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31.
Riadh Sahnoun Yuichi Fujimura Kuninobu Kabuto Yoshio Takeuchi Ryoji Noyori 《Journal of Physical Organic Chemistry》2009,22(10):903-912
In connection with study of chiral derivatizing agents (CDAs) for NMR determination of absolute configuration of organic compounds, factors controlling the conformational preference between syn‐ and anti‐forms in α‐substituted α‐fluorophenylacetic acid methyl ester (FC(X)(Ph)COOMe) model systems were theoretically investigated. Substituents X at the stereogenic carbon atom were X = H, C?CH and CH3, the electronic and steric properties of which were significantly different from each other. The model system with X = C?CH and that with X = CH3 were found to be possible candidates for fluorine‐containing CDAs. The syn conformation is stable compared with the anti one by 0.7 kcal mol?1 for the ester with X = C?CH. On the other hand, the anti conformation is stable compared with the syn one by 0.5 kcal mol?1 for the ester with X = CH3. Both natural bond orbital (NBO) analysis and deletion of selected orbitals based on the donor–acceptor NBO scheme were adopted for semi‐quantitative estimation of factors responsible for the conformational preference as well as a qualitative inspection of occupied canonical molecular orbitals (MOs). It was shown that [σ–(σ* + π*)(C?O)] and [σ–σ*(Ph) and π(Ph)–σ*] hyperconjugations are the main factors controlling the conformational preferences between the syn and anti conformations. Other types of effects such as electrostatic effects were also investigated. The role of the fluorine atom was also clarified. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
32.
Riadh Marzouki Abderrahmen Guesmi Ahmed Driss 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(10):i95-i98
The title compound, tetrasodium cobalt aluminium hexaarsenate, Na4Co7−xAl2/3x(AsO4)6 (x = 1.37), is isostructural with K4Ni7(AsO4)6; however, in its crystal structure, some of the Co2+ ions are substituted by Al3+ in a fully occupied octahedral site (site symmetry 2/m) and a partially occupied tetrahedral site (site symmetry 2). A third octahedral site is fully occupied by Co2+ ions only. One of the two independent tetrahedral As atoms and two of its attached O atoms reside on a mirror plane, as do two of the three independent Na+ cations, all of which are present at half‐occupancy. The proposed structural model based on a careful investigation of the crystal data is supported by charge‐distribution (CHARDI) analysis and bond‐valence‐sum (BVS) calculations. The correlation between the X‐ray refinement and the validation results is discussed. 相似文献
33.
Mohamed Nazih Rhimi Riadh El-Bahi 《International Journal of Theoretical Physics》2008,47(4):1095-1111
The Landau problem of a charged particle in a plane with a uniform perpendicular magnetic field is analysed in two oscillator
modes. The coherent states for the problem have been found out using a general definition of displaced states. The time evolution
and the associated nonadiabatic geometric phase for both initially displaced and non-displaced wave packets have been studied.
The path integral is derived in a simple way through the calculation of Gaussian integrals via the concept of coherent state
wavefunctions. 相似文献
34.
Michihisa Koyama Riadh Sahnoun Nozomu Hatakeyama Hiromitsu Takaba Carlos A. Del Carpio 《Applied Surface Science》2008,254(23):7774-7776
Efficient development of highly functional porous materials, used as catalysts in the automobile industry, demands a meticulous knowledge of the nano-scale interface at the electronic and atomistic scale. However, it is often difficult to correlate the microscopic interfacial interactions with macroscopic characteristics of the materials; for instance, the interaction between a precious metal and its support oxide with long-term sintering properties of the catalyst. Multi-scale computational chemistry approaches can contribute to bridge the gap between micro- and macroscopic characteristics of these materials; however this type of multi-scale simulations has been difficult to apply especially to porous materials. To overcome this problem, we have developed a novel mesoscopic approach based on a porous structure simulator. This simulator can construct automatically irregular porous structures on a computer, enabling simulations with complex meso-scale structures. Moreover, in this work we have developed a new method to simulate long-term sintering properties of metal particles on porous catalysts. Finally, we have applied the method to the simulation of sintering properties of Pt on alumina support. This newly developed method has enabled us to propose a multi-scale simulation approach for porous catalysts. 相似文献
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36.
The present paper investigates Gaussian bilateral inequalities in view of solving related probability maximization problems. Since the function f representing the probability of satisfaction of a given Gaussian bilateral inequality is not concave everywhere, we first state and prove a necessary and sufficient condition for negative semi-definiteness of the Hessian. Then, the (nonconvex) problem of globally maximizing f over a given polyhedron in \(\mathbb {R}^{n}\) is adressed, and shown to be polynomial-time solvable, thus yielding a new-comer to the (short) list of nonconvex global optimization problems which can be solved exactly in polynomial time. Application to computing upper bounds to the maximum joint probability of satisfaction of a set of m independent Gaussian bilateral inequalities is discussed and computational results are reported. 相似文献
37.
Sahnoun R Fujimura Y Kabuto K Takeuchi Y Noyori R 《The Journal of organic chemistry》2007,72(21):7923-7929
The origin of conformational preference in alpha-cyano-alpha-fluorophenylacetic acid (CFPA) methyl ester that is a model system of alpha-cyano-alpha-fluoro-p-tolylacetic acid (CFTA) esters was theoretically investigated by means of DFT and MP2 calculations. Two stable conformations having the C-F bond syn and anti to the C=O bond, respectively, were obtained for CFPA methyl ester. A small energy difference (0.9 kcal mol-1 at the MP2(fc)/6-31++G(d,p)) was found between the two conformations. From the molecular orbital analysis based on the Natural Bond Orbital analysis and supported by calculations using the Orbital Deletion Procedure technique, we found that sigma-(sigma*+pi*)(C=O) and sigma-sigma*(Ph) and pi(Ph)-sigma* hyperconjugations are the main factors responsible for the conformational preference. The role of the fluorine atom on the stereogenic center was also clarified. 相似文献
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Mariem Saada Hanen Wasli Ins Jallali Rim Kboubi Karl Girard-Lalancette Vakhtang Mshvildadze Riadh Ksouri Jean Legault Susana M. Cardoso 《Molecules (Basel, Switzerland)》2021,26(19)
The fractionation of the methanolic extract (MeOH-E) of Retama raetam (Forssk.) Webb & Berthel and further analysis by thin layer chromatography resulted in four fractions (F1, F2, F3 and F4) that, in parallel with the MeOH-E, were screened for antioxidant, cytotoxic, antidiabetic and antibacterial properties. In addition, chemical characterization of their bioactive molecules was performed using LC-DAD-ESI/MSn. The results indicated that F3 was the most promising regarding antioxidant and cytotoxicity abilities, possibly due to its richness in flavonoids class, particularly isoflavones. In turn, F1 was characterized by the presence of the most polar compounds from MeOH-E (organic acids and piscidic acid) and showed promising abilities to inhibit α-amylase, while F4, which contained prenylated flavonoids and furanoflavonoids, was the most active against the tested bacteria. The gathered results emphasize the distinct biological potentials of purified fractions of Retama raetam. 相似文献
40.
Amel Ben Abda Riadh Ben Fatma Damien Tromeur-Dervout 《Comptes Rendus Mathematique》2010,348(1-2):93-97
This Note is concerned with the severely ill-posed Cauchy–Helmholtz problem. This Cauchy problem being rephrased through an “interfacial” equation, we resort to an Aitken–Schwarz method for solving this equation. Numerical trials highlight the efficiency of the present method. 相似文献