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.

本研究旨在探讨所选金属螯合物对其过氧化物酶活性的构象和宏环效应。通过合成以乙二胺四乙酸（EDTA）的宏环衍生物和邻苯二胺（简称为edtaodH2）及其新型开环类似物（edtabzH2）为配体的Cu2+和Fe3+配合物，研究了Fe3+配合物edtaodH2表现出过氧化物酶样活性，而edtabzH2的配合物则不具备该活性。X射线研究表明，前者形成了[Fe-(edtaod)]2O的二聚分子，其中每个八面体配位的金属离子因其刚性的宏环骨架而位于宏环腔内，从而形成Fe-O-Fe桥；中心金属离子暴露于环境中，有利于氧气的捕获，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)]+组成，其金属离子适合于畸变的五角双锥形结构，从而避免环境氧气的侵害。与铁(III)配合物相比，具有单核结构和较高热力学稳定性的铜(II)配合物不显示过氧化物酶活性。空间效应在生物模拟活性中发挥着根本的作用。