From specific γ‐CD / [Nb6Cl12(H2O)6]2+ recognition to biological activity tuning

Specific molecular recognition of gamma-cyclodextrin (gamma-CD) toward cationic hexanuclear niobium [Nb6Cl12(H2O)6]2+ cluster complex in aqueous solutions results in a 1:1 supramolecular assembly {[Nb6Cl12(H2O)6]@gamma-CD}2+. NMR, ITC and ESI-MS techniques were used to study the interaction between the inorganic cluster and the organic macrocycle. 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 the reagents ratio, but crystallization by slow evaporation produces a 1:2 host-guest complex [Nb6Cl12(H2O)6@(gamma-CD)2]Cl220H2O featuring the cluster encapsulated between two molecules of gamma-CD. The 1:2 complex was characterized by XRD, EA, IR and TGA. Quantum chemical calculations were performed to model host-guest interaction.