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Under a standard set of conditions, the melting point of a substance is a characteristic property. The melting point is often equal to the freezing point. However, under carefully created conditions, supercooling, or superheating past the melting or freezing point can occur. Water on a very clean glass surface will often supercool several degrees below the freezing point without freezing. Fine emulsions of pure water have been cooled to −38 °C without nucleation to form ice. Nucleation occurs due to fluctuations in the properties of the material. If the material is kept still there is often nothing (such as physical vibration) to trigger this change, and supercooling (or superheating) may occur. Thermodynamically, the supercooled liquid is in the metastable state with respect to the crystalline phase, and it is likely to crystallize suddenly. | 0 | Theoretical and Fundamental Chemistry |
The longitudinal (or spin-lattice) relaxation time T is the decay constant for the recovery of the z component of the nuclear spin magnetization, M, towards its thermal equilibrium value, . In general,
In specific cases:
*If M has been tilted into the xy plane, then and the recovery is simply
i.e. the magnetization recovers to 63% of its equilibrium value after one time constant T.
*In the inversion recovery experiment, commonly used to measure T values, the initial magnetization is inverted, , and so the recovery follows
T relaxation involves redistributing the populations of the nuclear spin states in order to reach the thermal equilibrium distribution. By definition, this is not energy conserving. Moreover, spontaneous emission is negligibly slow at NMR frequencies. Hence truly isolated nuclear spins would show negligible rates of T relaxation. However, a variety of relaxation mechanisms allow nuclear spins to exchange energy with their surroundings, the lattice, allowing the spin populations to equilibrate. The fact that T relaxation involves an interaction with the surroundings is the origin of the alternative description, spin-lattice relaxation.
Note that the rates of T relaxation (i.e., 1/T) are generally strongly dependent on the NMR frequency and so vary considerably with magnetic field strength B. Small amounts of paramagnetic substances in a sample speed up relaxation very much. By degassing, and thereby removing dissolved oxygen, the T/T of liquid samples easily go up to an order of ten seconds. | 0 | Theoretical and Fundamental Chemistry |
The society publishes the magazine Australian Biochemist with three issues per year. The publication started in 1998, following on from the ABS/ASBMB newsletter, which was started in 1970. | 1 | Applied and Interdisciplinary Chemistry |
In practice, the atomic mass constant is determined from the electron rest mass m and the electron relative atomic mass A(e) (that is, the mass of electron divided by the atomic mass constant). The relative atomic mass of the electron can be measured in cyclotron experiments, while the rest mass of the electron can be derived from other physical constants.
where c is the speed of light, h is the Planck constant, α is the fine-structure constant, and R is the Rydberg constant.
As may be observed from the old values (2014 CODATA) in the table below, the main limiting factor in the precision of the Avogadro constant was the uncertainty in the value of the Planck constant, as all the other constants that contribute to the calculation were known more precisely.
The power of the presently defined values of universal constants can be understood from the table below (2018 CODATA). | 0 | Theoretical and Fundamental Chemistry |
In July 1987, Lower Saxony’s minister of Science and Art approved the establishment of the ICBM as a cooperation of the university departments of mathematics, biology, physics and chemistry. In 1991, the ICBM was approved as a central organisation of the University of Oldenburg. The registered association „Centre for Research on Shallow seas, Coastal Zones and the Marine Environment – Research Centre Terramare” (Zentrum für Flachmeer-, Küsten- und Meeresumweltforschung e.V. – Forschungszentrum Terramare) which was founded in 1990 in Wilhelmshaven and financed through federal state resources was incorporated into the ICBM in 2008.
The former directors of the ICBM are Wolfgang Krumbein, Ulrich Kattmann, Hans Joachim Schellnhuber, Bruno Eckhardt, Wolfgang Ebenhöh, Heribert Cypionka, Meinhard Simon, Hans-Jürgen Brumsack, Ulrike Feudel, Jürgen Rullkötter, Helmut Hillebrand, Bernd Blasius and Oliver Zielinski. At present, the institute is headed by Heinz Wilkes. | 0 | Theoretical and Fundamental Chemistry |
Thermolysin is an enzyme produced by Bacillus thermoproteolyticus that catalyses the hydrolysis of peptides containing hydrophobic amino acids. Therefore, it is also a target for antibacterial agents. The enzymatic reaction mechanism starts form the small peptide molecule and replaces the zinc binding water molecule towards Glu143 of thermolysin. The water molecule is then activated by both the zinc ion and the Glu143 residue and attacks the carbonyl carbon to form a tetrahedral transition state (see figure). Holden and coworkers then mimicked that tetrahedral transition state to design a series of phosphonamidate peptide analogues. Among the synthesized analogues, R = -Leu possesses the most potent inhibitory activity (K = 9.1 nM). | 1 | Applied and Interdisciplinary Chemistry |
Rewrite the second equation as
In the neighborhood of the weak discontinuity, the quantities to the first order (such as ) reduces the above equation to
At this point, it is worth mentioning that in general, disturbances in gases are propagated with respect to the gas at the local sound speed. In other words, in the fixed frame, the disturbances are propagated at the speed (the other possibility is although it is of no interest here). If the gas is at rest , then the disturbance speed is . This is just a normal sound wave propagation. If however is non-zero but a small quantity, then one find the correction for the disturbance propagation speed as obtained using a Taylor series expansion, where is a necessarily a positive constant (for ideal gas, , where is the specific heat ratio). This means that the above equation can be written as
whose solution is
where is a constant. This determines implicitly in the neighborhood of the week discontinuity where is small. This equation shows that at , , , but all higher-order derivatives are discontinuous. In the above equation, subtract from the left-hand side and from the right-hand side to obtain
which implies that if is a small quantity. It can be shown that the relation not only holds for small , but throughout the rarefaction wave. | 1 | Applied and Interdisciplinary Chemistry |
Jones became interested in science as a freshman at high school, where she took part in a national Science Technology Engineering Program. She earned a BS in biochemistry at Syracuse University in 1999. Jones completed her PhD at Georgia State University and specialized in structural biology.
Jones received postdoctoral training in structural virology at the University of Alabama at Birmingham. She was a Pfizer postdoctoral researcher at Washington University in St. Louis working with Michael Gross on MassSpec-based protein foot-printing. | 1 | Applied and Interdisciplinary Chemistry |
The law can be expressed in terms of attenuation coefficient, but in this case is better called the Bouguer-Lambert's law. The (Napierian) attenuation coefficient and the decadic attenuation coefficient of a material sample are related to its number densities and amount concentrations asrespectively, by definition of attenuation cross section and molar attenuation coefficient. Then the law becomesand
In many cases, the attenuation coefficient does not vary with , in which case one does not have to perform an integral and can express the law as:where the attenuation is usually an addition of absorption coefficient (creation of electron-hole pairs) or scattering (for example Rayleigh scattering if the scattering centers are much smaller than the incident wavelength). Also note that for some systems we can put (1 over inelastic mean free path) in place of | 0 | Theoretical and Fundamental Chemistry |
Marrow is part of I'm a Scientist, Get me out of here! energy generation zone. He has also been a key developer and academic consultant for the Dissemination of IT for the Promotion of Materials Science (DoITPoMS). Global Cycle Network Technology (GCN Tech) interviewed James about carbon fibre fatigue and strain in 2022. | 1 | Applied and Interdisciplinary Chemistry |
Asymmetric ester hydrolysis with pig liver esterase is the enantioselective conversion of an ester to a carboxylic acid through the action of the enzyme pig liver esterase (EC 3.1.1.1). Asymmetric ester hydrolysis involves the selective reaction of one of a pair of either enantiotopic (within the same molecule and related by a symmetry plane of the molecule) or enantiomorphic (in enantiomeric molecules and related as mirror images) ester groups. | 0 | Theoretical and Fundamental Chemistry |
There are two digits. The first digit is the priority number of the ligand on the fourfold (C) axis of the idealised pyramid the second digit is the priority number of the ligand trans to ligand of lowest priority in the plane perpendicular to the 4 fold axis. (If there is more than one choice then the highest numerical value second digit is taken.) | 0 | Theoretical and Fundamental Chemistry |
Filtration is movement of water and solute molecules across the cell membrane due to hydrostatic pressure generated by the cardiovascular system. Depending on the size of the membrane pores, only solutes of a certain size may pass through it. For example, the membrane pores of the Bowman's capsule in the kidneys are very small, and only albumins, the smallest of the proteins, have any chance of being filtered through. On the other hand, the membrane pores of liver cells are extremely large, but not forgetting cells are extremely small to allow a variety of solutes to pass through and be metabolized. | 1 | Applied and Interdisciplinary Chemistry |
There are many classes of neutral homoaromatic compounds although there is much debate as to whether they truly exhibit homoaromatic character or not.
One class of neutral homoaromatics are called monohomoaromatics, one of which is cycloheptatriene, and numerous complex monohomoaromatics have been synthesized. One particular example is a 60-carbon fulleroid derivative that has a single methylene bridge. UV and NMR analysis have shown that the aromatic character of this modified fulleroid is not disrupted by the addition of a homoconjugate linkage, therefore this compound is definitively homoaromatic.
Substituted neutral barbaralane derivatives (homoannulenes) have been disclosed as stable ground state homoaromatic molecules in 2023. Evidence for the homoaromatic character in this class of molecules stems from bond length analysis (X-Ray structural analysis) as well as shifts in the NMR spectrum. The homoannulenes also act as photoswitches by which means a local 6π homoaromaticity can be switched to a global 10π homoaromaticity. | 0 | Theoretical and Fundamental Chemistry |
While characterizing the compound resulting from deprotonation of cyclooctatriene by H NMR spectroscopy, the group observed that the resonance corresponding to two protons bonded to the same methylene bridge carbon exhibited an astonishing degree of separation in chemical shift.
From this observation, Pettit, et al. concluded that the classical structure of the cyclooctatrienyl cation must be incorrect. Instead, the group proposed the structure of the bicyclo[5.1.0]octadienyl compound, theorizing that the cyclopropane bond located on the interior of the eight-membered ring must be subject to considerable delocalization, thus explaining the dramatic difference in observed chemical shift. Upon further consideration, Pettit was inclined to represent the compound as the "homotropylium ion," which shows the "internal cyclopropane" bond totally replaced by electron delocalization. This structure shows how delocalization is cyclic and involves 6 π electrons, consistent with Huckel's rule for aromaticity. The magnetic field of the NMR could thus induce a ring current in the ion, responsible for the significant differences in resonance between the exo and endo protons of this methylene bridge. Pettit, et al. thus emphasized the remarkable similarity between this compound and the aromatic tropylium ion, describing a new "homo-counterpart" to an aromatic species already known, precisely as predicted by Winstein.
