Study of the interaction between two newly synthesized cyclometallated platinum (II) complexes and human serum albumin: Spectroscopic characterization and docking simulation

This study describes HSA binding properties of two cyclometalated platinum (II) complexes with non-leaving lipophilic ligands; deprotonated 2-phenylpyridine (ppy): C₁ and deprotonated benzo [h]quinolone (bhq): C₂, using UV–vis, fluorescence and circular dichroism (CD) spectroscopy. The absorption spectra of HSA decreased in the presence of increasing concentration of these complexes, reflecting HSA structural alteration after drug's binding. Also the thermodynamic parameters (ΔG, ΔH and ΔS) that obtained from Trp fluorescence study revealed that the interaction between these complexes and HSA were spontaneous. In addition, C₁ with flexible chemical structure indicated significantly higher fluorescence quenching and binding affinity to HSA than C₂ which possesses a higher structural rigidity. The ANS fluorescence results also indicated that two Pt (II) complexes were competing for binding to the hydrophobic regions of HSA. Moreover, CD results demonstrated that C₂ complex induced alteration of HSA conformation to more significant extent compared to C₁. The molecular docking results revealed the involvement of π–π stacking and hydrophobic interaction between these complexes and the protein. Overall, this study may highlight the significance of structural flexibility in designing of future anticancer Pt (II) complexes with improved binding affinity for HSA. - Highlights: • HSA is a general transport carrier for a wide variety of ligands such as metabolites and pharmaceutical drugs. • The HSA binding properties of two structurally related cyclometallated platinum (II) complexes (C₁ and C₂) were studied. • The complexes can bind to HSA and induce structural alteration in this protein. • The thermodynamic parameters revealed that the interactions were spontaneous and mainly hydrophobic driven. • C₁ with flexible chemical structure indicated a higher binding affinity for HSA than C₂