Synthesis and characterization of N3S2 donors macrocyclic copper(II) complexes. Catechol oxidase and phenoxazinone synthase biomimetic catalytic activity
A new series of copper(II) complexes have been synthesized with macrocyclic ligands L1 and L2 having N3S2-donating atoms in the 12-membered macrocyclic ring. The structure characterization of these newly synthesized copper(II) complexes was achieved by various physicochemical techniques. It has been shown that the stereochemistry of complexes is dependent on the type of counter anions incorporated in the complex molecule. Mimicking copper oxidase enzymes, namely catechol oxidase and phenoxazinone synthase, was investigated and the results obtained demonstrated that there is a correlation between the structural properties of these copper(II) complexes and the oxidase biomimetic catalytic activities. Kinetic measurements revealed second-order dependence on the catalyst concentration for 3,5-DTBCH2 and first order in the case of OAPH. On the other hand, for the substrate concentration dependence, a saturation-type behavior was detected for both 3,5-DTBCH2 and OAPH. Addition of Lewis base, triethylamine, in both systems exhibits dramatic effect on the rate of these catalytic aerobic oxidation reactions. The probable mechanistic implications of both catalytic systems are discussed.