EXAFS STUDIES OF AN AQUEOUS FE(IV) INTERMEDIATE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The mechanistic complexity and wide-spread involvement of the Fenton reaction in catalytic chemistry, atmospheric and environmental processes, aging and disease have made it one of the most studied and debated reactions of all time. Strictly speaking, the Fenton reaction is the oxidation of aqueous iron(II) ions with hydrogen peroxide in acidic aqueous solutions. This transformation is also proposed to occur in biological milieu where the pH is closer to 7-8 and the iron(II) center is presumably coordinated to ligands available within the cell. Such chemistry has been used to rationalize the production of some reactive oxygen species and to explain the effects of the combination of iron complexes, H2O2 and a reductant on DNA cleavage. Regarding the nature of the reactive intermediate(s), experimental evidence and arguments have been advanced for hydroxyl radicals, [(H2O)nFeIVO]2+, and metal-coordinated peroxide, [(H2O)5Fe(H2O2)]2+. In principle, the answer to this mechanistic question lies in reactivity studies of each proposed intermediate that can be generated independently. Until recently, only hydroxyl radicals can be obtained independently from other chemical sources. Recently, we have established that an FeIV intermediate is generated at pH 1 in aqueous solution from the reaction of [Fe(H2O)6]2+ and O3. This short-lived species was freeze-trapped and characterized by M¿ssbauer spectroscopic studies that confirm the existence of a high-spin FeIV species with an S = 2 ground state. We carried out initial XAS studies on two samples for which M¿ssbauer spectroscopy established the purity of 50% and 58%. We noted a pronounced 1s 3d transition in the XANES spectrum. The current project will continue these studies.