A pillar[5]arene-based multiple-stimuli responsive metal-organic gel was constructed for facile removal of mercury ions

An Encyclopedic Compendium on Chemosensing Supramolecular Metal-Organic Gels

Chemosensing, an interdisciplinary scientific domain, plays a pivotal role ranging from environmental monitoring to healthcare diagnostics and (inter)national security. Metal-organic gels (MOGs) are recognized for their stability, selectivity, and responsiveness, making them valuable for chemosensing applications. Researchers have explored the development of MOGs based on different metal ions and ligands, allowing for tailored properties and sensitivities, and have even demonstrated their applications as portable sensors such as paper-based test strips for practical use. Herein, several studies related to MOGs development and their applications in the chemosensing field via UV-visible or luminance along with electrochemical approach are presented. These papers explored MOGs as versatile materials with their use in sensing bio or environmental analytes. This review provides a foundational understanding of key concepts, methodologies, and recent advancements in this field, fostering the scientific community.

Pillararene-Based Supramolecular Polymers for Adsorption and Separation

Supramolecular polymers have attracted increasing attention in recent years due to their perfect combination of supramolecular chemistry and traditional polymer chemistry. The design and synthesis of macrocycles have driven the rapid development of supramolecular chemistry and polymer science. Pillar[n]arenes, a new generation of macrocyclic compounds possessing unique pillar-shaped structures, nano-sized cavities, multi-functionalized groups, and excellent host-guest complexation abilities, are promising candidates to construct supramolecular polymer materials with enhanced properties and functionalities. This review summarizes recent progress in the design and synthesis of pillararene-based supramolecular polymers (PSPs) and illustrates their diverse applications as adsorption and separation materials. All performances are evaluated and analyzed in terms of efficiency, selectivity, and recyclability. Typically, PSPs can be categorized into three typical types according to their topologies, including linear, cross-linked, and hybrid structures. The advances made in the area of functional supramolecular polymeric adsorbents formed by new pillararene derivatives are also described in detail. Finally, the remaining challenges and future perspectives of PSPs for separation-based materials science are discussed. This review will inspire researchers in different fields and stimulate creative designs of supramolecular polymeric materials based on pillararenes and other macrocycles for effective adsorption and separation of a variety of targets.

Synthesis of Thiapillar[6]arenes Bearing Redox-Active (Hydro)quinone Groups. Electrochemical and XRD Study

Pillar[n]arenes are among the newest members of the macrocyclic family. Nevertheless, their conformational behavior and binding properties as well as redox properties of dealkylated pillar[n]arenes are well-studied. At the same time, introducing a heteroatom into a cyclophane macrocycle is already known to alter all the above properties drastically. This study presents a simple synthetic approach based on thia-Michael addition cyclization that readily resulted into hexathiapillar[6]arene with four phenylene units alternated by two redox-active hydroquinone moieties. The straightforward synthesis of the macrocycle enabled a systematic study of its conformation and redox behavior. The modification of hexathiapillar[6]arene afforded five functionalized derivatives, which were studied structurally in detail. The findings revealed interesting redox and structural properties of the macrocycle and its derivatives including the formation of crystal lattices with continuous channels and empty voids.

Progress in Research and Application of Metal-Organic Gels: A Review

In recent years, metal-organic gels (MOGs) have attracted much attention due to their hierarchical porous structure, large specific surface area, and good surface modifiability. Compared with MOFs, the synthesis conditions of MOGs are gentler and more stable. At present, MOGs are widely used in the fields of catalysis, adsorption, energy storage, electrochromic devices, sensing, analysis, and detection. In this paper, literature metrology and knowledge graph visualization analysis are adopted to analyze and summarize the literature data in the field of MOGs. The visualization maps of the temporal distribution, spatial distribution, authors and institutions' distribution, influence of highly cited literature and journals, keyword clustering, and research trends are helpful to clearly grasp the content and development trend of MOG materials research, point out the future research direction for scholars, and promote the practical application of MOGs. At the same time, the paper reviews the research and application progress of MOGs in recent years by combining keyword clustering, time lines, and emergence maps, and looks forward to their challenges, future development trend, and application prospects.

