Molecular Recognition with Macrocyclic Receptors for Application in Precision Medicine

Photoinduced Proton-Transfer-Mediated Molecular Recognition in Molecular Crystals

Molecular recognition has traditionally been focused on ground-state interactions. However, leveraging photoenergy to access excited-state molecular recognition, which may enable enhanced sensitivity or selectivity that is unattainable in the ground state, remains underexplored. In this study, we demonstrate a novel photoinduced molecular recognition mechanism using self-assembled crystalline microribbons composed of a donor-acceptor (D-A) molecule with a twisted molecular backbone for ultratrace phenol vapor detection. We confirm that photoinduced proton transfer occurs from phenol to the C═N group in the pyridine moiety of the D-A system, generating a protonated D-A molecule and a phenoxide ion that triggers fluorescence quenching. This proton-transfer-mediated recognition mechanism endows the microribbons with exceptional sensitivity and selectivity toward phenol vapor, achieving a limit of detection (LOD) of 0.6 parts per trillion (ppt). Our findings reveal that harnessing light energy to drive molecular recognition opens new avenues for advancing fluorescence sensing technologies.

Exploring Supramolecular Frustrated Lewis Pairs

Frustrated Lewis pairs (FLPs) have rapidly become one of the key metal-free catalysts for a variety of chemical transformations. Embedding these catalysts within a supramolecular assembly can offer improvements to factors such as recyclability and selectivity. In this review we discuss advances in this area, covering key supramolecular assemblies such as metal organic frameworks (MOFs), covalent organic frameworks (COFs), polymers and macrocycles.

α-Synuclein targeted therapy with multiple pathological improvement for Parkinson's disease by macrocyclic amphiphile nanomedicine

The toxic species formed by the pathological aggregation of α-synuclein (α-Syn) is one of the core pathogenic mechanisms in Parkinson's disease, leading to mitochondrial dysfunction, oxidative stress and ultimately degeneration and loss of dopaminergic neurons. Developing effective inhibitors targeting α-Syn fibrillization critically requires the simultaneous achievement of (1) strong and selective binding of α-Syn for efficient disintegration of fibrils, as well as (2) robust transmembrane capability for efficient cellular uptake. Herein, the co-assembly of guanidinium-modified calixarene (GCA) and cyclodextrin (CD), termed GCA-CD, is screened fully accommodating these conditions. GCA-CD binds tightly and selectively towards α-Syn, thereby effectively inhibiting α-Syn aggregation and disintegrating its fibrils, meanwhile the guanidinium of GCA can additionally improve the transmembrane capability of the co-assembly. In vivo investigations demonstrate that the GCA-CD nanomedicine significantly rescues motor deficits and nigrostriatal degeneration of PD-like rats by decreasing the content of α-Syn as well as restoring mitochondrial dysfunction and suppressing oxidative stress. Astonishingly, transcriptome analysis further reveals the role of GCA-CD in dampening cuproptosis through inhibiting FDX1/LIAS signaling pathway, highlighting the multifaceted therapeutic effects of the co-assembly in PD. The findings in this study underscore the comprehensive exposition on the actual function mechanisms of the therapeutic agents, thereby providing valuable insights for informing material design.

High-affinity 1 : 2 recognition based on naphthyl-azocalix[4]arene and its application as a cleavable noncovalent connector in constructing responsive supramolecular polymeric materials

Macrocyclic hosts which can bind two guests simultaneously with high affinity, such as cucurbit[8]uril, are highly useful for a wide range of applications by acting as noncovalent connectors. However, the integration of stimuli-controlled release properties into such robust noncovalent connectors would be even more desirable. Here, we introduce Naph-SAC4A, a naphthyl-extended deep-cavity azocalix[4]arene with hypoxia-responsiveness, which exhibits exceptional 1 : 2 hosting abilities for organic dyes in aqueous solution with affinities ranging from 1014 to 1016 M-2. Furthermore, Naph-SAC4A was employed as a robust hypoxia-cleavable noncovalent connector to construct linear supramolecular polymers and crosslinked supramolecular hydrogels. Both structures exhibit responsiveness to hypoxic stimuli. With its high-affinity 1 : 2 recognition, unique hypoxia-responsiveness, and easy accessibility, Naph-SAC4A holds great potential for smart supramolecular polymeric materials.