Subsequent NMR studies undertaken by Winstein and others sought to evaluate the properties of metal carbonyl complexes with the homotropylium ion. Comparison between a molybdenum-complex and an iron-complex proved particularly fruitful. Molybdenum tricarbonyl was expected to coordinate to the homotropylium cation by accepting 6 π electrons, thereby preserving the homoaromatic features of the complex. By contrast, iron tricarbonyl was expected to coordinate to the cation by accepting only 4 π electrons from the homotropylium ion, creating a complex in which the electrons of the cation are localized. Studies of these complexes by H NMR spectroscopy showed a large difference in chemical shift values for methylene protons of the Mo-complex, consistent with a homoaromatic structure, but detected virtually no comparable difference in resonance for the same protons in the Fe-complex. | 0 | Theoretical and Fundamental Chemistry |
Sometimes it is more convenient to display graphical spectra with vertical axes that show the relative spectral flux density. In this case, the spectral flux density at a given wavelength is expressed as a fraction of some arbitrarily chosen reference value. Relative spectral flux densities are expressed as pure numbers without any units.
Spectra showing the relative spectral flux density are used when we are interested in comparing the spectral flux densities of different sources; for example, if we want to show how the spectra of blackbody sources vary with absolute temperature, it is not necessary to show the absolute values. The relative spectral flux density is also useful if we wish to compare a sources flux density at one wavelength with the same sources flux density at another wavelength; for example, if we wish to demonstrate how the Suns spectrum peaks in the visible part of the EM spectrum, a graph of the Suns relative spectral flux density will suffice. | 0 | Theoretical and Fundamental Chemistry |
Between November 2015 and October 2018, the Wellcome Trust supported a project to develop the [http://www.guidetoimmunopharmacology.org IUPHAR Guide to IMMUNOPHARMACOLOGY] (GtoImmuPdb), based on the GtoPdb schema. The GtoImmuPdb is an open-access resource that brings an immunological perspective to the high-quality, expert-curated pharmacological data found in the existing IUPHAR/BPS Guide to PHARMACOLOGY. Protein targets and ligands relevant to immunopharmacology have been tagged and curated into GtoImmuPdb. These have also been associated with new immunological data types such as immunological processes, cell types, and disease. GtoImmuPdb provides a knowledge base that connects immunology with pharmacology, bringing added value and supporting research and development of drugs targeted at modulating immune, inflammatory or infectious components of the disease. | 1 | Applied and Interdisciplinary Chemistry |
The key to the two-hybrid screen is that in most eukaryotic transcription factors, the activating and binding domains are modular and can function in proximity to each other without direct binding. This means that even though the transcription factor is split into two fragments, it can still activate transcription when the two fragments are indirectly connected.
The most common screening approach is the yeast two-hybrid assay. In this approach the researcher knows where each prey is located on the used medium (agar plates). Millions of potential interactions in several organisms have been screened in the latest decade using high-throughput screening systems (often using robots) and over thousands of interactions have been detected and categorized in databases as [https://thebiogrid.org BioGRID]. This system often utilizes a genetically engineered strain of yeast in which the biosynthesis of certain nutrients (usually amino acids or nucleic acids) is lacking. When grown on media that lacks these nutrients, the yeast fail to survive. This mutant yeast strain can be made to incorporate foreign DNA in the form of plasmids. In yeast two-hybrid screening, separate bait and prey plasmids are simultaneously introduced into the mutant yeast strain or a mating strategy is used to get both plasmids in one host cell.
The second high-throughput approach is the library screening approach. In this set up the bait and prey harboring cells are mated in a random order. After mating and selecting surviving cells on selective medium the scientist will sequence the isolated plasmids to see which prey (DNA sequence) is interacting with the used bait. This approach has a lower rate of reproducibility and tends to yield higher amounts of false positives compared to the matrix approach.
Plasmids are engineered to produce a protein product in which the DNA-binding domain (BD) fragment is fused onto a protein while another plasmid is engineered to produce a protein product in which the activation domain (AD) fragment is fused onto another protein. The protein fused to the BD may be referred to as the bait protein, and is typically a known protein the investigator is using to identify new binding partners. The protein fused to the AD may be referred to as the prey protein and can be either a single known protein or a library of known or unknown proteins. In this context, a library may consist of a collection of protein-encoding sequences that represent all the proteins expressed in a particular organism or tissue, or may be generated by synthesising random DNA sequences. Regardless of the source, they are subsequently incorporated into the protein-encoding sequence of a plasmid, which is then transfected into the cells chosen for the screening method. This technique, when using a library, assumes that each cell is transfected with no more than a single plasmid and that, therefore, each cell ultimately expresses no more than a single member from the protein library.
If the bait and prey proteins interact (i.e., bind), then the AD and BD of the transcription factor are indirectly connected, bringing the AD in proximity to the transcription start site and transcription of reporter gene(s) can occur. If the two proteins do not interact, there is no transcription of the reporter gene. In this way, a successful interaction between the fused protein is linked to a change in the cell phenotype.
The challenge of separating cells that express proteins that happen to interact with their counterpart fusion proteins from those that do not, is addressed in the following section. | 1 | Applied and Interdisciplinary Chemistry |
ATP has recently been proposed to act as a biological hydrotrope and has been shown to affect proteome-wide solubility. | 1 | Applied and Interdisciplinary Chemistry |
A useful heuristic is to imagine air starting from rest, experiencing a force directed from areas of high pressure toward areas of low pressure, called the pressure gradient force. If the air began to move in response to that force, however, the Coriolis "force" would deflect it, to the right of the motion in the northern hemisphere or to the left in the southern hemisphere. As the air accelerated, the deflection would increase until the Coriolis forces strength and direction balanced the pressure gradient force, a state called geostrophic balance. At this point, the flow is no longer moving from high to low pressure, but instead moves along isobars. Geostrophic balance helps to explain why, in the northern hemisphere, low-pressure systems (or cyclones) spin counterclockwise and high-pressure systems (or anticyclones') spin clockwise, and the opposite in the southern hemisphere. | 1 | Applied and Interdisciplinary Chemistry |
Photoluminescence (PL) is a phenomenon related to the ability of some compounds that, after absorbing specific electromagnetic radiation, relax to a lower energy state through emission of photons. This spectroelectrochemical technique is limited to those compounds with fluorescent or luminescent properties. The experiments are strongly interfered by ambient light. This technique provides structural information and quantitative information with great detection limits. | 0 | Theoretical and Fundamental Chemistry |
The defendants were pipemakers who were operating in agreement. When municipalities offered projects available to the lowest bidder, all companies but the one designated would overbid, guaranteeing the success of the designated low bidder if no bidder outside the group submitted a bid.
The government argued that some antitrust violations, such as bid rigging, were such egregious anti-competitive acts that they were always illegal (the so-called "per se" rule). The defendants asserted that it was a reasonable restraint of trade and that the Sherman Act could not have meant to prevent such restraints. | 1 | Applied and Interdisciplinary Chemistry |
To obtain the effect, it is necessary to achieve a phase separation, one of these phases works as the trigger for the temporary form, using a transition temperature that can be Tm or Tg and in this effect is called T. A second phase has the higher transition temperature and above this temperature the polymer melts and is processed by conventional methods.
The ratio of the elements forming the phase separation largely regulates the T transition temperature; this is much easier to control than in metallic alloys.
An example of this is the poly(ethylene oxide-ethylene terephthalate) or EOET copolymer. The polyethylene terephthalate (PET) segment has a relatively high Tg and its Tm is commonly referred to as the "hard" segment, whereas polyethylene ethylene oxide (PEO), has a relatively low Tm and Tg and is referred to as the "soft" segment. In the final polymer these segments separate into two phases in the solid state. PET has a high degree of crystallinity and the formation of these crystals provides for the flow and rearrangement of the PEO chains as they are stretched at temperatures higher than their Tm. | 0 | Theoretical and Fundamental Chemistry |
Monomers undergoing supramolecular polymerization are considered to be in equilibrium with the growing polymers, and thermodynamic factors therefore dominate the system. However, when the constituent monomers are connected via strong and multivalent interactions, a "metastable" kinetic state can dominate the polymerization. An externally supplied energy, in the form of heat in most cases, can transform the "metastable" state into a thermodynamically stable polymer. A clear understanding of multiple pathways exist in supramolecular polymerization is still under debate, however, the concept of "pathway complexity", introduced by E.W. "Bert" Meijer, shed a light on the kinetic behavior of supramolecular polymerization. Thereafter, many dedicated scientists are expanding the scope of "pathway complexity" because it can produce a variety of interesting assembled structures from the same monomeric units. Along this line of kinetically controlled processes, supramolecular polymers having "stimuli-responsive" and "thermally bisignate" characteristics is also possible.
In conventional covalent polymerization, two models based on step-growth and chain-growth mechanisms are operative. Nowadays, a similar subdivision is acceptable for supramolecular polymerization; isodesmic also known as equal-K model (step-growth mechanism) and cooperative or nucleation-elongation model (chain-growth mechanism). A third category is seeded supramolecular polymerization, which can be considered as a special case of chain-growth mechanism. | 0 | Theoretical and Fundamental Chemistry |
In biochemistry there are many instances of acyl groups, in all major categories of biochemical molecules.
Acyl-CoAs are acyl derivatives formed via fatty acid metabolism. Acetyl-CoA, the most common derivative, serves as an acyl donor in many biosynthetic transformations. Such acyl compounds are thioesters.
Names of acyl groups of amino acids are formed by replacing the -ine suffix with -yl. For example, the acyl group of glycine is glycyl, and of lysine is lysyl.
Names of acyl groups of ribonucleoside monophosphates such as AMP (5′-adenylic acid), GMP (5′-guanylic acid), CMP (5′-cytidylic acid), and UMP (5′-uridylic acid) are adenylyl, guanylyl, cytidylyl, and uridylyl respectively.
In phospholipids, the acyl group of phosphatidic acid is called phosphatidyl-.
Finally, many saccharides are acylated. | 0 | Theoretical and Fundamental Chemistry |
Limit values for VOC emissions into indoor air are published by AgBB, AFSSET, California Department of Public Health, and others. These regulations have prompted several companies in the paint and adhesive industries to adapt with VOC level reductions their products. VOC labels and certification programs may not properly assess all of the VOCs emitted from the product, including some chemical compounds that may be relevant for indoor air quality. Each ounce of colorant added to tint paint may contain between 5 and 20 grams of VOCs. A dark color, however, could require 5–15 ounces of colorant, adding up to 300 or more grams of VOCs per gallon of paint. | 0 | Theoretical and Fundamental Chemistry |
Surface conductivity may refer to the electrical conduction across a solid surface measured by surface probes. Experiments may be done to test this material property as in the n-type surface conductivity of p-type. Additionally, surface conductivity is measured in coupled phenomena such as photoconductivity, for example, for the metal oxide semiconductor ZnO. Surface conductivity differs from bulk conductivity for analogous reasons to the electrolyte solution case, where the charge carriers of holes (+1) and electrons (-1) play the role of ions in solution. | 0 | Theoretical and Fundamental Chemistry |
This timeline of biology and organic chemistry captures significant events from before 1600 to the present. | 1 | Applied and Interdisciplinary Chemistry |
Most liquids freeze by crystallization, formation of crystalline solid from the uniform liquid. This is a first-order thermodynamic phase transition, which means that as long as solid and liquid coexist, the temperature of the whole system remains very nearly equal to the melting point due to the slow removal of heat when in contact with air, which is a poor heat conductor. Because of the latent heat of fusion, the freezing is greatly slowed and the temperature will not drop anymore once the freezing starts but will continue dropping once it finishes.
