Twisted Cucurbit[n]urils.

Two new twisted cucurbiturils, cucurbit[13]uril (tQ[13]) and cucurbit[15]uril (tQ[15]), have been synthesized and separated, and their structures have been confirmed by NMR spectroscopy and MALDI-TOF mass spectrometry together with the X-ray structures of two new complexes, {Dy(H2O)4Cd(H2O)4tQ[13]}·2.5[CdCl4]·65H2O and {Cd0.5(H2O)2tQ[15]}·[CdCl4]·47H2O. tQ[15] is the largest cucurbit[n]uril (Q[n]) in the Q[n] family reported to date. The X-ray diffraction studies of both complexes indicated that these large tQ[n]s effectively exhibit two different cavities-a central cavity and two side cavities. Preliminary host-guest behavior by each of the new systems was investigated by NMR studies.

Supramolecular Recognition of Amino Acids by Twisted Cucurbit[14]uril.

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.

Synthesis and separation of cucurbit[n]urils and their derivatives.

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[8]uril with Thionine and Carbendazim with Spectroscopic Method].

In this paper, the interaction of cucurbit [8]uril(Q[8]) with thionine (TH) and carbendazim (CBZ) were investigated with fluorescence and UV-Vis spectroscopy. The experimental results showed that the inclusion complex between Q[8] and TH informed was at molar ratios of 1∶2 in 0.01 mol·L-1 hydrochloric acid solution. The fluorescence intensity of the Q[8]/TH complexes quenched when Q[8] was added to TH solution, but fluorescence increasing of the Q[8]/TH complex with the addition of CBZ was observed. The fluorescence increasing values show a good linear relationship with the CBZ concentration within 0~3.5 µmol·L-1. The linear regression equation relating fluorescence intensity (If) to CBZ concentration (c) is If=0.45c+32.24 (r=0.999). The detection limit was 9.39×10-8 mol·L-1. Forthemore, the influence of foreign species on the analytical signal of the Q[8]/TH complex in the presence of carbendazim was established. No interference was observed from commonly used foreign species such as metal ions (Fe3+, Mg2+, Ca2+). In particular, benzimidazole compounds thiabendazole and fuberidazole do not interfere with CBZ determination at a specific concentration. The results revealed that complexation of Q[8] and TH with CBZ offers a fluorescent switching "on-off" effect which will supply a potential application in pesticide residues test.

A Hemimethyl-Substituted Cucurbit[7]uril Derived from 3α-Methyl-glycoluril.

A novel hemimethyl-substituted cucurbit[7]uril (HMeQ[7]) derived from 3α-methyl-glycoluril has been prepared. HMeQ[7] is readily soluble in both water and dimethyl sulfoxide (DMSO) and displays not only host-guest interaction properties similar to those of the normal cucurbit[7]uril but also unusual properties in DMSO.

A novel shell-like supramolecular assembly of 4,4'-bipyridyl derivatives and a twisted cucurbit[14]uril molecule.

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.

Encapsulation of haloalkane 1-(3-chlorophenyl)-4-(3-chloropropyl)-piperazinium in symmetrical α,α',δ,δ'-tetramethyl-cucurbit[6]uril.

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].

Coordination of alkaline earth metal ions in the inverted cucurbit[7]uril supramolecular assemblies formed in the presence of [ZnCl4]2- and [CdCl4]2-.

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.

[Interaction of Cucurbit[8]uril with ß-Indoleacetic Acid and Methylviologen].

The interaction between Q[8] with ß-indoleacetic acid and the methylviologen was studied in aqueous solution with electronic absorption spectroscopy (UV-Vis), fluorescence spectroscopy, 1H NMR spectroscopy and isothermal titration calorimetry (ITC) in details. The authors explored the mode of action, action site and thermodynamic properties of the host-guest system. The electronic absorption and fluorescence spectroscopy data showed that the Q[8]/IAA system and Q[8]/MV²âº system informed 1:1 inclusion complexes in aqueous solution. ITC results showed that the changes of Gibbs free energy and enthalpy are all negative, it suggested that complex formation was spontaneous and exothermic reaction. Moreover, ITC results for the Q [8] and IAA with MV²âº indicate that the association constants of the Q[8]-IAA and Q[8]-MV²âº complexes were (3.22 ± 0.96) x 105 L · mol⁻¹ and (3.90 ± 0.91) x 106 L · mol⁻¹, respectively. Therefore, the interaction between Q[8] and IAA with the MV²âº was a competitive process. This likely occurs because the MV²âº and IAA molecules attempt to occupy the Q[8] cavity, which reduces the fluorescence and absorption spectra intensity of Q[8]-IAA because of the formation of a new inclusion complex between Q[8] and IAA with MV²âº. In addition, with the addition of MV²âº to a Q[8]/IAA complex, 1H NMR results showed that the indole moieties of ß-indoleacetic acid and bipyridyl group of methylviologen can be incorporated into Q[8] cavities because of electronic transfer MV²âº with PQ in a Q[8] cavity with ternary complexes. These results provides the potential applications for the supramolecular self-assembly in cucurbit[n]urils field.

