THE FENTON OXIDATION MECHANISM - REACTIVITIES OF BIOLOGICALLY RELEVANT SUBSTRATES WITH 2 OXIDIZING INTERMEDIATES DIFFER FROM THOSE PREDICTED FOR THE HYDROXYL RADICAL

The application of kinetic probes that allow one to determine relative reactivities of biologically relevant substrates with oxidizing inter mediates in the Fenton reagent H2O2 plus Fe2+ in acidic aqueous soluti on) is described, These results lead to the conclusion that there are two key intermediates with very different reactivity patterns. One (X) is proposed to be an iron complex formed via direct reaction of H2O2 with Fe2+, which reacts with N-nitrosodimethylamine to generate a stro ng transient absorption at 450 nm. This provides a sensitive spectroph otometric probe of the competitive reactivities toward X of biological ly relevant substrates such as nucleic acid components and amino acids . The second intermediate (Y) is probed by its oxidation of the Ru(bpy )(3)(2+) ion (bpy = 2,2' bipyridine) to a product with an absorption b and centered at 500 nm. In the absence of other substrates, Ru(bpy)(3) (2+) is oxidized at rates independent of the Ru concentration, but the product yield is diminished by competing reactions with substrates th at can intercept X. Competition studies demonstrate reactivity pattern s for X and Y that are clearly distinct from the pattern predicted For the hydroxyl radical, the intermediate commonly invoked in discussion s of Fenton oxidations. These data require reevaluation of the mechani sms by which the Fenton reagent oxidizes biological substrates.