三重らせん多糖シゾフィランの水溶液中での秩序－無秩序転移

抄録

A triple helical polysaccharide, schizophyllan, undergoes an order-disorder transition which is concerned with the side chain glucose residues and water molecules in aqueous solution. The order-disorder transition exhibits a strong molecular weight dependence, indicating a highly cooperative conformational change of side-chain glucose residues, and it was treated in terms of a linear cooperative theory originally proposed for the helix-coil transition of polypeptides. From concentration dependences of the transition temperature and the transition enthalpy, we divided the solvated water around the triple helix into four layers from of loosely structured water to of strongly bound water. The order-disorder transition of the schizophyllan triple helix is also reflected on characteristic temperature dependences of the dielectric dispersion and the cholesteric pitch of aqueous solutions of schizophyllan. The dielectric dispersion data demonstrated increase of free water and decrease of structured water at the transition from the order state to the disorder state. Abrupt change of the cholesteric pitch with temperature corresponds to the change of the side chain conformation and solvated water structure during the order-disorder transition.