Pillararene-based supramolecular polymers

ROS-responsive hydrogels: from design and additive manufacturing to biomedical applications

Hydrogels with intricate 3D networks and high hydrophilicity have qualities resembling those of biological tissues, making them ideal candidates for use as smart biomedical materials. Reactive oxygen species (ROS) responsive hydrogels are an innovative class of smart hydrogels, and are cross-linked by ROS-responsive modules through covalent interactions, coordination interactions, or supramolecular interactions. Due to the introduction of ROS response modules, this class of hydrogels exhibits a sensitive response to the oxidative stress microenvironment existing in organisms. Simultaneously, due to the modularity of the ROS-responsive structure, ROS-responsive hydrogels can be manufactured on a large scale through additive manufacturing. This review will delve into the design, fabrication, and applications of ROS-responsive hydrogels. The main goal is to clarify the chemical principles that govern the response mechanism of these hydrogels, further providing new perspectives and methods for designing responsive hydrogel materials.

A Pillararene-Based Cavitand: Synthesis and Solid-State Capsular Assemblies Induced by Linear Alkanes with Specific Lengths

Herein, a novel pillararene-based cavitand with fixed planar chirality was synthesized by the SuFEx reaction. As demonstrated by single crystal X-ray analysis, host-guest capsules involving this cavitand and linear alkanes with specific lengths are observed in the solid state. The formation of each capsule is driven by hydrogen bonding interactions between a linear alkane molecule and two cavitand molecules, as well as noncovalent interactions between the two cavitand molecules in this capsule.

A Review of Macrocycles Applied in Electrochemical Energy Storge and Conversion

Macrocycles composed of diverse aromatic or nonaromatic structures, such as cyclodextrins (CDs), calixarenes (CAs), cucurbiturils (CBs), and pillararenes (PAs), have garnered significant attention due to their inherent advantages of possessing cavity structures, unique functional groups, and facile modification. Due to these distinctive features enabling them to facilitate ion insertion and extraction, form crosslinked porous structures, offer multiple redox-active sites, and engage in host-guest interactions, macrocycles have made huge contributions to electrochemical energy storage and conversion (EES/EEC). Here, we have summarized the recent advancements and challenges in the utilization of CDs, CAs, CBs, and PAs as well as other novel macrocycles applied in EES/EEC devices. The molecular structure, properties, and modification strategies are discussed along with the corresponding energy density, specific capacity, and cycling life properties in detail. Finally, crucial limitations and future research directions pertaining to these macrocycles in electrochemical energy storage and conversion are addressed. It is hoped that this review is able to inspire interest and enthusiasm in researchers to investigate macrocycles and promote their applications in EES/EEC.

Double-cavity cucurbiturils: synthesis, structures, properties, and applications

Double-cavity Q[n]s are relatively new members of the Q[n] family and have garnered significant interest due to their distinctive structures and novel properties. While they incorporate n glycoluril units, akin to their single-cavity counterparts, their geometry can best be described as resembling a figure-of-eight or a handcuff, distinguishing them from single-cavity Q[n]s. Despite retaining the core molecular recognition traits of single-cavity Q[n]s, these double-cavity variants introduce fascinating new attributes rooted in their distinct configurations. This overview delves into the synthesis, structural attributes, properties, and intriguing applications of double-cavity Q[n]s. Some of the applications explored include their role in supramolecular polymers, molecular machinery, supra-amphiphiles, sensors, artificial light-harvesting systems, and adsorptive separation materials. Upon concluding this review, we discuss potential challenges and avenues for future development and offer valuable insights for other scholars working in this area with the aim of stimulating further exploration and interest.

Synergistically Boosting the Circularly Polarized Luminescence of Functionalized Pillar[5]arenes by Polymerization and Aggregation

Supramolecular polymers based on chiral macrocycles have attracted increasing attention in the field of circularly polarized luminescence (CPL) owing to their unique properties. However, the construction of macrocyclic supramolecular polymers with highly efficient CPL properties in aggregate states still remains challenging. Herein, w e constructed a class of macrocycle-based coordination polymers by combining the planar chiral properties of pillar[5]arene with the excellent fluorescence properties of aggregation-induced emission luminogens. The formation of polymers enhances both the fluorescence and chiral properties, resulting in chiral supramolecular polymers with remarkable CPL properties. Increasing the aggregation degree of the polymers can further improve their CPL properties, as evidenced by a 21-fold increase in the dissymmetry factor and an over 25-fold increase in the fluorescence quantum yield in the aggregate state compared to the solution state. Such a synergistic effect of polymerization- and aggregation-enhanced CPL can be explained by the restriction of intramolecular motions and aggregation-induced conformation confinement. This work provides a promising method for developing highly efficient CPL supramolecular polymers.

