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Lithium (medication) Lithium bromide and lithium chloride have been used in the past as table salt; however, they fell out of use in the 1940s, when it was discovered they were toxic in those large doses. Many other lithium salts and compounds exist, such as lithium fluoride and lithium iodide, but they are presumed to be as toxic or more so than the chloride and have never been evaluated for pharmacological effects. As of 2017 lithium was marketed under many brand names worldwide, including Cade, Calith, Camcolit, Carbolim, Carbolit, Carbolith, Carbolithium, Carbolitium, Carbonato de Litio, Carboron, Ceglution, Contemnol, D-Gluconsäure, Lithiumsalz, Efadermin (Lithium and Zinc Sulfate), Efalith (Lithium and Zinc Sulfate), Elcab, Eskalit, Eskalith, Frimania, Hypnorex, Kalitium, Karlit, Lalithium, Li-Liquid, Licarb, Licarbium, Lidin, Ligilin, Lilipin, Lilitin, Limas, Limed, Liskonum, Litarex, Lithane, Litheum, Lithicarb, Lithii carbonas, Lithii citras, Lithioderm, Lithiofor, Lithionit, Lithium, Lithium aceticum, Lithium asparagicum, Lithium Carbonate, Lithium Carbonicum, Lithium Citrate, Lithium DL-asparaginat-1-Wasser, Lithium gluconicum, Lithium-D-gluconat, Lithiumcarbonaat, Lithiumcarbonat, Lithiumcitrat, Lithiun, Lithobid, Lithocent, Lithotabs, Lithuril, Litiam, Liticarb, Litijum, Litio, Litiomal, Lito, Litocarb, Litocip, Maniprex, Milithin, Neurolepsin, Plenur, Priadel, Prianil, Prolix, Psicolit, Quilonium, Quilonorm, Quilonum, Téralithe, and Theralite | https://en.wikipedia.org/wiki?curid=39923620 |
Lithium (medication) Tentative evidence in Alzheimer's disease showed that lithium may slow progression. | https://en.wikipedia.org/wiki?curid=39923620 |
Sublimation sandwich method The sublimation sandwich method (also called the sublimation sandwich process and the sublimation sandwich technique) is a kind of physical vapor deposition used for creating man-made crystals. Silicon carbide is the most common crystal grown this way, though others crystals may also created with it (notably gallium nitride). In this method, the environment around a single crystal or a polycrystaline plate is filled with vapor heated to between 1600°C and 2100°C-- changes to this environment can affect the gas phase stoichiometry. The source-to-crystal distance is kept between 0.02-0.03mm (very low). Parameters that can affect crystal growth include source-to-substrate distance, temperature gradient, and the presence of tantalum for gathering excess carbon. High growth rates are the result of small source-to-seed distances combined with a large heat flux onto a small amount of source material with no more than a moderate temperature difference between the substrate and the source (0.5-10°C). The growth of large boules, however, remains quite difficult using this method, and it is better suited to the creation of epitaxial films with uniform polytype structures. Ultimately, samples with a thickness of up to 500µm can be produced using this method. | https://en.wikipedia.org/wiki?curid=39933282 |
Eigenstate thermalization hypothesis The eigenstate thermalization hypothesis (or ETH) is a set of ideas which purports to explain when and why an isolated quantum mechanical system can be accurately described using equilibrium statistical mechanics. In particular, it is devoted to understanding how systems which are initially prepared in far-from-equilibrium states can evolve in time to a state which appears to be in thermal equilibrium. The phrase "eigenstate thermalization" was first coined by Mark Srednicki in 1994, after similar ideas had been introduced by Josh Deutsch in 1991. The principal philosophy underlying the eigenstate thermalization hypothesis is that instead of explaining the ergodicity of a thermodynamic system through the mechanism of dynamical chaos, as is done in classical mechanics, one should instead examine the properties of matrix elements of observable quantities in individual energy eigenstates of the system. In statistical mechanics, the microcanonical ensemble is a particular statistical ensemble which is used to make predictions about the outcomes of experiments performed on isolated systems that are believed to be in equilibrium with an exactly known energy. The microcanonical ensemble is based upon the assumption that, when such an equilibrated system is probed, the probability for it to be found in any of the microscopic states with the same total energy have equal probability | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis With this assumption, the ensemble average of an observable quantity is found by averaging the value of that observable formula_1 over all microstates formula_2 with the correct total energy: Importantly, this quantity is independent of everything about the initial state except for its energy. The assumptions of ergodicity are well-motivated in classical mechanics as a result of dynamical chaos, since a chaotic system will in general spend equal time in equal areas of its phase space. If we prepare an isolated, chaotic, classical system in some region of its phase space, then as the system is allowed to evolve in time, it will sample its entire phase space, subject only to a small number of conservation laws (such as conservation of total energy). If one can justify the claim that a given physical system is ergodic, then this mechanism will provide an explanation for why statistical mechanics is successful in making accurate predictions. For example, the hard sphere gas has been rigorously proven to be ergodic. This argument cannot be straightforwardly extended to quantum systems, even ones that are analogous to chaotic classical systems, because time evolution of a quantum system does not uniformly sample all vectors in Hilbert space with a given energy | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis Given the state at time zero in a basis of energy eigenstates the expectation value of any observable formula_5 is Even if the formula_7 are incommensurate, so that this expectation value is given for long times by the expectation value permanently retains knowledge of the initial state in the form of the coefficients formula_9. In principle it is thus an open question as to whether an isolated quantum mechanical system, prepared in an arbitrary initial state, will approach a state which resembles thermal equilibrium, in which a handful of observables are adequate to make successful predictions about the system. However, a variety of experiments in cold atomic gases have indeed observed thermal relaxation in systems which are, to a very good approximation, completely isolated from their environment, and for a wide class of initial states. The task of explaining this experimentally observed applicability of equilibrium statistical mechanics to isolated quantum systems is the primary goal of the eigenstate thermalization hypothesis. Suppose that we are studying an isolated, quantum mechanical many-body system. In this context, "isolated" refers to the fact that the system has no (or at least negligible) interactions with the environment external to it. If the Hamiltonian of the system is denoted formula_10, then a complete set of basis states for the system is given in terms of the eigenstates of the Hamiltonian, where formula_12 is the eigenstate of the Hamiltonian with eigenvalue formula_13 | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis We will refer to these states simply as "energy eigenstates." For simplicity, we will assume that the system has no degeneracy in its energy eigenvalues, and that it is finite in extent, so that the energy eigenvalues form a discrete, non-degenerate spectrum (this is not an unreasonable assumption, since any "real" laboratory system will tend to have sufficient disorder and strong enough interactions as to eliminate almost all degeneracy from the system, and of course will be finite in size). This allows us to label the energy eigenstates in order of increasing energy eigenvalue. Additionally, consider some other quantum-mechanical observable formula_5, which we wish to make thermal predictions about. The matrix elements of this operator, as expressed in a basis of energy eigenstates, will be denoted by We now imagine that we prepare our system in an initial state for which the expectation value of formula_5 is far from its value predicted in a microcanonical ensemble appropriate to the energy scale in question (we assume that our initial state is some superposition of energy eigenstates which are all sufficiently "close" in energy) | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis The eigenstate thermalization hypothesis says that for an arbitrary initial state, the expectation value of formula_5 will ultimately evolve in time to its value predicted by a microcanonical ensemble, and thereafter will exhibit only small fluctuations around that value, provided that the following two conditions are met: These conditions can be written as where formula_23 and formula_24 are smooth functions of energy, formula_25 is the many-body Hilbert space dimension, and formula_26 is a random variable with zero mean and unit variance. Conversely if a quantum many-body system satisfies the ETH, the matrix representation of any local operator in the energy eigen basis is expected to follow the above ansatz. We can define a long-time average of the expectation value of the operator formula_27 according to the expression If we use the explicit expression for the time evolution of this expectation value, we can write The integration in this expression can be performed explicitly, and the result is Each of the terms in the second sum will become smaller as the limit is taken to infinity | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis Assuming that the phase coherence between the different exponential terms in the second sum does not ever become large enough to rival this decay, the second sum will go to zero, and we find that the long-time average of the expectation value is given by This prediction for the time-average of the observable formula_27 is referred to as its predicted value in the "diagonal ensemble", The most important aspect of the diagonal ensemble is that it depends explicitly on the initial state of the system, and so would appear to retain all of the information regarding the preparation of the system. In contrast, the predicted value in the microcanonical ensemble is given by the equally-weighted average over all energy eigenstates within some energy window centered around the mean energy of the system where formula_34 is the number of states in the appropriate energy window, and the prime on the sum indices indicates that the summation is restricted to this appropriate microcanonical window. This prediction makes absolutely no reference to the initial state of the system, unlike the diagonal ensemble. Because of this, it is not clear why the microcanonical ensemble should provide such an accurate description of the long-time averages of observables in such a wide variety of physical systems. However, suppose that the matrix elements formula_18 are effectively constant over the relevant energy window, with fluctuations that are sufficiently small | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis If this is true, this one constant value A can be effectively pulled out of the sum, and the prediction of the diagonal ensemble is simply equal to this value, where we have assumed that the initial state is normalized appropriately. Likewise, the prediction of the microcanonical ensemble becomes The two ensembles are therefore in agreement. This constancy of the values of formula_18 over small energy windows is the primary idea underlying the eigenstate thermalization hypothesis. Notice that in particular, it states that "the expectation value of" formula_27 "in a single energy eigenstate is equal to the value predicted by a microcanonical ensemble constructed at that energy scale." This constitutes a foundation for quantum statistical mechanics which is radically different from the one built upon the notions of dynamical ergodicity. Several numerical studies of small lattice systems appear to tentatively confirm the predictions of the eigenstate thermalization hypothesis in interacting systems which would be expected to thermalize. Likewise, systems which are integrable tend not to obey the eigenstate thermalization hypothesis. Some analytical results can also be obtained if one makes certain assumptions about the nature of highly excited energy eigenstates. The original 1994 paper on the ETH by Mark Srednicki studied, in particular, the example of a quantum hard sphere gas in an insulated box. This is a system which is known to exhibit chaos classically | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis For states of sufficiently high energy, Berry's conjecture states that energy eigenfunctions in this many-body system of hard sphere particles will appear to behave as superpositions of plane waves, with the plane waves entering the superposition with "random" phases and Gaussian-distributed amplitudes (the precise notion of this random superposition is clarified in the paper). Under this assumption, one can show that, up to corrections which are negligibly small in the thermodynamic limit, the momentum distribution function for each individual, distinguishable particle is equal to the Maxwell–Boltzmann distribution where formula_41 is the particle's momentum, m is the mass of the particles, k is the Boltzmann constant, and the "temperature" formula_42 is related to the energy of the eigenstate according to the usual equation of state for an ideal gas, where N is the number of particles in the gas. This result is a specific manifestation of the ETH, in that it results in a prediction for the value of an observable in "one energy eigenstate" which is in agreement with the prediction derived from a microcanonical (or canonical) ensemble. Note that no averaging over initial states whatsoever has been performed, nor has anything resembling the H-theorem been invoked. Additionally, one can also derive the appropriate Bose–Einstein or Fermi–Dirac distributions, if one imposes the appropriate commutation relations for the particles comprising the gas | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis Currently, it is not well understood how high the energy of an eigenstate of the hard sphere gas must be in order for it to obey the ETH. A rough criterion is that the average thermal wavelength of each particle be sufficiently smaller than the radius of the hard sphere particles, so that the system can probe the features which result in chaos classically (namely, the fact that the particles have a finite size ). However, it is conceivable that this condition may be able to be relaxed, and perhaps in the thermodynamic limit, energy eigenstates of arbitrarily low energies will satisfy the ETH (aside from the ground state itself, which is required to have certain special properties, for example, the lack of any nodes ). Three alternative explanations for the thermalization of isolated quantum systems are often proposed: The condition