Dynamics of water at membrane surfaces: Effect of headgroup structure.

Atomistic molecular dynamics simulations of fully hydrated 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE), and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) bilayers in the liquid-crystalline state were carried out to investigate the effect of different lipid headgroups on the dynamics of water at the bilayer surface in short 80 ps time scales. Results obtained in these studies show that the hydrogen bonding amine group of POPE and the glycerol group of POPG slow water motion more than the equivalent choline group of POPC. Therefore, it is surprising that the effect of a POPC bilayer surface on water dynamics is similar to that of POPE and POPG bilayers. That result is due to a much higher number of water molecules interacting with the choline group of POPC than hydrogen-bonded molecules interacting with amine or glycerol groups of POPE and POPG.