Comparative studies on the interactions of honokiol and magnolol with human serum albumin

In this study, the binding modes of honokiol (HK) and magnolol (MG) with human serum albumin (HSA) have been established under imitated physiological condition, which was very important to understand the pharmacokinetics and toxicity of HK or MG. The experimental results proved that the fluorescence of HSA was quenched by HK or MG through a static quenching procedure. The binding constants of HK–HSA and MG–HSA complexes were 5.304 and 263.755 × 104 L mol−1 at 298 K, respectively. The binding process was a spontaneous molecular interaction procedure, in which the hydrophobic interaction played a major role in the formation of the HK–HSA complex, whereas, the binding interaction between MG and HSA might involve the hydrophobic interaction strongly and electrostatic interaction. In addition, the effect of HK/MG on the secondary structure of HSA was analyzed using CD, UV–vis absorption, Fourier transform infrared (FT-IR), synchronous fluorescence and three-dimensional fluorescence spectra. According to Förster no-radiation energy transfer theory, the binding distance of HSA to HK or MG was calculated to be 1.842 or 1.238 nm. Besides, the effects of common ions on the binding constants of HSA–HK/MG systems were also discussed.