Controlling factors in the synthesis of cucurbituril and its homologues

Coordination-Adaptive Polydentate Pseudorotaxane Ligand for Capturing Multiple Uranyl Species

The propensity of uranyl for hydrolysis in aqueous environments prevents precise control of uranyl species in the scenarios of on-demand separation and tailored synthesis. Herein, using cucurbit[7]uril (CB[7]) as the macrocyclic molecule and 4,4'-bipyridine-N,N'-dioxide (DPO) as the string molecule, we propose a new kind of multidentate pseudorotaxane ligand, DPO@CB[7] for capturing uranyl species at different pH's. With the aprotic nature of DPO for metal coordination, the coordination ability of the DPO@CB[7] ligand is less affected by pH and can work in a wide range of pH's. Furthermore, by adaptive uranyl coordination, this aprotic pseudorotaxane ligand achieves effective recognition for different uranyl species ranging from monomeric to tetrameric originating from hydrolysis at varying pH's, and four novel uranyl-rotaxane compounds (URC1-4) are successfully obtained. Single-crystal X-ray diffraction analysis reveals that the DPO@CB[7] ligand coordinates with uranyl centers from monomeric to tetrameric in four different modes, as a result of structural flexibility of the DPO@CB[7] pseudorotaxane ligand. A detailed discussion for conformation flexibility of the DPO@CB[7] ligand has been conducted on the position changes of the DPO ligand trapped in the CB[7], which thus reveals good adaptivity of DPO@CB[7] that is noncovalently bonded as a supramolecular motif. In addition, characterization of the physicochemical properties of URC1 and URC2 with high phase purity, including powder X-ray diffraction (PXRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and luminescence properties, are also provided. This work provides a good case of an adaptive pseudorotaxane ligand for the recognition and capture of different uranyl species and will bring valuable hints to the design of multifunctional supramolecular ligands for actinide separation in the future.

Bioinspired tunable hydrogels: An update on methods of preparation, classification, and biomedical and therapeutic applications

Hydrogels exhibit water-insoluble three-dimensional polymeric networks capable of absorbing large amounts of biological fluids. Both natural and synthetic polymers are used for the preparation of hydrogel networks. Such polymeric networks are fabricated through chemical or physical mechanisms of crosslinking. Chemical crosslinking is accomplished mainly through covalent bonding, while physical crosslinking involves self-healing secondary forces like H-bonding, host-guest interactions, and antigen-antibody interactions. The building blocks of the hydrogels play an important role in determining the mechanical, biological, and physicochemical properties. Hydrogels are used in a variety of biomedical applications like diagnostics (biodetection and bioimaging), delivery of therapeutics (drugs, immunotherapeutics, and vaccines), wound dressing and skin materials, cardiac complications, contact lenses, tissue engineering, and cell culture because of the inherent characteristics like enhanced water uptake and structural similarity with the extracellular matrix (ECM). This review highlights the recent trends and advances in the roles of hydrogels in biomedical and therapeutic applications. We also discuss the classification and methods of hydrogels preparation. A brief outlook on the future directions of hydrogels is also presented.

Thermodynamics of Pillararene•Guest Complexation: Blinded Dataset for the SAMPL9 Challenge

We report an investigation of the complexation between a water soluble pillararene host (WP6) and a panel of hydrophobic cationic guests (G1 - G20) by a combination of ¹H NMR spectroscopy and isothermal titration calorimetry in phosphate buffered saline. We find that WP6 forms 1:1 complexes with K_a values in the 10⁴ - 10⁹ M^-1 range driven by favorable enthalpic contributions. This thermodynamic dataset serves as blinded data for the SAMPL9 challenge.