Crystallization consists of two major events, nucleation and crystal growth. "Nucleation" is the step wherein the molecules start to gather into clusters, on the nanometer scale, arranging in a defined and periodic manner that defines the crystal structure. "Crystal growth" is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. | 1 | Applied and Interdisciplinary Chemistry |
The term "ionic liquid" in the general sense was used as early as 1943.
The discovery date of the "first" ionic liquid is disputed, along with the identity of its discoverer. Ethanolammonium nitrate (m.p. 52–55 °C) was reported in 1888 by S. Gabriel and J. Weiner. In 1911 Ray and Rakshit, during preparation of the nitrite salts of ethylamine, dimethylamine, and trimethylamine observed that the reaction between ethylamine hydrochloride and silver nitrate yielded an unstable Ethylammonium nitrite ()· , a heavy yellow liquid which on immersion in a mixture of salt and ice could not be solidified and was probably the first report of room temperature ionic liquid. Later in 1914, Paul Walden reported one of the first stable room temperature ionic liquids ethylammonium nitrate ()· (m.p. 12 °C). In the 1970s and 1980s, ionic liquids based on alkyl-substituted imidazolium and pyridinium cations, with halide or tetrahalogenoaluminate anions, were developed as potential electrolytes in batteries.
For the imidazolium halogenoaluminate salts, their physical properties—such as viscosity, melting point, and acidity—could be adjusted by changing the alkyl substituents and the imidazolium/pyridinium and halide/halogenoaluminate ratios. Two major drawbacks for some applications were moisture sensitivity and acidity or basicity. In 1992, Wilkes and Zawarotko obtained ionic liquids with neutral weakly coordinating anions such as hexafluorophosphate () and tetrafluoroborate (), allowing a much wider range of applications. | 0 | Theoretical and Fundamental Chemistry |
Since development of the aluminium gallium nitride LED in the early 2000s, UV LED technology has seen sustained growth in the UV curing marketplace. Generating energy most efficiently in the 365-405 nm UVA wavelengths, continued technological advances, have allowed for improved electrical efficiency of UV LEDs as well as significant increases in output. UV LED lamps generate high energy directed to a specific area which strengthen the uniformity. Benefiting from lower-temperature operation and the lack of hazardous mercury, UV LEDs have replaced medium-pressure lamps in many applications. Major limitations include difficulties in designing optics for curing on complex three-dimensional objects, and poor efficiency at generating lower-wavelength energy, though development work continues. | 0 | Theoretical and Fundamental Chemistry |
The hydrolysis reaction for a hydrated metal ion in aqueous solution can be written as:
:p M + q HO ⇌ M(OH) + q H
and the corresponding formation constant as:
and associated equilibria can be written as:
:MO(OH)(s) + z H ⇌ M + (z–x) HO
:MO(OH)(s) + x HO ⇌ M + z OH
:p MO(OH)(s) + (pz–q) H ⇌ M(OH) + (pz–px–q) HO | 0 | Theoretical and Fundamental Chemistry |
Solutions to wave propagation problems in linear elastic transversely isotropic media can be constructed by superposing solutions for the quasi-P wave, the quasi S-wave, and a S-wave polarized orthogonal to the quasi S-wave.
However, the equations for the angular variation of velocity are algebraically complex and the plane-wave velocities are functions of the propagation angle are. The direction dependent wave speeds for elastic waves through the material can be found by using the Christoffel equation and are given by
where is the angle between the axis of symmetry and the wave propagation direction, is mass density and the are elements of the elastic stiffness matrix. The Thomsen parameters are used to simplify these expressions and make them easier to understand. | 0 | Theoretical and Fundamental Chemistry |
Suppose we are interested in finding the maximum power that can be extracted from the fluid. The power in the fluid is given by the following expression:
where is the fluid density as before, is the fluid velocity, and is the area of an imaginary surface through which the fluid is flowing. The power extracted from the fluid by a rotor in the scenario described above is some fraction of this power expression. We will call the fraction the power co-efficient, . Thus the power extracted, is given by the following expression:
Our question is this: what is the maximum value of using the Betz model?
Let us return to our derived expression for the power transferred from the fluid to the rotor (). We can see that the power extracted is dependent on the axial induction factor. If we differentiate with respect to , we get the following result:
If we have maximised our power extraction, we can set the above to zero. This allows us to determine the value of which yields maximum power extraction. This value is a . Thus we are able to find that . In other words, the rotor cannot extract more than 59 per cent of the power in the fluid. | 1 | Applied and Interdisciplinary Chemistry |
Gheorghe Spacu (December 5, 1883 – July 23, 1955) was a Romanian inorganic chemist.
Born in Iași, he attended the city's National College from 1894 to 1901. He subsequently enrolled in the physics and chemistry section of the sciences faculty at the University of Iași. There, his professors included Petru Poni (inorganic chemistry), Vasile Buțureanu (mineralogy and crystallography), Anastasie Obregia (organic chemistry) and Dragomir Hurmuzescu (electrochemistry). Upon graduating in 1905, he went to deepen his studies at the universities of University of Vienna and then Berlin. He returned in 1907, when he began working as an assistant in the inorganic chemistry laboratory of Neculai Costăchescu, and was promoted to head of operations in 1916. That year, he received a doctorate in chemistry, having submitted a thesis on iron compounds. After Costăchescu, he was the second individual to receive a doctorate in chemistry from a Romanian university. Subsequently, he was named associate professor at Iași University.
In 1919, following the union of Transylvania with Romania and the establishment of the University of Cluj, he was invited to teach as associate professor of inorganic and analytic chemistry. He was promoted to full professor in 1922. While at Cluj, he put together a school of chemistry, founding and supplying laboratories for students and researches and advising sixteen doctoral students. Among those he trained were Raluca Ripan, Ilie G. Murgulescu, Petru Spacu and Coriolan Drăgulescu. Petru, his only son, worked in his fathers department after obtaining a doctorate, later moving to Bucharest. Of Gheorghe Spacus 274 scientific articles, around two-thirds were written while he was at Cluj. These were generally published in the bulletin of the local scientific society, of which he was a founding member in 1921. He was elected a corresponding member of the Romanian Academy in 1927, and was promoted to titular member in 1935. He was assistant dean of the science faculty in 1923–1924, dean in 1924–1925, rector of the university in 1925–1926 and assistant rector in 1926–1927.
In 1939, he was asked to join the inorganic and analytic chemistry department of the University of Bucharest, where he began work in October 1940. As before, he focused on establishing laboratories and training chemists. Maria Brezeanu was one of his doctoral students. During his Bucharest period, his work appeared in the bulletin of the Academy's scientific section. He received three awards from the communist authorities: the state prize (1952 and 1954) and the order of labor (1953). He continued working until his death in 1955. | 0 | Theoretical and Fundamental Chemistry |
Combustion (in a fireplace, gas heater, candle, oil lamp, etc.) consumes oxygen while producing carbon dioxide and other unhealthy gases and smoke, requiring ventilation air. An open chimney promotes infiltration (i.e. natural ventilation) because of the negative pressure change induced by the buoyant, warmer air leaving through the chimney. The warm air is typically replaced by heavier, cold air.
Ventilation in a structure is also needed for removing water vapor produced by respiration, burning, and cooking, and for removing odors. If water vapor is permitted to accumulate, it may damage the structure, insulation, or finishes. When operating, an air conditioner usually removes excess moisture from the air. A dehumidifier may also be appropriate for removing airborne moisture. | 1 | Applied and Interdisciplinary Chemistry |
The compound was protected by a patent which was assigned to the German pharmaceutical company Hoechst AG (since merged into Aventis) on 29 October 1991. The patent was scheduled to expire on 29 October 2008. On 11 September 2007, in an appeal by the Indian company Lupin Ltd., the United States Court of Appeals for the Federal Circuit reversed a district court trial verdict and found that Aventis's patent on ramipril was invalid for "obviousness", opening this drug to generic manufacturers. | 0 | Theoretical and Fundamental Chemistry |
The concept of selectivity is used to quantify the extent to which one chemical substance, A, binds each of two other chemical substances, B and C. The simplest case is where the complexes formed have 1:1 stoichiometry. Then, the two interactions may be characterized by equilibrium constants and .
where [X] represents the concentration of substance X (A, B, C, …).
A selectivity coefficient is defined as the ratio of the two equilibrium constants.
This selectivity coefficient is in fact the equilibrium constant for the displacement reaction
It is easy to show that the same definition applies to complexes of a different stoichiometry, AB and AC. The greater the selectivity coefficient, the more the ligand C will displace the ligand B from the complex formed with the substrate A. An alternative interpretation is that the greater the selectivity coefficient, the lower the concentration of C that is needed to displace B from AB. Selectivity coefficients are determined experimentally by measuring the two equilibrium constants, and . | 0 | Theoretical and Fundamental Chemistry |
Organocerium chemistry is the science of organometallic compounds that contain one or more chemical bond between carbon and cerium. These compounds comprise a subset of the organolanthanides. Most organocerium compounds feature Ce(III) but some Ce(IV) derivatives are known. | 0 | Theoretical and Fundamental Chemistry |
Early process control breakthroughs came most frequently in the form of water control devices. Ktesibios of Alexandria is credited for inventing float valves to regulate water level of water clocks in the 3rd century BC. In the 1st century AD, Heron of Alexandria invented a water valve similar to the fill valve used in modern toilets.
Later process controls inventions involved basic physics principles. In 1620, Cornelis Drebbel invented a bimetallic thermostat for controlling the temperature in a furnace. In 1681, Denis Papin discovered the pressure inside a vessel could be regulated by placing weights on top of the vessel lid. In 1745, Edmund Lee created the fantail to improve windmill efficiency; a fantail was a smaller windmill placed 90° of the larger fans to keep the face of the windmill pointed directly into the oncoming wind.
With the dawn of the Industrial Revolution in the 1760s, process controls inventions were aimed to replace human operators with mechanized processes. In 1784, Oliver Evans created a water-powered flourmill which operated using buckets and screw conveyors. Henry Ford applied the same theory in 1910 when the assembly line was created to decrease human intervention in the automobile production process.
For continuously variable process control it was not until 1922 that a formal control law for what we now call PID control or three-term control was first developed using theoretical analysis, by Russian American engineer Nicolas Minorsky. Minorsky was researching and designing automatic ship steering for the US Navy and based his analysis on observations of a helmsman. He noted the helmsman steered the ship based not only on the current course error, but also on past error, as well as the current rate of change; this was then given a mathematical treatment by Minorsky.
His goal was stability, not general control, which simplified the problem significantly. While proportional control provided stability against small disturbances, it was insufficient for dealing with a steady disturbance, notably a stiff gale (due to steady-state error), which required adding the integral term. Finally, the derivative term was added to improve stability and control. | 1 | Applied and Interdisciplinary Chemistry |
Counting d electrons is a formalism. Often it is difficult or impossible to assign electrons and charge to the metal center or a ligand. For a high-oxidation-state metal center with a +4 charge or greater it is understood that the true charge separation is much smaller. But referring to the formal oxidation state and d electron count can still be useful when trying to understand the chemistry. | 0 | Theoretical and Fundamental Chemistry |
The discovery of paper chromatography in 1943 by Martin and Synge provided, for the first time, the means of surveying constituents of plants and for their separation and identification. Erwin Chargaff credits in Weintraub's history of the man the 1944 article by Consden, Gordon and Martin. There was an explosion of activity in this field after 1945. | 0 | Theoretical and Fundamental Chemistry |
From 1943 on, Booth started working on the determination of crystal structures using X-ray diffraction data. The computations involved were extremely tedious and there was ample incentive for automating the process and he developed an analogue computer to compute the reciprocal spacings of the diffraction pattern.
