A cylinder-shaped macrocycle formed via Friedel-Crafts reaction

By performing Friedel-Crafts reaction with a mixture of 1,3,5-tri(furan-2-yl) benzene (TFB) and acetone, we successfully synthesized a cylinder-shaped macrocycle. The isolated yield of 36% is relatively high, considering that twelve C-C bonds are formed simultaneously. The structure of this macrocycle was confirmed using 1H NMR spectroscopy, mass spectrometry and X-ray crystallography. This macrocycle is able to recognize a variety of cationic guests driven by cation-dipole and CH-π interactions.

Grafting Dendrons onto Pillar[5]Arene Scaffolds

With their ten peripheral substituents, pillar[5]arenes are attractive compact scaffolds for the construction of nanomaterials with a controlled number of functional groups distributed around the macrocyclic core. This review paper is focused on the functionalization of pillar[5]arene derivatives with small dendrons to generate dendrimer-like nanomaterials and bioactive compounds. Examples include non-viral gene vectors, bioactive glycoclusters, and liquid-crystalline materials.

Thermally Responsive Poly(ethylene oxide)-Based Polyrotaxanes Bearing Hydrogen-Bonding Pillar[5]arene Rings*

Poly(ethylene oxide)s (PEOs) are useful polymers with good water solubility, biological compatibility, and commercial availability. PEOs with various end groups were threaded into pillar[5]arene rings in a mixture of water and methanol to afford pseudopolyrotaxanes. Corresponding polyrotaxanes were also constructed by capping COOH-terminated pseudopolyrotaxanes with bulky amines, in which multiple hydrogen bonds involving the pillar[5]arene OH groups were critically important to prevent dethreading. The number of threaded ring components could be rationally controlled in these materials, providing a simple and versatile method to tune the mechanical and thermal properties. Specifically, a polyrotaxane with a high-molecular-weight axle became elastic upon heating above the melting point of PEOs and exhibited temperature-dependent shape memory property because of the topological confinement and crosslinked hydrogen bonds.

Effective enantiomeric identification of aromatic amines by tyrosine-modified pillar[5]arenes as chiral NMR solvating agents

Two novel tyrosine-modified pillar[5]arenes have been synthesized and applied as chiral NMR solvating agents to establish an efficient ¹H NMR method for enantioselective recognition and configuration assignment towards α-aromatic ethylamines.

3,6-Fluoren[5]arenes: synthesis, structure and complexation with fullerenes C60 and C70

3,6-Fluoren[5]arenes with big and rich-electron cavities were conveniently synthesized, which could form stable 1 : 1 complexes with fullerenes in solution.

Diverse binding of cationic guests by highly substituted [3 + 3] Schiff-base macrocycles

Schiff-base macrocycles interact with ammonium-based guests to form threaded pseudorotaxanes or unthreaded external complexes, and tautomerize in the process.

Stereoselectivity in dehydrative cyclic trimerization of substituted 4-alkylaminobenzoic acids

Cyclic trimerization of two 4-alkylaminobenzoic acids was performed to investigate the stereochemistry.

Pillar[6]quinone: facile synthesis, crystal structures and electrochemical properties

A novel electron-deficient macrocycle, pillar[6]quinone (P[Q]6), has been synthesized for the first time by both chemical and electrochemical oxidation of pillar[6]arene, showing clear hexagonal columnar stacking in the solid state. Cathodic voltammetric studies of P[Q]6 revealed that three electrons are injected first, followed by stepwise one-electron reductions.

Stimuli-Responsive Internally Ion-Paired Supramolecular Polymer Based on a Bis-pillar[5]arene Dicarboxylic Acid Monomer

A novel bis-pillar[5]arene dicarboxylic acid self-assembles in the presence of 1,12-diaminododecane to yield overall neutral, internally ion-paired supramolecular polymers. Their aggregation, binding mode, and morphology can be tuned by external stimuli such as solvent polarity, concentration, and base treatment.

Enantioselective Synthesis of Polycyclic Aromatic Hydrocarbon (PAH)-Based Planar Chiral Bent Cyclophanes by Rhodium-Catalyzed [2+2+2] Cycloaddition

The enantioselective synthesis of polycyclic aromatic hydrocarbon (PAH)-based planar chiral cyclophanes was achieved for the first time by the rhodium-catalyzed intramolecular regio- and enantioselective [2+2+2] cycloaddition of tethered diyne-benzofulvenes followed by stepwise oxidative transformations. The thus synthesized planar chiral bent cyclophanes, that possess bent p-terphenyl- and 9-fluorenone-cores, were converted to 9-fluorenol-based ones with excellent ee values of >99 % by diastereoselective 1,2-reduction. These 9-fluorenol-based cyclophanes exhibited high fluorescence quantum yields, which were significantly higher than that of an acyclic reference molecule (78-82 % vs. 48 %). The bending effect on the chiroptical property was also examined, which revealed that the anisotropy factors (g_abs values) for electronic circular dichroism (ECD) of these 9-fluorenol-based planar chiral bent cyclophanes increase as the tether length becomes shorter.

