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81.
Summary The enantioselectivity of native and derivatized cyclodextrin stationary phases for aromatic and aliphatic chiral sulfoxides
was evaluated using high performance liquid chromatography (HPLC). Many sulfoxide enantiomers could be baseline resolved using
the derivatized cyclodextrin stationary phases in the reverse phase mode. The most important factor influencing enantioselectivity
is the presence of steric bulk alpha to the chiral center. However, substituents on an aromatic ring bonded to the sulfoxide
have less pronounced effects on enantioselectivity. The 2,3-dimethyl β-cyclodextrin exhibits the broadest anantioselectivity
for neutral chiral sulfoxides. Native cyclodextrins and hydroxypropyl-β-cyclodextrins were much less effective in separating
this class of molecules. The hydrogen bonding ability of the organic modifier does not significantly affect enantioselectivity. 相似文献
82.
Neutron activation γ-spectrometry is sufficiently sensitive for the determination of traces of rare earth elements but quantitative separation from uranium is essential. The rare earth elements in 0.2 M ammonium carbonate medium are quantitatively retained on Chelex-100, and are quantitatively separated from uranium by recycling the eluate. When 10-g samples are used, neutron activation provides detection limits of 1–20 μg kg?1. Recoveries of rare earths, checked by spiking with radiotracers, are essentially complete. 相似文献
83.
J.D. Desai 《Applied Surface Science》2006,252(23):8039-8042
Quantum dots (QDs) of iron oxide have been deposited onto ITO coated glass substrates by spray pyrolysis technique, using ferric chloride (FeCl3·7H2O) in non-aqueous medium as a starting material. The non-aqueous solvents namely methanol, ethanol, propanol, butanol and pentanol were used as solvents. The effect of solvents on the film structure and morphology was studied. The structural, morphological, compositional and optical properties were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), and optical absorption measurement techniques. 相似文献
84.
85.
S C Bhatia S N Revankar K J Doshi N D Desai E D Bharucha C G Sahajwalla 《Journal of chromatography. A》1988,434(1):296-302
86.
H. S. Dang H. B. Desai S. R. Kayasth D. D. Jaiswal C. N. Wadhwani S. Somasundaram 《Journal of Radioanalytical and Nuclear Chemistry》1984,84(1):177-183
The daily intakes of trace elements by infants showing optimal pattern of growth are used as the basis to estimate the requirements of Fe, Co and Se during infancy. Since milk is the only food and source of nutrition in the first few months of life, the requirements of these elements are calculated from their average concentrations in human milk and the volume of milk required to supply sufficient amount of energy for maintenance and healthy growth of infants. The concentrations of the three elements in human milk were determined, using the technique of neutron activation followed by radiochemical separation. 相似文献
87.
Functionalization of 4-methyl group in cycloartane-type triterpenoids has been accomplished utilizing, in the key step, photolytic decomposition of an hypoiodite derived from a 3β-hydroxymethyl-4,4-dimethyl precursor. The synthesis of cycloeucalanone from cyclolaudanone is reported. 相似文献
88.
Abstract— The emission spectra of radiation induced isothermal luminescence (ITL) and the thermolu-minescence (TL) of purines and pyrimidines of nucleic acids and analogue 6-azauracil in the form of pellets of dry polycrystalline powders have been studied at 77 K, and compared with their low temperature fluorescence and phosphorescence spectra. The qualitative and quantitative measurements of isothermal luminescence and thermoluminescence show that the two result from the same radiative transitions. The thermoluminescence emission was observed to coincide with the phosphorescence emission of the compounds in all the cases. The thermoluminescence of the pyrimidines and their analogue, however, have shown an additional component corresponding to their fluorescence in the ultraviolet region. An extension of the Weissbluth model based on the location of the electron traps in relation to the excited states of the compounds is proposed to explain their thermoluminescence emission. 相似文献
89.
The finite-size scaling technique is extended to a microcanonical ensemble. As an application, equilibrium magnetic properties of anL×L square lattice Ising model are computed using the microcanonical ensemble simulation technique of Creutz, and the results are analyzed using the microcanonical ensemble finite-size scaling. The computations were done on the multitransputer system of the Condensed Matter Theory Group at the University of Mainz. 相似文献
90.