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


Abstract: The synthesis and characterisation including $^{1}$H and $^{13}$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 (k$_{cat})$ recorded for complex 3. The catalytic process as monitored by $^{1}$H NMR spectroscopy (isolation of 3, 5-DTBQ) and iodometric titration revealed the formation of H$_{2}$O$_{2}$ and thus implied that the mechanism of oxidation is through the formation of a semiquinolate species.

Keywords: Mannich base, thiocyanate, isothiocyanate, catecholase activity, turnover rates

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