Slow reorganization of small phosphatidylcholine vesicles upon adsorption of amphiphilic polymers

Static or dynamic light scattering measurements were performed in parallel, on dilute mixtures of DPPC/DPPA vesicles (typical radius 60 nm) and hydrop hobically modified polymers. This technique gave evidence of the slow kinet ics involved in both the reorganization of an adsorbed polymer layer and th e membrane breakage. Hours, or sometimes days, were required in order to fo llow the variation of both the hydrodynamic radius and the scattering inten sity at intermediate stages. Images of the intermediate species were collec ted using freeze-fracture electron microscopy (FFEM). Comparison of differe nt polymers (of varying molecular weight or structure) revealed the prime i mportance of hydrophobicity on the disruption of membranes. Although the pr esence of a few percent of pendant alkyl chains along the polymer backbone induced adsorption to membranes, only the association with the more hydroph obic ones (> 25 mol% of pendant octyl groups) resulted in small mixed objec ts of micellar size (radius about 10 nm). The drop of the mean radius of in termediate structures formed upon the vesicle breakage was also sensitive t o temperature. A tentative mechanism was proposed on the basis of kinetics and FFEM studies. (C) 2001 Academic Press.