Interaction of 1-Propanol and 2-Propanol with Dipalmitoylphosphatidylcholine Bilayer: A Calorimetric Study

Differential scanning calorimetry (DSC) was employed to study the effects of 1-propanol and 2-propanol on the thermotropic behavior of dipalmitoylphosphatidylcholine (DPPC) bilayer membranes. The biphasic effect was observed in both systems based on an abrupt reversal in trend of the gel-to-liquid crystalline main transition temperatures upon heating. At this inflection point, a large hysteresis also occurred between the heating and cooling main transition temperatures, and the pretransition peaks disappeared. Such evidence indicated the formation of the interdigitated gel phase at this critical concentration, which was determined to be 0.39 mol.L-1 and 0.52 mol.L-1 for 1-propanol and 2-propanol, respectively. This threshold concentration was found to be higher for 2-propanol than for 1-propanol, suggesting that the shorter chain length and branching in 2-propanol caused it to be a less effective inducer for the interdigitated phase in DPPC. On some heating and cooling scans, an extra peak is observed around and beyond the critical concentration, indicating the presence of mixed phases as the interdigitated phase forms.