Water compatible supramolecular polymers: recent progress

Application of Organic Gel on Skin Realized by Hydrogel/Organic Gel Adhesion

Diversity in solvent selection bestows the organic gel with appealing characteristics embracing antidrying, anti-icing, and antifouling abilities. However, organic gel, subjected to the "toxic" inherent property of solvent, is not able to be manipulated on skin. Herein, introducing the hydrogel layer amid organic gel and skin is envisaged to realize application of organic gel on skin. Hydrogel, inserted as the medium layer, works for the coupling role between skin and organic gel, also avoids the direct contact of organic gel toward skin. First, hydrogel system composed of acrylic acid is fabricated, meanwhile organic gel is prepared employing 2-hydroxyethyl methacrylate, ethylene glycol (EG) as solvent. Organic gel is able to adhere to hydrogel by hydrogen bonding resulting from carboxyl groups of polyacrylic acid chains and hydroxyl groups occurring on 2-hydroxyethyl methacrylate or EG. Additionally, hydrogen bonding enables the hydrogel to be firmly attached to skin, thus organic gel/hydrogel/skin assembly is produced. The further application of organic gel is exploited by incorporating stimuli-responsive dyes including spiropyran and rhodamine derivative.

Adaptive and Robust Vitrimers Fabricated by Synergy of Traditional and Supramolecular Polymers

Vitrimers offer a unique combination of mechanical performance, reprocessability, and recyclability that makes them highly promising for a wide range of applications. However, achieving dynamic behavior in vitrimeric materials at their intended usage temperatures, thus combining reprocessability with adaptivity through associative dynamic covalent bonds, represents an attractive but formidable objective. Herein, we couple boron-nitrogen (B-N) dative bonds and B-O covalent bonds to generate a new class of vitrimers, boron-nitrogen vitrimers (BNVs), to endow them with dynamic features at usage temperatures. Compared with boron-ester vitrimers (BEVs) without B-N dative bonds, the BNVs with B-N dative bonds showcase enhanced mechanical performance. The excellent mechanical properties come from the synergistic effect of the dative B-N supramolecular polymer and covalent boron-ester networks. Moreover, benefiting from the associative exchange of B-O dynamic covalent bonds above their topological freezing temperature (Tv), the resultant BNVs also possess the processability. This study leveraged the structural characteristics of a boron-based vitrimer to achieve material reinforcement and toughness enhancement, simultaneously providing novel design concepts for the construction of new vitrimeric materials.

Characterization by Gel Permeation Chromatography of the Molecular Weight of Supramolecular Polymers Generated by Forming Polyrotaxanes through the Introduction of External Stoppers

Supramolecular polymers find wide applications across diverse domains, and the molecular weight exerts a critical influence on their applicability. Consequently, the measurement of molecular weight for supramolecular polymers assumes paramount significance. Gel Permeation Chromatography (GPC) requiring low-concentration condition is a common characterization employed for molecular weight determination, which is not suitable for supramolecular polymers possessing concentration-independence property. Here, to break this threshold, we synthesized M1 embodying dibenzo-24-crown-8 (DB24C8) moiety as well as dibenzylammonium salt (DBA) group, which was capable of self-assembling into supramolecular polymers terminated with aldehyde groups at its end. Upon the addition of (4- (1,2,2-Triphenylvinyl) phenyl) methylamine (TPE-NH2), supramolecular polymers underwent a transition into polyrotaxanes, for which it was led by the generation of imine bonds. By virtue of GPC, the molecular weight of polyrotaxanes was obtained, then it was available to gain the molecular weight of supramolecular polymers with the help of transformation efficiency.

Nanotechnology for brain tumor imaging and therapy based on π-conjugated materials: state-of-the-art advances and prospects

In contemporary biomedical research, the development of nanotechnology has brought forth numerous possibilities for brain tumor imaging and therapy. Among these, π-conjugated materials have garnered significant attention as a special class of nanomaterials in brain tumor-related studies. With their excellent optical and electronic properties, π-conjugated materials can be tailored in structure and nature to facilitate applications in multimodal imaging, nano-drug delivery, photothermal therapy, and other related fields. This review focuses on presenting the cutting-edge advances and application prospects of π-conjugated materials in brain tumor imaging and therapeutic nanotechnology.

