Tomoji Ozeki
Tokyo Institute of Technology
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Featured researches published by Tomoji Ozeki.
Science | 2010
Qing-Fu Sun; Junji Iwasa; Daichi Ogawa; Yoshitaka Ishido; Sota Sato; Tomoji Ozeki; Yoshihisa Sei; Kentaro Yamaguchi; Makoto Fujita
Two Molecular Spheres Viruses form highly symmetrical coat structures, capsids, through the assembly of multiple lower-symmetry protein precursors. Recently, chemists have sought to emulate this process on a smaller scale, relying on the assembly of organic molecular struts and metal ions, rather than proteins. Sun et al. (p. 1144, published online 29 April; see the Perspective by Stefankiewicz and Sanders) now demonstrate that a mixture of palladium ions and V-shaped bridging ligands can self-assemble into a hollow, nearly spherical polyhedron with 24 vertices and a central diameter of 4 nanometers. The assembly process was highly sensitive to the ligand angle; a subtle average decrease generated instead a smaller 12-vertex product. A slight change in ligand geometry determines whether a 12- or 24-vertex polyhedron will form. Self-assembly is a powerful technique for the bottom-up construction of discrete, well-defined nanoscale structures. Large multicomponent systems (with more than 50 components) offer mechanistic insights into biological assembly but present daunting synthetic challenges. Here we report the self-assembly of giant M24L48 coordination spheres from 24 palladium ions (M) and 48 curved bridging ligands (L). The structure of this multicomponent system is highly sensitive to the geometry of the bent ligands. Even a slight change in the ligand bend angle critically switches the final structure observed across the entire ensemble of building blocks between M24L48 and M12L24 coordination spheres. The amplification of this small initial difference into an incommensurable difference in the resultant structures is a key mark of emergent behavior.
Science | 2006
Sota Sato; Junya Iida; Kosuke Suzuki; Masaki Kawano; Tomoji Ozeki; Makoto Fujita
The distinct properties of fluorous phases are practically useful for separation, purification, and reaction control in organic synthesis. Here, we report the formation of a liquid-like fluorous droplet, composed of 24 perfluoroalkyl chains confined in the interior of a 5-nanometer-sized, roughly spherical shell that spontaneously assembled in solution from 12 palladium ions and 24 bridging ligands. Crystallographic analysis confirmed the rigid shell framework and amorphous interior. Perfluoroalkanes can dissolve in this well-defined fluorous phase, whereas they can hardly dissolve in a surrounding polar organic solution, and their solubility (up to ∼eight perfluoroalkane molecules per spherical complex) can be finely controlled by tuning the length of perfluoroalkyl chains tethered to the shell.
Journal of the American Chemical Society | 2008
Sayaka Shishido; Tomoji Ozeki
The pH dependence of the structures of {Mo(154-x)} mixed-valence oxomolybdate giant clusters were investigated by synchrotron X-ray diffraction of systematically prepared crystals containing [Mo138O410(OH)20(OH2)46](40-) (1), [Mo138O410(OH)20(OH2)38](40-) (2), [Mo138O406(OH)16(OH2)46](28-) (3), [Mo142O400(OH)52(OH2)38](28-) (4), [Mo142O432(OH2)58](40-) (5), [Mo148O436(OH)15(OH2)56](27-) (6), [Mo150O451(OH)5(OH2)61](35-) (7), and both [Mo150O442.5(OH)11.5(OH2)64](24.5-) and [Mo152O446(OH)20(OH2)54](28-) (8). Crystals 1, 4, and 5 contain discrete clusters while intercluster Mo-O-Mo bonds connect the clusters into chains in crystal 7, into two-dimensional networks in crystals 2 and 3, and into a three-dimensional framework structure in crystal 6. Crystal 8 contains both discrete and linearly catenated clusters: discrete {Mo150} are located between the chains of {Mo152}. Direct correlation was observed between the nuclearity of the clusters with the pH of the mother liquor. On the other hand, the geometries of extended structures do not show apparent correlation with the pH. They turned out to be governed by the tectonics of the component clusters. The pH of the mother liquor exerts influence on the extended structure through the structures of the constituent clusters.
Organic Letters | 2012
Teigo Asai; Yu-Ming Chung; Hiroaki Sakurai; Tomoji Ozeki; Fang Rong Chang; Kouwa Yamashita; Yoshiteru Oshima
The concomitant addition of the histone deacetylase inhibitor and the DNA methyltransferase inhibitor to the culture medium of an entomopathogenic fungus, Isaria tenuipes, greatly enhanced its secondary metabolite production and led to the isolation of tenuipyrone (1), a novel polyketide with an unprecedented tetracyclic ring system bearing a spiroketal structural component, along with two known C(10)-polyketides, cephalosporolide B (2), which is a plausible biosynthetic precursor of 1, and cephalosporolide F (3).
