Spectroscopic Study of Protein Complexes with Low-Molecular Compounds

The binding peculiarities of methylene blue (MB), methyl violet (MV), and Hoechst 33258 (H33258) with human serum albumin (HSA) have been studied using the fluorescence spectroscopy method. Based on the fluorescence spectra analysis, it was shown that the HSA binds to the all mentioned ligands and forms complexes, meanwhile, a quenching of the ligand fluorescence occurs, which was found to be a static quenching type. The thermodynamic parameters (the entropy, enthalpy, and Gibbs free energy) were computed and it was revealed that the complex-formation takes place due to the hydrogen bonds and van der Waals interactions between the ligands and HSA. On the other hand, this process was revealed to be thermodynamically advantageous. The H33258 binds to HSA stronger as compared to the other two ligands, which becomes obvious because of the fluorescence spectra. It was also shown that in the case of MB binding to HSA at relatively high concentrations of HSA, the quenching occurs in two ways: by both static and dynamic modes.