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

A water-soluble fluorescent sensor based on the interaction of twisted cucurbit[14]uril (tQ[14]) and thiazole orange (TO) in aqueous solution was developed. Formation of the tQ[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 tQ[14]/TO complex with metal ions revealed that, from a series of nineteen selected common metal ions, 1) only Hg2+ can lead to fluorescence enhancement and then quenching of the tQ[14]/TO (2:1) complex in neutral aqueous solution; 2) only Ba2+ can induce fluorescence quenching of the tQ[14]/TO (2:1) complex in aqueous HCl solution (pH 2); furthermore, the tQ[14]/TO/Ba2+ systems exhibit reversible changes in fluorescent intensity on successively adding SO42- and Ba2+ ; and 3) only Ba2+ or Pb2+ can induce fluorescence quenching of the tQ[14]/TO (15:1) complex in aqueous HCl solution (pH 2). Thus, the tQ[14]/TO complex can act as a supramolecular fluorescence-based sensor for the determination of Hg2+ , Ba2+ , and Pb2+ ions.

A New Member of the Inverted Cucurbit[n]uril Family.

A new inverted cucurbituril, namely inverted hexamethylcucurbit[3,3]uril (iMe6 Q[3,3]), has been isolated and characterized. It incorporates a single inverted un-substituted glycoluril unit oriented towards the interior of the cavity, shows good solubility in water and organic solvents (DMSO), and exhibits different selectivity for guests to those of iQ[6] and other known Q[6]s.

Encapsulation of alkyldiammonium ions within two different cavities of twisted cucurbit[14]uril.

Binding interactions between twisted cucurbit[14]uril (tQ[14]) and a series of alkyldiammonium ions both in aqueous solution and DMSO media were investigated by NMR spectroscopy and ITC. Experimental data indicate that tQ[14] possesses two kinds of cavities with different space environments, which can encapsulate two or even three guest molecules with suitable shape and size.

Twisted Cucurbit[n]urils.

Two new twisted cucurbiturils, cucurbit[13]uril (tQ[13]) and cucurbit[15]uril (tQ[15]), have been synthesized and separated, and their structures have been confirmed by NMR spectroscopy and MALDI-TOF mass spectrometry together with the X-ray structures of two new complexes, {Dy(H2O)4Cd(H2O)4tQ[13]}·2.5[CdCl4]·65H2O and {Cd0.5(H2O)2tQ[15]}·[CdCl4]·47H2O. tQ[15] is the largest cucurbit[n]uril (Q[n]) in the Q[n] family reported to date. The X-ray diffraction studies of both complexes indicated that these large tQ[n]s effectively exhibit two different cavities-a central cavity and two side cavities. Preliminary host-guest behavior by each of the new systems was investigated by NMR studies.