Effects of ether vs. ester linkage on lipid bilayer structure and water permeability

The structure and water permeability of bilayers composed of the ether-linked lipid, dihexadecylphosphatidylcholine (DHPC), were studied and compared with the ester-linked lipid, dipalmitoylphosphaditdylcholine (DPPC). Wide angle X-ray scattering on oriented bilayers in the fluid phase indicate that the area per lipid A is slightly larger for DHPC than for DPPC. Low angle X-ray scattering yields A = 65.1 Å2 for DHPC at 48 °C. LAXS data provide the bending modulus, KC = 4.2 × 10−13 erg, and the Hamaker parameter H = 7.2 × 10−14 erg for the van der Waals attractive interaction between neighboring bilayers. For the low temperature phases with ordered hydrocarbon chains, we confirm the transition from a tilted Lβ′ gel phase to an untilted, interdigitated LβI phase as the sample hydrates at 20 °C. Our measurement of water permeability, Pf = 0.022 cm/s at 48 °C for fluid phase DHPC is slightly smaller than that of DPPC (Pf = 0.027 cm/s) at 50 °C, consistent with our triple slab theory of permeability.