Takashi Kato

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (245)1187.5 Total impact

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    ABSTRACT: Molecular assemblies that change photoluminescence color in response to thermal or mechanical stimulation without dissociation into the monomeric states in water are described herein. A dumbbell-shaped amphiphilic compound forms micellar molecular assemblies in water and exhibits yellow photoluminescence derived from excimer formation of the luminescent core, which contains a 2,6-diethynylanthracene moiety. Annealing of the aqueous solution induces a photoluminescence color change from yellow to green (λem, max=558525 nm). The same photoluminescence color change is also achieved by rubbing the yellow-photoluminescence-emitting molecular assemblies adsorbed on glass substrates with cotton wool in water. The observed green photoluminescence is ascribed to micelles that are distinct from the yellow-photoluminescence-emitting micelles, on the basis of transmission electron microscopy observations, atomic force microscopy observations, and dynamic light scattering measurements. We examined the relationship between the structure of the molecular assemblies and the photophysical properties of the anthracene derivative in water before and after thermal or mechanical stimulation and concluded that thermal or mechanical stimuli-induced slight changes of the molecular-assembled structures in the micelles result in the change in the photoluminescence color from yellow to green in water.
    Chemistry 07/2014; · 5.93 Impact Factor
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    ABSTRACT: The photocontrol of macroscopic alignment of nanostructured 2D ion-transporting pathways is described. The uniplanar homogenous alignment of thermotropic smectic (Sm) liquid-crystalline (LC) phase has been successfully achieved via photoinduced reorientation of the azobenzene groups of the imidazolium-based LC material. The ionic layers of the Sm LC phase are macroscopically oriented perpendicular to the surface of the glass substrate. The oriented films show anisotropic ion conduction in the Sm phase. This is the first example of the macroscopic photoalignment of ion-conductive LC arrays. Reversible switching of homeotropic and homogeneous alignments has also been achieved for the LC material. These materials and the alignment methodology may be useful in the development of ion-based circuits and memory devices.
    Journal of the American Chemical Society 06/2014; · 10.68 Impact Factor
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    ABSTRACT: Covalent attachment of mechanoresponsive luminescent organic or organometallic compounds to other materials is a promising approach to develop a wide variety of mechanoresponsive luminescent materials. Here, we report covalently linkable mechanoresponsive micelles that change their photoluminescence from yellow to green in response to mechanical stimulation under aqueous conditions. These micelles are composed of a dumbbell-shaped amphiphilic pyrene derivative having amine groups at the peripheral positions of its dendrons. Using a well-established cross-linker, the micelles were covalently linked via their peripheral amine groups to the surface of glass beads, polylactic acid (PLA) beads, and living cells under aqueous conditions. Vortexing of glass beads bearing the micelles in a glass vial filled with water caused a photoluminescence color change from yellow to green. PLA beads bearing the micelles showed no change in photoluminescence color under the same conditions. We ascribe this result to the lower density and stiffness of the PLA beads, because the color of the PLA beads changed on vortexing in the presence of bare glass beads. HeLa cells and HL 60 cells bearing the micelles showed no obvious photoluminescence color change under vortexing. The structure, photophysical properties and mechanism of photoluminescence color change of the micellar assemblies were examined.
    Journal of the American Chemical Society 02/2014; · 10.68 Impact Factor
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    ABSTRACT: Nanostructured inorganic/polymer hybrid thin films comprising aragonite nanorods derived from aqueous suspensions of amorphous calcium carbonate (ACC) are prepared. For the formation of calcium carbonate (CaCO3 )/polymer hybrids, spincoated and annealed films of poly(vinyl alcohol) (PVA) that function as polymer matrices are soaked in aqueous colloidal solutions dispersing ACC stabilized by poly(acrylic acid) (PAA). In the initial stage, calcite thin films form on the surface. Subsequently, aragonite crystals start to form inside the PVA matrix that contains PVA crystallites which induce aragonite nucleation. Nanostructured hybrids composed of calcite thin films consisting of nanoparticles and assembled aragonite nanorods are formed in the matrices of PVA.
