Pillararene-based self-assembled amphiphiles

Cyclodextrin-pillar[n]arene hybridized macrocyclic systems

Cyclodextrin (CD) and pillar[n]arene are significant macrocyclic host molecules in supramolecular chemistry, and have either similar or contrasting physicochemical properties, for example, both can provide capable cavities available for recognizing various favorite guest molecules, while they usually possess different solubility in aqueous solutions, and exhibit diverse chiral characteristics. To balance their similarity and differences inherited from each chemical structure and incorporate both advantages, the CD-pillar[n]arene hybrid macrocyclic system was recently developed. In this review, we will focus on the preparation and application of CD-pillar[n]arene hybrid macrocyclic systems. Both noncovalent interactions and covalent bonds were employed in the synthesis strategies of building the hybrid macrocyclic system, which was in the form of host-guest inclusion, self-assembly, conjugated molecules, and polymeric structures. Furthermore, the CD-pillar[n]arene hybrid macrocyclic system has been primarily applied for the removal of organic pollutants from water, induced chirality, as well as photocatalysis due to the integration of both cavities from CD and pillar[n]arene as hybrid hosts and chiral characteristics inherited from their chemical structures.

The coming of age of water channels for separation membranes: from biological to biomimetic to synthetic

Water channels are one of the key pillars driving the development of next-generation desalination and water treatment membranes. Over the past two decades, the rise of nanotechnology has brought together an abundance of multifunctional nanochannels that are poised to reinvent separation membranes with performances exceeding those of state-of-the-art polymeric membranes within the water-energy nexus. Today, these water nanochannels can be broadly categorized into biological, biomimetic and synthetic, owing to their different natures, physicochemical properties and methods for membrane nanoarchitectonics. Furthermore, against the backdrop of different separation mechanisms, different types of nanochannel exhibit unique merits and limitations, which determine their usability and suitability for different membrane designs. Herein, this review outlines the progress of a comprehensive amount of nanochannels, which include aquaporins, pillar[5]arenes, I-quartets, different types of nanotubes and their porins, graphene-based materials, metal- and covalent-organic frameworks, porous organic cages, MoS₂, and MXenes, offering a comparative glimpse into where their potential lies. First, we map out the background by looking into the evolution of nanochannels over the years, before discussing their latest developments by focusing on the key physicochemical and intrinsic transport properties of these channels from the chemistry standpoint. Next, we put into perspective the fabrication methods that can nanoarchitecture water channels into high-performance nanochannel-enabled membranes, focusing especially on the distinct differences of each type of nanochannel and how they can be leveraged to unlock the as-promised high water transport potential in current mainstream membrane designs. Lastly, we critically evaluate recent findings to provide a holistic qualitative assessment of the nanochannels with respect to the attributes that are most strongly valued in membrane engineering, before discussing upcoming challenges to share our perspectives with researchers for pathing future directions in this coming of age of water channels.

Supramolecular Detoxification of Macromolecular Biotoxin through the Complexation by a Large-Sized Macrocycle

Biotoxins are diverse, complex, and hypertoxic, ultimately serving as grave and lasting menaces to humanity. Here, it is aimed to introduce a new detoxification methodology for macromolecular biotoxin through complexation by a very large macrocycle. A 25-mer peptide isolated from Lycosa erythrognatha spider venom (LyeTxI) is selected as the model macromolecular biotoxin. Quaterphen[4]arene, with a side length of ≈1.6 nm, has a sufficient cavity to bind LyeTxI. Hence, the water-soluble derivative of Quaterphen[4]arene (H) is designed and synthesized. H exhibits an overall host-guest complexation toward LyeTxI, resulting in a considerably high association constant of (7.01 ± 0.18) × 10⁷  m^-1 . This encapsulation of peptide is interesting as traditional macrocycles can only engulf the amino acid residues of peptides due to their limited cavity size. In vitro assay verifies that complexation by H inhibits the interactions of LyeTxI with cell membranes, thereby reducing its cytotoxicity, suppressing hemolysis, and decreasing the release of lactate dehydrogenase. Notably, the intravenous administration of H has a significant therapeutic effect on LyeTxI-poisoned mice, alleviating inflammation and tissue damage, and markedly improving the survival rate from 10% to 80%. An efficient and potentially versatile approach is provided to detoxify macromolecular biotoxins, with giant macrocycle serving as an antidote.

