Cucurbit[ n ]urils for Supramolecular Catalysis

Investing in entropy: the strategy of cucurbit[n]urils to accelerate the intramolecular Diels-Alder cycloaddition reaction of tertiary furfuryl amines

Cucurbit[n]urils, renowned for their host-guest chemistry, are becoming versatile biomimetic receptors. Herein, we report that cucurbit[7]uril (CB[7]) accelerates the intramolecular Diels-Alder (IMDA) reaction for previously elusive and unreactive tertiary N-methyl-N-(homo)allyl-2-furfurylamines by up to 4 orders of magnitude under mild conditions. Using 1H NMR titrations and ITC experiments, we characterize the dissimilar thermodynamic and kinetic properties of the complexes. We also determine the activation parameters (ΔG ≠, ΔH ≠ and ΔS ≠) leading to the transition state of the IMDA reactions, both in the bulk and included in CB[7], to shed light on the key role of the receptor on the acceleration observed. CB[7] acts as an "entropy trap" utilizing guest binding to primarily pay the entropy penalty for reorganizing the substrate in a high-energy reactive conformation that resembles the geometry of the highly ordered transition state required for the IMDA reaction. This study underscores the potential of cucurbit[n]urils as artificial active sites, emulating specific aspects of enzymatic catalysis.

Supramolecularly modulated carbon-centered radicals: toward selective oxidation from benzyl alcohol to aldehyde

The reactivity of ketyl radicals and benzoyl radicals, two key intermediates of photo-induced oxidation of benzyl alcohol, can be stabilized by the host-guest interaction of the radicals with cucurbit[7]uril. As a result, the selectivity of photo-induced oxidation from benzyl alcohol to aldehyde is significantly improved by diminishing side reactions and inhibiting the generation of carboxylic acid products. This work presents a new route to modulate the reactivity of radical intermediates, enriching the chemistry of supramolecular intermediates and the toolbox of supramolecular catalysis.

Polymerizable rotaxane of cucurbituril protecting dopamine based adhesive hydrogels

The catechol moiety found within mussel proteins plays a pivotal role in enhancing their adhesive properties. Nonetheless, catechol compounds, such as dopamine (DOP) derivatives, are susceptible to oxidation, leading to the formation of quinone. This oxidation process poses a significant challenge in the development of DOP-based hydrogels, hampering their adhesion capabilities and hindering polymerization. To protect DOP moieties from oxidation, DOP and N-(3-aminopropyl)methacrylamide (AMA) moieties were grafted onto the side groups of biocompatible poly(glutamic acid) (PGA). Subsequently, the DOP unit, serving as a second guest, would be captured by a polymerizable rotaxane of cucurbituril (CB[n]), in which the host molecule CB[8] complexed with the first guest, polymerizable methyl viologen (MV), forming a protective function and dynamic cross-linking. Upon exposure to light curing, a composite network emerged through the synergy of covalent cross-linking and supramolecular host-guest complexation of DOP with CB[8]. The generated complexation between DOP and CB[8] could protect the DOP moieties, resulting in photocured hydrogels with exceptional adhesive strength and remarkable tensile capabilities. Moreover, 3D printing technology was used to create various models with these DOP-based hydrogels, demonstrating their promising applications in future.

Reversing the stereoselectivity of intramolecular [2+2] photocycloaddition utilizing cucurbit[8]uril as a molecular flask

Macrocyclic hosts, such as cucurbit[8]uril (CB8), can significantly influence the outcomes of chemical reactions involving encapsulated reactive guests. In this study, we demonstrate that CB8 completely reverses the stereoselectivity of intramolecular [2+2] photo-cycloaddition reactions. Notably, it was also found that CB8 can trigger the unreactive diene to be reactive.

Macrocycle-Based Hierarchically Porous Hydrogen-Bonded Organic Frameworks

Hydrogen-bonded organic frameworks (HOFs) are porous crystalline materials. The pores in HOFs are usually non-covalent extrinsic pores constructed through the formation of the framework. Supramolecular macrocycles with intrinsic pores in their structures are good candidates for constructing HOFs with intrinsic pores from the macrocycles themselves, thus leading to hierarchically porous structures. Combining the macrocycle and HOFs will endow these hierarchically porous materials with enhanced properties and special functionalities. This review summarizes recent advances in macrocycle-based HOFs, including the macrocycles used for constructing HOFs, the hierarchically porous structures of the HOFs, and the applications induced by the hierarchically HOFs porous structures. This review provides insights for future research on macrocycle-based hierarchically porous HOFs and the appropriate applications of the unique structures.

