Isostructural square planar mononuclear copper(II) and nickel(II) complexes: Catecholase and phenoxazinone synthase activity, protein and DNA-binding insights, and molecular docking

Two new isostructural mononuclear [Cu(L)₂] (1) and [Ni(L)₂] (2) complexes (where ligand: (3-ethoxypropyl)imino) methyl)naphthalene-2-ol) were synthesized and characterized using various spectroscopic and structural characterizations. Single-crystal X-ray diffraction analysis unveiled that both the complexes (1 and 2) manifest an ideal square planar geometry surrounding the Cu(II) and Ni(II) metal ions, arises from the coordination of the N₂O₂ donor atoms from two deprotonated Schiff base ligands HL. TD-DFT analysis was conducted to gain better insight into the electronic properties of the ligand HL and its complexes 1 and 2. Among these two complexes, only [Cu(L)₂] (1) demonstrates catalytic oxidation reactivity towards the model substrates, 3,5-di-tert-butyl-catechol and o-aminophenol, effectively mimicking the enzymes catechol oxidase and phenoxazinone synthase, respectively, with turnover numbers (k_cat) of 32.40 h⁻¹ and 9.59 h⁻¹ in MeOH. Furthermore, the efficacy of the protein binding interaction of the ligand HL and complexes 1 and 2 with bovine serum albumin (BSA), human serum albumin (HSA), and DNA was investigated at the atomistic level. The simulation analysis suggested that [Ni(L)₂] (2) complex binds more strongly with BSA, HSA and DNA than the HL and [Cu(L)₂] (1) with the binding energies of −8.88, −11.88 and −8.73 kcal/mole.