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91.
Determination of tea catechins 总被引:5,自引:0,他引:5
An overview of analytical methods for the measurement of biologically important tea catechins is presented. Liquid chromatography and capillary electrophoresis are the most cited techniques for catechin separation, identification and quantitation. Liquid chromatography with ultraviolet detection is frequently used; however, mass spectrometry, electrochemical, fluorescence and chemiluminescence detection are also utilized in cases where more sensitive or selective detection is needed. Two modes of capillary electrophoresis, capillary zone electrophoresis and micellar electrokinetic capillary chromatography, have been employed for the determination of catechins. Both modes of capillary electrophoresis are based on ultraviolet detection. Additional analytical techniques, such as gas chromatography, thin-layer chromatography, paper chromatography, spectrophotometry, biosensing, chemiluminescence and nuclear magnetic resonance spectroscopy have also been utilized for the determination of catechins and are reviewed herein. 相似文献
92.
Catalyzed asymmetric acyl halide-aldehyde cyclocondensation (AAC) reactions afford highly enantiomerically enriched 3,4-disubstituted-2-oxetanones. These reactions constitute catalytic asymmetric propionate aldol additions. An optically active Al(III)-triamine complex (10 mol %) catalyzes the di(isopropyl)ethylamine-mediated cyclocondensation of propionyl bromide and a variety of aldehydes to afford beta-lactone adducts with uniformly high enantioselection (90 --> 98% ee), diastereoselection (74 --> 98% de), and chemical yields (78-90%). Lactone ring opening reveals that the enantiomerically enriched beta-lactones act as surrogates for syn propionate aldol adducts. 相似文献
93.
[reaction: see text] Optically active 4-substituted 2-oxetanones provide conduits for preparing 2,3-dihydro-4H-pyrone heterocycles. Enantioenriched beta-lactones are prepared by asymmetric catalytic acyl halide-aldehyde cyclocondensation reactions. Hydrazone anion-mediated beta-lactone ring opening and ensuing cyclization-dehydroamination of the derived beta-ketohydrazone afford the desired dihydropyrones (68-81%). Optimized lactone ring-opening-cyclization reaction conditions render a variety of optically active 4-substituted-2-oxetanones as effective precursors to enantioenriched 2,3-dihydro-4H-pyrones. 相似文献
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Kubota Y Nelson JK Perticone D Poling R Schrenk S Crawford G Fulton R Jensen T Johnson DR Kagan H Kass R Malchow R Morrow F Whitmore J Wilson P Bortoletto D Brown D Dominick J McIlwain RL Miller DH Modesitt M Ng CR Schaffner SF Shibata EI Shipsey IP Battle M Kroha H Sparks K Thorndike EH Wang C Alam MS Kim IJ Li WC Nemati B Romero V Sun CR Wang P Zoeller MM Goldberg M Haupt T Horwitz N Jain V Mestayer MD Moneti GC Rozen Y Rubin P Skwarnicki T Stone S Thusalidas M Yao W Zhu G Barnes AV Bartelt J 《Physical review D: Particles and fields》1991,44(3):593-600
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The complexes [1,3-diphenyl-1,3-propanedionato]tricyclohexyltin(IV), (tropolonato)triphenyltin(IV), and (tropolonato)tricyclohexyltin(IV) have been prepared for the first time and have been found to be five-coordinate in the solid state. These and related five-coordinate complexes prepared previously have been studied by a variety of physical methods; 13C NMR, UV, IR, Raman, dipole moments and the Kerr effect. While all structures are demonstrably five-coordinate, and all chelates bidentate in the solid state, the geometries of two of the complexes in solution appear to vary somewhat from the expected fac or mer. There is evidence from the solution Kerr effect and 13C NMR that cyclohexyl derivatives may disproportionate. 相似文献
100.
X-ray diffraction analysis reveals the thiogermanic acid H(4)Ge(4)S(10) possesses discrete adamantane-like Ge(4)S(10)(4)(-) complex anions. Each thioanion is composed of four corner shared GeS(2.5)(-) tetrahedral units. Crystals were grown from anhydrous liquid hydrogen sulfide reactions with glassy germanium sulfide at room temperature. The crystal structure was solved and refined from single crystal diffractometer data (Mo Kalpha radiation) obtained at 173 K. H(4)Ge(4)S(10) is triclinic, centrosymmetric space group Ponemacr;, with a = 8.621(4) A, b = 9.899(4) A, c = 10.009(4) A, alpha = 85.963(7) degrees, beta = 64.714(7) degrees, gamma = 89.501(8) degrees, and Z = 2. Average bridging and terminal d(Ge-S) distances are 2.229 and 2.206 A, respectively. Vibrational mode assignments are reported from Raman scattering and IR absorption spectra of polycrystalline samples. The nu(s)(Ge-S-Ge) and nu(s)(Ge-S(-)) stretching modes are observed at 354 and 405 cm(-)(1), respectively. 相似文献