that the ETH imposes on the diagonal elements of an observable is responsible for the equality of the predictions of the diagonal and microcanonical ensembles. However, the equality of these long-time averages does not guarantee that the fluctuations in time around this average will be small. That is, the equality of the long-time averages does not ensure that the expectation value of formula_27 will settle down to this long-time average value, and then stay there for "most" times | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis In order to deduce the conditions necessary for the observable's expectation value to exhibit small temporal fluctuations around its time-average, we study the mean squared amplitude of the temporal fluctuations, defined as where formula_54 is a shorthand notation for the expectation value of formula_27 at time t. This expression can be computed explicitly, and one finds that Temporal fluctuations about the long-time average will be small so long as the off-diagonal elements satisfy the conditions imposed on them by the ETH, namely that they become exponentially small in the system size. Notice that this condition allows for the possibility of isolated "resurgence times", in which the phases align coherently in order to produce large fluctuations away from the long-time average. The amount of time the system spends far away from the long-time average is guaranteed to be small so long as the above mean squared amplitude is sufficiently small. The expectation value of a quantum mechanical observable represents the average value which would be measured after performing repeated measurements on an ensemble of "identically prepared" quantum states. Therefore, while we have been examining this expectation value as the principal object of interest, it is not clear to what extent this represents physically relevant quantities. As a result of quantum fluctuations, the expectation value of an observable is not typically what will be measured during one experiment on an isolated system | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis However, it has been shown that for an observable satisfying the ETH, quantum fluctuations in its expectation value will typically be of the same order of magnitude as the thermal fluctuations which would be predicted in a traditional microcanonical ensemble. This lends further credence to the idea that the ETH is the underlying mechanism responsible for the thermalization of isolated quantum systems. Currently, there is no known analytical derivation of the eigenstate thermalization hypothesis for general interacting systems. However, it has been verified to be true for a wide variety of interacting systems using numerical exact diagonalization techniques, to within the uncertainty of these methods. It has also been proven to be true in certain special cases in the semi-classical limit, where the validity of the ETH rests on the validity of Shnirelman's theorem, which states that in a system which is classically chaotic, the expectation value of an operator formula_27 in an energy eigenstate is equal to its classical, microcanonical average at the appropriate energy. Whether or not it can be shown to be true more generally in interacting quantum systems remains an open question. It is also known to explicitly fail in certain integrable systems, in which the presence of a large number of constants of motion prevent thermalization | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis It is also important to note that the ETH makes statements about "specific observables" on a case by case basis - it does not make any claims about whether every observable in a system will obey ETH. In fact, this certainly cannot be true. Given a basis of energy eigenstates, one can always explicitly construct an operator which violates the ETH, simply by writing down the operator as a matrix in this basis whose elements explicitly do not obey the conditions imposed by the ETH. Conversely, it is always trivially possible to find operators which "do" satisfy ETH, by writing down a matrix whose elements are specifically chosen to obey ETH. In light of this, one may be led to believe that the ETH is somewhat trivial in its usefulness. However, the important consideration to bear in mind is that these operators thus constructed may not have any "physical relevance." While one can construct these matrices, it is not clear that they correspond to observables which could be realistically measured in an experiment, or bear any resemblance to physically interesting quantities. An arbitrary Hermitian operator on the Hilbert space of the system need not correspond to something which is a physically measurable observable. Typically, the ETH is postulated to hold for "few-body operators," observables which involve only a small number of particles. Examples of this would include the occupation of a given momentum in a gas of particles, or the occupation of a particular site in a lattice system of particles | https://en.wikipedia.org/wiki?curid=39937659 |
Eigenstate thermalization hypothesis Notice that while the ETH is typically applied to "simple" few-body operators such as these, these observables need "not" be local in space - the momentum number operator in the above example does not represent a local quantity. There has also been considerable interest in the case where isolated, non-integrable quantum systems fail to thermalize, despite the predictions of conventional statistical mechanics. Disordered systems which exhibit many-body localization are candidates for this type of behavior, with the possibility of excited energy eigenstates whose thermodynamic properties more closely resemble those of ground states. It remains an open question as to whether a completely isolated, non-integrable system without static disorder can ever fail to thermalize. One intriguing possibility is the realization of "Quantum Disentangled Liquids." It also an open question whether "all" eigenstates must obey the ETH in a thermalizing system. | https://en.wikipedia.org/wiki?curid=39937659 |
G-strain In EPR spectroscopy, g-strain refers to broadening of g-values owing to small sample inhomogeneity owing to slight variations in the orientation of the paramagnetic centers. The phenomenon is indicated by broadening of the g-values that depends on the frequency of the spectrometer, such as X- or Q-band. If the line width were determined only by hyperfine coupling (which are field-independent), then the line widths would also be field independent, but they often are not. In iron-sulfur proteins, some other metalloproteins, as well as some solids, g-strain can be substantial. | https://en.wikipedia.org/wiki?curid=39941202 |
Plasmonic lens In nano-optics, a plasmonic lens generally refers to a lens for surface plasmon polaritons (SPPs), i.e. a device that redirects SPPs to converge towards a single focal point. Because SPPs can have very small wavelength, they can converge into a very small and very intense spot, much smaller than the free space wavelength and the diffraction limit. A simple example of a plasmonic lens is a series of concentric rings on a metal film. Any light that hits the film from free space at a 90 degree angle, known as the normal, will get coupled into a SPP (this part works like a diffraction grating coupler), and that SPP will be heading towards the center of the circles, which is the focal point. Another example is a tapered "dimple". In 2007, a novel, or technologically new, plasmonic lenses and waveguide by modulating light a mesoscale dielectric structure on a metallic film with arrayed nano-slits, which have constant depth but variant widths. The slits transport electromagnetic energy in the form of SPPs in nano meter sized waveguides and provide desired phase adjustments for manipulating the beam of light. The scientists claim that it is an improvement over other subwavelength imaging techniques, such as "superlenses", where the object and image are confined to the near field. These devices have been suggested for various applications that take advantage of the small size and high intensity of the SPPs at the focal point | https://en.wikipedia.org/wiki?curid=39950774 |
Plasmonic lens These include photolithography, heat-assisted magnetic recording, microscopy, biophotonics, biological molecule sensors, and solar cells, as well as other applications. The term "plasmonic lens" is also sometimes used to describe something different: Any free-space lens (i.e., a lens that focuses free-space light, rather than SPPs), that has something to do with plasmonics. These often come up in discussions of superlenses. | https://en.wikipedia.org/wiki?curid=39950774 |
Marmesin (nodakenetin) is a chemical compound precursor in psoralen and linear furanocoumarins biosynthesis. | https://en.wikipedia.org/wiki?curid=39951630 |
C4H7Cl The molecular formula CHCl may refer to: | https://en.wikipedia.org/wiki?curid=39953225 |
C23H38O2 The molecular formula CHO may refer to: | https://en.wikipedia.org/wiki?curid=39953261 |
C19H25NO3 The molecular formula CHNO may refer to: | https://en.wikipedia.org/wiki?curid=39953304 |
Thiolate-protected gold cluster Thiolate-protected gold clusters are a type of ligand-protected metal cluster, synthesized from gold ions and thin layer compounds that play a special role in cluster physics because of their unique stability and electronic properties. They are considered to be stable compounds. These clusters can range in size up to hundreds of gold atoms, above which they are classified as passivated gold nanoparticles. The wet chemical synthesis of thiolate-protected gold clusters is achieved by the reduction of gold(III) salt solutions, using a mild reducing agent in the presence of thiol compounds. This method starts with gold ions and synthesizes larger particles from them, therefore this type of synthesis can be regarded as a "bottom-up approach" in nanotechnology to the synthesis of nanoparticles. The reduction process depends on the equilibrium between different oxidation states of the gold and the oxidized or reduced forms of the reducing agent, or thiols. Gold(I)-thiolate polymers have been identified as important in the initial steps of the reaction. Several synthesis recipes exist that are similar to the Brust synthesis of colloidal gold, however the mechanism is not yet fully understood. The synthesis produces a mixture of dissolved, thiolate-protected gold clusters of different sizes. These particles can then be separated by gel electrophoresis (PAGE) | https://en.wikipedia.org/wiki?curid=39953452 |
Thiolate-protected gold cluster If the synthesis is performed in a kinetically controlled manner, particularly stable representatives can be obtained with particles of uniform size (monodispersely), avoiding further separation steps. Rather than starting from "naked" gold ions in solution, template reactions can be used for directed synthesis of clusters. The high affinity of the gold ions to electronegative and (partially) charged atoms of functional groups yields potential seeds for cluster formation. The interface between the metal and the template can act as a stabilizer and steer the final size of the cluster. Some potential templates are dendrimers, oligonucleotides, proteins, polyelectrolytes and polymers. Top-down synthesis of the clusters can be achieved by the "etching" of larger metallic nanoparticles with redox-active, thiol-containing biomolecules. In this process, gold atoms on the nanoparticles' surface react with the thiol, dissolving as gold-thiolate complexes until the dissolution reaction stops; this leaves behind a residual species of thiolate-protected gold clusters that is particularly stable. This type of synthesis is also possible using other non thiol-based ligands. The electronic structure of the thiolate-protected gold clusters is characterized by strongly pronounced quantum effects. These result in discrete electronic states, and a nonzero HOMO/LUMO gap | https://en.wikipedia.org/wiki?curid=39953452 |
Thiolate-protected gold cluster This existence of discrete electronic states was first indicated by the discrepancy between their optical absorption and the predictions of classical Mie scattering. The discrete optical transitions and occurrence of photoluminescence in these species are areas where they behave like molecular, rather than metallic, substances. This molecular optical behavior sharply distinguishes thiolate-protected clusters from gold nanoparticles, whose optical characterisics are driven by Plasmon resonance. Some of thiolate-protected clusters' properties can be described using a model in which the clusters are treated like "superatoms". According to this model they exhibit atomic-like electronic states, that are labeled S,P,D,F according to their respective angular momentum on the atomic level. Those clusters that have a ""closed superatomic shell"" configuration have indeed been identified as the most stable ones. This electronic shell closure and the resulting gain in stability is responsible for the discrete distribution of a few stable cluster sizes (magic numbers) observed in their synthesis, rather than a quasi-continuous distribution of sizes. Magic numbers are connected with the number of metal atoms in those thiolate-protected clusters which display an outstanding stability. Such clusters can be synthesized monodispersely and are end products of the etching procedure after an addition of excess thiols does not lead to further metal dissolution | https://en.wikipedia.org/wiki?curid=39953452 |
Thiolate-protected gold cluster Some important clusters with magic numbers are (SG:Glutathione): Au(SG), Au(SG), Au(SG), Au(SG), Au(SG), Au(SG), Au(SG), Au(SG), and Au(SG). Au(SCHPh) is also well-known. It was greater than representatives Au(p-MBA) with the para-mercaptobenzoice (para-mercapto-benzoic acid, p-MBA) produced ligand. Worthy of note is that in 2013, a structural prediction of the Au (SCH) cluster, based on Density Functional Theory (DFT) was confirmed in 2015. This result represents the maturity of this field where calculations are able to guide the experimental work. The following table features some sizes. In bionanotechnology, intrinsic properties of the clusters (for example, fluorescence) can be made available for bionanotechnological applications by linking them with biomolecules through the process of bioconjugation. The protected gold particles' stability and fluorescence makes them efficient emitters of electromagnetic radiation that can be tuned by varying the cluster size and the type of ligand used for protection. The protective shell can function (have functional groups added) in a way that selective binding (for example, as a complementary protein receptor of DNA-DNA-interaction) qualifies them for the use as biosensors. | https://en.wikipedia.org/wiki?curid=39953452 |
