Reactions of polycyclic aromatic hydrocarbon radical cations with model biological nucleophiles

The determination of gas-phase reactivity of a series of polycyclic aromatic hydrocarbons (PAHs) with nucleophiles is directed at achieving isomer differentiation through ion-molecule reactions and collisionally activated decomposition spectra. A series of PAH isomers form gas-phase [adduct - H]⁺ ions with the reagent nucleophiles pyridine and N- methylimidazole. Collisionally activated decomposition spectra of the [adduct - H]⁺ ions of the pyridine/PAH systems are dominated by products formed by losses of C₅H₄N, C₅H₅N (presumably neutral pyridine), and C₅H₆N. Collisional activation of PAH/N-methylimidazole [adduct- H]⁺ ions causes analogous losses of C₄H₅N₂, C₄H₆N₂ (presumably neutral N- methylimidazole), and C₄H₇N₂. The relative abundances of the ions that result from these losses are highly isomer specific for N-methylimidazole but less so for pyridine. Furthermore, PAH/N-methylimidazole [adduct - H]⁺ ions undergo a series of metastable-ion decompositions that also provide highly isomer-specific information. The C₄H₇N₂ (from PAH/N-methylimidazole product ions) and C₅H₆N (from PAH/pyridine product ions) losses tend to increase with the ΔH(f) of the PAH radical cation. In addition, it is shown that the fragmentation patterns of these gas-phase PAH/nucleophile adducts are similar to fragmentation patterns of PAH/nucleoside adducts generated in solution, which suggests that the structures of products formed in gas-phase reactions are similar to those produced in solution.