Visualization and quantitation of electronic communication pathways in a series of redox-active pillar[6]arene-based macrocycles

While oxidized pillar[5]arenes with 1-5 benzoquinone units are known, very few examples of oxidized pillar[6]arenes have been reported. We describe here the synthesis, characterization and electrochemical behavior of a series of macrocyclic hosts prepared by the stepwise oxidation of 1,4-diethoxypillar[6]arene, resulting in high-yield and high-purity isolation of two constitutional isomers for each macrocycle, in which two, three or four 1,4-diethoxybenzene units are replaced by benzoquinone residues. A careful structural comparison with their counterparts in the pillar[5]arene framework indicates that the geometries of the macrocycles are better described as non-Euclidean hyperbolic hexagons and elliptic pentagons, respectively. A comprehensive computational study to determine anisotropic induced current density (ACID) allows us to visualize and quantify through-space and through-bond communication pathways along the macrocyclic belt. Experimental and simulated voltammetric data, as well as UV-vis spectra, of the new macrocycles afford insights into the various electronic communication pathways in these compounds.

Catechol[4]arene: The Missing Chiral Member of the Calix[4]arene Family

A missing, inherently chiral member of the calix[4]arene family denoted "catechol[4]arene" was synthesized. Its properties were studied and compared to the ones of its close relatives resorcin[4]arene and pyrogallol[4]arene. This novel supramolecular host exhibits binding capabilities that are superior to its sister molecules in polar media. The enantiomerically pure forms of the macrocycle display modest recognition of chiral ammonium salts.

Aliphatic polyketones as classic yet new molecular ropes for structural diversity in organic synthesis

Polyketone compounds play an important role in organic chemistry as a prominent source of reactivity and functionality. Their chemical properties vary widely depending on the ketone sequence in carbon chains. Although vicinal and β-polyketones have been used for more than 150 years, the recent development of new ketone sequences composed of alternating 1,3- and 1,4-diketones has demonstrated the further potential of polyketones as structurally flexible molecular ropes capable of derivatization to π-conjugated chromophores and molecular assemblies. In this Feature Article, we review the synthetic strategies and reactivities of polyketones with respect to their ketone sequence. Furthermore, recent research on polyketones with hybrid ketone sequences is also discussed, focussing on their structural diversity in chemical transformations including intramolecular cyclization and stereoselective oxidation.

Facile One-Step Electrodeposition Preparation of Cationic Pillar[6]arene-Modified Graphene Films on Glassy Carbon Electrodes for Enhanced Electrochemical Performance

In the present work, we have developed a facile one-step route for preparing electrochemically reduced graphene oxide-cationic pillar[6]arene (ErGO-CP6) nanocomposite films on glassy carbon electrodes (GCEs) directly from graphene oxide-cationic pillar[6]arene (GO-CP6) colloidal solution by using a pulsed electrodeposition technique. The electrocatalytic activity of ErGO-CP6 was examined by studying the oxidations of five purine bases [adenine (A), guanine (G), xanthine (X), hypoxanthine (HX), and uric acid (UA)]. It enhanced the oxidation currents of A, G, X, HX, and UA when compared to unmodified ErGO films and bare GCE, which is considered to be the synergetic effects of the graphene (excellent electrical properties and large surface area) and CP6 molecules (high inclusion complexation and enrichment capability).

Nanochannel sensor for sensitive and selective adamantanamine detection based on host-guest competition

The abuse of adamantanamine (ADA) and its derivatives as veterinary drugs in the poultry industry could cause severe health problems for humans. It is of great need to develop a rapid, cheap and ultrasensitive method for ADA detection. In this study, a sensitive conical nanochannel sensor was established for the rapid quantitative detection of ADA with the distinctive design of the host-guest competition. The sensor was constructed by functionalizing the nanochannel surface with p-toluidine and was then assembled with Cucurbit [7]uril (CB [7]). When ADA is added, it could occupy the cavity of CB [7] due to the host-guest competition and makes CB [7] to release from the CB [7]-p-toluidine complex, resulting in a distinct change of hydrophobicity of the nanochannel, which could be determined by the ionic current. Under the optimal conditions, the strategy permitted sensitive detection of ADA in a linear range of 10-1000 nM. The nanochannel based ADA sensing platform showed both high sensitivity and excellent reproducibility and the limit of detection was 4.54 nM. For the first time, the rapid and sensitive recognition of an illegal medicine was realized based on the host-guest competition method with the nanochannel system and the principle and feasibility of this method were described at length. This strategy provides a simple, reliable, and effective way to apply host-guest system in the development of nanochannel sensor for small-molecule drug detection.

