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941.
Three chiral compounds were successfully separated in a short time with two enantiomer separation models on packed-capillary electrochromatography (CEC). (i) 75 μm I.D. capillaries were packed with 5 μm β-cyclodextrin (β-CD) chiral stationary phase (CSP). Effects of voltage, pH and concentration of organic modifier on electroosmotic flow (EOF) and chiral separations were investigated systematically. Enantiomers of a neutral compound (benzoin) and a neutral drug (mephenytoin) were separated within a short time with high efficiency. Efficiency of 32 000 theoretical plates per meter and resolution (R_s) of 1.42 were achieved for enantiomers of benzoin using a βCD packed column with 6.2 cm packed length. Efficiency of 45 000 theoretical plates per meter and R_s of 3.40 were obtained for enantiomers of mephenytoin. Especially, the enantiomer separation of mephenytion was performed in just 3.4 min with R_s of 2.60. (ⅱ) 75 μm I.D. capillary was packed with octadecylsilica particles (ODS). Chiral separat 相似文献
942.
Kozitsyna N. Yu. Martens M. V. Stolyarov I. P. Gekhman A. E. Vargaftik M. N. Moiseev I. I. 《Russian Chemical Bulletin》1999,48(9):1673-1681
The effects of the solvent and the ligand chirality on the regioselectivity of oxidative esterification of propylene and cyclohexene
by PdII carboxylates were studied using achiral (MeCO2
−, Me2CHCH2CO2
−), racemic ((±)-CF3CF2CF2OC*F(CF3)CO2
−), and chiral ((S)−(+)−MeC*H(Et)CO2
−, (+)−CF3CF2CF2OC*F(CF3)CO2
−) carboxylate ligands. The oxidation of alkenes in aprotic media (CHCl3, CH2Cl2, CO2, THF) affords mainly allylic esters (in the case of cyclohexene also homoallylic esters) and the oxidative esterification
at the vinylic position is absent. In weakly solvating media (CHCl3, CH2Cl2) the regioselectivity of cyclohexene oxidation (the allyl to homoallyl ratio) increases substantially on going from achiral
or racemic acido ligands to chiral acido ligands. In a more donor medium (THF) the ligand chirality effect almost vanishes.
The effects of the ligand chirality and the nature of the solvent on the mechanism of alkene oxidation by PdII complexes are discussed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1695–1703, September, 1999. 相似文献
943.
O. I. Kolodiazhnyi E. V. Grishkun S. Sheiko O. Demchuk H. Thoennessen P. Jones R. Schmutzler 《Russian Chemical Bulletin》1999,48(8):1568-1573
Chiral C2-symmetrical dialkyl phosphites and C3-symmetrical trialkyl phosphites, derived from (−)-borneol, (−)-menthol, and 1,2∶5,6-di-O-isopropylidene-α-d-glucofuranose, were studied as the starting reagents for the preparation of chiral organophosphorus compounds. The reactions
of C2-symmetrical dialkyl phosphites and C3-symmetrical trialkyl phosphites with aldehydes and amines or aldehydes are accompanied by asymmetrical induction at the α-carbon
atom to yield optically active α-aminoalkylphosphanates or α-hydroxyalkylphosphonates, respectively. The stereoselectivity
of the reaction depends on the structure of the starting compounds and the reaction conditions.
Translated fromIzvestiya Akademii, Nauk, Seriya Khimicheskaya, No. 8, pp. 1588–1593, August, 1999. 相似文献
944.
945.
A multiple-order-parameter mean-field theory of ordering on a binary hexagonal- close-packed (HCP) crystal structure is developed, and adapted to provide a continuum formulation that incorporates the underlying symmetries of the HCP crystal in both the bulk and gradient energy terms of the free energy. The work is an extension of the previous treatment by Braun et al. [Phil. Trans. Roy. Soc. Lond. A
355:1787 (1997)] of order–disorder transitions on a face-centered-cubic crystal (FCC) lattice. The theory is used to compute the orientation dependence of the structure and energy of interphase and antiphase boundaries in ordering to the Cd3Mg and CdMg structures, which are the HCP analogs of Cu3Au and CuAu structures in FCC. As in the corresponding FCC case, the multiple order parameters do not form a vector. Anisotropy is a natural consequence of the underlying crystal symmetries and the multiple-order-parameter continuum formation presented here. The isotropy transverse to the sixfold axis expected for a scalar order parameter is not found. 相似文献
946.
