Experimental and molecular simulation investigation of interaction between acyclovir and bovine serum albumin

The interaction between acyclovir (ACV) and bovine serum albumin (BSA) in Tris-HCl buffer solutions at pH = 7.40 was investigated by means of fluorescence and ultraviolet-visible (UV-vis) spectroscopy. At 298 and 310 K, with the wavelength of the excitation (lambda(ex)) at 282 nm, the fluorescence intensity decreased significantly with an increasing concentration of ACV. Fluorescence static quenching was observed for BSA, which was attributed to the formation of a complex between ACV and BSA during the binding reaction. This was illuminated further by the UV-vis absorption spectra and the decomposition of the fluorescence spectra. The thermodynamic parameters (Delta G, Delta H and Delta S) were calculated. The results showed that the forces acting between ACV and BSA were typical hydrophobic forces and the interaction process was spontaneous. The interaction distance r between ACV and BSA, evaluated according to the fluorescence resonance energy transfer theory, suggested that there is a high possibility that the energy transfer from BSA to ACV can occur. Theoretical investigations based on homology modelling and molecular docking suggested that the binding between ACV and BSA was dominated by hydrophilic forces and hydrogen bonding. The theoretical investigations provided a good structural basis to explain the phenomenon of fluorescence quenching between ACV and BSA.