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Metal ions have multiple roles during the reaction. Firstly it can bind to negatively charged substrate groups so they will not repel electron pairs from active site's nucleophilic groups. It can attract negatively charged electrons to increase electrophilicity. It can also bridge between active site and substrate. At last, they may change the conformational structure of the substrate to favour reaction. | 1 | Biochemistry |
Steel with an ultimate tensile strength of less than 1000 MPa (~145,000 psi) or hardness of less than HRC 32 on the Hardness Rockwell Scale is not generally considered susceptible to hydrogen embrittlement. As an example of severe hydrogen embrittlement, the elongation at failure of 17-4PH precipitation hardened stainless steel was measured to drop from 17% to only 1.7% when smooth specimens were exposed to high-pressure hydrogen
As the strength of steels increases, the fracture toughness decreases, so the likelihood that hydrogen embrittlement will lead to fracture increases. In high-strength steels, anything above a hardness of HRC 32 may be susceptible to early hydrogen cracking after plating processes that introduce hydrogen. They may also experience long-term failures anytime from weeks to decades after being placed in service due to accumulation of hydrogen over time from cathodic protection and other sources. Numerous failures have been reported in the hardness range from HRC 32-36 and more above; therefore, parts in this range should be checked during quality control to ensure they are not susceptible.
Testing the fracture toughness of hydrogen-charged, embrittled specimens is complicated by the need to keep charged specimens very cold, in liquid nitrogen, to prevent the hydrogen diffusing away. | 7 | Physical Chemistry |
The data feeds several key products, primarily abundance profiles. These profiles summarize and reorganize the information found in the similarity files in a more easily digestible format. | 1 | Biochemistry |
The most common side effects (more than 10% of patients) are hot flashes and sweating, which are typical of estrogen deficiency as caused by exemestane, and also insomnia, headache, and joint pain. Nausea and fatigue are mainly observed in patients with advanced breast cancer.
An occasional decrease in lymphocytes has been observed in approximately 20% of patients receiving Aromasin, particularly in patients with pre-existing lymphopenia.
Exemestane has androgenic properties similarly to formestane and can produce androgenic side effects such as acne and weight gain, although these are generally associated with supratherapeutic dosages of the drug. | 4 | Stereochemistry |
After his arrival at Oxford and during World War II, Cornforth significantly influenced the work on penicillin, particularly in purifying and concentrating it. Penicillin is usually very unstable in its crude form; as a consequence of this, researchers at the time were building upon Howard Floreys work on the drug. In 1940, Cornforth and other chemists measured the yield of penicillin in arbitrary units to understand the conditions that favoured penicillin production and activity, and he contributed to the writing of The Chemistry of Penicillin'.
In 1946, the Cornforths, who had by now married, left Oxford and joined the Medical Research Council (MRC), working at the National Institute for Medical Research (NIMR), where they continued on earlier work in synthesising sterols, including cholesterol. The Cornforths' collaboration with Robinson continued and flourished. In 1951, they completed, simultaneously with Robert Burns Woodward, the first total synthesis of the non-aromatic steroids. At the NIMR, Cornforth collaborated with numerous biological scientists, including George Popják, with whom he shared an interest in cholesterol. Together, they received the Davy Medal in 1968 in recognition of their distinguished joint work on the elucidation of the biosynthetic pathway to polyisoprenoids and steroids.
While working at the MRC, Cornforth was appointed a professor at the University of Warwick and was employed there from 1965 to 1971.
In 1975, Cornforth was awarded a share of the Nobel Prize in Chemistry, alongside Vladimir Prelog. In his acceptance speech, Cornforth said:
Also in 1975, he moved to the University of Sussex in Brighton as a Royal Society Research Professor. Cornforth remained there as a professor and was active in research until his death. | 0 | Organic Chemistry |
* [http://bioinformatics.ai.sri.com/ptools/ Pathway Tools]: A bioinformatics software package that assists in the construction of pathway/genome databases such as EcoCyc. Developed by Peter Karp and associates at the SRI International Bioinformatics Research Group, Pathway Tools has several components. Its PathoLogic module takes an annotated genome for an organism and infers probable metabolic reactions and pathways to produce a new pathway/genome database. Its MetaFlux component can generate a quantitative metabolic model from that pathway/genome database using flux-balance analysis. Its Navigator component provides extensive query and visualization tools, such as visualization of metabolites, pathways, and the complete metabolic network.
* [http://ergo.integratedgenomics.com/ ERGO]: A subscription-based service developed by Integrated Genomics. It integrates data from every level including genomic, biochemical data, literature, and high-throughput analysis into a comprehensive user friendly network of metabolic and nonmetabolic pathways.
* [http://www.cogsys.cs.uni-tuebingen.de/software/KEGGtranslator/ KEGGtranslator]: an easy-to-use stand-alone application that can visualize and convert KEGG files (KGML formatted XML-files) into multiple output formats. Unlike other translators, KEGGtranslator supports a plethora of output formats, is able to augment the information in translated documents (e.g., MIRIAM annotations) beyond the scope of the KGML document, and amends missing components to fragmentary reactions within the pathway to allow simulations on those. KEGGtranslator converts these files to SBML, BioPAX, SIF, SBGN, SBML with qualitative modeling extension, GML, GraphML, JPG, GIF, LaTeX, etc.
* [http://modelseed.org/ ModelSEED]: An online resource for the analysis, comparison, reconstruction, and curation of genome-scale metabolic models. Users can submit genome sequences to the RAST annotation system, and the resulting annotation can be automatically piped into the ModelSEED to produce a draft metabolic model. The ModelSEED automatically constructs a network of metabolic reactions, gene-protein-reaction associations for each reaction, and a biomass composition reaction for each genome to produce a model of microbial metabolism that can be simulated using Flux Balance Analysis.
* MetaMerge: algorithm for semi-automatically reconciling a pair of existing metabolic network reconstructions into a single metabolic network model.
* [https://github.com/esaskar/CoReCo CoReCo]: algorithm for automatic reconstruction of metabolic models of related species. The first version of the software used KEGG as reaction database to link with the EC number predictions from CoReCo. Its automatic gap filling using atom map of all the reactions produce functional models ready for simulation. | 1 | Biochemistry |
To extract quantities of interest, the autocorrelation data can be fitted, typically using a nonlinear least squares algorithm. The fit's functional form depends on the type of dynamics (and the optical geometry in question). | 7 | Physical Chemistry |
One short inscription on the pillar is associated with the Tomara king Anangpal, although it is hard to decipher.. Alexander Cunningham (1862–63) read the inscription as follows:
Based on this reading, Cunningham theorized that Anangpal had moved the pillar to its current location while establishing the city of Delhi. However, his reading has been contested by the later scholars. Buddha Rashmi Mani (1997) read it as follows: | 8 | Metallurgy |
NaDMSO condenses with esters (1) to form β-ketosulfoxides (2), which can be useful intermediates. Reduction of β-ketosulfoxides with aluminium amalgam gives methyl ketones (3). Reaction with alkyl halides followed by elimination gives α,β-unsaturated ketones (4). β-ketosulfoxides can also be used in the Pummerer rearrangement to introduce nucleophiles alpha to a carbonyl (5). | 0 | Organic Chemistry |
The final steps from the common corrinoid intermediate E-37/HE-44 to cobyric acid E-44/HE-51 were carried out by the two groups collaboratively and in parallel, the ETH group working with material produced by the A/D approach, and the Harvard group with that from the A/B approach. What the two groups in fact accomplished thus were the common final steps of two different syntheses.
The tasks in this end phase of the project were the regioselective introduction of methyl groups at the two meso positions C-5 and C-15 of E-37/HE-44, followed by conversion of all its peripheral carboxyl functions into primary amide groups, excepting that in side chain f at ring D, which had to end up as free carboxyl. These conceptually simple finishing steps turned out to be rather complex in execution, including unforeseen pitfalls like a dramatic loss of precious synthetic material in the so-called "Black Friday" (July 9, 1971). | 0 | Organic Chemistry |
According to Lord Kelvin's equation of 1871,
If the particle is assumed to be spherical, then ; hence,
Note: Kelvin defined the surface tension as the work that was performed per unit area by the interface rather than on the interface; hence his term containing has a minus sign. In what follows, the surface tension will be defined so that the term containing has a plus sign.
Since , then ; hence,
Assuming that the vapor obeys the ideal gas law, then
where:
: = mass of a volume of vapor
: = molecular weight of vapor
: = number of moles of vapor in volume of vapor
: = Avogadro constant
: = ideal gas constant =
Since is the mass of one molecule of vapor or liquid, then
: volume of one molecule .
Hence
: where .
