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HDXsite is an online websever which includes some applications such as HDX modeller increasing the resolution of experimental HDX data and modeling protection factors for individual residues. | 7 | Physical Chemistry |
pRb is able to be localize to sites of DNA breaks during the repair process and assist in non-homologous end joining and homologous recombination through complexing with E2F1. Once at the breaks, pRb is able to recruit regulators of chromatin structure such as the DNA helicase transcription activator BRG1. pRb has been shown to also be able to recruit protein complexes such as condensin and cohesin to assist in the structural maintenance of chromatin.
Such findings suggest that in addition to its tumor suppressive role with E2F, pRb is also distributed throughout the genome to aid in important processes of genome maintenance such as DNA break-repair, DNA replication, chromosome condensation, and heterochromatin formation. | 1 | Biochemistry |
Gadolinium is given to patients for magnetic resonance imaging, or an MRI.It is used as a contrast agent for the exam to improve clarity of the images formed. However, it can react in the human body and have detrimental effects. Therefore, the agent should be removed. One of these gadolinium based agents is gadodiamide. Calcium in the body should be determined accurately to ensure that the Gadodiamide does not have adverse effects on the patient. There are two o-cresolphthalein methods to determine amount of calcium. The o-cresolpthalein methods are effective because it is a calcium binding dye. The gadolinium ion with a charge of +3 can be removed from gadodiamide using o-cresolphthalein. For these methods, glomerular filtration rate, or GFR, and time since gadodiamide was given should be recorded. Ultimately, these two factors and the impact of gadodiamide on calcium levels calculated by the o-cresolphthalein method helps to reveal an amount of time that patients must wait after receiving gadodiamide to have blood drawn again, or avoid pseudohypocalcemia. | 3 | Analytical Chemistry |
Epigenetic modifications of histone tails in specific regions of the brain are of central importance in addictions, and much of the work on addiction has focused on histone acetylation. Once particular epigenetic alterations occur, they appear to be long lasting "molecular scars" that may account for the persistence of addictions.
Cigarette smokers (about 21% of the US population) are usually addicted to nicotine. After 7 days of nicotine treatment of mice, acetylation of both histone H3 and histone H4 was increased at the FosB promoter in the nucleus accumbens of the brain, causing 61% increase in FosB expression. This would also increase expression of the splice variant Delta FosB. In the nucleus accumbens of the brain, Delta FosB functions as a "sustained molecular switch" and "master control protein" in the development of an addiction.
About 7% of the US population is addicted to alcohol. In rats exposed to alcohol for up to 5 days, there was an increase in histone 3 lysine 9 acetylation in the pronociceptin promoter in the brain amygdala complex. This acetylation is an activating mark for pronociceptin. The nociceptin/nociceptin opioid receptor system is involved in the reinforcing or conditioning effects of alcohol.
Cocaine addiction occurs in about 0.5% of the US population. Repeated cocaine administration in mice induces hyperacetylation of histone 3 (H3) or histone 4 (H4) at 1,696 genes in one brain "reward" region [the nucleus accumbens (NAc)] and deacetylation at 206 genes. At least 45 genes, shown in previous studies to be upregulated in the NAc of mice after chronic cocaine exposure, were found to be associated with hyperacetylation of H3 or H4. Many of these individual genes are directly related to aspects of addiction associated with cocaine exposure.
In rodent models, many agents causing addiction, including tobacco smoke products, alcohol, cocaine, heroin and methamphetamine, cause DNA damage in the brain. During repair of DNA damages some individual repair events may alter the acetylations of histones at the sites of damage, or cause other epigenetic alterations, and thus leave an epigenetic scar on chromatin. Such epigenetic scars likely contribute to the persistent epigenetic changes found in addictions.
In 2013, 22.7 million persons aged 12 or older needed treatment for an illicit drug or alcohol use problem (8.6 percent of persons aged 12 or older). | 0 | Organic Chemistry |
Common bioactive materials available commercially for clinical use include 45S5 bioactive glass, A/W bioactive glass ceramic, dense synthetic HA, and bioactive composites such as a polyethylene–HA mixture. All these materials form an interfacial bond with adjacent tissue.
High-purity alumina bioceramics are currently commercially available from various producers. U.K. manufacturer Morgan Advanced Ceramics (MAC) began manufacturing orthopaedic devices in 1985 and quickly became a recognised supplier of ceramic femoral heads for hip replacements. MAC Bioceramics has the longest clinical history for alumina ceramic materials, manufacturing HIP Vitox® alumina since 1985. Some calcium-deficient phosphates with an apatite structure were thus commercialised as "tricalcium phosphate" even though they did not exhibit the expected crystalline structure of tricalcium phosphate.
Currently, numerous commercial products described as HA are available in various physical forms (e.g. granules, specially designed blocks for specific applications). HA/polymer composite (HA/polyethyelene, HAPEXTM) is also commercially available for ear implants, abrasives, and plasma-sprayed coating for orthopedic and dental implants.
Bioceramics are also been used in cannabis or delta 8 devices as wicks for the vaporization of such extracts. | 7 | Physical Chemistry |
Rasagiline was tested for efficacy in people with multiple system atrophy in a large randomized, placebo-controlled, double-blind disease-modification trial; the drug failed.
Teva conducted clinical trials attempting to prove that rasagiline did not just treat symptoms, but was a disease-modifying drug - that it actually prevented the death of the dopaminergic neurons that characterize Parkinson's disease and slowed disease progression. They conducted two clinical trials, called TEMPO and ADAGIO, to try to prove this. The FDA advisory committee rejected their claim in 2011, saying that the clinical trial results did not prove that rasagiline was neuroprotective. The main reason was that in one of the trials, the lower dose was effective at slowing progression, but the higher dose was not, and this made no sense in light of standard dose-response pharmacology. | 4 | Stereochemistry |
Consider a semi-ideal heat engine, in which heat transfer takes time, according to Fourier's law of heat conduction: , but other operations happen instantly.
Its maximal efficiency is the standard Carnot result, but it requires heat transfer to be reversible (quasistatic), thus taking infinite time. At maximum power output, its efficiency is the Chambadal–Novikov efficiency:
Due to occasional confusion about the origins of the above equation, it is sometimes named the Chambadal–Novikov–Curzon–Ahlborn efficiency. | 7 | Physical Chemistry |
Murexide is used in analytical chemistry as a complexometric indicator for complexometric titrations, most often of calcium ions, but also for copper, nickel, cobalt, thorium and rare-earth metals. It functions as a tridentate ligand.
Its use has been eclipsed by calcium-ion selective electrodes. | 3 | Analytical Chemistry |
The erosive effect of electrical discharges was first noted in 1770 by English physicist Joseph Priestley. | 8 | Metallurgy |
The initial step in this method involves the formation of a silyl ether at the C-2 hydroxy group of the glycosyl donor upon addition of dimethyldichlorosilane in the presence of a strong base such as butyllithium (BuLi); then the glycosyl acceptor is added to form a mixed silaketal. Activation of the anomeric leaving group in the presence of a hindered base then leads to the β-glycoside.
A modified silicon-tethering method involves mixing of the glycosyl donor with the glycosyl acceptor and dimethyldichlorosilane in the presence of imidazole to give the mixed silaketal in one pot. Activation of the tethered intermediate then leads to the β-glycoside product. | 0 | Organic Chemistry |
The exact timing at which life emerged on Earth is unknown. Minimum age estimates are based on evidence from the geologic rock record. The earliest physical evidence of life so far found consists of microbialites in the Nuvvuagittuq Greenstone Belt of Northern Quebec, in banded iron formation rocks at least 3.77 and possibly as old as 4.32 Gya. The micro-organisms lived within hydrothermal vent precipitates, soon after the 4.4 Gya formation of oceans during the Hadean. The microbes resembled modern hydrothermal vent bacteria, supporting the view that abiogenesis began in such an environment.
Biogenic graphite has been found in 3.7 Gya metasedimentary rocks from southwestern Greenland and in microbial mat fossils from 3.49 Gya cherts in the Pilbara region of Western Australia. Evidence of early life in rocks from Akilia Island, near the Isua supracrustal belt in southwestern Greenland, dating to 3.7 Gya, have shown biogenic carbon isotopes. In other parts of the Isua supracrustal belt, graphite inclusions trapped within garnet crystals are connected to the other elements of life: oxygen, nitrogen, and possibly phosphorus in the form of phosphate, providing further evidence for life 3.7 Gya. In the Pilbara region of Western Australia, compelling evidence of early life was found in pyrite-bearing sandstone in a fossilized beach, with rounded tubular cells that oxidized sulfur by photosynthesis in the absence of oxygen. Carbon isotope ratios on graphite inclusions from the Jack Hills zircons suggest that life could have existed on Earth from 4.1 Gya.
The Pilbara region of Western Australia contains the Dresser Formation with rocks 3.48 Gya, including layered structures called stromatolites. Their modern counterparts are created by photosynthetic micro-organisms including cyanobacteria. These lie within undeformed hydrothermal-sedimentary strata; their texture indicates a biogenic origin. Parts of the Dresser formation preserve hot springs on land, but other regions seem to have been shallow seas. A molecular clock analysis suggests the LUCA emerged prior to the Late Heavy Bombardment (3.9 Gya). | 9 | Geochemistry |
Promiscuity is not only a primordial trait, but also a very widespread property in modern genomes. A series of experiments have been conducted to assess the distribution of promiscuous enzyme activities in E. coli. In E. coli 21 out of 104 single-gene knockouts tested (from the Keio collection) could be rescued by overexpressing a noncognate E. coli protein (using a pooled set of plasmids of the ASKA collection). The mechanisms by which the noncognate ORF could rescue the knockout can be grouped into eight categories: isozyme overexpression (homologues), substrate ambiguity, transport ambiguity (scavenging), catalytic promiscuity, metabolic flux maintenance (including overexpression of the large component of a synthase in the absence of the amine transferase subunit), pathway bypass, regulatory effects and unknown mechanisms. Similarly, overexpressing the ORF collection allowed E. coli to gain over an order of magnitude in resistance in 86 out 237 toxic environment. | 1 | Biochemistry |
* CHCHDCH and CHCHCHD are a pair of structural isotopomers of propane.
* (R)- and (S)-CHCHDOH are isotopic stereoisomers of ethanol.
