Polycatenanes

Adhesive supramolecular polymeric materials constructed from macrocycle-based host–guest interactions

This review describes recent progress in adhesive supramolecular polymeric materials constructed from macrocycle-based host–guest interactions.

Differences in solubilities, crystal structures, NMR spectra and fluorescence emissions induced by potassium cation/benzo-21-crown-7 molecular recognition

Changes of the fundamental properties of host–guest pairs induced by potassium cation complexation were investigated.

Fluorescent supramolecular polymers with aggregation induced emission properties

This review summarizes the recent developments in AIE fluorescent supramolecular polymeric materials based on different types of intermolecular noncovalent interactions, and their wide ranging applications as chemical sensors, organic electronic materials, bio-imaging agents and so on.

Recent developments in the construction of metallacycle/metallacage-cored supramolecular polymers via hierarchical self-assembly

Supramolecular polymers have received considerable attention during the last few decades due to their scientific value in polymer chemistry and profound implications for future developments of advanced materials. Discrete supramolecular coordination complexes (SCCs) with well-defined size, shape, and geometry have been widely employed to construct hierarchical systems by coordination-driven self-assembly with the spontaneous formation of metal-ligand bonds, which results in the formation of well-defined two-dimensional (2D) metallacycles or three-dimensional (3D) metallacages with high functionalities. The incorporation of discrete SCCs into supramolecular polymers by the orthogonal combination of metal-ligand coordination and other noncovalent interactions or covalent bonding could further facilitate the construction of novel supramolecular polymers with hierarchical architectures and multiple functions including controllable uptake and release of guest molecules, providing a flexible platform for the development of smart materials. In this review, the recent progress in metallacycle/metallacage-cored supramolecular polymers that were constructed by the combination of metal-ligand interactions and other orthogonal interactions (including hydrophobic or hydrophilic interactions, hydrogen bonding, van der Waals forces, π-π stacking, electrostatic interactions, host-guest interactions and covalent bonding) has been discussed. In addition, the potential applications of metallacycle/metallacage-cored supramolecular polymers in the areas of light emitting, sensing, bio-imaging, delivery and release, etc., are also presented.

Mechanically interlocked materials. Rotaxanes and catenanes beyond the small molecule

An overview of the progress in mechanically interlocked materials is presented. In particular, we focus on polycatenanes, polyrotaxanes, metal–organic rotaxane frameworks (MORFs), and mechanically interlocked derivatives of carbon nanotubes (MINTs).

Dynamic hydrogels mediated by macrocyclic host-guest interactions

Hydrogels have attracted increasing research interest in recent years due to their dynamic properties and potential applications in biomaterials. Concurrently, macrocycle-based host-guest interactions have played an important role in the development of supramolecular chemistry. Recently, research towards dynamic hydrogels mediated by various macrocyclic host-guest interactions has been gradually disclosed. In this review, we will outline the burgeoning progress in the development of functional hydrogels mediated by various host molecules, such as cyclodextrins, cucurbit[n]urils, calix[n]arenes, pillar[n]arenes, and other macrocycles. Smart hydrogels with outstanding properties, like biocompatibility, toughness, and self-healing, are mainly focused. We believe that this review will highlight the potential of dynamic hydrogels mediated by macrocycle-based host-guest interactions.

Active DNA Olympic Hydrogels Driven by Topoisomerase Activity

Biological systems are equipped with a diverse repertoire of proteins that regulate DNA topology with precision that is beyond the reach of conventional polymer chemistry. Here, we harness the unique properties of topoisomerases to synthesize Olympic hydrogels formed by topologically interlinked DNA rings. Using dynamic light scattering microrheology to probe the viscoelasticity of DNA topological networks, we show that topoisomerase II enables the facile preparation of active, adenosine triphosphate-driven Olympic hydrogels that can be switched between liquid and solid states on demand. Our results provide a versatile system for engineering switchable topological materials that may be broadly leveraged to model the impact of topological constraints and active dynamics in the physics of chromosomes and other polymeric materials.

Topological Effects in Isolated Poly[n]catenanes: Molecular Dynamics Simulations and Rouse Mode Analysis

Poly[n]catenanes are mechanically interlocked polymers consisting of interlocking ring molecules. Over the years, researchers have speculated that the permanent topological interactions within the poly[n]catenane backbone could lead to unique dynamical behaviors. To investigate these unusual polymers, molecular dynamics simulations of isolated poly[n]catenanes have been conducted, along with a Rouse mode analysis. Owing to the mechanical bonds within the molecule, the dynamics of poly[n]catenanes at short length scales are significantly slowed and the distribution of relaxation times is broadened; these same behaviors have been observed in melts of linear polymers and are associated with entanglement. Despite these entanglement-like effects, at large length scales poly[n]catenanes do not relax much slower than isolated linear polymers and are less strongly impacted by increased segmental stiffness.

