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, Cu2+ and Fe3+ complexes were synthesized
with a macrocyclic derivative of ethylenediaminetetraacetic acid and o-phenylenediamine (abbreviated as edtaodH2)
and its new open-chain analogue (edtabzH2). The Fe3+ complex of edtaodH2 has a peroxidase-like activity,
whereas the complex of edtabzH2 does not. The X-ray study
of the former shows the formation of a dimeric molecule {[Fe­(edtaod)]2O} 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 Fe3+ complex consists of a mononuclear complex ion [Fe­(edtabz)­(H2O)]+, 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.

本研究旨在探讨选定金属螯合物对其过氧化物酶活性的构象和巨环效应。通过合成具有巨环衍生物的乙二胺四乙酸（EDTA）及其新的开环类似物（EDTABZ）的Cu2+和Fe3+配合物（以下简称EDTAodH2和EDTABZH2），以研究其对过氧化物酶活性的影响。EDTAodH2的Fe3+配合物展现出类似过氧化物酶的活性，而EDTABZH2的配合物则不具备此活性。X射线研究表明，EDTAodH2的Fe3+配合物形成了一种二聚分子{[Fe-(edtaod)]2O}，其中每个具有八面体配位的金属离子均位于巨环腔内，由于刚性的巨环框架，形成Fe-O-Fe桥；中心金属离子的暴露于环境中有助于捕获氧气，从而驱动生物模拟活性。过氧化物酶无活性的Fe3+配合物由单核配合物离子[Fe-(edtabz)-(H2O)]+构成，其中金属离子适合于扭曲的五角双锥形结构，从而抵御环境中的氧气。与铁(III)配合物相比，具有单核结构且热力学稳定性较高的铜(II)配合物显示出无过氧化物酶活性。立体效应在生物模拟活性中起着根本作用。