* (Z)- and (E)-CHCH=CHD are examples of isotopic stereoisomers of propene. | 4 | Stereochemistry |
He was born in Tel Aviv, Israel and sent to an English boarding school at the age of 7. After completing his secondary education he returned to Israel to carry out his military service before moving back to England to study the Natural Sciences Tripos at the University of Cambridge. He received his Ph.D. in Physics from Christ's College, Cambridge in 1972 under the supervision of David Tabor. He then became a Research Fellow at the Biophysics Institute, University of Stockholm and at the Karolinska Institute, Sweden until 1974.
He moved to Australia to take a post as fellow in the Research School of Physical Science and the Research School of Biological Sciences at the Institute of Advanced Studies, Australian National University in Canberra from 1974 to 1977. He was then appointed senior fellow in the Department of Applied Mathematics and Department of Neurobiology at the Institute of Advanced Studies, Australian National University in Canberra.
He relocated to California to join UCSB in 1986, where he worked till his death on the 20th of September 2018. | 6 | Supramolecular Chemistry |
Dissolved load is the portion of a streams total sediment load that is carried in solution, especially ions from chemical weathering. It is a major contributor to the total amount of material removed from a rivers drainage basin, along with suspended load and bed load. The amount of material carried as dissolved load is typically much smaller than the suspended load, though this is not always the case, particularly when the available river flow is mostly harnessed for purposes such as irrigation or industrial uses. Dissolved load comprises a significant portion of the total material flux out of a landscape, and its composition is important in regulating the chemistry and biology of the stream water.
The dissolved load is primarily controlled by the rate of chemical weathering, which depends on climate and weather conditions such as moisture and temperature. Dissolved load has many useful applications within the field of geology, including erosion, denudation, and reconstructing climate in the past. | 9 | Geochemistry |
The CARS process can be physically explained by using either a classical oscillator model or by using a quantum mechanical model that incorporates the energy levels of the molecule. Classically, the Raman active vibrator is modeled as a (damped) harmonic oscillator with a characteristic frequency of ω. In CARS, this oscillator is not driven by a single optical wave, but by the difference frequency (ω-ω) between the pump and the Stokes beams instead. This driving mechanism is similar to hearing the low combination tone when striking two different high tone piano keys: your ear is sensitive to the difference frequency of the high tones. Similarly, the Raman oscillator is susceptible to the difference frequency of two optical waves. When the difference frequency ω-ω approaches ω, the oscillator is driven very efficiently. On a molecular level, this implies that the electron cloud surrounding the chemical bond is vigorously oscillating with the frequency ω-ω. These electron motions alter the optical properties of the sample, i.e. there is a periodic modulation of the refractive index of the material. This periodic modulation can be probed by a third laser beam, the probe beam. When the probe beam is propagating through the periodically altered medium, it acquires the same modulation. Part of the probe, originally at ω will now get modified to ω+ω-ω, which is the observed anti-Stokes emission. Under certain beam geometries, the anti-Stokes emission may diffract away from the probe beam, and can be detected in a separate direction.
While intuitive, this classical picture does not take into account the quantum mechanical energy levels of the molecule. Quantum mechanically, the CARS process can be understood as follows. Our molecule is initially in the ground state, the lowest energy state of the molecule. The pump beam excites the molecule to a virtual state. A virtual state is not an eigenstate of the molecule and it can not be occupied but it does allow for transitions between otherwise unoccupied real states. If a Stokes beam is simultaneously present along with the pump, the virtual state can be used as an instantaneous gateway to address a vibrational eigenstate of the molecule. The joint action of the pump and the Stokes has effectively established a coupling between the ground state and the vibrationally excited state of the molecule. The molecule is now in two states at the same time: it resides in a coherent superposition of states. This coherence between the states can be probed by the probe beam, which promotes the system to a virtual state. Again, the molecule cannot stay in the virtual state and will fall back instantaneously to the ground state under the emission of a photon at the anti-Stokes frequency. The molecule is no longer in a superposition, as it resides again in one state, the ground state. In the quantum mechanical model, no energy is deposited in the molecule during the CARS process. Instead, the molecule acts like a medium for converting the frequencies of the three incoming waves into a CARS signal (a parametric process). There are, however, related coherent Raman processes that occur simultaneously which do deposit energy into the molecule. | 3 | Analytical Chemistry |
A significant second-order effect on the Perturbation Molecular Orbital model of homoaromaticity is the addition of a second homoconjugate linkage and its influence on stability. The effect is often a doubling of the instability brought about by the addition of a single homoconjugate linkage, although there is an additional term that depends on the proximity of the two linkages. In order to minimize δβ and thus keep the coupling term to a minimum, bishomoaromatic compounds form depending on the conformation of greatest stability by resonance and smallest steric hindrance. The synthesis of the 1,3-bishomotropenylium cation by protonating cis-bicyclo[6.1.0]nona-2,4,6-triene agrees with theoretical calculations and maximizes stability by forming the two methylene bridges at the 1st and 3rd carbons. | 7 | Physical Chemistry |
Nucleobases, such as guanine and adenine, can be synthesized from simple carbon and nitrogen sources, such as hydrogen cyanide (HCN) and ammonia. Formamide produces all four ribonucleotides when warmed with terrestrial minerals. Formamide is ubiquitous in the Universe, produced by the reaction of water and HCN. It can be concentrated by the evaporation of water. HCN is poisonous only to aerobic organisms (eukaryotes and aerobic bacteria), which did not yet exist. It can play roles in other chemical processes such as the synthesis of the amino acid glycine.
DNA and RNA components including uracil, cytosine and thymine can be synthesized under outer space conditions, using starting chemicals such as pyrimidine found in meteorites. Pyrimidine may have been formed in red giant stars or in interstellar dust and gas clouds. All four RNA-bases may be synthesized from formamide in high-energy density events like extraterrestrial impacts.
Other pathways for synthesizing bases from inorganic materials have been reported. Freezing temperatures are advantageous for the synthesis of purines, due to the concentrating effect for key precursors such as hydrogen cyanide. However, while adenine and guanine require freezing conditions for synthesis, cytosine and uracil may require boiling temperatures. Seven amino acids and eleven types of nucleobases formed in ice when ammonia and cyanide were left in a freezer for 25 years. S-triazines (alternative nucleobases), pyrimidines including cytosine and uracil, and adenine can be synthesized by subjecting a urea solution to freeze-thaw cycles under a reductive atmosphere, with spark discharges as an energy source. The explanation given for the unusual speed of these reactions at such a low temperature is eutectic freezing, which crowds impurities in microscopic pockets of liquid within the ice, causing the molecules to collide more often.] | 9 | Geochemistry |
As all other fluorescent proteins, Kaede can be the regional optical markers for gene expression and protein labeling for the study of cell behaviors.
One of the most useful applications is the visualization of neurons. Delineation of an individual neuron is difficult due to the long and thin processes which entangle with other neurons. Even when cultured neurons are labeled with fluorescent proteins, they are still difficult to identify individually because of the dense package.
In the past, such visualization could be done conventionally by filling neurons with Lucifer yellow or sulforhodamine, which is a laborious technique.[1] After the discovery of Kaede protein, it was found to be useful in delineating individual neurons. The neurons are transfected by Kaede protein cDNA, and are UV irradiated. The red, photoconverted Kaede protein has free diffusibility in the cell except for the nucleus, and spreads over the entire cell including dendrites and axon. This technique help disentangle the complex networks established in a dense culture. Besides, by labeling neurons with different colors by UV irradiating with different duration times, contact sites between the red and green neurons of interest are allowed to be visualized.
The ability of visualization of individual cells is also a powerful tool to identify the precise morphology and migratory behaviors of individual cells within living cortical slices. By Kaede protein, a particular pair of daughter cells in neighboring Kaede-positive cells in the ventricular zone of mouse brain slices can be followed. The cell-cell borders of daughter cells are visualized and the position and distance between two or more cells can be described.
As the change in the fluorescent colour is induced by UV light, marking of cells and subcellular structures is efficient even when only a partial photoconversion is induced. | 1 | Biochemistry |
Draper wrote a number of books and articles for magazines and journals ([https://scholar.google.com/citations?hl=en&pli=1&user=YcnAATAAAAAJ Google Scholar]). His books include:
* [https://archive.org/details/elementschemist02drapgoog Elements of Chemistry, Including the Most Recent Discoveries and Applications of the Science to Medicine and Pharmacy, and to the Arts.] by Robert Kane and John William Draper. New York: Harper and Brothers, 1842.
* [https://archive.org/details/bub_gb_IoAR-SpiFGQC History of the American Civil War.] New York: Harper & Brothers, 1867–70.
* [https://www.gutenberg.org/ebooks/1185 History of the Conflict Between Religion and Science.] New York: D. Appleton, 1874.
* [http://www.h-net.org/~bahai/diglib/books/A-E/D/draper/draptoc.htm History of the Intellectual Development of Europe.] New York: Harper & Brothers, 1863, [https://archive.org/details/historyintellec00drapgoog 1900 edition, v.1],[https://archive.org/details/historyintellec03drapgoog v.2]
* Human Physiology, Statistical and Dynamical; or, the Conditions and Course of the Life of Man. New York: Harper & Brothers, 1856.
* Life of Franklin, Edited by Ronald S. Wilkinson. Washington, D.C.: Library of Congress: U.S. Government Printing Office, 1977.
* Draper, John William. (1875). History of the Conflict between Religion and Science. Henry S. King & Co (reissued by Cambridge University Press, 2009; )
* [https://archive.org/details/scienceinameric00drapgoog Science in America: Inaugural address of Dr. John W. Draper, as president of the American Chemical Society] New York: J.F. Trow & Son, Printers, 1876.
* [https://archive.org/details/scientificmemoi00drapgoog Scientific Memoirs; Being Experimental Contributions to a Knowledge of Radiant Energy.] New York: Harper & Brothers, 1878.
* Text-Book on Chemistry. For the Use of Schools and Colleges. New York: Harper & Brothers, 1851, [https://archive.org/details/atextbookonchem03drapgoog 1861 edition]
* [https://archive.org/details/bub_gb_GgQ5AAAAMAAJ Text-Book on Natural Philosophy.] New York: Harper & Brothers, 1847.
* [https://archive.org/details/thoughtsonfutur00drapgoog Thoughts on the Future Civil Policy of America.] 3rd ed. New York: Harper & Brothers, 1867.
