Association of κ-carrageenan induced by Cs+ ions in iodide aqueous solution:: A light scattering study

Light scattering (LS) investigations have additionally confirmed the intramolecular nature of the fundamental ordered conformation (single helix) of kappa-carrageenan in aqueous 0.1 M NaI. The partial replacement of sodium with cesium ions induces a (thermoreversible) intermolecular association of the polysaccharide in the ordered conformation. The association-inducing effect can be observed already at the lowest investigated concentration of the cation. We found no significant change of the thermodynamic properties related to an alleged composition threshold value in the range of the cesium equivalent fraction, X-Cs from 0.12 to 0.40. The extent and the rate of the association process strongly increase with the concentration of cesium. Equilibrium values for the association constant could be obtained except for the case of X-Cs = 0.40, where the process is too massive to allow long-time LS investigation. In the latter condition, some additional stiffening of the chain was noticed.