Acyclic Cucurbit[n]uril Receptors Function as Solid State Sequestrants for Organic Micropollutants

The accumulation of organic micropollutants (OMP) in aquatic systems is a major societal problem that can be addressed by approaches including nanofiltration, flocculation, reverse osmosis and adsorptive methods using insoluble materials (e.g. activated carbon, MOFs, nanocomposites). More recently, polymeric versions of supramolecular hosts (e.g. cyclodextrins, calixarenes, pillararenes) have been investigated as OMP sequestrants. Herein, we report our study of the use of water insoluble dimethylcatechol walled acyclic cucurbit[n]uril (CB[n]) hosts as solid state sequestrants for a panel of five OMPs. A series of hosts (H1-H4) were synthesized by reaction of glycoluril oligomer (monomer-tetramer) with 3,6-dimethylcatechol and fully characterized by spectroscopic means and x-ray crystallography. The solid hosts sequester OMPs from water with removal efficiencies exceeding 90 % in some cases. The removal efficiencies of the new hosts parallel the known molecular recognition properties of analogous water soluble acyclic CB[n]. OMP uptake by solid host occurs rapidly (≈120 seconds). Head-to-head comparison with CB[6] in batch-mode separation and DARCO activated carbon in flow-through separation mode show that tetramer derived host (H4) performs very well under identical conditions. The work establishes insoluble acyclic CB[n]-type receptors as a promising new platform for OMP sequestration.

Enantiopure Corral[4]BINOLs as Ultrastrong Receptors for Recognition and Differential Sensing of Steroids

The precise recognition and sensing of steroids, a type of vital biomolecules, hold immense practical value across various domains. In this study, we introduced corral[4]BINOLs (C[4]BINOLs), a pair of enantiomeric conjugated deep-cavity hosts, as novel synthetic receptors for binding steroids. Due to the strong hydrophobic effect of their deep nonpolar, chiral cavities, the two enantiomers of C[4]BINOLs demonstrated exceptionally high recognition affinities (up to 1012 M-1) for 16 important steroidal compounds as well as good enantioselectiviy (up to 15.5) in aqueous solutions, establishing them as the most potent known steroid receptors. Harnessing their ultrahigh affinity, remarkable enantioselectivity, and fluorescence emission properties, the two C[4]BINOL enantiomers were employed to compose a fluorescent sensor array which achieved discrimination and sensing of 16 structurally similar steroids at low concentrations.

Metal-Organic Cage Receptors for Encapsulation and Sensing of Bile Acids

Developing synthetic supramolecular receptors to solubilize, scavenge, recognize, encapsulate, and sense steroids is challenging. Despite a limited number of receptors having affinity with steroids, none exists to bind steroidal bile acids selectively. Herein, we report a C2-symmetric metal-organic cage [Pd6L24]12+ and an expanded version of the Fujita cage [Pd6L14]12+, built with a conformationally flexible ligand L2, accessed through coordination-driven self-assembly. We examined both cages for steroid recognition in water: both have certain shared characteristics and distinctive features. [Pd6L14]12+ binds hydrophobic bile acids and other steroids by forming a 1:1 complex. In contrast, the expanded [Pd6L24]12+ cage exhibits an affinity for amphiphilic bile acids and selective steroids to encapsulate them as dimers, promoted by cooperative interguest hydrogen bonding. [Pd6L24]12+ has a 5 times stronger solubility enhancement ability for cholic acid compared to [Pd6L14]12+. Further, the expanded [Pd6L24]12+ cage can selectively sense bile acids in nanomolar detection limits through indicator displacement assay by employing sulforhodamine 101 (SR101).

Trapping and reversing neuromuscular blocking agent by anionic pillar[5]arenes: Understanding the structure-affinity-reversal effects

Selective relaxant binding agents (SRBA) have great potential in clinical surgeries for the precise reversal of neuromuscular blockades. Understanding the relationship between the structure-affinity-reversal effects of SRBA and neuromuscular blockade is crucial for the design of new SRBAs, which has rarely been explored. Seven anionic pillar[5]arenes (AP5As) with different aliphatic chains and anionic groups at both edges were designed. Their binding affinities to the neuromuscular blocking agent decamonium bromide (DMBr) were investigated using 1H NMR, isothermal titration calorimetry (ITC), and theoretical calculations. The results indicate that the capture of DMBr by AP5As is primarily driven by electrostatic interactions, ion-dipole interactions and C-H‧‧‧π interactions. The optimal size matching between the carboxylate AP5As and DMBr was ∼0.80. The binding affinity increased with an increase in the charge quantity of AP5As. Further animal experiments indicated that the reversal efficiency increased with increasing binding affinity for carboxylate or phosphonate AP5As. However, phosphonate AP5As exhibited lower reversal efficiencies than carboxylate AP5As, despite having stronger affinities with DMBr. By understanding the structure-affinity-reversal relationships, this study provides valuable insights into the design of innovative SRBAs for reversing neuromuscular blockade.

