Effect of Triton X-100 on the physical properties of liposomes

The interaction of the nonionic detergent Triton X-100 with phospholipid bilayers of liposomes made of egg yolk phosphatidylcholine was studied through the behavior of several physical properties. The dielectric permittivity spectra between 30 kHz and 13 MHz, the viscosity, the density, and the d.c. conductivity (1 kHz) of aqueous liposomes suspensions at various mole ratios were measured at 22 degrees C. For detergent-to-phospholipid ratios lower than 3, a dielectric relaxation process of characteristic frequency of about 50 kHz was recorded. This process does not appear for the liposomes in water, and becomes smaller and smaller for detergent-to-phospholipid ratios higher than 3. The viscosity of these suspensions showed a biphasic behavior, being remarkably increased by the detergent for concentration ratios lower than 3. The measured d.c. conductivity of these samples showed no relation with this process, being slightly increased when the detergent content is increased. As a conclusion of these results a well defined concentration range appears where the phospholipid organization changes forming highly asymmetrical structures.