Formation of a ripple phase in nanotubular dimyristoylphosphatidylcholine bilayers confined inside nanoporous aluminum oxide substrates observed by DSC

Phase properties of substrate-supported nanotubular dimyristoylphosphatidylcholine (DMPC) bilayers confined within nanoporous channels of anodic aluminum oxide were characterized by DSC and compared with unsupported vesicles. In addition to the main phase transition, all samples exhibited a pretransition with a characteristic midpoint hysteresis between heating and cooling scans. The pretransition indicates that nanotubular bilayers could exist in a ripple phase, whereas hysteresis points to a similarity in the phase transition mechanisms. Observance of the ripple phase in lipid nanotubes is an indication of fully hydrated and only slightly perturbed bilayer surface.