DNA replication, stores of chemical energy, chiefly Adenosine triphosphate (ATP) and more. | 1 | Biochemistry |
The following table lists some reported reactions that are relevant to photogeochemical study, including reactions that involve only naturally occurring compounds as well as complementary reactions that involve synthetic but related compounds. The selection of reactions and references given is merely illustrative and may not exhaustively reflect current knowledge, especially in the case of popular reactions such as nitrogen photofixation for which there is a large body of literature. Furthermore, although these reactions have natural counterparts, the probability of encountering optimal reaction conditions may be low in some cases; for example, most experimental work concerning CO photoreduction is intentionally performed in the absence of O, since O almost always suppresses the reduction of CO. In natural systems, however, it is uncommon to find an analogous context where CO and a catalyst are reached by light but there is no O present. | 5 | Photochemistry |
SNPs can be easily assayed due to only containing two possible alleles and three possible genotypes involving the two alleles: homozygous A, homozygous B and heterozygous AB, leading to many possible techniques for analysis. Some include: DNA sequencing; capillary electrophoresis; mass spectrometry; single-strand conformation polymorphism (SSCP); single base extension; electrochemical analysis; denaturating HPLC and gel electrophoresis; restriction fragment length polymorphism; and hybridization analysis. | 1 | Biochemistry |
Crystal luciferin was found to be fluorescent, absorbing ultraviolet light with a peak at 327 nm and emitting light with a peak at 530 nm. Visible emission occurs upon relaxation of the oxyluciferin from a singlet excited state down to its ground state. Alkaline solutions caused a redshift of the absorption likely due to deprotonation of the hydroxyl group on the benzothiazole, but did not affect the fluorescence emission. It was found that the luciferyl adenylate (the AMP ester of luciferin) spontaneously emits light in solution.
Different species of fireflies all use the same luciferin, however the color of the light emitted can differ greatly. The light from Photuris pennsylvanica was measured to be 552 nm (green-yellow) while Pyrophorus plagiophthalamus was measured to emit light at 582 nm (orange) in the ventral organ. Such differences are likely due to pH changes or differences in primary structure of the luciferase. Modification of the firefly luciferin substrate has led to "red-shifted" emissions (up to emission wavelength of 675 nm). | 1 | Biochemistry |
Ethyl cyanohydroxyiminoacetate is obtained in the reaction of ethyl cyanoacetate and nitrous acid (from sodium nitrite and acetic acid) in 87% yield.
Because of the rapid hydrolysis of the ester, the reaction should be carried out at pH 4.5, in buffered phosphoric acid the product can even be obtained in virtually quantitative yield.
The compound can be purified by recrystallization from ethanol or ethyl acetate.
Compared with the benzotriazole derivatives 1-hydroxybenzotriazole (HOBt) and 1-hydroxy-7-azabenzotriazole (HOAt) (which are widely used as peptide-linking reagents but are explosive), ethyl cyanohydroxyiminoacetate exhibits a markedly slowed thermal decomposition on heating. | 0 | Organic Chemistry |
Matrix-assisted inlet ionization (MAII) has shown that the laser is not necessary for the ionization process. Ions are formed when matrix-analyte is introduced to the vacuum of a mass spectrometer through an inlet aperture. LSI is a subset of MAII and is now called laserspray inlet ionization (LSII). Laser spray inlet ionization and matrix-assisted inlet ionization can be coupled to a fourier transform ion cyclotron resonance (FT-ICR) mass analyzer to improve detection of peptides and proteins. | 3 | Analytical Chemistry |
Bound to the 5-untranslated region of messenger RNA (mRNA), Morpholinos can interfere with progression of the ribosomal initiation complex from the 5 cap to the start codon. This prevents translation of the coding region of the targeted transcript (called "knocking down" gene expression). This is useful experimentally when an investigator wishes to know the function of a particular protein; Morpholinos provide a convenient means of knocking down expression of the protein and learning how that knockdown changes the cells or organism. Some Morpholinos knock down expression so effectively that, after degradation of preexisting proteins, the targeted proteins become undetectable by Western blot.
In 2016 a synthetic peptide-conjugated PMO (PPMO) was found to inhibit the expression of New Delhi Metallo-beta-lactamase, an enzyme that many drug-resistant bacteria use to destroy carbapenems. | 1 | Biochemistry |
The polypyrimidine tract is a region of pre-messenger RNA (mRNA) that promotes the assembly of the spliceosome, the protein complex specialized for carrying out RNA splicing during the process of post-transcriptional modification. The region is rich with pyrimidine nucleotides, especially uracil, and is usually 15–20 base pairs long, located about 5–40 base pairs before the 3' end of the intron to be spliced.
A number of protein factors bind to or associate with the polypyrimidine tract, including the spliceosome component U2AF and the polypyrimidine tract-binding protein (PTB), which plays a regulatory role in alternative splicing. PTB's primary function is in exon silencing, by which a particular exon region normally spliced into the mature mRNA is instead left out, resulting in the expression of an isoform of the protein for which the mRNA codes. Because PTB is ubiquitously expressed in many higher eukaryotes, it is thought to suppress the inclusion of "weak" exons with poorly defined splice sites. However, PTB binding is not sufficient to suppress "robust" exons.
