Two New Mononuclear Mn(II) and Cu(II) Mixed-Ligand Complexes Incorporating 2,6-Di(1H-pyrazol-1-yl)pyridine and 2-Hydroxy Naphthaldehyde-Derived Schiff Base: Structural, Theoretical, and Phenoxazinone Synthase Mimicking Activity

The current investigation involved the synthesis and detailed characterization of novel mixed-ligand complexes of Mn(II) (MnDPPNPH) and Cu(II) (CuDPPNPH). These complexes incorporate 2,6-di(1H-pyrazol-1-yl)pyridine (DPP) and a Schiff base derived from 2-hydroxy naphthaldehyde (NPH). The synthesized complexes revealed a stoichiometric ratio of 1:1:1 (metal:DPP:NPH), indicative of an octahedral coordination geometry around the Mn(II) and Cu(II) centers, as represented by the chemical formula [M (DPP)(NPH)(Cl)]. To elucidate their structural and electronic properties, theoretical calculations were performed. These calculations facilitated the optimization of the geometrical structures and provided insights into the molecular orbital characteristics of the complexes. The MnDPPNPH and CuDPPNPH complexes demonstrated potential phenoxazinone synthase mimicking activity by catalyzing aerial coupling of o-aminophenol (OAPh) to form phenoxazine-2-one (phenox). The mimicking activity of these complexes was quantitatively assessed using Michaelis-Menten enzymatic kinetics. Various enzyme kinetics plots were employed to determine several kinetic parameters, including the specificity constant and turnover number (kcat), which are crucial for understanding the efficiency of the catalytic cycles. Remarkably, the synthesized MnDPPNPH and CuDPPNPH complexes exhibited significantly higher turnover numbers (kcat) compared to previously reported complexes. This finding suggests that these new complexes possess superior catalytic activity, highlighting their potential as effective catalysts for reactions mimicking the function of phenoxazinone synthase.