Sterols stabilize the ripple phase structure in dihexadecylphosphatidylcholine

AbstractThe presence of various sterols in mixtures with dihexadecylphosphatidylcholine (DHPC) was studied using static X-ray diffraction of temperature equilibrated samples, and real-time X-ray diffraction of samples undergoing temperature scans. It was found that these sterols eliminate the interdigitation of the alkyl chains in the DHPC sub-gel and gel-state bilayers while stabilizing the ripple gel-state at the expense of the gel-state bilayer phase. The ripple-ripple phase transition previously observed for dipalmitoylphosphatidylcholine in the presence of low molar concentrations of sterols (Wolfe et al. (1992) Phys. Rev. Lett. 68, 1085–1088) was also observed for similar DHPC-sterol mixtures. In addition, we show the first evidence that the presence of 5α-cholestane-3β,5,6β-triol will cause the lipid mixtures to continue to adopt a ripple mesophase structure even after the DHPC alkyl chain becomes disordered