PERMEABILITY CHANGES IN THE PHOSPHOLIPID-BILAYER CAUSED BY NONIONIC SURFACTANTS

The liposome-nonionic surfactant interaction is investigated through the disrupting effect promoted by these surfactant molecules on unilamellar liposome vesicles (mean vesicle size 100 nm) prepared by reverse-phase evaporation. This interaction leads, at the outset, to modifications in the permeability of vesicles which are monitored by changes in the release of the fluorescent dye 5 (6)-carboxyfluorescein (CF) trapped inside the phospholipid bilayers. The nonionic surfactant tested was octylphenol polyethoxylated with, on average, between 8.5 and 20.0 ethylene oxide units, in the subsolubilizing range of surfactant concentrations. The coefficient of the equilibrium partition of each surfactant between the aqueous phase and the lipid bilayer is investigated. The surfactant that shows the highest value from the partition coefficients obtained is the octylphenol with 9.5 ethylene oxide units. There seems to exist a positive correlation between the partition coefficient of the surfactant and its ability to modify the permeability of liposomes. The importance of the hydrophilic-lipophilic balance (HLB) of each surfactant tested on the modification of partition coefficients versus the liposomes is noted. © 1992.