Host-Guest-Interaction Enhanced Nitric Oxide Photo-Generation within a Pillar[5]arene Cavity for Antibacterial Gas Therapy

Supramolecular macrocycles with intrinsic cavities have been widely explored as containers to fabricate versatile functional materials via specific host-guest recognitions. However, relatively few studies have focused on the modulation of guest reactivity within a macrocyclic cavity. Here, we demonstrate the confinement effect of pillar[5]arene with an electron-rich and precise cavity that can dramatically enhance guest photoactivity and nitric oxide (NO) generation upon visible light irradiation. Mechanism studies reveal that it is achieved through increasing the ground state nitro-aromatic torsion angle, suppressing the intersystem crossing relaxation path of the S1 state, and accelerating the isomerization reaction path of guest molecules. This NO-generating system displays broad-spectrum antibacterial, biofilm inhibition, and dispersal activities. Moreover, it can accelerate the healing of methicillin-resistant Staphylococcus aureus (MRSA)-infected wounds in vivo.

The Synthesis and Antibacterial Properties of Pillar[5]arene with Streptocide Fragments

The growing problem of bacterial resistance to antimicrobials actualizes the development of new approaches to solve this challenge. Supramolecular chemistry tools can overcome the limited bacterial resistance and side effects of classical sulfonamides that hinder their use in therapy. Here, we synthesized a number of pillar[5]arenes functionalized with different substituents, determined their ability to self-association using DLS, and characterized antimicrobial properties against S. typhimurium, K. pneumoniae, P. aeruginosa, S. epidermidis, S. aureus via a resazurin test. Biofilm prevention concentration was calculated for an agent with established antimicrobial activity by the crystal-violet staining method. We evaluated the mutagenicity of the macrocycle using the Ames test and its ability to affect the viability of A549 and LEK cells in the MTT-test. It was shown that macrocycle functionalized with sulfonamide residues exhibited antimicrobial activity an order higher than pure streptocide and also revealed the ability to prevent biofilm formation of S. aureus and P. aeruginosa. The compound did not show mutagenic activity and exhibited low toxicity to eukaryotic cells. The obtained results allow considering modification of the macrocyclic platforms with classic antimicrobials as an opportunity to give them a "second life" and return to practice with improved properties.

Crystal structure and supra-molecular features of a bis-urea-functionalized pillar[5]arene

The crystal structure of a bis-urea derivative based on A1/A2-functionalized pillar[5]arene (DUP) that encapsulates dimethyl formamide (DMF) inside the macrocyclic cavity is reported. The crystal structure of DUP·DMF, C63H70N4O12·C3H7NO, reveals that out of two urea functionalized spacers, one arm is oriented above the macrocyclic cavity with strong hydrogen-bonding inter-actions between the urea H atoms and DMF guest, whereas, the other arm is positioned away from the macrocycle, leading to inter-molecular hydrogen-bonding inter-actions between the urea H atoms of two adjacent pillar[5]arene macrocycles, resulting in the formation of a supra-molecular dimer.

Macrocycle-Strutted Coordination Microparticles for Fluorescence-Monitored Photosensitization and Substrate-Selective Photocatalytic Degradation

The prosperous advancement of supramolecular chemistry has motivated us to construct supramolecular hybrid materials with integrated functionalities. Herein, we report an innovative type of macrocycle-strutted coordination microparticle (MSCM) using pillararenes as the struts and "pockets", which performs unique activities of fluorescence-monitored photosensitization and substrate-selective photocatalytic degradation. Prepared via a convenient one-step solvothermal method, MSCM showcases the incorporation of supramolecular hybridization and macrocycles, endowed with well-ordered spherical architectures, superior photophysical properties, and photosensitizing capacity, where a self-reporting fluorescence response is exhibited upon photoinduced generation of multiple reactive oxygen species. Importantly, photocatalytic behaviors of MSCM show marked divergence toward three different substrates and reveal pronounced substrate-selective catalytic mechanisms, attributing to the variety in the affinity of substrates toward MSCM surfaces and pillararene cavities. This study brings new insight into the design of supramolecular hybrid systems with integrated properties and further exploration of functional macrocycle-based materials.

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.

