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Yoshikazu Ito,
Akira Miyazaki,
Kazuyuki Takai,
Vajiravelu Sivamurugan,
Takashi Maeno,
Takeshi Kadono,
Masaaki Kitano,
Yoshihiro Ogawa, Naotake Nakamura,
Michikazu Hara,
Suresh Valiyaveettil,
Toshiaki Enoki
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ABSTRACT: The magnetic dipole-dipole interaction between nanomagnets having huge magnetic moments can have a strength comparable to that of the van der Waals interaction between them, and it can be manipulated by applying an external magnetic field of conventional strength. Therefore, the cooperation between the dipole-dipole interaction and the applied magnetic field allows the magnetic moments of nanomagnets to be aligned and organized in an ordered manner. In this work, a network of magnetic nanoparticles connected with flexible long-alkyl-chain linkers was designed to develop a "magnetic sponge" capable of absorbing and desorbing guest molecules with changes in the applied magnetic field. The magnetization of the sponge with long-alkyl-chain bridges (30 C atoms) exhibited a 500% increase after cooling in the presence of an applied field of 7 T relative to that in the absence of a magnetic field. Cooling in a magnetic field leads to anisotropic stretching in the sponge due to reorganization of the nanomagnets along the applied field, in contrast to the isotropic organization under zero-field conditions. Such magnetic-responsive organization and reorganization of the magnetic particle network significantly influences the gas absorption capacity of the nanopores inside the material. The absorption and desorption of guests in an applied magnetic field at low temperature can be regarded as a fascinating "breathing feature" of our magnetic sponge.
Journal of the American Chemical Society 08/2011; 133(30):11470-3. · 9.91 Impact Factor
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ChemPhysChem 11/2008; 9(17):2457-60. · 3.41 Impact Factor
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ABSTRACT: The mol-ecular structure of the title compound, C(16)H(32)I(2), is centrosymmetric and the mol-ecular skeleton, including both terminal I atoms, has an all-trans conformation. The mol-ecules form layers of thickness a. These features are similar to those of the smectic C phase of liquid crystals.
Acta Crystallographica Section E Structure Reports Online 01/2008; 64(Pt 2):o418. · 0.35 Impact Factor
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ABSTRACT: Crystal structures of long-chain alkane-α,ω-diols with an even number of carbon atoms from 20 to 24 are determined. The molecular structures are similar to those of the lower homologues with an even number of carbon atoms analyzed previously; however, the methylene chain packings are different from each other. In the newly analyzed structure, it is found that the crystal structure type has an advantage in the close packing for the methylene part with increasing hydrophobic interactions. Crystal structures of a different polymorphic form in the even number of carbon atoms from 16 to 24 are also determined. The molecular and crystal structures are similar to those of an odd number of carbon atoms analyzed previously. However, the structures are slightly different from self-assembled multilayer structures whose models are derived from a grazing incidence synchrotron X-ray diffraction data. The carbon number starting to exhibit a polymorphic form coincides with that starting to show a rotator phase which are observed just below their melting points. From the viewpoint of the epitaxial growth at the surface and of the calculated density, it is found that the crystal structure of the polymorphic form has an advantage in exhibiting the rotator phase.
12/2007;
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ABSTRACT: The phase transition behavior of liquid crystalline cyclic-siloxanes containing fluorine atoms in the terminal mesogenic groups is reported. The series has different spacer length and the number of fluorine atoms that are included in the terminal mesogenic group. The thermal property of the compounds was investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The influence of the spacer length between cyclic-siloxane core and the terminal mesogenic groups on the mesomorphic properties was discussed. Moreover, we measured rheological property of these compounds in the presence of electric field. We described their electro-rheological effect (ER effect) in consideration of the influence of molecular structure. The cyclic compounds exhibited considerably large ER effect of which the response time to an electric field was fast. They were expected to be used as novel ER fluids in engineering field. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007
Journal of Applied Polymer Science 05/2007; 105(5):2474 - 2481. · 1.29 Impact Factor
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ABSTRACT: A side‐chain liquid crystalline polysiloxane derivative possessing mesogens was synthesized. The mesogens included a large dielectrically‐anisotropic moiety. Phase transition behaviour was investigated and the electrorheological (ER) effect of the polymer considered. No ER effect was observed in non‐sheared polysiloxane derivative because of its high inherent viscosity. However, a large ER effect was observed after pre‐shearing. Pre‐shearing, i.e. shearing with a high shear rate before the measurements, arranges the terminal mesogens in the shearing direction. Furthermore, a dilution of the sample led to a larger ER effect exceeding 10 000 Pa. We thus were able to demonstrate a new approach for the appearance of the ER effect.
