Multinuclear NMR Study on the Sol–Gel Transition of Aqueous κ- and λ-carrageenan Solutions: Selective Site Binding of Group I Cations

Multinuclear NMR study was carried out to study the interaction between group I cations (Na + , K + , Rb + and Cs + ) and κ- and λ-carrageenans. κ- and λ-carrageenans showed a marked difference in their physical properties, particularly in their gel-forming ability. Unlike aqueous λ-carrageenan solution, the gelation of κ- carrageenan produces highly selective 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 of selective site binding of ions to form the cross-linking domains in κ-carrageenan.