Hang Cong

Hydroquinone-induced framework based on direct coordination of rubidium ions to cucurbit[7]uril

A strategy of using organic guest-induced formation of polymers or frameworks based on the coordination of metal ions and cucurbit[n]urils was developed. Using this strategy, a compound with a stoichiometry of {Rb2(μ-OH)(H2O)2(Hyq@Q[7])2}·Cl has been synthesized. X-ray crystallography, shows the crystal structure to be a novel three dimensional infinite framework, constructed by the Q[7] pairs through the hydroquinone-induced coordination of the rubidium unit to the portal oxygens of the Q[7]s.

p-Hydroxybenzoic acid-induced formation of a novel framework based on direct coordination of caesium ions to cucurbit[8]uril

A novel three dimensional framework, generated by crystallisation of the ternary mixture of Q[8], CsCl and p-hydroxybenzoic acid (Hyb) has the formula {Cs(H2O)[(Hyb)2@Q[8]]2}+2Hyb·Cl−·24H2O. The crystal structure shows that the 3D framework is constructed from the four Q[8] molecule units through the Hyb-induced coordination of the caesium pair to the portal oxygens of the Q[8]s.

Chemo-selective oxidation of hydroxybenzyl alcohols with IBX in the presence of hemicucurbit[6]uril

The chemo-selective oxidation of bifunctional substrates via a supramolecular strategy has been achieved. IBX (o-iodoxybenzoic acid) oxidations of hydroxybenzyl alcohols produce the corresponding aldehyde and o-quinones, while the presence of HemiQ[6] can restrain the IBX oxidation of phenolic hydroxyl groups to afford the aldehyde product. The conversion and reaction rate are greatly affected by the structures of substrates, and the stereo effect and electronic effect play very important roles in the selective oxidation system. Various spectroscopies, including 1H NMR (proton nuclear magnetic resonance), IR (infrared), and UV-vis (ultra violet-visible) have been employed to confirm the host–guest interaction of HemiQ[6] with hydroxybenzyl alcohols.

Host-guest interaction of hemicucurbiturils with phenazine hydrochloride salt

The host–guest interactions between phenazine hydrochloride salt (PheH+) and hemicucurbit[n]uril (n = 6 or 12) (HemiQ[6 or 12]) have been studied by 1H NMR, UV–vis, IR, mass spectrometry (MS) and quantum chemistry. In 1H NMR spectra, the broadening of proton resonances of the hosts suggests the interactions of PheH+ with HemiQs. The quantitative stabilities of the host–guest systems have been obtained by UV–vis titration experiments, that is, the stoichiometric interactions of PheH+ with HemiQ[6] have been observed with an association constant of Ka = (2.5 ± 1.2) × 106 L mol− 1, while the 2:1 ratio complexes of PheH+ with HemiQ[12] are formed with stepwise association constants of K1 = (9.2 ± 2.8) × 104 L mol− 1 and K2 = (6.4 ± 0.9) × 105 L mol− 1, respectively, which induce a total association constant of Ka = 5.9 × 1010 L2 mol− 2. Both the 1:1 and 2:1 complexes have been detected by MS. Quantum chemistry calculations have been used to understand the static structures and thermodynamic stabilities of the supramolecular assemblies.

A Hemimethyl-Substituted Cucurbit[7]uril Derived from 3α-Methyl-glycoluril.

A novel hemimethyl-substituted cucurbit[7]uril (HMeQ[7]) derived from 3α-methyl-glycoluril has been prepared. HMeQ[7] is readily soluble in both water and dimethyl sulfoxide (DMSO) and displays not only host-guest interaction properties similar to those of the normal cucurbit[7]uril but also unusual properties in DMSO.

A highly selective and sensitive fluorescent chemosensor for Hg2+ based on a pyridine-appended π-conjugated ligand

A pyridine-appended π-conjugated ligand 1,4-bis[2-(4-pyridyl)ethenyl]benzene (bpeb) has proved to be highly selective and sensitive as a chemosensor for Hg2+ in buffered aqueous solution. Remarkable changes in the UV-vis and fluorescence emission spectra were observed upon addition of Hg2+ ions to a solution of bpeb. In particular, the interaction of the lone-pair electrons on the pyridine nitrogen with Hg2+ ions results in a significant red-shift in the fluorescence spectrum and a large Stokes shift of up to 65 nm. DFT calculations have revealed that the energy levels of the HOMO and LUMO of bpeb are critically decreased upon coordination to Hg2+ ions, thereby accounting for this red-shift of the fluorescence spectrum. Furthermore, bpeb has been shown to be applicable as a fluorescent probe for imaging Hg2+ ions in PC3 cell lines, which may help in the understanding of relevant biological processes at the molecular level.

