  A hydrated 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC) lipid
membrane is investigated using an all atom molecular dynamics simulation at
308K to find out the physical sources of universal slow relaxation of hydration
layers. Continuously residing interface water (IW) hydrogen bonded to each
other and concertedly to different moieties of lipid heads are identified. The
non-gaussian parameter of all IW show a crossover from cage vibration to
translational diffusion. A significant non-gaussianity is observed for the IW
prevailing large length correlations in translational van Hove functions. Two
time-scales for the ballisitic motions and hopping transitions are obtained
from the self intermediate scattering functions of the IW with an additional
long relaxation which disappears for the BW. This is attributed to the coupled
dynamics of IW cages hydrogen bonded to lipid heads. Our calculations reveal
that the water near membranes are slowed down due to dynamical heterogeneities
above room temperature and have implications to bioprotection mechanism at
freezing conditions.
