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941.
Mhadgut SC Palaniappan K Thimmaiah M Hackney SA Török B Liu J 《Chemical communications (Cambridge, England)》2005,(25):3207-3209
beta-cyclodextrin immobilized on Pd nanoparticles was successfully employed as an efficient phase-transfer catalyst in aqueous biphasic hydrogenation reactions. 相似文献
942.
High-speed counter-current chromatography (HSCCC) technique in semi-preparative scale has been successfully applied to the separation of bioactive flavonoid compounds, liquiritigenin and isoliquiritigenin in one step from the crude extract of Glycyrrhiza uralensis Risch. The HSCCC was performed using a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-acetonitrile-water (2:2:1:0.6:2, v/v). Yields of liquiritigenin (98.9% purity) and isoliquiritigenin (98.3% purity) obtained were 0.52% and 0.32%. Chemical structures of the purified liquiritigenin and isoliquiritigenin were identified by electrospray ionization-MS (ESI-MS) and NMR analysis. 相似文献
943.
Bromoiodomethane photodissociation in the low-lying excited states has been characterized using unrestricted Hartree-Fock, configuration-interaction-singles, and complete active space self-consistent field calculations with the SDB-aug-cc-pVTZ, aug-cc-pVTZ, and 3-21g** basis sets. According to the results of the vertical excited energies and oscillator strengths of these low-lying excited states, bond selectivity is predicted. Subsequently, the minimum energy paths of the first excited singlet state and the third excited state for the dissociation reactions were calculated using the complete active space self-consistent field method with 3-21g** basis set. Good agreement is found between the calculations and experimental data. The relationships of excitations, the electronic structures at Franck-Condon points, and bond selectivity are discussed. 相似文献
944.
945.
The cyclocondensation of 3-amino-2-iminonaphtho[1,2-d]thiazole ( 1 ) with a series of α-keto mono- and dicarboxylic acid derivatives 5a-i under different conditions was investigated. When the experiments were performed by refluxing in glacial acetic acid, the corresponding cyclized products, 2-substituted 3-oxo-3H-naphtho[1′,2′:4,5]thiazolo[3,2-b][1,2,4]triazines 4 were obtained in fair to good yields. On the other hand, when the reaction was conducted in boiling ethanol, it gave only the open chain condensates 6 , or in rare cases, together with minor amount of 4 . Since the intermediates 6 exist as mixture of both E- and Z-isomers, cyclization through heating was found insufficient. In any event representative compounds 4b,g,i have been evaluated for anti-HIV activity, but none of them were active. 相似文献
946.
Two natural products databases, the marine natural products database (MNPD) and the traditional Chinese medicines database (TCMD), were used to find novel structures of potent SARS-CoV protease inhibitors through virtual screening. Before the procedure, the databases were filtered by Lipinski's ROF and Xu's extension rules. The results were analyzed by statistic methods to eliminate the bias in target-based database screening toward higher molecular weight compounds for enhancing the hit rate. Eighteen lead compounds were recommended by the screening procedure. They were useful for experimental scientists in prioritizing drug candidates and studying the interaction mechanism. The binding mechanism was also analyzed between the best screening compound and the SARS protein. 相似文献
947.
Chen CH Liu KY Sudhakar S Lim TS Fann W Hsu CP Luh TY 《The journal of physical chemistry. B》2005,109(38):17887-17891
Thin films of silica hybrid materials consisting of two to three covalently bound organic chromophores at different ratios were conveniently synthesized and fabricated. The photophysical properties of these materials have been studied. The fluorescence spectra reveal complete fluorescence resonance energy transfer (FRET) from donor to acceptor, and the light-harvesting ability of these hybrid materials increases with increasing the molar fraction of donor chromophore. In a three-chromophore system, the energy is transferred from 300 to 530 nm successfully. Time-resolved fluorescence experiments are employed to elucidate the average rates and efficiencies (84-97%) of energy transfer in these organic/inorganic hybrid systems. The hybrid materials have been shown to provide antenna effect to facilitate energy transfer and light harvesting. 相似文献
948.
Aza-Morita-Baylis-Hillman reactions of N-(benzylidene)polyfluoroanilines 1 with methyl acrylate or acrylonitrile were studied. It was found that Lewis base, solvent and reaction temperature can significantly affect the reaction. Using 3-hydroxyquinuclidine (3-HQD) as a Lewis base in the reactions of 1 with methyl acrylate in DMF, the normal aza-Morita-Baylis-Hillman adducts 3 were formed in moderate to excellent yields. For the reactions of 1 with acrylonitrile, 1,4-diazabicyclo[2.2.2]octane (DABCO) is the best Lewis base giving the corresponding aza-Morita-Baylis-Hillman adducts 4 as the sole product in good to moderate yield. However, upon treatment of 1 with acrolein 2c, the corresponding reaction did not occur even in the presence of a variety of catalysts. 相似文献
949.
James V. Beitz C.W. Williams K.-S. Hong G.K. Liu 《Journal of solid state chemistry》2005,178(2):511-520
We have assessed the feasibility of carrying out time- and wavelength-resolved laser-induced fluorescence measurements of radiation damage in glassy silica. The consequences of alpha decay of Es-253 in LaPO4 nanophases embedded in silica were probed based on excitation of 5f states of Cm3+, Bk3+, and Es3+ ions. The recorded emission spectra and luminescence decays showed that alpha decay of Es-253 ejected Bk-249 decay daughter ions into the surrounding silica and created radiation damage within the LaPO4 nanophases. This conclusion is consistent with predictions of an ion transport code commonly used to model ion implantation. Luminescence from the 6D7/2 state of Cm3+was used as an internal standard. Ion-ion energy transfer dominated the dynamics of the observed emitting 5f states and strongly influenced the intensity of observed spectra. In appropriate sample materials, laser-induced fluorescence provides a powerful method for fundamental investigation of alpha-induced radiation damage in silica. 相似文献
950.
Liu Q Fang D Zheng J 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(7):1453-1457
Infrared spectroscopy studies of methyl 4-hydroxybenzoate (MHB) in 17 different organic solvents and in ethanol/CCl4 binary solvent were undertaken to investigate the solvent-solute interactions. The frequencies of carbonyl stretching vibration nu(C=O) of MHB in single solvents were correlated with the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The assignments of the two bands of nu(C=O) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of nu(C=O) of MHB in ethanol/CCl4 binary solvents showed that several kinds of solute-solvent hydrogen bonding interactions coexisted in the mixture solvents, with a change in the mole fraction of ethanol in the binary solvents. 相似文献