Spectroscopic and molecular modeling studies on the interaction between a fluorine-containing triazole derivative and human serum albumin.

The interaction between 4-(4-fluorobenzylideneamino)-5-propyl-4H-1,2,4-triazole-3-thiol (FBTZ) and human serum albumin (HSA) under simulative physiological conditions was investigated by fluorescence, UV-vis absorption and circular dichroism (CD) spectroscopy as well as molecular modeling method. Fluorescence spectroscopic data showed that the fluorescence quenching of HSA was a result of the formation of FBTZ-HSA complex. According to the modified Stern-Volmer equation, the effective quenching constants (K (a)) of FBTZ to HSA were obtained at three different temperatures. The enthalpy change (ΔH) and entropy change (ΔS) were calculated on the basis of van't Hoff equation, and the results showed that hydrogen-bonding and van der Waals forces were the dominant intermolecular forces to stabilize the complex. Site marker competitive replacement experiments demonstrated that the binding of FBTZ to HSA primarily took place in sub-domain IIA (Sudlow's site I). The binding distance (r) between FBTZ and the tryptophan residue of HSA was estimated according to the theory of fluorescence resonance energy transfer. The conformational investigation showed that the presence of FBTZ induced some changes of secondary structure of HSA. Molecular modeling study further confirmed the binding mode obtained by experimental study.