Supramolecular Interactions Research Articles

Bioinspired "Intermolecular Pocket" in Soft Molecular Crystal of Porous Organic CageExhibiting Reversible Guest Recognition.

Porous Organic Cages (POCs) have gathered a lot of attention in sorts of fields. Previous studies often focused on the functionalization of their intrinsic porosity, while the utilization of the extrinsic porosity has been seldom reported. To date, the rational construction of functionalized extrinsic porosity in POCs is a serious challenge, which still relies on trial and error. Inspired by hydrophobic proteins, in the contribution, a POC (namely NKPOC-DS) is obtained with hydrophobic "intermolecular pocket" as extrinsic porosity constructed through the assembly of disulfide bonds with hydrophobic groups, facilitating strong supramolecular interactions as confirmed by Electrostatic Potential (ESP) maps and single-crystal X-ray diffraction analysis. Notably, NKPOC-DS exhibits a unique C2H6-selective "breathing behaviour" due to the presence of softness in its extrinsic porosity, which does not extend to other gases such as C2H4, CH4, CO2, N2, and H2. Such specific recognition of C2H6 thus provides NKPOC-DS with the ability to preferentially adsorb C2H6 from a C2H6/C2H4 mixture. The innovative approach of biomimicry in the design of functional POCs provides new insights into manipulating the packing of cages, paving the way for potential applications in guest recognition and adsorption separations.

Bioinspired “Intermolecular Pocket” in Soft Molecular Crystal of Porous Organic Cage Exhibiting Reversible Guest Recognition

Porous Organic Cages (POCs) have gathered a lot of attention in sorts of fields. Previous studies often focused on the functionalization of their intrinsic porosity, while the utilization of the extrinsic porosity has been seldom reported. To date, the rational construction of functionalized extrinsic porosity in POCs is a serious challenge, which still relies on trial and error. Inspired by hydrophobic proteins, in the contribution, a POC (namely NKPOC‐DS) is obtained with hydrophobic “intermolecular pocket” as extrinsic porosity constructed through the assembly of disulfide bonds with hydrophobic groups, facilitating strong supramolecular interactions as confirmed by Electrostatic Potential (ESP) maps and single‐crystal X‐ray diffraction analysis. Notably, NKPOC‐DS exhibits a unique C2H6‐selective "breathing behaviour" due to the presence of softness in its extrinsic porosity, which does not extend to other gases such as C2H4, CH4, CO2, N2, and H2. Such specific recognition of C2H6 thus provides NKPOC‐DS with the ability to preferentially adsorb C2H6 from a C2H6/C2H4 mixture. The innovative approach of biomimicry in the design of functional POCs provides new insights into manipulating the packing of cages, paving the way for potential applications in guest recognition and adsorption separations.

Vertically Expanded Crystalline Porous Covalent Organic Frameworks.

Covalent organic frameworks (COFs) can be developed for molecular confinement and separation. However, their proximate π stacks limit the interlayer distance to be only 3-6 Å, which is too small for guests to enter. As a result, COFs block access to the x-y space and limit guest entry/exit strictly to only the pores along the z direction. Therefore, the extended faces of each layer are hidden between layers, precluding any interactions with guest molecules. Here, we report a strategy for opening interlayer spaces of COFs to attain newly accessible nanospaces between layers. This becomes possible using coordination bonds to replace the conventional π-π stacks between layers. We demonstrate this concept by synthesizing two-dimensional covalent cobalt(II) porphyrin layers through topology-guided polymerization, which were piled up by bidentate axial pillars through coordination bonds with cobalt(II) porphyrin along the z direction, assembling vertically expanded COFs via a one-pot reaction. The resultant frameworks separate the layers with axial pillars and create discrete apertures between layers defined by the molecular length of the pillars. Consequently, the originally inaccessible interlayers are open for guest access, while the polygonal π planes are exposed to trigger various supramolecular interactions. Vapor sorption, breakthrough experiments, and computational studies mutually revealed that the vertically expanded frameworks with optimal interlayer slits induce additional interactions to discriminate benzene and cyclohexane and separate their mixtures efficiently under ambient conditions.

