The dynamics of water at the phospholipid bilayer surface: a molecular dynamics simulation study

Molecular dynamics (MD) simulations of a fully hydrated 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer in the liquid-crystalline state were carried out to investigate the effect of the membrane on the dynamics of water. Translational and rotational motions of water near the membrane surface were restricted. The effect was the strongest for water molecules that were hydrogen (H) bonded to the phosphate (Op) and carbonyl (Oc) oxygen atoms as well as those clathrating choline group of POPC. The translational motion of Oc H bonded water was slower than that of the Op H bonded water, while the rotational motion was faster. Water clatrathing the POPC choline group was less affected than Op and Oc H bonded water. Translational diffusion of all membrane water was faster along the membrane plane than along the membrane normal.