Takashi Kato

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (266)1479.3 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Ionic liquid-based 2D ion-conductive liquid crystals are obtained by co-assembly of imidazolium salts and cationic calamitic liquid crystals with an imidazolium moiety at the end of the molecule through a flexible spacer. They exhibit smectic A phases. The two components are compatible over a wide range of compositions for ionic liquids with various anions. This organization of ionic liquids enhances the ionic conductivities of calamitic ionic liquid crystals. These liquid-crystalline mixtures dissolve lithium salts. The 2D ion-conductive pathways formed by the ionic liquid crystals and ionic liquids act as ion-conductive media for lithium ions.
    New Journal of Chemistry 03/2015; DOI:10.1039/C5NJ00085H · 3.16 Impact Factor
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    ABSTRACT: We describe the development of self-assembled one- and three-dimensional lithium ion conductors composed of zwitterionic liquid crystals, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and propylene carbonate (PC). Two types of wedge-shaped zwitterions based on imidazolium dicyanoethenolate and sulfonate were synthesized. These compounds alone show liquid-crystalline (LC) columnar hexagonal (Colh) phases and low ionic conductivities (10-8-10-7 S cm-1). The increase in the ionic conductivities was achieved by the addition of LiTFSI (10-5 S cm-1) followed by that of PC (10-4 S cm-1). Moreover, LC bicontinuous cubic (Cubbi) phases are induced by tuning the ionic nature of the zwitterionic liquid crystal with the ratio of LiTFSI and PC. The dissociation of LiTFSI in the zwitterions and the ion-dipole interaction between the lithium ion and PC are shown to be significant keys for the enhancement of the conductivities and stabilization of the nanosegregated LC structures.
    03/2015; DOI:10.1039/C5TA00814J
  • Polymer Journal 02/2015; 47(2):77-77. DOI:10.1038/pj.2014.132 · 1.55 Impact Factor
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    ABSTRACT: Ionic liquids have attracted a considerable attention as the next generation electrolytes for energy devices. We have developed new free-standing and nanostructured polymer films in which ionic liquids are confined into one-dimensionally ordered nanochannels. These polymer films have been obtained by photopolymerization of hydrogen-bonded supramolecular columnar liquid-crystalline self-assemblies of an imidazolium-based ionic liquid and a wedge-shaped diol compound containing polymerizable groups. The macroscopically parallel alignment of the columnar structures on a glass substrate has been achieved by the application of mechanical shearing, and subsequently fixed into polymer films by UV irradiation. This ionic liquid-containing polymer film exhibits higher ionic conductivity than that of the previously reported one-dimensional polymer film obtained by in situ photopolymerization of a covalent-type columnar liquid-crystalline imidazolium salt. The noncovalent supramolecular approach to one-dimensionally ion-conductive polymer films has led to improvement on conductive properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014
    Journal of Polymer Science Part A Polymer Chemistry 01/2015; 53(2). DOI:10.1002/pola.27380 · 3.54 Impact Factor
  • Polymer Journal 12/2014; 47(2):122-127. DOI:10.1038/pj.2014.123 · 1.55 Impact Factor
  • Polymer Journal 12/2014; 47(2):158-163. DOI:10.1038/pj.2014.127 · 1.55 Impact Factor
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    ABSTRACT: Thermotropic liquid-crystalline (LC) electrolytes for lithium-ion batteries are developed for the first time. A rod-like LC molecule having a cyclic carbonate moiety is used to form self-assembled two-dimensional ion-conductive pathways with lithium salts. Electrochemical and thermal stability, and efficient ionic conduction is achieved for the liquid crystal. The mixture of the carbonate derivative and lithium bis(trifluoromethylsulfonyl)imide is successfully applied as an electrolyte in lithium-ion batteries. Reversible charge–discharge for both positive and negative electrodes is observed for the lithium-ion batteries composed of the LC electrolyte.
    Advanced Functional Materials 12/2014; 25(8). DOI:10.1002/adfm.201402509 · 10.44 Impact Factor
  • Chemistry of Materials 11/2014; 26(22):6496-6502. DOI:10.1021/cm503090z · 8.54 Impact Factor
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    ABSTRACT: Organisms produce various organic/inorganic hybrid materials, which are called biominerals. They form through the self-organization of organic molecules and inorganic elements under ambient conditions. Biominerals often show highly organized and hierarchical structures from nanometer to macroscopic length scales, resulting in remarkable physical and chemical properties that cannot be obtained by simple accumulation of their organic and inorganic constituents. These observations motivate us to create novel functional materials exhibiting properties superior to those of conventional materials-both synthetic and natural. Herein, we introduce recent progresses in understanding biomineralization processes at molecular levels and the development of organic/inorganic hybrid materials by these processes. We specifically outline fundamental molecular studies on silica, iron oxide, and calcium carbonate biomineralization and describe material synthesis based on these mechanisms. These approaches allow us to design a variety of advanced hybrid materials with desired morphologies, sizes, compositions, and structures through environmentally friendly synthetic routes using functions of organic molecules.
