Molecular organization in DODAC membrane fragments

We have studied the molecular organization of surfactants in DODAC membrane fragments. The membrane phase transition has been probed by measuring the EPR spectra of incorporated 16-doxylstearic acid and by the study of the kinetics of pyrene excimer formation. In sonicated samples no phase transition is observed. At room temperature disks are still in a fluid state (as probed by pyrene) but with a high local viscosity (as probe by EPR). We describe the phase of DODAC in disk at room temperature as a glass. This glass state is distinct from the disordered state that might be expected from DODAC “micelles.” In a multi-layered DODAC membrane, we observed a phase transition at the temperature of 38°C (EPR) and 40°C (pyrene), close to the reported values. Hysteresis is observed only in the experiment of intermolecular excimer formation. We interpret this hysteresis as the time it takes for pyrene to drain out of DODAC crystalline microdomains.