Removal of Nerve Agent Simulants from Water Using Light-Responsive Molecular Baskets

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.

Ditopic Covalent Cage for Ion-Pair Binding: Influence of Anion Complexation on the Cation Exchange Rate

A new hemicryptophane host with a ditopic molecular cavity combining a cyclotriveratrylene (CTV) unit with a tris-urea moiety was synthesized. The complexation of halides, tetramethylammonium (TMA+) cation, and ion pairs was investigated. A positive cooperativity was observed, since halides display a higher binding constant when a TMA+ cation is already present inside the cage. When TMA+ was complexed alone, a decrease of temperature from 298 K to 230 K was required to switch from a fast to a slow exchange regime on the NMR time scale. Nevertheless, the prior complexation of a halide guest in the lower part of the host resulted in significant decrease of the exchange rate of the subsequent complexation of the TMA+ cation. Under these conditions, the 1H NMR signals characteristic of a slow exchange regime were observed at 298 K. Addition of an excess of salts, increases the ionic strength of the solution, restoring the fast exchange dynamics. This result provides insight on how the exchange rate of a cation guest can be modulated by the complexation of a co-guest anion.

Dynamic and Assembly Characteristics of Deep-Cavity Basket Acting as a Host for Inclusion Complexation of Mitoxantrone in Biotic and Abiotic Systems

We describe the preparation, dynamic, assembly characteristics of vase-shaped basket 13- along with its ability to form an inclusion complex with anticancer drug mitoxantrone in abiotic and biotic systems. This novel cavitand has a deep nonpolar pocket consisting of three naphthalimide sides fused to a bicyclic platform at the bottom while carrying polar glycines at the top. The results of 1 H Nuclear Magnetic Resonance (NMR), 1 H NMR Chemical Exchange Saturation Transfer (CEST), Calorimetry, Hybrid Replica Exchange Molecular Dynamics (REMD), and Microcrystal Electron Diffraction (MicroED) measurements are in line with 1 forming dimer [12 ]6- , to be in equilibrium with monomers 1(R) 3- (relaxed) and 1(S) 3- (squeezed). Through simultaneous line-shape analysis of 1 H NMR data, kinetic and thermodynamic parameters characterizing these equilibria were quantified. Basket 1(R) 3- includes anticancer drug mitoxantrone (MTO2+ ) in its pocket to give stable binary complex [MTO⊂1]- (Kd =2.1 μM) that can be precipitated in vitro with UV light or pH as stimuli. Both in vitro and in vivo studies showed that the basket is nontoxic, while at a higher proportion with respect to MTO it reduced its cytotoxicity in vitro. With well-characterized internal dynamics and dimerization, the ability to include mitoxantrone, and biocompatibility, the stage is set to develop sequestering agents from deep-cavity baskets.

Supramolecular detoxification of nitrogen mustard via host-guest encapsulation by carboxylatopillar[5]arene

Nitrogen mustard (NM), a kind of alkylating agent similar to sulfur mustard, remains a threat to public health. However, there is nearly no satisfactory antidote for nitrogen mustard. Herein, we developed a supramolecular antidote to nitrogen mustard through efficient complexation of NM by carboxylatopillar[5]arene potassium salts (CP[5]AK). The cavity of methoxy pillar[5]arene (P5A) is sufficient to encapsulate NM with an association constant of 1.27 × 10² M^-1, which was investigated by ¹H NMR titration, density functional theory studies and independent gradient model studies. NM degrades to the reactive aziridinium salt (2) in the aqueous phase which irreversibly alkylates DNA and proteins, causing severe tissue damage. Considering the size/charge matching with toxic intermediate 2, water-soluble CP[5]AK was selected to encapsulate the toxic aziridinium salt (2), resulting in a high association constant of 4.10 × 10⁴ M^-1. The results of protection experiments of guanosine 5'-monophosphate (GMP) by CP[5]AK indicated that the formation of a complex could effectively inhibit the alkylation of DNA. Besides, in vitro and in vivo experiments also indicated that the toxicity of the aziridinium salt (2) is inhibited with the formation of a stable host-guest complex, and CP[5]AK has a good therapeutic effect on the damage caused by NM. This study provides a new mechanism and strategy for the treatment of NM exposure-induced skin injuries.

Enantioselective Construction of Modular and Asymmetric Baskets

The precise positioning of functional groups about the inner space of abiotic hosts is a challenging task and of interest for developing more effective receptors and catalysts akin to those found in nature. To address it, we herein report a synthetic methodology for preparing basket-like cavitands comprised of three different aromatics as side arms with orthogonal esters at the rim for further functionalization. First, enantioenriched A (borochloronorbornene), B (iodobromonorbornene), and C (boronorbornene) building blocks were obtained by stereoselective syntheses. Second, consecutive A-to-B and then AB-to-C Suzuki-Miyaura (SM) couplings were optimized to give enantioenriched ABC cavitand as the principal product. The robust synthetic protocol allowed us to prepare (a) an enantioenriched basket with three benzene sides and each holding either tBu, Et, or Me esters, (b) both enantiomers of a so-called "spiral staircase" basket with benzene, naphthalene, and anthracene groups surrounding the inner space, and (c) a photo-responsive basket bearing one anthracene and two benzene arms.

