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71.
Francisco Garcia-Sevilla Manuela Garcia-Moreno Maria D. Masia Ricardo Gomez-Ladron de Guevara Maria M. Garcia-Molina Enrique Arribas Milagros Molina-Alarcon Maria L. Amo Ramon Varon 《Journal of mathematical chemistry》2014,52(7):1675-1689
Software application is implemented in this work to take full advantage of the characteristics of current operating systems and to provide the optimized symbolic kinetic equations for both enzyme and ligand species involved in enzyme reactions. This software, called SKEE-w2013, is implemented using C# language and runs under all operating systems from Windows XP up to Windows 8. It is applicable to any enzyme reaction mechanism that fits the general reaction scheme proposed previously by our group. It can be downloaded, free of charge, from http://oretano.iele-ab.uclm.es/~BioChem-mg/software.php. Besides the optimized equations, the software can provide non-optimized equations, so that the user can compare the advantage of using optimized equations rather than the non-optimized ones, whenever they do not coincide. Moreover, the software circumvents the limitations of other existing previous software tools implemented with what are nowadays obsolete programming languages and that, moreover, are limited to non-optimized kinetic equations. 相似文献
72.
Francisco Garcia-Sevilla Manuela Garcia-Moreno Maria D. Masia Ricardo Gomez-Ladron de Guevara Maria M. Garcia-Molina Enrique Arribas Milagros Molina-Alarcon Maria L. Amo Ramon Varon 《Journal of mathematical chemistry》2014,52(7):1647-1674
In this paper we extend to enzyme systems the results previously obtained in paper I of this series for linear compartmental systems. We obtain the time course equations for both the enzyme and ligand species involved in the reaction mechanisms, which fit a general enzyme system model when the connections between the different enzyme species are of first or pseudofirst order. The kinetic equations obtained here for a given species, enzyme or ligand have the advantage over all previous equations described in the literature, in that they are in the most simplified form possible, since they only contain the kinetic parameters and initial concentrations of the enzymatic reaction which really have some influence on the time progress curves of the species under study. These kinetic equations are denominated optimized equation to distinguish them from the others, which shall call non-optimized equations. We discuss those cases when both types of equation coincide and we show how, when they do not coincide, the non-optimized equations can be simplified to the optimized ones. Therefore, we show that the optimized equations could be used in all cases to avoid the need of subsequent simplifications to eliminate the parameters that play no role in the corresponding time equations. To illustrate the use of this procedure we will apply it to two simple examples of enzymatic reactions. 相似文献
73.
Jasna Huremović Milena Horvat Jože Kotnik David Kocman Suzana Žižek Sergio Ribeiro Guevara 《Analytical letters》2017,50(6):1049-1064
Tuzla is among the most polluted cities of Bosnia and Herzegovina. The main source of pollution in the area is soil heavily contaminated by mercury released from a former chloralkali plant. This paper is focused on the characterization of mercury contaminated soil and air surrounding the chloralkali plant. In soil, the mobility and transformation of mercury were investigated by sequential extraction, while the methylation and reduction potentials were determined by the use of a radioactive tracer. Mercury emission from soil was determined by laboratory and by flux chamber measurements in the field. In addition, mercury concentrations in air were estimated by the analysis of air and the transplanted lichen Hypogymnia physodes. Mercury in soils in the vicinity of the chloralkali plant exceeded the background value by a factor of more than 3000. The fractionation of mercury in surface soil by sequential extraction showed that the mercury in soil was primarily bound to organic matter and a fraction containing elemental mercury and mercury (I) chloride is also significant. The obtained methylation and reduction potentials are low. The mercury flux from soil was estimated by two approaches. Fluxes of up to 8000?ng/m2/day were measured at the most polluted site; evaporation from soil was shown to be the primary source of elevated mercury in air. Air concentration mapping also revealed other sources of mercury; the most likely is the 715 MW coal power plant in the vicinity of former chloralkali facility. 相似文献
74.
