Solubilizing effects caused by alkyl pyridinium surfactants in phosphatidylcholine liposomes

The solubilization of neutral and electrically charged liposomes by a series of alkyl pyridinium surfactants (alkyl chain lengths C10-C14) was 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 at which the surfactant saturated the liposomes Re(sat) and led to a complete solubilization of these structures Re(sol). From these parameters the corresponding surfactant partition coefficients were determined. The Re and K parameters fell as the surfactant alkyl chain length decreased or both the critical micellar concentration (CMC) and the hydrophilic/lipophilic balance (HLB number) increased, regardless of the bilayers electrical charge. Thus, although decyl-pyridinium bromide (DePB) showed the highest ability for saturation and solubilization of bilayers, its concentration was always higher than that needed for dodecyl-pyridinium bromide (DoPB) and tetradecyl-pyridinium bromide (TePB), the last one being the most active. These results emphasize the influence of the hydrophilic/lipophilic balance of these surfactants on liposome solubilization and the minor influence of the electrostatic factors in this process.