    Small 01/2014; · 7.82 Impact Factor
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    ABSTRACT: We here report the use of carboxylated polyrotaxanes as supramolecular templates for the formation of CaCO3 thin films. Polyrotaxanes consisting of carboxylated [small alpha]-cyclodextrins ([small alpha]-CD-COOH) and poly(ethylene glycol) have been obtained as an inducer of CaCO3 crystals. Poly(vinyl alcohol) has been used as a matrix to interact with the polyrotaxanes for this crystallization. These polyrotaxanes induce the formation of CaCO3 thin films, while the simple mixture of monomeric [small alpha]-CD-COOH and capped poly(ethylene glycol) only leads to the formation of granular crystals. The assembled carboxyl groups due to the construction of the polyrotaxane structure play an essential role for the development of CaCO3 thin films. Moreover, morphology and orientation of the obtained CaCO3 thin films are dependent on the amount of [small alpha]-CD-COOH incorporated into the polyrotaxane structure. This approach to the use of supramolecular templates will bring new designs for hybrid materials.
    CrystEngComm 01/2014; 16(8):1496-1501. · 3.88 Impact Factor
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    ABSTRACT: Switching of the luminescence properties of molecular materials in response to mechanical stimulation is of fundamental interest and also has a range of potential applications. Herein, a water-soluble mechanochromic luminescent pyrene derivative having two hydrophilic dendrons is reported. This pyrene derivative is the first example of a mechanochromic luminescent organic compound that responds to relative humidity. Mechanical stimulation (grinding) of this pyrene derivative in the solid state results in a change of the photoluminescence from yellow to green. Subsequent exposure to water vapor induces recovery of the initial yellow photoluminescence. The color change is reversible through at least ten cycles. It is also demonstrated that this compound can be applied as a mechano-sensing material in frictional wear testing for grease, owing to its immiscibility in non-polar solvents and its non-crystalline behavior. Transmission electron microscope and atomic force microscope observations of samples prepared from dilute aqueous solutions of the pyrene derivative on suitable substrates, together with dynamic light scattering measurements for the compound in aqueous solution, indicate that this amphiphilic dumbbell-shaped molecule forms micelles in water.
    Advanced Functional Materials 11/2013; 23(42). · 9.77 Impact Factor
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    ABSTRACT: Amino acid ionic liquids provide suitable media for lyotropic liquid-crystalline systems whose self-organisation behaviour is tuneable by the selection of amino acid anions.
    Chemical Communications 11/2013; · 6.38 Impact Factor
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    ABSTRACT: Molecular dynamics simulations were conducted to elucidate the effects of Mg2+ and H2O additives on the structure of amorphous calcium carbonate (ACC). New potential parameters for Mg2+ ions were developed. The distribution function of the angle formed by three nearest neighbor atoms was introduced to analyze the short-range, local structure of ACC. The simulation indicated that ACC had a weakly ordered local structure resembling the local structure of a CaCO3 crystal. The local structure of pure ACC resembled that of vaterite. The formation of the vaterite-like local structure was hindered by Mg2+ ions, whereas H2O molecules did not significantly influence the structure of ACC when the fraction of H2O molecules was low. However, when the fraction of H2O was high, the formation of a monohydrocalcite-like local structure was promoted. The effects of the additives on the structure of ACC were verified using the size of the additives, and the interaction between the additives and CaCO3. The simulated structure of ACC was compared with the structure of CaCO3 crystals nucleated through the formation of prenucleation ACC particles in real systems.
    The Journal of Physical Chemistry B 11/2013; · 3.61 Impact Factor
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    ABSTRACT: Herein we describe anhydrous proton transportation through 3D interconnected pathways formed by self-assembled molecular complexes. A thermotropic bicontinuous cubic (Cubbi) phase has been successfully obtained by mixing a wedge-shaped sulfobetaine with benzenesulfonic acid in different ratios. These ionic complexes exhibit the Cubbi phase in a wide range of temperatures while the single zwitterionic compound shows only a columnar hexagonal phase and benzenesulfonic acid is nonmesomorphic. Anhydrous proton conduction on the order of 10(-4) S cm(-1) has been achieved for the mixture in the Cubbi phase over 100 ºC, which can be useful for the development of new electrolytes for the next generation of fuel cells.
