Spectroscopic investigation on the interaction of 3,7-dihydroxyflavone with different isomers of human serum albumin

The interaction mechanism of 3,7-dihydroxyflavone (3,7-diHF) and human serum albumin (HSA) was investigated by fluorescence quenching, fluorescence enhancement, steady-state and time-resolved fluorescence emission and UV–vis absorption spectrometry. The binding site of 3,7-diHF on protein was determined by investigating the spectroscopic properties of 3,7-diHF–HSA complex at pH 7.4 and pH 3.5 individually, and confirmed by the site marker competitive experiments. The binding parameters of 3,7-diHF–HSA complex were estimated by fluorescence quenching experiments, and the data were in good agreement with the results obtained from fluorescence enhancement measurements. A remarkable increase in the fluorescence anisotropy values suggested that 3,7-diHF bound at a motional restricted pocket on HSA. The results indicated that 3,7-diHF, in anionic form, was bound within the hydrophobic pockets of the subdomain IIA of HSA (site I), and stabilised mainly by electrostatic force and ionic interactions. The binding mode of drug–protein was discussed based on above experimental results.