Supramolecular-Macrocycle-Based Crystalline Organic Materials

Supramolecular macrocycles are well known as guest receptors in supramolecular chemistry, especially host-guest chemistry. In addition to their wide applications in host-guest chemistry and related areas, macrocycles have also been employed to construct crystalline organic materials (COMs) owing to their particular structures that combine both rigidity and adaptivity. There are two main types of supramolecular-macrocycle-based COMs: those constructed from macrocycles themselves and those prepared from macrocycles with other organic linkers. This review summarizes recent developments in supramolecular-macrocycle-based COMs, which are categorized by various types of macrocycles, including cyclodextrins, calixarenes, resorcinarenes, pyrogalloarenes, cucurbiturils, pillararenes, and others. Effort is made to focus on the structures of supramolecular-macrocycle-based COMs and their structure-function relationships. In addition, the application of supramolecular-macrocycle-based COMs in gas storage or separation, molecular separation, solid-state electrolytes, proton conduction, iodine capture, water or environmental treatment, etc., are also presented. Finally, perspectives and future challenges in the field of supramolecular-macrocycle-based COMs are discussed.

Diversity Oriented Preparation of Pillar[5]arene-Containing [2]Rotaxanes by a Stopper Exchange Strategy

Rotaxane building blocks bearing 3,5-bis(trifluoromethyl) benzenesulfonate (BTBS) stoppers have been efficiently prepared from a pillar[5]arene derivative, 3,5-bis(trifluoromethyl) benzenesulfonyl chloride (BTBSCl) and different diols, namely 1,10-decanediol and 1,12-dodecanediol. The BTBS moieties of these compounds are good leaving groups and stopper exchange reactions could be achieved by treatment with different nucleophiles thus affording rotaxanes with ester, thioether or ether stoppers.

Vapochromic crystals: understanding vapochromism from the perspective of crystal engineering

Vapochromic materials, which undergo colour and/or emission changes upon exposure to certain vapours or gases, have received increasing attention recently because of their wide range of applications in, e.g., chemical sensors, light-emitting diodes, and environmental monitors. Vapochromic crystals, as a specific kind of vapochromic materials, can be investigated from the perspective of crystal engineering to understand the mechanism of vapochromism. Moreover, understanding the vapochromism mechanism will be beneficial to design and prepare task-specific vapochromic crystals as one kind of low-cost 'electronic nose' to detect toxic gases or volatile organic compounds. This review provides important information in a broad scientific context to develop new vapochromic materials, which covers organometallic or coordination complexes and organic crystals, as well as the different mechanisms of the related vapochromic behaviour. In addition, recent examples of supramolecular vapochromic crystals and metal-organic-framework (MOFs) vapochromic crystals are introduced.

Supramolecular metallacyclic hydrogels with tunable strength switched by host–guest interactions

A new family of supramolecular hydrogels with tunable strength was successfully constructed through a combination of coordination-driven self-assembly, post-assembly polymerization and host–guest interactions.

Coordination-driven self-assembly of discrete supramolecular double-metallacycles

This review comprehensively summarizes the recent advances in the coordination-driven self-assembly of discrete supramolecular double-metallacycles.

Preparation of a mechanically interlocked polymer from a linear supramolecular polymer

We transformed a linear supramolecular polymer into a mechanically interlocked polymer by photoisomerization.

A reversible, switchable pH-driven quaternary ammonium pillar[5]arene nanogate for mesoporous silica nanoparticles

Here we describe the assembly and pH-driven operation of two nanocarriers based on non-functionalized (MCM-41) and carboxylate-functionalized (MCM-41-COOH) containers loaded with the anticancer drug doxorubicin (DOX) and capped by quaternary ammonium pillar[5]arene (P[5]A) nanogates. MCM-41 and MCM-41-COOH containers were synthesized and transmission and scanning electron microscopies showed nanoparticles with spherical morphology and dimensions of 85 ± 13 nm. The nanochannels of MCM-41 loaded with DOX were gated through the electrostatic interactions between P[5]A and the silanolate groups formed at the silica-water interface, yielding the MCM-41-DOX-P[5]A nanocarrier. The second nanocarrier was gated through the electrostatic interactions between the carboxylate groups mounted on the surface of MCM-41 and P[5]A, resulting in the MCM-41-COO-DOX-P[5]A nanocarrier. The DOX release profiles from both nanocarriers were investigated by UV-vis spectroscopy at different pH values (2.0, 5.5 and 7.4) and also in the presence of ions, such as citrate^3- (19 mmol L^-1) and Zn²⁺ (1.2 and 50 mmol L^-1) at 37 °C. MCM-41-COO-DOX-P[5]A can be turned on and off eight times through the formation and breaking of electrostatic interactions. In vitro studies show that MCM-41-COO-DOX-P[5]A can penetrate and release DOX in the nucleus of human breast adenocarcinoma MCF-7 cancer cells leading to a pronounced cytotoxic effect. Therefore, the fabricated nanocarrier based on a water-soluble cationic pillar[5]arene nanogate, which is reversibly opened and closed by electrostatic interactions, can be considered as a promising drug transport and delivery technique for future cancer therapy.