Interaction of Ln3+ with Methyl-Substituted Cucurbit[n]urils (n=5,6) Derived from 3α-Methyl Glycoluril.

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].

Extended and contorted conformations of alkanediammonium ions in symmetrical α,α',δ,δ'-tetramethylcucurbit[6]uril cavity.

Binding interactions between symmetrical α,α',δ,δ'-tetramethylcucurbit[6]uril (TMeQ[6]) and a series of alkyldiammonium ions in aqueous solution and in the solid state were investigated by (1)H NMR spectroscopy, MALDI-TOF mass spectrometry, X-ray crystallography, and isothermal titration calorimetry (ITC). Their (1)H NMR spectra reveal that the actual binding behaviors vary depending upon the alkyl chain length. Their single-crystal X-ray diffraction analyses indicate the guest 1,2-ethanediammonium is located outside of the TMeQ[6] portal, while the other four alkyldiammonium guests can be accommodated in the TMeQ[6] cavity, forming 1:1 inclusion complexes. Most importantly, the long-chain alkyldiammoniums (1,8-octanediammonium and 1,10-decanediammonium) take a contorted conformation when bound within the TMeQ[6] cavity. Additionally, ITC experiments show that the complexation of the alkyldiammonium guests with TMeQ[6] is mainly enthalpy driven, which benefits from ion-dipole interactions.

Self-assemblies based on the "outer-surface interactions" of cucurbit[n]urils: new opportunities for supramolecular architectures and materials.

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.

Tetrachloridometallate dianion-induced cucurbit[8]uril supramolecular assemblies with large channels and their potential applications for extraction coating on solid-phase microextraction fibers.

Q[8]-based porous materials were synthesized in the presence of [Md-blockCl4](2-) anions as structure inducers. The driving forces of the structure-directing effect of the [Md-blockCl4](2-) anions may be due to the ion-dipole interaction and hydrogen bonding between the [Md-blockCl4](2-) anions and ≡CH or ═CH2 groups on the backs of Q[8] molecules. Moreover, the tests of potential applications show that these porous materials can not only capture organic molecules through the cavity of Q[8] moieties but also adsorb larger organic molecules with different selectivities.

[CdCl4]2- anion-induced coordination of alkaline earth metal ions to cucurbit[7]uril, corresponding supramolecular self-assemblies and potential application.

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.

Cucurbit[n]uril-based coordination chemistry: from simple coordination complexes to novel poly-dimensional coordination polymers.

Cucurbit[n]urils are a family of molecular container hosts bearing a rigid hydrophobic cavity and two identical carbonyl fringed portals. They have attracted much attention in supramolecular chemistry because of their superior molecular recognition properties in aqueous media. This review highlights the recent advances and challenges in the field of cucurbit[n]uril-based coordination chemistry. It not only presents progress in the knowledge of such macrocyclic compounds, which range from simple to complicated architectures, but also presents new routes of synthesis and their advantages in hybrid porous solids. The concept of structure "inducer" for their structural design to achieve predictable structures and controlled pores is described. The large pore sizes and hydrophobic cavities of these compounds that lead to unprecedented properties and potential applications are also discussed.

[Recognition of symmetrical tetramethyl-substituted cucurbit[6]uril and 2-(butane-1,4-diyl) dibenzimidazolium dichloride with spectroscopy].

The molecular inclusions of symmetrical tetramethyl-substituted cucurbit[6] uril and 2-(butane-1,4-diyl)dibenzimidazolium dichloride were investigated by using electronic absorption spectroscopy and fluorescence spectroscopy. The experimental results reveal that the formation of host-guest inclusion complexes between TMeQ[6] and SBB were formed with stoichiometry ratios of 1 : 1 and 2 : 1. The calculated binding constants are K(1 : 1 = (4.79 +/- 0.01) x 10(4) L x mol(-1) and, K(2 : 1) = (8.51 +/- 0.01) x 10(10) L2 x mol(-2) respectively based on the absorption spectrophotometric analysis, while the calculated binding constants are K(1 : 1) = 7.02 x 10(4) L x mol(-1) and K(2 : 1) = 2. 88 x 10(10) L2 x mol(-2) respectively based on the fluorescence spectroscopy analysis. The values of K are reasonably consistent.

Construction of cucurbit[7]uril based tubular nanochannels incorporating associated [CdCl4]2- and lanthanide ions.

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

Cucurbit[5]uril-metal complex-induced room-temperature phosphorescence of α-naphthol and ß-naphthol.

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 ß-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].

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

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