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].     

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.     

Achieving Enhanced Photochromic Properties of Diarylethene through Host-Guest Interaction in Aqueous Solution

Diarylethene (DTE) has been widely used in fluorescence probes, molecular logic gates, optical data-storage devices owing to the excellent photochromic property, while constructing high-performance photochromic DTE in aqueous media remains a big challenge. Herein we present several host-guest systems formed between cucurbit[n]uril (CB[n], n=7, 8, 10) and two water-soluble DTE derivatives 1 and 2 . It was found that host-guest interactions not only affect the photophysical properties of photochromic guests, but also make great differences on the photoreaction process. Different host-guest binding behaviors also lead to different effects on the photochromic properties of guests. In the presence of CB[n], both 1 and 2 showed enhanced emission and higher fluorescence quenching ratio at photostationary state. Besides, CB[10] ⋅1 exhibited faster response rate in cyclization reaction and better photofatigue resistance than free 1 in aqueous solution, while the supramolecular assembly of (CB[8])_n ⋅ ( 2 )_n showed slower response rate in both directions of the reversible photoreaction. Besides, the photofatigue resistance of 2 can be greatly improved through binding with CB[7]. Our results suggest that host-guest interactions could be an efficient way to improve photochromic properties of DTE in aqueous solution.     

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.     

Pseudo[n,m]rotaxanes of Cucurbit[7/8]uril and Viologen‐Naphthalene Derivative: A Precise Definition of Rotaxane

Rotaxane is a kind of classic supramolecule, which is usually constructed from a number of macrocycles and one axis molecule. Herein, we have expanded the supramolecular structure of [n]rotaxane to offer a precise definition of (pseudo)[n,m]rotaxane for accurately describing the two kinds of (pseudo)rotaxanes structures, which are self‐assembled from cucurbit[7/8]uril (CB[7/8]) and viologen‐naphthalene derivative, respectively. Furthermore, these CB‐based pseudorotaxanes exhibit varied photophysical properties, stimuli‐responsive behavior triggered by competitive guest, and self‐sorting behavior.     

Synthesis and crystal structures of sumpramolecular compounds of cucurbit[n]urils (n = 6, 8) with polynuclear strontium aqua complexes

Crystals of the {[Sr₄(H₂O)₁₂(NO₃)₄](C₃₆H₃₆N₂₄O₁₂)}(NO₃)₄·3H₂O and {[Sr₂(H₂O)₁₂][Sr(H₂O)₃(NO₃)₂]₂(C₄₈H₄₈N₃₂O₁₆)}(NO₃)₄·8H₂O were prepared by slow concentration of aqueous solutions containing strontium nitrate and macrocyclic cavitands, viz., cucurbit[6]uril and cucurbit[8]uril ([C₆H₆N₄O₂] _n , n = 6 and 8), respectively. According to the results of X-ray diffraction analysis, the crystal structures of these supramolecular compounds are built from polymeric chains, which consist of the alternating cucurbit[n]uril molecules and Sr²⁺ cations linked through the bridging aqua ligands and nitrate anions. The supramolecular compound of cucurbit[8]uril provides the first example of compounds in which this macrocycle is bound to metal aqua complexes.     

Cucurbit[7]uril⋅Guest Pair with an Attomolar Dissociation Constant

Host?guest complexes between cucurbit[7] (CB[7]) or CB[8] and diamantane diammonium ion guests 3 or 6 were studied by ¹H NMR spectroscopy and X‐ray crystallography. ¹H NMR competition experiments revealed that CB[7]? 6 is among the tightest monovalent non‐covalent complexes ever reported in water with K_a=7.2×10¹⁷ M ^?1 in pure D₂O and 1.9×10¹⁵ M ^?1 in D₂O buffered with NaO₂CCD₃ (50 mM ). The crystal structure of CB[7]? 6 allowed us to identify some of the structural features responsible for the ultratight binding, including the distance between the NMe₃⁺ groups of 6 (7.78 Å), which allows it to establish 14 optimal ion‐dipole interactions with CB[7], the complementarity of the convex van der Waals surface contours of 6 with the corresponding concave surfaces of CB[7], desolvation of the C?O portals within the CB[7]? 6 complex, and the co‐linearity of the C₇ axis of CB[7] with the N⁺???N⁺ line in 6 . This work further blurs the lines of distinction between natural and synthetic receptors.     

