Abstract
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. H2LCl2 belongs to the class of diacetylpyridine bis(hydrazone) ligands and bears two positively charged quaternary ammonium functionalities. The complexes 1–3 possess a pentagonal‐bipyramidal geometry, whereas 4 has 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. Complexes 1–3 do not have SOD activity, whereas 4 exhibits a high catalytic rate constant for the superoxide dismutation, kcat = 1.73 × 107 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.
Highlights
Diacetylpyridine bis(hydrazone) ligands and their derivatives represent a versatile class of polydentate ligands that are suit-[a] M
Besides standard physico-chemical and structural characterization of the Co(II), Zn(II), Fe(III) and Cu(II) complexes of the 2,6diacetylpyridine dihydrazone type ligand, we have investigated their redox behavior and tested their potential superoxide dismutase (SOD) activity
Knowing that the structurally related Fe(III) complex [Fe(dapsox)(H2O)2]ClO4, which was previously studied by some of us, possesses the SOD activity,[17] we wanted to probe whether the presence of two positively charged quaternary ammonium residues on the zwitterionic ligand L induce an effect on a potential SOD activity and general redox behavior
Summary
Diacetylpyridine bis(hydrazone) ligands and their derivatives represent a versatile class of polydentate ligands that are suit-. We have been studied PBP 3d metal complexes of diacetylpyridine bis(hydrazone) ligands,[2,17,31,32] as well as hydrazine complexes with positively charged quaternary ammonium groups from the Girard's T reagent.[33] Motivated by above discussed aspects of such complexes, we have synthesized and characterized Co(II), Zn(II), Fe(III) and Cu(II) complexes of 2,2′-[2,6-pyridinediylbis(ethylidyne-1-hydrazinyl-2ylidene)]bis[N,N,N-trimethyl-2-oxoethanaminium] dichloride (H2LCl2). Besides their single-crystal X-ray diffraction (sc-XRD), NMR and EPR analysis, we have studied their electrochemical behavior and SOD activity. The obtained results enabled us to gain new insights into the effects of positively charged functionalities on the redox properties and potential SOD catalysis of the diacetylpyridine bis(hydrazone) complexes
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