The suppression or selection of exons is critical to the proper expression of tissue-specific isoforms. For example, smooth muscle and skeletal muscle express alternate isoforms distinguished by mutually exclusive exon selection in alpha-tropomyosin. | 1 | Biochemistry |
Abrasive blasting also known as sandblasting, involves using compressed air to fire a steam of clean, sharp, crushed steel grit or aluminum oxide onto the surface of the component. Aluminum is a good option as it is relatively cheap. The fired grit breaks off small chucks of the substrate surface creating an evenly rough surface for good mechanical bonds to form. The substrate needs to be cleaned of any debris and residual grit from blasting prior to spraying. | 8 | Metallurgy |
The solvent is heated to reflux. The solvent vapour travels up a distillation arm, and floods into the chamber housing the thimble of solid. The condenser ensures that any solvent vapour cools, and drips back down into the chamber housing the solid material. The chamber containing the solid material slowly fills with warm solvent. Some of the desired compound dissolves in the warm solvent. When the Soxhlet chamber is almost full, the chamber is emptied by the siphon. The solvent is returned to the distillation flask. The thimble ensures that the rapid motion of the solvent does not transport any solid material to the still pot. This cycle may be allowed to repeat many times, over hours or days.
During each cycle, a portion of the non-volatile compound dissolves in the solvent. After many cycles the desired compound is concentrated in the distillation flask. The advantage of this system is that instead of many portions of warm solvent being passed through the sample, just one batch of solvent is recycled.
After extraction the solvent is removed, typically by means of a rotary evaporator, yielding the extracted compound. The non-soluble portion of the extracted solid remains in the thimble, and is usually discarded.
Like Soxhlet extractor, the Kumagawa extractor has a specific design where the thimble holder/chamber is directly suspended inside the solvent flask (having a vertical large opening) above the boiling solvent. The thimble is surrounded by hot solvent vapour and maintained at a higher temperature compared to the Soxhlet extractor, thus allowing better extraction for compounds with higher melting points such as bitumen. The removable holder/chamber is fitted with a small siphon side arm and, in the same way as for Soxhlet, a vertical condenser ensures that the solvent drips back down into the chamber which is automatically emptied at every cycle. | 3 | Analytical Chemistry |
Corrosion Science is a peer-reviewed scientific journal published by Elsevier in 16 issues per year. Established in 1961, it covers a wide range of topics in the study of pure/applied corrosion and corrosion engineering, including but not limited to oxidation, biochemical corrosion, stress corrosion cracking, and corrosion control methods, as well as surface science and engineering. The editors-in-chief are J.M.C. Mol (Delft University of Technology) and O.R. Mattos (Federal University of Rio de Janeiro). | 8 | Metallurgy |
Spatial particle-based methods differ from the methods described above by their explicit representation of space.
One example of a particle-based simulator that allows for a representation of cellular compartments is SRSim. SRSim is integrated in the LAMMPS molecular dynamics simulator and allows the user to specify the model in BNGL. SRSim allows users to specify the geometry of the particles in the simulation, as well as interaction sites. It is therefore especially good at simulating the assembly and structure of complex biomolecular complexes, as evidenced by a recent model of the inner kinetochore.
MCell allows individual molecules to be traced in arbitrarily complex geometric environments which are defined by the user. This allows for simulations of biomolecules in realistic reconstructions of living cells, including cells with complex geometries like those of neurons. The reaction compartment is a reconstruction of a dendritic spine.
MCell uses an ad-hoc formalism within MCell itself to specify a multi-state model: In MCell, it is possible to assign "slots" to any molecular species. Each slot stands for a particular modification, and any number of slots can be assigned to a molecule. Each slot can be occupied by a particular state. The states are not necessarily binary. For instance, a slot describing binding of a particular ligand to a protein of interest could take the states "unbound", "partially bound", and "fully bound".
The slot-and-state syntax in MCell can also be used to model multimeric proteins or macromolecular complexes. When used in this way, a slot is a placeholder for a subunit or a molecular component of a complex, and the state of the slot will indicate whether a specific protein component is absent or present in the complex. A way to think about this is that MCell macromolecules can have several dimensions: A "state dimension" and one or more "spatial dimensions". The "state dimension" is used to describe the multiple possible states making up a multi-state protein, while the spatial dimension(s) describe topological relationships between neighboring subunits or members of a macromolecular complex. One drawback of this method for representing protein complexes, compared to Meredys, is that MCell does not allow for the diffusion of complexes, and hence, of multi-state molecules. This can in some cases be circumvented by adjusting the diffusion constants of ligands that interact with the complex, by using checkpointing functions or by combining simulations at different levels. | 1 | Biochemistry |
Via the process known as spontaneous resolution, 5-10% of all racemates crystallize as mixtures of enantiopure crystals. This phenomenon allowed Louis Pasteur to separate left-handed and right-handed sodium ammonium tartrate crystals. These experiments underpinned his discovery of optical activity. In 1882 he went on to demonstrate that by seeding a supersaturated solution of sodium ammonium tartrate with a d-crystal on one side of the reactor and a l-crystal on the opposite side, crystals of opposite handedness will form on the opposite sides of the reactor.
