Host-guest Interactions Research Articles

Surprisingly fast self-healing coatings with anti-fog and antimicrobial activities via host-guest interaction

Dual functional coatings with anti-fog and antimicrobial performances greatly enhance the safety and reliability of medical detection devices, but are prone to mechanical damage, resulting in reduced performance and a shorter service lifespan. Herein, a semi-interpenetrating polymer network (SIPN) coating, featuring hydrophobic-hydrophilic balanced copolymers as bulk chains and host–guest inclusion compounds (HGICs) as cross-linkers, is reported, which demonstrates particularly effective anti-fog and antibacterial performances, along with a surprisingly fast self-healing capability under various scenarios. This HGIC-based coating displayed remarkable anti-fog capability over a wide temperature range from −20 ℃ to 85 ℃ and exhibited reliable antibacterial activities (≥98 %) against both gram-positive and gram-negative bacteria. Also, this coating showed extremely high self-healing ability (≥92 % recovery rate) within just 20 s, significantly outperforming traditional self-healing systems. These findings support the development of functional coatings that can highly maintain rapid self-healing performance while also providing anti-fog and antibacterial properties in medical detection devices.

Flexible Mesopores in Nanoscrolls: Extraordinarily Large Alteration of Pore Sizes and Their Reversibility.

Flexible porous materials have gained considerable interest for their potential applications in selective absorption and controlled release/storage of specific molecules or compounds. Here, nanoscrolls are proposed as a type of inorganic solids with reversibly flexible mesopores. Nanoscrolls exhibit a rolled-up structure composed of nanosheets with a 1D rod-like morphology, possessing two distinct nanospaces. The first space comprises 1D tubular mesopores located at the center of the rod, while the second space exists in the interlayer regions on the wall of the mesopore, resulting from the layer stacking caused by the scrolling of nanosheets. By replacing the interlayer cations on the nanoscroll walls with other cations, a drastic alteration in the size of the 1D mesopores is observed. For instance, exchanging bulky dodecylammonium cations with small NH4 + cations leads to a substantial change in pore size, with differences ranging from 10 to 20nm-a notably larger variation compared to previous reports on flexible porous materials. Importantly, the alteration of pore size induced by the exchange reaction is found to be reversible. This reversible alteration in pore size holds promise for applications in host-guest chemistry involving large moieties such as nanoparticles and enzymes.

Cyclic Oxothiomolybdates: Building Blocks for Cyclodextrin-Based Open Frameworks.

Desolvation processes, though common in self-assembled biological structures, are rarely evidenced and utilized in the design of crystalline architectures. In this study, we introduce a novel approach using the [Mo8S8O8(OH)8(guest)]2- complex, formed by the self-condensation of four [MoV 2O2S2]2- fragments around a guest unit (MoVIO6H4 or oxalate), as a chaotropic scaffold for crystallizing hybrid organic-inorganic systems with natural cyclodextrins. Our findings reveal that β-cyclodextrin (β-CD) facilitates the formation of host-guest complexes, while α-cyclodextrin (α-CD) induces the formation of a Kagome-type structure with significant voids. These new compounds were thoroughly characterized using X-ray diffraction (both powder and single-crystal), N2 adsorption, elemental and thermogravimetric analysis. Additionally, solution studies using 1H NMR titration and small-angle X-ray scattering (SAXS) demonstrated pre-association of the building units in solution. These results enhance our understanding of the design principles for supramolecular structures composed of inorganic polyanions and cyclodextrins.

Amino-Functionalized Metal-Organic Frameworks Featuring Ultra-Strong Ethane Nano-Traps for Efficient C2H6/C2H4 Separation.

