Controllable macrocyclic supramolecular assemblies in aqueous solution

Highly pre-organized fluorescent naphthotube for efficient detection of uranyl ions

Supramolecular fluorescent sensors have garnered extensive research attention and found broad applications in biochemical sensing attributed to their high selectivity, rapid response, stimulus responsiveness, and ease of modification, which stem from their inherent molecular recognition and self-assembly capabilities. Herein, supramolecular fluorescent sensors based on anthracene-functionalized naphthotubes have been successfully developed and utilized for the efficient detection of uranyl ions. Owing to the highly pre-organized carboxyl groups on the naphthotubes, uranyl ions are effectively captured, forming a non-fluorescent or weakly fluorescent complex to quench the fluorescence of anthracene. The fluorescent sensor exhibited a limit of detection as low as 53 nM, coupled with high sensitivity, rapid response time, and high selectivity. Moreover, it maintained robust detection capabilities in diverse aqueous environments such as seawater, river water, and tap water, demonstrating its promising potential for uranyl ions detection. This study provides a new idea for the development of detection methods for uranyl ions in complex environmental samples.

Supramolecular phosphorescent assemblies based on cucurbit[8]uril and bromophenylpyridine derivatives for dazomet recognition

A bromophenylpyridine derivative (N1) was designed, synthesized, and the molecule was incorporated into the cavity of the cucurbit[8]uril (Q[8]) as a guest to form a 2:1 host-guest complex. This complex demonstrates good room temperature phosphorescence (RTP) properties in aqueous solution. The host-guest interaction and optical properties of N1@Q[8] in aqueous solution were studied by means of 1H NMR, ultraviolet-visible absorption spectroscopy, fluorescence spectroscopy, phosphorescence spectroscopy, scanning electron microscopy and inverted fluorescence microscopy. The results show that the bromophenyl part of the guest molecule enters the cavity of Q[8], while the other part of N1 remains outside the cavity, resulting in a 2:1 supramolecular structure. This assembly exhibits specific recognition of dazomet on the phosphorescence spectrum with a detection limit of 8.8329 × 10-7 mol·L-1. Collectively, this finding opens up a new possibility for the potential application of room temperature phosphorescent materials in analytical detection.

A supramolecular bactericidal material for preventing and treating plant-associated biofilms

Treating bacterial biofilms on plants poses challenges due to biofilm induced resistance and poor agent adhesion on plant leaves. Here, we report on a host-guest self-assembled material which is biocompatible, has a lamellar supramolecular structure for leaf retention and prevents and treats bacterial biofilms. Phosphate/isopropanolamine-modified ferrocene forms a host-guest complex with β-CD which assembles into a lamella structure. The agent shows control efficacy against bacterial blight, bacterial leaf streak, and citrus canker in testing.

Photoswitchable Topological Regulation of Covalent Macrocycles, Molecular Recognition, and Interlocked Structures

Macrocycles represent one important class of functional molecules, and dynamic macrocycles with the potential of cleavability, adaptability, and topological conversion are challenging. Herein we report photoswitchable allosteric and topological control of dynamic covalent macrocycles and further the use in guest binding and mechanically interlocked molecules. The manipulation of competing ring-chain equilibria and bond formation/scission within reaction systems enabled light-induced structural regulation over dithioacetal and thioacetal dynamic bonds, accordingly realizing bidirectional switching between crown ether-like covalent macrocycles and their linear counterparts. The on-demand photoswitchable topological transformation of macrocycles further allowed guest recognition/release exhibiting controllable binding affinity and selectivity. To showcase the capability light-triggered assembly/disassembly of diverse mechanically interlocked structures, such as rotaxanes and catenanes, was achieved. The realization of photoswitchable topological conversion of covalent macrocycles, which has been rarely reported before, demonstrates the potential of light-triggered reactivity control and structural reconfiguration for enhanced complexity and sophisticated function. The strategies and results should be appealing to endeavors in molecular recognition, dynamic assemblies, molecular machines, and intelligent materials.

Non-Covalent Self-Assembly Behaviors Based on Racemic Binaphthol Scaffolds

Understanding the fundamental mechanisms involved in the construction and organization of multi-scale structures is crucial for the design and manufacture of complex functional systems with long-range molecular arrangements. In this paper, a series of compounds have been synthesized using racemic binaphthols as the skeleton and a Suzuki coupling reaction for derivatization at the 6,6' positions, which resulted in various structures bearing different functional groups. Control over the self-assembly of these racemic binaphthol derivatives was successfully achieved by adjusting the types and positions of the substituents in the parent binaphthol compound, which revealed the key factors influencing the types of the non-covalent interactions and the self-assembly process. For example, the single-crystal structures of the resulting compounds indicated that assembly structures such as single helix and double helix based on non-traditional hydrogen bond motifs could be obtained, and fascinating non-covalent self-assembly structures such as molecular ladders and catenane discovered.

Recent progress using novel tetraphenylethylene-based macrocyclic hosts in water

Macrocyclic structures are popular in supramolecular chemistry and have enjoyed considerable success as platforms for elaboration to container compounds and new materials. Host/guest studies in organic media have relied heavily on structures derived from crown ethers, calixarenes, cucurbiturils, resorcinarenes and pillararenes over the past decades. More recently, their water-soluble versions have been developed for potential applications in biology. Inspired by nature and the need for large-sized containers, Cao and co-workers have designed and synthesized a series of novel macrocyclic hosts based on the tetraphenylethylene (TPE) platform. These compounds have cationic frameworks with well-defined hydrophobic cavities for recognition of biomolecules (e.g. amino acids, nucleosides, peptides, proteins, coenzyme factors) in water. They offer multiple adaptive responses as sensors through fluorescence, circular dichroism and circularly polarized luminescence. These TPE-based hosts also show promising applications as stimuli-responsive fluorescent materials, in drug delivery and as artificial photofunctional systems. Herein, this review highlights this work as it establishes a new class of biomimetic, water-soluble supramolecular macrocyclic hosts.

