LIGHT-SCATTERING-STUDIES OF THE DILUTE-SOLUTION BEHAVIOR OF KAPPA-CARRAGEENEN, IOTA-CARRAGEENAN AND LAMBDA-CARRAGEENAN

An extensive study of the dilute solution behaviour of the carrageenan s, mainly by light scattering techniques, is presented. Both kappa- an d lambda-carrageenan exhibit ion-specific interaction. Normal polyelec trolyte behaviour is observed for kappa-carrageenan and a conformation al transition without a change in molar mass is reported, hence, exclu ding a coil-to-double-helix transition under the experimental conditio ns used in this study. A concentration-dependent association of iota-c arrageenan is observed as a function of increasing salt concentration; however all light scattering measurements extrapolate to the same mol ar mass at infinite dilution under conditions where the single helix p revails. The influence of counterion on chain stiffness, as judged by comparison of experimental results with theoretical predictions, is di scussed in terms of the persistence length. As all results have been o btained on polydisperse samples, attempts have been made to fractionat e the carrageenans. This can be successfully done for kappa- and lambd a-carrageenan, but not for iota-carrageenan. The present light scatter ing study on iota-carrageenan provides guidelines for a move appropria te strategy to fractionate polydisperse carrageenan samples.