ABSTRACT
Free radicals and transition metal ions are ubiquitous in biological systems. The variable valency of transition metal ions plays a key role in the catalysis of redox processes in which the oxidation states of the metal are inherently unstable and/or have only a transient existence during the reaction sequence. A characteristic property of the transition metals in solution is that they are coordinated to ligands, so that one must consider the complete entity—metal center and ligands—in its reaction with free radicals. In aqueous media it is important to recognize that free radicals with a dissociable proton exist in acidic and basic forms that can have quite different reactivities. In order to study the kinetics and mechanisms of the reactions of free radicals, fast time-resolved methods are required because the rates of these processes often approach the diffusion-controlled limit.