Ribosomal pause refers to the queueing or stacking of ribosomes during translation of the nucleotide sequence of mRNA transcripts. These transcripts are decoded and converted into an amino acid sequence during protein synthesis by ribosomes. Due to the pause sites of some mRNA’s, there is a disturbance caused in translation. Ribosomal pausing occurs in both eukaryotes and prokaryotes. It's been known since the 1980s that different mRNAs are translated at different rates. The main reason for these differences was thought to be the concentration of varieties of rare tRNAs limiting the rate at which some transcripts could be decoded. However, with research techniques such as ribosome profiling, it was found that at certain sites there were higher concentrations of ribosomes than average, and these pause sites were tested with specific codons. No link was found between the occupancy of specific codons and amount of their tRNAs. Thus, the early findings about rare tRNAs causing pause sites doesn't seem plausible. Two techniques can localize the ribosomal pause site in "vivo"";" a micrococcal nuclease protection assay and isolation of polysomal transcript. Isolation of polysomal transcripts occurs by centrifuging tissue extracts through a sucrose cushion with translation elongation inhibitors, for example cycloheximide. Ribosome pausing can be detected during preprolactin synthesis on free polysomes, when the ribosome is paused the other ribosomes are tightly stacked together | https://en.wikipedia.org/wiki?curid=39954585 |
Ribosomal pause When the ribosome pauses, during translation, the fragments that started to translate before the pause took place are overrepresented. However, along with the mRNA if the ribosome pauses then specific bands will be improved in the trailing edge of the ribosome. Some of the elongation inhibitors, such as: cycloheximide (in eukaryotes) or chloramphenicol, cause the ribosomes to pause and to accumulate in the start codons. Elongation Factor P regulates the ribosomal pause at polyproline in bacteria, and when there is no EFP the density of ribosomes decreases from the polyproline motifs. If there are multiple ribosome pauses, then the EFP won't resolve it. During protein synthesis, rapidly changing conditions in the cell can cause ribosomal pausing. In bacteria, this can affect growth rate and trigger translational abandonment. This releases the ribosome from the mRNA and the incomplete polypeptide is targeted for destruction. In eukaryotes, ribosomal pausing can initiate an analogous process which triggers endonucleolytic attack of the mRNA, a process termed mRNA no-go decay. Ribosomal pausing also aids co-translational folding of the nascent polypeptide on the ribosome, and delays protein translation while its encoding mRNA; this can trigger ribosomal frameshifting. Protein synthesis must occur in a specific way for ribosomal pausing to impact or change the outcome of this process. The products that are made because of the ribosomal pausing can be broken down by Ribosome Quality Control (RQC) | https://en.wikipedia.org/wiki?curid=39954585 |
Ribosomal pause RQC can happen after the ribosomal pausing. Even though RQC works to undo the effects of the ribosomal pause, there are specific situations relating to proteins when the ribosomal pause is needed. Ribosomal pausing does have an impact on the rate of protein synthesis and it may decrease the rate that it occurs. When the ribosome movement on the mRNA is not linear, the ribosome gets paused at different regions without a precise reason. The ribosome pause position will help to identify the mRNA sequence features, structure, and the transacting factor that modulates this process. The advantage of ribosomal pause sites that are located at protein domain boundaries are aiding the folding of a protein. There are times when the ribosomal pause does not cause an advantage and it needs to be restricted. In translation, elF5A inhibits ribosomal pausing for translation to function better. Ribosomal pausing can cause more non-canonical start codons without elF5A in eukaryotic cells. When there is a lack of elF5A in the eukaryotic cell, it can cause an increase in ribosomal pausing. The ribosomal pausing process can also be used by amino acids to control translation. It is known that ribosomes pause at distinct sites, but the reasons for these pauses are mostly unknown. Also, the ribosome pauses if the pseudoknot is disrupted. 10% of the ribosome pauses at the pseudoknot and 4% of the ribosomes are terminated. Before the ribosome is obstructed it passes the pseudoknot | https://en.wikipedia.org/wiki?curid=39954585 |
Ribosomal pause An assay was put together by a group from the University of California in an effort to show a model of mRNA. The translation was monitored in two in vitro systems. It was found that translating ribosomes aren't uniformly distributed along an mRNA. Protein folding "in vivo" is also important and is related to protein synthesis. For finding the location of the ribosomal pause "in vivo", the methods that have been used to find the ribosomal pause "in vitro" can be changed to find these specific locations "in vivo." Ribosome Profiling is a method that can reveal pausing sites through sequencing the ribosome protected fragments (RPFs or footprints) to map ribosome occupancy on the mRNA. Ribosome profiling has the ability to reveal the ribosome pause sites in the whole transcriptome. When the kinetics layer is added, it discloses the time of the pause, and the translation takes place. Ribosome profiling is however still in early stages and has biases that need to be explored further. Ribosome profiling allows for translation to be measured more accurately and precisely. During this process, translation needs to be stopped in order for ribosome profiling to be performed. This may cause a problem with ribosome profiling because the methods that are used to stop translation in an experiment can impact the outcome, which causes incorrect results. Ribosome profiling is useful for getting specific information on translation and the process of protein synthesis | https://en.wikipedia.org/wiki?curid=39954585 |
Ribosomal pause Ribosome profiling has been used successfully in several recent studies. | https://en.wikipedia.org/wiki?curid=39954585 |
Hexafluorotitanic acid (systematically named oxonium hexafluoridotitanate(2-)) is an inorganic compound with the chemical formula (HO)[TiF]. As with most oxonium salts, it is not stable when undissolved, or under neutral to basic conditions, tending to decompose in those conditions to titanium fluorides or oxyfluorides. Under highly acidic conditions, it decomposes to titania, which accelerated by fluoride scavengers. Under highly basic conditions, it is hydrolysed to titanium hydroxide. A related salt, is the anhydrous fluoronium hexafluoridotitanate(2-) or (HF)[TiF]. | https://en.wikipedia.org/wiki?curid=39956692 |
Martin Schröder (chemist) Martin Schröder is a British inorganic chemist. He is Vice President and Dean for the Faculty of Engineering and Physical Sciences and Professor of Chemistry in the Department of Chemistry at the University of Manchester since June 2015. Previously served as executive dean of the Faculty of Science from 2011 to 2015 and Professor of Inorganic Chemistry at the University of Nottingham from 1995 to 2015. Schröder was born of Estonian parents in Buckinghamshire in 1954, and educated at the local Slough Grammar School. He was awarded a Bachelor of Science degre in Chemistry from the University of Sheffield in 1975 followed by a PhD from Imperial College London in 1978 where his research was supervised by William P. Griffith. During Schröder's career he has held the following appointments: Schröder moved to the University of Manchester in 2015 as Vice President and Dean of the Faculty of Engineering and Physical Sciences and Professor of Chemistry. Schröder was elected a Fellow of the Royal Society of Chemistry (FRSC) and Fellow of the Royal Society of Edinburgh (FRSE). His awards include the Corday-Morgan Medal and Prize of the Royal Society of Chemistry in 1991, a Royal Society of Edinburgh Support research fellowship in 1991-2, Tilden Prize in 2001, the Royal Society of Chemistry award for the chemistry of transition metals in 2003, a Royal Society Wolfson Research Merit Award in 2005. | https://en.wikipedia.org/wiki?curid=39965610 |
Copper (heraldry) In heraldry, copper is the tincture of metallic copper. Copper has been introduced in Canadian heraldry. It is considered a metal along with Argent (silver) and Or (gold) and should be depicted as bright, new copper metal. While not commonly used, it features prominently in the arms of the City of Whitehorse, Yukon. | https://en.wikipedia.org/wiki?curid=39969498 |
Ailanthone is an allelopathic chemical that is produced by the "Ailanthus altissima" tree which inhibits the growth of other plants. | https://en.wikipedia.org/wiki?curid=39972514 |
Cayman Chemical Company is an American biotechnology company founded in 1980, headquartered in Ann Arbor, MI. The company provides chemicals that are used primarily by universities and pharmaceutical companies for research and the development of medicines. The company is also known as a provider of reference standards to state and federal crime labs for use in the detection of rapidly evolving designer drugs. Small quantities of these known reference standards are analyzed using mass spectrometry and gas chromatography techniques to match against forensic evidence, usually confiscated by law enforcement, or forensic toxicological evidence collected in the form of biological samples such as urine, blood, or tissue. was incorporated on June 6, 1980 in Denver, Colorado. It was initially a marine natural products company. Building on earlier environmental studies in the North Sound of Grand Cayman Island, Cayman initially sold prostaglandin standards as research chemicals. The company operated in Denver for several years before relocating to Ann Arbor, Michigan. Commercializing the patented work of Philippe Pradelles and others, Cayman exploited the acetylcholinesterase enzyme of electric eels to develop a range of sensitive enzyme immunoassays for prostaglandins in the late 1980s. The availability of these assays enabled the development of Celebrex by Searle/Monsanto, relying on measurements of Prostaglandin E2 and Thromboxane B2, and of Singulaire by Merck & Co, relying on measurements of unstable Leukotrienes | https://en.wikipedia.org/wiki?curid=39975065 |
Cayman Chemical Company Cayman Europe was established in January, 2005 in Tallinn, Estonia. Their operations focus on the distribution of Cayman Chemical products in Europe. Facilities are located in Neratovice, a town 18 miles north of Prague in the Czech Republic. Production is focused on pharmaceutical ingredients for generic drug formulators, specifically bulk prostaglandins. Founded in 1968, Biomol GmbH in Hamburg, Germany, distributes more than 300,000 research antibodies, assay kits, specialty reagents and related life science products to research, diagnostic and biopharmaceutical customers in Germany and Europe. | https://en.wikipedia.org/wiki?curid=39975065 |
Geworkbench geWorkbench (genomics Workbench) is an open-source software platform for integrated genomic data analysis. It is a desktop application written in the programming language Java. geWorkbench uses a component architecture. , there are more than 70 plug-ins available, providing for the visualization and analysis of gene expression, sequence, and structure data. geWorkbench is the Bioinformatics platform of MAGNet, the National Center for the Multi-scale Analysis of Genomic and Cellular Networks, one of the 8 National Centers for Biomedical Computing funded through the NIH Roadmap (NIH Common Fund). Many systems and structure biology tools developed by MAGNet investigators are available as geWorkbench plugins. Demonstrations of each feature described can be found at http://wiki.c2b2.columbia.edu/workbench/index.php/Tutorials. | https://en.wikipedia.org/wiki?curid=39982437 |
ConverDyn is a general partnership between American multinational firms General Atomics and Honeywell that provides uranium hexafluoride (UF) conversion and related services to utilities operating nuclear power plants in North America, Europe, and Asia. The company is the sole marketing agent of UF produced at the Honeywell Uranium Hexafluoride Processing Facility in Metropolis, Illinois. From 1970 to 1992, there were two operating uranium hexafluoride conversion facilities in the United States. These included Allied Signal's Metropolis Works Facility and General Atomics' Sequoyah Fuels Facility in Gore, Oklahoma. Facing low conversion prices and the implementation of the Megatons to Megawatts Program, both companies recognized the forthcoming struggles surrounding excess market supply of conversion services. In 1992, Allied Signal and General Atomics agreed to close the Gore, Oklahoma facility and take joint and equal ownership of profits from Allied Signal's plant in Metropolis, Illinois. was formed as a general partnership between the two companies as the sole marketing organization of uranium hexafluoride produced at the Metropolis plant. As a result, any and all uranium hexafluoride produced at Metropolis Works is marketed and sold by ConverDyn. In 1999, Honeywell and Allied Signal merged resulting in the partnership structure that exists currently. Built in 1958, the Honeywell Metropolis Works Facility is the only uranium hexafluoride conversion facility in the United States | https://en.wikipedia.org/wiki?curid=39986067 |
ConverDyn The plant has an annual conversion capacity of approximately 15,000 tU as UF accounting for approximately 20% of worldwide production capacity. The plant feeds UO yellowcake received from uranium mines and produces uranium hexafluoride gas for enrichment at one of the primary enrichment sites around the world. After being enriched, product is fabricated into nuclear fuel that ends up generating electricity at a nuclear power plant. Honeywell Metropolis Works deploys a unique technology and process by which it converts yellowcake to uranium hexafluoride gas. The other Western conversion facilities, Areva and Cameco, each utilize a process that requires two different facilities, one to convert yellowcake to either uranium tetrafluoride or uranium trioxide and another to convert to uranium hexafluoride. Honeywell developed a process known as the dry fluoride volatility conversion process that allows for complete yellowcake to UF at a single facility and also yielding a greater level of UF purity at 99.99% or higher. The dry fluoride volatility conversion process at Metropolis works goes through five basic steps: feed preparation, reduction, hydrofluorination, fluorination, and distillation. The aim of this initial step it to ensure that uranium concentrates have the optimum particle size and density necessary to move forward in the process of conversion. During this stage, uranium ore concentrates are converted to uranium dioxide and impurities are removed from the system into a waste gas stream | https://en.wikipedia.org/wiki?curid=39986067 |
