Unveiling the binding interaction of zinc (II) complexes of homologous Schiff‐base ligands on the surface of BSA protein: A combined experimental and theoretical approach
Tania Chowdhury, Kaushik Bera, Debabrata Samanta, Sandip Dolui, Suvendu Maity, Nakul C. Maiti, Prasanta Ghosh, Debasis Das
Abstract
Four new zinc (II) complexes [Zn (HL 1 H)Br 2 ] (1), [Zn (HL 1 H)Cl 2 ] (2), [Zn 2 (HL 2 )Br 3 ] (3), and [Zn (HL 2 )Cl] (4) have been synthesized by adopting template synthetic strategy and utilizing two homologous Schiff base ligands (H 2 L 1 = 4‐bromo‐2‐{[2‐(2‐hydroxyethylamino)‐ethylimino]‐methyl}‐6‐methoxyphenol, H 2 L 2 = 4‐bromo‐2‐{[3‐(2‐hydroxyethylamino)propylimino]methyl}‐6‐methoxyphenol), differing in one ‐CH 2 ‐ unit in the ligating backbone, by adopting template synthetic strategy. All the complexes have been characterized by single crystal X‐ray diffraction analysis as well as by other routine physicochemical techniques. Ligand mediated structural variations have been observed and rationalized by density functional theoretical (DFT) calculations. Interaction of the complexes 1–4 with Bovine Serum Albumin protein (BSA) has been studied by different spectroscopic techniques. A complete thermodynamic profile ( ΔH o , ΔS o and ΔG o ) was evaluated initially from the change in absorption and fluorescence spectra upon addition of BSA to the complexes. Appreciable binding constant values in the range ~ 0.94–4.51 × 10 4 M −1 indicate efficient binding tendency of the complexes to BSA with the sequence 1 ≅ 2 > 3 ≅ 4. Circular dichroism (CD), isothermal calorimetric titration experiments, molecular docking and molecular dynamics have been performed to gain deep insight into the binding regions of complex 1 to BSA. Experimental evidences suggest an interaction of zinc complexes at the surface of BSA protein and this particular binding has been exploited to determine unknown concentration of BSA protein. For this purpose complex 1 was explored as a BSA protein quantification tool.