Thus
Since
then
Since , then . If , then . Hence
Therefore
which is the Ostwald–Freundlich equation. | 7 | Physical Chemistry |
Normally, the Wnt signaling pathway leads to stabilization of β-catenin through inactivation of a protein complex containing the tumor suppressors APC and Axin. This destruction complex normally triggers β-catenin phosphorylation, inducing its degradation. De-regulation of the autocrine Wnt signaling pathway via mutations in APC and Axin have been linked to activation of various types of human cancer. Genetic alterations that lead to de-regulation of the autocrine Wnt pathway result in transactivation of epidermal growth factor receptor (EGFR) and other pathways, in turn contributing to proliferation of tumor cells. In colorectal cancer, for example, mutations in APC, axin, or β-catenin promote β-catenin stabilization and transcription of genes encoding cancer-associated proteins. Furthermore, in human breast cancer, interference with the de-regulated Wnt signaling pathway reduces proliferation and survival of cancer. These findings suggest that interference with Wnt signaling at the ligand-receptor level may improve the effectiveness of cancer therapies. | 1 | Biochemistry |
Ding Kuiling (; born March 1966) is a Chinese organic chemist. He has been Executive Vice President of Shanghai Jiao Tong University since October 2018, and formerly served as President of the Shanghai Institute of Organic Chemistry. He is an academician of the Chinese Academy of Sciences. | 0 | Organic Chemistry |
The NMR spectrum of the product formed from the reaction of the substrate with a CDA at room temperature is compared with one of the following: | 4 | Stereochemistry |
Neuromedin N is a neuropeptide derived from the same precursor polypeptide as neurotensin, and with similar but subtly distinct expression and effects. Composed of the amino acid sequence Lys-Ile-Pro-Tyr-Ile-Leu, neuromedin N is homologous to neurotensin, both of whose sequences are found on the pro neurotensin/neuromedin N precursor C-terminus. Both sequences of neuromedin N as well as neurotensin are flanked by Lys-Arg amino acids, which comprise a consensus sequence for the endoprotease proprotein convertase. Neuromedin N is primarily synthesized in the neural and intestinal tissues of mammals; in studies performed in mice, neuromedin Ns physiological effects were shown to include hypothermia and analgesia, arising from the peptides ligand association to and interaction with neurotensin type 2 (NTS2) G protein-coupled receptors. | 1 | Biochemistry |
In a sense, any spectrum analyzer that has vector signal analyzer capability is a realtime analyzer. It samples data fast enough to satisfy Nyquist Sampling theorem and stores the data in memory for later processing. This kind of analyser is only realtime for the amount of data / capture time it can store in memory and still produces gaps in the spectrum and results during processing time. | 7 | Physical Chemistry |
For U.S. food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For vitamin A labeling purposes 100% of the Daily Value was set at 5,000 IU, but it was revised to 900 μg RAE on 27 May 2016. A table of the old and new adult daily values is provided at Reference Daily Intake. | 1 | Biochemistry |
Radon concentration in the atmosphere is usually measured in becquerels per cubic meter (Bq/m), which is an SI derived unit. As a frame of reference, typical domestic exposures are about 100 Bq/m indoors and 10–20 Bq/m outdoors. In the US, radon concentrations are often measured in picocuries per liter (pCi/L), with 1 pCi/L = 37 Bq/m.
The mining industry traditionally measures exposure using the working level (WL) index, and the cumulative exposure in working level months (WLM): 1 WL equals any combination of short-lived progeny (, , , and ) in 1 liter of air that releases 1.3 × 10 MeV of potential alpha energy; one WL is equivalent to 2.08 × 10 joules per cubic meter of air (J/m). The SI unit of cumulative exposure is expressed in joule-hours per cubic meter (J·h/m). One WLM is equivalent to 3.6 × 10 J·h/m. An exposure to 1 WL for 1 working month (170 hours) equals 1 WLM cumulative exposure.
A cumulative exposure of 1 WLM is roughly equivalent to living one year in an atmosphere with a radon concentration of 230 Bq/m.
The radon () released into the air decays to and other radioisotopes. The levels of can be measured. The rate of deposition of this radioisotope is dependent on the weather. | 2 | Environmental Chemistry |
In biochemistry, intercalation is the insertion of molecules between the planar bases of deoxyribonucleic acid (DNA). This process is used as a method for analyzing DNA and it is also the basis of certain kinds of poisoning.
There are several ways molecules (in this case, also known as ligands) can interact with DNA. Ligands may interact with DNA by covalently binding, electrostatically binding, or intercalating. Intercalation occurs when ligands of an appropriate size and chemical nature fit themselves in between base pairs of DNA. These ligands are mostly polycyclic, aromatic, and planar, and therefore often make good nucleic acid stains. Intensively studied DNA intercalators include berberine, ethidium bromide, proflavine, daunomycin, doxorubicin, and thalidomide. DNA intercalators are used in chemotherapeutic treatment to inhibit DNA replication in rapidly growing cancer cells. Examples include doxorubicin (adriamycin) and daunorubicin (both of which are used in treatment of Hodgkins lymphoma), and dactinomycin (used in Wilms tumour, Ewing's Sarcoma, rhabdomyosarcoma).
Metallointercalators are complexes of a metal cation with polycyclic aromatic ligands. The most commonly used metal ion is ruthenium(II), because its complexes are very slow to decompose in the biological environment. Other metallic cations that have been used include rhodium(III) and iridium(III). Typical ligands attached to the metal ion are dipyridine and terpyridine whose planar structure is ideal for intercalation.
In order for an intercalator to fit between base pairs, the DNA must dynamically open a space between its base pairs by unwinding. The degree of unwinding varies depending on the intercalator; for example, ethidium cation (the ionic form of ethidium bromide found in aqueous solution) unwinds DNA by about 26°, whereas proflavine unwinds it by about 17°. This unwinding causes the base pairs to separate, or "rise", creating an opening of about 0.34 nm (3.4 Å). This unwinding induces local structural changes to the DNA strand, such as lengthening of the DNA strand or twisting of the base pairs. These structural modifications can lead to functional changes, often to the inhibition of transcription and replication and DNA repair processes, which makes intercalators potent mutagens. For this reason, DNA intercalators are often carcinogenic, such as the exo (but not the endo) 8,9 epoxide of aflatoxin B and acridines such as proflavine or quinacrine.
Intercalation as a mechanism of interaction between cationic, planar, polycyclic aromatic systems of the correct size (on the order of a base pair) was first proposed by Leonard Lerman in 1961. One proposed mechanism of intercalation is as follows: In aqueous isotonic solution, the cationic intercalator is attracted electrostatically to the surface of the polyanionic DNA. The ligand displaces a sodium and/or magnesium cation present in the "condensation cloud" of such cations that surrounds DNA (to partially balance the sum of the negative charges carried by each phosphate oxygen), thus forming a weak electrostatic association with the outer surface of DNA. From this position, the ligand diffuses along the surface of the DNA and may slide into the hydrophobic environment found between two base pairs that may transiently "open" to form an intercalation site, allowing the ethidium to move away from the hydrophilic (aqueous) environment surrounding the DNA and into the intercalation site. The base pairs transiently form such openings due to energy absorbed during collisions with solvent molecules. | 6 | Supramolecular Chemistry |
The recrystallization behavior of materials containing a wide distribution of particle sizes can be difficult to predict. This is compounded in alloys where the particles are thermally-unstable and may grow or dissolve with time. In various systems, abnormal grain growth may occur giving rise to unusually large crystallites growing at the expense of smaller ones. The situation is more simple in bimodal alloys which have two distinct particle populations. An example is Al-Si alloys where it has been shown that even in the presence of very large (<5 μm) particles the recrystallization behavior is dominated by the small particles (Chan & Humphreys 1984). In such cases the resulting microstructure tends to resemble one from an alloy with only small particles. | 8 | Metallurgy |
Due to the lone pair of electrons, halogen groups are available for donating electrons. Hence they are therefore ortho / para directors. | 0 | Organic Chemistry |
Natural fermentation predates human history. Since ancient times, humans have exploited the fermentation process. The earliest archaeological evidence of fermentation is 13,000-year-old residues of a beer, with the consistency of gruel, found in a cave near Haifa in Israel. Another early alcoholic drink, made from fruit, rice, and honey, dates from 7000 to 6600 BC, in the Neolithic Chinese village of Jiahu, and winemaking dates from ca. 6000 BC, in Georgia, in the Caucasus area. Seven-thousand-year-old jars containing the remains of wine, now on display at the University of Pennsylvania, were excavated in the Zagros Mountains in Iran. There is strong evidence that people were fermenting alcoholic drinks in Babylon ca. 3000 BC, ancient Egypt ca. 3150 BC, pre-Hispanic Mexico ca. 2000 BC, and Sudan ca. 1500 BC. | 1 | Biochemistry |
Most of the existing hydrophobicity scales are derived from the properties of amino acids in their free forms or as a part of a short peptide. Bandyopadhyay-Mehler hydrophobicity scale was based on partitioning of amino acids in the context of protein structure. Protein structure is a complex mosaic of various dielectric medium generated by arrangement of different amino acids. Hence, different parts of the protein structure most likely would behave as solvents with different dielectric values. For simplicity, each protein structure was considered as an immiscible mixture of two solvents, protein interior and protein exterior. The local environment around individual amino acid (termed as "micro-environment") was computed for both protein interior and protein exterior. The ratio gives the relative hydrophobicity scale for individual amino acids. Computation was trained on high resolution protein crystal structures. This quantitative descriptor for microenvironment was derived from the octanol-water partition coefficient, (known as Rekker's Fragmental Constants) widely used for pharmacophores. This scale well correlate with the existing methods, based on partitioning and free energy computations. Advantage of this scale is it is more realistic, as it is in the context of real protein structures. | 6 | Supramolecular Chemistry |
Thallium compounds such as thallium sulfate have been used for impregnating wood and leather to kill fungal spores and bacteria, and for the protection of textiles from attack by moths. Thallium sulfate has been used as a depilatory and in the treatment of venereal disease, skin fungal infections, and tuberculosis. | 1 | Biochemistry |
The sum of the mass concentrations of all components (including the solvent) gives the density of the solution:
Thus, for pure component the mass concentration equals the density of the pure component. | 3 | Analytical Chemistry |
The α-aminoadipate pathway is a biochemical pathway for the synthesis of the amino acid -lysine. In the eukaryotes, this pathway is unique to several species of yeast, higher fungi (containing chitin in their cell walls), and the euglenids. It has also been reported from bacteria of the genus Thermus and also in Pyrococcus horikoshii, potentially suggesting a wider distribution than previously thought. This uniqueness of the pathway makes it a potentially interesting target for antimycotics. | 1 | Biochemistry |
The Marchywka effect refers to electrochemical cleaning of diamond using an electric field induced with remote electrodes. | 7 | Physical Chemistry |
Mikhail Tsvet invented chromatography in 1900 during his research on plant pigments. He used liquid-adsorption column chromatography with calcium carbonate as adsorbent and petrol ether/ethanol mixtures as eluent to separate chlorophylls and carotenoids. The method was described on 30 December 1901 at the XI Congress of Naturalists and Physicians (XI съезд естествоиспытателей и врачей) in St. Petersburg. The first printed description was in 1905, in the Proceedings of the Warsaw Society of Naturalists, biology section. He first used the term "chromatography" in print in 1906 in his two papers about chlorophyll in the German botanical journal, Berichte der Deutschen botanischen Gesellschaft. In 1907 he demonstrated his chromatograph for the German Botanical Society.
