Topic
Acetal
About: Acetal is a research topic. Over the lifetime, 10600 publications have been published within this topic receiving 137215 citations. The topic is also known as: acetal.
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TL;DR: This mechanistic proposal is supported by a kinetic isotope effect of 1.4(5) for the hydrosilation of acetophenone, the observation that B(C(6)F(5))(3) catalyzes H/D and H/H scrambling in silanes in the absence of substrate, computational investigations, the synthesis of models for proposed intermediates, and other isotope labeling and crossover experiments.
Abstract: The strong organoborane Lewis acid B(C6F5)3 catalyzes the hydrosilation (using R3SiH) of aromatic and aliphatic carbonyl functions at convenient rates with loadings of 1−4%. For aldehydes and ketones, the product silyl ethers are isolated in 75−96% yield; for esters, the aldehydes produced upon workup of the silyl acetal products can be obtained in 45−70% yield. Extensive mechanistic studies point to an unusual silane activation mechanism rather than one involving borane activation of the carbonyl function. Quantitative kinetic studies show that the least basic substrates are hydrosilated at the fastest rates; furthermore, increased concentrations of substrate have an inhibitory effect on the observed reaction rate. Paradoxically, the most basic substrates are reduced selectively, albeit at a slower rate, in competition experiments. The borane thus must dissociate from the carbonyl to activate the silane via hydride abstraction; the incipient silylium species then coordinates the most basic function, whic...
610 citations
533 citations
TL;DR: Lac-conjugated gold nanoparticles exhibited selective aggregation when exposed to Recinus communis agglutinin (RCA120), a bivalent lectin specifically recognizing the β-d-galactose residue, inducing significant changes in the absorption spectrum with concomitant visible color change from pinkish-red to purple.
Abstract: Gold nanoparticles (1−10 nm size range) were prepared with an appreciably narrow size distribution by in situ reduction of HAuCl4 in the presence of heterobifunctional poly(ethylene glycol) (PEG) derivatives containing both mercapto and acetal groups (α-acetal-ω-mercapto-PEG). The α-acetal-PEG layers formed on gold nanoparticles impart appreciable stability to the nanoparticles in aqueous solutions with elevated ionic strength and also in serum-containing medium. The PEG acetal terminal group was converted to aldehyde by gentle acid treatment, followed by the reaction with p-aminophenyl-β-d- lactopyranoside (Lac) in the presence of (CH3)2NHBH3. Lac-conjugated gold nanoparticles exhibited selective aggregation when exposed to Recinus communis agglutinin (RCA120), a bivalent lectin specifically recognizing the β-d-galactose residue, inducing significant changes in the absorption spectrum with concomitant visible color change from pinkish-red to purple. Aggregation of the Lac-functionalized gold nanoparticle...
501 citations
447 citations
TL;DR: In this article, the stereochemistry of many alternating (1,3,5...) polyol chains can be determined by preparation and 13C NMR analysis of two frame-shifted polyacetonide derivatives.
446 citations