Ultrahigh-Affinity Molecular Recognition in Water and Biomedical Applications

Aqueous-phase molecular recognition pairs with ultrahigh binding affinity hold immense value in biotechnology and chemical applications. However, the rational design of synthetic pairs with such exceptional binding strength has long remained a significant challenge, with notable progress achieved only in recent years. In this minireview, we begin by defining the term "ultrahigh-affinity" through a comprehensive analysis of available data on aqueous-phase molecular recognition by water-soluble macrocyclic hosts. Based on this foundation, we provide a detailed overview of the latest advancements in various classes of ultrahigh-affinity receptors, extracting key design principles that drive their remarkable performance. We further highlight emerging applications of ultrahigh-affinity molecular pairs in biomedical materials, spanning bioorthogonal chemistry, biosensing, bioimaging, drug delivery, and toxin sequestration. These examples underscore the transformative potential of ultrahigh-affinity recognition in addressing real-world biomedical challenges. Finally, we offer a forward-looking perspective on the future of this rapidly evolving field, exploring potential directions for designing more diverse and functional ultrahigh-affinity molecular recognition tools. By bridging the gap between fundamental science and practical applications, this minireview aims to inspire the development of next-generation molecular recognition systems and foster deeper integration between supramolecular chemistry and biomedical materials, paving the way for innovative solutions to pressing biomedical needs.

Alexidine and Pentamidine Fold Inside the Bowl-shaped Cavity of p-Sulfonato-calix[4]arene

We report on the U-shaped folding of flexible guest molecules of medicinal interest upon their inclusion into macrocyclic cavity of p-sulfonato-calix[4]arene in aqueous media. Alexidine and pentamidine are FDA-approved drug compounds currently rediscovered as potent membrane-targeting antibiotic adjuvants helping restore antibiotic activity against multidrug resistant bacteria pathogens. We have adopted host-guest and crystal engineering approach to study these drugs with a view of potential supramolecular formulations and/or crystal forms. We focus on the host-guest conformational and structural behaviour of alexidine and pentamidine under macrocyclic confinement conditions benefitting from single crystal X-ray diffraction analysis, self-assembly studies in solution by NMR spectroscopy, dynamic light scattering and atomic force microscopy, and ion mobility mass spectrometry (IM-MS) analysis complemented by theoretical calculations. Our findings show that the simple bowl-shaped host promotes conformational fixing and crystallization of these guest molecules of high conformational freedom that are otherwise challenging to crystallize. The IM-MS structural studies of p-sulfonato-calix[4]arene complexes with pentamidine and alexidine revealed significant guest reorganization in the solution/gas phase, compared to the binding modes observed in the crystal structures. Despite these changes, the host-guest complexation remained consistent, with new interactions highlighting the increased role of electrostatic forces in the gas phase.

Dendritic Molecular Baskets for Selective Binding of Toxic Methotrexate

We describe the preparation, assembly, recognition characteristics, and bioactivity of dendritic basket 612-. This novel cavitand has a deep aromatic pocket with three (S)-glutamic acid dendrons at the rim to amplify water solubility and prevent self-association. 1H NMR spectroscopy, calorimetry (ITC), and mass spectrometry (ESI-MS) measurements validate the formation of an inclusion complex between 612- and anticancer drug methotrexate (MTX2-) in water (Kd=9.2 μM). To identify the docking pose, a comparison of computed (DFT and MM) and experimental 1H NMR chemical shifts suggests that MTX2- folds inside 612- (π⋅⋅⋅π), forming HBs with the peptidic dendrons while anchoring (C-H⋅⋅⋅π) to the aromatic pocket through its N-methyl group. In consequence, 612- selectively binds MTX2- in competition with structurally similar folic acid and leucovorin (reversal poisoning agent). While the host is biocompatible (HEK293; IC50>150 μM) and produces inclusion complex [MTX⊂6]14- in cell media, it experiences limitation in pharmacokinetic sequestration of MTX2- as dihydrofolate reductase's affinity to the drug is suggested to prevail over that of 612-. Nonetheless, considering the basket's biocompatibility, tunability, and chemoselectivity, it stands as the leading candidate in the pursuit of an effective abiotic antidote for methotrexate poisoning.

