Sai-Feng Xue

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.

Construction of Cucurbit[7]uril Based Tubular Nanochannels Incorporating Associated [CdCl4]2- and Lanthanide Ions

There is intensive interest in the design of tubular channels because of their novel structures and various applications in a variety of research fields. Herein, we present a series of coordination-driven Q[7]-derived organic nanochannels using an anion-induced strategy under different acid concentrations. An advantage of this approach is that the tubular channels not only retain the original character of the parent macrocyclic receptors but also provide deep hydrophobic cavities possessing guest binding sites. Importantly, this study also emphasizes the efficiency of the macrocyclic receptors in providing a tubular hydrophobic cavity by directly stacking on top of one another with the anion-fixed and by acid control. The resulting combination of hydrogen bonding, C-H···Cl, and ion-dipole interactions helps to stabilize these supramolecular architectures. Such systems are both tunable and versatile and allow for interconvertibility in the construction of nanochannels based on these macrocyclic receptors.

Cucurbit[n]urils (n=7, 8) binding of camptothecin and the effects on solubility and reactivity of the anticancer drug

The interaction between cucurbit[n]uril (n = 7, 8)(Q[n]) with two forms namely lactone modality and carboxylate modality of anticancer drug camptothecin (CPT) was studied. The results revealed that the combination of Q[n] with the lactone form of CPT was observed by electronic absorption spectroscopy, fluorescence spectroscopy and 1H NMR technique in the acid solution (pH 2) and the total stability constants β were also obtained by Job plot with a host:guest ratio of 2:1; while in the phosphate buffer solution (pH 7.4), only Q[8] bound the carboxylate form of CPT in ratio 1:1, but no obvious interaction between Q[7] and the carboxylate form of CPT was observed. The solubility of CPT was enhanced up to about 70 and 8 times at pH 2 due to the formation of interaction complexes with Q[7] and Q[8], respectively, by using phase solubility method. The cytotoxicity tests revealed that compared with the free CPT, the complexes of Q[n] and CPT had the same cytotoxic activity on the human lung cancer cell line A549 and murine macrophage cell line P388D1 and the moderate depressed activity on human leukaemia cell line K562.

Inorganic anion-aided coordination of lanthanide metal ions to cucurbituril and supramolecular self-assembly: potential applications in the separation of light lanthanides

Linear coordination polymers have been assembled from lanthanide cations (Ln3+) and cucurbituril (Q[6]) in the presence of [CdCl4]2− or [ZnCl4]2− anions as inorganic structure inducers in HCl solution. X-ray diffraction analysis has revealed honeycomb-patterned supramolecular assemblies, in which [CdCl4]2− or [ZnCl4]2− anions form the honeycomb and the hexagonal cells are occupied by Ln3+–Q[6] linear coordination polymers. For the Ln3+–Q[6]–[CdCl4]2− systems, the solid-state structures of the obtained compounds were all isomorphous, with the Ln3+ cations coordinated to Q[6] to form zigzag coordination polymers that fill the [CdCl4]2− honeycombs. For the Ln3+–Q[6]–[ZnCl4]2− systems, the obtained compounds were divided into two groups of four and five isomorphous complexes, respectively. Besides the zigzag coordination polymers, tubular coordination polymers occupying the [ZnCl4]2− honeycombs were also observed. The most remarkable phenomenon in the present work was the rapid precipitation of the Ln3+–Q[6]–[CdCl4]2− or –[ZnCl4]2− systems when the Ln3+ cations were La, Ce, Pr or Nd. This may offer a means of separating light lanthanides cations from their heavier counterparts.

Locating the cyclopentano cousins of the cucurbit[n]uril family.

The synthesis of the first family of fully substituted cucurbit[n]uril is discussed, and the structural features of precursor glycolurils are highlighted in their importance to achieving higher homologues. The members of the family, where n = 5-7, have been fully characterized, and increased binding affinities have been identified for dioxane in CyP(6)Q[6] and adamantyl NH(3)(+) in CyP(7)Q[7]. A higher homologue is indicated but not conclusively identified.

Stable cucurbit[5]uril MOF structures as ‘beaded’ rings built on a p-hydroxybenzoic acid template—a small molecule absorption material

p-Hydroxybenzoic acid acts as a template in the presence of KI for the self-assembly of cucurbit[5]uril, which arranges into 6-membered ring structures. These form hexagonal netting sheets, superimposed upon one another to create continuous channels. This solid material is absorbent to volatile organics, ranging in size from methanol to 1,4-dioxane.

Coordination nanotubes self-assembled from cucurbit[7]uril and lanthanide cations

A series of complexes based on the macrocyclic ligand cucurbit[7]uril (Q[7]) with formulas {La2(H2O)12Q[7]}·2(ZnCl4)·2Cl·31H2O (1), {Ln2(H2O)12Q[7]}·2(ZnCl4)·2Cl·xH2O [isomorphous with Ln = Ce (2), Pr (3) and Nd (4), x = 25 (2), 29 (3) and 25 (4)], and {Ln2(H2O)10Q[7]}·2(ZnCl4)·2Cl·xH2O [isomorphous with Ln = Sm (5), Gd (6), Tb (7), Er (8), Tm (9), Yb (10) and Lu (11), x = 24 (5), 27 (6), 27 (7), 33 (8), 27 (9), 18 (10) and 29 (11)], have been synthesized by the self-assembly of Q[7] with the corresponding lanthanide species in the presence of ZnCl2. The single-crystal X-ray diffraction analyses reveal that the eleven complexes are separated into three types of coordination nanotubes given different coordination environments of the lanthanide(III) ions. The eleven complexes display interesting structural progressions, which are mainly ascribed to the effect of lanthanide contraction. Their thermal and IR properties were also examined.

Novel Supramolecular Assemblies Based on Coordination of Samarium Cation to Cucurbit[5]uril

In the present study, we introduce the coordination of samarium-Q[5] systems in the absence and presence of the third species, and the corresponding supramolecular assemblies are dependent upon the addition of the third species. In the absence of the third species, a samarium cation (nitrate salt) coordinates to a Q[5] molecule and forms a molecular bowl; in the presence of an organic molecule (hydroquinone), a one-dimensional polymer of ···Sm-Q[5]-Sm-Q[5]-Sm··· is formed through direct coordination of Sm cation to the portal carbonyl oxygens. In the presence of nickel cations (chloride salt), an infinite 1D supramolecular chain is constructed of samarium/cucurbit[5]uril molecular bowl through ion-dipole interaction and hydrogen binding; in addition, the stacking of the supramolecular chains forms a novel hexagonal open framework. Remarkably, in the presence of copper cations (chloride salt), Q[5]-based hexagonal netting sheets are constructed of 6-Q[5]-ring structures.

[CdCl4]2− anion-induced coordination of Ln3+ to cucurbit[8]uril and the formation of supramolecular self-assemblies: potential application in isolation of light lanthanides

The coordination and supramolecular assemblies of Q[8] with lanthanides in the presence of [CdCl4]2− anions show significant differences, which could be used for the isolation of light lanthanides from their heavier counterparts.

Homochiral 1D-helical coordination polymers from achiral cucurbit[5]uril: hydroquinone-induced spontaneous resolution

Compared to a linear 1D coordination polymer of cucurbit[5] uril with Dy3+ ion, a pair of homochiral 1D-helical coordination polymers of cucurbit[5] uril with Dy3+ were obtained by spontaneous resolution upon crystallization in the presence of achiral hydroquinone, suggesting hydroquinone acts as an inducer of chiral helix.