Synthesis of the first amphiphilic pillar[6]arene and its enzyme-responsive self-assembly in water

A Visible-Light Regulated ATP Transport in Retinal-Modified Pillar[6]arene Layer-by-Layer Self-Assembled Sub-Nanochannel

Natural light-responsive rhodopsins play a critical role in visual conversion, signal transduction, energy transmission, etc., which has aroused extensive interest in the past decade. Inspired by these gorgeous works of living beings, scientists have constructed various biomimetic light-responsive nanochannels to mimic the behaviors of rhodopsins. However, it is still challenging to build stimuli-responsive sub-nanochannels only regulated by visible light as the rhodopsins are always at the sub-nanometer level and regulated by visible light. Pillar[6]arenes have an open cavity of 6.7 Å, which can selectively recognize small organic molecules. They can be connected to ions of ammonium or carboxylate groups on the rims. Therefore, we designed and synthesized the amino and carboxyl-derived side chains of pillar[6]arenes with opposite charges. The sub-nanochannels were constructed through the electrostatic interaction of layer-by-layer self-assembled amino and carboxyl-derived pillar[6]arenes. Then, the natural chromophore of the retinal with visible light-responsive performance was modified on the upper edge of the sub-nanochannel to realize the visible light switched on and off. Finally, we successfully constructed a visible light-responsive sub-nanochannel, providing a novel method for regulating the selective transport of energy-donating molecules of ATP.

Antibacterial Activity of Various Morphologies of Films Based on Guanidine Derivatives of Pillar[5]arene: Influence of the Nature of One Substitute on Self-assembly

The progress of the pillar[5]arene chemistry allowed us to set out a new concept on application of the supramolecular assemblies to create antimicrobial films with variable surface morphologies and biological activities. Antibacterial films were derived from the substituted pillar[5]arenes containing nine pharmacophoric guanidine fragments and one thioalkyl substituent. Changing the only thioalkyl fragment in the macrocycle structure made it possible to control the biological activity of the resulting antibacterial coating. Pretreatment of the surface with aqueous solution of the amphiphilic pillar[5]arenes reduced the biofilm thickness by 56 ± 10% of Gram-positive Staphylococcus aureus in the case of the pillar[5]arene containing a thiooctyl fragment and by 52 ± 7% for the biofilm of Gram-negative Klebsiella pneumoniae in the case of pillar[5]arene containing a thiooctadecyl fragment. Meanwhile, the cytotoxicity of the synthesized macrocycles was examined at a concentration of 50 μg/mL, which was significantly lower than that of bis-guanidine-based antimicrobial preparations.

Supramolecular host-guest nanosystems for overcoming cancer drug resistance

Cancer drug resistance has become one of the main challenges for the failure of chemotherapy, greatly limiting the selection and use of anticancer drugs and dashing the hopes of cancer patients. The emergence of supramolecular host-guest nanosystems has brought the field of supramolecular chemistry into the nanoworld, providing a potential solution to this challenge. Compared with conventional chemotherapeutic platforms, supramolecular host-guest nanosystems can reverse cancer drug resistance by increasing drug uptake, reducing drug efflux, activating drugs, and inhibiting DNA repair. Herein, we summarize the research progress of supramolecular host-guest nanosystems for overcoming cancer drug resistance and discuss the future research direction in this field. It is hoped that this review will provide more positive references for overcoming cancer drug resistance and promoting the development of supramolecular host-guest nanosystems.

Dual-Responsive Drug-Delivery System Based on PEG-Functionalized Pillararenes Containing Disulfide and Amido Bonds for Cancer Theranostics

The construction of a smart drug-delivery system based on amphiphilic pillararenes with multiple responsiveness properties has become an important way to improve the efficacy of tumor chemotherapy. Here, a new PEG-functionalized pillararene (EtP5-SS-PEG) containing disulfide and amido bonds was designed and synthesized, which has been used to construct a novel supramolecular nanocarrier through a host-guest interaction with a perylene diimide derivative (PDI-2NH4 ) and their supramolecular self-assembly. This nanocarrier showed good drug loading capability, and dual stimulus responsiveness to enzyme and GSH (glutathione). After loading of doxorubicin (DOX), the prepared nanodrugs displayed efficient DOX release and outstanding cancer theranostics ability.

