Ionic Covalent Organic Framework-Based Membranes for Selective and Highly Permeable Molecular Sieving.

Two-dimensional covalent organic frameworks (COFs) with uniform pores and large surface areas are ideal candidates for constructing advanced molecular sieving membranes. However, a fabrication strategy to synthesize a free-standing COF membrane with a high permselectivity has not been fully explored yet. Herein, we prepared a free-standing TpPa-SO3H COF membrane with vertically aligned one-dimensional nanochannels. The introduction of the sulfonic acid groups on the COF membrane provides abundant negative charge sites in its pore wall, which achieve a high water flux and an excellent sieving performance toward water-soluble drugs and dyes with different charges and sizes. Furthermore, the COF membrane exhibited long-term stability, fouling resistance, and recyclability in rejection performance. We envisage that this work provides new insights into the effect of ionic ligands on the design of a broad range of COF membranes for advanced separation applications.

Biomimetic Mineralization for Smart Biostimulant Delivery and Crop Micronutrients Fortification.

Sustainable and precise fortification practices are necessary to ensure food security for the increasing human population. Precision agriculture aims to minimize the use of fertilizers and pesticides by developing smart materials for real-life agricultural practices. Here, we show that biomimetic mineralization can be efficiently employed to encapsulate and controllably release plant biostimulants (MiZax-3) to improve the quality and yield of capsicum (Capsicum annum) crops in field experiments. ZIF-8 encapsulation of MiZax-3 (MiZIFs) could significantly enhance its stability up to around 679 times (6p value = 0.0072) at field conditions. Our results demonstrate that the coordinating Zn ions and the MiZax-3 play a vital role in improving Zn content in the produced fruits by 2-fold, which is the first report of this nature on Zn content in fruits. We envision this platform as a starting point to investigate other biocompatible coordination-based platforms for micronutrient delivery in precision agriculture.

An Amphiphilic Cell-Penetrating Macrocycle for Efficient Cytosolic Delivery of Proteins, DNA, and CRISPR Cas9.

The discovery of safe platforms that can circumvent the endocytic pathway is of great significance for biological therapeutics that are usually degraded during endocytosis. Here we show that a self-assembled and dynamic macrocycle can passively diffuse through the cell membrane and deliver a broad range of biologics, including proteins, CRISPR Cas9, and ssDNA, directly to the cytosol while retaining their bioactivity. Cell-penetrating macrocycle CPM can be easily prepared from the room temperature condensation of diketopyrrolopyrrole lactams with diamines. We attribute the high cellular permeability of CPM to its amphiphilic nature and chameleonic properties. It adopts conformations that partially bury polar groups and expose hydrophobic side chains, thus self-assembling into micellar-like structures. Its superior fluorescence makes CPM trackable inside cells where it follows the endomembrane system. CPM outperformed commercial reagents for biologics delivery and showed high RNA knockdown efficiency of CRISPR Cas9. We envisage that this macrocycle will be an ideal starting point to design and synthesize biomimetic macrocyclic tags that can readily facilitate the interaction and uptake of biomolecules and overcome endosomal digestion.

Industrial Separation Challenges: How Does Supramolecular Chemistry Help?

The chemical industry and the chemical processes underscoring it are under intense scrutiny as the demands for the transition to more sustainable and environmentally friendly practices are increasing. Traditional industrial separation systems, such as thermally driven distillation for hydrocarbon purification, are energy intensive. The development of more energy efficient separation technologies is thus emerging as a critical need, as is the creation of new materials that may permit a transition away from classic distillation-based separations. In this Perspective, we focus on porous organic cages and macrocycles that can adsorb guest molecules selectively through various host-guest interactions and permit molecular sieving behavior at the molecular level. Specifically, we summarize the recent advances where receptor-based adsorbent materials have been shown to be effective for industrially relevant hydrocarbon separations, highlighting the underlying host-guest interactions that impart selectivity and permit the observed separations. This approach to sustainable separations is currently in its infancy. Nevertheless, several receptor-based adsorbent materials with extrinsic/intrinsic voids or special functional groups have been reported in recent years that can selectively capture various targeted guest molecules. We believe that the understanding of the interactions that drive selectivity at a molecular level accruing from these initial systems will permit an ever-more-effective "bottom-up" design of tailored molecular sieves that, in due course, will allow adsorbent material-based approaches to separations to transition from the laboratory into an industrial setting.