Liquid Crystals 02/2007; 34(2):229-234. · 1.86 Impact Factor
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ABSTRACT: Poly{3-[(S)-2-methylbutoxy]phenyl isocyanate} was shown to be locally helical, but a rather flexible wormlike chain of persistence length 3 nm. Its optical activity changed remarkably on temperature−solvent and molecular weight, vanishing at a specific temperature Tc irrespective of molecular weight, exhibiting a cooperative transition of helical conformations. Such optical activity data were well explained by a theory of Lifson et al. on the helix reversal model, taking the conformations of the terminal residues explicitly. This polymer is locally helical and rodlike because of its conjugating main-chain amide bonds, which are conjugating also with side-chain phenyl rings. However, the latter conjugation weakens the main-chain stiffness, with almost no contribution to the global stiffness from helix reversal points.
04/2006;
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ABSTRACT: Dielectric dispersion measurements were made on aqueous solutions of a triple-helical polysaccharide schizophyllan over a wide concentration range 10−50 wt % at −45 to +30 °C. In the solution state, three different water structures with the different relaxation times τ were found, namely, bound water (τl), structured water (τs), and loosely structured water (τls) in addition to free water (τP). Structured water is less mobile and loosely structured water is nearly as mobile as free water, but bound water with τl is much less mobile, thus τl τs τls τP. The order−disorder transition accompanies the conversion between structured water and loosely structured water. However, the species with τs remains even in the disordered state and constitutes part of bound water in the entire temperature range. In the frozen state, in addition to bulk water formed by partial melting, two mobile species existed, which were assigned to liquidlike bound water and found to be a continuation of bound water in the solution state. These relaxation time data are discussed in connection with the entropy levels of the four structures deduced from heat capacity data (cf. Yoshiba, K.; et al. Biomacromolecules 2003, 4, 1348−1356).
09/2004;
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ABSTRACT: Heat capacity measurements were made on aqueous solutions of a triple-helical polysaccharide schizophyllan by precision adiabatic calorimetry over a wide range of concentrations 30.45−90.93 wt % at temperatures between 5 and 315 K. The heat capacity curves obtained were divided into four groups depending on the weight fraction of schizophyllan w regions I−IV. In region I, triple-helices with the sheath of bound water, structured water, and loosely structured water forming layers around the helix core are embedded in free water. In region II, there is no free water, and loosely structured water decreases until it vanishes, but structured water stays constant with increasing w. In region III, bound water remains unaffected, but structured water decreases with increasing w by overlapping each other. Finally, in region IV, only schizophyllan and bound water exist, the latter decreasing upon increasing w. The maximum thickness of each layer is 0.183 nm for bound water, 0.134 nm for structured water, and 0.236 nm for loosely structured water, and these layers of water are at the enthalpy levels of 53%, 93.7%, and nearly 100%, respectively, between ice (0%) and free water (100%).