Separation of Low-Molecular-Weight Organics by Water-Soluble Macrocyclic Arenes

In this study, we fabricate a series of water-soluble anionic macrocyclic arenes, including pillar[5]arene (WP5), pillar[6]arene (WP6), leaning pillar[6]arene (WLT6), and biphenyl-extended pillar[6]arene (WBpP6), which show different separation capabilities toward low-molecular-weight organics, such as short chain haloalkanes, cyclic aliphatics, and aromatics, in water. The liquid-liquid distribution experiments are carried out at room temperature. The separation factor for low-molecular-weight organics is evaluated in the extraction of equimolar mixtures. WP6 demonstrates a high extraction efficiency of up to 89% in separating toluene/methylcyclohexane mixtures. These adsorbents also have the advantages of rapid adsorption, high separation efficiency, remarkable selectivity, and good recyclability. This work not only expands the application scope of macrocyclic chemistry, but also has practical research value for organics separation and water purification.

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.

An Ultraviolet/Visible Light Regulated Protein Transport Gate Constructed by Pillar[6]arene-based Host-Guest System

Protein transport is an interesting and intrinsic life feature that is highly relevant to physiology and disease in living beings. Herein, inspired by nature, based on the supramolecular host-guest interaction, we have introduced the classical azobenzene light switches and L-phenylalanine derived pillar[6]arene (L-Phe-P6) into the artificial nanochannel to construct light-responsive nanochannels that could regulate protein transport effectively under the control of ultraviolet (UV) and visible (Vis) light. The light-controlled distribution of L-Phe-P6 in the channel led to the difference in surface charges in the nanochannel, which eventually brought the difference in protein transport. This research may not only provide a convenient theoretical model for biological research, but also a flexible light-responsive protein transport model, which will play a crucial role in light-controlled release of protein drugs and so on.

Orthogonal Design of Supramolecular Prodrug Vesicles via Water-Soluble Pillar[5]arene and Betulinic Acid Derivative for Dual Chemotherapy

Supramolecular prodrug vesicles with efficient property for dual chemotherapy have been successfully constructed based on the orthogonal self-assembly between a water-soluble pillar[5]arene host (WP5) and a betulinic acid guest (BA-D) as well as doxorubicin (DOX). Under the acidic microenvironment of cancer cells, both the encapsulated anticancer drug DOX and prodrug BA-D can be effectively released from DOX-loaded WP5⊃BA-D prodrug vesicles for combinational chemotherapy. Furthermore, bioexperiments indicate that DOX-loaded prodrug vesicles can obviously enhance the anticancer efficiency based on the cooperative effect of DOX and BA-D, while remarkably reducing the systematic toxicity in tumor-mice, displaying great potential applications in combinational chemotherapy for cancer treatments.

Stabilization of Antitumor Agent Busulfan through the Encapsulation within a Water-Soluble Pillar[5]arene

The complexation of antitumor agent busulfan by negatively charged carboxylatopillar[5]arenein water is reported. The encapsulation within carboxylatopillar[5]arenein reduces the hydrolytic degradation of busulfan from 90.7 % to 25.2 % after 24 days and accordingly enhances its stability by providing a hydrophobic shelter for busulfan in water. Moreover, the complexation result in 12 times improvement of water solubility for busulfan. Our result provides a supramolecular approach for stabilizing the anticancer agent busulfan.

Carboxylato-Pillar[6]arene-Based Fluorescent Indicator Displacement Assays for Caffeine Sensing

In the present work, we have developed a new indicator displacement system based on pillararene for anionic water-soluble carboxylato pillar [6] arene (WP6) and aromatic fluorescent dye safranine T (ST). A large fluorescence enhancement and colour change of ST were observed after complexation with electron-rich cavity in WP6 because of host-guest twisted intramolecular charge-transfer interactions. The constructed pillararene-indicator displacement system can be applied for caffeine selective detection in water.

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.

