A Series of Novel Rare Earth Molybdotungstosilicate Heteropolyoxometalates Binding to Bovine Serum Albumin: Spectroscopic Approach

Heteropolyoxometalate complexes have been widely applied in many fields. In this paper, the interaction between a series of novel rare earth molybdotungstosilicate heteropolyoxometalates, K₁₀H₃[Ln(SiMo₆W₅O₃₉)₂]·xH₂O (abbr. LnW₅, Ln = Pr (x = 30), Gd (x = 29), Dy (x = 28), and Yb (x = 31)), and bovine serum albumin (BSA) was investigated by spectroscopic approach under the physiological conditions. In the mechanism discussion, it was proved that the fluorescence quenching of BSA by LnW₅ is a result of the formation of LnW₅–BSA complex. Fluorescence quenching constants were determined using the Stern–Volmer equation to provide a measure of the binding affinity between LnW₅ and BSA. The binding affinity ranked in the order GdW₅ > DyW₅ > PrW₅ > YbW₅. The results of thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures indicate that van der Waals interactions and hydrogen bonds play a major role for LnW₅–BSA association. Furthermore, the distance r between donor (BSA) and acceptor (LnW₅) was obtained according to fluorescence resonance energy transfer.