07/2003;
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ABSTRACT: Cholesteric pitch P was measured on D2O solutions of a triple-helical polysaccharide schizophyllan as functions of temperature and concentration. The value of P varied with concentration and temperature and showed different concentration dependencies at lower and higher temperatures, with a sudden decrease in P in between. This is due to the order−disorder transition in schizophyllan solutions around 17 °C in D2O. These data were analyzed by a statistical theory taking into account chiral repulsive and attractive interactions proposed by Sato et al. A subtle imbalance between the attractive and repulsive interactions gave rise to a large change in P. For the schizophyllan solutions, the attractive interaction changed according to the transition, while the change of the repulsive one was less remarkable. Similar analyses were performed on poly(γ-benzyl l-glutamate) data, elucidating the roles of the two interactions in determining the cholesteric structure.
02/2003;
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ABSTRACT: Deuterium oxide solutions of schizophyllan, a triple-helical polysaccharide, undergoing an order-disorder transition centered at 17 degrees C, were studied by optical rotation (OR) and heat capacity (C(p)) to elucidate the molecular mechanism of the transition and water structure in the solution and frozen states. The ordered structure at low temperature consisted of the side chains and water in the vicinity forming an ordered hydrogen-bonded network surrounding the helix core and was disordered at higher temperature. In the solution state appeared clearly defined transition curves in both the OR and C(p) data. The results for three samples of different molecular weights were analyzed theoretically, treating this transition as a typical linear cooperative transition from the ordered to disordered states and explained quantitatively if the molecular weight polydispersity of the sample was considered. The excess heat capacity C(EX)(p) defined as the C(p) minus the contributions from schizophyllan and D(2)O was estimated. In the frozen state it increased with raising temperature above 150 K until the mixture melted. This was compared with the dielectric increment observed in this temperature range and ascribed to unfreezable water. From the heat capacity and dielectric data, unfreezable water is mobile but more ordered than free water. In the solution state, the excess heat capacity originates from the interactions of D(2)O molecules as bound water and structured water, and so forth. Thus the schizophyllan triple helix molds water into various structures of differing orders in solution and in the solid state.
Biopolymers 06/2002; 63(6):370-81. · 2.87 Impact Factor
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ABSTRACT: Deuterium oxide solutions of a triple-helical polysaccharide schizophyllan, undergoing an order-disorder transition centered around 17 degrees C, were studied by the time-domain reflectometry (TDR) to obtain dielectric dispersions in the solution and frozen states. In the solution state, the dispersion below the transition temperature is resolved in three dispersions (relaxation times at 0 degrees C) ascribed to side chain glucose residue (1; 102 ns), structured water (s; 2.0 ns) and bulk water (h), respectively, from low to high frequencies. Bulk water is divided into slow water (h2; 0.04 ns) and free or pure water (h1; 0.02 ns). Above the transition temperature structured water almost disappears and is compensated by slow water. Structured water is similar to bound water for proteins but different from it because of this transition behavior. Another dispersion (l) seen at the lowest frequency is assigned to the rotation of side-chain glucose residue coupled with hydrated water. Parts of this dispersion and structured water are suggested to constitute bound water. In the frozen state were observed a major dispersion (h; 0.14 ns) and a minor one (m; 28 ns), which were ascribed to considerably mobile and less mobile waters. They are similar to but not exactly the same as that for unfreezable water in bovine serum albumin solutions argued by Miura et al. (Biopolymers, 1995, Vol. 36, p. 9). Water is molded into different structures by the triple helix.
Biopolymers 02/2002; 63(1):21-31. · 2.87 Impact Factor
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ABSTRACT: Ten narrow-distribution samples of poly{n-hexyl-[(S)-3-methylpentyl]silylene} (PH3MPS) ranging in weight-average molecular weight from 3.1 × 103 to 8.7 × 105 in isooctane, n-hexane, and methylcyclohexane were studied by circular dichroism and ultraviolet absorption over a wide temperature range (from −75 to 85 °C). To follow the conformational transition, Kuhn's dissymmetry factor gabs as a measure of helicity was determined as a function of molecular weight and temperature from the ratio of circular dichroism to absorbency. The molecular weight dependence of gabs was analyzed by a statistical mechanical theory based on a conformational picture of an alternating sequence of right-handed and left-handed helices intervened by helix reversals. The free energy of the helix reversal was much smaller than those for polyisocyanates investigated previously [poly((R)-1-deuterio-n-hexyl isocyanate) and poly((R)-2-deuterio-n-hexyl isocyanate)] at the same temperatures although its solutions showed large circular dichroism. Therefore, it was shown that the correlation lengths of the helix for this polymer were much shorter than the polyisocyanates at the same temperature. Thus, the helix reversal is the dominant molecular process in the conformational properties of PH3MPS.
