Slow dynamics of supercooled trehalose hydration water in comparison with bulk water

Trehalose aqueous solutions are relevant in many technological applications, for example in cryopreservation of biomolecules. It is known that the presence of this disaccharide is able to slow down the dynamics of nearby water molecules and to modify their spatial rearrangement, nevertheless, a complete understanding of the properties of water-trehalose solutions and of trehalose cryoprotective properties is still lacking. Here we discuss recent molecular dynamics simulation results of water-trehalose solutions, performed at different temperatures upon cooling, and we compare the results with the behavior of the bulk phase. In particular we focus on the dynamical properties of hydration water, i.e., the water molecules in the hydration shell of the disaccharide. Hydration water shows a sub-diffusive behavior with respect to bulk water, the same structural relaxation typical of glass formers liquids, albeit slightly slower than in the bulk, and an additional relaxation process at longer timescales completely absent in the bulk. The analysis of hydrogen bond autocorrelation functions allows to connect the structural and long relaxation processes of hydration water to the dynamics of two distinct population of hydrogen bonds in the system, the water-water and water-trehalose hydrogen bonds.