Efficient catenane synthesis by cucurbit[6]uril-mediated azide-alkyne cycloaddition

We report here the efficient synthesis of a series of [3]catenanes featuring the use of cucurbit[6]uril to simultaneously mediate the mechanical and covalent bond formations. By coupling the mechanical interlocking with covalent macrocyclization, formation of topological isomers is eliminated and the [3]catenanes are formed exclusively in good yields. The efficient access to these [3]catenanes and the presence of other recognition units render them promising building blocks for the construction of other high-order interlocked structures.

A Nanosized Phenylene-Ethynylene-Butadiynylene [2]Catenane

In a convergent, template-directed synthesis, an efficient route to a phenylene-ethynylene-butadiynylene based [2]catenane is described. The key step is performed by the aminolysis of the corresponding precatenane, which is obtained by a sequence of metal-catalyzed cross-coupling and desilylation reactions. The cyclization reaction leads besides the [2]precatenane to a variety of larger precatenanes and offers an attractive approach to mechanically interlocked structures of different size.

Synthesis and Characterization of Poly(1,4,7-Trioxacycloundecane-8,11-dione) Macrocyclic Functionalized Hydrogel for High Selectivity Adsorption and Complexation of Bismuth Ion

Macrocyclic functional hydrogels incorporating new poly cyclic active sites (1,4,7-trioxacycloundecane-8,11-dione) within their entire network, have been synthesized. Using the high-dilution coupling of the bi-functional monomers maleic acid and bis(chloroethyl)ether in a sol-gel chemistry synthesis, 11-membered chelate rings infused with three oxygen donor atoms were created and characterized, and their structures confirmed using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic analyses. The macrocyclic gel, designed for selective host-guest adsorption and complexation of metal substrates, was initially tested against an aqueous set of 14 metal competitive solutions, where it demonstrated exclusive selectivity for Bi3+aq, with the other metals exhibiting zero adsorption. Further analysis using binary and single ion Bi3+-containing solutions showed a near-complete removal of Bi3+ using this polycyclic hydrogel, with 98% extraction efficiency and q = 9.80 mg/g. These results clearly confirm that the 1,4,7-trioxacycloundecane-8,11-dione cyclic sites are most suitable for high selectivity and capture of Bi. The metal substrates were entrapped within the 1,4,7-trioxacycloundecane-8,11-dione cyclic sites. Evidently, by exploiting the host-guest complexation chemistry of macrocycles, we were able to design hydrogel adsorbents whose networks were comprised entirely of macrocyclic active groups for possible purification works of copper involving bismuth impurities, and/or for efficient selective uptake and recovery of bismuth trace ions existing in highly competitive environments such as sea water.

Supramolecular Hybrid Material Constructed from Graphene Oxide and Pillar[6]arene-Based Host-Guest Complex as a Ultrasound and Photoacoustic Signals Nanoamplifier

Photoacoustic imaging combines the merits of ultrasound imaging and optical imaging that allows a fascinating imaging paradigm with deeper tissue penetration than optical imaging and higher spatial resolution than ultrasound imaging. Herein, we develop a supramolecular hybrid material composed of graphene oxide (GO) and a pillar[6]arene-based host-guest complex (CP6⊃PyN), which can be used as a ultrasound (US) and photoacoustic (PA) signal nanoamplifier. Triggered by the near-infrared (NIR) light mediated photothermal effect, CO2 nanobubbles are generated on the surface of GO@CP6⊃PyN due to the decomposition of bicarbonate counterions, thus strongly amplifying its US and PA performances. Our study, for the first time, demonstrates enhanced US and PA activity in supramolecular hybrid material on the basis of host-guest chemistry as a photoacoustic nanoplatform.

Vapour-driven crystal-to-crystal transformation showing an interlocking switch of the coordination polymer chains between 1D and 3D

A rare crystal-to-crystal transformation occurs between 1D coordination polymer chains and 3D mechanically interlocked structures via reversible opening and closing of the homogeneous chains without any change in the coordination mode and composition.

A novel supramolecular polymer network based on a catenane-type crosslinker

A novel supramolecular mechanically interlocked crosslinker was designed and used to prepare a supramolecular polymer network.

An AIEE fluorescent supramolecular cross-linked polymer network based on pillar[5]arene host–guest recognition: construction and application in explosive detection

A novel fluorescent supramolecular cross-linked polymer network with aggregation induced enhanced emission properties was constructed and further used for explosive detection.