Preparation, characterization, and biological activity study of thymoquinone-cucurbit[7]uril inclusion complex

In this study, the formation of a host–guest inclusion complex between cucurbit[7]uril (CB[7]) and thymoquinone (TQ) was investigated in aqueous solution. The formation of a stable inclusion complex, CB[7]–TQ, was confirmed by using different techniques, such as ¹H NMR and UV-visible spectroscopy. The aqueous solubility of TQ was clearly enhanced upon the addition of CB[7], which provided an initial indication for supramolecular complexation. The complexation stoichiometry and the binding constant of the inclusion complex were determined through a combination of two sets of titration methods, including UV-visible and fluorescence displacement titrations. Both methods suggested the formation of a 1 : 1 stoichiometry between CB[7] and TQ with moderate binding affinity of 3 × 10³ M⁻¹. Density functional theory (DFT) calculations were also performed to verify the structure of the resulted host–guest complex and to support the complexation stoichiometry. The theoretical calculations were in agreement with experimental results obtained by ¹H NMR spectroscopy. Most importantly, the cytotoxic effect of the CB[7]–TQ complex was investigated against cancer and normal cell lines. The results showed that the anticancer activity of TQ against MDA-MB-231 cells was enhanced by the complexation with CB[7], while no significant effect was observed in MCF-7 cells. The results also confirmed the low toxicity of the CB[7] host molecule that supports the use of CB[7] as a drug carrier.

The host–guest inclusion complexation of thymoquinone by cucurbit[7]uril in aqueous solution is established, which results in an enhanced biological activity.

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.

Cinnamaldehyde–cucurbituril complex: investigation of loading efficiency and its role in enhancing cinnamaldehyde in vitro anti-tumor activity

This study aimed to clarify the physico-chemical properties of cucurbit[7]uril (CB[7]) and cinnamaldehyde (Cinn) inclusion complexes (CB[7]–Cinn) and their resulting antitumor activity.

The cucurbit[7]uril effect on reference substances for NMR in deuterium oxide solution

The effect of macrocyclic molecule cucurubit[7]uril on the chemical shifts of internal reference substances for NMR studies in deuterium oxide solution and the cause were investigated.

Inclusion complexation and self-association of cucurbit[n]uril (n = 6, 7) and diquat under pseudo-physiological conditions

The formation and steric structure of the inclusion complex of cucurbit[n]uril (CB[n]; n = 6, 7) and diquat (DQ) were investigated through NMR measurements under the pH conditions of human pseudo-gastric or body fluids, in physiological saline.

Encapsulation of l-valine, d-leucine and d-methionine by cucurbit[8]uril

The binding interactions of cucurbit[8]uril (Q[8]) with l-valine, d-leucine, and d-methionine, both in aqueous solution and solid state, have been studied by 1H NMR spectroscopy and X-ray crystallography.

Evaluation of negolyte properties of supramolecular binary complexes based on viologen-cucurbit[7]urils

Viologen-based redox materials have become popular as electrolytes for aqueous organic redox flow batteries (AORFBs) in recent years because of their reversible nature.

Recent Advances in High-strength and High-toughness Polyurethanes Based on Supramolecular Interactions

Recent developments in supramolecular chemistry have generated increasing interest in supramolecular polymers and opened a window for the exploitation of various supramolecular polymeric materials and their multifunctional composites. High-performance polyurethanes,...

An inclusion complex of cucurbit[7]uril with benzimidazolyl benzyl viologen exhibits fluorescence and photochromic properties

A self-assembled supramolecular inclusion complex of Q[7] with benzimidazolyl benzyl viologen exhibits interesting fluorescence emission and reversible photochromism.

Fine-Tuning Macrocycle Cavity to Selectively Bind Guests in Water for Near-Infrared Photothermal Conversion

The rational and specific synthesis of the required organic macrocycles to bind the size-matched targeted guests without undesired macrocyclic byproducts remains a great challenge. Herein, based on a new naphthalimide...

