SOLUBILIZATION OF UNILAMELLAR LIPOSOMES CAUSED BY QUATERNARY AMMONIUM SURFACTANTS

The mechanisms governing the solubilization of neutral and electrically charged liposomes by a series of quaternary ammonium surfactants (alkyl chain lengths C-12 (DoTAB), C-14 (TeTAB) and C-16 (HeTAB)) were investigated. Solubilization was detected as a decrease in static light scattering of liposome suspensions. Two parameters were regarded as corresponding to the effective surfactant/lipid molar ratios (Re) at which the surfactant saturated the liposomes Re-sat and led to a complete solubilization of these structures Re-sol. From these parameters the surfactant partition coefficients for these two steps (K-sat and K-sol) were determined. Liposomes were formed by phosphatidylcholine, to which phosphatidic acid (PA) or stearylamine (SA) was added when required to increase the negative or positive surface charge. The Re and K parameters fell as the surfactant alkyl chain length decreased or their CMC increased regardless of the bilayer's electrical charge. Thus, despite the fact that DoTAB showed the highest efficiency in this interaction, its concentration for saturation and solubilization of bilayers was higher than that needed for TeTAB and HeTAB in all cases. These results emphasize the major influence of the hydrophobic character of these surfactants on liposome solubilization as well as the minor influence of the electrostatic factors in this process.