* Treatise on the Forces Which Produce the Organization of Plants. With an Appendix Containing Several Memoirs on Capillary Attraction, Electricity, and the Chemical Action of Light. New York: Harper & Brothers, 1844. | 5 | Photochemistry |
Although rare, flutamide has been associated with severe hepatotoxicity and death. By 1996, 46 cases of severe cholestatic hepatitis had been reported, with 20 fatalities. There have been continued case reports since, including liver transplants and death. A 2021 review of the literature found 15 cases of serious hepatotoxicity in women treated with flutamide, including 7 liver transplantations and 2 deaths.
Based on the number of prescriptions written and the number of cases reported in the MedWatch database, the rate of serious hepatotoxicity associated with flutamide treatment was estimated in 1996 as approximately 0.03% (3 per 10,000). However, other research has suggested that the true incidence of significant hepatotoxicity with flutamide may be much greater, as high as 0.18 to 10%.
Flutamide is also associated with liver enzyme elevations in up to 42 to 62% of patients, although marked elevations in liver enzymes (above 5 times upper normal limit) occur only in 3 to 5%. The risk of hepatotoxicity with flutamide is much higher than with nilutamide or bicalutamide. Lower doses of the medication appear to have a possibly reduced but still significant risk. Liver function should be monitored regularly with liver function tests during flutamide treatment. In addition, due to the high risk of serious hepatotoxicity, flutamide should not be used in the absence of a serious indication.
The mechanism of action of flutamide-induced hepatotoxicity is thought to be due to mitochondrial toxicity. Specifically, flutamide and particularly its major metabolite hydroxyflutamide inhibit enzymes in the mitochondrial electron transport chain in hepatocytes, including respiratory complexes I (NADH ubiquinone oxidoreductase), II (succinate dehydrogenase), and V (ATP synthase), and thereby reduce cellular respiration via ATP depletion and hence decrease cell survival. Inhibition of taurocholate (a bile acid) efflux has also been implicated in flutamide-induced hepatotoxicity. In contrast to flutamide and hydroxyflutamide, which severely compromise hepatocyte cellular respiration in vitro, bicalutamide does not significantly do so at the same concentrations and is regarded as non-mitotoxic. It is thought that the nitroaromatic group of flutamide and hydroxyflutamide enhance their mitochondrial toxicity; bicalutamide, in contrast, possesses a cyano group in place of the nitro moiety, greatly reducing the potential for such toxicity.
The hepatotoxicity of flutamide appears to depend on hydrolysis of flutamide catalyzed by an arylacetamide deacetalyse enzyme. This is analogous to the hepatotoxicity that occurs with the withdrawn paracetamol (acetominophen)-related medication phenacetin. In accordance, the combination of paracetamol (acetaminophen) and flutamide appears to result in additive to synergistic hepatotoxicity, indicating a potential drug interaction.
Hepatotoxicity with flutamide may be cross-reactive with that of cyproterone acetate. | 4 | Stereochemistry |
Protons can also interact with the nucleus of the atoms in the sample through elastic collisions, Rutherford backscattering, often repelling the proton at angles close to 180 degrees. The backscatter give information on the sample thickness and composition. The bulk sample properties allow for the correction of X-ray photon loss within the sample. | 7 | Physical Chemistry |
Born in Keresley on the outskirts of Coventry, Warwickshire, England, on 10 September 1936, Hartshorn was the son of Bernard Hartshorn and Christine Evelyn Hartshorn (née Bennett). He studied at Imperial College London, from where he graduated BSc and ARCS, and at University College, Oxford, where he obtained a DPhil in 1960. His doctoral thesis was titled Steroid hormone analogues.
Hartshorn married Jacqueline Joll in 1963, and the couple went on to have four sons. He became a naturalised New Zealand citizen in 1965. | 0 | Organic Chemistry |
Zn is an essential biological nutrient in the oceans, and its concentration is largely controlled by uptake by phytoplankton and remineralization. In addition to its critical role in many metalloenzymes (see Zinc Biology section), Zn is an important component of the carbonate shells of foraminifera and siliceous frustules in diatoms. The main inputs of Zn to the ocean are thought to be from rivers and dust. In some photic zones in the ocean, Zn is a limiting nutrient for phytoplankton, and thus its concentration in surface waters serves as one control on marine primary productivity. Zn concentrations are extremely low in the surface ocean (<0.1 nM) but are maximal at depth (~2 nM in the deep Atlantic; ~10 nM in the deep Pacific), indicating a deep regeneration cycle. The deep/surface ratio of Zn is typically on the order of 100, significantly larger than that observed for Cu.
A multitude of complex processes fractionate Zn isotopes in the marine environment. As seen with copper isotopes, the bulk isotopic composition of zinc in the oceans (δZn = +0.5‰) is heavier than that of the riverine input (δZn = +0.3‰), reflecting both equilibrium, biological and other processes that affect Zn isotope ratios in the ocean. In the surface ocean, phytoplankton preferentially uptake Zn, and as a result have average δZn values of ~+0.16‰ (i.e., 0.34‰ lighter than the bulk ocean). This preferential removal of Zn by photosynthetic marine organisms in the photic zone is most prominent in the spring and summer seasons when primary productivity is highest, and the seasonal variability of Zn isotope ratios is reflected in the δZn values of settling materials, which are heavier (e.g., by ~+0.20‰ in the Atlantic Ocean) during spring and summer than during the colder seasons. Additionally, the surface layers of FeMn-nodules are Zn enriched at high-latitudes (average δZn = +1‰), while δZn values of low-latitude samples are smaller and more variable (spanning +0.5 to +1‰). This observation has been interpreted as due to high levels of Zn consumption and preferential uptake of Zn above the seasonal thermocline at high latitudes during warmer seasons, and transfer of this heavy δZn signal to the settling sedimentary Fe-Mn hydroxides.
Sources and sinks for Zn isotopes are further highlighted in the vertical profile of Zn/Zn in the water column. In the upper 2,000 m of the Atlantic Ocean, δZn values are highly variable near the surface (δZn = +0.05 to +0.33‰) due to biological uptake and other surface processes, then gradually increase to ~+0.50‰ at 2,000 m depth. Potential sinks for light Zn isotopes, which enrich the residual bulk Zn isotope ratios in the ocean, include binding to and burial with sinking particulate matter, as well as Zn sulfide precipitation in buried sediments. As a result of preferential burial of Zn over the heavier Zn isotopes, sediments in the ocean are generally isotopically lighter than that of bulk seawater. For example, δZn values in 8 sedimentary cores from three different continental margins were depleted in Zn relative to the bulk ocean (δZn = -0.15 to +0.2‰), and furthermore the vertical profiles of δZn values in the cores showed no downcore isotopic variability, suggesting diagenesis does not significantly fractionate Zn isotopes. | 9 | Geochemistry |
Light-activated resins have found a place in floor refinishing applications, offering an instant return to service not available with any other chemical due to the need to cure at ambient temperatures. Because of application constraints, these coatings are exclusively UV cured with portable equipment containing high intensity discharge lamps. Such UV coatings are now commercially available for a variety of substrates, such as wood, vinyl composition tile and concrete, replacing traditional polyurethanes for wood refinishing and low durability acrylics for VCT. | 5 | Photochemistry |
Non-metallic inclusions are chemical compounds and nonmetals that are present in steel and other alloys. They are the product of chemical reactions, physical effects, and contamination that occurs during the melting and pouring process. These inclusions are categorized by origin as either endogenous or exogenous. Endogenous inclusions, also known as indigenous, occur within the metal and are the result of chemical reactions. These products precipitate during cooling and are typically very small. Exogenous inclusions are caused by the entrapment of nonmetals. Their size varies greatly and their source can include slag, dross, flux residues, and pieces of the mold. | 8 | Metallurgy |
In molecular biology, an amplicon is a piece of DNA or RNA that is the source and/or product of amplification or replication events. It can be formed artificially, using various methods including polymerase chain reactions (PCR) or ligase chain reactions (LCR), or naturally through gene duplication. In this context, amplification refers to the production of one or more copies of a genetic fragment or target sequence, specifically the amplicon. As it refers to the product of an amplification reaction, amplicon is used interchangeably with common laboratory terms, such as "PCR product."
Artificial amplification is used in research, forensics, and medicine for purposes that include detection and quantification of infectious agents, identification of human remains, and extracting genotypes from human hair.
Natural gene duplication plays a major role in evolution. It is also implicated in several forms of human cancer including primary mediastinal B cell lymphoma and Hodgkins lymphoma. In this context the term amplicon' can refer both to a section of chromosomal DNA that has been excised, amplified, and reinserted elsewhere in the genome, and to a fragment of extrachromosomal DNA known as a double minute, each of which can be composed of one or more genes. Amplification of the genes encoded by these amplicons generally increases transcription of those genes and ultimately the volume of associated proteins. | 1 | Biochemistry |
Some molecular compounds that adopt square pyramidal geometry are XeOF, and various halogen pentafluorides (XF, where X = Cl, Br, I). Complexes of vanadium(IV), such as vanadyl acetylacetonate, [VO(acac)], are square pyramidal (acac = acetylacetonate, the deprotonated anion of acetylacetone (2,4-pentanedione)). | 4 | Stereochemistry |
*[http://www.amkor.com/index.cfm?objectid=C55AF2CE-D1A3-1153-5E9522117EE0826C "Flip Chip Bump Electromigration Reliability A comparison of Cu Pillar, High Pb, SnAg and SnPb Bump Structures", White Paper] | 7 | Physical Chemistry |
Panel edge staining is a naturally occurring problem that occurs to anodized aluminium and stainless steel panelling and façades. It is semi-permanent staining that dulls the panel or façade's surface (in particular the edges of the panelling), reducing the natural lustre and shine produced by the anodizing processes used on the aluminium. Panel edge staining may also appear on powder coated aluminium, painted aluminium, stainless steel and titanium surfaces. | 8 | Metallurgy |
Generally speaking for highly expressed genes, translation elongation rates are faster along transcripts with higher codon adaptation to tRNA pools, and slower along transcripts with rare codons. This correlation between codon translation rates and cognate tRNA concentrations provides additional modulation of translation elongation rates, which can provide several advantages to the organism. Specifically, codon usage can allow for global regulation of these rates, and rare codons may contribute to the accuracy of translation at the expense of speed. | 1 | Biochemistry |
At physiological pHs, hydrogen fluoride is usually fully ionised to fluoride. In biochemistry, fluoride and hydrogen fluoride are equivalent. Fluorine, in the form of fluoride, is considered to be a micronutrient for human health, necessary to prevent dental cavities, and to promote healthy bone growth. The tea plant (Camellia sinensis L.) is a known accumulator of fluorine compounds, released upon forming infusions such as the common beverage. The fluorine compounds decompose into products including fluoride ions. Fluoride is the most bioavailable form of fluorine, and as such, tea is potentially a vehicle for fluoride dosing. Approximately, 50% of absorbed fluoride is excreted renally with a twenty-four-hour period. The remainder can be retained in the oral cavity, and lower digestive tract. Fasting dramatically increases the rate of fluoride absorption to near 100%, from a 60% to 80% when taken with food. Per a 2013 study, it was found that consumption of one litre of tea a day, can potentially supply the daily recommended intake of 4 mg per day. Some lower quality brands can supply up to a 120% of this amount. Fasting can increase this to 150%. The study indicates that tea drinking communities are at an increased risk of dental and skeletal fluorosis, in the case where water fluoridation is in effect. Fluoride ion in low doses in the mouth reduces tooth decay. For this reason, it is used in toothpaste and water fluoridation. At much higher doses and frequent exposure, fluoride causes health complications and can be toxic. | 1 | Biochemistry |
A point mutation is a genetic mutation where a single nucleotide base is changed, inserted or deleted from a DNA or RNA sequence of an organism's genome. Point mutations have a variety of effects on the downstream protein product—consequences that are moderately predictable based upon the specifics of the mutation. These consequences can range from no effect (e.g. synonymous mutations) to deleterious effects (e.g. frameshift mutations), with regard to protein production, composition, and function. | 1 | Biochemistry |
An action spectrum is a graph of the rate of biological effectiveness plotted against wavelength of light. It is related to absorption spectrum in many systems. Mathematically, it describes the inverse quantity of light required to evoke a constant response. It is very rare for an action spectrum to describe the level of biological activity, since biological responses are often nonlinear with intensity.