Phosphorescent acyclic cucurbituril solid supramolecular multicolour delayed fluorescence behaviour

Organic photoluminescent macrocyclic hosts have been widely advanced in many fields. Phosphorescent hosts with the ability to bind organic guests have rarely been reported. Herein, acyclic cucurbituril modified with four carboxylic acids (ACB-COOH) is mined to present uncommon purely organic room-temperature phosphorescence (RTP) at 510 nm with a lifetime of 1.86 μs. Its RTP properties are significantly promoted with an extended lifetime up to 2.12 s and considerable quantum yield of 6.29% after assembly with a polyvinyl alcohol (PVA) matrix. By virtue of the intrinsic self-crimping configuration of ACB-COOH, organic guests, including fluorescence dyes (Rhodamine B (RhB) and Pyronin Y (PyY)) and a drug molecule (morphine (Mor)), could be fully encapsulated by ACB-COOH to attain energy transfer involving phosphorescent acyclic cucurbituril. Ultimately, as-prepared systems are successfully exploited to establish multicolor afterglow materials and visible sensing of morphine. As an expansion of phosphorescent acyclic cucurbituril, the host afterglow color can be readily regulated by attaching different aromatic sidewalls. This study develops the fabrication strategies and application scope of a supramolecular phosphorescent host and opens up a new direction for the manufacture of intelligent long-lived luminescent materials.

Macrocycles and Acyclic Cucurbit[n]urils as Pseudo[2]catenane Partners for Long-Acting Neuromuscular Blocks and Rapid Reversal In Vivo

Long-acting neuromuscular blocks followed by rapid reversal may provide prolonged surgeries with improved conditions by omitting repetitive or continuous administration of the neuromuscular blocking agent (NMBA), eliminating residual neuromuscular block and minimizing postoperative recovery, which, however, is not clinically available. Here, we demonstrate that imidazolium-based macrocycles (IMCs) and acyclic cucurbit[n]urils (ACBs) can form such partners by functioning as long-acting NMBAs and rapid reversal agents through a pseudo[2]catenation mechanism based on stable complexation with Ka values of over 109 M-1. In vivo experiments with rats reveal that, at the dose of 2- and 3-fold ED90, one IMC attains a duration of action corresponding to 158 or 442 min for human adults, covering most of prolonged surgeries. The block can be reversed by one ACB with recovery time significantly shorter than that achieved by sugammadex for reversing the block of rocuronium, the clinically most widely used intermediate-acting NMBA.

Water-soluble terphen[3]arene macrocycle: a versatile reversal agent of neuromuscular blockers

Herein we report the design and synthesis of a terphen[n]arene derivative functionalised with sulfate acid ester groups. This water-soluble terphen[3]arene host effectively encapsulates a multitude of neuromuscular blocking agents (NMBAs) with high affinity, showing great potential as a NMBAs reversal agent in pharmaceutical research.

Host-guest binding of tetracationic cyclophanes to photodynamic agents inhibits posttreatment phototoxicity and maintains antitumour efficacy

In the past two decades, photodynamic therapy (PDT) has become an effective method for the treatment of cancer. However, the posttreatment residue of photodynamic agents (PDAs) causes long-term skin phototoxicity. Here, we apply naphthalene-derived, box-like tetracationic cyclophanes, named NpBoxes, to bind to clinically used porphyrin-based PDAs to alleviate their posttreatment phototoxicity by reducing their free content in skin tissues and 1O2 quantum yield. We show that one of the cyclophanes, 2,6-NpBox, could include the PDAs to efficiently suppress their photosensitivity for the generation of reactive oxygen species. A tumour-bearing mouse model study revealed that, when Photofrin, the most widely used PDA in clinic, was administrated at a dose corresponding to the clinical one, 2,6-NpBox of the same dose could significantly suppress its posttreatment phototoxicity on the skin induced by simulated sunlight irradiation, without imposing a negative influence on its PDT efficacy.

Highly Water-Soluble Cucurbit[8]uril Derivative as a Broad-Spectrum Neuromuscular Block Reversal Agent

Broad-spectrum agents for the reversal of residual curarization induced by neuromuscular blocking agents are of great significance. Here, we report a highly water-soluble cucurbit[8]uril (CB[8]) derivative as a broad-spectrum neuromuscular block reversal agent induced by both benzylisquinolinium and aminosteroid neuromuscular block agents by the supramolecular sequestration strategy. The UV/Vis competition titration assays suggest the high binding affinity of the CB[8] derivative toward both benzylisquinolinium-type cisatracurium besylate and aminosteroid-type rocuronium, vecuronium, and pancuronium, at the level of 10⁷ M^-1. In vivo studies demonstrate that the administration of the CB[8] derivative could significantly accelerate the recovery time compared to the placebo or neostigmine groups. The reversal activity of the CB[8] derivative is comparable to or higher than that of clinically approved sugammadex. Acute toxicity evaluations reveal that the CB[8]-derivative displays outstanding biocompatibility, with the maximum tolerance dose as high as 960 mg kg^-1.

Drug in Drug: A Host-Guest Formulation of Azocalixarene with Hydroxychloroquine for Synergistic Anti-Inflammation

Macrocyclic delivery and therapeutics are two significant topics in supramolecular biomedicine. The functional integration of these topics would open new avenues for treating diseases synergistically. However, these two individual topics have only been occasionally merged, probably because of the lack of functionalized design of macrocyclic host and the lack of efficient recognition between host and guest drugs. Herein, a "drug-in-drug" strategy is proposed, in which an active drug is encapsulated by a macrocycle possessing therapeutic activity to form a multifunctional supramolecular active pharmaceutical ingredient. As a proof-of-concept, a complex of hydroxychloroquine (HCQ) with sulfonated azocalix[4]arene (HCQ@SAC4A) is prepared to treat rheumatoid arthritis (RA) in a combined fashion. SAC4A is a therapeutic agent that exhibits scavenging capacity for reactive oxygen species and exerts an anti-inflammatory effect. It is also a hypoxia-responsive carrier that can deliver HCQ directly to the inflammatory articular cavity. Consequently, HCQ@SAC4A achieves the synergistic anti-inflammatory effect on both inflamed RAW 264.7 cells and RA rats. This effect is attributed to the temporal and spatial consistency of the two active ingredients of the complex. As a new paradigm for combinational therapy, the drug-in-drug strategy advances in easy preparation, mix-and-match combination, and precise ratiometric control.