In 1947, along with his collaborator and future spouse Kathleen Britten, he spent a few months with von Neumann's team, which was the leading edge in computer research at the time. | 0 | Theoretical and Fundamental Chemistry |
A drug carrier or drug vehicle is a substrate used in the process of drug delivery which serves to improve the selectivity, effectiveness, and/or safety of drug administration. Drug carriers are primarily used to control the release of drugs into systemic circulation. This can be accomplished either by slow release of a particular drug over a long period of time (typically diffusion) or by triggered release at the drug's target by some stimulus, such as changes in pH, application of heat, and activation by light. Drug carriers are also used to improve the pharmacokinetic properties, specifically the bioavailability, of many drugs with poor water solubility and/or membrane permeability.
A wide variety of drug carrier systems have been developed and studied, each of which has unique advantages and disadvantages. Some of the more popular types of drug carriers include liposomes, polymeric micelles, microspheres, and nanoparticles. Different methods of attaching the drug to the carrier have been implemented, including adsorption, integration into the bulk structure, encapsulation, and covalent bonding. Different types of drug carrier utilize different methods of attachment, and some carriers can even implement a variety of attachment methods. | 1 | Applied and Interdisciplinary Chemistry |
Some evidence shows that alternatives to pesticides can be equally effective as the use of chemicals. A study of Maize fields in northern Florida found that the application of composted yard waste with high carbon to nitrogen ratio to agricultural fields was highly effective at reducing the population of plant-parasitic nematodes and increasing crop yield, with yield increases ranging from 10% to 212%; the observed effects were long-term, often not appearing until the third season of the study. Additional silicon nutrition protects some horticultural crops against fungal diseases almost completely, while insufficient silicon sometimes leads to severe infection even when fungicides are used.
Pesticide resistance is increasing and that may make alternatives more attractive. | 1 | Applied and Interdisciplinary Chemistry |
In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to the energy difference (often expressed in electronvolts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is the energy required to promote an electron from the valence band to the conduction band. The resulting conduction-band electron (and the electron hole in the valence band) are free to move within the crystal lattice and serve as charge carriers to conduct electric current. It is closely related to the HOMO/LUMO gap in chemistry. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move within the solid because there are no available states. If the electrons are not free to move within the crystal lattice, then there is no generated current due to no net charge carrier mobility. However, if some electrons transfer from the valence band (mostly full) to the conduction band (mostly empty), then current can flow (see carrier generation and recombination). Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances having large band gaps (also called "wide" band gaps) are generally insulators, those with small band gaps (also called "narrow" band gaps) are semiconductor, and conductors either have very small band gaps or none, because the valence and conduction bands overlap to form a continuous band. | 0 | Theoretical and Fundamental Chemistry |
Anabolic processes build organs and tissues. These processes produce growth and differentiation of cells and increase in body size, a process that involves synthesis of complex molecules. Examples of anabolic processes include the growth and mineralization of bone and increases in muscle mass. | 1 | Applied and Interdisciplinary Chemistry |
CCAAT-enhancer-binding proteins (or C/EBPs) is a family of transcription factors composed of six members, named from C/EBPα to C/EBPζ. They promote the expression of certain genes through interaction with their promoters. Once bound to DNA, C/EBPs can recruit so-called co-activators (such as CBP) that in turn can open up chromatin structure or recruit basal transcription factors. | 1 | Applied and Interdisciplinary Chemistry |
As they require the conjunction of specific environmental conditions to form, particular mineral deposit types tend to occupy specific geodynamic niches, therefore, this page has been organised by metal commodity. It is also possible to organise theories the other way, namely according to geological criteria of formation. Often ores of the same metal can be formed by multiple processes, and this is described here under each metal or metal complex. | 0 | Theoretical and Fundamental Chemistry |
During the fading, colourant molecules undergo various chemical processes which result in fading.
When a UV-photon reacts with a molecule acting as colourant, the molecule is excited from the ground state to an excited state. The excited molecule is highly reactive and unstable. During the quenching of the molecule from excited state to ground state, atmospheric triplet oxygen reacts with the colourant molecule to form singlet oxygen and superoxide oxygen radical. The oxygen atom and the superoxide radical resulting from the reaction are both highly reactive and capable of destroying the colourants. | 0 | Theoretical and Fundamental Chemistry |
Peggoty Mutai is a Kenyan chemist. Born in Kericho, her interests include medicinal chemistry, in particular working with the search for new treatments against parasitic worms.
After studying at the University of Nairobi, Kenya, where she obtained her Bachelor of Science and her Masters degree in pharmacy and pharmaceutical analysis, she was accepted at McGill University in Canada to continue pursuing her doctorate, which she had started at the University of Cape Town, South Africa. Mutai returned to the University of Cape town to finish her doctorate in 2014. Mutai was among the fifteen Fellows chosen by the LOréal-UNESCO Awards for Women in Science to receive an international scholarship to pursue their research projects in 2012. She is currently a lecturer for the department of Pharmacology and Pharmacognosy at the University of Nairobi and the section head of Pharmacognosy. | 1 | Applied and Interdisciplinary Chemistry |
Hot tapping, or pressure tapping, is the method of making a connection to existing piping or pressure vessels without the interrupting or emptying of that section of pipe or vessel. This means that a pipe or tank can continue to be in operation whilst maintenance or modifications are being done to it. The process is also used to drain off pressurized casing fluids and add test points or various sensors such as temperature and pressure. Hot taps can range from a ½ inch hole designed for something as simple as quality control testing, up to a 48-inch tap for the installation of a variety of ports, valves, t-sections or other pipes.
Hot Tap Procedures:
A. A hot tap saddle, service saddle or welded threadolet, valve installed, assembly is pressure tested and hot tap machine attached.
B. Valve opened, hot tap completed, coupon or cut portion retained by latches on pilot drill. Pressure is contained within the hot tapping machine.
C. Cutter and coupon retracted and valve closed. Fluid is drained and hot tapping machine is removed. The tapped valve is now ready for the contractors tie-in or IFTs linestop/stopple equipment to be inserted.
Hot tapping is also the first procedure in line stopping, where a hole saw is used to make an opening in the pipe, so a line plugging head can be inserted.
Situations in which welding operations are prohibited on equipment which contains:
* Mixtures of gases or vapours within their flammable range or which may become flammable as a result of heat input in welding operations.
* Substances which may undergo reaction or decomposition leading to a dangerous increase in pressure, explosion or attack on metal. In this context, attention is drawn to the possibility that under certain combinations of concentration, temperature and pressure, acetylene, ethylene and other unsaturated hydrocarbons may decompose explosively, initiated by a welding hot spot.
* Oxygen-enriched atmospheres in the presence of hydrocarbons which may be present either in the atmosphere or deposited on the inside surface of the equipment or pipe.
* Compressed air in the presence of hydrocarbons which may be present either in the air or deposited on the inside surfaces of the equipment or pipe.
* Gaseous mixtures in which the partial pressure of hydrogen exceeds 700 kPa gauge, except where evidence from tests has demonstrated that hot-tapping can be done safely.
Based on the above, welding on equipment or pipe which contains hazardous substances or conditions as listed below (even in small quantities) shall not be performed unless positive evidence has been obtained that welding/hot tapping can be applied safely.
Substances
* Acetylene
* Acetonitrile
* Butadiene
* Caustic soda*
* Chlorine
* Compressed air at a pressure in excess of 3000 kPa gauge;
* Ethylene
* Ethylene oxide
* Fat/lean DEA/MEA;
* High pressure steam (pressure in excess of 5000 kPa (ga))
* Hydraulic Oil
* Hydrogen (partial pressure in excess of 700 kPa (ga))
* Hydrogen sulphide*
* Hydrofluoric acid
* Oxygen
* Propene
* Propene oxide
* Sulphuric acid
* Toxic substances.*
Constraints based on general hazard in the event of line puncturing during welding, not the welding process. Conditions:
* Vacuum conditions;
* Dissolved hydrogen in the pipe wall (e.g. due to service history);
* Pyrophoric scale deposits.
Note: The above list is not exhaustive, but gives an indication only. | 1 | Applied and Interdisciplinary Chemistry |
The idea of synthetic fibre reinforced pipe has origins in the flexible hose and offshore industry where it has been frequently used for applications such as control lines in umbilicals and production flowlines for over 30 years. However, the commercialisation and realisation of a competitive product for the onshore oil industry came from a partnership between Teijin Aramid (supplier of aramid fibre Twaron) and Wavin Repox (manufacturer of reinforced thermoset pipes), where Bert Dalmolen initiated a project to develop such a pipe. He was later employed by Pipelife where a state of the art production line was developed to produce RTP. Pipelife also developed a pipe reinforced with steel wire to achieve even higher pressure ratings of over using steel reinforcement. Mr Chevrier (Tubes d'Aquitaine) also developed machinery that could produce such pipes, but was not successful in commercialising RTP. | 1 | Applied and Interdisciplinary Chemistry |
Differences in the abundance of isotopes among natural samples are extremely small (almost always below 0.1% or 1 per mille). Nevertheless, these very small differences can record meaningful geological processes. To compare these tiny but meaningful differences, isotope abundances in natural materials are often reported relative to isotope abundances in designated standards, with the delta (δ) notation. The absolute values of Xe isotopes are normalized to atmospheric Xe. Define where i = 124, 126, 128, 129, 131, 132, 134, 136. | 0 | Theoretical and Fundamental Chemistry |
The chute-type machine has a lower footprint and fewer moving parts which results in lower investment and operating costs. In general, it is more applicable to well liberated material and surface detection, because a double sided scanning is possible on a more reliable on the system. The applicable top size of the chute-type machine is bigger, as material handling of particles up to is only technically viable on this setup.
The cost for most average farmers and industry workers is around $500 for the study and ergonomic design of the sensor. The sensor itself is still a prototype not yet built but looking to be approved by FDA around 2003 | 0 | Theoretical and Fundamental Chemistry |
Chloromethane is an abundant organohalogen, anthropogenic or natural, in the atmosphere. Natural sources produce an estimated 4,100,000,000 kg/yr. | 1 | Applied and Interdisciplinary Chemistry |
An electron avalanche happens between two unconnected electrodes in a gas when an electric field exceeds a certain threshold. Random thermal collisions of gas atoms may result in a few free electrons and positively charged gas ions, in a process called impact ionization. Acceleration of these free electrons in a strong electric field causes them to gain energy, and when they impact other atoms, the energy causes release of new free electrons and ions (ionization), which fuels the same process. If this process happens faster than it is naturally quenched by ions recombining, the new ions multiply in successive cycles until the gas breaks down into a plasma and current flows freely in a discharge.
