Exploring the binding interaction of rupatadine with bovine serum albumin using multi-spectroscopic and molecular modeling approaches

Rupatadine (RUPA), a second-generation H₁-receptor antagonist, is used to treat allergies with a further antagonistic action on platelet-activating factor. Here, the binding interaction between RUPA and bovine serum albumin (BSA) has been investigated via various approaches, including spectrofluorimetric techniques, thermodynamic studies, Fourier transform infrared spectroscopy (FTIR), ultraviolet (UV) spectroscopy, and molecular docking (MD). The spectrofluorimetric titration study was displayed at various temperatures, and the data revealed that the BSA native fluorescence is quenched by RUPA via a static quenching process, which has been signified by UV absorption and fluorescence spectroscopy. The thermodynamic analysis revealed that the stoichiometry between RUPA and BSA is 1:1, and their binding affinity was weak to moderate. As revealed by the enthalpy change (ΔH) and entropy change (ΔS) values of 133.024 kJ mol^{- 1} and 0.487 kJ mol^{- 1}, respectively. The hydrophobic forces are the main binding forces in the interaction between BSA and RUPA. The negative values of Gibbs free energy change (ΔG) indicate that the binding process between RUPA and BSA was spontaneous. Furthermore, results of the site marker technique and synchronous fluorescence measurements indicate that RUPA binding interaction occurs at site (I) on BSA in the vicinity of tryptophan residues, which was then confirmed by MD.