Comparison of quantum mechanical methods to compute the biologically relevant reactivities of cyclopenta-polycyclic aromatic hydrocarbons

In computational studies to understand the interaction of polycyclic aromatic hydrocarbons (PAHs) with biomolecular systems, the semiempirical method AM 1 has been used previously to determine the geometry of the PAH and its metabolites and relevant intermediates. A number of studies have shown that AM 1 provides geometries for parent PAHs that are acceptably close to experimentally determined structures. However, many of the properties that determine the manner by which PAHs interact with biological nucleophiles depend on the structure of metabolites and reactive intermediates where less experimental information is available. In a previous study, we used AM 1 to obtain the molecular geometries of reactive intermediates of cyclopenta-PAHs (cPAHs) and then used single-point Hartree-Fock calculations, with the gaussian 3-21g basis set, to obtain molecular energies and charge distributions, in order to predict the direction of epoxide ring opening. Recent advances in the availability of computational hardware and software have provided other, more rigorous, methods for approaching this problem. In this study, we used hartree-fock methods in the gaussian series of programs employing the 3-21_g and 6-31_g basis sets and the local density functional method Dmol to obtain molecular geometries, energies, and charge distributions of the epoxides and the two potential hydroxycarbocations that could result from protonated ring opening, for a series of cPAHs. We have also performed the same calculations with AMSOL /SM 2, a semiempirical method that adds the effect of the aqueous environment to the AM 1 Hamiltonian. The division of the cPAHs into classes is not altered by these more rigorous calculations. The inclusion of water in the Hamiltonian has a greater effect on the results than using the ab initio methods to obtain the structure. © 1994 John Wiley & Sons, Inc.