Catechol oxidase activity of comparable dimanganese and dicopper complexes

Abstract

Synthetic Cu^II₂ complexes have been widely investigated as model systems for catechol oxidase enzymes. The catechol oxidase reactivity of Mn^II₂ complexes has been less explored, and the effect of metal substitution in catecholase mimics has not been explored. A series of Mn^II₂ and Cu^II₂ complexes supported by the same poly-benzimidazole ligand framework have been synthesised and investigated in catecholase activity in acetonitrile medium using 3,5-di-tert-butylcatechol (3,5-DTBC) as a substrate. The Cu^II₂ complexes proved to be good catechol oxidase mimics with moderate k_cat values (∼45 h⁻¹). The kinetic parameters for Mn^II₂ complexes exhibited lower k_cat values (∼8–40 h⁻¹) when compared to the Cu^II₂ complexes. Our findings demonstrate that later transition metals supported by relatively electron rich ligands yield the highest k_cat values for catechol oxidation.