Synthesis of Glycoluril Dimers with the Ability to Form Polymeric Self-Associates in Water

Supramolecular self-assembly in water resulting in polymeric structures is emerging because of its potential in the preparation of adaptive materials with applications in biology and medicine. Here, we report the first example of host molecules based on glycoluril dimers, which self-associate into linear oligomers in water. The degree of polymerization for the resulting supramolecular aggregates was calculated using the isodesmic model and the Carothers equation. The model compound was prepared to enable a deeper understanding of the forces responsible for the self-association of the glycoluril dimer-based monomers in water.

Functional supramolecular micelles driven by the amphiphilic complex of biotin-acyclic cucurbituril and cannabidiol for cell-targeted drug delivery

Precise delivery of hydrophobic drugs has always been a great challenge for drug delivery systems. To overcome this problem, we designed and synthesized a novel supramolecular host biotin-acyclic cucurbituril (ACBB) at the first time, and we have developed a host-guest amphiphilic complex based on ACBB and amantadine-conjugated cannabinoids (AD-CBD) that self-assembles to form functionalized supramolecular micelles (FSMs) for cell-targeted drug delivery. The 1:1 stoichiometric ratio of the amphiphilic complex and its possible host-guest inclusion behaviors are obtained by fluorescence titration, nuclear magnetic resonance (NMR), Fourier transform-infrared spectroscopy (FT-IR) and thermal analysis (TGA and DSC). Using transmission electron microscope (TEM) and dynamic light scattering (DLS), we have observed that the shape of FSMs was spherical and size was 137-192 nm. In addition, MTT test results show that FSMs have good antitumor activity, taking MCF-7 as an example, the in vitro half-maximal inhibitory concentration (IC₅₀) values of FSMs were 1.53 μM and 5.02 μM, which were better than 30.83 μM of cisplatin. Confocal laser scanning microscopy (CLSM) results showed that FSMs loaded with Rhodamine B can specifically aggregate on the surface of tumor cells and the targeting ability has been directly verified. Flow cytometry results showed that FSMs could promote tumor cell apoptosis. All results indicated that FSMs had high bioavailability, stability, accurate targeting and excellent delivery efficiency, which had great application potential in the field of drug delivery.

When Molecules Meet in Water-Recent Contributions of Supramolecular Chemistry to the Understanding of Molecular Recognition Processes in Water

Molecular recognition processes in water differ from those in organic solvents in that they are mediated to a much greater extent by solvent effects. The hydrophobic effect, for example, causes molecules that only weakly interact in organic solvents to stay together in water. Such water‐mediated interactions can be very efficient as demonstrated by many of the synthetic receptors discussed in this review, some of which have substrate affinities matching or even surpassing those of natural binders. However, in spite of considerable success in designing such receptors, not all factors determining their binding properties in water are fully understood. Existing concepts still provide plausible explanations why the reorganization of water molecules often causes receptor‐substrate interactions in water to be strongly exothermic rather than entropically favored as predicted by the classical view of the hydrophobic effect.

Anthracene Walled Acyclic CB[n] Receptors: In Vitro and In Vivo Binding Properties Toward Drugs of Abuse

We report studies of the interaction of six acyclic CB[n]-type receptors toward a panel of drugs of abuse by a combination of isothermal titration calorimetry and 1H NMR spectroscopy.  Anthracene walled acyclic CB[n] host (M3) displays highest binding affinity toward methamphetamine (Kd = 15 nM) and fentanyl (Kd = 4 nM).  Host M3 is well tolerated by Hep G2 and HEK 293 cells up to 100 mM according to MTS metabolic and adenylate kinase release assays.  An in vivomaximum tolerated dose study with Swiss Webster mice showed no adverse effects at the highest dose studied (44.7 mg kg-1). Host M3 is not mutagenic based on the Ames fluctuation test and does not inhibit the hERG ion channel.  In vivoefficacy studies showed that pretreatment of mice with M3 significantly reduces the hyperlocomotion after treatment with methamphetamine, but M3 does not function similarly when administered 30 seconds after methamphetamine.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Flexible organic frameworks sequester neuromuscular blocking agents in vitro and reverse neuromuscular block invivo

Supramolecular sequestration and reversal of neuromuscular block (NMB) have great clinical applications. Water-soluble flexible organic frameworks (FOFs) cross-linked by disulfide bonds are designed and prepared. Different linker lengths are introduced to FOFs to give them varied pore sizes. FOFs are anionic nanoscale polymers and capable of encapsulating cationic neuromuscular blocking agents (NMBAs), including rocuronium (Roc), vecuronium (Vec), pancuronium (Panc) and cisatracurium (Cis). A host–guest study confirms that FOFs bind NMBAs in water. The multivalency interaction between FOFs and NMBAs is able to sequester NMBAs, and prevent them from escaping. These FOFs are non-toxic and biocompatible. Animal studies show that FOFs are effective for the reversal of NMB induced by Roc, Vec and Cis, which shorten the time to a train-of-four ratio of 0.9 by 2.6, 3.8 and 5.7-fold compared to a placebo, respectively.

