Supramolecular Self‐Assembly of Cucurbit[6]uil and Ionic Liquid in Non‐aqueous System

A novel [2]pseudorotaxane of cucurbit[6]uril(CB[6]) and 1‐butyl‐3‐methyl‐imidazolium bromide ([C₄mim]Br) was synthesized by directly mixing the host and the guest molecules in non‐aqueous system. Structural characterizations of the [2]pseudorotaxane were carried out by 1D, 2D NMR and X‐ray crystallography techniques both in solution and in crystal structure. The crystal structure demonstrated that CB[6] and [C₄mim]Br formed a complex with the ratio 1:1, in which one guest [C₄mim]Br was included inside the CB[6], while two other [C₄mim]Br molecules were free and surrounded the [2]pseudorotaxane as solvent molecules, which could stabilize the crystal structure through hydrogen bonds. Moreover, parallel solvent channels consisting by free [C₄mim]Br molecules occupied the pores among the frame of the pseudorotaxanes and formed zigzag lines in the crystal structure. [C₄mim]Br can serve as not only the guest reactant but also the solvent in the formation of [2]pseudorotaxane formation.     

In the twilight zone between [2]pseudorotaxanes and [2]rotaxanes

A [2]pseudorotaxane, based on a semi-dumbbell-shaped component containing asymmetrically substituted monopyrrolotetrathiafulvalene and 1,5-dioxynaphthalene recognition sites for encirclement by cyclobis(paraquat-p-phenylene) and with a "speed bump" in the form of a thiomethyl group situated between the two recognition sites, has been self-assembled. This supramolecular entity is a mixture in solution of two slowly interconverting [2]pseudorotaxanes, one of which is on the verge of being a [2]rotaxane at room temperature, allowing it to be isolated by employing flash column chromatography. These two [2]pseudorotaxanes were both characterized in solution by UV/Vis and (1)H NMR spectroscopies (1D and 2D) and also by differential pulse voltammetry. The spectroscopic and electrochemical data reveal that one of the complexes behaves wholly as a [2]pseudorotaxane, while the other has some [2]rotaxane character to it. The kinetics of the shuttling of cyclobis(paraquat-p-phenylene) between the monopyrrolotetrathiafulvalene and the 1,5-dioxynaphthalene recognition sites have been investigated at different temperatures. The shuttling processes, which are accompanied by detectable color changes, can be monitored using UV/Vis and (1)H NMR spectroscopies; the spectroscopic data have been employed in the determination of the rate constants, free energies of activation, enthalpies of activation, and the entropies of activation for the translation of cyclobis(paraquat-p-phenylene) between the two recognition sites.     

Versatile formation of [2]catenane and [2]pseudorotaxane structures; threading and noncovalent stoppering by a self-assembled macrocycle

A self-assembled dimeric macrocycle between 4,4'-bis(4-pyridylmethoxy)biphenyl (L) and (en)Pd(NO(3))(2) was constructed, and its interactions with cyclodextrins of different cavity size resulted in the formation of [2]catenane and [2]pseudorotaxane systems, respectively. The structures were identified by 1D and 2D NMR spectroscopy and cold spray ionization mass (CSI-MS) spectrometry.     

A novel two-dimensional polyrotaxane network self-assembled by heterowheel [4]pseudorotaxane

A novel heterowheel pseudorotaxane comprised of one guest, one cucurbit[7]uril and two cucurbit[6]urils was synthesised and characterised by ¹H NMR, single crystal X-ray diffraction analysis and thermogravimetric analysis. Single crystal X-ray diffraction analysis demonstrates that the heterowheel pseudorotaxane self-assembles into two-dimensional polyrotaxane network with the aid of water molecules and hydrogen bonds. Every four heterowheel pseudorotaxanes self-assemble into a parallelogram, which is the basic unit of the 2D network.     

