Unique similarity of the asymmetric trehalose solid-state hydration and the diluted aqueous-solution hydration

The structural and dynamical features of the hydration of the disaccharide alpha,alpha-trehalose have been derived from a 2.5 ns molecular dynamics wi th an explicit representation of the water molecules. The study aims at est ablishing a comprehensive understanding of the hydration pattern of trehalo se and comparing such features with those displayed by sucrose. The homonuc lear and heteronuclear coupling constants, the overall molecular tumbling t ime, and self-diffusion coefficient of the trehalose in aqueous solutions w ere established from the molecular dynamics simulations and compare well wi th experimental data. While the calculated translational diffusion of treha lose is very similar to that of sucrose, the calculated rotational diffusio n is much slower; The presence of water in the simulation induces significa nt changes in the mean potential acting on trehalose. It generates an asymm etric mean structure between the two glucose rings, in the otherwise symmet rical trehalose. The analysis of the hydration characteristics provides an average molecular hydration number of 7.8 water molecules in the first hydr ation shell which is close to that derived experimentally from viscosity an d apparent molar volume. Average and maximum residence times for water mole cules around the trehalose solute were also characterized. The analysis rev ealed that the water molecules around the O-2 hydroxyl groups were the most resident and that the water molecules around the acetalic oxygens in the " central cavity" of trehalose were particular mobile. 2D radial pair distrib utions were calculated to analyze the solute surroundings for localized wat er densities, e.g., bridging water molecules between the two pyranose rings . This analysis revealed no strong first hydration shell interactions, as f ound in the case of sucrose, but revealed that the water molecules of the d ihydrate solid-state structure are largely capable of satisfying the "hydra tion requirements" of the solute.