Cobalt(II), Zinc(II), Iron(III), and Copper(II) Complexes Bearing Positively Charged Quaternary Ammonium Functionalities: Synthesis, Characterization, Electrochemical Behavior, and SOD Activity

We have synthesized and characterized Co(II) (1), Zn(II) (2), Fe(III) (3) and Cu(II) (4) complexes of 2,2'-[2,6-pyridinediylbis(ethylidyne-1-hydrazinyl-2-ylidene)]bis[N,N,N-trimethyl-2-oxoethanaminium] dichloride (H2LCl2) by NMR, IR, and X-Band EPR spectroscopy, respectively, as well as by single-crystal X-ray structural analysis.H(2)LCl(2)belongs to the class of diacetylpyridine bis(hydrazone) ligands and bears two positively charged quaternary ammonium functionalities. The complexes1-3possess a pentagonal-bipyramidal geometry, whereas4has square-pyramidal geometry. Redox reactivity and SOD activity of the complexes was studied by means of electrochemical measurements in aqueous-buffer and DMF or DMSO solutions, respectively, as well as by stopped-flow measurements. Complexes1-3do not have SOD activity, whereas4exhibits a high catalytic rate constant for the superoxide dismutation,k(cat)= 1.73 x 10(7)m(-1) s(-1)(in MOPS buffer solution of pH = 7.4). The results were discussed in terms of complex redox potentials, electrostatic interactions and their spatial distribution, kinetic lability of metal centers, and stability of peroxo intermediates, respectively.