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961.
不对称催化是由潜手性反应物合成光活性化合物的有效途径,α,β-不饱和氨基酸的氢化立体选择性已达90%以上,L-Dopa的工业化生产则标志着不对称催化氢化开始走向实际应用。高选择性的催化剂一般是一价铑的手性双膦配体络合物,其中DIOP[2,3-O-异丙叉- 相似文献
962.
An expectation value approach to calculations of first-order properties using the non-iterative, triple-excitation amplitudes
in the coupled cluster wave function is exploited. Three methods are suggested and analysed using the many body perturbation
theory (MBPT) expansion arguments. The first method, in which non-iterative triple-excitation amplitudes are used in the expression
for the expectation values, makes the wave function accurate through the second order of MBPT. In the second method, which
is an extension of the first, effects of triple-excitation amplitudes are coupled with single- and double-excitation amplitudes.
The correlated density matrix equivalent through the fourth order to that obtained when CCSDT-la amplitudes are used is employed
in the third method. The suggested methods are tested on dipole moment and polarizability calculations for several diatomic
closed-shell molecules and are compared to other related approaches.
Received: 15 May 1997 / Accepted: 5 June 1997 相似文献
963.
Wolfgang A. Herrmann Jo o D. G. Correia Georg R. J. Artus Richard W. Fischer Carlos C. Rom o 《Journal of organometallic chemistry》1996,520(1-2):139-142
Methyl(oxo)bis(η2-peroxo)rhenium(VII)1, the active species of the system CH3ReO3/H2O2 in the catalytic oxidation of different organic and organometallic compounds, is stabilized by a water molecule attached to the rhenium center. This water molecule can be removed and substituted by hexamethylphosphoramide (HMPA) to yield (hexamethylphosphoramide)methyl(oxo)bis(η2-peroxo rhenium(VII) (3). The synthesis, crystal structure (X-ray difraction study), and catalytic properties of which compound are reported. Crystal data are as follows: monoclinic, space group P21/n, A = 900.76(7) pm, B = 1229.80(11) pm, C = 1318.57(11) pm, β = 90.251(7)°, Rw = 0.034 for 1878 reflections. The catalytic properties of compound 3 in the oxidation of olefins with H2O2 are similar to those of 1. 相似文献
964.
The investigation of the electrochemical reduction and the adsorption of meso-tetra(4-trimethylammoniumphenyl)porphine (T(4-TMAP)P) at a mercury electrode in alkaline solution shows that the overall reduction involves three two-electron steps, of which the first step is reversible and the latter two are irreversible. In addition, T(4-TMAP)P and its metal complexes of Cu(II) and Mg(II) can be strongly adsorbed on the surface of a mercury electrode. The adsorption phenomena have been utilized as a preconcentration step for the determination of trace amounts of the two ions by single sweep polarography. For copper, the detection limit is 1 × 10–8 mol dm–3, for magnesium, 1 × 10–7 mol dm–3, the latter being limited by the reagent blank. The proposed method was applied to the determination of Cu and Mg in various types of samples (chemicals, hair and liver tissues) with satisfactory results. 相似文献
965.
Hisanobu Wakita Georg Johansson Magnus Sandström Peter L. Goggin Hitoshi Ohtaki 《Journal of solution chemistry》1991,20(7):643-668
Structures of the complexes formed in aqueous solutions between zinc(II) and iodide ions have been determined from large-angle X-ray scattering, Raman and far-IR measurements. The coordination in the hydrated Zn2+ hexaaqua ion and the first iodide complex, [ZnI]+, is octahedral, but is changed into tetrahedral in the higher complexes, [ZnI2(H2O)2], [ZnI3(H2O)]– and [ZnI4]2–. The Zn-I bond length is 2.635(4)Å in the [ZnI4]2– ion and slightly shorter, 2.592(6)Å, in the two lower tetrahedral complexes. In the octahedral [ZnI(H2O)5]+ complex the Zn-I bond length is 2.90(1)Å. The Zn-O bonding distances in the complexes are approximately the same as that in the hydrated Zn2+ ion, 2.10(1)Å. 相似文献
966.
