論文リスト

学術論文 2013

Formation of a Pd@Au12 Superatomic Core in Au24Pd1(SC12H25)18  Probed by 197Au Mössbauer and Pd K-edge EXAFS Spectroscopy

Y. Negishi, W. Kurashige, Y. Kobayashi, S. Yamazoe, N. Kojima, M. Seto, T. Tsukuda*
J. Phys. Chem. Lett., 4, 3579-3584 (2013).

Recently, a variety of thiolated gold alloy clusters with well-defined compositions have been synthesized and the effect of doping on their properties and stability has been studied extensively. We examined the occupation site of the Pd dopant within Au24Pd1(SC12H25)18 by probing complementarily the local environments of Au and Pd elements using 197Au Mössbauer and Pd K-edge EXAFS spectroscopy, respectively. The experimental results suggest that the doped single Pd atom is preferentially located at the center of Au24Pd1(SC12H25)18 to form the superatomic Pd@Au12 core, which supports recent theoretical predictions. These spectroscopic measurements also clarified intracluster electron transfer from the Pd atom to the surrounding Au atoms.

Selenolate-protected Au38 Nanoclusters: Isolation and Structural Characterization

W. Kurashige, S. Yamazoe, K. Kanehira, T. Tsukuda, Y. Negishi
J. Phys. Chem. Lett., 4, 3181-3185 (2013).

We report the isolation and structural characterization of dodecaneselenolate-protected Au38 clusters (Au38(SeC12H25)24). These clusters were synthesized via the reaction of phenylethanethiolate-protected Au38 clusters (Au38(SC2H4Ph)24) with didodecyldiselenide ((C12H25Se)2). Characterization of the product by mass spectrometry and thermogravimetric analysis confirmed that highly pure Au38(SeC12H25)24 had been obtained. The electronic and geometrical structures, bonding characteristics, and stability of the Au38(SeC12H25)24 clusters were assessed using extended X-ray fine structure and X-ray absorption near edge structure measurements, optical absorption spectroscopy, electrochemical measurements, and stability testing.

Direct Atomic Imaging and Density Functional Theory Study of Au24Pd1 Cluster Catalyst

A. Bruma, F. R. Negreiros, S. Xie, T. Tsukuda, R. L. Johnston, A. Fortunelli, Z. Y. Li
Nanoscale, 5, 9620-9625 (2013). Selected as front cover

In this study we report a direct, atomic-resolution imaging of calcined Au24Pd1 clusters supported on multiwall carbon nanotubes by employing aberration-corrected scanning transmission electron microscopy. Using gold atoms as mass standards, we confirm the cluster size to be 25±2, in agreement with the Au24Pd1(SR)18 precursor used in the synthesis. Concurrently, a Density-Functional/Basin-Hopping computational algorithm is employed to locate the low-energy configurations of free Au24Pd1 cluster. Cage structures surrounding a single core atom are found to be favored, with a slight preference for Pd to occupy the core site. The cluster shows a tendency toward elongated arrangements, consistent with experimental data. The degree of electron transfer from the Pd dopant to Au is quantified through a Löwdin charge analysis, suggesting that Pd may act as an electron promoter to the surrounding Au atoms whenthey are involved in catalytic reactions.


Binding Motif of Terminal Alkynes on Gold Clusters

P. Maity, S. Takano, S. Yamazoe, T. Wakabayashi, T. Tsukuda*
J. Am. Chem. Soc. 135, 9450-9457 (2013).

Gold clusters protected by terminal alkynes (1–octyne (OC–H), phenyl acetylene (PA–H) and 9–ethenyl phenanthrene (EPT–H)) were prepared by the ligand exchange of small (diameter <2 nm) Au clusters stabilized by polyvinylpyrrolidone. The bonding motif of these alkynes on Au clusters was investigated using various spectroscopic methods. FTIR and Raman spectroscopy revealed that alkyenic hydrogen is lost during the ligand exchange and that the C≡C bond of the alkynyl group is weakened upon attachment to the Au clusters. Acidification of the water phase after the ligand exchange indicated that the ligation of alkynyl groups to the Au clusters proceeds via deprotonation of the alkynes. A series of precisely defined Au clusters, Au34(PA)16, Au54(PA)26, Au30(EPT)13, Au35(EPT)18, and Au41-43(EPT)21-23, were synthesized and characterized in detail to obtain further insight into the interfacial structures. Careful mass analysis confirmed the ligation of the alkynes in the dehydrogenated form. An upright configuration of the alkynes on Au clusters was suggested from the Au–to–alkyne ratios and photoluminescence from the excimer of the EPT ligands. EXAFS analysis implied that alkynyl carbon is bound to bridged or hollow sites on the cluster surface.