Grid‐based algorithm to search critical points,in the electron density,accelerated by graphics processing units 下载免费PDF全文
Raymundo Hernández‐Esparza Sol‐Milena Mejía‐Chica Andy D. Zapata‐Escobar Alfredo Guevara‐García Apolinar Martínez‐Melchor Julio‐M. Hernández‐Pérez Rubicelia Vargas Jorge Garza 《Journal of computational chemistry》2014,35(31):2272-2278
Using a grid‐based method to search the critical points in electron density, we show how to accelerate such a method with graphics processing units (GPUs). When the GPU implementation is contrasted with that used on central processing units (CPUs), we found a large difference between the time elapsed by both implementations: the smallest time is observed when GPUs are used. We tested two GPUs, one related with video games and other used for high‐performance computing (HPC). By the side of the CPUs, two processors were tested, one used in common personal computers and other used for HPC, both of last generation. Although our parallel algorithm scales quite well on CPUs, the same implementation on GPUs runs around 10× faster than 16 CPUs, with any of the tested GPUs and CPUs. We have found what one GPU dedicated for video games can be used without any problem for our application, delivering a remarkable performance, in fact; this GPU competes against one HPC GPU, in particular when single‐precision is used. © 2014 Wiley Periodicals, Inc. 相似文献
75.
Cerruela García G Luque Ruiz I Gómez-Nieto MA Cabrero Doncel JA Guevara Plaza A 《Journal of chemical information and modeling》2005,45(2):231-238
In this paper we present an algorithm for the generation of molecular graphs with a given value of the Wiener index. The high number of graphs for a given value of the Wiener index is reduced thanks to the application of a set of heuristics taking into account the structural characteristics of the molecules. The selection of parameters as the interval of values for the Wiener index, the diversity and occurrence of atoms and bonds, the size and number of cycles, and the presence of structural patterns guide the processing of the heuristics generating molecular graphs with a considerable saving in computational cost. The modularity in the design of the algorithm allows it to be used as a pattern for the development of other algorithms based on different topological invariants, which allow for its use in areas of interest, say as involving combinatorial databases and screening in chemical databases. 相似文献
76.
Ribeiro Guevara S Zizek S Repinc U Pérez Catán S Jaćimović R Horvat M 《Analytical and bioanalytical chemistry》2007,387(6):2185-2197
Mercury tracers are powerful tools that can be used to study mercury transformations in environmental systems, particularly
mercury methylation, demethylation and reduction in sediments and water. However, mercury transformation studies using tracers
can be subject to error, especially when used to assess methylation potential. The organic mercury extracted can be as low
as 0.01% of the endogenous labeled mercury, and artefacts and contamination present during methylmercury (MeHg) extraction
processes can cause interference. Solvent extraction methods based on the use of either KBr/H2SO4 or HCl were evaluated in freshwater sediments using 197Hg radiotracer. Values obtained for the 197Hg tracer in the organic phase were up to 25-fold higher when HCl was used, which is due to the coextraction of 197Hg2+ into the organic phase during MeHg extraction. Evaluations of the production of MeHg gave similar results with both MeHg
extraction procedures, but due to the higher Hg2+ contamination of the controls, the uncertainty in the determination was higher when HCl was used. The Hg2+ contamination of controls in the HCl extraction method showed a nonlinear correlation with the humic acid content of sediment
pore water. Therefore, use of the KBr/H2SO4 method is recommended, since it is free from these interferences. 197Hg radiotracer (T
1/2 = 2.673 d) has a production rate that is about 50 times higher than that of 203Hg (T
1/2 = 46.595 d), the most frequently used mercury radiotracer. Hence it is possible to obtain a similar level of performance
to 203Hg when it is used it in short-term experiments and produced by the irradiation of 196Hg with thermal neutrons, using mercury targets with the natural isotopic composition. However, if the 0.15% natural abundance
of the 196Hg isotope is increased, the specific activity of the 197Hg tracer can be significantly improved. In the present work, 197Hg tracer was produced from mercury 51.58% enriched in the 196Hg isotope, and a 340-fold increase in specific activity with respect to natural mercury targets was obtained. When this high
specific activity tracer is employed, mercury methylation and reduction experiments with minimum mercury additions are feasible.
Tracer recovery in methylation experiments (associated with Me197Hg production from 197Hg2+ spike, but also with Hg2+ contamination and Me197Hg artefacts) with marine sediments was about 0.005% g−1 WS (WS: wet sediment) after 20 h incubation with mercury additions of 0.05 ng g−1 WS, which is far below natural mercury levels. In this case, the amount of Hg2+ reduced to Hg0 (expressed as the percent 197Hg0 recovered with respect to the 197Hg2+ added) varied from 0.13 to 1.6% g−1 WS. Me197Hg production from 197Hg2+ spike after 20 h of incubation of freshwater sediment ranged from 0.02 to 0.13% g−1 WS with mercury additions of 2.5 ng g−1 WS, which is also far below natural levels. 197Hg0 recoveries were low, 0.0058 ± 0.0013% g−1 WS, but showed good reproducibility in five replicates. Me197Hg production from 197Hg2+ spiked in freshwater samples ranged from 0.1 to 0.3% over a period of three days with mercury additions of 10 ng L−1. A detection limit of 0.05% for Me197Hg production from 197Hg2+ spike was obtained in seawater in a 25 h incubation experiment with mercury additions of 12 ng L−1. 相似文献
77.