Synthesis and inclusion behavior of a heterotritopic receptor based on hexahomotrioxacalix[3]arene

A heterotritopic hexahomotrioxacalix[3]arene receptor with the capability of binding two alkali metals and a transition metal in a cooperative fashion was synthesized. The binding model was investigated by using 1H NMR titration experiments in CDCl3–CD3CN (10 : 1, v/v), and the results revealed that the transition metal was bound at the upper rim and the alkali metals at the lower and upper rims. Interestingly, the alkali metal ions Li+ and Na+ bind at the lower and upper rim respectively depending on the dimensions of the alkali metal ions versus the size of the cavities formed by the calix[3]arene derivative. The hexahomotrioxacalix[3]arene receptor acts as a heterotritopic receptor, binding with the transition metal ion Ag+ and the alkali metals ions Li+ and Na+. These findings were not applicable to other different sized alkali metals, such as K+ and Cs+.

Kinetic and thermodynamic inclusion complexes of symmetric teramethyl-substituted cucurbit[6]uril with HCl salts of N,N′-bis(pyridylmethyl)-1,6-hexanediamine

The host–guest interaction of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) with the hydrochloride salts of N,N′-bis(4-pyridylmethyl)-1,6-hexanediamine (P6), N,N′-bis(3-pyridyl-methyl)-1,6-hexanediamine (M6) and N,N′-bis(2-pyridylmethyl)-1,6-hexanediamine (O6) was investigated via single crystal X-ray diffraction, 1H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy. Single crystal X-ray diffraction showed that the hexyl moiety of P6 or M6 was incorporated in the cavity of TMeQ[6], while the two pyridylmethyl moieties of O6 were incorporated in the TMeQ[6] cavity in the solid state. The 1H NMR results in aqueous solution revealed that the TMeQ[6]-P6 and TMeQ[6]-M6 host–guest interaction systems produce a kinetic dumbbell-shaped inclusion complex at the initial stage and then an equilibrium pseudorotaxane-shaped inclusion complex as the only product after heating. However, only the pseudorotaxane-shaped inclusion complex was observed for the TMeQ[6]-O6 host–guest interaction system. Aqueous absorption spectrophotometric analysis showed that the dumbbell-shaped inclusion complexes were stable at pH 5.6, had a host–guest ratio of 2:1 and formed quantitatively at ∼1011 l2/mol2 for the TMeQ[6]-M6 and TMeQ[6]-O6 systems. The transformation from dumbbell to pseudorotaxane-shaped inclusion complexes for the TMeQ[6]-P6 and TMeQ[6]-M6 host–guest systems yielded activation energies of 59.35 ± 1.55 and 78.7 ± 3.45 kJ/mol, respectively. The pseudorotaxane-shaped inclusion complexes were stable at pH 5.6, had a host–guest ratio of 1:1 and formed quantitatively at ∼107 l/mol for the TMeQ[6]-M6 and TMeQ[6]-P6 systems.

Synthesis and inclusion properties of C3-symmetric triazole derivatives based on hexahomotrioxacalix[3]arene

A series of metal ion receptors cone-7,15,23-tri-tert-butyl-25,26,27-tris{[1H-(1-arylmethyl)(1,2,3-triazolyl)]-4-methoxy}hexahomotrioxacalix[3]arenes, cone-3–cone-5, have been synthesized from 7,15,23-tri-tert-butyl-25,26,27-tris(propargyloxy)hexahomotrioxacalix[3]arene 2via click chemistry. The complexation properties of the receptors cone-3–cone-5 toward the selected binding of heavy metal and transition metal ions have been evaluated. The structure of cone-3 was elucidated by single-crystal X-ray crystallography.

Cucurbit[7]uril-improved recognition by a fluorescent sensor for cadmium and zinc cations

Abstract The host–guest interaction of cucurbit[7]uril (Q[7]) with the new fluorescent sensor guest molecule (BIBPAH+), formed by alkylation of the secondary amine site in N,N-bis(2-pyridylmethyl)amine with 2-(bromomethyl)benzimidazole, was investigated by fluorescence and 1H NMR spectroscopy. The results indicate the formation of an inclusion complex in a 1:1 ratio with an association constant of Ka = (2.9 ± 0.7) × 105 L ∙ mol−1. There is minimal difference in the fluorescence intensities upon the introduction of each of Mn2+, Ni2+, Co2+, Cr3+, Ho3+ and Lu3+. However, the emission was slightly quenched on the addition of Cu2+ or Fe3+ whether Q[7] is present or not. Further investigation showed that encapsulation of BIBPAH+ in Q[7] improves Cd2+ and Zn2+ recognition by enhancing the fluorescence intensity, leading to an improvement in the limits of detection. In contrast, comparative parallel experiments in which Cu2+, Mn2+, Ni2+, Co2+, Fe3+, Cr3+, Ho3+ or Lu3+ were substituted for Zn2+ or Cd2+ resulted in minimal changes in the fluorescence that occurs for the corresponding metal-free system. The natures of the encapsulated Zn2+ and Cd2+ complexes have been investigated using fluorescence and 1H NMR spectroscopy as well as by quantum chemistry. The selectivity of a fluorescent sensor for Cd2+ and Zn2+ was improved by its encapsulation within the cavity of cucurbit[7]uril.