論文リスト

学術論文 2005

Subnanometer-Sized Gold Clusters with Dual Molecular Receptors: Synthesis and Assembly in One-Dimensional Arrangements

Y. Negishi, H. Tsunoyama, Y. Yanagimoto, and T. Tsukuda*
Chem. Lett., 34, 1638-1639 (2005).

Subnanometer-sized gold clusters protected by thiolated-β-cyclodextrin (HS-β-CD) were successfully isolated using polyacrylamide gel electrophoresis. Thermogravimetric measurements reveal that two β-CD ligands are bound to the Au clusters. One-dimensional assemblies of the β-CD-modified gold clusters are formed through binding interactions with ferrocene dimers.

Large-Scale Synthesis of Thiolated Au25 Clusters via Ligand Exchange Reactions of Phosphine-Stabilized Au11 Clusters

Y. Shichibu, Y. Negishi, T. Tsukuda*, and T. Teranishi*
J. Am. Chem. Soc. (communications), 127, 13464-13465 (2005).

Phosphine-stabilized Au11 clusters in chloroform were reacted with glutathione (GSH) in water under a nitrogen atmosphere. The resulting Au:SG clusters exhibit an optical absorption spectrum similar to that of Au25(SG)18, which was isolated as one of the major products from chemically prepared Au:SG clusters (Negishi, Y. et al. J. Am. Chem. Soc. 2005, 127, 5261). Rigorous characterization by optical spectroscopy, electrospray ionization mass spectrometry, and polyacrylamide gel electrophoresis confirms that the Au25(SG)18 clusters were selectively obtained on the sub-100-mg scale by ligand exchange reaction under aerobic conditions. The ligand exchange strategy offers a practical and convenient method of synthesizing thiolated Au25 clusters on a large scale.

Size-Specific Catalytic Activity of Polymer-Stabilized Gold Nanoclusters for Aerobic Alcohol Oxidation in Water

H. Tsunoyama, H. Sakurai, Y. Negishi, and T. Tsukuda*
J. Am. Chem. Soc. (communications), 127, 9374-9375 (2005).

Gold nanoclusters (φ=1.3 nm) stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP NCs) readily oxidize benzylic alcohols to the corresponding aldehydes and/or carboxylic acids under ambient temperature in water. Kinetic measurement has revealed that the smaller Au:PVP NCs exhibit higher catalytic activity as compared with the larger homologues and, more surprisingly, than the Pd:PVP NCs. A reaction mechanism for the alcohol oxidation catalyzed by Au:PVP NCs is proposed in which a superoxo like molecular oxygen adsorbed on small Au NCs surface abstracts hydrogen atom from the alkoxide, on the basis of the marked difference in the kinetic isotope effect and activation energy between Au:PVP and Pd:PVP NCs.

Glutathione-Protected Gold Clusters Revisited: Bridging the Gap between Gold(I)-Thiolate Complexes and Thiolate-Protected Gold Nanocrystals

Y. Negishi, K. Nobusada, and T. Tsukuda*
J. Am. Chem. Soc. (communications), 127, 5261-5270 (2005).

Small gold clusters (~1 nm) protected by molecules of a tripeptide, glutathione (GSH), were prepared by reductive decomposition of Au(I)-SG polymers at a low temperature and separated into a number of fractions by polyacrylamide gel electrophoresis (PAGE). Chemical compositions of the fractionated clusters determined previously by electrospray ionization (ESI) mass spectroscopy (Negishi, Y. et al. J. Am. Chem. Soc. 2004, 126, 6518) were reassessed by taking advantage of freshly-prepared samples, higher mass resolution and more accurate mass calibration; the nine smallest components are reassigned to Au10(SG)10, Au15(SG)13, Au18(SG)14, Au22(SG)16, Au22(SG)17, Au25(SG)18, Au29(SG)20, Au33(SG)22, and Au39(SG)24. These assignments were further confirmed by measuring the mass spectra of the isolated Au:S(h-G) clusters, where h-GSH is a homo-glutathione. It is proposed that a series of the isolated Au:SG clusters correspond to kinetically trapped intermediates of the growing Au cores. The relative abundance of the isolated clusters was correlated well with the thermodynamic stabilities against unimolecular decomposition. The electronic structures of the isolated Au:SG clusters were probed by X-ray photoelectron spectroscopy (XPS) and optical spectroscopy. The Au(4f) XPS spectra illustrate substantial electron donation from the gold cores to the GS ligands in the Au:SG clusters. The optical absorption and photoluminescence spectra indicate that the electronic structures of the Au:SG clusters are well quantized: embryos of the sp band of the bulk gold evolve remarkably depending on the numbers of the gold atoms and GS ligands. The comparison of these spectral data with those of sodium Au(I) thiomalate and 1.8 nm Au:SG nanocrystals (NCs) reveals that the Au:SG clusters constitute a distinct class of binary system which lies between the Au(I)-thiolated complexes and thiolate-protected Au NCs.

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