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MOF-hydrogel composites are an emerging class of composite materials with many potential biomedical applications. In this review article, we discuss the state-of-the-art and prospects for future development.

Adipic acid, an industrially-important chemical that can be sustainably derived from biomass and post-consumer nylon, is traditionally overlooked as a linker for MOFs. Herein, we report the first direct one-pot method for synthesising UiO-66 MOFs with an unprecedented 69 mol% adipate content, as well as the feasibility of these materials for MOF defect engineering by rapid and selective adipate thermolysis.

The first working lithium-ion battery containing polymer electrolytes derived from waste poly(ethylene terephthalate) beverage bottles is demonstrated.

Herein, we consider the possibility and future prospects of using waste plastic feedstock as an overlooked resource to develop polymeric adsorbents, metal–organic frameworks and porous carbon materials for CO2 capture and utilization.

A solvent-free approach for the post-synthetic functionalisation of polyethylene with carbonyl groups exclusively is described using oxygen as the oxidant, with industrially-relevant benzoic acid being the sole organic side product of the reaction.

Nonbiodegradable plastics with inert and saturated C–C backbones comprise the majority of global annual plastics produced, including the ubiquitous polyolefins (polyethylene and polypropylene) and ...

Thermogels, a class of hydrogels which show spontaneous sol-gel phase transition when warmed, are an important class of soft biomaterials. To date, however, most amphiphilic polymers that are able to form thermogels in aqueous solution are uncharged, and the influence of ionisable groups on thermogelation are largely unknown. Herein, we report the first example of a polyanionic amphiphilic multi-block copolymer, containing multiple pendant carboxylate groups, that can form transparent thermogels spontaneously when warmed up to physiological temperature. We demonstrate that introducing negative charges onto thermogelling polymers could significantly alter the properties of the micelles and thermogels formed. Furthermore, the polymer's polyanionic character provides new options for modulating the gel rheological properties, such as stiffness and gelation temperatures, through electrostatic interactions with different cations. We also demonstrated that the polyanionic thermogel allowed slower sustained release of a cationic model drug compound compared to an anionic one over 2 weeks. The findings from our study demonstrate exciting new possibilities for advanced biomedical applications using charged polyelectrolyte thermogel materials.

The structural battery is a multifunctional energy storage device that aims to address the weight and volume efficiency issues that conventional batteries face, especially in electric transportation. By combining the functions of mechanical load bearing and energy storage, structural batteries can reduce the reliance on, or even eventually replace the main power source in an electric vehicle or a drone. However, one of the key challenges to be addressed before achieving multifunctionality in structural batteries would be the design of a suitable multifunctional structural battery electrolyte. The structural battery electrolyte is the constituent that provides mechanical integrity under flexural loads or impact and hence determines the electrochemical and much of the mechanical performance of a structural battery device. This concept paper aims to cover the key considerations and challenges facing the design of structural battery electrolytes. In addition, the main approaches to surmount these challenges are highlighted, keeping design aspects like sustainability and recyclability in view. The authors would like to acknowledge the Structural Power for portable and electrified transportation grant (Grant number A20H3b0140, AME programmatic) for the support of this work.

Injectable hydrogels have gained considerable attention, but they are typically mechanically weak and subject to repeated physiological stresses in the body. Herein, we prepared polyurethane diacrylate (EPC-DA) hydrogels, which are injectable and can be photocrosslinked into fatigue-resistant implants. The mechanical properties can be tuned by changing photocrosslinking conditions, and the hybrid-crosslinked EPC-DA hydrogels exhibited high stability and sustained release properties. In contrast to common injectable hydrogels, EPC-DA hydrogels exhibited excellent antifatigue properties with90% recovery during cyclic compression tests and showed shape stability after application of force and immersion in an aqueous buffer for 35 days. The EPC-DA hydrogel formed a shape-stable hydrogel depot in an

Polymeric hydrogels are promising biomaterials to be used as vitreous tamponade in the eye. However, while the clinical need and the required attributes of a vitreous replacement hydrogel are clear, there is a major gap in understanding the various polymer requirements to achieve the "ideal" hydrogel. In this study, we investigated the effect of the polymer molecular weight on polyurethane thermogel properties and found that there is a theoretical minimum number of hydrophobic blocks required for gelation. We then used these polymers as vitreous replacements. We found that there is a preferred molecular weight range, whereby hydrogels with lower molecular weights can cause retinal atrophy and corresponding functional visual loss, while those with higher molecular weights lead to opacity issues. Thermogels in the preferred molecular weight range retained the normal retinal structure and exhibited full visual recovery within 3 months. The effect of the molecular weight was further demonstrated by the effects of postsynthetic autoclaving on the retinal structure and function. The effect of the polymer molecular weight on the functional characteristics of hydrogels demonstrated herein is an important design parameter for polymeric hydrogels for ocular applications.

