Cucurbit[7]uril/CuCl promoting decomposition of 4-nitrobenzenediazonium in aqueous solution

The host-guest complex between cucurbit[7]uril and 4-nitro-benzendiazonium is decomposed into a nitrobenzene/4-nitrophenol mixture in a high total yield in the presence of CuCl.     

Cucurbit[7]uril stabilization of a diarylmethane carbocation in aqueous solution

The stability of the 4,4′-bis(dimethylamino)diphenylmethane carbocation is significantly enhanced in aqueous solution by its inclusion in the cucurbit[7]uril host cavity. The formation of the host-guest complex (K_CB[7] = 2.0 × 10⁴ M⁻¹) shifts the carbinol-carbocation equilibrium, maximizing the formation of the intensely blue carbocation to 90% at pH 5.2.     

Cucurbit[8]uril-mediated photodimerization of alkyl 2-naphthoate in aqueous solution

The photodimerization of methyl 2-naphthoate (1), ethyl 2-naphthoate (2) and butyl 2-naphthoate (3) in cucurbituril (CB) aqueous solution was investigated. The product distribution and fluorescence spectral changes suggest that CB[8] can encapsulate two molecules of alkyl 2-naphthoate (1 or 2) and thereby facilitate a cubane-like photodimer formation. Subtle changes in either cavity size of CB[n] or alkyl substitutes can significantly modulate the interaction of CB[n] with 2-naphthoate derivatives affording remarkable alterations in their photochemical reactivity.     

Cucurbit[7]uril host-guest complexes with small polar organic guests in aqueous solution

The host-guest stability constants for the inclusion of a series of small neutral polar organic guests in cucurbit[7]uril (CB[7]) have been determined in aqueous solution by (1)H NMR titrations. The dependence of the stability constant on the nature of the guests indicates that hydrophobic and dipole-quadrupole interactions are responsible for the binding. The complexation-induced chemical shift changes in the guest proton resonances, coupled with energy-minimization calculations, suggest that the guests are located such that their dipole moment is aligned perpendicular with the quadrupole moment of the CB[7] host. The stability constants for acetone and acetophenone decrease in the presence of Na(+) or K(+) cations as a result of cation capping of the CB[7] portals.     

Cucurbit[7]uril complexations of bis(isoquinolinium)alkane dications in aqueous solution

The 1:1 and 2:1 host–guest complexation of a series of 1,n-bis(isoquinolinium)alkane dications (Iq(CH₂)_nIq²⁺, n = 2, 4, 5, 6, 8, 9, 10 and 12, and Iq(p-xylene)Iq²⁺) by cucurbit[7]uril (CB[7]) in aqueous solution has been investigated by ¹H NMR spectroscopy and ESI mass spectrometry. The site of binding of the first CB[7] is dependent on the nature of the central linker group, with encapsulation of the p-xylene group or the polymethylene chain when n = 6–10.With shorter (n = 2–5) or longer (n = 12) chains, the first CB[7] binds over an isoquinolinium group. With a second CB[7], the binding of the central group is abandoned in favour of the CB[7] hosts encapsulating the two cationic isoquinolinium termini. The 1:1 and 2:1 host–guest stability constants are related to modes of binding and the nature of the central linkers, and are compared with dicationic guests bearing different terminal groups.     

Cucurbit[8]uril/cucurbit[7]uril controlled off/on fluorescence of the acridizinium and 9-aminoacridizinium cations in aqueous solution

The blue fluorescence of acridizinium bromide (ADZ+) and the green fluorescence of 9-aminoacridizinium bromide (AADZ+) in aqueous solutions can be almost entirely switched off upon the double inclusion of these guests in the cavity of cucurbit[8]uril (CB[8]) owing to the formation of a nonfluorescent, noncovalent dimer complex, and then fluorescence can be effectively restored by adding cucurbit[7]uril (CB[7]) to the complex because it competitively extracts the fluorophores out of the CB[8] cavity.     

