Supramolecular Assembly Mediated by Metal Ions in Aqueous Solution and Its Application in Their Analysis

Graphical Uniquely responsive : The interaction of thiazole orange (TO) with twisted cucurbit[14]uril ( t Q[14]) was investigated, and formation of a stable fluorescent t Q[14]/TO complex was observed. The t Q[14]/TO complex exhibited unique fluorescence responses to Hg 2+ , Ba 2+ , and Pb 2+ cations in different aqueous media (see figure). Thus, a fluorescent sensor for three heavy-metal ions was developed. A water-soluble fluorescent sensor based on the interaction of twisted cucurbit[14]uril ( t Q[14]) and thiazole orange (TO) in aqueous solution was developed. Formation of the t Q[14]/TO complex gives rise to stronger fluorescence in both neutral and acidic aqueous solutions compared with that of free TO. Further experiments on the interaction of the t Q[14]/TO complex with metal ions revealed that, from a series of nineteen selected common metal ions, 1) only Hg 2+ can lead to fluorescence enhancement and then quenching of the t Q[14]/TO (2:1) complex in neutral aqueous solution; 2) only Ba 2+ can induce fluorescence quenching of the t Q[14]/TO (2:1) complex in aqueous HCl solution (pH 2); furthermore, the t Q[14]/TO/Ba 2+ systems exhibit reversible changes in fluorescent intensity on successively adding SO 4 2− and Ba 2+ ; and 3) only Ba 2+ or Pb 2+ can induce fluorescence quenching of the t Q[14]/TO (15:1) complex in aqueous HCl solution (pH 2). Thus, the t Q[14]/TO complex can act as a supramolecular fluorescence-based sensor for the determination of Hg 2+ , Ba 2+ , and Pb 2+ ions.