The ligand N-(2,5-dihydroxybenzyl)-N,N’-bis(2-pyridinylmethyl)-1,2-ethanediamine (H2qtp1) was previously used to prepare a Mn(II) complex that served as both as a sensor for H2O2 and a functional mimic of superoxide dismutase (SOD). Zn(II) complexes with H2qtp1 were prepared and characterized in both the solid state and aqueous solution. The complex was found to catalytically degrade superoxide, with a kcat of 3.4 × 106 M-1 s-1 in 60 mM HEPES solution buffered to pH 7.4. When phosphate is used as the buffer, the kcat at pH 7.4 increases to 19 × 106 M-1 s-1; with Mn(II)-containing SOD mimics, the use of phosphate has invariably decreased SOD activity. The ligand by itself does not catalyze the degradation of superoxide. When the Zn(II) complex reacts with discrete electron and proton abstractors, a transient EPR feature with g = 1.99 is observed. We believe that this corresponds a Zn(II)-quinoxyl radical species and speculate that similar species are intermediates in the SOD activity.

Catalysis of superoxide degradation by a Zn(II) complex with a quinol-containing ligand

255th National Meeting (2018)

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