Selective Targeting of Proteins by Hybrid Polyoxometalates: Interaction Between a Bis-Biotinylated Hybrid Conjugate and Avidin.

The Keggin-type polyoxometalate [γ-SiWO] was covalently modified to obtain a bis-biotinylated conjugate able to bind avidin. Spectroscopic studies such as UV-vis, fluorimetry, circular dichroism, coupled to surface plasmon resonance technique were used to highlight the unique interplay of supramolecular interactions between the homotetrameric protein and the bis-functionalized polyanion. In particular, the dual recognition mechanism of the avidin encompasses (i) a complementary electrostatic association between the anionic surface of the polyoxotungstate and each positively charged avidin subunit and (ii) specific host-guest interactions between each biotinylated arm and a corresponding pocket on the tetramer subunits. The assembly exhibits peroxidase-like reactivity and it was used in aqueous solution for L-methionine methyl ester oxidation by HO. The recognition phenomenon was then exploited for the preparation of layer-by-layer films, whose structural evolution was monitored by ATR-FTIR spectroscopy. Finally, cell tracking studies were performed by exploiting the specific interactions with a labeled streptavidin.