Phosphatidylcholine vesicle solubilization by glucosidic non-ionic surfactants: a turbidity and x-ray diffraction study.

The solubilization mechanism of egg phosphatidylcholine (PC) vesicles by octyl glucoside (OG) and hecameg (HG) was examined at 25°C by turbidity and small-angle x-ray scattering (SAXS) analysis. Turbidity was recorded upon continuous surfactant addition to PC vesicles in the highly diluted region of the lipid-surfactant-water phase diagram. SAXS analysis was performed on more concentrated samples with the same surfactant and lipid compositions as in the diluted domain studied by turbidity. Very similar vesciel-to-micelle transition mechanisms are observed for OG and HG. The solubilization process involves four steps, the limits of which univocally correspond to precise surfactant-to-Pc molar ratios in the aggregates and surfactant concentrations in the aqueous continuum. However, HG shows a better efficiency to dissolve PC vehicles than OG. These limits correspond to the boundaries of distinct structural states observed in the more concentrated region. With increasing surfactant-to-lipid ratios, these states are successively: 1) a lamellar structure characterized by a main repeat distance close to that observed for the PC L\ga phase, beside one or more other apparently lamellar structure(s) of smaller periodicity, 2) a unique lamellar phase, 3) coexisting lamellar and micellar assemblies, and 4) interacting micelles. [ABSTRACT FROM AUTHOR]