Permeability changes of phospholipid vesicles caused by surfactants

The partition coefficient at equilibrium of different surfactants between the aqueous phase and the lipid bilayer of small unilamellar vesicle (SUV) liposome has been determined. The release of the fluorescent agent 5-(6) carboxyfluorescein from the interior of liposomes, induced by a nonionic surfactant octylphenol ethoxylated with 10 units of ethylene oxide (Triton X-100), by two anionic surfactants — sodium dodecyl sulphate and sodium dodecyl ether sulphate — and by an amphoteric surfactant dodecyl betaine was studied at sub-solubilizing concentrations. The following increasing order of the partition coefficients obtained for each surfactant can be observed: Triton X-100 > sodium dodecyl ether sulphate > sodium dodecyl sulphate > dodecyl betaine. There was a strong positive association between coefficient of partition and the ability of the different surfactants to modify the permeability of liposomes. The importance of the presence of ethylene oxide units in the molecular structure of the surfactant in relation to alter the partition coefficient in front of SUV liposomes is indicated.