Takahiro Sato

Osaka University, Suika, Ōsaka, Japan

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Publications (117)486.75 Total impact

  • Ken Morishima, Takahiro Sato
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    ABSTRACT: We have investigated aqueous micellar solutions of mixtures of a surfactant (dodecylpyridinium chloride) and a hydrophobe (1-dodecanol) near the critical micelle concentration (cmc), using simultaneous static and dynamic light scattering measurements. The static light scattering intensity for the aqueous solutions was separated into fast and slow relaxation components using dynamic light scattering results. The slow relaxation component gave us the information about the large scattering component. It turned out from this component that the amount of large colloidal particles of the hydrophobe was very tiny in the solution and hardly affects the association-dissociation equilibrium of the hydrophobe-uptake micelle. The free surfactant molecule and the hydrophobe-uptake spherical micelle in the solutions belong to the fast relaxation component. We have characterized the spherical micelle and also analyzed the association-dissociation equilibrium of the hydrophobe-uptake micelle up to near the cmc, using this scattering component extracted.
    Langmuir 09/2014; · 4.38 Impact Factor
  • Polymer Journal 02/2014; 46(5):264-271. · 1.55 Impact Factor
  • Kōbunshi rombun shū 01/2014; 71(8):361-366. · 0.22 Impact Factor
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    ABSTRACT: Lyotropic liquid crystallinity was investigated for amylose tris(n-butylcarbamate) (ATBC), amylose tris(ethylcarabamate) (ATEC), and amylose tris(n-hexylcarbamate) (ATHC) in tetrahydrofuran (THF) and ethyl lactates (ELs) by using phase separation experiments, polarized microscopic observation, small-angle X-ray diffraction, and circular dichroism measurements. Concentrated THF solution of ATBC has selective reflection at visible light wavelength, indicating the formation of cholesteric phase. A current theory well explains the phase diagram of ATBC, ATEC, and ATHC in THF. On the other hand, ELs solution forms smectic phase and it has significantly different phase diagram, that is, the biphasic range is much wider than that in THF. In other words, highly concentrated smectic phase can be obtained from semidilute and rather low viscosity ELs solution. This is likely because amylose alkylcarbamate chains may have significant anisotropic intermolecular attractive interaction in between polymer chains in ELs or intermolecular interactions between the chain ends are much more different from those in THF.
    Macromolecules 07/2013; 46(11):4589-4595. · 5.93 Impact Factor
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    ABSTRACT: Small-angle X-ray scattering measurements were made for nine cyclic amylose tris(n-butylcarbamate) (cATBC) samples ranging in the weight-average molar mass Mw from 1.6 × 104 to 1.1 × 105 to determine the z-average mean-square radius of gyration S2z and the particle scattering function P(q) in two good solvents, tetrahydrofuran (THF) and methanol (MeOH) at 25 °C and in a Θ solvent, 2-propanol (2PrOH) at the Θ temperature (35 °C). Static and dynamic light scattering measurements were carried out for cATBC in 2PrOH to determine Mw, the second virial coefficient A2, and the hydrodynamic radius RH. The dimensional and hydrodynamic properties are consistently explained by the current theories for wormlike ring having substantially the same model parameters obtained for linear analogues, that is, the Kuhn segment length λ–1 of THF, 2PrOH, and MeOH are 75, 20, and 11 nm, respectively. Furthermore, number of hydrogen bonds decreases with the order of THF, 2PrOH, and MeOH, as is the case with linear ATBC. These results indicate that cATBC has rigid helical backbone stabilized by intramolecular hydrogen bonds in THF and it loosens with increasing solvent polarity. Indeed, lyotropic liquid crystallinity was found for cATBC in THF. In the Θ condition, 2PrOH at 35 °C, cATBC has large positive A2 values, (1.3–1.4) × 10–4 mol g–2 cm3. It is successfully explained by the simulation results considering intermolecular topological interaction.
    Macromolecules 07/2013; 46(13):5355-5362. · 5.93 Impact Factor
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    ABSTRACT: The self-association behavior of a thermosensitive amphiphilic block copolymer, poly(N-isopropylacrylamide)-b-poly(N-vinyl-2-pyrrolidone) (PNIPAM-b-PNVP) in water upon heating was investigated by static and dynamic light scattering (SLS and DLS), small-angle X-ray scattering (SAXS), and pulsed field gradient NMR (PFG-NMR). Combining SLS and DLS with SAXS and PFG-NMR, we conclude that above 40 degrees C, the unimer or a few arms star micelle of the copolymer coexists with large spherical particles of uniform density, which should be regarded as concentrated-phase droplets produced by a liquid liquid phase separation. The spherical particles of PNIPAM-b-PNVP samples with the PNIPAM content less than 0.32 became smaller with increasing temperature. This temperature dependence was explained in terms of the packing parameter for amphiphiles.