Cucurbituril-based supramolecular host-guest complexes: single-crystal structures and dual-state fluorescence enhancement

Two supramolecular complexes were prepared using cucurbiturils [CBs] as mediators and a four-armed p-xylene derivative (M1) as a guest molecule. The single crystals of these two complexes were obtained and successfully analyzed by single-crystal X-ray diffraction (SCXRD). An unexpected and intriguing 1 : 2 self-assembly arrangement between M1 and CB[8] was notably uncovered, marking its first observation. These host-guest complexes exhibit distinctive photophysical properties, especially emission behaviors. Invaluable insights can be derived from these single-crystal structures. The precious single-crystal structures provide both precise structural information regarding the supramolecular complexes and a deeper understanding of the intricate mechanisms governing their photophysical properties.

Synthesis of Novel Phosphorus-Containing Derivatives of 1,3,4-Trimethylglycoluril via the Birum-Oleksyszyn Reaction

This work presents the synthesis of a new compound, 1-[aryl-(diphenylphosphono)methyl]-3,4,6-trimethylglycolurils, via the interaction of benzaldehyde and its mononitro- and monohydroxyderivatives with 1,3,4-trimethylglycoluril and triphenylphosphite. By varying the reaction conditions and the catalysts, the obtained product yields ranged from satisfactory to good. The diastereomers formed during the reaction were separated by semipreparative HPLC on the C18 stationary phase. The isolated diastereomers were characterized by 1H, 13C, and 31P NMR, and the structures of the diastereomers were confirmed using a single-crystal X-ray crystal structure analysis and quantum chemical calculations.

Complexation of Fluorofenidone by Cucurbit[7]uril and β-Cyclodextrin: Keto-Enol Tautomerization to Enhance the Solubility

This study is designed to compare drug encapsulation by cucurbit[7]uril and β-cyclodextrin, using fluorofenidone as a model drug. Single-crystal X-ray diffraction analysis was employed to successfully determine the crystal structures of fluorofenidone·H+@cucurbit[7]uril Form, fluorofenidone@cucurbit[7]uril Form, and fluorofenidone@β-cyclodextrin Form. Keto-enol tautomerization of fluorofenidone mediated by cucurbit[7]uril in acid solution is confirmed by crystal structures, pH titration, and nuclear magnetic resonance experiments. However, β-cyclodextrin cannot cause the keto-enol tautomerization of fluorofenidone under similar conditions. The phase solubility study demonstrates that cucurbit[7]uril has a much higher solubilization capacity for fluorofenidone than β-cyclodextrin in 0.1 M HCl since the Kc values of fluorofenidone with cucurbit[7]uril and β-cyclodextrin were 1223.97 ± 452.68 and 78.49 ± 10.56 M-1, respectively. Excellent solubility can be attributed to the keto-enol tautomerization of fluorofenidone under the conditions of cucurbit[7]uril in acid solution. The enol form of fluorofenidone is encapsulated by cucurbit[7]uril by hydrogen bonding interaction and hydrophobic interaction to increase binding affinity. Rat pharmacokinetic studies demonstrate that the area under the plasma concentration-time curve from time 0 to 7 h value of fluorofenidone@cucurbit[7]uril complex is 1.70-fold greater than that of free fluorofenidone, and the mean residence time from time 0 to 7 h is slightly prolonged from 1.29 to 1.76 h (P < 0.01) after oral administration. However, no significant difference is found between fluorofenidone and fluorofenidone@β-cyclodextrin complex. This work indicates that the induction of keto-enol tautomerization of drugs using macrocyclic molecules has the potential to be an effective method to improve their solubility and bioavailability, providing valuable insights for the application of macrocyclic molecules in the biomedical field.

Stabilization of Carbocation Intermediate by Cucurbit[7]uril Enables High Photolysis Efficiency

A cucurbit[7]uril-based host-guest strategy is employed to enhance the efficiency of photolysis reactions that release caged molecules from photoremovable protecting groups. The photolysis of benzyl acetate follows a heterolytic bond cleavage mechanism, thereby leading to the formation of a contact ion pair as the key reactive intermediate. The Gibbs free energy of the contact ion pair is lowered by 3.06 kcal/mol through the stabilization of cucurbit[7]uril, as revealed by DFT calculations, which results in a 40-fold increase in the quantum yield of the photolysis reaction. This methodology is also applicable to the chloride leaving group and the diphenyl photoremovable protecting group. We anticipate that this research presents a novel strategy to improve reactions involving active cationics, thereby enriching the field of supramolecular catalysis.

