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991.
992.
Yang‐Wen Ou Su‐Yao Xiao Wang‐Huang Lin Yong Cao Min Zhang Li‐Chao Zhao Long‐Fang Li 《Helvetica chimica acta》2010,93(1):84-89
A further chemical investigation of the plant Rubus corchorifolius L. f., collected in Hunan Province, afforded three new ent‐kauranoids 3 – 5 . Their structures were elucidated by various spectroscopic methods. 相似文献
993.
Liu Airong Lu Hanwen Fu Jiyang Pi Yong-Lin Huang Youqin Li Jing Ma Yuwei 《Nonlinear dynamics》2017,87(1):677-694
Nonlinear Dynamics - Little research about the out-of-plane dynamic stability of arches under in-plane loading has been reported in the literature hitherto. This paper presents analytical and... 相似文献
994.
Endo-β-N-acetylglucosaminidases are a class of endoglycosidases that deglycosylate N-glycans from glycoproteins. We describe here a facile synthesis of a complex type N-glycan thiazoline as a new mechanism-based inhibitor for this class of enzymes. The synthesis started with the readily available sialoglycopeptide (SGP) and its conversion into the glycan thiazoline through several enzymatic and chemical reactions. The synthetic glycan thiazoline showed potent inhibitory activity against several endoglycosidases including the two antibody-deactivating enzymes, Endo-S and Endo-S2, from human pathogen Streptococcus pyogenes, which would be useful as tools for structural and functional studies of these enzymes. 相似文献
995.
Two novel derivatives of TTDA (3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid), TTDA-BOM and TTDA-N'-BOM, each having a benzyloxymethyl group, were synthesized. (17)O NMR longitudinal and transverse relaxation rates and chemical shifts of aqueous solutions of their Gd(III) complexes were measured at variable temperature with a magnetic field strength of 9.4 T. The water exchange rate (k(ex)(298)) values for [Gd(TTDA-BOM)(H(2)O)](2-) (117 x 10(6) s(-1)) and [Gd(TTDA-N'-BOM)(H(2)O)](2-) (131 x 10(6) s(-1)) are significantly higher than those of [Gd(DTPA)(H(2)O)](2-) (4.1 x 10(6) s(-1)) and [Gd(BOPTA)(H(2)O)](2-) (3.45 x 10(6) s(-1)). The rotational correlation time (tau) values for [Gd(TTDA-BOM)(H(2)O)](2-) (119 ps) and [Gd(TTDA-N'-BOM)(H(2)O)](2-) (125 ps) are higher than those of [Gd(DTPA)(H(2)O)](2-) (103 ps) and [Gd(TTDA)(H(2)O)](2-) (104 ps). The stepwise stoichiometric binding constants of [Gd(TTDA-BOM)(H(2)O)](2)(-) and [Gd(TTDA-N'-BOM)(H(2)O)](2)(-) bound to HSA are obtained by ultrafiltration studies. Fluorescent probe displacement studies exhibit that [Gd(TTDA-BOM)(H(2)O)](2-) and [Gd(TTDA-N'-BOM)(H(2)O)](2-) can displace dansylsarcosine from HSA with inhibition constants (K(i)) of 1900 and 1600 microM, respectively; however, they are not able to displace warfarin. These results indicate that [Gd(TTDA-BOM)(H(2)O)](2-) and [Gd(TTDA-N'-BOM)(H(2)O)](2-) have a weak binding to site II on HSA. In addition, the mean bound relaxivity (r(1b)) and bound relaxivity (r(1)(b)) values for the [Gd(TTDA-BOM)(H(2)O)](2-)/HSA and [Gd(TTDA-N'-BOM)(H(2)O)](2-)/HSA adducts are obtained by ultrafiltration and relaxivity studies, respectively. The bound relaxivity of these adducts values are significantly higher than those of [Gd(BOPTA)(H(2)O)](2-)/HSA and [Gd(DTPA-BOM(3))(H(2)O)](2-)/HSA. These results also suggest that bound relaxivity is site dependent. In binding sites studies of Gd(III) chelates to HSA, a significant decrease of the relaxation rates (R(1obs)) was observed for the [Eu(TTDA-BOM)(H(2)O)](2-) complex which was added to the [Gd(TTDA-N'-BOM)(H(2)O)](2-)/HSA solution, and this indicated that these Gd(III) complexes share the same HSA binding site. Finally, as measured by the Zn(II) transmetalation process, the kinetic stability of these Gd(III) complexes are significantly higher than that of [Gd(DTPA-BMA)(H(2)O)]. 相似文献
996.
A method for direct determination of DL-tetrahydropalmatine (DL-THP) in Corydalis yanhusuo, a traditional Chinese herb, by L-THP imprinted monolithic precolumn on-line/off-line coupling with reversed-phase high performance liquid chromatography (RP-HPLC) was developed. The L-THP imprinted monolithic column has been prepared by in situ polymerization using methacrylic acid (MAA) and ethylene dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. With the optimization of chromatographic conditions, such as mobile phase composition, flow rate, column temperature and sample loading, for the separation of enantiomer, DL-THP was base-line separated on the MIP. The imprinted monolithic column was used as a precolumn for fractionation of the C. yanhusuo extract. Both the non-retained and retained fractions were separated by RP-HPLC. Meanwhile, the D-THP and L-THP can be detected in the non-retained and retained fractions, respectively. Additionally, direct determination of L-THP using molecularly imprinted monolith on-line coupling with a reversed-phase column was acquired. 相似文献
997.
The critical reverse micelle concentrations of C(12)-s-C(12).2Br (s=2,3,4,5,6,8,12) in n-heptane/n-hexanol solutions, cmc(I)s, have been determined by absorption spectrum method using iodine as probe. The values of cmc(I)s are smaller than those of the critical micelle concentrations (cmc(aq)s) in aqueous solution and reach a maximum at s=4, which is similar to the variation of cmc(aq) with s. The variation of cmc(I) with s is attributed to the alteration in the spacer chain conformation, i.e. when the spacer is short enough, it may adopt stretch configuration and when the spacer is long, it tends to bend towards the continuous oil phase to achieve a more densely packing of the quaternary ammonium heads on the surface of the core. 相似文献
998.
A sugar-quinoline fluorescent chemosensor for selective detection of Hg2+ ion in natural water 总被引:1,自引:0,他引:1
A selective and sensitive fluorescent sensor for detection of Hg2+ in natural water was achieved by incorporating the well-known fluorophore quinoline group and a water-soluble D-glucosamine group within one molecule. 相似文献
999.
Ionic liquid buffers: a new class of chemicals with potential for controlling pH in non-aqueous media 总被引:2,自引:0,他引:2
Ionic liquids with buffering characteristics, synthesized by the reaction of [RMIM]OH base moieties with phthalic and tartaric acid, respectively, are potential reagents for controlling pH in non-aqueous media; remarkable [Base]/[Acid] molar ratio dependence of the catalytic activities has been observed in the hydrogenation of olefins with [RuCl2(PPh3)3] complex in DMF and [BMIM][BF4]. 相似文献