Pillararene-Based Variable Stoichiometry Co-Crystallization: A Versatile Approach to Diversified Solid-State Superstructures.

Variable stoichiometry co-crystals are important in solid-state supramolecular chemistry as they allow studies of structure-property relationships while permitting the synthesis of new scaffolds using identical synthons. In this work, we extend the concept of variable stoichiometry co-crystals into the realm of pillararene chemistry and show that this permits the rational construction of a diverse set of supramolecular structures in the solid state. Specifically, we report a series of variable stoichiometry co-crystals based on pillar[n]arenes and tetracyanobenzene (TCNB) and show that the combination of in-cavity complexation by pillar[n]arenes (n = 5,6) and outside binding with TCNB allows several types of co-crystals with different self-assembled superstructures to be isolated. The variable stoichiometry co-crystals of this study display different solid-state physicochemical properties, including colors and luminescence features. Among these pillar[n]arene-based co-crystals, we discovered unique crystallographic architectures wherein two sets of individual host-guest complexes co-exist in the solid state. These mixed co-crystal systems allow for vapochromic-based detection of n-bromoalkanes. This work highlights a new strategy for the construction of self-assembled superstructures in the solid state and for tuning their intrinsic characteristics, including their luminescent and substrate-responsive features.

Caging the Hofmeister Effect by a Biomimetic Supramolecular Receptor.

The effect of anions on the solubility and function of proteins was recognized in 1888 and is now termed the Hofmeister effect. Numerous synthetic receptors are known that overcome the associated anion recognition bias. However, we are unaware of a synthetic host being used to overcome Hofmeister effect perturbations to natural proteins. Here, we report a protonated small molecule cage complex that acts as an exo-receptor and displays non-Hofmeister solubility behavior, with only the chloride complex remaining soluble in aqueous media. This cage allows for the activity of lysozyme to be retained under conditions where anion-induced precipitation would otherwise cause it to be lost. To our knowledge, this is the first time a synthetic anion receptor is used to overcome the Hofmeister effect in a biological system.

Smart Materials Based on Synthetic Host Molecules: The Role of Host-Guest Chemistry in the Fabrication and Application.

Stimuli-responsive or smart materials have recently shown a significant impact on the frontier of material science and engineering. The exponential development of synthetic host molecules (SHMs) over the last decades and their corresponding host-guest chemistry, have empowered researchers with new opportunities to design and construct tailored or guest-specific smart materials. In this Minireview, we present the recent advancements in synthetic host based smart materials, ranging from the fabrication strategies to the state-of-art applications including adsorption, separation, luminescence, self-healing and actuation. The role that the host-guest chemistry plays in these systems is highlighted throughout to give a better prospective of the available possibilities for emerging materials of future economies.

Dynamic Hydrogen-Bonded Zinc Adeninate Framework (ZAF) for Immobilization of Catalytic DNA.

Effective immobilization and delivery of genetic materials is at the forefront of biological and medical research directed toward tackling scientific challenges such as gene therapy and cancer treatment. Herein we present a biologically inspired hydrogen-bonded zinc adeninate framework (ZAF) consisting of zinc adeninate macrocycles that self-assemble into a 3D framework through adenine-adenine interactions. ZAF can efficiently immobilize DNAzyme with full protection against enzyme degradation and physiological conditions until it is successfully delivered into the nucleus. As compared to zeolitic imidazolate frameworks (ZIFs), ZAFs are twofold more biocompatible with a significant loading efficiency of 96 %. Overall, our design paves the way for expanding functional hydrogen-bonding-based systems as potential platforms for the loading and delivery of biologics.

Fluorine-Boosted Kinetic and Selective Molecular Sieving of C6 Derivatives.

Porous molecular sorbents have excellent selectivity towards hydrocarbon separation with energy saving techniques. However, to realize commercialization, molecular sieving processes should be faster and more efficient compared to extended frameworks. In this work, we show that utilizing fluorine to improve the hydrophobic profile of leaning pillararenes affords a substantial kinetic selective adsorption of benzene over cyclohexane (20 : 1 for benzene). The crystal structure shows a porous macrocycle that acts as a perfect match for benzene in both the intrinsic and extrinsic cavities with strong interactions in the solid state. The fluorinated leaning pillararene surpasses all reported organic molecular sieves and is comparable to the extended metal-organic frameworks that were previously employed for this separation such as UIO-66. Most importantly, this sieving system outperformed the well-known zeolitic imidazolate frameworks under low pressure, which opens the door to new generations of molecular sieves that can compete with extended frameworks for more sustainable hydrocarbon separation.