A fluorescent probe for detection of Hg2+ ions constructed by tetramethyl cucurbit[6]uril and 1,2-bis(4-pyridyl)ethene

In this paper, tetramethyl cucurbit[6]uril (TMeQ[6]) and 1,2-bis(4-pyridyl)ethene (G) were used to construct a supramolecular fluorescent probe G@TMeQ[6]. The host-guest interaction between TMeQ[6] and G was investigated using ¹H NMR spectroscopy, single-crystal X-ray diffraction and various experimental techniques. The results show that TMeQ[6] and G form an inclusion complex with a host-guest ratio of 1:1 and the equilibrium association constant (K_a) was 2.494 × 10⁴ M^-1. The G@TMeQ[6] fluorescent probe can sensitively recognize Hg²⁺ ions by fluorescence enhancement. The linear range is 0.33 × 10^-5-1.65 × 10^-5 mol·L^-1, R² = 0.9926, and the limit of detection is 4.12 × 10^-8 mol·L^-1. The fluorescent probe can be used to detect the concentration of Hg²⁺ ions in aqueous solution, and provides a theoretical basis for the development of new fluorescent probes for detecting heavy metal ions.

Mechanochemical Defluorinative Arylation of Trifluoroacetamides: An Entry to Aromatic Amides

The amide bond is prominent in natural and synthetic organic molecules endowed with activity in various fields. Among a wide array of amide synthetic methods, substitution on a pre-existing (O)C-N moiety is an underexplored strategy for the synthesis of amides. In this work, we disclose a new protocol for the defluorinative arylation of aliphatic and aromatic trifluoroacetamides yielding aromatic amides. The mechanochemically induced reaction of either arylboronic acids, trimethoxyphenylsilanes, diaryliodonium salts, or dimethyl(phenyl)sulfonium salts with trifluoroacetamides affords substituted aromatic amides in good to excellent yields. These nickel-catalyzed reactions are enabled by C-CF₃ bond activation using Dy₂O₃ as an additive. The current protocol provides versatile and scalable routes for accessing a wide variety of substituted aromatic amides. Moreover, the protocol described in this work overcomes the drawbacks and limitations in the previously reported methods.

Development and Application of a Supramolecular Brønsted Acid Catalyst Based on the Noria Macrocycle

The synthesis of derivatives of the Noria macrocycle and the structurally similar macrocycle, R3, each containing 12 sulfonic acid groups, is reported. Herein, we demonstrate their utility as reusable Brønsted acid catalysts for the Biginelli synthesis of dihydropyrimidinones and the Pechmann synthesis of coumarins. We also demonstrate that the supramolecular structure directs the reagents to interact with the sulfonic acid catalytic sites, thus increasing the catalyst's efficiency compared to other monomeric, macrocyclic, and polymeric sulfonic acid catalysts.

Regulation of Antimicrobial Effect of Hemicyanine-Based Photosensitizer via Supramolecular Assembly

An intelligent "antimicrobial switch" has been constructed to reduce prolonged exposure of pathogenic bacteria to antibiotics, which could reversibly "turn off" or "turn on" the antimicrobial activity of hemicyanines through self-assembly or dis-assembly of cucurbit[7]uril (CB[7]). This assembly effectively inhibited the production of ROS under light, shielding the active site of hemicyanines and achieving on-demand antimicrobial ability. Moreover, CB[7] differentially inhibits ROS of molecules with different alkyl chain lengths, which provided reference for the subsequent design of materials with antimicrobial activity regulation, and could effectively delay or even prevent the development of pathogens resistance.

Investigation of the Complexation between 4-Aminoazobenzene and Cucurbit[7]uril through a Combined Spectroscopic, Nuclear Magnetic Resonance, and Molecular Simulation Studies

Cucurbiturils are well known for their ability to form supramolecular systems with ultrahigh affinities binding. Inclusion complex between 4-aminoazobenzene and cucurbit[7]uril has been investigated in aqueous solution by ultraviolet (UV)-spectroscopy, ¹H NMR, and molecular simulations. 4-aminoazobenzene shows high affinity in acidic solutions while no association was detected in neutral solutions. The thermodynamic properties of complex formation are investigated using both UV spectroscopy and nuclear magnetic resonance (NMR) measurements. Our results highlight that the high binding constant between CB7 and 4AA (log K = 4.9) is the result of a large negative change in Δ_r H° (-19 kJ/mol) and a small positive change in TΔ_r S° (9 kJ/mol). The analysis of the experimental data lead to hypothesis on the structure of the complex. We have used molecular dynamics simulation to interpret experiments. Interestingly, the cis-trans isomerization of aminoazobenzene is considered. All the results are discussed and compared with those previously obtained with other host molecules.