The matere bond

This perpective delves into the emerging field of matere bonds, a novel type of noncovalent interaction involving group 7 elements such as manganese, technetium, and rhenium. Matere bonds, a new member of the σ-hole family where metal atoms act as electron acceptors, have been shown experimentally and theoretically to play significant roles in the self-assembly and stabilization of supramolecular structures both in solid-state and solution-phase environments. This perspective article explores the physical nature of these interactions, emphasizing their directionality and structural influence in various supramolecular architectures. Recent studies have expanded the understanding of matere bonds beyond classical metal-ligand coordination, highlighting their potential in crystal engineering and catalysis. This perspective article also examines the occurrence of matere bonds in biological systems, particularly within manganese-containing proteins, where they contribute to the structural integrity and catalytic activity. Theoretical and computational analyses, including molecular electrostatic potential surfaces and density functional theory, further elucidate the properties and applications of matere bonds, offering new insights for the design of advanced materials and biomimetic systems. This comprehensive overview underscores the versatility of matere bonds, paving the way for future innovations in supramolecular chemistry involving metals.

Metal-Free Electrocatalytic Alkaline Water Splitting by Porous Macrocyclic Proton Sponges

Macrocycles are unique as they encapsulate and transfer guest molecules or ions and facilitate catalytic processes. Although metalated macrocycles are pivotal in electrocatalytic processes, using metal-free analogs has been rare. Following the strategy of Kanbara et al., we synthesized an azacalixarene macrocycle-N, N', N''-tris(p-aminophenyl)azacalix[3](2,6)pyridine (CalixNH2). The macrocycle encapsulates a proton in its cavity, maintaining the protonation even in highly alkaline media. Notably, it retains almost 50 % protonated form in 1 M KOH (~pH 14)-acting as a proton sponge. As hydrogen evolution is complex in alkaline media owing to sluggish water dissociation, we implemented the proton sponge (CalixNH2) in an alkaline hydrogen evolution reaction. Conjugated Porous polymers, TpCalix and DhaCalix, have been synthesized from the triamine-CalixNH2. The most efficient catalyst, TpCalix, has shown excellent performance in alkaline HER and OER in 1 M KOH (~pH 14), with low overpotentials of only 112(±2) and 290(±2) mV at 10 mA cm-2, respectively, and durable up to 24 hours. A full-cell reaction using TpCalix in both the cathode and anode exhibited a low full-cell voltage of 1.73 V and was stable for 12 hours. DFT calculations verified the tripyridinic core, which acts as the principal site for proton abstraction and binding.

Supramolecular Organic Framework that Enables Multifunctional Doxorubicin Delivery, Photofrin Post-treatment Phototoxicity Inhibition, and Heparin Neutralization

Although porous frameworks are structurally ideal for the development of biomaterials through drug adsorption, sequestration, and delivery, integration of multiple biofunctions into a biocompatible porous framework would greatly improve its potential for preclinical investigations by increasing both therapeutic value and research and development efficiency. Herein, we report the preparation of a highly biocompatible supramolecular organic framework from an imidazolium-derived tetrahedral monomer and cucurbit[8]uril. The supramolecular organic framework has been revealed to have regular intrinsic porosity and adsorb doxorubicin, photofrin, and heparins driven by hydrophobicity and/or ion-pairing electrostatic interactions. In vivo or in vitro assays illustrate that this adsorption leads to efficient intracellular delivery of doxorubicin, which enhances its antitumor efficacy, elimination of photofrin, which inhibits its post-treatment phototoxicity without reducing its photodynamic therapeutic activity, and sequestration of (low-molecular-weight) heparins, which neutralizes their anticoagulation activity more efficiently than clinically used protamine.