Molecular sensors respond to target molecules in their surroundings to detect and sometimes even quantify their concentrations. Traditionally comprised of small organic molecules or metal complexes...

DNA-templated silver nanoclusters (AgNCs) are an emerging class of ultrasmall (

Current treatments for oral mucosa-related ulcers use drugs to relieve pain and promote healing, but rarely consider drug resistance to bacterial infection in the microenvironment of the oral cavity or the prevention of bleeding from gingival mucosa ulcers. We herein report an injectable, thermogelling chitosan-based system to address these concerns. An aqueous solution of chitosan-based conjugates (chitosan-g-poly(N-isopropylacrylamide) [CS-g-PNIPAAM] including 1a [CS-g-PNIPAAM with less PNIPAAM] and 1b [CS-g-PNIPAAM with more PNIPAAM], and chitosan-g-poly(N-isopropylacrylamide)-g-polyacrylamide [CS-g-PNIPAAM-g-PAM] 3) could reversibly form semi-solid gels at physiological temperatures for easy application to oral cavity ulcer sites by injection. The chitosan-based conjugate thermogels prepared could inhibit both Gram-positive and Gram-negative bacteria and the two with higher chitosan and poly(N-isopropylacrylamide) contents (1a and 1b) promoted proliferation of gingival fibroblasts in vitro. These two thermogels also exhibited improved blood clotting in an in vivo rat study. Thermogels 1a and 1b effectively promoted ulcer healing and shortened ulcer healing times in an oral gingival mucosa ulcer model using Sprague Dawley (SD) rats. These thermogels showed no obvious toxicity to the main organs of SD rats undergoing gingival ulcer treatment. These results suggest that this antibacterial biomaterial could be a promising injectable therapeutic agent for the treatment for oral mucosa ulcers.

Zinc dithiocarbamates are traditionally highly-efficient catalysts for accelerating rubber vulcanization reactions, but have thus far not found substantial use in other forms of polymerisations. Herein, we demonstrate a new application of zinc diethyldithiocarbamate (ZDTC) for the synthesis of polyurethanes suitable for biomedical applications. Compared with other organozinc compounds such as zinc acetylacetonate and zinc neodecanoate, ZDTC showed exceptional catalytic performance, capable of forming high molecular weight polyurethanes, with the reaction tolerant to different organic solvents. The ZDTC-catalysed biocompatible amphiphilic polyurethanes comprising PEG and PPG blocks form thermo-responsive hydrogels which showed remarkably low sol-to-gel transition temperatures at surprisingly low concentrations in water. Microstructural analysis of the polyurethane aqueous solutions by small-angle X-ray scattering (SAXS) experiments revealed considerable supramolecular self-assembly of the polyurethanes even at 4 °C. Valuably, cell viability studies revealed that residual ZDTC catalysts present in unpurified polyurethane polymers exerted considerably lower cytotoxicities than those catalysed by tin(IV) catalysts such as dibutyltin dilaurate (DBTL). As demonstrated herein, ZDTC may be a possible alternative to highly-toxic organotin catalysts for the synthesis of polyurethanes, with further potential for other polymerization reactions reliant on organotin Lewis acidity such as polyester synthesis.

One common cause of vision loss after retinal detachment surgery is the formation of proliferative and contractile fibrocellular membranes. This aberrant wound healing process is mediated by epithelial-mesenchymal transition (EMT) and hyper-proliferation of retinal pigment epithelial (RPE) cells. Current treatment relies primarily on surgical removal of these membranes. Here, we demonstrate that a bio-functional polymer by itself is able to prevent retinal scarring in an experimental rabbit model of proliferative vitreoretinopathy. This is mediated primarily via clathrin-dependent internalisation of polymeric micelles, downstream suppression of canonical EMT transcription factors, reduction of RPE cell hyper-proliferation and migration. Nuclear factor erythroid 2–related factor 2 signalling pathway was identified in a genome-wide transcriptomic profiling as a key sensor and effector. This study highlights the potential of using synthetic bio-functional polymer to modulate RPE cellular behaviour and offers a potential therapy for retinal scarring prevention.