Arylazopyrazole as a photo-switch for controllable self-assembly of pillar[6]arene-based supramolecular amphiphiles

A photo-responsive host-guest molecular recognition between a cationic pillar[6]arene host and an arylazopyrazole derived guest was established. Based on this novel recognition motif, a photo-controllable supra-amphiphile was constructed. The spontaneous aggregation can be reversibly controlled by irradiation with UV (365 nm) and green light (520 nm), leading to a switch between spherical nanoparticles and vesicle-like aggregates.

Porous pillararene-based polymer as adsorbent and solid disinfectant for water treatment

Pillararene polymers have been widely used as excellent adsorbents for water treatment, but pillararene polymers with ultra-high specific surface area and versatility are still rarely reported. Herein, a quaternary ammonium salt modified pillar [5] arene polymer, QPBP [5], with specific surface area of 1844 m2 g-1 was successfully synthesized. Since QPBP [5] has abundant different adsorption sites, it exhibits excellent performance for the simultaneously removal of organic pollutants with different charges from water. The selected three model pollutants, Rhodamine B (RhB, positively charged), Sulfamethazine (SMT, electrically neutral) and Fulvic acid (FA, negatively charged), could be rapidly and efficiently removed from water by QPBP [5] within 10 min, which are much faster than them by most of the reported adsorbents. RhB and SMT are mainly adsorbed through hydrophobic interactions with the QPBP [5] surface, while FA is mainly removed through ion exchange. In addition, QPBP [5] also showed excellent reusability and adsorption performance for the environmentally relevant concentration of pollutants. Furthermore, the quaternary ammonium groups on QPBP [5] makes it a solid disinfectant with excellent antibacterial properties. In conclusion, QPBP [5] is a promising multifunctional adsorbent for the treatment of complex pollutants in water.

Effect on the conformation of monosubstituted pillar[5]arene: solvent, temperature, concentration and linker length

A series of monosubstituted pillar[5]arenes (PIn) bearing a fluorescent probe (E)-4-[4-(dimethylamino)styryl-]-1-pyridinium were synthesized and characterized. The conformations of the monosubstituted pillar[5]arenes were investigated systematically by NMR and fluorescence spectroscopy and were found to be dependent on solvent polarity, concentration, temperature and linker length. PI1 with a short linker remained uncomplexed in DMSO, whereas it formed a polymer at high concentration in chloroform. As the linker length increased, PI2-4 could exist in equilibrium between self-inclusion monomer and intermolecular complexes. The increase of concentration led to the formation of a polymer in DMSO and a self-penetrating dimer in chloroform. The results provided information on the modulation of supramolecular assemblies by various factors.

Harnessing Pillar[5]arene Host-Guest Complexation To Improve pH Stability and Affect Enzymatic Degradation of the Anticancer Prodrug Capecitabine: A 19 F NMR Study

Cancer is a global health problem, and supramolecular chemotherapy is emerging as a novel strategy to battle the disease. Here, we first evaluated the thermodynamic and kinetic stability of the complexes formed between several water-soluble per-substituted pillar[5]arene derivatives and capecitabine (1), a widely used oral chemotherapeutic prodrug. The exchange rate was studied, for the first time in pillararene chemistry, by the 19 F guest exchange saturation transfer (GEST) NMR technique. Importantly, when we evaluated the effect of complexation on the characteristics of 1, we found that the complexation of 1 with such pillar[5]arene hosts increased capecitabine stability at acidic pH very significantly and slowed its enzymatic degradation by the carboxylesterase enzyme in a manner that depended on the host. These interesting findings could have implications on the clinical use of this heavily used prodrug and might affect the management of cancer patients.

Synthesis of Thiapillar[6]arenes Bearing Redox-Active (Hydro)quinone Groups. Electrochemical and XRD Study

Pillar[n]arenes are among the newest members of the macrocyclic family. Nevertheless, their conformational behavior and binding properties as well as redox properties of dealkylated pillar[n]arenes are well-studied. At the same time, introducing a heteroatom into a cyclophane macrocycle is already known to alter all the above properties drastically. This study presents a simple synthetic approach based on thia-Michael addition cyclization that readily resulted into hexathiapillar[6]arene with four phenylene units alternated by two redox-active hydroquinone moieties. The straightforward synthesis of the macrocycle enabled a systematic study of its conformation and redox behavior. The modification of hexathiapillar[6]arene afforded five functionalized derivatives, which were studied structurally in detail. The findings revealed interesting redox and structural properties of the macrocycle and its derivatives including the formation of crystal lattices with continuous channels and empty voids.