Host-guest interaction and properties of cucurbit[8]uril with chloramphenicol

The interaction between cucurbit[8]uril (Q[8]) and chloramphenicol (CPE) was investigated using single-crystal X-ray diffraction spectroscopy, isothermal titration calorimetry (ITC) and UV–vis, NMR and IR spectroscopy. The effects of Q[8] on the stability, in vitro release performance and antibacterial activity of CPE were also studied. The results showed that CPE and Q[8] formed a 1:1 inclusion complex (CPE@Q[8]) with an inclusion constant of 5.474 × 10⁵ L/mol. The intervention of Q[8] did not affect the stability of CPE, but obviously reduced the release rate of CPE in artificial gastric and intestinal juice; Q[8] has a slow-release effect on CPE. The antibacterial results showed that the minimum inhibitory concentration (MIC) of CPE and CPE@Q[8] toward Escherichia coli (E. coli) was 1.5 × 10^–3 and 1.0 × 10^–3 mol/L, respectively, and toward Staphylococcus aureus (S. aureus), the MIC was 2.0 × 10^–3 mol/L for both CPE and CPE@Q[8]. Therefore, Q[8] enhanced the inhibitory activity of CPE against E. coli.

Nanocollision mediated electrochemical sensing of host-guest chemistry at a nanoelectrode surface

Electrochemical (EC) measurements of dynamic nanoparticle collisions on a support electrode provide a powerful approach to study the electrical properties of interfacial molecules self-assembled on the electrode surface. By introducing a special cage-shaped macrocyclic molecule, cucurbit[7]uril (CB7), onto a gold nanoelectrode surface, we show that the dynamic interactions between CB7 and the colliding nanoparticles can be real-time monitored via the appearance of distinct EC current switching signals. When a guest molecule is included in the CB7 cavity, the changed host-guest chemistry can be probed via the amplitude change of the EC current signals. In addition, different guest molecules can be recognized by CB7 on the nanoelectrode surface, giving rise to distinguishable current jump signals for different host-guest systems. Remarkably, two well-defined current states are observed in the EC measurements of the CB7-ferrocene complex, indicating two orientation geometries of ferrocene inside the CB7 cavity can be resolved in this EC sensing platform. This work demonstrates an effective approach for studying the dynamics of host-guest chemistry at the liquid-solid interface and sheds light on a convenient EC sensor for the recognition of target molecules with the aid of CB7.

Study on the host-guest complex of dicyclohexanocucurbit[6]uril and 2-phenylbenzimidazole, and its recognition effect toward Fe3

This paper has selected dicyclohexanocucurbit[6]uril (CyH2Q[6]) as the host and 2-phenylbenzimidazole (G) as the guest to investigate the host-guest interaction mode between CyH2Q[6] and G. Under acidic conditions, the complex was characterized using nuclear magnetic resonance, ultraviolet and fluorescence spectroscopy. The results show that the molecular ratio of CyH2Q[6] to G is 2 : 1. The crystals were cultured with ZnCl2 as a structural inducer under acidic conditions and single crystal X-ray diffraction showed that the molecular ratio of CyH2Q[6] to G is 1 : 3. The G@CyH2Q[6] was used as a fluorescent probe to identify metal cations. The probe exhibits a good selective recognition effect toward Fe3+ ions, which involves a reduced fluorescence intensity with a limit of detection of 1.321 × 10-6 mol l-1.

Cucurbiturils as Effectors on the Self-Assembly of Pd(II) and Pt(II) Metallacycles

Four bidentate, dicationic ligands (L1²⁺-L4²⁺) were prepared and investigated as guests for binding by the cucurbit[7]uril (CB[7]) host and structural components for metal (Pd and Pt)-coordinated self-assembly into metallacycles. In aqueous solutions, all the ligands were found to form stable complexes of variable stoichiometries with CB[7], and only one (L2²⁺) failed to self-assemble, induced by the presence of suitable Pd or Pt complexes, into metallacycles. Exposure of the Pd-based metallacycles to CB[7] led to their disassembly at room temperature, while the Pt-based metallacycles remained stable under these conditions. However, heating of the Pt metallacycles in the presence of CB[7] also led to their disassembly. This interplay between the interactions in aqueous media of the L1²⁺, L3²⁺, and L4²⁺ ligands with the CB[7] host and Pd (or Pt) complexes suggests the possibility of using these or related systems for controlled drug delivery applications.

