Concentration Dependence of the Order‐Disorder Transition of Carrageenans

The temperature-induced changes in optical rotation which are associated with the order-disorder transition of carrageenans have been analysed to investigate the concentration dependence and hence to attempt to derive the number of polysaccharide chains involved in the ordered species at equilibrium. The consequences of the known polydispersity have been analysed by computer-modelling and it is shown that this need not cause misleading results. For iota-carrageenan segments of 0.1 M NaCl and 0.1 M KCl solution the results point to a two-chain state and therefore support the proposed double helix model. For chi-carrageenan segments the apparent average number of molecules involved in the ordered state at equilibrium is 3.7, suggesting that if double helices form here 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.