Synthesis of Naphthalimide Derivatives and Their Luminescence upon Complexation with Cucurbit[n]uril Hosts

A series of naphthalimide derivatives are synthesized and their binding behavior upon complexation with cucurbit[n]urils (CB[n]s) has been investigated. With a heavy atom (bromine) on the naphthalimide core, 4-bromo-1,8-naphthalimide derivatives 1-4 show short room-temperature phosphorescence (RTP) lifetimes with low quantum yields. Their RTP properties are significantly enhanced in the presence of CB[8] or CB[10] both in aqueous solution and solid state owing to the efficient suppression of nonradiative decay and isolation of quenching factors by the rigid cavity of CB[n]. Without the bromine atom, 1,8-naphthalimide derivatives 5 and 6 show strong excimer emission upon complexation with CB[10] accompanied by fluorescence transition from blue to cyan. The fluorescence colors of 4-(dimethylamino)-1,8-naphthalimide derivatives 7 and 8 change from blue to white to yellow with the addition of CB[n]. This host-guest complexation strategy to modulate the luminescence of the luminophore would further broaden the application of luminescent materials.

Pillar[5]arene-based supramolecular pseudorotaxane polymer material for ultra-sensitive detection of Fe3+ and F. RSC Adv 2023;13:12270-12275. [PMID: 37091614 PMCID: PMC10113919 DOI: 10.1039/d3ra00997a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Recent advancements in ultra-sensitive detection, particularly the Aggregation Induced Emission (AIE) materials, have demonstrated a promising detection method due to their low cost, real-time detection, and simplicity of operation. Here, coumarin functionalized pillar[5]arene (P5C) and bis-bromohexyl pillar[5]arene (DP5) were successfully combined to create a linear AIE supramolecular pseudorotaxane polymer (PCDP-G). The use of PCDP-G as a supramolecular AIE polymer material for recyclable ultra-sensitive Fe³⁺ and F^- detection is an interesting application of the materials. According to measurements, the low detection limits of PCDP-G for Fe³⁺ and F^- are 4.16 × 10^-10 M and 6.8 × 10^-10 M, respectively. The PCDP-G is also a very effective logic gate and a material for luminous displays.

Supramolecular chiral sensing by supramolecular helical polymers

A tetrakis(porphyrin) with branched side chains self-assembled to form supramolecular helical polymers both in solution and in the solid state. The helicity of the supramolecular polymers was determined by the chirality of solvent molecules, which permitted the polymer chains to be used in chiral sensing.

Solvent-Dependent Self-Assembly of a Pillar[5]arene-Based Poly-Pseudo-Rotaxane Linked and Threaded by Silver(I) Trifluoroacetate: A Double Role

In the supramolecule area, the fabrication of a new concept called polyrotaxanes or poly-pseudo-rotaxanes remains challenging. We herein report the formation of a poly-pseudo-rotaxane in which the same salt-type guest serves both linking and threading in the resulting structure. The combination of A1/A2-thiopyridyl pillar[5]arene (L) and silver(I) trifluoroacetate in CHCl₃/CH₃OH afforded a one-dimensional (1D) poly-pseudo-rotaxane. In this structure, to our surprise, the AgCF₃CO₂ guest not only links the di-armed L ligands via an infinite -L-Ag-L-Ag- arrangement but also threads into a pillar[5]arene cavity in a dimer form, (AgCF₃CO₂)₂. In contrast, the same reaction in CH₂Cl₂/CH₃OH yielded a simple 1D coordination polymer because an included CH₂Cl₂ molecule in the pillar[5]arene cavity prevents the threading of the silver(I) trifluoroacetate guest. Comparative ¹H- and ¹⁹F-NMR studies support the solvent-dependent poly-pseudo-rotaxane formation at a lower concentration of L.

Pillararene-Based Supramolecular Polymers for Cancer Therapy

Supramolecular polymers have attracted considerable interest due to their intriguing features and functions. The dynamic reversibility of noncovalent interactions endows supramolecular polymers with tunable physicochemical properties, self-healing, and externally stimulated responses. Among them, pillararene-based supramolecular polymers show great potential for biomedical applications due to their fascinating host-guest interactions and easy modification. Herein, we summarize the state of the art of pillararene-based supramolecular polymers for cancer therapy and illustrate its developmental trend and future perspective.

