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.     

From Packed “Sandwich” to “Russian Doll”: Assembly by Charge‐Transfer Interactions in Cucurbit[10]uril

As the host possessing the largest cavity in the cucurbit[n]uril (CB[n]) family, CB[10] has previously displayed unusual recognition and assembly properties with guests but much remains to be explored. Herein, we present the recognition properties of CB[10] toward a series of bipyridinium guests including the tetracationic cyclophane known as blue box along with electron‐rich guests and detail the influence of encapsulation on the charge‐transfer interactions between guests. For the mono‐bipyridinium guest (methylviologen, MV ²⁺), CB[10] not only forms 1:1 and 1:2 inclusion complexes, but also enhances the charge‐transfer interactions between methylviologen and dihydroxynaphthalene ( HN ) by mainly forming the 1:2:1 packed “sandwich” complex (CB[10] ? 2 MV ²⁺ ?HN ). For guest 1 with two bipyridinium units, an interesting conformational switching from linear to “U” shape is observed by adding catechol to the solution of CB[10] and the guest. For the tetracationic cyclophane‐blue box, CB[10] forms a stable 1:1 inclusion complex; the two bipyridinium units tilt inside the cavity of CB[10] according to the X‐ray crystal structure. Finally, a supramolecular “Russian doll” was built up by threading a guest through the cavities of both blue box and CB[10].     

瓜环对氨基酸的分子识别研究

使用¹H NMR和UV-Vis光谱法研究了七、八元瓜环对九种天然氨基酸盐酸盐的分子识别作用. 结果表明, 瓜环对芳香侧基取代的L-酪氨酸、L-色氨酸、L-苯丙氨酸均能进行有效识别, 而侧链上不带芳香基团的氨基酸, 如L-组氨酸、L-谷氨酸、L-蛋氨酸、L-缬氨酸、L-白氨酸、L-丙氨酸, 与这些瓜环的作用相对较弱. 对于七元瓜环, 主客体间都以1∶1化学计量比形成包结物, 并得到它们相互作用的稳定常数; 八元瓜环与L-酪氨酸及L-色氨酸也以1∶1形成包结物, 而与L-苯丙氨酸以1∶2形成包结物. L-酪氨酸、L-色氨酸和L-苯丙氨酸荧光性质研究表明, 七、八元瓜环既可成为这些氨基酸荧光性质的增敏试剂, 也可成为它们荧光淬灭试剂, 这与氨基酸的结构有关.     

Four Polyoxometalate-Viologen Discoloration Materials for UV Probing,Inkless and Erasable Printing and Visual Detection of Hg2+

In this work, four POM-based compounds containing viologen ligands were synthesized, namely {Cu^II(tybipy)₂(DMF)₂[H₂(β-Mo₈O₂₆)]₂} ⋅ 4 C₂H₇N ( 1 ), (Htybipy)₂ ⋅ (β-Mo₈O₂₆) ( 2 ) (tybipy⋅Br=1-Thiophen-3-ylmethyl-[4,4’]bipyridinyl-1-ium bromide), [Cu^II(nibipy)₂(4,4’-bipy)] ⋅ (SiW₁₂O₄₀) ( 3 ), (Hnibipy)₂ ⋅ (δ-Mo₈O₂₆) ( 4 ) (nibipy⋅Cl=1-(4-Nitro-benzyl)-[4,4’]bipyridinyl-1-ium chloride, 4,4’-bipy=4,4’-bipyridine). In compounds 1 and 3 , Cu²⁺ and mixed organic ligands modify POM anions. On the other hand, 2 and 4 are supramolecular structures only containing ligands and anions. Under Xe lamp with filter (300-400 nm) irradiation, these four compounds showed good photoresponse and photochromic ability, which can be used in mixed matrix films for visible UV detectors. Compounds 1 – 4 also have photoluminescence property and show good fluorescence quenching effect. A suspension of four compounds can be evenly spread on filter paper as inkless and erasable printing materials. Compounds 1 and 2 were also used as Hg²⁺ fluorescence detectors. The fluorescence intensity of 1 decreased by ca. 90 % when the concentration of Hg²⁺ increased to 40 mM. Moreover, we also prepared composites 1 / 2 @Hg²⁺, 1 @Cu²⁺, 1 @Co²⁺ by introducing 1 / 2 and Hg²⁺, Cu²⁺ and Co²⁺ to detection paper respectively, which can act as photochromic materials with features of fast color recovery.     