For several reasons, Tsvets work was long ignored: the violent political upheaval in Russia at the beginning of the 20th century, the fact that Tsvet originally published only in Russian (making his results largely inaccessible to western scientists), and an article denying Tsvets findings. Richard Willstätter and Arthur Stoll tried to repeat Tsvets experiments, but because they used an overly aggressive adsorbent (destroying the chlorophyll), were not able to do so. They published their results and Tsvets chromatography method fell into obscurity. It was revived 10 years after his death thanks to Austrian biochemist Richard Kuhn and his student, German scientist Edgar Lederer as well as the work of A. J. Martin and R. L. Synge. | 3 | Analytical Chemistry |
Although most plasmids are double-stranded DNA molecules, some consist of single-stranded DNA, or predominantly double-stranded RNA. RNA plasmids are non-infectious extrachromosomal linear RNA replicons, both encapsidated and unencapsidated, which have been found in fungi and various plants, from algae to land plants. In many cases, however, it may be difficult or impossible to clearly distinguish RNA plasmids from RNA viruses and other infectious RNAs. | 1 | Biochemistry |
Addition across the unsaturated carbon-carbon bond can be Markovnikov or anti-Markovnikov depending on the catalyst. When considering the possibly of R/S chirality, four products can be obtained: Markovnikov with R or S and anti-Markovnikov addition with R or S. Although there have been many reports of catalytic hydroamination with a wide range of metals, there are far fewer describing enantioselective catalysis to selectively make one of the four possible products. Recently, there have been reports of selectively making the thermodynamic or kinetic product, which can be related to the racemic Markovnikov or anti-Markovnikov structures (see Thermodynamic and Kinetic Product below). | 0 | Organic Chemistry |
Yu was awarded a Royal Society University Research Fellowship in 2003, which allowed him to start his independent research towards the development of asymmetric C–H activation reactions. In 2004, he moved to Brandeis University as an assistant professor of chemistry. He moved to The Scripps Research Institute as an associate professor in 2007 and was promoted to full professor in 2010. In 2012, he was appointed the Frank and Bertha Hupp Professor of Chemistry. | 0 | Organic Chemistry |
Metal aromaticity or metalloaromaticity is the concept of aromaticity, found in many organic compounds, extended to metals and metal-containing compounds. The first experimental evidence for the existence of aromaticity in metals was found in aluminium cluster compounds of the type where M stands for lithium, sodium or copper. These anions can be generated in a helium gas by laser vaporization of an aluminium / lithium carbonate composite or a copper or sodium / aluminium alloy, separated and selected by mass spectrometry and analyzed by photoelectron spectroscopy. The evidence for aromaticity in these compounds is based on several considerations. Computational chemistry shows that these aluminium clusters consist of a tetranuclear plane and a counterion at the apex of a square pyramid. The unit is perfectly planar and is not perturbed the presence of the counterion or even the presence of two counterions in the neutral compound . In addition its HOMO is calculated to be a doubly occupied delocalized pi system making it obey Hückel's rule. Finally a match exists between the calculated values and the experimental photoelectron values for the energy required to remove the first 4 valence electrons. The first fully metal aromatic compound was a cyclogallane with a Ga core discovered by Gregory Robinson in 1995.
D-orbital aromaticity is found in trinuclear tungsten and molybdenum metal clusters generated by laser vaporization of the pure metals in the presence of oxygen in a helium stream. In these clusters the three metal centers are bridged by oxygen and each metal has two terminal oxygen atoms. The first signal in the photoelectron spectrum corresponds to the removal of the valence electron with the lowest energy in the anion to the neutral compound. This energy turns out to be comparable to that of bulk tungsten trioxide and molybdenum trioxide. The photoelectric signal is also broad which suggests a large difference in conformation between the anion and the neutral species. Computational chemistry shows that the anions and dianions are ideal hexagons with identical metal-to-metal bond lengths. Tritantalum oxide clusters (TaO) also are observed to exhibit possible D-orbital aromaticity.
The molecules discussed thus far only exist diluted in the gas phase. A study exploring the properties of a compound formed in water from sodium molybdate () and iminodiacetic acid also revealed evidence of aromaticity, but this compound has actually been isolated. X-ray crystallography showed that the sodium atoms are arranged in layers of hexagonal clusters akin to pentacenes. The sodium-to-sodium bond lengths are unusually short (327 pm versus 380 pm in elemental sodium) and, like benzene, the ring is planar. In this compound each sodium atom has a distorted octahedral molecular geometry with coordination to molybdenum atoms and water molecules. The experimental evidence is supported by computed NICS aromaticity values. | 7 | Physical Chemistry |
The oldest surviving Watt engine is Old Bess of 1777, now in the Science Museum, London.
The oldest working engine in the world is the Smethwick Engine, brought into service in May 1779 and now at Thinktank in Birmingham (formerly at the now defunct Museum of Science and Industry, Birmingham).
The oldest still in its original engine house and still capable of doing the job for which it was installed is the 1812 Boulton and Watt engine at the Crofton Pumping Station in Wiltshire. This was used to pump water for the Kennet and Avon Canal; on certain weekends throughout the year the modern pumps are switched off and the two steam engines at Crofton still perform this function.
The oldest extant rotative steam engine, the Whitbread Engine (from 1785, the third rotative engine ever built), is located in the Powerhouse Museum in Sydney, Australia.
A Boulton-Watt engine of 1788 may be found in the Science Museum, London, while an 1817 blowing engine, formerly used at the Netherton ironworks of M W Grazebrook now decorates Dartmouth Circus, a traffic island at the start of the A38(M) motorway in Birmingham.
The Henry Ford Museum in Dearborn, Michigan houses a replica of a 1788 Watt rotative engine. It is a full-scale working model of a Boulton-Watt engine. The American industrialist Henry Ford commissioned the replica engine from the English manufacturer Charles Summerfield in 1932. The museum also holds an original Boulton and Watt atmospheric pump engine, originally used for canal pumping in Birmingham, illustrated below, and in use in situ at the Bowyer Street pumping station, from 1796 until 1854, and afterwards removed to Dearborn in 1929.
An other one is preserved at Fumel factory, France. | 7 | Physical Chemistry |
Pets, especially dogs, can contribute to fecal contamination of surface waters. Runoff from roads, parking lots, and yards can carry animal wastes to streams through storm sewers. Birds can be a significant source of fecal coliform bacteria. Swans, geese, seagulls, and other waterfowl can all elevate bacterial counts, especially in wetlands, lakes, ponds, and rivers. | 3 | Analytical Chemistry |
Dioxane is used in a variety of applications as a versatile aprotic solvent, e. g. for inks, adhesives, and cellulose esters. It is substituted for tetrahydrofuran (THF) in some processes, because of its lower toxicity and higher boiling point (101 °C, versus 66 °C for THF).
While diethyl ether is rather insoluble in water, dioxane is miscible and in fact is hygroscopic. At standard pressure, the mixture of water and dioxane in the ratio 17.9:82.1 by mass is a positive azeotrope that boils at 87.6 C.
The oxygen atoms are weakly Lewis-basic. It forms adducts with a variety of Lewis acids. It is classified as a hard base and its base parameters in the ECW model are E =1.86 and C = 1.29.
Dioxane produces coordination polymers by linking metal centers. In this way, it is used to drive the Schlenk equilibrium, allowing the synthesis of dialkyl magnesium compounds. Dimethylmagnesium is prepared in this manner:
:2 CHMgBr + (CHO) → MgBr(CHO) + (CH)Mg | 6 | Supramolecular Chemistry |
Since the late 1970s, the use of CFCs has been heavily regulated because of their destructive effects on the ozone layer. After the development of his electron capture detector, James Lovelock was the first to detect the widespread presence of CFCs in the air, finding a mole fraction of 60 ppt of CFC-11 over Ireland. In a self-funded research expedition ending in 1973, Lovelock went on to measure CFC-11 in both the Arctic and Antarctic, finding the presence of the gas in each of 50 air samples collected, and concluding that CFCs are not hazardous to the environment. The experiment did however provide the first useful data on the presence of CFCs in the atmosphere. The damage caused by CFCs was discovered by Sherry Rowland and Mario Molina who, after hearing a lecture on the subject of Lovelocks work, embarked on research resulting in the first publication suggesting the connection in 1974. It turns out that one of CFCs most attractive features—their low reactivity—is key to their most destructive effects. CFCs lack of reactivity gives them a lifespan that can exceed 100 years, giving them time to diffuse into the upper stratosphere. Once in the stratosphere, the suns ultraviolet radiation is strong enough to cause the homolytic cleavage of the C-Cl bond. In 1976, under the Toxic Substances Control Act, the EPA banned commercial manufacturing and use of CFCs and aerosol propellants. This was later superseded in the 1990 amendments to the Clean Air Act to address stratospheric ozone depletion.
By 1987, in response to a dramatic seasonal depletion of the ozone layer over Antarctica, diplomats in Montreal forged a treaty, the Montreal Protocol, which called for drastic reductions in the production of CFCs. On 2 March 1989, 12 European Community nations agreed to ban the production of all CFCs by the end of the century. In 1990, diplomats met in London and voted to significantly strengthen the Montreal Protocol by calling for a complete elimination of CFCs by 2000. By 2010, CFCs should have been completely eliminated from developing countries as well.
Because the only CFCs available to countries adhering to the treaty is from recycling, their prices have increased considerably. A worldwide end to production should also terminate the smuggling of this material. However, there are current CFC smuggling issues, as recognized by the United Nations Environmental Programme (UNEP) in a 2006 report titled "Illegal Trade in Ozone Depleting Substances". UNEP estimates that between 16,000–38,000 tonnes of CFCs passed through the black market in the mid-1990s. The report estimated between 7,000 and 14,000 tonnes of CFCs are smuggled annually into developing countries. Asian countries are those with the most smuggling; as of 2007, China, India and South Korea were found to account for around 70% of global CFC production, South Korea later to ban CFC production in 2010. Possible reasons for continued CFC smuggling were also examined: the report noted that many of the refrigeration systems that were designed to be operated utilizing the banned CFC products have long lifespans and continue to operate. The cost of replacing the equipment of these items is sometimes cheaper than outfitting them with a more ozone-friendly appliance. Additionally, CFC smuggling is not considered a significant issue, so the perceived penalties for smuggling are low. In 2018 public attention was drawn to the issue, that at an unknown place in east Asia an estimated amount of 13,000 metric tons annually of CFCs have been produced since about 2012 in violation of the protocol. While the eventual phaseout of CFCs is likely, efforts are being taken to stem these current non-compliance problems.
