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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 since the first member of the Q[n]-family, cucurbit[6]uril (Q[6]), was structurally identified in 1981 by Mock and co-workers. The interactions of the rigid cavities and negative portals of Q[n]s have resulted in the development of two almost mutually exclusive areas of study, namely Q[n]-based host–guest chemistry and Q[n]-based coordination chemistry. However, researches has revealed that Q[n]-based host–guest inclusion interactions may be influenced by metal ion coordination at the Q[n] portals, and in turn, coordination of metal ions at the Q[n] portals could be promoted by the formation of Q[n]-based inclusion host–guest complexes. Thus, this review provides an overview of related advances and achievements involving such a combination of Q[n]-based host–guest chemistry and Q[n]-based coordination chemistry, which could become an emerging branch, that is, Q[n]-based host–guest-metal ion chemistry. In particular, it could be useful in the treatment of wastewater, kinetic studies, drug delivery, the construction of novel supramolecular frameworks, metal-catalyzed reactions, recognition or response to metal cations, and so on.

A novel supramolecular host–guest complex of anti-tuberculosis drug isoniazid (INH) with symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) has been investigated using 1H NMR spectroscopy methods, mass spectrometer and single-crystal X-ray diffraction analysis. The result revealed that the INH guest is located the portal of the TMeQ[6] host in both the solutions and the solid state. The driving forces for the association between the guest INH and the host TMeQ[6] are made by a balance between hydrogen bonding interactions and ion-dipole interactions.

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.

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’.

Lanthanide coordination complexes have attracted considerable attention because of their unique electronic, magnetic, and optical properties. Early work showed that the large size of lanthanide ions, their propensity for ionic bonding and steric dictates in the coordination sphere are crucial factors influencing the coordination number and geometry of individual lanthanide (Ln) complexes. This review provides an overview of recent advances and achievements in the chemistry of the lanthanides involving cucurbit[n]uril {Q[n]}ligands. The two preorganised (identical) carbonyl fringed portals in Q[n]s are each ideal for acting as a rigid platform for developing a variety of lanthanide-containing metallo-supramolecular assemblies. Further, the ability to employ Q[n]s with different portal sizes provides a means for influencing metal coordination behaviour. A range of examples in which the use of a “structure inducer” (often an anionic species or an organic molecule) is employed to promote the isolation of new Ln3+-Q[n] species is discussed. Particular Q[n] metal complex systems have been demonstrated to discriminate the light lanthanide cations from their heavier counterparts suggesting possible application in lanthanide separation processes.

The interaction of alkaline-earth cations (AE2+) with hexanohydroxyhexanomethylcucurbit[6]uril (HHQ[6]) in the presence of CdCl2 in aqueous HCl solution was investigated. Single crystal X-ray diffraction analysis revealed that the interaction results in the formation of one-dimensional coordination polymers of HHQ[6] with AE2+ (Ca, Sr or Ba). In addition, compounds containing Ca and Sr are isomorphous. Moreover, the compound obtained from the HHQ[6]–MgCl2–CdCl2–HCl system contained only a metal-free HHQ[6]-based supramolecular assembly. ITC experiments showed that the interaction between HHQ[6] and Mg2+ could not be effectively measured, and that the interaction of Ca2+ or Sr2+ with HHQ[6] are driven by ΔH and ΔS, whereas the interaction between Ba2+ and HHQ[6] is driven by ΔH.

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.

Host–guest interactions in an aqueous solution of an inverted cucurbit[7]uril (iQ[7]) with α,ω-alkyldiammonium guests (H3N(CH2)xNH3Cl2, x = 2, 4, 6, 8, 10, and 12 named 1–6) were investigated by nuclear magnetic resonance (NMR) and isothermal titration calorimetry (ITC). 1H NMR spectroscopy revealed that all alkyldiammonium cations are involved in interactions with iQ[7] that fall into three groups. Averaged signals of free and bound guests with shorter alkyl chains including 1–3 indicate a higher binding and unbinding exchange ratio, within the time scale of the NMR experiments. Averaged signals for the guest 1 compound exhibited a downfield shift indicative of a dominant portal interaction between 1 and iQ[7], in contrast to guest 2 and 3 compounds that exhibited an upfield shift. Averaged signals of guests with longer alkyl chains such as 4–6 displayed a lower binding and unbinding exchange ratio on the NMR time scale. The occurrence of upfield shifts for all guests except 1 indicate a dominant inclusion interaction between the guests and iQ[7]. ITC experiments showed that the thermodynamics of complexation of the alkyldiammonium guests with iQ[7] were both enthalpically and entropically driven. Interestingly, complexation was predominantly entropically driven for the first guest group, with the exception of guest 3, but was enthalpically driven for the third guest group. Host–guest interactions of the more conventional cucurbit[7]uril (Q[7]) with these α,ω-alkyldiammonium guests were also investigated under the same conditions for comparison.