Enhanced Desalination Polyamide Membranes Incorporating Pillar[5]arene through in-Situ Aggregation-Interfacial Polymerization-isAGRIP

Membrane-based desalination have an important role in water purification. Inspired by highly performant biological proteins, artificial water channels (AWC) have been proposed as active components to overcome the permeability/selectivity trade-off of desalination processes. Promising performances have been reported with Pillararene crystalline phases revealing impressive molecular-scale separation performances, when used as selective porous materials. Herein, we demonstrate that Pillar[5]arene PA[5] aggregates are in-situ generated and incorporated during the interfacial polymerization, within industrially relevant reverse osmosis polyamide-PA membranes. In particular, we explore the best combination between PA[5] aggregates and m-phenylenediamine (MPD) and trimesoylchloride (TMC) monomers to achieve their seamless incorporation in a defect-free hybrid polyamide PA[5]-PA membranes for enhanced desalination. The performances of the reference and hybrid membranes are evaluated by cross-flow filtration under real reverse osmosis conditions (15.5 bar of applied pressure) by filtration of brackish feed streams. The optimized membranes achieve a ∼40 % improvement, in water permeance of ∼2.76±0.5 L m^-2  h^-1  bar^-1 and high 99.5 % NaCl rejection with respect to the reference TFC membrane and a similar water permeance compared to one of the best commercial BW30 membranes (3.0 L m^-2  h^-1  bar^-1 and 99.5 % NaCl rejection).

Tetraphenylethene-Embedded Pillar[5]arene and [15]Paracyclophane: Distorted Cavities and Host-Guest Binding Properties

Two aggregation-induced emission (AIE) macrocycles (DMP[5]-TPE and PCP[5]-TPE) were prepared by embedding Tetraphenylethene (TPE) unit into the skeletons of Dimethoxypillar[5]arene (DMP[5]) and [15]Paracyclophane ([15]PCP) at meso position, respectively. In crystal, the PCP[5]-TPE showed a distorted cavity, and the incubation of hexane inside the DMP[5]-TPE cavity caused a distinct change in the molecular conformation compared to PCP[5]-TPE. There was no complexation between PCP[5]-TPE and 1,4-dicyanobutane (DCB). UV absorption experiments showed the distorted cavity of DMP[5]-TPE hindered association with DCB.

A Stretchable Pillararene-Containing Supramolecular Polymeric Material with Self-Healing Property

Constructing polymeric materials with stretchable and self-healing properties arise increasing interest in the field of tissue engineering, wearable electronics and soft actuators. Herein, a new type of supramolecular cross-linker was constructed through host-guest interaction between pillar[5]arene functionalized acrylate and pyridinium functionalized acrylate, which could form supramolecular polymeric material via photo-polymerization of n-butyl acrylate (BA). Such material exhibited excellent tensile properties, with maximum tensile strength of 3.4 MPa and strain of 3000%, respectively. Moreover, this material can effectively dissipate energy with the energy absorption efficiency of 93%, which could be applied in the field of energy absorbing materials. In addition, the material showed self-healing property after cut and responded to competitive guest.

Antimicrobial Activity of Calixarenes and Related Macrocycles

Calixarenes and related macrocycles have been shown to have antimicrobial effects since the 1950s. This review highlights the antimicrobial properties of almost 200 calixarenes, resorcinarenes, and pillararenes acting as prodrugs, drug delivery agents, and inhibitors of biofilm formation. A particularly important development in recent years has been the use of macrocycles with substituents terminating in sugars as biofilm inhibitors through their interactions with lectins. Although many examples exist where calixarenes encapsulate, or incorporate, antimicrobial drugs, one of the main factors to emerge is the ability of functionalized macrocycles to engage in multivalent interactions with proteins, and thus inhibit cellular aggregation.

Pillar[5]arene-Based Switched Supramolecular Photosensitizer for Self-Amplified and pH-Activated Photodynamic Therapy

Photodynamic therapy (PDT) has emerged as a promising and spatiotemporally controllable cancer treatment modality. However, serious skin photosensitization during the PDT process limits the clinical application of PDT. Thus, the construction of "smart" and multifunctional photosensitizers has attracted substantial interest. Herein, we develop a mitochondria-targeting and pH-switched hybrid supramolecular photosensitizer by the host-guest interaction. The PDT efficacy of supramolecular photosensitizers can be quenched by the Förster resonance energy transfer (FRET) effect during long circulation and activated by the dissociation of supramolecular photosensitizers in an acidic tumor microenvironment, benefitting from the dynamic feature of the host-guest interaction and pH responsiveness of the water-soluble pillar[5]arene on gold nanoparticles. The rational integration of mitochondria-targeting and reductive glutathione (GSH) elimination in the hybrid switchable supramolecular photosensitizer prolongs the lifetime of reactive oxygen species generated in the PDT near mitochondria and further amplifies the PDT efficacy. Thus, the facile and versatile construction of switchable supramolecular photosensitizer offers not only the targeted and precise phototherapy but also high therapeutic efficacy, which would provide a new path for the clinic application of PDT.

