Tripodal Organic Cages with Unconventional CH···O Interactions for Perchlorate Remediation in Water

Sensing features, on-site detection and bio-imaging application of a tripodal tris(hydroxycoumarin) based probe towards Cu2+/His

A new tripodal tris(hydroxycoumarin) based Schiff base, HCTN was synthesized and characterized by FT-IR, 1H NMR, 13C NMR and ESI-HRMS. The probe, HCTN exhibits cyan emission in DMSO/HEPES buffer (9:1, v/v) which selectively detects Cu2+ ion via turn-off fluorescence. The quenching of the fluorescence was due to the binding of the probe, HCTN towards paramagnetic Cu2+ ion resulting in chelation enhanced quenching effect (CHEQ). From the spectroscopic results, the limit of detection of Cu2+ ion was obtained as very low as 0.40 × 10-9 M. The complexation of the metal ion, Cu2+ towards the probe HCTN was confirmed by the ESI-HRMS and Job's plot analysis which supports 1:1 binding stochiometric ratio. In order to validate the affinity of Cu2+ ion towards histidine, the HCTN+Cu2+ system was utilized for the detection of histidine via turn-on mode by the metal displacement approach. The detection limit of His was found to be 7.31 × 10-10 M. In addition to the above, the probe was utilized for various detection applications such as paper strips, cotton swabs, logic gates and thin film applications. The probe, HCTN extends its application to the confocal bioimaging to sense the Cu2+ and Histidine intracellularly.

Near-Quantitative Removal of Oxalate and Terephthalate from Water by Precipitation with a Rigid Bis-Amidinium Compound

A simple, readily-prepared precipitant (1⋅Cl2) precipitates oxalate or terephthalate from water with very high efficacy, removing these anions at sub-millimolar concentrations using only one equivalent of precipitant. A simple aqueous base/acid cycle can be used to regenerate 1⋅Cl2 after use. The resulting precipitates, 1⋅oxalate and 1⋅terephthalate, are anhydrous and closely-packed, with each anion receiving eight charge-assisted hydrogen bonds from amidinium N-H donors. Precipitation of oxalate and terephthalate occurs at much lower concentrations than other dicarboxylates, and direct competition experiments with the biologically/environmentally relevant divalent anions CO3 2-, HPO4 2- and SO4 2- reveal very high selectivity for oxalate or terephthalate over these competitors.

The Versatile Applications of Calix[4]resorcinarene-Based Cavitands

The advancement of synthetic host-guest chemistry has played a pivotal role in exploring and quantifying weak non-covalent interactions, unraveling the intricacies of molecular recognition in both chemical and biological systems. Macrocycles, particularly calix[4]resorcinarene-based cavitands, have demonstrated significant utility in receptor design, facilitating the creation of intricately organized architectures. Within the realm of macrocycles, these cavitands stand out as privileged scaffolds owing to their synthetic adaptability, excellent topological structures, and unique recognition properties. So far, extensive investigations have been conducted on various applications of calix[4]resorcinarene-based cavitands. In this review, we will elaborate on their diverse functions, including catalysis, separation and purification, polymeric materials, sensing, battery materials, as well as drug delivery. This review aims to provide a holistic understanding of the multifaceted roles of calix[4]resorcinarene-based cavitands across various applications, shedding light on their contributions to advancing the field of supramolecular chemistry.

From small changes to big gains: pyridinium-based tetralactam macrocycle for enhanced sugar recognition in water

The complex distribution of functional groups in carbohydrates, coupled with their strong solvation in water, makes them challenging targets for synthetic receptors. Despite extensive research into various molecular frameworks, most synthetic carbohydrate receptors have exhibited low affinities, and their interactions with sugars in aqueous environments remain poorly understood. In this work, we present a simple pyridinium-based hydrogen-bonding receptor derived from a subtle structural modification of a well-known tetralactam macrocycle. This small structural change resulted in a dramatic enhancement of glucose binding affinity, increasing from 56 M-1 to 3001 M-1. Remarkably, the performance of our synthetic lectin surpasses that of the natural lectin, concanavalin A, by over fivefold. X-ray crystallography of the macrocycle-glucose complex reveals a distinctive hydrogen bonding pattern, which allows for a larger surface overlap between the receptor and glucose, contributing to the enhanced affinity. Furthermore, this receptor possesses allosteric binding sites, which involve chloride binding and trigger receptor aggregation. This unique allosteric process reveals the critical role of structural flexibility in this hydrogen-bonding receptor for the effective recognition of sugars. We also demonstrate the potential of this synthetic lectin as a highly sensitive glucose sensor in aqueous solutions.

Highly selective recognition of fluoride using a trapezoidal cage

By using a trapezoidal cage (1), highly selective recognition of F- (S > 1000) was achieved in highly competitive environments composed of a large excess of various common anions. Through NMR, fluorescence, UV-vis and HRMS studies, the binding behavior and binding affinity (β2 = ∼107 M-2) of 1 + F- are shown.