ConverDyn The sized yellowcake is reacted with hydrogen in a fluidizing medium to form uranium dioxide The UO resulting from the previous reduction stage is then converted into uranium tetrafluoride intermediate (Green Salt) and additional impurities are removed from the system. The Metropolis Works Plant operates the largest gaseous fluorine capacity in the world. Fluorine is produced in this process by the electrolysis of HF in a Potassium Bifluoride substrate. The fluorine is pulled to the fluorination process under vacuum so as to increase the safety of this step. The result of this step is crude uranium hexafluoride gas. Finally, uranium hexafluoride from the previous step is purified in a two-stage distillation system. The crude UF is vaporized and transferred through a boiling system into cold traps. After cooling, the final product is filled into cylinders for transport. This stage is proprietary Honeywell technology which allows output of 99.99% or greater UF. After the Fukushima Daiichi nuclear disaster in 2011, the United States Nuclear Regulatory Commission conducted inspections at all US nuclear facilities for seismic deficiencies and general resistance to natural disasters. Although initial inspections confirmed that the Metropolis Works Facility was in full compliance with its operating license, the NRC shutdown the plant in May 2012 and required a series of upgrades to improve resilience to natural disasters including earthquakes and tornadoes | https://en.wikipedia.org/wiki?curid=39986067 |
ConverDyn Honeywell elected to complete required upgrades and the plant restarted production of uranium hexafluoride in July 2013, after more than a year offline. | https://en.wikipedia.org/wiki?curid=39986067 |
BIOPAN is a multi-user research program by the European Space Agency (ESA) designed to investigate the effect of the space environment on biological material. The experiments in are exposed to solar and cosmic radiation, the space vacuum and weightlessness, or a selection thereof. Optionally, the experiment temperature can be stabilized. hosts astrobiology, radiobiology and materials science experiments. The facility is installed on the external surface of Russian Foton descent capsules protruding from the thermal blanket that envelops the satellite. The program started in the early nineties with an ESA contract for the a joint development by Kayser-Threde and Kayser Italia. It was based on the heritage of a low-tech Russian exposure container called KNA ("Kontejner Nauchnoj Apparatury"). The facilities are installed on the external surface of Foton descent capsules. It has a motor-driven hinged lid, which opens 180° in Earth orbit to expose the experiment samples to the harsh space environment. For re-entry, the closed facility is protected with an Ablative heat shield. The facilities are equipped with thermometers, UV sensors, a radiometer, a pressure sensor and an active radiation dosimeter. Data acquired by the sensors is stored by throughout each mission and can be accessed after flight. The possibility of overheating during atmospheric re-entry was acknowledged early during the development, therefore, a quite massive heat shield was designed for it | https://en.wikipedia.org/wiki?curid=39993849 |
BIOPAN While the total weight of is close to 27 kg, including the experiments, the heat shield is responsible for 12 kg of that figure. The electronics consists of the following units: signal acquisition board, microcontroller board with its flight software, memory board and EGSE. The missions flown so far are: | https://en.wikipedia.org/wiki?curid=39993849 |
Ligation (molecular biology) In molecular biology, ligation is the joining of two nucleic acid fragments through the action of an enzyme. It is an essential laboratory procedure in the molecular cloning of DNA whereby DNA fragments are joined together to create recombinant DNA molecules, such as when a foreign DNA fragment is inserted into a plasmid. The ends of DNA fragments are joined together by the formation of phosphodiester bonds between the 3'-hydroxyl of one DNA terminus with the 5'-phosphoryl of another. RNA may also be ligated similarly. A co-factor is generally involved in the reaction, and this is usually ATP or NAD. Ligation in the laboratory is normally performed using T4 DNA ligase, however, procedures for ligation without the use of standard DNA ligase are also popular. The mechanism of the ligation reaction was first elucidated in the laboratory of I. Robert Lehman. Two fragments of DNA may be joined together by DNA ligase which catalyzes the formation of a phosphodiester bond between the 3'-OH at one end of a strand of DNA and the 5'-phosphate group of another. In animals and bacteriophage, ATP is used as the energy source for the ligation, while In bacteria, NAD is used. The DNA ligase first reacts with ATP or NAD, forming a ligase-AMP intermediate with the AMP linked to the ε-amino group of lysine in the active site of the ligase via a phosphoamide bond. This adenylyl group is then transferred to the phosphate group at the 5' end of a DNA chain, forming a DNA-adenylate complex | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) Finally, a phosphodiester bond between the two DNA ends is formed via the nucleophilic attack of the 3'-hydroxyl at the end of a DNA strand on the activated 5′-phosphoryl group of another. A nick in the DNA (i.e. a break in one strand of a double-stranded DNA) can be repaired very efficiently by the ligase. However, a complicating feature of ligation presents itself when ligating two separate DNA ends as the two ends need to come together before the ligation reaction can proceed. In the ligation of DNA with sticky or cohesive ends, the protruding strands of DNA may be annealed together already, therefore it is a relatively efficient process as it is equivalent to repairing two nicks in the DNA. However, in the ligation of blunt-ends, which lack protruding ends for the DNA to anneal together, the process is dependent on random collision for the ends to align together before they can be ligated, and is consequently a much less efficient process. The DNA ligase from "E. coli" cannot ligate blunt-ended DNA except under conditions of molecular crowding, and it is therefore not normally used for ligation in the laboratory. Instead the DNA ligase from phage T4 is used as it can ligate blunt-ended DNA as well as single-stranded DNA. Factors that affect an enzyme-mediated chemical reaction would naturally affect a ligation reaction, such as the concentration of enzyme and the reactants, as well as the temperature of reaction and the length of time of incubation | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) Ligation is complicated by the fact that the desired ligation products for most ligation reactions should be between two different DNA molecules and the reaction involves both inter- and intra-molecular reactions, and that an additional annealing step is necessary for efficient ligation. The three steps to form a new phosphodiester bond during ligation are: enzyme adenylylation, adenylyl transfer to DNA, and nick sealing. Mg(2+) is a cofactor for catalysis, therefore at high concentration of Mg(2+) the ligation efficiency is high. If the concentration of Mg(2+) is limited, the nick- sealing is the rate- limiting reaction of the process, and adenylylated DNA intermediate stays in the solution. Such adenylylation of the enzyme restrains the rebinding to the adenylylated DNA intermediate comparison of an Achilles' heel of LIG1, and represents a risk if they are not fixed. The concentration of DNA can affect the rate of ligation, and whether the ligation is an inter-molecular or intra-molecular reaction. Ligation involves joining up the ends of a DNA with other ends, however, each DNA fragment has two ends, and if the ends are compatible, a DNA molecule can circularize by joining its own ends. At high DNA concentration, there is a greater chance of one end of a DNA molecule meeting the end of another DNA, thereby forming intermolecular ligation | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) At a lower DNA concentration, the chance that one end of a DNA molecule would meet the other end of the same molecule increases, therefore intramolecular reaction that circularizes the DNA is more likely. The transformation efficiency of linear DNA is also much lower than circular DNA, and for the DNA to circularize, the DNA concentration should not be too high. As a general rule, the total DNA concentration should be less than 10 μg/ml. The relative concentration of the DNA fragments, their length, as well as buffer conditions are also factors that can affect whether intermolecular or intramolecular reactions are favored. The concentration of DNA can be artificially increased by adding condensing agents such as cobalt hexamine and biogenic polyamines such as spermidine, or by using crowding agents such as polyethylene glycol (PEG) which also increase the effective concentration of enzymes. Note however that additives such as cobalt hexamine can produce exclusively intermolecular reaction, resulting in linear concatemers rather than the circular DNA more suitable for transformation of plasmid DNA, and is therefore undesirable for plasmid ligation. If it is necessary to use additives in plasmid ligation, the use of PEG is preferable as it can promote intramolecular as well as intermolecular ligation. The higher the ligase concentration, the faster the rate of ligation. Blunt-end ligation is much less efficient than sticky end ligation, so a higher concentration of ligase is used in blunt-end ligations | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) High DNA ligase concentration may be used in conjunction with PEG for a faster ligation, and they are the components often found in commercial kits designed for rapid ligation. Two issues are involved when considering the temperature of a ligation reaction. First, the optimum temperature for DNA ligase activity which is 37C, and second, the melting temperature (T) of the DNA ends to be ligated. The melting temperature is dependent on length and base composition of the DNA overhang—the greater the number of G and C, the higher the T since there are three hydrogen bonds formed between G-C base pair compared to two for A-T base pair—with some contribution from the stacking of the bases between fragments. For the ligation reaction to proceed efficiently, the ends should be stably annealed, and in ligation experiments, the T of the DNA ends is generally much lower than 37C. The optimal temperature for ligating cohesive ends is therefore a compromise between the best temperature for DNA ligase activity and the T where the ends can associate. However, different restriction enzymes generates different ends, and the base composition of the ends produced by these enzymes may also differ, the melting temperature and therefore the optimal temperature can vary widely depending on the restriction enzymes used, and the optimum temperature for ligation may be between 4-15C depending on the ends | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) Ligations also often involve ligating ends generated from different restriction enzymes in the same reaction mixture, therefore it may not be practical to select optimal temperature for a particular ligation reaction and most protocols simply choose 12-16C, room temperature, or 4C. The ionic strength of the buffer used can affect the ligation. The kinds of cations presence can also influence the ligation reaction, for example, excess amount of Na can cause the DNA to become more rigid and increase the likelihood of intermolecular ligation. At high concentration of monovalent cation (>200 mM) ligation can also be almost completely inhibited. The standard buffer used for ligation is designed to minimize ionic effects. Restriction enzymes can generate a wide variety of ends in the DNA they digest, but in cloning experiments most commonly-used restriction enzymes generate a 4-base single-stranded overhang called the sticky or cohesive end (exceptions include "Nde"I which generates a 2-base overhang, and those that generate blunt ends). These sticky ends can anneal to other compatible ends and become ligated in a sticky-end (or cohesive end) ligation. "Eco"RI for example generates an AATT end, and since A and T have lower melting temperature than C and G, its melting temperature T is low at around 6C. For most restriction enzymes, the overhangs generated have a T that is around 15C | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) For practical purposes, sticky end ligations are performed at 12-16C, or at room temperature, or alternatively at 4C for a longer period. For the insertion of a DNA fragment into a plasmid vector, it is preferable to use two different restriction enzymes to digest the DNA so that different ends are generated. The two different ends can prevent the religation of the vector without any insert, and it also allows the fragment to be inserted in a directional manner. When it is not possible to use two different sites, then the vector DNA may need to be dephosphorylated to avoid a high background of recircularized vector DNA with no insert. Without a phosphate group at the ends the vector cannot ligate to itself, but can be ligated to an insert with a phosphate group. Dephosphorylation is commonly done using calf-intestinal alkaline phosphatase (CIAP) which removes the phosphate group from the 5′ end of digested DNA, but note that CIAP is not easy to inactivate and can interfere with ligation without an additional step to remove the CIAP, thereby resulting in failure of ligation. CIAP should not be used in excessive amount and should only be used when necessary. Shrimp alkaline phosphatase (SAP) or Antarctic phosphatase (AP) are suitable alternative as they can be easily inactivated. Blunt end ligation does not involve base-pairing of the protruding ends, so any blunt end may be ligated to another blunt end. Blunt ends may be generated by restriction enzymes such as "Sma"I and "Eco"RV | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) A major advantage of blunt-end cloning is that the desired insert does not require any restriction sites in its sequence as blunt-ends are usually generated in a PCR, and the PCR generated blunt-ended DNA fragment may then be ligated into a blunt-ended vector generated from restriction digest. Blunt-end ligation, however, is much less efficient than sticky end ligation, typically the reaction is 100X slower than sticky-end ligation. Since blunt-end does not have protruding ends, the ligation reaction depends on random collisions between the blunt-ends and is consequently much less efficient. To compensate for the lower efficiency, the concentration of ligase used is higher than sticky end ligation (10x or more). The concentration of DNA used in blunt-end ligation is also higher to increase the likelihood of collisions between ends, and longer incubation time may also be used for blunt-end ligations. If both ends needed to be ligated into a vector are blunt-ended, then the vector needs to be dephosphorylated to minimize self-ligation. This may be done using CIAP, but caution in its use is necessary as noted previously. Since the vector has been dephosphorylated, and ligation requires the presence of a 5'-phosphate, the insert must be phosphorylated. Blunt-ended PCR product normally lacks a 5'-phosphate, therefore it needs to be phosphorylated by treatment with T4 polynucleotide kinase. Blunt-end ligation is also reversibly inhibited by high concentration of ATP | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) PCR usually generates blunt-ended PCR products, but note that PCR using "Taq" polymerase can add an extra adenine (A) to the 3' end of the PCR product. This property may be exploited in TA cloning where the ends of the PCR product can anneal to the T end of a vector. TA ligation is therefore a form of sticky end ligation. Blunt-ended vectors may be turned into vector for TA ligation with dideoxythymidine triphosphate (ddTTP) using terminal transferase. For the cloning of an insert into a circular plasmid: Sometimes ligation fail to produce the desired ligated products, and some of the possible reasons may be: A number of commercially available DNA cloning kits use other methods of ligation that do not require the use of the usual DNA ligases. These methods allow cloning to be done much more rapidly, as well as allowing for simpler transfer of cloned DNA insert to different vectors. These methods however require the use of specially designed vectors and components, and may lack flexibility. Topoisomerase can be used instead of ligase for ligation, and the cloning may be done more rapidly without the need for restriction digest of the vector or insert. In this TOPO cloning method a linearized vector is activated by attaching topoisomerase I to its ends, and this "TOPO-activated" vector may then accept a PCR product by ligating to both of the 5' ends of the PCR product, the topoisomerase is released and a circular vector is formed in the process | https://en.wikipedia.org/wiki?curid=40002050 |