Stable pillar [5] arene-based pseudo [1] rotaxanes formed in polar solution

Mono-alkyl-functionalized pillar[5] arenes P1,P2,and P3 were synthesized by click reaction,which exhibited different self-assembly behavior in polar solvent DMSO.Stable pseudo [1] rotaxane was formed by the self-complexation from P1 or P2,whereas,concentration-dependent pseudorotaxane structures were generated by P3 which bearing more flexible side chain.Interestingly,the obtained pseudo[1] rotaxanes exhibited a dynamic fast assembly process upon adding NaBF₄,resulting in the formation of Na⁺-induced pseudorotaxanes.     

Complexation of sym-bis(benzimidazole)-2, 2’-ethylene salts with cucurbit[6]uril derivatives：A potential axle molecule for pseudorotaxanes

Sym-bis(benzimidazole)-2,2'-ethylene cations act as a new axle template for threading cucurbit[6]uril derivatives on, forming [2]pseudorotaxane and [3]pseudorotaxane. These new complexes have been studied using 1H NMR, UV-vis absorption spectroscopy and X-ray analysis. Changes in the 1H NMR spectra indicate that the two types of pseudorotaxane can be formed by varying the host concentration. UV-vis absorption titration experiments at different pH values demonstrate that interesting pKa shifts of the bis-benzimidazole derivatives can be induced by the host-guest complexation. The associated constants were calculated to be 2.81×104 L/mol and 9.06×106 L/mol for the [2]pseudorotaxanes and [3]pseudorotaxanes, respectively. Furthermore, X-ray diffraction studies of the solid state structures provide unequivocal proof of the host concentration dependent pseudorotaxane, which is strongly in line with the evidences in solution.     

含有葫芦[6]脲的新型准轮烷的合成

通过葫芦[6]脲(CB[6])与两个质子化的1,4-丁二胺在水溶液中于室温下进行超分子自组装, 得到一种新型的准轮烷. 通过¹H NMR, 质谱和¹H ROESY NMR对其结构进行了表征, 证实CB[6]位于质子化1,4-丁二胺的脂肪链上, 通过非共价键与1,4-丁二胺结合, 并且主体(CB[6])与客体的结合的物质的量之比为2∶1.     

Isomeric [2]rotaxanes and unidirectional [2]pseudorotaxane composed of alpha-cyclodextrin and aliphatic chain-linked carbazole-viologen compounds

[structure: see text] Capping the alpha-cyclodextrin (alpha-CD) complex of 1-(N-carbazole)-10-[4-(4-pyridinio)-1-pyridinio]decane with 3,5-dimethoxybenzyl bromide in DMF gives two isomeric [2]rotaxanes, 2a and 2b, while alpha-CD and 1-(N-carbazole)-10-[4-(1-methyl-4-pyridnino)-1-pyridinio]decane 3 in water form mostly a unidirectional [2]pseudorotaxane having the same alpha-CD orientation as 2b. Structures were elucidated from 1H NMR and circular dichroism spectra. The orientational specificity of alpha-CD in the 3/alpha-CD [2]pseudorotaxane is due to the slow dethreading rate of the 2b-type isomer.     

SYNTHESIS AND PROPERTIES OF COPOLYMERS CONTAINING CUCURBIT[6]URIL-BASED PSEUDOROTAXANE STRUCTURE

Novel copolymers based on acrylamide（AM）and complex pseudorotaxane monomer N’-（3-vinylbenzyl）-1,4- diaminobutane dihydrochloride with cucurbit[6]uril（CB[6]）（3VBCB）were prepared via free-radical polymerization in aqueous solution,and characterized by ¹H-NMR,FT-IR,elemental analysis and static light scattering.The compositions of the copolymers（PAM3VBCB）with pseudorotaxane units were determined by ¹H-NMR and elemental analysis.Thermal properties of the copolymers were studied by TGA,and the effects of the copolymer concentration and pH on the average hydrodynamic radius（R_h）of the copolymer molecules were studied by dynamic light scattering（DLS）.The experiment data show that CB[6]beads are localized on 1,4-diaminobutane units in side chains of the copolymers.TGA results show that thermal stability of the copolymer increases with increasing the content of pseudorotaxane unit because of the enhanced rigidity and the bulky steric hindrance of 3VBCB in side chains of PAM3VBCB.DLS data show that the average hydrodynamic radius of copolymer molecules increases with the increase in the copolymer concentration,and both the pH and electrical conductivity of PAM3VBCB solutions demonstrate an acute change with addition of NaOH because of CB[6] dethreading from the side chains of PAM3VBCB.CB[6]threading and dethreading of PAM3VBCB could be controlled by addition of BaCl₂ and Na₂SO₄     

