TRANSMISSION ELECTRON-MICROSCOPY AND LIGHT-SCATTERING-STUDIES ON THE INTERACTION OF A NONIONIC ANIONIC SURFACTANT MIXTURE WITH PHOSPHATIDYLCHOLINE LIPOSOMES/

The interaction of an equimolecular mixture of nonylphenol polyethoxyl ated [NP(EO)(10)] and sodium dodecyl sulfate (SDS) surfactants with ph osphatidylcholine (PC) liposomes was studied by means of transmission electron microscopy (TEM) and changes in the mean particle size (quasi elastic light scattering; QELS) and in the static light scattering (SL S) of the system during liposome solubilization. A good correlation wa s found between the TEM diameter of particles and the mean hydrodynami c diameter (HD) determined by QELS. The aggregates resulting in this i nteraction were dependent on the surfactant concentration in the syste m. Thus, an initial vesicle growth occurred when the surfactant concen tration was 15.98 mol%, together with the formation of a very small pe rcentage of smaller particles. Additional surfactant amounts (28.32 mo l%) led first to the formation of largest vesicles (HD 418 nm) and sec ond to a fall in the vesicle diameter and in the SLS of the system. Th us, for 38.27 mol%, the TEM picture still showed the presence of vesic les, albeit with signs of disintegration. When additional amounts of s urfactant were added to the system, the size curve started to show a b imodal distribution. Thus, for 51.81 mol% surfactant concentration, a sharp curve appeared at 51 nm, corresponding to the formation of small particles and TEM pictures clearly showed vesicle disintegration with formation of tubular structures. It is noteworthy that additional sur factant amounts (from 52 to 60 mol%) led to the formation of unclosed multilayered structures together with smaller aggregates. The gradual increase in the proportion of these smaller aggregates (mixed micelles ) led to the complete solubilization liposomes. (C) 1998 Wiley-Liss, I nc.