A multitechnique study of europium decatungstate and human serum albumin molecular interaction

Polyoxometalates (POMs) show promising biological activities, but the mechanism of these potential therapeutic effects remains to be elucidated at a molecular level. As a step in this direction, the interaction between the Eu-containing decatungstate [EuW10O36](9-) and human serum albumin (HSA) has been studied by several techniques. Fluorescence/luminescence analysis showed the existence of a strong interaction between the POM and HSA. This interaction has key effects both on luminescence of the POM and on the behaviours of HSA. An enhancement of the POM luminescence is observed upon interaction. The presence of increasing concentrations of the POM results in the progressive quenching of the fluorescence of the single tryptophan of HSA. Circular dichroism led to the conclusion that the binding of the POM did not alter the secondary structure of HSA. Isothermal titration calorimetry revealed an enthalpy-driven binding reaction between HSA and the POM, resulting in the formation of a 1 : 1 complex. The present work is meaningful in finding novel solid state bio-image or fluorescence/luminescence labelling agents.