Bimodal Visual Sensors Based on Mechanoluminescence and Biosensing for Artificial Intelligence‐Assisted Orthodontics

AbstractFlexible visual sensors hold great potential for application in wearable electronics and health monitoring. However, the separate acquisition of various visual signals without mutual interference and their functional integration in internal biomedical devices remains a significant challenge. Here, a functional material that integrates mechanoluminescent units with biosensing units through supramolecular interactions, enabling bimodal non‐interfering visual detection of orthodontic force and bacterial infection is presented. The orthodontic force induces fluorescence by facilitating the release of electrons from trapped energy levels, caused by the disruption or rearrangement of defect structures within strontium aluminate crystals. Meanwhile, the seamlessly integrated biosensing component can effectively detect lactic acid in a dose‐dependent manner, underscoring its multifunctional capabilities in biosensing applications. Moreover, the development of a cloud‐based deep learning server can achieve a 97.7% accuracy in the precise decoupling of visual signals, facilitating remote monitoring and enabling early intervention during orthodontic treatment. The proposed artificial intelligence‐enhanced bimodal visual sensors represent a new paradigm for orthodontic monitoring, suitable for a wide range of biomedical applications.

A Strong and Tough Ion‐gel Enabled by Hierarchical Meshing and Ion Hybridizations Collaboration

AbstractIon‐gels, with inherent flexibility, tunable conductivity, and multi‐stimulus response, have attracted significant attention in flexible/wearable electronics. However, the design of ion‐gels that exhibit both strength and toughness is challenging. In this study, a novel ion‐gel design is proposed that mimics the hierarchical meshing structure of leaves in combination with ion hybridization. Polyacrylamide (PAM) is incorporated in TEMPO oxidized cellulose nanofibers (TOCNFs) clusters by in situ polymerization, generating a hydrogel with micro/nanoscale entangled networks. Replacement of water by a metal halide ionic liquid ([BMIm]ZnxCly) in the hydrogel resulted in the formation of an ion hybrid network with supramolecular interactions. The integration of the PAM/TOCNF polymer network with [BMIm]ZnxCly resulted in ion‐gels with high strength (5.9 MPa), toughness (22 MJ m−3), and enhanced elastic modulus (30 MPa) combined with non‐flammability, heat and cold resistance. While having fast responsiveness (36 ms) of sensing signal and stability of power supply even at 4000 cycle collisions. Stable signal output even at high (200 °C) /sub‐zero temperatures. The proposed strategy offers a new approach to the material design of flexible/wearable electronics.

Host‐Guest Assemblies of Polyoxovanadate Clusters as Supramolecular Catalysts

Supramolecular functional materials can be used to overcome some of the most challenging tasks in materials science, where the dynamic nature of supramolecular interactions can be leveraged to fine‐tune the properties of the material. The Lindqvist hexavanadate family of polyoxometalates are interesting candidates for supramolecular materials due to their redox and Lewis acid properties that enable their application in energy conversion or catalysis. Despite their promising potential, hexavanadate clusters are underrepresented in supramolecular materials, mainly due to the synthetic challenges related to their inherent reactivity. In this work, pillar[5]arene was successfully grafted onto a Lindqvist hexavanadate and the resulting structure was confirmed by single crystal X‐ray diffraction, presenting the first example of a crystal structure of a polyoxometalate covalently functionalized with a pillar[5]arene. By introducing a ditopic guest molecule that could interlink pillar[5]arene moieties, host‐guest interactions were leveraged as the driving force for the formation of supramolecular assemblies incorporating hexavanadate clusters in a controlled manner. The enhanced catalytic performance of the resulting aggregates confirmed their potential application as functional catalytic materials. This novel approach for developing hexavanadate‐based catalysts reported here showcases the potential of using host‐guest interactions as a means to introduce catalytically active metal‐oxo clusters into supramolecular frameworks.

Host-Guest Assemblies of Polyoxovanadate Clusters as Supramolecular Catalysts.

