Biomimetic simazine oxidation catalyzed by metalloporphyrins

The metalloporphyrin-mediated simazine oxidation was investigated, in order to evaluate whether metalloporphyrins were good biomimetic models for the oxidation of this herbicide. The commercially available second-generation metalloporphyrins: 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin metal(III) chloride, [M(TDCPP)]Cl; 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin metal(III) chloride, [M(TFPP)]Cl; and 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin metal(III) chloride, [M(TMPyP)]Cl5 (metal = Fe or Mn), and the oxidants iodosylbenzene (PhIO), hydrogen peroxide, and 3-chloroperoxy benzoic acid (m-CPBA) were employed in this study. Results demonstrated that these metalloporphyrins can mimic both the in vivo and in vitro action of cytochrome P450 for simazine oxidation, with formation of the dechlorinated metabolites OEET and OEAT mainly, as well as production of two other unknown compounds, identified by HPLC/mass spectrometry as ODET and ODDT. Among the systems, [Fe(TDCPP)]Cl/m-CPBA was the most efficient for simazine oxidation, giving up to 49% total conversion. Although hydrogen peroxide did not afford the best results (about 14% simazine conversion), it can be considered the most efficient oxidant from the point of view of toxicity, because it leads to less toxic products, namely OAAT and OEAT. The effect of some reaction conditions was investigated, and product evolution as a function of time was also monitored. Based on these results, simplified reaction mechanisms have been proposed.

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► Metalloporphyrins have efficiently catalyzed the persistent herbicide simazine.
► Metalloporphyrins can mimic the in vivo action of cytochrome P450 for simazine oxidation.
► Dehalogenated products predominate, although one chlorinated product is also observed.
► Dechlorination or dealkylation pathways occur through different intermediate species.