Green, Efficient Detection and Removal of Hg2+ by Water-Soluble Fluorescent Pillar[5]arene Supramolecular Self-Assembly

Developing a water-soluble supramolecular system for the detection and removal of Hg²⁺ is extremely needed but remains challenging. Herein, we reported the facile construction of a fluorescent supramolecular system (H⊃G) in 100% water through the self-assembly of carboxylatopillar[5]arene sodium salts (H) and diketopyrrolopyrrole-bridged bis(quaternary ammonium) guest (G) by host–guest interaction. With the addition of Hg²⁺, the fluorescence of H⊃G could be efficiently quenched. Since Hg²⁺ showed synergistic interactions (coordination and Hg²⁺- cavity interactions with G and H, respectively), crosslinked networks of H⊃G@Hg²⁺ were formed. A sensitive response to Hg²⁺ with excellent selectivity and a low limit of detection (LOD) of 7.17 × 10⁻⁷ M was obtained. Significantly, the quenching fluorescence of H⊃G@Hg²⁺ can be recovered after a simple treatment with Na₂S. The reusability of H⊃G for the detection of Hg²⁺ ions was retained for four cycles, indicating the H⊃G could be efficiently used in a reversible manner. In addition, the H⊃G could efficiently detect Hg²⁺ concentration in real samples (tap water and lake water). The developed supramolecular system in 100% water provides great potential in the treatment of Hg²⁺ detection and removal for environmental sustainability.

GOx-assisted synthesis of pillar[5]arene based supramolecular polymeric nanoparticles for targeted/synergistic chemo-chemodynamic cancer therapy

Background

Cancer is the most serious world's health problems on the global level and various strategies have been developed for cancer therapy. Pillar[5]arene-based supramolecular therapeutic nano-platform (SP/GOx NPs) was constructed successfully via orthogonal dynamic covalent bonds and intermolecular H-bonds with the assistance of glucose oxidase (GOx) and exhibited efficient targeted/synergistic chemo-chemodynamic cancer therapy.

Methods

The morphology of SP/GOx NPs was characterized by DLS, TEM, SEM and EDS mapping. The cancer therapy efficinecy was investigated both in vivo and in vitro.

Results

SP/GOx NPs can load drug molecules (Dox) and modify target molecule (FA-Py) on its surface conveniently. When the resultant FA-Py/SP/GOx/Dox NPs enters blood circulation, FA-Py will target it to cancer cells efficiently, where GOx can catalyst the overexpressed glucose to generate H₂O₂. Subsequently, the generated H₂O₂ in cancer cells catalyzed by ferrocene unit to form •OH, which can kill cancer cells. Furthermore, the loaded Dox molecules released under acid microenvironment, which can further achieve chemo-therapy.

Conclusion

All the experiments showed that the excellent antitumor performance of FA-Py/SP/GOx/Dox NPs, which provided an new method for pillar[5]arene-based supramolecular polymer for biomedical applications.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01237-0.

Hierarchical porous metal–organic gels and derived materials: from fundamentals to potential applications

This review summarizes recent progress in the development and applications of metal–organic gels (MOGs) and their hybrids and derivatives dividing them into subclasses and discussing their synthesis, design and structure–property relationship.

A simple pillar[5]arene assembled multi-functional material with ultrasensitive sensing, self-healing, conductivity and host-guest stimuli-responsive properties

Multi-functional materials have received wide attention due to their potential applications in various fields; therefore, developing a simple and easy strategy for the preparation of multi-functional materials is an interesting issue. In this work, a novel supramolecular gel, TP-QG, has been successfully constructed via the assembly of a simple methoxyl-pillar[5]arene host (TP) and a tripodal (tri-pyridine-4-yl)-amido-benzene guest (Q). Interestingly, TP-QG could act as a multi-functional material and showed strong fluorescence, good self-healing, host-guest stimuli-responsiveness and conductive properties. Due to these properties, TP-QG shows a fascinating application prospect. For instance, TP-QG could exhibit ultrasensitive fluorescence response for Fe³⁺ and F^- in water via the fluorescence "ON-OFF-ON" pathway; the lowest detection limit (LOD) of TP-QG for Fe³⁺ was 2.32 × 10^-10 M and the LOD of TP-QG-Fe for F^- was 4.30 × 10^-8 M. These properties permit TP-QG to act as not only a Fe³⁺ and F^- sensor, but also an "ON-OFF-ON" fluorescence display material and an efficient logic gate. Meanwhile, the xerogel of TP-QG could remove Fe³⁺ from water, and the adsorption ratio was 98.68%; the xerogel of TP-QG-Fe could also remove F^- from water; the removal ratio was about 87.92%. This work provides a feasible way to construct multi-functional smart materials by host-guest assembly.