Solid Lipid Nanoparticles Based on Monosubstituted Pillar[5]arenes: Chemoselective Synthesis of Macrocycles and Their Supramolecular Self-Assembly

Novel monosubstituted pillar[5]arenes with one or two terminal carboxyl groups were synthesized by the reaction of succinic anhydride with pillar[5]arene derivative containing a diethylenetriamine function. The ability for non-covalent self-assembly in chloroform, dimethyl sulfoxide, as well as in tetrahydrofuran-water system was studied. The ability of the synthesized macrocycles to form different types of associates depending on the substituent nature was established. The formation of stable particles with average diameter of 192 nm in chloroform and of 439 nm in DMSO was shown for pillar[5]arene containing two carboxyl fragments. Solid lipid nanoparticles (SLN) based on monosubstituted pillar[5]arenes were synthesized by nanoprecipitation in THF-water system. Minor changes in the structure of the macrocycle substituent can dramatically influence the stability and shape of SLN (spherical and rod-like structures) accordingly to DLS and TEM. The presence of two carboxyl groups in the macrocycle substituent leads to the formation of stable spherical SLN with an average hydrodynamic diameter of 364-454 nm. Rod-like structures are formed by pillar[5]arene containing one carboxyl fragment, which diameter is about of 50-80 nm and length of 700-1000 nm. The synthesized stable SLN open up great prospects for their use as drug storage systems.

Supramolecular Combination Cancer Therapy Based on Macrocyclic Supramolecular Materials

Supramolecular combination therapy adopts supramolecular materials to design intelligent drug delivery systems with different strategies for cancer treatments. Thereinto, macrocyclic supramolecular materials play a crucial role in encapsulating anticancer drugs to improve anticancer efficiency and decrease toxicity towards normal tissue by host-guest interaction. In general, chemotherapy is still common therapy for solid tumors in clinics. However, supramolecular combination therapy can overcome the limitations of the traditional single-drug chemotherapy in the laboratory findings. In this review, we summarized the combination chemotherapy, photothermal chemotherapy, and gene chemotherapy based on macrocyclic supramolecular materials. Finally, the application prospects in supramolecular combination therapy are discussed.

Supramolecular Organic Frameworks: Exploring Water-Soluble, Regular Nanopores for Biomedical Applications

In past decades, regular porous architectures have received a great amount of attention because of their versatile functions and applications derived from their efficient adsorption of various guests. However, most reported porous architectures exist only in the solid state. Therefore, their applications as biomaterials may face several challenges, such as phase separation, slow degradation, and long-term accumulation in the body. This Account summarizes our efforts with respect to the development and biomedical applications of water-soluble 3D diamondoid supramolecular organic frameworks (dSOFs), a family of supramolecular polymers that possess intrinsic regular nanoscale porosity.dSOFs have been constructed from tetratopic components and cucurbit[8]uril (CB[8]) through hydrophobically driven encapsulation by CB[8] for intermolecular dimers formed by peripheral aromatic subunits of the tetratopic components in water. All dSOFs exhibit porosity regularity or periodicity in aqueous solution, which is confirmed by solution-phase synchrotron SAXS and XRD experiments. Dynamic light scattering (DLS) reveals that their sizes range from 50 to 150 nm, depending on the concentrations of the components. As nonequilibrium supramolecular architectures, dSOFs can maintain their nanoscale sizes at micromolar concentrations for dozens of hours. Their diamondoid pores have aperture sizes ranging from 2.1 to 3.6 nm, whereas their water solubility and porosity regularity allow them to rapidly include discrete guests driven by ion-pair electrostatic attraction, hydrophobicity, or a combination of the two interactions. The guests may be small molecule or large macromolecular drugs, photodynamic agents (PDAs), or DNA.The rapid inclusion of bioactive guests into dSOFs has led to two important biofunctions. The first is to function as antidotes through including residual drugs. For heparins, the inclusion results in full neutralization of their anticoagulant activity. For clinically used porphyrin PDAs, the inclusion can alleviate their long-term posttreatment phototoxicity but does not reduce their photodynamic efficacy. The second is to function as in situ loading carriers for the intracellular delivery of antitumor drugs or DNA. Their nanoscale sizes bring out their ability to overcome the multidrug resistance of tumor cells, which leads to a remarkable enhancement of the bioactivity of the included drugs. By conjugating aldoxorubicin to tetrahedral components, albumin-mimicking prodrugs have also been constructed, which conspicuously improves the efficacy of aldoxorubicin toward multi-drug-resistant tumors through the delivery of the frameworks. As new supramolecular drugs and carriers, dSOFs are generally biocompatible. Thus, further efforts might lead to medical benefits in the future.