Synthesis and investigation of new cyclic molecules using the stilbene scaffold

A new approach to the synthesis of asymmetrical cyclic compounds using a stilbene scaffold has been developed. The use of boron trifluoride diethyl etherate as the catalyst, both with and without paraformaldehyde, allows us to obtain new substituted dioxanes, oxanes, cyclic compounds or dimer. The analysis of products was run using experimental and theoretical methods.

A new approach to the synthesis of asymmetrical cyclic compounds using a stilbene scaffold has been developed.

Polymeric crown ethers: LCST behavior in water and stimuli-responsiveness

A crown ether-functionalized poly(vinyl alcohol) (PVA) system shows lower critical solution temperature (LCST) phase separation behavior in water.

An ATP/ATPase responsive supramolecular fluorescent hydrogel constructedviaelectrostatic interactions between poly(sodiump-styrenesulfonate) and a tetraphenylethene derivative

We report a supramolecular fluorescent hydrogel based on poly(sodiump-styrenesulfonate) and a tetraphenylethene derivative.

Supramolecular chemotherapeutic drug constructed from pillararene-based supramolecular amphiphile

A therapeutic supramolecular amphiphile, P5⊃CPT-ss-Py, with GSH-responsiveness was constructed using pillar[5]arene-based host–guest molecular recognition. Cellular internalization and anticancer efficacy were greatly increased through this supramolecular strategy.

The geometry of periodic knots, polycatenanes and weaving from a chemical perspective: a library for reticular chemistry

The geometry of the most regular polycatenanes and weavings, as an extended family of discrete knots and catenanes, is described in terms of sticks and corners in their optimal embeddings.

Barium cation-responsive supra-amphiphile constructed by a new twisted cucurbit[15]uril/paraquat recognition motif in water

A new, strong, and barium cation-responsive host–guest recognition motif based on twisted cucurbit[15]uril and paraquat was established in water.

Poly[n]catenanes: Synthesis of molecular interlocked chains

As the macromolecular version of mechanically interlocked molecules, mechanically interlocked polymers are promising candidates for the creation of sophisticated molecular machines and smart soft materials. Poly[n]catenanes, where the molecular chains consist solely of interlocked macrocycles, contain one of the highest concentrations of topological bonds. We report, herein, a synthetic approach toward this distinctive polymer architecture in high yield (~75%) via efficient ring closing of rationally designed metallosupramolecular polymers. Light-scattering, mass spectrometric, and nuclear magnetic resonance characterization of fractionated samples support assignment of the high-molar mass product (number-average molar mass ~21.4 kilograms per mole) to a mixture of linear poly[7-26]catenanes, branched poly[13-130]catenanes, and cyclic poly[4-7]catenanes. Increased hydrodynamic radius (in solution) and glass transition temperature (in bulk materials) were observed upon metallation with Zn².

Catenane Crosslinked Mechanically Adaptive Polymer Gel

A new strategy is introduced to prepare an adaptive polymer gel that has a unique adaptability in response to environmental stimuli. This gel is prepared by the thiol-ene "click" reaction between a bisvinyl [2]catenane and a poly(ethylene glycol) derivative containing multiple thiol groups. The catenane crosslinker is responsive to external stimuli due to the existence of intercomponent hydrogen bonding (IHB). The strong IHB restricts the rotation and movement of the crosslinker, giving it a rigid feature; however, the crosslinker becomes flexible when the IHB is destroyed. In consequence, the resulting gel can be reversibly switched between tough and soft states under stimulations.

Supramolecular polymerization of a ureidopyrimidinone-based [2]catenane prepared via ring-closing metathesis

The synthesis and supramolecular polymerization of a ureidopyrimidinone‐based Sauvage‐type [2]catenane is reported. The monomer synthesis explores many routes using the elegant metathesis catalysts of Bob Grubbs, yielding a catenane with one ureidopyrimidinone in each cycle. The supramolecular polymer obtained features both mechanical bonds and quadruple hydrogen bonding connections.

Pillar[5]arene-Diketopyrrolopyrrole Fluorescent Copolymer: A Promising Recognition and Adsorption Material for Adiponitrile by Selective Formation of a Conjugated Polypseudorotaxane

Conjugated pillar[5]arene-diketopyrrolopyrrole copolymer (P1) is synthesized by the copolymerization of a difunctionalized pillar[5]arene and a diketopyrrolopyrrole-based monomer, which shows large extinction coefficients (1.1 × 10⁴ m^-1 cm^-1 ) at 519 nm and strong emission at 587 nm. P1 exhibits very strong host-guest binding affinity towards adiponitrile but low binding affinity towards 1,4-dihalobutane and 1,4-bis(imidazol-1-yl)butane. Such an enhanced selectivity is first found in the polypseudorotaxane between pillararene and neutral guests in organic solution and is successfully used for the recognition and adsorption of adiponitrile by the formation of a P1-adiponitrile polypseudorotaxane.

