Investigation of kinetics and thermodynamics in the interaction process between two pyridine derived Schiff base complexes and catalase

Abstract

In the present study, two new Zn(II) complexes had been prepared by an N2 bidentate Schiff base ligand 4-pyridylimine-1,2-diacetylmonoxime (PIAO) (a: [Zn(PIAO)2]Cl2, b: [Zn(PIAO)Cl2]). Spectroscopic methods were employed to characterize complexes. The antioxidant properties of PIAO and the complexes were studied in vitro by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging method. Our findings showed that PIAO binding to the metal center enhances the antioxidant properties with this trend: a > b > PIAO. Biophysical techniques were adopted to study the binding of these complexes with bovine liver catalase (BLC). The catalytic function of BLC decreased after interaction with both complexes (to 66% and 81% in the presence of a and b, respectively). Inhibitory activity of complexes occurs by a mixed-type inhibitory mechanism. Fluorescence results showed that the combination of BLC with both complexes undergoes static quenching mechanism (Kb = 6.1 × 106 M−1 for a and 0.73 × 104 M−1 for b at 310 K). The interaction process was spontaneous, exothermic and van der Waals and hydrogen bonds forces played major roles. UV–Vis, 3D, and synchronous fluorescence measurements indicated the changes in the microenvironment residues in the presence of Zn complexes. Molecular docking studies indicated that a cavity among the wrapping domain, N-Terminal arm and β-barrel is the best binding site of the prepared complexes on BLC. In conclusion, the above complexes in addition to providing antioxidant properties can interact with catalase and so inhibit its catalytic activity.