Study of interaction of Potassium Dodecatangestato Cobaltate(III) with Bovine Serum Albumin using Fluorescence Spectroscopy

The binding of potassium dodecatangestato cobaltate(III) (PDC) as a water-soluble polyoxometal with bovine serum albumin (BSA) as a major transporting protein of plasma, has been investigated at pH 7.2, 5 mM phosphate buffer, 27°C and various ionic strength by fluorescence spectroscopy. The results show that the binding of PDC to BSA quenches BSA emission and the Stern–Volmer linear relationship can be applied for the quenching process. The values of Stern–Volmer constant, K sv, which can be considered as a binding constant for formation of 1:1 complex at 0.01, 0.1 and 0.2 M NaCl are 8.56 × 105, 5.72 × l05 and 9.60 × 105, respectively. The interpretation of the results represents that binding affinity depends on both electrostatic forces and conformational stability of BSA. A step-by-step aggregation model, which has been developed by Borissevich et al., was used to determine the average aggregation number of BSA, ⟨J⟩, from the fluorescence quenching. The results show that the binding of PDC to BSA does not induce any considerable aggregation in BSA molecules. Therefore, it can be concluded that there are no considerable conformational changes in BSA molecules during its interaction with PDC.