Influence of a Single Catenane on the Solid-State Properties of Mechanically Linked Polymers

We report on mechanically linked polymers containing a single catenane in the middle of the chain. These polymers were synthesized by a simple procedure consisting in "clicking" polymer chains onto a functionalized palladium-templated [2]catenane, allowing the preparation of a variety of mechanically linked polymers. The flexibility of the catenane junction was modulated by removing the Pd ion from the catenane to unlock the macrocycles and increase their mobility. We show that this mobility change has a strong impact on the solid-state properties of the polymers. This is illustrated by studying the glass transition temperature of polystyrene-based polymers and the crystallization behavior of poly(ethylene oxide)-based polymers. Our study proves that a change of flexibility of a single catenane inserted into a polymer chain drastically influences the polymer behavior in the solid state.

Fluorescent Supramolecular Polymeric Materials

Fluorescent supramolecular polymeric materials are rising stars in the field of fluorescent materials not only because of the inherent optoelectronic properties originating from their chromophores, but also due to the fascinating stimuli-responsiveness and reversibility coming from their noncovalent connections. Especially, these noncovalent connections influence the fluorescence properties of the chromophores because their state of aggregation and energy transfer can be regulated by the assembly-disassembly process. Considering these unique properties, fluorescent supramolecular polymeric materials have facilitated the evolution of new materials useful for applications in fluorescent sensors, probes, as imaging agents in biological systems, light-emitting diodes, and organic electronic devices. In this Review, fluorescent supramolecular polymeric materials are classified depending on the types of main driving forces for supramolecular polymerization, including multiple hydrogen bonding, electrostatic interactions, π-π stacking interactions, metal-coordination, van der Waals interactions and host-guest interactions. Through the summary of the studies about fluorescent supramolecular polymeric materials, the status quo of this research field is assessed. Based on existing challenges, directions for the future development of this field are furnished.

Carboxylatopillar[n]arenes: a versatile class of water soluble synthetic receptors

Carboxylatopillar[n]arenes (CP[n]As, n = 5, 6, 7, 9, 10) constitute a family of water soluble synthetic receptors. These receptors are excellent hosts for a wide range of cationic organic molecules and have shown promising application in the fields of stimuli-responsive supramolecular assemblies, targeted drug delivery vehicles and sensors. Analogous metal-coordinated prismatic structures have shown excellent affinities for analytes.

A supramolecular polymer network gel with stimuli-responsiveness constructed by orthogonal metal ion coordination and pillar[5]arene-based host–guest recognition

A novel external stimuli-responsive supramolecular polymer network gel was fabricated by orthogonal Ag-coordination and pillar[5]arene-based host–guest interactions.

Pillar[5]arene-based amphiphilic supramolecular brush copolymer: fabrication, controllable self-assembly and application in self-imaging targeted drug delivery

Supramolecular brush copolymers have attracted continuing interest due to their unusual architectures, fascinating properties, and potential applications in many fields involving smart stimuli-responsive drug delivery systems. Herein, the first pillararene-based amphiphilic supramolecular brush copolymer (P5-PEG-Biotin⊃PTPE) was constructed on the basis of the host-guest molecular recognition between a water-soluble pillar[5]arene (P5) and a viologen salt (M). P5-PEG-Biotin⊃PTPE self-assembled into supramolecular nanoparticles (SNPs), which were utilized as a self-imaging drug delivery vehicle by taking advantage of the aggregation-induced emission (AIE) effect. Encapsulation of anticancer drug doxorubicin (DOX) caused deactivation of the fluorescences of both the tetraphenylethene (TPE) and DOX chromophores due to the energy transfer relay (ETR) effect, mediated by Förster resonance energy transfer (FRET) and aggregation-caused quenching (ACQ). The release of loaded DOX molecules can be triggered by low pH and reductase, recovering the "silenced" fluorescence caused by the interruption of the ETR effect, achieving in situ visualization of the drug release process by observing the location and magnitude of the energy transfer-dependent fluorescence variation. The biotin ligands on the surfaces of the DOX-loaded SNPs act as targeting agents to deliver DOX preferentially to cancer cells over-expressing biotin receptor. In vitro studies demonstrated that the loading of DOX by this supramolecular nanomaterial exhibited selective cytotoxicity towards cancer cells over normal cells. The potency of this sophisticated supramolecular drug delivery system in cancer therapy was further evaluated in HeLa tumor-bearing mice. In vivo experiments confirmed that the DOX-loaded SNPs possess excellent antitumor efficacy with negligible systemic toxicity.