Pillar[n]MaxQ: A New High Affinity Host Family for Sequestration in Water

We report the synthesis, X-ray crystal structure, and molecular recognition properties of pillar[n]arene derivative P[6]AS, which we refer to as Pillar[6]MaxQ along with analogues P[5]AS and P[7]AS toward guests 1-18. The ultratight binding affinity of P[5]AS and P[6]AS toward quaternary (di)ammonium ions renders them prime candidates for in vitro and in vivo non-covalent bioconjugation, for imaging and delivery applications, and as in vivo sequestration agents.

per-Alkoxy-pillar[5]arenes as Electron Donors: Electrochemical Properties of Dimethoxy-Pillar[5]arene and Its Corresponding Rotaxane

1,4-dimethoxypillar[5]arene undergoes reversible multielectron oxidations forming stable radical cations, a property retained when incorporated in [2]rotaxanes, suggesting that pillar[5]arenes can be employed as viable, yet unreported, electron donors.

Cross-Linked Pillar[6]arene Nanosponges Fabricated by the Use of a Supra-Amphiphilic Template: Cargo Encapsulation and Overcoming Multidrug Resistance

We report a general fabrication method for water-soluble pillar[n]arene nanosponges (NS) by the use of a supra-amphiphilic template. For the first time, a supra-amphiphilic template is used to conveniently control the size of host molecule-based NS. The intrinsic cavity of water-soluble pillar[6]arene could stably encapsulate dyes (acridine orange and indocyanine green) and antitumor drugs (doxorubicin hydrochloride and mitoxantrone) by host-guest interaction. NS could deliver antitumor drugs to cancer cells. Multidrug resistance (MDR) of cancer cells (MCF-7/ADR) is overcome by the use of NS with a ninefold reduction in the IC₅₀ value compared to that of the free drug (3.4 μM vs 34.4 μM). Mechanistic studies show that stable encapsulation of the antitumor drug is the reason to overcome MDR.

pH-Induced Transition Between Single-Chain Macrocyclic Amphiphile and [c2]Daisy Chain-Based Bola-Type Amphiphile and the Related Self-Assembly Behavior in Water

Macrocyclic amphiphiles, a type of amphiphiles synthesized based on macrocyclic compounds, have attracted much attention over the past decades due to their unique superiority in the construction of various functional nanomaterials. The regulation of the state of macrocyclic amphiphiles by introducing stimuli-responsive motif to macrocyclic amphiphiles is an efficient way to extend their applications in diverse fields. Herein, pillararene-based macrocyclic amphiphile H1 was prepared. H1 can act as single-chain amphiphile to self-assemble into micelles in water when the pH was ≥5.0. H1 can be protonated to turn into H2 when pH changed to <5.0. Interestingly, H2 formed [c2]daisy chain-based bola-type supramolecular amphiphile. This bola-type supramolecular amphiphile self-assembled into nanosheets in water. Therefore, pH-induced transition between single-chain macrocyclic amphiphile and bola-type amphiphile and the corresponding self-assembly system based on pillararene in water were constructed.

Supramolecular therapeutics to treat the side effects induced by a depolarizing neuromuscular blocking agent

Succinylcholine (Sch) is the only depolarizing neuromuscular blocking agent widely used for rapid sequence induction in emergency rooms. Unfortunately, a variety of (sometimes lethal) adverse effects, such as hyperkalemia and cardiac arrest, are associated with its use, and currently there are no specific antidotes to reverse Sch or to treat these side-effects. Methods: The binding behaviors of Sch and several synthetic receptors, including cucurbit[7]uril, sulfo-calix[4]arene and water-soluble carboxylatopillar[6]arene (WP[6]), were first investigated. With a mouse model, a leathal dose of Sch was selected for evaluation of the antidotal effects of these synthetic receptors on Sch induced mortality. The antidotal effects of a selected synthetic receptor, WP[6], on Sch induced cardiac arrhythmias, hyperkalemia, rhabdomyolysis and paralysis were subsequently evaluated with rat and mouse models. The reversal mechanism was also investigated at a cellular level. Results: All of these macrocyclic molecules exhibited relatively high binding affinities with Sch in vitro. In a Sch-overdosed mouse model, immediate injection of these synthetic receptors right after Sch administration increased the overall survival rate, with WP[6] standing out with the most effective antidotal effects. In addition, administration of WP[6] also reversed the paralysis induced by Sch in a mouse model. Moreover, infusion of WP[6] to Sch-overdosed rats reduced the incidence of cardiac arrhythmia, inhibited the otherwise abnormally high serum potassium levels, and relieved the muscular damage. At the cellular level, WP[6] reversed the Sch induced depolarization and reduced the efflux of intracellular potassium. Conclusion: Synthetic receptors, particularly WP[6], exhibited high binding affinities towards Sch, and presented a significant potential as supramolecular therapeutics to treat the various side effects of Sch by specifically sequestering Sch in vivo.

