Effect of water on solvation structure and dynamics of ions in the peptide bond environment: importance of hydrogen bonding and dynamics of the solvents.

The solvation structure and dynamics of ions in aqueous N-methylacetamide (NMA) solutions are calculated using classical molecular dynamics simulations. Our results are analyzed in terms of varying composition ranging from pure NMA to pure water. We also examined the effect of varying water content on the structure and dynamics of a neutral solute. Altogether we have simulated 38 different systems in the present work. It is found that water molecules have preference over NMA for the ions irrespective of their charge and size, whereas the neutral solute is preferably solvated by methyl groups of NMA. The calculated self-diffusion coefficient values show comparatively slower dynamics for ions than the neutral solute which can be attributed to the stronger solvation of ions in aqueous NMA mixtures. Various dynamical properties associated with translational and rotational motion of solvents are also calculated, and similar slower dynamics of solvents is observed which can be attributed to the enhanced stability of the hydrogen bonds and formation of interspecies complexes in the mixtures.