SOLUBILIZATION OF UNILAMELLAR LIPOSOMES CAUSED BY QUATERNARY AMMONIUMSURFACTANTS

The mechanisms governing the solubilization of neutral and electricall y charged liposomes by a series of quaternary ammonium surfactants (al kyl chain lengths C-12 (DoTAB), C-14 (TeTAB) and C-16 (HeTAB)) were in vestigated. Solubilization was detected as a decrease in static light scattering of liposome suspensions. Two parameters were regarded as co rresponding to the effective surfactant/lipid molar ratios (Re) at whi ch 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 wh ich phosphatidic acid (PA) or stearylamine (SA) was added when require d to increase the negative or positive surface charge. The Re and K pa rameters fell as the surfactant alkyl chain length decreased or their CMC increased regardless of the bilayer's electrical charge. Thus, des pite the fact that DoTAB showed the highest efficiency in this interac tion, its concentration for saturation and solubilization of bilayers was higher than that needed for TeTAB and HeTAB in all cases. These re sults emphasize the major influence of the hydrophobic character of th ese surfactants on liposome solubilization as well as the minor influe nce of the electrostatic factors in this process.