Effects of monovalent cation and anion species on the conformation of gellan chains in aqueous systems

The effects of monovalent cation and anion species on the conformation of gellan chains in aqueous solutions were examined by optical rotation (OR) and fluorescence anisotropy measurements. The OR measurement suggested that a cation species with a large ionic radius aggregates the gellan chains to form supramolecular structures that have negative optical rotations even in the solution state. The anion species F− lowered the coil-helix transition temperature and suppressed the aggregation of gellan chains, while the anion species Cl−, Br−, and I− showed no influence on the coil-helix transition temperature or the aggregation behavior. The coil-helix transition of gellan chains was affected by the cation concentration rather than by the type of cation species; however, the latter was the predominant factor with respect to the aggregation of gellan chains.