Theoretical insights into the formation, structure, and electronic properties of anticancer oxaliplatin drug and cucurbit[n]urils n = 5 to 8

Geometries, formation and electronic properties of cucurbit[n]uril-oxaliplatin n = 5–8, host-guest complexes are investigated with DFT calculations. The formation of inclusion complexes of CB[n]-oxaliplatin are facile in CB[n] n = 6–8. In the complex, the cyclohexyl group is found to be deep inside the cavity, with the formation of a hydrogen bonding between the portal oxygen atoms and the amine nitrogen of the oxaliplatin guest. NBO analysis shows the transfer of charge from the metal center to the CB[7] unit and the existence of hydrogen bonding between the oxygen portal and amine nitrogen. The HOMO orbital is localized on the carboxylate group and the LUMO orbital are localized on the cucurbituril unit in CB[7]-oxaliplatin complex. The strength of the interaction determined here reflects the ability of CB[n] to act as a host for suitably oxaliplatin guests, even in aqueous solution.     

Inclusion compounds of cucurbit[<Emphasis Type="Italic">n</Emphasis>]urils with metal complexes

A new class of supramolecular compounds—inclusion compounds of metal complexes encapsulated in organic macrocyclic cavitands cucurbit[n]urils (CB[n], C_6n H_6n N_4n O_2n , n = 7−10)—has been surveyed. A unique combination of a rather rigid hydrophobic intramolecular cavity and negatively charged portals favors the formation of stable host-guest compounds. Basic methods of synthesis of inclusion compounds of CB[n] with metal complexes have been reported, and the structures of the resulting products isolated as crystals and characterized by X-ray crystallography have been considered. The effect of encapsulation on the geometric and spectral characteristics of the complexes and their redox properties has been traced. It has been shown that encapsulation in CB[n] can lead to a change in the reactivity of the complexes in thermolysis and isomerization and aquation reactions. Encapsulation of biologically active metal complexes in CB[n] is a promising strategy for designing new-generation prolonged-action pharmaceuticals.     

Acyclic Cucurbit[n]uril-Type Receptors: Aromatic Wall Extension Enhances Binding Affinity,Delivers Helical Chirality,and Enables Fluorescence Sensing

We report the linear extension from M1 to M2 to anthracene walled M3 which adopts a helical conformation (X-ray) to avoid unfavorable interactions between sidewalls. M3 is water soluble (=30 mm ) and displays enhanced optical properties (ϵ=1.28×10⁵ m ⁻¹ cm⁻¹, λ_max=370 nm) relative to M2 . The binding properties of M3 toward guests 1 – 29 were examined by ¹H NMR and ITC. The M3 ⋅guest complexes are stronger than the analogous complexes of M2 and M1 . The enhanced binding of M3 toward neuromuscular blockers 25 , 27 – 29 suggests that M3 holds significant promise as an in vivo reversal agent. The changes in fluorescence observed for M3 ⋅guest complexes are a function of the relative orientation of the anthracene sidewalls, guest concentration, K_a, and guest electronics which rendered M3 a superb component of a fluorescence sensing array. The work establishes M3 as a next generation sequestering agent and a versatile component of fluorescence sensors.     

A Series of Polyoxometalate-Viologen Photochromic Materials for UV Probing,Amine Detecting and Inkless and Erasable Printing

In this work, by using two kinds of viologen ligands three POM-based Compounds were obtained under hydrothermal conditions, namely [Ag^I(bmypd)_0.5(β-Mo₈O₂₆)_0.5] (1) (bmypd ⋅ 2Cl=1,1′-[Biphenyl-4,4′-bis(methylene)]bis(4,4′-bipyridyinium)dichloride), [Ag^I₂(bypy)₄(HSiW₁₂O₄₀)₂] ⋅ 14H₂O (2) and [Ag^I(bypy)(γ-Mo₈O₂₆)_0.5] (3) (bypy⋅Cl=1-Benzyl-4,4′-bipyridyinium chloride). The structures were characterized by Fourier transform infrared spectroscopy (FT–IR), Powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS) and single crystal X-ray diffraction. Compounds 1–3 show excellent photochromic ability with fast photoresponse under the irradiation of ultraviolet light with different degrees of color changes. So compounds 1–3 can be used as visible ultraviolet detectors. Compounds 1–3 also possess photoluminescence properties with fast and excellent fluorescence quenching effect. Compounds 1–3 also can be used as inkless and erasable printing materials with suspensions of 1–3 applied to filter paper. Compounds 1–3 can also produce color changes in amine vapor environment, especially in an NH₃ atmosphere. Compounds 1–3 can be used as organic amine detectors.     