The traditional intravitreal injection delivery of anti-vascular endothelial growth factor (anti-VEGF) to the posterior segment of the eye for treatment of retinal diseases is invasive and associated with sight-threatening complications. To avoid such complications, there has been significant interest in developing polymers for topical drug delivery to the retina. This study reports a nanomicelle drug delivery system made of a co-polymer EPC (nEPCs), which is capable of delivering aflibercept to the posterior segment topically through corneal-scleral routes. EPC is comprised of polyethylene glycol (PEG), polypropylglycol (PPG) and polycaprolactone (PCL) segments. In this study, aflibercept-loaded nEPCs (nEPCs+A) is capable of penetrating the cornea in ex-vivo porcine eye models and deliver a clinically significant amount of aflibercept to the retina of laser-induced choroidal neovascularisation (CNV) murine models, causing CNV regression. nEPCs+A also demonstrates biocompatibility in-vitro and in-vivo. Interestingly, this study also suggests that nEPCs have intrinsic anti-angiogenic properties. The ability to deliver anti-VEGF drugs and the intrinsic anti-angiogenic properties of nEPCs may result in synergistic effects which can be harnessed for effective therapeutics. nEPCs may be a promising topical anti-VEGF delivery platform for the treatment of retinal diseases. This article is protected by copyright. All rights reserved.

Vitreous endotamponades play essential roles in facilitating retina recovery following vitreoretinal surgery, yet existing clinically standards are suboptimal as they can cause elevated intra-ocular pressure, temporary loss of vision, and cataracts while also requiring prolonged face-down positioning and removal surgery. These drawbacks have spurred the development of next-generation vitreous endotamponades, of which supramolecular hydrogels capable of in-situ gelation have emerged as top contenders. Herein, we demonstrate thermogels formed from hyper-branched amphiphilic copolymers as effective transparent and biodegradable vitreous endotamponades for the first time. These hyper-branched copolymers are synthesised via polyaddition of polyethylene glycol, polypropylene glycol, poly(e-caprolactone)-diol, and glycerol (branch inducing moiety) with hexamethylene diisocyanate. The hyper-branched thermogels are injected as sols and undergo spontaneous gelation when warmed to physiological temperatures in rabbit eyes. We found that polymers with an optimal degree of hyper-branching showed excellent biocompatibility and was able to maintain retinal function with minimal atrophy and inflammation, even at absolute molecular weights high enough to cause undesirable in-vivo effects for their linear counterparts. The hyper-branched thermogel is cleared naturally from the vitreous through surface hydrogel erosion and negates surgical removal. Our findings expand the scope of polymer architectures suitable for in-vivo intraocular therapeutic applications beyond linear constructs.

Gel polymer electrolytes are an important advancement in energy storage technology due to their enhanced safety and practical ionic conductivities at ambient temperatures. Herein, a simple one-step facile synthesis of chemically crosslinked polyurethanes containing polyethylene oxide (PEO) and polypropylene oxide (PPO) macromolecular segments was developed, using ubiquitous non-toxic tetrabutylammonium or potassium chloride and bromide salts as catalysts. These salts were shown to catalyze the gelation of diol-diisocyanate polyaddition reactions within minutes. When impregnated with a liquid electrolyte, the resulting gel electrolyte exhibited a practical ionic conductivity of 1.1×10-4 S cm-1 at 40 °C and low segmental chain motion activation energy (11 kJ mol-1 ). These findings further promote PEO-PPO polyurethanes as a biocompatible class of materials suitable for further exploration as gel polymer electrolytes for supercapacitors.

