AN INTEGRAL-EQUATION TO DESCRIBE THE SOLVATION OF POLAR-MOLECULES IN LIQUID WATER

We developed and implemented a statistical mechanical integral equatio n theory to describe the hydration structure of complex molecules. The theory, which is an extension of the reference interaction site model (RISM) in three dimensions, yields the average density from the solve nt interactions sites at all points r around a molecular solute of arb itrary shape. Both solute-solvent electrostatic and van der Waals inte ractions are fully included, and solvent packing is taken into account . The approach is illustrated by calculating the average oxygen and hy drogen density of liquid water around two molecular solutes: water and N-methylacetamide. Molecular dynamics simulations are performed to te st the results obtained from the integral equation. It is observed tha t important microscopic structural features of the average water densi ty due to hydrogen bonding are reproduced by the integral equation. Th e integral equation has a simple formal structure and is easy to imple ment numerically. It offers a powerful alternative to computer simulat ions with explicit solvent molecules and to continuum solvent represen tations for incorporating solvation effects in a wide range of applica tions.