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排序方式: 共有646条查询结果,搜索用时 15 毫秒
631.
Petr Vašek 《Supramolecular chemistry》2013,25(7):529-536
Interactions of a new porphyrin–β-cyclodextrin conjugate (1) with a number of aromatic compounds have been studied after covalent immobilization of 1 onto a solid matrix of 3-aminopropylated silica particles. The effects of both porphyrin and β-cyclodextrin moieties on interactions with achiral aromatic compounds were studied and the influence of the achiral porphyrin spacer on chiral recognition of binaphthyl derivatives by the β-cyclodextrin moiety of 1 is discussed. 相似文献
632.
一种改进的共轭梯度法及全局收敛性 总被引:1,自引:0,他引:1
本文在DY共轭梯度法的基础上对解决无约束最优化问题提出一种改进的共轭梯度法.该方法在Wolfe线搜索下能够保证充分下降性,并在目标函数可微的条件下,证明了算法的全局收敛性.大量数值试验表明,该方法是很有效的. 相似文献
633.
Conjugate function theory is used to develop dual programs for nonseparable convex programs involving the square root function.
This function arises naturally in finance when one measures the risk of a portfolio by its variance–covariance matrix, in
stochastic programming under chance constraints and in location theory. 相似文献
634.
The aim of the paper was to investigate the effect of ultrasonic emulsification treatment on the fabrication mechanism and stability of the emulsion. The covalent conjugate made with rice bran protein hydrolysate (RBPH) and ferulic acid (FA) was used as the emulsifier. The effects of high intensity ultrasound (HIU) power with different level (0 W, 150 W, 300 W, 450 W and 600 W) on the stability of emulsion were evaluated. The results showed that ultrasonic emulsification can significantly improve the stability of the emulsions (p < 0.05). The emulsion gained better stability and emulsifying property at 300 W. It was able to fabricate emulsion with smaller particle size, more uniform distribution and higher interfacial protein content. It was confirmed by fluorescent microscopy and cryo-scanning electron microscopy (cryo-SEM) furtherly. And it was also proved that the emulsion treated by proper HIU treatment at 300 W had better storage stability. Excessive HIU treatment (450 W, 600 W) had negative effects on the stability of emulsion. The stability of emulsion (300 W) against different environmental stresses was further explored, which established a theoretical basis for the industrial application of emulsion in food industry. 相似文献
635.
WeiWang Lian-shengZhang Yi-fanXu 《计算数学(英文版)》2005,23(2):217-224
A revised conjugate gradient projection method for nonlinear inequality constrained optimization problems is proposed in the paper, since the search direction is the combination of the conjugate projection gradient and the quasi-Newton direction. It has two merits. The one is that the amount of computation is lower because the gradient matrix only needs to be computed one time at each iteration. The other is that the algorithm is of global convergence and locally superlinear convergence without strict complementary condition under some mild assumptions. In addition the search direction is explicit. 相似文献
636.
Christopher J. Chapman Kelly J. Wadsworth Christopher G. Frost 《Journal of organometallic chemistry》2003,680(1-2):206-211
The enantioselective rhodium-catalysed conjugate addition of aryl boronic acids to dehydroalanine derivatives has been successfully carried out in the presence of C2-symmetric aryl diphosphite ligand (R,R,R-4) to prepare unnatural amino acid esters. The products have been obtained in up to 72% ee and with good isolated yield. 相似文献
637.
The total synthesis of panaginsene has been accomplished in 11 linear steps starting from methyl 3,3-dimethyl-5-oxocyclopent-1-ene-1-carboxylate. The key steps are a Sharpless asymmetric epoxidation and Ti(III)-mediated reductive epoxide opening-radical cyclization to construct the chiral quaternary carbon stereocenter followed by a very challenging HWE olefination reaction on an 1,3-keto aldehyde and a late stage McMurry olefination using low valent titanium to construct the highly constrained angular tetrasubstituted olefin in a five-membered ring. 相似文献
638.
Stephen G. Davies Jairton Dupont Robert J.C. Easton Osamu Ichihara Jeffrey M. McKenna Andrew D. Smith José A.A. de Sousa 《Journal of organometallic chemistry》2004,689(24):4184-4209
Conjugate addition of achiral lithium dimethylamide to the chiral iron cinnamoyl complexes (S,E)- and (S,Z)-[(η5-C5H5)Fe(CO)(PPh3)(COCHCHPh)] proceeds with high diastereoselectivity, with this protocol being used to establish unambiguously the absolute configuration of Winterstein’s acid (3-N,N-dimethylamino-3-phenylpropanoic acid) as (R). The highly diastereoselective conjugate addition of lithium N-benzyl-N-trimethylsilylamide to a range of α,β-unsaturated iron acyl complexes, followed by in-situ elaboration of the derived enolate by either alkylation or aldol reactions is also demonstrated, facilitating the stereoselective synthesis of both cis- and trans-β-lactams. This methodology has been used to effect the formal asymmetric syntheses of (±)-olivanic acid and (±)-thienamycin. Addition of chiral lithium amides derived from primary and secondary amines to the iron crotonyl complex [(η5-C5H5)Fe(CO)(PPh3)(COCHCHMe)] indicates that lithium N-α-methylbenzylamide shows low levels of enantiorecognition, while lithium N-3,4-dimethoxybenzyl-N-α-methylbenzylamide and lithium N-benzyl-N-α-methylbenzylamide show high levels of enantiodiscrimination. The high level of observed enantiorecognition was used to facilitate a kinetic resolution of (RS)-[(η5-C5H5)Fe(CO)(PPh3)(COCHCHMe)] with homochiral lithium (R)-N-3,4-dimethoxybenzyl-N-α-methylbenzylamide. Further mechanistic studies show that conjugate additions of (RS)-lithium N-benzyl-N-α-methylbenzylamide to either the (RS)- or homochiral iron crotonyl complex show 2:1 stoicheiometry, while homochiral lithium N-benzyl-N-α-methylbenzylamide shows 1:1 stoicheiometry. 相似文献
639.
Sang Bok Kim Marcus D. Faust Dwight A. Sweigart 《Journal of organometallic chemistry》2009,694(1):52-1595
The η6-hydroquinone iridium complex [(η6-H2Q)Ir(COD)]BF4 undergoes facile double deprotonation to the η4-quinone anionic analogue. The latter has been shown to be the first example of an iridium complex that catalyzes 1,4 conjugate addition reactions of aryl boronic acids to electron deficient olefins. 相似文献
640.
Christopher A. Lee 《Tetrahedron letters》2004,45(39):7193-7196
Several dihydroagarofuran esters have been reported to be effective multidrug resistance (MDR) reversing agents for both cancer cells and bacteria. We report a rapid synthesis of the dihydroagarofuran ring system from carvone in a sequence that is highlighted by a sequential conjugate addition/aldol sequence, a ring closing metathesis reaction, and a diastereoselective alkene reduction to provide an axial methyl group. The synthesis allows for differential esterification reactions as required to study the roles of these groups in MDR reversal. 相似文献