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Using the one-pot, direct strategy reported by Su and co-workers, we have synthesised a series of cucurbit[n]urils (Q[n], n = 5–8) and alkyl-substituted cucurbit[6]urils (SQ[6]s) anchored on polymers. Acrylamide, as a typical monomer, was used to synthesise a series of Q[n]s (n = 5–8) and SQ[6]-anchored polyacrylamides (PAMs) using a persulfate salt as initiator and oxidant. The Q[n]s (n = 5–8) and SQ[6]-anchored PAM samples have been characterised by 1H NMR, 1H NMR titrations of probe guests, Fourier-transform infrared and thermogravimetric analyser. The results confirmed that PAM chains had been successfully grafted on the back of the Q[n]s (n = 5–8) and SQ[6]s through an in situ radical polymerisation approach. It was further confirmed that the hydrophobic cavities of the Q[n]s on the polymers were still freely accessible. This synthetic approach may be extended to a variety of Q[n]s that are difficult to functionalise.

Supramolecular architectures and materials have attracted immense attention during the last decades because they not only open the possibility of obtaining a large variety of aesthetically interesting structures but also have applications in gas storage, sensors, separation, catalysis, and so on. On the other hand, cucurbit[n]urils (Q[n]s), a relatively new class of macrocyclic hosts with a rigid hydrophobic cavity and two identical carbonyl fringed portals, have attracted much attention in supramolecular chemistry. Because of the strong charge-dipole and hydrogen bonding interactions, as well as hydrophobic and hydrophilic effect derived from the negative portals and rigid cavities of Q[n]s, nearly all research in Q[n]s has been focused on utilizing the portals and cavities to construct supramolecular assemblies similar to other macrocyclic receptors such as cyclodextrin and calixarenes. Interestingly, a recent study revealed that other weak noncovalent interactions such as hydrogen bonding and π···π stacking, as well as C-H···π and ion-dipole interactions, could also be defined as "outer-surface interactions", which are derived from the electrostatically positive outer surface of Q[n]s. These interactions could be the driving forces in the formation of various novel Q[n]-based supramolecular architectures and functional materials. In this Account, we provide a comprehensive overview of supramolecular self-assemblies based on the outer-surface interactions of Q[n]s. These outer-surface interactions include those between Q[n]s, Q[n]s and aromatic molecules, Q[n]s and calixarenes, Q[n]s and inorganic complex ions, and Q[n]s and polyoxometalates. Pioneering work has shown that such weak noncovalent interactions play very important roles in the formation of various Q[n]-based functional materials and supramolecular architectures. For example, hydrogen bonds in outer-surface interactions between Q[n] molecules not only function as the sole driving force in the formation of one-dimensional Q[n] porous channels but also assist the bonding forces of the channels in capturing and accommodating acetylene molecules and carbon dioxide in the channel cavities. Moreover, upon introduction of a third species such as an aromatic molecule or inorganic anion into the Q[n]/metal system, "outer-surface interactions" could lead to Q[n]/metal-based self-assemblies from simple finite supramolecular coordination complexes to infinite polydimensional supramolecular architectures and other structures. Overall, this Account focuses on the novel self-assembly driving force derived from Q[n]s including (i) concepts of the outer-surface interactions of Q[n]s, (ii) providing plausible explanations of the mechanisms of the outer-surface interactions of Q[n]s, and (iii) introduction of an overview of the developments and practical applications of outer-surface interactions of Q[n]s in supramolecular chemistry. It is hoped that this study based on the outer-surface interactions of Q[n]s can enrich the field of molecular engineering of functional supramolecular systems and provide new opportunities for the construction of functional materials and architectures.

In the present work, we describe four previously unreported cucurbituril-based coordination supramolecular self-assemblies, formed in the presence of alkali metal and cadmium ions. Unexpectedly, in the presence of potassium or rubidium and cadmium cations, cucurbituril prefers to coordinate with cadmium to form three dimensional frameworks. The alkali metal ions seem to play a role of structure inducer in HCl medium and are not present in the final structures. In neutral aqueous solution, cadmium cations also show stronger coordination to cucurbituril and form one-dimensional supramolecular chains through static electronic interactions. When the alkali metal ion is sodium in HCl solution, sodium ions show stronger coordination to cucurbituril and form one-dimensional coordination polymers. [CdCl4]2– anions link the linear polymers through static electronic interactions between coordinated chloride anions and sodium cations, which results in the formation of two-dimensional networks.

In the present work, we demonstrate the formation of a typical cucurbit[6]uril (Q[6])-based porous material in the presence of the hexachloroplatinate(IV) anion [PtCl6]2– as an inorganic structure inducer. The driving forces for the structure directing effect of the [PtCl6]2– anion could be attributed to ion–dipole and hydrogen-bonding interactions between the anion and the ≡CH or =CH2 groups on the back of the Q[6] molecule.

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.

