Hydration of cytosine using combined discrete SCRF models:: influence of the number of discrete solvent molecules

The solvation of cytosine has been investigated using a combined discrete/SCRF model. Molecular structures and gas phase binding energies were obtained at the HF/6-31G(d) level for ten cytosine-nH(2)O complexes, where n ranges from 1 to 13. Furthermore, gas-phase binding were also computed at the MP2/6-31G(d) level for complexes with n less than or equal to 7. The Polarizable Continuum Model self-consistent reaction-field (SCRF) were applied to such complexes in order to investigate the effect of the explicit water on the free energy of solvation and on the electronic structure of the solute. The results were compared with those provided by SCRF methods revealing that the discrete/SCRF models constitute a very reliable strategy. (C) 1999 Published by Elsevier Science B.V. All rights reserved.