The conformational transition of ι-carrageenan in different salt solutions under nongelling conditions has been studied by light scattering (WALLS). The focus is on the thermodynamic interactions and the concentration dependence of the reduced scattering intensity at zero angle. An upward curvature of (KC p /R 0) in conditions of conformational ordering has been interpreted as due to a concentration-dependent reversible chain association. The open association model of Elias has been applied to analyze the data. In conditions of conformational ordering a decrease of polymer concentration, C p , is accompanied by a decrease of (M̄ w)assoc. These results have been confirmed by using low-angle light scattering (LALLS). In the lowest range of C p , the decreasing values of (M̄ w)assoc are already very close to that of the single-stranded disordered conformation. In the same range, the values of the specific optical activity remain constant. This is a confirmatory evidence that the fundamental ordered conformation of ι-carrageenan is a single helix.

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