Developing high-performance porous materials to separate ethane from ethylene is an important but challenging task in the chemical industry, given their similar sizes and physicochemical properties. Herein, a new type of ultra-strong C2H6 nano-trap, CuIn(3-ain)4 is presented, which utilizes multiple guest-host interactions to efficiently capture C2H6 molecules and separate mixtures of C2H6 and C2H4. The ultra-strong C2H6 nano-trap exhibits the high C2H6 (2.38mmolg-1) uptake at 6.25kPa and 298K and demonstrates a remarkable selectivity of 3.42 for C2H6/C2H4 (10:90). Additionally, equimolar C2H6/C2H4 exhibited a superior high separation potential ∆Q (2286mmolL-1) at 298K. Kinetic adsorption tests demonstrated that CuIn(3-ain)4 has a high adsorption rate for C2H6, establishing it as a new benchmark material for the capture of C2H6 and the separation of C2H6/C2H4. Notably, this exceptional performance is maintained even at a higher temperature of 333K, a phenomenon not observed before. Theoretical simulations and single-crystal X-ray diffraction provide critical insights into how selective adsorption properties can be tuned by manipulating pore dimensions and geometry. The excellent separation performance of CuIn(3-ain)4 has been confirmed through breakthrough experiments for C2H6/C2H4 gas mixtures.

Probing Noncovalent Interaction Strengths of Host-Guest Complexes Using Negative Ion Photoelectron Spectroscopy.

Noncovalent interactions (NCIs) are crucial for the formation and stability of host-guest complexes, which have wide-ranging implications across various fields, including biology, chemistry, materials science, pharmaceuticals, and environmental science. However, since NCIs are relatively weak and sensitive to bulk perturbation, direct and accurate measurement of their absolute strength has always been a significant challenge. This concept article aims to demonstrate the gas-phase electrospray ionization (ESI)-negative ion photoelectron spectroscopy (NIPES) as a direct and precise technique to measure the absolute interaction strength, probe nature of NCIs, and reveal the electronic structural information for host-guest complexes. Our recent studies in investigating various host-guest complexes that involve various types of NCIs such as anion-π, (di)hydrogen bonding, charge-separated ionic interactions, are overviewed. Finally, a summary and outlook are provided for this field.

Evaluation of All-Atom and Martini 3 Coarse-Grained Force Fields from the Structural Investigation of Nitroxide Spin Probes and Their Confinement in Beta-Cyclodextrin.

Nitroxide radicals have found wide applications as spin labels or probes, and their guest-host interactions with cyclodextrins exhibit enhanced applications in electron spin resonance (ESR) spectroscopy and imaging due to improved biostability toward reducing agents. Although the computational prediction of the guest-host binding has become increasingly common for small ligands, molecular simulations regarding the conformational preferences of hosted spin probes have not been conducted. Here we present molecular dynamics simulations at an atomistic level for a set of four TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) spin probes and thereafter develop coarse-grained models compatible with the recent version of the Martini force field (v 3.0) to tackle their encapsulation in the cavity of β-cyclodextrin (βCD) for which experimental ESR data are available. The results indicate that the atomistic descriptions perform well in relation to the structural parameters derived from X-ray diffraction as well as hydrogen bonding and hydrogen patterns and predict that the guest-host complexation is hydrophobically driven by the presence of a methyl group pair of the spin probe at the cavity center of βCD. The spin probe mobility at the binding site reveals the nitroxide group orientation toward the secondary rim of the cyclodextrin and the alternating presence of the two methyl group pairs inside the cavity, features in agreement with the experimental behavior of the ESR parameters. The coarse-grained parameterizations of TEMPO probes and βCD rely on optimizing the bonded and nonbonded parameters with references to the atomistic simulation results, and they are capable of recovering the orientation and location of the spin probe inside the cyclodextrin cavity predicted by the atomistic guest-host complexes. The results suggest the cyclodextrin host-guest system as a powerful validation suite to evaluate new coarse-grained parameterizations of small ligands and future extensions to functionalized cyclodextrins in inclusion complexes.

Exploring the host compound dynamics of 1,4-phenylene-bis(di-p-fluorophenylmethanol) in mixed pyridines

AbstractIn this investigation, the wheel-and-axle host compound, 1,4-phenylene-bis(di-p-fluorophenylmethanol) (H), was demonstrated to have inclusion ability for each of PYR, 2MP, 3MP and 4MP (1:1, 1:2, 1:2 and 1:2 were the H: G ratios). In the equimolar guest competition experiments, H was observed to have an overwhelming affinity for PYR and 4MP relative to 2MP and 3MP. In fact, selectivity coefficients calculated from the non-equimolar binary guest competition experiments suggested that this host compound would be an efficient candidate for the separation of all PYR/2MP mixtures and a 40:60 4MP/3MP solution through host-guest chemistry strategies. SCXRD analyses established the preferred guests (PYR and 4MP) to be involved in significantly shorter stabilizing classical hydrogen bonding interactions with H, explaining the selectivity behaviour of this host compound in the guest mixtures. Additionally, Hirshfeld surface considerations also explained this behaviour, but only for PYR. Furthermore, thermal analyses were used to ascertain the relative thermal stabilities of the four complexes and, satisfyingly, the PYR- and 4MP-containing complexes possessed the greater thermal stabilities compared with H·2(2MP) and H·2(3MP), as was demonstrated by a comparison of their guest release onset temperatures.

