The Recognition Of Metal Ions By A Supramolecular Probe With A Melon Ring As The Main Body

Three supramolecular probes for metal cationson the basis of formation of ternary host-guest complexes ofcucurbit[n]uril-organic molecule-metal ion have been developed in this work. Three guest molecules,Guest1, Guest2, and Guest3 have synthesized, which were encapsulated with Q[7], Q[8] and TMe Q[6], respectively, to form the novel supramolecular probes, and the host-guest interactions have been characterized by UV-vis, 1HNMR, fluorescence, and IR spectroscopies. Guest1 was a new fluorescent sensor guest molecule,formed by alkylation of the secondary amine site in N,N-bis?2-pyridylmethyl?amine with 2-?bromomethyl?benzimidazole. The stable inclusion complex between Guest1 and Q[7] wes formed with an association constant of Ka =?2.9 ±0.7? × 10⁵L/mol. Further investigation showed that benzimidazole groups of Guest1 entered into the cavity of the Q[7], meanwhile, two pyridine groups,which could coordinated with metal ion, resided outside the cavity of Q[7].The encapsulation of Guest1 in Q[7] improves Cd²⁺ and Zn²⁺ recognition by enhancing the fluorescence intensity. And both the molar ratio method and Job method showed that the ratio of the host guest inclusion complex to Cd²⁺or Zn²⁺was 1:1, respectively. The limitation of dectation for metal ions in inclusion complex is as low as 10-9mol/L.The host–guest interaction of Q[8] with Guest2, consisting ofnaphthalene 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 amoderate association constant of Ka =?1.1 ± 0.2? × 10⁶ L/mol. The formation of thehost-geust complex wasdriven by the markedly enhanced charge-transfer interaction between the electron-rich and electron-deficient moities inside the hydrophobic cavity of Q[8], while the carbon oxygen chain stay ed outside of Q[8] to form a supramolecular crown ether.Screening of the metal cation substrates suggestedthat the inclusion complex performed an obvious recognition to Ag⁺ ions with the absorption changes of UV-Vis spectra.Guest3 was synthesized by the reaction of 1,10-phenanthroline andPyridine-4-carboxaldehyde. The host–guest interaction of TMe Q[6] with Guest3 was investigatedby1 HNMR, fluorescencespectroscopy and X-raysingle-crystal diffraction. The results indicated the formation of an inclusion complex in a ratio of 1 : 1 with amoderate association constant of Ka = 4.0× 10⁶ L/mol, and caused the dramatic enhancement of fluorescence intensity. The analysis of the crystal structure of the inclusion complex showed that the phenanthrolinemoiety on Guest3 resided outside the cavity of TMe Q[6], which was able tocoordinate to metal ion. In the experiments of screening for rare earth metals, it was found that the inclusion complexformed by Guest3 and TMe Q[6] recognized for La³⁺ and Ce³⁺.