Role of a perhydroxyl radical in the chelator-mediated Fenton reaction

The chelator-mediated Fenton (CMF) chemistry is one of the main biological non-enzymatic systems for oxygen-centered radical generation. A perhydroxyl radical (HO2 center dot) is a secondary radical specie in CMF systems, however, despite being reported as an iron reducer, its production and role in the CMF redox chemistry are not yet well understood. We assessed the production profiles of HO2 center dot and HO center dot generated in situ in CMF systems by EPR, iron-reducing capacity with and without HO2 center dot, and ligand concentration using CMF systems with p-substituted catecholates between pH values 3.0 and 7.0. The results showed that HO2 center dot was generated as a secondary radical in all CMF systems but it also showed evidence of a HO2 center dot-independent pathway that contributes to the reduction of Fe3+. Along with the current knowledge of the reaction mechanism of the CMF chemistry, the SQ of the ED ligand is proposed to contribute to the generation of HO2 center dot.