Molecular gels are promising new classes of materials for the treatment of polluted water owing to their large surface area for pollutant sorption and ease of chemical modification. In recent years, exceptional gel performance in the removal of pollutants such as oil, excess and/or toxic cations and anions, as well as dyes and pharmaceutical products have been reported. However, for them to be used in real-life settings, numerous practical considerations such as gel mechanical properties and recyclability also need to be taken into account. In this review, we highlight key advances in the development of this class of sorbent materials with an emphasis on hydrogels, comprising small molecule supramolecular gelators, polymers and composites comprising graphene/graphene oxide, microorganisms and iron nanoparticles achieved during the last decade. In our ‘bottom-up’ approach, we emphasise the key design features of each gel material accounting for its target pollutant adsorption characteristics and material properties, together with the most important practical considerations necessary for real-life usage. By putting these into perspective, we hope that this review will stimulate further strategic translational research into practical gel remediators capable of integrating with and complementing existing water treatment technologies.

Thermogels are temperature-responsive hydrogels which are most commonly formed by supramolecular self-assembly of polymer amphiphiles comprising of both hydrophobic and hydrophilic segments. Although polyurethane thermogels have shown great promise as biomaterials, their synthesis by step-growth polymerisation of diols and diisocyanates can also result in formation of allophanate branches, which arise from the reaction between free isocyanate groups and urethane linkages along the polymer backbone. In this paper, we investigate the effects of different synthetic conditions on the degree of allophanate branching on polyurethane amphiphiles, and explore the influences of these branches on the polymers' critical micelle concentration (CMC), thermodynamics of micellization and subsequent thermogel properties. Our findings offer new insights into the relationship between polymer structure, micelle and gel properties. These results highlight the importance of taking polymer branching into account for understanding the hierarchical self-assembly of polymer amphiphiles and the resulting thermogel properties and behaviour.

An integrated multiplex all-solid-state, polymer membrane-based ion-selective-electrode was designed and fabricated. The device includes an on-chip Pt pseudo-reference electrode and three independent Au working electrode. Nitrate, potassium, and phosphate selective membranes are coated on three electrodes independently. The sensitivity, selectivity, and stability of the device are evaluated using a laboratory-made measurement circuit board for ion concentrations from 10 μM to 100 mM.

Viral epidemics develop from the emergence of new variants of infectious viruses. The lack of effective antiviral treatments for the new viral infections coupled with rapid community spread of the infection often result in major human and financial loss. Viral transmissions can occur via close human‐to‐human contact or via contacting a contaminated surface. Thus, careful disinfection or sanitization is essential to curtail viral spread. A myriad of disinfectants/sanitizing agents/biocidal agents are available that can inactivate viruses, but their effectiveness is dependent upon many factors such as concentration of agent, reaction time, temperature, and organic load. In this work, we review common commercially available disinfectants agents available on the market and evaluate their effectiveness under various application conditions. In addition, this work also seeks to debunk common myths about viral inactivation and highlight new exciting advances in the development of potential sanitizing agents., Virus pandemics are recurrent in human history, and one of the major means of human‐to‐human viral transmissions occur through contact with contaminated surfaces. Herein, we provide a summary of the major commercially available sanitizing agents used to inactivate viruses and critically evaluate their effectiveness to do so.

The increasing prevalence of infectious diseases in recent decades has posed a serious threat to public health. Routes of transmission differ, but the respiratory droplet or airborne route has the greatest potential to disrupt social intercourse, while being amenable to prevention by the humble face mask. Different types of masks give different levels of protection to the user. The ongoing COVID-19 pandemic has even resulted in a global shortage of face masks and the raw materials that go into them, driving individuals to self-produce masks from household items. At the same time, research has been accelerated towards improving the quality and performance of face masks, e.g., by introducing properties such as antimicrobial activity and superhydrophobicity. This review will cover mask-wearing from the public health perspective, the technical details of commercial and home-made masks, and recent advances in mask engineering, disinfection, and materials and discuss the sustainability of mask-wearing and mask production into the future.

The ability of natural enzymes to regulate their guest binding affinities and preferences through the use of co-ligands which alter the features of the binding site is fundamental to biological homeostatic control. Herein, the rarely exploited orthosteric control of guest binding is demonstrated using neutral halogen bonding [2]rotaxanes, in which a chemical stimulus (acid) interacting with the interlocked host binding site switches the host's native guest preference from metal cations to anions. When neutral, the rotaxanes exhibit pronounced transition metal cation affinity and comparatively weak anion binding properties. However, the addition of acid attenuates the rotaxanes' ability to coordinate cations, while concurrently enabling strong binding of halides through charge assisted halogen bonding and hydrogen bonding interactions in competitive aqueous solvent media. The appendage of a fluorescent anthracene reporter group to the rotaxane framework also enables diagnostic sensory responses to cation/anion binding.