Self-Healing Thiolated Pillar[5]arene Films Containing Moxifloxacin Suppress the Development of Bacterial Biofilms

Polymer self-healing films containing fragments of pillar[5]arene were obtained for the first time using thiol/disulfide redox cross-linking. These films were characterized by thermogravimetric analysis and differential scanning calorimetry, FTIR spectroscopy, and electron microscopy. The films demonstrated the ability to self-heal through the action of atmospheric oxygen. Using UV-vis, 2D 1H-1H NOESY, and DOSY NMR spectroscopy, the pillar[5]arene was shown to form complexes with the antimicrobial drug moxifloxacin in a 2:1 composition (logK11 = 2.14 and logK12 = 6.20). Films containing moxifloxacin effectively reduced Staphylococcus aureus and Klebsiella pneumoniae biofilms formation on adhesive surfaces.

Hybrid Macrocyclic Polymers: Self-Assembly Containing Cucurbit[m]uril-pillar[n]arene

Supramolecular self-assembly by hybrid macrocycles containing both cucurbit[m]uril (CB[m]) and pillar[n]arene was discussed and summarized in this review. Due to different solubility, diverse-sized cavities, and various driving forces in recognizing guests, the role of CB[m] and pillar[n]arene in such hybrid macrocyclic systems could switch between competitor in capturing specialized guests, and cooperator for building advanced hybridized macrocycles, by controlling their characteristics in host-guest inclusions. Furthermore, both CB[m] and pillar[n]arene were employed for fabricating advanced supramolecular self-assemblies such as mechanically interlocked molecules and supramolecular polymers. In those self-assemblies, CB[m] and pillar[n]arene played significant roles in, e.g., microreactor for catalyzing particular reactions to bridge different small pieces together, molecular "joint" to connect different monomers into larger assemblies, and "stabilizer" in accommodating the guest molecules to adopt a favorite structure geometry ready for assembling.

pH-Triggered Transition from Micellar Aggregation to a Host-Guest Complex Accompanied by a Color Change

A pH-triggered transition from micellar aggregation to a host-guest complex was achieved based on the supramolecular interactions between calixpyridinium and pyrroloquinoline quinone disodium salt (PQQ-2Na) accompanied by a color change. Our design has the following three advantages: (1) a regular spherical micellar assembly is fabricated by the supramolecular interactions between calixpyridinium and PQQ-2Na at pH 6 in an aqueous solution, (2) increasing the pH can lead to a transition from micellar aggregation to a host-guest complex due to the deprotonation of calixpyridinium, and at the same time (3) increasing the pH can lead to a color change owing to the deprotonation of calixpyridinium and the complexation of deprotonated calixpyridinium with PQQ-2Na. Benefitting from the low toxicity of calixpyridinium and PQQ-2Na, this pH-induced transition from micellar aggregation to a host-guest complex was further studied as a controllable-release model.

GOx-assisted synthesis of pillar[5]arene based supramolecular polymeric nanoparticles for targeted/synergistic chemo-chemodynamic cancer therapy

Background

Cancer is the most serious world's health problems on the global level and various strategies have been developed for cancer therapy. Pillar[5]arene-based supramolecular therapeutic nano-platform (SP/GOx NPs) was constructed successfully via orthogonal dynamic covalent bonds and intermolecular H-bonds with the assistance of glucose oxidase (GOx) and exhibited efficient targeted/synergistic chemo-chemodynamic cancer therapy.

Methods

The morphology of SP/GOx NPs was characterized by DLS, TEM, SEM and EDS mapping. The cancer therapy efficinecy was investigated both in vivo and in vitro.

Results

SP/GOx NPs can load drug molecules (Dox) and modify target molecule (FA-Py) on its surface conveniently. When the resultant FA-Py/SP/GOx/Dox NPs enters blood circulation, FA-Py will target it to cancer cells efficiently, where GOx can catalyst the overexpressed glucose to generate H₂O₂. Subsequently, the generated H₂O₂ in cancer cells catalyzed by ferrocene unit to form •OH, which can kill cancer cells. Furthermore, the loaded Dox molecules released under acid microenvironment, which can further achieve chemo-therapy.

Conclusion

All the experiments showed that the excellent antitumor performance of FA-Py/SP/GOx/Dox NPs, which provided an new method for pillar[5]arene-based supramolecular polymer for biomedical applications.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01237-0.