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.

Complexation of specific residues by carboxylatopillar[6]arene for improving the zymolytic stability of arginine-containing peptides

A general strategy for improving the zymolytic stability against proteases is reported. Carboxylatopillar[6]arene (CP6A) could effectively bind arginine and arginine-containing peptides, thereby improving the stability of angiotensin peptides in the presence of trypsin by the complexation of the side chain of the arginine residue.

Supramolecular Radiosensitizer Based on Hypoxia-Responsive Macrocycle

Radiotherapy (RT) has been viewed as one of the most effective and extensively applied curatives in clinical cancer therapy. However, the radioresistance of tumor severely discounts the radiotherapy outcomes. Here, an innovative supramolecular radiotherapy strategy, based on the complexation of a hypoxia-responsive macrocycle with small-molecule radiosensitizer, is reported. To exemplify this tactic, a carboxylated azocalix[4]arene (CAC4A) is devised as molecular container to quantitatively package tumor sensitizer banoxantrone dihydrochloride (AQ4N) through reversible host-guest interaction. Benefited from the selective reduction of azo functional groups under hypoxic microenvironment, the supramolecular prodrug CAC4A•AQ4N exhibits high tumor accumulation and efficient cellular internalization, thereby significantly amplifying radiation-mediated tumor destruction without appreciable systemic toxicity. More importantly, this supramolecular radiotherapy strategy achieves an ultrahigh sensitizer enhancement ratio (SER) value of 2.349, which is the supreme among currently reported noncovalent-based radiosensitization approach. Further development by applying different radiosensitizing drugs can make this supramolecular strategy become a general platform for boosting therapeutic effect in cancer radiotherapies, tremendously promising for clinical translation.

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.

Supramolecular systems prepared using terpyridine-containing pillararene

Recent progresses about the preparation of terpyridine-containing pillararene, as well as the utilization of those building blocks for making external stimulud-responsive supramolecular systems were summarized in this review.

Fine-Tuning Macrocycle Cavity to Selectively Bind Guests in Water for Near-Infrared Photothermal Conversion

The rational and specific synthesis of the required organic macrocycles to bind the size-matched targeted guests without undesired macrocyclic byproducts remains a great challenge. Herein, based on a new naphthalimide...

Molecular Recognition by Pillar[5]arenes: Evidence for Simultaneous Electrostatic and Hydrophobic Interactions

The formation of inclusion complexes between alkylsulfonate guests and a cationic pillar[5]arene receptor in water was investigated by NMR and ITC techniques. The results show the formation of host-guest complexes stabilized by electrostatic interactions and hydrophobic effects with binding constants of up to 10⁷ M⁻¹ for the guest with higher hydrophobic character. Structurally, the alkyl chain of the guest is included in the hydrophobic aromatic cavity of the macrocycle while the sulfonate groups are held in the multicationic portal by ionic interactions.

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.

