Investigation of two blood proteins binding to Cantharidin and Norcantharidin by multispectroscopic and chemometrics methods

The interactions of Cantharidin/Norcantharidin (CTD/NCTD) with two blood proteins, i.e., bovine serum albumin (BSA) and bovine hemoglobin (BHb), have been investigated by the fluorescence, UV-vis absorption, and FT-IR spectra under imitated physiological condition. The binding characteristics between CTD/NCTD and BSA/BHb were determined by fluorescence emission and resonance light scattering (RLS) spectra. The quenching mechanism of two blood proteins with CTD/NCTD is a static quenching. Moreover, the experimental data were further analyzed based on multivariate curve resolution-alternating least squares (MCR-ALS) technique to obtain the concentration profiles and pure spectra for three species (BSA/BHb, CTD/NCTD and CTD/NCTD-BSA/BHb complexes) which existed in the interaction procedure. The number of binding sites n and binding constants Kb were calculated at various temperatures. The thermodynamic parameters (such as, ΔG, ΔH, and ΔS) for BSA-CTD/NCTD and BHb-CTD/NCTD systems were calculated by the Van't Hoff equation and also discussed. The distance r between CTD/NCTD and BSA/BHb were evaluated according to Förster no-radiation energy transfer theory. The results of Fourier transform infrared (FT-IR), synchronous fluorescence and three-dimensional fluorescence spectra showed that the conformations of BSA/BHb altered with the addition of CTD/NCTD. In addition, the effects of common ions on the binding constants of BSA-CTD/NCTD and BHb-CTD/NCTD systems were also discussed.