Spontaneous resolution has also been demonstrated with racemic methadone. In a typical setup 50 grams dl-methadone is dissolved in petroleum ether and concentrated. Two millimeter-sized d- and l-crystals are added and after stirring for 125 hours at 40 °C two large d- and l-crystals are recovered in 50% yield.
Another form of direct crystallization is preferential crystallization also called resolution by entrainment of one of the enantiomers. For example, seed crystals of (−)- induce crystallization of this enantiomer from an ethanol solution of (±)-. | 4 | Stereochemistry |
The invention and widespread application of hydraulic mining, namely hushing and ground-sluicing, aided by the ability of the Romans to plan and execute mining operations on a large scale, allowed various base and precious metals to be extracted on a proto-industrial scale only rarely matched until the Industrial Revolution.
The most common fuel by far for smelting and forging operations, as well as heating purposes, was wood and particularly charcoal, which is nearly twice as efficient. In addition, coal was mined in some regions to a fairly large extent: almost all major coalfields in Roman Britain were exploited by the late 2nd century AD, and a lively trade along the English North Sea coast developed, which extended to the continental Rhineland, where bituminous coal was already used for the smelting of iron ore. The annual iron production at Populonia alone accounted for an estimated 2,000 to 10,000 tons. | 8 | Metallurgy |
The Cariaco Basin in Venezuela has been used to study the cycle of organic material in euxinic marine environments. An increase in productivity coincident with post glacial nutrient loading probably caused a transition from oxic to anoxic and subsequently euxinic conditions around 14.5 thousand years ago. High productivity at the surface produces a rain of particulate organic matter to the sub surface where anoxic, sulfidic conditions persist. The organic matter in this region is oxidized with sulfate, producing reduced sulfur (HS) as a waste product. Free sulfur exists deep in the water column and up to 6m in depth in the sediment. | 9 | Geochemistry |
The pillar does not bear an inscription mentioning its erector, date or purpose. It is located at Dhar, which was the capital of the Paramara dynasty. According to the local tradition, the pillar commemorates a military victory of the 11th century Paramara king Bhoja, whose knowledge of iron metallurgy can be seen in his book Yuktikalpataru. Henry Cousens of Archaeological Survey of India (ASI) theorized that it was constructed by the later Paramara king Arjunavarman in 1210 CE, from the molten arms of an enemy force.
The Lat Masjid, in whose compound the pillar is located, was constructed with spolia from Hindu and Jain temples. R. Balasubramaniam theorizes that a Shiva temple previously occupied the site, and the pillar was originally located at the front of this temple, with a trishula (trident) at the top.
The two largest fragments have a number of holes at irregular intervals, on all sides. The depth of the holes ranges from , and their diameter ranges from . Because they are distributed unevenly, they do not appear to be slots for lamps (as in a deepa-stambha). Cousens speculated that these were used by the forgers and welders to handle the pillar with their instruments during the manufacturing process. Roessler agreed with this hypothesis, and proposed that these slots were also used to hold the pillar upright using iron anchors.
The pillar appears to have been built using horizontal forge welding technique. Brahm Prakash theorized that smaller sections, measuring to in length, were joined together to form the pillar. | 8 | Metallurgy |
TOXMAP was a geographic information system (GIS) from the United States National Library of Medicine (NLM) that was deprecated on December 16, 2019. The application used maps of the United States to help users explore data from the United States Environmental Protection Agency's (EPA) Toxics Release Inventory (TRI) and Superfund programs with visual projections and maps. | 1 | Biochemistry |
In contrast with jawed vertebrates whose immunity is based on variable, diverse, and joining gene segments (VDJs) of immunoglobulins, the jawless invertebrates, such as lamprey and hagfish, create a receptor diversity by somatic DNA rearrangement of leucine-rich repeat (LRR) modules that are incorporate in *vlr* genes (variable leukocyte receptors). Those LRR form 3D structures resembling curved solenoids that selectively bind specific glycans.
A study from University of Maryland has shown that lamprey antibodies (lambodies) could selectively bind to tumor-associated carbohydrate antigens (such as Tn and TF) at nanomolar affinities. The T-nouvelle antigen (Tn) and TF are present in proteins in as much as 90% of different cancer cells after post-translational modification, whereas in healthy cells those antigens are much more complex. A selection of lambodies that could bind to aGPA, a human erythrocyte membrane glycoprotein that is covered with 16 TF moieties, through magnetic-activated cell sorting (MACS) and fluorescence-activated cell sorting (FACS) has yielded a leucine-rich lambody VLRB.aGPA.23. This lambody selectively stained (over healthy samples) cells from 14 different types of adenocarcinomas: bladder, esophagus, ovary, tongue, cheek, cervix, liver, nose, nasopharynx, greater omentum, colon, breast, larynx, and lung. Moreover, patients whose tissues stained positive with VLRB.aGPA.23 had a significantly smaller survival rate.