Supramolecular functional materials can be used to overcome some of the most challenging tasks in materials science, where the dynamic nature of supramolecular interactions can be leveraged to fine-tune the properties of the material. The Lindqvist hexavanadate family of polyoxometalates are interesting candidates for supramolecular materials due to their redox and Lewis acid properties that enable their application inenergy conversion or catalysis. Despite their promising potential, hexavanadate clusters are underrepresented in supramolecular materials, mainly due to the synthetic challenges related to their inherent reactivity. In this work, pillar[5]arene was successfully grafted onto a Lindqvist hexavanadate and the resulting structure was confirmed by single crystal X-ray diffraction, presenting the first example of a crystal structure of a polyoxometalate covalently functionalized with a pillar[5]arene. By introducing a ditopic guest molecule that could interlink pillar[5]arene moieties, host-guest interactions were leveraged as the driving force for the formation of supramolecular assemblies incorporating hexavanadate clusters in a controlled manner. The enhanced catalytic performance of the resulting aggregates confirmed their potential application as functional catalytic materials. This novel approach for developing hexavanadate-based catalysts reported here showcases the potential of using host-guest interactions as a means to introduce catalytically active metal-oxo clusters into supramolecular frameworks.

Liquid Phase Exfoliation of Protein Parent Crystals into Nanosheets and Fibrils Based on Orthogonal Supramolecular Interactions.

Proteins are attractive building blocks for fabricating diverse and precise nanomaterials. However, the facile fabrication of multidimensional artificial assemblies is highly challenging. Here, inspired by the large-scale production technique of inorganic nanomaterials, we demonstrate the application of liquid phase exfoliation (LPE) on native protein ConA by the design of synthetic ligands. These ligands provide distinct in-plane and out-of-plane supramolecular interactions, allowing the generation of multidimensional architectures based on the same protein by dissociating a single interaction in solution, including 3D porous protein crystals, 2D sizable nanosheets, and 1D fibrils. Importantly, the exfoliated 2D sheets were dozens of times larger than the self-assembled nanosheets, resulting in a dramatic enhancement of the intrinsic bioactivity of the building blocks by receptor clustering and less endocytosis. These findings enable the successful application of LPE on biomacromolecules and open up an alternative avenue to generate advanced multidimensional nanomaterials, without the need for complex protein design and careful adjustment of self-assembly conditions.

Dual-Redox Responsive Interfaces Based on Donor-Acceptor Interactions.

Nanoparticle surfactant (NPS) is a highly competitive means for stabilizing liquid-liquid interfaces, endowing interfacial assemblies with functionalities, and enabling the construction of all-liquid devices. Integrating different types of supramolecular interactions into NPSs would open possibilities to generate interfaces that are responsive to multiple stimuli. Here, by using donor-acceptor interactions between polydopamine nanoparticles (PDA NPs) and methyl viologen (MV2+) terminated polystyrene, the formation, assembly, and jamming of a supramolecular NPS at the water-toluene interface is demonstrated. Harnessing the redox properties of both catechol and MV2+, the dual-redox responsiveness can be achieved, allowing the reconfiguration of NPS-based structured liquids. Using NPS as an emulsifier, oil-in-water (O/W), water-in-oil (W/O), and oil-in-water-in-oil (O/W/O) Pickering emulsions can be obtained in one step, which exhibit smart responsiveness to redox reagents. Taking advantage of the adsorption capacity of PDA NPs, the purification of dye-polluted water can be achieved through O/W Pickering emulsions. We envision that this unique dual-redox responsive biphasic system would hold great potential for developing sophisticated controlled-release systems as well as other intelligent, functional materials.

Solvent and additive-controlled supramolecular isomerism in zinc coordination polymers.

A new series of Zn(II) supramolecular isomers containing ditopic 1,3-di(pyridin-4-yl)urea (4bpu) ligand were synthesized and characterized by infrared analysis, elemental analysis and TGA as well as single-crystal X-ray diffraction analysis. Four solvent-induced pseudopolymorphic zinc (II) coordination polymers (CPs), namely, {[Zn(4bpu)(OAc)2](CH3OH)}n (1), {[Zn(4bpu)(OAc)2](C2H5OH)}n (2), {[Zn(4bpu)(OAc)2](HOCH2CH2OH)}n (3), and {[Zn(4bpu)(OAc)2](0.5H2O)}n (4), were prepared by the reaction of Zn(OAc)2.2H2O and 4bpu via self-assembly under varying solvent systems. Also, a pair of polymorphic coordination polymers namely, {[Zn(4bpu)(OAc)2](CH3OH)}n (1α) and {[Zn3(4bpu)3(OAc)6](CH3OH)2}n(1β), was prepared in the presence of different organic additives. Single-crystal X-ray diffraction confirmed that 1-4 and 1α display 1D polymeric zig-zag chains and 1β exhibits 1D triple-stranded ladders that were self-assembled through various supramolecular interactions. In addition, a series of dissolution-recrystallization structural transformations (DRST) were performed on these supramolecular isomers.

