Complexation of HSA with Different Forms of Antimony (Sb): An Application of Fluorescence Spectroscopy

Antimony (Sb) has been considered as an emerging pollutant recently. Sb is toxic to microorganisms, plants and human being. Sb has become one global emerging contaminant and this caused more and more concern from the government and scientists.

Sb exists in environment in many kinds of forms and the toxicity of Sb depends on its form. Sb enters human body via drinking water, inhalation and food chain, unavoidably interacts with human serum albumin (HSA) in blood plasma, and consequently does harm to human health. The harmful effects of Sb on human health depend on the Sb species and their binding ability to HSA.

Most studies on toxic effects of Sb focused on drug toxicology due to the wide use of Sb-containing drugs. It was observed that exposure to trivalent forms of Sb led to liver damage, hemolysis, hematuria, apoptosis in human fibroblasts, sister chromatid exchanges and circulatory disease. However, the mechanism of human organ or blood interacting with Sb is still not well known.

To quantitatively study interaction of HSA with different forms of Sb, binding of three forms of Sb with HSA was investigated by excitation-emission matrix (EEM) fluorescence spectroscopy. Conditional stability constants and binding constants for Sb-HSA system were reported and the possible binding mechanisms were also discussed.

All of antimony potassium tartrate, antimony trichloride and potassium pyroantimonate quenched fluorescence of HSA. Values of conditional stability constant K_a (×10⁵/M) for Sb and HSA systems were 8.13–9.12 for antimony potassium tartrate, 2.51–4.27 for antimony trichloride and 3.63–9.77 for potassium pyroantimonate. The binding constant K_b (×10⁴/M) values of HAS with antimony potassium tartrate, antimony trichloride and potassium pyroantimonate were 0.02–0.07, 3.55–5.01, and 0.07–1.08, respectively.

There was one independent class of binding site for antimony trichloride towards HAS and more than one Sb binding sites and negative cooperativity between multiple binding sites for potassium pyroantimonate and antimony potassium tartrate towards HSA. The binding ability of HAS to complex Sb followed the order: antimony trichloride > potassium pyroantimonate > antimony potassium tartrate. The result was published in Journal of Luminescence in March 2013.