Action spectra are typically written as unit-less responses with peak response of one, and it is also important to distinguish if an action spectrum refers to quanta at each wavelength (mol or log-photons), or to spectral power (W).
It shows which wavelength of light is most effectively used in a specific chemical reaction. Some reactants are able to use specific wavelengths of light more effectively to complete their reactions. For example, chlorophyll is much more efficient at using the red and blue regions than the green region of the light spectrum to carry out photosynthesis. Therefore, the action spectrum graph would show spikes above the wavelengths representing the colours red and blue.
The first action spectrum was made by T. W. Engelmann, who split light into its components by the prism and then illuminated Cladophora placed in a suspension of aerobic bacteria. He found that bacteria accumulated in the region of blue and red light of the split spectrum. He thus discovered the effect of the different wavelengths of light on photosynthesis and plotted the first action spectrum of photosynthesis.
Action spectra have a wide variety of uses in biological and chemical research, particularly in understanding the effect of ultraviolet (UV) light on biological molecules and systems. UV light wavelengths range between 295 nm-400 nm and are known to induce skin and DNA damage. As a result, action spectra have been used to measure the efficiency of different light wavelengths in disinfecting water, the rate and mechanism of photodegradation of folic acid in the blood, and the chirality of molecules to determine secondary structure. Further examples include suppression of melatonin by wavelength and a variety of hazard functions, related to tissue damage from visible and near-visible light. | 5 | Photochemistry |
There are several software tools available for RNA velocity analysis.Each of these tools has its own strengths and applications, so the choice of tool would depend on the specific requirements of your analysis: | 1 | Biochemistry |
Sumerians from 4500 years ago have said to use insecticides in the form of sulfur compounds. Additionally, the Chinese from about 3200 years ago used mercury and arsenic compounds to control the body lice.
Agrochemicals were introduced to protect crops from pests and enhance crop yields. The most common agrochemicals include pesticides and fertilizers. Chemical fertilizers in the 1960s were responsible for the beginning of the "Green Revolution", where using the same surface of land using intensive irrigation and mineral fertilizers such as nitrogen, phosphorus, and potassium has greatly increased food production. Throughout the 1970s through 1980s, pesticide research continued into producing more selective agrochemicals. Due to the adaptation of pests to these chemicals, more and new agrochemicals were being used, causing side effects in the environment. | 2 | Environmental Chemistry |
Lithium amides like the diisopropylamide (LDA) and the (tetramethylpiperidide (LiTMP)) generally work well for the deprotonation of all types of salts, providing that not too much LiOH is present in the n-butyllithium used to make the lithium amide. Titration of lithium amide can be used to determine the amount of hydroxide in solution. The deprotonation of precursor salts with metal hexamethyldisilazides works very cleanly for the deprotonation of all types of salts, except for unhindered formamidinium salts, where this base can act as a nucleophile to give a triaminomethane adduct. | 0 | Organic Chemistry |
Although the epoxidation of ethylene is routinely achieved in the industry with selectivities as high as 90% on Ag catalysts, most catalysts provided efficiency, and 433 K (160 °C). The active species in these catalysts were identified to be hemispherical gold nano-crystals of less than 2 nm in diameter in intimate contact with the support.
Alkene epoxidation has been demonstrated in absence of H reductant in the liquid phase. For example, using 1% Au/graphite, ~80% selectivities of cis-cyclooctene to cyclooctene oxide (analogous to cyclohexene oxide) were obtained at 7-8% conversion, 353 K (80 °C), and 3 MPa O in absence of hydrogen or solvent. Other liquid-phase selective oxidations have been achieved with saturated hydrocarbons. For instance, cyclohexane has been converted to cyclohexanone and cyclohexanol with a combined selectivity of ~100% on gold catalysts. Product selectivities can be tuned in liquid phase reactions by the presence or absence of solvent and by the nature of the latter, viz. water, polar, or nonpolar. With gold catalysts, the catalyst's support has less influence on reactions in the liquid phase than on reactions in the gas phase. | 7 | Physical Chemistry |
Chloroplasts develop from proplastids when seedlings emerge from the ground. Thylakoid formation requires light. In the plant embryo and in the absence of light, proplastids develop into etioplasts that contain semicrystalline membrane structures called prolamellar bodies. When exposed to light, these prolamellar bodies develop into thylakoids. This does not happen in seedlings grown in the dark, which undergo etiolation. An underexposure to light can cause the thylakoids to fail. This causes the chloroplasts to fail resulting to the death of the plant.
Thylakoid formation requires the action of vesicle-inducing protein in plastids 1 (VIPP1). Plants cannot survive without this protein, and reduced VIPP1 levels lead to slower growth and paler plants with reduced ability to photosynthesize. VIPP1 appears to be required for basic thylakoid membrane formation, but not for the assembly of protein complexes of the thylakoid membrane. It is conserved in all organisms containing thylakoids, including cyanobacteria, green algae, such as Chlamydomonas, and higher plants, such as Arabidopsis thaliana. | 5 | Photochemistry |
The most commonly applied methods are MS and HPLC, in which the glycan part is cleaved either enzymatically or chemically from the target and subjected to analysis. In case of glycolipids, they can be analyzed directly without separation of the lipid component.
N-glycans from glycoproteins are analyzed routinely by high-performance-liquid-chromatography (reversed phase, normal phase and ion exchange HPLC) after tagging the reducing end of the sugars with a fluorescent compound (reductive labeling).
A large variety of different labels were introduced in the recent years, where 2-aminobenzamide (AB), anthranilic acid (AA), 2-aminopyridin (PA), 2-aminoacridone (AMAC) and 3-(acetylamino)-6-aminoacridine (AA-Ac) are just a few of them. Different labels have to be used for different ESI modes and MS systems used.
O-glycans are usually analysed without any tags, due to the chemical release conditions preventing them to be labeled.
Fractionated glycans from high-performance liquid chromatography (HPLC) instruments can be further analyzed by MALDI-TOF-MS(MS) to get further information about structure and purity. Sometimes glycan pools are analyzed directly by mass spectrometry without prefractionation, although a discrimination between isobaric glycan structures is more challenging or even not always possible. Anyway, direct MALDI-TOF-MS analysis can lead to a fast and straightforward illustration of the glycan pool.
In recent years, high performance liquid chromatography online coupled to mass spectrometry became very popular. By choosing porous graphitic carbon as a stationary phase for liquid chromatography, even non derivatized glycans can be analyzed. Detection is here done by mass spectrometry, but in instead of MALDI-MS, electrospray ionisation (ESI) is more frequently used. | 0 | Organic Chemistry |
Magnetic refrigeration, or adiabatic demagnetization, is a cooling technology based on the magnetocaloric effect, an intrinsic property of magnetic solids. The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms.
A strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. A heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off. This increases the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the heat sink.
Because few materials exhibit the needed properties at room temperature, applications have so far been limited to cryogenics and research. | 7 | Physical Chemistry |
Given that a virtually uncountable variety of octahedral complexes exist, it is not surprising that a wide variety of reactions have been described. These reactions can be classified as follows:
* Ligand substitution reactions (via a variety of mechanisms)
* Ligand addition reactions, including among many, protonation
* Redox reactions (where electrons are gained or lost)
* Rearrangements where the relative stereochemistry of the ligand changes within the coordination sphere.
Many reactions of octahedral transition metal complexes occur in water. When an anionic ligand replaces a coordinated water molecule the reaction is called an anation. The reverse reaction, water replacing an anionic ligand, is called aquation. For example, the slowly yields in water, especially in the presence of acid or base. Addition of concentrated HCl converts the aquo complex back to the chloride, via an anation process. | 4 | Stereochemistry |
Sephadex is a cross-linked dextran gel used for gel filtration. It was launched by Pharmacia in 1959, after development work by Jerker Porath and Per Flodin. The name is derived from separation Pharmacia dextran. It is normally manufactured in a bead form and most commonly used for gel filtration columns. By varying the degree of cross-linking, the fractionation properties of the gel can be altered.
These highly specialized gel filtration and chromatographic media are composed of macroscopic beads synthetically derived from the polysaccharide dextran. The organic chains are cross-linked to give a three-dimensional network having functional ionic groups attached by ether linkages to glucose units of the polysaccharide chains.
Available forms include anion and cation exchangers, as well as gel filtration resins, with varying degrees of porosity; bead sizes fall in discrete ranges between 20 and 300 µm.
Sephadex is also used for ion-exchange chromatography.