A Comparative Study of Complexation of β-Cyclodextrin,Calix[4]arenesulfonate and Cucurbit[7]uril with Dye Guests: Fluorescence Behavior and Binding Ability

The complexation behaviors of acridine red (AR), neutral red (NR) and rhodamine B (RhB) dye guest molecules by three kinds of supramolecular hosts, including β-cyclodextrin (β-CD), calix[4]arene tetrasulfonate (C4AS) and cucurbit[7]uril (CB[7]), have been investigated by means of fluorescence spectra in aqueous citrate buffer solution (pH 6.0). The results obtained show that the three hosts, possessing different types of cavity, lead to various complexation-induced fluorescence of dye guests, and present different binding ability and molecular selectivity. The complexation stability constants decrease in the order of NR > AR > RhB for C4AS and CB[7] hosts, while in the order of RhB > AR > NR for β-CD host. Particularly, CB[7] displays the strongest binding ability with NR (K _S = 33300 M^? 1), and provides the molecular selectivity of 4.8 for NR/AR pairs. Although the binding ability of C4AS for present dye guests is weaker than CB[7], but the molecular selectivity of the two hosts are nearly equivalent. β-CD shows stronger binding ability with RhB (K _S = 5880 M^? 1) as comparison with CB[7] and C4AS. Furthermore, the solvent effects and salt effects during the course of complexation have also been investigated.     

Aurophilicity-Mediated Construction of Emissive Porous Molecular Crystals as Versatile Hosts for Liquid and Solid Guests

The first examples of porous molecular crystals that are assembled through Au⋅⋅⋅Au interactions of gold complex 1 are here reported along with their exchange properties with respect to their guest components. Single-crystal X-ray diffraction (XRD) analyses indicate that the crystal structure of 1 /CH₂Cl₂⋅pentane is based on cyclic hexamers of 1 , which are formed through six Au⋅⋅⋅Au interactions. The packing of these cyclic hexamers affords a porous architecture, in which the one-dimensional channel segment contains CH₂Cl₂ and pentane as guests. These guests can be exchanged through operationally simple methods under retention of the host framework of 1 , which furnished 1 /guest complexes with 26 different guests. A single-crystal XRD analysis of 1 /eicosane, which contains the long linear alkane eicosane (n-C₂₀H₄₂), successfully provided its accurately modeled structure within the porous material. These host–guest complexes show chromic luminescence with both blue- and redshifted emissions. Moreover, this porous organometallic material can exhibit luminescent mechanochromism through release of guests.     

One Guest or Two? A Crystallographic and Solution Study of Guest Binding in a Cubic Coordination Cage

A crystallographic investigation of a series of host–guest complexes in which small-molecule organic guests occupy the central cavity of an approximately cubic M₈L₁₂ coordination cage has revealed some unexpected behaviour. Whilst some guests form 1:1 H⋅G complexes as we have seen before, an extensive family of bicyclic guests—including some substituted coumarins and various saturated analogues—form 1:2 H⋅G₂ complexes in the solid state, despite the fact that solution titrations are consistent with 1:1 complex formation, and the combined volume of the pair of guests significantly exceeds the Rebek 55±9 % packing for optimal guest binding, with packing coefficients of up to 87 %. Re-examination of solution titration data for guest binding in two cases showed that, although conventional fluorescence titrations are consistent with 1:1 binding model, alternative forms of analysis—Job plot and an NMR titration—at higher concentrations do provide evidence for 1:2 H⋅G₂ complex formation. The observation of guests binding in pairs in some cases opens new possibilities for altered reactivity of bound guests, and also highlights the recently articulated difficulties associated with determining stoichiometry of supramolecular complexes in solution.     