Monofunctionalized Fluorinated Bambusurils and Their Conjugates for Anion Transport and Extraction

Bambusurils are macrocyclic molecules that are known for their high binding affinity and selectivity toward anions. Here, we present the preparation of two bambusurils bearing fluorinated substituents and one carboxylic function. These monofunctionalized bambusurils were conjugated with crown ether and cholesterol units. The resulting conjugates were successfully tested in liquid-liquid extraction of inorganic salts and chloride/bicarbonate transport across lipid bilayers.

Effect of Na+ and K+ on the cucurbituril-mediated hydrolysis of a phenyl acetate

The environment around the active site affects the catalytic activity of enzymes. Studying the cucurbit[7]uril-promoted acid hydrolysis of a cationic phenyl acetate derivative, we found that the hydrophobic cavity of the macrocycle screens the reaction centre from the positively charged neighbouring group. Moreover, the chelation of alkali metal cations with the cucurbit[7]uril portal and acetyl group of the substrate reduces the hydrolysis rate of the encapsulated ester in an aqueous solution. This type of inhibition corresponds to a rare uncompetitive model in contrast to the more common competitive model that relies on substrate displacement.

Regiodivergent C-N Coupling of Quinazolinones Controlled by the Dipole Moments of Tautomers

Herein, we report that the dipole moments of tautomers can be the controlling factor for regiodivergent synthesis of either 14H-quinazolino[3,2-f]phenanthridin-14-ones or 6H-quinazolino[1,2-f]phenanthridin-6-ones, selectively, from unmasked 2-([1,1'-biphenyl]-2-yl)quinazolin-4(3H)-one. An intramolecular C(sp²)-NH coupling reaction mediated by PhI(OCOOCF₃)₂ could lead to two different regioisomers selectively at different temperatures when the dielectric constants of solvents like hexafluoroisopropanol and trifluoroacetic acid matched with the tautomer's dipole moments.

Back electron transfer rates determine the photoreactivity of donor-acceptor stilbene complexes in a macrocyclic host

Host-guest 2 : 1 complexation of photoreactive alkene guests improves the selectivity of [2 + 2] photodimerizations by templating alkene orientation prior to irradiation. Host-guest chemistry can also provide 1 : 1 : 1 complexes through the inclusion of electronically complementary donor and acceptor guests, but the photoreactivity of such complexes has not been investigated. We imagined that such complexes could enable selective cross-[2 + 2] photocycloadditions between donor and acceptor stilbenes. In pursuit of this strategy, we investigated a series of stilbenes and found 1 : 1 : 1 complexes with cucurbit[8]uril that exhibited charge-transfer (CT) absorption bands in the visible and near-IR regions. Irradiation of the CT band of an azastilbene, 4,4'-stilbenedicarboxylate, and cucurbit[8]uril ternary complex led to a selective cross-[2 + 2] photocycloaddition, while other substrate pairs exhibited no productive chemistry upon CT excitation. Using transient absorption spectroscopy, we were able to understand the variable photoreactivity of different stilbene donor-acceptor complexes. We found that back electron transfer following CT excitation of the photoreactive complex is positioned deep in the Marcus inverted region due to electrostatic stabilization of the ground state, allowing [2 + 2] to effectively compete with this relaxation pathway. Control reactions revealed that the cucurbit[8]uril host not only serves to template the reaction from the ground state, but also protects the long-lived radical ions formed by CT from side reactions. This protective role of the host suggests that donor-acceptor host-guest ternary complexes could be used to improve existing CT-initiated photochemistry or access new reactivity.