Generation of Triplet States by Host‐Stabilized Through‐Space Conjugation for the Construction of Efficient Supramolecular Photocatalysts

AbstractPromoting the generation of triplet states is essential for developing efficient photocatalytic systems. This research presents a novel approach of host‐stabilized through‐space conjugation via the combination of covalent and non‐covalent methods. The designed building block, 4,4′‐(1,4(1,4)‐dibenzene cyclohexaphane‐1,4‐diyl)bis(1‐phenylpyridinium) chloride, features inherently stable through‐space conjugation. When this block forms a 1 : 1 host–guest complex with cucurbit[8]uril, the through‐space conjugation is further stabilized within the confined cavity. Both the generation and lifetime of triplet state are significantly increased, resulting from the host‐stabilized through‐space conjugation. Additionally, the ultrahigh binding constant of 6.58×1014 M−1 ensures the persistence of host‐stabilization effect. As a result, the host–guest complex acts as a highly efficient catalyst in the photocatalytic oxidation of thioether and aromatic alcohol. In the photodegradation of lignin, a complex natural product, the host–guest complex also exhibits high efficiency, demonstrating its robustness. This line of research is anticipated to enrich the toolbox of supramolecular photochemistry and provide a strategy for fabricating efficient supramolecular photocatalysts.

Reimagining Anti-Inflammatory Drugs Delivery: The Integration of Ordered Mesoporous Silica and MOF Materials for Enhanced Therapeutic Outcomes

Abstract Migraine, one of the neurological conditions, affects approximately 15% of the global population. It is characterized by intense headaches accompanied by nausea, vomiting, and heightened sensitivity to light. The first line of drugs for treating migraine are non-steroidal anti-inflammatory drugs. Unfortunately, these medications suffer from poor solubility in water, uncontrolled release, and numerous adverse side effects. In order to maximize their therapeutic effect by preventing premature release and degradation, novel drug delivery systems based on composites are being dynamically developed. Herein, the biocompatible ketoprofen, naproxen sodium, and diclofenac sodium vehicles integrating ordered mesoporous silica (SBA-16) with Fe-based metal–organic frameworks (MIL-101(Fe)) were synthesized via the solvothermal method. The composites were characterized by different percentages of MIL-101(Fe) 
(25 and 50 wt.%), which had a significant impact on their porosity, structure, and number of functional groups. The SBA-16@MIL-101(Fe)-25 and SBA-16@MIL-101(Fe)-50 samples exhibited BET surface areas of 768 and 324 m2/g, respectively. Their sorption capacities towards selected anti-inflammatory drugs were in the range of 141-318 mg/g for ketoprofen, 481-490 mg/g for naproxen sodium, and 246-589 mg/g for diclofenac sodium, notably exceeding the values obtained for pure mesoporous silica (5-9 mg/g). Morphological defects and specific functional groups, derived from SBA-16 and MIL-101(Fe), contributed to generating new adsorption sites in composites, enhancing host-guest interactions. The drug release profiles were determined by the carrier porosity, surface charge, and the presence of functional groups. The diffusion of ketoprofen and diclofenac sodium from the composites into the phosphate buffer (pH 7.7), mimicking rectal fluid, occurred in a more controlled manner compared to pristine silica. The SBA-16@MIL-101(Fe)-50 carrier released 82% of ketoprofen and 90% of diclofenac sodium over 24 hours.

A novel electrochemical sensor based on ꞵ-cyclodextrin/bismuth oxybromide/multi-walled carbon nanotubes modified electrode with in situ addition of tetrabutylammonium bromide for the simultaneous detection and degradation of tebuconazole.

