Solvation structure and dynamics of ions in concentrated urea solution

The solvation structure and dynamics of ions and a neutral hydrophobic solute in aqueous urea solutions are investigated using classical molecular dynamics simulations. Our results are analyzed in terms of varying concentrations ranging from pure water to ~ 6.9 M solution of urea. It is found that except K+, other ions prefer to interact with water molecules in the solution irrespective of their charge and size whereas the neutral solute does not prefer to interact either with water or urea. The calculated diffusion coefficient values show comparatively slower dynamics for ions than the neutral solute in aqueous urea mixtures. The residence time of ions in water is found to be increased with increasing urea concentration whereas for the neutral solute it remains same for the entire range of urea concentration. There is no significant change observed for the structural relaxation time and lifetime of hydrogen bonded water molecules in the solution.