By the time of the Montreal Protocol, it was realised that deliberate and accidental discharges during system tests and maintenance accounted for substantially larger volumes than emergency discharges, and consequently halons were brought into the treaty, albeit with many exceptions. | 2 | Environmental Chemistry |
Nucleoside diphosphate (NDP) kinase catalyzes in vivo ATP-dependent synthesis of ribo- and deoxyribonucleoside triphosphates. In mutated Escherichia coli that had a disrupted nucleoside diphosphate kinase, adenylate kinase performed dual enzymatic functions. ADK complements nucleoside diphosphate kinase deficiency. | 1 | Biochemistry |
The model is based on seasonal input data and returns seasonal outputs. The number of seasons per year can be chosen between a minimum of one and a maximum of four. One can distinguish for example dry, wet, cold, hot, irrigation or fallow seasons. Reasons of not using smaller input/output periods are:
#short-term (e.g., daily) inputs would require much information, which, in large areas, may not be readily available;
#short-term outputs would lead to immense output files, which would be difficult to manage and interpret;
#this model is especially developed to predict long-term trends, and predictions for the future are more reliably made on a seasonal (long-term) than on a daily (short-term) basis, due to the high variability of short-term data;
#though the precision of the predictions for the future may be limited, a lot is gained when the trend is sufficiently clear. For example, it need not be a major constraint to the design of appropriate soil salinity control measures when a certain salinity level, predicted by SahysMod to occur after 20 years, will in reality occur after 15 or 25 years. | 9 | Geochemistry |
Conserved cycles in a biochemical network can be identified by examination of the stoichiometry matrix, The stoichiometry matrix for a simple cycle with species A and AP is given by:
The rates of change of A and AP can be written using the equation:
Expanding the expression leads to:
Note that . This means that , where is the total mass of moiety .
Given an arbitrary system:
elementary row operations can be applied to both sides such that the stoichiometric matrix is reduced to its echelon form, giving:
The elementary operations are captured in the matrix. We can partition to match the echelon matrix where the zero rows begin such that:
By multiplying out the lower partition, we obtain:
The matrix will contain entries corresponding to the conserved cycle participants. | 1 | Biochemistry |
Multiple isoforms of the Fas receptor protein are produced by alternative splicing. Two normally occurring isoforms in humans are produced by an exon-skipping mechanism. An mRNA including exon 6 encodes the membrane-bound form of the Fas receptor, which promotes apoptosis, or programmed cell death. Increased expression of Fas receptor in skin cells chronically exposed to the sun, and absence of expression in skin cancer cells, suggests that this mechanism may be important in elimination of pre-cancerous cells in humans. If exon 6 is skipped, the resulting mRNA encodes a soluble Fas protein that does not promote apoptosis. The inclusion or skipping of the exon depends on two antagonistic proteins, TIA-1 and polypyrimidine tract-binding protein (PTB).
* The 5' donor site in the intron downstream from exon 6 in the pre-mRNA has a weak agreement with the consensus sequence, and is not bound usually by the U1 snRNP. If U1 does not bind, the exon is skipped (see "a" in accompanying figure).
* Binding of TIA-1 protein to an intronic splicing enhancer site stabilizes binding of the U1 snRNP. The resulting 5 donor site complex assists in binding of the splicing factor U2AF to the 3 splice site upstream of the exon, through a mechanism that is not yet known (see b).
* Exon 6 contains a pyrimidine-rich exonic splicing silencer, ure6, where PTB can bind. If PTB binds, it inhibits the effect of the 5' donor complex on the binding of U2AF to the acceptor site, resulting in exon skipping (see c).
This mechanism is an example of exon definition in splicing. A spliceosome assembles on an intron, and the snRNP subunits fold the RNA so that the 5 and 3 ends of the intron are joined. However, recently studied examples such as this one show that there are also interactions between the ends of the exon. In this particular case, these exon definition interactions are necessary to allow the binding of core splicing factors prior to assembly of the spliceosomes on the two flanking introns. | 1 | Biochemistry |
Woodward and Hoffmann developed the pericyclic selection rules after performing extensive orbital-overlap calculations. At the time, Woodward wanted to know whether certain electrocyclic reactions might help synthesize vitamin B. Chemists knew that such reactions exhibited striking stereospecificity, but could not predict which stereoisomer a reaction might select. In 1965, Woodward–Hoffmann realized that a simple set of rules explained the observed stereospecificity at the ends of open-chain conjugated polyenes when heated or irradiated. In their original publication, they summarized the experimental evidence and molecular orbital analysis as follows:
*In an open-chain system containing 4n π electrons, the orbital symmetry of the highest occupied molecule orbital is such that a bonding interaction between the ends must involve overlap between orbital envelopes on opposite faces of the system and this can only be achieved in a conrotatory process.
*In open systems containing (4n + 2) π electrons, terminal bonding interaction within ground-state molecules requires overlap of orbital envelopes on the same face of the system, attainable only by disrotatory displacements.
*In a photochemical reaction an electron in the HOMO of the reactant is promoted to an excited state leading to a reversal of terminal symmetry relationships and stereospecificity.
In 1969, they would use correlation diagrams to state a generalized pericyclic selection rule equivalent to that now attached to their name: a pericyclic reaction is allowed if the sum of the number of suprafacial 4q + 2 components and number of antarafacial 4r components is odd. .
In the intervening four years, Howard Zimmerman and Michael J. S. Dewar proposed an equally general conceptual framework: the Möbius-Hückel concept, or aromatic transition state theory. In the Dewar-Zimmerman approach the orbital overlap topology (Hückel or Möbius) and electron count (4n + 2 or 4n) results in either an aromatic or antiaromatic transition state.
Meanwhile, Kenichi Fukui analyzed the frontier orbitals of such systems. A process in which the HOMO-LUMO interaction is constructive (results in a net bonding interaction) is favorable and considered symmetry-allowed, while a process in which the HOMO-LUMO interaction is non-constructive (results in bonding and antibonding interactions that cancel) is disfavorable and considered symmetry-forbidden.
Though conceptually distinct, aromatic transition state theory (Zimmerman and Dewar), frontier molecular orbital theory (Fukui), and orbital symmetry conservation (Woodward and Hoffmann) all make identical predictions. The Woodward–Hoffmann rules exemplify molecular orbital theory's power, and indeed helped demonstate that useful chemical results could arise from orbital analysis. The discovery would earn Hoffmann and Fukui the 1981 Nobel Prize in Chemistry. By that time, Woodward had died, and so was ineligible for the prize. | 7 | Physical Chemistry |
Interferome is managed by a team at Monash University :Monash Institute of Medical Research and the University of Cambridge | 1 | Biochemistry |
An environment's plasmidome refers to the plasmids present in it.
The term is a portmanteau of the two English words Plasmid and Kingdom.
In biological research, plasmidome may refer to the actual plasmids that were found and isolated from a certain microorganism by means of culturing isolated microorganism and investigating the plasmids it possesses or by taking an environmental sample and performing a metagenomic survey using next generation sequencing methods in order to reveal and characterize plasmid genomes that belong to that environment. | 1 | Biochemistry |
To describe dynamics of the systems that obey the generalized mass action law, one has to represent the activities as functions of the concentrations c and temperature. For this purpose, use the representation of the activity through the chemical potential:
where μ is the chemical potential of the species under the conditions of interest, is the chemical potential of that species in the chosen standard state, R is the gas constant and T is the thermodynamic temperature.
The chemical potential can be represented as a function of c and T, where c is the vector of concentrations with components c. For the ideal systems, and : the activity is the concentration and the generalized mass action law is the usual law of mass action.
Consider a system in isothermal (T=const) isochoric (the volume V=const) condition. For these conditions, the Helmholtz free energy measures the “useful” work obtainable from a system. It is a functions of the temperature T, the volume V and the amounts of chemical components N (usually measured in moles), N is the vector with components N. For the ideal systems,
The chemical potential is a partial derivative: .
The chemical kinetic equations are
If the principle of detailed balance is valid then for any value of T there exists a positive point of detailed balance c:
Elementary algebra gives
where
For the dissipation we obtain from these formulas:
The inequality holds because ln is a monotone function and, hence, the expressions and have always the same sign.
Similar inequalities are valid for other classical conditions for the closed systems and the corresponding characteristic functions: for isothermal isobaric conditions the Gibbs free energy decreases, for the isochoric systems with the constant internal energy (isolated systems) the entropy increases as well as for isobaric systems with the constant enthalpy. | 7 | Physical Chemistry |
A pulsed Fourier-transform spectrometer does not employ transmittance techniques. In the most general description of pulsed FT spectrometry, a sample is exposed to an energizing event which causes a periodic response. The frequency of the periodic response, as governed by the field conditions in the spectrometer, is indicative of the measured properties of the analyte. | 7 | Physical Chemistry |
An advantage of the microscope spectrometer is its ability to use microscope apertures to precisely control the area of sample analysis. Flat capillaries can be used for analyzing small liquid samples, up to about 10 micro-liters in volume. Quartz or mirror-based optics can be used for studying samples from the ultraviolet (UV), down to 200 nm, to the near infrared (NIR) up to 2100 nm. Samples that emit electromagnetic radiation via fluorescence, phosphorescence or photoluminescence when exposed to light, can be quantitatively investigated using a variety of excitation and barrier filters. A variety of observations can be made on samples of interest by using different illumination sources such as halogen, xenon, deuterium and mercury lamps. Plane polarized light can also be used for studying birefringent samples. | 7 | Physical Chemistry |
At 15 GPa graphite changes to a hard transparent form, that is not diamond. Diamond is very resistant to pressure, but at about 1 TPa (1000 GPa) transforms to a BC-8 form. | 9 | Geochemistry |
Sodium methoxide, also called sodium methylate and sodium methanolate, is a white powder when pure. It is used as an initiator of an anionic addition polymerization with ethylene oxide, forming a polyether with high molecular weight. Both sodium methoxide and its counterpart prepared with potassium are frequently used as catalysts for commercial-scale production of biodiesel. In this process, vegetable oils or animal fats, which chemically are fatty acid triglycerides, are transesterified with methanol to give fatty acid methyl esters (FAMEs).
