From Specific Gamma-Cd/[Nb6cl12(H2o)(6)](2+) Recognition To Biological Activity Tuning

Specific molecular recognition of gamma-cyclodextrin (gamma-CD) by the 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 spectroscopy, isothermal titration calorimetry (ITC), and ESI-MS 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)]Cl-2.20 H2O featuring the cluster encapsulated between two molecules of gamma-CD. The 1:2 complex was characterized by XRD, elemental analysis, IR spectroscopy, and thermogravimetric analysis (TGA). Quantum chemical calculations were performed to model host-guest interaction.