Leveraging supramolecular systems in biomedical breakthroughs

Supramolecular systems, intricate assemblies of molecular subunits organized through various intermolecular interactions, offer versatile platforms for diverse applications, including gene therapy, antimicrobial therapy, and cellular engineering. These systems are cost-effective and environmentally friendly, contributing to their attractiveness in biomaterial design. Furthermore, supramolecular biomaterials based on acyclic, macrocyclic compounds and lipid-based assembly offer potential applications in distinct types of biomedical approaches. In this context, they can transport several therapeutic agents very effectively to the target site. Supramolecular hydrogels exhibit potent antimicrobial activity by disrupting microbial membranes, offering promising solutions to combat drug-resistant pathogens. Additionally, supramolecular luminescent nanoparticles enable targeted cell imaging, facilitating disease diagnosis and treatment with high specificity and sensitivity. In cellular engineering, supramolecular assemblies of small molecules demonstrate biological activities, overcoming challenges in cancer treatment by inhibiting signaling pathways and inducing apoptosis in cancer cells. This review emphasizes the applications of supramolecular systems from gene therapy to cellular imaging, tissue engineering, and antimicrobial therapy, showcasing their potential to drive innovation and address pressing healthcare challenges.

Cyclodextrin supramolecular assembly confined luminescent materials

The macrocyclic supramolecular assembly confinement effect not only induces or extends the fluorescence/phosphorescence luminescence behavior of guest molecules but has also been widely applied in the research fields of chemistry, biology, and materials. This review primarily describes recent advances in cyclodextrin (CD) supramolecular assembly confined luminescent materials. Taking advantage of their hydrophobic cavity, CDs and their derivatives effectively encapsulate guest molecules and special functional groups or further assemble and polymerize to restrict the motion of guest chromophores, inducing and enhancing the luminescence behavior and realizing intelligent stimulus-responsive luminescence depending on changes in temperature, light, redox reactions and solvent polarity, which are successfully applied in targeted cell imaging, sensing, information encryption, anti-counterfeiting and flexible electronic light-emitting devices. With the emergence of new chromophores and CD primitives, spatial confinement within CD supramolecular assemblies will further realize the rapid development of supramolecular science and technology in circularly polarized luminescence, fluorescence/phosphorescence cascade energy transfer, light-harvesting energy-transfer systems and long persistent luminescent materials.

Research progress of fluorescent composites based on cyclodextrins: Preparation strategies, fluorescence properties and applications in sensing and bioimaging

Fluorescence analysis has been regarded as one of the commonly used analytical methods because of its advantages of simple operation, fast response, low cost and high sensitivity. So far, various fluorescent probes, with noble metal nanoclusters, quantum dots, organic dyes and metal organic frameworks as representatives, have been widely reported. However, single fluorescent probe often suffers from some deficiencies, such as low quantum yield, poor chemical stability, low water solubility and toxicity. To overcome these disadvantages, the introduction of cyclodextrins into fluorescent probes has become a fascinating approach. This review (with 218 references) systematically covers the research progress of fluorescent composites based on cyclodextrins in recent years. Preparation strategies, fluorescence properties, response mechanisms and applications in sensing (ions, organic pollutants, bio-related molecules, temperature, pH) and bioimaging of fluorescent composites based on cyclodextrins are summarized in detail. Finally, the current challenges and future perspectives of these composites in relative research fields are discussed.

Host-Guest Chemistry in Binary and Ternary Complexes Utilizing π-Conjugated Carbon Nanorings

The carbon nanorings, possessing a radial π system, have garnered significant attention primarily due to their size-dependent photophysical properties and the presence of a unique curved π-conjugated cavity. This is evidenced by the rapid proliferation of publications. Furthermore, the integration of building blocks into CPP skeletons can confer [n]CPPs with novel and exceptional photophysical and electronic characteristics, as well as chiral properties and host-guest interactions, thereby augmenting the diversity of [n]CPPs. Notably, the curved π surface structures and concave cavity of carbon nanorings enable them to host aromatic or non-aromatic guests with a complementarily curved surface, resulting in interesting binary or ternary complexes. This review provides a comprehensive treatment of literature reports on binary and ternary complexes, focusing on both their host-guest interactions and properties. It is important to note that the scope of this review is limited to host-guest chemistry in binary and ternary complexes based on π-conjugated carbon nanorings.

Heat-Set Supramolecular Hydrogelation by Regulating the Hydrophilic-Lipophilic Balance for a Tunable Circularly Polarized Luminescent Switch

Heat-set supramolecular gels exhibited totally opposite phase behaviors of dissolution upon cooling and gelation on heating. They are commonly discovered by chance and their rational design remains a great challenge. Herein, a rational design strategy is proposed to realize heat-set supramolecular hydrogelation through regulation of the hydrophilic-lipophilic balance of the system. A newly synthesized amphiphile hydrogelator with pyrene embedded in its lipophilic terminal can self-assemble into a hydrogel through a heating and cooling cycle. However, the host-guest complex of the gelator and hydrophilic γ-cyclodextrin (γ-CyD) results in a sol at room temperature. Thus, heat-set hydrogelation is realized from the sol state in a controllable manner. Heat-set gelation mechanism is revealed by exploring critical heat-set supramolecular gelation and the related findings provide a general strategy for developing new functional molecular gels with tunable hydrophilic-lipophilic balance.

