Interaction energies between oxide surfaces and multiple phosphatidylcholine bilayers from extended-DLVO theory
Interaction energies between dipalmitoylphosphatidylcholine (DPPC) bilayers and corundum (α-Al(2)O(3)) or quartz (α-SiO(2)) are calculated according to extended-Derjaguin-Landau-Verwey-Overbeek (DLVO) theory in order to examine oxide-dependent multiple bilayer adsorption. Energies are investigated at two ionic strengths (I=17 or 217 mM) and compared to corresponding DPPC adsorption experiments on corundum and quartz particles. The repulsive hydration interaction diminishes sharply with separation distance, and beyond ∼3 nm, the interaction energy is determined by the electrostatic and van der Waals contributions only. We revise the electrostatic interaction to account for solution exclusion by the bilayers, extending the distance over which this interaction occurs. Calculated oxide-bilayer interaction energies explain our experimentally-observed adsorption of three bilayers on corundum compared to two on quartz at low I, and only two bilayers on both oxides at high I. The results are consistent with our hypothesis that electric double-layer extension at low I allows oxide-bilayer electrostatic interactions to contribute to deposition of DPPC bilayers at large (∼14 nm) separations. Theoretically-predicted pseudo-infinite supported bilayer stacks formed from vesicles are not observed experimentally due to kinetic considerations. Potential relevance to biomedical applications and to the role of mineral surfaces in proto-cell membrane self-assembly is discussed.