  Water molecules play an important role in providing unique environments for
biological reactions on cell membranes. It is widely believed that water
molecules form bridges that connect lipid molecules and stabilize cell
membranes. Using all-atom molecular dynamics simulations, we show that
translational and rotational diffusion of water molecules on lipid membrane
surfaces exhibit subdiffusion. Moreover, we provide evidence that both
divergent mean trapping time (continuous-time random walk) and long-correlated
noise (fractional Brownian motion) contribute to this subdiffusion. These
results suggest that subdiffusion on cell membranes causes the water
retardation, an enhancement of cell membrane stability, and a higher reaction
efficiency.