Time-Resolved Encryption via a Kinetics-Tunable Supramolecular Photochromic System

With the advancement of forgery and decryption methods, conventional static encryption technology is becoming more and more powerless, which strongly demands the development of multistate anticounterfeiting materials as well as advanced multidimensional encryption strategies and technologies. Here a new strategy to realize time-resolved encryption based on a self-assembled supramolecular ternary complex is presented, which exhibits tunable dynamic photochromic features caused by the reversible photodimerization/cleavage reactions of the guest chromophores inside the cavity of cucurbit[8]uril (CB[8]). This supramolecular system shows excellent photochromic properties, including extremely rapid response time, high conversion rate, and product-stereoselectivity, etc. More importantly, the kinetics of the photoreaction can be modulated by simply varying the host-guest ratios in aqueous or quasi-solid phase, providing the material with finely tunable time-dependent features, which cannot only be employed in data processing with more extended information, but also construct confidential materials by time-resolved multidimensional encryption and dynamic anticounterfeiting. The strategic design of kinetics-tunable supramolecular photochromic materials may provide valuable guidance for the development of more advanced materials for information security.

Cucurbit[7]uril-Modulated H/D Exchange of α-Carbonyl Hydrogen: Deceleration in Alkali and Acceleration in Acid Conditions

Supramolecular catalysis based on host-guest interactions has aroused much attention in past decades. Among the various strategies, modulation of the reactivity of key intermediates is an effective strategy to achieve high-efficiency supramolecular catalysis. Here, we report that by utilizing the host-guest interaction of cucurbit[7]uril (CB[7]), the reactivity of anionic enolate and cationic oxonium, the intermediates of H/D exchange of the α-carbonyl hydrogen in alkali and acid conditions, respectively, could be modulated effectively. On one hand, in alkaline conditions, both the electrostatic effect and the steric hindrance effect of CB[7] disfavored formation of the enolate anion intermediate. On the other hand, in acidic conditions, the oxonium was stabilized and the solvent effect was weakened by the electrostatic effect of CB[7]. As a result, the H/D exchange of 1-(4-acetylphenyl)-N,N,N-trimethylmethanaminium bromide is decelerated in alkaline and accelerated in acidic conditions. It is promising that the highly polar portals of CB[n] molecules together with their well-defined host-guest chemistry may be applied to modulate the reactivity of other kinds of ionic intermediates in an effective and convenient way, thus enriching the toolkit of supramolecular catalysis.

Controllable synthesis of Co nanoparticles with the assistance of cucurbit[6]uril and its efficient photoelectrochemical catalysis in water splitting on a g-C3N4 photoanode

An innovative photoanode was developed for efficient PEC water splitting by the deposition of a Co nano-catalyst on the surface of a g-C3N4 film, producing the significant photocurrent density of 393 μA cm−2 at 1.23 V vs. RHE.

Single-crystal structures of cucurbituril-based supramolecular host-guest complexes for bioimaging

Two single-crystal structures of cucurbit[n]uril mediated supramolecular complexes were obtained in which [1+3] and [2+3] self-assembly modes are adopted due to the different sizes of cucurbit[7]uril and cucurbit[8]uril. An obvious red-shift in absorption and emission was observed compared to the guest molecule itself which makes them good biolabels.

New horizons for catalysis disclosed by supramolecular chemistry

The adoption of a supramolecular approach in catalysis promises to address a number of unmet challenges, ranging from activity (unlocking of novel reaction pathways) to selectivity (alteration of the innate selectivity of a reaction, e.g. selective functionalization of C-H bonds) and regulation (switch ON/OFF, sequential catalysis, etc.). Supramolecular tools such as reversible association and recognition, pre-organization of reactants and stabilization of transition states upon binding offer a unique chance to achieve the above goals disclosing new horizons whose potential is being increasingly recognized and used, sometimes reaching the degree of ripeness for practical use. This review summarizes the main developments that have opened such new frontiers, with the aim of providing a guide to researchers approaching the field. We focus on artificial supramolecular catalysts of defined stoichiometry which, under homogeneous conditions, unlock outcomes that are highly difficult if not impossible to attain otherwise, namely unnatural reactivity or selectivity and catalysis regulation. The different strategies recently explored in supramolecular catalysis are concisely presented, and, for each one, a single or very few examples is/are described (mainly last 10 years, with only milestone older works discussed). The subject is divided into four sections in light of the key design principle: (i) nanoconfinement of reactants, (ii) recognition-driven catalysis, (iii) catalysis regulation by molecular machines and (iv) processive catalysis.

