Probing the binding of vitexin to human serum albumin by multispectroscopic techniques

The interaction between vitexin and human serum albumin (HSA) has been studied by using different spectroscopic techniques viz., fluorescence, UV–vis absorption, circular dichroism (CD) and Fourier transform infrared (FT–IR) spectroscopy under simulated physiological conditions. Fluorescence results revealed the presence of static type of quenching mechanism in the binding of vitexin to HSA. The binding constants (Ka) between vitexin and HSA were obtained according to the modified Stern–Volmer equation. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) were calculated to be –57.29 kJ mol−1 and –99.01 J mol−1 K−1 via the vanʹt Hoff equation, which indicated that the interaction of vitexin with HSA was driven mainly by hydrogen bond and van der Waals forces. Fluorescence anisotropy data showed that warfarin and vitexin shared a common binding site I corresponding to the subdomain IIA of HSA. The binding distance (r) between the donor (HSA) and the acceptor (vitexin) was 4.16 nm based on the Förster theory of non-radioactive energy transfer. In addition, the results of synchronous fluorescence, CD and FT–IR spectra demonstrated that the microenvironment and the secondary structure of HSA were changed in the presence of vitexin.