"Rim-Differentiated" Pillar[6]arenes

A "rim-differentiated" pillar[6]arene (RD-P[6]) was obtained successfully, with the assistance of a dimeric silver trifluoroacetate template, among eight different constitutional isomers in a direct and regioselective manner. The solid-state conformation of this macrocycle could switch from the 1,3,5-alternate to a truly rim-differentiated one upon guest inclusion. This highly symmetric RD-P[6] not only hosts metal-containing molecules inside its cavity, but also can form a pillar[6]arene-C₆₀ adduct through co-crystallization on account of donor-acceptor interactions. The development of synthetic strategies to desymmetrize pillararenes offers new opportunities for engineering complex molecular architectures and organic electronic materials.

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.

A pH-Responsive Supramolecular Drug Delivery System Constructed by Cationic Pillar[5]arene for Enhancing Antitumor Activity

Drug delivery systems have good biocompatibiliy and low side effects for cancer treatment, but overcoming high efficiency of drug-loading and the drug-targeting controlled release still remains challenging. In this work, supramolecular vesicles, with pH-triggering effect, have been successfully constructed for drug delivery, which are fabricated by the complexation between a cationic pillar[5]arene (DAWP5) and a sodium dodecyl sulfonate (SDS) in aqueous solution. Drug-loading and releasing results demonstrated that anticancer drug doxorubicin (DOX) could be loaded efficiently by such cationic vesicles in neutral condition, and the drug release could be controlled in the simulated weak acid environment of tumor cells. Moreover, the vesicles had low cytotoxicity to normal human cell (L02), while the DOX-loaded vesicles could significantly enhance the cytotoxicity of free DOX for normal cell L02 and four tested tumor cells (Hela, HepG2, MGC-803 and T24). Especially for HepG2, after 24 h incubation time, IC₅₀ of DOX-loaded vesicles was only 0.79 μM, about 23% of that of DOX (3.43 μM). These results suggested that such novel vesicles have promising potential to construct nano-drug delivery systems for various biomedical applications.

Cationic Water-Soluble Pillar[5]arene-Modified Cu2-xSe Nanoparticles: Supramolecular Trap for ATP and Application in Targeted Photothermal Therapy in the NIR-II Window

With the rapid progress of nanotechnology, near-infrared (NIR), light-assisted phototherapy as a minimally invasive local cancer therapy, especially photothermal therapy (PTT), has captured broad research attention in recent years. However, combined target molecules with a PTT system through reversible supramolecular interactions has been reported rarely. In this work, we constructed a supramolecular nanosystem combining ATP capture and target PTT based on cationic pillar[5]arene (CWP5)-functionalized Cu_2-xSe nanoparticles (Cu_2-xSe@CWP5 NPs). Cu_2-xSe@CWP5 NPs, with an average diameter of approximately 100 nm and strong absorption in the near-infrared-II window, were prepared in water through a facile one-step in situ synthesis method, then (4-carboxybutyl)triphenylphosphonium bromide (TPP), a mitochondria-targeted molecule, was modified on the surface of the particles through the host-guest recognition. Upon irradiation with a 1064 nm laser, the obtained Cu_2-xSe@CWP5/TPP NPs showed remarkably photothermal ablation capability to HeLa cells. Importantly, our Cu_2-xSe@CWP5/TPP NPs exhibited excellent therapeutic effect due to the combination of inhibited hydrolysis of ATP and targeted photothermal therapy upon in vitro and in vivo studies. Significantly, through host-guest interactions, we can modify different types of target molecules within this PTT system at will.