The synthesis and anion binding properties of a novel pyrrole-containing dicationic halogen bonding (XB) motif is described. When incorporated into an acyclic cleft-type receptor, rare selectivity for tetrahedral oxoanions (H2PO4− and SO42−) over halides is observed in aqueous solvent media.

The end-of-life treatment for post-consumer plastic waste constitutes one of modern society’s greatest problems, whereby highly unsustainable landfilling and incineration are the two main disposal routes. At present, the chemical upcycling of plastic waste is largely limited to its pyrolytic conversion into hydrocarbon fuels or nanomaterials. Herein, we demonstrate the upcycling of high-volume plastic waste by turning them into catalysts for biomass valorization. Many existing studies synthesize organocatalysts from a bottom-up approach using specialized monomers. Yet, transforming widely available waste polymers into functionalized materials for catalysis remains relatively unexplored. In this study, homogeneous and cross-linked heterogeneous catalysts derived from waste polystyrene food containers are shown to convert readily available saccharide precursors from biomass into 5-hydroxymethylfurfural (5-HMF), a key biorefinery platform chemical, under short reaction times and mild conditions. In addition, the heterogeneous catalyst can be reused multiple times with little loss of yield between repeated runs. Other than 5-HMF, doping the reaction with water or halide salts also allowed the formation of valuable products such as formic acid and diformylfuran. Our work expands on existing upcycling options for post-consumer plastic waste by giving them a new lease of life as value-added catalysts.

The application of chiral interlocked host molecules for discrimination of guest enantiomers has been largely overlooked, which is surprising given their unique three-dimensional binding cavities capable of guest encap-sulation. Herein, we combined the stringent linear geometric interaction constraints of halogen bonding (XB), the non-covalent interaction between an electrophilic halogen atom and a Lewis base, with highly preorganized and conforma-tionally restricted chiral cavities of [2]rotaxanes to achieve enantioselective anion recognition. Representing the first detailed investigation of the use of chiral XB rotaxanes for this purpose, extensive 1H NMR binding studies and mo-lecular dynamics (MD) simulation experiments revealed that the chiral rotaxane cavity significantly enhances enantio-discrimination compared to the non-interlocked free axle and macrocycle components. Furthermore, by examining the enantioselectivities of a family of structurally similar XB [2]rotaxanes containing different combinations of chiral and achiral macrocycle and axle components, the dominant influence of the chiral macrocycle in our rotaxane design for determining the effectiveness of chiral discrimination is demonstrated. MD simulations reveal the crucial geometric roles played by the XB interactions in orientating the bound enantiomeric anion guests for chiral selectivity, as well as the critical importance of the anions’ hydration shells in governing binding affinity and enantio-discrimination.

Electron-deficient heavy chalcogen atoms contain Lewis acidic σ-holes which are able to form attractive supramolecular interactions, known as chalcogen bonding (ChB), with Lewis bases. However, their potential in solution-phase anion binding applications is only just beginning to be realized in simple acyclic systems. Herein, we explore the 5-(methylchalcogeno)-1,2,3-triazole (chalcogen = Se, Te) motif as a novel ChB donor for anion binding. Other than being chemically robust enough to be incorporated into macrocyclic structures, thereby significantly expanding the scope and complexity of ChB host systems, we also demonstrate, by 1H NMR and DFT calculations, that the chalcogen atoms oriented within the macrocycle cavity are able to chelate copper(I) endotopically. Exploiting this property, the first examples of mechanically interlocked [2]rotaxanes containing ChB-donor groups are prepared via an active metal template strategy. Solution-phase 1H NMR and molecular modeling studies provide compelling evidence for the dominant influence of ChB in anion binding by these interlocked host systems. In addition, unprecedented charge-assisted ChB-mediated anion binding was also studied in aqueous solvent mixtures, which revealed considerable differences in anion recognition behavior in comparison with chalcogen-free host analogues. Moreover, DFT calculations and molecular dynamics simulations in aqueous solvent mixtures indicate that the selectivity is determined by the different hydrophilic characters of the anions allied to the hydration of the binding units in the presence of the anions. Exploiting the NMR-active nuclei of the ChB-donor chalcogen atoms, heteronuclear 77Se and 125Te NMR were used to directly study how anion recognition influences the local electronic environment of the chalcogen atoms in the mechanically bonded rotaxane binding sites in organic and aqueous solvent mixtures.

