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A nitrate-water cluster [(NO 3 ) 2 (H 2 O) 8 ] 2− confined in the hydrophobic cavity of a cucurbit[8]uril complex with Sr 2+ has been observed. It represents the first example of inorganic anion-water cluster formation inside the cucurbit[ n ]uril hydrophobic cavity.

Two Q[n]-based porous compounds, Q[5]·[PtCl6]2 −·2H3O·12H2O and 2Q[8]·[PtCl6]2 −·2H3O·74H2O in cooperating the hexachloroplatinate(IV) anion ([PtCl6]2 −) as an inorganic structure directing agent are demonstrated. The driving forces for the formation of such novel Q[n]-based porous compounds are considered to be the outer surface interactions of Q[n]s, including dipole interactions between Q[n]s and ion-dipole interactions between [PtCl6]2 − anions and Q[n]s. Moreover, the Q[5]-based porous compound displays absorption distinctness for tetrachloromethane, whereas the Q[8]-based porous compound displays absorption distinctness for methanol.

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.

Compared to isolated, simple Ln3+/Q[6] complexes in the absence of polychloridometallate ions, linear coordination polymers have been assembled from lanthanide cations (Ln3+) and cucurbituril (Q[6]) in the presence of polychloridometallate ions as inorganic structure inducers in HCl solution. X-ray diffraction analysis has revealed that not only [CuCl4]2− anions but also [FeCl2(H2O)4]+ cations can induce the coordination of Ln3+ cations to Q[6] so as to form Ln3+/Q[6]-based tubular coordination polymers. The driving forces are considered to be interaction of the electron-deficient carbon sites of the carbonyl dipoles of Q[n] molecules with the chloride ends of the Md-block−Cl bonds in the [Md-blockClx]n− anions or [Md-blockClx]m+ cations, as well as unusual hydrogen bonding between the methine and methylene groups on the back of adjacent Q[n] molecules and the chlorine atoms of the [Md-blockClx]n− ions. We have classified such interactions as ‘back-interaction of Q[n]s’.

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.

The interactions between a series of lanthanide cations (Ln3+ ) and methyl-substituted cucurbiturils (SPMeQ[5] and SHMeQ[6]) derived from a 3α-methyl glycoluril have been investigated. Single-crystal X-ray diffraction analysis revealed that both SPMeQ[5] and SHMeQ[6] selectively interact with certain lanthanide ions. SPMeQ[5] forms coordination capsules in the presence of [CdCl4 ]2- . The Ln3+ cations that interact are the four light lanthanides, La3+ , Ce3+ , Pr3+ , and Nd3+ , whereas the remaining lanthanide cations remain in solution. SHMeQ[6] formed adducts of SHMeQ[6] with aqua complexes of lanthanide cations ([Ln(H2 O)8 ]3+ ); for SHMeQ[6]-Ln(NO3 )3 -CdCl2 -HCl systems (Ln=Gd-Lu), no solid crystals were obtained from systems that contained La, Ce, Pr, Nd, Sm, or Eu. Whereas solid crystals of adducts of SHMeQ[6] with aqua complexes of lanthanide cations (Ln=Sm-Lu) formed SHMeQ[6]-Ln(NO3 )3 systems in neutral solution, no solid crystals were obtained from systems that contained La, Ce, Pr, or Nd. These results suggest that SPMeQ[5]- and SHMeQ[6]-Ln(NO3 )3 systems could be useful for the selective isolation of these lighter or heavier lanthanide cations from mixtures. Energy-dispersive spectrometry indicated that the lighter or heavier lanthanide cations could be isolated from their heavier or lighter counterparts through interaction with SPMeQ[5] and SHMeQ[6].