A dendritic polyamidoamine supramolecular system composed of pillar[5]arene and azobenzene for targeting drug-resistant colon cancer

Fusobacterium nucleatum caused drug-resistant around tumor sites often leads to the failure of chemotherapy during colorectal cancer (CRC) treatment. Multifunctional cationic quaternary ammonium materials have been widely used as broad-spectrum antibacterial agents in antibacterial and anticancer fields. Herein, we design a smart supramolecular quaternary ammonium nanoparticle, namely quaternary ammonium PAMAM-AZO@CP[5]A (Q-P-A@CP[5]A), consisting of azobenzene (AZO)-conjugated dendritic cationic quaternary ammonium polyamidoamine (PAMAM) as the core and carboxylatopillar[5]arene (CP[5]A)-based switch, for antibacterial and anti-CRC therapies. The quaternary ammonium-PAMAM-AZO (Q-P-A) core endows the supramolecular system with enhanced antibacterial and anticancer properties. -N⁺CH₃ groups on the surface of Q-P-A are accommodated in the CP[5]A cavity under normal conditions, which significantly improves the biocompatibility of Q-P-A@CP[5]A. Meanwhile, the CP[5]A host can be detached from -N⁺CH₃ groups under pathological conditions, achieving efficient antibacterial and antitumor therapies. Furthermore, azoreductase in the tumor site can break the -NN- bonds of AZO in Q-P-A@CP[5]A, leading to the morphology recovery of supramolecular nanoparticles and CRC therapy through inducing cell membrane rupture. Both in vitro and in vivo experiments demonstrate that Q-P-A@CP[5]A possesses good biocompatibility, excellent antibacterial effect, and CRC treatment capability with negligible side effects. This supramolecular quaternary ammonium system provides an effective treatment method to overcome chemotherapy-resistant cancer caused by bacteria.

Bioapplication of cyclodextrin-containing montmorillonite

Recent progresses in the integration of CDs and montmorillonite, as well as applications of CD-containing montmorillonite hybrid host systems are summarized in this review. Several efficient synthesis strategies, such as ion exchange, metal coordination, supramolecular strategies, polymerizations and organic synthesis methods, have been discussed during the preparation of CDs/montmorillonite hybrid composites. In particular, diverse instrumental techniques were highly recommended for characterizing the as-obtained hybrid systems, including their chemical composition and structures, crystallinity, surface/self-assembled morphologies, as well as other particular physiochemical properties, providing a direct guide for promoting the desired structures and exploring various applications. It should be noted that the introduction of functional groups, as well as the integration of CDs and montmorillonite granted the thus obtained CD-containing montmorillonite hybrid host systems a lot of unique features, providing great opportunities for expanding the practical applications to a series of biological and environmental areas, such as biosensors, sorption and decontamination of bio/environmental hazardous materials, biostudies about aqueous dispersity, stability and biocompatibility, drug loading and target delivery, controlled and sustained drug release, as well as antibacterial.

Pillar[6]arene-Based Supramolecular Nanocatalysts for Synergistically Enhanced Chemodynamic Therapy by the Intracellular Cascade Reaction

Chemodynamic therapy (CDT) based on the intracellular Fenton reaction has become increasingly explored in cancer treatment. However, the mildly acidic tumor microenvironment and the limited amount of intracellular hydrogen peroxide (H₂O₂) will create issues for CDT to perform a sustained and high-efficiency treatment. Therefore, how to selectively reduce the pH value and augment the amount of H₂O₂ in tumor tissues has become the key factor for realizing excellent CDT. Besides, the majority of the reported CDT systems have been constructed from iron-based inorganic or metal-organic framework nanomaterials due to the decisive role of metals in CDT, which restricts the development of CDT. In this study, inspired by the host-guest interactions between pillar[6]arene and ferrocene, a ternary pillar[6]arene-based supramolecular nanocatalyst (GOx@T-NPs) for CDT is reported for the first time. GOx@T-NPs not only exhibited a high-efficiency catalytic ability to convert glucose into hydroxyl radicals (^•OH) and to reduce the pH value inside cancer cells for significant enhancement of the CDT effect, but they also showed sensitive glutathione-induced camptothecin (CPT) prodrug release capacity for further improving the efficiency of CDT. Hence, GOx@NPs possessed excellent ability to synergistically enhance the CDT. Additionally, an antitumor mechanism study showed that the prominent tumor inhibition capacity of GOx@T-NPs was derived from trimodal synergistic interactions of CDT, starvation therapy, and chemotherapy. Moreover, GOx@T-NPs manifested good biocompatibility and tumor selectivity with few side effects in major organs. This work broadens the range of materials available for CDT and demonstrates new developments in pillar[n]arene-based multimodal synergistic treatment systems.