    Journal of the American Chemical Society 10/2013; · 10.68 Impact Factor
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    ABSTRACT: Thin-film growth of aragonite CaCO3 on annealed poly(vinyl alcohol) (PVA) matrices is induced by adding Mg(2+) into a supersaturated solution of CaCO3 . Both the growth rate and surface morphology of the aragonite thin films depend upon the concentration of Mg(2+) in the mineralization solution. In the absence of PVA matrices, no thin films are formed, despite the presence of Mg(2+) . Molecular dynamics simulation of the CaCO3 precursor suggests that the transition of amorphous calcium carbonate to crystals is suppressed in the presence of Mg(2+) . The role for ionic additives in the crystallization of CaCO3 on organic templates obtained in this study may provide useful information for the development of functional hybrid materials.
    Chemistry - An Asian Journal 09/2013; · 4.57 Impact Factor
  • Junji Sakuda, Takuma Yasuda, Takashi Kato
    ChemInform 04/2013; 44(17).
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    ABSTRACT: Smectic liquid crystals consisting of an aromatic moiety based on 10,10′-bis(phenylethynyl)-9,9′-bianthryl at the central part and one and two mesogenic moieties on each side connected through oxyethylene spacers have been prepared to develop stimuli-responsive materials. The compound having two mesogenic moieties on each side (i.e. four total) forms an ordered smectic phase. Mechanochromic luminescence is observed for the smectic liquid crystal. A sample of this molecule formed by thermal annealing shows green photoluminescence at room temperature. The photoluminescent color changes from green to blue-green with mechanical stimulation at room temperature. The change of the photoluminescent color by mechanical shearing is ascribed to the disturbance of the π–π interactions between the adjacent molecules. Moreover, the original green photoluminescent color is recovered by heating followed by cooling to room temperature. The effects of the number, and thus volume of mesogenic moieties were also examined. Smaller mesogenic moieties lead to stronger ground state interactions between adjacent luminescent molecules and red-shifted emission. In contrast, the compound having three mesogenic moieties on each side shows no mechanochromic luminescence. The large mesogenic moieties disturb intermolecular interactions, resulting in no detectable change in the assembled structure of luminescent moieties upon mechanical stimulation. These results suggest that the present molecular design is useful for fabricating new stimuli-responsive materials with liquid-crystalline behavior.
    J. Mater. Chem. C. 03/2013; 1(15):2648-2656.
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    ABSTRACT: Functional peptides play an important role in the formation of biominerals. Here we focus on peptides involved in mineralization of the exoskeleton of a crayfish. New recombinant peptides are designed and synthesized on the basis of an acidic functional peptide, CAP-1, derived from the exoskeleton of a crayfish. We have examined the effect of these peptides on the hybrid formation of calcium carbonate and organic molecules in aqueous solution. In the presence of these recombinant peptides having chitin binding moieties, platelike tripodal calcite crystals are formed on the chitin matrix with unidirectional crystallographic orientation. Two kinds of interactions, (1) interactions between an acidic part of the peptides and calcium ions and (2) specific binding interactions of the peptides to chitin, are essential for the formation of the oriented crystals and the induction of specific morphologies. Moreover, the sizes of crystallites decrease with increasing the number of acidic parts of mutational peptides. The bioinspired design of peptides that control the interface of inorganic and organic domains may pave the way for an opportunity to build new hybrid structures.
    Faraday Discussions 03/2013; 159(1):483-494. · 3.82 Impact Factor
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    ABSTRACT: The introduction of bulky tert-butyl substituents into smectic liquid-crystalline 9,10-bis(phenylethynyl)anthracene derivatives influences excimer structures and luminescence properties.
    Chemical Communications 02/2013; · 6.38 Impact Factor
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    ABSTRACT: Thin‐film growth of aragonite CaCO3 on annealed poly(vinyl alcohol) (PVA) matrices is induced by adding Mg2+ into a supersaturated solution of CaCO3. Both the growth rate and surface morphology of the aragonite thin films depend upon the concentration of Mg2+ in the mineralization solution. In the absence of PVA matrices, no thin films are formed, despite the presence of Mg2+. Molecular dynamics simulation of the CaCO3 precursor suggests that the transition of amorphous calcium carbonate to crystals is suppressed in the presence of Mg2+. The role for ionic additives in the crystallization of CaCO3 on organic templates obtained in this study may provide useful information for the development of functional hybrid materials.
