Light scattering studies of the dilute solution behaviour of κ-, ι- and λ-carrageenan

Abstract

An extensive study of the dilute solution behaviour of the carrageenans, mainly by light scattering techniques, is presented. Both κ- and λ-carrageenan exhibit ion-specific interaction. Normal polyelectrolyte behaviour is observed for κ-carrageenan and a conformational transition without a change in molar mass is reported, hence, excluding a coil-to-double-helix transition under the experimental conditions used in this study. A concentration-dependent association of ι-carrageenan is observed as a function of increasing salt concentration; however all light scattering measurements extrapolate to the same molar mass at infinite dilution under conditions where the single helix prevails. The influence of counterion on chain stiffness, as judged by comparison of experimental results with theoretical predictions, is discussed in terms of the persistence length. As all results have been obtained on polydisperse samples, attempts have been made to fractionate the carrageenans. This can be successfully done for κ- and λ-carrageenan, but not for ι-carrageenan. The present light scattering study on ι-carrageenan provides guidelines for a more appropriate strategy to fractionate polydisperse carrageenan samples.