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Thermal and photochemical reactivity of oxygen atoms on gold nanocluster surfaces
T. Matsumoto, P. Nickut, H. Tsunoyama, K.
Watanabe, T. Tsukuda, K. Al-Shamery, Y. Matsumoto*
Surf. Sci., 601, 5226-5231 (2007).
Deposition and Fabrication of Alkanethiolate Gold Nanocluster Films on TiO2(110) and the Effects of Plasma Etching
T. Matsumoto, P. Nickut, T. Sawada, H.
Tsunoyama, K. Watanabe, T. Tsukuda, K. Al-Shamery, Y. Matsumoto*
Surf. Sci., 601, 5121-5126 (2007).
Thermosensitive Gold Nanoclusters Stabilized by Well-Defined Vinyl Ether Star Polymers: Reusable and Durable Catalysts for Aerobic Alcohol Oxidation
S. Kanaoka, N. Yagi, Y. Fukuyama, S. Aoshima,* H.
Tsunoyama, T. Tsukuda, and H. Sakurai
J. Am. Chem. Soc. (communications), 129, 12060-12061 (2007).
Au nanoclusters of less than 4 nm with a narrow size distribution were prepared and supported in thermosensitive vinyl ether star polymers obtained by living cationic polymerization. The thermosensitivity of the star polymers permitted easy separation of the clusters from the reaction mixture without any negative aggregation. Thus, the Au clusters could be recovered for reuse several times to induce alcohol oxidation with similar reactivity in each run.
Origin of Magic Stability of Thiolated Gold Clusters: A Case Study on Au25(SC6H13)18
Y. Negishi, N. K. Chaki, Y. Shichibu, R. L.
Whetten, and T. Tsukuda*
J. Am. Chem. Soc. (communications), 129, 11322-11323 (2007).
The present work aims to test the validity of the electronic shell model for Au25(SC6H13)18 by monitoring the charge state of the Au:S core and thereby to elucidate the origin of magic stability. Electrospray ionization mass spectrometry revealed that the Schiffrin method yields [Au25(SC6H13)18]x with a distribution of charge states, which shifts toward negative values with reduction time. The stable ions [Au25(SC6H13)18]1+ and [Au25(SC6H13)18]1− can be synthesized by chemical oxidation and reduction of [Au25(SC6H13)18]0, respectively. These findings lead us to conclude that electronic shell closing is not a crucial factor for the high stability of [Au25(SC6H13)18]x (x = 1-, 0, 1+). We ascribe magic stability to the core-in-cage structure predicted theoretically.
Synthesis of Normal and Inverted Gold-Silver Core-Shell Architectures in β-Cyclodextrin and Their Applications in SERS
S. Pande, S. K. Ghosh, S. Praharaj, S. Panigrahi,
S. Basu, S. Jana, A. Pal, T. Tsukuda, and T. Pal*
J. Phys. Chem. C, 111, 10806-10813 (2007).
Electronic Structure of Dendrimer-encapsulated Au Nanocluster
M. Imamura,* T. Miyashita, A. Tanaka, H. Yasuda, Y. Negishi, T. Tsukuda
Eur. Phys. J. D, 43, 233-236 (2007).
Thiolate-Induced Structural Reconstruction of Gold Clusters Probed by 197Au Mössbauer Spectroscopy
K. Ikeda, Y. Kobayashi, Y. Negishi, M. Seto, T.
Iwasa, K. Nobusada, T. Tsukuda,* and N. Kojima*
J. Am. Chem. Soc. (communications), 129, 7230-7231 (2007).
We investigated the structures of a series of glutathionate-protected gold clusters, Aun(SG)m with n=10-45, using 197Au Mössbauer spectroscopy, which allows us to probe the local environment of the Au sites via isomer shift (IS) and quadrupole splitting (QS). The spectral analysis, with the help of recent theoretical results on methanethiolated gold clusters, revealed that Au-SG oligomeric rings are preferentially formed around the Au core. Specifically, a core-in-cage structural motif theoretically predicted for [Au25(SCH3)18]+ explains the Mössbauer spectra of Au25(SG)18 fairly well and thereby explains the high stability against the core etching reaction. The positive IS and QS values for the Au cores of Aun(SG)m suggest a nontrivial effect of thiolate ligation on the electronic structure of the underlying gold clusters
Biicosahedral Gold Clusters [Au25(PPh3)10(SCnH2n+1)5Cl2]2+ (n=2-18): a Stepping Stone to Cluster-Assembled Materials
Y. Shichibu, Y. Negishi, T. Watanabe, N. K. Chaki,
H. Kawaguchi, and T. Tsukuda*
J. Phys. Chem. C (Letters), 111, 7845-7847 (2007).
The chemical reaction between [Au11(PPh3)8Cl2]+ and n-alkanethiol CnH2n+1SH (n=2, 8, 10, 12, 14, 16, 18) serendipitously yielded stable Au25 cluster compounds with the formula, [Au25(PPh3)10(SCnH2n+1)5Cl2]2+. Single-crystal X-ray structural analysis of [Au25(PPh3)10(SCnH2n+1)5Cl2](SbF6)2 revealed that the Au25 core is constructed by bridging two icosahedral Au13 clusters with thiolates sharing a vertex atom. Optical absorption spectroscopy showed that coupling between the Au13 building blocks gives rise to new electronic levels in addition to those of the Au13 constituents.