Supramolecular Drug Delivery System from Macrocycle-Based Self-Assembled Amphiphiles for Effective Tumor Therapy

Intelligent drug delivery systems (DDSs) that can improve therapeutic outcomes of antitumor agents and decrease their side effects are urgently needed to satisfy special requirements of treatment of malignant tumors in clinics. Here, the fabrication of supramolecular self-assembled amphiphiles based on the host-guest recognition between a cationic water-soluble pillar[6]arene (WP6A) host and a sodium decanesulfonate guest (G) is reported. The chemotherapeutic agent doxorubicin hydrochloride (DOX) can be encapsulated into the formed vesicle (G/WP6A) to construct supramolecular DDS (DOX@G/WP6A). WP6A affords strong affinities to G to avoid undesirable off-target leakage during delivery. Nanoscaled DOX@G/WP6A is capable of preferentially accumulating in tumor tissue via enhanced permeability and retention (EPR) effect. After internalization by tumor cells, the abundant adenosine triphosphate (ATP) binds competitively with WP6A to trigger the disintegration of self-assembled vesicles with the ensuing release of DOX. In vitro and in vivo research confirmed that DOX@G/WP6A is not only able to promote antitumor efficacy but also reduce DOX-related systemic toxicity. The above favorable findings are ascribed to the formation of ternary self-assembly, which profits from the combination of the factors of the EPR effect and the ATP-triggered release.

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.

MOF-based multi-stimuli-responsive supramolecular nanoplatform equipped with macrocycle nanovalves for plant growth regulation

Controllable and on-demand delivery of agrochemicals such as plant hormones is conducive to improving agrochemicals utilization, tackling water and environmental pollution, reducing soil acidification, and realizing the goals of precision agriculture. Herein, a smart plant hormone delivery system based on metal-organic frameworks (MOFs) and supramolecular nanovalves, namely gibberellin (GA)-loaded CLT6@PCN-Q, is constructed through supramolecular host-guest interaction to regulate the growth of dicotyledonous Chinese cabbage and monocotyledonous wheat. The porous nanoscale MOF (NMOF) with a uniform diameter of 97 nm modified by quaternary ammonium (Q) stalks is served as a cargo reservoir, followed by the decoration of carboxylated leaning tower[6]arene (CLT6) based nanovalves on NMOF surfaces through host-guest interactions to fabricate CLT6@PCN-Q with a diameter of ∼101 nm and a zeta potential value of -13.2 mV. Interestingly, the as-fabricated supramolecular nanoplatform exhibits efficient cargo loading and multi-stimuli-responsive release under various external stimuli including pH, temperature, and competitive agent spermine (SPM), which can realize the on-demand release of cargo. In addition, GA-loaded CLT6@PCN-Q is capable of effectively promoting the seeds germination of wheat and stem growth of dicotyledonous Chinese cabbage and monocotyledonous wheat (1.86 and 1.30 times of control groups, respectively). The smart supramolecular nanoplatform based on MOFs and supramolecular nanovalves paves a way for the controlled delivery of plant hormones and other agrochemicals for promoting plant growth, offering new insights and methods to realize precision agriculture. STATEMENT OF SIGNIFICANCE: To achieve controllable and sustainable release of cargos such as agrochemicals, a smart MOF-based multi-stimuli-responsive supramolecular nanoplatform equipped with supramolecular nanovalves was fabricated via the host-guest interaction between quaternary ammonium stalks-functionalized nanoMOFs and water-soluble leaning tower[6]arene. The as-prepared supramolecular nanoplatform with uniform diameter distribution demonstrated good cargo release in response to various external stimuli. The installation of synthetic macrocycles could effectively reduce cargo loss in the pre-treatment process. This type of supramolecular nanoplatform exhibited good promoting effect on seed germination and plant growth dicotyledonous Chinese cabbage and monocotyledonous wheat. As an eco-friendly, controlled, and efficient cargo delivery system, this supramolecular nanoplatform will be a promising candidate in precision agriculture and controlled drug release to attract the broad readership.

