Synthesis, characterization, and polyphenol oxidase activity of CuII, MnII, and FeIII complexes with a N2O2 ligand

Abstract

To explore the effect of the metal center on catechol oxidase and tyrosinase activities, four complexes, Cu2(μ-Cl)2(hbpg)2 (1), [Cu2(μ-OH2)2(hbpg)2](NO3)2(H2O)2 (2), [Fe2(μ-Cl)2(hbpg)2]Cl2(H2O)2 (3), and [Mn2(μ-Cl)2(hbpg)2](H2O)2 (4) (hbpg = N-(2-hydroxybenzyl)-N-(2-picolyl)glycine), were synthesized and characterized with elemental analysis, single-crystal X-ray diffraction, molar conductivity measurements, mass spectrometry, UV-Visible, and FT-IR spectroscopies. The X-ray crystal structural analysis indicates that 1 has a binuclear copper, coordinated with N2O2 ligands. Complementary characterizations suggested that 2, 3, and 4 have similar coordination sphere. Complex 3 exhibits much higher catechol oxidase and tyrosinase-like activity than 1, 2, and 4. The results suggested that with a similar coordination sphere, the redox potential of the metal center is critical for catalytic activity. This work provides valuable information for improving the polyphenol oxidase activity of metal complexes for phenolic degradation.