A novel electrochemical sensor-based glassy carbon electrode (GCE) was fabricated and appliedtosimultaneous detection and degradation of tebuconazole (TBZ) for the first time.TheGCE was consecutively modified by multi-walled carbon nanotubes (MWCNTs), bismuth oxybromide (BiOBr), ꞵ-cyclodextrin (ꞵ-CD), and in situ addition of tetrabutylammonium bromide (TBABr). The detection was based on the decreasing of Bi signal at its anodic potential (Epa) of 0.05V. Under the optimum conditions, the modified electrode exhibited a linear response to TBZ in the concentration range 1-100μg L-1 with a detection limit of 0.9μg L-1. TBZ was firstly adsorbed on the surface of the modified electrode through host-guest molecule interactions of the ꞵ-CD. The adsorption was further enhanced by the large surface area of BiOBr and MWCNTs. The adsorbed TBZ on the electrode surface hindered the electron transfer of Bi, thus decreasing the oxidation of Bi. In addition, the in situ addition of tetrabutylammonium bromide (TBABr) enriched TBZ via electrostatic interactions, increasing its detection sensitivity. The fabricated electrochemical sensor was applied to determine TBZ in water and soil samples from rice fields with recoveries of 80.5-100.5% and 87.6-112%, respectively. Furthermore, the degradation of TBZ on the modified electrode was studied under a solar light simulator. The degradation percentage (100%) of TBZ (50µg L-1) was achieved in5min owing to the excellent photocatalytic properties of BiOBr.

The Swiss Army Knife of Electrodes: Pillar[6]arene‐Modified Electrodes for Molecular Electrocatalysis Over a Wide pH Range

AbstractMolecularly‐modified electrode materials that maintain stability over a broad pH range are rare. Typically, each electrochemical transformation necessitates a specifically tuned system to achieve strong binding and high activity of the catalyst. Here, we report the functionalisation of mesoporous indium tin oxide (mITO) electrodes with the macrocyclic host molecule pillar[6]arene (PA[6]). These electrodes are stable within the pH range of 2.4–10.8 and can be equipped with electrochemically active ruthenium complexes through host–guest interactions to perform various oxidation reactions. Benzyl alcohol oxidation serves as a model reaction in acidic media, while ammonia oxidation is conducted to assess the systems performance under basic conditions. PA[6]‐modified electrodes demonstrate catalytic activity for both reactions when complexed to different guest molecules and can be reused by reabsorption of the catalyst after its degradation. Furthermore, the system can be employed to perform subsequent reactions in electrolyte with varying pH, enabling the same electrode to be utilised in multiple different electrocatalytic reactions.

Hydrogen‐Bonded Organic Frameworks as a Carrier for Nanodrugs with Host–Guest Interaction for Smart Wound Dressing Applications

AbstractThis study introduces surface modification to conventional dressings utilizing adducts of a hydrogen‐bonded organic framework (HOF) with curcumin, curcumin–silver, curcumin‐zinc oxide nanoparticles, and citric acid drugs. Accordingly, eight HOF‐AMs and dressings modified with them were studied. The synthesized structures underwent characterization using various methods, including IR, 1H NMR, XRD, FE‐SEM, and EDX. FE‐SEM results show that the hexagonal morphology is maintained along with the crystal growth in the form of hexagonal tubes. In order to confirm the nanoscale nature of the structures, TEM analysis was conducted specifically for curcumin‐Ag nanoparticles and curcumin–ZnO nanoparticles which confirms the particle size smaller than 50 nm. Knowing the sensitivity of the release of the incorporated substances to temperature and pH, the controlled release of the drugs at two different temperatures (37 °C and 40 °C) and pH levels of 5.5, 7.4, and 9 at the modified dressings was investigated. Investigating the release of HOF‐AMs particles and modified dressings indicates that these products in both cases provide the possibility of drug release in alkaline and acidic pHs. Also, the results showed that increasing the temperature increases the release of curcumin particles in all its types. The modified dressings showed a loading capacity of more than 50 mg g−1.

Color-Tunable Thermally Activated Delayed Fluorescence Polymeric Materials Constructed by Host–Guest Complexation Revealing Rewritable Advanced Information Encryption

Color-Tunable Thermally Activated Delayed Fluorescence Polymeric Materials Constructed by Host–Guest Complexation Revealing Rewritable Advanced Information Encryption

Assembling a new generation of radiopharmaceuticals with supramolecular theranostics.

