Catalases are a class of metalloenzymes present in most aerobic forms of life and are responsible for the protection of cell from damage caused by hydrogen peroxide, by converting it into water and oxygen. Manganese-based catalase (MnCAT) has been identified in different organisms, raising the interest in developing small molecules as biomimetic models. Mn(III) complexes of pyclen, a 12-membered ring pyrinophane macrocycle, have previously shown to be a functional mimic of MnCAT in our laboratory. In this study, modifications of the pyridinophane macrocycle were used to evaluate their impact on the catalytic disproportionation of hydrogen peroxide. Two series of ligands were studied: (1) varying the number of pyridine moieties within the macrocycle, and (2) substitutions in the 4-position of the pyridine ring. pH-potentiometric titrations were used to determine the formation constants of each manganese complex (log <i>ß</i>), which allowed us to derive speciation curves in solution. The initial rates method was used to calculate the kinetic-relevant parameters for the disproportionation reaction. The results emphasize the effect of structural differences of the ligand on modulating the reactivity of manganese, which are the basis of a mechanistic study of the reaction that is currently underway.

Catalytic disproportionation of hydrogen peroxide by manganese complexes of 12-membered pyridinophane macrocycles

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