Changes in the polyelectrolyte-amphiphile interaction due to helix-coil transition induced by specific counterions or...

For the system kappa-carrageenan/amitriptyline it is shown that the degree of binding of amitriptyline is closely related to the carrageenan conformation as regulated by the counterions (Na+ or K+). The adsorption becomes much more pronounced when the carrageenan molecule is in the helix form (counterion K+) than when it has a coil conformation (counterion Na+). Furthermore, for the helical state the adsorption becomes strongly cooperative. It is also shown experimentally that the release from the adsorbed state has a conversion temperature at about 42 degrees C (helix-coil transition). The effect is also related to the linear charge density. For iota-carrageenan with a higher charge density the adsorption is strong and cooperative both in the presence of Na+ and K+ ions.