Electron avalanches are essential to the dielectric breakdown process within gases. The process can culminate in corona discharges, streamers, leaders, or in a spark or continuous electric arc that completely bridges the gap. The process may extend huge sparks — streamers in lightning discharges propagate by formation of electron avalanches created in the high potential gradient ahead of the streamers advancing tips. Once begun, avalanches are often intensified by the creation of photoelectrons as a result of ultraviolet radiation emitted by the excited mediums atoms in the aft-tip region. The extremely high temperature of the resulting plasma cracks the surrounding gas molecules and the free ions recombine to create new chemical compounds.
The process can also be used to detect radiation that initiates the process, as the passage of a single particles can be amplified to large discharges. This is the mechanism of a Geiger counter and also the visualization possible with a spark chamber and other wire chambers. | 0 | Theoretical and Fundamental Chemistry |
The Papkovich–Neuber solution represents the velocity and pressure fields of an incompressible Newtonian Stokes flow in terms of two harmonic potentials. | 1 | Applied and Interdisciplinary Chemistry |
Standard monolayer cell culturing on tissue culture plastic has notably improved the understanding of basic cell biology, but it does not replicate the complex 3D architecture of in vivo tissue, and it can significantly modify cell properties. This often compromises experiments in basic life science, leads to misleading drug-screening results on efficacy and toxicity, and produces cells that may lack the characteristics needed for developing tissue regeneration therapies.
The future of cell culturing for fundamental studies and biomedical applications lies in the creation of multicellular structure and organization in three dimensions. Many schemes for 3D culturing are being developed or marketed, such as bio-reactors or protein-based gel environments.
A 3D cell culturing system known as the Bio-Assembler uses biocompatible polymer-based reagents to deliver magnetic nanoparticles to individual cells so that an applied magnetic driver can levitate cells off the bottom of the cell culture dish and rapidly bring cells together near the air-liquid interface. This initiates cell-cell interactions in the absence of any artificial surface or matrix. Magnetic fields are designed to rapidly form 3D multicellular structures in as little as a few hours, including expression of extracellular matrix proteins. The matrix, protein expression, and response to exogenous agents of resulting tissue show great similarity to in vivo results. | 0 | Theoretical and Fundamental Chemistry |
Microglobulin is a globulin of relatively small molecular weight. It can be contrasted to macroglobulin.,
Examples include:
* Beta-2 microglobulin
* Alpha-1-microglobulin | 1 | Applied and Interdisciplinary Chemistry |
Fluorides include compounds that contain ionic fluoride and those in which fluoride does not dissociate. The nomenclature does not distinguish these situations. For example, sulfur hexafluoride and carbon tetrafluoride are not sources of fluoride ions under ordinary conditions.
The systematic name fluoride, the valid IUPAC name, is determined according to the additive nomenclature. However, the name fluoride is also used in compositional IUPAC nomenclature which does not take the nature of bonding involved into account.
Fluoride is also used non-systematically, to describe compounds which release fluoride upon dissolving. Hydrogen fluoride is itself an example of a non-systematic name of this nature. However, it is also a trivial name, and the preferred IUPAC name for fluorane. | 1 | Applied and Interdisciplinary Chemistry |
Stationary phases can react with CDAs to form chiral stationary phases which can resolve chiral molecules. By reacting with alcohols on a silicate stationary phase, CDAs add a chiral center to the stationary phase, which allows for the separation of chiral molecules. | 0 | Theoretical and Fundamental Chemistry |
The hydrolysis of nitriles RCN proceeds in the distinct steps under acid or base treatment to first give carboxamides and then carboxylic acids RCOOH. The hydrolysis of nitriles to carboxylic acids is efficient. In acid or base, the balanced equations are as follows:
Strictly speaking, these reactions are mediated (as opposed to catalyzed) by acid or base, since one equivalent of the acid or base is consumed to form the ammonium or carboxylate salt, respectively.
Kinetic studies show that the second-order rate constant for hydroxide-ion catalyzed hydrolysis of acetonitrile to acetamide is 1.6 M s, which is slower than the hydrolysis of the amide to the carboxylate (7.4 M s). Thus, the base hydrolysis route will afford the carboxylate (or the amide contaminated with the carboxylate). On the other hand, the acid catalyzed reactions requires a careful control of the temperature and of the ratio of reagents in order to avoid the formation of polymers, which is promoted by the exothermic character of the hydrolysis. The classical procedure to convert a nitrile to the corresponding primary amide calls for adding the nitrile to cold concentrated sulfuric acid. The further conversion to the carboxylic acid is disfavored by the low temperature and low concentration of water.
Two families of enzymes catalyze the hydrolysis of nitriles. Nitrilases hydrolyze nitriles to carboxylic acids:
Nitrile hydratases are metalloenzymes that hydrolyze nitriles to amides.
These enzymes are used commercially to produce acrylamide.
The "anhydrous hydration" of nitriles to amides has been demonstrated using an oxime as water source: | 0 | Theoretical and Fundamental Chemistry |
Oxidative lesions are an umbrella category of lesions caused by reactive oxygen species (ROS), reactive nitrogen species (RNS), other byproducts of cellular metabolism, and exogenous factors such as ionizing or ultraviolet radiation. Byproducts of oxidative respiration are the main source of reactive species which cause a background level of oxidative lesions in the cell. DNA and RNA are both affected by this, and it has been found that RNA oxidative lesions are more abundant in humans compared to DNA. This may be due cytoplasmic RNA having closer proximity to the electron transport chain. Known oxidative lesions characterized in DNA and RNA are many in number, as oxidized products are unstable and may resolve quickly. The hydroxyl radical and singlet oxygen are common reactive oxygen species responsible for these lesions. 8-oxo-guanine (8-oxoG) is the most abundant and well characterized oxidative lesion, found in both RNA and DNA. Accumulation of 8-oxoG may cause dire damage within the mitochondria and is thought to be a key player in the aging process. RNA oxidation has direct consequences in the production of proteins. mRNA affected by oxidative lesions is still recognized by ribosome, but the ribosome will undergo stalling and dysfunction. This results in proteins having either decreased expression or truncation, leading to aggregation and general dysfunction. | 1 | Applied and Interdisciplinary Chemistry |
The head group classification of a surfactant is determined by the head group ion type. Ionic surfactants derive their amphiphilicity from a charged hydrophilic head group and tend to be small, low molecular weight molecules. Ionic surfactants will stabilize particles suspended in a paint by electrostatic repulsion and are easily adsorbed and desorbed from a surface due to their small size.
Anionic head groups are negatively charged, and commonly used in cleaning products. Anionic surfactants can be found in products such as shampoos, laundry detergents, and soaps because of their ability to remove dirt from soft mediums such as fabric. Anionic surfactants are easily suspended in water due to the polarity of the charged head group. However, hard water can deactivate the molecule. Some of the more commonly used anionic head groups are sulfates and ethoxylates.
Cationic head groups have a positive charge and cationic surfactants are used in several different applications. One common use for cationic surfactants is in fabric softeners. Cationic head groups are also added to laundry detergent in conjunction with anionic surfactants because they help to improve the dirt removal properties of the anionic surfactants. Cationic head groups also increase the disinfecting properties of household cleaners. Some common cationic surfactants head groups include amines and quaternary ammonium ions.
Among the many types of surfactants, cationic surfactants are very useful corrosion inhibitors due of their protective effectiveness in neutral and acidic media.
Nonionic head groups have no charge and they function very well as grease removers. Nonionic surfactants are commonly used in detergents, soaps, and household cleaners. In solutions of hard water, nonionic surfactants are used to help limit the deactivation of ionic surfactants caused by the calcium and magnesium ions. Some common nonionic surfactant head groups include fatty acids and glycols. | 0 | Theoretical and Fundamental Chemistry |
Fancy and Kodadek's invention of PICUP in 1999 was the first time proteins cross-linking was able to be performed in such a short period of time (1 second) and without modifying the structure of the proteins in question. Additionally, PICUP was able to be performed at physiological pH of 7.4, which opened doors for further application of protein cross-linking such as studying the biochemical mechanisms that proteins participate in the human body. In addition, irradiation by visible light in PICUP is useful because many biomolecules that participate in metabolic pathways to be analyzed do no absorb light with wavelengths below the range for UV light, allowing for cross-links without denaturation. | 1 | Applied and Interdisciplinary Chemistry |
Cyclopropanation of olefins with diazocarbonyl compounds is commonly accomplished using rhodium carboxylate complexes, although copper was originally used. The scope of the olefin is generally quite broad—electron-rich, neutral, and electron-poor olefins have all been cyclopropanated efficiently using rhodium-based catalyst systems. This section describes the various classes of diazocarbonyl compounds that react with olefins under rhodium catalysis to afford cyclopropanes.
Diazoacetates that possess a single carbonyl substituent attached to the diazo carbon, have been used for the cyclopropanation of a wide array of olefins. Diastereoselectivity for the (E) cyclopropane increases as the size of the ester group increases. In addition, adding electron density to the catalyst (for instance by replacing acetate ligands with acetamide, acam) increases the diastereoselectivity of the reaction.
Diazocarbonyl compounds substituted with two electron-withdrawing groups, such as diazomalonates, are prone to experience side reactions under cyclopropanation conditions. [3+2] Cycloaddition and C-H insertion side products have been observed.
Diazoacetates substituted with a vinyl or aryl group on the diazo carbon are unreactive towards trans-alkenes. This result has been explained by invoking the transition state model in Eq. (2). Reactions of these substrates are highly selective for the (E) cyclopropane isomer.
Vinyl diazoacetates react with dienes to afford divinyl cyclopropanes, which undergo Cope rearrangement to afford cycloheptadienes. The more substituted double bond of the diene reacts preferentially.
Furans react similarly with vinyl diazoacetates, although the intermediate cyclopropane may transform either into the Cope rearrangement product or an opened unsaturated carbonyl compound. The distribution of these products is highly dependent on the substitution pattern of the furan.
Pyrroles react with vinyl diazoacetates to form nitrogen-bridged cycloheptadienes. The use of methyl lactate as a chiral auxiliary on the vinyl diazoacetate led to moderate diastereoselectivity in the tandem cyclopropanation/Cope rearrangement of Boc-protected pyrrole.
The enantioselectivity of asymmetric cyclopropanations may depend profoundly on the solvent. | 0 | Theoretical and Fundamental Chemistry |
The components of bitumen include four main classes of compounds:
* Naphthene aromatics (naphthalene), consisting of partially hydrogenated polycyclic aromatic compounds
* Polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material
* Saturated hydrocarbons; the percentage of saturated compounds in asphalt correlates with its softening point
* Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds
Bitumen typically contains, elementally 80% by weight of carbon; 10% hydrogen; up to 6% sulfur; and molecularly, between 5 and 25% by weight of asphaltenes dispersed in 90% to 65% maltenes. Most natural bitumens also contain organosulfur compounds, Nickel and vanadium are found at <10 parts per million, as is typical of some petroleum. The substance is soluble in carbon disulfide. It is commonly modelled as a colloid, with asphaltenes as the dispersed phase and maltenes as the continuous phase. "It is almost impossible to separate and identify all the different molecules of bitumen, because the number of molecules with different chemical structure is extremely large".