A reference scale of cucurbit[7]uril binding affinities

The accurate determination of ultra-high binding affinities in supramolecular host-guest chemistry is a challenging endeavour because direct binding titrations are generally limited to affinities <10⁶ M^-1 due to sensitivity constraints of common titration methods. To determine higher affinities, competitive titrations are usually performed, in which one compound with a well established binding affinity serves as a reference. Herein, we propose a reference scale for such competitive titrations with the host cucurbit[7]uril (CB7) comprising binding affinities in the range from 10³ to 10¹⁵ M^-1. The suggested reference compounds are commercially available and will aid in the future determination of CB7 binding affinities for stimuli-responsive host-guest systems.

Selective Separation of Hexachloroplatinate(IV) Dianions Based on Exo-Binding with Cucurbit[6]uril

The recognition and separation of anions attracts attention from chemists, materials scientists, and engineers. Employing exo-binding of artificial macrocycles to selectively recognize anions remains a challenge in supramolecular chemistry. We report the instantaneous co-crystallization and concomitant co-precipitation between [PtCl₆ ]^2- dianions and cucurbit[6]uril, which relies on the selective recognition of these dianions through noncovalent bonding interactions on the outer surface of cucurbit[6]uril. The selective [PtCl₆ ]^2- dianion recognition is driven by weak [Pt-Cl⋅⋅⋅H-C] hydrogen bonding and [Pt-Cl⋅⋅⋅C=O] ion-dipole interactions. The synthetic protocol is highly selective. Recognition is not observed in combinations between cucurbit[6]uril and six other Pt- and Pd- or Rh-based chloride anions. We also demonstrated that cucurbit[6]uril is able to separate selectively [PtCl₆ ]^2- dianions from a mixture of [PtCl₆ ]^2- , [PdCl₄ ]^2- , and [RhCl₆ ]^3- anions. This protocol could be exploited to recover platinum from spent vehicular three-way catalytic converters and other platinum-bearing metal waste.

The Effect of Cucurbit[7]uril on the Antitumor and Immunomodulating Properties of Oxaliplatin and Carboplatin

Cucurbit[7]uril (CB[7]) is a molecular container that may form host–guest complexes with platinum(II) anticancer drugs and modulate their efficacy and safety. In this paper, we report our studies of the effect of CB[7]–oxaliplatin complex and the mixture of CB[7] and carboplatin (1:1) on viability and proliferation of a primary cell culture (peripheral blood mononuclear cells), two tumor cell lines (B16 and K562) and their activity in the animal model of melanoma. At the same time, we studied the impact of platinum (II) drugs with CB[7] on T cells and B cells in vitro. Although the stable CB[7]–carboplatin complex was not formed, the presence of cucurbit[7]uril affected the biological properties of carboplatin. In vivo, CB[7] increased the antitumor effect of carboplatin, but, at the same time, increased its acute toxicity. Compared to free oxaliplatin, its complex with CB[7] shows a greater cytotoxic effect on tumor cell lines B16 and K562, while in vivo, the effects of the free drug and encapsulated drug were comparable. However, in vivo studies also demonstrated that the encapsulation of oxaliplatin in CB[7] lowered the toxicity of the drug.

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].

Preparation and characterization of a new type of symmetrical dicyclopentyl substituted cucurbit[6]uril

A symmetrical dicyclopentyl substituted cucurbit[6]uril (CyP2Q[6]) was synthesized, and crystallized under the conditions of 3 mol/L hydrochloric acid solution and the induction of ZnCl2. The crystal structure was characterized by X-ray single crystal diffractometer, 1H NMR and MS, and the results show that the crystal belongs to the monoclinic crystal system with P21/n space group, a = 13.095 (2), b = 33.002 (6), c = 15.770 (3), α = 90°, β = 102.828(5)°, γ = 90°, Z = 4, and a macroporous honeycomb structure appears in the crystal.

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.

