Hydration studies on lipid membranes: Classification of water molecules in different bilayers in gel and liquid phase.

L. M. ALARCÓN; A. DISALVO; G.A. APPIGNANESI; A. VERDE

Buenos Aires

Workshop; Structure and Dynamics of Glassy, Supercooled and Nanoconfined Fluids; 2019

We use molecular dynamics simulations to study the hydration properties of lipid membranes, both in the gel state and in the crystalline fluid. We show that while the hydration centers remain significantly hydrated in both phases, the gel-fluid transition implies significant changes in the second hydration layer, particularly in the region of the hydrocarbon tails. Thus, while the water population is almost nil in the hydrocarbon tails zone in gel state, this region becomes partially accessible to water in crystalline liquid state in membranes of dipalmitoylphosphatidylcholine (DPPC). In the case of membranes composed of unsaturated lipids, the presence of double bonds modifies the hydration map particularly in the hydrocarbon zone. We also showed that the water molecules located in the non-polar zone have a lower hydrogen bridge (HB) coordination in comparison with the molecules of the first hydration layer, which are arranged in relatively compact ´nanoclusters´. The water molecules in the hydrocarbon tails zone tend to be organized in less compact structures, like branched chains, with a small population of isolated molecules. This behavior is similar to that observed in other hydration contexts, such as water penetrating carbon nanotubes or hydrophobic pores, reflecting the poor predisposition of water to sacrifice HB coordination.