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Josephsohn NS Snapper ML Hoveyda AH 《Journal of the American Chemical Society》2003,125(14):4018-4019
An efficient Ag-catalyzed method for asymmetric addition of the Danishefsky diene to various aryl imines to afford cycloadducts in > or =89% ee and > or =85% isolated yield is reported. Reactions are effected with 0.1-1 mol % catalyst (4 degrees C), and the chiral ligand is readily prepared from commercially available materials, including the inexpensive i-Leu. These catalytic asymmetric cycloadditions can be carried out without the use of solvent or with undistilled THF in air. A first generation supported chiral catalyst that effectively promotes the cycloaddition reaction and can be recycled (five cycles) is described. 相似文献
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本文利用荧光光谱和园二色光谱了新开花粉蛋白的盐酸胍去折叠过程。结果显示:新开花粉蛋白的盐酸胍去折叠是一个只包含天然蛋白和变性终态的二态过程,与已经报道的天花粉蛋白的盐酸胍去折叠的过程不同。 相似文献
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Review of nanofluids for heat transfer applications 总被引:2,自引:0,他引:2
Saeid Vafaei 《中国颗粒学报》2009,7(2)
Research on nanofluids has progressed rapidly since its enhanced thermal conductivity was first repotted about a decade ago,though much controversy and inconsistency have been reported,and insufficient understanding of the formulation and mechanism of nanofluids further limits their applications.This work presents a critical review of research on heat transfer applications of nanofluids with the aim of identifying the limiting factors so as to push forward their further development. 相似文献
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Vijay NS Bhagawati-Prasad Evy De Leenheer Nadine P Keefe Lorna A Ryan Jennifer Carlring Andrew W Heath 《Journal of immune based therapies and vaccines》2010,8(1):1
Active vaccination can be effective as a post-exposure prophylaxis, but the rapidity of the immune response induced, relative
to the incubation time of the pathogen, is critical. We show here that CD40mAb conjugated to antigen induces a more rapid
specific antibody response than currently used immunological adjuvants, alum and monophosphoryl lipid A™. 相似文献
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Josephsohn NS Snapper ML Hoveyda AH 《Journal of the American Chemical Society》2004,126(12):3734-3735
An efficient catalytic and enantioselective method (up to >98% ee) for Mannich reactions between trimethylsilyl enol ethers derived from acetone and acetophenone and aryl, alkenyl, alkynyl, and alkyl imines is disclosed. A large variety of beta-amino ketones can be synthesized in the presence of 1-5 mol % AgOAc and an inexpensive and readily available amino acid-derived phosphine. All Ag-catalyzed asymmetric Mannich reactions can be run in undistilled THF and air. The o-anisyl activating groups of product amines can be removed in >70% isolated yield through a single vessel operation. The synthetic utility of the catalytic asymmetric method is illustrated by a four-pot synthesis of optically pure alkaloid (-)-sedamine. 相似文献
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[reaction: see text] A readily available iso-leucine-based phosphine ligand is used to promote Ag-catalyzed Mannich reactions between silylketene acetals and various alkynyl imines. Reactions can be effected in the presence of 5 mol % catalyst, without the need for rigorous exclusion of air, and with commercially available solvents (without purification) to afford the desired beta-alkynyl-beta-amino esters in 84-94% ee and 61-91% isolated yield. 相似文献
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Arun Kumar NS Prashanth Shivappa Adarakatti Ashoka S Pandurangappa Malingappa 《Journal of Solid State Electrochemistry》2018,22(6):1711-1719
A simple strategy has been proposed to quantify Zn2+ ions using CeO2 nanoparticle-modified glassy carbon electrode. The CeO2 nanoparticles were prepared by sucrose-nitrate decomposition method, and it was characterized by X-ray diffraction (XRD), FT-IR, TEM, and surface area analyzer. The synthesized CeO2 nanoparticles were used as modifier molecules as a thin film on glassy carbon electrode (GCE) in the trace level quantification of Zn2+ by using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) techniques. The fabricated sensor exhibited a good analytical response towards Zn2+ ions. The modified electrode showed a wide linearity in the concentration range 20–380 μg L?1 with a limit of detection 0.36 μg L?1. The proposed electrochemical sensor was successfully applied to trace level Zn2+ quantification from real sample matrices. 相似文献
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FTIR光谱法研究天花粉蛋白的热去折叠过程 总被引:4,自引:0,他引:4
本文利用FTIR光谱技术和计算机辅助解析技术(二阶导数、去卷积和曲线拟合)研究了天花粉蛋白的热诱导去折叠过程。结果表明:在25~85℃温度范围内,天花粉蛋白的热去折叠是一个不可逆的分子间聚集的过程;二级结构随温度的变化暗示了折叠中间体的存在。 相似文献
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N S Josephsohn K W Kuntz M L Snapper A H Hoveyda 《Journal of the American Chemical Society》2001,123(47):11594-11599
Kinetic, structural, and stereochemical data regarding the mechanism of Ti-catalyzed addition of cyanide to imines in the presence of Schiff base peptide ligands are disclosed. The reaction is first order in the Ti-ligand complex; kinetic studies reveal DeltaS(dagger) = -45.6 +/- 4.1 cal K(-1) mol(-1), indicating a highly organized transition structure for the turnover-limiting step of the catalytic cycle. A mechanistic model consistent with the kinetic and stereochemical data is presented, where the Ti center is coordinated to the Schiff base unit of the ligand and the AA2 moiety of the peptidic segment of the chiral ligand associates and delivers HNC to the activated bound substrate. Thus, these studies illustrate that these non-C2-symmetric catalysts likely operate in a bifunctional fashion. 相似文献
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