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991.
The 13C NMR spectra of a number of 2,3-dihdyro-1,4-diazepinium salts, like 1H NMR spectra, confirm shape, and charge distribution for these compounds. The ring has a half-chair shape which is inverting rapidly at room temperature. The atoms in the conjugated portion of the ring show alternating polarity, and phenyl groups attached to these positions act, respectively, as electron-donors or electron-acceptors. A methyl substituent in the saturated portion of the ring shows equal preference for quasi-equatorial and quasi-axial conformations. Some comparisons are drawn between present results and similar results obtained with related benzene derivatives. 相似文献
992.
993.
Metoprolol is a lipophilic, cardioselective beta-adrenergic blocking agent commercially available as a racemic compound. A normal phase high-performance liquid chromatographic method was developed to directly determine individual enantiomeric concentrations of metoprolol in human serum. Separation of the enantiomers was accomplished by a cellulose-tris(3,5-dimethylphenylcarbamate) chiral stationary phase. Metoprolol enantiomers were detected by means of fluorescence with excitation and emission wavelengths of 275 and 315 nm, respectively. Standard curves were linear over the concentration range 12.5-400 ng/ml for each enantiomer. Within-day coefficient of variation was less than 15% at all concentrations and the between-day coefficient of variation ranged from 4.1 to 11.2%. The limit of detection was determined to be 5 ng/ml for each enantiomer and the stereoselective resolution (alpha) of R- and S-metoprolol was 3.08. The assay was employed to determine enantiomeric serum concentrations of metoprolol in healthy male volunteers. 相似文献
994.
995.
996.
Several exact results are presented for a one-dimensional tight-binding model of layered binary metallic structures for the cases of arbitrary, random, incommensurate, and commensurate layer sequences. 相似文献
997.
High-resolution Stark-hyperfine transition measurements have been made on the J = 1, K = 0 and J = 1, K = 1 levels of ammonia using molecular beam electric resonance spectroscopy. The dipole moments measured are μ(J = 1, K = 0) = 1.47149(15) D and μ(J = 1, K = 1) = 1.47179(15) D. The polarizability anisotropy was found to be positive and hyperfine properties for both states were accurately measured. 相似文献
998.
The combined effects of off-diagonal disorder and electron-hole pair production (the X-ray edge effect) are studied for a one-dimensional Anderson model of a liquid metal with a half-full band. 相似文献
999.
1000.
M. B. Shiran K. M. Quan D. J. Watmough K. Abdellatif J. R. Mallard D. Marshall D. W. Gregory 《Ultrasonics》1990,28(6):411-414
The mapping of ultrasound fields using the dye paper method is described. The mode of action by which the dye concentration is increased has been investigated. Microbubbles on the paper surface and microstreaming of dye solution seem to be essential features of the mapping method. The streaming is thought to inhibit the formation of a dye depletion layer near the paper to an extent dependent on local sound intensity A linear relation between streaming velocity and intensity is derived. 相似文献