Biomimetic complexes of Mn(II), Fe(III), Co(II), and Ni(II) with 1,10-phenanthroline and a salen type ligand: tailored synthesis, characterization, DFT, enzyme kinetics, and antibacterial screening

A symmetrical tetradentate Schiff base, o-HACPHENEN, was prepared by condensation of 1,2-bis(ethylenediamine) with o-hydroxyacetophenone in 1:2 molar ratio. The Schiff base ligand and 1,10-phenanthroline were used for the tailored synthesis of four mixed-ligand complexes, [Mn(o-HACPHENEN)(1,10-phen)] (1), [Fe(o-HACPHENEN)(1,10-phen)]Cl (2), [Co(o-HACPHENEN)(1,10-phen)] (3), and [Ni(o-HACPHENEN)(1,10-phen)] (4). The ligand and complexes were characterized on the basis of elemental analyses, ESI-MS, molar conductance, electronic, FT-IR, ¹H-NMR, and ¹³C-NMR spectra. DFT study was used to optimize the geometry of the investigated compounds. Using Gaussian09 molecular modeling, HOMO-LUMO study, bond lengths, bond angles, molecular electrostatic potential map (MEP), and Mulliken charge were also evaluated. Complexes displayed remarkable catalase-like activity in the disproportion reactions of hydrogen peroxide. The kinetics of the activity were investigated and data are fitted in Lineweaver Burk plot, revealing Michaelis Menten behavior. The catalase activity of ligand and complexes were found in the order 1 > 2 > 4 > 3 > o-HACPHENEN. Compounds were screened for their antibacterial activity against gram-negative bacteria Escherichia coli in comparison to standard drugs. Complexes were more potent than Schiff base. The MIC of complexes was also studied.