ADP-iron as a fenton reactant: Radical reactions detected by spin trapping, hydrogen abstraction, and aromatic hydroxylation

Abstract

A mixture of ADP, ferrous ions, and hydrogen peroxide (H 2O 2) generates hydroxyl radicals (.OH) that attack the spin trap DMPO (5,5-dimethyl-pyrollidine- N-oxide) to yield the hydroxyl free radical spin-adduct, degrade deoxyribose and benzoate with the release of thiobarbituric acid-reactive material, and hydroxylate benzoate to give fluorescent products. Inhibition studies, with scavengers of the .OH radical, suggest that the behavior of iron-ADP in the reaction is complicated by the formation of ternary complexes with certain scavengers and detector molecules. In addition, iron-ADP reacting with H 2O 2 appears to release a substantial number of .OH radicals free into solution. During the generation of .OH radicals the ADP molecule was, as expected, damaged by the iron bound to it. Damage to the iron ligand in this way is not normally monitored in reaction systems that use specific detector molecules for .OH radical damage. Under certain reaction conditions the ligand may be the major recipient of .OH radical damage thereby leading to the incorrect assumption that the iron ligand is a poor Fenton reactant.