Stuffed pumpkins: mechanochemical synthesis of host-guest complexes with cucurbit[7]uril

Solvent-free mechanochemical synthesis (ball-milling) was used to prepare inclusion complexes with cucurbit[7]uril and four model guest molecules (adamantane, adamantyl-1-amine hydrochloride, toluidine hydrochloride, and p-phenylenediamine dihydrochloride). Successful formation of individual inclusions was independently confirmed by one- and two-dimensional solid-state NMR techniques and differential scanning calorimetry. Mechanochemical synthesis represents an alternative path towards new types of cucurbit[n]uril/guest inclusion complexes that are not accessible due to limited solubility of the individual components.

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 Modulation of Antibacterial Activity of Ambroxol by Cucurbit[7]uril

Supramolecular encapsulation by cucurbit[7]uril (CB[7]) was recently demonstrated to provide a simple and efficient method for antibacterial activity regulation of antibiotics. In this work, CB[7] was shown to form binary host-guest complex with ambroxol hydrochloride (ABX), a clinical mucokinetic and expectorant drug, which was reported to exhibit certain antibacterial activity. ¹ H NMR titration and isothermal titration calorimetry experiment results suggested that the 4-hydroxyl cyclohexylamine group of ABX was included inside the CB[7] cavity, with a binding constant K_a of (6.69±0.11)×10⁵  M^-1 in phosphate buffered saline (PBS) solution, thermodynamically driven by both enthalpy change (ΔH=-12.2 kJ/mol) and entropy change (TΔS=21.1 kJ/mol). More importantly, ABX's inhibitory activity (MIC₅₀ ) against bacillary strains towards Pseudomonas aeruginosa and Escherichia coli strains was decreased from (5.11±0.31)×10^-6  M^-1 and (2.63±0.34)×10^-5  M^-1 to zero upon encapsulation by CB[7], and was subsequently recovered to almost its original activity when a competitive guest, amantadine hydrochloride, for disassembling CB[7]-ABX complex, was added, suggesting that the antibacterial activity of ABX could be readily "turned off/on" upon its complexation and decomplexation with CB[7].

Cucurbit[10]uril-Encapsulated Cationic Porphyrins with Enhanced Fluorescence Emission and Photostability for Cell Imaging

Porphyrins are widely applied for imaging, diagnosis, and treatment of diseases because of their excellent photophysical properties. However, porphyrins easily tend to aggregate driven by hydrophobic interaction and π-π stacking in an aqueous medium, which causes fluorescence quenching of the porphyrins as well as limitation of cell uptake and intracellular accumulation. Herein, cucurbit[10]uril (CB[10]) was used to fully encapsulate cationic porphyrin (CPor) in the large cavity with strong binding affinity in aqueous solutions, and the CPor aggregates were efficient disassembled, companying remarkable enhancing its fluorescence intensity. The CB[10]-based host-guest complex provided excellent protection to CPor, resulting in less susceptibility to oxidation and imparting higher photostability to CPor for cell imaging. In addition, by complexation with CB[10], it was found that the fluorescence signals and photostability of CPor were also effectively improved in cells with different reactive oxygen species levels. It is highly anticipated that the large macrocyclic host cavity-triggered large-guest encapsulation strategy in this work will provide a convenient and efficient method for designing supramolecular porphyrin dyes, thus broadening the diagnosis and imaging application in cells and microorganisms.

Host-guest modes and supramolecular frameworks of complexes of tetramethyl cucurbit[6]uril with 4-chloroaniline and 4,4'-diaminostilbene

Since the first reportal on decamethylcucurbit[5]uril (Me₁₀Q[5]) in 1992, substituted cucurbit[n]urils have attracted considerable research interest. In this study, the host–guest modes between the tetramethyl cucurbit[6]uril (TMeQ[6]) as a host and 4-chloroaniline and 4,4′-diaminostilbene (G1 and G2) as guests were investigated by single-crystal X-ray diffraction, NMR, ITC, UV-Vis spectrum, and MALDI-TOF mass spectrometry analyses. The experimental results showed that TMeQ[6] formed a 1 : 1 inclusion compound with G1, and the carbonyl portal of TMeQ[6] formed a 1 : 1 self-assembly with G2. Further, multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C–H⋯π interactions, ion–dipole interactions, and dipole–dipole interactions).