Redox-Driven Chiral Inversion of Water-Soluble Pillar[5]arene with l-Cystine Derivative in the Aqueous Medium

In the aqueous solution, l-CySS-OMe induced pS-WP5 from racemic WP5. Upon the addition of dithiothreitol as a reducing reagent to the above system, pS-WP5 was then converted to pR-WP5 for the reason that l-CySS-OMe was reduced to l-Cys-OMe. Followed by the addition of H₂O₂ as an oxidation reagent, pR-WP5 was converted back to pS-WP5. The chiral conformational transferring process between pR-WP5 and pS-WP5 can be easily and visually observed by reading the CD signal.

Mono-mercapto-functionalized pillar[5]arene: a host-guest complexation accelerated reversible redox dimerization

A mono-mercapto-functionalized pillar[5]arene and its dimer, capable of being reversibly interconverted, were successfully synthesized. Fascinatingly, a faster reversible redox conversion involving a dynamic disulfide bond was observed between their host-guest complexes compared with the hosts themselves.

Construction of a hydroxide responsive C3-symmetric supramolecular gel for controlled release of small molecules

A C3-symmetric acylhydrazone-based low molecular weight gelator (BHTP) bearing three pyridine units was synthesized and it was found to form a stable supramolecular gel in the mixture solvent of DMSO-H2O. The morphology of the gel as observed by FE-SEM showed a dense sheet structure. Hydrogen bonding and π-π stacking between the gelators were determined as the non-covalent interactions for the gelation, which were investigated thoroughly using XRD, UV-Vis, 1H NMR and FT-IR instruments. BHTP could form pH tolerant supramolecular gels in the widest range of pH values from 1 to 11. The DMSO-H2O (v : v = 1 : 1) gel exhibited selective response to OH- over a series of other anions through the color change from a white gel to a yellow solution, and the OH- response mechanism was proved by 1H NMR experiments. In solution, the lowest detection limit of BHTP for OH- was calculated to be as low as 1.62 × 10-7 M via UV-Vis titration experiments. Finally, encapsulation and controlled release of small molecules such as rhodamine B, crystal violet and methyl orange have been successfully carried out, demonstrating the potential for drug delivery application of this C3-symmetric supramolecular gel. This work opens a novel avenue for the preparation of supramolecular gel-based multiple functional smart materials.

Multifunctional Pillar[n]arene-Based Smart Nanomaterials

The construction of smart nanomaterials from host macrocycles that are responsive to specific stimuli has gained significant attention in recent years. The application of pillar[n]arenes has been of particular interest given their ease of functionalization and tunability of the intrinsic cavity electronic properties that allows them to encapsulate a great variety of guests and complex with metal ions with high selectivity via noncovalent interactions, endowing them with captivating properties and functions. Herein, we present the most recent advances in the design and functionalization of pillar[n]arene-based smart nanomaterials, and their applications for sensing, catalysis, drug delivery, and artificial transmembrane channels.