瓜环与2,2'-联吡啶衍生物的相互作用

利用¹H NMR技术、紫外吸收光谱及荧光光谱方法, 考察了对六、七以及八元瓜环与多种2,2'-联吡啶衍生物相互作用形成的主客体配合物结构及光谱性质. 研究结果显示, 不同的2,2'-联吡啶衍生物与瓜环作用不仅形成多种不同包结比的稳定包结配合物, 且所形成的主客体包结配合物的结构及光谱性质也各不相同; 同时用几种方法协同考察起到了互为补充、互为验证的良好效果.     

Photodimerization of azaanthracene derivatives mediated by cucurbit[10]uril

Challenges of achieving efficient photodimerization of azaanthracene derivatives remain due to the low selectivity and slow reaction rate. In this paper, cucurbit[10]uril (CB[10]), with the largest rigid and hydrophobic cavity among CB[n]s, was used to affect the photodimerization reaction of four water-soluble 1-(2-)substituted azaanthracene derivatives (1-4). It revealed that 1-4 could form 1:2 host-guest complexes with CB[10] in aqueous solution. Irradiation of 1 in the presence of 0.5 equiv. of CB[10] selectively produced a head-to-tail (anti-HT) photodimer product. As for 2-4, CB[10] acted as a nanoreactor accelerating their photodimerization reaction in water. Our results suggest that photodimerization of azaanthracene derivatives could be promoted by the CB[10]-based host-guest strategy with high efficiency and selectivity.     

Acyclic cucurbituril congener binds to local anaesthetics

The recognition properties of acyclic cucurbit[n]uril (CB[n]) congener 1 towards seven local anaesthetic drugs (2–8) are reported. Job plots constructed from ¹H NMR experiments confirm the 1:1 host:guest nature of these complexes, whereas the changes in chemical shift observed upon complex formation (Δδ values) provide information about the geometry of the host–guest complexes. For complexes between host 1 and guests 2–5 and 8, a single geometry was preferred, whereas for guests 6 and 7 a mixture of two diastereomeric complexes was indicated. The K _a values for complexes between 1 and 2–8 fall in the range of 10³–10⁸ M^? 1 as determined by UV–vis and ¹H NMR competition experiments. The results further establish that acyclic CB[n]-type receptor 1 is preorganised into the C-shape required for binding and that its aromatic o-xylylene walls endow it with a potency towards aromatic ammonium ions. The K _a values reported in this paper constitute a blind data-set used in the SAMPL3 challenge aimed at testing computational methods relevant to protein√ligand systems. The work thus highlights the great potential of CB[n] receptors as model systems to promote synergy between the supramolecular and computational chemistry communities.     

Cucurbit[n]urils for Supramolecular Catalysis

The control over chemical reactivity and selectivity are always pursued. Using non-covalent interactions to achieve efficient and selective catalysis is an essential goal of supramolecular catalysis. Supramolecular catalysis based on cucurbit[n]urils (CB[n]s) possesses distinct characteristics for the unique structure of CB[n]s. CB[n]s are a family of pumpkin-shaped host molecules with various molecular sizes, rigid structures, electronegative portals and wealthy host-guest chemistry. Herein, we summarize the three major mechanisms of CB[n]s based supramolecular catalysis. Owing to the structural properties of CB[n]s, CB[n]s can serve as nanoreactors and steric hindrance to modulate the reactivity of substrates. They can also catalyze the reactions by modulating the reactivity of ionized intermediates. Recent progresses on the CB[n]s based supramolecular catalysis are introduced in this Minireview and the future development in this field is discussed. It is anticipated that this review provides insights into the mechanism of CB[n]s based supramolecular catalysis and may help scientists find new opportunities in this field.     

Dynamic Interfacial Adhesion through Cucurbit[n]uril Molecular Recognition

Supramolecular building blocks, such as cucurbit[n]uril (CB[n])‐based host–guest complexes, have been extensively studied at the nano‐ and microscale as adhesion promoters. Herein, we exploit a new class of CB[n]‐threaded highly branched polyrotaxanes (HBP‐CB[n]) as aqueous adhesives to macroscopically bond two wet surfaces, including biological tissue, through the formation of CB[8] heteroternary complexes. The dynamic nature of these complexes gives rise to adhesion with remarkable toughness, displaying recovery and reversible adhesion upon mechanical failure at the interface. Incorporation of functional guests, such as azobenzene moieties, allows for stimuli‐activated on‐demand adhesion/de‐adhesion. Macroscopic interfacial adhesion through dynamic host–guest molecular recognition represents an innovative strategy for designing the next generation of functional interfaces, biomedical devices, tissue adhesives, and wound dressings.     

