A molecular dynamics study of the urea/water mixture

The short time dynamics of the water-urea mixture is studied herein by molecular dynamics simulations. The local anisotropy of the dynamical properties arising from the highly directional hydrogen bonding interactions and their modification under the influence of increasing the urea concentration is the major focus of the present report. Study of the direction dependant translation and rotation self-diffusion coefficients of both species, as well as that of velocity autocorrelation functions and corresponding power spectra, indicate that the addition of urea leads to an overall isotropy and stiffening of the short time dynamics of both species. It is speculated that some of the well-known properties of the urea/water mixture, such as the denaturation of proteins for example, could find an explanation in these features. (C) 2000 American Institute of Physics. [S0021-9606(00)52120-5].