The mechanism of interaction between 2,3-dihydro-4',5,7-trihydroxyflavone (naringenin, NAR) and human serum albumin (HSA) has been investigated by UV absorption, fluorescence and Fourier transform infrared spectroscopic methods. The UV absorption spectra revealed that the hydroxyl group at 7 position was partially dissociated at physiological pH (7.4) to cause significant red shift of UV absorption band originated from the conjugated system between the ring A and the carbonyl group of ring B. Further red shift of this band after interaction of NAR with human serum albumin signified that the conjugated system participated in the interaction. There was only one binding site (probably site I) in the drug to protein molar ratios ranging from 0.1 to 10, and the binding affinity was 1.27×10⁵ L•mol^－1 (n＝5, RSD＜5%). The effects of pH on the protein fluorescence quenching after interaction with NAR were studied to find that the active functional group in neutral state played key role in the binding process. The alterations of protein secondary structure before and after interaction with NAR were determined both in H₂O and D₂O buffer solutions. The percentage of protein α-helix structure was decreased with the increase of drug concentration, and that of β-sheet and β-turn structure increased. The content of random coil was also slightly increased in higher drug concentration. Combining the results of UV absorption, fluorescence and Fourier transform infrared spectroscopic methods, the binding mode of NAR with HSA was discussed.

Key words: 2,3-dihydro-4',5,7-trihydroxyflavone, human serum albumin, Fourier transform infrared spectroscopy, fluorescence spectroscopy, UV absorption spectroscopy