Coordination in supramolecular assemblies was investigated by reacting a series of lanthanide cations (Ln3+) and a new alkyl-substituted cucurbituril, the ortho-tetramethyl-substituted cucurbituril (o-TMeQ[6]), in the presence of cadmium nitrate as an inorganic structure inducer in neutral solution. X-ray diffraction analysis revealed that the coordination of lanthanide cations gives rise to two isomorphous groups bound to three and eight isomorphous compounds, respectively. One group is typical of the coordination of o-TMeQ[6] with light lanthanide cations such as Nd3+, Sm3+ and Eu3+, while the other group is characteristic of the coordination of o-TMeQ[6] with heavy lanthanide cations such as Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+ and Lu3+. Most interestingly, no solid crystals were obtained for any compounds containing La, Ce, or Pr, suggesting that these compounds may be suitable for the separation of heavier lanthanide cations from their lighter counterparts.

In the present work, we describe three cucurbit[7]uril-based coordination supermolecular self-assemblies in the presence of [M(trans)Cl4](2-). It can affect the construction of Q[7]/metal ions-based coordination polymers, at the same time it can result in the formation of Q[7]-based supramolecular assemblies when introducing the [M(trans)Cl4](2-) into the Q[7]/metal ions system.

A symmetrical octamethyl-substituted cucurbituril has been synthesized in a controlled manner by using a dimer of dimethyl-substituted glycoluril, which was in turn synthesized under formaldehyde-deficient conditions. The dimer of dimethyl-substituted glycoluril and the symmetrical octamethyl-substituted cucurbituril have been characterized by NMR spectrometry, ESI mass spectrometry and single-crystal X-ray diffraction analysis. The structure of the dimer of dimethyl-substituted glycoluril is notable because it constitutes a useful new building block that could permit the formation of such cucurbit[n]urils with substituents in certain positions or with limited numbers of methine groups on their backbones.

The host–guest interactions between a symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril and three 4-pyrrolidinopyridine derivatives, specifically 4-pyrrolidinopyridine, N-butyl-4-pyrrolidinopyridine, and N-amyl-4-pyrrolidinopyridine, have been investigated both in aqueous solution and in the solid state using NMR spectroscopic methods, electronic absorption spectroscopy, isothermal titration calorimetry (ITC), and single-crystal X-ray diffraction analysis. In aqueous solution, TMeQ[6] forms 1 : 1 inclusion complexes with these guests. Generally, TMeQ[6] preferentially accommodates the pyridyl moiety of these guests, which was confirmed by the crystal structures of its complexes with 4-pyrrolidinopyridine and N-butyl-4-pyrrolidinopyridine. Moreover, TMeQ[6] can form a thermodynamic inclusion complex with 4-pyrrolidinopyridine at elevated temperatures. The unthreading and rethreading of the TMeQ[6] ring can simulate a molecular-level plug/socket system, that can be reversibly driven by Ba2+/SO42−, and is accompanied by obvious changes in the UV absorption spectrum, both in wavelength and intensity.

The host–guest interactions of macrocyclic hosts cucurbit[7,8]urils (Q[7,8]) with prototropic forms of the drug gefitinib (diprotonated: GH2+ and neutral: G) were investigated by electronic absorption spectroscopy. The two hosts Q[7,8] showed strong binding to the diprotonated form due to the ion–dipole interaction between the polar carbonyl oxygens of the hosts and the cationic GH2+. Q[7] and Q[8] showed similar binding to the neutral gefitinib, shifting its pKa by about 1.4 units and 0.7 units downward, respectively. Determination of the thermodynamic parameters of complex formation showed that the formation of inclusion complexes between gefitinib and Q[7,8] was enthalpy controlled, suggesting that hydrophobic and van der Waals interactions were the main driving forces. Moreover, the formation of inclusion complexes between Q[7] and Q[8] and gefitinib was confirmed by 1H NMR, which showed that the phenyl moiety of gefitinib was entrapped in the Q[7] cavity or likely located on the outside of the Q[7] cavity. The two models showed a fast dynamic equilibrium. Our results indicate that the complexation of gefitinib with Q[7] could enhance the solubility and dissolution rate of gefitinib in aqueous solution.

We prepared two new types of (HO)10Q[5]-based supramolecular assemblies by using the [PMo12O40]3– anion as a structure inducer. Single-crystal X-ray diffraction analysis revealed that these two types of (HO)10Q[5]/[PMo12O40]3– hydrides were constructed from (HO)10Q[5]/[PMo12O40]3–-based 2D networks in which [PMo12O40]3– plays a key rule in attracting (HO)10Q[5] molecules through (1) classical hydrogen bonding of the functionalized hydroxy groups on the back of the (HO)10Q[5] molecules, (2) unusual hydrogen bonding of the methylene groups on the back of the (HO)10Q[5] molecules, and (3) interaction between electron-deficient carbon sites of the carbonyl groups of the (HO)10Q[5] molecules with electron-rich oxygen sites of the Mo–O groups from the [PMo12O40]3– anions. An additional electrostatic interaction could exist in K+-coordinated (HO)10Q[5] complexes.