Guest–host inclusion complexes between thiabendazole (TBZ) and cucurbit[7]uril (Q[7]), symmetrical tetra-methylcucurbit[6]uril (TMeQ[6]) and meta-hexamethyl-substituted cucurbit[6]uril (HMeQ[6]) in aqueous solution were investigated by 1H NMR spectroscopy and phase solubility studies. The antifungal activities of the inclusion complexes were also determined. Analysis of the 1H NMR spectra revealed that the host Q[7] selectively binds the benzimidazole ring moiety of the guest molecule and that the thiazole ring is encapsulated into the cavities of TMeQ[6] and HMeQ[6]. Phase solubility diagrams were analysed using rigorous procedures to obtain estimates of the complex formation constants for Q[n]-TBZ complexation. The phase solubility studies showed that TBZ solubility increased as a function of Q[7], TMeQ[6] and HMeQ[6] concentrations. We found that complexation of TBZ with Q[n] increased the inhibitory effect of TBZ on the growth of Fusarium graminearum. Our results thus demonstrate that complexation of TBZ with Q[n] could be used to improve the solubility and antifungal activity of TBZ.

A one-pot strategy was employed to synthesize a series of water-soluble cucurbit[7]uril-anchored polyacrylic acids (Q[7]-anchored PAAs) with high yields in the presence of an ammonium persulfate salt as both an initiator and an oxidant. The effects of acrylic acid, Q[7] feed mass and APS concentration on the formation of polymer nanocapsules have been investigated. The Q[7]-anchored PAAs can be further esterified with 2-naphthol to yield water-insoluble derivatives, which are characteristic of the stationary phase for absorption of basic dyes, especially neutral red.

The supramolecular interactions among thioflavin T (ThT), two herbicides paraquat (PQ) and diquat (DQ), and macrocyclic cucurbit[8]uril (Q[8]), were studied using spectrofluorimetry, ultraviolet-visible absorbance spectrometry, 1H nuclear magnetic resonance spectroscopy, and isothermal titration calorimetry. A new method based on fluorescence quenching of the fluorescent host–guest complexes of Q[8]–ThT (the probe) upon cooperative binding with PQ or DQ to form a ternary complex, was proposed for the analytical determination of the two herbicides in aqueous solutions. Detection limits of 7.95 × 10−9 mol L−1 and 8.07 × 10−9 mol L−1 were obtained for PQ and DQ, respectively. Recoveries obtained by the proposed method in real-world examples such as river water and cabbage extracts were 104–108%. Interestingly, this method demonstrated high selectivity towards PQ and DQ in the presence of various metal ions and quaternary ammonium substances. Such a method provides a rapid, selective, sensitive and facile strategy for herbicides detection and quantification.

A one-pot strategy was employed to synthesize a series of cucurbit[5]uril-anchored (Q[5]-anchored) polymers with high yields. The acrylic acid (AA) monomer, an ammonium persulfate salt (APS) initiator, and an oxidant were used in the polymerization. The Q[5]-anchored polyacrylic acid aggregates (Q[5]-PAA) have been characterized by 1H NMR, 13C NMR, 2D NMR, FTIR, TGA, GPC, TEM and SEM measurements. The experimental results confirm that PAA chains can be grafted to Q[5] in a controlled manner through an in situ radical polymerization approach. The effects of acrylic acid and Q[5] feed mass and APS concentration on the formation of polymer nanocapsules have been investigated. The experiments reveal that the feed mass of acrylic acid greatly influences the properties of Q[5]-PAA when the ratio of Q[5]/APS is fixed at 0.5. In particular, when APS/Q[5] = 46 and 72, vesicle structures are observed in the Q[5]-anchored polymers. Moreover, such polymer nanocapsules show selective absorption of some volatile compounds, particularly methanol.

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.

o-Tetramethyl-substituted cucurbituril (o-TMeQ[6]), a polydentate ligand, has been synthesized and isolated in a controlled manner by using a dimer of dimethyl-substituted glycoluril and a dimer of unsubstituted glycoluril. Coordination assemblies have been investigated by reactions between alkaline earth cations and o-TMeQ[6] in the presence of [CdCl4]2–, a structure inducer, in HCl aqueous solution. X-ray diffraction analysis revealed that o-TMeQ[6] coordinates with Ca2+ or Sr2+ and forms centrosymmetric tetranuclear assemblies in the presence of [CdCl4]2–. [CdCl4]2– typically produces the “honeycomb effect” by forming honeycomb-like frameworks, which assist metal ions in coordinating to o-TMeQ[6]. The driving forces of this effect are the “outer-surface interactions” of cucurbit[n]urils.

