The mutagenic modulating effect of p-phenylenediamine on the oxidation of o- or m-phenylenediamine with hydrogen peroxide in the Salmonella test

The mutagenicity of o- and m-phenylenediamine (PD) was remarkedly enhanced by oxidation; their major mutagenic oxidation products were 2,3- and 2,7-diaminophenazine, respectively. In order to evaluate the modulation effect of p-PD on the oxidation of m- or o-PD, p-PD and mixtures of m- and p-PD (m-PD/p-PD) and o- and p-PD (o-PD/p-PD) were oxidized with hydrogen peroxide and their mutagenicity was tested in Salmonella typhimurium TA98 in the presence or absence of a mammalian metabolic activation system (S9 mix). The H2O2-oxidized m-PD/p-PD and o-PD/p-PD were potent mutagens with S9 mix, whereas H2O2-oxidized p-PD was slightly mutagenic. The major mutagenic oxidation products of m-PD/p-PD and o-PD/p-PD were identified as 2,7- and 2,3-diaminophenazine, respectively, by TLC and HPLC. 2,8-Diaminophenazine was also found as a reaction product in oxidized m-PD/p-PD, and it was weakly mutagenic. The mutagenic potency of oxidized m-PD/p-PD or o-PD/p-PD was lower than that of singly oxidized m-PD or o-PD. The yield of 2,7- and 2,3-diaminophenazine was obviously decreased with increases in p-PD, and it was concluded that the declined mutagenic potency of oxidized m-PD/p-PD or o-PD/p-PD was due to the decrease in diaminophenazines. But the formation of diaminophenazines was not completely inhibited by the addition of a 9-fold molar ratio of p-PD to m-PD or o-PD, 8.6 nmole of 2,7-diaminophenazine and 1882.4 nmole of 2,3-diaminophenazine were formed from 1 mmole of m-PD and o-PD, respectively.