Water structures of differing order and mobility in aqueous solutions of schizophyllan, a triple-helical polysaccharide as revealed by dielectric dispersion measurements

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).