Synthesis of a Pd2L4 Hydrazone Molecular Cage Through Multiple Reaction Pathways

Molecular cages are preorganized molecules with a central cavity, typically formed through the reaction of their building blocks through chemical bonds. This requires, in most cases, forming and breaking reversible bonds during the cage formation reaction pathway for error correction to drive the reaction to the cage product. In this work, we focus on both Pd-ligand and hydrazone bonds implemented in the structure of a Pd2L4 hydrazone molecular cage. As the cage contains two different types of reversible bonds, we envisaged a cage formation comparative study by performing the synthesis of the cage through three different reaction pathways involving the formation of Pd-ligand bonds, hydrazone bonds, or a combination of both. The three reaction pathways produce the cage with yields ranging from 73% to 79%. Despite the complexity of the reaction, the cage is formed in a high yield, even for the reaction pathway that involves the formation of 16 bonds. This research paves the way for more sophisticated cage designs through complex reaction pathways.

Expedient Decagram-Scale Synthesis of Robust Organic Cages That Bind Sulfate Strongly and Selectively in Water

Selective anion recognition remains a key challenge in supramolecular chemistry: only a very small number of systems that can function in water are known, and these nearly always preferentially bind hydrophobic anions. In this work, we report three robust hexa-cationic cages that can be prepared on scales up to 14 g in two simple and high-yielding steps from commercially available materials. One of these cages displays unusually strong sulfate binding in water (Ka = 12,000 M-1), and demonstrates high selectivity for this anion over H2PO4-/HPO42- in DMSO/buffer mixtures. These results demonstrate that relatively large, three-dimensional supramolecular hosts can be prepared in high yields and on large scales, and can be highly potent receptors.

Charge-assisted hydrogen bonding in a bicyclic amide cage: an effective approach to anion recognition and catalysis in water

Hydrogen bonding is prevalent in biological systems, dictating a myriad of life-sustaining functions in aqueous environments. Leveraging hydrogen bonding for molecular recognition in water encounters significant challenges in synthetic receptors on account of the hydration of their functional groups. Herein, we introduce a water-soluble hydrogen bonding cage, synthesized via a dynamic approach, exhibiting remarkable affinities and selectivities for strongly hydrated anions, including sulfate and oxalate, in water. We illustrate the use of charge-assisted hydrogen bonding in amide-type synthetic receptors, offering a general molecular design principle that applies to a wide range of amide receptors for molecular recognition in water. This strategy not only revalidates the functions of hydrogen bonding but also facilitates the effective recognition of hydrophilic anions in water. We further demonstrate an unconventional catalytic mechanism through the encapsulation of the anionic oxalate substrate by the cationic cage, which effectively inverts the charges associated with the substrate and overcomes electrostatic repulsions to facilitate its oxidation by the anionic MnO4 -. Technical applications using this receptor are envisioned across various technical applications, including anion sensing, separation, catalysis, medical interventions, and molecular nanotechnology.

Hydrogen-Bonded Fibrous Nanotubes Assembled from Trigonal Prismatic Building Blocks

In reticular chemistry, molecular building blocks are designed to create crystalline open frameworks. A key principle of reticular chemistry is that the most symmetrical networks are the likely outcomes of reactions, particularly when highly symmetrical building blocks are involved. The strategy of synthesizing low-dimensional networks aims to reduce explicitly the symmetry of the molecular building blocks. Here we report the spontaneous formation of hydrogen-bonded fibrous structures from trigonal prismatic building blocks, which were designed to form three-dimensional crystalline networks on account of their highly symmetrical structures. Utilizing different microscopic and spectroscopic techniques, we identify the structures at the early stages of the assembly process in order to and understand the growth mechanism. The symmetrical molecular building blocks are incorporated preferentially in the longitudinal direction, giving rise to anisotropic hydrogen-bonded porous organic nanotubes. Entropy-driven anisotropic growth provides micrometer-scale unidirectional nanotubes with high porosity. By combining experimental evidence and theoretical modeling, we have obtained a deep understanding of the nucleation and growth processes. Our findings offer fundamental insight into the molecular design of tubular structures. The nanotubes evolve further in the transverse directions to provide extended higher-order fibrous structures [nano- and microfibers], ultimately leading to large-scale interconnected hydrogen-bonded fiber-like structures with twists and turns. Our work provides fundamental understanding and paves the way for innovative molecular designs in low-dimensional networks.