Chiral halogen bonding (S)-BINOL-based receptors are demonstrated to enhance the enantioselective recognition and sensing of chiral anions compared to their hydrogen bonding analogues. Computational studies attribute this behaviour to the strict linearity of halogen bonding (XB) and steric environment conferred by the XB donor groups bridged by the (S)-BINOL motif.

Polylactide (PLA) is a fully biodegradable and recyclable plastic, produced from a bio‐derived monomer: it is a circular economy plastic. Its properties depend upon its stereochemistry and isotactic PLA shows superior thermal‐mechanical performances. Here, a new means to control tacticity by exploiting rotaxane conformational dynamism is described. Dynamic achiral [2]rotaxanes can show high isoselectivity (Pi=0.8, 298 K) without requiring any chiral additives and enchain by a chain end control mechanism. The organocatalytic dynamic stereoselectivity is likely applicable to other small‐molecule and polymerization catalyses.

Vitreous endo-tamponades are commonly used in the treatment of retinal detachments and tears. They function by providing a tamponading force to support the retina after retina surgery. Current clinical vitreous endo-tamponades include expansile gases (such as sulfur hexafluoride (SF6) and perfluoropropane (C3F8)) and also sislicone oil (SiO). They are effective in promoting recovery but are disadvantaged by their lower refractive indices and lower densities as compared to the native vitreous, resulting in immediate blurred vision after surgery and necessitating patients to assume prolonged face-down positioning respectively. While the gas implants diffuse out over time, the SiO implants are non-biodegradable and require surgical removal. Therefore, there is much demand to develop an ideal vitreous endo-tamponade that can combine therapeutic effectiveness with patient comfort. Polymeric hydrogels have since attracted much attention due to their favourable properties such as high water content, high clarity, suitable refractive indices, suitable density, tuneable rheological properties, injectability, and biocompatibility. Many design strategies have been employed to design polymeric hydrogel-based vitreous endo-tamponades and they can be classified into four main strategies. This review seeks to analyse these various strategies and evaluate their effectiveness and also propose the key criteria to design successful polymeric hydrogel vitreous endo-tamponades.

Novel chiral halogen and chalcogen bonding receptors exhibit different selectivities for stereo- and geometric dicarboxylate isomers compared to a hydrogen bonding analogue. The unique geometric and electronic properties of the chalcogen bonding receptor facilitate the diagnostic fluorescence sensing of geometric dicarboxylate isomer guest species.

The application of chalcogen bonding (ChB) to anion recognition is an underdeveloped area of host–guest supramolecular chemistry. The chemical instability of heavier chalcogen derivatives may in part be responsible for the lack of progress. Herein, the synthesis of a new structurally simple, tellurium‐based ChB binding motif is reported, the robust stability of which has enabled the thermodynamic properties for ChB halide anion binding in polar aprotic and wet protic organic solvent media to be elucidated. The thermodynamic data reveals how the subtle interplay between ChB host, anion guest and solvent dictates halide binding selectivity and affinity trends. These findings help to provide a deeper insight into the nature of the ChB–anion interaction.

Summary Sigma (σ)-holes are electron-deficient regions that arise from the anisotropic distribution of electron density on the atom of group 14 (tetrels), 15 (pnictogens), 16 (chalcogens), and 17 (halogens) elements when covalently bonded to electron-withdrawing groups. Named after the donor atom's group, the σ-hole interactions, halogen bonding, and chalcogen bonding with anionic species have found ground-breaking applications in anion supramolecular chemistry within the last decade. In this review, we feature key recent discoveries and advances across the whole range of σ-hole interactions for anion recognition, from the familiar halogen bonding to the almost unknown pnictogen and tetrel bonding. In particular, the novel anion recognition properties and applications that result from the unique aspects of each σ-hole interaction, together with detailed design considerations of anion-binding receptor motifs, are highlighted.

The immobilisation of electrocatalysts for CO2 reduction onto light harvesting semiconductors is proposed to be an important step towards developing more efficient CO2 reduction photoelectrodes. Here, we report a low cost nickel cyclam complex covalently anchored to a metal oxide surface. Using transient spectroscopy we validate the role of surface immobilisation on enhancing the rate of photoelectron transfer. Furthermore [Ni(1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid)]2+ (2) is shown to be a very active electrocatalyst in solution.