Based on the formation of the ternary host–guest inclusion complex between veratryl alcohol, o-iodoxybenzoic acid (IBX) and cucurbit[8]uril (Q[8]), the effect of substrate substituents on the IBX oxidation of aryl alcohols to the corresponding aldehyde subject to supramolecular catalysis by Q[8] in aqueous solvent is described. Aryl alcohols with different substituent effect on electron, for example, 2,3,4-methoxybenzyl alcohols and 2,3,4-pyridinemethanol hydrochlorides, have been subjected to the procedure for IBX oxidizing in the absence and presence of Q[8] at room temperature. The catalytic ability of Q[8] reveals that the electronic effect of the substituent on the α-carbon of the aryl alcohol is crucial to the Q[8]-catalytic oxidation, and the supramolecular catalysis of Q[8] is mechanistically suggested to contribute to the alcohols with mainly negative inductive effect of substituent.

The supramolecular properties of cucurbit[7]uril and 1,ω-bisbenzimidazolyl derivatives have been studied by 1H NMR, fluorescence emission spectroscopy, and X-ray single crystal analysis. The distinctly fluorescent response behaviors indicated that the benzimidazole moiety here not only acts as the optical signaling unit for the pseudorotaxane system, but also behaves as a proton acceptor during the host–guest complexation. Furthermore, the fluorescent signals intensity could be adjusted by varying the alkylene spacer between the two benzimidazole moieties.

The coordination of pentacyclohexanocucurbit[5]uril (PCyHQ[5]) to alkali metal cations and the formation of supramolecular assemblies in the absence and presence of [CdCl4]2– or [ZnCl4]2– anions as inorganic structure inducers have been investigated by single-crystal X-ray diffraction analysis. Studies of the crystal structures have revealed that the [CdCl4]2– or [ZnCl4]2– anions do not form honeycomb structures owing to the presence of alkyl substituents on the surface of the outer walls of PCyHQ[5], which can seriously perturb the interaction of the anions with the outer walls. Moreover, in the presence of [ZnCl4]2– anions, the formation of a new Rb-PCyHQ[5]-based 2D six-membered “bracelet” network suggests that larger ions such as Ba2+ and even Ra2+ could form this new type of supramolecular assembly.

Sym -bis(benzimidazole)-2,2′-ethylene cations act as a new axle template for threading cucurbit[6]uril derivatives on, forming [2] pseudo rotaxane and [3] pseudo rotaxane. These new complexes have been studied using 1 H NMR, UV–vis absorption spectroscopy and X-ray analysis. Changes in the 1 H NMR spectra indicate that the two types of pseudo rotaxane can be formed by varying the host concentration. UV–vis absorption titration experiments at different pH values demonstrate that interesting p K a shifts of the bis-benzimidazole derivatives can be induced by the host–guest complexation. The associated constants were calculated to be 2.81 × 10 4 L/mol and 9.06 × 10 6 L/mol for the [2] pseudo rotaxanes and [3] pseudo rotaxanes, respectively. Furthermore, X-ray diffraction studies of the solid state structures provide unequivocal proof of the host concentration dependent pseudo rotaxane, which is strongly in line with the evidences in solution.

In the present study, the lanthanide(III) contraction effect induced coordination architectures of HCyHQ[6] have been studied. The results, including fifteen crystal structures, indicate that although lanthanide metal ions have similar chemical properties mostly, their slightly different ionic radii play a key role in the formation of different supramolecular self-assembly types of HCyHQ[6]. As a result, the ionic radius-dependent complexes of HCyHQ[6] can be structurally classified into four groups: HCyHQ[6]-pair, HCyHQ[6]-molecular bowl, Ln–HCyHQ[6] one dimensional coordination polymer, and HCyHQ[6]-molecular capsule.

Binding interactions between twisted cucurbit[14]uril (tQ[14]) and twenty standard amino acids (AAs) have been investigated by NMR spectroscopy and isothermal titration calorimetry (ITC) in aqueous HCl solutions and in DMSO. The results showed that tQ[14] displays clear binding affinity for AAs with a positively charged side chain or containing an aromatic ring, but weaker binding affinity for AAs with hydrophobic or polar side chains, with the binding mode depending on the type of side chain present in the AAs.

Cucurbit[n]uril chemistry has become an important part of contemporary supramolecular chemistry since cucurbit[n]urils (Q[n]s) are not only able to encapsulate various guests, but are also capable of coordinating to a wide range of metal ions, leading to the establishment of Q[n]-based host–guest chemistry and coordination chemistry. Each of these impressive developments can be attributed to the growth of protocols for obtaining Q[n]s. In this review, we survey synthetic procedures for obtaining cucurbit[n]urils and their substituted derivatives together with the separation and purification of these remarkable compounds. The coverage is aimed at both existing workers in the field as well as at those requiring an “entry” into Q[n]-based research.

