Electrostatic molecular potential contour maps generated from ab-hitio MODPOT/VRDDO/MERGE wave functions of carcinogenic benzo(a)pyrene and its metabolites

The electrostatic molecular potential contour maps were calculated for carcinogenic benzo(a)-pyrene and a number of its metabolites (BP 7.8-oxide; BP 7.8-dihydrodiols [several stereoisomers: A trans (equatorial, equatorial), B trans (axial, axial), B cis (axial, equatorial)]; BP 7,8-dihydrodiol-9,IO-epoxide A α,β,α and 7,8-dihydrodiol-9,1O-epoxideB α,α,α with the epoxide ring open at Clo with the oxygen on C9, and open at C9 with the oxygen on Cl0} The maps were generated from our ab-inirio MODPOT/VRDDO/MERGE wave functions calculated for these species. The results of the maps for BP show that these electrostatic molecular potential contour maps can be used to indicate favored positions of attack for electrophilic species, such as “electrophilic” oxygen, to form an epoxide as well as for positive ion attack. The BP maps not only indicate the favored position for attack but also that the oxygen would attack from below the molecular plane and the epoxide would form below the plane, in accord with experiment. The maps around BP 7.8-oxide and around BP 7,8-dihydrodiol-9,1O-epoxidein dicate the directional preferences for proton assisted epoxide ring opening. The maps around the BP 7,8-dihydrodiol indicate that while for certain stereoisomers the “electrophilic” oxygen will prefer to attack from below, for other isomers it will prefer to attack from above. This gives great insight into the stereochemical preference for formation of different BP 7.8-dihydrodiol-9, I 0-epoxides. Electrostatic molecular potential contour maps can also be used as an “electrophilicity” index. The farther out in space a positive contour extends, the more electrophilic is this species compared to a congener. The maps generated around BP 7.8-dihydrodiol-9,IO-epoxide with the epoxide open at C10 with the oxygen remaining on C9 or open at C9 with the oxygen remaining on C10 indicate that the former is the more electrophilic species, in accord with experiment