ChemFET Anion Sensor Based on MOF Nanoparticles.

Nanoparticles of metal-organic frameworks (nanoMOFs) possess the unusual combination of both internal and external surfaces. While internal surfaces have been the focus of fundamental and applications-based MOF studies, the chemistry of the external surfaces remains scarcely understood. Herein we report that specific ion interactions with nanoparticles of Cu(1,2,3-triazolate)2 (Cu(TA)2) resemble the Hofmeister behavior of proteins and the supramolecular chemistry of synthetic macromolecules. Inspired by these anion-selective interactions, we tested the performance of Cu(TA)2 nanoparticles as chemical field effect transistor (ChemFET) anion sensors. Rather than size-based selectivity, the detection limits of the devices exhibit a Hofmeister trend, with the greatest sensitivity towards anions perchlorate, iodide, and nitrate. These results highlight the importance of the pore-based supramolecular interactions, rather than localized donor-acceptor pairs, in designing MOF-based technologies.

Sequence-Controlled Copolymerization of Structurally Well-Defined Multinuclear Zinc Acrylate Complexes and Styrene.

The copolymerization of two or more monomers produces polymeric materials with unique properties that cannot be achieved with homopolymers. However, precise control over the polymer sequence remains challenging because the sequence is determined by the inherent reactivity of comonomers. Therefore, only limited methods using modified monomers or supramolecular interactions are reported. In this study, the sequence control of acrylate-styrene copolymerization using multinuclear zinc complexes is reported. The copolymerization of the zinc acrylate complex with a polymeric sheet-like structure and styrene in benzene affords a copolymer with a higher content of acrylate triad than calculated for the statistical random model, whereas tetranuclear zinc acrylate (TZA) affords a copolymer with fewer adjacent acrylate sequences. The copolymer with a higher content of acrylate triad exhibits a lower glass transition temperature because of the higher mobility of the longer polystyrene segments. These results highlight the promise of multinuclear zinc acrylate complexes as monomers for sequence-controlled copolymerization.

Gold Nanoparticles Stabilized by δ‐Cyclodextrin in Aqueous Media: Characterization and Evaluation of their Catalytic Properties in the Reduction of 4‐Nitrophenol

AbstractThe synthesis of gold nanoparticles stabilized by cyclomaltononaose (δ‐CD) in aqueous phase was performed. Protection of the gold nanoparticles by standard native cyclodextrins such as α‐CD, β‐CD and γ‐CD has also been considered for comparison. All of these colloidal suspensions were fully characterized by FT‐IR, DLS, UV‐Vis spectroscopy, TEM, XPS and also NMR experiments. Finally, their catalytic activity was evaluated in the reduction of 4‐nitrophenol to 4‐aminophenol in the presence of an excess of sodium borohydride. Gold nanoparticles stabilized by δ‐CD presented good activity and exhibited better long‐term stability. This study highlighted the fact that the obtention of the best catalytic activity corresponds to not only a compromise between the size of the nanoparticles and the interaction of the substrate with the metal nanoparticles surface, but also the supramolecular interactions between the substrate and the cyclodextrin.

Comprehensive analysis of dye adsorption and supramolecular interaction between dyes and cotton fibers in non-aqueous media/less water dyeing system