From Supramolecular Vesicles to Micelles: Controllable Construction of Tumor-Targeting Nanocarriers Based on Host-Guest Interaction between a Pillar[5]arene-Based Prodrug and a RGD-Sulfonate Guest

The targeting ability, drug-loading capacity, and size of the drug nanocarriers are crucial for enhancing the therapeutic index for cancer therapy. Herein, the morphology and size-controllable fabrication of supramolecular tumor-targeting nanocarriers based on host-guest recognition between a novel pillar[5]arene-based prodrug WP5-DOX and a Arg-Gly-Asp (RGD)-modified sulfonate guest RGD-SG is reported. The amphiphilic WP5-DOX⊃RGD-SG complex with a molar ratio of 5:1 self-assembles into vesicles, whereas smaller-sized micelles can be obtained by changing the molar ratio to 1:3. This represents a novel strategy of controllable construction of supramolecular nanovehicles with different sizes and morphologies based on the same host-guest interactions by using different host-guest ratios. Furthermore, in vitro and in vivo studies reveal that both these prodrug nanocarriers could selectively deliver doxorubicin to RGD receptor-overexpressing cancer cells, leading to longer blood retention time, enhanced antitumor efficacy, and reduced systematic toxicity in murine tumor model, suggesting their potential application for targeted drug delivery.

Gated Materials: Installing Macrocyclic Arenes-Based Supramolecular Nanovalves on Porous Nanomaterials for Controlled Cargo Release

Supramolecular nanovalves are an emerging class of important elements that are functionalized on the surfaces of inorganic or hybrid nanocarriers in the constructions of smart cargo delivery systems. Taking advantage of the pseudorotaxane structure via host-guest complexation and the dynamic nature of supramolecular interactions, macrocyclic arene-based supramolecular nanovalves have shown great promise in the applications of drug delivery and controlled release. Careful selection of diverse external stimuli, such as pH variations, temperature changes, redox, enzymes, light irradiation, and competitive binding, can activate the opening and closing of the nanovalves by altering the supramolecular structure or binding affinities. Meanwhile, the porous solid supports in controlled release systems also play an important role in the functionalities of the nanocarriers, which include, but not limited to, mesoporous silica nanoparticles (MSNs), metal-organic frameworks (MOFs), core-shell nanomaterials, and rare-earth porous nanomaterials. The elaborate decoration by macrocyclic arenes-based supramolecular nanovalves on porous nanomaterials has provided intelligent controlled release platforms. In this review, we will focus on the overview of supramolecular nanovalves based on two typical macrocyclic arenes, that is, calixarenes and pillarenes, and their operation manners in the controlled release processes.

Crystalline Cyclophane-Protein Cage Frameworks

Cyclophanes are macrocyclic supramolecular hosts famous for their ability to bind atomic or molecular guests via noncovalent interactions within their well-defined cavities. In a similar way, porous crystalline networks, such as metal-organic frameworks, can create microenvironments that enable controlled guest binding in the solid state. Both types of materials often consist of synthetic components, and they have been developed within separate research fields. Moreover, the use of biomolecules as their structural units has remained elusive. Here, we have synthesized a library of organic cyclophanes and studied their electrostatic self-assembly with biological metal-binding protein cages (ferritins) into ordered structures. We show that cationic pillar[5]arenes and ferritin cages form biohybrid cocrystals with an open protein network structure. Our cyclophane-protein cage frameworks bridge the gap between molecular frameworks and colloidal nanoparticle crystals and combine the versatility of synthetic supramolecular hosts with the highly selective recognition properties of biomolecules. Such host-guest materials are interesting for porous material applications, including water remediation and heterogeneous catalysis.

