VESICLE TO MICELLE STRUCTURAL TRANSITIONS INVOLVED IN THE INTERACTIONOF DODECYLBETAINE WITH LIPOSOMES - TRANSMISSION ELECTRON-MICROSCOPY AND LIGHT-SCATTERING-STUDIES

The interaction of the amphoteric surfactant dodecylbetaine (C-12-Bet) with phosphatidylcholine (PC) liposomes was studied by means of trans mission electron microscopy (TEM) and changes in the mean particle siz e (quasi-elastic light scattering, QELS) and in static light scatterin g (SLS) of the system were observed during liposome solubilization. A good correlation was found between the TEM diameter of the particles a nd the mean hydrodynamic diameter (HD) determined by QELS. The aggrega tes resulting in this interaction were dependent on the C-12-Ber conce ntration in the system. Thus, an initial vesicle growth occurred when the surfactant concentration was 16.66 mol%. Additional surfactant amo unts led first to the formation of largest vesicles (HD 306 nm for 37. 50 mol% C-12-Bet concentration) and second to a fall in the vesicle di ameter an in the SLS of the system. Thus, For 47.36 mol%, (Re-SAT, sur factant to PC molar ratio for liposome saturation), the TEM picture st ill showed the presence of vesicles albeit with signs of disintegratio n and vesicle fusion. When additional amounts of surfactant were added to the system the size curve started to show a bimodal distribution. Thus, for 52.38 mol% a sharp curve appeared at 9 nm corresponding to t he formation of small particles and the TEM picture showed vesicle dis integration with formation of tubular structures as a crucial intermed iate. Up to a surfactant mole percent of 60% progressive vesicle disin tegration took place with increasing presence of small aggregates (tub ular structures and bilayer fragments) and without formation of comple x multilayered structures. The gradual increase in the proportion of t hese small aggregates (mixed micelles) led to the complete solubilizat ion of liposomes. (C) 1998 Elsevier Science Ltd. All rights reserved.