Influence of the support and the size of gold clusters on catalytic activity for glucose oxidation.

Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo 192-0397, Japan.
Angewandte Chemie International Edition (Impact Factor: 13.73). 11/2008; 47(48):9265-8. DOI: 10.1002/anie.200802845
Source: PubMed
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    ABSTRACT: In recent years supported gold nanoparticles have emerged as efficient catalysts with considerable synthetic potential for liquid-phase oxidation reactions based on molecular oxygen as oxidant. Here we critically review the most attractive applications related to the selective oxidation of functional groups containing O, N, or Si heteroatoms. The reactions include the oxidation of alcohols, aldehydes, and organosilanes; the diverse transformations of amines; benzylic oxidations; and some one-pot multistep reactions starting with alcohol or amine oxidation. In complex liquid-phase transformations relying on bifunctional catalysis, appropriate choice of the support is frequently more important than the size of the gold particles. In some oxidation reactions gold nanoparticles outperform the traditional platinum-group metal catalysts, but the latest results indicate the superiority of bimetallic particles containing gold and platinum, palladium, or rhodium. The environmentally benign nature of the transformations is discussed.
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    ABSTRACT: Noble metal nanoparticles have attracted much interest in the heterogeneous catalysis. Particularly, efficient manipulation of the responsive catalytic properties of the metal nanoparticles is an interesting topic. In this work, a simple and efficient strategy is developed to regulate the pH-responsive catalytic activities of glucose oxidase (GOx)-mimicking gold nanoparticles (AuNPs). Four DNA strands (regulating strands) that differ slightly in sequences are used to interact non-covalently with citrate-capped AuNPs, resulting in markedly distinct pH-dependent catalytic behavior of AuNPs. This is ascribed to the characteristic pH-induced conformational change of the DNA strands that leads to the different adsorption capability to the NPs surface, as demonstrated by pH-CD profiles of the respective DNA molecules. The pH-dependent catalysis of AuNPs is also encoded with structural information of the double-stranded DNA (including regulating strands and their complementary strands) that has conformation resistant or responsive to pH change. As a result, the catalysis can be programmed into an AND gate, a XNOR gate or a NOT gate, using pH and complementary strand as the inputs, the nanoparticle activity as the output and the regulating strands as the programs. This work can be expanded by engineering the catalytic behavior of noble metal nanoparticles to respond smartly to a variety of environmental stimuli, such as metal ions or light wavelengths. These results may provide insight into understanding ligand-regulated nanometallic catalysis.
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    ABSTRACT: We have developed a quantitative particle size analytical method at the single atomic level employing electron microscopy and image processing for the investigation of supported metal catalysts. In the present study, a supported gold (Au) catalyst containing sub-nano clusters and individual atoms was globally observed by high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) using spherical aberration (Cs)-corrected TEM. To fully extract structural information of the Au clusters and individual atoms from the HAADF-STEM images, a morphological image-processing operation was applied. The resulting mean particle size was in good agreement with particle sizes estimated from average information provided by X-ray absorption fine structure analysis. It is demonstrated that the present HAADF-STEM image analysis gives a quantitative particle size distribution measurement of supported Au clusters and individual atoms.
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