Hybrid Molecular Container Based on Glycoluril and Triptycene: Synthesis, Binding Properties, and Triggered Release

We designed and synthesized a "hybrid" molecular container 1, which is structurally related to both cucurbit[n]uril (CB[n]) and pillar[n]arene type receptors. Receptor 1 was fully characterized by ¹ H NMR, ¹³ C NMR, IR, MS and X-ray single crystal diffraction. The self-association behavior, host-guest recognition properties of 1, and the [salt] dependence of K_a were investigated in detail by ¹ H NMR and isothermal titration calorimetry (ITC). Optical transmittance and TEM measurements provide strong evidence that receptor 1 undergoes co-assemble with amphiphilic guest C10 in water to form supramolecular bilayer vesicles (diameter 25.6±2.7 nm, wall thickness ≈3.5 nm) that can encapsulate the hydrophilic anticancer drug doxorubicin (DOX) and the hydrophobic dye Nile red (NR). The release of encapsulated DOX or NR from the vesicles can be triggered by hexamethonium (8 c) or spermine (10) which leads to the disruption of the supramolecular vesicles.

Supramolecular Polymer-Based Fluorescent Microfibers for Switchable Optical Waveguides

We report the switchable optical waveguide microfibers based on fluorescent supramolecular polymer for the first time. The pillar[5]arene-based supramolecular polymeric microfibers were prepared easily from the viscous solution of bispillar[5]arene host (bisP5A) and diphenylanthracene-derived guest (GD). The resulting microfibers  act as an active optical waveguide material with long propagation distance (400 μm) and low optical propagation loss (0.01 dB/μm). When photoresponsive dithienylethene-derived guest (GDTE) was added, the resulting ternary microfibers show switchable optical waveguide by the noninvasive control of UV/vis light with negligible fatigue over four cycles. This convenient preparation method is also applied for the quadruple-hydrogen-bonded fluorescent supramolecular polymeric microfibers which imply good light propagation property with an optical loss coefficient of 0.02 dB/μm.

Formation of Twisted β-Sheet Tapes from a Self-Complementary Peptide Based on Novel Pillararene-GCP Host-Guest Interaction with Gene Transfection Properties

Small peptides capable of assembling into well-defined nanostructures have attracted extensive attention due to their interesting applications as biomaterials. This work reports the first example of a pillararene functionalized with a guanidiniocarbonyl pyrrole (GCP)-conjugated short peptide segment. The obtained amphiphilic peptide 1 spontaneously self-assembles into a supramolecular β-sheet in aqueous solution based on host-guest interaction between pillararene and GCP unit as well as hydrogen-bonding between the peptide strands. Interestingly, peptide 1 at low concentration shows transitions from small particles to "pearl necklace" assemblies, and finally to branched fibers in a time-dependent process. At higher concentration, it directly assembles into twisted β-sheet tapes. Notably, without pillararene moiety, the control peptide A forms α-helix structure with morphology changing from particles to bamboo-like assemblies depending on concentration, indicating a significant role of the pillararene-GCP host-guest interaction for the secondary structure formation. Moreover, peptide 1 can serve as an efficient gene transfection vector.

Smart Self-Assembled Nanosystem Based on Water-Soluble Pillararene and Rare-Earth-Doped Upconversion Nanoparticles for pH-Responsive Drug Delivery

Exploring novel drug delivery systems with good stability and new structure to integrate pillararene and upconversion nanoparticles (UCNPs) into one system continues to be an important challenge. Herein, we report a novel preparation of a supramolecular upconversion nanosystem via the host-guest complexation based on carboxylate-based pillar[5]arene (WP5) and 15-carboxy-N,N,N-trialkylpentadecan-1-ammonium bromide (1)-functionalized UCNPs to produce WP5⊃1-UCNPs that can be loaded with the chemotherapeutic drug doxorubicin (DOX). Importantly, the WP5 on the surface of the drug-loaded nanosystem can be efficiently protonated under acidic conditions, resulting in the collapse of the nanosystem and drug release. Moreover, cellular uptake confirms that the nanosystem can enter human cervical cancer (HeLa) cells, resulting in drug accumulation in the cells. More importantly, cytotoxicity experiments demonstrated the excellent biocompatibility of WP5⊃1-UCNPs without loading DOX and that the nanosystem DOX-WP5⊃1-UCNPs exhibited an ability of killing HeLa cells effectively. We also investigated magnetic resonance imaging and upconversion luminescence imaging, which may be employed as visual imaging agents in cancer diagnosis and treatment. Thus, in the present work, we show a simple yet powerful strategy to combine UCNPs and pillar[5]arene to produce a unified nanosystem for dual-mode bioimaging-guided therapeutic applications.

