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11.
Five paeonol glycosides, suffruticosides A, B, C, D, and E, and a monoterpene glucoside, galloyl-oxypaeoniflorin, were isolated from the glycosidic fraction of Chinese Moutan Cortex, the root cortex of Paeonia suffruticosa Andrews, together with paeonolide, apiopaeonoside, galloyl-paeoniflorin, oxypaeoniflorin, and paeoniflorin. The structures of five suffruticosides and galloyl-oxypaeoniflorin were elucidated on the basis of chemical and physicochemical evidence. Suffruticosides A, B, C, and D, galloyl-oxypaeoniflorin, and galloyl-paeoniflorin exhibited more potent radical scavenging effects than alpha-tocopherol. 相似文献
12.
Mass spectra of ginsenoside-Rg1 deca-acetate 1 Siehe Lit.2. and the related dammaran-type triterpene saponin acetates have been studied and a comment is given on the structure of panaxoside A (=ginsenoside-Rg1) proposed by Elyakov, et al . 相似文献
13.
Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a metal tube atomizer has been applied to the determination of lead in Bangladeshi fish samples. The slurry sampling conditions, such as slurry stabilizing agent, slurry concentration, pyrolysis temperature for the slurried fish samples, particle size and ultrasonic agitation time, were optimized for electrothermal atomic absorption spectrometry with the Mo tube atomizer. Thiourea was used as the chemical modifier for the interference of matrix elements. The detection limit was 53 fg (3S/N). The determined amount of lead in Bangladeshi fish samples was consistent with those measured in the dissolved acid-digested samples. The advantages of the proposed methods are easy calibration, simplicity, low cost and rapid analysis. 相似文献
14.
Phosphorus has been determined by electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser. The effects of interferents on the phosphorus signal have been investigated. Chemical interferences were eliminated by high-temperature pyrolysis. The detection limit for the molybdenum tube system was 2.3 ng (corresponding to 2.3 micrograms ml-1 when 1 microliter was injected into the atomiser) and the characteristic mass was 1.9 ng of phosphorus. A calibration graph method combined with high-temperature pyrolysis has been evaluated through the determination of phosphorus in biological materials. The sensitivity, accuracy and precision of the method were superior to or nearly equal to those of graphite furnace atomic absorption spectrometry. The advantages of the high-temperature pyrolysis method are its simplicity and low cost. 相似文献
15.
16.
[reaction in text] The first total synthesis of (+/-)-linderol A, a hexahydrodibenzofuran isolated from Lindera umbellata bark, with potent inhibitory activity on melanin biosynthesis of cultured B-16 melanoma cells was achieved via a 20-step of reaction in 7.64% overall yield starting from 4,6-dimethoxysalicylaldehyde. 相似文献
17.
[reaction: see text] Chiral C(4)-substituted (E)- or (Z)-1-alkynyl-1-trimethylsilyloxy-2-butene systems provide anti-(Z) or syn-(Z) conjugated dienyne, with a very high level of stereocontrol, on treatment with BF(3).OEt(2) in CH(2)Cl(2) at -50 degrees C in the presence of allyltrimethylsilane. The Cieplak conformation for (E)-substrates and neighboring-group participation for (Z)-substrates are considered to be responsible for the stereochemical consequences. 相似文献
18.
Nakai I Kondoh H Amemiya K Nagasaka M Shimada T Yokota R Nambu A Ohta T 《The Journal of chemical physics》2005,122(13):134709
The mechanism of CO oxidation reaction on oxygen-precovered Pt(111) surfaces has been studied by using time-resolved near-edge x-ray absorption fine structure spectroscopy. The whole reaction process is composed of two distinct paths: (1) a reaction of isolated oxygen atoms with adsorbed CO, and (2) a reaction of island-periphery oxygen atoms after the CO saturation. CO coadsorption plays a role to induce the dynamic change in spatial distribution of O atoms, which switches over the two reaction paths. These mechanisms were confirmed by kinetic Monte Carlo simulations. The effect of coadsorbed water in the reaction mechanism was also examined. 相似文献
19.
The title hydride and its deuteride were successfully synthesized. The crystal structure of the deuteride was determined by time-of-flight neutron powder diffraction. BaAlD(5) crystallizes with a new orthorhombic structure in space group Pna2(1) (No. 33), cell parameters a = 9.194(1) A, b = 7.0403(9) A, and c = 5.1061(6) A, Z = 4. BaAlH(5) is the first example that contains one-dimensional zigzag chains of [AlH(6)] along the crystallographic c axis. 相似文献
20.
Yoichiro Iwase Koichi Kondo Kenji Kamada Koji Ohta 《Journal of polymer science. Part A, Polymer chemistry》2002,40(20):3534-3541
1,4‐Bis(4‐benzylpyridinium)butadiyne triflate was aggregated in dimethylformamide and spontaneously converted into the 1,4‐addition type of polydiacetylene. The polymerization took place in a dipolar aprotic solvent with a large dielectric constant that could enhance the aggregation of the ionic diacetylene salt through the electrostatic interaction. The molecular weight of the diacetylene was leveled off after 30 h at 80 °C to reach 1.5 × 104 (number‐average molecular weight) that consisted of the 1,4‐addition type of polydiacetylene similar to polydiacetylenes obtained in the conventional solid‐state polymerization. Electron spin resonance spectra revealed that diradicals were generated at the earlier state aggregation to give rise to a solution polymerization. The UV spectra also suggested the presence of the activated aggregation associated with the polymerization as well as the eximer emission spectra. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3534–3541, 2002 相似文献