Two inclusion complexes formed on self-assembly of the Q[8] host with dihexyl-4,4′-bipyridinium (HV2+) dibromide and 1,3-bis(4-butylpiperazin-1-yl)-propane (C3PA2+) dibromide guests have been characterized by X-ray crystallography, which clearly shows how the hosts and the guests interlock with each other using supramolecular interactions, eventually generating novel polypseudorotaxanes.

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.

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 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.

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.

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...

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.

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.

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.

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.

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 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.

Four crystal structures of inclusion complexes of amino acid and cucurbit[n]uril have been synthesized and characterized by X-ray diffractions. The used four amino acids are l -Glutamate ( l -Glu), l -Tyrosine ( l -Tyr), l -Hisdine ( l -His), l -Leucine ( l -Leu) and the hosts are α,α′,δ,δ′-tetramethylcucurbit[6]uril (TMeQ[6]), the normal cucurbit[8]uril (Q[8]). The corresponding compounds based on the inclusion complexes of amino acid and cucurbit[n]uril have stoichiometry of { l -Glu@TMeQ[6]} + ·Cl − ·13H 2 O ( 1 ), {( l -Tyr) 2 @Q[8]}·27H 2 O ( 2 ), {( l -His) 2 @Q[8]}·19H 2 O ( 3 ) and {( l -Leu) 2 @Q[8]} 2+ ·2Cl − ·32H 2 O ( 4 ). The crystal structure of the compound 1 reveals that a l -Glu molecule is captured by a host TMeQ[6] with a 1:1 host:guest ratio. The crystal structures of compounds 2 , 3 and 4 show that all three inclusion complexes of l -Tyr@Q[8], l -His@Q[8] and l -Leu@Q[8] are in 1:2 host:guest ratio. The host Q[8] can include not only two aromatic moieties from two same guests (such as in the cases of 2 and 3 ) but also two alkyl chains of two l -Leu molecules (the case of 4 ).

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.

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...

Interactions of cucurbit[7]uril (Q[7] host) with guest adenine (g1), adenosine (g2) and 2′,3′-o-isopropylideneadenosine (g3) were studied in details by 1H NMR, UV absorption spectroscopy, fluorescence spectroscopy and high performance liquid chromatography (HPLC) methods. We found that the suitable pH range for interaction was between 1 and 7, and the optimal pH range was between 2 and 4. The 1H NMR analysis indicated that Q[7] selectively interacted with the adenine moiety of the guests g1 and g2, while Q[7] selectively interacted with the D-ribose sugar ring moiety of the guest g3. Moreover, 1H NMR spectra showed that the exchange between the bound guest and the free guest was fast on the NMR time scale for the Q[7]-g1 and Q[7]-g2 systems. However, an obvious equilibrium between the bound host/guest and the unbound host/guest were observed in the Q[7]-g3 complex. Several methods were used to determine quantitatively the stability of the three host–guest inclusion complexes formed between Q[7] and the 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.

The interaction between cucurbit[8]uril (Q[8]) and a series of symmetric viologen derivatives having aliphatic substituents of variable length [N,N′-dialkyl-4,4′-bipyridinium dianions; alkyl = CH3(CH2) n –, n = 0 (MV2+), 1 (EV2+), 2 (PV2+), 3 (BV2+), 4 (FV2+), 5 (HV2+) or 6 (SV2+); BPY2+ = diprotonated 4,4-bipyridine], determined by 1H NMR and electronic absorption spectroscopy methods, is described. Some different binding models were observed in this work when compared to the interactions between cucurbit[7]uril (Q[7]) and these guests. The experimental results revealed that the binding site of the guests by Q[8] depended strongly on the length of the aliphatic substituents on the 4,4′-bipyridinium nucleus. While a 1:2 complex was observed for Q[8]-BPY2+ under acidic conditions, a 1:1 complex was formed for Q[8]-viologen derivatives with chains shorter than four carbon atoms. However, multiple Q[8] molecules could be threaded on the longer-chain FV2+, HV2+ or SV2+ molecules to form 2:1 and even possibly 3:1 complexes.

