The role of electronic properties to the mutagenic activity of 1,6- and 3,6-dinitrobenzo[ a]pyrene isomers

Abstract

Equilibrium geometries, infrared spectra, vertical first ionization potential (IP), electronic affinity (EA), dipole moment ( μ) and electronic dipole polarizability ( α) of 1,6- and 3,6-dinitrobenzo[ a]pyrene isomers (1,6-DNB aP and 3,6-DNB aP) were evaluated by means of Density Functional Theory (DFT) and recent semiempirical PM6 method. Structural, energetic and vibrational properties of DNB aP isomers are substantially similar to each other. Calculated IP, EA and α values of these isomers are practically identical, while μ of 3,6-DNB aP (8.2 D at DFT level) is predicted to be ca. 4 times the value of 1,6-DNB aP isomer (1.9 D at DFT level), owing to favorable mutual orientation of the individual nitro group vectors. Higher direct-mutagenic activities of 3,6-DNB aP with respect to 1,6-DNB aP isomer by 1–2 orders of magnitude might be determined by its peculiar electronic charge distribution, which through stronger electrostatic and inductive interactions, can promote much more effectively binding to active-site of enzymes involved in mutagenic pathways. On the other hand, orientation of the nitro substituents relatively to the plane of the aromatic moiety, molecular sizes, as well as nitroreduction and oxidation reactions seem not to have a key role in the determination of the different mutagenic behaviour of these isomers.