Intrinsically Porous Molecular Materials (IPMs) for Natural Gas and Benzene Derivatives Separations.

ConspectusSeparating and purifying chemicals without heat would go a long way toward reducing the overall energy consumption and the harmful environmental footprint of the process. Molecular separation processes are critical for the production of raw materials, commodity chemicals, and specialty fuels. Over 50% of the energy used in the production of these materials is spent on separation and purification processes, which primarily includes vacuum and cryogenic distillations. Chemical manufacturers are now investigating modest thermal approaches, such as membranes and adsorbent materials, as they are more cognizant than ever of the need to save energy and prevent pollution. Porous materials, such as zeolites, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs), have dominated the field of industrial separations as their high surface areas and robust pores make them ideal candidates for molecular separations of gases and hydrocarbons. Separation processes involving porous materials can save 70%-90% of energy costs compared to that of thermally driven distillations. However, most porous materials have low thermal, chemical, and moisture stability, in addition to limited solution processability, which tremendously constrain their broad industrial translation. Intrinsically porous molecular materials (IPMs) are a subclass of porous molecular materials that are comprised of molecular host macrocycles or cages that absorb guests in or around their intrinsic cavity. IPMs range from discrete porous molecules to assemblies with amorphous or highly crystalline structures that are held together by weak supramolecular interactions. Compared to the coordination or dynamic covalent bond-constructed porous frameworks, IPMs possess high thermal, chemical, and moisture stability and maintain their porosity under critical conditions. Moreover, the intrinsic porosity endows IPMs with excellent host-guest properties in solid, liquid (organic or aqueous), and gas states, which can be further utilized to construct diverse separation strategies, such as solid-gas adsorption, solid-liquid absorption, and liquid-liquid extraction. The diversity of host-guest interactions in the engineered IPMs affords a plethora of possibilities for the development of the ideal "molecular sieves". Herein, we present a different take on the applicability of intrinsically porous materials such as cyclodextrin (CD), cucurbiturils (CB), pillararene (P), trianglamines (T), and porous organic cages (POCs) that showed an impressive performance in gas purification and benzene derivatives separation. IPMs can be easily scaled up and are quite stable and solution processable that consequently facilitates a favorable technological transformation from the traditional energy-intensive separations. We will account for the main advances in molecular host-guest chemistry to design "on-demand" separation processes and also outline future challenges and opportunities for this promising technology.

Functional Supramolecular Polymeric Networks: The Marriage of Covalent Polymers and Macrocycle-Based Host-Guest Interactions.

Covalent polymers connected by non-covalent interactions constitute a fascinating set of materials known as supramolecular polymer networks (SPNs). A key feature of SPNs is that the underlying covalent polymers endow the resulting self-assembled materials with features, such as structural and mechanical integrity, good processability, recyclability, stimuli-responsiveness, self-healing, and shape memory, that are not recapitulated in the case of classic covalent polymer systems. The unique nature of SPNs derives from the controlled marriage of traditional covalent polymers and macrocycle-based host-guest interactions. As a consequence, supramolecular polymeric networks have played important roles in a number of diverse fields, including polymer science, supramolecular chemistry, materials science, biomedical materials, and information storage technology. In this Review, we summarize advances made in the area of functional SPNs, with a focus on original literature reports appearing in the past five years. The treatment is organized according to the key macrocycle-based host-guest interactions used to produce various SPNs. The role of the underlying polymer backbones is also discussed.

Water compatible supramolecular polymers: recent progress.

Water compatible supramolecular polymers (WCSPs) combine aqueous compatibility with the reversibility and environmental responsiveness of supramolecular polymers. WCSPs have seen application across a number of fields, including stimuli-responsive materials, healable materials, and drug delivery, and are attracting increasing attention from the design, synthesis, and materials perspectives. In this review, we summarize the chemistry of WCSPs from 2016 to mid-2021. For the sake of discussion, we divide WCSPs into five categories based on the core supramolecular approaches at play, namely hydrogen-bonding arrays, electrostatic interactions, large π-conjugated subunits, host-guest interactions, and peptide-based systems, respectively. We discuss both synthesis and polymer structure, as well as the underlying design expectations. The goal of this overview is to deepen our understanding of the strategies that have been exploited to prepare WCSPs, as well as their properties and uses. Thus, a section devoted to potential applications is included in this review.