Morphology transformation of pillararene-based supramolecular nanostructures

In this feature article, the construction methods and the factors that influence the morphological transformation of pillararene-based supramolecular nanostructures are reviewed.

Discovery of non-classical complex models between a cationic water-soluble pillar[6]arene and naphthalenesulfonate derivatives and their self-assembling behaviors

Molecular recognition based on cationic water-soluble pillar[n]arenes shows considerable advantages in their application in biological and environmental systems, such as excellent anion-binding ability and antimicrobial properties. Unique complex models are discovered in this work where a cationic water-soluble pillar[6]arene binds with disodium 1,5-naphthalenedisulfonate and disodium 2,6-naphthalenedisulfonate at the ratio of 1 : 2, which is proven by results from nuclear magnetic resonance spectroscopy, isothermal titration calorimetry, fluorescence spectroscopy experiments and transmission electron microscopy.

Supramolecular nanotheranostics based on pillarenes

With the rapid development of supramolecular chemistry and nanomaterials, supramolecular nanotheranostics has attracted remarkable attention owing to the advantages compared with conventional medicine. Supramolecular architectures relying on non-covalent interactions possess reversible and stimuli-responsive features; endowing supramolecular nanotheranostics based on supramolecular assemblies great potentials for the fabrication of integrated novel nanomedicines and controlled drug delivery systems. In particular, pillarenes, as a relatively new class of synthetic macrocycles, are important candidates in the construction of supramolecular therapeutic systems due to their excellent features such as rigid and symmetric structures, facile substitution, and unique host-guest properties. This review summarizes the development of pillarene-based supramolecular nanotheranostics for applications in biological mimicking, virus inhibition, cancer therapy, and diagnosis, which contains the following two major parts: (a) pillarene-based hybrid supramolecular nanotheranostics upon hybridizing with porous materials such as mesoporous silica nanoparticles, metal-organic frameworks, metal nanoparticles, and other inorganic materials; (b) pillarene-based organic supramolecular therapeutic systems that include supramolecular amphiphilic systems, artificial channels, and prodrugs based on host-guest complexes. Finally, perspectives on how pillarene-based supramolecular nanotheranostics will advance the field of pharmaceuticals and therapeutics are given.

Supramolecular vesicles based on pillar[n]arenes: design, construction, and applications

Supramolecular vesicles have attracted considerable attention due to their advantages of facile construction, high-cargo-loading capacity, and good biocompatibility. Pillar[n]arenes are a unique family of supramolecular macrocycles, exhibiting excellent features and broad applications due to their intrinsic topology and high functionality. In the past decade, the construction of pillar[n]arene-based supramolecular vesicles has been continuously attempted and developed rapidly. In this review, we mainly summarize the significant advancements of such supramolecular vesicles in the last three years. By showing some representative examples, the design strategies, construction methods, and potential applications of these dynamic nanocarriers are discussed in detail. In particular, the responsiveness of such vesicles to various external stimuli and their applications in drug delivery are highlighted. The outstanding performance of pillar[n]arene-based supramolecular vesicles would definitely enrich the family of supramolecular vesicles and promote the development of dynamic supramolecular materials.

Stimuli-responsive supramolecular nano-systems based on pillar[n]arenes and their related applications

Stimuli-responsive supramolecular nano-systems (SRNS) have been a trending interdisciplinary research area due to the responsiveness upon appropriate stimuli, which makes SRNS very attractive in multiple fields where precise control is vital.

Functionalization of inorganic nanomaterials with pillar[n]arenes

Pillar[n]arenes, which consist of hydroquinone units linked by -CH2- bridges at 2,5-positions, are a relatively new class of synthetic macrocycles since 2008. Their facile preparation and flexible modification properties make them ideal stabilizers for inorganic nanomaterials. Furthermore, their symmetrical and columnar architectures with very rigid and π-rich cavities endow them with rich host-guest properties. This Feature Article provides an overview of the functionalization of inorganic nanomaterials with pillar[n]arenes and their applications. These inorganic nanomaterials are classified into three major classes according to different types of compositions: (1) novel metal nanomaterials; (2) hybrid metal nanomaterials; and (3) porous materials. The applications of these nanomaterials such as catalysis, drug delivery, cancer therapy, and sensing have been comprehensively discussed.