Bioinspired Ion Host with Buried and Consecutive Binding Sites for Controlled Ion Dislocation

This study presents a bioinspired ion host featuring continuous binding sites arranged in a tunnel-like structure, closely resembling the selectivity filter of natural ion channels. Our investigation reveals that ions traverse these sites in a controlled, sequential manner due to the structural constraints, effectively mimicking the ion translocation process observed in natural channels. Unlike systems with open binding sites, our model facilitates sequential ion recognition state transitions, enabled by the deliberate design of the tunnel. Notably, we observe dual ion release kinetics, highlighting the system's capacity to maintain ion balance in complex environments and adapt to changing conditions. Additionally, we demonstrate selective binding of two different ions-a challenging task for systems lacking structured tunnels.

Macrocyclic receptors for anion recognition

Macrocyclic receptors have emerged as versatile and efficient molecular tools for the recognition and sensing of anions, playing a pivotal role in molecular recognition and supramolecular chemistry. The following review provides an overview of the recent advances in the design, synthesis, and applications of macrocyclic receptors specifically tailored for anion recognition. The unique structural features of macrocycles, such as their well-defined structures and pre-organised binding sites, contribute to their exceptional anion-binding capabilities that have led to their application across a broad range of the chemical and biological sciences.

Sulfonated Azocalix[4]arene: A Universal and Effective Taste-Masking Agent

Many active pharmaceutical ingredients have a specific bitter taste. To enhance patient compliance and treatment efficacy, taste-masking agents are crucial in oral drug formulations. Confronting numerous bitter drug molecules with varied structures, the pharmaceutical field strives to explore and develop universal and effective masking approaches. Here, we reported sulfonated azocalix[4]arene (SAC4A), a universal supramolecular masking agent with deep cavity that provides stronger hydrophobic effect and larger interaction area during recognition, allowing high binding affinity to bitter drug molecules. Moreover, bitter drugs could deeply buried in the cavity, with the bitterness effectively masked. As a result, SAC4A can bind to 16 different bitter drugs with high affinities, encompassing alkaloids, flavonoids, terpenoids, and more, while maintaining high biocompatibility. As anticipated, SAC4A effectively masks the unpalatable bitter taste associated with these drugs. Consequently, SAC4A is a promising universal and effective supramolecular masking agent.

Analyzing urinary hippuric acid as a metabolic health biomarker through a supramolecular architecture

The prevalence of metabolic disorders has been found to increase concomitantly with alternations in habitual diet and lifestyle, indicating the importance of metabolic health monitoring for early warning of high-risk status and suggesting effective intervention strategies. Hippuric acid (HA), as one of the most abundant metabolites from the gut microbiota, holds potential as a regulator of metabolic health. Accordingly, it is imperative to establish an efficient, sensitive, and affordable method for large-scale population monitoring, revealing the association between HA level and metabolic disorders. Upon systematic screening of macrocycle•dye reporter pair, a supramolecular architecture (guanidinomethyl-modified calix[5]arene, GMC5A) was employed to sense urinary HA by employing fluorescein (Fl), whose complexation behavior was demonstrated by theoretical calculations, accomplishing quantification of HA in urine from 249 volunteers in the range of 0.10 mM and 10.93 mM. Excitedly, by restricted cubic spline, urinary HA concentration was found to have a significantly negative correlation with the risk of metabolic disorders when it exceeded 0.76 mM, suggesting the importance of dietary habits, especially the consumption of fruits, coffee, and tea, which was unveiled from a simple questionnaire survey. In this study, we accomplished a high throughput and sensitive detection of urinary HA based on supramolecular sensing with the GMC5A•Fl reporter pair, which sheds light on the rapid quantification of urinary HA as an indicator of metabolic health status and early intervention by balancing the daily diet.