Interaction of host-guest complexes of cucurbit[<Emphasis Type="Italic">n</Emphasis>] urils with double probe guests

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.     

Supramolecular interaction of cucurbit[n]urils and coptisine by spectrofluorimetry and its analytical application

The supramolecular interaction of a homologous series of cucurbit[n]uril (CB[n], n = 5, 6, 7, 8) hosts and coptisine (COP) was studied by spectrofluorimetry. All of the CB[n]s were found to react with COP to form 1:1 host-guest stable complexes and the fluorescence intensity of the complexes was greatly enhanced. The apparent association constants of the complexes were 1.44 × 10⁴, 1.28 × 10⁴, 1.86 × 10⁴ and 1.26 × 10⁴ L mol⁻¹ for CB[5], CB[6], CB[7] and CB[8], respectively. In addition, CB[5] and CB[7] exhibited a higher fluorescence signal than CB[6] and CB[8]. The fluorescence intensity of the complex with CB[7] was enhanced 70-fold compared to that of the studied drug itself. Based on the significant enhancement of fluorescence intensity of supramolecular complex, a simple, rapid, highly sensitive, and selective spectrofluorimetric method was developed for the determination of COP in aqueous solution in the presence of CB[7]. At the optimum reaction conditions, a linear relationship was obtained in the range from 0.05 to 1700 ng mL⁻¹ with a detection limit of 0.012 ng mL⁻¹. The proposed method was successfully applied for the determination of the drug in urine and serum samples.     

Regulation of Charge Delocalization in a Heteronuclear Fe2Ru System by a Stepwise Photochromic Process

Heteronuclear complexes FeCp₂?DTE?C?C?Ru(dppe)₂Cl ( 1 o ; dppe=1,2‐bis(diphenylphosphino)ethane, Cp=cyclopentadienyl, DTE=dithienylethene) and FeCp₂?DTE?C?C?Ru(dppe)₂?C?C?DTE?FeCp₂ ( 2 oo ), with redox‐active ferrocenyl and ruthenium centers separated by a photochromic DTE moiety, were prepared to achieve photoswitchable charge delocalization and Fe???Ru electronic communication. Upon UV‐light irradiation of 2 oo , the Fe???Ru heterometallic electronic interaction is increasingly facilitated with stepwise photocyclization, 2 oo → 2 co → 2 cc ; this is ascribed to the gradual increase in π‐conjugated systems. The near‐infrared absorptions in mixed‐valence species [ 2 oo ]⁺/[ 2 co ]⁺/[ 2 cc ]⁺ are gradually intensified following the conversion of [ 2 oo ]⁺→[ 2 co ]⁺→[ 2 cc ]⁺, which demonstrates that the extent of charge delocalization shows progressive enhancement with stepwise photocyclization. As revealed by electrochemical, spectroscopic, and theoretical studies, complex 2 exhibits nine switchable states through stepwise photochromic and reversible redox processes.     

The Role of Packing,Dispersion, Electrostatics,and Solvation in High-Affinity Complexes of Cucurbit[n]urils with Uncharged Polar Guests

The rationalization of non-covalent binding trends is both of fundamental interest and provides new design concepts for biomimetic molecular systems. Cucurbit[n]urils (CBn) are known for a long time as the strongest synthetic binders for a wide range of (bio)organic compounds in water. However, their host-guest binding mechanism remains ambiguous despite their symmetric and simple macrocyclic structure and the wealth of literature reports. We herein report experimental thermodynamic binding parameters (ΔG, ΔH, TΔS) for CB7 and CB8 with a set of hydroxylated adamantanes, di-, and triamantanes as uncharged, rigid, and spherical/ellipsoidal guests. Binding geometries and binding energy decomposition were obtained from high-level theory computations. This study reveals that neither London dispersion interactions, nor electronic energies or entropic factors are decisive, selectivity-controlling factors for CBn complexes. In contrast, peculiar host-related solvation effects were identified as the major factor for rationalizing the unique behavior and record-affinity characteristics of cucurbit[n]urils.