Modification and crosslinking strategies for hyaluronic acid-based hydrogel biomaterials

Hyaluronic acid (HA) is an attractive extracellular matrix-derived polymer. The related HA-based hydrogels are emerging to be the hotspots in the cutting edge of biomaterials. The continuous sights concentrate on exploring modification methods and crosslinking strategies to promote the advancement of HA-based hydrogels with enhanced physical/chemical properties and enriched biological performance. Here, the advances on modification methods and crosslinking strategies for fabricating HA-based hydrogels with diverse capacities are summarized. Firstly, the modification reactions that occur on the active hydroxyl, carboxyl and N-acetyl groups of HA molecule are discussed. Next, the emphasis is put on various crosslinking strategies including physical crosslinking, covalent crosslinking and dynamic covalent crosslinking. Finally, we provide a general summary and give a critical viewpoint on the remaining challenges and the future development of HA-based hydrogels. It is hoped that this review can provide new proposals for the specific design of functional hydrogel biomaterials.

Synthesis of a water-soluble naphthalene-based macrocycle and its host-guest properties

Reported here is the synthesis of a naphthalene-based macrocycle bearing anionic carboxylato groups on the rims along with its complexation with cationic guests in aqueous media. The macrocycle could strongly bind guests in a molecular clip model with association constants of 106-107 M-1.

One-Pot Cyclization to Large Peptidomimetic Macrocycles by In Situ-Generated β-Turn-Enforced Folding

Macrocycles have been targets of extensive synthetic efforts for decades because of their potent molecular recognition and self-assembly capabilities. Yet, efficient syntheses of macrocyclic molecules via irreversible covalent bonds remain challenging. Here, we report an efficient approach to large peptidomimetic macrocycles by using the in situ-generated β-turn structural motifs afforded in the amidothiourea moieties from the early steps of the reaction of 2 molecules of bilateral amino acid-based acylhydrazine with 2 molecules of diisothiocyanate. Four chiral and achiral peptidomimetic large macrocycles were successfully synthesized in high yields of 45-63% in a feasible one-pot reaction under sub-molar concentration conditions and were purified by simple filtration. X-ray crystallographic characterization of three macrocycles reveals an important feature that their four β-turn structures, each maintained by four 10-membered intramolecular hydrogen bonds, alternatively network the four aromatic arms. This affords an interesting conformation switching mode upon anion binding. Binding of SO₄^2- to 1L or 1D that contains 4 alanine residues (with the lowest steric hinderance among the macrocycles) leads to an inside-out structural change of the host macrocycle, as confirmed by the X-ray crystal structure of 1L-SO₄^2- and 1D-SO₄^2- complexes, accompanied by an inversion of the CD signals. On the basis of the strong sulfate affinity of the macrocycles, we succeeded in the removal of sulfate anions from water via a macrocycle-mediated liquid-liquid extraction method. Our synthetic protocol can be easily extended to other macrocycles of varying arms and/or chiral amino acid residues; thus, a variety of structurally and functionally diverse macrocycles are expected to be readily made.

MXenes Functionalized with Macrocyclic Hosts: From Molecular Design to Applications

Two-dimensional (2D) MXene has aroused wide attention for its excellent physical and chemical properties. The interlayer engineering formed by layer-by-layer stacking of MXene nanosheets can be employed for molecular sieving and water purification by incorporating specific groups onto the exterior surface of MXene. Macrocyclic hosts exhibiting unique structural features and recognition ability can construct smart devices for external stimuli with reversible features between macrocycles and guests. On that basis, macrocyclic hosts can be anchored to MXene to provide numerous insights into their compositions and intercalation states. In this review, the MXene prepared based on macrocyclic hosts from molecular design to applications is highlighted. Various MXenes functionalized with macrocyclic hosts are empowered in functional membrane (including water purification, organic solvent nanofiltration, and electromagnetic shielding), photocatalysis, sensing, and adsorption (interactions with specific guest). Hopefully, this review can bring new inspiration to the design of multifunctional MXene-based materials and improving its practical applications.

Supramolecular Room Temperature Phosphorescent Materials Based on Cucurbit[8]uril for Dual Detection of Dodine

In recent years, host-guest interactions of macrocycles have attracted much attention as an emerging method for enhancing the intersystem crossing of pure organic room-temperature phosphorescence. In this work, we utilize cucurbit[8]uril (Q[8]) to specifically recognize synthetic bromophenyl pyridine derivatives (BPCOOH) to construct a highly stable charge-transfer dimer, where the bromophenyl pyridine moiety of BPCOOH is encapsulated by Q[8] in a 1:2 host/guest ratio. The assemblies exhibit specific recognition and detection properties for dodine on both fluorescence and phosphorescence spectra. Subsequently, the solid films were prepared by introducing carboxymethylcellulose sodium into the assemblies, which greatly enhanced its RTP performance by increasing the noncovalent bonding interactions, enabling the visualization of high-strength RTP and quantitative testing of the solid state. Finally, this material was used for the application of portable indicator papers to achieve rapid and visualized detection of dodine in daily life, which provides more possibilities for the potential applications of cucurbit[n]uril-based room-temperature phosphorescence material.