A new amphiphilic pillar[5]arene: synthesis and controllable self-assembly in water and application in white-light-emitting systems

A new amphiphilic pillar[5]arene with excellent surface activity was designed and synthesized successfully for the first time. Interestingly, this pillar[5]arene shows controllable self-assembly behaviour in water and can be applied in white-light-emitting systems.

Pillararene-based self-assembled amphiphiles

Pillararenes are a unique group of supramolecular macrocycles, presenting important features and potential applications on account of their intrinsic structural properties and functionality. Developing pillararene-based self-assembled amphiphiles (PSAs) is an efficient approach to translate pillararenes into functional systems and materials for facilitating their practical applications. In this review article, we highlight recent significant advancements in PSAs. A new standard according to the number, solubility, and amphiphilicity of building blocks is employed for dividing PSAs into different categories. The fabrication of PSAs based on various building blocks and supramolecular interactions, and the formation of amphiphile-based self-assemblies are then discussed based on this standard. Furthermore, interesting stimulus-responsiveness to various factors, such as pH, redox, temperature, light, ionic effect, and host-guest competition, generated by the functional groups on various building blocks is summarized, and the corresponding supramolecular interactions in PSAs and their self-assemblies are elaborated. In addition, some important applications of PSAs and their assemblies are discussed. This review not only provides fundamental findings on the construction of PSAs, but also foresees future research directions in this rapidly developing area.

Enhancing the solubility and bioactivity of anticancer drug tamoxifen by water-soluble pillar[6]arene-based host-guest complexation

A water-soluble pillar[6]arene functions as a solubilizing agent to enhance the solubility and bioactivity of poorly water-soluble anticancer drug tamoxifen by host-guest complexation between it and tamoxifen.

Biological and related applications of pillar[n]arenes

Pillar[n]arenes are a new class of synthetic supramolecular macrocycles streamlined by their particular pillar-shaped architecture which consists of an electron-rich cavity and two fine-tuneable rims. The ease and diversity of the functionalization of the two rims open possibilities for the design of new architectures, topological isomers, and scaffolds. Significantly, this emerging class of macrocyclic receptors offers a unique platform for biological purposes. This review article covers the most recent contributions from the pillar[n]arene field in terms of artificial membrane transport systems, controlled drug delivery systems, biomedical imaging, biosensors, cell adhesion, fluorescent sensing, and pesticide detection based on host-guest interactions. The review also uniquely describes the properties of sub-units that make pillar[n]arenes suitable for biological applications and it provides a detailed outline for the design of new innovative pillar-like structures with specific properties to open up a new avenue for pillar[n]arene chemistry.

Nucleobases, nucleosides, and nucleotides: versatile biomolecules for generating functional nanomaterials

The incorporation of biomolecules into nanomaterials generates functional nanosystems with novel and advanced properties, presenting great potential for applications in various fields. Nucleobases, nucleosides and nucleotides, as building blocks of nucleic acids and biological coenzymes, constitute necessary components of the foundation of life. In recent years, as versatile biomolecules for the construction or regulation of functional nanomaterials, they have stimulated interest in researchers, due to their unique properties such as structural diversity, multiplex binding sites, self-assembly ability, stability, biocompatibility, and chirality. In this review, strategies for the synthesis of nanomaterials and the regulation of their morphologies and functions using nucleobases, nucleosides, and nucleotides as building blocks, templates or modulators are summarized alongside selected applications. The diverse applications range from sensing, bioimaging, and drug delivery to mimicking light-harvesting antenna, the construction of logic gates, and beyond. Furthermore, some perspectives and challenges in this emerging field are proposed. This review is directed toward the broader scientific community interested in biomolecule-based functional nanomaterials.

