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.

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.

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].

[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.

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.

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.

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.

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.

[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.

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.

Difference of coordination between alkali- and alkaline-earth-metal ions to a symmetrical α,α',δ,δ'-tetramethylcucurbit[6]uril.

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

A novel strategy to assemble achiral ligands to chiral helical polyrotaxane structures.

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.

Novel supramolecular assemblies based on coordination of samarium cation to cucurbit[5]uril.

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.

Cucurbituril-resisted acylation of the anti-tuberculosis drug isoniazid via a supramolecular strategy.

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

[Interaction of cucurbit [n = 7, 8] with methylindoles via fluorescence spectroscopy].

In the present work, the authors investigated interaction of cucurbit [n=7, 8] urils(Q[7], Q[8]) with 2-methylindol (Me) and 3-methylindol(Sk), influences of pH and temperature on the interaction of Q[7], Q[8] with the guests and calculations of the stability constants and thermodynamic parameters by using fluorescence spctroscopy. The results show that: the interation ratios are 1 : 1 of host: guest for all systems, except the Q[8]-Sk system, for which the ratio is 1 : 2 of host: guest; the interaction ratios of the host: guest systems did not change in the range of pH 1-11 and temperature between 298 and 313 K; the stability constant is the largest at pH 1 and room temperature. The thermodynamic parameter revealed that the interaction of the host and the guest of spontaneitied.

Complexation of cyclohexanocucurbit[6]uril with cadmium ions: X-ray crystallographic and electrochemical study.

Complexation of cyclohexanocucurbit[6]uril (Q*[6]), a water-soluble cucurbit[n]uril derivative, with Cd(2+) ions has been studied by means of cyclic voltammetry and differential pulse voltammetry. The electrochemical experimental data prove the formation of a highly stable 1:6 Q*[6]/Cd(2+) complex. We also obtained the single-crystal X-ray structure of a cadmium ion complex with Q*[6], in which each portal of Q*[6] chelates three cadmium ions. The present study suggests the potential utility of Q*[6] as an effective cadmium ion chelator and extractant.

[Interaction between cucurbit[n]urils (n = 7 and 8) and 2-amino-phenyl-thiazole].

The interaction between cucurbiturils(Q[7], Q[8]) and the 2-amino-benzothiazole (g) was investigated by 1H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy. The results show that with 2 < pH < 9, using different spectrum methods was able to observe the interaction between the cucurbit[n]urils and the guest at pH between 2 and 9, Q[7] interacts with the guest with a 1 : 1 host : guest ratio, and Q[8] interacts with the guest with a 1 : 2 host : guest ratio. Also, the inclusion constant and the thermodynamic parameters of the interaction systems, such as the entropy and enthalpy of systems, were considered.

[Cucurbit[8]urils-induced room temperature phosphorescence of phenanthrene and fluorene].

In this paper, a new room temperature phosphorescence for phenanthrene and fluorene were first reported with cucurbit[8]uril as the revulsant, KI as the heavy atomperturber, and Na2SO3 as deoxygenation. The RTP maximum wavelengths were lambda(ex)/lambda(em) = 282/509 nm and lambda(ex)/lambda(em) = 276/518 nm and the RTP lifetimes of the two systems were 1.82 and 3.68 ms respectively. Under optimum experimental conditions, the RTP intensity was liner with phenanthrene and fluorene concentration in the range of 1.0 x 10(-7) -1. 5 x 10(-6) mol x L(-1), 1.5 x 10(-6)-1.0 x 10(-5) mol x L(-1) and 8.0 x 10(-7)-8.0 x 10(-6) mol x L(-1), respectively. The detection limits were 4.8 x 10(-9) mol x L(-1) and 8.0 x 10(-9) mol x L(-1) respectively.

[A new probe for Ca2+ based on the rhodamine B amide armed homotrioxacalix[3] arene-Sb3+ complex].

A new fluorescence probe based on the rhodamine B amide-armed homotrioxacalix[3]arene (1) has been synthesized, and its Ca(2+)-selective chromogenic properties were investigated in acetonitrile Tris-HCl buffer (pH 7) solution by UV-Vis and fluorescence spectroscopies. Upon the addition of Sb3+ ion, the spirocyclic ring of 1 was opened and a significant fluorescence enhancement and colorimetric change was observed. However, addition of Ca2+ ion to the solution of 1-Sb3+ complex leads to a strong fluorescence quenching of the original 1-Sb3+ complex. The phenomenon exhibited a pronounced Ca2+ selective fluoroionophoric behavior over other coexistent metal ions and provided the ratiometric determination as well as naked-eye detection of Ca2+ ions.