A close look at the crystal structure of VLRB.aGPA.23 reveals a tryptophan residue at position 187 right over the carbohydrate binding pocket. | 1 | Biochemistry |
Piezoelectricity is the ability of crystals to generate a voltage in response to an applied mechanical stress. The piezoelectric effect is reversible in that piezoelectric crystals, when subjected to an externally applied voltage, can change shape by a small amount. Polymer materials like rubber, wool, hair, wood fiber, and silk often behave as electrets. For example, the polymer polyvinylidene fluoride (PVDF) exhibits a piezoelectric response several times larger than the traditional piezoelectric material quartz (crystalline SiO). The deformation (~0.1%) lends itself to useful technical applications such as high-voltage sources, loudspeakers, lasers, as well as chemical, biological, and acousto-optic sensors and/or transducers. | 7 | Physical Chemistry |
The permanent hardness of water is determined by the water's concentration of cations with charges greater than or equal to 2+. Usually, the cations have a charge of 2+, i.e., they are divalent. Common cations found in hard water include Ca and Mg, which frequently enter water supplies by leaching from minerals within aquifers. Common calcium-containing minerals are calcite and gypsum. A common magnesium mineral is dolomite (which also contains calcium). Rainwater and distilled water are soft, because they contain few of these ions.
The following equilibrium reaction describes the dissolving and formation of calcium carbonate and calcium bicarbonate (on the right):
:CaCO (s) + CO (aq) + HO (l) Ca (aq) + 2 (aq)
The reaction can go in either direction. Rain containing dissolved carbon dioxide can react with calcium carbonate and carry calcium ions away with it. The calcium carbonate may be re-deposited as calcite as the carbon dioxide is lost to the atmosphere, sometimes forming stalactites and stalagmites.
Calcium and magnesium ions can sometimes be removed by water softeners.
Permanent hardness (mineral content) is generally difficult to remove by boiling. If this occurs, it is usually caused by the presence of calcium sulfate/calcium chloride and/or magnesium sulfate/magnesium chloride in the water, which do not precipitate out as the temperature increases. Ions causing the permanent hardness of water can be removed using a water softener, or ion-exchange column. | 3 | Analytical Chemistry |
The element carbon plays a central role in climate and life on Earth. It is capable of moving among and between the geosphere, cryosphere, atmosphere, biosphere and hydrosphere. This flow of carbon is referred to as the Earths carbon cycle. It is also intimately linked to the cycling of other elements and compounds. The ocean plays a fundamental role in Earths carbon cycle, helping to regulate atmospheric CO concentration. The biological pump is a set of processes that transfer organic carbon from the surface to the deep ocean, and is at the heart of the ocean carbon cycle.
The biological pump depends on the fraction of primary produced organic matter that survives degradation in the euphotic zone and that is exported from surface water to the ocean interior, where it is mineralized to inorganic carbon, with the result that carbon is transported against the gradient of dissolved inorganic carbon (DIC) from the surface to the deep ocean. This transfer occurs through physical mixing and transport of dissolved and particulate organic carbon (POC), vertical migrations of organisms (zooplankton, fish) and through gravitational settling of particulate organic carbon.
The biological pump can be divided into three distinct phases, the first of which is the production of fixed carbon by planktonic phototrophs in the euphotic (sunlit) surface region of the ocean. In these surface waters, phytoplankton use carbon dioxide (CO), nitrogen (N), phosphorus (P), and other trace elements (barium, iron, zinc, etc.) during photosynthesis to make carbohydrates, lipids, and proteins. Some plankton, (e.g. coccolithophores and foraminifera) combine calcium (Ca) and dissolved carbonates (carbonic acid and bicarbonate) to form a calcium carbonate (CaCO) protective coating.
Once this carbon is fixed into soft or hard tissue, the organisms either stay in the euphotic zone to be recycled as part of the regenerative nutrient cycle or once they die, continue to the second phase of the biological pump and begin to sink to the ocean floor. The sinking particles will often form aggregates as they sink, greatly increasing the sinking rate. It is this aggregation that gives particles a better chance of escaping predation and decomposition in the water column and eventually making it to the sea floor.
The fixed carbon that is decomposed by bacteria either on the way down or once on the sea floor then enters the final phase of the pump and is remineralized to be used again in primary production. The particles that escape these processes entirely are sequestered in the sediment and may remain there for millions of years. It is this sequestered carbon that is responsible for ultimately lowering atmospheric CO.
The diagram immediately above illustrates the components of the biological pump. Biology, physics and gravity interact to pump organic carbon into the deep sea. The processes of fixation of inorganic carbon in organic matter during photosynthesis, its transformation by food web processes (trophodynamics), physical mixing, transport and gravitational settling are referred to collectively as the biological pump.