Ligation (molecular biology) Another method of cloning without the use of ligase is by DNA recombination, for example as used in the Gateway cloning system. The gene, once cloned into the cloning vector (called entry clone in this method), may be conveniently introduced into a variety of expression vectors by recombination. | https://en.wikipedia.org/wiki?curid=40002050 |
Isovalent hybridization In chemistry, isovalent or second order hybridization is an extension of orbital hybridization, the mixing of atomic orbitals into hybrid orbitals which can form chemical bonds, to include fractional numbers of atomic orbitals of each type (s, p, d). It allows for a quantitative depiction of bond formation when the molecular geometry deviates from ideal bond angles. Only bonding with 4 equivalent substituents results in exactly hybridization. For molecules with different substituents, we can use isovalent hybridization to rationalize the differences in bond angles between different atoms. In the molecule methyl fluoride for example, the HCF bond angle (108.73°) is less than the HCH bond angle (110.2°). This difference can be attributed to more character in the C−F bonding and more character in the C−H bonding orbitals. The hybridisation of bond orbitals is determined by Bent's rule: "Atomic s character concentrates in orbitals directed toward electropositive substituents". The bond length between similar atoms also shortens with increasing s character. For example, the C−H bond length is 110.2 pm in ethane, 108.5 pm in ethylene and 106.1 pm in acetylene, with carbon hybridizations sp (25% s), sp (33% s) and sp (50% s) respectively. To determine the degree of hybridization of each bond one can utilize a "hybridization parameter" (). For hybrids of s and p orbitals, this is the coefficient formula_1multiplying the p orbital when the hybrid orbital is written in the form formula_2 | https://en.wikipedia.org/wiki?curid=40006957 |
Isovalent hybridization The square of the hybridization parameter equals the "hybridization index" () of an orbital. formula_3. The fractional s character of orbital "i" is formula_4, and the s character of all the hybrid orbitals must sum to one, so that formula_5 The fractional character of orbital "i" is formula_6, and the p character of all the hybrid orbitals sums to the number of p orbitals involved in the formation of hybrids: These hybridization parameters can then be related to physical properties like bond angles. Using the two bonding atomic orbitals and we are able to find the magnitude of the interorbital angle. The orthogonality condition implies the relation known as Coulson's theorem: For two identical ligands the following equation can be utilized: The hybridization index cannot be measured directly in any way. However, one can find it indirectly by measuring specific physical properties. Because nuclear spins are coupled through bonding electrons, and the electron penetration to the nucleus is dependent on s character of the hybrid orbital used in bonding, "J-"coupling constants determined through NMR spectroscopy is a convenient experimental parameter that can be used to estimate the hybridization index of orbitals on carbon. The relationships for one-bond C-H and C-C coupling are where "J" is the one-bond NMR spin-spin coupling constant between nuclei X and Y and χ(α) is the s character of orbital α on carbon, expressed as a fraction of unity | https://en.wikipedia.org/wiki?curid=40006957 |
Isovalent hybridization As an application, the C-H coupling constants show that for the cycloalkanes, the amount of s character in the carbon hybrid orbital employed in the C-H bond decreases as the ring size increases. The value of "J" for cyclopropane, cyclobutane and cyclopentane are 161, 134, and 128 Hz, respectively. This is a consequence of the fact that the C-C bonds in small, strained rings (cyclopropane and cyclobutane) employ excess p character to accommodate their molecular geometries (these bonds are famously known as 'banana bonds'). In order to conserve the total number of s and p orbitals used in hybridization for each carbon, the hybrid orbital used to form the C-H bonds must in turn compensate by taking on more s character. Experimentally, this is also demonstrated by the significantly higher acidity of cyclopropane (p"K" "~" 46) compared to, for instance, cyclohexane (p"K" ~ 52). | https://en.wikipedia.org/wiki?curid=40006957 |
Gérard Maugin Gérard A. Maugin (born December 2, 1944 in Angers – September 22, 2016 in Villejuif) was a French engineering scientist. Maugin acquired his engineering degree in mechanical engineering in 1966 at the Ecole Nationale Supérieure d'Arts et Métiers (Ensam) and he continued his studies at the school of aeronautics Sup Aéro in Paris until 1968. In 1966 he worked for the French Ministry of Defence on ballistic missiles. In 1968 he received his (DEA) degree in hydrodynamics in Paris. In 1969, he earned his master's degree from Princeton University, where he graduated in 1971 (Ph.D.). He was a NASA International Fellow between 1968 and 1970. In 1971/72 he was an officer in the French Air Force. In 1975 he received his doctorate in mathematics (Doctorat d'Etat) at the University of Paris VI (Pierre et Marie Curie), where he also taught and directed a team at the Laboratoire de Mécanique Théorique conducting research since 1985 on Continuum mechanics and Theoretical Mechanics. After its name change to the Laboratoire de Modélisation en Mécanique (LMM), he headed this from 1998. From 1979 he was Director of Research at CNRS. He was a visiting professor and visiting scientist at Princeton, Belgrade, Warsaw, Istanbul, at the Royal Institute of Technology in Stockholm, at the TU Berlin, Rome, Tel Aviv, the Lomonosov University, Kyoto, Darmstadt and Berkeley | https://en.wikipedia.org/wiki?curid=40007354 |
Gérard Maugin His work deals with continuum mechanics, including relativistic continuum mechanics, micro magnetism, electrodynamics of continua, thermo mechanics, surface waves and nonlinear waves in continua, lattice dynamics, material equations and biomechanical applications (tissue growth). In 2001 he received the Max Planck Research Award, was the 1991/92 Fellow of the Berlin Institute for Advanced Study, and in 2001 received an honorary doctorate from the Technical University of Darmstadt . In 1982 he received the Prix Paul Doistau–Émile Blutet of the French Academy of Sciences and in 1977 the Medal of the CNRS in physics and engineering. He was a member of the Polish Academy of Sciences (1994), of the Estonian Academy of Sciences and was awarded an honorary professorship by the Moscow State University. In 2003, he received the A. Cemal Eringen Medal. | https://en.wikipedia.org/wiki?curid=40007354 |
Ahmed Cemal Eringen Ahmet Cemal Eringen (February 15, 1921, in Kayseri, Turkey – December 7, 2009) was a Turkish- American engineering scientist. He was a professor at Princeton University and the founder of the Society of Engineering Science. The Eringen Medal is named in his honor. Eringen studied at the Technical University of Istanbul and graduated with a diploma degree in 1943 and then worked for the Turkish Aircraft Co. until 1944. In 1944/45, he was a trainee at the Glenn L. Martin Company and in 1945 was group leader at the Turkish Air League Company. He continued his studies at the Polytechnic Institute of Brooklyn in New York City where he received his doctorate in applied mechanics in 1948 under the supervision of Nicholas J. Hoff. He became assistant professor at the Illinois Institute of Technology in 1948, associate professor in 1953 and professor in 1955 at Purdue University. He was appointed as professor of aerospace and mechanical engineering at Princeton University in 1966. He became professor of continuum mechanics in the departments of "civil and geological engineering" and "the program in applied and computational mathematics" at Princeton University. He retired in 1991 as the dean of the School of Engineering and Applied Science at Princeton University and died in 2009. Eringen had been married since 1949 and had four children. His work deals with continuum mechanics, electrodynamics of continua and material theories. In 1981 he received an honorary doctorate from the University of Glasgow (D. Sc.) | https://en.wikipedia.org/wiki?curid=40007405 |
Ahmed Cemal Eringen In 1973 he received the Distinguished Service Award and the 1976 as named in his honor A. C. Eringen Medal of the Society of Engineering Science, whose president he was in 1963 to 1973. | https://en.wikipedia.org/wiki?curid=40007405 |
440C is a 400 series stainless steel, and is the highest carbon content from 400 stainless steel series. It is usually heat treated to reach hardness of 58–60 HRC. It is a bearing steel, and used in rolling contact stainless bearings, e.g. ball and roller bearings. It is also used to make knife blades. can be oil quenched to achieve maximum hardness. has the highest strength, hardness, and wear resistance of all the commonplace 440-series stainless alloys with high carbon content and moderate corrosion resistance. | https://en.wikipedia.org/wiki?curid=40016771 |
Rafael Moure-Eraso (born May 2, 1946) is a former chairman and chief executive of the U.S. Chemical Safety and Hazard Investigation Board (CSB). Moure-Eraso was born in Cali, Colombia, in 1946. He grew up in Bogotá where he was educated by Augustinian friars and at the University of Los Andes. He received his B.Sc. in chemical engineering from the University of Pittsburgh in 1967 and M.Sc. in chemical engineering from Bucknell University in 1970. He received his M.Sc. and Ph.D. from the University of Cincinnati in Environmental Health-Industrial Hygiene in 1974 and 1982. For over 30 years, Moure-Eraso has been involved in workplace safety issues. Prior to joining the CSB Moure-Eraso served as a member of the National Advisory Committee on Occupational Health (NACOSH) for the Occupational Safety and Health Administration (OSHA) and as a member of the Scientific Advisory Committee of the National Institute for Occupational Safety and Health (NIOSH). Moure-Eraso has also worked as a chemical engineer for Rohm and Haas and the Dow Chemical Company. He was a faculty member at the University of Massachusetts Lowell for 22 years and chairman of the university's Department of Work Environment for 5 years. He has also served as an industrial hygienist engineer with the national offices of the United Automobile Workers union and the Oil, Chemical and Atomic Workers International Union. Moure-Eraso was nominated by President Barack Obama to the U.S. Chemical Safety Board in March 2010 and confirmed by the Senate in June 2010 | https://en.wikipedia.org/wiki?curid=40032774 |
Rafael Moure-Eraso In March 2015, he was called to testify in front of the House Oversight Committee regarding the management of the Chemical Safety Board. Following that testimony fourteen members of the committee issued a letter to the White House calling on the president to use his statutory authority to remove Moure-Eraso from his position as chairman of the CSB. The letter cited a pattern of retaliation against whistleblowers, disenfranchisement of fellow board members, low morale in the organization, and possible violations of the Federal Records Act by using personal email accounts for official business. Moure-Eraso told the "Los Angeles Times": "A lot of it is political. The mission of the organization is to produce good reports that make a difference for safety. We are doing that. I can show that we are producing the best reports ever produced in the agency. I stand by that. All of this other talk is peripheral... There have been a lot of accusations, but none of those have ever ended in any findings. The Office of Special Counsel has made no recommendations. Anybody can claim actions against whistleblowers, but there’s no evidence of this. To just say it is not enough. What I would like to be judged for is the quality of the product and the fulfillment of our mission. There will always be people complaining. But they are all rumors." He resigned his post on March 26, 2015. | https://en.wikipedia.org/wiki?curid=40032774 |
Indium Corporation is a refiner, producer, and supplier of indium and indium compounds. The company also has various products based on other metals. The company was founded in 1934, headquartered in Clinton, NY. was known as "The of America" in 1934. For many years the founders/scientists Dr. William S. Murray and Daniel Gray researched the metal called indium, hoping they would find some new ways to commercialize the metal. After several years of trial and error, they discovered methods for obtaining indium and how to change it chemically. The first breakthrough was in 1934 when the company developed indium plating for aircraft engine bearings. In the mid to late 1970s, the Huari Huari zinc mine was the principal source of indium for The Indium cooperation offers Indium, Gallium, Tin and Germanium as bare metals. They also offer Indium, Gallium and Germanium compounds. Their products also include various solder pastes (with different alloys and fluxes) and other PCB assembly materials (like epoxies and fluxes). | https://en.wikipedia.org/wiki?curid=40040442 |
Chromotropism is the (reversible) change in color of a substance due to the physical and chemical properties of its ambient surrounding medium, such as temperature and pressure, light, solvent, and presence of ions and electrons. | https://en.wikipedia.org/wiki?curid=40045124 |