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.

Cucurbituril-activated photoreaction of dithienylethene for controllable targeted lysosomal imaging and anti-counterfeiting

Supramolecular macrocycle-mediated photoreaction has been a research hotspot recently. Herein, we fabricated a photo-responsive intelligent supramolecular assembly that consisted of a water-soluble dithienylethene derivative (DTE-MPBT) and cucurbit[n]urils (CB[n]). Importantly, CB[n], especially CB[8], could act as activators and trigger conformational alteration of the arm parts (typical molecular rotors) of DTE-MPBT, achieving dual functions, i.e. high-efficiency visible-light-cyclization reaction of the DTE core and fluorescence enhancement of DTE-MPBT, resulting in the formation of a dual visible light-driven fluorescent switch. These unexpected discoveries prompted the supramolecular assembly to be applied to dual-visible-light-controlled targeted lysosomal imaging and QR code information recognition. Moreover, the solid-state assembly exhibited more outstanding fluorescence and visible-light-switched fluorescence performance because of the host-guest-induced aggregation synergistic effect, showing fascinating applications, such as light-manipulative data storage and anti-counterfeiting. In brief, we unprecedentedly adopted a supramolecular strategy of "killing two birds with one stone", i.e. assembly-activated photochromism (AAP) and assembly-activated emission enhancement (AAEE), to fabricate dual-visible-light-driven fluorescent switches, which show promising application prospects in biomimetic smart nanomaterials based on supramolecular self-assembly systems.

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.

A [15]paracyclophenone and its fluorenone-containing derivatives: syntheses and binding to nerve agent mimics via aryl-CH hydrogen bonding interactions

A [1₅]paracyclophenone and its fluorenone-containing derivatives were synthesized. The novel macrocyclic host I binds nerve agent mimics through the ‘non-traditional’ aryl-CH hydrogen bonding interactions.

Photolysis of the BODIPY dye activated by pillar[5]arene

Here, a pseudo[3]rotaxane comprising a fluorescent BODIPY derivative and pillar[5]arene was conveniently fabricated via host–guest complexation. Importantly, in this system, the efficient photodecomposition of the BODIPY derivative in the presence of pillar[5]arene was witnessed upon irradiation at 311 nm light, which was demonstrated via UV-Vis absorption, fluorescence emission, NMR and HR-MS spectroscopy techniques, but the only BODIPY dye in the absence of pillar[5]arene couldn't undergo photodegradation. We demonstrated that pillar[5]arene could act as an activator to trigger the photodegradation reaction of BODIPY derivatives via free radical reactions even without supramolecular interactions. The present results provide a new strategy for the efficient photolysis of organic dyes.

Here, a pseudo[3]rotaxane comprising a fluorescent BODIPY derivative and pillar[5]arene was conveniently fabricated via host–guest complexation.

A highly diastereoselective synthesis of deep molecular baskets

We describe a preparative method for directing Mizoroki-Heck cyclotrimerization of enantioenriched bromonorbornenes into molecular baskets having increasingly deeper and extendable aromatic cavities. Such diastereoselective cyclotrimerizations of the bromo-olefinic substrates resulted from prevalent β migratory insertions without the formation of palladacycle intermediate(s). The facile access to multigram quantity of a new series of basket-like hosts clears the way for creating novel supramolecular materials for storage, sequestration and catalysis.

Catalytic Degradation of Nerve Agents

Nerve agents (NAs) are a group of highly toxic organophosphorus compounds developed before World War II. They are related to organophosphorus pesticides, although they have much higher human acute toxicity than commonly used pesticides. After the detection of the presence of NAs, the critical step is the fast decontamination of the environment in order to avoid the lethal effect of these organophosphorus compounds on exposed humans. This review collects the catalytic degradation reactions of NAs, in particular focusing our attention on chemical hydrolysis. These reactions are catalyzed by different catalyst categories (metal-based, polymeric, heterogeneous, enzymatic and MOFs), all of them described in this review.

Influence of cyclic and acyclic cucurbiturils on the degradation pathways of the chemical warfare agent VX

The highly toxic nerve agent VX is a methylphosphonothioate that degrades via three pathways in aqueous solution, namely through the hydrolysis of the P-O or P-S bonds, or the cleavage of the C-S bond at the 2-aminoethyl residue. In the latter case, an aziridinium ion and a phosphonothioate is formed. Here it is shown that acyclic or cyclic cucurbiturils inhibit these reactions in phosphate buffer at physiological pH and thus stabilise the nerve agent. When using unbuffered basic solutions as the reaction medium, however, in which the P-S or P-O bonds are normally hydrolysed preferentially, cucurbiturils turned out to strongly shift VX degradation towards the cleavage of the C-S bond. Cucurbit[7]uril, in particular, has a so pronounced effect under suitable conditions that it almost completely suppresses the formation of products resulting from the other degradation pathways. Investigations involving VX analogues in combination with computational methods suggest that one reason for the reaction control exerted by the cucurbiturils is the preorganisation of VX for aziridinium ion formation. In addition, cucurbit[7]uril also lowers the transition state of the reaction by stabilising the positive charge developing on the way to the product. Cucurbiturils thus have a marked effect on the reactivity of a highly toxic nerve agent, which potentially allows using them for decontamination purposes.

