Selective complexation of n-alkanes with pillar[5]arene dimers in organic media

A pillar[5]arene dimer was synthesized by linking a mono-hydroxylated pillar[5]arene with 1,4-bis(bromomethyl)benzene. The pillar[5]arene dimer formed stronger complexes with n-alkanes than did a monomeric pillar[5]arene.     

Photoreversible transformation between seconds and hours time-scales: threading of pillar[5]arene onto the azobenzene-end of a viologen derivative

Photoswitching of the transformation between seconds and hours time-scales is demonstrated using the threading of per-hydroxylated pillar[5]arene onto the azobenzene-end of a viologen derivative. When the azobenzene moiety was in the trans form, the threading of per-hydroxylated pillar[5]arene quickly took place at 25 °C and could not be monitored directly. The exchange rate (k) and half-life time (t(1/2)) examined by 2D EXSY NMR spectroscopy were found to be 0.209 ± 0.013 s(-1) and 3.33 ± 0.21 s, respectively. In contrast, the cis form of the azobenzene moiety required very long time (k = 2.14 ± 0.27 × 10(-5) s(-1), t(1/2) = 9.13 ± 1.2 h) to thread per-hydroxylated pillar[5]arene at 25 °C. Photoisomerization from the trans to the cis form generated the following increment of free energy of activation at 25 °C: ΔG(in)(?) (cis form) - ΔG(in)(?) (trans form) = 22.8 ± 0.24 kJ mol(-1), which led to the time-scale transformation. The tuning of the threading was also accomplished by heating/cooling: the rate constants increased on heating and decreased on cooling.     

Host–Guest Complexation Using Pillar[5]arene Crystals: Crystal-Structure Dependent Uptake,Release, and Molecular Dynamics of an Alkane Guest

Host–guest complexation has been mainly investigated in solution, and it is unclear how guest molecules access the assembled structures of host and dynamics of guest molecules in the crystal state. In this study, we studied the uptake, release, and molecular dynamics of n-hexane vapor in the crystal state of pillar[5]arenes bearing different substituents. Pillar[5]arene bearing 10 ethyl groups yielded a crystal structure of herringbone-type 1:1 complexes with n-hexane, whereas pillar[5]arene with 10 allyl groups formed 1:1 complexes featuring a one-dimensional (1D) channel structure. For pillar[5]arene bearing 10 benzyl groups, one molecule of n-hexane was located in the cavity of pillar[5]arene, and another n-hexane molecule was located outside of the cavity between two pillar[5]arenes. The substituent-dependent differences in molecular arrangement influenced the uptake, release, and molecular dynamics of the n-hexane guest. The substituent effects were not observed in host–guest chemistry in solution, and these features are unique for the crystal state host–guest chemistry of pillar[5]arenes.     

Dual Electroactivity in a Covalent Organic Network with Mechanically Interlocked Pillar[5]arenes

The synthesis and characterization of a polyrotaxanated covalent organic network (CON) based on the association between the viologen and pillar[5]arene (P[5]OH) units are reported. The mechanical bond allows for the irreversible insertion of n-type redox centers (P[5]OH macrocycles) within a pristine structure based on p-type viologen redox centers. Both redox units are active on a narrow potential range and, in water, the presence of P[5]OH greatly increases the electroactivity of the material.     

基于柱[5]芳烃主客体包结构筑分子响应型超分子水凝胶

主客体相互作用是在水溶液中与大环主体分子形成稳定的包结物的理想驱动力.以功能化的苯并咪唑衍生物为客体(M),水溶性柱[5]芳烃为主体构建了一种分子响应型超分子水凝胶.通过1H NMR, 2D NOESY和扫描电子显微镜(SEM)研究了水凝胶的成凝胶机理.有趣的是,主客体包结作用、柱[5]芳烃间有序的"外腔"π-π相互作用和分层堆积对于获得超分子水凝胶是必不可少的,非共价键相互作用的动态可逆性使凝胶体系对温度变化/化学刺激产生响应.此外,加入竞争性客体己二腈(ADN)/百草枯(PQ)后,柱[5]芳烃基水凝胶可转化为溶胶.因此,该超分子水凝胶可以选择性识别有机分子.     

Water-soluble pillar[4]arene[1]quinone: Synthesis,host-guest property and application in the fluorescence turn-on sensing of ethylenediamine in aqueous solution,organic solvent and air

Water-soluble pillar[5]arenes are a class of typical macrocycles and have aroused tremendous attention for its easy to modify, abundant host-guest properties and extensive applications. However, up to now, all the reported water-soluble pillar[5]arenes acted as the host molecules, whereas they failed to be postsynthetically modified, which seriously impeded the development of the pillar[5]arene-based supramolecular chemistry. In this work, a new water-soluble pillar[5]arene, pillar[4]arene[1]quinone, was designed and synthsized with eight quaternary ammonium groups as well as a quinone units. Such a new water-soluble pillar[4]arene[1]quinone was capable of forming 1:1 stable complex with sodium 1-octanesulfonate in aqueous solution. Since the 1,4-quinone unit of WP[4]Q[1] could react with ethylenediamine (EDA) to form a conjugated quinoxaline structure, so pillar[4]arene[1]quinone could apply to the facile fluorescence turn-on sensing of EDA in aqueous solution, organic solvent and air.     