Water-soluble flexible organic frameworks are prepared and used to sequester neuromuscular blocking agents, and reverse their neuromuscular block in vivo.

Detoxification of the Toxic Sulfur Mustard Simulant by a Supramolecular Antidote in Vitro and in Vivo

Although great potential hazards and threats still occur from sulfur mustard, there are no specific medicine or therapy for the intoxication of sulfur mustard. Herein, we have demonstrated a supramolecular approach for the detoxification of the sulfur mustard simulant CEES (4) in vitro and in vivo by carboxylatopillar[5]arene potassium salts (CP[5]AK 1) efficiently based on host-guest interactions. The encapsulation of CEES (4) by the cavity of the pillar[5]arene 2 is driven by C-H···π interactions between CEES (4) and the electron-rich cavity of pillar[5]arene 2, which was investigated by 1H NMR titration, density functional theory studies, and the independent gradient model studies. CEES (4) is degradated to the reactive sulfonium salts quickly in aqueous media, resulting in the alkylation of DNA and proteins. The sulfonium salts can be encapsulated by CP[5]AK 1 efficiently, which accelerates the degradation of the sulfonium salts about 14 times. The cell and animal experiments indicated that the bioactivities of the sulfonium salts are inhibited with the formation of stable host-guest complexes, and CP[5]AK 1 has a good therapeutic effect on the damages caused by CEES (4) at either pre- or post-treatments. Due to the low cytotoxicity and good therapeutic effect, the anionic pillar[5]arenes are expected to be developed as specific antidotes against sulfur mustard (HD).

In Vitro and In Vivo Sequestration of Methamphetamine by a Sulfated Acyclic CB[n]-Type Receptor

We report the synthesis of two new acyclic sulfated acyclic CB[n]-type receptors (TriM0 and Me4 TetM0) and investigations of their binding properties toward a panel of drugs of abuse (1-13) by a combination of 1 H NMR spectroscopy and isothermal titration calorimetry. TetM0 is the most potent receptor with Ka ≥106  M-1 toward methamphetamine, fentanyl, MDMA and mephedrone. TetM0 is not cytotoxic toward HepG2 and HEK 293 cells below 100 μM according to MTS metabolic and adenylate kinase release assays and is well tolerated in vivo when dosed at 46 mg kg-1 . TetM0 does not inhibit the hERG ion channel and is not mutagenic based on the Ames fluctuation test. Finally, in vivo efficacy studies show that the hyperlocomotion of mice treated with methamphetamine can be greatly reduced by treatment with TetM0 up to 5 minutes later. TetM0 has potential as a broad spectrum in vivo sequestrant for drugs of abuse.

Template-Directed Synthesis of Bivalent, Broad-Spectrum Hosts for Neuromuscular Blocking Agents*

We report on the synthesis of bivalent water-soluble calix[4]arene and calix[5]arene hosts, Super-sCx4 and Super-sCx5 as new broad-spectrum supramolecular binders of neuromuscular blocking agents (NMBAs). Synthesis was achieved using the target bisquaternary amine NMBAs as a template to link two highly anionic p-sulfonatocalixarene building blocks in aqueous solution. Bivalent anionic hosts Super-sCx4 and Super-sCx5 bind by engaging both quaternary amines present on a variety of NMBAs. We report low μM binding to structurally diverse alkyl, steroidal, curarine and benzylisoquinoline NMBAs with high selectivity over the neurotransmitter acetylcholine and a variety of other hydrophobic amines.

Binding Methylarginines and Methyllysines as Free Amino Acids: A Comparative Study of Multiple Host Classes*

Methylated free amino acids are an important class of targets for host‐guest chemistry that have recognition properties distinct from those of methylated peptides and proteins. We present comparative binding studies for three different host classes that are each studied with multiple methylated arginines and lysines to determine fundamental structure‐function relationships. The hosts studied are all anionic and include three calixarenes, two acyclic cucurbiturils, and two other cleft‐like hosts, a clip and a tweezer. We determined the binding association constants for a panel of methylated amino acids using indicator displacement assays. The acyclic cucurbiturils display stronger binding to the methylated amino acids, and some unique patterns of selectivity. The two other cleft‐like hosts follow two different trends, shallow host (clip) following similar trends to the calixarenes, and the other more closed host (tweezer) binding certain less‐methylated amino acids stronger than their methylated counterparts. Molecular modelling sheds some light on the different preferences of the various hosts. The results identify hosts with new selectivities and with affinities in a range that could be useful for biomedical applications. The overall selectivity patterns are explained by a common framework that considers the geometry, depth of binding pockets, and functional group participation across all host classes.

Molecular Recognition of Nerve Agents and Their Organophosphorus Surrogates: Toward Supramolecular Scavengers and Catalysts

Nerve agents are tetrahedral organophosphorus compounds (OPs) that were developed in the last century to irreversibly inhibit acetylcholinesterase (AChE) and therefore impede neurological signaling in living organisms. Exposure to OPs leads to a rapid development of symptoms from excessive salivation, nasal congestion and chest pain to convulsion and asphyxiation which if left untreated may lead to death. These potent toxins are prepared on a large scale from inexpensive staring materials, making it feasible for terrorist groups or states to use them against military and civilians. The existing antidotes provide limited protection and are difficult to apply to a large number of affected individuals. While new prophylactics are currently being developed, there is still need for therapeutics capable of both preventing and reversing the effects of OP poisoning. In this review, we describe how the science of molecular recognition can expand the pallet of tools for rapid and safe sequestration of nerve agents.