Supramolecular assembly confined purely organic room temperature phosphorescence and its biological imaging

Purely organic room temperature phosphorescence, especially in aqueous solution, is attracting increasing attention owing to its large Stokes shift, long lifetime, low preparation cost, low toxicity, good processing performance advantages, and broad application value. This review mainly focuses on macrocyclic (cyclodextrin and cucurbituril) hosts, nanoassembly, and macromolecule (polyether) confinement-driven RTP. As an optical probe, the assembly and the two-stage assembly strategy can realize the confined purely organic RTP and achieve energy transfer and light-harvesting from fluorescence to delayed fluorescence or phosphorescence. This supramolecular assembly is widely applied for luminescent materials, cell imaging, and other fields because it effectively avoids oxygen quenching. In addition, the near-infrared excitation, near-infrared emission, and in situ imaging of purely organic room temperature phosphorescence in assembled confinement materials are also prospected.

Advances in modified hyaluronic acid-based hydrogels for skin wound healing

Hyaluronic acid (HA) is a natural linear anionic polysaccharide with many unique characteristics such as excellent biocompatibility and biodegradability, native biofunctionality, hydrophilicity, and non-immunoreactivity. HA plays crucial roles in numerous biological processes, including the inflammatory response, cell adhesion, migration, proliferation, differentiation, angiogenesis, and tissue regeneration. All these properties and biological functions of HA make it an appealing material for the synthesis of biomedical hydrogels for skin wound healing. Since HA is not able to be gelate alone, it must be processed and functionalized through chemical modifications and crosslinking to generate versatile HA-based hydrogels. In recent years, different physical and chemical crosslinking strategies for HA-based hydrogels have been developed and designed, such as radical polymerization, Schiff-base crosslinking, enzymatic crosslinking, and dynamic covalent crosslinking, and they have broad and promising applications in skin wound healing and tissue engineering. In this review, we focus on chemical modification and crosslinking strategies for HA-based hydrogels, aiming to provide an overview of the latest advances in the development of HA-based hydrogels for skin wound healing. We summarize and propose feasible measures for the application of HA-based hydrogels for skin treatment, and discuss future application trends, which may ultimately promote HA-based hydrogels as a promising biomaterial for clinical applications.

Multicharged cyclodextrin supramolecular assemblies

Multicharged cyclodextrin (CD) supramolecular assemblies, including those based on positively/negatively charged modified mono-6-deoxy-CDs, per-6-deoxy-CDs, and random 2,3,6-deoxy-CDs, as well as parent CDs binding positively/negatively charged guests, have been extensively applied in chemistry, materials science, medicine, biological science, catalysis, and other fields. In this review, we primarily focus on summarizing the recent advances in positively/negatively charged CDs and parent CDs encapsulating positively/negatively charged guests, especially the construction process of supramolecular assemblies and their applications. Compared with uncharged CDs, multicharged CDs display remarkably high antiviral and antibacterial activity as well as efficient protein fibrosis inhibition. Meanwhile, charged CDs can interact with oppositely charged dyes, drugs, polymers, and biomacromolecules to achieve effective encapsulation and aggregation. Consequently, multicharged CD supramolecular assemblies show great advantages in improving drug-delivery efficiency, the luminescence properties of materials, molecular recognition and imaging, and the toughness of supramolecular hydrogels, in addition to enabling the construction of multistimuli-responsive assemblies. These features are anticipated to not only promote the development of CD-based supramolecular chemistry but also contribute to the rapid exploitation of these assemblies in diverse interdisciplinary applications.

Advances of supramolecular interaction systems for improved oil recovery (IOR)

Improved oil recovery (IOR) includes enhanced oil recovery (EOR) and other technologies (i.e. fracturing, water injection optimization, etc.), have become important methods to increase the oil/gas production in petroleum industry. However, conventional flooding systems always encounter the problems of low efficiency, high cost and complicated synthetic procedures for harsh reservoirs conditions. In recent decades, the supramolecular interactions are introduced into IOR processes to simplify the synthetic procedures, alter their structures and properties with bespoke functionalities and responsiveness suitable for different conditions. Herein, we primarily review the fundamentals of several supramolecular interactions, including hydrophobic association, hydrogen bond, electrostatic interaction, host-guest recognition, metal-ligand coordination and dynamic covalent bond from intrinsic principles and extrinsic functions. Then, the descriptions of supramolecular interactions in IOR processes from categories and advances are focused on the following variables: polymer, surfactant, surfactant/polymer (SP) complex for EOR and viscoelasticity surfactant (VES) for clean hydraulic fracturing aspects. Finally, the field applications, challenges and prospects for supramolecular interactions in IOR processes are involved and systematically addressed. The development of supramolecular interactions can open the way toward adaptive and evolutive IOR technology, a further step towards the cost-effective production of petroleum industry.