Synthesis and structure characterization of novel calix[4]（aza）crown derivatives

Three novel calix[4](aza)crown deravatives have been synthesized,including a new [2]pseudorotaxane in which calix[4]- azacrown behaves as a stopper,a novel‘tren’type calix[4]azacrown and a novel‘spiro’type calix[4]azacrown containing morpholine unit.The structures of these compounds have been confirmed by NMR and MS.     

Helic[6]arene-Based Chiral Pseudo[1]rotaxanes and [1]Rotaxanes

Chiral pseudo[1]rotaxanes and [1]rotaxanes constructed from macrocyclic arenes still remain a big challenge mainly owing to the lack of such chiral macrocycles. In this work, a new system of chiral pseudo[1]rotaxanes formed by self-inclusion of helic[6]arene containing amide linked with the terminal tertiary amines was first discovered. Based on an atom-economic stopping strategy, a pair of chiral [1]rotaxanes were conveniently obtained in almost quantitative yields by blocking the pseudo[1]rotaxanes with monobenzyl bromide of tetraphenylethene. The structures of pseudo[1]rotaxanes and [1]rotaxanes were characterized by 2D NMR spectra in solution, combined with DFT calculations. The photophysical properties further revealed the efficient chirality transfer of helic[6]arene to the tetraphenylethene moiety, compared to their unthreaded chiral isomers. The discovery of the chiral pseudo[1]rotaxanes allows for a wide and available synthesis of chiral [1]rotaxanes, and also opening a new avenue to the design of chiral supramolecular materials.     

八元瓜环与二(2-亚甲基-1,2,3,4-四氢异喹啉)的自组装模式

以用1,2,3,4-四氢喹啉和二溴乙烷合成的二(2-亚甲基-1,2,3,4-四氢异喹啉)的溴化氢酸盐为客体, 八元瓜环为主体, 利用1H NMR技术, 单晶X射线衍射方法以及理论计算等方法, 考察了两者的自组装模式. 1H NMR分析结果表明, 在溶液状态条件下, 不仅每一个八元瓜环分子同时与两个客体分子的芳环部分相互作用, 而且每一个客体分子两端的芳环部分同时与两个八元瓜环分子相互作用, 从而形成一维的自组装超分子链; 而在固体状态下, 每一个八元瓜环也可同时包结两个客体的芳环部分而形成三元的自组装结构, 但八元瓜环包结两个客体形成一独立的三元自组装结构. 利用晶体结构建立模型的计算结果说明, 模拟溶液状态比固体状态条件下的主客体包结更有利于体系能量的降低, 与主客体在溶液中1H NMR实验结果相符.     

Synthesis and characterization of a new pillar[5]arene-based [1]rotaxane

In this study, we reported the synthesis of three kinds of mono-functional pillar[5]arene derivatives PRI, PRII and R and their structures were studied by 1D and 2D NMR spectra and mass spectra. The 2D NMR spectra including ¹H-¹³C HSQC, ¹H-¹H COSY and NOESY spectra indicated that PRI and PRII are both stable self-included pseudo[1]rotaxanes in CDCl₃. These original structures are promising compounds for the design of pillar[5]-based [1]rotaxane. And the results showed that R could exist stable in CDCl₃ and DMSO because of the coordination of N-H?O hydrogen bonding interaction and C-H?π interaction.     