Synthesis and X-ray crystal structure of a difunctionalized pillar[5]arene at A1/B2 positions by in situ cyclization and deprotection

The reaction of 1,4-dimethoxybenzene and paraformaldehyde using AlBr(3) yields multiple-deprotected pillar[5]arenes. A1/B2 di-deprotected pillar[5]arene can be isolated by silica gel chromatography and washing procedures. The X-ray structure and polymerization of the A1/B2 di-deprotected pillar[5]arene are reported.     

Construction of [1]rotaxanes with pillar[5]arene as the wheel and terpyridine as the stopper

The condensation reaction ofω-aminoalkyleneamide-functionalized pillar[5]arenes with 2-(4-([2,2’:6’,2〃-terpyridin]-4’-yl)phenoxy)acetic acid or 4-(4-([2,2’:6’,2"-terpyridin]-4’-yl)phenoxy)butanoic acid in dry chloroform at room temperature under the catalysis of HOBT/EDCl resulted in novel pillar[5]arene diamido-bridged terpyridine derivatives.~1 H NMR and 2 D NOESY spectra clearly indicated that the interesting[1]rotaxanes were formed by longer alkylene such as propylene,butylene and hexylenediamido chains threading into the cavity of the pillar[5]arene and with larger terpyridine acting as the stopper.However,the shorter ethylenediamido chain only exists outer of cavity of pillar[5]arene and the molecule exist on free form.     

Monofunctionalized pillar[5]arene as a host for alkanediamines

Alkanediamines serve as neutral guests for the recently discovered host pillar[5]arene. The proposed [2]pseudorotaxane nature of the superstructure of the 1:1 host-guest complexes is supported by the template-directed synthesis of a related [2]rotaxane. A synthetic route to monofunctional pillar[5]arenes has also been developed, allowing for the creation of a fluorescent sensor for alkylamine binding. The precursors to this host could act as starting points for a large library of monofunctional pillar[5]arene macrocycles.     

Construction of π‐Surface‐Metalated Pillar[5]arenes which Bind Anions via Anion–π Interactions

By simple ligand exchange of the cationic transition‐metal complexes [(Cp*)M(acetone)₃](OTf)₂ (Cp*=pentamethylcyclopentadienyl and M=Ir or Rh) with pillar[5]arene, mono‐ and polynuclear pillar[5]arenes, a new class of metalated host molecules, is prepared. Single‐crystal X‐ray analysis shows that the charged transition‐metal cations are directly bound to the outer π‐surface of aromatic rings of pillar[5]arene. One of the triflate anions is deeply embedded within the cavity of the trinuclear pillar[5]arenes, which is different to the host–guest behavior of most pillar[5]arenes. DFT calculation of the electrostatic potential revealed that the metalated pillar[5]arenes featured an electron‐deficient cavity due to the presence of the electron‐withdrawing transition metals, thus allowing encapsulation of electron‐rich guests mainly driven by anion–π interactions.     

Monofunctionalized pillar[5]arenes: synthesis and supramolecular structure

The first synthesis of a monohydroxy pillar[5]arene has been carried out, by controlling the de-O-methylation of per-methylated pillar[5]arene. Using monohydroxy pillar[5]arene as an intermediate, mono-guest-functionalized pillar[5]arene was prepared. It formed a self-inclusion complex in CDCl(3) whereas in acetone-d(6) dethreading of the guest moiety took place.     

Separation of Linear and Branched Alkanes Using Host–Guest Complexation of Cyclic and Branched Alkane Vapors by Crystal State Pillar[6]arene

Activated crystals of pillar[6]arene produced by removing the solvent upon heating were able to take up branched and cyclic alkane vapors as a consequence of their gate‐opening behavior. The uptake of branched and cyclic alkane vapors by the activated crystals of pillar[6]arene induced a crystal transformation to form one‐dimensional channel structures. However, the activated crystals of pillar[6]arene hardly took up linear alkane vapors because the cavity size of pillar[6]arene is too large to form stable complexes with linear alkanes. This shape‐selective uptake behavior of pillar[6]arene was further utilized for improving the research octane number of an alkane mixture of isooctane and n‐heptane: interestingly, the research octane number was dramatically improved from a low research octane number (17 %) to a high research octane number (>99 %) using the activated crystals of pillar[6]arene.     

A self-complexing and self-assembling pillar[5]arene

A monofunctionalised pillar[5]arene derivative carrying a viologen side chain which exhibits self-complexation in dilute dichloromethane solutions forms supramolecular daisy chain polymers and eventually organogels as its concentration is increased three-fold over the range from 0.1 to 100 mM.     