Fabrication of Host-Guest Complexes between Adamantane-Functionalized 1,3,4-Oxadiazoles and β-Cyclodextrin with Improved Control Efficiency against Intractable Plant Bacterial Diseases

Supramolecular chemistry provides huge potentials and opportunities in agricultural pest management. In an attempt to develop highly bioactive, eco-friendly, and biocompatible supramolecular complexes for managing intractable plant bacterial diseases, herein, a type of interesting adamantane-functionalized 1,3,4-oxadiazole was rationally prepared to facilitate the formation of supramolecular complexes via β-cyclodextrin-adamantane host-guest interactions. Initial antibacterial screening revealed that most of these adamantane-decorated 1,3,4-oxadiazoles were obviously bioactive against three typically destructive phytopathogens. The lowest EC₅₀ values could reach 0.936 (III₁₈), 0.889 (III₁₈), and 2.10 (III₁₉) μg/mL against the corresponding Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and Pseudomonas syringae pv. actinidiae (Psa). Next, the representative supramolecular binary complex III₁₈@β-CD (binding mode 1:1) was successfully fabricated and characterized by ¹H nuclear magnetic resonance (NMR), isothermal titration calorimetry (ITC), high-resolution mass spectrometry (HRMS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Eventually, correlative water solubility and foliar surface wettability were significantly improved after the formation of host-guest assemblies. In vivo antibacterial evaluation found that the achieved supramolecular complex could distinctly alleviate the disease symptoms and promote the control efficiencies against rice bacterial blight (from 34.6-35.7% (III₁₈) to 40.3-43.6% (III₁₈@β-CD)) and kiwi canker diseases (from 41.0-42.3% (III₁₈) to 53.9-68.0% (III₁₈@β-CD)) at 200 μg/mL (active ingredient). The current study can provide a feasible platform and insight for constructing biocompatible supramolecular assemblies for managing destructive bacterial infections in agriculture.

Multivalent supramolecular assembly with ultralong organic room temperature phosphorescence, high transfer efficiency and ultrahigh antenna effect in water

Multivalent supramolecular assemblies have recently attracted extensive attention in the applications of soft materials and cell imaging. Here, we report a novel multivalent supramolecular assembly constructed from 4-(4-bromophenyl)pyridine-1-ium bromide modified hyaluronic acid (HABr), cucurbit[8]uril (CB[8]) and laponite® clay (LP), which could emit purely organic room-temperature phosphorescence (RTP) with a phosphorescence lifetime of up to 4.79 ms in aqueous solution via multivalent supramolecular interactions. By doping the organic dyes rhodamine B (RhB) or sulfonated rhodamine 101 (SR101) into the HABr/CB[8]/LP assembly, phosphorescence energy transfer was realized with high transfer efficiency (energy transfer efficiency = 73–80%) and ultrahigh antenna effect (antenna effect value = 308–362) within the phosphorescent light harvesting system. Moreover, owing to the dynamic nature of the noncovalent interactions, a wide-range spectrum of phosphorescence energy transfer outputs could be obtained not only in water but also on filter paper and a glass plate by adjusting the donor–acceptor ratio and, importantly, white-light emission was obtained, which could be used in the application of information encryption.

An ultralong lifetime supramolecular assembly was constructed via multivalent supramolecular interactions and achieved phosphorescence light harvesting. Multicolor (including white) broad-spectrum outputs could be achieved in water and also on filter paper and a glass plate.

Nanosized Carbon Macrocycles Based on a Planar Chiral Pseudo Meta- [2.2]Paracyclophane

Structural designs combining cycloparaphenylenes (CPPs) backbone with planar chiral [2.2]Paracyclophane ([2.2]PCP) lead to optical-active chiral macrocycles with intriguing properties. X-ray crystal analysis revealed aesthetic necklace-shaped structures and size-dependent packages with long-range channels. The macrocycles exhibit unique photophysical properties with high fluorescence quantum yield of up to 82%, and the fluorescent color varies with ring size. In addition, size-dependent chiroptical properties with moderately large CPL dissymmetry factor of 10 -3 and CPL brightness in the range of 30 - 40 M -1 cm -1 were observed.

Pillararene-containing polymers with tunable fluorescence properties based on host-guest interactions

Linear polymers containing pillar[5]arenes as the pendant groups were designed and synthesized via a ring-opening metathesis polymerization. Such polymers could form supramolecular brush polymers and exhibited tunable fluorescence properties based on the host-guest interactions.

Luminescent lanthanide-macrocycle supramolecular assembly

A series of macrocyclic compounds, including crown ether, cyclodextrin, cucurbituril and pillararene, bound to various specific organic/inorganic/biological guest molecules and ions through various non-covalent interactions, can not only make a single system multifunctional but also endow the system with intelligence, especially for luminescent materials. Due to their excellent luminescence properties, such as long-lived excited states, sharp linear emission bands and large Stokes shift, lanthanides have shown great advantages in luminescence, and have been more and more applied in the design of advanced functional luminescent materials. Based on reported research, we summarize the progress of lanthanide luminescent materials based on different macrocyclic compounds from ion or molecule recognition to functional nano-supramolecular assembly of the lanthanide-macrocycle supramolecular system including photo-reaction mediated switch of lanthanide luminescent molecules, multicolor luminescence, ion detection and cell imaging of rare-earth up-conversion of macrocyclic supramolecular assembly. Finally, we put forward the prospects of future development of lanthanide luminescent macrocyclic supramolecular materials.