Selective Hydrogenation of Nitroaromatics by Colloidal Iridium Nanoparticles

Md. J. Sharif, P. Maity, S. Yamazoe, T. Tsukuda*
Chem. Lett., 42, 1023-1025 (2013).  Editor's choice

Poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized iridium nanoparticles (Ir NPs) showed high chemoselectivity for hydrogenation of nitroaromatics having –CHO, >C=O, –CN and –Cl functional groups to afford the corresponding aniline compounds under atmospheric hydrogen at room temperature in aqueous/organic biphasic medium.

Structural Characterization of Unprecedented Al14O and Al15O2: Photoelectron Spectroscopy and Density Functional Calculations

T. Watanabe, T. Tsukuda*
J. Phys. Chem. C, 117, 6664-6668 (2013).

New aluminum oxide clusters Al14O and Al15O2 were observed unprecedentedly in the gas-phase reaction of Aln and O2. Photoelectron spectroscopic measurements and density functional calculations indicated that Al14O and Al15O2 are composed of an icosahedral Al13 moiety bonded by one and two OAl unit(s), respectively. The preferential formation of Al14O and Al15O2 is explained in terms of the high stability associated with the Al13 moiety and efficient collisional trapping as intermediates of oxidative etching reactions.

Correction to "Dendrimer Encapsulated Copper Cluster as a Chemoselective and Regenerable Hydrogenation Catalyst"

P. Maity, S. Yamazoe, T. Tsukuda*
ACS Catal., 3, 554 (2013).

Dendrimer Encapsulated Copper Cluster as a Chemoselective and Regenerable Hydrogenation Catalyst

P. Maity, S. Yamazoe, T. Tsukuda*
ACS Catal., 3, 182-185 (2013).

A copper cluster encapsulated within a poly(amidoamine) dendrimer with hydroxyl surface groups (PAMAM-OH) acted as a chemoselective catalyst for hydrogenation of carbonyl and olefin groups in water. The activity was dependent on the molar ratio of Cu2+ and PAMAM-OH used in the synthesis which was ascribed to the size specific chemical properties of Cu clusters. The dendrimer encapsulated Cu cluster was oxidized into Cu2+ ions under aerobic condition, but could be regenerated by reduction with NaBH4 for catalytic application.

Enhanced Magnetization in Highly-Crystalline and Atomically-Mixed bcc Fe-Co Nanoalloys Prepared by Hydrogen Reduction of Oxide Composites

Md Jafar Sharif, M. Yamauchi,* S. Toh, S. Matsumura, S. Noro, K. Kato, M. Takata, T. Tsukuda
Nanoscale, 5, 1489-1493 (2013)

FexCo100-x nanoalloys (NAs) with 20≤x≤80 were prepared by hydrogen reduction of Fe-Co oxide nano-composites, which were composed of mixed phases (or domains) of Fe2O3 and CoO. In situ X-ray diffraction (XRD) measurements using synchrotron radiation clearly showed development of solid-solution Fe-Co phase by hydrogen reduction from the oxide composites. High–resolution transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM and powder XRD revealed that Fe-Co NAs form a single crystal structure and the two elements are mixed homogeneously. The saturation magnetization depends on the size and the metal composition and shows the highest value (250 emu/g) for the Fe70Co30 NA in the size range of 30-55 nm, which is comparable to than that of the Fe70Co30 bulk alloy (245 emu/g). This high magnetization was attributable to high crystallinity and homogeneous mixing of constituent atom, which are attained by thermal treatment of oxide phases under hydrogen atmosphere.

Structural Evolution of Glutathionate-protected Gold Clusters Studied by Means of 197Au Mössbauer Spectroscopy

N. Kojima,* Y. Kobayashi, Y. Negishi, M. Seto, T. Tsukuda

Hyperfine Interactions, 217, 91-98 (2013).

197Au Mössbauer spectra of a series of glutathionate-protected gold clusters, Aun(SG)m, with n = 10 – ~55 were re-analyzed to understand the structure evolution behavior. The numbers of gold atoms coordinated by different numbers (0, 1, and 2) of the GS ligands were successfully determined by assuming individual isomer shifts and quadrupole splittings for the three sites in Au25(SG)18 (Tsukuda, T., Negishi, Y., Kobayashi, Y., Kojima, N.: Chem. Lett. 40, 1292 (2011)) The analysis revealed the drastic structural evolution of Aun(SG)m in the range of n = 10 – ~55.

Production of Oxidation-Resistant Copper Nanoparticles on Carbon Nanotubes by Photoreduction

N. Nishida, A. Miyashita, T. Tsukuda, H. Tanaka*
Chem. Lett., 42, 168-170 (2013).

Copper nanoparticles (Cu NPs) were produced by photoreduction of a mixture of copper acetate solution and carbon nanotubes (CNTs) at room temperature. The diameter of NPs could be controlled by the photoirradiation time. HRTEM and XRD measurements revealed that the NPs were composed of a metallic Cu core and a Cu2O shell which act as a passive layer.


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