Asphalt may be confused with coal tar, which is a visually similar black, thermoplastic material produced by the destructive distillation of coal. During the early and mid-20th century, when town gas was produced, coal tar was a readily available byproduct and extensively used as the binder for road aggregates. The addition of coal tar to macadam roads led to the word "tarmac", which is now used in common parlance to refer to road-making materials. However, since the 1970s, when natural gas succeeded town gas, bitumen has completely overtaken the use of coal tar in these applications. Other examples of this confusion include La Brea Tar Pits and the Canadian tar sands, both of which actually contain natural bitumen rather than tar. "Pitch" is another term sometimes informally used at times to refer to asphalt, as in Pitch Lake. | 0 | Theoretical and Fundamental Chemistry |
The emission of electromagnetic radiation (EMR) during plastic deformation and crack propagation in metals and rocks has been studied. The EMR emissions from metals and alloys have also been explored and confirmed. Molotskii presented a dislocation mechanism for this type of EMR emission. In 2005, Srilakshmi and Misra reported an additional phenomenon of secondary EMR during plastic deformation and crack propagation in uncoated and metal-coated metals and alloys.
EMR during the micro-plastic deformation and crack propagation from several metals and alloys and transient magnetic field generation during necking in ferromagnetic metals were reported by Misra (1973–75), which have been confirmed and explored by several researchers. Tudik and Valuev (1980) were able to measure the EMR frequency during tensile fracture of iron and aluminum in the region 100 THz by using photomultipliers. Srilakshmi and Misra (2005a) also reported an additional phenomenon of secondary electromagnetic radiation in uncoated and metal-coated metals and alloys. If a solid material is subjected to stresses of large amplitudes, which can cause plastic deformation and fracture, emissions such as thermal, acoustic, ions, and exo-emissions occur. | 0 | Theoretical and Fundamental Chemistry |
An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts:
* The chemical gradient, or difference in solute concentration across a membrane.
* The electrical gradient, or difference in charge across a membrane.
When there are unequal concentrations of an ion across a permeable membrane, the ion will move across the membrane from the area of higher concentration to the area of lower concentration through simple diffusion. Ions also carry an electric charge that forms an electric potential across a membrane. If there is an unequal distribution of charges across the membrane, then the difference in electric potential generates a force that drives ion diffusion until the charges are balanced on both sides of the membrane.
Electrochemical gradients are essential to the operation of batteries and other electrochemical cells, photosynthesis and cellular respiration, and certain other biological processes. | 0 | Theoretical and Fundamental Chemistry |
Unlike the hormones with which it competes, flutamide is not a steroid; rather, it is a substituted anilide. Hence, it is described as nonsteroidal in order to distinguish it from older steroidal antiandrogens such as cyproterone acetate and megestrol acetate. | 0 | Theoretical and Fundamental Chemistry |
Mining is the largest source of uranium contamination in the environment. Uranium milling creates radioactive waste in the form of tailings, which contain uranium, radium, and polonium. Consequently, uranium mining results in "the unavoidable radioactive contamination of the environment by solid, liquid and gaseous wastes".
Seventy percent of global uranium resources are on or adjacent to traditional lands belonging to Indigenous people, and perceived environmental risks associated with uranium mining have resulted in environmental conflicts involving multiple actors wherein local campaigns become national or international debates.
Some of these environmental conflicts have limited uranium exploration. Incidents at Ranger uranium mine in the Northern Territory of Australia and disputes over Indigenous land rights led to increased opposition to development of the nearby Jabiluka deposits and suspension of that project in the early 2000s. Similarly, environmental damage from Uranium mining on traditional Navajo lands in the southwestern United States resulted in restrictions on additional mining in Navajo lands in 2005. | 0 | Theoretical and Fundamental Chemistry |
The data stored in SABIO-RK in a comprehensive manner is mainly extracted manually from literature. This includes reactions, their participants (substrates, products), modifiers (inhibitors, activators, cofactors), catalyst details (e.g. EC enzyme classification, protein complex composition, wild type / mutant information), kinetic parameters together with corresponding rate equation, biological sources (organism, tissue, cellular location), environmental conditions (pH, temperature, buffer) and reference details. Data are adapted, normalized and annotated to controlled vocabularies, ontologies and external data sources including KEGG, UniProt, ChEBI, PubChem, NCBI, Reactome, BRENDA, MetaCyc, BioModels, and PubMed.<br/>
As of October 2021 SABIO-RK contains about 71.000 curated single entries extracted from more than 7.300 publications.
<br/>
Several tools, databases and workflows in Systems Biology make use of SABIO-RK biochemical reaction data by integration into their framework including
SYCAMORE,
MeMo-RK,
CellDesigner,
PeroxisomeDB,
Taverna workflows
or tools like KineticsWizard software for data capture and analysis.
Additionally, SABIO-RK is part of MIRIAM registry, a set of guidelines for the annotation and curation of computational models | 1 | Applied and Interdisciplinary Chemistry |
In Japan, "clarke" is translated as . The word is always added, which happens to make the term appear similar in form with scientific constants such as . The term may have a narrower sense than Fersman's. Several of the following constraints may apply:
* Only of Earth's crust
* Lithosphere approximated as a 10 mile-deep layer from sea level
* Must include all of three layers: lithosphere (93.06%), hydrosphere (0.91%) and atmosphere (0.03%)
* Only mass ratio)
* Denote in percents) (not in ppm or ppb)
* (What the quoter believes to be) data from Clarke and Washington(1924)
Another peculiarity in Japan is the existence of a popular version of data, which was tabulated in reference books such as the annual "Chronological Scientific Tables" (RCST1939(1938)), the "Dictionary of Physics and Chemistry" (IDPC(1939)) and other prominent books on geochemistry and chemistry. This version Kimura(1938) was devised by chemist . It was often quoted as The "Clarke numbers" (unsourced examples:,). The numbers differed from any versions by Clarke / Clarke&Washington (1889–1924), or anything listed in foreign (non-Japanese) articles such as the USGS compilation , thus unknown outside of Japan. Yet the numbers were sometimes quoted in English articles without citation (example:).
As geological definition of "Earths crust" evolved, the "10 mile-deep" approximation were deemed out-of-date, and some people considered the term "clarke number" obsolete too. Yet other people may have meant broader senses, not limiting to Earths crust, leading to confusion. RCST1961(1961) switched their "clarke number" table from Kimura(1938) to Mason(1958) based, and the label "clarke number" on table was removed in RCST1963(1962). IDPC(1971) removed the "clarke number" table which was a Kimura(1938)s variant. IDPC(1981) said the term is mostly abandoned, and the dictionary entry for "clarke number" itself was removed from IDPC(1998). So "clarke numbers" became associated almost solely with Kimura(1938)s data, but Kimuras name forgotten. Incidentally, in major reference books, there was no data table titled "clarke numbers" which showed Clarkes original tables.
Despite being removed from major reference books, data from Kimura(1938) and phrases such as "the Clarke number of iron is 4.70", unsourced, continue to circulate, even in the 2010s (example:). | 0 | Theoretical and Fundamental Chemistry |
Consider a typical chemical reaction in which two reactants A and B combine to form a product C:
This can also be written
The prefactors −1, −2 and 3 (with negative signs for reactants because they are consumed) are known as stoichiometric coefficients. One molecule of A combines with two of B to form 3 of C, so if we use the symbol [X] for the molar concentration of chemical X,
If the reaction takes place in a closed system at constant temperature and volume, without a build-up of reaction intermediates, the reaction rate is defined as
where is the stoichiometric coefficient for chemical X, with a negative sign for a reactant.
The initial reaction rate has some functional dependence on the concentrations of the reactants,
and this dependence is known as the rate equation or rate law. This law generally cannot be deduced from the chemical equation and must be determined by experiment. | 0 | Theoretical and Fundamental Chemistry |
Mayeda worked initially as a laboratory assistant to Harold Urey at the University of Chicago, where she was hired initially to wash glassware. They used mass spectrometry to measure oxygen isotopes in the shells of marine molluscs which gave information on the prehistoric temperatures of ocean waters and hence paleoclimates. Urey developed the field of cosmochemistry and with Mayeda studied primitive meteorites, also by using oxygen isotope analysis. Later, she worked with Cesare Emiliani on isotopic evaluation of the ice age. When Urey retired from the university in 1958, Mayeda was persuaded to remain there by Robert N. Clayton, and collaborate with him on applications of mass spectroscopy. She was described as an indomitable research assistant.
Mayeda and Clayton's first research paper considered the use of Bromine pentafluoride to extract Isotopes of oxygen from rocks and minerals. It remains their most cited work. From the 1970s until the late 1990s Mayeda and Clayton became famous for their use of oxygen isotopes to classify meteorites. They developed several tests that were used across the field of meteorite and lunar sample analysis. They studied variations in the abundances of the stable isotopes of oxygen, oxygen-16, oxygen-17 and oxygen-18, and deduced differences in the formation temperatures of the meteorites. They also worked on the mass spectroscopy and chemistry of the Allende meteorite. They published many scientific papers on the "oxygen thermometer" and analysed approximately 300 lunar samples that had been collected during NASAs Apollo Program.
In 1992, a new type of meteorite, the Brachinite, was identified. Clayton and Mayeda studied the Achondrite meteorites and showed that variations in the oxygen-17 isotope ratios within a planet are due to inhomogeneities in the Solar Nebula. They analysed Shergotty meteorites, proposing that there could have been a water-rich atmosphere on Mars and studied the Bocaiuva meteorite, finding that the Eagle Station meteorite was formed due to impact heating.
In 2002 Mayeda was awarded the Society Merit Prize from the Geochemical Society of Japan. In the same year, an asteroid was named after her. Mayedas husband, Harry, died in 2003. Mayeda suffered from cancer and died on February 13, 2004. In 2008, the book Oxygen in the Solar System' was dedicated to Clayton and Mayeda. | 0 | Theoretical and Fundamental Chemistry |
In 1832, the family settled in Mecklenburg County, Virginia, east of Christiansville (now Chase City). Although he arrived too late to obtain the prospective teaching position, John William established a laboratory in Christiansville. Here he conducted experiments and published eight papers before entering medical school. His sister Dorothy Catherine Draper provided finances through teaching drawing and painting for his medical education. In March 1836, he graduated from the University of Pennsylvania School of Medicine. That same year, he began teaching at Hampden–Sydney College in Virginia. | 0 | Theoretical and Fundamental Chemistry |
Air is liquefied by the Linde process, in which air is alternately compressed, cooled, and expanded, each expansion results in a considerable reduction in temperature. With the lower temperature the molecules move more slowly and occupy less space, so the air changes phase to become liquid. | 0 | Theoretical and Fundamental Chemistry |
Bioglass 8625, also called Schott 8625, is a soda-lime glass used for encapsulation of implanted devices. The most common use of Bioglass 8625 is in the housings of RFID transponders for use in human and animal microchip implants. It is patented and manufactured by Schott AG. Bioglass 8625 is also used for some piercings.