A supramolecular host-guest interaction-mediated injectable hydrogel system with enhanced stability and sustained protein release

Injectable hydrogels have been studied as drug delivery systems because of their minimal invasiveness and sustained drug release properties. Pluronic F127, consisting of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers, exhibits thermo-responsive properties and hence is injectable due to its rapid sol-gel transition. Unmodified Pluronic F127-based hydrogels, however, have limited long-term stability and controllable release of drugs entrapped within them. In this study, host-guest interactions between adamantane-conjugated Pluronic F127 (F127-Ad) and polymerized β-cyclodextrin (CDP) were employed to develop a hydrogel-based protein delivery system. Single or multiple adamantane units were successfully introduced at the termini of Pluronic F127 with a 100% conversion yield, and the synthesized F127-Ad polymer produced a physically crosslinked micelle-packing structure when mixed with CDP. As the number of adamantanes at the terminal ends of Pluronic F127 increased, the critical gelation concentration of F127-Ad/CDP hydrogel decreased from 15 to 6% (w/v). The F127/CDP hydrogel was able to maintain its structure even with lower polymer content, and its injectability improved with a reduction of the hydrogel viscosity. The long-term stability of F127/CDP hydrogels was evaluated in vitro and in vivo, and it was demonstrated that the subcutaneously injected hydrogel did not disintegrate for up to 30 d. Throughout the drug release test using gelatin and insulin as model drugs, it was demonstrated that their release rates could be regulated via complexation between the protein drugs and the β-cyclodextrin molecules inside the hydrogel. In conclusion, the F127-Ad/CDP hydrogel is expected to be a versatile protein delivery system with controllable durability and drug release characteristics. STATEMENT OF SIGNIFICANCE: Pluronic F127 is one of the widely studied polymeric materials for thermo-sensitive injectable hydrogels due to its high biocompatibility and rapid sol-gel transition. Since the Pluronic F127-based hydrogel has some limitations in its long-term stability and mechanical property, it is inevitable to modify its structure for the application to drug delivery. In this study, mono- or multi- adamantane-conjugated Pluronic F127s were synthesized and mixed with β-cyclodextrin polymers to form hydrogels with host-guest interaction-mediated micelle-packing structures. The host-guest interaction introduced into the hydrogel system endowed it a sustained protein drug release behavior as well as high durability in vitro and in vivo. By increasing the number of adamantane molecules at the end of the Pluronic F127, both the stability and injectability of the hydrogel could be also modulated.

Cucurbituril-activated photoreaction of dithienylethene for controllable targeted lysosomal imaging and anti-counterfeiting

Supramolecular macrocycle-mediated photoreaction has been a research hotspot recently. Herein, we fabricated a photo-responsive intelligent supramolecular assembly that consisted of a water-soluble dithienylethene derivative (DTE-MPBT) and cucurbit[n]urils (CB[n]). Importantly, CB[n], especially CB[8], could act as activators and trigger conformational alteration of the arm parts (typical molecular rotors) of DTE-MPBT, achieving dual functions, i.e. high-efficiency visible-light-cyclization reaction of the DTE core and fluorescence enhancement of DTE-MPBT, resulting in the formation of a dual visible light-driven fluorescent switch. These unexpected discoveries prompted the supramolecular assembly to be applied to dual-visible-light-controlled targeted lysosomal imaging and QR code information recognition. Moreover, the solid-state assembly exhibited more outstanding fluorescence and visible-light-switched fluorescence performance because of the host-guest-induced aggregation synergistic effect, showing fascinating applications, such as light-manipulative data storage and anti-counterfeiting. In brief, we unprecedentedly adopted a supramolecular strategy of "killing two birds with one stone", i.e. assembly-activated photochromism (AAP) and assembly-activated emission enhancement (AAEE), to fabricate dual-visible-light-driven fluorescent switches, which show promising application prospects in biomimetic smart nanomaterials based on supramolecular self-assembly systems.

Multicharge β-cyclodextrin supramolecular assembly for ATP capture and drug release

A hyaluronidase-responsive polysaccharide supramolecular assembly was constructed from an amphiphilic β-cyclodextrin bearing seven hexylimidazolium units (AMCD), adamantyl-grafted hyaluronic acid, and chlorambucil, which showed specific cancer cell targeting and controlled drug release abilities. Interestingly, ternary supramolecular assembly can disassemble in the presence of hyaluronidase, and the released AMCD can assemble with ATP to form a stable 1 : 1 complex, which enhanced the efficacy of chlorambucil on cancer chemotherapy by inhibiting ATP hydrolysis.

2-Hydroxypropyl-β-cyclodextrin encapsulates dimethyl disulfide producing a controlled release formulation

Dimethyl disulfide (DMDS), a soil fumigant, is an effective, broad-spectrum compound that often replaces bromomethane (MB) in the prevention and treatment of soil-borne diseases. However, the disadvantages of DMDS include toxicity, volatility, pungent odor, risk of human exposure, and environmental pollution. Cyclodextrin (CD) has been widely used as a carrier of chemicals in many industries due to its functional advantages and safety. In this study, a DMDS-controlled release formulation was developed by encapsulating DMDS in the cavity of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD). This formulation reduced DMDS usage and production costs. Orthogonal experimental design, Fourier transform infrared (FT-IR), Scanning electron microscopy (SEM), Thermal gravity analysis (TGA) characterization, efficacy comparison, safety, and other aspects of the evaluation showed that under the best preparation conditions, the encapsulation rate was 81.49%. The efficacy of DMDS@HP-β-CD was similar to unformulated DMDS. The efficacy duration of the formulation was about two times longer than DMDS, and it was safer to use. This study reveals a cyclodextrin-DMDS formulation with reduced toxicity, longer duration, environmental safety and sustainability.