Cucurbit[7]uril pseudorotaxane-based photoresponsive supramolecular nanovalve

Light relief! Mesoporous silica materials equipped with photoresponsive cucurbit[7]uril-pseudorotaxane nanovalves operate in biological media to trap cargo molecules within nanopores, but undergo controlled release when irradiated with light of a suitable wavelength (see figure). Significantly, a "ladder"-release pattern is obtained to balance maximal therapeutic efficacy and minimal dose frequency in the development of "pulsed" drug therapy.     

Enantioselective [2 + 2] photodimerization reactions of coumarins in solution

[reaction: see text] The [2 + 2]photodimerization reactions of coumarin to an optically active anti-head-to-head dimer in the presence of an optically active host compound in cyclohexane solution proceeded with high enantioselectivity.     

Host-guest interaction of Hoechst 34580 and Cucurbit[7]uril

To track nuclear dynamic processes by fluorescence imaging, nuclear stains should be highly fluorescent, resistant to photobleaching, and inert to nuclear processes. The nuclear stains of the Hoechst family, such as Hoechst 34580, show bright fluorescence only on groove binding to DNA, and therefore may interfere with visualization of nuclear dynamic processes induced by other stimuli. We study host-guest interactions between Hoechst 34580 and Cucurbit[7]uril (CB7) in aqueous solutions. The formation of CB7-Hoechst 34580 inclusion complexes with stoichiometry of 2:1 in water and 1:1 in phosphate-buffered saline (PBS) solution (pH 7.0) is confirmed by (1)H NMR, absorption spectra, fluorescence spectra, MALDI-TOF MS, and molecular modeling. Compared to Hoechst 34580, the inclusion complex exhibits redshifted absorption, intensified fluorescence, improved photostability, weakened DNA binding affinity, comparable ability to penetrate cell nuclei, and better nuclear-staining capability, and thus a new avenue for the application of cucurbituril in fluorescence imaging is opened.     

Cucurbit[7]uril Complexation of Near-Infrared Fluorescent Azobenzene-Cyanine Conjugates

Two new azobenzene heptamethine cyanine conjugates exist as dispersed monomeric molecules in methanol solution and exhibit near-infrared (NIR) cyanine absorption and fluorescence. Both conjugates form non-emissive cyanine H-aggregates in water, but the addition of cucurbit[7]uril (CB7) induces dye deaggregation and a large increase in cyanine NIR fluorescence emission intensity. CB7 encapsulates the protonated azonium tautomer of the 4-(N,N-dimethylamino)azobenzene component of each azobenzene–cyanine conjugate and produces a distinctive new absorption band at 534 nm. The complex is quite hydrophilic, which suggests that CB7 can be used as a supramolecular additive to solubilize this new family of NIR azobenzene–cyanine conjugates for future biomedical applications. Since many azobenzene compounds are themselves potential drug candidates or theranostic agents, it should be possible to formulate many of them as CB7 inclusion complexes with improved solubility, stability, and pharmaceutical profile.     

Supramolecular Inhibition of Amyloid Fibrillation by Cucurbit[7]uril

Amyloid fibrils are insoluble protein aggregates comprised of highly ordered β‐sheet structures and they are involved in the pathology of amyloidoses, such as Alzheimer’s disease. A supramolecular strategy is presented for inhibiting amyloid fibrillation by using cucurbit[7]uril (CB[7]). CB[7] prevents the fibrillation of insulin and β‐amyloid by capturing phenylalanine (Phe) residues, which are crucial to the hydrophobic interactions formed during amyloid fibrillation. These results suggest that the Phe‐specific binding of CB[7] can modulate the intermolecular interaction of amyloid proteins and prevent the transition from monomeric to multimeric states. CB[7] thus has potential for the development of a therapeutic strategy for amyloidosis.     