Modulation of Multiple Signaling Pathways of the Plant-Derived Natural Products in Cancer

Natural compounds are highly effective anticancer chemotherapeutic agents, and the targets of plant-derived anticancer agents have been widely reported. In this review, we focus on the main signaling pathways of apoptosis, proliferation, invasion, and metastasis that are regulated by polyphenols, alkaloids, saponins, and polysaccharides. Alkaloids primarily affect apoptosis-related pathways, while polysaccharides primarily target pathways related to proliferation, invasion, and metastasis. Other compounds, such as flavonoids and saponins, affect all of these aspects. The association between compound structures and signaling pathways may play a critical role in drug discovery.

Colorimetric sensing towards spermine based on supramolecular pillar[5]arene reduced and stabilized gold nanoparticles

We develop a novel and fast colorimetric sensing platform for spermine (Sp) by using macrocyclic host hydroxyl pillar[5]arene (P5) molecule reduced and stabilized Au nanoparticles via the supramolecular host-guest recognition interaction between P5 and Sp. The P5-modified Au nanoparticles (P5-Au) are easily obtained by redox reaction between hydroxyl groups in P5 and Au³⁺ in HAuCl₄, where hydroxyl groups are oxidized to carboxyl groups and Au³⁺ is reduced to Au⁰⁺ under alkali catalysis at room temperature without NaBH₄ or other reducing agent. A uniform diameter of about 5.0 nm and wine red color P5-Au nanoparticles can be synthesized by this green and rapid method. The mechanism of redox reaction between P5 and HAuCl₄ is studied by the XPS and ¹³C NMR, and the P5-Au is characterized by the TEM, XRD and XPS.

Pillar[5]arene Based [1]rotaxane Systems With Redox-Responsive Host-Guest Property: Design, Synthesis and the Key Role of Chain Length

Pillar[n]arenes are a new type of macrocyclic compounds, which were first reported in 2008 by Ogoshi. They not only have cylindrical, symmetrical, and rigid structures, but also have many advantages, including easy functionalization and rich host-guest properties. On the other hand, mechanically interlocked molecules (MIMs) exist extensively in nature which have been artificially synthesized and widely applied in the fields of nanotechnology and biology. Although pillar[5]arene-based MIMs have been investigated much over recent years, pillar[5]arene-based [1]rotaxanes are very limited. In this report, we synthesized a series of amide-linked pillar[5]arene-based [1]rotaxanes with ferrocene unit as the stopper. Under the catalysis of HOBT/EDCL, the mono-amido-functionalized pillar[5]arenes were amidated with ferrocene carboxylic acid to constructed ferrocene-based [1]rotaxanes, respectively. The structure of the [1]rotaxanes were characterized by ¹H NMR, ¹³C NMR, 2D NMR, mass spectroscopy, and single-crystal X-ray structural determination. In the experiment, the monofunctionalized pillar[5]arene was synthesized with a self-inclusion property, which allows for forming a pseudo-rotaxane. The key role is the length of the imine chain in this process. The formation of a rotaxane was realized through amidation of ferrocene dicarboxylic acid, which acted as a plug. In addition, due to the ferrocene units, the pillar[5]arene-based [1]rotaxanes perform electrochemically reversible property. Based on this nature, we hope these pillar[5]arene-based [1]rotaxanes can be applied in battery devices in the future.

Host-Guest Chemistry in Supramolecular Theranostics

Macrocyclic hosts, such as cyclodextrins, calixarenes, cucurbiturils, and pillararenes, exhibit unparalleled advantages in disease diagnosis and therapy over the past years by fully taking advantage of their host-guest molecular recognitions. The dynamic nature of the non-covalent interactions and selective host-guest complexation endow the resultant nanomaterials with intriguing properties, holding promising potentials in theranostic fields. Interestingly, the differences in microenvironment between the abnormal and normal cells/tissues can be employed as the stimuli to modulate the host-guest interactions, realizing the purpose of precise diagnosis and specific delivery of drugs to lesion sites. In this review, we summarize the progress of supramolecular theranostics on the basis of host-guest chemistry benefiting from their fantastic topological structures and outstanding supramolecular chemistry. These state-of-the-art examples provide new methodologies to overcome the obstacles faced by the traditional theranostic systems, promoting their clinical translations.