The biological pump is responsible for transforming dissolved inorganic carbon (DIC) into organic biomass and pumping it in particulate or dissolved form into the deep ocean. Inorganic nutrients and carbon dioxide are fixed during photosynthesis by phytoplankton, which both release dissolved organic matter (DOM) and are consumed by herbivorous zooplankton. Larger zooplankton - such as copepods - egest fecal pellets which can be reingested and sink or collect with other organic detritus into larger, more-rapidly-sinking aggregates. DOM is partially consumed by bacteria (black dots) and respired; the remaining refractory DOM is advected and mixed into the deep sea. DOM and aggregates exported into the deep water are consumed and respired, thus returning organic carbon into the enormous deep ocean reservoir of DIC. About 1% of the particles leaving the surface ocean reach the seabed and are consumed, respired, or buried in the sediments. There, carbon is stored for millions of years. The net effect of these processes is to remove carbon in organic form from the surface and return it to DIC at greater depths, maintaining the surface-to-deep ocean gradient of DIC. Thermohaline circulation returns deep-ocean DIC to the atmosphere on millennial timescales. | 9 | Geochemistry |
Although beneficial for the effectiveness of the reaction, the use of copper salts in "classical" Sonogashira reaction is accompanied with several drawbacks, such as the application of environmentally unfriendly reagents, the formation of undesirable alkyne homocoupling (Glaser side products), and the necessity of strict oxygen exclusion in the reaction mixture. Thus, with the aim of excluding copper from the reaction, a lot of effort was undertaken in the developments of Cu-free Sonogashira reaction. Along the development of new reaction conditions, many experimental and computational studies focused on elucidation of reaction mechanism. Until recently, the exact mechanism by which the Cu-free reaction occurs was under debate, with critical mechanistic questions unanswered. It was shown in 2018 by Košmrlj et al. that the reaction proceeds along the two interconnected Pd/Pd catalytic cycles.
* Similar to the original mechanism, the Pd cycle begins with the oxidative addition of the aryl halide or triflate to the Pd catalyst, forming complex B and activating aryl halide substrate for the reaction.
* Acetylene is activated in the second, Pd mediated cycle. Phenylacetylene was proven to form Pd monoacetylide complex D as well as Pd bisacetylide complex F under mild reaction conditions.
* Both activated species, namely complexes B and F, are involved in the transmetallation step, forming complex C and regenerating D.
* The resulting products of reductive elimination, disubstituted alkyne product as well as regenerated Pd catalytic species, complete the Pd catalytic cycle.
It was demonstrated that amines are competitive to the phosphines and can also participate as ligands L in the described reaction species. Depending on the rate of the competition between amine and phosphines, a dynamic and complex interplay is expected when using different coordinative bases. | 0 | Organic Chemistry |
The shuttle consists of four protein parts:
*malate dehydrogenase in the mitochondrial matrix and intermembrane space.
*aspartate aminotransferase in the mitochondrial matrix and intermembrane space.
*malate-alpha-ketoglutarate antiporter in the inner membrane.
*glutamate-aspartate antiporter in the inner membrane. | 1 | Biochemistry |
It was found that pyruvate dehydrogenase enzyme found in the mitochondria of eukaryotic cells closely resembles an enzyme from Geobacillus stearothermophilus, which is a species of gram-positive bacteria. Despite similarities of the pyruvate dehydrogenase complex with gram-positive bacteria, there is little resemblance with those of gram-negative bacteria. Similarities of the quaternary structures between pyruvate dehydrogenase and enzymes in gram-positive bacteria point to a shared evolutionary history which is distinctive from the evolutionary history of corresponding enzymes found in gram-negative bacteria. Through an endosymbiotic event, pyruvate dehydrogenase found in the eukaryotic mitochondria points to ancestral linkages dating back to gram-positive bacteria.
Pyruvate dehydrogenase complexes share many similarities with branched chain 2-oxoacid dehydrogenase (BCOADH), particularly in their substrate specificity for alpha-keto acids. Specifically, BCOADH catalyzes the degradation of amino acids and these enzymes would have been prevalent during the periods on prehistoric Earth dominated by rich amino acid environments. The E2 subunit from pyruvate dehydrogenase evolved from the E2 gene found in BCOADH while both enzymes contain identical E3 subunits due to the presence of only one E3 gene. Since the E1 subunits have a distinctive specificity for particular substrates, the E1 subunits of pyruvate dehydrogenase and BCOADH vary but share genetic similarities. The gram-positive bacteria and cyanobacteria that would later give rise to mitochondria and chloroplast found in eukaryotic cells retained the E1 subunits that are genetically related to those found in the BCOADH enzymes. | 1 | Biochemistry |
From the kinetic energy formula it can be shown that
where v is in m/s, T is in kelvin, and m is the mass of one molecule of gas in kg. The most probable (or mode) speed is 81.6% of the root-mean-square speed , and the mean (arithmetic mean, or average) speed is 92.1% of the rms speed (isotropic distribution of speeds).
See:
* Average,
* Root-mean-square speed
* Arithmetic mean
* Mean
* Mode (statistics) | 7 | Physical Chemistry |
Yu was born on January 10, 1966, in Zhejiang, China. He received his B.Sc. in chemistry at East China Normal University in 1987. Yu then went on to the Guangzhou Institute of Chemistry, Chinese Academy of Sciences where he worked on heterogeneous reactions of terpenes with zeolite materials with Prof. Shu-De Xiao, obtaining his M.Sc. in 1990. He remained at the Guangzhou Institute of Chemistry for four years as a research associate.