Hindrance of photodimerization of coumarin derivative induced by pillar[5]arene-based molecular recognition in water

An easy and simple method for the impediment of the photodimerization of coumarin derivative induced by pillar[5]arene-based molecular recognition was provided. Moreover, we successfully use this system in supra-amphiphile self-assembly in water.

A redox-responsive selenium-containing pillar[5]arene-based macrocyclic amphiphile: synthesis, controllable self-assembly in water, and application in controlled release

A selenium-containing pillar[5]arene-based macrocyclic amphiphile was prepared. This amphiphile self-assembled in water to form vesicles with redox responsiveness. Then, these pillar[5]arene-based vesicles were used in the controlled release of DOX.

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).

Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry

In 2008, we reported a new class of pillar-shaped macrocyclic hosts, known as "pillar[n]arenes". Today, pillar[n]arenes are recognized as key players in supramolecular chemistry because of their facile synthesis, unique pillar shape, versatile functionality, interesting host-guest properties, and original supramolecular assembly characteristics, which have resulted in numerous electrochemical and biomedical material applications. In this Review, we have provided historical background to macrocyclic chemistry, followed by a detailed discussion of the fundamental properties of pillar[n]arenes, including their synthesis, structure, and host-guest properties. Furthermore, we have discussed the applications of pillar[n]arenes to materials science, as well as their applications in supramolecular chemistry, in terms of their fundamental properties. Finally, we have described the future perspectives of pillar[n]arene chemistry. We hope that this Review will provide a useful reference for researchers working in the field and inspire discoveries concerning pillar[n]arene chemistry.

Improved in vivo tumor therapy via host–guest complexation

A decomposable and intracellular pH-responsive drug delivery system by immobilizing a water-soluble pillar[5]arene onto hollow mesoporous nanoparticles through host–guest complexation was successfully prepared and its application in controlled drug delivery in vitro and in vivo was also investigated.

Fluorescence indicator displacement detection based on pillar[5]arene-assisted dye deprotonation

A fluorescence switch based on a pH-sensitive dye and a cationic pillar[5]arene was employed in fluorescence indicator displacement detection of phenolic contaminants.

Host–guest interaction enhanced aggregation-induced emission and its application in cell imaging

A host–guest inclusion complex based on a monofunctionalized pillar[5]arene and a tetraphenylethene derivative was prepared, resulting in an enhanced emission from the tetraphenylethene-based guest, which was applied in cell imaging.

A cationic water-soluble biphen[3]arene: synthesis, host–guest complexation and fabrication of a supra-amphiphile

The first cationic water-soluble biphen[3]arene was synthesized, which was used to change the aggregation of the amphiphilic guest in water.

Synthesis of a disulfide-bridged bispillar[5]arene and its application in supramolecular polymers

A disulfide-bridged bispillar[5]arene was synthesized efficiently and applied to fabricate supramolecular polymers, which were redox-responsive and could be used to prepare fluorescent water-dispersible nanospheres.

A water-soluble biphen[3]arene: synthesis, host–guest complexation, and application in controllable self-assembly and controlled release

The first water-soluble biphen[3]arene was synthesized. Its pH-responsive host–guest complexation with secondary ammonium salts in water was investigated. This novel recognition motif was further used in controllable self-assembly and controlled release.

A γ-ray and dual redox-responsive supramolecular polymer constructed by a selenium containing pillar[5]arene dimer and a neutral guest

A novel linear supramolecular polymer was fabricated by self-assembly of a selenium containing pillar[5]arene dimer 1 and a neutral guest 2. This supramolecular polymer can be destroyed by irradiating γ-radiation, or adding H₂O₂ or GSH.

Supramolecular assembly-induced yellow emission of 9,10-distyrylanthracene bridged bis(pillar[5]arene)s

Newly synthesized DSA-bridged bis(pillar[5]arene)s with AIE properties form linear supramolecular polymers upon binding to a neutral guest linker, exhibiting supramolecular assembly-induced yellow fluorescence emission.