A Rotaxane Scaffold for the Construction of Multiporphyrinic Light-Harvesting Devices

A sophisticated photoactive molecular device has been prepared by combining recent concepts for the preparation of multifunctional nanomolecules (click chemistry on multifunctional scaffolds) with supramolecular chemistry (self-assembly to prepare rotaxanes). Specifically, a clickable [2]rotaxane scaffold incorporating a free-base porphyrin stopper has been prepared and functionalized with ten peripheral Zn(II)-porphyrin moieties. Electrochemical investigations of the final compound revealed a peculiar behavior resulting from the intramolecular coordination of the Zn(II) porphyrin moieties to 1,2,3-triazole units. Finally, steady state investigations of the compound combining Zn(II) and free-base porphyrin moieties have shown that this compound is a light-harvesting device capable of channeling the light energy from the peripheral Zn(II)-porphyrin subunits to the core by singlet-singlet energy transfer.

Fluorescence Resonance Energy Transfer Systems in Supramolecular Macrocyclic Chemistry

The fabrication of smart materials is gradually becoming a research focus in nanotechnology and materials science. An important criterion of smart materials is the capacity of stimuli-responsiveness, while another lies in selective recognition. Accordingly, supramolecular host-guest chemistry has proven a promising support for building intelligent, responsive systems; hence, synthetic macrocyclic hosts, such as calixarenes, cucurbiturils, cyclodextrins, and pillararenes, have been used as ideal building blocks. Meanwhile, manipulating and harnessing light artificially is always an intensive attempt for scientists in order to meet the urgent demands of technological developments. Fluorescence resonance energy transfer (FRET), known as a well-studied luminescent activity and also a powerful tool in spectroscopic area, has been investigated from various facets, of which the application range has been broadly expanded. In this review, the innovative collaboration between FRET and supramolecular macrocyclic chemistry will be presented and depicted with typical examples. Facilitated by the dynamic features of supramolecular macrocyclic motifs, a large variety of FRET systems have been designed and organized, resulting in promising optical materials with potential for applications in protein assembly, enzyme assays, diagnosis, drug delivery monitoring, sensing, photosynthesis mimicking and chemical encryption.

Pillar[5]arene-Based Supramolecular Plasmonic Thin Films for Label-Free, Quantitative and Multiplex SERS Detection

Novel plasmonic thin films based on electrostatic layer-by-layer (LbL) deposition of citrate-stabilized Au nanoparticles (NPs) and ammonium pillar[5]arene (AP[5]A) have been developed. The supramolecular-induced LbL assembly of the plasmonic nanoparticles yields the formation of controlled hot spots with uniform interparticle distances. At the same time, this strategy allows modulating the density and dimensions of the Au aggregates, and therefore the optical response, on the thin film with the number of AuNP-AP[5]A deposition cycles. Characterization of the AuNP-AP[5]A hybrid platforms as a function of the deposition cycles was performed by means of visible-NIR absorption spectroscopy, and scanning electron and atomic force microscopies, showing larger aggregates with the number of cycles. Additionally, the surface enhanced Raman scattering efficiency of the resulting AuNP-AP[5]A thin films has been investigated for three different laser excitations (633, 785, and 830 nm) and using pyrene as Raman probe. The best performance was shown by the AuNP-AP[5]A film obtained with two deposition cycles ((AuNP-AP[5]A)₂) when excited with a 785 laser line. The optical response and SERS efficiency of the thin films were also simulated using the M³ solver and employing computer aided design models built based on SEM images of the different films. The use of host molecules as building blocks to fabricate (AuNP-AP[5]A)₂) films has enabled the ultradetection, in liquid and gas phase, of low molecular weight polyaromatic hydrocarbons, PAHs, with no affinity for gold but toward the hydrophobic AP[5]A cavity. Besides, these plasmonic platforms allowed achieving quantitative detection within certain concentration regimes. Finally, the multiplex sensing capabilities of the AuNP-AP[5]A)₂ were evaluated for their ability to detect in liquid and gas phase three different PAHs.