Interconversion between [5]pseudorotaxane and [3]pseudorotaxane by pasting/detaching two axle molecules

An acceptor-donor-acceptor-type linear molecule 1(2+) containing one electron-rich naphthoxy (NP) unit and two monocharged viologen (MCV) units was synthesized. Through the noncovalent interaction of cucurbit[8]uril (CB[8]) with one NP and one MCV in 1(2+), we first obtained a [2]pseudorotaxane ([1(2+)]?CB[8]), and the excess CB[8] included simultaneously the two bare MCV units of two [2]pseudorotaxanes to form a [5]pseudorotaxane ([1(2+)](2)?[CB[8]](3)). Its transformation to [3]pseudorotaxane was achieved through detaching the two axle molecules in the presence of acid, and then the addition of base may result in a reversible switch between two different pseudorotaxanes. This novel methodology elongating reversibly linear molecules by noncovalent interactions will benefit the development of stimuli-responsive functional molecular devices.     

Toward High‐Generation Rotaxane Dendrimers That Incorporate a Ring Component on Every Branch: Noncovalent Synthesis of a Dendritic [10]Pseudorotaxane with 13 Molecular Components

By taking advantage of the fact that cucurbit[6]uril (CB[6]) forms exceptionally stable host–guest complexes with protonated amines, and that its homologue CB[8] can encapsulate a pair of electron‐rich and electron‐deficient guest molecules to form a stable 1:1:1 complex, we synthesized a novel dendritic [10]pseudorotaxane, or second‐generation rotaxane dendrimer (from a topological point of view), in which 13 molecular components are held together by noncovalent interactions. A triply branched molecule containing an electron‐deficient bipyridinium unit on each branch formed a branched [4]pseudorotaxane with 3 equivalents of CB[8]. Addition of 3 equivalents of 2,6‐dihydroxynaphthalene produced a first‐generation rotaxane dendrimer, which was characterized by NMR spectroscopy and CSI‐MS. The reaction of the branched [4]pseudorotaxane with 3 equivalents of a triply branched molecule that has an electron‐donor unit at one arm and CB[6]‐containing units at the other two gave the dendritic [10]pseudorotaxane, the structure of which was confirmed by NMR spectroscopy, UV/Vis titration experiments, and CSI‐MS.     

Face-selective [2]- and [3]rotaxanes: kinetic control of the threading direction of cyclodextrins

New [2]- and [3]pseudorotaxanes containing alpha-cyclodextrin (alpha-CDs) molecules as rotors and alkyl pyridinium derivatives as axles were prepared by a slipping process. The inclusion behavior of these rotaxanes was investigated by using one- and two-dimensional NMR spectroscopy. The methyl group at the 2-position of the pyridinium moiety at the end of each axle molecule was found to control the rates of threading of the alpha-CD onto the axle molecules. alpha-CD can approach axle molecules from a particular direction to form inclusion complexes. Axle molecules that contain a 2-methylpyridinium moiety at one end and a bulky stopper at the other end can regulate the direction of approach to give a [2]pseudorotaxane such as 2 b-alpha-CD. A [3]pseudorotaxane in which two alpha-CD molecules are arranged facing in the same direction at two stations of the tetracationic axle molecule was also obtained. These face-selective behaviors are dominated by kinetic processes rather than thermodynamic processes.     

A fluorophoric-axle-based, nonfluororescent, metallo anti-[3]pseudorotaxane: recovery of fluorescence by means of an axle substitution reaction

