Solubilization of Nonionic Monoalkyl Amphiphile−Cholesterol Vesicles by Octyl Glucoside: Cryo-Transmission Electron Microscopy of the Intermediate Structures

The micellization by octyl glucoside (OG) of diglycerol hexadecyl ether−cholesterol (1:1 wt %) sonicated vesicles containing a small amount of dicetyl phosphate has been studied by quasielastic light scattering, turbidity measurement, and cryogenic transmission electron microscopy. By using a controlled environment vitrification system (CEVS), this last technique provides new information about the vesicle−micelle transition structures without introducing artifacts due to changes in temperature or saturation. The intermediate structures have been visualized as a function of increasing surfactant composition. In the 0−0.5 range of the OG to lipid molecular ratio in the aggregates, profound vesicle rearrangements, mainly fusion and deformation processes, occur. At higher OG concentrations, the vesicles significantly decrease in size and form clusters which originate from a dense precipitate and coexist with mixed micelles, the proportion of lamellar structures being progressively reduced in favor of micellization. Beyond a OG to lipid ratio of 6.7 in the aggregates, only mixed micelles are depicted.