Coordination-Driven Folding in Multi-ZnII -Porphyrin Arrays Constructed on a Pillar[5]arene Scaffold

Pillar[5]arene derivatives bearing peripheral porphyrin subunits have been efficiently prepared from a deca-azide pillar[5]arene building block (17) and Zn^II -porphyrin derivatives bearing a terminal alkyne function (9 and 16). For the resulting deca-Zn^II -porphyrin arrays (18 and 20), variable temperature NMR studies revealed an intramolecular complexation of the peripheral Zn^II -porphyrin moieties by 1,2,3-triazole subunits. As a result, the molecules adopt a folded conformation. This was further confirmed by UV/Vis spectroscopy and cyclic voltammetry. In addition, we have also demonstrated that the coordination-driven unfolding of 18 and 20 can be controlled by an external chemical stimulus. Specifically, addition of an imidazole derivative (22) to solution of 18 or 20 breaks the intramolecular coordination at the origin of the folding. The resulting molecular motions triggered by the addition of the imidazole ligand mimic the blooming of a flower.

Pillararene-Based Aggregation-Induced-Emission-Active Supramolecular System for Simultaneous Detection and Removal of Mercury(II) in Water

Supramolecular polymers are polymers based on monomeric units held together with directional and reversible noncovalent interactions. Compared with traditional polymers, they possess better processability and better recycling properties, owing to their reversible monomer-to-polymer transition. Herein, we report the construction of a new supramolecular system through self-assembly of a thymine-substituted copillar[5]arene 1 and a tetraphenylethylene (TPE) derivative 2 in the presence of Hg²⁺. Copillar[5]arene 1 can coordinate with Hg²⁺ tightly through T-Hg²⁺-T pairings. On the other hand, 1 can bind with guest molecule 2 through host-guest interactions between the pillararene cavity and the nitrile moiety of 2. These joint interactions generate crisscrossed networks composed of 1, 2, and Hg²⁺, which eventually wrap into spherical nanoparticles. Due to the aggregation-induced emission (AIE) properties of 2, the formed supramolecular polymer exhibits strong fluorescence which renders convenient the detection of the Hg²⁺-containing nanoparticles and the subsequent removal procedure. Furthermore, the polymer precipitate can be readily isolated by simple treatment, and the pseudorotaxane 2 ⊂ 1 can be recycled and reused. Our study has demonstrated a practical strategy for the sensing and removal of heavy metal ions in water by the construction of supramolecular polymers.

Pillar[6]arene-valved mesoporous silica nanovehicles for multiresponsive controlled release

The synthesis and host-guest chemistry of pillararene (PA) derivatives are a hot research topic, and the applications of PAs in relevant research fields are essential to explore. Carboxylate-substituted pillar[6]arene (CPA[6])-valved mesoporous silica nanoparticles (MSNs) functionalized with dimethylbenzimidazolium (DMBI) and bipyridinium (BP) stalks were constructed, respectively, for multiresponsive controlled release. CPA[6] encircled the DMBI or BP stalks to develop supramolecular nanovalves for encapsulation of cargo within the MSN pores. The release of cargo was triggered by acidic pH or competitive binding for the dethreading of CPA[6] and the opening of the nanovalves; moreover, coordination chemistry is the first strategy to activate CPA nanovalves by metal chelating with the carboxylate groups of CPA for cargo release. The controlled release of the CPA[6]-valved MSN delivery systems can meet diverse requirements and has promising biological applications in targeted drug therapy.

Pillar[5]arene-based supramolecular organic frameworks for highly selective CO2-capture at ambient conditions

Low-density, solid-state, porous supramolecular organic frameworks are constructed using pillarenes. The frameworks have a honeycomb-like structure, permanent porosity, high thermal stability, and selective and reversible sorption properties toward CO2. The exceptionally selective CO2-sorption properties (375/1, 339/1) of one framework over N2 and CH4 indicate potential applications in CO2-capture for post-combustion power plants and natural gas sweetening.