    Macromolecules 01/2013; 46(1):226-235. · 5.93 Impact Factor
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    ABSTRACT: Six amylose-2-acetyl-3,6-bis(phenylcarbamate) (AAPC) samples ranging in weight-average molar mass M(w) from 1.8 × 10(4) g mol(-1) to 1.1 × 10(6) g mol(-1) have been prepared from enzymatically synthesized amylose samples. Static light scattering, small-angle X-ray scattering, sedimentation equilibrium, and viscosity measurements were made for the samples in 1,4-dioxane (DIOX), 2-ethoxyethanol (2EE), and 2-butanone (MEK) all at 25°C to determine particle scattering functions, z-average radii of gyration, intrinsic viscosities, as well as M(w) . The data were analyzed in terms of the wormlike cylinder model mainly to yield the helix pitch per residue h and the Kuhn segment length λ(-1) , which corresponds to twice of the persistence length. The latter parameters (λ(-1) ) in 2EE (11 nm) and MEK (12 nm) are quite smaller than those for amylose tris(phenylcarbamate) (ATPC) in the same solvent (16 nm in 2EE and 18 nm in MEK) whereas those for AAPC (21 nm) and ATPC (22 nm) in DIOX are essentially the same as each other. This indicates that the chain stiffness of AAPC is more strongly influenced by the solvents since the number of intramolecular H-bonds of AAPC is more changeable than that for ATPC. © 2012 Wiley Periodicals, Inc. Biopolymers 97:1010-1017, 2012.
    Biopolymers 12/2012; 97(12):1010-7. · 2.29 Impact Factor
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    ABSTRACT: Six cyclic amylose tris(phenylcarbamate) (ATPC) samples have been prepared from enzymatically synthesized cyclic amylose ranging in the number of repeat units N from 24 to 290. Synchrotron-radiation small-angle X-ray scattering measurements were made for the samples in 1,4-dioxane (DIOX) and 2-ethoxyethanol (2EE) to determine the z-average radius of gyration ?S2?z and the particle scattering function P(q). Molar mass dependencies of ?S2?z in the two solvents were successfully explained by the current theories for the wormlike ring with the same parameters for linear ATPC in the corresponding solvent, that is, the helix pitch h (or contour length) per residue and the Kuhn segment length ??1 (stiffness parameter, twice the persistence length). The latter parameter ??1 is 22 and 16 nm in DIOX and 2EE, respectively. Except for the low-q region, P(q) was also explained by the rigid ring having the same contour length Nh as that for linear ATPC. Further, their local conformation estimated from circular dichroism spectra is essentially unaltered from that for linear ATPC at least when N ≥ 24.
    ACS Macro Letters 11/2012; 1(11):1291-1294. · 5.24 Impact Factor
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    ABSTRACT: Eight amylose tris(ethylcarbamate) (ATEC) samples ranging in the weight-average molar mass M(w) from 1.0 × 10(4) to 1.1 × 10(6) g mol(-1) and five amylose tris(n-hexylcarbamate) (ATHC) samples of which M(w) varies from 4.9 × 10(4) to 2.2 × 10(6) g mol(-1) have been prepared from enzymatically synthesized amylose samples having narrow dispersity indices and no branching. Small-angle angle X-ray scattering (SAXS), light scattering, viscometry, and infrared (IR) absorption measurements were carried out for their dilute solutions, that is, ATEC in tetrahydrofuran (THF), 2-methoxyethanol (2ME), methanol (MeOH), and ATHC in THF and 1-propanol (1PrOH) to determine M(w), particle scattering functions, intrinsic viscosities, and IR spectra. SAXS and viscosity measurements were also made on ATEC in d- and l-ethyl lactates. The data were analyzed in terms of the wormlike cylinder model to estimate the helix pitch (or contour length) per residue h and the Kuhn segment length λ(-1) (stiffness parameter, twice the persistence length). Both ATEC and ATHC have large λ(-1) in THF, that is, 33 and 75 nm, respectively, and smaller λ(-1) were obtained in alcohols, indicating that they have rigid helical conformation stabilized by intramolecular hydrogen bonds in THF. On the contrary, the helical structure estimated from the h value significantly depends on the alkyl side groups in a complex fashion, that is, h = 0.36 nm for ATEC, h = 0.29 nm for ATHC, and h = 0.26 nm for amylose tris(n-butylcarbamate) (ATBC). This is likely related to the bulkiness of side groups packed inside the amylosic helices. The solvent dependence of h, λ(-1), and the fraction f(hyd) of intramolecular hydrogen bonds for ATEC can be explained by a current model as is the case with ATBC [ Terao , K. ; Macromolecules 2010 , 43 , 1061 ], in which each contour point along the chain takes loose helical and rigid helical sequences independently.