Highly stretchable and self-healing photoswitchable supramolecular fluorescent polymers for underwater anti-counterfeiting

Thanks to the non-destructiveness and spatial-controllability of light, photoswitchable fluorescent polymers (PFPs) have been successfully applied in advanced anti-counterfeiting and information encryption. However, most of them are not suitable for use in harsh underwater environments, including high salinity seawater. In this study, by integrating photochromic molecules into a hydrophobic polymer matrix with the fluorine elastomer, including dipole-dipole interactions, we describe a class of novel photoswitchable supramolecular fluorescent polymers (PSFPs) that can adaptively change their fluorescence between none, green and red by the irradiation of different light. The PSFPs not only exhibited excellent photoswitchable properties, including fast photo-responsibility, prominent photo-reversibility, and photostability, but also exhibited some desired properties, including exceptional stretchability, hydrophobicity, antifouling, self-healing ability, simple preparation process, and processability. We thus demonstrated their applications in underwater data encryption and anti-counterfeiting labels.

Insights into the Correlation of Cross-linking Modes with Mechanical Properties for Dynamic Polymeric Networks

Simultaneously introducing covalent and supramolecular cross-links into one system to construct dually cross-linked networks, has been proved an effective approach to prepare high-performance materials. However, so far, features and advantages of dually cross-linked networks compared with those possessing individual covalent or supramolecular cross-linking points are rarely investigated. Herein, on the basis of comparison between supramolecular polymer network (SPN), covalent polymer network (CPN) and dually cross-linked polymer network (DPN), we reveal that the dual cross-linking strategy can endow the DPN with integrated advantages of CPN and SPN. Benefiting from the energy dissipative ability along with the dissociation of host-guest complexes, the DPN shows excellent toughness and ductility similar to the SPN. Meanwhile, the elasticity of covalent cross-links in the DPN could rise the structural stability to a level comparable to the CPN, exhibiting quick deformation recovery capacity. Moreover, the DPN has the strongest breaking stress and puncture resistance among the three, proving the unique property advantages of dual cross-linking method. These findings gained from our study further deepen the understanding of dynamic polymeric networks and facilitate the preparation of high-performance elastomeric materials.

Rational Design of the β-Bulge Gate in a Green Fluorescent Protein Accelerates the Kinetics of Sulfate Sensing

Detection of anions in complex aqueous media is a fundamental challenge with practical utility that can be addressed by supramolecular chemistry. Biomolecular hosts such as proteins can be used and adapted as an alternative to synthetic hosts. Here, we report how the mutagenesis of the β-bulge residues (D137 and W138) in mNeonGreen, a bright, monomeric fluorescent protein, unlocks and tunes the anion preference at physiological pH for sulfate, resulting in the turn-off sensor SulfOFF-1. This unprecedented sensing arises from an enhancement in the kinetics of binding, largely driven by position 138. In line with these data, molecular dynamics (MD) simulations capture how the coordinated entry and gating of sulfate into the β-barrel is eliminated upon mutagenesis to facilitate binding and fluorescence quenching.

Blends of nitrophenylmaleimide isomers with carboxymethylcellulose for the preparation of supramolecular polymers

