Multinuclear NMR study on the sol-gel transition of aqueous kappa-and lambda-carrageenan solutions: Selective site binding of group I cations

Multinuclear NMR study was carried out to study the interaction between gro up I cations (Na+, K+, Rb+ and Cs+) and kappa- and lambda-carrageenans. kap pa- and lambda-carrageenans showed a marked difference in their physical pr operties, particularly in their gel-forming ability. Unlike aqueous lambda- carrageenan solution, the gelation of kappa- carrageenan produces highly se lective binding sites for alkali metal ions, in which Rb+, K+ and Cs+ ions bind more strongly than Na+. The alkali metal NMR suggests the occurrence o f selective site binding of ions to form the cross-linking domains in kappa -carrageenan.