Sephadex is crosslinked with epichlorohydrin. | 1 | Biochemistry |
Radical elimination can be viewed as the reverse of radical addition. In radical elimination, an unstable radical compound breaks down into a spin-paired molecule and a new radical compound. Shown below is an example of a radical elimination reaction, where a benzoyloxy radical breaks down into a phenyl radical and a carbon dioxide molecule. | 2 | Environmental Chemistry |
Since glyceroneogenesis is related to lipid regulation, it can be found in adipose tissue and the liver. In adipose tissue, glyceroneogenesis restrains the release of free fatty acids (FFA) by re-esterifying them. In the liver, triglycerides are synthesized for lipid distribution. | 1 | Biochemistry |
Demasking is the process of clearing the part of etchant and maskant. Etchant is generally removed with a wash of clear, cold water. A de-oxidizing bath may also be required in the common case that the etching process left a film of oxide on the surface of the material. Various methods may be used to remove the maskant, the most common being hand removal using scraping tools. This is frequently time-consuming and laborious, and for large-scale processes may be automated. | 8 | Metallurgy |
A drinking bird consists of two glass bulbs joined by a glass tube (the bird's neck/body). The tube extends nearly all the way into the bottom bulb, and attaches to the top bulb but does not extend into it.
The space inside the bird contains a fluid, usually colored for visibility. (This dye might fade when exposed to light, with the rate depending on the dye/color).
The fluid is typically dichloromethane (DCM), also known as methylene chloride.
Earlier versions contained trichlorofluoromethane.
Miles V. Sullivan's 1945 patent suggested ether, alcohol, carbon tetrachloride, or chloroform.
Air is removed from the apparatus during manufacture, so the space inside the body is filled by vapor evaporated from the fluid. The upper bulb has a "beak" attached which, along with the head, is covered in a felt-like material. The bird is typically decorated with paper eyes, a plastic top hat, and one or more tail feathers. The whole device pivots on a crosspiece attached to the body. | 7 | Physical Chemistry |
Any sort of saturated molecule can be the starting point for generating isolobal fragments. The molecule's bonding and nonbonding molecular orbitals (MOs) should be filled and the antibonding MOs empty. With each consecutive generation of an isolobal fragment, electrons are removed from the bonding orbitals and a frontier orbital is created. The frontier orbitals are at a higher energy level than the bonding and nonbonding MOs. Each frontier orbital contains one electron. For example, consider Figure 5, which shows the production of frontier orbitals in tetrahedral and octahedral molecules.
As seen above, when a fragment is formed from CH, one of the sp hybrid orbitals involved in bonding becomes a nonbonding singly occupied frontier orbital. The frontier orbital’s increased energy level is also shown in the figure. Similarly when starting with a metal complex such as d-ML, the dsp hybrid orbitals are affected. Furthermore, the t nonbonding metal orbitals are unaltered. | 0 | Organic Chemistry |
The most common phosphonium compounds have four organic substituents attached to phosphorus. The quaternary phosphonium cations include tetraphenylphosphonium, (CH)P and tetramethylphosphonium .
Quaternary phosphonium cations () are produced by alkylation of organophosphines. For example, the reaction of triphenylphosphine with methyl bromide gives methyltriphenylphosphonium bromide:
:PPh + CHBr → [CHPPh]Br
The methyl group in such phosphonium salts is mildly acidic, with a pK estimated to be near 15:
:[CHPPh] + base → CH=PPh + [Hbase]
This deprotonation reaction gives Wittig reagents. | 0 | Organic Chemistry |
In microbiology, methyl red is used in the methyl red test (MR test), used to identify bacteria producing stable acids by mechanisms of mixed acid fermentation of glucose (cf. Voges–Proskauer test).
The MR test, the "M" portion of the four IMViC tests, is used to identify enteric bacteria based on their pattern of glucose metabolism. All enterics initially produce pyruvic acid from glucose metabolism. Some enterics subsequently use the mixed acid pathway to metabolize pyruvic acid to other acids, such as lactic, acetic, and formic acids. These bacteria are called methyl-red positive and include Escherichia coli and Proteus vulgaris. Other enterics subsequently use the butylene glycol pathway to metabolize pyruvic acid to neutral end products. These bacteria are called methyl-red-negative and include Serratia marcescens and Enterobacter aerogenes. | 3 | Analytical Chemistry |
There are various uses of DNA molecular modeling in Genomics and Biotechnology research applications, from DNA repair to PCR and DNA nanostructures. Two-dimensional DNA junction arrays have been visualized by Atomic force microscopy.
DNA molecular modeling has various uses in genomics and biotechnology, with research applications ranging from DNA repair to PCR and DNA nanostructures. These include computer molecular models of molecules as varied as RNA polymerase, an E. coli, bacterial DNA primase template suggesting very complex dynamics at the interfaces between the enzymes and the DNA template, and molecular models of the mutagenic, chemical interaction of potent carcinogen molecules with DNA. These are all represented in the gallery below.
Technological application include a DNA biochip and DNA nanostructures designed for DNA computing and other dynamic applications of DNA nanotechnology.
The image at right is of self-assembled DNA nanostructures. The DNA "tile" structure in this image consists of four branched junctions oriented at 90° angles. Each tile consists of nine DNA oligonucleotides as shown; such tiles serve as the primary "building block" for the assembly of the DNA nanogrids shown in the AFM micrograph.
Quadruplex DNA may be involved in certain cancers. Images of quadruplex DNA are in the gallery below. | 4 | Stereochemistry |
By placing the hybrid proteins under the control of IPTG-inducible lac promoters, they are expressed only on media supplemented with IPTG. Further, by including different antibiotic resistance genes in each genetic construct, the growth of non-transformed cells is easily prevented through culture on media containing the corresponding antibiotics. This is particularly important for counter selection methods in which a lack of interaction is needed for cell survival.
The reporter gene may be inserted into the E. coli genome by first inserting it into an episome, a type of plasmid with the ability to incorporate itself into the bacterial cell genome with a copy number of approximately one per cell.
The hybrid expression phagemids can be electroporated into E. coli XL-1 Blue cells which after amplification and infection with VCS-M13 helper phage, will yield a stock of library phage. These phage will each contain one single-stranded member of the phagemid library. | 1 | Biochemistry |
The disulfide bonds are strong, with a typical bond dissociation energy of 60 kcal/mol (251 kJ mol). However, being about 40% weaker than and bonds, the disulfide bond is often the "weak link" in many molecules. Furthermore, reflecting the polarizability of divalent sulfur, the bond is susceptible to scission by polar reagents, both electrophiles and especially nucleophiles (Nu):
The disulfide bond is about 2.05 Å in length, about 0.5 Å longer than a bond. Rotation about the axis is subject to a low barrier. Disulfides show a distinct preference for dihedral angles approaching 90°. When the angle approaches 0° or 180°, then the disulfide is a significantly better oxidant.
Disulfides where the two R groups are the same are called symmetric, examples being diphenyl disulfide and dimethyl disulfide. When the two R groups are not identical, the compound is said to be an asymmetric or mixed disulfide.
Although the hydrogenation of disulfides is usually not practical, the equilibrium constant for the reaction provides a measure of the standard redox potential for disulfides:
This value is about −250 mV versus the standard hydrogen electrode (pH = 7). By comparison, the standard reduction potential for ferrodoxins is about −430 mV. | 0 | Organic Chemistry |
Monte Carlo and molecular dynamic approaches became useful tools for theoretical calculations aiming at predictions of adsorption equilibria and diffusivities in small pores of various simple geometries. The interactions between adsorbate molecules are represented by the Lenard-Jones potential:
where r is the interparticle distance, is the point at which the potential is zero, and is the well depth. | 7 | Physical Chemistry |
RNA silencing or RNA interference refers to a family of gene silencing effects by which gene expression is negatively regulated by non-coding RNAs such as microRNAs. RNA silencing may also be defined as sequence-specific regulation of gene expression triggered by double-stranded RNA (dsRNA). RNA silencing mechanisms are conserved among most eukaryotes. The most common and well-studied example is RNA interference (RNAi), in which endogenously expressed microRNA (miRNA) or exogenously derived small interfering RNA (siRNA) induces the degradation of complementary messenger RNA. Other classes of small RNA have been identified, including piwi-interacting RNA (piRNA) and its subspecies repeat associated small interfering RNA (rasiRNA). | 1 | Biochemistry |
When an electron moves through a gas, its interactions with the gas atoms cause scattering to occur. These interactions are classified as inelastic if they cause excitation or ionization of the atom to occur and elastic if they do not.
The probability of scattering in such a system is defined as the number of electrons scattered, per unit electron current, per unit path length, per unit pressure at 0 °C, per unit solid angle. The number of collisions equals the total number of electrons scattered elastically and inelastically in all angles, and the probability of collision is the total number of collisions, per unit electron current, per unit path length, per unit pressure at 0 °C.
Because noble gas atoms have a relatively high first ionization energy and the electrons do not carry enough energy to cause excited electronic states, ionization and excitation of the atom are unlikely, and the probability of elastic scattering over all angles is approximately equal to the probability of collision. | 7 | Physical Chemistry |
TBS is isotonic and non-toxic. It can be used to dilute substances used in laboratory experiments. Additives can be used to add to a compound's functionality.
TBS is often used in immuno-blotting for both membrane washing and antibody dilution. | 1 | Biochemistry |
The Comparative Toxicogenomics Database (CTD) is a public website and research tool that curates scientific data describing relationships between chemicals, genes/proteins, diseases, taxa, phenotypes, GO annotations, pathways, and interaction modules, launched on November 12, 2004.
