Spectroscopic studies of the interaction of anti-coagulant rodenticide diphacinone with human serum albumin

Abstract

The interaction of diphacinone with human serum albumin (HSA) was studied by the methods of fluorescence and Fourier transform infrared (FT-IR) spectroscopy under simulative physiological conditions. Diphacinone can strongly quench the intrinsic fluorescence of HSA by static quenching. The apparent binding constants K T at four different temperatures (291, 300, 310, and 318 K) were obtained according to Scatchard procedure. The Stern–Volmer and Scatchard plots both had an intersection at C diphacinone/C HSA≈1.2, which indicated that diphacinone binded to different binding sites on HSA. The analytical results of fluorescence data showed when C diphacinone/C HSA was lower than 1.2, the numbers of binding sites were near 1.1, and C diphacinone/C HSA was higher than 1.2, the number of binding sites was approximately 1.8. The FT-IR spectra had proved that the secondary structure of HSA changed after interacting with diphacinone in aqueous solution. The thermodynamic parameters were calculated by van't Hoff equation. The enthalpy change (Δ H 0) and entropy change (Δ S 0) were −14.59 kJ mol −1 and 62.49 J mol −1 K −1, respectively. The results suggested that the hydrophobic interaction might play a main role in the interaction of diphacinone with the HSA. The binding distance ( r) between diphacinone and tryptophan in HSA was obtained according to the Förster energy transfer theory. Furthermore, the study of molecular modeling indicated that diphacinone could bind to the site I of HSA and hydrophobic interaction was the major acting force, which was in agreement with the binding mode study.