On the role of short- and long-range forces in aqueous systems

Effects of short- and long-range forces upon the properties of aqueous syst ems is examined using a decomposition into trial potentials which can be co nstructed from any realistic water-water potential. Both pure water and dil uted aqueous solutions of nonelectrolytes are considered over a wide range of thermodynamic conditions. It is shown that, regardless of the thermodyna mic conditions, the structure of water is determined by short range forces which may be both repulsive and attractive; however, with increasing temper ature the effect of the short range attractive forces rapidly lessens. As r egards the aqueous solutions of non-polar compounds, it is shown that only the short range water-water interactions and simple exclusion effects are e ssential for the arrangement and orientation of water molecules in the hydr ation shell. (C) 2000 Elsevier Science B.V. All rights reserved.