A multi-responsive organogel and colloid based on the self-assembly of a Ag(i)-azopyridine coordination polymer

In this work, through the coordination of C₃ symmetric azopyridine ligands and Ag(i), coordination polymers with azo groups on the main chain were prepared. The trans coordination polymer formed an organogel with a network of nanofibers at low critical gelation concentrations, and it exhibited the abilities of self-healing and multi-stimuli response to heating, light, mechanical shearing, and chemicals due to the presence of dynamic coordinating bonds. On the other hand, the cis coordination polymer was found to assemble into nanoparticles to give a responsive colloid, which can produce fibrous precipitation in several days upon visible light irradiation due to the isomerization of the azo groups. This work provides a novel example for the design of a multi-responsive organogel and colloid based on the structural transformation of coordination polymers.

Concentration-dependent supramolecular self-assembly of A1/A2-asymmetric-difunctionalized pillar[5]arene

A series of A1/A2-bromoalkoxy-and-hydroxy-difunctionalized pillar[5]arenes were synthesized by the removal of the pillar[5]arene-bearing benzyl group using catalytic hydrogenation. The difunctionalized pillar[5]arene bearing 8-bromooctoxy and benzyloxy substituents at the A1/A2 positions formed pseudo[1]rotaxane at low concentration and double-threaded supramolecular dimer at high concentration. The supramolecular self-assembly behavior has been probed with multiple methods including varying (variable) concentration 1H NMR spectroscopy, diffusion-ordered spectroscopy (DOSY), dynamic light scattering (DLS) measurements, isothermal titration calorimetry (ITC), and single-crystal X-ray analysis.

Pillararene-based conjugated porous polymers

The synthesis and application of promising polymeric materials–pillararene-based conjugated porous polymers–are discussed and summarized in this review.

Molecularly Imprinted Polymers Doped with Carbon Nanotube with Aid of Metal-Organic Gel for Drug Delivery Systems

PURPOSE

The incidence of breast cancer worldwide has been on the rise since the late 1970s, and it has become a common tumor that threatens women's health. Aminoglutethimide (AG) is a common treatment of breast cancer. However, current treatments require frequent dosing that results in unstable plasma concentration and low bioavailability, risking serious adverse reactions. Our goal was to develop a molecularly imprinted polymer (MIP) based delivery system to control the release of AG and demonstrate the availability of this drug delivery system (DDS), which was doped with carbon nanotube with aid of metal-organic gel.

METHODS

Preparation of MIP was optimized by key factors including composition of formula, ratio of monomers and drug loading concentration.

RESULTS

By using multi-walled carbon nanotubes (MWCNT) and metal-organic gels (MOGs), MIP doubled the specific surface area, pore volume tripled and the IF was 1.6 times than the reference. Compared with commercial tablets, the relative bioavailability was 143.3% and a more stable release appeared.

CONCLUSIONS

The results highlight the influence of MWCNT and MOGs on MIP, which has great potential as a DDS.

Functional supramolecular gels based on pillar[n]arene macrocycles

Supramolecular gels constructed from low-molecular-weight gelators via noncovalent interactions have received increasing attention. The rapid development of stimuli-responsive supramolecular gels with attractive properties is highly desirable to meet the ever-growing demand of materials science and chemistry. The inherent reversible and dynamic nature of noncovalent interactions in supramolecular gels endows the materials with sensing, processing, and actuating functions in response to specific environmental changes and offers them great potential in flexible biomaterials and intelligent devices. In particular, pillar[n]arenes with symmetrical pillar-shaped architectures have been recognized as an emerging class of synthetic macrocycles after crown ethers, cyclodextrins, calixarenes, and cucurbiturils, and proven to be excellent candidates for the fabrication of functional supramolecular gels due to their many advantages including facile synthesis, diverse functionalization, and appealing host-guest properties. This review provides a comprehensive overview of recent progress in supramolecular gels involving pillar[n]arenes and their derivatives as synthetic macrocyclic arenes, from the viewpoints of the synthetic approach, controllable assembly, stimuli-responsiveness, and functions. Perspectives of this burgeoning field of research are also given at the end.