Supramolecular chemistry has been used to tackle some of the major challenges in modern science, including cancer therapy and diagnosis. Supramolecular platforms provide synthetic flexibility, rapid generation through self-assembly, facile labelling, unique topologies, tunable reversibility of the enabling noncovalent interactions, and opportunities for host-guest chemistry and mechanical bonding. In this Review, we summarize recent advances in the design and radiopharmaceutical application of discrete self-assembled coordination complexes and mechanically interlocked molecules - namely, metallacages and rotaxanes, respectively - as well as in situ-forming supramolecular aggregates, specifically pinpointing their potential as next-generation radiotheranostic agents. The outlook of suchsupramolecular constructs for potential applications in the clinic is discussed.

The Swiss Army Knife of Electrodes: Pillar[6]arene-Modified Electrodes for Molecular Electrocatalysis Over a Wide pH Range.

Molecularly-modified electrode materials that maintain stability over a broad pH range are rare. Typically, each electrochemical transformation necessitates a specifically tuned system to achieve strong binding and high activity of the catalyst. Here, we report the functionalisation of mesoporous indium tin oxide (mITO) electrodes with the macrocyclic host molecule pillar[6]arene (PA[6]). These electrodes are stable within the pH range of 2.4-10.8 and can be equipped with electrochemically active ruthenium complexes through host-guest interactions to perform various oxidation reactions. Benzyl alcohol oxidation serves as a model reaction in acidic media, while ammonia oxidation is conducted to assess the systems performance under basic conditions. PA[6]-modified electrodes demonstrate catalytic activity for both reactions when complexed to different guest molecules and can be reused by reabsorption of the catalyst after its degradation. Furthermore, the system can be employed to perform subsequent reactions in electrolyte with varying pH, enabling the same electrode to be utilised in multiple different electrocatalytic reactions.

Solvent- and Concentration-Induced Topological Transformation of a Ruthenium(II)-Based Trigonal Prism to a Triply Interlocked [2] Catenane.

Synthesis of interlocked supramolecular cages has been a growing field of interest due to their structural diversity. Herein, we report the template-free synthesis of a Ru(II) triply interlocked [2] catenane using coordination-driven self-assembly. The self-assembly of a triazine-based tripyridyl donor L (2,4,6-tris(5-(pyridin-4-yl)thiophen-3-yl)-1,3,5-triazine) with a dinuclear Ru(II) acceptor M (Ru2(dhnq)(η6-p-cymene)2)(CF3SO3)2) yielded two distinct structures depending on the solvent and concentration. In methanol, a triply interlocked metalla [2] catenane (MC2) was formed, whereas in nitromethane, a non-interlocked cage (MC1) was obtained. The non-interlocked cage MC1 was gradually converted to MC2 in nitromethane by the increase in the concentration of cage MC1 from 0.5 to 9 mM. The interlocked cage (MC2) was stable after formation and was unaffected by the change in concentration. Notably, the free cage (MC1) exhibited host-guest interactions with polycyclic aromatic aldehydes, stabilizing the non-interlocked structure even at higher concentrations. In contrast, the triply interlocked [2] catenane (MC2) remains stable due to self-penetration and does not encapsulate guest molecules. This work showcases the stimuli-induced irreversible structural transformation of a triangular prismatic cage to its triply interlocked [2] catenane by employing metal-ligand coordination chemistry.

In Situ Self-Assembly of Antibody-Rhamnose Complex as a Pre-Targeting Strategy for Enhanced Cancer Immunotherapy.

Enhancing the Fc effector functions of monoclonal antibodies (mAbs) is a proven strategy for improving cancer immunotherapy. In this study, we present a novel pre-targeting approach that integrates host-guest chemistry with an antibody-recruiting concept to create mAbs with superior effector functions. Using rituximab (RTX), a clinically approved anti-CD20 mAb, as our model, we modified RTX by conjugating it with adamantane (Ada) derivatives and various polyethylene glycol (PEG) linkers to produce RTX-Ada conjugates. These conjugates effectively formed RTX-rhamnose (Rha) complexes in situ through self-assembly, driven by host-guest interactions with Rha-modified β-cyclodextrin. This mechanism successfully redirected endogenous anti-Rha antibodies to target cells, enhancing the availability of Fc domains for improved effector functions, including complement-dependent cytotoxicity (CDC). A structure-activity relationship study indicated that the potency of these in situ complexes was significantly influenced by the length of the PEG linker used; shorter PEG linkers correlated with higher CDC activity. Given the variability in endogenous antibody levels among individuals, this strategy presents a flexible and promising platform for enhancing the efficacy of mAb-based cancer immunotherapy.

