Enhanced entrapment of a quaternary ammonium compound in liposomes by ion-pairing

The encapsulation of a quaternary ammonium compound by multilamellar liposomes was enhanced by formation of ion-pairs with a counterion. Thus, [14C]methantheline bromide was synthesized and paired with a 25 M excess of trichloroacetate. Under these conditions, the amount of radioactivity entrapped by phosphatidylcholine liposomes was three times greater than when no trichloroacetate was present. The increased liposomal loading was probably due to the solubilization of the ion-pair in the lipid membrane of the liposome.