Recognition of silver cations by a cucurbit[8]uril-induced supramolecular crown ether

Abstract

The host–guest interaction of cucurbit[8]uril (Q[8]) with a synthesized guest molecule, consisting of naphthalene and viologen moieties bridged by a carbon oxygen chain, was investigated by ¹H NMR and UV-Vis spectroscopy. The results indicated the formation of an inclusion complex in a ratio of 1 : 1 with a moderate association constant of K_a = (1.1 ± 0.2) × 10⁶ L mol⁻¹. The formation of this special complex is driven by the markedly enhanced charge-transfer interaction between the electron-rich and electron-deficient guest molecule inside the hydrophobic cavity of Q[8], while the carbon oxygen chain stays outside of Q[8] to form a supramolecular crown ether. Screening of the metal cation substrate suggested that the inclusion complex recognizes Ag⁺ ions with high selectivity, as shown by UV-Vis spectroscopy.