Sodium methoxide is produced on an industrial scale and available from a number of chemical companies. | 0 | Organic Chemistry |
Contact between a contaminant and an organism can occur through any route. The possible routes of exposure are: inhalation, if the contaminant is present in the air; ingestion, through food, drinking or hand-to-mouth behavior; and dermal absorption, if the contaminant can be absorbed through the skin.
Exposure to a contaminant can and does occur through multiple routes, simultaneously or at different times. In many cases the main route of exposure is not obvious and needs to be investigated carefully. For example, exposure to byproducts of water chlorination can obviously occur by drinking, but also through the skin, while swimming or washing, and even through inhalation from droplets aerosolized during a shower. The relative proportion of exposure from these different routes cannot be determined a priori. Therefore, the equation in the previous section is correct in a strict mathematical sense, but it is a gross oversimplification of actual exposures, which are the sum of the integrals of all activities in all microenvironments. For example, the equation would have to be calculated with the specific concentration of a compound in the air in the room during the time interval. Similarly, the concentration in the ambient air would apply to the time that the person spends outdoors, whereas the concentration in the food that the person ingests would be added. The concentration integrals via all routes would be added for the exposure duration, e.g. hourly, daily or annually as
where is the initial time and the ending time of last in the series of time periods spent in each microenvironment over the exposure duration. | 2 | Environmental Chemistry |
Because of the decreased basicity compared to pyridine, electrophilic substitution of pyrimidine is less facile. Protonation or alkylation typically takes place at only one of the ring nitrogen atoms. Mono-N-oxidation occurs by reaction with peracids.
Electrophilic C-substitution of pyrimidine occurs at the 5-position, the least electron-deficient. Nitration, nitrosation, azo coupling, halogenation, sulfonation, formylation, hydroxymethylation, and aminomethylation have been observed with substituted pyrimidines.
Nucleophilic C-substitution should be facilitated at the 2-, 4-, and 6-positions but there are only a few examples. Amination and hydroxylation have been observed for substituted pyrimidines. Reactions with Grignard or alkyllithium reagents yield 4-alkyl- or 4-aryl pyrimidine after aromatization.
Free radical attack has been observed for pyrimidine and photochemical reactions have been observed for substituted pyrimidines. Pyrimidine can be hydrogenated to give tetrahydropyrimidine. | 1 | Biochemistry |
Tin extraction and use can be dated to the beginning of the Bronze Age around 3000 BC, during which copper objects formed from polymetallic ores had different physical properties. The earliest bronze objects had tin or arsenic content of less than 2% and are therefore believed to be the result of unintentional alloying due to trace metal content in copper ores such as tennantite, which contains arsenic. The addition of a second metal to copper increases its hardness, lowers the melting temperature, and improves the casting process by producing a more fluid melt that cools to a denser, less spongy metal. This was an important innovation that allowed for the much more complex shapes cast in closed molds of the Bronze Age. Arsenical bronze objects appear first in the Middle East where arsenic is commonly found in association with copper ore, but the health risks were quickly realized and the quest for sources of the much less hazardous tin ores began early in the Bronze Age. This created the demand for rare tin metal and formed a trade network that linked the distant sources of tin to the markets of Bronze Age cultures.
Cassiterite (SnO), oxidized tin, most likely was the original source of tin in ancient times. Other forms of tin ores are less abundant sulfides such as stannite that require a more involved smelting process. Cassiterite often accumulates in alluvial channels as placer deposits due to the fact that it is harder, heavier, and more chemically resistant than the granite in which it typically forms. These deposits can be easily seen in river banks, because cassiterite is usually black or purple or otherwise dark, a feature exploited by early Bronze Age prospectors. It is likely that the earliest deposits were alluvial and perhaps exploited by the same methods used for panning gold in placer deposits. | 8 | Metallurgy |
Many high-pressure, high-temperature materials have been observed in fulgurites. Many of these minerals and compounds are also known to be formed in extreme environments such as nuclear weapon tests, hypervelocity impacts, and interstellar space. Shocked quartz was first described in fulgurites in 1980. Other materials, including highly reduced silicon-metal alloys (silicides), the fullerene allotropes C (buckminsterfullerenes) and C, as well as high-pressure polymorphs of SiO, have since been identified in fulgurites.
Reduced phosphides have been identified in fulgurites, in the form of schreibersite ( and ), and titanium(III) phosphide. These reduced compounds are otherwise rare on Earth due to the presence of oxygen in Earth's atmosphere, which creates oxidizing surface conditions. | 9 | Geochemistry |
In 2020 a team at the University Hospital Heidelberg (Germany) re-gained the antibacterial power of vancomycin by modifying the molecule with a cationic oligopeptide. The oligopeptide consists of six arginin units in Position V. In comparison to the unmodified vancomycin the activity against vancomycin-resistant bacteria could be enhanced by a factor of 1,000. This pharmacon is still in preclinical development. | 0 | Organic Chemistry |
PCAF has been shown to interact with:
* BRCA2,
* CTNNB1,
* CREBBP,
* EVI1,
* HNF1A,
* IRF1,
* IRF2,
* KLF13,
* Mdm2
* Myc,
* NCOA1,
* POLR2A,
* RBPJ,
* TCF3,
* TRRAP, and
* TWIST1. | 1 | Biochemistry |
In conjunction with organosilicates, phosphonates are also used to treat "sudden oak death", which is caused by the fungus-like eukaryote Phytophthora ramorum. | 0 | Organic Chemistry |
Mitochondria and plastids evolved from free-living prokaryotes into current cytoplasmic organelles through endosymbiotic evolution. Mitochondria are thought to be necessary for eukaryotic life to exist. They are known as the cell's powerhouses because they provide the majority of the energy or ATP required by the cell. The mitochondrial genome (mtDNA) is replicated separately from the host genome. Human mtDNA codes for 13 proteins, most of which are involved in oxidative phosphorylation (OXPHOS). The nuclear genome encodes the remaining mitochondrial proteins, which are then transported into the mitochondria. The genomes of these organelles have become far smaller than those of their free-living predecessors. This is mostly due to the widespread transfer of genes from prokaryote progenitors to the nuclear genome, followed by their elimination from organelle genomes. In evolutionary timescales, the continuous entry of organelle DNA into the nucleus has provided novel nuclear genes. Furthermore, Mitochondria depend on nuclear genes for essential protein production as they cannot generate all necessary proteins independently. | 1 | Biochemistry |
Inductive cleavage, in organic chemistry, is the charge-initiated counterpoint to radical initiated alpha-cleavage. Since inductive cleavage does not require unpairing and re-pairing electrons it can occur at both radical cationic and cationic sites. | 0 | Organic Chemistry |
Increasing the substrate concentration increases the rate of reaction (enzyme activity). However, enzyme saturation limits reaction rates. An enzyme is saturated when the active sites of all the molecules are occupied most of the time. At the saturation point, the reaction will not speed up, no matter how much additional substrate is added. The graph of the reaction rate will plateau. | 1 | Biochemistry |
Low molecular weight polyols are widely used in polymer chemistry where they function as crosslinking agents and chain extenders. Alkyd resins for example, use polyols in their synthesis and are used in paints and in molds for casting. They are the dominant resin or "binder" in most commercial "oil-based" coatings. Approximately 200,000 tons of alkyd resins are produced each year. They are based on linking reactive monomers through ester formation. Polyols used in the production of commercial alkyd resins are glycerol, trimethylolpropane, and pentaerythritol. In polyurethane prepolymer production, a low molecular weight polyol-diol such as 1,4-butanediol may be used as a chain extender to further increase molecular weight though it does increase viscosity because more hydrogen bonding is introduced. | 7 | Physical Chemistry |
In physical chemistry, a hot atom is an atom that has a high kinetic or internal energy.
When molecule AB adsorbs on a surface dissociatively,
# both A and B adsorb on the surface, or
# only A adsorbs on the surface, and B desorbs from the surface.
In case 2, B gains a high translational energy from the adsorption energy of A, and hot atom B is generated. For example, the hydrogen molecule, because of its light mass, gets a high translational energy. Such a hot atom does not fly into vacuum but is trapped on the surface, where it diffuses with high energy.
Hot atoms are expected to play important roles in catalytic reactions. For example, a reaction of a hydrogen atom with hydrogen atoms on a silicon surface and a reaction of an oxygen atom with oxygen molecules on Pt(111) have been reported. Hot atoms can also be generated by degenerating molecules on a metal surface with UV light. It has been reported that the reactivity of an oxygen atom generated in such a way on a platinum surface is different from that of chemisorbed oxygen atoms. Elucidating the role of hot atoms on surfaces will lead to a deeper understanding of the mechanism of reactions. | 7 | Physical Chemistry |
Microcystins have a common structural framework of D-Ala-X--Z-Adda-D-γ-Glu-, where X and Z are variable amino acids; the systematic name "microcystin-XZ" (MC-XZ in short) is then assigned based on the one letter codes (if available; longer codes otherwise) of the amino acids. If the molecule show any other modification, the differences are noted in square brackets before "MC". Of these, several are uncommon non-proteinogenic amino acids:
* D-Masp is D-erythro-β-methyl-isoaspartic acid, a derivative of aspartic acid in β-amino acid form;
* Adda is (all-S,all-E)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid, a β-amino acid exclusively found in microcystin and the related nodularin;
* Mdha is N-methyldehydroalanine, a derivative of dehydroalanine. In nodularin it is replaced by Mdhb (N-methyldehydrobutyrine), another dehydroamino acid derivative. | 2 | Environmental Chemistry |
In chemistry, an activated complex represents a collection of intermediate structures in a chemical reaction when bonds are breaking and forming. The activated complex is an arrangement of atoms in an arbitrary region near the saddle point of a potential energy surface. The region represents not one defined state, but a range of unstable configurations that a collection of atoms pass through between the reactants and products of a reaction. Activated complexes have partial reactant and product character, which can significantly impact their behaviour in chemical reactions.