Supramolecular assembly of antibody-rhamnose complex to enhance the complement-dependent cytotoxicity for cancer immunotherapy

Enhancing the complement-dependent cytotoxicity (CDC) of monoclonal antibodies (mAbs) has the potential to improve their clinical performance. In this study, we describe an innovative antibody-hapten supramolecular complex strategy to amplify CDC activity. We selected Rituximab (RTX), an approved anti-CD20 mAb, and conjugated it with adamantane (Ada) to generate RTX-Ada. After targeting CD20-positive cells, this conjugate can interact with rhamnose (Rha)-modified β-cyclodextrin via host-guest interaction, in situ forming a supramolecular complex that can recruit anti-Rha antibodies onto CD20-positive cancer cells. This complex provides a larger number of Fc domains for complement system activation, leading to enhanced CDC. Our study demonstrates the potential of antibody-based supramolecular complexes for cancer immunotherapy, offering a promising approach to improve the efficacy of mAb-based cancer treatments.

Separation performances of extended pillar[6]arenes, a new stationary phase for gas chromatography

Pillar[n]arenes (P[n]As, n = 5–10), a new generation of macrocyclic hosts, display interesting properties such as 3D π-electron cavity, host-guest interactions, good stability, and easy functionalization, which make these polymers very promising for separation applications. In particular, extended P[n]As (EP[n]As) show large-sized cavities, structural flexibility, cavity adaptability, and synthetic accessibility. These characteristics have been exploited in this work, which reports for the first time the investigation of two EP[n]As (LP6A-C10 and BpP6A-C10) as stationary phases for gas chromatography (GC). LP6A-C10 and BpP6A-C10 columns exhibited moderate polarity (average polarity 117 and 118) and high column efficiencies (3000 plates/m and 3235 plates/m). These columns achieved complete challenging separation of halogenated benzene, benzaldehyde, phenol, and aniline isomers, which are difficult to resolve due to their high resemblance in structures and properties. Experimental results demonstrate the high selectivity and inertness of the prepared columns and their distinct advantages if compared with commercial HP-5 and HP-35 columns. EP[n]As columns displayed good separation repeatability with RSD values of 0.01%–0.02 % for run-to-run, 0.01%–0.22 % for day-to-day, and 1.36–3.56 % for column-to-column. This work demonstrates the promising future of EP[n]A stationary phases for chromatographic separations.

Rational screening of metal single-atom-doped ZSM-5 to promote ring-opening cracking of cycloalkanes to light olefins

The ring-opening cracking of cycloalkanes to light olefins poses a formidable challenge due to the sluggish activation of the C–C bond. In this study, we realize the rational screening of various single metal doped M−ZSM−5 catalysts (M = Mn, Co, Ni, Cu, Zn, Zr, Ru, Rh, Pd, Ag, Pt) to promote the ring-opening cracking of cycloalkanes to light olefins. Our calculation results show that methyl cyclopentane, a model compound of cycloalkanes, tends to adsorb in the form of a “half-chair” configuration in the intersecting channels of the M−ZSM−5, which is caused by the drastic distortion of the five-membered ring, accompanied by large changes in the bond angles. Based on the host–guest interaction between the active site and hydrocarbon in ring-opening cleavage, we reveal that the binding energies of metals to H and C can respectively quantify the metal’s ability to activate C–H and C–C bonds in cycloalkanes. By solving the microkinetic model, we plot activity-selectivity TOF volcano diagrams, where Mn, Ru, Rh-ZSM-5 within the EH range of −2.5 to −3.5 eV and the EC range of −6 to −8 eV can efficiently induce the ring-opening reaction of cycloalkanes without excessive dehydrogenation leading to aromatic hydrocarbon formation. The calculation shows good agreement with catalytic experimental tests and in situ DRIFT spectra results, providing a series of potential candidate catalysts for the ring-opening cracking of cycloalkane-rich diesel fuel.