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.

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.

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.

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.

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.

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.

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, 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...

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.

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.

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.

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.

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 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.

Four host–guest complexes, {(gI)@(CyH) 6 Q[6]}·3H 2 O ( 1 ), {(gIIH 2 ) 2+ @(CyH) 2 Q[6]}·2Cl − ·21H 2 O ( 2 ), {(gIII)@Q[6]}·27H 2 O ( 3 ), and {(gIVH) + @(CyH) 2 Q[6]}·Cl − ·13H 2 O ( 4 ), have been prepared from cyclohexanocucurbit[6]uril, {(CyH) 6 Q[6]}, symmetrical dicyclohexanocucurbit[6]uril {(CyH) 2 Q[6]}, and cucurbit[6]uril {Q[6]} as hosts, and four different guests, namely 2-phenyl-2 H -imidazole (gI), the HCl salt of N 1 , N 4 -bis(pyridin-3-ylmethyl)butane-1,4-diamine (gII), benzylamine (gIII), and the HCl salt of 4-(1 H -imidazolyl)phenol (gIV). Their crystal structures have been characterized by single-crystal X-ray diffraction analyses and revealed that these hosts can form supramolecular assemblies through iondipole interactions, hydrogen bonding, CH···π or NH···π interactions, and π···π stacking.

A new flexible tripodal compound 1 linked with three rhodamine groups as fluorophores and recognition sites was synthesized and its sensing behavior toward metal ions was investigated by UV–vis and fluorescence spectroscopy methods. It exhibited excellent selectivity for Cu(II) over miscellaneous metal ions including Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Cd(II), Al(III), Mg(II), Ca(II), Sr(II ) , Na(I), and K(I). While the fluorescence of the 1 -Cu(II) complex could be enhanced significantly upon the addition of Hg(II) compound 1 may therefore be applicable as an OFF-ON fluorescent chemosensor for Cu(II) and Hg(II).

A new fluorescent sensor 1 based on the rhodamine amide-armed homotrioxacalix[3]arene was synthesized, and its sensing behavior toward metal ions was investigated by UV–vis and fluorescence spectroscopies. Upon the addition of metal cations (Sb3+, Fe3+, Ni2+), a significant fluorescent enhancement in the range of 500–600 nm and colorimetric change was observed.

Three host–guest complexes of methylsubstituted cucurbit[6]urils host and anthracene derivatives guests were synthesized and structurally characterized by single crystal X-ray diffractions and 1H NMR technique. The hosts are dodecamethylcucurbit[6]uril (DDMeQ[6]), α,α′,δ,δ′-tetramethylcucurbit[6]uril (TMeQ[6]), and hexa-methylsubstituted cucurbituril (HSMeQ[6]) made from 3a-methyl-glycoluril. The guests are 9,10-bis[N-(aminoethylene)aminomethyl]anthracene (AN1), 9,10-bis[N-(aminopropylene) aminomethyl]anthracene (AN2) and 9,10-bis[N-(aminobutylene)aminomethyl]anthracene (AN3). The crystal structures show the compounds 1–3 with stoichiometry of {DDMeQ[6]-AN1}2+2NO3−24H2O (1), {TMeQ[6]-AN2}2+4NO3− 2H3O+10H2O (2) and {2HSMeQ[6]-AN3}2+2Cl−25H2O (3) respectively, and the formation of an exclusion or inclusion host–guest complex is dependent on the length of the substituted alkyl chains on the anthracene.