An azine-containing bispillar[5]arene-based multi-stimuli responsive supramolecular pseudopolyrotaxane gel for effective adsorption of rhodamine B

An azine-containing bispillar[5]arene was designed and synthesized by the reaction of aldehyde functionalized-pillar[5]arene and hydrazine. Then, a novel bispillar[5]arene-based supramolecular pseudopolyrotaxane has been successfully prepared via host-guest interaction. Interestingly, by taking advantage of the host-guest interactions, π-π stacking interactions and hydrogen bonding interactions, the multi-stimuli-responsive gel-sol phase transitions of such a supramolecular pseudopolyrotaxane gel were successfully realized under different stimuli, such as acid, temperature, concentration, and competitive guests. Moreover, this supramolecular system could effectively adsorb dye molecule rhodamine B. It is worth noting that this supramolecular pseudopolyrotaxane gel prepared in cyclohexanol solution (BP5·G·C) could be used as an adsorbent material for adsorbing rhodamine B with adsorption efficiency of 98.4%. Meanwhile, the adsorption efficiency was 97.6% for supramolecular pseudopolyrotaxane gel prepared in DMSO-H2O (v : v, 8 : 2) binary solution (BP5·G·D), also indicating the superior adsorption effect of BP5·G·D toward the dye molecule rhodamine B.

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

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

Supramolecular Gel as the Template for Catalysis, Inorganic Superstructure, and Pharmaceutical Crystallization

A supramolecular gel is a fascinating combination of flexibility and orderliness. While the supramolecular nature of crosslinking contributes towards the adaptivity and the reversibility of the system, orderliness at the molecular level amplifies the functional output and induces extraordinary selectivity into the system. Therefore, use of supramolecular gels as the soft template is an emerging area of research, which includes but not limited to catalysis of a chemical or a photochemical process, transcription of gel property to a substrate, or even controlling the nucleation of drug molecules. This review aims to highlight the template effect of supramolecular gels in the above-mentioned areas relevant to novel fundamental chemistry, technology, and healthcare.

Pillararenes as macrocyclic hosts: a rising star in metal ion separation

Pillararenes are macrocyclic oligomers of alkoxybenzene akin to calixarenes but tethered at the 2,5-positions via methylene bridges. Benefiting from their unique pillar-shaped architecture favorable for diverse functionalization and versatile host-guest properties, pillararenes decorated with chelating groups worked excellently as supporting platforms to construct extractants or adsorbents for metal ion separation. This feature article provides a detailed summary of pillararenes in Ln/An separation by liquid-liquid extraction and heavy metal separation by solid-liquid extraction. The preorganization effect of the rigid pillararene framework has a profound impact on the extraction of metal ions, and a unique extraction mechanism is observed when employing ionic liquids as solvents. The rich host-guest chemistry of pillararenes enables construction of a wide variety of supramolecular materials as metal ion adsorbents. We also discuss the differences between pillararenes and several well-known macrocycles, with a focus on the metal-ligand coordination and its influencing factors. We hope this review will provide useful information and unleash new opportunities in this field.

Emissive intelligent supramolecular gel for highly selective sensing of Al3+ and writable soft material

A fluorine-containing acylhydrazone was newly designed and found to form gels in a mixed solvent of DMSO-ethylene glycol. The gelator could show brilliant blue light upon mixing with Al3+, which could be erased by F- ions and thus forming an erasable gel.

Acylhydrazone functionalized benzimidazole-based metallogel for the efficient detection and separation of Cr3

Chromium(iii) is a kind of microelement and can be converted to the more toxic chromium(vi), which is a carcinogen, by redox cycling. Thus, the development of novel materials for the detection and removal of Cr³⁺ is a very important issue. A novel metallogel chemosensor (BMG-Fe) based on functionalized benzimidazole (BM) and Fe³⁺ was constructed, which could fluorescently detect and separate Cr³⁺. The detection limit of BMG-Fe for Cr³⁺ is 2.62 × 10^-8 M, and it exhibited high sensitivity and selectivity for Cr³⁺. Meanwhile, the absorbing percentage of BMG-Fe for Cr³⁺ is 96.36%, indicating a high separation rate. Interestingly, the sensitivity and ingestion capacity of BMG-Fe for Cr³⁺ are better than that of the simple organogel (BMG). So, the metallogel BMG-Fe could be utilized for the efficient removal of heavy metal ions from waste water.

