Hydrogen bonding structure and dynamics of water at the dimyristoylphosphatidylcholine lipid bilayer surface from a molecular dynamics simulation

An analysis of the structural and dynamical hydrogen bonding interactions at the lipid water interface from a 10 ns molecular dynamics simulation of a hydrated dimyristoylphosphatidylcholine (DMPC) lipid bilayer is presented. We find that the average number of hydrogen bonds per lipid oxygen atom varies depending on its position within the lipid. Radial distribution functions are reported for water interacting with lipid oxygen, nitrogen, and phosphor-us atoms, as well as for lipid-lipid interactions. The extent of inter- and intramolecular lipid-water-lipid hydrogen bond bridges is explored along with charge pair associations among headgroups of different lipid molecules. We also examine the hydrogen bonding dynamics of water at the lipid surface. A picture emerges of a sticky interface where water that is hydrogen bonded to lipid oxygen atoms diffuses slowly. Hydrogen bonds between water and the double bonded lipid oxygen atoms are longer lived than those to single bonded lipid oxygen atoms, and hydrogen bonds between water and the tail lipid oxygen atoms are longer lived than those to headgroup oxygen atoms. The implications of these results for lateral proton transfer at the interface are also discussed.