Permeability of cryptands through dihexadecyl phosphate bilayer membranes

The leakage of Ru(bpy)3(2+) across a membrane of dihexadecyl phosphate (DHP) vesicles was compared when induced by (2.1.1), (2.2.1), (2.2.2.), (2.2.1.)C10 and (2.2.2.)C10-cryptands, and by (2.2.) and (2.2.)-bishydroxyethyl, i.e., ionizable macrobicyclic and monocyclic amino polyethers. Ru(bpy)3(2+) leakage increased as the permeant concentrations rose and was much higher for the very lipophilic cryptands. It also increased as the pH fell, and was lower and less dependent on the permeant concentration when induced by addition of partially titrated than by non-pretitrated cryptand. The efficiency of the permeant decreased as the alkali cation concentration rose and was independent of the cation type. It also varied with the membrane type: the efficiency of the (2.2.2.)C10-cryptand was higher on permeation of the membrane of DHP vesicles made from dihexadecyl phosphate than that of large unilamellar vesicles (LUV) composed of alpha-phosphatidylcholine, alpha-phosphatidic acid and cholesterol in an 8:1:1 molar ratio. The results are discussed in terms of the structural, physico-chemical and electrical characteristics of the permeating agents and of the membranes.