Interaction studies of copper complex containing food additive carmoisine dye with human serum albumin (HSA): Spectroscopic investigations

In this study, the interaction between human serum albumin (HSA) and a copper complex of carmoisine dye; [Cu(carmoisine)(2)(H2O)(2)], was studied in vitro using multi-spectroscopic methods. It was found that the intrinsic fluorescence of HSA was quenched by the addition of the [Cu(carmoisine)(2)(H2O)(2)] complex and the quenching mechanism was considered as static quenching by formation of a [Cu(carmoisine)(2)(H2O)(2)]-HSA complex. The binding constant was about 10(4)M(-1) at room temperature. The values of the calculated thermodynamic parameters (H<0 and S>0) suggested that both hydrogen bonds and the hydrophobic interactions were involved in the binding process. The site marker competitive experiments revealed that the binding of [Cu(carmoisine)(2)(H2O)(2)] to HSA primarily occurred in subdomain IIIA (site II) of HSA. The results of circular dichroism (CD) and UV-vis spectroscopy showed that the micro-environment of amino acid residues and the conformation of HSA were changed after addition of the [Cu(carmoisine)(2)(H2O)(2)] complex. Finally, the binding of the [Cu(carmoisine)(2)(H2O)(2)] complex to HSA was modelled by a molecular docking method. Excellent agreement was obtained between the experimental and theoretical results with respect to the binding forces and binding constant.