Concentration Dependence of the Order‐Disorder Transition of Carrageenans

Abstract

The temperature-induced changes in optical rotation which are associated with the order-disorder transition of carrageenans [isolated from Eucheuma spinosum] were analyzed to investigate concentration dependence and to determine the number of polysaccharide chains involved in the ordered species at equilibrium. The consequences of the polydispersity were analyzed by computer-modelling. For l-carrageenan segments in 0.1 M NaCl and 0.1 M KCl solution, a 2-chain state supports the double helix model. For .kappa.-carrageenan segments the apparent average number of molecules involved in the ordered state at equilibrium is 3.7, suggesting that if double helices form they aggregate further. The method of investigation may be generally applicable to measuring the number of chains which associate in ordered states in aqueous solutions of polysaccharides.