Interactions between a symmetrical tetramethyl-substituted cucurbit[6]uril (host: TMeQ[6]) and 1,ω-alkylenedipyridine (ω = 2, 4, 6, 8, 10) dicationic guests were investigated using 1H NMR spectroscopy and single crystal X-ray crystallography. In these inclusion complexes, combined cavity and portal binding in TMeQ[6] were observed, and the length of the bridged alkylene was found to play an important role not only in balancing the overall hydrophilic/hydrophobic interaction between the host and the guest, but also in defining the structure of the resulting inclusion complexes. For the guest 1,2-ethylenedipyridine (Edpy), TMeQ[6] includes a positively charged pyridine ring of Edpy to form an unsymmetrical inclusion complex; for the guest 1,4-butylenedipyridine (Bdpy), TMeQ[6] includes a positively charged pyridine ring of Bdpy, but the different competitive interactions in and between the related inclusion complexes could lead to a fast exchange between the hosts and guests. For the guests with longer bridge chains, such as 1,6-hexamethylenedipyridine (Hdpy) or 1,8-octylenedipyridine (Odpy), a stable pseudorotaxane inclusion complex is formed by combining the hydrophobic cavity and the outer portal dipole-ion interactions. However, for 1,10-decatylenedipyridine (Ddpy), the two TMeQ[6] host molecules include the two end pyridine rings of Ddpy and form a dumbbell inclusion complex.

A new tripodal rhodamine B derivative 2 was designed and synthesized by tripodal trialdehyde and rhodamine B hydrazide for the first time. This derivative could be used as a fluorescent chemosensor for the selective and sensitive determination of copper(II) in Tris-HCl buffer and ethanol aqueous mixed media. Under the optimum conditions described herein, fluorescence enhancement at 557/577 nm was linearly related to the concentration of copper(II) in the range of 0.10 to 10.00×10−5 mol·L−1, with a correlation coefficient of R 2=0.9964 (n=15) and a detection limit of 1.129×10−7 mol·L−1 (the relative standard deviation for five repeated measurements at 4.00×10−5 mol·L−1 Cu(II) was 2.2%). The absorbance measurements at 557 nm were linearly related to the concentration of Cu(II) in the range of 0.50 to 25.00×10−5 mol·L−1, with a correlation coefficient of R 2=0.9948 (n=13) and a detection limit of 3.338×10−7mol·L−1.

Interaction between the normal cucurbit[n]urils (n = 6,7,8; Q[6], Q[7], Q[8]) and a sym-tetramethyl-substituted cucurbit[6]uril derivative (TMeQ[6]) with the hydrochloride salts of some imidazole derivatives N-(4-hydroxylphenyl)imidazole (g1), N-(4-aminophenyl)imidazole (g2), 2-phenylimidazole (g3) in aqueous solution was investigated by using 1H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy, as well as by using a single crystal X-ray diffraction determination. The 1H NMR spectra analysis established a basic interaction model in which inclusion complexes with a host:guest ratio of 1:1 forms for the Q[6]s and Q[7] cases, while with a host:guest ratio of 1:2 form for the Q[8] cases. It was common that the hosts selectively bound the phenyl moiety of the guests. Absorption spectrophotometric and fluorescence spectroscopic analysis in aqueous solution defined the stability of the host–guest inclusion complexes at pH 5.8 with a host:guest ratio of 1:1 form quantitatively as logK values between 4 and 5 for the smaller hosts Q[6 or 7]s, while with a host:guest ratio of 1:2 form quantitatively as logK values between 11 and 12 for the host Q[8]. Two single crystal X-ray structures of the inclusion complexes TMeQ[6]-g2 · HCl and TMeQ[6]-g3 · HCl showed the phenyl moiety of these two guests inserted into the host cavity, which supported particularly the 1H NMR spectroscopic study in solution.