Arsenic biochemistry refers to biochemical processes that can use arsenic or its compounds, such as arsenate. Arsenic is a moderately abundant element in Earth's crust, and although many arsenic compounds are often considered highly toxic to most life, a wide variety of organoarsenic compounds are produced biologically and various organic and inorganic arsenic compounds are metabolized by numerous organisms. This pattern is general for other related elements, including selenium, which can exhibit both beneficial and deleterious effects. has become topical since many toxic arsenic compounds are found in some aquifers, potentially affecting many millions of people via biochemical processes. The evidence that arsenic may be a beneficial nutrient at trace levels below the background to which living organisms are normally exposed has been reviewed. Some organoarsenic compounds found in nature are arsenobetaine and arsenocholine, both being found in many marine organisms. Some As-containing nucleosides (sugar derivatives) are also known. Several of these organoarsenic compounds arise via methylation processes. For example, the mold "Scopulariopsis brevicaulis" produces significant amounts of trimethylarsine if inorganic arsenic is present. The organic compound arsenobetaine is found in some marine foods such as fish and algae, and also in mushrooms in larger concentrations | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry In clean environments, the edible mushroom species Cyanoboletus pulverulentus hyperaccumulates arsenic in concentrations reaching even 1,300 mg/kg in dry weight; cacodylic acid is the major As compound. A very unusual composition of organoarsenic compounds was found in deer truffles ("Elaphomyces" spp.). The average person's intake is about 10–50 µg/day. Values about 1000 µg are not unusual following consumption of fish or mushrooms; however, there is little danger in eating fish since this arsenic compound is nearly non-toxic. A topical source of arsenic are the green pigments once popular in wallpapers, e.g. Paris green. A variety of illness have been blamed on this compound, although its toxicity has been exaggerated. Trimethylarsine, once known as Gosio's gas is an intensely malodorous organoarsenic compound that is commonly produced by microbial action on inorganic arsenic substrates. Arsenic (V) compounds are easily reduced to arsenic (III) and could have served as an electron acceptor on primordial Earth. Lakes that contain a substantial amount of dissolved inorganic arsenic, harbor arsenic-tolerant biota. Although phosphate and arsenate are structurally similar, there is no evidence that arsenic replaces phosphorus in DNA or RNA. A 2010 experiment involving the bacteria GFAJ-1 that made this claim was refuted by 2012. Anthropogenic (man-made) sources of arsenic, like the natural sources, are mainly arsenic oxides and the associated anions | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry Man-made sources of arsenic, include wastes from mineral processing, swine and poultry farms. For example, many ores, especially sulfide minerals, are contaminated with arsenic, which is released in roasting (burning in air). In such processing, arsenide is converted to arsenic trioxide, which is volatile at high temperatures and is released into the atmosphere. Poultry and swine farms make heavy use of the organoarsenic compound roxarsone as an antibiotic in feed. Some wood is treated with copper arsenates as a preservative. The mechanisms by which these sources affect "downstream" living organisms remains uncertain but are probably diverse. One commonly cited pathway involves methylation. The monomethylated acid, methanearsonic acid (CHAsO(OH)), is a precursor to fungicides (tradename Neoasozin) in the cultivation of rice and cotton. Derivatives of phenylarsonic acid (CHAsO(OH)) are used as feed additives for livestock, including 4-hydroxy-3-nitrobenzenearsonic acid (3-NHPAA or Roxarsone), ureidophenylarsonic acid, and "p"-arsanilic acid. These applications are controversial as they introduce soluble forms of arsenic into the environment. Despite, or possibly because of, its long-known toxicity, arsenic-containing potions and drugs have a history in medicine and quackery that continues into the 21st century. Starting in the early 19th century and continuing into the 20th century, Fowler's solution, a toxic concoction of sodium arsenite, was sold | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry The organoarsenic compound Salvarsan was the first synthetic chemotherapeutic agent, discovered by Paul Ehrlich. The treatment, however, led to many problems causing long lasting health complications. Around 1943 it was finally superseded by penicillin. The related drug Melarsoprol is still in use against late-state African trypanosomiasis (sleeping sickness), despite its high toxicity and possibly fatal side effects. Arsenic trioxide (AsO) inhibits cell growth and induces apoptosis(programmed cell death)i in certain types of cancer cells, which are normally immortal and can multiply without limit. In combination with all-trans retinoic acid, it is FDA-approved as first-line treatment for promyelocytic leukemia. Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolised (detoxified) through a process of methylation. The methylation occurs through alternating reductive and oxidative methylation reactions, that is, reduction of pentavalent to trivalent arsenic followed by addition of a methyl group (CH). In mammals, methylation occurs in the liver by methyltransferases, the products being the (CH)AsOH (dimethylarsinous acid) and (CH)As(O)OH (dimethylarsinic acid), which have the oxidation states As(III) and As(V), respectively. Although the mechanism of methylation of arsenic in humans has not been elucidated, the source of methyl is methionine, which suggests a role of S-adenosyl methionine | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry Exposure to toxic doses begin when the liver's methylation capacity is exceeded or inhibited. There are two major forms of arsenic that can enter the body, arsenic (III) and arsenic (V). Arsenic (III) enters the cells though aquaporins 7 and 9, which is a type of aquaglyceroporin. Arsenic (V) compounds use phosphate transporters to enter cells. The arsenic (V) can be converted to arsenic (III) by the enzyme purine nucleoside phosphorylase. This is classified as a bioactivation step, as although arsenic (III) is more toxic, it is more readily methylated. There are two routes by which inorganic arsenic compounds are methylated. The first route uses Cyt19 arsenic methyltransferase to methylate arsenic (III) to a mono-methylated arsenic (V) compound. This compound is then converted to a mono-methylated arsenic (III) compound using Glutathione S-Transferase Omega-1 (GSTO1). The mono-methylated arsenic (V) compound can then be methylated again by Cyt19 arsenic methyltransferase, which forms a dimethyl arsenic (V) compound, which can be converted to a dimethyl arsenic (III) compound by Glutathione S-Transferase Omega-1 (GTSO1). The other route uses glutathione (GSH) to conjugate with arsenic (III) to form an arsenic (GS) complex. This complex can form a monomethylated arsenic (III) GS complex, using Cyt19 arsenic methyltransferase, and this monomethylated GS complex is in equilibrium with the monomethylated arsenic (III) | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry Cyt19 arsenic methyltransferase can methylate the complex one more time, and this forms a dimethylated arsenic GS complex, which is in equilibrium with a dimethyl arsenic (III) complex. Both of the mono-methylated and di-methylated arsenic compounds can readily be excreted in urine. However, the monomethylated compound was shown to be more reactive and more toxic than the inorganic arsenic compounds to human hepatocites (liver), keratinocytes in the skin, and bronchrial epithelial cells (lungs). Studies in experimental animals and humans show that both inorganic arsenic and methylated metabolites cross the placenta to the fetus, however, there is evidence that methylation is increased during pregnancy and that it could be highly protective for the developing organism. Enzymatic methylation of arsenic is a detoxification process; it can be methylated to methylarsenite, dimethylarsenite or trimethylarsenite, all of which are trivalent. The methylation is catalyzed by arsenic methyltransferase (AS3MT) in mammals, which transfers a methyl group on the cofactor S-adenomethionine (SAM) to arsenic (III). An orthologue of AS3MT is found in bacteria and is called CmArsM. This enzyme was tested in three states (ligand free, arsenic (III) bound and SAM bound). Arsenic (III) binding sites usually use thiol groups of cyseine residues. The catalysis involves thiolates of Cys72, Cys174, and Cys224 | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry In an SN2 reaction, the positive charge on the SAM sulfur atom pulls the bonding electron from the carbon of the methyl group, which interacts with the arsenic lone pair to form an As−C bond, leaving SAH. In humans, the major route of excretion of most arsenic compounds is via the urine. The biological half-life of inorganic arsenic is about 4 days, but is slightly shorter following exposure to arsenate than to arsenite. The main metabolites excreted in the urine of humans exposed to inorganic arsenic are mono- and dimethylated arsenic acids, together with some unmetabolized inorganic arsenic. The biotransformation of arsenic for excretion is primarily done through the nuclear factor erythroid 2 related factor 2 (Nrf2) pathway. Under normal conditions the Nrf2 is bound to Kelch-like ECH associated protein 1 (Keap1) in its inactive form. With the uptake of arsenic within cells and the subsequent reactions that result in the production of reactive oxygen species (ROS), the Nrf2 unbinds and becomes active. Keap1 has reactive thiol moieties that bind ROS or electrophilic arsenic species such as monomethylted arsenic (III) and induces the release of Nrf2 which then travels through the cytoplasm to the nucleus. The Nrf2 then activates antioxidant responsive element (ARE) as well as electrophilic responsive element (EpRE) both of which contribute in the increase of antioxidant proteins | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry Of particular note in these antioxidant proteins is heme oxygenase 1 ([HO-1]), NAD(P)H-quinone oxidoreductase 1 (NQO1), and γ-glutamylcysteine synthase (γGCS) which work in conjunction to reduce the oxidative species such as hydrogen peroxide to decrease the oxidative stress upon the cell. The increase in γGCS causes an increased production of aresnite triglutathionine (As(SG)) an important adduct that is taken up by either multidrug associated protein 1 or 2 (MRP1 or MRP2) which removes the arsenic out of the cell and into bile for excretion. This adduct can also decompose back into inorganic arsenic. Of particular note in the excretion of arsenic is the multiple methylation steps that take place which may increase the toxicity of arsenic due to MMeAsIII being a potent inhibitor of glutathione peroxidase, glutathione reductase, pyruvate dehydrogenase, and thioredoxin reductase. Arsenic is a cause of mortality throughout the world; associated problems include heart, respiratory, gastrointestinal, liver, nervous and kidney diseases. Arsenic interferes with cellular longevity by allosteric inhibition of an essential metabolic enzyme pyruvate dehydrogenase (PDH) complex, which catalyzes the oxidation of pyruvate to acetyl-CoA by NAD. With the enzyme inhibited, the energy system of the cell is disrupted resulting in a cellular apoptosis episode. Biochemically, arsenic prevents use of thiamine resulting in a clinical picture resembling thiamine deficiency | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry Poisoning with arsenic can raise lactate levels and lead to lactic acidosis. Genotoxicity involves inhibition of DNA repair and DNA methylation. The carcinogenic effect of arsenic arises from the oxidative stress induced by arsenic. Arsenic's high toxicity naturally led to the development of a variety of arsenic compounds as chemical weapons, e.g. dimethylarsenic chloride. Some were employed as chemical warfare agents, especially in World War I. This threat led to many studies on antidotes and an expanded knowledge of the interaction of arsenic compounds with living organisms. One result was the development of antidotes such as British anti-Lewisite. Many such antidotes exploit the affinity of As(III) for thiolate ligands, which convert highly toxic organoarsenicals to less toxic derivatives. It is generally assumed that arsenates bind to cysteine residues in proteins. By contrast, arsenic oxide is an approved and effective chemotherapeutic drug for the treatment of acute promyelocytic leukemia (APL). Due to its similar structure and properties, pentavalent arsenic metabolites are capable of replacing the phosphate group of many metabolic pathways. The replacement of phosphate by arsenate is initiated when arsenate reacts with glucose and gluconate in vitro. This reaction generates glucose-6-arsenate and 6-arsenogluconate, which act as analogs for glucose-6-phosphate and 6-phosphogluconate | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry At the substrate level, during glycolysis, glucose-6-arsenate binds as a substrate to glucose-6-phosphate dehydrogenase, and also inhibits hexokinase through negative feedback. Unlike the importance of phosphate in glycolysis, the presence of arsenate restricts the generation of ATP by forming an unstable anhydride product, through the reaction with D-glyceraldehyde-3-phosphate. The anhydride 1-arsenato-3-phospho-D-glycerate generated readily hydrolyzes due to the longer bond length of As-O compared to P-O. At the mitochondrial level, arsenate uncouples the synthesis of ATP by binding to ADP in the presence of succinate, thus forming an unstable compound that ultimately results in a decrease of ATP net gain. Arsenite (III) metabolites, on the other hand, have limited effect on ATP production in red blood cells. Enzymes and receptors that contain thiol or sulfhydryl functional groups are actively targeted by arsenite (III) metabolites. These sulfur-containing compounds are normally glutathione and the amino acid cysteine. Arsenite derivatives generally have higher binding affinity compared to the arsenate metabolites. These bindings restrict activity of certain metabolic pathways. For example, pyruvate dehydrogenase (PDH) is inhibited when monomethylarsonous acid (MMA) targets the thiol group of the lipoic acid cofactor. PDH is a precursor of acetyl-CoA, thus the inhibition of PDH eventually limits the production of ATP in electron transport chain, as well as the production of gluconeogenesis intermediates | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry Arsenic can cause oxidative stress through the formation of reactive oxygen species (ROS), and reactive nitrogen species (RNS). Reactive oxygen species are produced by the enzyme NADPH oxidase, which transfers