Cationic pillar[6]arene/ATP host-guest recognition: selectivity, inhibition of ATP hydrolysis, and application in multidrug resistance treatment

Due to the differences in the cavity size of the hosts and the charge and length of the guests, a cationic water-soluble pillar[6]arene (WP6) selectively complexes with ATP to form a stable 1 : 1 inclusion complex WP6⊃ATP. This host-guest complexation was utilized to efficiently inhibit the hydrolysis of ATP, arising from the existence of the hydrophobic cavity of WP6. A folic acid functionalized diblock copolymer (FA-PEG-b-PAA) was employed to PEGylate WP6 to endow the polyion complex (PIC) micelles with specific targeting ability, preferentially delivering WP6 to folate receptor over-expressing KB cell. This host-guest complexation was further used to block the efflux pump to transport anticancer drugs out of cells by cutting off the energy source, which enhanced the efficacy of the cancer chemotherapy of DOX·HCl towards drug resistant MCF-7/ADR cell. This supramolecular method provides an extremely distinct strategy to potentially overcome multidrug resistance (MDR).

Formation of a series of stable pillar[5]arene-based pseudo[1]-rotaxanes and their [1]rotaxanes in the crystal state

A series of mono-amide-functionalized pillar[5]arenes with different lengths of N-ω-aminoalkyl groups as the side chain on the rim were designed and synthesized, which all formed pseudo[1]rotaxanes in the crystal state. And these pseudo[1]rotaxanes could be transformed into [1]rotaxanes or open forms in the crystal state. In addition, they were also studied in solution by (1)H NMR spectroscopy.

Supramolecular Copolymer Constructed by Hierarchical Self-Assembly of Orthogonal Host-Guest, H-Bonding, and Coordination Interactions

Supramolecular copolymers with complex architectures and emergent functions constitute a class of challenging but enticing synthetic targets in polymer science. Individual building blocks can be tailored to endow a resulting supramolecular copolymer with increased structural and functional complexity. Herein, we describe the construction of a linear supramolecular copolymer comprising mechanically interlocked segments with hydrogen-bonding metallorhomboidal units. Specifically, a hierarchical supramolecular polymerization of a crown ether-based [2]rotaxane and a discrete organoplatinum(II) metallacycle driven by 2-ureido-4-pyrimidinone (UPy) quadruple hydrogen bonding provides the impetus for its formation. This system demonstrates enhanced structural complexity accessed by the unification of orthogonal noncovalent interactions: metal coordination, host-guest chemistry, and multiple hydrogen bonding interfaces.

Catenane-based mechanically-linked block copolymers

An original strategy for the synthesis of diblock copolymers where the blocks are linked by a catenane junction is described. Starting from a functionalized catenane precursor, our strategy enables the preparation of a variety of copolymers by different techniques such as ROP, ATRP and CuAAC click reaction.

A pillar[5]arene-based [2]rotaxane lights up mitochondria

Subcellular organelle-specific reagents for simultaneous targeting, imaging and treatment are highly desirable for cancer therapy. However, it remains a challenge to fabricate a single molecular platform containing a targeting group, imaging and therapeutic agents through traditional synthesis. Due to their superior sensitivity and photostability, fluorescent probes with aggregation-induced emission (AIE) characteristics have attracted more and more attention in studying the process of translocation, drug release, and excretion of nanomedicines in vitro or in vivo. We construct a pillar[5]arene-based [2]rotaxane (R1) by employing tetraphenylethene (TPE) and triphenylphosphonium (TPP) moieties as stoppers; the TPE unit retains the aggregation-induced emission (AIE) attribute and the TPP group is used as a mitochondria-targeting agent. R1 exhibits enhanced AIE, high specificity to mitochondria, and superior photostability. By introducing doxorubicin (DOX) into R1, prodrug R2 is constructed as a dual-fluorescence-quenched Förster resonance energy transfer (FRET) system, in which the TPE-based axle acts as a donor fluorophore and the DOX unit acts as the acceptor. Upon hydrolysis of R2 in endo/lysosomes, the fluorescences of the carrier and the drug recover. R1 is further utilized as a drug delivery platform to conjugate other anticancer drugs containing amine groups through imine formation to prepare prodrugs. The anticancer drugs are released from these prodrugs in the cells upon hydrolysis of the pH-responsive imine bonds.