Ionization Potentials and Metabolic Activations of Carbazole and Acridine Derivatives

7H-Dibenzo[c,g]carbazole (DBC) and dibenz[a,j]acridine (DBA) representing environmental nitrogen-heterocyclic aromatic (NHA) genotoxicants undergo differing metabolism and exhibit differing DNA binding patterns and carcinogenic activities. Two chemical oxidation-related parameters, anodic peak potentials (E pa) and maximum absorption energies (E CT) of the charge-transfer complexes, were measured for a series of 18 derivatives of carbazole and acridine. On the basis of the E pa and E CT values and the ionization potential (IP) data of the parent carbazole and acridine that are available in the literature, with linear regression analyses, IP values of the 18 carbazoles and acridines were reported for the first time. The two sets of IP values determined from either E pa or E CT agreed with one another for most of the compounds. Carbazoles possessed IP values (ranging from 7.2 to 7.6 eV) that are lower than those of acridines (i.e., 7.8−8.1 eV). These data are consistent with the potential activation of carbazole and/or acridine derivatives. For DBC having an IP of ∼7.3 eV, both one-electron oxidation and monooxygenation pathways are involved in the metabolic activation. In contrast, DBA with a high IP of ∼8.0 eV is activated through the monooxygenation pathway only. Therefore, just as it is known for carcinogenic PAHs, IP appears to be an important parameter in predicting the metabolic activation for genotoxic NHA in the environment.