Interaction of styrene with DODAB bilayer vesicles. Influence on vesicle morphology and bilayer properties

The solubilization of styrene in large unilamellar DODAB vesicles is invest igated at a styrene to DODAB molar ratio of 2:1. The combination of various vesicle characterization methods allows a simultaneous look at vesicle mor phology (cryo-TEM, DLS) and molecular interactions (micro-DSC, various fluo rescence techniques) and gives a complete picture of the DODAB vesicles bef ore and after the addition of styrene. Cryo-TEM and DLS results reveal that the addition of styrene does not break up the DODAB vesicles as an entity, but the peculiar angular DODAB vesicle morphology becomes smoother and the geometries tend to be more curved. The change in morphology is explained b y an enhanced bilayer fluidity and the drastic depression of the phase tran sition temperature as determined from calorimetry and fluorescence experime nts. Moreover, micro-DSC scans and fluorescence experiments with two differ ent pyrene probes suggest a nonhomogeneous distribution and partial demixin g of solute and bilayer for temperatures below similar to 27 degrees C. Abo ve this temperature, the solute appears uniformly distributed and facilitat es molecular motion in the amphiphile aggregate. The diffusion coefficient for the lateral diffusion of an amphiphilic probe is then increased by a fa ctor of 2 compared to the pure DODAB vesicles. The observed solubilization phenomena are rationalized by interactions of the solute with both the hydr ocarbon part and the polar headgroup region of the bilayer.