A pyrazolone-based dinuclear Cu(II) Schiff-base complex: DFT studies on the rate-determining steps of the tautomerism in the ligand and molecular docking modelling with COVID-19 main protease (6LU7)

Abstract A new dinuclear Schiff-base complex, [Cu2L'2(μ-OAc)2], was synthesized and characterized by various spectroscopic methods and single-crystal X-ray diffraction (SCXRD). The symmetrical H2L ligand was synthesized from the reaction between 4-acetyl-3-methyl-1-phenyl-2-pyrazoline-5-one (or acylpyrazolone) with 1,3-propanediamine, but upon reaction with a metal salt, it gave the unsymmetrical HL'. The transition states and rates of interconversion between different tautomeric forms of HL' were studied by DFT computations. The imine-one (Z) in the gas phase and imine-ol (Z) in the solution were the most stable forms, most probably due to better hydrogen bonding. We also applied molecular docking modeling on the various tautomeric forms of the ligand as well as the complex with the main protease (6LU7) of the SARS-CoV-2 virus. Based on the obtained results, the complex had better interactions with the receptor. The order of the interactions was [Cu2L2(μ-OAc)2] > amine-one (Z) > imine-one (E) > imine-ol (Z) > amine-one (E) > imine-one (Z) > imine-ol (E).

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