Interaction between tetramethylcucurbit[6]uril (TMeQ[6], host) with hydrochloride salts of 2-phenylpridine (G1), 2-benzylpyridine (G2), and 4-benzylpyridine (G3) (guests) have been investigated by using 1H NMR spectroscopy and electronic absorption spectroscopy and theoretical calculations. The 1H NMR spectra analysis established an interaction model in which the host selectively included the phenyl moiety of the HCl salt of the above three guests, and formed inclusion complexes with a host-guest ratio of 1:1. Absorption spectrophotometric analysis allowed quantitative measurement of the stability of these host-guest inclusion complexes. Particularly, we have established a competitive interaction in which one host-guest inclusion complex pair is much more stable than another host-guest inclusion complex pair. The stability constants for the three host-guest inclusion complexes of TMeQ[6]-G1, TMeQ[6]-G2, and TMeQ[6]-G3 are approximately 2x10(6), 60.7, and 19.9 mol-1.L, respectively. To understand how subtle differences in the structure of the title guests lead to a significant difference in the stability of the corresponding host-guest inclusion complexes with the TMeQ[6], ab initio theoretical calculations have been performed, not only for the gas phase but also the solution phase (water as solvent) in all cases. The calculation results revealed that when the phenyl moiety of the three pyridine derivate guests was included, the host-guest complexation reached the minimum, and the corresponding energy differences for the formation of the title host-guest inclusion complexes are qualitatively consistent with the experimental results.

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.

This work showed that the 4,4′-bipyridyl group and alkyl chains of 4,4′-bipyridyl derivatives are completely located in the shell-like cavity of the twisted cucurbit[14]uril molecule and formed novel shell-like 1 : 1 inclusion complexes. As it is enthalpy-driven the complexation benefits from ion–dipole interactions.

Complexation of haloalkane 1-(3-chlorophenyl)-4-(3-chloropropyl)-piperazinium (PZ(+)) dihydrochloride with symmetrical α,α',δ,δ'-tetramethyl-cucurbit[6]uril (TMeQ[6]) has been investigated using NMR spectroscopy, MALDI-TOF mass spectrometry, isothermal titration calorimetry (ITC), and X-ray crystallography. Our data indicate that the chloropropyl group of PZ(+) resides within the cavity of TMeQ[6] in both aqueous solution and the solid state, generating a highly stable inclusion complex PZ(+)@TMeQ[6]. In aqueous solution, the formation of the inclusion complex PZ(+)@TMeQ[6] benefits from the ion-dipole interactions between the guest PZ(+) and the host TMeQ[6]. While in the solid state, hydrogen-bonding interactions also play an important role in stabilizing the inclusion complex PZ(+)@TMeQ[6].

A convenient method to isolate inverted cucurbit[7]uril (iQ[7]) from a mixture of water-soluble Q[n]s was established by eluting the soluble mixture of Q[n]s on a Dowex (H(+) form) column so that iQ[7] could be selected as a ligand for coordination and supramolecular assembly with alkaline earth cations (AE(2+)) in aqueous HCl solutions in the presence of [ZnCl(4)](2-) and [CdCl(4)](2-) anions as structure-directing agents. Single-crystal X-ray diffraction analysis revealed that both iQ[7]-AE(2+) -[ZnCl(4)](2-) -HCl and iQ[7]-AE(2+) -[CdCl(4)](2-) -HCl interaction systems yielded supramolecular assemblies, in which the [ZnCl(4)](2-) and [CdCl(4)](2-) anions presented a honeycomb effect, and this resulted in the formation of linear iQ[7]/AE(2+) coordination polymers through outer-surface interactions of Q[n]s.

Host–guest complexes of cucurbit[n=5–8]uril and some examples of ortho substituted pyridines or aminopyridines were examined by 1H NMR spectroscopy. Portal binding of two ortho aminopyridine free bases, by cucurbit[5]uril, was observed in 1H NMR spectra. Combined cavity and portal binding in cucurbit[6]uril were observed for both the free base 2-aminomethylpyridine, ampy, the HCl salt, ampy·1HCl, and the salt of 2,2′-bispyridine, bpy·1HCl. Two novel complexes were formed with cucurbit[6]uril. The free base ampyas a dual occupant, formed a 2:1 complex, and bpy·1HCl formed a stable asymmetric 1:1 complex. Only portal binding of 2,6-bisaminomethylpyridine and its salts was observed for cucurbit[6]uril. Fast exchange of the free base and pyridineammonium salts was observed for cucurbit[7-8]uril.