The database is maintained by the Department of Biological Sciences at North Carolina State University. | 1 | Biochemistry |
Kinetic binding experiments differ from saturation and competition experiments in that they are not done at equilibrium. Instead, they measure the course of binding of the radioligand during the experiment as well as the dissociation to determine calculation of the Kd, and rate constants of binding and dissociation. Kinetic binding experiments are also called dissociation binding experiments and can help evaluate the interaction of the radioligand and the targeted receptor. | 1 | Biochemistry |
Reaction progress kinetic analysis relies on the ability to accurately monitor the reaction conversion over time. This goal may be accomplished by a range of techniques, the most common of which are described below. While these techniques are sometimes categorized as differential (monitoring reaction rate over time) or integral (monitoring the amount of substrate and/or product over time), simple mathematical manipulation (differentiation or integration) allows interconversion of the data obtained by either of the two. Regardless of the technique implemented, it is generally advantageous to confirm the validity in the system of interest by monitoring with an additional independent method. | 7 | Physical Chemistry |
Berlin has undertaken research on a broad range of areas in both physical and theoretical chemistry, involving stochastic dynamics of complex systems, chemical kinetics and transport of active species in condensed phase and in biological molecules, physical chemistry of liquids and solids, theoretical biophysics and physical aspects of prebiotic evolution, physical methods for the initiation of chemical reactions, in particular cryochemistry, radiation chemistry, photo, and high pressure chemistry. His research covers a vast range of fields, such as the theory of excess electrons in non-polar liquids and liquid noble gases, charge transfer under extreme conditions, chemical processes coupled to structural rearrangements of molecular environment, dispersive kinetics, the effects of correlated fluctuations in chemical and biological properties, the role of static and dynamic disorder in the mechanism of chemical processes in condensed media. Later works are focused on mechanism and kinetics of charge transfer and transport in DNA, culminated in a series of studies of various DNA constructs as building blocks of molecular circuitry. Berlin has published over 170 papers in scientific journals. | 7 | Physical Chemistry |
In statistical mechanics, the entropy of an isolated system at thermodynamic equilibrium is defined as the natural logarithm of , the number of distinct microscopic states available to the system given the macroscopic constraints (such as a fixed total energy ):
This equation, which relates the microscopic details, or microstates, of the system (via ) to its macroscopic state (via the entropy ), is the central idea of statistical mechanics. Such is its importance that it is inscribed on Boltzmann's tombstone.
The constant of proportionality serves to make the statistical mechanical entropy equal to the classical thermodynamic entropy of Clausius:
One could choose instead a rescaled dimensionless entropy in microscopic terms such that
This is a more natural form and this rescaled entropy exactly corresponds to Shannon's subsequent information entropy.
The characteristic energy is thus the energy required to increase the rescaled entropy by one nat. | 7 | Physical Chemistry |
The first reported use of a PPG in the scientific literature was by Barltrop and Schofield, who in 1962 used 253.7 nm light to release glycine from N-benzylglycine. Following this initial report, the field rapidly expanded throughout the 1970s as Kaplan and Epstein studied PPGs in a variety of biochemical systems. During this time, a series of standards for evaluating PPG performance was compiled. An abbreviated list of these standards, which are commonly called the Lester rules, or Sheehan criteria are summarized below:
* In biological systems, the protected substrate, as well as the photoproducts should be highly soluble in water; in synthesis, this requirement is not as strict
* The protected substrate, as well as the photoproducts should be stable in the photolysis environment
* Separation of the PPG should exhibit a quantum yield greater than 0.10
* Separation of the PPG should occur through a primary photochemical process
* The chromophore should absorb incident light with reasonable absorptivity
* The excitation wavelength of light should be greater than 300 nm
* The media and photoproducts should not absorb the incident light
* A general, high-yield synthetic procedure should exist for attaching the PPG to an unprotected substrate
* The protected substrate and the photoproducts should be easily separated | 5 | Photochemistry |
The silicothermic reduction of dolomite was first developed by Amati in 1938 at the University of Padua. Immediately afterward, an industrial production was established in Bolzano (Italy), using what is now better known as the Bolzano process.
A few years later in 1939, when Canada and its allies entered WW2, they were short on supplies that required magnesium such as bombs, other military devices and aluminum alloys needed for aircraft. Dr. Lloyd Montgomery Pidgeon at the National Research Council was able to create a method for extracting magnesium from dolomite in a vacuum at high temperature with ferrosilicon as the reducing agent. At this time, the ferrosilicon method was known, however it had yet to be commercialized. By early 1942, a successful pilot test took place.
Since then, the Pidgeon process has continually been widely used, especially in China, the worlds largest magnesium producer. | 8 | Metallurgy |
Efficient ribosomal frameshifting generally requires the presence of an RNA secondary structure to enhance the effects of the slippery sequence. The RNA structure (which can be a stem-loop or pseudoknot) is thought to pause the ribosome on the slippery site during translation, forcing it to relocate and continue replication from the −1 position. It is believed that this occurs because the structure physically blocks movement of the ribosome by becoming stuck in the ribosome mRNA tunnel. This model is supported by the fact that strength of the pseudoknot has been positively correlated with the level of frameshifting for associated mRNA.
Below are examples of predicted secondary structures for frameshift elements shown to stimulate frameshifting in a variety of organisms. The majority of the structures shown are stem-loops, with the exception of the ALIL (apical loop-internal loop) pseudoknot structure. In these images, the larger and incomplete circles of mRNA represent linear regions. The secondary "stem-loop" structures, where "stems" are formed by a region of mRNA base pairing with another region on the same strand, are shown protruding from the linear DNA. The linear region of the HIV ribosomal frameshift signal contains a highly conserved UUU UUU A slippery sequence; many of the other predicted structures contain candidates for slippery sequences as well.
The mRNA sequences in the images can be read according to a set of guidelines. While A, T, C, and G represent a particular nucleotide at a position, there are also letters that represent ambiguity which are used when more than one kind of nucleotide could occur at that position. The rules of the International Union of Pure and Applied Chemistry (IUPAC) are as follows:
These symbols are also valid for RNA, except with U (uracil) replacing T (thymine). | 1 | Biochemistry |
Configurational electronic entropy is usually observed in mixed-valence transition metal oxides, as the charges in these systems are both localized (the system is ionic), and capable of changing (due to the mixed valency). To a first approximation (i.e. assuming that the charges are distributed randomly), the molar configurational electronic entropy is given by:
where is the fraction of sites on which a localized electron/hole could reside (typically a transition metal site), and is the concentration of localized electrons/holes. Of course, the localized charges are not distributed randomly, as the charges will interact electrostatically with one another, and so the above formula should only be regarded as an approximation to the configurational atomic entropy. More sophisticated approximations have been made in the literature. | 7 | Physical Chemistry |
In chemistry, the term supramolecular chirality is used to describe supramolecular assemblies that are non-superposable on their mirror images.
Chirality in supramolecular chemistry implies the non-symmetric arrangement of molecular components in a non-covalent assembly. Chirality may arise in a supramolecular system if one of its component is chiral or if achiral components arrange in a non symmetrical way to produce a supermolecule that is chiral. | 4 | Stereochemistry |
Omega oxidation (ω-oxidation) is a process of fatty acid metabolism in some species of animals. It is an alternative pathway to beta oxidation that, instead of involving the β carbon, involves the oxidation of the ω carbon (the carbon most distant from the carboxyl group of the fatty acid). The process is normally a minor catabolic pathway for medium-chain fatty acids (10-12 carbon atoms), but becomes more important when β oxidation is defective.
In vertebrates, the enzymes for ω oxidation are located in the smooth ER of liver and kidney cells, instead of in the mitochondria as with β oxidation. The steps of the process are as follows:
After these three steps, either end of the fatty acid can be attached to coenzyme A. The molecule can then enter the mitochondrion and undergo β oxidation. The final products after successive oxidations include succinic acid, which can enter the citric acid cycle, and adipic acid.
The first step in ω-oxidation, i.e. addition of a hydroxy residue to the omega carbon of short, intermediate, and long chain unsaturated or saturated fatty acids, can serve to produce or inactivate signaling molecules. In humans, a subset of Cytochrome P450 (CYP450) microsome-bound ω-hydroxylases (termed Cytochrome P450 omega hydroxylases) metabolize arachidonic acid (also known as eicosatetraenoic acid) to 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE possesses a range of activities in animal and cellular model systems, e.g. it constricts blood vessels, alters the kidneys reabsorption of salt and water, and promotes the growth of cancer cells; genetic studies in humans suggest that 20-HETE contributes to hypertension, myocardial infarction, and brain stroke (see 20-Hydroxyeicosatetraenoic acid). Among the CYP450 superfamily, members of the CYP4A and CYP4F subfamilies viz., CYP4A11, CYP4F2, CYP4F3, are considered the predominant cytochrome P450 enzymes responsible in most tissues for forming 20-HETE. CYP2U1 and CYP4Z1 contribute to 20-HETE production in a more limited range of tissues. The cytochrome ω-oxidases including those belonging to the CYP4A and CYP4F sub-families and CYPU21 also ω-hydroxylate and thereby reduce the activity of various fatty acid metabolites of arachidonic acid including LTB4, 5-HETE, 5-oxo-eicosatetraenoic acid, 12-HETE, and several prostaglandins that are involved in regulating various inflammatory, vascular, and other responses in animals and humans. This hydroxylation-induced inactivation may underlie the proposed roles of the cytochromes in dampening inflammatory responses and the reported associations of certain CYP4F2 and CYP4F3 single nucleotide variants with human Crohns disease and Celiac disease, respectively. | 1 | Biochemistry |
A biomaterial should perform its intended function within the living body without negatively affecting other bodily tissues and organs. In order to prevent unwanted organ and tissue interactions, biomaterials should be non-toxic. The toxicity of a biomaterial refers to the substances that are emitted from the biomaterial while in vivo. A biomaterial should not give off anything to its environment unless it is intended to do so. Nontoxicity means that biomaterial is: noncarcinogenic, nonpyrogenic, nonallergenic, blood compatible, and noninflammatory. However, a biomaterial can be designed to include toxicity for an intended purpose. For example, application of toxic biomaterial is studied during in vivo and in vitro cancer immunotherapy testing. Toxic biomaterials offer an opportunity to manipulate and control cancer cells. One recent study states: "Advanced nanobiomaterials, including liposomes, polymers, and silica, play a vital role in the codelivery of drugs and immunomodulators. These nanobiomaterial-based delivery systems could effectively promote antitumor immune responses and simultaneously reduce toxic adverse effects." This is a prime example of how the biocompatibility of a biomaterial can be altered to produce any desired function. | 1 | Biochemistry |
Hyperconjugation affects several properties.
# Bond length: Hyperconjugation is suggested as a key factor in shortening of sigma bonds (σ bonds). For example, the single C–C bonds in 1,3-butadiene and propyne are approximately 1.46 Å in length, much less than the value of around 1.54 Å found in saturated hydrocarbons. For butadiene, this can be explained as normal conjugation of the two alkenyl parts. But for propyne, it is generally accepted that this is due to hyperconjugation between the alkyl and alkynyl parts.
