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991.
Wei Sheng Feng Hong Wei Li Xiao Ke Zheng Sui Qing Chen 《中国化学快报》2007,18(12):1518-1520
Two new megastigmane O-glucopyranosides,named (2R,3R,5R,6S,9R)-3-hydroxy-5,6-epoxy-β-ionol-2-O-β-D-glucopyrano- side(1) and (2R,3R,5R,6S,9R)-3-hydroxyl-5,6-epoxy-acety-β-ionol-2-O-β-D-glucopyranoside(2) together with six known mega- stigmanes,were isolated from the leaves of Broussonetia papyrifera (Linn.) Vent.Their structures were established by chemical methods and spectroscopic techniques including 2D NMR. 相似文献
992.
Hong-Bing Ji Ting Ting Wang Le-Fu Wang Yan-Xiong Fang 《Reaction Kinetics and Catalysis Letters》2007,90(2):259-266
A reusable solid catalyst, MnFe1.8Cu0.15Ru0.05O4, has been developed as an effective catalyst for the aerobic oxidation of sulfides and sulfoxides to sulfones. The ruthenium
modified spinel catalyst is the first example reported for such reaction under mild condition with molecular oxygen as the
only oxidant. The oxidation reaction proceeded via an electrophilic attack of the oxygen atom of the catalyst on the electron-rich
sulfur atom of the substrate. 相似文献
993.
The addition of gem-difluorinated alkyl iodides to alkynes initiated by AIBN neatly gave the corresponding difluoromethylene vinyl iodides among which the stereoselectivity of aromatic acetylenes was high. The further coupling reaction of E-phenyl difluoromethylene vinyl iodides with terminal alkynes in the presence of catalytic palladium afforded the substituted difluorinated enynes. 相似文献
994.
Beatty KE Xie F Wang Q Tirrell DA 《Journal of the American Chemical Society》2005,127(41):14150-14151
We describe fluorescence labeling of newly synthesized proteins in Escherichia coli cells by means of Cu(I)-catalyzed cycloaddition between alkynyl amino acid side chains and the fluorogenic dye 3-azido-7-hydroxycoumarin. The method involves co-translational labeling of proteins by the non-natural amino acids homopropargylglycine (Hpg) or ethynylphenylalanine (Eth) followed by treatment with the dye. As a demonstration, the model protein barstar was expressed and treated overnight with Cu(I) and 3-azido-7-hydroxycoumarin. Examination of treated cells by confocal microscopy revealed that strong fluorescence enhancement was observed only for alkynyl-barstar treated with Cu(I) and the reactive dye. The cellular fluorescence was punctate, and gel electrophoresis confirmed that labeled barstar was localized in inclusion bodies. Other proteins showed little fluorescence. Examination of treated cells by fluorimetry demonstrated that cultures supplemented with Eth or Hpg showed an 8- to 14-fold enhancement in fluorescence intensity after labeling. Addition of a protein synthesis inhibitor reduced the emission intensity to levels slightly above background, confirming selective labeling of newly synthesized proteins in the bacterial cell. 相似文献
995.
JiChengCHU HongShengGUO JunBiaoCHANG KangZHAO 《中国化学快报》2004,15(7):785-786
The synthesis of novel nucleoside analog (3R)-2,3-dideoxy-3-(N-hydroxy-N-methylamino)-L-arabinofuranosyl uracil was studied. A twelve-step synthetic route, started from L-ascorbic acid, was designed, and the final product was obtained in 20.8% yield. 相似文献
996.
Determination of Dopamine in the Presence of Ascorbic Acid Using a Poly(Amidosulfonic Acid) Modified Glassy Carbon Electrode 总被引:3,自引:0,他引:3
Yuzhong?ZhangEmail author Guiying?Jin Zhousheng?Yang Hong?Zhao 《Mikrochimica acta》2004,147(4):225-230
A glassy carbon electrode (GCE) was modified with electropolymerized films of amidosulfonic acid in pH 7.0 phosphate buffer solution (PBS) by cyclic voltammetry (CV). The modified electrode showed an excellent electrocatalytical effect on the oxidation of dopamine (DA). In pH 7.0 PBS, the anodic peak current increased linearly with the concentration of DA in the range of 5.0×10–7 1.0×10–4moldm–3, with a correlation coefficient of 0.9932, and a detection limit (S/N=3) of 1.0× 10–7moldm–3. The relative standard deviation of 10 successive scans was 2.5% for 1.0×10–6moldm–3 DA. The interference of ascorbic acid (AA) with the determination of DA could be eliminated because of the very distinct attracting interaction between DA cations and the negatively poly(amidosulfonic acid) film in pH 7.0 PBS. The proposed method exhibited good recovery and reproducibility. 相似文献
997.
Kossen K Vaish NK Jadhav VR Pasko C Wang H Jenison R McSwiggen JA Polisky B Seiwert SD 《Chemistry & biology》2004,11(6):807-815
Many reports have suggested that target-activated ribozymes hold potential value as detection reagents. We show that a "half"-ribozyme ligase is activated similarly by three unstructured oligoribonucleotides representing the major sequence variants of a hepatitis C virus 5'-untranslated region (5'-UTR) target and by a structured RNA corresponding to the entire 5'-UTR. Half-ribozyme ligation product was detected both in an ELISA-like assay and in an optical immunoassay through the use of hapten-carrying substrate RNAs. Both assay formats afford a limit of detection of approximately 1 x 10(6) HCV molecules (1.6 attomol, 330 fM), a sensitivity which compares favorably to that provided by standard immunoassays. These data suggest that target-activated ribozyme systems are a viable approach for the sensitive detection of viral nucleic acids using high-throughput platforms. 相似文献
998.
A three-parametric modification equation and the least-squares approach are adopted to calibrating hybrid density-functional theory energies of C(1)-C(10) straight-chain aldehydes, alcohols, and alkoxides to accurate enthalpies of formation DeltaH(f) and Gibbs free energies of formation DeltaG(f), respectively. All calculated energies of the C-H-O composite compounds were obtained based on B3LYP6-311++G(3df,2pd) single-point energies and the related thermal corrections of B3LYP6-31G(d,p) optimized geometries. This investigation revealed that all compounds had 0.05% average absolute relative error (ARE) for the atomization energies, with mean value of absolute error (MAE) of just 2.1 kJ/mol (0.5 kcal/mol) for the DeltaH(f) and 2.4 kJ/mol (0.6 kcal/mol) for the DeltaG(f) of formation. 相似文献
999.
1000.
To isolate epigallocatechin gallate (EGCG) of catechin compounds from Korean green tea (Bosung, Chonnam), a C18 reversed-phase preparative column (250x22 mm) packed with packings of three different sizes (15, 40-63, and 150 microm) was used. The sample extracted with water was partitioned with chloroform and ethyl acetate to remove the impurities including caffeine. The mobile phases in this experiment were composed of 0.1% acetic acid in water, acetonitrile, methanol and ethyl acetate. The injection volume was fixed at 400 microl and the flow rate was increased as the particle size becomes larger. The isolation of EGCG with particle size was compared at a preparative scale and the feasibility of separation of EGCG at larger particle sizes was confirmed. The optimum mobile phase composition for separating EGCG was experimentally obtained at the particle sizes of 15 and 40-63 microm in the isocratic mode, but EGCG was not purely separated at the particle size of 150 microm. 相似文献