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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: 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
