Comparative Studies of Structures and Peroxidase-like Activities of Copper(II) and Iron(III) Complexes with an EDTA-Based Phenylene-Macrocycle and Its Acyclic Analogue

With the objective of studying the conformational and macrocyclic effects of selected metal chelates on their peroxidase activities, Cu 2+ and Fe 3+ complexes were synthesized with a macrocyclic derivative of ethylenediaminetetraacetic acid and o -phenylenediamine (abbreviated as edtaodH 2 ) and its new open-chain analogue (edtabzH 2 ). The Fe 3+ complex of edtaodH 2 has a peroxidase-like activity, whereas the complex of edtabzH 2 does not. The X-ray study of the former shows the formation of a dimeric molecule {[Fe(edtaod)] 2 O} in which each metal with an octahedral coordination is overposed over the macrocyclic cavity, as a result of rigid macrocyclic frame, to form an Fe-O-Fe bridge; the exposure of the central metal to the environment facilitates the capture of oxygen to drive the biomimetic activity. The peroxidase-inactive Fe 3+ complex consists of a mononuclear complex ion [Fe(edtabz)(H 2 O)] + , the metal ion of which is suited in a distorted pentagonal bipyramid to be protected from environmental oxygen. The copper(II) complexes, which have mononuclear structures with high thermodynamic stability compared with the iron(III) complexes, show no peroxidase activity. The steric effects play a fundamental role in the biomimetic activity.