Binding Between Cyclohexanohemicucurbit[n]urils and Polar Organic Guests

Inherently chiral, barrel-shaped, macrocyclic hosts such as cyclohexanohemicucurbit[n]urils (cycHC[n]) bind zinc porphyrins and trifluoroacetic acid externally in halogenated solvents. In the current study, we tested a set of eighteen organic guests with various functional groups and polarity, namely, thiophenols, phenols, and carboxylic and sulfonic acids, to identify a preference toward hydrogen bond–donating molecules for homologous cycHC[6] and cycHC[8]. Guests were characterized by Hirshfeld partial charges on acidic hydrogens and their binding by ¹H and ¹⁹F NMR titrations. Evaluation of association constants revealed the complexity of the system and indirectly proved an external binding with stoichiometry over 2:1 for both homologs. It was found that overall binding strength is influenced by the stoichiometry of the formed complexes, the partial atomic charge on the hydrogen atom of the hydrogen bond donor, and the bulkiness of the guest. Additionally, a study on the formation of complexes with halogen anions (Cl⁻ and Br⁻) in methanol and chloroform, analyzed by ¹H NMR, did not confirm complexation. The current study widens the scope of potential applications for host molecules by demonstrating the formation of hydrogen-bonded complexes with multisite hydrogen bond acceptors such as cycHC[6] and cycHC[8].

Tuneable Control of Organocatalytic Activity through Host-Guest Chemistry

Dynamic regulation of chemical reactivity is important in many complex chemical reaction networks, such as cascade reactions and signal transduction processes. Signal responsive catalysts could play a crucial role in regulating these reaction pathways. Recently, supramolecular encapsulation was reported to regulate the activities of artificial catalysts. We present a host-guest chemistry strategy to modulate the activity of commercially available synthetic organocatalysts. The molecular container cucurbit[7]uril was successfully applied to change the activity of four different organocatalysts and one initiator, enabling up- or down-regulation of the reaction rates of four different classes of chemical reactions. In most cases CB[7] encapsulation results in catalyst inhibition, however in one case catalyst activation by binding to CB[7] was observed. The mechanism behind this unexpected behavior was explored by NMR binding studies and pKa measurements. The catalytic activity can be instantaneously switched during operation, by addition of either supramolecular host or competitive binding molecules, and the reaction rate can be predicted with a kinetic model. Overall, this signal responsive system proves a promising tool to control catalytic activity.

Transforming a Fluorochrome to an Efficient Photocatalyst for Oxidative Hydroxylation: A Supramolecular Dimerization Strategy Based on Host-Enhanced Charge Transfer

The development of non-covalent synthetic strategy to fabricate efficient photocatalysts is of great importance in theranostic and organic materials. Herein, a fluorochrome N,N'-dimethyl 2,5-bis(4-pyridinium)thiazolo[5,4-d]thiazolediiodide (MPT) was transformed into an efficient photocatalyst through supramolecular dimerization in the cavity of cucurbit[8]uril (CB[8]). The host-enhanced charge transfer interaction within the supramolecular dimer 2MPT-CB[8] dramatically promoted intersystem crossing to produce triplet. In addition, the staggered conformation of 2MPT-CB[8] facilitated the energy transfer and electron transfer of the triplet. As a result, 2MPT-CB[8] could serve as a high-efficiency photocatalyst for the oxidative hydroxylation of arylboronic acids. This supramolecular dimerization strategy enriches the supramolecular engineering of functional π-systems. It is anticipated that this strategy can be extended to fabricate various π-systems with tailor-made functions.

Fluorescent Molecular Cages with Sucrose and Cyclotriveratrylene Units for the Selective Recognition of Choline and Acetylcholine

The synthesis of four fluorescent diastereoisomeric molecular cages containing cyclotriveratrylene and sucrose moieties connected via the naphthalene linkers is reported. These diastereoisomers were found to be selective and efficient receptors for acetylcholine and choline. Compound P-5a has a better affinity for choline over acetylcholine, while cage M-5a exhibits a higher association constant for acetylcholine over choline. The highest selectivity value was observed for compound M-5a (K_ACh/K_Ch = 3.1). Cages P-5a, P-5b, M-5a, and M-5b were fully characterized by the advanced NMR techniques, and ECD spectroscopy was supported by DFT calculations. The binding constants K_a of these receptors were determined by fluorescence titration experiments in acetonitrile.

Supramolecular electrocatalysis of a highly efficient oxygen evolution reaction with cucurbit[6]uril

A supramolecular ternary electrocatalyst, fabricated via the stepwise-coating of polypyrrole, rGO and cucurbit[6]uril, was developed for highly efficient oxygen evolution reaction with full electrochemical performance.