Mixed host co-assembled systems for broad-scope analyte sensing

Here we report a systems chemistry oriented approach for developing information-rich mixed host chemosensors. We show that co-assembling macrocyclic hosts from different classes, DimerDye sulfonatocalix[4]arenes and cucurbit[n]urils, effectively increases the scope of analyte binding interactions and therefore, sensory outputs. This simple dynamic strategy exploits cross-reactive noncovalent host-host complexation interactions while integrating a reporter dye, thereby producing emergent photophysical responses when an analyte interacts with either host. We first demonstrate the advantages of mixed host co-assembled chemosensors through an increased detection range of hydrophobic, cationic, neutral, and anionic drugs. We then implement mixed host sensors in an array-based platform for the differentiation of illicit drugs, including cannabinoids, benzodiazepine analogs, opiates, anesthetics, amphetamine, and common adulterating substances. Finally, the potential of this approach is applied to profiling real-world multi-component illicit street drug samples, proving to be more effective than classical sensor arrays.

Co-Assembled Nanoparticles toward Multi-Target Combinational Therapy of Alzheimer's Disease by Making Full Use of Molecular Recognition and Self-Assembly

The complex pathologies in Alzheimer's disease (AD) severely limit the effectiveness of single-target pharmic interventions, thus necessitating multi-pronged therapeutic strategies. While flexibility is essentially demanded in constructing such multi-target systems, for achieving optimal synergies and also accommodating the inherent heterogeneity within AD. Utilizing the dynamic reversibility of supramolecular strategy for conferring sufficient tunability in component substitution and proportion adjustment, amphiphilic calixarenes are poised to be a privileged molecular tool for facilely achieving function integration. Herein, taking β-amyloid (Aβ) fibrillation and oxidative stress as model combination pattern, a supramolecular multifunctional integration is proposed by co-assembling guanidinium-modified calixarene with ascorbyl palmitate and loading dipotassium phytate within calixarene cavity. Serial pivotal events can be simultaneously addressed by this versatile system, including 1) inhibition of Aβ production and aggregation, 2) disintegration of Aβ fibrils, 3) acceleration of Aβ metabolic clearance, and 4) regulation of oxidative stress, which is verified to significantly ameliorate the cognitive impairment of 5×FAD mice, with reduced Aβ plaque content, neuroinflammation, and neuronal apoptosis. Confronted with the extremely intricate clinical realities of AD, the strategy presented here exhibits ample adaptability for necessary alterations on combinations, thereby may immensely expedite the advancement of AD combinational therapy through providing an exceptionally convenient platform.

Expanding the Hydrophobic Cavity Surface of Azocalix[4]arene to Enable Biotin/Avidin Affinity with Controlled Release

The development of artificial receptors that combine ultrahigh-affinity binding and controllable release for active guests holds significant importance in biomedical applications. On one hand, a complex with an exceedingly high binding affinity can resist unwanted dissociation induced by dilution effect and complex interferents within physiological environments. On the other hand, stimulus-responsive release of the guest is essential for precisely activating its function. In this context, we expanded hydrophobic cavity surface of a hypoxia-responsive azocalix[4]arene, affording Naph-SAC4A. This modification significantly enhanced its aqueous binding affinity to 1013 M-1, akin to the naturally occurring strongest recognition pair, biotin/(strept-)avidin. Consequently, Naph-SAC4A emerges as the first artificial receptor to simultaneously integrate ultrahigh recognition affinity and actively controllable release. The markedly enhanced affinity not only improved Naph-SAC4A's sensitivity in detecting rocuronium bromide in serum, but also refined the precision of hypoxia-responsive doxorubicin delivery at the cellular level, demonstrating its immense potential for diverse practical applications.