Tuning the allosteric sequestration of anticancer drugs for developing cooperative nano-antidotes

Dual-cavity baskets, carrying six γ-aminobutyric acids sequester anticancer anthracyclines in a cooperative manner to be of interest for creating nano-antidotes.

Photoinduced interruption of interannular cooperativity for delivery of cationic guests in water

Photoinduced decarboxylation of two hexaanionic baskets, surrounding a divalent cationic guest, reduced the interannular cooperativity (i.e. multivalency) holding the complex together to result in the release of guests.

Reversible reduction drives anion ejection and C60 binding within an FeII 4L6 cage

Fe^II₄L₆ tetrahedral cage 1 was prepared from a redox-active dicationic naphthalenediimide (NDI) ligand. The +20 charge of the cage makes it a good host for anionic guests, with no binding observed for neutral aromatic molecules. Following reduction by Cp₂Co, the cage released anionic guests; subsequent oxidation by AgNTf₂ led to re-uptake of anions. In its reduced form, however, 1 was observed to bind neutral C₆₀. The fullerene guest was subsequently ejected following cage re-oxidation. The guest release process was found to be facilitated by anion-mediated transport from organic to aqueous solution. Cage 1 thus employs electron transfer as a stimulus to control the uptake and release of both neutral and charged guests, through distinct pathways.

Fe^II₄L₆ cage 1 binds anionic guests but not neutral guests. In its reduced form, the cage can bind neutral C₆₀. Reduction and oxidation of the cage could thus be used as a stimulus to control the uptake and release of both neutral and charged guests.

Photolysis of a calixpyridinium-based supramolecular amphiphilic assembly and its selective turn-on fluorescence recognition of lysine in water

A new calixpyridinium-based light-responsive host-guest recognition motif was found in this work. This host-guest recognition motif was further discovered to be applied as a selective turn-on fluorescent sensor for lysine over other natural amino acids.

Stereo- and Regioselective Synthesis of Molecular Baskets

We describe a stereoselective method for obtaining multigram quantities of molecular basket 1 _syn in overall 11% yield, using inexpensive cyclopentadiene and diethyl fumarate as starting materials. First, an asymmetric synthesis of enantioenriched bromo(trimethylstannyl)alkene (-)-8 was accomplished by the stereoselective bromination of dibromonorbornene (+)-4 guided by anchimeric assistance and subsequent syn- exo-elimination of tetrabromonorbornane (-)-5a as the key steps. Subsequent Cu(I)-catalyzed cyclotrimerization of (-)-8 was optimized to give 1 _{syn/ anti} in 85% yield and 1:1 ratio of diastereomers. Importantly, the results of our mechanistic experiments were in line with the cyclotrimerization occurring in a chain-type fashion with racemization of a Cu(I) homochiral dimeric intermediate, reducing the stereoselectivity of the transformation. Enabled by more facile access to molecular baskets of type 1 _syn, a range of recognition studies can now be completed for producing novel supramolecular catalysts, organophosphorus scavengers, and nanostructured materials.

Semi-Rigid Molecular-Clip-Based Molecular Crystal Gearshift

A new version of molecular clip, with a semi-rigid symmetrical crab-type architecture and flexible cavity size, has been successfully designed and synthesized via a one-pot Friedel-Crafts alkylation reaction. The X-ray single-crystal diffraction data provide a simple and intuitive explanation, not only for its well-preorganized and regulated conformation but also for its selective and tunable guest-binding capability. For the first time, the newly designed molecular clip was demonstrated to be not only a controllable variable-speed nonporous adsorption material in solution iodine capture, but also capable of on-off switching in volatile iodine capture. The presented new concept of molecular crystal gearshift directly from the molecular clip crystals represents an important advance in the development of synthetic receptor chemistry, which will exert a significant influence on small-molecule crystallography.

Stackable molecular chairs

Molecular chairs, carrying three amino acids or peptides, stack in an antiparallel fashion to give hexavalent assemblies for bottom-up construction of novel soft materials and therapeutics.

Photo-induced formation of organic nanoparticles possessing enhanced affinities for complexing nerve agent mimics

Organic nanoparticles, composed of molecular baskets, could act as nanocarriers for selective “mopping” of toxic CWAs or pesticides, after being assembled by a light stimulus.

Molecular recognition of organophosphorus compounds in water and inhibition of their toxicity to acetylcholinesterase

endo-Functionalized molecular tubes are able to recognize toxic organophosphorus compounds in water. They can be used as a fluorescent sensor and as an inhibitor to reduce the toxicity of paraoxon to acetylcholinesterase.