electrons from NADPH to oxygen, synthesizing a superoxide, which is a reactive free radical. This superoxide can react to form hydrogen peroxide and a reactive oxygen species. The enzyme NADPH oxidase is able to generate more reactive oxygen species in the presence of arsenic, due to the subunit p22phax, which is responsible for the electron transfer, being upregulated by arsenic. The reactive oxygen species are capable of stressing the endoplasmic reticulum, which increases the amount of the unfolded protein response signals. This leads to inflammation, cell proliferation, and eventually to cell death. Another mechanism in which reactive oxygen species cause cell death would be through the cytoskeleton rearrangement, which affects the contractile proteins. The reactive nitrogen species arise once the reactive oxygen species destroy the mitochondria. This leads to the formation of the reactive nitrogen species, which are responsible for damaging DNA in arsenic poisoning. Mitochondrial damage is known to cause the release of reactive nitrogen species, due to the reaction between superoxides and nitric oxide (NO). Nitric oxide (NO) is a part of cell regulation, including cellular metabolism, growth, division and death. Nitric oxide (NO) reacts with reactive oxygen species to form peroxynitrite | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry In cases of chronic arsenic exposure, the nitric oxide levels are depleted, due to the superoxide reactions. The enzyme NO synthase (NOS) uses L-arginine to form nitric oxide, but this enzyme is inhibited by monomethylated arsenic (III) compounds. Arsenic is reported to cause DNA modifications such as aneuploidy, micronuclei formation, chromosome abnormality, deletion mutations, sister chromatid exchange and crosslinking of DNA with proteins. It has been demonstrated that arsenic does not directly interact with DNA and it is considered a poor mutagen, but instead, it helps mutagenicity of other carcinogens. For instance, a synergistic increase in the mutagenic activity of arsenic with UV light has been observed in human and other mammalian cells after exposing the UV-treated cells to arsenic. A series of experimental observations suggest that the arsenic genotoxicity is primarily linked to the generation of reactive oxygen species (ROS) during its biotransformation. The ROS production is able to generate DNA adducts, DNA strand breaks, crosslinks and chromosomal aberrations. The oxidative damage is caused by modification of DNA nucleobases, in particular 8-oxoguanine (8-OHdG) which leads to G:C to T:A mutations. Inorganic arsenic can also cause DNA strand break even at low concentrations. Inhibition of DNA repair processes is considered one of main mechanism of inorganic arsenic genotoxicity | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry Nucleotide excision repair (NER) and base excision repair (BER) are the processes implicated in the repair of DNA base damage induced by ROS after arsenic exposure. In particular, the NER mechanism is the major pathway for repairing bulky distortions in DNA double helix, while the BER mechanism is mainly implicated in the repair of single strand breaks induced by ROS, but inorganic arsenic could also repress the BER mechanism. Arsenic is highly detrimental to the innate and the adaptive immune system of the body. When the amount of unfolded and misfolded proteins in endoplasmic reticulum stress is excessive, the unfolded protein response (UPR) is activated to increase the activity of several receptors that are responsible the restoration of homeostasis. The inositol-requiring enzyme-1 (IRE1) and protein kinase RNA-like endoplasmic reticulum kinase (PERK) are two receptors that restrict the rate of translation. On the other hand, the unfolded proteins are corrected by the production of chaperones, which are induced by the activating transcription factor 6 (ATF6). If the number of erroneous proteins elevates, further mechanism is active which triggers apoptosis. Arsenic has evidentially shown to increase the activity of these protein sensors. Arsenic exposure in small children distorts the ratio of T helper cells (CD4) to cytotoxic T cells (CD8), which are responsible for immunodepression. In addition, arsenic also increases the number of inflammatory molecules being secreted through macrophages | https://en.wikipedia.org/wiki?curid=29855647 |
Arsenic biochemistry The excess amount of granulocytes and monocytes lead to a chronic state of inflammation, which might result in cancer development. There are three molecules that serve as chelator agents that bond to arsenic. These three are British Anti-Lewisite (BAL, Dimercaprol), succimer (DMSA) and Unithiol (DMPS). When these agents chelate inorganic arsenic, it is converted into an organic form of arsenic because it is bound to the organic chelating agent. The sulfur atoms of the thiol groups are the site of interaction with arsenic. This is because the thiol groups are nucleophilic while the arsenic atoms are electrophilic. Once bound to the chelating agent the molecules can be excreted, and therefore free inorganic arsenic atoms are removed from the body. Other chelating agents can be used, but may cause more side effects than British Anti-Lewisite (BAL, Dimercaprol), succimer (DMSA) and (DMPS). DMPS and DMSA also have a higher therapeutic index than BAL. These drugs are efficient for acute poisoning of arsenic, which refers to the instantaneous effects caused by arsenic poisoning. For example, headaches, vomiting or sweating are some of the common examples of an instantaneous effect. In comparison, chronic poisonous effects arise later on, and unexpectedly such as organ damage. Usually it is too late to prevent them once they appear. Therefore, action should be taken as soon as acute poisonous effects arise. | https://en.wikipedia.org/wiki?curid=29855647 |
GFAJ-1 is a strain of rod-shaped bacteria in the family Halomonadaceae. It is an extremophile that was isolated from the hypersaline and alkaline Mono Lake in eastern California by geobiologist Felisa Wolfe-Simon, a NASA research fellow in residence at the US Geological Survey. In a 2010 "Science" journal publication, the authors claimed that the microbe, when starved of phosphorus, is capable of substituting arsenic for a small percentage of its phosphorus to sustain its growth. Immediately after publication, other microbiologists and biochemists expressed doubt about this claim which was robustly criticized in the scientific community. Subsequent independent studies published in 2012 found no detectable arsenate in the DNA of GFAJ-1, refuted the claim, and demonstrated that is simply an arsenate-resistant, phosphate-dependent organism. The bacterium was discovered by geomicrobiologist Felisa Wolfe-Simon, a NASA astrobiology fellow in residence at the US Geological Survey in Menlo Park, California. GFAJ stands for "Give Felisa a Job". The organism was isolated and cultured beginning in 2009 from samples she and her colleagues collected from sediments at the bottom of Mono Lake, California, U.S.A. Mono Lake is hypersaline (about 90 grams/liter) and highly alkaline (pH 9.8). It also has one of the highest natural concentrations of arsenic in the world (200 μM). The discovery was widely publicized on 2 December 2010 | https://en.wikipedia.org/wiki?curid=29856330 |
GFAJ-1 Molecular analysis based on 16S rRNA sequences shows to be closely related to other moderate halophile ("salt-loving") bacteria of the family Halomonadaceae. Although the authors produced a cladogram in which the strain is nested among members of "Halomonas", including "H. alkaliphila" and "H. venusta", they did not explicitly assign the strain to that genus. Many bacteria are known to be able to tolerate high levels of arsenic, and to have a proclivity to take it up into their cells. However, was controversially proposed to go a step further; when starved of phosphorus, it was proposed to instead incorporate arsenic into its metabolites and macromolecules and continue growing. The sequence of the genome of the bacterium is now posted in GenBank. In the "Science" journal article, is referred to as a strain of Halomonadaceae and not as a new species. The International Code of Nomenclature of Bacteria, the set of regulations which govern the taxonomy of bacteria, and certain articles in the International Journal of Systematic and Evolutionary Microbiology contain the guidelines and minimal standards to describe a new species, e.g. the minimal standards to describe a member of the "Halomonadaceae". Organisms are described as new species if they meet certain physiological and genetic conditions, such as generally less than 97% 16S rRNA sequence identity to other known species and metabolic differences allowing them to be discerned apart | https://en.wikipedia.org/wiki?curid=29856330 |
GFAJ-1 In addition to indicators to tell the novel species from other species, other analyses are required, such as fatty acid composition, respiratory quinone used and tolerance ranges and deposition of the strain in at least two microbiological repositories. New proposed names are given in italics followed by "sp. nov." (and "gen. nov." if it is a novel genus according to the descriptions of that clade). In the instance of the strain these criteria are not met, and the strain is not claimed to be a new species. When a strain is not assigned to a species (e.g. due to insufficient data or choice) it is often labeled as the genus name followed by "sp." (i.e., undetermined species of that genus) and the strain name. In the case of the authors chose to refer to the strain by strain designation only. Strains closely related to include "Halomonas" sp. GTW and "Halomonas" sp. G27, neither of which were described as valid species. If the authors had formally assigned strain to the genus "Halomonas", the name would be given as "Halomonas" sp. GFAJ-1. A phosphorus-free growth medium (which actually contained 3.1 ± 0.3 μM of residual phosphate, from impurities in reagents) was used to culture the bacteria in a regime of increasing exposure to arsenate; the initial level of 0.1 mM was eventually ramped up to 40 mM. Alternative media used for comparative experiments contained either high levels of phosphate (1.5 mM) with no arsenate, or had neither added phosphate nor added arsenate | https://en.wikipedia.org/wiki?curid=29856330 |
GFAJ-1 It was observed that could grow through many doublings in cell numbers when cultured in either phosphate or arsenate media, but could not grow when placed in a medium of a similar composition to which neither phosphate nor arsenate was added. The phosphorus content of the arsenic-fed, phosphorus-starved bacteria (as measured by ICP-MS) was only 0.019 (± 0.001) % by dry weight, one thirtieth of that when grown in phosphate-rich medium. This phosphorus content was also only about one tenth of the cells' average arsenic content (0.19 ± 0.25% by dry weight). The arsenic content of cells as measured by ICP-MS varies widely and can be lower than the phosphorus contents in some experiments, and up to fourteen times higher in others. Other data from the same study obtained with nano-SIMS suggest a ~75-fold excess of phosphate (P) over arsenic (As) when expressed as P:C and As:C ratios, even in cells grown with arsenate and no added phosphate. When cultured in the arsenate solution, only grew 60% as fast as it did in phosphate solution. The phosphate-starved bacteria had an intracellular volume 1.5 times normal; the greater volume appeared to be associated with the appearance of large "vacuole-like regions". When the researchers added isotope-labeled arsenate to the solution to track its distribution, they found that arsenic was present in the cellular fractions containing the bacteria's proteins, lipids and metabolites such as ATP, as well as its DNA and RNA | https://en.wikipedia.org/wiki?curid=29856330 |
GFAJ-1 Nucleic acids from stationary phase cells starved of phosphorus were concentrated via five extractions (one with phenol, three with phenol-chloroform and one with chloroform extraction solvent), followed by ethanol precipitation. Although direct evidence of the incorporation of arsenic into biomolecules is still lacking, radioactivity measurements suggested that approximately one-tenth (11.0 ± 0.1%) of the arsenic absorbed by these bacteria ended up in the fraction that contained the nucleic acids (DNA and RNA) and all other co-precipitated compounds not extracted by the previous treatments. A comparable control experiment with isotope-labeled phosphate was not performed. With the distribution of the strain in mid-2011, other labs began to independently test the validity of the discovery. Rosemary Redfield from the University of British Columbia, following issues with the growth conditions, investigated the growth requirements of GFAJ-1, and found that the strain grows better on solid agar medium than in liquid culture. Redfield attributed this to low potassium levels and hypothesized that the potassium levels in basal ML60 medium may be too low to support growth. Redfield after finding and addressing further issues (ionic strength, pH and the use of glass tubes instead of polypropylene) found that arsenate marginally stimulated growth, but didn't affect the final densities of the cultures, unlike what was claimed | https://en.wikipedia.org/wiki?curid=29856330 |
GFAJ-1 Subsequent studies using mass spectrometry by the same group found no evidence of arsenate being incorporated into the DNA of GFAJ-1. Arsenate esters, such as those that would be present in DNA, are generally expected to be orders of magnitude less stable to hydrolysis than corresponding phosphate esters. dAMAs, the structural arsenic analog of the DNA building block dAMP, has a half-life of 40 minutes in water at neutral pH. Estimates of the half-life in water of arsenodiester bonds, which would link the nucleotides together, are as short as 0.06 seconds—compared to 30 million years for the phosphodiester bonds in DNA. The authors speculate that the bacteria may stabilize arsenate esters to a degree by using poly-β-hydroxybutyrate (which has been found to be elevated in "vacuole-like regions" of related species of the genus "Halomonas" ) or other means to lower the effective concentration of water. Polyhydroxybutyrates are used by many bacteria for energy and carbon storage under conditions when growth is limited by elements other than carbon, and typically appear as large waxy granules closely resembling the "vacuole-like regions" seen in cells. The authors present no mechanism by which insoluble polyhydroxybutyrate may lower the effective concentration of water in the cytoplasm sufficiently to stabilize arsenate esters. Although all halophiles must reduce the water activity of their cytoplasm by some means to avoid desiccation, the cytoplasm always remains an aqueous environment | https://en.wikipedia.org/wiki?curid=29856330 |