Self-Assembling Systems Based on Pillar[5]arenes and Surfactants for Encapsulation of Diagnostic Dye DAPI

In this paper, we report the development of the novel self-assembling systems based on oppositely charged Pillar[5]arenes and surfactants for encapsulation of diagnostic dye DAPI. For this purpose, the aggregation behavior of synthesized macrocycles and surfactants in the presence of Pillar[5]arenes functionalized by carboxy and ammonium terminal groups was studied. It has been demonstrated that by varying the molar ratio in Pillar[5]arene-surfactant systems, it is possible to obtain various types of supramolecular systems: host-guest complexes at equimolar ratio of Pillar[5]arene-surfactant and interpolyelectrolyte complexes (IPECs) are self-assembled materials formed in aqueous medium by two oppositely charged polyelectrolytes (macrocycle and surfactant micelles). It has been suggested that interaction of Pillar[5]arenes with surfactants is predominantly driven by cooperative electrostatic interactions. Synthesized stoichiometric and non-stoichiometric IPECs specifically interact with DAPI. UV-vis, luminescent spectroscopy and molecular docking data show the structural feature of dye-loaded IPEC and key role of the electrostatic, π-π-stacking, cation-π interactions in their formation. Such a strategy for the design of supramolecular Pillar[5]arene-surfactant systems will lead to a synergistic interaction of the two components and will allow specific interaction with the third component (drug or fluorescent tag), which will certainly be in demand in pharmaceuticals and biomedical diagnostics.

Self Assembled Cages with Mechanically Interlocked Cucurbiturils

We report preparation of (bis)aniline ligand 4 which contains a central viologen binding domain and its subcomponent self-assembly with aldehyde 5 and Fe(OTf)2 in CH3CN to yield tetrahedral assembly 6. Complexation of ligand 4 with CB[7] in the form of CB[7]•4•2PF6 allows the preparation of assembly 7 which contains an average of 1.95 (range 1-3) mechanically interlocked CB[7] units. Assemblies 6 and 7 are hydrolytically unstable in water due to their imine linkages. Redesign of our system with water stable 2,2'-bipyridine end groups was realized in the form of ligands 11 and 16 which also contain a central viologen binding domain. Self-assembly of 11 with Fe(NTf2)2 gave tetrahedral MOP 12 as evidenced by 1H NMR, DOSY, and mass spectrometric analysis. In contrast, isomeric ligand 16 underwent self-assembly with Fe(OTf)2 to give cubic assembly 17. Precomplexation of ligands 11 and 16 with CB[7] gave the acetonitrile soluble CB[7]•11•2PF6 and CB[7]•16•2PF6 complexes. Self-assembly of CB[7]•11•2PF6 with Fe(OTf)2 gave tetrahedron 13 which contains on average 1.8 mechanically interlocked CB[7] units as determined by 1H NMR, DOSY, and ESI-MS analysis. Self-assembly of CB[7]•16•2PF6 with Fe(OTf)2 gave cube 13 which contains 6.59 mechanically interlocked CB[7] units as determined by 1H NMR and DOSY measurements.

Complexation of an Antimicrobial Peptide by Large-Sized Macrocycles for Decreasing Hemolysis and Improving Stability

Traditional macrocyclic hosts have finite cavity sizes, generally 5-10 Å, which are commonly adaptive to recognize small guests rather than biological macromolecules. Here two water-soluble large-sized quaterphen[n]arenes (WQPns, n=3, 4) were designed and synthesized. These two hosts present significantly distinct recognition abilities. Specifically, they could strongly complex an antimicrobial peptide, pexiganan (PXG) with the association constants (Ka ) of (4.20±0.23)×104  M-1 for PXG/WQP3 and (2.46±0.44)×105  M-1 for PXG/WQP4. Complexation of PXG by WQP3 and WQP4 served to decrease the hemolysis of PXG in rabbit red blood cells in a statistically significant way. Furthermore, host-guest complexation was shown to substantially enhance metabolic stability of PXG in presence of proteinase K, rat plasma and liver or kidney homogenates.