The interaction of cucurbit[7]uril (Q[7]) with a pro-virucide, adefovir bis(l-leucine propyl)ester (PMEA-Leu) in aqueous solutions and in solid state was studied by 1H NMR, UV absorption spectroscopy, fluorescence and IR spectroscopy. The 1H NMR revealed that the leucine propyl moiety of the compound could be entrapped in the cavity of the host Q[7], and the other moiety except for leucine propyl moieties, including aminopurine, was probably located at the portal area of Q[7]. Absorption and fluorescence spectroscopy proved that the interaction of Q[7] with PMEA-Leu led to the formation of host–guest inclusion complexes (2:1) that were controlled by the concentration of the host Q[7]. Formation of the inclusion complex between Q[7] and PMEA-Leu was confirmed by IR spectroscopy in solid state. In addition, deliquescent stability studies indicated that the moisture stability of the host–guest complex was significantly enhanced. The phenomenon was explained by the fact that the formation of solid inclusion c...

The supramolecular formation of an anticancer drug (6-mercaptopurine (6-MP)) in an acetate buffer solution was demonstrated through a host–guest interaction with the macrocyclic host cucurbit[7]uril (Q[7]) and bovine serum albumin (BSA). With the help of ultraviolet absorption and fluorescence spectroscopy, it was shown that a binary complex formed between 6-MP and Q[7] and/or BSA, and a specific binding interaction took place between 6-MP and Q[7] in the presence of BSA. The inclusion constants and thermodynamic parameters were determined at different temperatures. The data suggested that the formation of the binary 6-MP–Q[7] complex was driven by enthalpy in the presence of an unfavourable entropy, which was attributed to the van der Waals and hydrophobic interactions. The fluorescence quenching of BSA by 6-MP was a result of the formation of the 6-MP–BSA complex. This quenching occurred by a static quenching mechanism, and hydrophobic forces played predominant roles in the binding process. Moreover, th...

Interaction between tetramethylcucurbit[6]uril (TMeQ[6], host) and the hydrochloride salt of α-furaldehyde-isonicotinyl-hydrazone hydrochloride (FIHH+, guest) was investigated using X-ray crystallography and spectroscopic methods. X-ray crystallography showed that the π–π stacking effect and hydrogen bonding resulted in the formation of a dumbbell-shaped supramolecule which contained two FIHH+@TMeQ[6] host–guest inclusion complexes. The host–guest interaction provided identifiable changes in the vibrational frequencies in the IR spectra. 1H NMR spectral analysis established a similar interaction model and revealed that TMeQ[6] preferred to include the furan moiety over the pyridine moiety of the FIHH+ guest molecule. Absorption spectrophotometric analysis suggested that the host and guest interact in a ratio of 1:1 with a stability constant K s = (3.52 ± 0.74) × 106 l mol− 1.pH titration confirmed that the host–guest interaction led to a clear change in the protonation constant of the title guest. Quantum...

Four coordination compounds, namely [Na(H2O)(H2O)2⊂C40H50N20O10](C6H6O2)2Cl·8H2O (1), [K2(H2O)2(H2O)⊂C40H50N20O10](C6H6O2)2Cl2·7H2O (2), [Rb2(H2O)2(H2O)⊂C40H50N20O10](C6H6O2)2Cl2·7H2O (3) and [Cs(H2O)2(H2O⊂C40H50N20O10)](C6H6O2)2Cl·6H2O (4), were obtained by the reactions of the corresponding alkali metal salts with decamethylcucurbit[5]uril (Me10Q[5]) in the presence of hydroquinone, and their structures were determined by single-crystal X-ray diffraction. The results revealed that in compounds 1 and 4 each Me10Q[5] ligand coordinates one Na+ or Cs+ ion to form a molecular bowl structure, while in compounds 2 and 3 each Me10Q[5] ligand coordinates two K+ or Rb+ ions to form a closed molecular capsule structure, and adjacent molecular capsules bridge each other through water molecules to form 1D coordination polymers. In addition, we found that the coordination distances for the metal ions and the height of the metal ions out-of-portal-plane for the four compounds are in the same order, 1

In the present study, we report three crystal structures of heterometallic Q[5]-based complexes. They are complexes of heterometallic cadmium and potassium ions/Q[5] capsules with a stoichiometry of {(CdCl)[K(H 2 O)][Cl@Q[5]]} + [CdCl 3 (H 2 O) 2 ] − 7H 2 O ( 1 ), heterometallic praseodymium and calcium/Q[5] pairs with a stoichiometry of 2{[Ca(H 2 O)(OH)]- μ -[Pr(H 2 O) 3 [Cl@Q[5]]]} 3+ 6Cl − 32H 2 O ( 2 ) and discrete heterometallic neodymium and potassium ions/Q[5] capsules with a stoichiometry of {[Nd(H 2 O) 3 ][(NO 3 )@Q[5]][K(H 2 O)][Nd(H 2 O) 3 (NO 3 ) 4 ]} 2+ 2(NO 3 ) − 8H 2 O ( 3 ).