The pH and mercury ion stimuli-responsive supramolecular assemblies of cucurbit[7]uril and Hoechst 33342

In the present work, we have investigated the effect of pH and mercury ions on the host-guest complex formed between cucurbit[7]uril (Q[7]) and Hoechst 33342 (H33342). ¹H NMR, UV-vis and fluorescence spectroscopy revealed that acid/base stimulation could change the binding stoichiometry between Q[7] and H33342. The results suggest that two complexation equilibria (1:1 and 2:1) may exist between H33342 and Q[7] at pH 2.0 and 4.5, respectively. However, a 1:1 host-guest complex was formed between H33342 and Q[7] at pH 7.0 and 10.0. Q[7] shows differential affinities for the protonated and neutral forms of H33342 dye. Moreover, the switching between H33342∙2H⁺@2Q[7](1:2) at pH 4.5 and H33342∙H⁺@Q[7](1:1) at pH 7.0 was reversible. Furthermore, as a metal stimulus, Hg²⁺ ions could push (i) Q[7] from the piperazine ring to the benzimidazole position with a 1:1 guest-host ratio and (ii) a second Q[7] onto the ethyl position with a 1:2 guest-host stoichiometry. This stimulus response system will have potential applications in the field of molecular switch design.

Selective Identification of Phenylalanine Using Cucurbit[7,8]uril-Based Fluorescent Probes

The interactions of two host–guest inclusion complexes comprised of cucurbit[7]uril (Q[7]) and cucurbit[8]uril (Q[8]) with a derivative of toluidine blue O (TB) have been investigated using 1H NMR and fluorescence spectroscopy. The experimental results revealed that the Q[7] host interacts with a TB molecule to form a 1:1 inclusion complex and the Q[8] host interacts with two TB guest molecules to form a 1:2 inclusion complex. The inclusion of the TB guest molecule within the Q[7] host gave rise to significant fluorescence enhancement, whereas the inclusion of the TB guest molecule within the Q[8] host resulted in significant fluorescence quenching. Further recognition experiments involving a series of l-α-amino acids revealed that the TB@Q[7] inclusion fluorescence probe exhibits high selectivity for the recognition of phenylalanine via significant fluorescence quenching in an aqueous solution, whereas the TB@Q[8] inclusion fluorescence probe also exhibited high selectivity for phenylalanine recognition via fluorescence enhancement in an aqueous solution.

High-Efficiency Synergistic Effect of Supramolecular Nanoparticles Based on Cyclodextrin Prodrug on Cancer Therapy

Novel cyclodextrin-prodrug supramolecular nanoparticles (NPs) with cooperative-enhancing cancer therapy were constructed from a reduction-sensitive disulfide bond-linked permethyl-β-cyclodextrin-camptothecin prodrug, water-soluble adamantane-porphyrin photosensitizer, and hyaluronic acid grafted by triphenylphosphine and β-cyclodextrin through an orthogonal host-guest recognition strategy, displaying uniform nanoparticles with a diameter around 100 nm as revealed by dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Compared with 293T normal cells, the supramolecular NPs could be easily taken up by mitochondria of A549 cancer cells, then release the active anticancer drug camptothecin (CPT) in situ via the cleavage of the disulfide bond by the overexpressed glutathione, and could initiate the effective singlet oxygen (¹O₂) generation by porphyrin under light irradiation, ultimately resulting in severe mitochondrial dysfunction and a rising cell death rate with increasing micromolar concentration of NPs. These multicomponent supramolecular nanoassemblies effectively combined the two-step synergistic chemo-photodynamic therapy of reduction-release of CPT and light-triggered ¹O₂ generation within cancer cells presenting the synergistic effect of supramolecular nanoparticles on cancer therapy, which provide a new approach for efficient step-by-step cancer therapy.

Purely organic light-harvesting phosphorescence energy transfer by β-cyclodextrin pseudorotaxane for mitochondria targeted imaging

A new type of purely organic light-harvesting phosphorescence energy transfer (PET) supramolecular assembly is constructed from 4-(4-bromophenyl)-pyridine modified β-cyclodextrin (CD-PY) as a donor, cucurbit[8]uril (CB[8]) as a mediator, rhodamine B (RhB) as an acceptor, and adamantane modified hyaluronic acid (HA-ADA) as a cancer cell targeting agent. Interestingly, the complexation of free CD-PY, which has no RTP emission in aqueous solution, with CB[8] results in the formation of CD-PY@CB[8] pseudorotaxane with an RTP emission at 510 nm. Then the addition of RhB leads to an efficient light-harvesting PET process with highly efficient energy transfer and an ultrahigh antenna effect (36.42) between CD-PY@CB[8] pseudorotaxane and RhB. Importantly, CD-PY@CB[8]@RhB assembles with HA-ADA into nanoparticles with further enhanced delayed emission at 590 nm. The nanoparticles could be successfully used for mitochondria targeted imaging in A549 cancer cells. This aqueous-state PET based on a supramolecular assembly strategy has potential application in delayed fluorescence cell imaging.

A new type of purely organic light-harvesting PET supramolecular assembly is constructed with efficient energy transfer and ultrahigh antenna effect. Moreover, the assembly could be used for mitochondria targeted imaging in A549 cancer cells.

