Surface Charge and Overlayer pH Influence the Dynamics of Supported Phospholipid Films

Understanding the thermodynamics and kinetics of interactions between model lipid bilayers and planar supports is of critical importance in the furtherance of biosensing and the creation of biomimetic devices. Evaluating these properties can be accomplished through understanding the diffusional properties of the bilayer constituents. In this report, the dynamics of a model DMPC bilayer supported on a phosphorylated silica surface are studied in the presence and absence of interfacial Ca²⁺ as a function of pH of the aqueous overlayer. The data for this system reveal the importance of the balance of ionic interactions between the interfacial species, and the dependence of the diffusional, kinetic and thermodynamic properties of the system on pH. The thermodynamic data suggest that interactions between the bilayer and surface are mediated enthalpically rather than entropically.