From Specific γ‐CD/[Nb 6 Cl 12 (H 2 O) 6 ] 2+ Recognition to Biological Activity Tuning

International audience; Specific molecular recognition of γ-cyclodextrin (γ-CD) toward cationic hexanuclear niobium [Nb6Cl12(H2O)6] 2+ cluster complex in aqueous solutions results in a 1:1 supramolecular assembly {[Nb6Cl12(H2O)6]@γ-CD} 2+. NMR, ITC and ESI-MS techniques were used to study the interaction between the inorganic cluster and the organic macrocycle in water. Such molecular association affects the biological activity of [Nb6Cl12(H2O)6] 2+ , decreasing its cytotoxicity despite enhanced cellular uptake. The 1:1 stoichiometry is maintained in solution over a large window of composition, but crystallization by slow evaporation in air produces a 1:2 host-guest complex [Nb6Cl12(H2O)6@(γ-CD)2]Cl2·20H2O showing a cluster unit encapsulated between two molecules of γ-CD. The 1:2 complex was isolated and characterized by XRD, EA, IR and TGA. Quantum chemical calculations were performed to model host-guest interaction.