    The Journal of Physical Chemistry B 10/2012; 116(42):12714-20. · 3.38 Impact Factor
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    ABSTRACT: We have investigated the heat-induced self-association in water of a block copolymer (PIPOZ-b-PEOZ) comprising two thermosensitive blocks: a poly(2-isopropyl-2-oxazoline) block (degree of polymerization 71) and a poly(2-ethyl-2-oxazoline) block (degree of polymerization 38) using differential scanning calorimetry (DSC), static light scattering (SLS), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) together with visual observation on the macroscopic and microscopic scales. The dehydration temperatures of the PIPOZ and PEOZ blocks in water are 43 and 54 °C, respectively. When heated abruptly to 50 °C where PIPOZ-b-PEOZ is amphiphilic, the copolymer first forms star micelles that further aggregate to form large concentrated phase droplets, and finally the droplets coalesce into a bulk liquid phase, having a copolymer concentration as high as 0.8 g/cm 3. When heated abruptly to 70 °C, where both blocks are hydrophobic, the copolymer solution also separates into two liquid phases, consisting of phase-separated polymer-rich micrometer or submicrometer size droplets dispersed in a polymer-poor liquid phase, but the droplets do not coalesce into a liquid bulk phase. We discuss the role of the more hydrophilic PEOZ block in the macroscopic phase separation behavior. No microphase separation takes place in the concentrated phase of the aqueous PIPOZ-b-PEOZ block copolymer solution. © 2012 American Chemical Society.
    Macromolecules 08/2012; 45(15):6111-6119. · 5.93 Impact Factor
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    ABSTRACT: Light and small-angle X-ray scattering and viscosity measurements were made for four curdlan tris(phenylcarbamate) (CdTPC) samples having quite narrow dispersity indices (DI) and ranging in the molecular weight between 6 × 104 and 2 × 106, to determine weight-average molecular weights Mw, radii of gyration 〈S2〉〈S2〉, particle scattering functions P(q), and intrinsic viscosities [η] in tetrahydrofuran (THF) and 4-methyl-2-pentanone (MIBK). Size-exclusion chromatography equipped with light scattering and/or viscosity detectors was performed for some broad DI samples in THF also to determine 〈S2〉〈S2〉 and [η] as a function of Mw. The solution data were analyzed in terms of the wormlike-chain model to estimate the Kuhn segment length of 57 nm in THF and 17 nm in MIBK and the helix pitch per residue h of 0.39 nm in THF and 0.51 nm in MIBK. Since the former h value is almost equivalent to that for single helical curdlan and its acetate derivative in crystal, it is reasonably suggested that the local conformation of CdTPC in THF is close to the tightly wound helix stabilized by the intramolecular hydrogen bonding, which was detected from the solution IR spectra.
    Polymer 08/2012; 53(18):3946-3950. · 3.77 Impact Factor
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    ABSTRACT: This letter describes the phase behavior of aqueous solutions of an N-isopropylacrylamide (NIPAM) homopolymer and copolymers of N,N'-diisopropylfumaramide (DIPFAM) and NIPAM as studied by transmittance measurements, infrared spectroscopy, and differential scanning calorimetry to reveal the effect of the density of N-isopropylamide side chain upon the phase behavior. The clouding-point and clearing-point temperatures decreased with increasing the mole fraction of DIPFAM (x(D)). It was noteworthy that only an extra side chain per ca. 7 NIPAM units had a remarkable effect on the phase behavior; the interactions between side chains were stronger, the intrapolymer contraction was less favorable, and the cooperativity of phase transition was lower at x(D) = 0.15 presumably because of the steric hindrance of dense side chains.
