Spectroscopic Investigation and in Vitro Cytotoxic Activity Toward HepG2 Cells of a Copper Compound Complexed with Human Serum Albumin

The human serum albumin (HSA) interaction of a mixed-ligand copper compound (1) with an imidazole and taurine Schiff base derived from salicylaldehyde and taurine was investigated using fluorescence spectroscopy, UV-vis spectroscopy, time-resolved fluorescence spectroscopy, circular dichroism (CD) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and a molecular docking technique. The results of fluorescence and time-resolved fluorescence spectroscopy indicated that 1 can effectively quench the HSA fluorescence by a static mechanism. Binding constants (K) and the number of binding sites (n ≈ 1) were calculated using modified Stern-Volmer equations. The thermodynamic parameters were calculated. UV-vis, CD and FT-IR spectroscopy measurements confirm the alterations in the HSA secondary structure induced by 1. The site marker competitive experiment confirms that 1 is located in subdomain IB of HSA. The combination of molecular docking results and fluorescence experimental results reveal that hydrophobic interaction and hydrogen bonds are the predominant intermolecular forces stabilizing the 1-HSA complex. The 1-HSA complex increases approximately three times its cytotoxicity in cancer cells but has no effect on normal cells in vitro. Compared with unbound 1, the 1-HSA complex promotes HepG2 cells apoptosis and also has a stronger capacity for cell cycle arrest at the S phase of HepG2 cells.