Surfactant Effect on the Physicochemical Characteristics of Solid Lipid Nanoparticles Based on Pillar[5]arenes

Novel monosubstituted pillar[5]arenes containing both amide and carboxyl functional groups were synthesized. Solid lipid nanoparticles based on the synthesized macrocycles were obtained. Formation of spherical particles with an average hydrodynamic diameter of 250 nm was shown for pillar[5]arenes containing N-(amidoalkyl)amide fragments regardless of their concentration. It was established that pillar[5]arene containing N-alkylamide fragments can form spherical particles with two different sizes (88 and 223 nm) depending on its concentration. Mixed solid lipid nanoparticles based on monosubstituted pillar[5]arenes and surfactant (dodecyltrimethylammonium chloride) were obtained for the first time. The surfactant made it possible to level the effect of the macrocycle concentration. It was found that various types of aggregates are formed depending on the macrocycle/surfactant ratio. Changing the macrocycle/surfactant ratio allows to control the charge of the particles surface. This controlled property will lead to the creation of molecular-scale porous materials that selectively interact with various types of substrates, including biopolymers.

Fullerene-containing pillar[n]arene hybrid composites

The construction and application of fullerene-containing pillar[n]arene organic–inorganic hybrid composites/systems has been discussed and summarized.

Charged Tubular Supramolecule Boosting Multivalent Interactions for the Drastic Suppression of Aβ Fibrillation

Anti-Aβ therapy has dominated clinical trials for the prevention and treatment of Alzheimer's disease (AD). However, suppressing Aβ aggregation and disintegrating mature fibrils simultaneously remains a great challenge. In this work, we developed a new strategy using a charged tubular supramolecule (CTS) with pillar[5]arene as the backbone and modifying amino and carboxyl groups at the tubular terminals (noted as CTS-A, CTS-A/C, and CTS-C, respectively) to suppress Aβ fibrillation for the first time. According to the spectroscopic and microscopic characterizations, Aβ₄₀ fibrillation can be efficiently suppressed by CTS-A in a very low inhibitor:peptide (I:P) molar ratio (1:10). A greatly alleviated cytotoxic effect of Aβ peptides after the inhibition or disaggregation process is further disclosed. The well-organized supramolecular structure drives multivalent interaction and gains enhanced efficiency on amyloid fibrillar modulation. These results open a new path for the design of supramolecules in the application of AD treatment.

Crown Ether-Based Supramolecular Polymers: From Synthesis to Self-Assembly

Supramolecular polymers not only possess many advantages of traditional polymers, but also have many unique characteristics. Supramolecular polymers can be constructed by self-assembly of various noncovalent interactions. Host-guest interaction, as one important type of noncovalent interactions, has been widely applied to construct supramolecular polymers. From the perspective of classification of the recognition system motifs, host-guest recognition motifs mainly include crown ether, cyclodextrin, calixarene, cucurbituril, and pillararene-based host-guest recognition pairs. Crown ethers, as the first-generation macrocyclic hosts, have played a very important part in the development of supramolecular chemistry. Due to the easy modification of crown ethers, various crown ether derivatives have been prepared by attaching some functional groups to the edges of crown ethers, which endowed them with some interesting properties and made them ideal candidates for the fabrication of supramolecular polymers. This review gives a review of the preparation of crown ether-based supramolecular polymers (CSPs) and summarizes crown ether-based recognition pairs, organization methods, topological structures, stimuli-responsiveness, and functional characteristics.

Water-soluble pillar[5]arene sulfo-derivatives self-assemble into biocompatible nanosystems to stabilize therapeutic proteins

Pillar[5]arenes containing sulfonate fragments have been shown to form supramolecular complexes with therapeutic proteins to facilitate targeted transport with an increased duration of action and enhanced bioavailability. Regioselective synthesis was used to obtain a water-soluble pillar[5]arene containing the fluorescent label FITC and nine sulfoethoxy fragments. The pillar[5]arene formed complexes with the therapeutic proteins binase, bleomycin, and lysozyme in a 1:2 ratio as demonstrated by UV-vis and fluorescence spectroscopy. The formation of stable spherical nanosized macrocycle/binase complexes with an average particle size of 200 nm was established by dynamic light scattering and transmission electron microscopy. Flow cytometry demonstrated the ability of macrocycle/binase complexes to penetrate into tumor cells where they exhibited significant cytotoxicity towards A549 cells at 10^-5-10^-6 M while maintaining the enzymatic activity of binase.

Covalently bridged pillararene-based oligomers: from construction to applications

Covalently bridged pillararene-based oligomers (CBPOs) are formed by covalent bonding of pillararene monomers, and they play a critical role in expanding the multi-disciplinary application of pillararenes due to their excellent molecular complexing ability, specially designed geometry and multifunctional linking groups. This article provides a comprehensive review of the synthesis and applications of CBPOs. The design and synthetic strategies of a series of CBPOs (dimers, trimers, tetramers and others) are first introduced. Many CBPOs with multi-cavities and unique geometry are very attractive and efficient building blocks for constructing novel smart supramolecular polymers (SPs) with different topological structures through host-guest interactions. We describe the methods of constructing various SPs based on CBPOs in detail. Furthermore, the extensive applications of CBPOs and CBPO-based SPs in recognition and detection of ions and organic small molecules, selective adsorption and separation, artificial light-harvesting systems, catalysis, drug delivery systems, and others are systematically introduced. Finally, the future challenges and perspectives for CBPOs are also highlighted.