Hong Zheng Wei Yu Hon-bin Zhang Chi-xing Zhou 《高分子科学》2006,(1):1-11
Finite element method is used to simulate the high-speed melt spinning process,based on the equation system proposed by Doufas et al.Calculation predicts a neck-like deformation,as well as the related profiles of velocity,diameter, temperature,chain orientation,and crystallinity in the fiber spinning process.Considering combined effects on the process such as flow-induced crystallization,viscoelasticity,filament cooling,air drag,inertia,surface tension and gravity,the simulated material flow behaviors are consistent with those observed for semi-crystalline polymers under various spinning conditions.The structure change of polymer coils in the necking region described by the evolution of conformation tensor is also investigated.Based on the relaxation mechanism of macromolecules in flow field different types of morphology change of polymer chains before and in the neck are proposed,giving a complete prospect of structure evolution and crystallization of semi-crystalline polymer in the high speed fiber spinning process. 相似文献
967.
Diaminocarboxylic acid carrier ampholytes, such as L-histidine, 2,3-diaminopropionic acid, L-ornithine, and L-lysine, were reacted with glycerol-1,3-diglycidyl ether (GDGE) and poly(vinyl alcohol) (PVA) in the presence of sodium hydroxide to produce hydrolytically and mechanically stable hydrogels, supported on a PVA substrate, for use as buffering membranes in isoelectric trapping (IET) separations. The pH values of the DACAPVA membranes were determined with the help of small-molecule pI markers and proteins and were found to be in the 6 < pH < 8.5 range. The membranes were successfully used to isoelectrically trap small ampholytes, desalt ampholyte solutions in IET mode, and effect the binary separation of chicken egg white proteins. 相似文献
968.
A chemically modified carbon paste electrode with 3,4-tetra pyridinoporphirazinatocobalt(II) (Co(3,4 tppa) was applied to the determination of free cyanide ion. The electrode has a linear range between 1.5 × 10−5 M and 1.0 × 10−2 M with a Nernstian slope of 60 ± 1.5 mV/decade and its detection limit is 9 × 10−6 M. The response time of electrode is 5 min. The proposed electrode was applied successfully for the determination of cyanide in commercially available spring water. Some anions, such as SCN−, I−, Cl−, Br− and oxalate that are usually serious interfering species for most of cyanide selective electrodes, did not have any interfering effect for this proposed electrode. 相似文献
969.
970.
Chun Li 《Tetrahedron》2004,60(37):8037-8041
It has been confirmed that octasulfonatocalix[8]arene (Calx-S8) and tris(2,2′-bipyridine)ruthenium (II) (Ru(bpy)32+) can form a stable host-guest complex in aqueous solution. The binding constant for 1:1 [Calx-S88−·Ru(bpy)32+]6− complex formation was estimated to be (2.4±0.8)×104 dm3 mol−1 by fluorescence titration, which indicates that the [Calx-S88−·Ru(bpy)32+]6− complex is the main species in 1:1 molar ratio aqueous solution of Calx-S8 and Ru(bpy)32+. In situ UV-Vis spectroscopic measurements indicated that Ru(bpy)32+ complexes can be readily deposited onto ITO electrode through electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) using [Calx-S88−·Ru(bpy)32+]6− host-guest complex as a dopant anion owing to the electrostatic interaction between the cationic conductive polymer and the anionic host-guest complex. The loading degree of the composite film with Ru(bpy)32+ can be determined by Lambert-Beer law modified for the two-dimensional concentration. The obtained composite film showed good photoelectric conversion properties in response to visible light irradiation. This is a novel photocurrent generation system in which the photoexcited state energy is efficiently collected by the conductive polymeric layer. 相似文献