    Langmuir 03/2012; 28(13):5522-6. · 4.38 Impact Factor
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    ABSTRACT: Small-angle X-ray scattering (SAXA) measurements were made for three collagen model peptides, H-(Gly-Pro-4-(R)-Hyp)(9)-OH, H-(Pro-4-(R)-Hyp-Gly)(9)-OH, and H-(Gly-4-(R)-Hyp-4-(R)-Hyp)(9)-OH with or without sodium polyacrylate (NaPAA) in 20 mM and 100 mM aqueous NaCl at 15 and 75 degrees C. At 15 degrees C, almost all triple helical peptides form a complex with NaPAA when the molar ratio of acrylic acid unit to peptide molecules is larger than 10 whereas they are molecularly dispersed at 75 degrees C. Furthermore, the attached triple helices appreciably extend the main chain of NaPAA, and the radius of gyration for the complex is at most twice larger than the single NaPAA chain. Circular dichroism measurements demonstrated that the complexation noticeably stabilizes the triple helical structure and the melting midpoint temperature T(m) is 2-10 degrees C higher than that for the solution without NaPAA. This stabilization was also observed for negatively charged sodium carboxymethylamylose and sodium hyaluronate as well as for positively charged poly(vinly ammonium) chloride, but no appreciable stabilization of the triple helical structure by the polyelectrolytes was observed for an end-capped peptide Ac-(Gly-Pro-4-(R)-Hyp)(9)-NH(2). These results indicate that the complex formation is due to the electrostatic attraction between polyelectrolytes and the opposite charges at the end of uncapped triple helical peptides.
    Macromolecules 01/2012; 45(1):392-400. · 5.93 Impact Factor
  • Katsuyuki Ueno, Hitomi Ueno, Takahiro Sato
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    ABSTRACT: The colloidal polyion complex formed from sodium poly(acrylate) (NaPA) and poly(vinyl ammonium) chloride (PVACl) is almost stoichiometric but is slightly charged owing to the adsorption of an excess of the polyelectrolyte component onto the neutral complex. The charge stabilizes the colloidal polyacrylate–poly(vinyl ammonium) complex in an aqueous solution of a non-stoichiometric mixture of NaPA and PVACl, and the aggregation number of the colloidal complex increases as the stoichiometric composition is approached. This colloidal polyion complexation is an irreversible process, and the aggregation number depends on the method used to mix the NaPA and PVACl solutions. On the basis of the experimental results, we propose a simple model for colloidal polyion complex formation.
    Polymer Journal 01/2012; 44(1):59-64. · 1.55 Impact Factor
  • Hui-dan Liu, Takahiro Sato
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    ABSTRACT: The polyelectrolyte complex formed from the polyanion and polycation was studied by turbidimetry, static and electrophoretic light scattering, and elementary analysis. Sodium salts of polyacrylate (PA) and heparin (Hep) were chosen as the polyanion, and hydrochloric salts of poly(vinyl amine) (PVA) and chitosan (Chts) as the polycation. Although these vinyl polymers and polysaccharides have remarkably different backbone chemical structures and linear charge densities, all the four combinations PA-PVA, PA-Chts, Hep-PVA, and Hep-Chts provide almost stoichiometric polyelectrolyte complexes which are slightly charged owing to the adsorption of the excess polyelectrolyte component onto the neutral complex. The charges stabilize the complex colloids in aqueous solution of a non-stoichiometric mixture, and the aggregation number of the complex colloids increases with approaching to the stoichiometric mixing ratio. The mixing ratio dependence of the aggregation number for the four complexes is explained by the model proposed in the previous study.
    Chinese Journal of Polymer Science 01/2012; 31(1). · 1.42 Impact Factor
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    ABSTRACT: The z-average radius of gyration, the particle scattering function and the intrinsic viscosity have been determined for amylose tris(n-butylcarbamate) (ATBC) in D-, DL- and L-ethyl lactates, all at 25 degrees C, by light and small-angle X-ray scattering and viscometry as functions of the weight-average molecular weight ranging from 1.7 x 10(4) to 1.7 x 10(6) to investigate the chiral solvent dependence of the helical conformation of the amylose derivative. The data were analyzed in terms of the wormlike chain model to determine the Kuhn segment length lambda(-1) (the stiffness parameter) and the helix pitch per residue h. The lambda(-1) value of 49 nm in D-EL is 52% larger than 32 nm in L-ethyl lactate, an unmistakable chiral solvent effect to the helical conformation of the amylose derivative, and the relation between h and lambda(-1) is consistent with that obtained previously in nine different solvents [Polymer, 2010, 51, 4243]. The content of intramolecularly hydrogen bonding C=O groups in D-ethyl lactate is estimated to be 15% more than that in L-ethyl lactate, confirmed by heats of dilution for ethyl lactate solutions of ATBC estimated by isothermal titration calorimetry.