Bioglass 8625 does not bond to tissue or bone, it is held in place by fibrous tissue encapsulation. After implantation, a calcium-rich layer forms on the interface between the glass and the tissue. Without additional antimigration coating it is subject to migration in the tissue. The antimigration coating is a material that bonds to both the glass and the tissue. Parylene, usually Parylene type C, is often used as such material.
Bioglass 8625 has a significant content of iron, which provides infrared light absorption and allows sealing by a light source, e.g., a Nd:YAG laser or a mercury-vapor lamp. The content of FeO yields high absorption with maximum at 1100 nm, and gives the glass a green tint. The use of infrared radiation instead of flame or contact heating helps preventing contamination of the device.
After implantation, the glass reacts with the environment in two phases, in the span of about two weeks. In the first phase, alkali metal ions are leached from the glass and replaced with hydrogen ions; small amount of calcium ions also diffuses from the material. During the second phase, the Si-O-Si bonds in the silica matrix undergo hydrolysis, yielding a gel-like surface layer rich on Si-O-H groups. A calcium phosphate-rich passivation layer gradually forms over the surface of the glass, preventing further leaching.
It is used in microchips for tracking of many kinds of animals, and recently in some human implants. The U.S. Food and Drug Administration (FDA) approved use of Bioglass 8625 in humans in 1994. | 0 | Theoretical and Fundamental Chemistry |
Because many polymers are composed of primarily of hydrocarbon chains with at most slightly polar functional groups, they tend to have low surface energies and thus adsorb rather poorly. While this can be advantageous for some applications, modification of polymer surfaces is crucial for many other applications in which adhering a substrate to its surface is vital for optimal performance. For example, many applications utilize polymers as structural components, but which degrade rapidly when exposed to weather or other sources of wear. Therefore, coatings must be used which protect the structural layer from damage. However, the poor adhesive properties of nonpolar polymers makes it difficult to adsorb the protective coating onto its surface. These types of problems make the measurement and control of surface energies important to development of useful technologies.
The Gibbs energy of adsorption, , can be determined from the adsorption equilibrium constant:
Because is negative for a spontaneous process and positive for a nonspontaneous process, it can be used to understand the tendency for different compounds to adsorb to a surface. In addition, it can be divided into a combination of two components:
which are the Gibbs energies of physisorption and chemisorption, respectively. Many polymer applications, such as those which use polytetrafluoroethylene (PTFE, or Teflon) require the use of a surface with specific physisorption properties toward one type of material, while being firmly adhered in place to a different type of material. Because the physisorption energy is so low for these types of materials, chemisorption is used to form covalent bonds between the polymer coating and the surface of the object (such as a pan) which holds it in place. Because the relative magnitudes of chemisorption processes are generally much greater than magnitudes of physisorption processes, this forms a strong bond between the polymer and the surface it is chemically adhered to, while allowing the polymer to retain its physisorption characteristics toward other materials.
Experimentally, the enthalpy and entropy of adsorption are often used to fine-tune the adsorption properties of a material. The enthalpy of adsorption can be determined from constant pressure calorimetry:
where:
: is the heat exchanged,
: is the integral molar enthalpy of adsorption,
: is the number of moles adsorbed.
From the enthalpy of adsorption, the entropy of adsorption can be calculated:
where:
: is the integral molar entropy of adsorption,
: is the temperature in kelvins.
Together, these are used to understand the driving forces behind adsorption processes. | 0 | Theoretical and Fundamental Chemistry |
Since there is no rotation at large , becomes independent of resulting in . Hence and .
Here the boundary conditions for the fluid are
Self-similar solution is obtained by introducing following transformation,
where is the fluid density.
The self-similar equations are
with boundary conditions for the fluid are
The coupled ordinary differential equations need to be solved numerically and an accurate solution is given by Cochran(1934). The inflow axial velocity at infinity obtained from the numerical integration is , so the total outflowing volume flux across a cylindrical surface of radius is . The tangential stress on the disk is . Neglecting edge effects, the torque exerted by the fluid on the disk with large () but finite radius is
The factor is added to account for both sides of the disk. From numerical solution, torque is given by . The torque predicted by the theory is in excellent agreement with the experiment on large disks up to the Reynolds number of about , the flow becomes turbulent at high Reynolds number. | 1 | Applied and Interdisciplinary Chemistry |
Another type of drug delivery vehicle used is polymeric micelles. They are prepared from certain amphiphilic co-polymers consisting of both hydrophilic and hydrophobic monomer units. They can be used to carry drugs that have poor solubility. This method offers little in the terms of size control or function malleability. Techniques that utilize reactive polymers along with a hydrophobic additive to produce a larger micelle that create a range of sizes have been developed.
Dendrimers are also polymer-based delivery vehicles. They have a core that branches out in regular intervals to form a small, spherical, and very dense nanocarrier. | 1 | Applied and Interdisciplinary Chemistry |
Metals can be toxic in high quantities. Either ingestion or faulty metabolic pathways can lead to metal toxicity (metal poisoning). Sources of toxic metals include cadmium from tobacco, arsenic from agriculture and mercury from volcanoes and forest fires. Nature, in the form of trees and plants, is able to trap many toxins and can bring abnormally high levels back into equilibrium. Toxic metal poisoning is usually treated with some type of chelating agent. Heavy metal poisoning, such as from mercury, cadmium, or lead, is particularly pernicious.
Examples of specific types of toxic metals include:
* Copper: copper toxicity usually presents itself as a side effect of low levels of the protein ceruloplasmin, which normally is involved in copper storage. This is referred to as Wilson’s disease. Wilson's disease is an autosomal recessive genetic disorder whose mutation causes the ATPase that transports copper into bile and ultimately incorporates it into ceruloplasmin to malfunction.
* Plutonium: ever since the nuclear age, plutonium poisoning is a potential danger, especially among nuclear reactor employees; inhalation of Pu dust is particularly dangerous due to its intense alpha particle emission. There have been very few cases of plutonium poisoning.
* Mercury: mercury is usually ingested from agricultural sources or other environmental sources. Mercury poisoning can lead to neurological disease and kidney failure if left untreated.
* Iron: iron toxicity, iron poisoning, or iron overload is well known. Iron does test only very weakly positive for the Ames test for cancer, however, since it is such a strong catalyst and essential for the production of ATP and consequently DNA production, any excess soluble iron is toxic especially over time. Too much iron deposited in tissues or high levels in the blood stream has been successfully linked to a vast majority of human diseases from Alzheimer's to Malaria. In Botany, iron is a severe problem for the irrigation of plants like rice, maize, or wheat in Sub-Saharan Africa whose subterranean water contains excessive amounts of iron which then poisons these crops.
* Lead and cadmium: lead poisoning and cadmium poisoning can lead to gastrointestinal, kidney, and neurological dysfunction. The use of unleaded paints and gas has successfully decreased the number of cases of lead heavy metal poisoning.
* Nickel, chromium, and cadmium: via metal-DNA interactions, these metals can be carcinogenic.
* Nickel: allergies to nickel, particularly from skin to metal contact via jewelry, are common.
* Zinc, cadmium, magnesium, chromium: metal fume fever can be caused by ingestion of the fumes of these metals and leads to flu-like symptoms.
* Beryllium: The risk of beryllium poisoning is relevant to occupational safety and health for metalworkers or ore millers who work with alloys or ores that contain beryllium in greater than trace amounts. For alloys, this means those alloys in which beryllium is intentionally featured, and for ores, it means those pursued for beryllium or those with nonnegligible beryllium co-occurrence. | 1 | Applied and Interdisciplinary Chemistry |
The population of vibrationally excited states follows a Boltzmann distribution, so low-frequency vibrational states are appreciably populated even at room temperatures. As the moment of inertia is higher when a vibration is excited, the rotational constants (B) decrease. Consequently, the rotation frequencies in each vibration state are different from each other. This can give rise to "satellite" lines in the rotational spectrum. An example is provided by cyanodiacetylene, H−C≡C−C≡C−C≡N.
Further, there is a fictitious force, Coriolis coupling, between the vibrational motion of the nuclei in the rotating (non-inertial) frame. However, as long as the vibrational quantum number does not change (i.e., the molecule is in only one state of vibration), the effect of vibration on rotation is not important, because the time for vibration is much shorter than the time required for rotation. The Coriolis coupling is often negligible, too, if one is interested in low vibrational and rotational quantum numbers only. | 0 | Theoretical and Fundamental Chemistry |
Marquis reagent was first discovered in 1896 and described by the Russian (Estonian) pharmacologist, Eduard Markus (1871–1944) () in his magister dissertation in 1896; and named after him, and was tested for the first time at the University of Dorpat. The reagent should be stored in the freezer for maximum shelf life.
It is the primary presumptive test used in Ecstasy reagent testing kits. It can also be used to test for such substances as opiates (e.g. codeine, heroin), and phenethylamines (e.g. 2C-B, mescaline).
The test is performed by scraping off a small amount of the substance and adding a drop of the reagent (which is initially clear and colorless). The results are analyzed by viewing the color of the resulting mixture, and by the time taken for the change in color to become apparent: | 0 | Theoretical and Fundamental Chemistry |
AFM scanners are made from piezoelectric material, which expands and contracts proportionally to an applied voltage. Whether they elongate or contract depends upon the polarity of the voltage applied. Traditionally the tip or sample is mounted on a "tripod" of three piezo crystals, with each responsible for scanning in the x,y and z directions. In 1986, the same year as the AFM was invented, a new piezoelectric scanner, the tube scanner, was developed for use in STM. Later tube scanners were incorporated into AFMs. The tube scanner can move the sample in the x, y, and z directions using a single tube piezo with a single interior contact and four external contacts. An advantage of the tube scanner compared to the original tripod design, is better vibrational isolation, resulting from the higher resonant frequency of the single element construction, in combination with a low resonant frequency isolation stage. A disadvantage is that the x-y motion can cause unwanted z motion resulting in distortion. Another popular design for AFM scanners is the flexure stage, which uses separate piezos for each axis, and couples them through a flexure mechanism.
Scanners are characterized by their sensitivity, which is the ratio of piezo movement to piezo voltage, i.e., by how much the piezo material extends or contracts per applied volt. Due to the differences in material or size, the sensitivity varies from scanner to scanner. Sensitivity varies non-linearly with respect to scan size. Piezo scanners exhibit more sensitivity at the end than at the beginning of a scan. This causes the forward and reverse scans to behave differently and display hysteresis between the two scan directions. This can be corrected by applying a non-linear voltage to the piezo electrodes to cause linear scanner movement and calibrating the scanner accordingly. One disadvantage of this approach is that it requires re-calibration because the precise non-linear voltage needed to correct non-linear movement will change as the piezo ages (see below). This problem can be circumvented by adding a linear sensor to the sample stage or piezo stage to detect the true movement of the piezo. Deviations from ideal movement can be detected by the sensor and corrections applied to the piezo drive signal to correct for non-linear piezo movement. This design is known as a "closed loop" AFM. Non-sensored piezo AFMs are referred to as "open loop" AFMs.
