Relaxation time scales of interfacial water upon fluid to ripple to gel phase transitions of bilayers

Abstract

The slow relaxation of interface water (IW) across three primary phases of membranes is relevant to understand the influence of IW on membrane functions at supercooled conditions. To this objective, a total of [Formula: see text]s all-atom molecular dynamics simulations of 1,2-dimyristoyl-sn-glycerol-3-phosphocholine lipid membranes are carried out. A supercooling-driven drastic slow-down in heterogeneity time scales of the IW is found at the fluid to the ripple to the gel phase transitions of the membranes. At both fluid-to-ripple-to-gel phase transitions, the IW undergoes two dynamic crossovers in Arrhenius behavior with the highest activation energy at the gel phase due to the highest number of hydrogen bonds. Interestingly, the Stokes–Einstein (SE) relation is conserved for the IW near all three phases of the membranes for the time scales derived from the diffusion exponents and the non-Gaussian parameters. However, the SE relation breaks for the time scale obtained from the self-intermediate scattering functions. The behavioral difference in different time scales is universal and found to be an intrinsic property of glass. The first dynamical transition in the α relaxation time of the IW is associated with an increase in the Gibbs energy of activation of hydrogen bond breaking with locally distorted tetrahedral structures, unlike the bulk water. Thus, our analyses unveil the nature of the relaxation time scales of the IW across membrane phase transitions in comparison with the bulk water. The results will be useful to understand the activities and survival of complex biomembranes under supercooled conditions in the future.

Interface Water Assists in Dimethyl Sulfoxide Crossing and Poration in Model Bilayer

“…Note that τ HB obtained from C HB (t) = 1/e is analogous to τ HB obtained through a stretched exponential fitting procedure. 53,54 Figure S9a,b depicts the lifetime of the H-bond between water−water and DMSO− water extracted from Figures S7 and S8. τ HB increased with an increase in DMSO concentrations for both cases.…”

Dynamical Crossover of Interfacial Water upon Melting of a Lipid Bilayer: Influence of Different Parts of the Headgroups

“…The time scales of hydrogen bond relaxation of interfacial water was also investigated in this study. 44 However, the temperature dependence of rotational time scales of interfacial water or dissecting the dynamics of both translational and rotational motion of interfacial water near different headgroups or at different distances from the polar ends of the lipids along phase transition of the bilayer needs to be investigated. Besides, understanding the origin of dynamical crossover, if any, on bilayer melting in terms of changes in spatially resolved dynamical correlations of water at different chemical environments at different parts of the lipids is an important exercise that also needs to be carried out.…”

“…The carbonyl groups were found to terminate the water hydrogen bond network of uporiented waters from the bulk to the carbonyl groups. More recent studies of Malik et al , have investigated dynamical heterogeneity and relaxation time scales of water near DMPC lipid bilayers at varying temperatures from normal to deeply supercooled conditions and identified two dynamical crossovers in the diffusion of interfacial water associated with fluid to ripple to gel phase transitions of the lipid layers. The time scales of hydrogen bond relaxation of interfacial water was also investigated in this study .…”

“…More recent studies of Malik et al , have investigated dynamical heterogeneity and relaxation time scales of water near DMPC lipid bilayers at varying temperatures from normal to deeply supercooled conditions and identified two dynamical crossovers in the diffusion of interfacial water associated with fluid to ripple to gel phase transitions of the lipid layers. The time scales of hydrogen bond relaxation of interfacial water was also investigated in this study . However, the temperature dependence of rotational time scales of interfacial water or dissecting the dynamics of both translational and rotational motion of interfacial water near different headgroups or at different distances from the polar ends of the lipids along phase transition of the bilayer needs to be investigated.…”

“…There have also been many molecular dynamics simulations of different phases of lipid bilayers. − Zhang and Berkowitz performed a molecular dynamics simulation of dilauroylphosphatidylcholine phospholipids with different hydration levels. It was observed that the orientational relaxation slows down as the hydration level is reduced.…”