Novel water-compatible supramolecular polymers (WCSP) based on the non-covalent interaction between carboxymethylcellulose (CMC) and o, m, and p-nitrophenylmaleimide isomers are proposed. The non-covalent supramolecular polymer was obtained from high viscosity CMC with a degree of substitution 1.03 with o, m, and p-nitrophenylmaleimide molecules that were synthesized from maleic anhydride and its corresponding nitroaniline. Subsequently, blends were made at different nitrophenylmaleimide concentrations, stirring rate, and temperatures, with 1.5% CMC, to select the best conditions for each case and to evaluate the rheological properties. The selected blends were used to form films and analyze spectroscopic, physicochemical, and biological properties. Then, the interaction between a CMC monomer and each isomer of nitrophenylmaleimide was investigated using quantum chemistry computational calculations with the B3LYP/6-311 + G (d,p) method, providing a detailed explanation of their intermolecular interactions. The supramolecular polymers obtained exhibit an increase in viscosity of blends between 20% and 30% compared to CMC, a shift in the wavenumber of the OH infrared band by approximately 66 cm^-1, and the first decomposition peak at the glass transition temperature occurring between 70 and 110 °C. These changes in properties are attributed to the formation of hydrogen bonds between the species. However, the degree of substitution and the viscosity of the CMC affects the physical, chemical, and biological properties of the polymer obtained. The supramolecular polymers are biodegradable regardless of the type of blends made and are easily obtainable. Notably, the CMC with m-nitrophenylmaleimide yields the polymer with the best properties.

Multicolor Iridium(III) Complexes with Host-Guest Recognition Motifs for Enhanced Electrochemiluminescence and Modular Labeling

Cyclometalated Ir(III) complexes with high electrochemiluminescence (ECL) efficiency and appropriate bioconjugation sites are urgently needed in ECL immunoassays (ECLIA). Herein, we report the synthesis, photophysics, electrochemistry, and ECL of six new Ir(III) complexes bearing naphthyl (nap) or adamantane phenyl (adap) substitutions, four of which emit cyan, green, or red light and display 1.7- to 7.5-fold increases in ECL intensity. In combination with DFT/TDDFT calculations, this enhancement is rationalized to the augmented radiative rate that arises from both the strengthened spin-orbit coupling (SOC) and the increased transition dipole moment. In addition, the adap-based Ir(III) complex shows high binding affinity with β-cyclodextrin (β-CD) due to the strong hydrophobic interaction, which enables us to develop a modular strategy for the labeling of Ir(III) complexes with biomolecules and to use hydrophobic luminophores in the aqueous-phase detection. As demonstrated, a novel ECLIA is built up and exhibits a wide linear range from 1 ng/mL to 10 μg/mL and a detection limit of 72 pg/mL for the determination of C-reactive protein (CRP). These findings provide new insights into the design, synthesis, and bio-labeling of highly emissive Ir(III) complexes and pave the way for the development of novel ECLIA based on host-guest recognition motifs.

Press-N-Go On-Skin Sensor with High Interfacial Toughness for Continuous Healthcare Monitoring

On-skin electronic sensors are demanded for healthcare monitoring such as the continuous recording of biopotential and motion signals from patients. However, the mechanical mismatches and poor interface adhesion at the skin/sensor interfaces always cause high interfacial impedance and artifacts, frequent interfacial failure, and unexpected depletion of the device, which significantly limit the performance of the sensors. We here develop an on-skin sensor based on a conductive pressure-sensitive tape, which is assembled from supramolecular dual-cross-linked hydrogel composites. Both covalent and noncovalent cross-links in the hydrogel networks could harvest high flexibility, pressure-sensitive adhesion, and high interfacial toughness altogether, enabling a convenient "Press-N-Go" application of the sensor on human skin without additional pre/post-treatment on the skin or the senor. The high conformability and low resistivity of the tape can sustainably lower the interfacial impedance and thus improve signal quality in various measurement conditions. Our design provides a feasible path to develop interface-toughened on-skin electronics, which is desired in dynamic human-machine interfaces.

Carbon Dioxide-Mediated Desalination

Conventional desalination membrane technologies, although offer portable drinking water, are still energy-intensive processes. This paper proposes a potentially new approach for performing water desalination and purification by utilizing the reversible interaction of carbon dioxide (CO₂) with nucleophilic amines─reminiscent of the Solvay process. Based on our model studies with small molecules, CO₂-responsive amphiphilic insoluble diamines were prepared, characterized, and applied in the formation of soda and ammonium chloride upon exposure to ambient CO₂ (1 atm), thus removing chloride ions from model and real seawater. This ion-exchange process and separation of chloride from the aqueous phase are spontaneous in the presence of CO₂ without the need for external energy sources. We demonstrate a flow system to envisage energy-efficient CO₂-mediated desalination and simultaneous carbon capture and sequestration.