Self Assembled Cages with Mechanically Interlocked Cucurbiturils

We report preparation of (bis)aniline ligand 4 which contains a central viologen binding domain and its subcomponent self-assembly with aldehyde 5 and Fe(OTf)₂ in CH₃CN to yield tetrahedral assembly 6. Complexation of ligand 4 with CB[7] in the form of CB[7]•4•2PF₆ allows the preparation of assembly 7 which contains an average of 1.95 (range 1-3) mechanically interlocked CB[7] units. Assemblies 6 and 7 are hydrolytically unstable in water due to their imine linkages. Redesign of our system with water stable 2,2'-bipyridine end groups was realized in the form of ligands 11 and 16 which also contain a central viologen binding domain. Self-assembly of 11 with Fe(NTf₂)₂ gave tetrahedral MOP 12 as evidenced by ¹H NMR, DOSY, and mass spectrometric analysis. In contrast, isomeric ligand 16 underwent self-assembly with Fe(OTf)₂ to give cubic assembly 17. Precomplexation of ligands 11 and 16 with CB[7] gave the acetonitrile soluble CB[7]•11•2PF₆ and CB[7]•16•2PF₆ complexes. Self-assembly of CB[7]•11•2PF₆ with Fe(OTf)₂ gave tetrahedron 13 which contains on average 1.8 mechanically interlocked CB[7] units as determined by ¹H NMR, DOSY, and ESI-MS analysis. Self-assembly of CB[7]•16•2PF₆ with Fe(OTf)₂ gave cube 13 which contains 6.59 mechanically interlocked CB[7] units as determined by ¹H NMR and DOSY measurements.

Acyclic Cucurbituril Featuring Pendant Cyclodextrins

We report the design and synthesis of the acyclic cucurbit[n]uril-β-cyclodextrin chimeric host H1. The goal of the study is to deepen the cavity of the receptor to allow β-CD complexation of moieties on the guest (especially fentanyl) that protrude from the cavity of the primary acyclic CB[n] binding site to enhance binding affinity and deliver new supramolecular antidotes for fentanyl intoxication. 1H NMR spectroscopy was used to deduce the geometry of the complexes between H1 and H2 and the guest panel (G1 - G8 and fentanyl) whereas isothermal titration calorimetry was used to determine the thermodynamic parameters of complexation. Hosts H1 and H2 retain the essential molecular recognition features of CB[n] receptors, but chimeric host H1 binds slightly stronger toward the guest panel than H2 for reasons that remain unclear. Compared to tetraanionic hosts M1 and M2, the dianionic hosts H1 and H2 are less potent receptors which reflects the importance of electrostatic (ion-ion and ion-dipole) interactions in this series of hosts. The work highlights the challenges inherent in the optimization of binding affinity of hosts as potential supramolecular antidotes.

Chiroptical sensing of amino acids, amines, amino alcohols, alcohols and terpenes with π-extended acyclic cucurbiturils

The efficiency and scope of two acyclic π-wall extended cucurbiturils, M2 and M3, exhibiting rapidly interconverting helical conformers for chiroptical sensing of amines, amino acids, alcohols, and terpenes at micromolar concentrations in water is evaluated. The formation of 1 : 1 host-guest complexes results in spontaneous induction of circular dichroism signals that can be used for accurate determination of the absolute configuration and enantiomeric composition of the analyte based on a simple mix-and-measure protocol.

In Vitro and In Vivo Sequestration of Phencyclidine by Me4 Cucurbit[8]uril*

We report investigations of the use of cucurbit[8]uril (CB[8]) macrocycles as an antidote to counteract the in vivo biological effects of phencyclidine. We investigate the binding of CB[8] and its derivative Me4 CB[8] toward ten drugs of abuse (3-9, 12-14) by a combination of 1 H NMR spectroscopy and isothermal titration calorimetry in phosphate buffered water. We find that the cavity of CB[8] and Me4 CB[8] are able to encapsulate the 1-amino-1-aryl-cyclohexane ring system of phencyclidine (PCP) and ketamine as well as the morphinan skeleton of morphine and hydromorphone with Kd values ≤50 nm. In vitro cytotoxicity (MTS metabolic and adenylate kinase cell death assays in HEK293 and HEPG2 cells) and in vivo maximum tolerated dose studies (Swiss Webster mice) which were performed for Me4 CB[8] indicated good tolerability. The tightest host⋅guest pair (Me4 CB[8]⋅PCP; Kd =2 nm) was advanced to in vivo efficacy studies. The results of open field tests demonstrate that pretreatment of mice with Me4 CB[8] prevents subsequent hyperlocomotion induction by PCP and also that treatment of animals previously dosed with PCP with Me4 CB[8] significantly reduces the locomotion levels.

Supramolecular cancer nanotheranostics

Among the many challenges in medicine, the treatment and cure of cancer remains an outstanding goal given the complexity and diversity of the disease. Nanotheranostics, the integration of therapy and diagnosis in nanoformulations, is the next generation of personalized medicine to meet the challenges in precise cancer diagnosis, rational management and effective therapy, aiming to significantly increase the survival rate and improve the life quality of cancer patients. Different from most conventional platforms with unsatisfactory theranostic capabilities, supramolecular cancer nanotheranostics have unparalleled advantages in early-stage diagnosis and personal therapy, showing promising potential in clinical translations and applications. In this review, we summarize the progress of supramolecular cancer nanotheranostics and provide guidance for designing new targeted supramolecular theranostic agents. Based on extensive state-of-the-art research, our review will provide the existing and new researchers a foundation from which to advance supramolecular cancer nanotheranostics and promote translationally clinical applications.