In 1994, Yu moved to the United Kingdom to pursue graduate studies at the University of Cambridge with Prof. Jonathan B. Spencer. At Cambridge, he studied biosynthesis and the mechanistic details of the hydrometallation step in asymmetric hydrogenation reactions with heterogeneous and homogeneous catalysts, among the twenty-one papers he co-authored with Spencer. Yu graduated with his Ph.D. in 1999.
Between 1999 and 2001, Yu worked as a Junior Research Fellow of St John's College, Cambridge. From 2001-2002, Yu worked as a postdoctoral fellow at Harvard University in the laboratory of Prof. E. J. Corey on selective palladium-catalyzed allylic oxidation reactions. Yu returned to Cambridge in 2002 and continued in his position as a Junior Research Fellow. | 0 | Organic Chemistry |
Absolute configuration refers to the spatial arrangement of atoms within a chiral molecular entity (or group) and its resultant stereochemical description. Absolute configuration is typically relevant in organic molecules where carbon is bonded to four different substituents. This type of construction creates two possible enantiomers. Absolute configuration uses a set of rules to describe the relative positions of each bond around the chiral center atom. The most common labeling method uses the descriptors R or S and is based on the Cahn–Ingold–Prelog priority rules. R and S refer to rectus and sinister, Latin for right and left, respectively.
Chiral molecules can differ in their chemical properties, but are identical in their physical properties, which can make distinguishing enantiomers challenging. Absolute configurations for a chiral molecule (in pure form) are most often obtained by X-ray crystallography, although with some important limitations. All enantiomerically pure chiral molecules crystallise in one of the 65 Sohncke groups (chiral space groups). Alternative techniques include optical rotatory dispersion, vibrational circular dichroism, ultraviolet-visible spectroscopy, the use of chiral shift reagents in proton NMR and Coulomb explosion imaging. | 4 | Stereochemistry |
Due to the increased demand for iron for casting cannons, the blast furnace came into widespread use in France in the mid 15th century.
The direct ancestor of those used in France and England was in the Namur region, in what is now Wallonia (Belgium). From there, they spread first to the Pays de Bray on the eastern boundary of Normandy and from there to the Weald of Sussex, where the first furnace (called Queenstock) in Buxted was built in about 1491, followed by one at Newbridge in Ashdown Forest in 1496. They remained few in number until about 1530 but many were built in the following decades in the Weald, where the iron industry perhaps reached its peak about 1590. Most of the pig iron from these furnaces was taken to finery forges for the production of bar iron.
The first British furnaces outside the Weald appeared during the 1550s, and many were built in the remainder of that century and the following ones. The output of the industry probably peaked about 1620, and was followed by a slow decline until the early 18th century. This was apparently because it was more economic to import iron from Sweden and elsewhere than to make it in some more remote British locations. Charcoal that was economically available to the industry was probably being consumed as fast as the wood to make it grew.
The first blast furnace in Russia opened in 1637 near Tula and was called the Gorodishche Works. The blast furnace spread from there to central Russia and then finally to the Urals. | 8 | Metallurgy |
The Ferrier Research Institute at Victoria University of Wellington was named for Ferrier. It was created on 6 January 2014 to accommodate the group of carbohydrate chemists who left Callaghan Innovation on that date. (Callaghan Innovation was previously Industrial Research Ltd.) | 0 | Organic Chemistry |
In January 2011, the ASTM withdrew standard ASTM D 6002, which had provided plastic manufacturers with the legal credibility to label a plastic as compostable. Its description is as follows:
The ASTM has yet to replace this standard. | 7 | Physical Chemistry |
Sucrose esters are mainly manufactured by using interesterification, the transfer of fatty acid from one ester to another. In this case, it means that the fatty acids used for the synthesis of sucrose esters are themselves in the esterified form. There are three processes that have been developed. | 0 | Organic Chemistry |
Whiskers can cause short circuits and arcing in electrical equipment. The phenomenon was discovered by telephone companies in the late 1940s and it was later found that the addition of lead to tin solder provided mitigation. The European Restriction of Hazardous Substances Directive (RoHS), which took effect on July 1, 2006, restricted the use of lead in various types of electronic and electrical equipment. This has driven the use of lead-free alloys with a focus on preventing whisker formation . Others have focused on the development of oxygen-barrier coatings to prevent whisker formation.
Airborne zinc whiskers have been responsible for increased system failure rates in computer server rooms. Zinc whiskers grow from galvanized (electroplated) metal surfaces at a rate of up to a millimeter per year with a diameter of a few micrometers. Whiskers can form on the underside of zinc electroplated floor tiles on raised floors. These whiskers can then become airborne within the floor plenum when the tiles are disturbed, usually during maintenance. Whiskers can be small enough to pass through air filters and can settle inside equipment, resulting in short circuits and system failure.
