Reactions of tetraazamacrocyclic Fe-III complexes with hydrogen peroxide -Putative catalase mimics?

Iron(III) complexes of macrocyclic tetraaza ligands [Fe(III)-1-Fe(III)-3] w ere investigated for their putative catalase-like properties under physiolo gical conditions: i.e., in aqueous solution at pH = 7.0-7.4 and at micromol ar concentrations of the catalyst and hydrogen peroxide. Complex Fe(III)-1, originally studied by Busch et al. as a catalase model, at pH = 4.6, only degrades hydrogen peroxide to oxygen as a minor reaction at this pH (< 1% O -2 yield). Experiments with the analogous complex Fe(III)-2 at pH = 7.2 fou nd that no oxygen was formed under physiological conditions, although hydro gen peroxide was decomposed to an extent of more than 50%. Complex Fe(III)- 3 produced oxygen on reaction with H2O2, but only in stoichiometric amounts . Thus, the decomposition of hydrogen peroxide by these iron(III) complexes cannot reasonably be described as a catalase-like activity.