Vapor-Triggered Mechanical Actuation in Polymer Composite Films Based on Crystalline Organic Cages.

The fabrication of smart materials, which can efficiently mimic biological systems through the introduction of soft components, is of great importance in the emerging fields of sensors and actuators. Herein, a smart composite film that can mechanically respond to vapors trigger then readily restores its original shape upon the removal of the stimuli is reported. This actuating composite film was prepared by mixing the highly elastic poly (vinylidene fluoride) (PVDF) polymer with the flexible and crystalline organic cages (Oba-cage) at variable concentrations. The mechanism of the mechanical response could be accurately recorded due to the ordered cage crystals. This work highlights the importance of designing smart materials at the molecular level to precisely control the response or reaction upon the introduction of different triggers, which can ultimately lead to a monumental leap in the field of soft robotics.

Adsorptive Molecular Sieving of Styrene over Ethylbenzene by Trianglimine Crystals.

The separation of styrene (ST) and ethylbenzene (EB) mixtures is of great importance in the petrochemical and plastics industries. Current technology employs multiple cycles of energy-intensive distillation due to the very close boiling points of ST and EB. Here, we show that the molecular sieving properties of easily scalable and stable trianglimine crystals offer ultrahigh selectivity (99%) for styrene separation. The unique molecular sieving properties of trianglimine crystals are corroborated by DFT calculations, suggesting that the incorporation of the nonplanar EB requires a significant deformation of the macrocyclic cavity whereas the planar ST can be easily accommodated in the cavity.

Selective Separation of Lithium Chloride by Organogels Containing Strapped Calix[4]pyrroles.

Reported herein are two functionalized crown ether strapped calix[4]pyrroles, H1 and H2. As inferred from competitive salt binding experiments carried out in nitrobenzene-d5 and acetonitrile-d3, these hosts capture LiCl selectively over four other test salts, viz. NaCl, KCl, MgCl2, and CaCl2. Support for the selectivity came from density functional theory (DFT) calculations carried out in a solvent continuum. These theoretical analyses revealed a higher innate affinity for LiCl in the case of H1, but a greater selectivity relative to NaCl in the case of H2, recapitulating that observed experimentally. Receptors H1 and H2 were outfitted with methacrylate handles and subject to copolymerization with acrylate monomers and cross-linkers to yield gels, G1 and G2, respectively. These two gels were found to adsorb lithium chloride preferentially from an acetonitrile solution containing a mixture of LiCl, NaCl, KCl, MgCl2, and CaCl2 and then release the lithium chloride in methanol. The gels could then be recycled for reuse in the selective adsorption of LiCl. As such, the present study highlights the use of solvent polarity switching to drive separations with potential applications in lithium purification and recycling.

AIE-Based Fluorescent Triblock Copolymer Micelles for Simultaneous Drug Delivery and Intracellular Imaging.

Fluorescent drug delivery systems have received increasing attention in cancer therapy because they combine drug delivery and bioimaging into a single platform. For example, polymers with aggregation-induced emission (AIE) fluorophores, such as tetraphenylethylene (TPE), have emerged as an elegant choice for drug delivery/bioimaging applications. In this work, we report one-pot sequential organocatalytic ring-opening polymerization of ε-caprolactone (CL) and ethylene oxide (EO) using TPE-(OH)2 as a difunctional initiator, in the presence of a t-BuP2/TEB Lewis pair (catalyst), in THF at room temperature. Two well-defined triblock copolymers with inverse block sequences, TPE-(PCL-b-PEO)2 and TPE-(PEO-b-PCL)2, were synthesized by altering the sequential addition of CL and EO. The physicochemical properties, including hydrodynamic diameter, morphology, and AIE properties of the synthesized amphiphilic triblock copolymers were investigated in aqueous media. The block copolymer micelles were loaded with anticancer drugs doxorubicin and curcumin to serve as drug delivery vehicles. In vitro studies revealed the accelerated drug release at lower pH (5.5), which mimics the tumor microenvironment, different from the physiological pH (7.4). In vitro cytotoxicity studies demonstrated that the neat block copolymer micelles are biocompatible, while drug-loaded micelles exhibited a significant cytotoxic effect in cancer cells. Cellular uptake, examined by confocal laser scanning microscopy, showed that the block copolymer micelles were rapidly internalized by the cells with simultaneous emission of TPE fluorophore. These results suggest that these triblock copolymers can be utilized for intracellular bioimaging.