六～八元瓜环与三种N-苄基取代笼状客体的相互作用

合成了3种具有对不同瓜环选择性各异的双探针N-苄基取代笼状客体, 它们分别是N-苄基六次甲基四胺盐酸盐(1), N-苄基喹啉环啶盐酸盐(2), N-苄基-1,4-二氮杂双环[2.2.1]辛烷盐酸盐(3), 利用¹H NMR和MS等方法对这些客体进行了表征. ¹H NMR显示, 六元瓜环仅对这些客体的苄基探针部分具有选择性作用, 形成作用比为1∶1的不对称包结配合物; 七元瓜环对客体1和3的苄基探针部分具有选择性作用, 形成作用比为1∶1的不对称包结配合物, 而对客体2的笼状奎宁环啶基部分具有选择性作用, 也形成作用比为1∶1的包结配合物; 八元瓜环也仅对这些客体的苄基探针部分具有选择性作用, 形成作用比为1∶2的对称包结配合物.     

Cucurbit[7]uril Complexation Drives Thermal trans–cis‐Azobenzene Isomerization and Enables Colorimetric Amine Detection

Complexation of yellow diaminoazobenzenes 1 and 3 inside cucurbit[7]uril (CB[7]) results in the formation of purple‐colored CB[7] ? cis‐ 1? 2 H⁺ and CB[7] ? cis‐ 3? 2 H⁺ complexes, respectively. The high binding affinity and selectivity displayed by CB[7] toward 1 and 3 pays the >10 kcal mol^?1 thermodynamic cost for this isomerization. We investigated the behavior of these complexes as a function of pH and observed large pK_a shifts and high pH responsiveness, which are characteristic of cucurbit[n]uril molecular containers. The remarkable yellow to purple color change was utilized in the construction of an indicator displacement assay for biologically active amines 4 – 10 . This indicator displacement assay is capable of quantifying the pseudoephedrine ( 5 ) content in Sudafed tablets over the 5–350 μM range.     

Uptake of Hydrocarbons in Aqueous Solution by Encapsulation in Acyclic Cucurbit[n]uril‐Type Molecular Containers

The ability of two water‐soluble acyclic cucurbit[n]uril (CB[n]) type containers, whose hydrophobic cavity is defined by a glycoluril tetramer backbone and terminal aromatic (benzene, naphthalene) sidewalls, to act as solubilizing agents for hydrocarbons in water is described. ¹H NMR spectroscopy studies and phase‐solubility diagrams establish that the naphthalene‐walled container performs as well as, or better than, CB[7] and CB[8] in promoting the uptake of poorly soluble hydrocarbons into aqueous solution through formation of host–hydrocarbon complexes. The naphthalene‐walled acyclic CB[n] container is able to extract large hydrocarbons from crude oil into aqueous solution.     

瓜环与4,4'-二氨基二苯甲烷衍生物的相互作用

合成了三种长链多芳环多胺基客体, 它们分别由三种醛基吡啶异构体与4,4'-二氨基二苯甲烷形成的Schiff碱还原而成, 并得到¹H NMR以及质谱分析方法表征证实. 以核磁共振技术、紫外吸收光谱分析方法以及滴定¹H NMR方法为研究手段, 对瓜环(cucurbit[n]urils, n＝6～8)分别与三种4,4'-二[N-(吡啶甲基)氨基]二苯甲烷盐酸盐相互作用进行了考察. 实验结果表明, 六元瓜环与三种4,4'-二[N-(吡啶甲基)氨基]二苯甲烷盐酸盐相互作用均形成物质的量之比为2∶1的哑铃型包结配合物; 八元瓜环与三种N,N'-二(N-(吡啶甲基)二苯甲烷盐酸盐相互作用形成以类轮烷结构为主的包结配合物; 七元瓜环与三种N,N'-二(N-(吡啶甲基)二苯甲烷盐酸盐相互作用存在多种模式的竞争.     

Effects of the number and placement of positive charges on viologen–cucurbit[n]uril interactions

Recent developments in the synthesis and applications of the cucurbit[n]uril family of synthetic hosts has led to an increasing interest in the detailed studies of their interactions with a wide variety of guests. This paper describes a quantitative study of the effects of the number and placement of positive charges on the binding of viologen guests to cucurbit[7]uril and cucurbit[8]uril. A series of viologen derivatives with one to four charges was characterised by isothermal titration calorimetry, ¹H NMR spectroscopy and mass spectrometry to determine the stoichiometry, affinity and mode of binding. These data show that stoichiometry can be controlled by the placement of charge, and that affinity can be increased by the addition of positive charges. This study should serve as a guide for the design of supramolecular structures built from viologens and cucurbit[n]urils.

