Quantum–classical simulation of proton transport ia a phospholipid bilayer

Abstract

Proton transport ia a phospholipid membrane was studied using a mixed quantum–classical molecular dynamics simulation technique. We first investigated proton diffusion into the hydrophilic region of the membrane. The ammonium and phosphate groups of the lipid molecules were found to form a hydrogen bonded network. Permeation of this network is related to an activation energy of 20 kcal mol⁻¹. Close to the intermediate region between the head groups and the alkyl chains of the lipid bilayer proton association to the negatively charged phosphate groups results in a local minimum in the potential of mean force. Back diffusion was found to be inhibited by a barrier of 8 kcal mol⁻¹. Finally proton transfer through the hydrophobic interior of the membrane was investigated according to the solubility-diffusion and the pore mechanism. From our simulations the increase in proton permeability in the presence of water pores could be demonstrated qualitatively.