On the specific role of coions and counterions on kappa-carrageenan conformation.

The role of the nature and concentration of counterions and coions on the conformation of kappa-carrageenan is discussed; particularly, that of iodide compared with chloride based on the results obtained from optical rotation, viscometry and microcalorimetry. Iodide gives a more stable helical conformation, with a larger degree of order; at the same time, it represses aggregation of the helices and the gelation ability. Concerning the ordered conformation obtained in the presence of iodide coions, the results obtained are not conclusive. From the enthalpy of the conformational change, it seems that, even in the presence of iodide, the ordered conformation remains a double helix. On the other hand, no doubling of molecular weight was obtained by MALLS/GPC. Thus, this aspect remains still under discussion.