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891.
Immobilized polysaccharide-based chiral stationary phases (CSPs) are gaining importance in the resolution of racemic compounds due to their stable nature on working with normal solvents and those prohibited for use with coated phases (tetrahydrofuran, chloroform, dichloromethane, acetone, 1,4-dioxane, ethyl acetate, and certain other ethers). This review discusses the use of immobilized polysaccharide CSPs in the chiral resolution of various racemates by liquid chromatography. The discussion includes immobilization methodologies, enantioselectivities, efficiencies, and a comparison of chiral recognition capabilities of coated vs. immobilized CSPs. Some applications of immobilized CSPs to the chiral resolution of racemic compounds are also presented. 相似文献
892.
Salah Fayed A Abdel-Aaty Shehata M Yehia Hassan N El-Weshahy SA 《Journal of separation science》2006,29(18):2716-2724
Two sensitive, selective, and precise stability-indicating, high-performance liquid chromatography and high-performance thin-layer chromatography methods have been developed for the determination of alfuzosin hydrochloride in the presence of its degradation products. Alfuzosin.HCl was subjected to stress alkaline, acidic, oxidative, thermal, and photo-degradation. The drug could be well separated from the degradation products upon applying the two methods. Separation by HPLC was achieved using an Xterra RP18 column and acetonitrile/0.02 M KH2PO4 (pH=3) in a ratio of 20:80 as mobile phase. The flow rate was 1 mL/min. The linearity range was 0.25 to 11 microg/mL with mean percentage recovery of 100.26 +/- 1.54. The HPTLC method used ALUGRAM Nano-SIL silica gel 60 F254 plates; the optimized mobile phase was methanol/ammonia (100:1.2). Quantitatively the spots were scanned densitometrically at 245 nm. A second order polynomial equation was used for the regression. The range was 0.5-7 microg/spot. The mean percentage recovery was 100.13 +/- 1.67. Two main degradation products were obtained in most stress conditions, separated, and identified by FT-IR and NMR spectral analysis, from which the degradation pathway was proposed. The two methods were validated according to the International Conference on Harmonization. In addition, the HPLC method was used to study the kinetics of alkaline and acid degradation of the drug. 相似文献
893.
Chadi Hassan Taher 《manuscripta mathematica》2010,132(1-2):169-198
We calculate the parabolic Chern character of a bundle with locally abelian parabolic structure on a smooth strict normal crossings divisor, using the definition in terms of Deligne–Mumford stacks. We obtain explicit formulas for ch 1, ch 2 and ch 3, and verify that these correspond to the formulas given by Borne for ch 1 and Mochizuki for ch 2. 相似文献
894.
AbstractIn this article, we investigate the representation rings (or Green rings) of the Drinfeld doubles of the Taft algebras. It is shown that these Green rings are commutative rings generated by infinitely many elements subject to certain relations. The generators together with the subjecting relations are given. The stable Green rings of of the Drinfeld doubles of the Taft algebras are also described. 相似文献
895.
Applying integrated variational principles on fluid and deck plate to the large deflection analysis of floating roofs, this paper investigates the significance of the flexural and membrane components in the formulations of the deck plate. Integrated variational principles facilitate the treatment of the compatibility of deformation between floating roof and supporting liquid. Analysis results show that different assumptions about deck plate formulation commonly used in the literature, results in considerably different deflection and stress patterns on the floating roof. The results show that modeling of the deck plate as a flexural element rather than the membrane, by eliminating the need for nonlinear analysis, gives reasonable results for deflections and stresses in the deck plate. Finally, to check the results of the variational formulation, employing Bessel functions and ignoring membrane stiffness an approximate solution is derived and its results compared with those of the variational formulation. This comparison shows that the approximate solution closely follows the variational formulation. 相似文献
896.
Nabil M. Hassan Tetsuo Ishikawa Masahiro Hosoda Atsuyuki Sorimachi Shinji Tokonami Masahiro Fukushi Sarata K. Sahoo 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(1):15-21
The specific activities of 238U, 232Th, and 40K in selected building materials used in Japan were measured using a high-purity germanium detector. The uranium and thorium concentrations were determined from same samples using inductively coupled plasma mass spectrometry. There was a good agreement between the measurement of uranium and thorium with both methods (R 2 = 0.94, and 0.97, respectively). Based on the specific activities, we have estimated some hazard indexes such as radium equivalent activities (Ra eq), external hazard index (H ex), internal hazard index (H in), annual gonadal equivalent dose (AGED), internal alpha dose, mass exhalation rate and emanation coefficient of radon. 相似文献
897.
898.
M. Z. Kassaee Hassan Masrouri Farnaz Movahedi 《Monatshefte für Chemie / Chemical Monthly》2010,36(1):317-322
Abstract
Zinc oxide nanoparticles are used as an effective and reusable catalyst for one-pot, four-component couplings of aldehydes, dimedone, active methylene compounds, and ammonium acetate to produce polyhydroquinoline derivatives under solvent-free conditions at room temperature. Compared with other methods, satisfactory results are obtained with high yields, short reaction times, and simplicity in the experimental procedure. The catalyst could easily be recycled and reused four times without noticeable decrease in catalytic activity. 相似文献899.
900.
Han SB Hassan A Kim IS Krische MJ 《Journal of the American Chemical Society》2010,132(44):15559-15561
A total synthesis of the oxo-polyene macrolide (+)-roxaticin is achieved in 20 steps from 1,3-propanediol. In this approach, 9 of 10 C-C bonds formed in the longest linear sequence are made via metal catalysis, including 7 C-C bonds formed by iridium catalyzed alcohol C-C coupling. Notably, the present synthesis, which represents the most concise preparation of any oxo-polyene macrolide reported to date, is achieved in the absence of chiral reagents and chiral auxiliaries with minimal use of premetalated C-nucleophiles. 相似文献