Fluorescent Metallacycle-Cored Amphiphilic Nanoparticles Formed by β-Cyclodextrin-Based Host-Guest Interactions towards Cancer Theranostics

Theranostic agents, taking the advantages of both imaging and therapeutic functions, are anticipated to be key components in the development of personalized medicine in which the therapeutic response can be real-time monitored. Herein, three metallacycles with pendent adamantane groups are prepared by coordination-driven self-assembly of Pt^II ligands with anticancer activities and tetraphenylethylene derivatives with emission. β-Cyclodextrin, which shows good host-guest interactions with adamantane moieties, was added to form amphiphilic supramolecular nanoparticles with the aim to enhance the aqueous solubilities and bioactivities of these metallacycles. Moreover, when rhodamine-modified β-cyclodextrin was used as the carrier, the release of the metallacycles from the nanoparticles could be monitored in situ through the fluorescence changes owing to the efficient fluorescence resonance energy transfer from the metallacycles to rhodamine-modified β-cyclodextrin. In vitro and in vivo studies showed that these nanoparticles not only served as cell imaging contrast agents but also displayed improved anticancer activities, allowing them to serve as potential candidates for cancer theranostics. This study provides a simple and efficient method to prepare theranostic agents by hierarchical supramolecular self-assembly, which will pave the way for image-guided cancer therapy, targeted cancer therapy, and related biomedical fields.

Enzymatic Noncovalent Synthesis

Enzymatic reactions and noncovalent (i.e., supramolecular) interactions are two fundamental nongenetic attributes of life. Enzymatic noncovalent synthesis (ENS) refers to a process where enzymatic reactions control intermolecular noncovalent interactions for spatial organization of higher-order molecular assemblies that exhibit emergent properties and functions. Like enzymatic covalent synthesis (ECS), in which an enzyme catalyzes the formation of covalent bonds to generate individual molecules, ENS is a unifying theme for understanding the functions, morphologies, and locations of molecular ensembles in cellular environments. This review intends to provide a summary of the works of ENS within the past decade and emphasize ENS for functions. After comparing ECS and ENS, we describe a few representative examples where nature uses ENS, as a rule of life, to create the ensembles of biomacromolecules for emergent properties/functions in a myriad of cellular processes. Then, we focus on ENS of man-made (synthetic) molecules in cell-free conditions, classified by the types of enzymes. After that, we introduce the exploration of ENS of man-made molecules in the context of cells by discussing intercellular, peri/intracellular, and subcellular ENS for cell morphogenesis, molecular imaging, cancer therapy, and other applications. Finally, we provide a perspective on the promises of ENS for developing molecular assemblies/processes for functions. This review aims to be an updated introduction for researchers who are interested in exploring noncovalent synthesis for developing molecular science and technologies to address societal needs.

UV Accelerated Assemblies Constructed Using Calixpyridinium in Aqueous Solution

In this work, an irregular calixpyridinium-suramin sodium supramolecular assembly was constructed by the strong host-guest electrostatic interactions. More interestingly, a novel regular spherical supramolecular assembly was also fabricated by the hydrogen bonding interactions between suramin sodium and the UV accelerated addition product of deprotonated calixpyridinium in water. The same principle was also applied to construct a UV accelerated regular spherical self-assembly by the addition product of deprotonated calixpyridinium in water. Compared with the complicated and irreversible covalent connection of the light-responsive groups to the building block, which is one of the common means of obtaining light-responsive supramolecular systems, this finding not only provides a smart, facile, and universally applicable method to construct deprotonated calixpyridinium-based light-responsive host-guest systems but also provides a new idea for the development of other novel light-responsive building blocks.

Temperature-Dependent and pH-Responsive Pillar[5]arene-Based Complexes and Hydrogen-Bond-Based Supramolecular Pentagonal Boxes in Water

Supramolecular systems in water are of paramount importance and those based on hydrogen bonds are both intriguing and scarce. Here, after studying the peculiar host-guest complexes formed between per-dimethylamino-pillar[5]arene (1) and the bis-sulfonates 2 a-c, we describe the formation of the first hydrogen-bond-based supramolecular pentagonal boxes (SPBs), which are stable in water. These pH-responsive SPBs are constructed from 1 as a body, benzene polycarboxylic acids 3 a,b as lid compounds, and 2 a-c as guests. We demonstrate that encapsulation of 2 a-c in pillar[5]arene 1 and in the highly stable water-soluble SPBs, that is, 1(3 a)₂ and 1(3 b)₂ , is both temperature and pH dependent and, quite interestingly, depends, on the nature of the lid compounds used for capping the boxes even at high pH. We also highlight the difference in the ¹ H NMR characteristics of 2 b and 2 c in the cavity of 1 and the SPBs.

A Woven Supramolecular Metal-Organic Framework Comprising a Ruthenium Bis(terpyridine) Complex and Cucurbit[8]uril: Enhanced Catalytic Activity toward Alcohol Oxidation

The self-assembly of a diamondoid woven supramolecular metal-organic framework wSMOF-1 has been achieved from intertwined [Ru(tpy)₂ ]²⁺ (tpy=2,2',6',2''-terpyridine) complex M1 and cucurbit[8]uril (CB[8]) in water, where the intermolecular dimers formed by the appended aromatic arms of M1 are encapsulated in CB[8]. wSMOF-1 exhibits ordered pore periodicity in both water and the solid state, as confirmed by a combination of ¹ H NMR spectroscopy, UV-vis absorption, isothermal titration calorimetry, dynamic light scattering, small angle X-ray scattering and selected area electron diffraction experiments. The woven framework has a pore aperture of 2.1 nm, which allows for the free access of both secondary and primary alcohols and tert-butyl hydroperoxide (TBHP). Compared with the control molecule [Ru(tpy)₂ ]Cl₂ , the [Ru(tpy)₂ ]²⁺ unit of wSMOF-1 exhibits a remarkably higher heterogeneous catalysis activity for the oxidation of alcohols by TBHP in n-hexane. For the oxidation of 1-phenylethan-1-ol, the yield of acetophenone was increased from 10 % to 95 %.