Effects of the nitro-group on the mutagenicity and toxicity of some benzamines

The Ames Salmonella/microsomal assay was employed to test the mutagenicity of some benzamines (aniline, and o- and p-phenylenediamine) and their nitro-derivatives (p-nitroaniline, 2-nitro-p-phenylenediamine, 3- and 4-nitro-o-phenylenediamine), using strains TA98 and TA100 and their nitroreductase-deficient mutants, TA98NR and TA100NR, in the presence and absence of rat S9 mix. The addition of the nitro-group to benzamine molecules converted them into direct mutagens. Furthermore, the position of the nitro-group affected their mutagenic activities. Cytotoxicity testing with Chinese hamster ovary cells (CHO-K1) showed that the presence of the nitro-group in these compounds had no specific effect on toxicity. The test compounds all showed a dose-related increase in inducing chromosomal aberrations in CHO cells. However, the presence of the nitro-group did not affect potency in inducing chromosomal aberrations. Compounds containing the nitro-group had higher initial oxidation potentials and dipole moments (mu) than their nonnitro-containing counterparts. The mutagenicity and toxicity of these compounds were not related to physico-chemical properties, including oxidation potential, energy difference (deltaE) between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), ionization potential (I.P.), and mu.