The terms activated complex and transition state are often used interchangeably, but they represent different concepts. Transition states only represent the highest potential energy configuration of the atoms during the reaction, while activated complex refers to a range of configurations near the transition state. In a reaction coordinate, the transition state is the configuration at the maximum of the diagram while the activated complex can refer to any point near the maximum.
Transition state theory (also known as activated complex theory) studies the kinetics of reactions that pass through a defined intermediate state with standard Gibbs energy of activation . The transition state, represented by the double dagger symbol represents the exact configuration of atoms that has an equal probability of forming either the reactants or products of the given reaction.
The activation energy is the minimum amount of energy to initiate a chemical reaction and form the activated complex. The energy serves as a threshold that reactant molecules must surpass to overcome the energy barrier and transition into the activated complex. Endothermic reactions absorb energy from the surroundings, while exothermic reactions release energy. Some reactions occur spontaneously, while others necessitate an external energy input. The reaction can be visualized using a reaction coordinate diagram to show the activation energy and potential energy throughout the reaction.
Activated complexes were first discussed in transition state theory (also called activated complex theory), which was first developed by Eyring, Evans, and Polanyi in 1935. | 7 | Physical Chemistry |
PARP1 is involved in base excision repair (BER), single- and double-strand break repair, and chromosomal stability. It is also involved in transcriptional regulation through its facilitation of protein–protein interactions. PARP1 uses NAD in order to perform its function in apoptosis. If a PARP becomes overactive the cell will have decreased levels of NAD cofactor as well as decreased levels of ATP and thus will undergo necrosis. This is important in carcinogenesis because it could lead to the selection of PARP1 deficient cells (but not depleted) due to their survival advantage during cancer growth.
Susceptibility to carcinogenesis under PARP1 deficiency depends significantly on the type of DNA damage incurred. There are many implications that various PARPs are involved in preventing carcinogenesis. As stated previously, PARP1 and PARP2 are involved in BER and chromosomal stability. PARP3 is involved in centrosome regulation. Tankyrase is another (ADP-ribosyl)polymerase that is involved in telomere length regulation.
PARP1 inhibition has also been widely studied in anticancer therapeutics. The mechanism of action of a PARP1 inhibitor is to enhance the damage done by chemotherapy on the cancerous DNA by disallowing the reparative function of PARP1 in BRCA1/2 deficient individuals .
PARP14 is another ADP-ribosylating enzyme that has been well-studied in regards to cancer therapy targets; it is a signal transducer and activator of STAT6 transcription-interacting protein, and was shown to be associated with the aggressiveness of B-cell lymphomas. | 1 | Biochemistry |
Biosensors are attached to a substance of interest. Normally, this substance would not be able to absorb light, but with the attached biosensor, light can be absorbed and emitted on a spectrophotometer. Additionally, biosensors that are fluorescent can be viewed with the naked eye. Some fluorescent biosensors also have the ability to change color in changing environments (ex: from blue to red). A researcher would be able to inspect and get data about the surrounding environment based on what color he or she could see visibly from the biosensor-molecule hybrid species.
Colorimetric assays are normally used to determine how much concentration of one species there is relative to another. | 1 | Biochemistry |
Tablets are small, solid dosages suitable for the use of mucoadhesive coatings. The coating may be formulated to adhere to a specific mucosa, enabling both systemic and targeted local administration. Tablets are generally taken enterally, as the size and stiffness of the form results in poor patient compliance when administered through other routes. | 1 | Biochemistry |
After receiving his Ph.D., Herman T. Briscoe was appointed assistant professor of chemistry at Indiana University, working his way to professor of chemistry in 1928. Throughout his career, Briscoe authored or coauthored 23 publications on conductivity, physical properties, and the reactions of organic and inorganic molecules, supervised the graduate studies of 25 students, and published several general chemistry textbooks.
In 1938, President of Indiana University Herman B. Wells appointed Briscoe as the secretary of the newly established self-survey committee, which sought the feedback of faculty and proposed administrative changes accordingly. In the same year, Briscoe was appointed Chairman of the Department of Chemistry of Indiana University following the recommendation of retiring Chairman Robert E. Lyons. Herman Briscoe would continue on to become Indiana University's first Dean of Faculties in 1939 and Vice President of Indiana University in 1940. Briscoe gave up his appointment as Chairman of the Department of Chemistry in order to focus on his administrative roles as Vice President and Dean of Faculties, in which he served until his retirement in 1959. | 3 | Analytical Chemistry |
Rutherford backscattering spectrometry is named after Lord Rutherford, a physicist sometimes referred to as the father of nuclear physics. Rutherford supervised a series of experiments carried out by Hans Geiger and Ernest Marsden between 1909 and 1914 studying the scattering of alpha particles through metal foils. While attempting to eliminate "stray particles" they believed to be caused by an imperfection in their alpha source, Rutherford suggested that Marsden attempt to measure backscattering from a gold foil sample. According to the then-dominant plum-pudding model of the atom, in which small negative electrons were spread through a diffuse positive region, backscattering of the high-energy positive alpha particles should have been nonexistent. At most small deflections should occur as the alpha particles passed almost unhindered through the foil. Instead, when Marsden positioned the detector on the same side of the foil as the alpha particle source, he immediately detected a noticeable backscattered signal. According to Rutherford, "It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you."
Rutherford interpreted the result of the Geiger–Marsden experiment as an indication of a Coulomb collision with a single massive positive particle. This led him to the conclusion that the atoms positive charge could not be diffuse but instead must be concentrated in a single massive core: the atomic nucleus. Calculations indicated that the charge necessary to accomplish this deflection was approximately 100 times the charge of the electron, close to the atomic number of gold. This led to the development of the Rutherford model of the atom in which a positive nucleus made up of Ne positive particles, or protons, was surrounded by N' orbiting electrons of charge -e to balance the nuclear charge. This model was eventually superseded by the Bohr atom, incorporating some early results from quantum mechanics.
If the energy of the incident particle is increased sufficiently, the Coulomb barrier is exceeded and the wavefunctions of the incident and struck particles overlap. This may result in nuclear reactions in certain cases, but frequently the interaction remains elastic, although the scattering cross-sections may fluctuate wildly as a function of energy and no longer be calculable analytically. This case is known as "Elastic (non-Rutherford) Backscattering Spectrometry" (EBS). There has recently been great progress in determining EBS scattering cross-sections, by solving Schrödinger's equation for each interaction. However, for the EBS analysis of matrices containing light elements, the utilization of experimentally measured scattering cross-section data is also considered to be a very credible option. | 7 | Physical Chemistry |
It is prepared by disulfonation of naphthalene with oleum:
:CH + 2 SO → CH(SOH)
Further sulfonation gives The 1,3,5-trisulfonic acid derivative. | 0 | Organic Chemistry |
An inverted repeat sequence with no intervening nucleotides between the initial sequence and its downstream reverse complement is a palindrome. <br /> EXAMPLE:<br />
Step 1: start with an inverted repeat: <br />
Step 2: remove intervening nucleotides: <br />
This resulting sequence is palindromic because it is the reverse complement of itself.
::: test sequence (from Step 2 with intervening nucleotides removed)
::: complement of test sequence
::: reverse complement This is the same as the test sequence above, and thus, it is a palindrome. | 1 | Biochemistry |
Hydrolysis of a silyl enol ether results in the formation of a carbonyl compound and a disiloxane. In this reaction, water acts as an oxygen nucleophile and attacks the silicon of the silyl enol ether. This leads to the formation of the carbonyl compound and a trimethylsilanol intermediate that undergoes nucleophilic substitution at silicon (by another trimethylsilanol) to give the disiloxane. | 0 | Organic Chemistry |
The word electrolyte derives from Ancient Greek ήλεκτρο- (ēlectro-), prefix related to electricity, and λυτός (lytos), meaning "able to be untied or loosened". | 7 | Physical Chemistry |
For individuals not previously exposed to OC effects, the general feelings after being sprayed can be best likened to being "set alight". The initial reaction, should the spray be directed at the face, is the involuntary closing of the eyes, an instant sensation of the restriction of the airways and the general feeling of sudden and intense searing pain about the face, nose, and throat. This is due to irritation of mucous membranes. Many people experience fear and are disoriented due to sudden restriction of vision even though it is temporary. There is associated shortness of breath, although studies performed with asthmatics have not produced any asthma attacks in those individuals, and monitoring is still needed for the individuals after exposure. Police are trained to repeatedly instruct targets to breathe normally if they complain of difficulty, as the shock of the exposure can generate considerable panic as opposed to actual physical symptoms. | 1 | Biochemistry |
Bacterial populations interact in a similar manner to cells in tissue. They communicate through physical interactions and signaling molecules such as homoserine lactones and peptides as a means to control metabolism and regulate growth . A common example and one of the most studied forms of bacterial cell interactions is biofilm. Biofilm is a cell aggregate that can be attached to biological or abiotic surfaces. Bacteria form biofilms to adapt to various environments such as changes in substrate availability. For example, the formation of biofilm increases a bacterial cell's resistance to antibiotics compared to cells which are not part of the aggregate. | 1 | Biochemistry |
He became a member of the legislative assembly of the self-governing Colony of Victoria as a radical and supporter of the Land Convention, representing Castlemaine.
He was postmaster-general of Victoria in 1861. He resigned from the legislature in 1864. He had sponsored bills on medical practitioners and adulteration of food which became law in 1862 and 1863. | 3 | Analytical Chemistry |
In the general case of two convex bodies, the effective radius can be expressed as follows
where R and R" are the principal radii of curvature for the surfaces i' = 1 and 2, evaluated at points of closest approach distance, and φ is the angle between the planes spanned by the circles with smaller curvature radii. When the bodies are non-spherical around the position of closest approach, a torque between the two bodies develops and is given by
where
The above expressions for two spheres are recovered by setting R = R" = R. The torque vanishes in this case.