In the present study, the coordination and supramolecular self-assemblies of a series of alkali and alkaline earth metal ions to cucurbit[5]uril in the presence of nitrophenol are introduced. The experimental results have proven that the presence of nitrophenol and the ionic radiuses of the metal ions influence greatly the coordination and supramolecular self-assemblies of these metal ions to Q[5] molecule. Compared to in the absence of p-nitrophenol, the presence of p-nitrophenol seems to frustrate the formation of the K-Q[5] coordination polymer, while the presence of p-nitrophenol induces the formation of Rb- and Cs-Q[5] coordination polymers. Basically, one-dimensional supramolecular chains are constructed of alkaline earth metal ions and Q[5] molecules alternating; the sizes of their ionic radiuses influence the interaction modes in the chain. The formation of the Ca-Q[5] polymer results in the partial coordination of Ca cations to the portals of adjacent Q[5] molecules due to the smaller ionic radiu...

The complexation of thiabendazole (TBZ) with the cucurbit[6]uril (Q[6]), cucurbit[7]uril (Q[7]) and symmetric tetramethyl-cucurbit[6]uril (TMeQ[6]) in aqueous solution has been investigated using UV–vis and fluorespectrometry. The experimental results show 1:1 host–guest inclusion complexes at pH 6.5 for all three macrocyclic hosts, and the corresponding formation constants by UV and fluorescence methods are (5.37 ± 1.05) × 104 L mol−1 and (1.47 ± 0.41) × 104 L mol−1 for the Q[6]-TBZ system (7.76 ± 0.51) × 104 L mol−1 and (9.36 ± 0.22) × 104 L mol−1 for the Q[7]-TBZ system (1.28 ± 0.78) × 104 L mol−1 and (2.69 ± 0.55) × 104 L mol−1 for the TMeQ[6]-TBZ system, respectively. Based on the enhancement of the fluorescence intensity of TBZ with the addition of Q[n]s in neutral media, a fluorespectrometry method for the determination of TBZ in aqueous solution in the presence of Q[n] was established. In the range of 6.0 × 10−8 mol L−1–8.0 × 10−6 mol L−1 a linear relationship was obtained between fluorescence intensity and TBZ concentration. The detection limit was found to be between 5.51 and 8.85 × 10−9 mol L−1. The interference of coexisting ions was found to be slight. The proposed method has been successfully applied to the determination of TBZ in different aqueous solutions with satisfactory recoveries of 92–103%. The method seems to be suitable for environmental water analysis.

To explore differences in coordination between alkali- and alkaline-earth-metal ions and cucurbit[n]urils, a water-soluble α,α',δ,δ'-tetramethylcucurbit[6]uril (TMeQ[6]) was used to synthesize a series of complexes and their supramolecular assemblies, based on the coordination of TMeQ[6] with alkali- and alkaline-earth-metal ions. The complexes and corresponding supramolecular assemblies were structurally characterized by single-crystal X-ray diffraction. Unlike cucurbituril (Q[6]), which formed the metal-Q[6] polymers based on the direct coordination of carbonyl oxygen atoms to the alkali-metal ions, TMeQ[6] formed metal-TMeQ[6] polymers based on the direct coordination of carbonyl oxygen atoms with the alkaline-earth-metal ions rather than the alkali-metal ions.

Efficient selectivity for the supramolecular catalysis by cucurbit[8]uril (Q[8]) for the oxidation of aryl, allyl, and alkyl alcohols to corresponding aldehydes by o-Iodoxybenzoic acid (IBX) in aqueous solvent is reported. The relationship between the catalytic ability of Q[8] and the structure of the substrate has revealed that the catalyst prefers aryl and allyl alcohols to alkyl alcohols, and the conversions of most aryl and allyl alcohols have been increased by 30–50% in the presence of Q[8]. The catalytic selectivity suggests that the IBX oxidation proceeds via a stabilized α-Carbanion intermediate and the supramolecular catalysis should be mechanistically related to the electron density and reactivity of the α-Carbanion.

Using the achiral N,N'-bis(2-pyridylmethyl)-1,6-hexanediamine ligand bearing two end pyridyl groups as the source of conformational chirality, a novel type of TMeQ[6]-based helical polyrotaxane was prepared and characterized by X-ray crystallography and (1)H NMR spectroscopy. The chirality of the polyrotaxane was generated from twisting of the hexylidene of the N,N'-bis(2-pyridylmethyl)-1,6-hexanediamine "string" when bound within the hydrophobic cavity of TMeQ[6]. Two opposite chiral helical polyrotaxanes crystallize as a racemic compound.

The interaction products of normal cucurbit[n]urils (n = 7, 8; Q[7] Q[8]) and a sym- tetramethyl-substituted cucurbit[6]uril derivative (TMeQ[6]) with the hydrochloride salts of 2,4-diaminoazobenzene (g·HCl) were investigated in aqueous solution using 1H NMR spectroscopy, electronic absorption spectroscopy, as well as single crystal X-ray diffraction. The 1H NMR spectra analysis established a basic interaction model in which inclusion complexes with a host:guest ratio of 1:1 form for the TMeQ[6] and Q[7] cases, while they form with a host:guest ratio of 1:2 for the Q[8] case. Commonly, the hosts selectively bound to the phenyl moieties of the guests. Absorption spectrophotometric analysis in aqueous solution defined the stability of the host–guest inclusion complexes at pH 3.2. Quantitatively, at this pH, complexes with a host:guest ratio of 1:1—those with smaller hosts TMeQ[6] and Q[7]—formed with logK values between 6 and 7. That with host Q[8] and a host:guest ratio of 1:2 formed with a logK value of 10.8. Single crystal X-ray structures of the inclusion complexes TMeQ[6]–g·HCl and Q[8]–g·HCl showed the phenyl moiety of the guest inserted into the host cavity. This result supports the solution-based 1H NMR spectroscopic study.