# Dipole moments: The large increase in dipole moment of 1,1,1-trichloroethane as compared with chloroform can be attributed to hyperconjugated structures.
# The heat of formation of molecules with hyperconjugation are greater than sum of their bond energies and the heats of hydrogenation per double bond are less than the heat of hydrogenation of ethylene.
# Stability of carbocations:
#:(CH)C > (CH)CH > (CH)CH > CH
#: The three C–H σ bonds of the methyl group(s) attached to the carbocation can undergo the stabilization interaction but only one of them can be aligned perfectly with the empty p-orbital, depending on the conformation of the carbon–carbon bond. Donation from the two misaligned C–H bonds is weaker. The more adjacent methyl groups there are, the larger hyperconjugation stabilization is because of the increased number of adjacent C–H bonds. | 7 | Physical Chemistry |
Photoelectrochemical oxidation (PECO) is the process by which light enables a semiconductor to promote a catalytic oxidation reaction. While a photoelectrochemical cell typically involves both a semiconductor (electrode) and a metal (counter-electrode), at sufficiently small scales, pure semiconductor particles can behave as microscopic photoelectrochemical cells. PECO has applications in the detoxification of air and water, hydrogen production, and other applications. | 5 | Photochemistry |
Organic thiocyanates are organic compounds containing the functional group RSCN. the organic group is attached to sulfur: R−S−C≡N has a S–C single bond and a C≡N triple bond.
Organic thiocyanates are valued building blocks. They allow to access efficiently various sulfur containing functional groups and scaffolds. | 0 | Organic Chemistry |
The society publishes the magazine Australian Biochemist with three issues per year. The publication started in 1998, following on from the ABS/ASBMB newsletter, which was started in 1970. | 1 | Biochemistry |
In addition to the parallelepiped primitive cells, for every Bravais lattice there is another kind of primitive cell called the Wigner–Seitz cell. In the Wigner–Seitz cell, the lattice point is at the center of the cell, and for most Bravais lattices, the shape is not a parallelogram or parallelepiped. This is a type of Voronoi cell. The Wigner–Seitz cell of the reciprocal lattice in momentum space is called the Brillouin zone. | 3 | Analytical Chemistry |
One of the first dendrimers, the Newkome dendrimer, was synthesized in 1985. This macromolecule is also commonly known by the name arborol. The figure outlines the mechanism of the first two generations of arborol through a divergent route (discussed below). The synthesis is started by nucleophilic substitution of 1-bromopentane by triethyl sodiomethanetricarboxylate in dimethylformamide and benzene. The ester groups were then reduced by lithium aluminium hydride to a triol in a deprotection step. Activation of the chain ends was achieved by converting the alcohol groups to tosylate groups with tosyl chloride and pyridine. The tosyl group then served as leaving groups in another reaction with the tricarboxylate, forming generation two. Further repetition of the two steps leads to higher generations of arborol.
Poly(amidoamine), or PAMAM, is perhaps the most well known dendrimer. The core of PAMAM is a diamine (commonly ethylenediamine), which is reacted with methyl acrylate, and then another ethylenediamine to make the generation-0 (G-0) PAMAM. Successive reactions create higher generations, which tend to have different properties. Lower generations can be thought of as flexible molecules with no appreciable inner regions, while medium-sized (G-3 or G-4) do have internal space that is essentially separated from the outer shell of the dendrimer. Very large (G-7 and greater) dendrimers can be thought of more like solid particles with very dense surfaces due to the structure of their outer shell. The functional group on the surface of PAMAM dendrimers is ideal for click chemistry, which gives rise to many potential applications.
Dendrimers can be considered to have three major portions: a core, an inner shell, and an outer shell. Ideally, a dendrimer can be synthesized to have different functionality in each of these portions to control properties such as solubility, thermal stability, and attachment of compounds for particular applications. Synthetic processes can also precisely control the size and number of branches on the dendrimer. There are two defined methods of dendrimer synthesis, divergent synthesis and convergent synthesis. However, because the actual reactions consist of many steps needed to protect the active site, it is difficult to synthesize dendrimers using either method. This makes dendrimers hard to make and very expensive to purchase. At this time, there are only a few companies that sell dendrimers; Polymer Factory Sweden AB commercializes biocompatible bis-MPA dendrimers and Dendritech is the only kilogram-scale producers of PAMAM dendrimers. NanoSynthons, LLC from Mount Pleasant, Michigan, USA produces PAMAM dendrimers and other proprietary dendrimers. | 6 | Supramolecular Chemistry |
In column chromatography a mixture of substances is dissolved in a mobile phase and passed over a stationary phase in a column. A selectivity factor is defined as the ratio of distribution coefficients, which describe the equilibrium distribution of an analyte between the stationary phase and the mobile phase. The selectivity factor is equal to the selectivity coefficient with the added assumption that the activity of the stationary phase, the substrate in this case, is equal to 1, the standard assumption for a pure phase. The resolution of a chromatographic column, R is related to the selectivity factor by:
where α is selectivity factor, N is the number of theoretical plates k and k are the retention factors of the two analytes. Retention factors are proportional to distribution coefficients. In practice substances with a selectivity factor very close to 1 can be separated. This is particularly true in gas-liquid chromatography where column lengths up to 60 m are possible, providing a very large number of theoretical plates.
In ion-exchange chromatography the selectivity coefficient is defined in a slightly different way | 7 | Physical Chemistry |
In principle one can calculate all the above thermodynamic observables from a single differential scanning calorimetry thermogram of the system assuming that the is independent of the temperature. However, it is difficult to obtain accurate values for this way. More accurately, the can be derived from the variations in vs. which can be achieved from measurements with slight variations in pH or protein concentration. The slope of the linear fit is equal to the . Note that any non-linearity of the datapoints indicates that is probably not independent of the temperature.
Alternatively, the can also be estimated from the calculation of the accessible surface area (ASA) of a protein prior and after thermal denaturation as follows:
For proteins that have a known 3d structure, the can be calculated through computer programs such as Deepview (also known as swiss PDB viewer). The can be calculated from tabulated values of each amino acid through the semi-empirical equation:
where the subscripts polar, non-polar and aromatic indicate the parts of the 20 naturally occurring amino acids.
Finally for proteins, there is a linear correlation between and through the following equation: | 7 | Physical Chemistry |
The point groups are named according to their component symmetries. There are several standard notations used by crystallographers, mineralogists, and physicists.
For the correspondence of the two systems below, see crystal system. | 3 | Analytical Chemistry |
Lake Chichoj is located in the municipality of San Cristóbal Verapaz, department of Alta Verapaz, in Guatemala. The catchment of lake has been designated as a Protected Area, in an attempt to protect the lake from environmental degradation. Water routing through the catchment is made complex by karstic groundwater flow. It is estimated that the catchment of the lake drains . The lake in turn drains superficially to the Cahabón River, which flows to the Atlantic Ocean via Lake Izabal. | 2 | Environmental Chemistry |
Transcription factor TFA is a nuclear protein involved in the RNA polymerase II-dependent transcription of DNA. TFA is one of several general (basal) transcription factors (GTFs) that are required for all transcription events that use RNA polymerase II. Other GTFs include TFD, a complex composed of the TATA binding protein TBP and TBP-associated factors (TAFs), as well as the factors TFB, TFE, TFF, and TFH. Together, these factors are responsible for promoter recognition and the formation of a transcription preinitiation complex (PIC) capable of initiating RNA synthesis from a DNA template. | 1 | Biochemistry |
Common adverse drug reactions are nausea and vomiting. People who are allergic to penicillin and other β-lactam antibiotics should take caution if taking imipenem, as cross-reactivity rates are high. At high doses, imipenem is seizurogenic. | 4 | Stereochemistry |
One application of the technique includes detection of protein modifications in two bacterial species Ehrlichia- E. muris and IOE. Cholera toxin B subunit (which binds to gangliosides), concanavalin A (which detects mannose-containing glycans) and nitrophospho molybdate-methyl green (which detects phosphoproteins) were used to detect protein modifications. The technique showed that the antigenic proteins of the non-virulent E.muris is more post-translationally modified than the highly virulent IOE. | 0 | Organic Chemistry |
Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy, and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas:
*Leaching
*Solution concentration and purification
*Metal or metal compound recovery | 8 | Metallurgy |
Factors influencing habit include: a combination of two or more crystal forms; trace impurities present during growth; crystal twinning and growth conditions (i.e., heat, pressure, space); and specific growth tendencies such as growth striations. Minerals belonging to the same crystal system do not necessarily exhibit the same habit. Some habits of a mineral are unique to its variety and locality: For example, while most sapphires form elongate barrel-shaped crystals, those found in Montana form stout tabular crystals. Ordinarily, the latter habit is seen only in ruby. Sapphire and ruby are both varieties of the same mineral: corundum.
Some minerals may replace other existing minerals while preserving the originals habit, i.e. pseudomorphous replacement. A classic example is tigers eye quartz, crocidolite asbestos replaced by silica. While quartz typically forms prismatic (elongate, prism-like) crystals, in tigers eye the original fibrous' habit of crocidolite is preserved. | 3 | Analytical Chemistry |
A typical protein-coding gene is first copied into RNA as an intermediate in the manufacture of the final protein product. In other cases, the RNA molecules are the actual functional products, as in the synthesis of ribosomal RNA and transfer RNA. Some RNAs known as ribozymes are capable of enzymatic function, while others such as microRNAs and riboswitches have regulatory roles. The DNA sequences from which such RNAs are transcribed are known as non-coding RNA genes.
Some viruses store their entire genomes in the form of RNA, and contain no DNA at all. Because they use RNA to store genes, their cellular hosts may synthesize their proteins as soon as they are infected and without the delay in waiting for transcription. On the other hand, RNA retroviruses, such as HIV, require the reverse transcription of their genome from RNA into DNA before their proteins can be synthesized. | 1 | Biochemistry |
These codes typically use regular grids (cubical or rectangular cuboid), conjugate gradient method to solve large system of linear equations, and FFT-acceleration of the matrix-vector products which uses convolution theorem. Complexity of this approach is almost linear in number of dipoles for both time and memory. | 7 | Physical Chemistry |
The sigma-2 receptor is expressed in brain and retinal cells where it regulates key pathways involved in age-related diseases such as Alzheimers disease and synucleinopathies such as Parkinsons disease and dementia with Lewy bodies, as well as dry age-related macular degeneration (dry AMD). The normal activity of processes regulated by sigma-2, such as protein trafficking and autophagy, is impaired by cellular stresses such as oxidative stress and the build-up of amyloid-β and α-synuclein oligomers. Studies support that sigma-2 modulators can rescue biological processes that are impaired in neurodegenerative diseases.
