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
posted on 2019-12-18, 19:06authored byMelissa Beltran-Torres, Rocío Sugich-Miranda, Hisila Santacruz-Ortega, Lorena Machi, Motomichi Inoue, Enrique F. Velázquez-Contreras, Yedith Soberanes, Herbert Höpfl, Refugio Pérez-González, Rosa Elena Navarro, Alex J. Salazar-Medina, Rogerio R. Sotelo Mundo
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.