Novel Rare Earth Tungstoarsenate Heteropolyoxometalates K11[Ln(AsW11O39)2]•xH2O (Ln = La, Nd, Sm) Binding to Bovine Serum Albumin: Spectroscopic Approach

The rare earth salts of heteropoly have been widely applied in many fields. In this study, the biological activity of rare earth tungstoarsenate heteropolyoxometalates K-11[Ln(AsW11O39)(2)]center dot xH(2)O (abbr. LnW(11), Ln = La (x = 24), Nd (x = 17), and Sm (x = 19)) were investigated by spectroscopic methods including fluorescence spectroscopy and UV-vis absorption spectroscopy at different temperatures. In the mechanism discussion, it was proved that the fluorescence quenching of bovine serum albumin (BSA) by LnW(11) is initiated by complex formation. The thermodynamic parameters suggested that the binding of LnW(11) to BSA is spontaneous, and the mainly force is electrostatic interactions. Site marker competitive experiments demonstrated that LaW11 binds with high affinity to site I (subdomain IIA) of BSA; but SmW11 and NdW11 bind with affinity to both site I (subdomain IIA) and site II (subdomain IIIA) of BSA. The results of synchronous fluorescence spectrum indicate that the secondary structure of BSA molecules was changed in the presence of LnW(11). In addition, the binding parameters, binding site number, and effect of metal ions on LnW(11)-BSA were also discussed.