Structural, theoretical and enzyme-like activities of novel Cu(II) and Mn(II) complexes with coumarin based bidentate ligand

A novel ligand 4-hydroxy-3-(3-pyridineazo)-coumarin (HPYC) and its Cu(II) and Mn(II) complexes were synthesized. These compounds were characterized by elemental analysis, ICP-OES, FT-IR, XRD, thermal analysis, magnetic susceptibility and molar conductivity measurements. The free ligand HPYC was further characterized by 1H- and 13C-NMR spectra. Elemental analysis, stoichiometric and spectroscopic data of the synthesized molecules indicated that HPYC behaved as a bidentate and the metal:ligand ratio of the complexes was 1:2. The optimized molecular geometries, chemical shifts, vibrational frequencies, HOMO-LUMO energies and molecular electrostatic potential diagrams of the synthesized molecules in the ground state were calculated by using DFT/ B3LYP with 6-311G(d,p) basis set. LANL2DZ basis set with effective core potential for the Cu(II) and Mn(II) ions was used. All the theoretical data obtained as a result of quantum chemical calculations were compared with the experimental ones and it was observed that they were in good agreement. Studies were also conducted to model the functional properties of catecholase and phenoxazinone synthase of both synthesized complexes. For this purpose, the catalytic activities of each complex in the oxidation reactions of 3,5-di-tert-butylcatechol to 3,5-ditert-butyl-o-benzoquinone and 2-aminophenol to 2-aminophenoxazin-3-one were investigated under aerobic conditions. Cyclic voltammetry of the Cu(II) and Mn(II) complexes was used to explain their catalytic activity in enzymatic reactions. From the calculated rate constant values, it was determined that the [Cu(PYC)2(H2O)2] complex could have better biomimetic properties as it catalyzed both oxidation reactions better than [Mn (PYC)2(H2O)2].