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 adduci - 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 metastableion 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.