Ultradynamic Isoreticularly Expanded Porous Organic Crystals

Porous organic materials showcasing large framework dynamics present new paths for adsorption and separation with enhanced capacity and selectivity beyond the size-sieving limits, which is attributed to their guest-responsive sorption behaviors. Porous hydrogen-bonded crosslinked organic frameworks (HCOFs) are attractive for their remarkable ability to undergo guest-triggered expansion and contraction facilitated by their flexible covalent crosslinkages. However, the voids of HCOFs remain limited, which restrains the extent of the framework dynamics. In this work, we synthesized a series of HCOFs characterized by unprecedented size expansion capabilities induced by solvents. These HCOFs were constructed by isoreticularly co-crystallizing two complementary sets of hydrogen bonding building blocks to generate porous molecular crystals, which were crosslinked through thiol-ene/yne single-crystal-to-single-crystal transformations. The generated HCOFs exhibit enhanced chemical durability, high crystallinity, and extraordinary framework dynamics. For instance, HCOF-104 crystals featuring a pore diameter of 13.6 Å expanded in DMF to 300 ± 10% of their original lengths within just 1 min. This expansion allows the HCOFs to adsorb guest molecules that are significantly larger than the pore sizes of their crystalline states. Through methanol-induced contraction, these large guests were encapsulated in the fast-contracted HCOFs. These advancements in porous framework dynamics pave the way for new methods of encapsulating guests for targeted delivery.

Streamlining the automated discovery of porous organic cages

Self-assembly through dynamic covalent chemistry (DCC) can yield a range of multi-component organic assemblies. The reversibility and dynamic nature of DCC has made prediction of reaction outcome particularly difficult and thus slows the discovery rate of new organic materials. In addition, traditional experimental processes are time-consuming and often rely on serendipity. Here, we present a streamlined hybrid workflow that combines automated high-throughput experimentation, automated data analysis, and computational modelling, to accelerate the discovery process of one particular subclass of molecular organic materials, porous organic cages. We demonstrate how the design and implementation of this workflow aids in the identification of organic cages with desirable properties. The curation of a precursor library of 55 tri- and di-topic aldehyde and amine precursors enabled the experimental screening of 366 imine condensation reactions experimentally, and 1464 hypothetical organic cage outcomes to be computationally modelled. From the screen, 225 cages were identified experimentally using mass spectrometry, 54 of which were cleanly formed as a single topology as determined by both turbidity measurements and 1H NMR spectroscopy. Integration of these characterisation methods into a fully automated Python pipeline, named cagey, led to over a 350-fold decrease in the time required for data analysis. This work highlights the advantages of combining automated synthesis, characterisation, and analysis, for large-scale data curation towards an accessible data-driven materials discovery approach.

Modular Strategy for Constructing para-Cage[n]arenes, meta-Cage[n]arenes, and meta-Bimacrocyclic-Arenes

Here, we present a versatile modular strategy for crafting novel covalent organic cages (para-cage[n]arenes and meta-cage[n]arenes, n = 3,4) and bimacrocycles (meta-bimacrocyclic-arenes) with stable backbones and modifiable rims. These structures can be synthesized from commercially available aromatic multialdehydes in a three-step process: quantitative bromination, Suzuki-Miyaura reaction (yielding over 60%), and a rapid one-pot Friedel-Crafts reaction with paraformaldehyde. Notably, the cage[n]arenes exhibit a well-defined prismatic shape, and the bimacrocyclic-arenes display both dimeric and monomeric configurations.

3D-Printed Porous Supramolecular Sorbents for Cobalt Recycling

Electronic waste recycling is a recognized global challenge that requires new strategies to bind and release critical materials selectively, such as cobalt present in lithium-ion batteries. To address this challenge, hierarchical 3D-printed porous polymer scaffolds bearing supramolecular receptors were prepared using vat photopolymerization and their cobalt binding profiles were examined as a function of matrix polarity. By combining high-resolution digital light processing (DLP) with polymerization-induced phase separation (PIPS), functional acrylic copolymer networks with micrometer-level precision of geometry and nanometer-level pores were generated. Covalent integration of a methacrylate-functionalized bisdicyclohexyl acetamide (BDCA-MA) receptor enabled binding and release of cobalt(II) chloride (CoCl2) via a solvent polarity switch mechanism involving a change in solvent from ethanol to water. The present structures proved reusable as shown by sustained high binding efficiency over five bind and release cycles. This platform represents a "green" and energy conscious method for future electronic waste recycling.

Tuning CH Hydrogen Bond-Based Receptors toward Picomolar Anion Affinity via the Inductive Effect of Distant Substituents

Inspired by nature, artificial hydrogen bond-based anion receptors have been developed to achieve high anion selectivity; however, their binding affinity is usually low. The potency of these receptors is usually increased by the introduction of aryl substituents, which withdraw electrons from their binding site through the resonance effect. Here, we show that the polarization of the C(sp3 )-H binding site of bambusuril receptors, and thus their potency to bind anions, can be modulated by the inductive effect. The presence of electron-withdrawing groups on benzyl substituents of bambusurils significantly increases their binding affinities to halides, resulting in the strongest iodide receptor reported to date with an association constant greater than 1013  M-1 in acetonitrile. A Hammett plot showed that while the bambusuril affinity toward halides linearly increases with the electron-withdrawing power of their substituents, their binding selectivity remains essentially unchanged.