Tin whiskers do not have to be airborne to damage equipment, as they are typically already growing directly in the environment where they can produce short circuits, i.e., the electronic equipment itself. At frequencies above 6 GHz or in fast digital circuits, tin whiskers can act like miniature antennas, affecting the circuit impedance and causing reflections. In computer disk drives they can break off and cause head crashes or bearing failures. Tin whiskers often cause failures in relays and have been found upon examination of failed relays in nuclear power facilities. Pacemakers have been recalled due to tin whiskers. Research has also identified a particular failure mode for tin whiskers in vacuum (such as in space), where in high-power components a short-circuiting tin whisker is ionized into a plasma that is capable of conducting hundreds of amperes of current, massively increasing the damaging effect of the short circuit. The possible increase in the use of pure tin in electronics due to the RoHS directive drove JEDEC and IPC to release a tin whisker acceptance testing standard and mitigation practices guideline intended to help manufacturers reduce the risk of tin whiskers in lead-free products.
Silver whiskers often appear in conjunction with a layer of silver sulfide, which forms on the surface of silver electrical contacts operating in an atmosphere rich in hydrogen sulfide and high humidity. Such atmospheres can exist in sewage treatment plants and paper mills.
Whiskers over 20 µm in length were observed on gold-plated surfaces and noted in a 2003 NASA internal memorandum.
The effects of metal whiskering were chronicled on History Channels program Engineering Disasters' 19. | 8 | Metallurgy |
The Lifshitz theory can be expressed as an effective Hamaker constant in the van der Waals theory.
Consider, for example, the interaction between an ion of charge , and a nonpolar molecule with polarizability at distance . In a medium with dielectric constant , the interaction energy between a charge and an electric dipole is given by
with the dipole moment of the polarizable molecule given by , where is the strength of the electric field at distance from the ion. According to Coulomb's law:
so we may write the interaction energy as
Consider now, how the interaction energy will change if the right hand molecule is replaced with a medium of density of such molecules. According to the "classical" van der Waals theory, the total force will simply be the summation over individual molecules. Integrating over the volume of the medium (see the third figure), we might expect the total interaction energy with the charge to be
But this result cannot be correct, since It is well known that a charge in a medium of dielectric constant at a distance from the plane surface of a second medium of dielectric constant experiences a force as if there were an image charge of strength at distance D on the other side of the boundary. The force between the real and image charges must then be
and the energy, therefore
Equating the two expressions for the energy, we define a new effective polarizability that must obey
Similarly, replacing the real charge with a medium of density and polarizability gives an expression for . Using these two relations, we may restate our theory in terms of an effective Hamaker constant. Specifically, using McLachlan's generalized theory of VDW forces the Hamaker constant for an interaction potential of the form between two bodies at temperature is
with , where and are Boltzmanns and Plancks constants correspondingly. Inserting our relations for and approximating the sum as an integral , the effective Hamaker constant in the Lifshitz theory may be approximated as
We note that are real functions, and are related to measurable properties of the medium; thus, the Hamaker constant in the Lifshitz theory can be expressed in terms of observable properties of the physical system. | 7 | Physical Chemistry |
R-410A, sold under the trademarked names AZ-20, EcoFluor R410, Forane 410A, Genetron R410A, Puron, and Suva 410A, is a zeotropic but near-azeotropic mixture of difluoromethane (CHF, called R-32) and pentafluoroethane (CHFCF, called R-125) that is used as a refrigerant in air conditioning and heat pump applications. R-410A cylinders were colored rose but are no longer specially color-coded, now bearing a standard light gray color.
On December 27, 2020, the United States Congress passed the American Innovation and Manufacturing (AIM) Act, which directs US Environmental Protection Agency (EPA) to phase down production and consumption of hydrofluorocarbons (HFCs). HFCs have a high global warming potential and contribute to climate change. Rules developed under the AIM Act require HFC production and consumption to be reduced by 85% from 2022 to 2036. R-410A will be restricted by this Act because it contains the HFC R-125. Other refrigerants (like R-32 and R-454B) will replace R-410A in most applications, just as R-410A replaced the earlier refrigerant, R-22. | 2 | Environmental Chemistry |
In the case of schizophrenia, the overt symptom could be a psychosis, but the underlying phenotypes are, for example, a lack of sensory gating and a decline in working memory. Both of these traits have a clear genetic component and can thus be called endophenotypes. A strong candidate for schizophrenia endophenotype is prepulse inhibition, the ability to inhibit the reaction to startling stimuli. However, several other task-related candidate endophenotypes have been proposed for schizophrenia, and even resting measures extracted from EEG, such as, power of frequency bands and EEG microstates.
Endophenotypes are quantitative, trait-like deficits that are typically assessed by laboratory-based methods rather than by clinical observation.
The four primary criteria for an endophenotype are that it is present in probands with the disorder, that it is not state-related (that is, it does not occur only during clinical episodes) but instead is present early in the disease course and during periods of remission, that it is observed in unaffected family members at a higher rate than in the general population, and that it is heritable. The behavioral syndrome of schizophrenia is no longer thought to be a singular disease with a single underlying cause, as is once again becoming clear. Instead, it could have a number of different etiologies, and the symptoms could have many different origins. Such heterogeneity may explain some of the challenges in determining the genetics of schizophrenia and may also account for the clinical observations of schizophrenia treatment response variability.