A number of linear coordination polymers have been assembled from lanthanide cations (Ln3+) and cucurbit[7]uril (Q[7]) in the presence of [CuCl4]2−or [CoCl4]2− anions acting as inorganic structure inducers in HCl solution. X-ray diffraction analysis has revealed that they form three groups of isomorphous structures. Generally, the complexes of Q[7] with light lanthanide cations (those with atomic number below that of neodymium (Nd3+)) are in one group. The other two groups, in which the lanthanide cation has atomic number greater than that of europium (Eu3+), seem to follow no obvious rule. For example, the complexes of Q[7] with Eu3+ and Gd3+cations are in the second group in the presence of [CuCl4]2− anions, while they are in the third group in the presence of [CoCl4]2− anions. However, whatever group a given complex belongs to, they all show a common honeycomb-patterned supramolecular assembly, in which [CuCl4]2−or [CoCl4]2− anions form a honeycomb structure. The Ln3+ cations then coordinate to neighboring Q[7] molecules to form 1D coordination polymers that are inserted into the channels of the honeycomb framework, such that each individual coordination polymer is surrounded by [CuCl4]2−or [CoCl4]2− anions.

Similar to the larger members of the cucurbituril family, such as cucurbit[8]uril (Q[8]), the smallest member, cucurbit[5]uril (Q[5]), can also induce room-temperature phosphorescence (RTP) of α-naphthol (1) and β-naphthol (2). The relationship between the RTP intensity of 1 and 2 and the concentration of Q[5] or Q[8] suggests that the mechanism underlying the Q[5] complex-induced RTP is different from that of the Q[8]-induced RTP for these luminophores. The crystal structures of 1-Q[5]-KI, 2-Q[5]-KI, 1-Q[5]-TlNO(3), and 2-Q[5]-TlNO(3) systems show that in each case Q[5] and the respective metal ions, K(+) or Tl(+), form infinite ···Q[5]-M(+)-Q[5]-M(+)··· chains that surround the luminophores. Although these tube- or wall-like structures are likely destroyed in solution, the key interaction between the convex-shaped outer walls of Q[5] and the plane of the aromatic naphthols, via π···π stacking and C-H···π interactions, is postulated to be essentially maintained leading to a microenvironment that holds the luminophore and the heavy atom perturber together; such a model is supported by the observed Q[5] complex-induced RTP of the above naphthols. With respect to this, a high Q[5]/luminophore concentration was employed in an endeavour to promote the formation of π···π stacking and C-H···π interactions similar to those observed in the crystal structures of the 1- or 2-Q[5]-K(+) and -Tl(+) systems. In keeping with the proposed model, the RTP of each system is quenched when Q[5] is replaced by the alkyl-substituted Q[5] derivatives, decamethylQ[5] and pentacyclohexanoQ[5]. This is in agreement with the substituent groups on the surface of the metal-bond Q[5] obstructing the naphthol molecule from accessing the convex glycouril backbone of Q[5].

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

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

The long alkyl chain of N,N'-bis(4-dimethylaminobenzyl)dodecane-1,12-diamine (C(12)DA) adopts different chiral helical conformations, one left-handed and the other right-handed, when bound within the cavities of two distorted cucurbit[8]uril (Q[8]) units, as unequivocally established by X-ray crystallography.

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

In the present work, we describe a kind of novel cucurbit[8]uril-based coordination supramolecular self-assembly taking place in the presence of tetrachloride transition-metal dianions ([MtransCl4]2−, Mtrans = Cd, Zn, Cu, Co) in HCl solution. As reported previously, the “honeycomb effect” of the tetrachloride transition-metal dianion ([MtransCl4]2− has been observed in the coordination of strontium cations to cucurbit[8]uril molecules (Q[8]s). It seems that the [MtransCl4]2− anions form a honeycomb structure with hexagonal cells filled with Sr2+–Q[8] linear coordination polymers in which the Sr2+ cations coordinate to Q[8] molecules and form zigzag coordination polymers.

