A COMPARISON OF THERMALLY INDUCED CHANGES IN SONICATED PHOSPHOLIPID AND SURFACTANT VESICLES BY MEANS OF INTRA‐MOLECULAR EXCIMER‐FORMING PROBE

Abstract The molecule (1,l'‐dipyrenyl)‐methyl ether (dipyme) was used for monitoring the bilayer fluidity of surfactant and sonicated phospholipid vesicles. In the latter systems, the observed transition temperatures ( Tc ) are identical with those found by different methods. Surfactant vesicles prepared from dioctadecyldimethylammonium bromide (DODAB) and dihexadecylphosphate (DHP) molecules manifest a similar fluidity of their bilayers as those of sonicated phospholipid vesicles below their Tc. However, unlike in phospholipid vesicles, there was no significant change of the bilayer structure above Tc observed in surfactant vesicles. DHP vesicles formed in pure water provide a different solubilization site for dipyme than those prepared in a buffer solution. Such sites are characterized by a relatively high local concentration of the probe and the appearance of the blue shifted spectrum of the excimer.