SOLUBILIZATION OF LECITHIN VESICLES BY A CATIONIC SURFACTANT - INTERMEDIATE STRUCTURES IN THE VESICLE MICELLE TRANSITION OBSERVED BY CRYO-TRANSMISSION ELECTRON-MICROSCOPY

The morphological change of lecithin vesicles during solubilization with the cationic surfactant cetyltrimethylammonium chloride (CTAC) was studied by means of cryo-transmission electron microscopy (cryo-TEM). The observed changes in aggregate size and structure were in most respects similar to those observed for systems containing lecithin and nonionic surfactants. Addition of low concentrations of CTAC to sonicated small unilamellar vesicles do as previously found for nonionics, give rise to a significant increase in the vesicle size. The growth of vesicles was monitored in time resolved cryo-TEM measurements and was clearly shown to proceed through an intermediate state comprising open bilayered discs. Contrary to other systems the addition of CTAC to the present system gives rise, at a certain concentration range, to the formation of a new intermediate structure. The samples stabilize in vesicles or open fragments of bilayers filled with holes to form a mesh-structure. Such structures, previously not documented by cryo-TEM, may be viewed as intermediates between bilayers and cylindrical micelles. The effects of CTAC on aggregate size and structure described above pertain to systems containing 100 mM NaCl. In the absence of salt the vesicle growth at low surfactant concentrations is strongly supressed, and only a dissolution of vesicles directly into mixed cylindrical micelles is observed. © 1993 by Academic Press, Inc.