Conformations of adducts formed between the genotoxic benzo[a]pyrene-7,8-dione and 2′-deoxycytidine

Abstract

Benzo[a]pyrene-7,8-dione (BPQ) is formed by the activation of benzo[a]pyrene(B[a]P), which is an environmental toxic substance that is easily exposed in daily life, due to P450/epoxide hydrolase, and is a substance that induces DNA deformation by forming adducts with DNA. In this study, to investigate the form of bonding between BPQ and DNA, the structures of adducts between BPQ and 2′-deoxycytidine were examined. To examine BPQ–dC adduct conformation, geometry optimization of a total of 16 structural isomers was performed using the density functional theory method. In the structures of BPQ–dC adducts, for the cis-form, the angle between BPQ and dC is nearly perpendicular; but for the trans-form, the bending angle is small. The trans-form had a larger energy gap between ground state and excited state than the cis-form, and had a smaller HOMO–LUMO gap than the cis-form. Therefore, it was found that the trans-form absorbs stronger light and has higher reactivity than the cis-form. Molecular electrostatic potential was calculated and analyzed. The calculated ESP contour map shows the electrophilic and nucleophilic regions of the molecule.