Reactivity of gas-phase benzene and naphthalene radical cations with N-methylimidazole, a model DNA base

The focus of this research is to evaluate the gas-phase reactivity of benzene and naphthalene radical cations with the model DNA base, N-methylimidazole, by using mass spectrometric techniques. Results show that in ionized mixtures of benzene/N-methylimidazole and naphthalene/N-methylimidazole, radical-cation adducts are produced. Through ion selection experiments with a Fourier transform mass spectrometer, it is shown that benzene neutrals and N-methylimidazole radical cations are the reactants, leading to a radical-cation adduct of m/z 160, whereas naphthalene radical cations and N-methylimidazole neutrals are the reactants leading to a radical-cation adduct of m/z 210. Further, the adducts have structures in which the polycyclic aromatic hydrocarbon (PAH) moiety is predominantly attached to the N-3 position of the imidazole ring. This attachment is analogous to adducts formed in solution reactions of PAH radical cations with DNA as well as those isolated from biological systems wherein one-electron oxidation of the aromatic compound is thought to be the activating step.