Monosulfonicpillar[5]arene: Synthesis, Characterization, and Complexation with Tetraphenylethene for Aggregation-Induced Emission

A pillar[5]arene derivative with a hydrophilic sulfonic group, i.e., monosulfonicpillar[5]arene (MSP5), has been successfully synthesized for the first time, which exhibited strong binding affinity towards alcohol analogs. Significantly, fluorescent supramolecular ensemble was fabricated from the supramolecular complexation of MSP5 and a neutral guest with tetraphenylethene core. Enhanced fluorescent emission of this system can be detected both in dilute solution and the solid state, and its temperature and competitive guest multi-responsive properties suggest its promising application as a chemical sensor towards alcohol analogs, ethylenediamine, and temperature variations.

A multi-stimuli responsive metallosupramolecular polypseudorotaxane gel constructed by self-assembly of a pillar[5]arene-based pseudo[3]rotaxane via zinc ion coordination and its application for highly sensitive fluorescence recognition of metal ions

A novel pillar[5]arene-based metallosupramolecular polypseudorotaxane gel has been successfully prepared.

A novel thermo-responsive supramolecular organogel based on dual acylhydrazone: fluorescent detection for Al3+ ions

A new dual acylhydrazone-functionalized gelator (L) has been synthesized, which behaves as a thermal-responsive supramolecular organogel (L-gel) in DMSO. This L-gel exhibits very weak fluorescence based on the photoinduced electron transfer (PET) mechanism. The L-gel can recognize Al³⁺ and assemble into an enhanced blue-light-emitting supramolecular metallogel (Al@gel).

A thermo-responsive supramolecular gel and its luminescence enhancement induced by rare earth Y3

A new acylhydrazone-functionalized dual benzimidazole derivative gelator (L) was synthesized. L can self-assemble in DMSO-EG (ethylene glycol) or DMF-water mixtures to form a thermo-responsive supramolecular organogel (L-gel). In order to increase the fluorescence intensity of L-gel (DMSO-EG system), L-gel slowly turned into a clear solution upon addition of one equivalent of RE (rare earth) Y³⁺. Interestingly, this gelator L and Y³⁺ can be assembled into an enhanced blue-light-emitting supramolecular metallogel (Y@gel) in DMF-water mixtures.

Novel multi-analyte responsive ionic supramolecular gels based on pyridinium functionalized-naphthalimide

A novel ionic supramolecular gel (is-G) is synthesized using N-(pyridinium-4-yl)-naphthalimide (G1) and n-pentanoic acid. By rationally introducing competitive coordination into is-G, two ion coordinated ionic supramolecular gels is-IG and is-FeG (coordinated with I^- and Fe³⁺, respectively) are obtained. is-IG could fluorescently "turn-on" detect Hg²⁺ and l-Arg with specific selectivity, whereas, is-FeG could accurately identify l-Ser via fluorescence in water. Moreover, ion or amino acid responsive films based on these ionic supramolecular gels are prepared. These ionic supramolecular gels and films could act as multi-analyte detection materials as well as fluorescent display materials.

A novel supramolecular organogel based on acylhydrazone functionalized pillar[5]arene acts as an I- responsive smart material

A novel organic gelator (PZ) has been synthesized by rationally connecting a pillar[5]arene moiety and a bis(hexadecyloxy)phenyl functionalized acylhydrazone moiety. PZ could self-assemble into a supramolecular polymer and form a stable organogel (OPZ) in cyclohexanol by multi-self-assembly driving forces such as C-Hπ, ππ, vdW and hydrogen bonding interactions. The organogel (OPZ) shows blue aggregation-induced emission (AIE). Interestingly, the organogel OPZ could sense iodide ions (I^-) in the gel-gel state with high selectivity and sensitivity. The detection limit of OPZ for I^- is 9.4 × 10^-8 M, indicating high sensitivity to I^-. Furthermore, a thin film based on OPZ was prepared, which could be used as a smart material for the detection of I^- as well as a fluorescent security display material.

Pillararene-based fluorescent chemosensors: recent advances and perspectives

This feature article summarizes recent research in the pillararene-based fluorescent chemosensor field in terms of ion sensing, small molecule recognition, biomolecule detection, fluorescent supramolecular aggregates, and biomedical imaging.

Pillar[5]arene-based fluorescent polymer for selective detection and removal of mercury ions

A novel pillar[5]arene-based fluorescent polymer has been synthesized, and it is used for fluorescence detection and removal of the toxic mercury ions.