Lewis Acid Character of Zero-valent Gold Nanoclusters under Aerobic Conditions: Intramolecular Hydroalkoxylation of Alkenes
I. Kamiya, H. Tsunoyama, T. Tsukuda, and H. Sakurai*
Chem. Lett., 36, 646-647 (2007).
Gold nanoclusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP NCs, φ = 1.3 nm) behave as Lewis acid catalyst in aqueous media under aerobic conditions, to promote the intramolecular hydroalkoxylation of unactivated alkenes. Molecular oxygen generates a reaction center having the Lewis acidic character on the surface of Au NCs in which constituent gold atoms are formally in zero-valence state.
Effect of Ag-Doping on the Catalytic Activity of Polymer-Stabilized Au Clusters in Aerobic Oxidation of Alcohol
N. K. Chaki, H. Tsunoyama, Y. Negishi, H. Sakurai,
J. Phys. Chem. C (Letters), 111, 4885-4888 (2007).
A set of nearly monodisperse Au-Ag alloy clusters (size range 1.6 to 2.2 nm) with various Ag content (5-30%) was prepared by the co-reduction method in the presence of poly(N-vinyl-2-pyrrolidone) (PVP). The catalytic activities of the Au-Ag:PVP clusters were investigated for aerobic oxidation of p-hydroxybenzyl alcohol as a model reaction to understand the effect of Ag on the catalytic activity of Au clusters. It was found that the rate constants per unit surface area for Au-Ag:PVP clusters with small Ag content (< 10%) were larger than those of monometallic Au:PVP clusters of comparable size. The enhancement of the catalytic activity by Ag doping is discussed in light of the electronic structure of the Au-Ag cores probed by X-ray photoelectron spectroscopy. The present results indicate that the partial anionic character of the Au core is important for the aerobic oxidation reactions of Au:PVP clusters.
Extremely High Stability of Glutathionate-Protected Au25 Clusters Against Core Etching
Y. Shichibu, Y. Negishi, H. Tsunoyama, M. Kanehara,
T. Teranishi, and T. Tsukuda*
Small(communications), 3, 835-839 (2007).
The core etching reaction by free glutathione (GSH) was studied for size-selected, glutathionate-protected Aun(SG)m clusters with (n, m) = (10, 10), (15, 13), (18, 14), (22, 16), (25, 18), (29, 20), (33, 22), (39, 24). Only the Au25(SG)18 clusters remained unetched, whereas the Au25(SG)18 clusters with n<25 and n>25 were transformed into a Au(I):SG complex and stable Au25:SG, respectively. This remarkable dependence of size on etching reactivity opens up a new approach for the selective synthesis of Au25:SR on a large scale.
Formation of Alkanethiolate-Protected Gold Clusters with Unprecedented Core Sizes in the Thiolation of Polymer-Stabilized Gold Clusters
H. Tsunoyama, P. Nickut, Y. Negishi, K. Al-Shamery,
Y. Matsumoto, T. Tsukuda*
J. Phys. Chem. C, 111, 4153-4158 (2007).
Octadecanethiolate-protected gold (Au:SC18) clusters were prepared by the reaction of C18SH and Au clusters stabilized by poly(N-vinyl-2-pyrrolidone) (PVP). Four samples were fractionated by recycling size exclusion chromatography (SEC) of the as-prepared Au:SC18 clusters, and their core sizes were determined to be 8, 11, 21, 26 kDa by using laser desorption ionization mass spectrometry. Unexpectedly, the sequence of these core sizes is different from that (8, 14, 22, and 29 kDa) obtained by conventional reduction of Au(I)SC18 polymers, which is governed by kinetic factors. The present finding shows that the Au:SR (R=organic group) clusters with a high tolerance to thiol etching can be systematically synthesized by first populating precursory Au clusters in a PVP matrix with subsequent thiolation of the preformed Au clusters.
Synthetic Application of PVP-stabilized Au Nanocluster Catalyst to Aerobic Oxidation of Alcohols in Aqueous Solution under Ambient Conditions
H. Tsunoyama, T. Tsukuda, H. Sakurai*
Chem. Lett., 36, 212-213 (2007).
Gold nanoclusters (φ=1.3 nm) stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) were found to show a high catalytic activity toward the aerobic oxidation of alcohols. Various kinds of primary and secondary alcohols were converted to the corresponding carboxylic acids and ketones, respectively, in basic aqueous media at 300-360 K under air.
Oxidative Homo-coupling of Potassium Aryltrifluoroborates Catalyzed by Gold Nanocluster under Aerobic Conditions
H. Sakurai*, H. Tsunoyama, and T. Tsukuda
J. Organomet. Chem., 692, 368-374 (2007).
Gold(0) nanoclusters, stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP-n), catalyzed the oxidative homo-coupling reaction of potassium aryltrifluoroborate in water under air. Catalytic activity was dependent on the size of clusters. The smallest cluster Au:PVP-1 (dav = 1.3 ± 0.3 nm) gave the highest activity, while Au:PVP-7 (dav = 9.5 ± 1.0 nm) did not catalyze the homo-coupling. The catalyst was reusable for several times. Positively charged surface on the Au cluster, generated by the adsorption of molecular oxygen, would be the active site of the catalysis.