M.E. Saleta H.E. Troiani S. Ribeiro Guevara R.D. Snchez M. Malta R.M. Torresi 《Journal of magnetism and magnetic materials》2008,320(14):e268-e271
In this work, we present the synthesis and characterization of a hybrid nanocomposite constituted by iron oxide nanoparticles and vanadium oxide/Hexadecylamine (VOx/Hexa) nanotubes. Transmission Electron Microscopy (TEM) images show small particles (around 20 nm) in contact with the external wall of the multiwall tubes, which consist of alternate layers of VOx and Hexa. By Energy Dispersive Spectroscopy (EDS), we detected iron ions within the tube walls and we have also established that the nanoparticles are composed of segregated iron oxide. The samples were studied by Electron Paramagnetic Resonances (EPR) and dc-magnetization as a function of the magnetic field. The analysis of the magnetization and EPR data confirms that a fraction of the V atoms are in the V4+ electronic state and that the nanoparticles exhibit a superparamagnetic behavior. The percentage of V and Fe present in the nanocomposite was determined using Instrumental Neutron Activation Analysis (INAA). 相似文献
78.
M. A. Arribére S. Ribeiro Guevara A. J. Kestelman I. M. Cohen 《Journal of Radioanalytical and Nuclear Chemistry》1999,241(1):25-31
The feasibility of validating data obtained in the determination of chlorine, potassium, and calcium by neutron capture activation
analysis, through their determination using threshold reactions has been studied. To this purpose the authors experimentally
determined the following fission neutron spectrum averaged cross sections (in mb):37Cl(n,p)37S, 0.234±0.015;41K(n,α)38Cl, 0.740±0.044;42Ca(n,p)42K, 3.09±0.22;43Ca(n,p)43K, 2.27±0.12;44Ca(n,p)44K, 0.074±0.013. The application of these values to the analysis of some reference materials are presented. Also, the problem
of mutual interferences has been addressed for the following pairs:36S(n,Γ)37S and37Cl(n,p)37S;37Cl(n,Γ)38Cl and41K(n,α)38Cl;41K(n,ψ)42K and42Ca(n,p)42K. 相似文献
79.
Augusto Rivera James Guevara‐Pulido John Sadat‐Bernal Jaime Ríos‐Motta Guillermo Zaragoza 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(9):o435-o437
The title compound, 1,5:3,7‐dimethano‐1,3,5,7‐benzotetrazonine–hydroquinone (2/1), 2C11H14N4·C6H6O2, crystallizes with the hydroquinone molecule located on a center of inversion. In contrast to other hydroquinone–adamanzane adducts, which form extended hydrogen‐bonded networks, in the present case, one hydroquinone molecule is linked to two 1,5:3,7‐dimethano‐1,3,5,7‐benzotetrazonine molecules, forming a 2:1 cluster through O—H...N hydrogen bonds. 相似文献
80.
R. Daga S. Ribeiro Guevara M. L. Sánchez M. Arribére 《Journal of Radioanalytical and Nuclear Chemistry》2006,270(3):677-694
Summary Volcanic ashes erupted by recent magmatic events were collected from one sedimentary sequence of lake Nahuel Huapi (Patagonia,
Argentina) and then analyzed by Instrumental Neutron Activation Analysis. Primary volcanic components, including white and
brownish pumice fragments, scoriae and glass shards, as well as bulk sediments from four tephra layers identified in the sedimentary
sequence, were characterized by their major and trace element contents. The two tephra layers being in the upper section of
the sequence can be linked to the eruptions of Cordon Caulle fissure (Puyehue-Cordon Caulle region) occurred in 1921-1922
and 1960, according to core dating. The third tephra layer, which is clearly associated to an event occurred in the 1890-1900
decade, has different compositional patterns showing a different source from those upper tephras. Whereas, the fourth, which
could be associated to an event occurred at the end of the 18 th century, shows the same composition patterns as those registered
for the Cordon Caulle fissure. 相似文献