The unprecedented application of a chiral halogen-bonding [3]rotaxane host system for the discrimination of stereo- and E/Z geometric isomers of a dicarboxylate anion guest is described. Synthesised by a chloride anion templation strategy, the [3]rotaxane host recognises dicarboxylates through the formation of 1:1 stoichiometric sandwich complexes. This process was analysed by molecular dynamics simulations, which revealed the critical synergy of halogen and hydrogen bonding interactions in anion discrimination. In addition, the centrally located chiral (S)-BINOL motif of the [3]rotaxane axle component facilitates the complexed dicarboxylate species to be sensed via a fluorescence response.

A family of cationic halogen bonding [2]rotaxanes have been synthesised via an active-metal template synthetic strategy. 1H NMR spectroscopic anion titration investigations reveal these interlocked host systems recognize halides selectively over oxoanions in aqueous–organic solvent media. Furthermore, systematically modulating the rigidity and size of the rotaxanes’ anion binding cavities via metal complexation, as well as by varying the number of halogen bond-donor groups in the axle component, was found to dramatically influence halide anion selectivity.

A neutral redox-active acyclic halogen bonding (XB) receptor with a ferrocene core functionalised at the 1,3-positions of a cyclopentadienyl ring with iodotriazole motifs is prepared. Owing to favourable host-guest size-complementarity, the receptor was found to be selective for azide over a diverse range of anions with different geometries. Voltammetric studies revealed the unique ability of the XB ferrocene receptor to selectively sense azide via a significant cathodic shift of its ferrocene/ferrocenium redox couple. Notably, much weaker binding of azide was observed for the hydrogen bonding 1,3-bis-prototriazole ferrocene receptor analogue, which also displayed a poorer electrochemical response, suggesting that halogen bonding interactions play crucial roles in the binding and sensing of azide.

Neutral tetradentate halogen bond donor foldamers were synthesised and exhibit enhanced anion affinities over their hydrogen bonding analogues, displaying iodide selectivity over lighter halide, carboxylate and dihydrogen phosphate anions. A foldamer with a chiral (S)-binaphthol motif was demonstrated to distinguish between enantiomers of chiral anions.

The design and construction of neutral interlocked host molecules for anion recognition are rare. Using an active-metal template approach, the preparation of a family of neutral halogen bonding (XB) rotaxanes containing two, three and four iodotriazole groups integrated into the macrocycle and axle components is achieved. In spite of the interlocked hosts' neutrality, such rotaxane systems are capable of binding halide anions strongly and selectively in wet organic solvent mixtures. Importantly, halide-binding strength and selectivity can be modulated by varying the number and position of the halogen bond donor iodotriazole groups within the interlocked cavity; the rotaxane containing the largest number of halogen bond donor groups exhibits the highest halide anion-binding affinities. By varying the percentage of water content in the solvent, neutral XB donor-mediated anion-binding strength is also demonstrated to be highly sensitive to solvent polarity.

Supramolecular hydrogels held together by non-covalent interactions such as electrostatics, hydrogen bonding, and hydrophobic forces are among the most promising soft material platforms for modern biomedical applications. By virtue of their inherent reversibility and dynamism, they respond well to environmental stimuli and biochemical cues and can dissipate mechanical energy effectively. These important features are well suited for cell culture, tissue engineering, on-demand controlled release of therapeutics, tissue adhesion, and molecular sensing and as artificial gel substitutes in organs (e.g., vitreous humour and synovial fluids), which are not easily achieved by permanently cross-linked covalent hydrogels. Consequently, supramolecular hydrogels have grown in popularity and have witnessed rapid development for biomedical applications in recent years. Through the numerous applications and exciting advances during the last five years discussed in this mini-review, we highlight how the supramolecular interactions enabling gel formation also translates to their bulk material properties and resulting biomedical applications. Owing to their versatility and ease of ‘bottom-up’ engineering from the molecular level, supramolecular hydrogels are poised to offer a wide range of biomedical solutions to modern societal problems, including but not limited to wound healing, development of artificial tissues, cell therapies, and anticancer treatment. Keywords: Physically-crosslinked hydrogels, Hydrophobic interactions, Hydrogen bonding, Ionic interactions, Inclusion complexes