The effect of polyelectrolyte counterion specificity, charge density, and conformation on polyelectrolyte-amphiphile interaction:: The carrageenan/furcellaran amitriptyline system

The effect of polyelectrolyte cation specificity, charge density, and conformation on the interaction between furcelleran, kappa, iota, and lambda -carrageenan, respectively, and amitriptyline, an amphiphilic cationic drug molecule, was studies by means of a dialysis equilibrium technique. The carrageenans used in this study-furcelleran, kappa, iota, and lambda -carrageenan-had a charge density corresponding to 0.69, 0.92, 1.53, and 2.07 sulfate groups per disaccharide. In general, the binding isotherms followed the other Li+ < Na+ < N(CH3)(4)(+) < K+ <less than or equal to> Cs+ approximate to Rb+, i.e., the binding isotherms were shifted to higher concentration of free amphiphile according to the sequence indicated. This affinity sequence correlates well with that found for the dextran sulfate-amitriptyline system (A. Hugerth and L.-O. Sundelof, Langmuir 2000, 16, 313-317). The factor determining critical aggregation concentration in the presence of Na+ compared tp K+ was found to be as follows: the flexibility (conformation) in the case of the lower charged carrageenans, i.e., furcelleran and kappa -carrageenan, charge density for iota -carrageenan, and in the lambda -carrageenan case the difference in the ROSO3--alkali ion specificity. (C) 2001 John Wiley & Sons, Inc.