The expression for two perpendicularly crossing cylinders is obtained from R = R and R"' → ∞. In this case, torque will tend to orient the cylinders perpendicularly for repulsive forces.
For attractive forces, the torque will tend to align them.
These general formulas have been used to evaluate approximate interaction forces between ellipsoids. | 7 | Physical Chemistry |
As a long-acting injection, zuclopenthixol decanoate comes in a 200 mg and 500 mg ampoule. Doses can vary from 50 mg weekly to the maximum licensed dose of 600 mg weekly. In general, the lowest effective dose to prevent relapse is preferred. The interval may be shorter as a patient starts on the medication before extending to 3 weekly intervals subsequently. The dose should be reviewed and reduced if side effects occur, though in the short-term an anticholinergic medication benztropine may be helpful for tremor and stiffness, while diazepam may be helpful for akathisia. 100 mg of zuclopenthixol decanoate is roughly equivalent to 20 mg of flupentixol decanoate or 12.5 mg of fluphenazine decanoate.
In acutely psychotic and agitated inpatients, 50 – 200 mg of zuclopenthixol acetate may be given for a calming effect over the subsequent three days, with a maximum dose of 400 mg in total to be given. As it is a long-acting medication, care must be taken not to give an excessive dose.
In oral form zuclopenthixol is available in 2, 10, 25 and 40 mg tablets, with a dose range of 20–60 mg daily. | 4 | Stereochemistry |
The decline of filter-feeding shellfish populations, such as oysters, likely contribute to HAB occurrence. As such, numerous research projects are assessing the potential of restored shellfish populations to reduce HAB occurrence. | 3 | Analytical Chemistry |
The term "environmental toxin" can sometimes explicitly include synthetic contaminants such as industrial pollutants and other artificially made toxic substances. As this contradicts most formal definitions of the term "toxin", it is important to confirm what the researcher means when encountering the term outside of microbiological contexts.
Environmental toxins from food chains that may be dangerous to human health include:
* Paralytic shellfish poisoning (PSP)
* Amnesic shellfish poisoning (ASP)
* Diarrheal shellfish poisoning (DSP)
* Neurotoxic shellfish poisoning (NSP) | 1 | Biochemistry |
Sarıçiftçi has published more than 500 scientific publications in scientific journals. He is one of the most cited scientists in his field. In a global ranking of the best materials scientists Sarıçiftçi was classified as 14th. | 7 | Physical Chemistry |
The Thorpe–Ingold effect, gem-dimethyl effect, or angle compression is an effect observed in chemistry where increasing steric hindrance favours ring closure and intramolecular reactions. The effect was first reported by Beesley, Thorpe, and Ingold in 1915 as part of a study of cyclization reactions. It has since been generalized to many areas of chemistry.
The comparative rates of lactone formation (lactonization) of various 2-hydroxybenzenepropionic acids illustrate the effect. The placement of an increasing number of methyl groups accelerates the cyclization process.
One application of this effect is addition of a quaternary carbon (e.g., a gem-dimethyl group) in an alkyl chain to increase the reaction rate and/or equilibrium constant of cyclization reactions. An example of this is an olefin metathesis reaction: In the field of peptide foldamers, amino acid residues containing quaternary carbons such as 2-aminoisobutyric acid are used to promote formation of certain types of helices.
One proposed explanation for this effect is that the increased size of the substituents increases the angle between them. As a result, the angle between the other two substituents decreases. By moving them closer together, reactions between them are accelerated. It is thus a kinetic effect.
The effect also has some thermodynamic contribution as the in silico strain energy decreases on going from cyclobutane to 1-methylcyclobutane and 1,1-dimethylcyclobutane by a value between 8 kcal/mole and 1.5 kcal/mole.
A noteworthy example of the Thorpe-Ingold effect in supramolecular catalysis is given by diphenylmethane derivatives provided with guanidinium groups. These compounds are active in the cleavage of the RNA model compound HPNP. Substitution of the methylene group of the parent diphenylmethane spacer with cyclohexylidene and adamantylidene moieties enhances catalytic efficiency, with gem dialkyl effect accelerations of 4.5 and 9.1, respectively. | 4 | Stereochemistry |
It was not until 1666 that Isaac Newton showed that white lights from the sun could be dissipated into a continuous series of colors. So Newton introduced the concept which he called spectrum to describe this phenomenon. He used a small aperture to define the beam of light, a lens to collimate it, a glass prism to disperse it, and a screen to display the resulting spectrum. Newtons analysis of light was the beginning of the science of Later, It became clear that the Suns radiation might have components outside the visible portion of the spectrum. In 1800 William Hershel showed that the suns radiation extended into [https://www.livescience.com/50260-infrared-radiation.html ], and in 1801 John Wilhelm Ritter also made a similar observation in the . Joseph Von Fraunhofer extended Newtons discovery by observing the suns spectrum when sufficiently dispersed was blocked by a fine dark lines now known as Fraunhofer also developed which disperses the lights in much the same way as does a glass prism but with some advantages. the grating applied interference of lights to produce provides a direct measuring of wavelengths of diffracted beams. So by extending Thomas Youngs study which demonstrated that a light beam passes slit emerges in patterns of light and dark edges Fraunhofer was able to directly measure the wavelengths of spectral lines. However, despite his enormous achievements, Fraunhofer was unable to understand the origins of the special line in which he observed. It was not until 33 years after his passing that Gustav Kirchhoff established that each element and compound has its unique spectrum and that by studying the spectrum of an unknown source, one could determine its chemical compositions, and with these advancements, spectroscopy became a truly scientific method of analyzing the structures of chemical compounds. Therefore, by recognizing that each atom and molecule has its spectrum Kirchhoff and Robert Bunsen established spectroscopy as a scientific tool for probing atomic and molecular structures and founded the field of spectrochemical analysis for analyzing the composition of materials. | 7 | Physical Chemistry |
Levopropylhexedrine (Eventin) is an adrenergic alkylamine used as an anorectic in Germany and patented by Smith Kline & French in 1947. It has also been used in the anticonvulsant preparation barbexaclone in combination with phenobarbital to offset sedation. Levopropylhexedrine is the levorotatory S-enantiomer of propylhexedrine. The dextrorotatory counterpart is known as dextropropylhexedrine. | 4 | Stereochemistry |
Brevianamides are indole alkaloids that belong to a class of naturally occurring 2,5-diketopiperazines produced as secondary metabolites of fungi in the genus Penicillium and Aspergillus. Structurally similar to paraherquamides, they are a small class compounds that contain a bicyclo[2.2.2]diazoctane ring system. One of the major secondary metabolites in Penicillium spores, they are responsible for inflammatory response in lung cells. | 0 | Organic Chemistry |
Surfactants are in demand for a wide range of industrial applications as they increase solubility, foaming capacity and lower surface tensions. In particular, rhamnolipids have been used broadly in the cosmetic industry for products such as moisturisers, condom lubricant and shampoo. Rhamnolipids are efficacious in bioremediation of organic and heavy metal polluted sites. They also facilitate degradation of waste hydrocarbons such as crude oil and vegetable oil by Pseudomonas aeruginosa. The rhamnolipid surfactant itself is valuable in the cosmetic industry, and rhamnolipids are a source of rhamnose, which is an expensive sugar in itself.
Other bio-based surfactants include sophorolipids and mannose-erythritol lipids. | 0 | Organic Chemistry |
The space occupied by a polymer molecule is generally expressed in terms of radius of gyration, which is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of pervaded volume, which is the volume spanned by the polymer chain and scales with the cube of the radius of gyration.
The simplest theoretical models for polymers in the molten, amorphous state are ideal chains. | 7 | Physical Chemistry |
A frozen zoo is a storage facility in which genetic materials taken from animals (e.g. DNA, sperm, eggs, embryos and live tissue) are stored at very low temperatures (−196 °C) in tanks of liquid nitrogen. Material preserved in this way can be stored indefinitely and used for artificial insemination, in vitro fertilization, embryo transfer, and cloning. There are a few frozen zoos across the world that implement this technology for conservation efforts. Several different species have been introduced to this technology, including the Pyrenean ibex, Black-footed ferret, and potentially the white rhinoceros. | 1 | Biochemistry |
Raphaël Horace Dubois (20 June 1849, Le Mans – 21 January 1929) was a French pharmacologist known for his work on bioluminescence and anesthesia. He coined the terms proteon and bioproteon, from the Greek "proteon" for matter and "bios" for life. Bioproteon means "living matter". He concluded that there was no difference between matter and living matter.
Dubois bioluminescence work began when he became a research assistant to Paul Bert in 1882. While initially planning to study the effects of anesthesia on mollusks, witnessing the bioluminescence of Pyrophorus noctilucus inspired him to study the beetle more in depth. Dubois discovered that not only do the adults glow, but so do the unfertilized eggs, embryo, and larvae. Dubois later conducted studies on Scolioplanes crassipes, wherein Dubois discovered the source of its luminescence is in cells of the wall of the gut. Dubois published a paper studying the light production of Pholas dactylus' in 1887, in which he coined the terms luciferin and luciferase. | 1 | Biochemistry |
The major breakthroughs occurred during the Second World War as the result of research conducted independently in the United Kingdom and the United States into the potential use of herbicides in war. The compound 2,4-D was first synthesized by W. G. Templeman at Imperial Chemical Industries. In 1940, his work with indoleacetic acid and naphthaleneacetic acid indicated that "growth substances applied appropriately would kill certain broad-leaved weeds in cereals without harming the crops," though these substances were too expensive and too short-lived in soil due to degradation by microorganisms to be of practical agricultural use; by 1941, his team succeeded in synthesizing a wide range of chemicals to achieve the same effect at lower cost and better efficacy, including 2,4-D. In the same year, R. Pokorny in the US achieved this as well. Independently, a team under Juda Hirsch Quastel, working at the Rothamsted Experimental Station made the same discovery. Quastel was tasked by the Agricultural Research Council (ARC) to discover methods for improving crop yield. By analyzing soil as a dynamic system, rather than an inert substance, he was able to apply techniques such as perfusion. Quastel was able to quantify the influence of various plant hormones, inhibitors, and other chemicals on the activity of microorganisms in the soil and assess their direct impact on plant growth. While the full work of the unit remained secret, certain discoveries were developed for commercial use after the war, including the 2,4-D compound.
