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排序方式: 共有316条查询结果,搜索用时 15 毫秒
1.
本文将文献[9]中给出的一维广义函数的集值导数的某些结果,推广到n维情形,并给出一些与优化有关的其他结果. 相似文献
2.
Molecular dynamics simulations with a combined quantum mechanical and molecular mechanical (QM/MM) potential have been carried out to investigate the squalene-to-hopene carbocation cyclization mechanism in squalene-hopene cyclase (SHC). The present study is based on free energy simulations by constructing the free energy surface for the cyclization steps along the reaction pathway. The picture that emerges for the carbocation cyclization cascade is a delicate balance of thermodynamic and kinetic control that ultimately favors the formation of the final hopanoids carbon skeleton. A key finding is that the five- to six-membered ring expansion process is not a viable reaction pathway for either C- or D-ring formation in the cyclization reaction. The only significant intermediate is the A/B-bicyclic cyclohexyl cation (III), from which two asynchronous concerted reaction pathways lead to, respectively, the 6,6,6,5-tetracyclic carbon skeleton and the 6,6,6,6,5-pentacyclic hopanoids. Experimentally, these two products are observed to have 1% and 99% yields, respectively, in the wild-type enzyme. We conclude that the product distribution in the wild-type enzyme is dictated by kinetic control of these two reaction pathways. 相似文献
3.
地质样品中金,银,铊等元素的连续原子吸收光谱法测定 总被引:4,自引:0,他引:4
本文提出了一个一次称样连续测定金、银、铊的简便、快速的新方法。该法是以泡塑吸附金、铊,使银等定量地保留在溶液中。泡塑上的铊用EDTA解脱后,再用硫脲溶液继续解脱金,然后,采用原子吸收光谱法连续测定金、银、铊。方法用于黄铁矿、方铅等单矿矿物及岩石、土壤样品中xng/g~xxxμg/g金、银、铊的测定,获得满意结果。 相似文献
4.
5.
Nam K Prat-Resina X Garcia-Viloca M Devi-Kesavan LS Gao J 《Journal of the American Chemical Society》2004,126(5):1369-1376
Reactive flux molecular dynamics simulations have been carried out using a combined QM/MM potential to study the dynamics of the nucleophilic substitution reaction of dichloroethane by a carboxylate group in haloalkane dehalogenase and in water. We found that protein dynamics accelerates the reaction rate by a factor of 2 over the uncatalyzed reaction. Compared to the thermodynamic effect in barrier reduction, protein dynamic contribution is relatively small. However, analyses of the friction kernel reveal that the origins of the reaction dynamics in water and in the enzyme are different. In aqueous solution, there is significant electrostatic solvation effect, which is reflected by the slow reorganization relaxation of the solvent. On the other hand, there is no strong electrostatic coupling in the enzyme and the major effect on reaction coordinate motion is intramolecular energy relaxation. 相似文献
6.
7.
Yuanyou Yang Ning Liu Shunzhong Luo Jiali Liao Jiannan Jin Taiming Zhang Pengji Zhao 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(3):659-663
Biosorption of 241Am by a fungus A. niger, including the spore and hyphae, was investigated. The preliminary results showed that the adsorption of 241Am by the microorganism was efficient. More than 96% of the total 241Am could be removed from 241Am solutions of 5.6-111 MBq/l (C
o) by spore and hyphaeof A. niger, with adsorbed 241Am metal (Q) of 7.2-142.4 MBq/g biomass, and 5.2-106.5 MBq/g, respectively. The biosorption equilibrium was achieved within 1 hour and
the optimum pH range was pH 1-3. No obvious effects on 241Am adsorption by the fungus were observed at 10-45 °C, or in solutions containing Au3+ or Ag+, even 2000 times above the 241Am concentration. The 241Am biosorption by the fungus obeys the Freundlich adsorption equation. There was no significant difference between the adsorption
behavior of A. nigerspore and hyphae.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Ning Liu Shunzhong Luo Yuanyou Yang Taiming Zhang Jiannan Jin Jiali Liao 《Journal of Radioanalytical and Nuclear Chemistry》2002,252(1):187-191
The biosorption of radionuclide 241Am from solution by Saccharomyces cerevisiae (S. cerevisiae), and the effects of experimental conditions on the adsorption were investigated. The preliminary results showed thatS. cerevisiae is a very efficient biosorbent. An average of more than 99% of the total 241Am could be removed by S. cerevisiae of 2.1 g/l (dry weight) from 241Am solutions of 17.54–4386.0 mg/l (2.22 MBq/l–555 MBq/l) with adsorption capacities of 7.45–1880.0 mg/g biomass (dry weight) (0.94 MBq/g–237.9 MBq/g). The adsorption equilibrium was achieved within 1 hour and the optimum pH ranged 1–3. No significant differences on 241Am adsorption were observed at 10–45 °C, or in solutions containing Au3+ or Ag+, even 2000 times above 241Am concentration. The relationship between concentrations and adsorption capacities of 241Am indicated the biosorption process should be described by the Freundlich adsorption isotherm. 相似文献
9.
Zou Fan Zuo Jing Geng Chao Li Feng Huang Guan Liu Jiaying Jiang Jiali Fan Zhihua Li Xinyang 《Journal of Russian Laser Research》2021,42(4):462-467
Journal of Russian Laser Research - Laser aiming is one of the key technologies of laser atmospheric transmission. The beam actually is affected by atmospheric turbulence and mechanical vibration;... 相似文献
10.
本文以环状单萜醇α-萜品醇、L-薄荷醇及链状单萜醇香叶醇、香茅醇为先导化合物,采用酰氯酯化法合成肉豆蔻酸α-萜品醇酯(TER-C14)、肉豆蔻酸-L-薄荷醇酯(MEN-C14)、肉豆蔻酸香叶醇酯(GER-C14)和肉豆蔻酸香茅醇酯(CIT-C14),并考察单萜醇及其肉豆蔻酯作为促透剂对布南色林(Blo)的促透效果。通过体外经皮渗透实验、体外释放实验和分子模拟技术初步探究单萜醇及其肉豆蔻酯的促透机制。结果显示,当GER-C14或CIT-C14为促透剂时,均有显著的促透效果(P<0.05),并且24h经皮累积透过量是空白组的4.84倍和4.45倍。促透机制为肉豆蔻酸单萜醇酯破坏药物与神经酰胺之间的氢键相互作用,增加脂质迁移率和药物的自由能,从而促进药物的渗透。肉豆蔻酸单萜醇酯有望作为新型促透剂在经皮给药系统中广泛应用。 相似文献