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181.
Preparative high-speed counter-current chromatography for purification of shikonin from the Chinese medicinal plant Lithospermum erythrorhizon 总被引:8,自引:0,他引:8
The bioactive compound shikonin was successfully isolated and purified from the crude extract of the traditional Chinese medicinal plant Lithospermum erythrorhizon Sieb. et Zucc. by preparative high-speed counter-current chromatography (HSCCC). The preparative HSCCC was performed using a two-phase solvent system composed of n-hexane-ethylacetate-ethanol-water (16:14:14:5 (v/v)). A total amount of 19.6 mg of shikonin at 98.9% purity was obtained from 52 mg of the crude extract (containing 38.9% shikonin) with 96.9% recovery. The preparative isolation and purification of shikonin by HSCCC was completed in 200 min in a one-step separation. 相似文献
182.
Amorphous SiOx nanotubes with homogeneous diameters were fabricated in large-scale on silicon substrate by thermal evaporation method, with liquid gallium as medium. The average diameter of tubes is about 80 nm and the length is more than 10 1m, with small ratio between the inner and outer diameter of the tube. The silicon element in the substrate and the residual oxygen element in reaction chamber were first dissolved into liquid Ga. Then the SiOx precipitated from the surface of gallium droplet, forming the nanotube structure with Ga droplet being the center. The room temperature photoluminescence measurements under excitation at 260 nm show that the SiOx nanotubes has a strong blue emission at 453 nm with two shoulders at 410 and 480 nm respectively, which may be related to oxygen defects. The preparation method improved the traditional complicated method and also provided a new way to fabricate SiOx nanotubes in large quantity. 相似文献
183.
纳米金探针检测Hg 2+离子 总被引:1,自引:0,他引:1
利用Hg2+的核酸适体修饰纳米金形成探针建立了一种定量检测Hg2+离子的方法. Hg2+适体吸附在纳米金表面, 使纳米金的稳定性增强, 抑制氯化钠对纳米金的团聚作用. 溶液中有Hg2+离子存在时, 由于适体与纳米金的吸附作用小于适体与Hg2+离子的亲和作用, 纳米金失去适体保护在氯化钠作用下发生团聚. 溶液颜色由红变蓝, 紫外-可见光谱最大吸收峰由520 nm红移至620 nm. 在优化条件下, 吸光度的比值(A620/A520)与Hg2+离子浓度在5.0×10-9~7.2×10-7 mol8226;L-1范围内呈线性关系, 检测限可达3.3×10-10 mol8226;L-1. 研究了K+, Ca2+等常见离子的干扰, 结果表明该方法具有良好的选择性. 相似文献
184.
聚酰亚胺研究新进展 总被引:5,自引:0,他引:5
汪称意|李光|江建明|杨胜林|金俊弘 《化学进展》2009,21(1):174-181
聚酰亚胺(PI)是一类重要的高性能聚合物,广泛应用在航空航天、微电子、汽车、石油等高科技领域。由于其结构上的可设计性,世界上越来越多的研究者投入到这类高技术材料的研究开发中。本文分别从可溶性PI的分子设计与合成、功能性PI的合成与用途、PI绿色合成方法、PI纳米复合材料的制备4个方面综述了近年来PI的研究热点和新进展,为了解聚酰亚胺的研究提供了有价值的信息。 相似文献
185.
Chen H Peng C Sun L Liu H Hu Y Jiang J 《Langmuir : the ACS journal of surfaces and colloids》2007,23(22):11112-11119
We report a molecular simulation study on the assembly of an (A7B5)5/A7B5 copolymer blend on nanopatterned surfaces. The density distributions, anisotropic radii of gyration, and conformations of both copolymers are quantitatively characterized. As the width of stripes on the surface decreases, the shape and thickness of the assembled film are found to be in qualitative agreement with those from experiments. The simulation results indicate that the shape and conformation of ordered film can be modulated by tuning the adsorption energy between the surface and the polymer or by adjusting the width of the stripes on the surface. We can regulate the width of the stripes to obtain a desired polymer conformation without altering the assembled film. In remarkable contrast to the pure copolymer, the radii of gyration of the blend in three directions are consistently smaller. The simulation reveals that the addition of a short chain during assembly is of central importance in restructuring the conformations of the long chain. 相似文献
186.
Rui Liu Jing-fu Liu Xiao-xia Zhou Gui-bin Jiang Rui Liu 《Trends in analytical chemistry : TRAC》2011,30(9):1462-1476
Raman-based technologies have proved to be excellent tools for on-site and in-vivo analysis, due to the non-invasive nature of their detection, their capability of providing structure information, their high tolerance to aqueous samples, the ultra-sensitivity of surface-enhanced Raman scattering (SERS) and resonance Raman scattering (RRS), the high spatial resolution of tip-enhanced Raman scattering (TERS), and the ultrashort spectra-acquisition time for coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS).In this review, we highlight the recent success of Raman-based technologies in various applications, including:
(1)
on-site surface analysis and chemical-reaction monitoring; (2)
on-site identification of cultural objects, archeological studies and planetary science; (3)
in-vivo analysis of cells and microorganisms; (4)
in-vivo diagnosis inside human and animal bodies; (5)
in-vivo fast Raman imaging and mapping; (6)
the study of SERS processes; and, (7)
assessment of nanomaterial safety.
187.
Yue W Gao J Li Y Jiang W Di Motta S Negri F Wang Z 《Journal of the American Chemical Society》2011,133(45):18054-18057
Tetracene tetracarboxylic diimides have been synthesized based on direct double ring extension of electron-deficient naphthalene diimides involving metallacyclopentadienes. Atomic structure and electronic transitions responsible for their NIR absorption spectra are investigated with quantum-chemical calculations. In light of their unique structure and admirable photophysical and electronic properties, this new molecular skeleton is promising candidate for n-type semiconductors. 相似文献
188.
189.
The binding equilibrium between l? and human serum albumin (HSA) or bovine serum albumin (BSA) has been studied by means of the resonance Rayleigh scattering (RRS) and equilibrium dialysis. It has been found for the first time that RRS and multiple frequency scattering (MFS) are enhanced as the l? binding to the HSA and BSA, but fluorescence quenches. The equilibrium dialysis results suggest that the binding of l? to HSA and BSA fits a phase-distribution model other than Scatchard model, and that the order of magnitude of its phase-distribution constant was found to be 104. It is most probable that Cl? or other anion ions influence the binding of l? by changing the ionic strength in the solution. The dialysis at different pH indicates that the binding mechanism is due to the electrostatic forces between the l? and protonated basic amino-acid residues. 相似文献
190.
Several rare earth‐doped, calcium‐based magnetic catalysts were prepared for the synthesis of glycerol carbonate. The basicity and basic strength analysis of the catalysts showed that the doping of rare earth improved the basicity of the catalysts, and the doping of lanthanum maximized it. In addition, with the doping of lanthanum, the particle size of the catalyst became smaller to promote the organic reactants near the active sites of catalysts, thereby effectively improving the performance. NiFe2O4@[CaO‐La2O3] shows better catalytic performance with 99.0% yield of glycerol carbonate compared to the other catalysts. The NiFe2O4@(CaO‐La2O3) could be reused in six cycles without significant loss in activity. 相似文献