     

Cucurbituril‐Modulated Supramolecular Assemblies: From Cyclic Oligomers to Linear Polymers

Employing bis(p‐sulfonatocalix[4]arenes) (bisSC4A) and N′,N′′hexamethylenebis(1‐methyl‐4,4′‐bipyridinium) (HBV⁴⁺) as monomer building blocks, the assembly morphologies can be modulated by cucurbit[n]uril (CB[n]) (n=7, 8), achieving the interesting topological conversion from cyclic oligomers to linear polymers. The binary supramolecular assembly fabricated by HBV⁴⁺ and bisSC4A units, forms an oligomeric structure, which was characterized by NMR spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic light scattering (DLS), isothermal titration calorimetry (ITC), and gel permeation chromatography (GPC) experiments. The ternary supramolecular polymer participated by CB[8] is constructed on the basis of host–guest interactions by bisSC4A and the [2]pseudorotaxane HBV⁴⁺@CB[8], which is characterized by means of AFM, DLS, NMR spectroscopy, thermogravimetric analysis (TGA), UV/Vis spectroscopy, and elemental analysis. CB[n] plays vital roles in rigidifying the conformation of HBV⁴⁺, and reinforcing the host–guest inclusion of bisSC4A with HBV⁴⁺, which prompts the formation of a linear polymer. Moreover, the CB[8]‐participated ternary assembly could disassemble into the molecular loop HBV²⁺@CB[8] and free bisSC4A after reduction of HBV⁴⁺ to HBV²⁺, whereas the CB[7]‐based assembly remained unchanged after the reduction. CB[8] not only controlled the topological conversion of the supramolecular assemblies, but also improved the redox‐responsive assembly/disassembly property practically.     

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.     

Pseudopolyrotaxanes of Cucurbit[6]uril: A Three‐Dimensional Network Self‐assembled by ClO4−(H2O)2 Water Clusters

A pseudorotaxane of cucurbit[6]uril (CB[6]) with guest molecule N,N′‐hexamethylenebis (pyrazinyl perchlorate) (BPHP) was synthesized and characterized by ¹H NMR spectra, IR, single crystal X‐ray diffraction analysis and thermogravimetric analysis. The structure of the pseudorotaxane (CB[6]·BPHP) is stabilized by host‐guest hydrogen bonds. Self‐assembly of the pseudorotaxane produces infinite one‐dimensional and two‐dimensional networks with intermolecular hydrogen bonds. In the molecular packing of the CB[6]·BPHP, ClO₄^?(H₂O)₂ water clusters serve as bridges to associate these pseudorotaxanes and form three‐dimensional networked pseudopolyrotaxane.     

H3BTC‐Induced Supramolecular Assembly Based on Cucurbit[6]uril: Possible Application for Sensing Small Molecules

The compound 2[Ca(H₂O)₃ (DMF@CB[6])] · 2(BTC) · 15H₂O ( CCUT ‐ 102 , CB[6] = cucurbit[6]uril; H₃BTC = 1,3,5‐benzenetricarboxylic acid) was synthesized using the approach of organic guest‐induced formation of polymers or frameworks based on the coordination of metal ions and cucurbit[n]urils. The compound was characterized by X‐ray diffraction analysis, PXRD, IR spectroscopy, thermogravimetric and elemental analyses. According to the X‐ray diffraction data, the calcium atom is coordinated by the oxygen atoms of the CB[6] molecule, water molecules, and N ,N‐dimethylformamide (DMF). The internal cavity of CB[6] is occupied by DMF. Each H₃BTC molecule interacts the CB[6] molecules through π?π interactions between aromatic rings of H₃BTC and the rings of CB[6]. The luminescence behaviors and sensing properties of CCUT ‐ 102 in different solvents were also studied.     