Cotton textile dyeing consumes large amounts of energy and water and discharges large amount of wastewater and pollutants. Zero or less discharge of the wastewater and contaminants from the cotton textile dyeing has been under high demands from textile industry. Recently, a novel reactive dyeing technology of using a non-aqueous medium with little water (NMLW) was developed for cotton fabrics. However, the use of high concentration of reactive dyes in the system triggers aggregation of the dyes in cotton fibers, influencing the quality of dyed cotton textiles. In this investigation, adsorption, diffusion, and aggregation behavior of reactive dyes in cotton fibers were studied. Compared to traditional water-based dyeing system, cotton fabrics demonstrated superior color depth, as long with higher rates of dye uptake and fixation for reactive dyes. At low dye concentrations, the maximum absorption wavelengths of reactive dyes were unchanged, and complied with the Lambot-Beer law. However, when the dye concentration was excessively high, reactive dyes with different molecular structures, as well as multi-layer dye aggregates with π-π stacking and hydrogen bonding interactions, showed different light absorption spectral characteristics and photophysical properties. Moreover, the dye particle size and dye ionization were influenced by the dye concentration, molecular weight, molecular configuration, etc. Analysis of the molecular dynamics of reactive dyes revealed that the maximum dye aggregation size was predominantly dimer at low dye concentration. However, the dimer ratio significantly decreased, while the trimer ratio increased, and higher-order aggregates were observed at a higher dye concentration. The strength of hydrogen bonds between dye molecules and water molecules, as well as the number of water molecules surrounding dye molecules, was influenced by dye concentration and alkali. This study provides a foundation for understanding the micro-aggregation behavior of reactive dyes and offer guidance for optimizing the dyeing process in practical production settings.

Environment-tolerant, inherently conductive and self-adhesive gelatin-based supramolecular eutectogel for flexible sensor

Although hydrogels have attracted increasing attention in the stretchable devices, the low adhesion properties and poor environmental adaptation still seriously restrict their development and application. Herein, we focused on the interaction between polymer networks with disperse media and their resultant influence on gel performance, and constructed self-adhesive and environment-tolerant gelatin/polyacrylamide supramolecular-polymer double-network (Gelatin/PAM SP-DN) eutectogels using multiple supramolecular interactions between natural macromolecule and well-designed deep eutectic solvent (DES). The dual networks of Gelatin/PAM SP-DN eutectogels produced significant supramolecular forces with DES, including hydrogen bonding and electrostatic interaction, contributing to enhance the energy dissipation capacity. Additionally, the Gelatin-PAM SP-DN eutectogels were more prone to generate strong bonding force to various substrates, showcasing both in-situ and ex-situ adhesion performance, and even being used for wet and underwater adhesion. The eutectogels revealed excellent environmental tolerance to maintain excellent mechanical flexibility, conductivity and adhesion at high and low temperatures, ensuring the constructed sensor to sensitively and reliably perceive strain, pressure and human motions over a wide temperature range. Also, the eutectogel demonstrated great potential as a temperature sensor. This work opens up a new horizon in the design of multifunctional and environment-tolerant natural macromolecule-based gel materials for flexible electronics, human-machine interaction and health diagnosis.

Immobilization of laccase on Fe3O4@SiO2 core@shell magnetic nanoparticles for methylene blue biodegradation

Here we report the preparation and characterization of novel enzyme supports based on silica-coated Fe3O4 magnetic nanoparticles. These nanomaterials were modified at their outer silica surface with isocyanate, trimethylammonium and β-cyclodextrin moieties to immobilize laccase from Trametes versicolor through covalent, electrostatic and supramolecular interactions, respectively, with protein immobilization yields ranging from 21.7% to 53.5%. The effect of the immobilization approach on the activity, optimal working conditions, stability and reusability of the resulting biocatalysts were studied. Best results were achieved for native and adamantane-modified laccase supramolecularly immobilized on β-cyclodextrin bearing supports in terms of their catalytic properties, showing 18.0 U and 14.0 U of immobilized laccase activity per gram of support. However, high thermal stability was observed for the enzyme covalently immobilized on isocyanate-modified nanoparticles, with 14.8-fold increase in the half-life time at 65ºC in comparison with native laccase. Best reusability properties were also achieved by covalent immobilization, retaining over 88% of the initial catalytic activity after 13 cycles of magnetic reuses. All enzyme derivatives were evaluated for the catalytic degradation of methylene blue as pollutant model, showing significant reduction of the dye. In special, a 68-fold increase in the removal efficacy was observed for covalently immobilized enzyme compared to the free laccase. These results suggest high potential application of these biocatalysts in wastewater treatment.

