Catalase enzymes are a key antioxidant defense present in most aerobic forms of life and are responsible for the protection of cells from damage caused by hydrogen peroxide (H2O2). A range of diseases have been attributed to their absence or malfunction. The active site of MnCAT is composed of Mn ions bridged by a μ-carboxylate ligand and μ-oxygen bridges. Many synthetic, binuclear Mn complexes have been reported with the aim of mimicking the spectroscopic and/or extremely efficient catalytic reactivity of MnCAT. A challenge of bioinorganic chemistry has been to rationalize the involvement of the different redox couples participating in the H2O2 disproportionation reaction, along with the structural differences of the Mn centers modulated by the ligands. Our team has synthesized a series of PyN3 and Py2N2 monomers and μ-oxo dimer manganese complexes. The latter set of μ-oxo complexes yielded EPR spectra strikingly similar to that of MnCAT and prompted us to show that these complexes were competent for H2O2 disproportionation reactivity. Interestingly, spectroscopy experiments implicated the presence of dimeric species during catalysis. This presentation will focus on the measurements of k, Ea, and TON for a new series of Mn complexes. These parameters can be tuned by two main variables in ligand design (1) the number of pyridine rings and (2) electron-donating groups attached on the 4-position of the pyridine ring. This data will be integrated into a proposed mechanism to show how the dimeric form of the complexes can achieve H2O2 disproportionation.

MnCAT type H2O2 disproportionation reactivity can be controlled by tuning pyridinophane ring structure and pyridine substitution

ACS Spring 2022

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