    Chemistry - An Asian Journal 01/2013; 8(12). · 4.57 Impact Factor
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    ABSTRACT: Molecular Dynamics Biominerals have an organic–inorganic hybrid nature and hierarchical structures. A promising way to obtain environmentally benign and functional materials is to mimic the self‐organization processes of biomineralization and the elaborate structures of biominerals. In their Full Paper on page 3002 ff., Tatsuya Nishimura, Takashi Kato et al. report on aragonite thin‐film composites that have been obtained by using magnesium ions as an additive in combination with poly(vinyl alcohol) as a matrix. The image on the Back Cover shows a polarizing optical micrograph of obtained thin‐film CaCO3 crystals grown on the PVA matrix with an overlay of a simulated structure of the system.
    Chemistry - An Asian Journal 01/2013; 8(12). · 4.57 Impact Factor
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    ABSTRACT: Bisphenylsulfone-based hexacatenal molecules self-assemble to form thermotropic columnar liquid-crystalline phases through the dipole–dipole interactions of sulfonyl groups and nanosegregation of aliphatic and aromatic moieties. The vertical alignment of the columns has been achieved by applying electric fields to the samples sandwiched between ITO substrates. In addition, organogels are obtained by the formation of the self-assembled fibrous aggregates of a sulfone derivative in organic solvents such as dodecylbenzene. The dipole–dipole interactions of the sulfonyl moieties play a key role in the formation of these one-dimensional molecular assemblies.
    New Journal of Chemistry 12/2012; 37(1). · 2.97 Impact Factor
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    ABSTRACT: Magnetic fibers were obtained through self-assembly of a nitroxide radical gelator derived from an L-isoleucine-based scaffold. Spins in the fibers are aligned one-dimensionally due to the parallel β-sheet conformation of the intermolecular hydrogen bonds. The spin nanowires exhibit magnetic behavior reproducible by the Bonner–Fisher model.
    Chemical Science 08/2012; 3(10):3007-3010. · 8.31 Impact Factor
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    ABSTRACT: Co-organization of amphiphilic zwitterions and bis(trifluoromethanesulfonyl)imide led to the formation of bicontinuous cubic liquid-crystalline structures having 3D continuous hydrophilic gyroid minimal surface. The gyroid surface, incorporating a small amount of water, provided extremely thin but macroscopically continuous water nanosheet with a thickness of approximately 5 Å. The water nanosheet functioned as alignment free proton conduction pathway.
    Journal of the American Chemical Society 06/2012; 134(28):11354-7. · 10.68 Impact Factor
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    ABSTRACT: Three-dimensionally continuous ionic nanochannels have been developed by imidazolium-based ionic liquids and amphiphilic molecules having a diethanolamine moiety. Co-organisation of these two components into liquid–crystalline bicontinuous cubic phases leads to the formation of the 3D nanochannels. The induction of bicontinuous cubic phases is observed for the combination of an ionic liquid, 1-(2-methoxyethyl)-3-methylimidazolium bromide, and a diethanolamine derivative, N-{3-[N′, N′-bis(2-hydroxyethyl) aminopropyl]}-3,4-didodecyloxy benzoylamide. Compatibility enhanced by intermolecular interactions between the imidazoliums and the diethanolamine moiety plays an important role for the co-organisation of the two components. The three-dimensionally continuous ionic nanochannels function as efficient transportation pathways for ions. The material design using bicontinuous cubic liquid–crystalline structures will offer an opportunity for the development in the field of nanochannel material science.
    Chemical Science 05/2012; 3(6):2001-2008. · 8.31 Impact Factor

Publication Stats

2k Citations
1,187.50 Total Impact Points

Institutions

  • 1970–2014
    • The University of Tokyo
      • • Department of Medical Engineering
      • • Department of Chemistry and Biotechnology
      • • Faculty & Graduate School of Engineering
      • • Institute of Industrial Science
      Edo, Tōkyō, Japan
  • 2005–2013
    • Tokyo University of Agriculture and Technology
      Edo, Tōkyō, Japan
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan
  • 2007
    • Kyoto University
      • Department of Material Chemistry
      Kyoto, Kyoto-fu, Japan
    • University of California, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Angeles, CA, United States
  • 2002
    • Tokyo Institute of Technology
      • Chemical Resources Laboratory
      Tokyo, Tokyo-to, Japan