Dynamic covalent epoxy network of hyperbranched-synergistic-supramolecular: Catalyst-free reprocessing, and application in carbon fiber composites recycling

Plastic recycling, especially the recycling of thermosets, is a crucial step towards improving waste management and achieving economic recycling. Here, a method utilizing non-covalent supramolecular interactions and synergistic hyperbranched structures is reported to endow transesterification-based thermosetting materials with recyclability in the absence of a catalyst. A hyperbranched epoxy resin curing agent (HPCA) containing amide bonds, terminated by amine and ester, was designed and synthesized, and further cured with bisphenol A epoxy resin. The hyperbranched topological structure and its abundant amide bonds contribute to the formation of a dense hydrogen bonding network, enhancing the reprocessability, thermal, and mechanical properties of the material. As a result, the resin can be reprocessed by hot pressing at 190 °C and 10 MPa for 40 min without catalyst. Moreover, amide and ester bonds endow resin materials with excellent degradation performance in alkaline solutions, laying the foundation for the recycling and utilization of carbon fibers in composite materials.

Impact of Cations and Implicit Solvent on the Sensitivity of the Enol Tautomers of 3-Nitro-1,2,4-Triazole-5-One: A DFT Study

The explosive sensitivity of the supramolecular interaction between cations (Mn+ = Li+, Na+, K+, Be2+, Ca2+ and Mg2+) with enol tautomers (c0 and c1) of 3-nitro-1,2,4-triazole-5-one (NTO) complexes has been investigated using Density Functional Theory (DFT). The effect of water as the solvent was included via the CPCM approach. At the gas phase, the presence of the metal cations, especially Be2+, significantly increased the bond dissociation energy (BDE) of C-NO2 of the enol tautomers. However, in the presence of the solvent, the BDE was lower than in the gas phase, even in the supramolecular complex of Be2+ - c0 and Be2+ - c1.

Construction of Highly Porous and Robust Hydrogen-Bonded Organic Framework for High-Capacity Clean Energy Gas Storage.

Development of highly porous and robust hydrogen-bonded organic frameworks (HOFs) for high-pressure methane and hydrogen storage remains a grand challenge due to the fragile nature of hydrogen bonds. Herein, we report a strategy of constructing the double-walled framework to target highly porous and robust HOF (ZJU-HOF-5a) for extraordinary CH4 and H2 storage. ZJU-HOF-5a features a minimized twofold interpenetration with double-walled structure, in which multiple supramolecular interactions are existed between the interpenetrated walls. This structural configuration can notably enhance the framework robustness while maintaining its high porosity, affording one of the highest gravimetric and volumetric surface areas of 3102 m2 g-1 and 1976 m2 cm-3 among the reported HOFs so far. ZJU-HOF-5a thus exhibits an extremely high volumetric H2 uptake of 43.6 g L-1 at 77 K/100 bar and working capacity of 41.3 g L-1 under combined swing conditions (77 K/100 bar→160 K/5 bar), and also impressive methane storage performance with a 5-100 bar working capacity of 187 (or 159) cm3 (STP) cm-3 at 270 K (or 296 K), outperforming most of the reported porous organic materials. Single-crystal X-ray diffraction studies on CH4-loaded ZJU-HOF-5a reveal that abundant supramolecular binding sites combined with ultrahigh porosities account for its high CH4 storage capacities. Combined with high stability, super-hydrophobicity, and easy recovery, ZJU-HOF-5a is placed among the most promising materials for H2 and CH4 storage applications.

Detection of Layer Charge Density in Layered Double Hydroxides and Studies on Host‐Guest Interactions

AbstractThe layer charge density of layered double hydroxides (LDHs) significantly affects interlayer spacing, the arrangement of interlayer anions and water molecules, thermal stability, as well as adsorption performance. However, traditional methods for evaluating the layer charge density of LDHs are complex, prone to large errors, and impacted by numerous factors, rendering these methods unable to facilitate direct comparisons of layer charge density across different LDH compositions. Consequently, this study proposes a novel approach based on the host‐guest supramolecular interactions in LDHs to investigate the layer charge density by analyzing changes in the position of the infrared absorption peaks of interlayer guest species. The shifts in infrared absorption peak positions are employed to assess the layer charge density of MgAl‐LDHs with varying molar ratios (M2+/M3+=2, 2.5, 3, 3.5, 4). The validity of using infrared peak position shifts is corroborated through a combination of techniques, including Raman spectroscopy, TG‐DTG, XRD, Zeta potential, and adsorption analyses. Furthermore, the layer charge density of NiAl, CoAl, MgFe, and NiFe‐LDHs are evaluated, confirming the universality of the infrared method. By ranking layer charge density of LDHs with different compositions and ratios, this study resolves the challenge of comparing LDHs with diverse layer compositions.