排序方式: 共有38条查询结果,搜索用时 421 毫秒
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D. Zorrilla Cuenca J. Sánchez Márquez M. Fernández Núñez R. Rodríguez Huertas 《International journal of quantum chemistry》2007,107(4):879-893
This project consists of two parts. In the first part, a series of test calculations is performed to verify that the integrals involved in the determination of atomic and molecular properties by standard self‐consistent field (SCF) methods can be obtained through Halton, Korobov, or Hammersley quasi‐random integration procedures. Through these calculations, we confirm that all three methods lead to results that meet the levels of precision required for their use in the calculation of properties of small atoms or molecules at least at a Hartree–Fock level. Moreover, we have ensured that the efficiency of quasi‐random integration methods that we have tested is Halton=Korobov>Hammersley?pseudo‐random. We also find that these results are comparable to those yielded by ordinary Monte Carlo (pseudo‐random) integration, with a calculation effort of two orders of smaller magnitude. The second part, which would not have been possible without the integration method previously analyzed, contains a first study of atoms constrained in spherical boxes through SCF calculations with basis functions adapted to the features of the problem: Slater‐type orbitals (STOs) trimmed by multiplying them by a function that yields 1 for 0 < r < (R‐δ), polynomial values for (R‐δ) < r < R and null for r > R, R being the radius of the box and δ a variationally determined interval. As a result, we obtain a equation of state for electrons of small systems, valid just in the limit of low temperatures, but fairly simple. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
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Numerical Algorithms - In this contribution, we consider the sequence $\{Q_{n}^{\lambda }\}_{n\geq 0}$ of monic polynomials orthogonal with respect to the following inner product involving... 相似文献
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Maderna A Huertas R Hawthorne MF Luguya R Vicente MG 《Chemical communications (Cambridge, England)》2002,(16):1784-1785
A boron-rich, water-soluble porphyrin conjugate was synthesized by coupling of two carboranyl alcohols with 2-chlorophenoxyphosphorus dichloride, followed by conjugation to an amine-functionalized tetraphenyl-porphyrin via an amide linkage. 相似文献
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Ludivine Ferey Nathalie Delaunay Douglas N. Rutledge Alain Huertas Yann Raoul Pierre Gareil Jérôme Vial Isabelle Rivals 《Analytica chimica acta》2014
Because of their high toxicity, international regulatory institutions recommend monitoring specific polycyclic aromatic hydrocarbons (PAHs) in environmental and food samples. A fast, selective and sensitive method is therefore required for their quantitation in such complex samples. This article deals with the optimization, based on an experimental design strategy, of a cyclodextrin (CD) modified capillary zone electrophoresis separation method for the simultaneous separation of 19 PAHs listed as priority pollutants. First, using a central composite design, the normalized peak-start and peak-end times were modelled as functions of the factors that most affect PAH electrophoretic behavior: the concentrations of the anionic sulfobutylether-β-CD and neutral methyl-β-CD, and the percentage of MeOH in the background electrolyte. Then, to circumvent computational difficulties resulting from the changes in migration order likely to occur while varying experimental conditions, an original approach based on the systematic evaluation of the time intervals between all the possible pairs of peaks was used. Finally, a desirability analysis based on the smallest time interval between two consecutive peaks and on the overall analysis time, allowed us to achieve, for the first time in CE, full resolution of all 19 PAHs in less than 18 min. Using this optimized capillary electrophoresis method, a vegetable oil was successfully analyzed, proving its suitability for real complex sample analysis. 相似文献
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Hybrid catalysts containing CuO-ZnO or CuO-ZnO-Al2O3 as the metallic component and the zeolite H-ferrierite as support were prepared by both the coprecipitation-impregnation and coprecipitation-sedimentation methods. They were characterized by XRD, BET, and TEM. Aluminum was added to the metallic component, and the effects on the hybrid catalyst properties were studied. The metallic component blocked the zeolite micropore volume, and spaces were created between agglomerate particles of the first component, increasing mesopore volume. Aluminum introduction at a Cu/Zn/Al ratio of 55/30/15 favored the formation of hydrotalcite as a precursor to CuO/ZnO/Al2O3. In this case, small, highly dispersed particles of these oxides were obtained. In the coprecipitation-impregnation method, greater contact between the H-ferrierite zeolite and the metallic component was observed. 相似文献
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Farrera JA Canal I Hidalgo-Fernández P Pérez-García ML Huertas O Luque FJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(7):2277-2285
The tautomeric equilibria of 2-(4'-hydroxyphenylazo)benzoic acid (HABA) and 2-(3',5'-dimethyl-4'-hydroxyphenylazo)benzoic acid (3',5'-dimethyl-HABA) have been studied by a combination of spectroscopic and computational methods. For neutral HABA in solvents of different polarity (toluene, chloroform, DMSO, DMF, butanol, and ethanol) the azo tautomer (AT) is largely predominant. For monoanionic HABA, the hydrazone tautomer (HT) is the only detected species in apolar solvents such as toluene and chloroform, while the AT is the only detected species in water and a mixture of both tautomers is detected in ethanol. Comparison of the results obtained for HABA and its 3',5'-dimethylated derivative shows that dimethylation of the hydroxybenzene ring shifts the tautomeric preferences towards the hydrazone species. These findings have been used to examine the differences in binding affinity to streptavidin, as the lower affinity of HABA can be explained in terms of the larger energetic cost associated with the tautomeric shift to the bioactive hydrazone species. Overall, these results suggest that a balanced choice of chemical substituents, embedding environment, and pH can be valuable for exploitation of the azo-hydrazone tautomerism of HABA biomimetics in biotechnological applications. 相似文献
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A fast radical chain mechanism in the polyfluoroalkoxylation of aromatics through NO2 group displacement. Mechanistic and theoretical studies 总被引:1,自引:0,他引:1
Tejero I Huertas I González-Lafont A Lluch JM Marquet J 《The Journal of organic chemistry》2005,70(5):1718-1727
Introduction of polyfluoroalkoxy and polyfluoroalkylthio substituents in aromatic rings can be achieved with mild conditions and short times thorough reaction of concentrated solutions of dinitrobenzenes in DMF with polyfluoro alcohols and polyfluoro thiols in moderate excess, in the presence of excess tetrabutylammonium fluoride as a base. Mechanistic studies suggest that under these conditions a fast radical chain mechanism operates. This mechanism is elicited by oxidation of a Meisenheimer complex and proceeds through a radical aromatic substitution with the polyfluoroalkoxy or the polyfluoroalkylthio radicals as key intermediates. At low concentrations, entrainment can be achieved with superoxide anion. A rationale for this effect is discussed. Answers to particular questions about the proposed mechanism are achieved through a theoretical study at the B3LYP/6-31+G(d,p) level. Specifically, the competition between the radical mechanism and the corresponding polar one (classical S(N)Ar reaction) is studied in that way, with the conclusion that the key steps of the radical mechanism in our reaction conditions (polar aprotic solvent) are at least as efficient as the ones of the polar one, thus justifying the observed kinetic advantage for the chain reaction in the conditions where an efficient initiation occurs. 相似文献