title: Ordering in aqueous polysaccharide solutions. II. Optical rotation and heat capacity of aqueous solutions of a triple-helical polysaccharide schizophyllan.
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.
authors.affiliation: Department of Applied Chemistry, Faculty of Science and Engineering, Ritsumeikan University, Nojihigashi 1-1-1, Kusatsu, Siga 525-8577, Japan.
authors.forename: Kazuto
authors.initials: K
authors.lastname: Yoshiba
authors.forename: Tetsurou
authors.initials: T
authors.lastname: Ishino
authors.forename: Akio
authors.initials: A
authors.lastname: Teramoto
authors.forename: Naotake
authors.initials: N
authors.lastname: Nakamura
authors.forename: Yuji
authors.initials: Y
authors.lastname: Miyazaki
authors.forename: Michio
authors.initials: M
authors.lastname: Sorai
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Naoki
authors.initials: N
authors.lastname: Shinyashiki
authors.forename: Shin
authors.initials: S
authors.lastname: Yagihara
mesh_terms: D000276:Adjuvants, Immunologic / Q000737:chemistry; D002236:Carbohydrate Conformation; D009904:Optical Rotation; D012566:Sizofiran / Q000737:chemistry*; D012996:Solutions; D013816:Thermodynamics; D014867:Water
chemical_list: D000276:Adjuvants, Immunologic; D012996:Solutions; D014867:Water; D012566:Sizofiran