Journal of the American Chemical Society | 2011
Tatsuhiro Kojima; Mark R. Antonio; Tomoji Ozeki
Hydrogen-bond-assisted molecular aggregation of decavanadate anions, [H(n)V(10)O(28)]((6-n)-), in non-aqueous solutions was probed by systematic small-angle X-ray scattering and (1)H and (51)V NMR spectroscopic measurements in mixtures of acetone and 1,4-dioxane. Under acetone-rich conditions, the decavanadate anion prefers a self-associated hydrogen-bonded dimer of {[H(3)V(10)O(28)](2)}(6-), which dissociates into monomeric species as the proportion of 1,4-dioxane increases. The association/dissociation behaviors of the decavanadate anions were proven to be reversible and driven by the protophobic/protophilic nature of the solvent.
Chemical Communications | 2006
Kanji Takaoka; Masaki Kawano; Tomoji Ozeki; Makoto Fujita
In situ crystallography reveals that the solid state [2 + 2] photodimerization of acenaphthylene in a coordination cage takes place smoothly without preorganizaiton of reaction centers at a preferred geometry, because the substrate tumbles thermally in the large hollow of the cage.
Organic Letters | 2012
Teigo Asai; Shuntaro Morita; Naoki Shirata; Tohru Taniguchi; Kenji Monde; Hiroaki Sakurai; Tomoji Ozeki; Yoshiteru Oshima
Cultivation of Chaetomium mollipilium with nicotinamide, a NAD(+)-dependent HDAC inhibitor, stimulated its secondary metabolism, leading to the isolation of structurally diverse new C(13)-polyketides, mollipilin A-E (1-5) as well as two known compounds (6 and 7). Spectroscopic methods, X-ray single crystal diffraction analysis, and VCD elucidated the absolute configurations of structures 1-6, and plausible biosynthetic pathways for 1-7 were proposed based on structural relationships. Mollipilins A (1) and B (2) exhibited moderate growth inhibitory effects on HCT-116 cells.
Dalton Transactions | 2006
Hirokazu Chiba; Akihide Wada; Tomoji Ozeki
Two novel salts of lacunary tungstosilicates with guanidinium and alkali metal cations, (CH6N3)7Na[SiW11O39]·(CH3)2CO·8H2O (1) and (CH6N3)K6Na[SiW11O39]·11.5H2O (2), have been synthesized and their crystal structures have been determined by synchrotron X-ray diffraction. In both crystals, the Na+ cations link the lacunary Keggin-type tungstosilicate anions into linear structures. The neighboring [SiW11O39]8− anions are related by two-fold screw and translational operations in compounds 1 and 2, respectively. Second harmonic generation was observed for compound 1.
Journal of Alloys and Compounds | 1993
Tomoji Ozeki; Toshihiro Yamase
Abstract The photoluminescence properties of the potassium sodium salt of decatungstoterbate, K3Na4H2TbW10O36·20H2O, are studied and compared with those of its sodium salt. Photoexcitation of the ligand-to-metal (oxygen-to-tungsten) charge transfer (O → W LMCT) band of the W5O18 groups in this complex leads to green emission due to the f → f transition within terbium(III), as a result of an intramolecular energy transfer from the W5O18 groups to terbium(III). The quantum yields of the O → W LMCT excitation are comparable between the two salts, while the quantum yield of the direct excitation of terbium(III) in the potassium sodium salt is about three times greater than that in the sodium salt.
Organic Letters | 2013
Teigo Asai; Sae Otsuki; Hiroaki Sakurai; Kouwa Yamashita; Tomoji Ozeki; Yoshiteru Oshima
Graphiopsis chlorocephala was separated from the surface-sterilized healthy leaves of Paeonia lactiflora (Paeoniaceae) and cultivated with nicotinamide (an NAD(+)-dependent HDAC inhibitor). The culture conditions significantly enhanced secondary metabolite production in the fungus and led to the isolation of a structurally diverse set of new benzophenones, cephalanones A-F (1-6), and a known 2-(2,6-dihydroxy-4-methylbenzoyl)-6-hydroxybenzoic acid (7). The structures of 1-6 were determined from NMR data, single crystal X-ray diffraction, and chemical transformations.