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排序方式: 共有72条查询结果,搜索用时 31 毫秒
1.
Umar Farid Maria Luisa Aiello Prof. Stephen J. Connon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(43):10074-10079
A new catalytic methodology was developed to promote an efficient one-pot kinetic resolution of racemic aldehydes with selectivity (s*) of up to 91 (99:1 d.r., >99 % ee) in a cycloaddition reaction with enolizable anhydrides to afford dihydroisocoumarin products (a core prevalent in natural products and molecules of medicinal interest) containing three contiguous stereocentres. 相似文献
2.
The self-assembly and bioactivity of the peptide–polymer conjugate DGRFFF–PEG3000 containing the RGD cell adhesion motif has been examined, in aqueous solution. The conjugate is designed to be amphiphilic by incorporation of three hydrophobic phenylalanine residues as well as the RGD unit and a short poly(ethylene glycol) (PEG) chain of molar mass 3000 kg mol−1. Above a critical aggregation concentration, determined by fluorescence measurements, signals of β-sheet structure are revealed by spectroscopic measurements, as well as X-ray diffraction. At high concentration, a self-assembled fibril nanostructure is revealed by electron microscopy. The fibrils are observed despite PEG crystallization which occurs on drying. This suggests that DGRFFF has an aggregation tendency that is sufficiently strong not to be prevented by PEG crystallization. The adhesion, viability and proliferation of human corneal fibroblasts was examined for films of the conjugate on tissue culture plates (TCPs) as well as low attachment plates. On TCP, DGRFFF–PEG3000 films prepared at sufficiently low concentration are viable, and cell proliferation is observed. However, on low attachment surfaces, neither cell adhesion nor proliferation was observed, indicating that the RGD motif was not available to enhance cell adhesion. This was ascribed to the core–shell architecture of the self-assembled fibrils with a peptide core surrounded by a PEG shell which hinders access to the RGD unit. 相似文献
3.
Unstrained cycloalkenes undergo ruthenium-catalysed ring opening-cross metathesis reactions with simple alpha, beta-unsaturated carbonyl compounds under mild conditions. 相似文献
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The diffusion coefficient for Fe in Y from Mössbauer experiments is several orders of magnitude lower than from bulk diffusion measurements. This can be explained by a combination substitution-interstitial diffusion mechanism. 相似文献
6.
This paper presents an experimental study examining the behavior of a single droplet displaced radially from an infinite droplet stream. The displaced droplet behaves as a tracking particle that responds to the velocity profile generated by the droplet stream. This profile changes with droplet spacing. The measurements show that the velocity field of the infinite stream extends more than 15 droplet diameters from the stream axis, with the largest gradients residing within 5 diameters. The effects of drag and electrostatic forces are quantified to demonstrate that lift forces contribute to the displaced droplets's motion.The monetary support for this work was provided through a NSF Presidential Young and Investigator grant. The authors also recognize the laboratory efforts of Dameon Wood in setting up the charge deflection apparatus. 相似文献
7.
Bifunctional (thio)urea-based cinchona alkaloid derivatives have been shown to promote highly efficient enantioselective desymmetrization reactions of meso anhydrides. The most selective of these catalysts is capable of the enantioselective methanolysis of succinic and glutaric anhydride derivatives to form hemiester products with >90% yield and enantiomeric excess at 1 mol % loading and ambient temperature. 相似文献
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A new class of bifunctional organocatalyst promotes the chemoselective reduction of diketone electrophiles at catalytic loadings in the presence of an inorganic co-reductant. 相似文献
10.
In the presence of a highly efficient novel bifunctional organocatalyst at low loadings under mild conditions, enolizable homophthalic anhydrides can be added to a range of aromatic and aliphatic aldehydes to give dihydroisocoumarins, with excellent yields and diastereo- and enantiocontrol (up to 99% ee). 相似文献