Some distinct genes that could underlie certain endophenotypic traits in schizophrenia include:
* RELN – coding the reelin protein downregulated in patients' brains. In one 2008 study, its variants were associated with performance in verbal and visual working memory tests in the nuclear families of patients.
* FABP7, coding the Fatty acid-binding protein 7 (brain), one SNP of which was associated with schizophrenia in one 2008 study, is also linked to prepulse inhibition in mice. It is still uncertain though whether the finding will be replicated for human patients.
* CHRNA7, coding the neuronal nicotinic acetylcholine receptor alpha7 subunit. alpha7-containing receptors are known to improve prepulse inhibition, pre-attentive and attentive states. | 2 | Environmental Chemistry |
With increasing bainite content in steel, the hardness, yield and tensile strength remain almost constant for bainite content up to 50%, and then increase by ca. 30%. Hence meter-size shafts and plates of high-bainite steels have been commercially mass-produced by Rolls-Royce Holdings and Tata Steel.
In the railway industry, bainite steel is commonly alloyed with vanadium to produce rails of very high strength, with good wear and rolling contact fatigue resistance. Bainite rails fabricated by Corus were installed in the Channel Tunnel in 2006, and after 3 years showed no evidence of the cracks found in standard rails of the same age. | 8 | Metallurgy |
Protocols for conducting biosurveys of water resources have been published by state government agencies and the U.S. Environmental Protection Agency (EPA). Agencies use these protocols to implement the Clean Water Act. Similar protocols have been published by volunteer organizations. | 2 | Environmental Chemistry |
Urea in concentrations up to 10 M is a powerful protein denaturant as it disrupts the noncovalent bonds in the proteins. This property can be exploited to increase the solubility of some proteins. A mixture of urea and choline chloride is used as a deep eutectic solvent (DES), a substance similar to ionic liquid. When used in a deep eutectic solvent, urea gradually denatures the proteins that are solubilized.
Urea can in principle serve as a hydrogen source for subsequent power generation in fuel cells. Urea present in urine/wastewater can be used directly (though bacteria normally quickly degrade urea). Producing hydrogen by electrolysis of urea solution occurs at a lower voltage () and thus consumes less energy than the electrolysis of water ().
Urea in concentrations up to 8 M can be used to make fixed brain tissue transparent to visible light while still preserving fluorescent signals from labeled cells. This allows for much deeper imaging of neuronal processes than previously obtainable using conventional one photon or two photon confocal microscopes. | 0 | Organic Chemistry |
Spacecraft waste heat is ultimately rejected to space by radiator surfaces. Radiators can be of different forms, such as spacecraft structural panels, flat-plate radiators mounted to the side of the spacecraft, panels deployed after the spacecraft is on orbit, and droplets.
All radiators reject heat by infrared (IR) radiation from their surfaces. The radiating power depends on the surface's emittance and temperature.
The radiator must reject both the spacecraft waste heat plus any radiant-heat loads from the environment or other spacecraft surfaces.
Most radiators are therefore given surface finishes with high IR emittance ( > 0.8) to maximize heat rejection and low solar absorption ( < 0.2) to limit heat loads from the sun.
High-temperature radiators are preferred for better efficiency and size reduction considerations, however, fluid property and droplet cloud property are additional factors.
Droplet size formation and droplet density govern emission and reabsorption.
A smaller droplet is essential for obtaining effective radiation in the liquid droplet radiator. A droplet with a diameter of 1 μm has been calculated to cool from 500 K to 252 K in two seconds. A dense cloud of the droplet sheet will retard the cooling rate of the droplets because of the reabsorption of the emitted light.
A single droplet radiates heat as it travels through space and at any time this heat loss is given by:
where is the Stefan–Boltzmann constant,
is the droplet heat loss rate to space (joules/second),
is the droplet radius (meters),
is the average gray body view factor for droplet at stream center (less than one), and
is the absolute droplet temperature at any time (kelvin).
This equation models the droplet as a gray body with
constant average emissivity. The instantaneous radiation
rate is equal to the rate of energy loss resulting in this
equation:
where is the specific heat capacity,
is the density of droplet (kg/m),
is the droplet transit time (seconds). | 7 | Physical Chemistry |
Lassar Cohn, Lassar-Cohn or Ernst Lassar Cohn (6 September 1858 – 9 October 1922) was a Prussian chemist and professor at the University of Königsberg who wrote several influential textbooks on organic analysis including methods for the analysis of urine.
Cohn was born in the Jewish family of Jacob Marcus Cohen and Hanna Hewe in Hamburg. He studied at the Gymnasium in Königsberg before going the University of Heidelberg. He also studied at Bonn and Königsberg. After receiving a doctorate in 1880 and habilitation in 1888 he joined the University of Königsberg and became a professor in 1894. He worked for some time from 1897 at the Ludwig-Maximilians-University in Munich but returned to Königsberg in 1902. In 1907 he also began to work with the chemical industry. Cohn's major works included studies of organic compounds, tartaric acid and its esters, bile chemistry and the recycling of industrial wastes. He innovated methods for nitrogen measurement, saccharimetry, and urine analysis. | 1 | Biochemistry |