Wen-Xuan Zhao

A supramolecular assembly of methyl-substituted cucurbit[5]uril and its potential applications in selective absorption

A supramolecular assembly of a methyl-substituted cucurbit[5]uril (SPMeQ[5]) derived from 3-α-methyl-glycoluril is formed in the presence of the organic structure-directing agent, hydroquinone (Hyq). The structure-directing effect of Hyq is not only useful in the construction of novel supramolecular assemblies based on cucurbit[n]uril (Q[n]) and organic molecules but it could also enable the preparation of Q[n]-based porous materials for use in molecular sieves, and sensors, used in absorption and separation.

Supramolecular assembly of a methyl-substituted cucurbit[6]uril and its potential applications in selective sorption

Assembly of a methyl-substituted cucurbit[6]uril derived from 3α-methyl-glycoluril (HMeQ[6]) has been studied. A supramolecular assembly has been formed in aqueous HCl solution through the outer-surface interactions of HMeQ[6] molecules. This supramolecular assembly has a porous structure with potential for applications in the selective sorption of polar volatile organics, which may be useful in molecular sieves, sensors, absorption and separation.

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.

Outer Surface Interactions of Cucurbit[6]uril That Trigger the Assembly of Supramolecular Three-Dimensional Polycatenanes.

A supramolecular polycatenane stabilized by outer surface interactions between cucurbit[6]uril (Q[6] or CB[6]) cations and [CdCl4 ]2- is reported. The arrangement of the poly-interlocked supramolecular framework is evidently constructed by a favorable combination of weak non-covalent interactions such as hydrophobic effects, hydrogen bonding, ion-dipole interactions, and C-H⋅⋅⋅Cl interactions in the solid state. Further study suggests that such 3D poly-interlocked species could be rapidly precipitated from the mixture solution in high yield owing to electrostatic interaction of the [CdCl4 ]2- anion with the electropositive outer surface of Q[6] host. This work thus demonstrates a simple, low-cost, and efficient non-covalent approach for the construction of a infinite 3D interlocked structure in water besides through coordination or covalent bonds.

Methyl-substituted cucurbit[6]uril-based microporous supramolecular frameworks for highly selective Et2O/CH3OH adsorption

The interaction and supramolecular assemblies of two alkaline earth metal ions, Ca2+ and Ba2+, with methyl-substituted cucurbit[6]uril derived from 3α-methyl-glycoluril (HMeQ[6]) in aqueous HCl solution have been investigated. X-ray diffraction analysis revealed that coordination of HMeQ[6] with these metal ions resulted in the formation of one-dimensional coordination polymers in the presence of polychloride transition metal anions, such as [CdCl4]2−, as structure-directing agents. The supramolecular frameworks exhibit excellent thermal stability as well as permanent porosity. The activated desolvated materials show high Et2O and CH3OH adsorption capacity and selectivity compared with other porous organic materials assembled solely through hydrogen bonding under ambient conditions.

Coordination and recognition of lanthanide cations by a methyl-substituted cucurbit[6]uril derived from 3α-methyl-glycoluril

The interactions between a series of lanthanide cations (Ln3+) and a methyl-substituted cucurbit[6]uril derived from 3α-methyl-glycoluril (SHMeQ[6]) in the presence of [CdCl4]2 − as a structure-directing agent in aqueous HCl solutions (6.0 mol·L − 1) have been investigated. The formation of ionic radius-dependent complexes, the crystal structures of six of which have been obtained, shows the recognition ability of SHMeQ[6] towards lanthanide cations. For example, SHMeQ[6] forms molecular capsule-like complexes with the two lightest lanthanide cations, La3+ and Ce3+; molecular pairs with Nd3+, Sm3+, Eu3+ and Gd3+, and no solid crystals are formed with the heavier lanthanides.