Self‐Assembled Monolayers of Cucurbit[6]uril on a Gold Electrode for 4,4′‐Oxydianiline Determination. Analytical Application

Self‐assembled monolayers of cucurbit[6]uril (CB[6]) on a gold electrode have been used for 4,4′‐oxydialine (ODA) analysis. The formation of the supramolecular complex between ODA and CB[6] was used for the molecular selection and the electroanalytical determination of this analyte. In addition to this, all the parameters affecting the modification of the gold electrode and the determination of 4,4′‐oxydianiline were optimized by square wave voltammetry. Upon the electrode modification, pentanethiol was employed to fill up the exposed surface between CB[6] molecules. The calculated detection and determination limits were 0.06 µg mL^?1 and 0.19 µg mL^?1, respectively, with good accuracy and precision as shown by the calculated values for the relative error and relative standard deviation (E_r=0.1 % and RDS=2.9 %; n=10 ). Moreover, the developed methodology was successfully applied to the 4,4′‐oxydialine determination in real wastewaters and shoe‐dyeing samples.     

Comparative macrocycle binding of the anticancer drug phenanthriplatin by cucurbit[<Emphasis Type="Italic">n</Emphasis>]urils, β-cyclodextrin and <Emphasis Type="Italic">para</Emphasis>-sulfonatocalix[4]arene: a <Superscript>1</Superscript>H NMR and molecular modelling study

The potential anticancer drug phenanthriplatin, [cis-(NH₃)₂(phenanthridine)Cl]⁺, forms supramolecular complexes with cucurbit[n]urils (CB[n], n?=?7 or 8), β-cyclodextrin and para-sulfonatocalix[4]arene (sCX[4]) as determined by ¹H NMR spectroscopy and molecular modeling. The results show that cucurbit[7]uril binds over the long arm of the drug, where hydrophobic effects and two hydrogen bonds stabilise binding. For cucurbit[8]uril, two phenanthriplatin molecules can bind simultaneously within the macrocycle’s cavity. Unfortunately, Na⁺ was able to displace the drug from both CB[7] and CB[8] making the macrocycles unsuitable as delivery vehicles for phenanthriplatin. Drug binding to β-cyclodextrin occurs at the portal of the macrocycle with no part of the phenanthriplatin located within the cavity. Phenanthriplatin binding to sCX[4] occurs in a 2-to-1, macrocycle-to-drug, ratio with the formation of a capsule-like complex where each sCX[4] binds over opposing ends of the drug. The results indicate that para-sulfonatocalix[4]arene is the only suitable macrocycle of the four studied for further research into phenanthriplatin drug delivery.     

六～八元瓜环与咪唑[4,5-f]-1',10'-菲咯啉衍生物的相互作用

合成了2-苯基-咪唑[4,5-f]-1',10'-菲咯啉和对二甲氨基-2-苯基-咪唑[4,5-f]-1',10'-菲咯啉两种咪唑[4,5-f]-1',10'-菲咯啉衍生物, 并经过一、二维核磁共振谱以及质谱方法的验证. 利用¹H NMR、质谱以及紫外可见分光光度法, 考察了以六～八元瓜环为主体, 咪唑[4,5-f]-1',10'-菲咯啉衍生物为客体的作用体系, 以及形成的主客体包结配合物的结构特征. 研究结果表明: 三种瓜环均与2-苯基-咪唑[4,5-f]-1',10'-菲咯啉发生相互作用, 客体以较小的苯基一端穿过瓜环内腔直至苯基部分和菲咯啉部分分别露置在瓜环的两个端口外, 特别是八元瓜环能容纳两个客体分子. 而对二甲氨基-2-苯基-咪唑[4,5-f]-1',10'-菲咯啉仅能与七及八元瓜环相互作用, 作用模式与前者相同.     

Synthesis and crystal structures of supramolecular compounds of polynuclear aluminum(III) aqua hydroxo complexes with cucurbit[6]uril

Supramolecular compounds of the di-, trideca-, and triacontanuclear aluminum aqua hydroxo complexes, viz., [Al₂(OH)₂(H₂O)₈]⁴⁺, [Al₁₂(AlO₄)(OH)₂₄(H₂O)₁₂]⁷⁺, and [Al₃₀O₈(OH)₅₆(H₂O)₂₆]¹⁸⁺, respectively, with the organic macrocyclic cavitand cucurbit[6]uril (C₃₆H₃₆N₂₄O₁₂) were prepared by evaporation of aqueous solutions of aluminum nitrate and cucurbit[6]uril after the addition of pyridine, ammonia, KOH, or NaOH at pH 3.1–3.8. X-ray diffraction study demonstrated that the aqua hydroxo complexes are linked to the macrocycle through hydrogen bonds between the hydroxo and aqua ligands of the polycations and the portal oxygen atoms of cucurbit[6]uril. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 261—268, February, 2006.