Evaluation of the mutagenicity of nitration products derived from phenalenone (1H-phenalen-1-one)

1H-Phenalen-1-one (phenalenone) is one of the major oxygenated polyaromatic compounds present in the atmospheric environment. In order to gain detailed information regarding the mutagenicity and physicochemical properties of the nitration products of phenalenone, we measured Ames Salmonella mutagenicity, lower LUMO (lowest unoccupied molecular orbital) energy and octanol-water partition coefficient of the products obtained from the nitration reaction of phenalenone. Both nitration reactions of phenalenone, i.e. with mixed inorganic acids (a mixture of nitric acid and sulphuric acid) and with NO(2)-O(3) in an aprotic solvent, preferentially afforded the nitration products 2-nitrophenalenone and 5-nitrophenalenone. Formation of a 6-nitro derivative of phenalenone was, however, only observed in the nitration reaction with sulphuric acid. Moreover, dinitro derivatives of phenalenone and also two oxidatively decomposed products of nitrophenalenone, i.e. 3-nitro- and 4-nitronaphthalic anhydride, were isolated from the reaction mixture. The mutagenicities of the six nitro compounds obtained from the nitration reactions were tested with the Salmonella strains TA98, TA100, YG1021 and YG1024 in the absence of S9 mix. Among these products, 2-nitrophenalenone exhibited the most potent mutagenic activity against TA98, TA100 and YG1024 (160, 230 and 2800 revertants/nmol for strains TA100, TA98 and YG1024, respectively), whereas 2,5-dinitrophenalenone exerted the highest mutagenicity against YG1021. Semi-empirical calculation showed that among the mononitrophenalenone series, the mononitro derivatives possessing lower LUMO energy tended to exhibit greater mutagenic activity than those with higher LUMO energy. This tendency, however, did not extend to the compounds with different aromatic ring systems due to the considerable differences in the hydrophobicities of these compounds.