Host–guest complexation of HMeQ[7] with alkyldiammonium ions and alkyldiamines: a comparative study

This work presents the host–guest complexation of HMeQ[7] with a series of alkyldiammonium ions and the corresponding uncharged alkyldiamines (H2N(CH2)nNH2, n = 2, 4, 6, 8, 10, 12) in aqueous solution. 1H NMR data indicate that all alkyldiamines and alkyldiammonium ions have inclusion interactions with HMeQ[7] except for the ethanediamine. The driving force for the formation of HMeQ[7]–alkyldiammonium inclusion complexes appears to be the ion–dipole interaction, while the complexation of HMeQ[7] with alkyldiamines mostly depends on the hydrophobic effect. ITC study points out that the host–guest complexation of HMeQ[7] with alkyldiammonium ions is driven by enthalpy and entropy, while the host–guest complexation of HMeQ[7] with alkyldiamines is driven exclusively by enthalpy. The features of weak basicity and absence of charged groups of the alkyldiamines are responsible for the large negative entropy and large enthalpy change in the complexation process of HMeQ[7] with alkyldiamines.

Coordination of alkaline-earth metal cations to a symmetrical octamethyl-substituted cucurbituril in the presence of polychlorido cadmium(II) anions

The interaction of the alkaline-earth metal ions Mg2+, Ca2+, Sr2+ and Ba2+ with the symmetrical octamethyl-substituted cucurbituril, OMeQ[6], in the presence of [CdCl4]2−/[Cd2Cl8]4− anions as structure-directing agent(s) in 3 M HCl has been investigated. Ca2+ and Sr2+ yielded closely related metallosupramolecular assemblies whose X-ray structures show that in the former, [Cd2Cl8]4− anions are arranged to form parallelogram-like frameworks that surround linear OMeQ[6]/Ca2+ polymeric units. The structure of the OMeQ[6]/Sr2+ assembly is similar except that the [Cd2Cl8]4− anions in the OMeQ[6]/Ca2+ assembly are replaced by [Cd2(H2O)2Cl8]4− anions. In contrast to the above structures, interaction of the larger Ba2+ ion with OMeQ[6] gives rise to a different assembly type displaying a porous linear polymeric arrangement incorporating two different Ba2+ coordination modes; [Cd2Cl4]4− anions are associated with the Ba2+ bridges linking adjacent OMeQ[6] units in the polymeric chain. In contrast to Ca2+ and Sr2+, the smaller Mg2+ ion under similar synthetic conditions failed to yield a solid product. Isothermal titration calorimetry (ITC) studies revealed that OMeQ[6] interacts with Ca2+, Sr2+ and Ba2+, but not Mg2+, in neutral aqueous solution. The respective X-ray structures reveal the presence of both channels and other voids in the three assemblies. Following application of a vacuum until constant weight was obtained, samples of the Sr2+ and Ba2+ assemblies were subjected to the saturated vapour of each of the following volatile ligands: acetonitrile, methanol, ethanol, acetone, diethylether, dichloromethane, cyclohexane and n-hexane. The respective absorption profiles show maximum absorption for methanol, with reduced uptake for the remaining larger and/or less polar guest molecules.

Adducts of aqua complexes of Ln3+ with hexahydroxyhexamethylcucurbit[6]uril: potential application in the isolation of heavy lanthanides

The interactions of a series of lanthanide cations (Ln3+) with hexahydroxyhexamethylcucurbit[6]uril (HHQ[6]) have been investigated. The interaction results in the formation of solid crystals of adducts of HHQ[6] with aqua complexes of lanthanide cations of type ([Ln(H2O)8]3+) for Ln = Gd–Lu to yield HHQ[6]–Ln(NO3)3–CdCl2–H2O species in neutral solution. Conversely, no solid crystals were obtained for systems containing La, Ce, Pr, Nd, Sm, or Eu. Unit cell determination by X-ray diffraction shows all of these adducts to be isomorphous. Thermodynamic parameters, Ka, ΔH, and ΔS determined by ITC, show clear differences in the systems involving the six lightest lanthanides compared to those involving the eight heavier lanthanides. Energy-dispersive spectrometry indicated that the lighter or heavier lanthanide cations could be isolated from their heavier or lighter counterparts through interaction with HHQ[6].