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排序方式: 共有258条查询结果,搜索用时 218 毫秒
251.
Marco Ferrara Benedetta Crescenzi Monica Donghi Ester Muraglia Emanuela Nizi Silvia Pesci Vincenzo Summa Cristina Gardelli 《Tetrahedron letters》2007,48(47):8379-8382
The hexahydropyrimido[1,2-a]azepine-2-carboxamide derivative 1 could be obtained by three synthetic strategies, which allowed access to multigram amounts of material of high purity and ee. Two strategies involved alternative approaches to the bicyclic pyrimidone core, with the most efficient one being a two-step sequence from commercially available starting materials exploiting a little precedented cyclisation reaction. The remaining steps to 1 included an efficient crystallisation of an intermediate as a single stereoisomer. An alternative strategy employing a chiral starting material led to products of low optical purity but allowed the assignment of the configuration of the stereogenic centre of 1. 相似文献
252.
Aguilera-Venegas B Olea-Azar C Norambuena E Arán VJ Mendizábal F Lapier M Maya JD Kemmerling U López-Muñoz R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(3):1004-1012
Electrochemical and ESR studies were carried out in this work with the aim of characterizing the reduction mechanisms of 4-substituted and 1,4-disubstituted 7-nitroquinoxalin-2-ones by means of cyclic voltammetry in DMSO as aprotic solvent. Two reduction mechanisms were found for these compounds: the first, for compounds bearing a labile hydrogen by following a self-protonation mechanism (ECE steps), and the second, for compounds without labile hydrogen, based on a purely electrochemical reduction mechanism (typical of nitroheterocycles). The electrochemical results were corroborated using ESR spectroscopy allowing us to propose the hyperfine splitting pattern of the nitro-radical, which was later corroborated by the ESR simulation spectra. All these compounds were assayed as growth inhibitors against Trypanosoma cruzi: first, on the non-proliferative (and infective) form of the parasite (trypomastigote stage), and then, the ones that displayed activity, were assayed on the non-infective form (epimastigote stage). Thus, we found four new compounds highly active against T. cruzi. Finally, molecular modeling studies suggest the inhibition of the trypanothione reductase like one of the possible mechanisms involved in the trypanocidal action. 相似文献
253.
Multienzymatic conversion of sucrose into fructose and gluconic acid was studied through fed-batch and continuous (in a membrane reactor) processes. The law of substrate addition (sucrose or glucose) for the fed-batch process which led to a yield superior to 80% was the decreasing linear type, whose feeding rate (?; L/h) was calculated through the equation: ? = ?o ? k.t, where ?o (initial feeding rate, L/h), k (linear addition constant, L/h 2), and t (reaction time, h). In the continuous process, the yield of conversion of sucrose (Y) was superior to 70% under the following conditions: dilution rate?=?0.33 h?1, total duration of 15 h, pH 5.0, 37 °C and initial sucrose concentration of 64 g/L (Y?=?92%), 100 g/L (Y?=?83%), or 150 g/L (Y?=?76%). 相似文献
254.
255.
Agustín Blazquez-Martín Dr. Ester Verde-Sesto Prof. Arantxa Arbe Prof. José A. Pomposo 《Angewandte Chemie (International ed. in English)》2023,62(46):e202313502
We perform the conversion of a commodity plastic of common use in pipes, window frames, medical devices, flexible hoses, etc. like polyvinyl chloride (PVC) to single-chain nanoparticles (SCNPs). SCNPs are versatile, protein-mimetic soft nano-objects of growing interest for catalysis, sensing, and nanomedicine, among other uses. We demonstrate that the metamorphosis process -as induced through metal-free click chemistry- leads to well-defined, uniform SCNPs that are stable during storage in the solid state for months. All the conversion process (from PVC isolation to PVC-SCNPs synthesis) can be run in a green, dipolar aprotic solvent and involving, when required, a simple mixture of ethanol and water (1/1 vol.) as non-solvent. The resulting PVC-SCNPs are investigated as recyclable, metalloenzyme-mimetic catalysts for several representative Cu(II)-catalyzed organic reactions. The method could be valid for the metamorphosis and valorization of other commodity plastics in which it is feasible to install azide functional groups in their linear polymer chains. 相似文献
256.
Dr. Kumar Bhaskar Pal Dr. Ester Maria Di Tommaso Dr. A. Ken Inge Prof. Berit Olofsson 《Angewandte Chemie (International ed. in English)》2023,62(20):e202301368
We report an efficient radical-mediated C−C coupling through photoredox-catalyzed reactions of 4-alkyl-dihydropyridines (DHPs) and vinylbenziodoxol(on)es (VBX, VBO). This transition-metal-free and mild photocatalytic method has excellent functional group tolerance and affords vinylated products in good yields, with complete retention of the alkene configuration. The utility of the methodology is demonstrated by the diastereoselective synthesis of C-vinyl glycosides. Preliminary mechanistic studies suggest that the C−C bond formation is stereospecific and proceeds through a concerted radical coupling transition state. 相似文献
257.
Lucía Agud Albesa Macarena Boix García M. Leonor Pla Ferrando Salvador Cayetano Cardona Navarrete 《Mathematical Methods in the Applied Sciences》2023,46(2):2133-2164
We compare different solutions of the convection–diffusion–reaction problem with Danckwerts boundary conditions. Analytical solution is found, and method of lines and Crank–Nicholson method are described, applied, and compared for different values of Péclet and Damköhler numbers. The eigenvalues and eigenfunctions have been obtained for all the possible values of the dimensionless parameters. And the analytical expression of the concentration has been calculated with the optimum number of terms in the Fourier expansion. 相似文献
258.
Chelo Ferreira José L. López Ester Pérez Sinusía 《Studies in Applied Mathematics》2023,150(1):254-276
We consider the highly oscillatory integral for large positive values of w, , K and p positive integers with , and an entire function. The standard saddle point method is complicated and we use here a simplified version of this method introduced by López et al. We derive an asymptotic approximation of this integral when for general values of K and p in terms of elementary functions, and determine the Stokes lines. For , the asymptotic behavior of this integral may be classified in four different regions according to the even/odd character of the couple of parameters K and p; the special case requires a separate analysis. As an important application, we consider the family of canonical catastrophe integrals for large values of one of its variables, say , and bounded values of the remaining ones. This family of integrals may be written in the form for appropriate values of the parameters w, θ and the function . Then, we derive an asymptotic approximation of the family of canonical catastrophe integrals for large . The approximations are accompanied by several numerical experiments. The asymptotic formulas presented here fill up a gap in the NIST Handbook of Mathematical Functions by Olver et al. 相似文献