Local structure is critical for superoxide dismutase activity in copper complexes: Relationship between EPR parameters, structure and activity in some sterically hindered copper(II) bis(hydrazono-triazine) complexes

Electron paramagnetic resonance (EPR) spectrometry and molecular mechanics force field calculations have been performed on some sterically hindered copper(II) complexes with hydrazonotriazine ligands, in order to gain further insight into the relationship between their bonding, structures and biological activity. As was the case with Cu(II) bis(hydrazono-triazine) complexes studied previously, the most stable configuration for all of the complexes involves coordination of two nitrogen and two oxygen atoms (2N2O) in a distorted tetragonal arrangement. With the present complexes, however, the superoxide radical scavenging activities were very low, a result which may be explained by their inability to form a (nearly) square planar structure, which facilitates the copper redox cycling during superoxide dismutation.