Study of interaction between syringin and human serum albumin by multi-spectroscopic method and atomic force microscopy

The interaction between syringin and HSA has been studied by AFM, molecule modeling, fluorescence, UV–vis, FTIR and CD spectroscopy. Fluorescence results revealed that syringin can enhance the intensity of HSA fluorescence. The enhancement data was analyzed by the equation which developed by Bhattacharya et al. The results showed that there was one primary syringin binding site on HSA with a binding constant of 2.97 × 104 M−1 at 295 K. Thermodynamic analysis by Van Hoff equation found enthalpy change (ΔH0) and entropy change (ΔS0) were −5.23 kJ mol−1 and 103.34 J mol−1 K−1 respectively, which indicated the hydrophobic interaction was the predominant force in the binding process. Competitive experiments showed a displacement of warfarin by syringin, which indicated that the binding site was located at the drug site I. AFM results revealed that the dimension of the individual HSA molecules was larger after interaction with syringin. The secondary structure compositions of free HSA and HSA–syringin complex were estimated by FTIR and CD spectra.