Synthesis and evaluation of catecholase activities of metal complexes of 1,4-substituted piperazine Mannich base of 4-acetamidophenol

Abstract

The synthesis and characterisation including 11^{1}H and 1313^{13}C NMR spectroscopy of a Mannich~base~1,4-di-(5-acetamido-2-hydroxybenzyl)piperazine~is herein reported. The Mannich reaction leading to the formation of the ligand took place at both ends of piperazine. Four metal complexes [Cu(II) and Fe(III)] including those bearing thiocyanate groups (SCN-) in N- and S-bonding modes have been studied for their abilities to mimic catecholase oxidase. All the metal complexes are catalytically active with the highest turnover rate (kcat)cat)_{cat}) recorded for complex 3. The catalytic process as monitored by 11^{1}H NMR spectroscopy (isolation of 3, 5-DTBQ) and iodometric titration revealed the formation of H22_{2}O22_{2} and thus implied that the mechanism of oxidation is through the formation of a semiquinolate species.