Vesicle solubilization by alkyl sulfate surfactants: A cryo-TEM study of the vesicle to micelle transition

The solubilization of small unilamellar lecithin vesicles by some different alkyl sulfate surfactants (C10SO4-, C12SO4-, and C14SO4-) was investigated by means of light scattering and cryo-transmission electron microscopy. All surfactants were found to induce vesicle growth at subsolubilizing concentrations and a transformation into small globular lipid/surfactant mixed micelles at high surfactant concentrations. The surfactant chain length, however, was found to have a profound influence both on the amount of surfactant needed for solubilization of the lipid bilayer and on the type of structures formed during the vesicle to micelle transition. For C10SO4- a coexistence between vesicles composed of normal lamellar (L(alpha)) phase and thread-like micelles was observed, whereas during solubilization with C12SO4- and C14SO4- an intermediate, presumably holey lamellar, phase appeared before the bilayers were eventually solubilized into lipid/surfactant mixed micelles. The above observations pertain to measurements made in buffer solutions containing 150 mM NaCl. Upon decreasing the salt concentration, disk-shaped micelles, and at higher surfactant concentration thread-like micelles, frequently connected via three-way junctions, were observed during solubilization with C12SO4-. (C) 1996 Academic Press,Inc.