Coupling of solvent and solute dynamics-molecular dynamics simulations of aqueous urea solutions with different intramolecular potentials

摘要

The vibrational characteristics and the hydration of urea are studied by classical molecular dynamics simulations, using three different urea models that are dissolved in 1616 SPC/E waters. The urea models only differ in the frequency of nitrogen inversion, ranging from 645 to 170 cm~(-1) in the gas phase. Intermolecular interactions are described by additive potentials using the same parameters for all models. The effects of urea on local water properties are discussed in terms of radical profiles of excess coordination numbers, the extent of the hydrogen-bond network, and the water-water interaction energy. It is found that water properties beyond the first hydrate shell of an urea model with slow inverting pyramidal amino groups are similr to those beyond the second hydrate shell of a water molecule, whereas a planar quickly vibrating urea model induces perturbations similar to hydrophobic hydration. The results are discussed in the context of the suefulness of molecular dynamics simulations for the understanding of the denaturing effect of urea on water.