Fast kinetic studies of dioxygen-derived species and their metal complexes

The role of metals in the reactivity of HO2/O2- with compounds of biological interest is discussed. A scheme that illustrates the various reactions that a transition metal complex can undergo when reacting with HO2/O2- is presented in terms of ligand and pH effects. The decomposition of hydrogen peroxide catalysed by ferrous ion is reviewed in terms of new rate data for the reactions of ferric ion with perhydroxyl (HO2) and superoxide (O2-) radicals. The new results support a mechanism proposed by Barb and his coworkers (W.G. Barb, J.H. Baxendale, P. George & K.R. Hargrave, Trans. Faraday Soc. 47, 462-500 (1951] and negates the occurrence of the Haber-Weiss reaction in this system. In the presence of MnII complexes, O2- reacts to form MnO2+ transients and MnIII complexes. Their reactivities with ascorbate, Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) and NADH-NADPH is discussed.