Slow Relaxations of Chemically Confined Hydration Layers near Lipid Bilayers: Dynamical Heterogeneities above Supercooling

TL;DR

This study uses molecular dynamics simulations to reveal the slow, heterogeneous relaxation dynamics of hydration water near lipid membranes, highlighting their implications for biological protection mechanisms.

Contribution

It uncovers the microscopic origins of slow hydration layer relaxation and dynamical heterogeneities in water near lipid bilayers at physiological temperatures.

Findings

Identification of hydrogen-bonded interface water clusters

Observation of non-Gaussian diffusion behavior

Discovery of multiple relaxation time-scales for water motions

Abstract

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.