Piling Up Pillar[5]arenes To Self‐Assemble Nanotubes

New liquid‐crystalline pillar[5]arene derivatives have been prepared by grafting first‐generation Percec‐type poly(benzylether) dendrons onto the macrocyclic scaffold. The molecules adopt a disc‐shaped structure perfectly suited for self‐organization into a columnar liquid‐crystalline phase. In this way, the pillar[5]arene cores are piled up, thus forming a nanotubular wire encased within a shell of peripheral dendrons. The capability of pillar[5]arenes to form inclusion complexes has been also exploited. Specifically, detailed binding studies have been carried out in solution with 1,6‐dicyanohexane as the guest. Inclusion complexes have also been prepared in the solid state. Supramolecular organization into the Col_h mesophase has been deduced from X‐ray diffraction data and found to be similar to that observed within the crystal lattice of a model inclusion complex prepared from 1,4‐dimethoxypillar[5]arene and 1,6‐dicyanohexane.     

Synthesis and characterization of bis-[1]rotaxanes via salen-bridged bis-pillar[5]arenes

The series of salen-bridged bis-pillar[1]arenes were conveniently prepared by condensation reaction of5,5'-methylenebis(2-hydroxybenzalde hyde)or 5,5'-(propane-2,2-diyl)bis(2-hydroxybenzaldehyde)with mono-amido-functionalized pillar[5]arenes containing different terminal aminoalkyl groups in refluxing ethanol.The^1H NMR and 2D-NOESY spectra indicated that the salen-bridged bis-pillar[5]arenes with longer allcylene linker(n=3,4,6)formed the fascinating bis-[1]rotaxanes,while the salenbridged bis-pillar[5]arenes with short hydrazine and ethylenediamino linker(n=0,2)predominately existed in free form.The single crystal structure of the bis-pillar[5]are ne ambiguously indicated that two propylenediamino linker inserted in to two cavities of pillar[5]arene to form a novel bis-[1]rotaxanes.     

Synthesis of pillar[5]arene dimers and their cooperative binding toward some neutral guests

Three pillar[5]arene dimers, bridged by a flexible aliphatic chain (H1) or a relatively rigid phenylene unit (H2 and H3), were synthesized, with the possible synthetic strategies being discussed. The dimers could significantly enhance the binding affinities toward neutral model substrates in comparison with monomeric 1,4-dimethoxypillar[5]arene (H4) through the cooperative binding of two pillar[5]arene moieties. The molecular binding ability and selectivity are discussed from the viewpoints of the size/shape-fit concept and multiple recognition mechanism.     

Complexation of neutral 1,4-dihalobutanes with simple pillar[5]arenes that is dominated by dispersion forces

The complexation of neutral 1,4-dihalobutanes with simple pillar[5]arenes was investigated. The results indicate the formation of interpenetrated complexes, where the dispersive interactions dominate the complex stability. Typically, 1,4-diiodobutane displays the strongest binding strength with ethylpillar[5]arene [K(a) = (1.0 ± 0.1) × 10(4) M(-1)], up to 120 fold as compared with 1,4-difluorobutane.     

Enhanced head-to-head photodimers in the photocyclodimerization of anthracenecarboxylic acid with a cationic pillar[6]arene

The complexation behaviors of anthracenecarboxylic acid and water-soluble cationic pillararenes have been investigated by ¹H NMR, UV-vis and ITC methods. The cationic pillar[6]arene was found to stepwise form 1:1 and 1:2 complexes, having a large K₁ and a relatively small K₂ values. Photocyclodimerization of AC within the pillar[6]arene improved the yield of the head-to-head photodimers. Up to 4.97 HH/HT ratio has been reached by optimizing the reaction conditions.     

Pillar[5]arene-based [3]rotaxanes: Convenient construction via multicomponent reaction and pH responsive self-assembly in water

Four pillar[5]arene based [3]rotaxanes(1-4) involving two 1,4-diethoxypillar[5]arene(DEP5) rings and a dumbbell-shaped component were successfully synthesized.The dumbbell-shape molecules contain one longer bridge,two triazole sites and two multicomponent stoppers.After threading DEP5 rings with linear guests(G1-G4) which contain two benzaldehyde units,the base catalyzed three-component reaction of dimedone,malononitrile and benzaldehyde was performed to construct the stoppers and connected the pseudorotaxanes with stoppers to generate 1-4.The structures of [3]rotaxanes and their self-assembly behaviors were characterized by ~1 H NMR,~(13)C NMR,NOESY,HR-ESI-MS,DLS and TEM technologies.We hope that pillar[5]arene based [3]rotaxanes may have potential applications in drug delivery systems and molecular devices.     

Synthesis of pillar[5]arenes with a PH-containing fragment

The reactions of phosphorus(III) chloride and 2-chloro-1,3,2-dioxaphospholane with monohydroxypillar[5]arene afforded for the first time the corresponding PH-phosphonates. It was found that the newly formed P–O(Ar) bond is characterized by considerably reduced reactivity, which was rationalized by essential shielding of the phosphorus atom by the pillar[5]arene macrocycle. The pillar[5]arene scaffold stabilizes the highly reactive P^III–Cl fragment, so that the formation of macrocyclic dichlorophosphite can be detected under normal conditions.