Recent advances in supramolecular antidotes

Poisons always have fascinated humankind. Initially considered as deleterious or hazardous substances, the modern era has witnessed the controlled utilization of dangerous poisons in medicine and cosmetics. Simultaneously, antidotes have become crucial as reversal agents to counteract the effects of a poison, and they are also used today to positively cancel the benefits of a poison after use. Currently, the majority of poisons are composed of small molecules. This review focuses on recent developments to reverse or prevent toxic effects of poisons by encapsulation in host molecules. Cyclodextrins, cucurbiturils, acyclic cucurbituril derivatives, calixarenes, and pillararenes, have been reported to largely impact the effects of toxic compounds, thus extending the current paradigm of small molecule antidotes by adding a new family of macrocyclic compounds to the current arsenal of antidotes. Along this line of research, endogenous "harmful" species are also sequestered by one or more of these supramolecular host molecules, expanding the potential of supramolecular antidotes to diverse therapeutic areas.

Reversing cytotoxicity of uric acid by supramolecular encapsulation with acyclic cucurbit[n]uril

Supramolecular encapsulation removes harmful substances from organisms has evolved into a new strategy. In this article, we prepared three supramolecular complexes of acyclic cucurbit[n]urils (ACBs) with uric acid (UA), and studied the inclusion behaviors of ACBs and UA by fluorescence spectroscopy, UV-vis spectroscopy and nuclear magnetic resonance. Furthermore, we characterized the effect of the complexes of UA with ACBs on the expression of inflammatory biomarkers in human hepatoma HepG2 cell lines through C-reactive protein (CRP) western blot. The results showed UA molecules can be recognized by three ACBs with different binding constants, and ACBs successfully blocked the inflammatory stimulation of uric acid on HepG2 cell lines and inhibited the expression of the major inflammatory factor CRP by formations of complexes between UA and ACBs. This article proves that ACBs can efficiently reversing cytotoxicity of UA, which provides a new method to treating hyperuricemia disease.

Acyclic Cucurbit[n]uril-Type Receptors: Aromatic Wall Extension Enhances Binding Affinity, Delivers Helical Chirality, and Enables Fluorescence Sensing

We report the linear extension from M1 to M2 to anthracene walled M3 which adopts a helical conformation (X-ray) to avoid unfavorable interactions between sidewalls. M3 is water soluble (=30 mm) and displays enhanced optical properties (ϵ=1.28×105  m-1  cm-1 , λmax =370 nm) relative to M2. The binding properties of M3 toward guests 1-29 were examined by 1 H NMR and ITC. The M3⋅guest complexes are stronger than the analogous complexes of M2 and M1. The enhanced binding of M3 toward neuromuscular blockers 25, 27-29 suggests that M3 holds significant promise as an in vivo reversal agent. The changes in fluorescence observed for M3⋅guest complexes are a function of the relative orientation of the anthracene sidewalls, guest concentration, Ka , and guest electronics which rendered M3 a superb component of a fluorescence sensing array. The work establishes M3 as a next generation sequestering agent and a versatile component of fluorescence sensors.

Supramolecular hosts as in vivo sequestration agents for pharmaceuticals and toxins

Pharmaceutical agents, drugs of abuse, and toxic substances have a large impact, positive and negative, on modern society. Efforts to mitigate the side effects of pharmaceuticals and counteract the life threatening effects of drugs of abuse and toxins can occur either by pharmacodynamic (PD) approaches based on bioreceptor·drug antagonism or by pharmacokinetic (PK) approaches that seek to reduce the concentration of free drug. In this tutorial review, we present the use of supramolecular hosts (cyclodextrins, calixarenes, (acyclic) cucurbiturils, and pillararenes) as in vivo sequestration agents for neuromuscular blockers, drugs of abuse (methamphetamine and fentanyl), anesthetics, neurotoxins, the pesticide paraquat, and heparin anti-coagulants by the PK approach. The review presents the basic physical and molecular recognition features of the supramolecular hosts and some of the principles used in their selection and structural optimization for in vivo sequestration applications. The influence of host·guest complexation on other relevant in vivo properties of drugs (e.g. distribution, circulation time, excretion, redox properties) is also mentioned. The article concludes with a discussion of future directions.

Acyclic Cucurbit[n]uril-Type Containers as Receptors for Neuromuscular Blocking Agents: Structure-Binding Affinity Relationships

Acyclic cucurbit[n]uril molecular containers 1 and 2C3 have previously been shown to strongly bind to the neuromuscular blocking agents rocuronium, vecuronium, pancuronium, and cisatracurium in vitro by optical methods and to reverse neuromuscular block in vivo in rats. In this paper we study the in vitro binding of a panel of acyclic CB[n]-type receptors toward the four neuromuscular blocking agents and acetylcholine to develop structure-binding affinity relationships. The selected variants include those with different aromatic sidewalls (e.g. 1Me₄ with dimethyl o-xylylene walls; 3 with 1,8-linked naphthalene walls), with different glycoluril oligomer lengths (e.g. 4 and 5 based on glycoluril trimer), and with different linker lengths between aromatic wall and SO₃ ^- solubilizing group (e.g. 2C2 - 2C4). Based on the analysis of complexation induced changes in ¹H NMR chemical shift we conclude that the hydrophobic regions of the guests bind in the hydrophobic cavity of the hosts with the cationic moieties of the guest binding at the ureidyl C=O portals by ion-dipole and ion-ion interactions. The thermodynamic parameters of binding were determined by direct and competition isothermal titration calorimetry experiments. We find that hosts 4 and 5 based on glycoluril trimer form significantly weaker complexes with the streroidal NMBAs than with the analogues hosts based on glycoluril tetramer (1 and 2C3). Similarly, hosts 1Me₄ and 3 with different length and height aromatic walls do not exhibit the extreme binding constants displayed by 2C3 but rather behave similarly to 1. Finally, we find that hosts 2C2 and 2C4 bind only slightly more weakly to the NMBAs than 2C3, but retain the ability to discriminate against acetylcholine, and possess higher inherent water solubility than 2C3. Host 2C4, in particular, holds potential for future in vivo applications.