A Cu(2+)-templated, multinuclear, nonfluorescent, anti-[3]pseudorotaxane was synthesized on a fluorophoric axle. The Cu(2+)-templated [3]pseudorotaxane was characterized by the electrospray ionization mass spectroscopy (ESI-MS), UV/Vis and EPR spectroscopy, and single-crystal X-ray data. The ESI-MS showed peaks that support the formation of [3]pseudorotaxane. The UV/Vis spectrum of [3]pseudorotaxane in CH(3)CN showed a characteristic d-d band of a Cu(2+) complex at 650 nm. Further, the X-band in the EPR spectrum of [3]pseudorotaxane suggested a distorted square-pyramidal geometry of Cu(2+). Importantly, formation of the [3]pseudorotaxane was confirmed by the single-crystal X-ray structural analysis, which showed that one fluorophoric axle was threaded into two Cu(2+) macrocyclic wheels (MC-Cu(2+)) with an anti conformation. The UV/Vis and fluorescence titration experiments were carried out to follow the solution-state formation of [3]pseudorotaxane by MC-Cu(2+) and fluorophoric axle in CH(3)CN. In both studies, the sigmoidal curve fit supported the formation of 1:2 complex of the fluorophoric axle and MC-Cu(2+) complex. Secondly, the release of the fluorophoric axle from the nonfluorescent [3]pseudorotaxane through the formation of a [2]pseudorotaxane was demonstrated by titrating a solution of the [3]pseudorotaxane with a stronger bidentate chelating ligand, such as 1,10-phenanthroline (Phen). Substitution of the fluorophoric axle from the [3]pseudorotaxane with about 100% efficiency was achieved by the addition of approximately two equivalents of Phen, and the formation of a Phen-threaded [2]pseudorotaxane was established by ESI-MS of the resulting solution and a single-crystal X-ray study. Axle substitution was also confirmed by a fluorescence titration experiment, which showed a step-wise recovery of the fluorescence intensity of the fluorophoric axle. The association constants for the formation of the [3]- and [2]pseudrotaxanes were calculated from the fluorescence and UV/Vis data. In addition, 2,2'-bipyridine (BPy), which is a relatively weaker bidendate chelating ligand compared to Phen, showed an inefficient and incomplete axle substitution of the [3]pseudorotaxane, although BPy previously showed the formation of [2]pseudrotaxane with the MC-Cu(2+) wheel in solution and ESI-MS studies. In this context, the formation of a BPy-threaded [2]pseudrotaxane was further established by single-crystal X-ray diffraction study.     

Reversible 2D pseudopolyrotaxanes based on cyclodextrins and cucurbit[6]uril

In this paper, a pseudorotaxane (2) was synthesized by reaction of cucurbit [6]uril with 6-[(6-aminohexyl)amino]-6-deoxy-beta-cyclodextrin chloride. Subsequently, pseudorotaxanes 2 were further assembled to form a 2D pseudopolyrotaxane (3) through an alpha,omega-PPG2000 diamino polymer threading the cavities of cyclodextrins in 2, and the resulting pseudopolyrotaxane was comprehensively characterized by FT-IR, NMR, TG-DTA, elemental analysis, and transmission electron microscopy. Significantly, the 2D pseudopolyrotaxane can turn into a main-chain pseudopolyrotaxane in the presence of base, and then the addition of alpha-cyclodextrins may result in a reversible switch between two different 2D pseudopolyrotaxanes.     

Two [2]pseudorotaxane-like complexes and their corresponding [2]rotaxanes stabilized via interactions on opposite ends of the same macrocycle

A multiple-use macrocycle recognizes dibenzylammonium ions and 2,6-lutidine derivatives, each in a [2]pseudorotaxane-like manner, through interactions with its diethylene glycol (hydrogen bonding) and 2,6-pyridinedicarboxamide (Pd²⁺ chelation) spacers, respectively. We characterized these complexes in the solid state (X-ray crystallography) and in solution (¹H NMR spectroscopy). The synthesis of two corresponding [2]rotaxanes confirmed that these recognition systems possess [2]pseudorotaxane geometries in solution.     

Design and synthesis of self-included pillar[5]arene-based bis-[1]rotaxanes

Two strategies for the design of new pillar[5]arene-based mechanically self-interlocked molecules (MSMs) are reported here. The first strategy is based on the construction of an intermediate pseudo[1]rotaxane followed by the desired bis-[1]rotaxane. The other one is based on the construction of the desired bis-[1]-rotaxane directly via a condensation reaction through host-guest interactions between a mono-functionalized pillar[5]arene and the axle. This compound has interesting self-assembly properties in methanol and some extended applications of this compound will be reported in the near future.