    Polymer Chemistry 01/2012; 3(2):472-478. · 5.37 Impact Factor
  • Macromolecules 10/2011; 44(20):8343-8349. · 5.93 Impact Factor
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    ABSTRACT: We examined the antibacterial and hemolytic activities in a series of amphiphilic block and random copolymers of poly(vinyl ether) derivatives prepared by base-assisting living cationic polymerization. Block and random amphiphilic copolymers with similar monomer compositions showed the same level of activity against Escherichia coli . However, the block copolymers are much less hemolytic compared to the highly hemolytic random copolymers. These results indicate that the amphiphilic copolymer structure is a key determinant of activity. Furthermore, the block copolymers induced dye leakage from lipid vesicles consisting of E. coli -type lipids, but not mammalian lipids, while the random copolymers disrupted both types of vesicles. In addition, both copolymers displayed bactericidal and hemolytic activities at concentrations 1 or 2 orders of magnitude lower than their critical (intermolecular) aggregation concentrations (CACs), as determined by light scattering measurements. This suggests that polymer aggregation or macromolecular assembly is not a requisite for the antibacterial activity and selectivity against bacteria over human red blood cells (RBCs). We speculate that different single-chain conformations between the block and random copolymers play an important role in the antibacterial action and underlying antibacterial mechanisms.
    Biomacromolecules 08/2011; 12(10):3581-91. · 5.79 Impact Factor
  • Source
    Yusuke Sanada, Ken Terao, Takahiro Sato
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    ABSTRACT: The addition of methanol to dilute THF solutions of chiral-achiral random copolymers of fluorene derivatives and the chiral homopolymer showed thermo-reversible circular dichroism (CD) induction in the main-chain fluorene absorption region. This finding demonstrated the uneven population of the right- and left-handed helical conformations in the polymer chains. From the sign of the induced CD, two helical screw-sense inversions were found by changing the chiral monomer content. The Ising model for chirally interacting chiral-achiral random copolymers can explain the double screw-sense inversions. Polymer Journal (2011) 43, 832-837; doi: 10.1038/pj.2011.75; published online 3 August 2011
    Polymer Journal 08/2011; 43(10):832-837. · 1.50 Impact Factor
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    ABSTRACT: Aggregates formed from amphiphilic alternating copolymer samples of sodium maleate and dodecyl vinyl ether (MAL/C12) of different molecular weights or (weight-average) degrees of polymerization Nw1 (= 76−5000) were characterized by light scattering and fluorescence techniques in 0.05 M aqueous NaCl at pH 10 to investigate the molecular weight dependence of the micellar structure of amphiphilic polyelectrolytes. The light scattering and fluorescence data demonstrated a unicore−multicore transition of the MAL/C12 micelle at Nw1 ≈ 300. The structures of unicore and multicore micelles of MAL/C12 copolymers formed were analyzed using the flower micelle model and the flower necklace model, respectively. The data points for unicore micelles formed from the three low-molecular-weight MAL/C12 fractions were in good agreement with the flower micelle model of the minimum loop size determined by the rigidity of the polymer main chain, which we proposed previously [Kawata Macromolecules 2007, 40, 1174−1180]. On the other hand, the data points for the four high-molecular-weight MAL/C12 fractions were nicely fitted to the flower necklace model, the conformation of which was represented as the touched bead model.
    Macromolecules 03/2011; · 5.93 Impact Factor

Publication Stats

1k Citations
486.75 Total Impact Points

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Institutions

  • 1988–2013
    • Osaka University
      • Department of Macromolecular Science
      Suika, Ōsaka, Japan
  • 2010
    • Dainippon Sumitomo Pharma Co., Ltd.
      Ōsaka, Ōsaka, Japan
  • 2004
    • Nagoya University
      • Department of Molecular Design and Engineering
      Nagoya, Aichi, Japan
  • 2002
    • Ritsumeikan University
      • Research Organization of Science and Engineering
      Kioto, Kyōto, Japan