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921.
Two new saponins were isolated from leaves of Panax quinquefolium and their structures were elucidated as 3beta, 12beta, 20S-trihydroxy-25-methoxydammar-23-ene 3-O-{[beta-D-glucopyranosyl(1-->2)-beta-D-glucopyranosyl]-20-O-[alpha-L-arabinopyranosyl(1-->6)]-beta-D-glucopyranoside (1) and 3beta, 20S-dihydroxy-12beta, 23R-epoxydammar-24-ene 3-O-{[beta-D-glucopyranosyl(1-->2)-beta-D-glucopyranosyl]-20-O-[beta-D-xylopyanosyl(1-->6)]-beta-D-glucopyranoside (2) on the basis of (1)D and (2)D NMR (including (1)H, (13)C-NMR, (1)H-(1)H COSY, HSQC, TOCSY, HMBC, and NOESY), ESI-MS spectrometry and chemical methods. 相似文献
922.
Jijun Qiu Weidong Yu Xiangdong Gao Xiaomin Li Weizhen He Se-Jeong Park Hyung-Kook Kim Yong-Hwae Hwang 《Journal of Sol-Gel Science and Technology》2008,47(2):187-193
Silver nanoparticles well dispersed in a spherical Poly(vinylpyrollidone)(PVP) matrix were simply prepared by spray pyrolysis
of aqueous solutions of AgNO3 and PVP without any reducing agent. Highly monodisperse silver particles were obtained above the initial mass ratio of PVP/AgNO3 ∼ 1 and in a certain narrow temperature range. Below the critical mass ratio the silver particles grew to larger ones polydispersely.
As the ratio increased above it, they became smaller maintaining their monodispersity. The use of PVP considerably decreased
the reduction temperature of the silver nitrate from 450 °C to 250 °C under the same pyrolysis conditions, due to its reducing
nature. As the pyrolysis temperature increased above the decomposition temperature of PVP, the silver particles in the matrix
grew to merge to a single particle while their crystallite size did not increase as much. The spherical assemblies of the
silver nanoparticles were hardly disengaged even after severe washing off the matrix materials. The mechanism of the nanoparticle
growth was also discussed. 相似文献
923.
Jin H Qiu H Sakamoto Y Shu P Terasaki O Che S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(21):6413-6420
Using lipids (N-acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0 degrees C to 10, 15, or 20 degrees C. The structures were studied by electron microscopy. It was found that 1) the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2) these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid-solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3) the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L-form N-acyl amino acid was used as the lipid template; 4) the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries. 相似文献
924.
A simple, sensitive and accurate liquid chromatographic method with UV detection was developed and validated to determine voriconazole in a new emulsion formulation. Chromatographic separation was achieved on a Diamonsil C18 column (250 × 4.6 mm I.D., 5 μm) using a mobile phase consisting of acetonitrile-water-acetic acid (40:60:0.25, v/v/v) at a flow rate of 1.0 mL min?1. The UV detection wavelength was set at 256 nm. The linear calibration curves were obtained in the concentration range of 1.00–100 μg mL?1 with the limit of quantification of 1.00 μg mL?1. The within- and between-run precisions in terms of percentage relative standard deviation were lower than 7.4 and 7.1%, respectively. The accuracy in terms of percentage relative error ranged from ?1.5 to 1.4%. This validated method was successfully applied to the determination of the content of voriconazole in a new emulsion formulation. 相似文献
925.
A rapid and sensitive method was developed and validated for the determination of MCYST (microcystin)-RR, -LR, and [Dha7] MCYST-LR in rat plasma by liquid chromatography-tandem mass spectrometry. The analytes were extracted from rat plasma by protein precipitation, followed by solid-phase extraction. Liquid chromatography with electrospray ionization mass spectrometry, operating in selected reaction monitoring (SRM) mode, was used to quantify MCYST-RR, -LR, and [Dha7] MCYST-LR in rat plasma. The recoveries for each analyte in rat plasma ranged from 70.8 to 88.7%. The calibration curve was linear within the range from 0.005 to 1.25 μg mL?1. The limit of detection were 1.4, 1.0, 0.6 ng mL?1 for MCYST-RR, -LR, and [Dha7] MCYST-LR. The overall precision was determined on three different days. The values for within- and between-day precision in rat plasma were within 15%. This method was applied to the identification and quantification of microcystins in rat plasma with acute exposure of microcystins via intravenous injection. 相似文献
926.
