Light scattering investigation of iota-carrageenan aqueous solutions. Concentration dependence of association

The conformational transition of t-carrageenan in different salt solutions under nongelling conditions has been studied by light scattering (WALLS). T he focus is on the thermodynamic interactions and the concentration depende nce of the reduced scattering intensity at zero angle. An upward curvature of (KCp/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 conditi ons of conformational ordering a decrease of polymer concentration, C-p, is accompanied by a decrease of ((M) over bar (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 ((M) over bar (w))(assoc) are alread y very close to that of the single-stranded disordered conformation. In the same range, the values of the specific optical activity remain constant. T his is a confirmatory evidence that the fundamental ordered conformation of t-carrageenan is a single helix.