Three new alkyl-substituted cucurbit[6]urils, symmetrical tetracyclopentano cucurbit[6]uril {TCyPQ[6]}, meta-tricyclopentano cucurbit[6]uril {m-TriCyPQ[6]} and meta-dicyclopentano cucurbit[6]uril {m-(CyP)2Q[6]}, were synthesized by using the controlled synthesis utilizing the readily available dimer of the unsubstituted glycouril, diether of cyclopentano glycoluril and the unsubstituted glycouril. These partial cyclopentano-substituted cucurbit[6]urils were characterized by single-crystal X-ray diffractions. In the crystal structure of compounds 2{TCyPQ[6]}·57H2O (1) and {m-TriCyPQ[6]}·23H2O (2), both of Q[6]s formed a molecular capsule included water molecules, and the capsules assembled one-dimensional supramolecular chains through the hydrogen bonding. In the crystal structure of compound 2{m-(CyP)2Q[6]}·(HV)2+·4Cl−·2(H3O)+·44H2O (3), a dumbbell shape host–guest inclusion complex N,N-dihexyl-4,4′-bipyridinium(HV2+) with m-(CyP)2Q[6] was formed, the m-(CyP)2Q[6] host selectively included the alkyl moiety of the guest through the hydrophobic cavity interaction and the ion-dipole interaction.

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...

Interaction between tetramethylcucurbit[6]uril and 3-amino-5-phenylpyrazole hydrochloride in aqueous solution has been investigated by using 1H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy, as well as by a single crystal X-ray diffraction determination. The 1H NMR spectra analysis established a basic interaction model in which an inclusion complex with a host:guest ratio of 1:1 forms, in which the host selectively binds the phenyl moiety of the guest. Absorption spectrophotometric and fluorescence spectroscopic analysis in aqueous solution defined the stability of the host–guest inclusion complexes quantitatively as 6.8 × 105 mol− 1 L at pH 2.6; the interaction is pH dependent, decreasing as pH rises. The single crystal X-ray structure of the isolated inclusion complex shows the phenyl moiety of the guest inserted into the host cavity, which supports particularly the 1H NMR spectroscopic study in solution. In the crystal structure of the inclusion complex, the host–gu...

We explored the use of cucurbiturils to form inclusion complexes to overcome the solubility problems of kinetin, a plant cytokinin. Inclusion complexes between kinetin and Q[7], TMeQ[6] and HMeQ[6] in aqueous solution and in solid state were investigated by phase solubility studies, 1H NMR and IR. The effects of pH and temperature on complex stability were also investigated. Phase solubility studies showed that kinetin solubility increased in a linear fashion as a function of Q[7] and TMeQ[6] concentrations. However, kinetin solubility increased first, then decreased as the HMeQ[6] concentration increased, and the maximum solubility of kinetin was achieved at 4.95 mM in HMeQ[6]. The solubility of kinetin as well as the stability constant of its complex with Q[7] were affected by the pH of the medium. The thermodynamic parameters of the complex formation were also determined, and it showed that the formation of the inclusion complexes between kinetin and Q[7] was enthalpy controlled, suggesting that hydrophobic and van der Waals interactions were the main driving forces. Moreover, we found that the size of the cavity of cucurbituril played an important role in the association process. The formation of inclusion complexes between Q[7], TMeQ[6] and HMeQ[6] with kinetin was confirmed by 1H NMR, and IR spectroscopy showed the presence of inclusion complexes in solid state. Our results demonstrated that the complexation of kinetin with Q[n] could be used to improve the solubility of kinetin in aqueous solution.

Two partially methyl substituted cucurbituril, PMeQ[5] and HMeQ[6], were synthesized from 3a-methyl-glycoluril. They were characterized by 1 H NMR, ES-MS and single crystal X-ray diffraction. Ab initio calculations showed that each isolated methyl substituted cucurbit[ n ]uril is the most stable form among its all possbile isomers. One of the remarkable properties of these two partially substituted cucurbituril is their high solubility in the commonly used solvents such as water, methanol, and DMSO.

The interaction between tetramethylcucurbit[6]uril (host) and 5,5'-dimethyl-2,2'-bipyridyl hydrochloride (guest) was studied by 1H NMR, X-ray crystallography, electronic absorption spectroscopy, fluorescence emission spectra and quantum chemistry calculations. This experimental-computational study that indicated the host can orientationally encapsulate the guest with a moderate association constant value. Computation qualitatively explained the split UV-visible absorption peak of the inclusion complex.