Interaction between cucurbit[8]uril (Q[8]) with a fungicide, carboxin in aqueous solution, was investigated by 1H-NMR, electronic absorption spectroscopy, and fluorescence spectroscopy. Spectroscopy analysis established a basic interaction model which formed an inclusion complex with a host:guest ratio of 1:1. 1H-NMR showed that Q[8] encapsulated the phenyl ring into its cavity and the rest of the guest molecule stayed outside the host. Comparative in vitro evaluations of the growth inhibitory effects of the inclusion complex solution toward Rhizoctonia solani demonstrated appreciable improvements in the antifungal activity of carboxin through the addition of Q[8]. In comparison with the positive control, improvement was evaluated in terms of area covered by the mycelia of R. solani and their growth inhibition rate. Inclusion complexation of carboxin with Q[8] suggests a potential means for production of an environmentally friendly carboxin-based fungicide to counteract R. solani.

A bromide salt of 2,2′-(hexane-1,6-diyl) diisoquinolinium (K6) was designed, synthesized and introduced to construct a novel framework induced by π···π stacking of 2,2′-(alkylene-1,ω-diyl)diisoquinolinium from Q[6]-based pseudo-rotaxanes. The crystal structure of the compound revealed that the assembled framework based on the Q[6]-2,2′-(alkylene-1,6-diyl)diisoquinolinium pseudo-rotaxanes have stoichiometries of {(K6)@(Q[6])}2+·2Br−·7(H2O). The compound 1 has a novel three-dimensional framework constructed of two different channels―one containing stacked isoquinolyl moieties from the K6@Q[6] pseudorotaxanes and the other containing the bromide anions. 1H NMR spectra analysis was performed and confirmed the pseudorotaxane interaction model in which the 2,2′-(alkylene-1,6-diyl)diisoquinolinium guest threads into the cavity of Q[6] with the alkyl chain included inside the cavity and the two end isoquinolyl moieties protruding from the two opening portals. Absorption spectrophotometric and fluorescence spectroscopic analyses of the host–guest inclusion complex in aqueous solution found that the complexes were most stable at a host:guest mole ratio of 1:1. At this ratio, the complex has binding constants (K) ~106.

Five crystals based on para-dicyclohexanocucurbit[6]uil (DCyHQ[6]) were synthesized and structurally characterized by single-crystal X-ray diffractions. They are {Dioxane@DCyHQ[6]}·18H2O (1), { [ Cu ( H 2 O ) 6 ] 2 DCyHQ [ 6 ] } 4 + · 2 SO 4 2 - · 10 H 2 O (2), { [ Zn ( H 2 O ) 6 ] 2 DCyHQ [ 6 ] } 4 + · 2 SO 4 2 - · 10 H 2 O (3), { [ Sr ( H 2 O ) 5 ] 2 DCyHQ [ 6 ] } 4 + · 5 Cl - · ( H 3 O ) + · 8 H 2 O (4), { [ Na ( H 2 O ) 4 ] 2 DCyHQ [ 6 ] } 2 + · 4 Br - · 2 ( H 3 O ) + · 14 H 2 O (5). The compound 1 which is a dioxane@DCyHQ[6] inclusion host–guest complex; the other three crystal structures of the compounds 2, 3 and 4 show supramolecular assemblies comprising of DCyHQ[6] and metal ions or their aqueous complexes through hydrogen bonding; while the crystal structure of the compound 5 shows a one-dimensional supramolecular polymer through direct coordination of sodium cations to the portal carbonyl oxygen atoms of the DCyHQ[6].

The developments into the synthesis of networked rings, and channels generated in crystalline structures of substituted cucurbit[n]uril with metal ions and organic cations are reviewed. Pertinent chemical features and characteristics are discussed in the context of structural design and supramolecular architecture when utilizing substituted cucurbit[n]uril as building blocks.

Guest–host inclusion complexes between 6-benzyladenine (6-BA), cucurbit[7]uril (Q[7]), symmetrical tetramethylcucurbit[6]uril (TMeQ[6]) and meta-hexamethyl-substituted cucurbit[6]uril (HMeQ[6]) in aqueous solution were investigated by 1H NMR, UV absorption spectroscopy and phase solubility studies. The 1H NMR spectra analysis revealed that the hosts selectively bound the phenyl moiety of the guests. Absorption spectroscopic analysis defined the stability of the host–guest inclusion complexes. A host:guest ratio of 1:1 was measured quantitatively as (5.63 ± 0.26) × 104, (1.94 ± 0.17) × 103 and (2.89 ± 0.23) × 103 mol L− 1 for the Q[7]-6-BA, TMeQ[6]-6-BA and HMeQ[6]-6-BA systems, respectively. Phase solubility diagrams were analysed through rigorous procedures to obtain estimates of the complex formation constants for Q[n]-6-BA complexation. The formation constants were (1.29 ± 0.24) × 104 L mol− 1 for Q[7]-6-BA, (3.20 ± 0.17) × 103 L mol− 1 for TMeQ[6]-6-BA and (3.52 ± 1.01) × 103 L mol− 1 for TMeQ[6]-6-BA...