Solution NMR of synthetic cavity containing supramolecular systems: what have we learned on and from?

NMR has been instrumental in studies of both the structure and dynamics of molecular systems for decades, so it is not surprising that NMR has played a pivotal role in the study of host-guest complexes and supramolecular systems. In this mini-review, selected examples will be used to demonstrate the added value of using (multiparametric) NMR for studying macrocycle-based host-guest and supramolecular systems. We will restrict the discussion to synthetic host systems having a cavity that can engulf their guests thus restricting them into confined spaces. So discussion of selected examples of cavitands, cages, capsules and their complexes, aggregates and polymers as well as organic cages and porous liquids and other porous materials will be used to demonstrate the insights that have been gathered from the extracted NMR parameters when studying such systems emphasizing the information obtained from somewhat less routine NMR methods such as diffusion NMR, diffusion ordered spectroscopy (DOSY) and chemical exchange saturation transfer (CEST) and their variants. These selected examples demonstrate the impact that the results and findings from these NMR studies have had on our understanding of such systems and on the developments in various research fields.

Pillar[5]-bis-trithiacrown: Influence of Host-Guest Interactions on the Formation of Coordination Networks

A pillar[5]-bis-trithiacrown (L) capable of metal binding and organic guest threading simultaneously has been employed, and the influence of dinitrile guests [CN(CH₂)_nCN (n = 2-6: abbreviated C2-C6)] on the coordination behaviors has been investigated. When the ditopic ligand L was reacted with HgCl₂ in the presence of the C2-C6 guests, the shorter guests C2 and C3 afforded a two-dimensional coordination polymer [Hg₇Cl₁₄(C2@L)₂]_n (1) and a one-dimensional coordination polymer [(Hg₃Cl₆)₂(C3@L)₂]_n (2), respectively. In 1 and 2, each dinitrile guest threads into the pillararene cavity to form a C2@L or C3@L unit via the host-guest interaction. Further linking of these units by exocyclic Hg-S bonds and anion coordination lead to the formation of coordination products with different dimensionalities. While the use of the longer guests C4-C6 under the same reactions yielded a discrete dimercury(II) complex 3, [Hg₂Cl₄(CH₃CN@L)] which contains one acetonitrile solvent molecule because the longer dinitriles do not serve as effective guests. In the NMR and UV-vis studies, the association constants (log K_1:1) for the host-guest interactions of L with the dinitrile guests are C2 (4.75) > C3 (4.17) ≫ C4 (2.85) > C5 (2.45) > C6 (too small), indicating that the shorter guests C2 or C3 interact more strongly than longer ones due to the confined interior space of L. Taken collectively, the C2 and C3 guests with proper size-matching promote the formation of coordination polymers and vice versa, suggesting that the guest size could be a controlling factor.

Design Guidelines for Cationic Pillar[n]arenes that Prevent Biofilm Formation by Gram-Positive Pathogens

Bacterial biofilms are a major threat to human health, causing persistent infections that lead to millions of fatalities worldwide every year. Biofilms also cause billions of dollars of damage annually by interfering with industrial processes. Recently, cationic pillararenes were found to be potent inhibitors of biofilm formation in Gram-positive bacteria. To identify the structural features of pillararenes that result in antibiofilm activity, we evaluated the activity of 16 cationic pillar[5]arene derivatives including that of the first cationic water-soluble pillar[5]arene-based rotaxane. Twelve of the derivatives were potent inhibitors of biofilm formation by Gram-positive pathogens. Structure activity analyses of our pillararene derivatives indicated that positively charged head groups are critical for the observed antibiofilm activity. Although certain changes in the lipophilicity of the substituents on the positively charged head groups are tolerated, dramatic elevation in the hydrophobicity of the substituents or an increase in steric bulk on these positive charges abolishes the antibiofilm activity. An increase in the overall positive charge from 10 to 20 did not affect the activity significantly, but pillararenes with 5 positive charges and 5 long alkyl chains had reduced activity. Surprisingly, the cavity of the pillar[n]arene is not essential for the observed activity, although the macrocyclic structure of the pillar[n]arene core, which facilitates the clustering of the positive charges, appears important. Interestingly, the compounds found to be efficient inhibitors of biofilm formation were nonhemolytic at concentrations that are ∼100-fold of their MBIC₅₀ (the minimal concentration of a compound at which at least 50% inhibition of biofilm formation was observed compared to untreated cells). The structure–activity relationship guidelines established here pave the way for a rational design of potent cationic pillar[n]arene-based antibiofilm agents.

