The aim of the present study was to characterize the competition of propranolol (PROP) and taxifolin (TAX) in binding to human serum albumin (HSA) in physiological buffer (pH=7.4) using multiple spectroscopic, chemometrics and molecular dynamics simulation measurements. Fluorescence analysis was used to describe the binding and quenching properties of HSA-ligand complexes in binary and ternary systems. These spectral data were further analyzed by the multivariate curve resolution-alternating least squares (MCR-ALS) method. In addition, the concentration profiles and pure spectra of three species (HSA, ligand and HSA-ligand) and the apparent equilibrium constants Kapp were evaluated. Fluorescence spectroscopy showed that in the presence of TAX, the binding constant of HSA–PROP was increased. The effect of ligands on the secondary structure of protein has been analyzed by Fourier transform infrared spectra. Conformational change of protein was analyzed using synchronous fluorescence spectroscopy, three-dimensional fluorescence spectra and molecular dynamics (MD) simulation. The results of synchronous fluorescence and three-dimensional fluorescence spectra showed that PROP would alter the micro-environment around tryptophan (Trp) and tyrosine (Tyr) residues in the presence of TAX. According to MD simulation, results suggested that these ligands can interact with the protein, with affecting the secondary structure of HSA and with a modification of its tertiary structure. MD simulations and experimental data supported each other.

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