1,4-Butylidenedipyridinium (C 4 DP 2+ ) and 1,10-decylidenedipyridinium (C 10 DP 2+ ) cationic guests form highly stable 1:1 inclusion complexes in aqueous solution with a cucurbit[8]uril (Q[8]) host. Single-crystal structure analysis of the inclusion complexes revealed that the alkyl chain of the C n DP 2+ (n = 4, 10) cationic guest adopts an unconventional contorted conformation, which is attributed to favorable host-guest interactions (including charge―dipole and hydrophobic interactions) when bound within the cavity of the Q[8] host. Moreover, their crystal structures suggest that the alkyl chain and the aromatic group can be encapsulated into the Q[8] host simultaneously, and the alkyl chain is more favorably encapsulated into the Q[8] host than the aromatic group.

A chemical investigation reveals that the resistance to acylation of an anti-tuberculosis drug, isoniazid is a consequent result of the inclusion or exclusion of cucurbit[n]urils (n = 6 or 7). The (1)H NMR spectra analysis shows that the different interaction models of the isoniazid with the two cucurbiturils are dependent on the cavity size of the hosts. Quantum chemistry calculations with density functional theory method indicate that the interaction of the isoniazid with both cucurbiturils is through thermodynamic stabilization in both the gas phase and aqueous solution through hydrogen bonding on the portal carbonyls of the cucurbiturils. Electronic absorption titration spectra suggest the hosts and guest interact in a ratio of 1 : 1 with moderate binding constants. Acylation kinetics of isoniazid with various acylating agents in the presence of the cucurbiturils revealed that resistance is only dependent on the host-isoniazid ratio, and independent on the size of the cucurbiturils and the species of acylating agents.

The formation of 3D fused 10-membered “bracelet” frameworks derived from the alkyl-substituted curcurbit[5]urils (SQ[5]s), 1,2,4-hexamethylcucurbit[5]uril (1,2,4-HMeQ[5]), and pentacyclopentanocucurbit[5]uril (PCyHQ[5]) and K+ ions is described. These remarkable catenated structures feature trigonal-planar branching units involving three SQ[5]s connected via their bound K+ ions in a triangular manner in which the coordination of each K+ ion to the five portal carbonyl oxygen atoms of one SQ[5] as well as to a bridging portal carbonyl oxygen from an adjacent SQ[5] draws the edges of three portals into close proximity. The corresponding offset angle at each junction provides the basis for the 3D assembly of the observed fused 10-membered SQ[5] bracelet frameworks.

Cucurbit[n]urils (Q[n]) are promising ligands for the coordination of metal ions, metal complexes or clusters, and form various Q[n]-based complexes. Among the Q[n] complexes, those formed by direct coordination between Q[n]s and metal ions are particularly important. The direct coordination of metal ions to cucurbit[n]urils leads to the formation of Q[n]-based molecular capsules, tubular polymers and molecular bracelets, which could have nanoscale applications in drug delivery, molecular devices and new materials.

Three one-dimensional methyl-substituted cucurbituril-based polyrotaxanes, [Ag(H2O)(C4N3)(TMeQ[6])](NO3)3H2O (1), [Cu(H2O)2Cl2(C4N4)(TMeQ[6])]2H2O (2), and [Ag2(H2O)3(C4N4)(TMeQ[6])]2(NO3)14H2O (3) have been prepared with N,N′-bis(3-pyridylmethyl)-1,4-butanediamine (C4N3) and N,N′-bis(4-pyridylmethyl)-1,4-butane diamine (C4N4), incorporating a symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) using methods assisted by silver(I) and copper(II) ions. X-ray diffraction analyses reveal that all three polyrotaxanes have basically 1D linear chain structures with different shapes. However, the π···π stacking of the protruded pyridyl ring of the guest is observed and leads to the formation of two-dimensional networks in compound 1. Unlike most cases in which a metal ion coordinates to both of the terminal pyridyl nitrogen atoms of two neighboring pseudorotaxanes, the silver ion coordinates to only one terminal pyridyl nitrogen atom and simultaneously coordinates to two carbonyl oxygen atoms of the neigh...

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–gu...

The interaction of 6-mercaptopurine (6-MP), an antitumor drug, with cucurbit[7]uril (Q[7]) and DNA in an acetate buffer solution was studied by differential pulse voltammetry (DPV) and cyclic voltammetry(CV). The electrochemical data indicated a 1:1 complex formation of 6-MP with Q[7] and DNA. The formation constants of these complexes were determined based on the variations in the current. Moreover, the interactions of the 6-MP-Q[7] inclusion complex with DNA have been investigated by means of voltammetry. The results suggested that 6-MP displayed a high affinity for Q[7] and that the inclusion complex did not decompose when it bound to DNA. It can be inferred from the experimental data that the binding model of 6-MP to DNA may be ‘electrostatic binding’. In addition, the formation of inclusion complexes between Q[7] and 6-MP was confirmed by UV-Vis spectroscopy and the 1H NMR technique.