Eight coordination complexes, {LnCl2(H2O)3Q*[5]}·NO3·18.5H2O [isomorphous for Ln = La (1), Ce (2) and Pr (3)], {LnCl2(H2O)2Q*[5]}·NO3·14H2O [isomorphous for Ln = Nd (4) and Sm (5)], {Dy(H2O)2[Cl ⊂ Q*[5]]Dy(H2O)6}·5Cl·20H2O (6), {LnCl(H2O)[Cl ⊂ Q*[5]]Ln(H2O)6}·4Cl·13H2O [isomorphous for Ln = Ho (7) and Er (8)], were obtained by reactions of the corresponding lanthanide species with the macrocyclic ligand pentacyclohexanocucurbit[5]uril (Q*[5]) in aqueous solution, and their structures were determined by single-crystal X-ray diffraction. Crystal structure analysis reveals that, in complexes 1–5, each Q*[5] coordinates to one lanthanide(III) ion to form an opened molecular capsule structure, and then adjacent molecular capsules bridge each other to form a 1-D coordination polymer structure, while in complexes 6–8, each Q*[5] coordinates to two lanthanide(III) ions to form a 0-D half-opened molecular capsule structure. These complexes show that their structural variations are ascribed to the effect of lanthanide contraction.

A homochiral 1D-helical coordination polymer has been assembled from calcium ions (Ca2+) and cucurbit[5]uril (Q[5]) in the presence of p-hydroxybenzoic acid (Hyb) as an organic structure inducer. This result shows that a homochiral 1D-helical coordination polymer can be obtained from Q[5] with not only heavy lanthanides but also other metal ions, such as calcium dications in the present case, and that p-hydroxybenzoic acid (Hyb) can serve as an organic structure inducer in place of the previously used hydroquinone (Hyq). Control experiments by X-ray diffraction analysis have shown that Q[5] coordinates with the calcium cations to form a linear coordination polymer in the absence of Hyb, while a mixture of Q[5] and Hyb, without a metal salt under the same synthetic conditions, produces Q[5]-based linear supramolecular chains linked by hydrogen-bonding networks, which lie in a Hyb-based net.

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

Three novel coordination polymers {[K(H2O)](NO3⊂C30H28N20O20)[K(η2-NO3)]}Cl(H3O)22+·7H2O (1), {[Rb3(μ2-H2O)(μ3-H2O)(H2O)5SO4]+(H2O⊂C30H29N20O20)}Cl(H3O)+·2H2O (2), [Cs2(H2O⊂C30H26N20O20)]SO42−(H3O)44+ (3), were obtained by reactions of the corresponding alkali metal salts with an organic macrocyclic ligand perhydroxycucurbit[5]uril, (HO)10Q[5], and their structures were determined by single-crystal X-ray diffraction studies. The results revealed that, in complexes 1 and 3, the (HO)10Q[5] ligands are interlinked into two-dimensional networks through coordination of their carbonyl groups and hydroxy groups to the alkali metal ions (K+ and Cs+) in between, while in complex 2, the carbonyl groups and hydroxy groups of the (HO)10Q[5] ligands are coordinated by the Rb+ ions to form an acclivitous ‘ladder’ structure. Furthermore, solid-state packing of the complexes 1 and 3 shows the formation of open channels occupied by counterions and non-coordinating water molecules. The thermogravimetric analysis (TGA) of complex 1 was characterized.

The host-guest relationship between cucurbit[8]uril, phenanthrolines and some methyl substituted 1,10-phenanthrolines has been investigated by using 1H NMR spectroscopy and fluorescence spectroscopy. The results showed that phenanthrolines as molecular guests bind in the cavity and portal of cucurbit[8]uril in a ratio of 2:1 (guest to host). The phenanthroline isomers 1,10-,1,7- and 4,7- showed red shifts between 47 and 108 nm and pronounced increases in fluorescent intensity. These same isomers produced inclusion complexes with cucur-bit[8]uril which had moderate to fast exchange rates on the 1H NMR time scale. The methyl substituted 1,10-phenanthrolines studied gave stable inclusion complexes in a ratio of 2:1 which showed slow exchange rates. These guests formed п-п stacked pairs which were cavity bound but also partly protruded from only one portal forming unsymmetrical host-guest complexes. In addition, these п-п stacked pairs formed orientation isomers within the confines of the cucur-bit[8]uril cavity.

Three guests with two moiety probes for different Cucurbit[n = 6-8]urils have been synthesized. They are N-(2-methylenethiophen)-adamataneamine, N-(2-methylene pyrrole)-adamataneamine and N-(2-methylenefurfuran)-adamataneamine. The probes are methyle-nepyridyl typically for Q[6] and adamataneamine typically for Q[7]. The host-guest complexes of Cucurbit[n = 6-8]urils with these guests have been investigated by using NMR techniques and ESMS method. Also, thermoanalysis has been used for exploring relationship of enthalpy and stability of the host-guest complexes.