When 2,4-D was commercially released in 1946, it became the first successful selective herbicide, triggering a worldwide revolution in agricultural output. It allowed for greatly enhanced weed control in wheat, maize (corn), rice, and similar cereal grass crops, because it kills dicots (broadleaf plants), but not most monocots (grasses). The low cost of 2,4-D has led to continued usage today, and it remains one of the most commonly used herbicides in the world. Like other acid herbicides, current formulations use either an amine salt (often trimethylamine) or one of many esters of the parent compound. | 2 | Environmental Chemistry |
The dyes used in early experimental cells (circa 1995) were sensitive only in the high-frequency end of the solar spectrum, in the UV and blue. Newer versions were quickly introduced (circa 1999) that had much wider frequency response, notably "triscarboxy-ruthenium terpyridine" [Ru(4,4',4"-(COOH)-terpy)(NCS)], which is efficient right into the low-frequency range of red and IR light. The wide spectral response results in the dye having a deep brown-black color, and is referred to simply as "black dye". The dyes have an excellent chance of converting a photon into an electron, originally around 80% but improving to almost perfect conversion in more recent dyes, the overall efficiency is about 90%, with the "lost" 10% being largely accounted for by the optical losses in top electrode.
A solar cell must be capable of producing electricity for at least twenty years, without a significant decrease in efficiency (life span). The "black dye" system was subjected to 50 million cycles, the equivalent of ten years' exposure to the sun in Switzerland. No discernible performance decrease was observed. However the dye is subject to breakdown in high-light situations. Over the last decade an extensive research program has been carried out to address these concerns. The newer dyes included 1-ethyl-3 methylimidazolium tetrocyanoborate [EMIB(CN)] which is extremely light- and temperature-stable, copper-diselenium [Cu(In,GA)Se] which offers higher conversion efficiencies, and others with varying special-purpose properties.
DSSCs are still at the start of their development cycle. Efficiency gains are possible and have recently started more widespread study. These include the use of quantum dots for conversion of higher-energy (higher frequency) light into multiple electrons, using solid-state electrolytes for better temperature response, and changing the doping of the TiO to better match it with the electrolyte being used. | 5 | Photochemistry |
Sometimes grouped into the chemical mechanism of adhesion, hydrogen bonding can increase adhesive strength by the dispersive mechanism. Hydrogen bonding occurs between molecules with a hydrogen atom attached to a small, electronegative atom such as fluorine, oxygen or nitrogen. This bond is naturally polar, with the hydrogen atom gaining a slight positive charge and the other atom becoming slightly negative. Two molecules, or even two functional groups on one large molecule, may then be attracted to each other via Keesom forces. | 6 | Supramolecular Chemistry |
Using , , (assuming body temperature) and the fact that one volt is equal to one joule of energy per coulomb of charge, the equation
can be reduced to
which is the Nernst equation. | 7 | Physical Chemistry |
Von Stahel und Eysen (English: On Steel and Iron) is the first printed book on metallurgy, published in 1532 by several publishers: Kunegunde Hergot in Nuremberg, Melchior Sachs in Erfurt, and Peter Jordan in Mainz. It has been suggested that Hergot was probably the first to publish the text, as the material seems to come from Nuremberg: its material on tempering and quenching is similar to the short treatise on hardening iron beginning Von dem herten. Nu spricht meister Alkaym in the late fourteenth- or early fifteenth-century Nuremberg manuscript Nürnberger Handschrift GNM 3227a.
About half the text is on how to harden iron and steel through tempering and quenching, mentioning water, but also a range of recipes of varying degrees of elaborateness. The recipe take clarified honey, fresh urine of a he-goat, alum, borax, olive oil, and salt; mix everything well together and quench therein might, through the urea content of the urine (HNCONH), have helped to produce nitrated, case-hardened iron. Less likely to have been efficacious is: take varnish, dragons blood, horn scrapings, half as much salt, juice made from earthworms, radish juice, tallow, and vervain and quench therein. It is also very advantageous in hardening if a piece that is to be hardened is first thoroughly cleaned and well polished'.
A modern commentator on some of the more outlandish techniques in the book noted: "There isn't really much to say...except that perhaps it was meant to trip up rivals. However, this may not be the case because similar instructions were circulated in 1708 in Nuremberg."
The text also includes techniques for colouring, soldering, and etching. Etching was quite a new technology at the time, and Von Stahel und Eysen provides the first attested recipes. | 8 | Metallurgy |
The linear molecular geometry describes the geometry around a central atom bonded to two other atoms (or ligands) placed at a bond angle of 180°. Linear organic molecules, such as acetylene (), are often described by invoking sp orbital hybridization for their carbon centers.
According to the VSEPR model (Valence Shell Electron Pair Repulsion model), linear geometry occurs at central atoms with two bonded atoms and zero or three lone pairs ( or ) in the AXE notation. Neutral molecules with linear geometry include beryllium fluoride () with two single bonds, carbon dioxide () with two double bonds, hydrogen cyanide () with one single and one triple bond. The most important linear molecule with more than three atoms is acetylene (), in which each of its carbon atoms is considered to be a central atom with a single bond to one hydrogen and a triple bond to the other carbon atom. Linear anions include azide () and thiocyanate (), and a linear cation is the nitronium ion ().
Linear geometry also occurs in molecules, such as xenon difluoride () and the triiodide ion () with one iodide bonded to the two others. As described by the VSEPR model, the five valence electron pairs on the central atom form a trigonal bipyramid in which the three lone pairs occupy the less crowded equatorial positions and the two bonded atoms occupy the two axial positions at the opposite ends of an axis, forming a linear molecule. | 4 | Stereochemistry |
A neolithic-chalcolithic tell is located south of the town.
The first occupation phase at Aratashen was pre-ceramic, going back to 6500 BCE. Parallels are found in the southeastern Trans-Caucasia, and in the northeastern Mesopotamia, especially based on the construction techniques and the lithic and bone tools.
Also the pottery, after it appears, is somewhat similar. The best parallels are with Kul Tepe of Nakhichevan to the south, and with the northern Near East, such as the lower levels of Hajji Firuz Tepe, at Dalma Tepe, and at Tilki Tepe.
The Shulaveri-Shomutepe culture, that developed in the neighbouring Kura basin and the Karabakh steppe, does not have close parallels with the early Aratashen artifacts.
At Aratashen, obsidian was discovered that came from Turkish sources at Meydan Dağ, in the Lake Van basin; these samples were found in association with the very early Halaf culture ware, which probably also came to Aratashen from the same area.
Other types of pottery appear at the end of the fifth millennium BC. At this time, the plain of Ararat was in contact with the contemporary populations of northern Mesopotamia, and also with those of the ‘Sioni culture’ of the Kura basin.
The pottery of the second occupation phase of Aratashen is becoming close to that in the Ararat plain. Here we see the influence of the Late Chalcolithic horizon of approximately 4300–3500 BC in the whole of northern Mesopotamia, such as:
: "... development of straw-tempered ware, initial use of the slow wheel, early forms of standardization in manufacture and typological features ("Coba bowls"), a frequent surface treatment with light scraping..."
This pottery has many Transcaucasian, or Sioni culture features. Sioni culture generally succeeded the
Shulaveri-Shomutepe culture in some areas. Here we already see the features of the later Kura–Araxes culture pottery. | 8 | Metallurgy |
The usefulness of TD Diffuse optics lies in its ability to continually and noninvasive monitor optical properties of tissue. Making it a powerful diagnostic tool for long-term bedside monitoring in infants and adults alike. It has already been demonstrated that TD diffuse optics can be successfully applied to various biomedical applications such as cerebral monitoring, optical mammography, muscle monitoring, etc. | 7 | Physical Chemistry |
Joanna V. Clark is an American geoscientist working for Geocontrols Systems Inc on the JETS Contract at NASA Johnson Space Center. She is collaborator on the Sample Analysis at Mars (SAM) and Mars Science Lab (MSL) science teams. Her research includes oxychlorines, chlorides, phyllosilicates, manganese oxides and has also been involved with martian simulant development for In-Situ Resource Utilization. | 9 | Geochemistry |
Core subjects are similar to biochemistry courses and typically include gene expression, research methods, proteins, cancer research, immunology, biotechnology and many more. In some universities molecular medicine is combined with another discipline such as chemistry, functioning as an additional study to enrich the undergraduate program. | 1 | Biochemistry |
Tailings are also called mine dumps, culm dumps, slimes, refuse, leach residue, slickens, or terra-cone (terrikon). | 8 | Metallurgy |
* Full-length ncRNA capture – BoMoC has high processivity across modified RNA templates resulting in the production of more full-length cDNA products compared to common reverse transcriptase's, which are prone to premature termination at modified sites.
* Single tube reaction – All cDNA synthesis steps can be performed in a single tube, without the need for intermediate purification steps. This allows for automation of the OTTR approach. Additionally, this reduces the total amount of input RNA required purification steps, prone to loss of
* Capture of modified sites – Mis-incorporation signatures of BoMoC across modified RNA bases have been characterized. Therefore, OTTR allows for the identification of modification status of RNA transcripts where modified sites are known.
* Sequencing of both RNA and DNA templates – While RNA templates have been used to benchmark the OTTR technique, BoMoC is processive over DNA, meaning this library preparation approach could be adapted for DNA characterization. | 1 | Biochemistry |
The tail addition step in this synthesis (Scheme 6) was identical to that in the Nicolaou tail addition and was based on Oijma chemistry. The A ring was functionalized with a hydroxyl group through pyridinium chlorochromate oxidation of α-acylketone 49 to form ketone 50. Subsequent reduction using sodium borohydride produced alcohol 51 . Reaction of this alcohol with the Ojima lactam 52 and a concluding silyl deprotection step at two triethyl silyl positions in compound 53 gave Taxol. | 0 | Organic Chemistry |
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