Cucurbit[7]uril host-guest complexes of the histamine H2-receptor antagonist ranitidine

The macrocyclic host cucurbit[7]uril forms very stable complexes with the diprotonated (K(CB[7])(1) = 1.8 x 10(8) dm(3) mol(-1)), monoprotonated (K(CB[7])(2) = 1.0 x 10(7) dm(3) mol(-1)), and neutral (K(CB[7])(3) = 1.2 x 10(3) dm(3) mol(-1)) forms of the histamine H(2)-receptor antagonist ranitidine in aqueous solution. The complexation behaviour was investigated using (1)H NMR and UV-visible spectroscopy as a function of pH and the pK(a) values of the guest were observed to increase (DeltapK(a1) = 1.5 and DeltapK(a2) = 1.6) upon host-guest complex formation. The energy-minimized structures of the host-guest complexes with the cationic guests were determined and provide agreement with the NMR results indicating the location of the CB[7] over the central portion of the guest. The inclusion of the monoprotonated form of ranitidine slows the normally rapid (E)-(Z) exchange process and generates a preference for the (Z) isomer. The formation of the CB[7] host-guest complex greatly increases the thermal stability of ranitidine in acidic aqueous solution at 50 degrees C, but has no effect on its photochemical reactivity.     

A facile,stereoselective [2 + 2] photoreaction mediated by curcurbit[8]uril

The [2 + 2] photoreaction of (E)-diaminostilbene dihydrochloride proceeds with large rate acceleration and high stereoselectivity via formation of a stable 1:2 host-guest complex with curcurbit[8]uril in solution.     

葫芦脲的研究进展

葫芦脲(CB[n])及其衍生物是由n个苷脲单元连接成的穴状分子,因其结构特殊,受到广泛的关注与研究。本文综述了CB[n]的性质、合成以及近年来CB[n]在分子开关、催化剂、药物载体等方面的研究进展。     

Inclusion Interactions of Cucurbit[7]uril with Adenine and its Derivatives

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 guests. The formation constants by UV and fluorescence were 1.90 × 10⁵ L mol^? 1 and 1.34 × 10⁵ L mol^? 1 for Q[7]-g1, 9.41 × 10⁴ L mol^? 1 and 4.24 × 10⁴ L mol^? 1 for Q[7]-g2, 4.50 × 10⁴ L mol^? 1 and 3.62 × 10⁴ L mol^? 1 for Q[7]-g3, respectively. HPLC method was also introduced to explore the interactions between Q[7] and the adenine and its derivatives. The formation constants of the host–guest inclusion complexes, as determined by HPLC, were 6.76 × 10⁴ L mol^? 1 for Q[7]-g1, 1.80 × 10⁴ L mol^? 1 for Q[7]-g2, 3.01 × 10⁴ L mol^? 1 for Q[7]-g3 respectively. Our study suggested that Q[7] could be a suitable host for the delivery of bioactive molecules, such as the adenine and its derivatives.     

Cucurbit[7]uril promoting PdCl2-catalyzed cross-coupling reaction of benzyl halides and arylboronic acids in aqueous media

The research provides a novel approach for producing diarylmethane derivatives using CB[7]–NaCl–PdCl₂ catalyzed Suzuki cross-coupling reaction of benzyl chloride derivatives and arylboronic acids in ethanol aqueous solution.     

Determination of Paraquat by Cucurbit[7]uril Sensitized Fluorescence Quenching Method

A method for the determination of paraquat by cucurbit[7]uril (CB[7]) fluorescence quenching was developed. The assay was based on the reaction of the CB[7] with acridine orange. The fluorescence intensity of acridine orange regularly increased with the addition of CB[7]. However, while an appropriate amount of paraquat was added to the CB[7]- acridine orange system, the fluorescence intensity of the system was quenched which was employed to determine paraquat. Under the optimum conditions, a linear range of 3.0–800 nmol L^?1 and a detection limit of 1.61 nmol L^?1 for paraquat were obtained. The simple strategy reported here offers great practical potential for the determination of pesticide residues in agricultural products.     

Cucurbit[7]uril as a Tool in the Green Synthesis of Gold Nanoparticles

A simple, green, one‐pot synthesis of gold nanoparticles was achieved through the reaction of an aqueous mixture of potassium tetrachloroaurate(III) and the macrocycle cucurbit[7]uril in the presence of sodium hydroxide at room temperature without introducing any kind of traditional reducing agents and/or external energy. The as‐prepared gold nanoparticles showed catalytic activity for the reduction reaction of 4‐nitrophenol in the presence of NaBH₄, which has been established by visual inspection and UV/Vis spectroscopy. This report is the first for the preparation of gold nanoparticles using cucurbit[7]uril in aqueous media through chemical reduction without employing conventional reducing agents and/or external energy.