An ordered adlayer of sulfate or bisulfate has been found on the unreconstructed Au(100) surface in 0.1 M H2SO4 by in-situ STM. The ordered adlayer is formed concomitantly with lifting of the (hex)-reconstruction. The new structure consists of sulfate/bisulfate rows that run parallel to the edges of the islands that were created during the (hex)→(1×1) transition. The distance between the adions within the rows is 4.0±0.3 Å, and that between rows 10.4±0.7 Å, corresponding to a
superstructure with a surface coverage of about 0.2. 相似文献
947.
Tohru Shibata 《Macromolecular Symposia》2004,208(1):353-370
Cellulose acetate has been utilized in a variety of separation and purification processes. In membrane separation, cellulosics, in particular cellulose acetate, have played important roles. Hemodialysis and desalination are the established fields where acetate membranes have been applied. Recently, a new application, that is the purification of drinking water, is growing. The history of cellulosic membranes, preparation of acetate membranes, and applications will be reviewed. Cellulose acetate is also useful in chromatography and related separation technologies. These application will also be reviewed and the relationship between the superstructure of cellulose triacetate and its adsorptive behavior is briefly mentioned. 相似文献
948.
Frank Janssen Marco Sturm Leo van Ijzendoorn Arnoud Denier van der Gon Herman Schoo Martien de Voigt Hidde Brongersma 《Macromolecular Symposia》2004,212(1):225-230
The characteristics of polymer light emitting diodes (PLEDs) (ITO/PPV/Ca) depend strongly on the conditions during preparation and operation. We studied the effects of heat treatment (during and after preparation) of PLEDs with OC1C10-PPV as active layer. PLEDs showed a reduction of both the current and the light output to 40 % after annealing for only 30 min at 65 °C. Effects on I-V characteristics were studied by measuring single carrier devices (hole- and electron-dominated devices). The current reduction after heat treatment can be ascribed to degradation of the ITO/PPV and the Ca/PPV interfaces. 相似文献
949.
Yoshiro Tajitsu 《Macromolecular Symposia》2004,212(1):201-208
Polylactic acid (PLA) is a polymer material on which biodegradability research has been the most advanced. PLA is a chiral polymer in which molecules containing asymmetric carbon atoms have a helical structure. Two optical isomers of PLA exist, PLLA (poly(L-lactic acid)) and PDLA (poly(D-lactic acid)). In this study, using various physical processes, we fabricated various samples such as oriented PLLA film, PLLA fiber, rolled PLLA film and forged PLLA plate. We observed a large optical rotatory power ρ in the cylindrical plate fabricated using a forging process. ρ of forged PLLA plates is 7200°/mm which is approximately 300 times larger than that of α-quartz. 相似文献
950.
Alloy formation at the Ni–Al interface for thin nickel films deposited on Al(110) surfaces has been studied using high-energy ion scattering/channeling (HEIS) and X-ray photoelectron spectroscopy (XPS). For nickel atoms deposited at room temperature on Al(110), a large amount of nickel–aluminum intermixing occurs at the interface. For the first two monolayers (ML) of deposited nickel, an NiAl-like compound is formed. The intermixing continues with a different rate, forming an Ni3Al-like compound for nickel coverages from 2 to 8 ML, at which point a nickel metal film begins to grow on the surface. Nickel atoms deposited at 250°C on the Al(110) surface exhibit no surface compound formation, but diffuse up to 400 Å into the aluminum substrate. Interatomic potentials based on the embedded-atom method (EAM) are used in a Monte Carlo approach to simulate the evolution of the Ni–Al(110) interface as a function of the nickel coverage. The calculated ion-scattering yields and X-ray photoelectron intensities from nickel and aluminum atoms in these simulated interfaces are in good quantitative agreement with the experimental results. The simulations show a high-density Ni–Al alloy forming at the Al(110) surface which apparently inhibits outward diffusion of aluminum, leading to the more nickel-rich alloy and finally nickel film growth. The ion-scattering simulations show an unusually large amount of backscattering occurring below the Ni–Al(110) interface, apparently associated with defocusing of the incident ion beam. 相似文献