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991.
Hebbe-Viton V Desvergnes V Jodry JJ Dietrich-Buchecker C Sauvage JP Lacour J 《Dalton transactions (Cambridge, England : 2003)》2006,(17):2058-2065
Association of enantiopure TRISPHAT anion (1) with chiral spiro [Cu(LL')2] complexes (LL' = 2-R-phen, 2, 6-R-bpy, 3, and 2-iminopyridine, 4) leads to an efficient NMR enantiodifferentiation. Variable temperature 1H NMR spectroscopy has been used to determine the isomerisation kinetics of these pseudo-tetrahedral complexes and to evaluate their configurational stability; the latter depending on the structure of the diimine ligands. In the case of the 2-anthracenyl-phen derivative, a decent level of supramolecular stereocontrol was noted (d.e. up to 45%); the configuration of the complex being determined by electronic circular dichroism (ECD). 相似文献
992.
Péres VF Saffi J Melecchi MI Abad FC Martinez MM Oliveira EC Jacques RA Caramão EB 《Journal of chromatography. A》2006,1105(1-2):148-153
Piperaceae family is original from tropical regions and it shows more than 700 species around the world. Piper gaudichaudianum Kunth is the specie more abundant in Brazil, occurring from Northeast to South Brazil. In this paper, it was investigated the influence of some experimental parameters on the pressurized liquid extraction (PLE) of P. gaudichaudianum Kunth leaves, using petroleum ether as extractor solvent. The optimization of the main variables involved in the PLE process (extraction temperature and time) has been done by response surface methodology (RSM) using, as responses, the extraction yield and the chromatographic profile (GC/MS) of the extracts. The optimized procedure employed 3 g of ground leaves, 10 min of extraction and one cycle of extraction at 85 degrees C. The major compounds present in the petroleum ether extracts were: palmitic acid, stearic acid and nerolidol. The results presented in this work show the possibility of using a fast and easy process to recover compounds from P. gaudichaudianum Kunth. 相似文献
993.
K. A. Shaykhutdinov S. I. Popkov A. N. Lavrov L. P. Kozeeva M. Yu. Kameneva V. V. Val’kov D. M. Dzebisashvili A. D. Fedoseev 《JETP Letters》2010,92(5):332-337
The behavior of the low-temperature specific heat C(T) for YBa2Cu3O6 + x
single crystals with the doping level corresponding to the normal phase has been studied by the relaxation technique at different
values of the applied magnetic field. It has been found that the C(T)/T plot exhibits such an anomaly as a steep increase with decreasing temperature from T about 4 K down to T ≤ 2 K (the minimum temperature value accessible in the experiment). The applied magnetic field as high as 9 T inverts this
anomaly and leads to a sharp drop in C(T)/T during cooling within the same temperature range. A model involving the Schottky-type centers formulated in this work and
the data on spin correlation functions has allowed us to calculate the temperature dependence of the specific heat, which
fits the experimental curves quite well. 相似文献
994.
Valéria M. Rosa Patricio S. Letelier 《International Journal of Theoretical Physics》2010,49(2):316-323
The existence and stability under linear perturbation of closed timelike curves in the spacetime associated to Schwarzschild
black hole pierced by a spinning string are studied. Due to the superposition of the black hole, we find that the spinning
string spacetime is deformed in such a way to allow the existence of closed timelike geodesics. 相似文献
995.
It has been shown in the limit of the low density of band carriers that the inclusion of the strong intersite interaction between electrons within the framework of the periodic Anderson model results in two qualitatively new features in its energy structure. The first feature is associated with the appearance of an additional quasi-localized level, which significantly changes the structure of the electronic density of states. The second feature is the strong renormalization of the effective constant of hybridization with the bare localized level. 相似文献
996.
Jana Sopkov‐de Oliveira Santos Valrie Collot Isabelle Bureau Sylvain Rault 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(8):1035-1036
The crystal structure of 1‐benzyl‐3‐(5‐hydroxymethyl‐2‐furyl)indazole, C19H16N2O2, showed that the furan O and indazole N atoms lie on the same face of the molecule. The crystal packing consists of intermolecular hydrogen bonding, and indazole–indazole and indazole–phenyl interactions. 相似文献
997.
Amino and/or polyethyleneglycol (PEG) functionalized core-shell γFe2O3-SiO2 magnetic nanoparticles were synthesized and characterized. Amino-PEG-functionalized core-shell nanoparticles have calibrated sizes and a good colloidal stability. These bi-functionalized core-shell nanoparticles are potentially useful as biocompatible particles for magnetically targeted chemotherapy. 相似文献
998.
A. Yu. Val’kov V. P. Romanov M. V. Romanov 《Journal of Experimental and Theoretical Physics》2001,93(2):344-362
Spatial correlation functions of orientation fluctuations in bounded cells of smectic and nematic liquid crystals are calculated taking into account the effect of external fields and finiteness of the energy of anchoring to the surface. The cases of positive and negative anisotropies of magnetic susceptibility or permittivity are considered. The calculations are based on the division of degrees of freedom into bulk and surface ones and on the reduction of the computation of the continual integral determining the correlation function to the solution of the Euler equation with corresponding boundary conditions of the first or third kind. The obtained correlation functions are used for describing the intensity of light scattered in nematics for the planar and homeotropic orientations. It is shown, in particular, that the measurements of the angular dependence of the scattered light intensity may serve as a reliable method for determining the energy of anchoring of a liquid crystal to a substrate for different values of the external field. 相似文献
999.
Marc Rolland Tarek Kassem Valérie Rolland Jean Martinez 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(12):1415-1417
We present the crystal and molecular structures of 2,3,6,7,8,8a-hexahydro-6,8-methano-7,7,8a-trimethyl-3-(1-methyl-2-oxopropylidene)-5H-1,4-benzoxazin-2-one, C16H21NO3, (III), and 2,3,6,7,8,8a-hexahydro-3-(2-hydroxy-1-methylpropyl)-6,8-methano-7,7,8a-trimethyl-5H-1,4-benzoxazin-2-one, C16H25NO3, (V). These compounds are two of the four key intermediates in our synthetic route to (2R,3R,4R)-4-hydroxyisoleucine. The two structures provide a full understanding of the stereochemistry in successive steps. This synthesis was based on a new optically pure chiral oxazinone auxiliary derived from (1R,2R,5R)-2-hydroxypinan-3-one. 相似文献
1000.
Abraham Chemtob Valrie Hroguez Yves Gnanou 《Journal of polymer science. Part A, Polymer chemistry》2004,42(5):1154-1163
Latex particles based on 1,4‐polybutadiene were synthesized via dispersion ring‐opening metathesis copolymerization of 1,5‐cyclooctadiene with a α‐norbornenyl poly(ethylene oxide) macromonomer. Stable but polydisperse colloidal dispersions in the 50 nm to 10 μm size range were obtained. In this work, particular attention was paid to the effects of the kinetics of copolymerization on the structure of the graft copolymers formed and on the onset of turbidity. Strategies to prepare monodisperse polybutadiene particles were also designed through the growth of a polybutadiene shell from a well‐defined polynorbornene seed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1154–1163, 2004 相似文献