Wei Li Yi-Jun Wu Dong-Mei Qin Yan Ma Ying-Jian Sun Shao-Ping Qiu 《Chromatographia》2008,67(9-10):761-766
A relatively simple method for the determination of azoxystrobin residues in grapes and soil using gas chromatography equipped with electron capture detector (GC-ECD) is described. Samples were extracted with acetone, and further partitioned with dichloromethane and petroleum ether. The extracts were then cleaned up in a glass clean-up column filled with active charcoal and silica gel, and eluted with dichloromethane/ethyl acetate (70:30, v/v). The eluate was collected and concentrated for GC-ECD analysis. The results showed good linearity (r 2 = 0.9998) over the concentration range of 6.25–400 ng mL?1. The limits of detection (LOD) and quantification (LOQ) of azoxystrobin were 3 and 10 ng mL?1. Recovery from soil and grape samples was in the range of 83.52–107.36 and 82.21–107.31%, with corresponding relative standard deviations (RSD) of 5.21–9.11 and 4.53–5.90% for the three fortified levels. Inter- and intra-day RSDs were in the range of 0.87–6.76 and 2.01–5.46%. The accuracy and sensitivity of the GC-ECD method was independently confirmed by LC and GC-MS. It was demonstrated that the proposed method was simple and efficient, and particularly suitable for detecting azoxystrobin residues in grapes and soil. 相似文献
927.
Two new silica-based long-chain alkylimidazolium stationary phases were prepared and characterized for their use in high-performance liquid chromatography. The stationary phases were both prepared by the reaction of chloropropyl silica with long-chain alkylimidazoles and were used to separate common inorganic anions. Hydrophobic interactions were also studied by the comparison of differential retention of various organic compounds. The alkyl chain length did not show an impact on the anion-exchange process but affected the hydrophobic interaction of the stationary phases. 相似文献
928.
Zhong‐Quan Zhang Jian‐Chao Chen Xian‐Ming Zhang Zhong‐Rong Li Ming‐Hua Qiu 《Helvetica chimica acta》2008,91(8):1494-1499
Two new spirostanol saponins, (1β,3β,5β,25S)‐spirostan‐1,3‐diol 1‐(β‐D ‐xylopyranoside) ( 1 ) and (1β,3β,5β,25S)‐spirostan‐1,3‐diol 1‐[α‐L ‐rhamnopyranosyl‐(1→2)‐β‐D ‐fucopyranoside] ( 2 ), along with two known compounds, (1β,3β,5β,25S)‐spirostan‐1,3‐diol 1‐[α‐L ‐rhamnopyranosyl‐(1→2)‐β‐D ‐xylopyranoside] ( 3 ) and (1β,3β,4β,5β,25S)‐spirostan‐1,3,4,5‐tetrol 5‐(β‐D ‐glucopyranoside) ( 4 ) were isolated from the whole plant of Reineckia carnea. The structures of the new steroids were determined by detailed analysis of their 1D‐ and 2D‐NMR spectra and chemical methods, and by comparison with spectral data of known compounds. Compounds 3 and 4 were isolated from the genus Reineckia for the first time. 相似文献
929.
This work addresses the chemical nature of the catalytic activity of X-ray "pure" CoO nanocrystals. All samples were prepared by a solvothermal reaction route. X-ray diffraction indicates the formation of CoO in a cubic rock-salt structure, while infrared spectra and magnetic measurements demonstrate the coexistence of CoO and Co 3O 4. Therefore, X-ray "pure" CoO nanocrystals are a unique composite structure with a CoO core surrounded by an extremely thin Co 3O 4 surface layer, which is likely a consequence of the surface passivation of CoO nanocrystals from the air oxidation at room temperature. The CoO core shows a particle size of 22 or 280 nm, depending on the types of the precursors used. This composite nanostructure was initiated as a catalytic additive to promote the thermal decomposition of ammonium perchlorate (AP). Our preliminary investigations indicate that the maximum decomposition temperature of AP is significantly reduced in the presence of CoO/Co 3O 4 composite nanocrystals and that the maximum decomposition peak shifts toward lower temperatures as the loading amount of the composite nanocrystals increases. These findings are different from the literature reports when using many nanoscale oxide additives. Finally, the decomposition heat for the low-temperature decomposition stages of AP was calculated and correlated to the chemical nature of the CoO/Co 3O 4 composite nanostructures. 相似文献
930.