An Antitumor Dual-Responsive Host-Guest Supramolecular Polymer Based on Hypoxia-Cleavable Azocalix[4]arene

The exploitation of specific guests which can respond to external stimuli is the main approach for the construction of stimuli-responsive supramolecular polymers (SPs) based on host-guest interactions. Most functional guests, however, fail to manifest stimuli-responses. Herein, a hypoxia-responsive dimeric azocalixarene (D-SAC4A) with outstanding hosting properties was used as the macrocyclic building block for the preparation of host stimuli-responsive SPs. Since azocalixarenes can also be compatible with stimuli-responsive guests, an antitumor drug, camptothecin (CPT), was chosen and linked via a disulfide-containing linker to afford a glutathione (GSH)-responsive ditropic guest (D-CPT). A unique dual-responsive SP was obtained by 1 : 1 mixing of D-SAC4A and D-CPT in water, which further assembled into SP nanoparticles (DSPNs). DSPNs displayed outstanding stability against dilution and biological interferants, as well as precise CPT-release under GSH and hypoxia conditions. In vitro and in vivo experiments demonstrated the good biosafety and tumor-suppressive effects of DSPNs.

Supramolecular Combination Chemotherapy: Cucurbit[8]uril Complex Enhanced Platinum Drug Infiltration and Modified Nanomechanical Property of Colorectal Cancer Cells

Combination chemotherapy is recognized as a vital medical treatment for cancer, but it has not achieved clinical ideal effects of combination therapy. Herein, we designed a supramolecular combination chemotherapy strategy based on cucurbit[8]uril (CB[8]), which can be facilely assembled into dual platinum drugs. Interestingly, employing the CB[8] carrier led to a greater than 10-fold intracellular Pt content compared to that of dual drugs at 4 h, and the CB[8] complex (CLE) can enhance the infiltration of platinum drugs in colorectal tumor cells tremendously. The platinum drugs can be released from CLE through consuming more tumor biomarker spermidine. Through analyzing the nanomechanical property of the colorectal tumor cellular surface by bioscope AFM, it was revealed that CLE modified the property by decreasing the adhesion and increasing the stiffness. This study provided a facile and sensitive strategy for improving combination chemotherapy by supramolecular materials.

Bis-Pyridine-Based Organogel with AIE Effect and Sensing Performance towards Hg2

A novel gelator (1) based on a bis-pyridine derivative was designed and synthesized, which could form stable gels in methanol, ethanol, acetonitrile, ethyl acetate, DMF/H₂O (4/1, v/v) and DMSO/H₂O (4/1, v/v). The self-assembly process of gelator 1 was studied by field emission scanning electron microscopy (FESEM), UV–vis absorption spectroscopy, fluorescence emission spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction and a water contact angle experiment. Gelator 1 exhibited obvious AIE behavior. On the base of its AIE, the gel of 1 could detect Hg²⁺, which resulted in fluorescence quenching and a gel–sol transition. ¹H NMR titration experiments with Hg²⁺ revealed that the metal coordination interaction induced the fluorescence quenching and the breakdown of the noncovalent interaction in the gel system. This research provides a new molecular mode for designing a functional self-assembly gel system.

A Strategy Based on Aggregation-Induced Ratiometric Emission to Differentiate Molecular Weight of Supramolecular Polymers

Molecular weight has an important bearing on the properties of supramolecular polymers. However, the intuitive differentiation of the molecular weight of supramolecular polymers remains challenging. Given this situation, establishing a reliable relationship between fluorescence properties and molecular weight may be a promising strategy. Herein, we prepared a supramolecular monomer M1 with aggregation-induced ratiometric emission characteristics. With the increasing M1 concentration (0.100-100 mM), the average degree of polymerization (DP_DOSY ) rose from 1.00 to 293. Meanwhile, the color changed from dark blue to cyan, finally to yellow-green in the same concentration range. Hence, the intuitive relationship between DP_DOSY and fluorescence colors was constructed, allowing the visual differentiation of molecular weight. Moreover, the fluorescence color could be regulated by introducing a competitive molecule to induce the depolymerization of supramolecular polymers.

