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991.
Chemical Constituents of Ailanthus triphysa 总被引:2,自引:0,他引:2
Two new compounds,8(14),15-isopimaradiene-2α,3α,19-triol(1),and 6α,7β-dihydroxy-17(20)-cis-5α-pregna-16-one(2),together with four known copounds,a oxygenated rare phyllocladane,phyllocladan-16α,19-diol(3),kaempferol-3-0-β-D-galactopyranosied,kaempferol-3-0-α-L-rhamnopyranoside and scopoletin, were isolated from the leaves of Ailanthus tripysa.Structures of 1-3 were elucidated on the basis of spectroscopic data as compared with related compounds. 相似文献
992.
超声波作用下羰基化合物的还原偶联反应 总被引:5,自引:0,他引:5
超声波在一些有机反应中有明显的促进作用「“,Luche等认为超声波的作用有两种主要类型[’j.一类是涉及电子转移的自由基或离子一自由基型反应,由于超声波的空化作用所产生的局部高温高压可以促进电子转移,从而明显地加快反应速度;对大多数离子型反应,超声波只能起到机械的物理作用.我们曾报道偕二卤化合物在Li、Na、Mg等金属作用下产生卡宾的反应是单电子转移过程,该反应可由于超声辐射而大大加速[‘];而在芳基叔脚的断裂反应中,超声波可以促进三苯基俄与金属馊反应生成二苯基脚负离子,但对它进一步的亲核取代反应却没有明… 相似文献
993.
Yongyao Zhou Huaiwen Wang Gang Sun Yuquan Fan Xingguo Chen Zhide Hu 《Analytical and bioanalytical chemistry》2000,366(1):17-21
A methodology based on the coupling of experimental design and artificial neural networks (ANNs) is proposed in the optimization of a new flow injection system for the spectrophotometric determination of Al(III) with Arsenazo DBM, which has for the first time been used as chromogenic reagent in the quantitative analysis of aluminium. An orthogonal design is utilized to design the experimental protocol, in which three variables are varied simultaneously. Feedforward-type neural networks with faster back propagation (BP) algorithm are applied to model the system, and then optimization of the experimental conditions is carried out in the neural network with 3-7-1 structure, which have been confirmed to be able to provide the maximum performance. In contrast to traditional methods, the use of this methodology has advantages in terms of a reduction in analysis time and an improvement in the ability of optimization. The method has been applied to the determination of Al(III) in steel samples and provided satisfactory results. 相似文献
994.
The biosorption properties of cadmium(Ⅱ) by pre-treated biomass of Phanerochaete chrysosporium in the form of pellet were investigated. It was found that formaldehyde cross-linking and subsequent alkaline treatment could significantly improve the adsorption capacity of the biomass compared to other sorts of treatments, such as calcium chloride treatment, HCl treatment and,acetone treatment. Biosorption capacity of cadmium was examined as a function of physical and chemical factors including the pH of the metal solution pellet size, temperature and biomass concentration. The cadmium removal efficiency was strongly affected by pH. The maximal adsorption occurred around pH4.5. The pellet size also had a marked influence on the cadmium removal efficiency and the optimum size was the diameter range of 1.5-2.0 mm. The effect of biosorption temperature on cadmium uptake was inconspicuous between 25℃ and 35℃, but there was a notable decrease in cadmium uptake when the temperature reached 40℃. The cadmium removal efficiency increased as the biomass concentration when the initial cadmium ion concentration was 10 mg/L. When the biomass concentration was 2 g/L,the removal efficiency was 99.56%. However, the augment of the. removal efficiency was not obvious when the biomass concentration was more than 2 g/L. On the optimum conditions mentioned above,cadmium concentration could be reduced from 10 ppm down to 0.04 ppm that was below the Chinese National Waste Water Integrated Discharge Standard. In the biosotption process, most of the metal uptake happened during a short period immediately after the adsorption process started. It was observed that the biomass pellets had already adsorbed 83.36% of the total amount of cadmium finally adsorbed within the initial 10 minutes. The cadmium uptake rate decreased gradually afterwards. Sorption equilibrium could almost be established in 12 hours. This indicated that biosorption might consist of two processes:a fast surface binding process opcurring first and a slow membrane diffusion process taking place subsequently. 相似文献
995.
LiAgSO4-Al2O3复合电解质的导电性研究 总被引:6,自引:0,他引:6
研究了分散第二相α-Al2O3对LiAgSO4的离子导电性的影响,发现LiAgSO4-Al2O3的电导率随a-Al2O3含量的增加而升高,在300-500℃间电导率高于纯LiAgSO4,a-Al2O3含量摩尔比约为40时最高。TG-DTA和XRD分析表明,在高温稳定的体立心LiAgSO4降温后以Ag2SO4的正交β相形式存在,但在H2O存在下,生成Li2SO4.H2O和Ag2SO4.FT-IR分析 相似文献
996.
耐高温α-淀粉酶结合Ca2+的研究 总被引:1,自引:0,他引:1
测定了耐高温α-淀粉酶分子中含10个Ca2+,脱钙酶逐量补钙后的活力及稳定性研究表明:酶分子中前8个Ca2+参与酶的催化作用,后2个Ca2+抖对酶结构起稳定作用.脱钙酶加钙后室温下的荧光光谱和CD谱表明:酶的构象虽有变化,但不显著,说明酶的构象对ca2+的依赖性很小.脱钙酶结合不同数目的Ca2+,于90℃加热15 min后,测其荧光光谱,结果表明,结合10个Ca2+时,酶保持最大的稳定构象;CD谱表明脱钙酶加热时仍具有一定的螺旋结构.这再次说明,酶的构象对ca2+依赖性较低. 相似文献
997.
一类新型的双β-氨基醇的合成及催化硼烷对芳酮的不对称还原反应 总被引:7,自引:0,他引:7
以L-半胱氨酸盐酸盐出发,经与二卤代烷偶联,成酯和格氏反应制得三种双手性β-氨基醇,1,2-双[R-2-氨基-3-羟基-3,3-二苯基丙硫基]乙烷(4a),1,3-双[R-2-氨基-3-羟基-3,3-二苯基丙硫基]丙烷(4b),1,4-双[R-2-氨基-3-羟基-3,3-二苯基丙硫基]丁烷(4c)。将此类双手性β-氨基醇与硼烷在THF溶液中反应,in situ制备双手性恶唑硼烷催化硼烷对芳酮的不对称还原,产物苯乙醇的光学收率达72.8%、α-溴代苯乙醇的光学收率达91.4%。 相似文献
998.
999.
1000.
Gang Xue Wen Xu Wentao Yu Qi Fang 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(1):m27-m29
The title compound, (C7H10N)[Ni(C3S5)2] or (Etpy)[Ni(dmit)2] (where Etpy is the N‐ethylpyridinium cation, C7H10N+, and dmit is the 2‐thioxo‐1,3‐dithiole‐4,5‐dithiolate dianion, C3S52−), crystallizes in the P space group with two molecules in the asymmetric unit. The [Ni(dmit)2]− monoanion has a planar D2h conformation, with the central Ni atom and the four coordinated S atoms forming an NiS4 square plane. The six‐membered ring of the Etpy cation also shows good planarity, as expected. There are two main types of disorder in the two Etpy cations. Several short intermolecular interactions are present, such as S⋯S, Ni⋯S and Ni⋯Ni, which help to form the enhanced three‐dimensional structure of the crystal. 相似文献