In vitro studies of experimental sigma-2 receptor modulators demonstrated an ability to prevent the binding of amyloid-β oligomers to neurons and also to displace bound amyloid-β oligomers from neuronal receptors. In addition, transgenic mice treated sigma-2 receptor modulators performed significantly better in the Morris water maze task than did vehicle-treated mice. Taken together, these studies suggest that sigma-2 receptor modulation may be a viable approach for treating certain neurodegenerative diseases of the CNS and retina. | 1 | Biochemistry |
Bose first sent a paper to Einstein on the quantum statistics of light quanta (now called photons), in which he derived Plancks quantum radiation law without any reference to classical physics. Einstein was impressed, translated the paper himself from English to German and submitted it for Bose to the Zeitschrift für Physik, which published it in 1924. (The Einstein manuscript, once believed to be lost, was found in a library at Leiden University in 2005.) Einstein then extended Boses ideas to matter in two other papers. The result of their efforts is the concept of a Bose gas, governed by Bose–Einstein statistics, which describes the statistical distribution of identical particles with integer spin, now called bosons. Bosons, particles that include the photon and atoms such as helium-4 (), are allowed to share a quantum state. Einstein proposed that cooling bosonic atoms to a very low temperature would cause them to fall (or "condense") into the lowest accessible quantum state, resulting in a new form of matter.
In 1938, Fritz London proposed the BEC as a mechanism for superfluidity in and superconductivity.
The quest to produce a Bose–Einstein condensate in the laboratory was stimulated by a paper published in 1976 by two program directors at the National Science Foundation (William Stwalley and Lewis Nosanow). This led to the immediate pursuit of the idea by four independent research groups; these were led by Isaac Silvera (University of Amsterdam), Walter Hardy (University of British Columbia), Thomas Greytak (Massachusetts Institute of Technology) and David Lee (Cornell University).
On 5 June 1995, the first gaseous condensate was produced by Eric Cornell and Carl Wieman at the University of Colorado at Boulder NIST–JILA lab, in a gas of rubidium atoms cooled to 170 nanokelvins (nK). Shortly thereafter, Wolfgang Ketterle at MIT produced a Bose–Einstein Condensate in a gas of sodium atoms. For their achievements Cornell, Wieman, and Ketterle received the 2001 Nobel Prize in Physics. These early studies founded the field of ultracold atoms, and hundreds of research groups around the world now routinely produce BECs of dilute atomic vapors in their labs.
Since 1995, many other atomic species have been condensed, and BECs have also been realized using molecules, quasi-particles, and photons. | 7 | Physical Chemistry |
Schwartz's reagent reduces amides to aldehydes.
Vinylation of ketones in high yields is a possible use of Schwartz's reagent.
Schwartz's reagent has been used in the synthesis of some macrolide antibiotics, (−)-motuporin, and antitumor agents. | 0 | Organic Chemistry |
General transcription factors (GTFs) or basal transcription factors are protein transcription factors that have been shown to be important in the transcription of class II genes to mRNA templates. Many of them are involved in the formation of a preinitiation complex, which, together with RNA polymerase II, bind to and read the single-stranded DNA gene template. The cluster of RNA polymerase II and various transcription factors is known as a basal transcriptional complex (BTC). | 1 | Biochemistry |
The next major change in shutter hardware coincided with the American Civil War era. Heavy presses and punches were in use in factories around the country and a maturing rail transportation system opened inland areas for the products of the factories. Iron was the norm up until that time – steel had been expensive to produce. Hardware makers were quick to take advantage of this new material. They produced the first of the "butt" and "H" or "Parliament" style lift-off hinges. Quick and easy to produce and strong enough to hold heavy shutters, they found favor in the new construction of the period.
Around 1880 the first examples of "New York" style hardware appeared. Plate steel elements were assembled by unskilled labor in sprawling factories. This hardware style evolved into the many imported forms seen today. It provided the ability to surface mount hinges and tie the wooden elements of the shutters together, and also allowed for smaller and less expensive window and shutter elements. About this time the first commercially produced "S" style tie-backs were seen – manufactured by Stanley Works in Connecticut. Historically an "S" is a very difficult form to forge. Stanley forged the first simple styles for commercial consumption but it wasn't until the 1930s that they started to stamp them. | 8 | Metallurgy |
Energetic polymers (e.g. nitro or azido derivates of polymers) can be used as a binder to increase the explosive power in comparison with inert binders. Energetic plasticizers can be also used. The addition of a plasticizer lowers the sensitivity of the explosive and improves its processibility. | 7 | Physical Chemistry |
Iron can be stored in ferritin as ferric iron due to the ferroxidase activity of the ferritin heavy chain. Dysfunctional ferritin may accumulate as hemosiderin, which can be problematic in cases of iron overload. The ferritin storage iron pool is much larger than the labile iron pool, ranging in concentration from 0.7 mM to 3.6 mM. | 1 | Biochemistry |
Neuromuscular blocking agents exert their effect by modulating the signal transmission in skeletal muscles. An action potential is, in other words, a depolarisation in neurone membrane due to a change in membrane potential greater than the threshold potential leads to an electrical impulse generation. The electrical impulse travels along the pre-synaptic neurone axon to synapse with the muscle at the neuromuscular junction (NMJ) to cause muscle contraction.
When the action potential reaches the axon terminal, it triggers the opening of the calcium ion gated channels, which causes the influx of Ca. Ca will stimulate the release of neurotransmitter in the neurotransmitter containing vesicles by exocytosis (vesicle fuses with the pre-synpatic membrane).
The neurotransmitter, acetylcholine(ACh) binds to the nicotinic receptors on the motor end plate, which is a specialised area of the muscle fibre's post-synaptic membrane. This binding causes the nicotinic receptor channels to open and allow the influx of Na into the muscle fibre.
Fifty percent of the released ACh is hydrolysed by acetylcholinesterase (AChE) and the remaining bind to the nicotinic receptors on the motor end plate. When ACh is degraded by AChE, the receptors are no longer stimulated and the muscle can be repolarised.
If enough Na enter the muscle fibre, it causes an increase in the membrane potential from its resting potential of -95mV to -50mV (above the threshold potential -55V) which causes an action potential to spread throughout the fibre. This potential travels along the surface of the sarcolemma. The sarcolemma is an excitable membrane that surrounds the contractile structures known as myofibrils that are located deep in the muscle fibre. For the action potential to reach the myofibrils, the action potential travels along the transverse tubules (T-tubules) that connects the sarcolemma and center of the fibre.
Later, action potential reaches the sarcoplasmic reticulum which stores the Ca needed for muscle contraction and causes Ca to be released from the sarcoplasmic reticulum. | 1 | Biochemistry |
Homoenolates are a type of functional group that have been used in synthetic organic chemistry since the 1980s. They are related to enolates, but represent an umpolung of their reactivity. Homoenolates can be formed with a variety of different metal counterions, including lithium, iron, silver, lead, titanium, tin, tellurium, zirconium, niobium, mercury, zinc, antimony, bismuth, nickel, palladium, and copper. Homoenolates stability and reactivity varies by counterion identity and other nearby functional groups. Common pathways of decomposition include proto-demetalation and β-hydride elimination. Multiple reviews on the topic of homoenolates and their reactivity have been published. | 0 | Organic Chemistry |
One of the most famous reversible photochromic applications is color changing lenses for sunglasses. The largest limitation in using photochromic technology is that the materials cannot be made stable enough to withstand thousands of hours of outdoor exposure so long-term outdoor applications are not appropriate at this time.
The switching speed of photochromic dyes is highly sensitive to the rigidity of the environment around the dye. As a result, they switch most rapidly in solution and slowest in the rigid environment like a polymer lens. In 2005 it was reported that attaching flexible polymers with low glass transition temperature (for example siloxanes or polybutyl acrylate) to the dyes allows them to switch much more rapidly in a rigid lens. Some spirooxazines with siloxane polymers attached switch at near solution-like speeds even though they are in a rigid lens matrix. | 5 | Photochemistry |
The double bond of a glycal allows many other functional groups to be introduced into a monosaccharide. Like an alkene, a glycal can undergo electrophilic addition across the double bond to add in these new atoms such as halogens, epoxides, and nitrogen. The glycal double bond also allows a deoxy position (carbon in the ring that doesn’t have an oxygen bonded to it) to be easily introduced.
Glycals have many uses in synthetic carbohydrate chemistry. They are commonly used as glycosylation donors, meaning that they can react with other monosaccharides to form a longer chain of monosaccharides called an oligosaccharide.
Glycals can also have interesting applications in studying biological systems, particularly enzymes. D-glucal and radiolabelled D-galactal have been used to selectively bind with amino acids in the active sites of several enzymes. These enzyme-glycal complexes allow these amino acids that are essential for catalysis to be identified and allow for a better understanding of how these enzymes function. | 0 | Organic Chemistry |
Hydrophilic interaction chromatography (or hydrophilic interaction liquid chromatography, HILIC) is a variant of normal phase liquid chromatography that partly overlaps with other chromatographic applications such as ion chromatography and reversed phase liquid chromatography. HILIC uses hydrophilic stationary phases with reversed-phase type eluents. The name was suggested by Andrew Alpert in his 1990 paper on the subject. He described the chromatographic mechanism for it as liquid-liquid partition chromatography where analytes elute in order of increasing polarity, a conclusion supported by a review and re-evaluation of published data. | 1 | Biochemistry |
In quantum mechanics, a doublet is a composite quantum state of a system with an effective spin of 1/2, such that there are two allowed values of the spin component, −1/2 and +1/2. Quantum systems with two possible states are sometimes called two-level systems. Essentially all occurrences of doublets in nature arise from rotational symmetry; spin 1/2 is associated with the fundamental representation of the Lie group SU(2). | 7 | Physical Chemistry |
Amorphous solids in general have a unique magnetic property because of their atomic disorder as explained above. They are rather soft metals and each has its own specific magnetic property depending on the means of production. In the splat quenching process, the metals are very soft and have superparamagnetic properties or shifting polarity behavior caused by the rapid and intense heat transfer. | 8 | Metallurgy |
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