Towards Universal Stimuli-Responsive Drug Delivery Systems: Pillar[5]arenes Synthesis and Self-Assembly into Nanocontainers with Tetrazole Polymers

In this work, we have proposed a novel universal stimulus-sensitive nanosized polymer system based on decasubstituted macrocyclic structures-pillar[5]arenes and tetrazole-containing polymers. Decasubstituted pillar[5]arenes containing a large, good leaving tosylate, and phthalimide groups were first synthesized and characterized. Pillar[5]arenes containing primary and tertiary amino groups, capable of interacting with tetrazole-containing polymers, were obtained with high yield by removing the tosylate and phthalimide protection. According to the fluorescence spectroscopy data, a dramatic fluorescence enhancement in the pillar[5]arene/fluorescein/polymer system was observed with decreasing pH from neutral (pH = 7) to acidic (pH = 5). This indicates the destruction of associates and the release of the dye at a pH close to 5. The presented results open a broad range of opportunities for the development of new universal stimulus-sensitive drug delivery systems containing macrocycles and nontoxic tetrazole-based polymers.

Pillararene-based self-assemblies for electrochemical biosensors

The ingenious design and synthesis of novel macrocycles bring out renewed vigor of supramolecular chemistry in the past decade. As an intriguing class of macrocycles, pillararene and pillararene-based functional materials that are constructed through the noncovalent bond self-assembly approach have been undergoing a rapid growth, benefiting from their unique structures and physiochemical properties. This review elaborates recent significant advances of electrochemical studies based on pillararene systems. Fundamental electrochemical behavior of pillar[n]arene[m]quinone and pillararene-based self-assemblies as well as their applications in electrochemical biosensors are highlighted. In addition, the advantages and functions of pillararene self-assembly systems resulted from the unique molecular architectures are analyzed. Finally, current challenges and future development tendency in this burgeoning field are discussed from the viewpoint of both fundamental research and applications. Overall, this review not only manifests the main development vein of pillararene-based electrochemical systems, but also conquers a solid foundation for their further bioelectrochemical applications.

Difunctionalized pillar[5]arene-based polymer nanosheets for photodynamic therapy of Staphylococcus aureus infection

Bacterial infections pose severe threats to global public health security. Developing antibacterial agents with both high efficiency and safety to handle this problem has become a top priority. Here, highly stable and effective polymer nanosheets have been constructed by the covalent co-assembly of a pillar[5]arene derivative and metalloporphyrin for photodynamic antibacterial therapy (PDAT). The monolayer nanosheets are strongly positively charged and thus capable of binding with Staphylococcus aureus (SA) through electrostatic interactions. Additionally, the nanosheets can be activated to generate reactive oxygen species (ROS) under white-light irradiation, and exhibit satisfactory antibacterial performance towards SA. More importantly, cell viability assays demonstrate that the nanosheets show little to no cytotoxicity impact on mammalian cells even when the concentrations are much higher than those employed in the antibacterial studies. The above results suggest that the polymer nanosheets could be an effective antibacterial agent to overcome bacterial infections and hold a broad range of potential applications in real life.

Synergistic enhancement of the emergency treatment effect of organophosphate poisoning by a supramolecular strategy

Poisoning by organophosphorus agents (OPs) is a serious public health issue across the world. These compounds irreversibly inhibit acetylcholinesterase (AChE), resulting in the accumulation of acetylcholine (ACh) and overstimulation of ACh receptors. A supramolecular detoxification system (SDS) has been designed with a view to deliver pyridine-2-aldoxime methochloride (PAM) with a synergistic inhibition effect on the ACh-induced hyperstimulation through host-guest encapsulation. NMR and fluorescence titration served to confirm the complexation between carboxylatopillar[6]arene (CP6A) and PAM as well as ACh with robust affinities. Patch-clamp studies proved that CP6A could exert an inhibition effect on the ACh-induced hyperstimulation of ACh receptors. Support for the feasibility of this strategy came from fluorescence imaging results. In vivo studies revealed that complexation by CP6A serves to increase the AChE reactivation efficiency of PAM. The formation of the PAM/CP6A complex contributed to enhance in a statistically significant way the ability of PAM not only to relieve symptoms of seizures but also to improve the survival ratio in paraoxon-poisoned model rats. These favorable findings are attributed to synergistic effects that PAM reactivates AChE to hydrolyze ACh and excess ACh is encapsulated in the cavity of CP6A to relieve cholinergic crisis symptoms.