Three supramolecular assemblies [(C 14 H 17 N 2 ) 2 ⊂C 48 H 48 N 32 -O 16 ]Cl 2 ·23H 2 O (1), {[C 14 H 17 N 2 Cu(H 2 O) 5 ] 2 ⊂C 48 H 48 N 32 O 16 }-[(C 14 H 17 N 2 ) 2 ⊂C 48 H 48 N 32 O 16 ]Cl 4 (NO 3 ) 4 ·32H 2 O (2), and {[C 14 H 17 N 2 Ni(H 2 O) 5 ] 2 ⊂C 48 H 48 N 32 O 16 }[(C 14 H 17 N 2 ) 2 ⊂C 48 H 48 -N 32 O 16 ]Cl 2 (NO 3 ) 6 ·22H 2 O (3) were synthesized in aqueous solution and characterized by X-ray diffraction. The crystal structures of these supramolecular assemblies show that Q[8] can selectively encapsulate either the bipyridinium or butyl moiety of the 1-butyl-4,4'-bipyridinium guest in its hydrophobic cavity to form ternary complexes through the influence of metal-ligand coordination. The main driving force of the selective formation of these supramolecular assemblies may be due to ion-dipole interactions.

Nine supramolecular self-assembly entities consisting of cucurbit[5]uril, potassium salts, and hydroxybenzene or its derivatives were constructed by conventional methods. In this supramolecular architectural system, Q[5]s and the metal ions (K+) form infinite chains through coordination and ion−dipole interaction, and the stacking of these supramolecular chains then forms wavelike “walls”. The layers of hydroxybenzene or its derivatives are sandwiched by these wavelike walls, and the counteranions are captured in the molecular channels formed by the supramolecular chains. The gap between the adjacent walls is dependent on the size of the hydroxybenzene or its derivatives.

The crystal structure of {K[(H 2 O)@Q[5]][Zn(H 2 O) 3 Cl]} ZnCl 4 ·6(H 2 O) ( 1 ) is reported. It consists of an infinite 1D supramolecular chain constructed of heterometallic zinc and potassium ions/cucurbit[5]uril capsules held together through ion–dipole interactions and hydrogen bonding, and forms a novel hexagonal open framework.

The novel fluorescent sensor 1, which is comprised of two rhodamine B lactams as fluorophores that are 1,3-alternately linked to a thiacalix[4]arene, behaves as a highly sensitive ion-induced fluorescent sensor for Fe3+ and Cr3+. This compound was synthesized, and its recognition of metal ions was evaluated by fluorescence and absorption spectroscopy. The possible mechanism of Fe3+- and Cr3+-induced spirocycle opening of 1 leads to fluorescent and colorimetric enhancement, and these properties were investigated by spectroscopy, 1H NMR and IR. The stoichiometric ratios and association constants of the complexes between 1 and these ions have been measured and calculated, and showed that the presence of Fe3+ or Cr3+ induced sensor 1 to form a stable 1:1 complex.

A new rhodamine B schiff-base fluorescent sensor (1) was synthesized by a one-step condensation reaction of rhodamine B ethylenediamine and acetylacetone. The structure of 1 was characterized by single crystal X-ray crystallography, 1H NMR, MS and IR spectroscopy. Studying its fluorogenic and colorimetric behaviors towards various metal ions, high sensitivity and selectivity were achieved for Fe3+ over other commonly coexistent metal ions, which were accompanied by ring opening of a rhodamine spirocycle framework. In the ethanol aqueous medium (v/v = 4/6, Tris–HCl buffer, pH = 7.0), the presence of Fe3+ induces the formation of a 1-ion complex, which was deduced by spectroscopy, HPLC and electrochemical methods. The limit of detection for Fe3+ determinations was low to 0.11 μM (fluorescence measurement) and 1.6 μM (UV–vis measurement), respectively, indicating the potential application of 1 for the determination of trace Fe3+ ions in neutral medium.

The molecular binding behaviour of the symmetrically substituted tetramethylcucurbit[6]uril (TMeQ[6]) was examined in relationship to the two pyridine-based molecular guests 1,6-hexanedipyridinium dication (Hdipy2+) and the HCl salt of N,N′-bis(3-pyridylmethyl)-diaminoethane (Ediamp). The interactions and binding modes of each guest with TMeQ[6] are discussed using solution results (1H NMR spectroscopy) and solid-state findings (single-crystal X-ray diffraction), to evaluate interactions in common. Supramolecular structures are formed that rely on a combination of the now typical driving forces associated with Q[n] as a molecular host, which are dipole–ion, hydrophobic, H-bonding and in the present examples include π…π and C–H…π interactions.