GFAJ-1 NASA's announcement of a news conference "that will impact the search for evidence of extraterrestrial life" was criticized as sensationalistic and misleading; an editorial in "New Scientist" commented "although the discovery of alien life, if it ever happens, would be one of the biggest stories imaginable, this was light-years from that". In addition, many experts who have evaluated the paper have concluded that the reported studies do not provide enough evidence to support the claims made by the authors. In an online article on "Slate", science writer Carl Zimmer discussed the skepticism of several scientists: "I reached out to a dozen experts ... Almost unanimously, they think the NASA scientists have failed to make their case". Chemist Steven A. Benner has expressed doubts that arsenate has replaced phosphate in the DNA of this organism. He suggested that the trace contaminants in the growth medium used by Wolfe-Simon in her laboratory cultures are sufficient to supply the phosphorus needed for the cells' DNA. He believes that it is more likely that arsenic is being sequestered elsewhere in the cells. University of British Columbia microbiologist Rosemary Redfield said that the paper "doesn't present any convincing evidence that arsenic has been incorporated into DNA or any other biological molecule", and suggests that the experiments lacked the washing steps and controls necessary to properly validate their conclusions | https://en.wikipedia.org/wiki?curid=29856330 |
GFAJ-1 Harvard microbiologist Alex Bradley said that arsenic-containing DNA would be so unstable in water it could not have survived the analysis procedure. On 8 December 2010, "Science" published a response by Wolfe-Simon, in which she stated that criticism of the research was expected. In response, a "Frequently Asked Questions" page to improve understanding of the work was posted on 16 December 2010. The team plans to deposit the strain in the ATCC and DSMZ culture collections to allow widespread distribution. In late May 2011, the strain has also been made available upon request directly from the laboratory of the authors. "Science" has made the article freely available. The article was published in print six months after acceptance in the 3 June 2011 issue of "Science". The publication was accompanied by eight technical comments addressing various concerns regarding the article's experimental procedure and conclusion, as well as a response by the authors to these concerns. The editor in chief Bruce Alberts has indicated that some issues remain and that their resolution is likely to be a long process. A review by Rosen "et al.", in the March 2011 issue of the journal "BioEssays" discusses the technical issues with the "Science" paper, provides alternative explanations, and highlights known biochemistry of other arsenic resistant and arsenic utilizing microbes. On 27 May 2011, Wolfe-Simon and her team responded to the criticism in a follow-up "Science" journal publication | https://en.wikipedia.org/wiki?curid=29856330 |
GFAJ-1 Then on January 2012 a group of researchers led by Rosie Redfield at the University of British Columbia analyzed the DNA of using liquid chromatography–mass spectrometry and could not detect any arsenic, which Redfield calls a "clear refutation" of the original paper's findings. A simple explanation for the growth in medium supplied with arsenate instead of phosphate was provided by a team of researchers at the University of Miami in Florida. After labeling the ribosomes of a laboratory strain of "Escherichia coli" with radioactive isotopes (forming a radioactive tracer), they followed bacterial growth in medium containing arsenate but no phosphate. They found that arsenate induces massive degradation of ribosomes, thus providing sufficient phosphate for the slow growth of arsenate tolerant bacteria. Similarly, they suggest, cells grow by recycling phosphate from degraded ribosomes, rather than by replacing it with arsenate. Following the publication of the articles challenging the conclusions of the original "Science" article first describing GFAJ-1, the website Retraction Watch argued that the original article should be retracted because of misrepresentation of critical data. So far, as of January 2019, the paper has not yet been retracted. | https://en.wikipedia.org/wiki?curid=29856330 |
Moeller stain Moeller staining involves the use of a steamed dye reagent in order to increase the stainability of endospores; carbol fuchsin is the primary stain used in this method. Endospores are stained red, while the counterstain methylene blue stains the vegetative bacteria blue. Endospores are surrounded by a highly resistant spore coat, which is highly resistant to excessive heat, freezing, desiccation, as well as chemical agents. More importantly, for identification, spores are resistant to commonly employed staining techniques; therefore alternative staining methods are required. Carbol fuchsin is applied to a heat-fixed slide. The slide is then heated over a bunsen burner, or suspended over a hot water bath, covered with a paper towel, and steamed for 3 minutes. The slide is rinsed with acidified ethanol, and counter-stained with Methylene blue. An improved method involves the addition of the surfactant Tergitol 7 to the carbol fuchsin stain, and the omission of the steaming step. | https://en.wikipedia.org/wiki?curid=29858554 |
Leukocyte immunoglobulin-like receptors The leukocyte immunoglobulin-like receptors (LILR) are a family of receptors possessing extracellular immunoglobulin domains. They are also known as CD85, ILTs and LIR, and can exert immunomodulatory effects on a wide range of immune cells. The human genes encoding these receptors are found in a gene cluster at chromosomal region 19q13.4. They include A subset of LILR recognise MHC class I (also known as HLA class I in humans). Of these, the inhibitory receptors LILRB1 and LILRB2 show a broad specificity for classical and non-classical MHC alleles with preferential binding to b2m-associated complexes. In contrast, the activating receptors LILRA1 and LILRA3 prefer b2m-independent free heavy chains of MHC class I, and in particular HLA-C alleles. | https://en.wikipedia.org/wiki?curid=29859320 |
Reverse electron flow (also known as reverse electron transport) is a mechanism in microbial metabolism. Chemolithotrophs using an electron donor with a higher redox potential than NAD(P)/NAD(P)H, such as nitrite or sulfur compounds, must use energy to reduce NAD(P). This energy is supplied by consuming proton motive force to drive electrons in a reverse direction through an electron transport chain and is thus the reverse process as forward electron transport. In some cases, the energy consumed in reverse electron transport is five times greater than energy gained from the forward process. Autotrophs can use this process to supply reducing power for inorganic carbon fixation. | https://en.wikipedia.org/wiki?curid=29863201 |
Royal Gold is a precious metals company with royalty claims on gold, silver, copper, lead and zinc at mines in over 20 countries (12 in the Americas, most of the rest spread between Africa, Western Europe and Australia). Over half of the developmental properties it has interests in are producing however most (130 representing 70% of all properties) have not passed the exploration stage. Not all contracts are the same, some like the one it has with Thompson Creek Metals regarding a quarter of the gold produced at Mount Milligan lasts the length of the mine's life while others like Taparko in West Africa which ranges depending on the price of gold and the one in Pascua Lama (El Indio Gold Belt) where the 5.23% royalty is contingent on gold prices (must be higher than $800 an ounce) are structured differently; Most claims are between 1% and 5% but a few like Andacolo (75%) and Taparko (15%) are over 10%. It also has an interest in Osisko Mining's Malartic gold project within the abitibi gold belt (1.0-1.5%, will be Canada's largest when production begins in 2012). The royalties are either bought (paid Thompson Creek Metals $311.5 million in October 2010 for a guaranteed, fixed share of gold production at Mount Milligan) or acquired through project financing arrangements. Similar to silver streaming companies, royalty companies are not exposed to the operational risks associated with mining | https://en.wikipedia.org/wiki?curid=29866399 |
Royal Gold Royal Gold's business has over a short period of time become more internationalized and diversified (in 2010 60% of revenue came from abroad compared to 44% the year before). In 2010 40% of revenue came from the USA compared to 79% in 2008; Canada down to 4% from 27% in 2008 however most assets in Canada are in the developmental phase while Africa nearly tripled to 29%. is one of the world's leading precious metals royalty companies. In the 2009 edition of the Fortune Small Business Magazine (FSB) it ranked 10th among the fastest growing small businesses in the United States, 79 spots higher than in 2008. reported record operating cash flow of $69.7 million during fiscal Q2 2017 as well as $107 million in revenue and earnings per share of $0.43. 2010 was the year the company experienced the most growth with over a billion of the $1.86 billion in assets it has (September 2010) added during the year. In 2007 it purchased an interest in the Penasquito mine which did not begin producing until 2010. January 2010 acquired 75% of gold produced at Andacolo copper mine in Chile from Teck Resources. The royalty claim gets cut by 33.3% (down to 50% total) after it receives 910,000 ounces. February 2010 completed the acquisition of another royalty company, IRC which has claims in Chile (Pascua Lama) and Canada (Voisey's Bay). International Royalty Company was quick to accept the $702 million deal from after Franco-Nevada attempted a hostile $640 million takeover | https://en.wikipedia.org/wiki?curid=29866399 |
Royal Gold In the summer of 2011 paid Seabridge Gold C$160 million for a 2% net smelter return royalty claim on the KSM gold-copper-silver-molybdenum project in northern British Columbia. By the end of the 2010 fiscal year the company was receiving royalty payments from 34 mines (July 2010). The developmental projects in which has the highest percentage claims are Wolverine, Yukon (9.445% of the gold and silver) and Pine Cove, Newfoundland (7.5% of the gold). There are two molybdenum properties, one in Saskatchewan (Allan that has started producing) and another in British Columbia (Schaft Creek, not producing). Andacollo, the property Royal has the highest stake in (75%) was estimated by Teck Resources to have 2P reserves (Proved + Probable) of 1.631 million ounces of gold. Voisey's Bay (3-4% royalty) has reserves of about 1.5 billion pounds of nickel, 873 million pounds of copper and 74 million pounds of cobalt. In the first nine months of 2010 the largest producing mines that it has a royalty interest on were Leeville for gold (321,247 ounces), Robinson for copper (83.1 million pounds), Penasquito for lead (56 million pounds), zinc (86.3 million pounds), nickel (37.2 million pounds) and silver (8.5 million ounces). In addition to the following properties there are another 19 in production that only produce gold. In the last three months of the 2011 calendar year relied on Andacollo (23.5%), Voisey's Bay (17.5%), Penasquito (9.2%), Holt (6.1%) for more than half of its revenue | https://en.wikipedia.org/wiki?curid=29866399 |
Royal Gold Those mines produced in total 92,358 ounces of gold during the quarter up from 65,862 ounces during the same period a year earlier, only two of them produced anything besides gold. Voisey's Bay and Las Cruces are the only major mining operations that don't produce gold. | https://en.wikipedia.org/wiki?curid=29866399 |
Semenov Institute of Chemical Physics The of Russian Academy of Sciences (RAS) (now known as the Semenov ICP in Moscow ), was established in 1931 under the direction of Professor Nikolay Semyonov, Nobel Laureate in Chemistry (1956) on the basis of the Physico-Chemical Sector of the Leningrad Physical Technical Institute (Ioffe Institute). The staff of the Institute includes about 450 researchers. The Institute has been situated in Moscow since 1943. It is affiliated with the Moscow State University and has chairs at the Moscow Institute of Physics and Technology and other institutions of higher education. The Institute's aim has been defined as "the implementation of physical theories and methods into chemistry, chemical industry and some other branches of national economy". Its main areas of scientific inquiry are the kinetics and mechanism of chemical reactions, catalysis of chemical reactions, theory and dynamics of elementary processes, physics and chemistry of solids, structure and properties of polymers and composites, fundamentals of polymerization processes, physics and chemistry of combustion, shock waves and detonation. In 1956, a branch of the Institute of Chemical Physics was established in Chernogolovka; this was reorganized in 1997 as the independent Institute of Problems of Chemical Physics (IPCP RAS). Another department of the Semenov Institute was reorganized in 1994 as the N. M. Emanuel Institute of Biochemical Physics in Moscow of the Russian Academy of Sciences. | https://en.wikipedia.org/wiki?curid=29870342 |
MassTag-PCR MassTag PCR is a modification of PCR based on mass-spectrometric detection of an end product. This technology was pioneered by a scientist from Center for Infection and Immunity (CII) of the Mailman School of Public Health at Columbia University, USA. Like conventional PCR, uses primer pairs. The difference is primers used for MassTag PCR are tagged with molecules of known masses or MassCodes. Instead of single pair of primers this technology uses a number of primers, making it a multiplex system. Unlike, conventional Multiplex PCR system, in MassTag PCR more than 15 primer pairs could be used. If DNA from any of the agent of primer panel is present, it will be amplified. Each amplified product will carry its specific Masscodes. The PCR product is then purified to remove unbound primers, dNTPs, enzyme and other impurities. Finally, the purified PCR products are subjected to UV light as the chemical bond between the nucleic acids and primers is photolabile. As the Masscodes are liberated from PCR products they are detected with a Mass Spectrometer. Presence of specific MassCode indicates the presence of specific pathogen. This technique has been found to detect a previously uncharacterized clade of rhinovirus. MassTag PCR is a more comprehensive and sensitive diagnostic technique, CII was able to determine the cause of this illness for 26 out of 79 previously unknown cases. MassTag PCR demonstrated its tripartite value as a tool for surveillance, outbreak detection, and epidemiology. | https://en.wikipedia.org/wiki?curid=29872545 |
K factor (crude oil refining) The K factor or characterization factor is a systematic way of classifying a crude oil according to its paraffinic, naphthenic, intermediate or aromatic nature. 12.5 or higher indicate a crude oil of predominantly paraffinic constituents, while 10 or lower indicate a crude of more aromatic nature. The K factor is also referred to as the UOP K factor or just UOPK. | https://en.wikipedia.org/wiki?curid=29882763 |
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