Pillar[n]MaxQ: A New High Affinity Host Family for Sequestration in Water

We report the synthesis, X-ray crystal structure, and molecular recognition properties of pillar[n]arene derivative P[6]AS, which we refer to as Pillar[6]MaxQ along with analogues P[5]AS and P[7]AS toward guests 1-18. The ultratight binding affinity of P[5]AS and P[6]AS toward quaternary (di)ammonium ions renders them prime candidates for in vitro and in vivo non-covalent bioconjugation, for imaging and delivery applications, and as in vivo sequestration agents.

Acyclic Cucurbit[n]uril-Type Receptors: Optimization of Electrostatic Interactions for Dicationic Guests

The synthesis of acyclic CB[n]-type host (1) is reported. By optimizing the placement of the sulfate groups nearby the electrostatically negative ureidyl C═O portals, the binding affinity of this class of receptors toward hydrophobic (di)ammonium guest molecules (5-23) is maximized. The X-ray crystal structures of 1·6a and 1·6d are reported.

Conformationally Mobile Acyclic Cucurbit[n]uril-Type Receptors Derived from an S-shaped Methylene Bridged Glycoluril Pentamer

We report the synthesis of the conformationally mobile S-shaped glycoluril pentamer building block 3a and two new acyclic CB[n]-type receptors P1 and P2. P1 (9 mM) and P2 (11 mM) have moderate aqueous solubility but their host•guest complexes are poorly soluble. Host P1 does not undergo intermolecular self-association whereas P2 does (K_s = 189±27 M^-1). ¹H NMR titrations show that P1 and P2 are poor hosts toward hydrophobic (di)cations 6 - 11 (P1: K_a = 375-1400 M^-1; P2: K_a = 1950-19800 M^-1) compared to Tet1 and Tet2 (Tet1: K_a = 3.09 × 10⁶ to 4.69 × 10⁸ M^-1; Tet2: K_a = 4.59 × 10⁸ to 1.30 × 10¹⁰ M^-1). Molecular modelling shows that P1 and P2 exist as a mixture of three different conformers due to the two S-shaped methylene bridged glycoluril dimer subunits that each possess two different conformations. The lowest energy conformers of P1 and P2 do not feature a well-defined central cavity. In the presence of guests, P2 adapts its conformation to form 1:1 P2•guest complexes; the binding free energy pays the energetic price of conformer selection. This energetically unfavorable conformer selection results in significantly decreased K_a values of P1 and P2 compared to Tet1 and Tet2.

Supramolecular neuromuscular blocker inhibition by a pillar[5]arene through aqueous inclusion of rocuronium bromide

A water-soluble pillar[5]arene, decafunctionalized with thioether and carboxylate fragments, was synthesized as a structural analogue of Sugammadex. Its ability to restore the contraction of the diaphragm muscle by encapsulating the muscle relaxant rocuronium bromide was demonstrated. Using UV-vis, NMR and fluorescence spectroscopy, it was shown that the muscle relaxant is associated with the pillar[5]arene with an association constant of 4500 M-1 and a stoichiometry of 1 : 1. The structure of the inclusion complex of the pillar[5]arene with rocuronium bromide was additionally investigated by quantum chemical methods.

Triptycene Walled Glycoluril Trimer: Synthesis and Recognition Properties

We report the synthesis of a new acyclic CB[n]-type host (1) that features a central glycoluril trimer capped by triptycene sidewalls. Host 1 has good solubility in water (≈ 3 mM) and does not undergo strong self-association (K_s = 480 M^-1). We probed the geometry of the complexes by analyzing the complexation induced changes in the ¹H NMR spectra and measured the complexation thermodynamics by isothermal titration calorimetry. The conformation of 1 and its packing in the solid state was revealed by single crystal x-ray diffraction measurements.

