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MALDI Mass Analysis of 11 kDa Gold Clusters Protected by Octadecanethiolate Ligands
Risako Tsunoyama, Hironori Tsunoyama, Panvika
Pannopard, Jumras Limtrakul, and Tatsuya Tsukuda*
J. Phys. Chem. C, 114 (38), 16004-16009 (2010).
We previously reported the isolation of octadecanethiolate-protected Au (Au:SC18H37) clusters having a core mass of 11 kDa from the crude Au:SC18H37 samples obtained in the reaction between octadecanethiol (C18H37SH) and poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized Au clusters. This stable Au:SC18H37 compound was assigned to be Au55(SCnH2n+1)32 by destructive mass spectrometry and thermogravimetry (TG) performed in the framework of the classical structure model, in which the thiolates are bound to the surface of a magic Au55 core. In the present study, the molecular formula of the Au:SC18H37 (11 kDa) cluster was reassessed by non-destructive matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), and it was confirmed that the Au:SC18H37 (11 kDa) cluster is a mixture of Au54(SC18H37)30 and Au55(SC18H37)31. On the basis of our present understanding of the structures of other stable Au:SR clusters, we proposed that Au54(SC18H37)30 and Au55(SC18H37)31 have a structural motif comprising a Au37 cluster core that is completely protected by -SR-[Au(I)-SR-]x oligomers (x = 1 and 2). The nonformation of the Au:SR (11 kDa) cluster during the conventional chemical reduction of Au(I)-SR oligomers is ascribed to the kinetics of Au:SR formation.
Chirality and Electronic Structure of the Thiolate-Protected Au38 Nanocluster
Olga Lopez-Acevedo, Hironori Tsunoyama, Tatsuya Tsukuda, Hannu Häkkinen and Christine M. Aikens*
J. Am. Chem. Soc., 132 (23), 8210-8218 (2010).
Structural, electronic, and optical properties of the thiolate-protected Au38(SR)24 cluster are studied by density-functional theory computations (R = CH3 and R = C6H13) and by powder X-ray crystallography (R = C12H25). A low-energy structure which can be written as Au23@(Au(SR)2)3(Au2(SR)3)6 having a bi-icosahedral core and a chiral arrangement of the protecting gold-thiolate Aux(SR)y units yields an excellent match between the computed (for R = C6H13) and measured (for R = C12H25) powder X-ray diffraction function. We interpret in detail the electronic structure of the Au23 core by using a particle-in-a-cylinder model. Although the alkane thiolate ligands are achiral, the chiral structure of the ligand layer yields strong circular dichroism (CD) in the excitations below 2.2 eV for Au38(SCH3)24. Our calculated CD spectrum is in quantitative agreement with the previously measured low-energy CD signal of glutathione-protected Au38(SG)24. Our study demonstrates a new mechanism for the strong chiral response of thiolate-protected gold clusters with achiral metal cores and ligands.
Fluorescent Fe(II) Metallo-supramolecular Polymers: Metal-ion-directed Self-assembly of New Bisterpyridines Containing Triethylene Glycol Chains
Ravindra R Pal, Masayoshi Higuchi*, Yuichi Negishi,
Tatsuya Tsukuda and Dirk G Kurth
POLYMER JOURNAL, 42, 336-341 (2010).
We synthesized new ditopic bisterpyridine (BTPY) ligands (L2 and L4) containing triethylene glycol (TEG) chains at the ortho-position of the peripheral pyridine ring and succeeded in obtaining fluorescent Fe(II) metallo-supramolecular polyelectrolytes (FeL2-MEPE and FeL4-MEPE) through complexation of Fe(II) ions with L2 and L4, respectively. The Fe(II) ion is known to quench fluorescence, but FeL2-MEPE shows a retention of quantum yield that is nearly threefold higher than that of the unsubstituted analog (FeL3-MEPE). We investigated the substituent effects of TEG chains on metallo-supramolecular polymers and their fluorescent and electrochemical properties in detail.
Size Effect of Silica-supported Gold Clusters in the Microwave-assisted Oxidation of Benzyl Alcohol with H2O2
Yongmei Liu, Hironori Tsunoyama, Tomoki Akita, and
Chem. Lett., 39, 159-161 (2010).
Gold clusters with average diameters of 0.8, 1.5, and 1.9 nm were prepared on mesoporous silica (SBA-15) by controlling the calcination time of an Au11(PPh3)7Cl3/SBA-15 composite. It was found that the catalytic activity for benzyl alcohol oxidation decreased monotonically with the increase in size.
Efficient and Selective Epoxidation of Styrene with TBHP Catalyzed by Au25 Clusters on Hydroxyapatite
Yongmei Liu, Hironori Tsunoyama, Tomoki Akita, and Tatsuya Tsukuda*
Chem. Commun., 46, 550-552 (2010).
Au25 clusters supported on hydroxyapatite oxidized styrene in toluene with 100% conversion and 92% selectivity to the epoxide, under optimum conditions and using anhydrous tert-butyl hydroperoxide (TBHP) as an oxidant.