    Organic & Biomolecular Chemistry 10/2014; 46(11). DOI:10.1039/C4OB01796J · 3.49 Impact Factor
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    ABSTRACT: We prepared pyridinium-based amphiphilic zwitterions and examined their liquid-crystalline (LC) phase behavior in the presence and absence of lithium salts. Addition of lithium salts induced nanosegregated LC phases such as bicontinuous cubic phase and smectic phase depending on the anion species of the lithium salts. For example, an equimolar mixture of dodecylcarbamoyl-1-(4-sulfobutyl)pyridinium betaine and lithium bis(trifluoromethanesulfonyl)imide (LiTf2N) exhibited a bicontinuous cubic phase between 40 and 100 C. The exhibition of these nanosegregated phases was attributed to the formation of an ionic liquid-like ion pair composed of the pyridinium cation and the Tf2N anion. The preferential interaction between the pyridinium cation and the Tf2N anion was confirmed with Raman spectroscopic measurement. Moreover, the amphiphilic zwitterions were found to show not only thermotropic LC behavior but also lyotropic LC behavior in the presence of polar solvents such as protic ionic liquids. The results presented here indicate that the combination of amphiphilic zwitterions and suitable additive ions is a potential method to construct nanostructured LC materials showing tuneable phase behavior.
    Bulletin of the Chemical Society of Japan 07/2014; 87(7):792-796. DOI:10.1246/bcsj.20140049 · 2.22 Impact Factor
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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 - A European Journal 07/2014; 20(33). DOI:10.1002/chem.201403025 · 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; 136(27). DOI:10.1021/ja5041573 · 11.44 Impact Factor
  • Yulai Han, Tatsuya Nishimura, Takashi Kato
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    ABSTRACT: Thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) brushes have been synthesized and employed as the crystallization matrices for the development of polymer/strontium carbonate hybrid materials. The use of PNIPAm brush matrices results in the formation of patterned polymer/strontium carbonate hybrid thin films in the presence of poly(acrylic acid) additives. Moreover, the conformational change in the thermoresponsive PNIPAm brush matrices induces the change in the surface morphologies of the obtained polymer/SrCO3 hybrid thin films. The strategy of using stimuli-responsive polymer brush matrices is expected to be a promising method for controlling the surface morphology of two-dimensional hybrid thin film materials.
    Polymer Journal 05/2014; 46(8):499-504. DOI:10.1038/pj.2014.36 · 1.55 Impact Factor
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    ABSTRACT: Stiff yet flexible and strong transparent film materials mimicking the structure of crustacean exoskeletons were obtained from calcium carbonate and cellulose. These biobased materials have the composite structure of a three-dimensional nanoscale network of surface-carboxylated crystalline cellulose incorporated into an amorphous inorganic-based hybrid matrix of nanosegregated calcium carbonate and acidic polymers.
    05/2014; 1(3):321. DOI:10.1039/c3mh00134b
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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 04/2014; 10(8). DOI:10.1002/smll.201302745 · 7.51 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; 136(11). DOI:10.1021/ja412670g · 11.44 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(8-8):1496-1501. DOI:10.1039/c3ce41649f · 3.86 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). DOI:10.1002/adfm.201300180 · 10.44 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; 49(100). DOI:10.1039/c3cc45429k · 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; 117(47). DOI:10.1021/jp407721x · 3.38 Impact Factor

Publication Stats

7k Citations
1,479.30 Total Impact Points

Institutions

  • 1970–2013
    • The University of Tokyo
      • • Department of Chemistry and Biotechnology
      • • Institute of Industrial Science
      Edo, Tōkyō, Japan
  • 2005
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan
  • 2002–2004
    • Shinshu University
      Shonai, Nagano, Japan
  • 1992–2002
    • Cornell University
      Итак, New York, United States
  • 1998–2001
    • Shimane University
      • Department of Physics and Material Science
      Matsu, Shimane, Japan
  • 2000
    • Radboud University Nijmegen
      • Department of Organic Chemistry
      Nymegen, Gelderland, Netherlands