Metallo-Supramolecular Coordination Polymers Based on Amidopyridine Derivatives of Pillar[5]arene and Cu(II) and Pd(II) Cations: Synthesis and Recognition of Nitroaromatic Compounds

Decasubstituted pillar[5]arenes containing amidopyridine fragments have been synthesized for the first time. As was shown by UV-vis spectroscopy, the pillar[5]arenes with p-amidopyridine fragments form supramolecular associates with Cu(II) and Pd(II) cations in methanol in a 2:1 ratio. Using a sol-gel approach these associates are transformed into metallo-supramolecular coordination polymers (supramolecular gels) which were characterized as amorphous powders by scanning electron microscopy (SEM) and dynamic light scattering (DLS). The powders are able to selectively adsorb up to 46% of nitrophenols from water and were incorporated into an electrochemical sensor to selectively recognize them in aqueous acidic solution.

Construction of Supramolecular Polymers with Different Topologies by Orthogonal Self-Assembly of Cryptand-Paraquat Recognition and Metal Coordination

Recently, metal-coordinated orthogonal self-assembly has been used as a feasible and efficient method in the construction of polymeric materials, which can also provide supramolecular self-assembly complexes with different topologies. Herein, a cryptand with a rigid pyridyl group on the third arm derived from BMP32C10 was synthesized. Through coordination-driven self-assembly with a bidentate organoplatinum(II) acceptor or tetradentate Pd(BF4)2•4CH3CN, a di-cryptand complex and tetra-cryptand complex were prepared, respectively. Subsequently, through the addition of a di-paraquat guest, linear and cross-linked supramolecular polymers were constructed through orthogonal self-assembly, respectively. By comparing their proton nuclear magnetic resonance (1H NMR) and diffusion-ordered spectroscopy (DOSY) spectra, it was found that the degrees of polymerization were dependent not only on the concentrations of the monomers but also on the topologies of the supramolecular polymers.

Pillararene-based AIEgens: research progress and appealing applications

The pillararene-based AIEgens and AIE materials, constructed using different assembly forms, show attractive applications in various areas.

Supramolecular brush polymers prepared from 1,3,4-oxadiazole and cyanobutoxy functionalised pillar[5]arene for detecting Cu2+

The self-assembly of an A1/A2 disubstituted pillar[5]arene was used to construct a supramolecular brush polymer.

Hierarchical self-assembly and controlled disassembly of a cavitand-based host–guest supramolecular polymer

Two hierarchical aggregation modes of cavitand-based supramolecular polymers allow implementing orthogonal disassembly procedures: electrochemical reduction for linear chains and solvent-driven dissolution for bundles.

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.

β-Cyclodextrin modified Pt(II) metallacycle-based supramolecular hyperbranched polymer assemblies for DOX delivery to liver cancer cells

Despite the widespread clinical application of chemotherapeutic anticancer drugs, their adverse side effects and inefficient performances remain ongoing issues. A drug delivery system (DDS) designed for a specific cancer may therefore overcome the drawbacks of single chemotherapeutic drugs and provide precise and synergistical cancer treatment by introducing exclusive stimulus responsiveness and combined chemotherapy properties. Herein, we report the design and synthesis of a supramolecular drug delivery assembly 1 constructed by orthogonal self-assembly technique in aqueous media specifically for application in liver cancer therapy. Complex 1 incorporates the β-cyclodextrin host molecule-functionalized organoplatinum(II) metallacycle 2 with two specific stimulus-responsive motifs to the signaling molecule nitric oxide (NO), in addition to the three-armed polyethylene glycol (PEG) functionalized ferrocene 3 with redox responsiveness. With this molecular design, the particularly low critical aggregation concentration (CAC) of assembly 1 allowed encapsulation of the commercial anticancer drug doxorubicin (DOX). Controlled drug release was also achieved by morphological transfer via a sensitive response to the endogenous redox and NO stimuli, which are specifically related to the microenvironment of liver tumor cells. Upon combination of these properties with the anticancer ability from the platinum acceptor, in vitro studies demonstrated that DOX-loaded 1 is able to codeliver anticancer drugs and exhibit therapeutic effectiveness to liver tumor sites via a synergistic effect, thereby revealing a potential DDS platform for precise liver cancer therapeutics.