Cyclodextrin-pillar[n]arene hybridized macrocyclic systems

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

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.

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

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

Metal-ligand Interactions and Oligo(p-Phenylene Vinylene) Derivatives Based Supramolecular Polymer Possessing Variable Fluorescence Colors

Fluorescent supramolecular polymers combine the benefits of supramolecular polymers in terms of dynamic nature with the optoelectronic features of incorporated fluorophores. However, the majority of fluorescent supramolecular polymers can only exhibit a single fluorescent state, restricting their applications. Incorporating J-type dyes into supramolecular monomers is expected to impart supramolecular polymers with variable fluorescence colors, because the aggregation mode of J-type dyes is closely related to the formation of supramolecular polymers. Herein, we report a supramolecular polymer [M1·Zn(OTf)₂ ]_n , in which the monomer M1 contains a J-type dye, oligo(p-phenylene vinylene) (OPV) derivative, and two terpyridine ends. The M1 + Zn(OTf)₂ solutions exhibit fluorescence color changes varying from cyan to yellow-green in the monomer concentration ranging from 0.04 to 1.00 mM. Moreover, based on the outputs from laser scanning confocal microscopy (LSCM), the fluorescence color transition during the formation of supramolecular polymers is intuitively proven. Additionally, considering the close relationship between the supramolecular polymer structure and the fluorescence color, the fluorescence color can be regulated by introducing tetraethylammonium hydroxide (TBAOH) that can bind with Zn²⁺ competitively to break up the structure of the supramolecular polymer. This article is protected by copyright. All rights reserved.

Injectable self-healing cellulose hydrogel based on host-guest interactions and acylhydrazone bonds for sustained cancer therapy

Tumor local chemotherapy employing injectable hydrogel reservoirs is a promising platform to achieve precise drug administration. However, balanced injectability, pH-responsiveness and long-term hydrolysis resistance of self-healing hydrogels remain appealing challenges. Herein, a modular preassembly strategy combining host-guest interactions with dynamic acylhydrazone bonds, was exploited to fabricate injectable cellulose-based hydrogels (CAAs) dressed with self-healing properties, pH-responsiveness and hydrolytic degradation resistance. Attributed to the host-guest interaction between β-cyclodextrin (CD) and 1-adamantane (AD), the hydrogels exhibited injectability, self-healing properties (healing efficiency of 97.5%) and rapid recovery (< 10 min) without external stimuli in physiological environment. Moreover, the hydrogels equipped with dynamic acylhydrazone linkages underwent slow hydrolytic degradation (> 30 days) and pH-responsive behavior, endowing the hydrogels with precise spatiotemporal drug release administration. The in vivo application of CAA as a carrier was studied using doxorubicin (DOX) model drug, and the results shows that using CAA as DOX carrier not only greatly enhances the anti-tumor efficacy of DOX, but also reduced the side effects of DOX. STATEMENT OF SIGNIFICANCE: With the preassemble approach combining host-guest interactions with dynamic acylhydrazone bonds, this work demonstrated a multi-functional self-healing hydrogel as drug carrier developed by using natural polysaccharides, which offers a new avenue for the high-value utilization of biomass. The strategy demonstrated in the present work may also supply a pathway for the preparation and regulation of hydrogels as intelligent biomedicine materials.

Supramolecular systems prepared using terpyridine-containing pillararene

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

A cucurbit[8]uril-stabilized 3D charge transfer supramolecular polymer with a remarkable confinement effect for enhanced photocatalytic proton reduction and thioether oxidation

A water-soluble porous supramolecular polymer is assembled through a CB[8]-based 2 + 2 host–guest binding motif, which can greatly increase the efficiency of photocatalysis.