Single Molecular Nanomedicines Based on Macrocyclic Carrier-Drug Conjugates for Concentration-Independent Encapsulation and Precise Activation of Drugs

Nanomedicines often rely on noncovalent self-assembly and encapsulation for drug loading and delivery. However, challenges such as reproducibility issues due to the multicomponent nature, off-target activation caused by premature drug release, and complex pharmacokinetics arising from assembly dissociation have hindered their clinical translation. In this study, we introduce an innovative design concept termed single molecular nanomedicine (SMNM) based on macrocyclic carrier-drug conjugates. Through the covalent linkage of two chemotherapy drugs to a hypoxia-cleavable macrocyclic carrier, azocalix[4]arene, we obtained two self-included complexes to serve as SMNMs. The intramolecular inclusion feature of the SMNMs has not only demonstrated comprehensive shielding and protection for the drugs but also effectively prevented off-target drug leakage, thereby significantly reducing their side effects and enhancing their antitumor therapeutic efficacy. Additionally, the attributes of being a single component and molecularly dispersed confer advantages such as ease of preparation and good reproducibility for SMNMs, which is desirable for clinical applications.

Pillarurilarenes: Glycoluril-Expanded Pillararenes

Glycoluril-expanded pillararenes composed of glycoluril and dialkoxybenzene units, namely, pillarurilarenes (PURA), were synthesized through a fragment coupling macrocyclization strategy. Partial replacement of dialkoxybenzene with glycoluril endows PURA with polarized equatorial methine protons for derivatization or CH-anion binding. Crystal structures of pillar[2]uril[4]arene and pillar[1]uril[4]arene containing two glycoluril units and one glycoluril unit, respectively, indicated the inward orientation of the glycoluril unit, as also suggested by 1H nuclear magnetic resonance and density functional theory calculation. This work lays a good foundation for expanding pillararenes using non-aromatic rings.

Sulfonated Azocalix[4]arene-Modified Metal-Organic Framework Nanosheets for Doxorubicin Removal from Serum

Chemotherapy is one of the most commonly used methods for treating cancer, but its side effects severely limit its application and impair treatment effectiveness. Removing off-target chemotherapy drugs from the serum promptly through adsorption is the most direct approach to minimize their side effects. In this study, we synthesized a series of adsorption materials to remove the chemotherapy drug doxorubicin by modifying MOF nanosheets with sulfonated azocalix[4]arenes. The strong affinity of sulfonated azocalix[4]arenes for doxorubicin results in high adsorption strength (Langmuir adsorption constant = 2.45-5.73 L mg-1) and more complete removal of the drug. The extensive external surface area of the 2D nanosheets facilitates the exposure of a large number of accessible adsorption sites, which capture DOX molecules without internal diffusion, leading to a high adsorption rate (pseudo-second-order rate constant = 0.0058-0.0065 g mg-1 min-1). These adsorbents perform effectively in physiological environments and exhibit low cytotoxicity and good hemocompatibility. These features make them suitable for removing doxorubicin from serum during "drug capture" procedures. The optimal adsorbent can remove 91% of the clinical concentration of doxorubicin within 5 min.

Pillar[6]MaxQ functions as an in vivo sequestrant for rocuronium and vecuronium

The binding affinity of pillar[6]MaxQ toward a panel of neuromuscular blockers and neurotransmitters was measured in phosphate buffered saline by isothermal titration calorimetry and 1H NMR spectroscopy. In vivo efficacy studies showed that P6MQ sequesters rocuronium and vecuronium and reverses their influence on the recovery of the train-of-four (TOF) ratio.

Optically Pure Calixarenyl Phosphine via Stereospecific Alkylation on Evans' Oxazolidinone Moiety

A convenient protocol for the synthesis of 25,26,27-tribenzoyl-28-[((S)-1-diphenylphos- phanyl-propan-2-yl)oxy]-calix[4]arene via stereospecific methylation on Evans' oxazolidinone moiety was reported. According to the 13C NMR analysis of this phosphine, the calix[4]arene skeleton adopted a 1,3-alternate conformation. The latter conformation of the macrocycle and the (S)-chirality of the carbon atom bearing the methyl substituent were confirmed by a single-crystal X-ray diffraction study. After coordination of the phosphinated ligand to the dimeric [RuCl2(p-cymene)]2 organometallic precursor, the resulting arene-ruthenium complex was tested in the asymmetric reduction of acetophenone and alcohol was obtained with modest enantiomeric excess.