ABSTRACT
This chapter focuses on proton permeation of lipid bilayers. It examines an alternative mechanism for permeation of ions across lipid bilayers and aims to compare experimental results with theoretical predictions from both models. A. Parsegian first described the barrier properties of lipid bilayers in terms of the Born energy required to bring an ion from a high-dielectric aqueous phase to the low-dielectric medium of the hydrocarbon chains composing the membrane interior. The nonelectrostatic portion of the total Gibbs energy is usually assumed to arise from the energy of solvation of a hypothetical ion that lacks electrical charge, but with all other characteristics unchanged. Two types of pore structures in the lipid bilayer are possible, which can be roughly classified as hydrophobic and hydrophilic defects. Partitioning models are consistent with some features of ionic permeation, particularly if solvophobic energy is taken into account.