Macrocyclic-Amphiphile-Based Self-Assembled Nanoparticles for Ratiometric Delivery of Therapeutic Combinations to Tumors

Combination chemotherapy refers to the use of multiple drugs to treat cancer. In this therapy, the optimal ratio of the drugs is essential to achieve drug synergism and the desired therapeutic effects. However, most delivery strategies are unable to precisely control the ratio of the drugs during the drug loading and delivery processes, resulting in inefficient synergy and unpredictable efficacy. Herein, a macrocyclic-amphiphile-based self-assembled nanoparticle (MASN) that achieves precise loading and ratiometric delivery of therapeutic combinations is presented. By integrating multiple macrocyclic cavities within a single nanoparticle, the MASN can load multiple drug molecules via the host-guest interaction, and the ratio of the drugs loaded can be predicted with their initial concentrations and characteristic binding affinity. Moreover, MASNs are readily degraded under a hypoxic microenvironment, allowing spontaneous release of the drugs upon reaching tumor tissues. With precise drug loading and controlled release mechanisms, MASNs achieve ratiometric delivery of multiple commercial drugs to tumors, thereby achieving optimal anti-tumor effects. Since the optimal drug ratio of a therapeutic combination can be quickly determined in vitro, MASNs can translate this optimal ratio to the therapeutic benefits in vivo, providing a potential platform for the rapid development of effective combination cancer therapies involving multiple drugs.

Highly Selective Separation of Isopropylbenzene and α-Methylstyrene by Nonporous Adaptive Crystals of Perbromoethylated Pillararene via Vapor- and Liquid-Phase Adsorptions

Isopropylbenzene (IPB) and α-methylstyrene (AMS), two members of C9 aromatics, are important in both industrial production and laboratory research, but the separation of IPB/AMS mixtures is still a big challenge. Here, we provide a new strategy to separate IPB and AMS using nonporous adaptive crystals of four pillararenes, perethylated pillar[5]arene, perethylated pillar[6]arene, perbromoethylated pillar[5]arene, and perbromoethylated pillar[6]arene (BrP6). Among them, BrP6 selectively adsorbs IPB from an equal volume mixture of IPB and AMS with >95% purity for solid-vapor phase adsorption and >94% purity for solid-liquid phase adsorption, while the selectivities for the other three pillararenes are unsatisfactory. Single-crystal structural analyses combined with powder X-ray diffraction and differential scanning calorimetry experiments demonstrate that the selectivity arises from the different stabilities of guest-loaded BrP6 crystals. Moreover, the reversible transitions between guest-free and IPB-loaded structures indicate the preeminent recycling performance of BrP6 crystals.

Pressure-driven, solvation-directed planar chirality switching of cyclophano-pillar[5]arenes (molecular universal joints)

Planar chiral cyclophanopillar[5]arenes with a fused oligo(oxyethylene) or polymethylene subring (MUJs), existing as an equilibrium mixture of subring-included (in) and -excluded (out) conformers, respond to hydrostatic pressure to exhibit dynamic chiroptical property changes, leading to an unprecedented pressure-driven chirality inversion and the largest ever-reported leap of anisotropy (g) factor for the MUJ with a dodecamethylene subring. The pressure susceptivity of MUJs, assessed by the change in g per unit pressure, is a critical function of the size and nature of the subring incorporated and the solvent employed. Mechanistic elucidations reveal that the in-out equilibrium, as the origin of the MUJ's chiroptical property changes, is on a delicate balance of the competitive inclusion of subrings versus solvent molecules as well as the solvation of the excluded subring. The present results further encourage our use of pressure as a unique tool for dynamically manipulating various supramolecular devices/machines.