Comparative study of urea and tetramethylurea in water by molecular dynamics simulations

The hydration of urea and tetramethylurea (TMU) is studied by molecular dynamics simulations. A perturbed structure of the H-bond network is shown in the hydration shell of urea around carbonyl oxygen, and an enhanced mobility of water is found in the region corresponding to the hydration of the carbonyl oxygen beyond the first hydration shell. The influence of urea on the water structure is reflected by a relative increase in the mobility of the low-energetic, five-coordinated molecules, i.e., an acceleration of switching within the tetrahedral H-bond network by the formation of "bifurcated" bonds. (C) 1999 Elsevier Science B.V. All rights reserved.