The sensitivity of piezoelectric materials decreases exponentially with time. This causes most of the change in sensitivity to occur in the initial stages of the scanner's life. Piezoelectric scanners are run for approximately 48 hours before they are shipped from the factory so that they are past the point where they may have large changes in sensitivity. As the scanner ages, the sensitivity will change less with time and the scanner would seldom require recalibration, though various manufacturer manuals recommend monthly to semi-monthly calibration of open loop AFMs. | 0 | Theoretical and Fundamental Chemistry |
Due to their toxicity, use of first-generation glycopeptide antibiotics is restricted to patients who are critically ill, who have a demonstrated hypersensitivity to the β-lactams, or who are infected with β-lactam-resistant species, as in the case of methicillin-resistant Staphylococcus aureus. These antibiotics are effective principally against Gram-positive cocci. First-generation examples exhibit a narrow spectrum of action, and are bactericidal only against the enterococci. Some tissues are not penetrated very well by glycopeptides, and they do not penetrate into the cerebrospinal fluid.
The second-generation glycopeptides, or "lipoglycopeptides", have better binding to Lipid II due to the lipophilic moieties, expanding the antibacterial spectrum. Telavancin also has a hydrophilic moiety attached to enhance tissue distribution and reduce nephrotoxicity. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, an alkali (; from ) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline, and less often, alkalescent, is commonly used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases. | 0 | Theoretical and Fundamental Chemistry |
*Chandler Chemistry Laboratory at Lehigh University, constructed in 1884
*Joseph Priestley House, U.S. home of Joseph Priestley, discoverer of oxygen, from 1798 to 1804 | 1 | Applied and Interdisciplinary Chemistry |
Modified bisulfite sequencing was optimized for rRNA, tRNA, and miRNA molecules from Drosophila.
Bisulfite treatment has been most widely used to detect dm5C (DNA m5C). The treatment essentially converts a cytosine to a uridine, but methylated cytosines would be unchanged by the treatment.
Previous attempts to develop m5C sequencing protocols using bisulfite treatment were not able to effectively address the problem of the harsh treatment of RNA which causes significant degradation of the molecules. Specifically, bisulfite deamination treatment (high pH) of RNA is detrimental to the stability of phosphodiester bonds. As a result, it is difficult to pre-enrich RNA molecules or to obtain enough PCR product of the correct size for deep sequencing.
A modified version of bisulfite sequencing was developed by Schaefer et al. (2009) which decreased the temperature at which bisulfite treatment of RNA from 95 °C to 60 °C. The rationale behind the modification was that since RNA, unlike DNA, is not double-stranded, but rather, consists of regions of single-strandedness, double-stranded stem structures and loops, it could be possible to unwind RNA at a much lower temperature. Indeed, RNA could be treated for 180 minutes at 60C without significant loss of PCR amplicons of the expected size. Deamination rates were determined to be 99% at 180min of treatment.
After bisulfite treatment of fragmented RNA, reverse transcription is performed, followed by PCR amplification of the cDNA products, and finally deep sequencing was done using the Roche 454 platform.
Since the developers of the method used the Roche platform, they also used GS Amplicon Variant Analyzer (Roche) for analyzing deep sequencing data to quantify sequence-specific cytosine content.
However, recent papers have suggested that the method have several flaws: (1) Incomplete conversion of regular cytosines in double-stranded regions of RNA; (2) areas containing other modifications that resulted in bisulfite-treatment resistance; and (3) sites containing potential false-positives due to (1) and (2) In addition, it is possible the sequencing depth is still not high enough to correctly detect all methylated sites. | 1 | Applied and Interdisciplinary Chemistry |
Another technique that has been gaining ground for single molecule experiments is the use of optical tweezers for applying mechanical forces on molecules. A strongly focused laser beam has the ability to catch and hold particles (of dielectric material) in a size range from nanometers to micrometers. The trapping action of optical tweezers results from the dipole or optical gradient force on the dielectric sphere. The technique of using a focused laser beam as an atom trap was first applied in 1984 at Bell laboratories. Until then experiments had been carried out using oppositely directed lasers as a means to trap particles. Later experiments, at the same project at Bell laboratories and others since, showed damage-free manipulation on cells using an infrared laser. Thus, the ground was made for biological experiments with optical trapping.
Each technique has its own advantages and disadvantages. For example, AFM cantilevers, can measure angstrom-scale, millisecond events and forces larger than 10 pN. While glass microfibers cannot achieve such fine spatial and temporal resolution, they can measure piconewton forces. Optical tweezers allow the measurement of piconewton forces and nanometer displacements which is an ideal range for many biological experiments. Magnetic tweezers can measure femtonewton forces, and additionally they can also be used to apply torsion. AFS devices allow the statistical analysis of the mechanical properties of biological systems by applying picoNewton forces to hundreds of individual particles in parallel, with sub-millisecond response time. | 0 | Theoretical and Fundamental Chemistry |
In 1992, Hunter was jointly awarded the Meldola Medal and Prize by the Royal Society of Chemistry. It is awarded to a British chemist who was under 32 years of age for promising original investigations in chemistry. In 1999, he was jointly awarded the Corday–Morgan Medal and Prize by the Royal Society of Chemistry. It is awarded for the most meritorious contributions to chemistry. In 2008, he was elected a Fellow of the Royal Society (FRS), the premier learned society for science in the United Kingdom. | 0 | Theoretical and Fundamental Chemistry |
His medical interest led him to investigate the gases the miners breathed – fire damp (methane) and choke damp (oxygen depleted air). Carlisle Spedding helped to build a laboratory for Brownrigg and fed it with gases from a nearby coal mine through lead pipes. Brownrigg developed methods of collecting and transferring the gases and supplied James Lowther with gas filled bladders to show to The Royal Society which then elected Brownrigg as a Fellow.
His experiments on gases continued and after visiting a spa resort in Germany he became interested in gases to be found in mineral waters. A paper he published entitled "Experimental inquiry concerning the nature of the mineral elastic spirit or air contained in the Pouhon water, and other acidulae" earned him the prestigious Copley Medal in 1766. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, many reactions depend on the absorption of photons to provide the energy needed to overcome the activation energy barrier and hence can be labelled light-dependent. Such reactions range from the silver halide reactions used in photographic film to the creation and destruction of ozone in the upper atmosphere. This article discusses a specific subset of these, the series of light-dependent reactions related to photosynthesis in living organisms. | 0 | Theoretical and Fundamental Chemistry |
Several methods have been proposed for technetium-99 separation including: crystallization, liquid-liquid extraction, molecular recognition methods, volatilization, and others.
In 2012 the crystalline compound Notre Dame Thorium Borate-1 (NDTB-1) was presented by researchers at the University of Notre Dame. It can be tailored to safely absorb radioactive ions from nuclear waste streams. Once captured, the radioactive ions can then be exchanged for higher-charged species of a similar size, recycling the material for re-use. Lab results using the NDTB-1 crystals removed approximately 96 percent of technetium-99. | 0 | Theoretical and Fundamental Chemistry |
Anhydrous can be prepared from zinc and hydrogen chloride gas at 700 °C:
Aqueous solutions may be readily prepared similarly by treating Zn metal, zinc carbonate, zinc oxide, and zinc sulfide with hydrochloric acid:
Hydrates can be produced by evaporation of an aqueous solution of zinc chloride. Different evaporation temperatures produce different hydrates; for example, evaporation at room temperature produces the 1.33-hydrate. Lower evaporation temperatures produce higher hydrates.
Commercial samples of zinc chloride typically contain water and products from hydrolysis as impurities. Such samples may be purified by recrystallization from hot dioxane. Anhydrous samples can be purified by sublimation in a stream of hydrogen chloride gas, followed by heating the sublimate to 400 °C in a stream of dry nitrogen gas. Finally, the simplest method relies on treating the zinc chloride with thionyl chloride. | 0 | Theoretical and Fundamental Chemistry |
Aerobic respiration is the most preferred remineralisation reaction due to its high energy yield. Although oxygen is quickly depleted in the sediments and is generally exhausted centimeters from the sediment-water interface. | 0 | Theoretical and Fundamental Chemistry |
Two oligonucleotides are used for this step (Figure 1: Adapter oligos). One of the oligonucleotides contains a 12-nucleotide single-stranded random tag sequence followed by a fixed 5' nucleotide sequence (black sequence in Figure 1). In this step, oligonucleotides are annealed in a complementary region by incubation at the required temporal condition. | 1 | Applied and Interdisciplinary Chemistry |
This gene encodes a member of the tyrosine kinase and, to be more specific, the Janus kinases (JAKs) protein families. This protein associates with the cytoplasmic domain of type I and type II cytokine receptors and promulgate cytokine signals by phosphorylating receptor subunits. It is also component of both the type I and type III interferon signaling pathways. As such, it may play a role in anti-viral immunity.
Cytokines play pivotal roles in immunity and inflammation by regulating the survival, proliferation, differentiation, and function of immune cells, as well as cells from other organ systems. Hence, targeting cytokines and their receptors is an effective means of treating such disorders. Type I and II cytokine receptors associate with Janus family kinases (JAKs) to affect intracellular signaling. Cytokines including interleukins, interferons and hemopoietins activate the Janus kinases, which associate with their cognate receptors.
The mammalian JAK family has four members: JAK1, JAK2, JAK3 and tyrosine kinase 2 (TYK2). The connection between Jaks and cytokine signaling was first revealed when a screen for genes involved in interferon type I (IFN-1) signaling identified TYK2 as an essential element, which is activated by an array of cytokine receptors. TYK2 has broader and profound functions in humans than previously appreciated on the basis of analysis of murine models, which indicate that TYK2 functions primarily in IL-12 and type I-IFN signaling. TYK2 deficiency has more dramatic effects in human cells than in mouse cells. However, in addition to IFN-α and -β and IL-12 signaling, TYK2 has major effects on the transduction of IL-23, IL-10, and IL-6 signals. Since, IL-6 signals through the gp-130 receptor-chain that is common to a large family of cytokines, including IL-6, IL-11, IL-27, IL-31, oncostatin M (OSM), ciliary neurotrophic factor, cardiotrophin 1, cardiotrophin-like cytokine, and LIF, TYK2 might also affect signaling through these cytokines. Recently, it has been recognized that IL-12 and IL-23 share ligand and receptor subunits that activate TYK2. IL-10 is a critical anti-inflammatory cytokine, and IL-10 mice suffer from fatal, systemic autoimmune disease.
TYK2 is activated by IL-10, and its deficiency affects the ability to generate and respond to IL-10. Under physiological conditions, immune cells are, in general, regulated by the action of many cytokines and it has become clear that cross-talk between different cytokine-signalling pathways is involved in the regulation of the JAK–STAT pathway. | 1 | Applied and Interdisciplinary Chemistry |
In its simplest form, photosynthesis is adding water to to produce sugars and oxygen, but a complex chemical pathway is involved, facilitated along the way by a range of enzymes and co-enzymes. The enzyme RuBisCO is responsible for "fixing" – that is, it attaches it to a carbon-based molecule to form a sugar, which can be used by the plant, releasing an oxygen molecule along the way. However, the enzyme is notoriously inefficient, and just as effectively will also fix oxygen instead of in a process called photorespiration. This is energetically costly as the plant has to use energy to turn the products of photorespiration back into a form that can react with . | 0 | Theoretical and Fundamental Chemistry |
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