Role of residual water hydrogen bonding in sugar/water/biomolecule systems: a possible explanation fortrehalose peculiarity

We report on the set of experimental and simulative evidences which enabled us to suggest how biological structures embedded in a non-liquid water–saccharide solvent are anchored to the surrounding matrix via a hydrogen bond network. Such a network, whose rigidity increases by decreasing the sample water content, couples the degrees of freedom of the biostructure to those of the matrix and gives place to protein–saccharide–water structures ( protein–solvent conformational substates ). In particular, the whole set of data evidences that, while the protein–sugar interaction is well described in terms of a water entrapment hypothesis, the water replacement hypothesis better describes the sugar–membrane interaction; furthermore, it gives a hint towards the understanding of the origin of the trehalose peculiarity since the biomolecule–matrix coupling, specific to each particular sugar, always results in being the tightest for trehalose. In line with the heterogeneous dynamics in supercooled fluids and in carbohydrate glasses of different residual water contents, recent results confirm, at the single molecule level, the existence of protein–solvent conformational substates , spatially heterogeneous and interconverting, whose rigidity increases by lowering the sample hydration.