Interactions of Three Chalcones with Human Serum Albumin Revealed by Spectroscopic Techniques

Chalcones are the proverbial precursors of many naturally occurring compounds and possess a variety of biological activities and a broad spectrum of pharmacological properties. The interaction mechanism between three chalcones, 2',4',4-trihydroxyflavone (also called isoliquiritigenin, 2',4',4-triHC), 2',4'-dihydroxyflavone (2',4'-diHC), and 4-hydroxyflavone (4-HC) and human serum albumin (HSA) was investigated using fluorescence quenching, fluorescence enhancement and UV absorption spectra. The binding parameters of chalcone-HSA complexes were evaluated by fluorescence quenching measurements, and the results were consistent with those obtained from fluorescence enhancement methods. The binding affinities of three chalcones with HSA at pH 7.4 were ranked in the order (the binding constants in the range 0.28 - 2.39 × 10⁵ L mol^-1), 2',4',4-triHC > 2',4'-diHC > 4-HC, indicating that the three chalcones displayed tight affinities for HSA and the hydroxyl group in chalcones played a key role in their binding affinities with HSA. The results of the UV absorption and the fluorescence enhancement elucidated that the chalcones may lead to micro-environmental and conformational changes of HSA. The binding site of the chalcone 2',4',4-triHC on the HSA was explored by the spectroscopic properties of the 2',4',4-triHC-HSA complex at pH 7.4 and 3.5, and the results demonstrated that 2',4',4-triHC bound within the hydrophobic pockets of subdomain IIA of HSA, namely site I, and the electrostatic force and ionic interactions played a crucial role in the binding interaction between chalcones and protein. The obtained results provided scientific evidence for the binding property of the chalcones and protein, which would be helpful for development of novel drugs with the skeleton of chalcones.