07/2001;
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ABSTRACT: Light scattering and vicosity measurements were made on fractionated samples of poly{n-hexyl-{(S)-2-methylbutyl]silylene)} (PH2MBS, 1) and poly{n-hexyl-[(S)-3-methylpentyl]silylene} (PH3MPS, 2) in isooctane to determine their stiffness, which are expressed in terms of the persistence length q of Kraty and Porod. The q of polymer 1 is as large as 85 nm and depends only slightly on temperature, indicating that its conformation is almost rodlike, whereas the q of polymer 2 is 6.2 nm, its global conformation being close to a random coil. It is concluded that the global conformation of polysilylene is determined by its side chain; polysilylene with a β-branch is much stiffer compared to those without it.
03/2001;
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ABSTRACT: Electro-rheological (ER) effect of a blend composed of two liquid crystalline materials with different molecular weights is described in this article. The results indicated that ER effect of the blend was observed at the temperature range where each neat sample did not show ER effect. Furthermore, both storage modulus (G′) and loss modulus (G″) decreased drastically at the temperature range for the blend in dynamic viscoelastic measurements. We show that steady ER effect could be obtained by using a blend made up of two liquid crystalline components, whereas remarkable increment in shear stress was not observed for each component under applied electric field.
Polymer. 48(25):7264-7270.
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ABSTRACT: Dielectric dispersion measurements were made on aqueous solutions of a triple-helical polysaccharide schizophyllan over a wide concentration range 10-50 wt % at -45 to +30 degrees C. In the solution state, three different water structures with the different relaxation times tau were found, namely, bound water (taul), structured water (taus), and loosely structured water (tauls) in addition to free water (tauP). Structured water is less mobile and loosely structured water is nearly as mobile as free water, but bound water with taul is much less mobile, thus taul > taus > tauls greater, similar tauP. The order-disorder transition accompanies the conversion between structured water and loosely structured water. However, the species with taus remains even in the disordered state and constitutes part of bound water in the entire temperature range. In the frozen state, in addition to bulk water formed by partial melting, two mobile species existed, which were assigned to liquidlike bound water and found to be a continuation of bound water in the solution state. These relaxation time data are discussed in connection with the entropy levels of the four structures deduced from heat capacity data (cf. Yoshiba, K.; et al. Biomacromolecules 2003, 4, 1348-1356).
Biomacromolecules 5(6):2137-46. · 5.48 Impact Factor
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ABSTRACT: Heat capacity measurements were made on aqueous solutions of a triple-helical polysaccharide schizophyllan by precision adiabatic calorimetry over a wide range of concentrations 30.45-90.93 wt % at temperatures between 5 and 315 K. The heat capacity curves obtained were divided into four groups depending on the weight fraction of schizophyllan w regions I-IV. In region I, triple-helices with the sheath of bound water, structured water, and loosely structured water forming layers around the helix core are embedded in free water. In region II, there is no free water, and loosely structured water decreases until it vanishes, but structured water stays constant with increasing w. In region III, bound water remains unaffected, but structured water decreases with increasing w by overlapping each other. Finally, in region IV, only schizophyllan and bound water exist, the latter decreasing upon increasing w. The maximum thickness of each layer is 0.18(3) nm for bound water, 0.13(4) nm for structured water, and 0.23(6) nm for loosely structured water, and these layers of water are at the enthalpy levels of 53%, 93.7%, and nearly 100%, respectively, between ice (0%) and free water (100%).
Biomacromolecules 4(5):1348-56. · 5.48 Impact Factor
