Studies on Heterobinuclear Copper-Zinc Complexes of Amino Acids as Biomimic Systems of Superoxide Dismutase

Abstract

Superoxide dismutase (SOD) contains two metal ions Cu(II) and Zn(II), active sites being bridged
by the imidazolate anion. A model system for this enzyme has been investigated by attempted
syntheses of copper-zinc complexes of amino acids [CuZn(L1)4(H2O)2] where L1 = glycine and
[CuZn(L2)3(H2O)2] where L2 = histidine. The characterization of these compounds was carried
out by conductance measurements, electronic, electron paramagnetic resonance (EPR) spectroscopy, fourier transform infrared spectra (FT-IR) and cyclic voltammetry along with the catalytic
decomposition of hydrogen peroxide. From the above studies, it is interesting to note that the
complex [CuZn(his)3(H2O)2] alone forms a mixed metal complex, which mimics the native
enzyme both structurally and spectroscopically whereas glycine complexes form only the
mechanical mixture of CuL1 and ZnL1. The peculiar coordination behaviour of histidine is its
ability to act as a bridging ligand between the two metal atoms through the nitrogen atoms of
imidazolate anions as observed in the native superoxide dismutase enzyme.