Investigation of the interaction between sophoricoside and human serum albumin by optical spectroscopy and molecular modeling methods

The interaction of sophoricoside and human serum albumin (HSA) was investigated by UV-absorption, fluorescence spectroscopy and Fourier transform infrared (FT-IR) spectroscopy at simulative physiological pH with sophoricoside concentrations of 3.0 × 10−6 to 2.3 × 10−5 mol L−1. The experimental results suggested that the intrinsic fluorescence of HSA was quenched by addition of sophoricoside through static quenching mechanism. The interaction between sophoricoside and HSA was occurred via a single class of binding site. The binding constants at 290, 301, 310 and 318 K were 6.19 × 104, 4.69 × 104, 3.54 × 104, 3.11 × 104 L mol−1, respectively. In the presence of sophoricoside the protein secondary structure changed in aqueous solution. The standard enthalpy change (−19.44 kJ mol−1) and standard entropy change (24.71 J mol−1 K−1) of the binding reaction revealed that hydrophobic interaction was the predominant binding force. In addition, molecular modeling showed that sophoricoside was bound within the subdomain IIA of the HSA.