Calix[4]pyrrole-Crosslinked Porous Polymeric Networks for the Removal of Micropollutants from Water.

Calix[4]pyrrole-based porous organic polymers (P1-P3) for removing organic micropollutants from water were prepared. A bowl-shaped α,α,α,α-tetraalkynyl calix[4]pyrrole and diketopyrrolopyrrole monomer were crosslinked via Sonogashira coupling to produce a 3D network polymer, P1. P1 proved too hydrophobic for use as an adsorbent and was converted to the corresponding neutral polymer P2 (containing carboxylic acid groups) and its anionic derivative P3 (containing carboxylate anion groups). Anionic P3 outperformed P2 in screening studies involving a variety of model organic micropollutants of different charge, hydrophilicity and functionality. P3 proved particularly effective for cationic micropollutants. The theoretical maximum adsorption capacity (qmax,e ) of P3 reached 454 mg g-1 for the dye methylene blue, 344 mg g-1 for the pesticide paraquat, and 495 mg g-1 for diquat. These uptake values are significantly higher than those of most synthetic adsorbent materials reported to date.

From Capsule to Helix: Guest-Induced Superstructures of Chiral Macrocycle Crystals.

Predicting, controlling, understanding, and elucidating the phase transition from gel to crystal are highly important for the development of various functional materials with macroscopic properties. Here, we show a detailed and systematic description of the self-assembly process of an enantiopure trianglimine macrocyclic host from gel to single crystals. This proceeds via an unprecedented formation of capsule-like or right-handed helix superstructures as metastable products, depending on the nature of the guest molecule. Mesitylene promotes the formation of capsule-like superstructures, whereas toluene results in the formation of helices as intermediates during the course of crystallization. Single-crystal results demonstrate that the crystals obtained via the direct self-assembly from the gel phase are different from the crystals obtained from the stepwise assembly of the intermediate superstructures. Hence, investigating the phase-transition superstructures that self-assemble through the process of crystallization can unravel new molecular ordering with unexplored host-guest interactions. Such understanding will provide further tools to control hierarchical assemblies at the molecular level and consequently design or dictate the properties of evolved materials.

Cell-Type-Specific CRISPR/Cas9 Delivery by Biomimetic Metal Organic Frameworks.

Effective and cell-type-specific delivery of CRISPR/Cas9 gene editing elements remains a challenging open problem. Here we report the development of biomimetic cancer cell coated zeolitic imidazolate frameworks (ZIFs) for targeted and cell-specific delivery of this genome editing machinery. Coating ZIF-8 that is encapsulating CRISPR/Cas9 (CC-ZIF) with a cancer cell membrane resulted in the uniformly covered C3-ZIF(cell membrane type). Incubation of C3-ZIFMCF with MCF-7, HeLa, HDFn, and aTC cell lines showed the highest uptake by MCF-7 cells and negligible uptake by the healthy cells (i.e., HDFn and aTC). As to genome editing, a 3-fold repression in the EGFP expression was observed when MCF-7 were transfected with C3-ZIFMCF compared to 1-fold repression in the EGFP expression when MCF-7 were transfected with C3-ZIFHELA. In vivo testing confirmed the selectivity of C3-ZIFMCF to accumulate in MCF-7 tumor cells. This supports the ability of this biomimetic approach to match the needs of cell-specific targeting, which is unquestionably the most critical step in the future translation of genome editing technologies.

Adhesive supramolecular polymeric materials constructed from macrocycle-based host-guest interactions.

Nature uses the power of non-covalent interactions as the basis for many kinds of adhesion phenomena. Inspired by nature, scientists have prepared various synthetic adhesive materials that rely on a number of non-covalent interactions at the interfaces. Commonly used non-covalent interactions include hydrogen bonding, π-π stacking, charge transfer interactions, electrostatic interactions, hydrophobic interactions, macrocycle-based host-guest interactions, among others. Within this context, macrocycle-based host-guest interactions are of particular interest. Often they give rise to distinct properties, such as multiple combined noncovalent interactions and a diversity of stimuli-based responsiveness. In this tutorial review, we will summarise recent advances in adhesive supramolecular polymeric materials that rely primarily on macrocycle-based host-guest interactions. An overview of future challenges and a perspective of this sub-field are also provided.