Implication of manganese (III), oxalate, and oxygen in the degradation of nitroaromatic compounds by manganese peroxidase (MnP) |
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Authors: | B. Van Aken S. Agathos |
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Affiliation: | Department of Civil and Environmental Engineering, University of Iowa, Iowa City 52242, USA. |
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Abstract: | The fungal ligninolytic enzyme manganese peroxidase (MnP) is known to function by oxidizing Mn(II) to Mn(III), a powerful oxidant. In this work, an abiotic system consisting of Mn(III) in oxalate buffer under aerobic conditions (Mn(III)/oxalate/O2 system) was shown to be capable of extensively transforming 2-amino-4,6-dinitrotoluene (2A46DNT)--one of the main reduction products of 2,4,6-trinitrotoluene (TNT). No significant transformation occurred in the presence of other organic acids or under anaerobic conditions. The Mn(III)/oxalate/O2 system was also able to transform other nitroaromatic compounds such as 2-nitrotoluene, 4-nitrotoluene, 2,4-dinitrotoluene, TNT - the latter to a lesser extent -, and their reduction derivatives. The Mn(III)/oxalate/O2 system mineralized 14C-U-ring labeled 2A46DNT slightly, while no significant mineralization of 14C-U-ring labeled TNT was observed. Unidentified 14C-transformation products were highly polar. Electron spin resonance experiments performed on the Mn(III)/oxalate/O2 system revealed the generation of formyl free radicals (*COO-). The oxygen requirement for the transformation of nitroaromatic compounds suggests the involvement of superoxide free radicals (O2-*). produced through autoxidation of *COO- by molecular oxygen. The implication of such a Mn(III)/oxalate/O2 system in the MnP-catalyzed degradation of nitroaromatic pollutants by white-rot fungi is further discussed. |
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