Molecular Lysine Tweezers Counteract Aberrant Protein Aggregation

Molecular tweezers (MTs) are supramolecular host molecules equipped with two aromatic pincers linked together by a spacer (Gakh, 2018). They are endowed with fascinating properties originating from their ability to hold guests between their aromatic pincers (Chen and Whitlock, 1978; Zimmerman, 1991; Harmata, 2004). MTs are finding an increasing number of medicinal applications, e.g., as bis-intercalators for DNA such as the anticancer drug Ditercalinium (Gao et al., 1991), drug activity reverters such as the bisglycoluril tweezers Calabadion 1 (Ma et al., 2012) as well as radioimmuno detectors such as Venus flytrap clusters (Paxton et al., 1991). We recently embarked on a program to create water-soluble tweezers which selectively bind the side chains of lysine and arginine inside their cavity. This unique recognition mode is enabled by a torus-shaped, polycyclic framework, which is equipped with two hydrophilic phosphate groups. Cationic amino acid residues are bound by the synergistic effect of disperse, hydrophobic, and electrostatic interactions in a kinetically fast reversible process. Interactions of the same kind play a key role in numerous protein-protein interactions, as well as in pathologic protein aggregation. Therefore, these particular MTs show a high potential to disrupt such events, and indeed inhibit misfolding and self-assembly of amyloidogenic polypeptides without toxic side effects. The mini-review provides insight into the unique binding mode of MTs both toward peptides and aggregating proteins. It presents the synthesis of the lead compound CLR01 and its control, CLR03. Different biophysical experiments are explained which elucidate and help to better understand their mechanism of action. Specifically, we show how toxic aggregates of oligomeric and fibrillar protein species are dissolved and redirected to form amorphous, benign assemblies. Importantly, these new chemical tools are shown to be essentially non-toxic in vivo. Due to their reversible moderately tight binding, these agents are not protein-, but rather process-specific, which suggests a broad range of applications in protein misfolding events. Thus, MTs are highly promising candidates for disease-modifying therapy in early stages of neurodegenerative diseases. This is an outstanding example in the evolution of supramolecular concepts toward biological application.

Applications of Cucurbiturils in Medicinal Chemistry and Chemical Biology

The supramolecular chemistry of cucurbit[n]urils (CBn) has been rapidly developing to encompass diverse medicinal applications, including drug formulation and delivery, controlled drug release, and sensing for bioanalytical purposes. This is made possible by their unique recognition properties and very low cytotoxicity. In this review, we summarize the host-guest complexation of biologically important molecules with CBn, and highlight their implementation in medicinal chemistry and chemical biology.

Triazole functionalized acyclic cucurbit[n]uril-type receptors: host·guest recognition properties

We report the synthesis of three new triazole functionalized acyclic CB[n]-type receptors (2-4) by click chemistry. The compounds have good solubility in water (≥8 mM) and do not undergo strong self-association (Ks ≤ 903 M-1). We measured the binding constants of 2-4 toward guests 9-24 and compared the results to those obtained for the prototypical acyclic CB[n]-type receptor 1. The X-ray crystal structure of 4 is also described.

Supramolecular therapeutics to treat the side effects induced by a depolarizing neuromuscular blocking agent

Succinylcholine (Sch) is the only depolarizing neuromuscular blocking agent widely used for rapid sequence induction in emergency rooms. Unfortunately, a variety of (sometimes lethal) adverse effects, such as hyperkalemia and cardiac arrest, are associated with its use, and currently there are no specific antidotes to reverse Sch or to treat these side-effects. Methods: The binding behaviors of Sch and several synthetic receptors, including cucurbit[7]uril, sulfo-calix[4]arene and water-soluble carboxylatopillar[6]arene (WP[6]), were first investigated. With a mouse model, a leathal dose of Sch was selected for evaluation of the antidotal effects of these synthetic receptors on Sch induced mortality. The antidotal effects of a selected synthetic receptor, WP[6], on Sch induced cardiac arrhythmias, hyperkalemia, rhabdomyolysis and paralysis were subsequently evaluated with rat and mouse models. The reversal mechanism was also investigated at a cellular level. Results: All of these macrocyclic molecules exhibited relatively high binding affinities with Sch in vitro. In a Sch-overdosed mouse model, immediate injection of these synthetic receptors right after Sch administration increased the overall survival rate, with WP[6] standing out with the most effective antidotal effects. In addition, administration of WP[6] also reversed the paralysis induced by Sch in a mouse model. Moreover, infusion of WP[6] to Sch-overdosed rats reduced the incidence of cardiac arrhythmia, inhibited the otherwise abnormally high serum potassium levels, and relieved the muscular damage. At the cellular level, WP[6] reversed the Sch induced depolarization and reduced the efflux of intracellular potassium. Conclusion: Synthetic receptors, particularly WP[6], exhibited high binding affinities towards Sch, and presented a significant potential as supramolecular therapeutics to treat the various side effects of Sch by specifically sequestering Sch in vivo.

Host-Guest Chemistry in Supramolecular Theranostics

Macrocyclic hosts, such as cyclodextrins, calixarenes, cucurbiturils, and pillararenes, exhibit unparalleled advantages in disease diagnosis and therapy over the past years by fully taking advantage of their host-guest molecular recognitions. The dynamic nature of the non-covalent interactions and selective host-guest complexation endow the resultant nanomaterials with intriguing properties, holding promising potentials in theranostic fields. Interestingly, the differences in microenvironment between the abnormal and normal cells/tissues can be employed as the stimuli to modulate the host-guest interactions, realizing the purpose of precise diagnosis and specific delivery of drugs to lesion sites. In this review, we summarize the progress of supramolecular theranostics on the basis of host-guest chemistry benefiting from their fantastic topological structures and outstanding supramolecular chemistry. These state-of-the-art examples provide new methodologies to overcome the obstacles faced by the traditional theranostic systems, promoting their clinical translations.

A glycoluril dimer-triptycene hybrid receptor: synthesis and molecular recognition properties

The strategic combination of the methylene bridged glycoluril dimer and triptycene skeletons delivers acyclic water soluble hybrid receptor 1 which is analogous to cucurbit[6]uril. The molecular recognition properties of host 1 toward hydrophobic cationic guests are investigated in detail by a combination of 1H NMR spectroscopy and isothermal titration calorimetry (ITC) studies. The fluorescence emission of 1 can be selectively and efficiently quenched upon the formation of 1·26 and 1·28 complexes.