Non-Covalent and Covalent Binding of New Mixed-Valence Cage-like Polyoxidovanadate Clusters to Lysozyme.

The high-resolution X-ray structures of the model protein lysozyme in the presence of the potential drug [V IV O(acetylacetonato) 2 ] from crystals grown in 1.1 M NaCl, 0.1 M sodium acetate at pH 4.0 reveal the binding to the protein of different and unexpected mixed-valence cage-like polyoxidovanadates (POVs): [V 15 O 36 (OH 2 )] 5- , which non-covalently interacts with the lysozyme surface, [V 15 O 33 (OH 2 )] + and [V 20 O 51 (OH 2 )] n- (this latter based on an unusual {V 18 O 43 } cage) which covalently bind the protein. EPR spectroscopy confirms the partial oxidation of V IV to V V and the formation of mixed-valence species. The results indicate that the interaction with proteins can stabilize the structure of unexpected - both for dimension and architecture - POVs, not observed in aqueous solution.