Two TMeQ[6]-based multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C–H... π interactions, ion–dipole interactions, and dipole–dipole interactions).

Electron transfer photochromism of solid-state supramolecules constructed by cucurbit[n]uril (n = 5–8) and 1-(4-carboxybenzyl)-4-[2-(4-pyridyl)-vinyl]-pyridinium chloride

Solid-state supramolecular complexes of a bispyridinium ethylene derivative with cucurbit[n = 5–8]uril exhibit fast responsive photochromic properties, which are caused by the electron transfer from the host to the guest.

Fluorescence visualization of cucurbit[8]uril-triggered dynamic host–guest assemblies

Dynamic assemblies of π-conjugated bispyridinium guests with cucurbit[8]uril in aqueous solution could be distinguished by real-time naked-eye observation of the resulting quantitative fluorescence emissions.

Assemblies of cucurbit[6]uril-based coordination complexes with disulfonate ligands: from discrete complexes to one- and two-dimensional polymers

Nine assemblies of Q[6]-based coordination complexes incorporating disulfonate ligands were obtained and two of them were found to have the ability to sense Fe³⁺via a fluorescence quenching effect.

Cucurbituril-assisted formation of tunable carbon dots from single organic precursors in water

A facile method by utilizing the host–guest interaction of Q[n]s for the catalytic fabrication of CDs with high emitting qualities and a tunable particle size from a single organic precursor in water with high output has been demonstrated.

Cucurbituril-Oriented Nanoplatforms in Biomedical Applications

Cucucrbituril (CB) belongs to a family of macrocycles that are easily accessible. Their structural specificity provides excellent molecular recognition capabilities, with the ability to be readily chemically modified. Because of these properties, researchers have found CB to be a useful molecular carrier for delivering drug molecules and therapeutic biomolecules. Their significance lies in the fact that CB not only increases the solubility and stability of an encapsulated guest but also provides the possibility to achieve targeted delivery of the guest molecule. Therefore, the emergence of CB undoubtedly provides opportunities for the development of targeted drug delivery in an era where intelligent drugs have attracted considerable attention. It has also been found that CB can enhance fluorescent dyes, allowing the preparation of biosensors with enhanced sensitivity for use in clinical settings. In the present review, the acquisition, properties, and structural modifications of CB are first comprehensively described, and then the value of this macrocycle in applications within the medical field is discussed. In addition, we have also summarized patent applications of CB in this field over recent years, aiming to illustrate the current status of developments of this molecule. Finally, we discuss the challenges faced by CB in the medical field and future trends in its development.

Suppression of Malachite Green-Induced Toxicity to Human Liver Cells Utilizing Host-Guest Chemistry of Cucurbit[7]uril

We investigated a host-guest complex between cucurbit[7]uril and malachite green, and its effect on the toxicity to human liver cells. The host-guest complexation was evaluated by a UV/vis titration and electrospray-ionization mass spectrometry. Interestingly, the host-guest complex resulted in remarkable suppression of the toxicity of malachite green in its practical concentration range (ca. ∼6 μM). This study is one step forward to the active control of the biological effects of potent toxicants utilizing host-guest chemistry.

Separating Enthalpic, Configurational, and Solvation Entropic Components in Host-Guest Binding: Application to Cucurbit[7]uril Complexes through a Full In Silico Approach via Water Nanodroplets

Cucurbiturils are a family of supramolecular hosts obtained by condensation of glycoluril and formaldehyde. Cucurbit[7]uril, CB[7], is the most prominent member of the family for its biomolecular interest, arising from its mild solubility in water and for its strong binding with a large variety of guests containing nonpolar fragments such as adamantanes and ferrocene. For instance, CB[7] encapsulates diamantane diammonium iodide with an attomolar dissociation constant, a value unmatched even in natural encapsulation processes. Computational chemistry has been extensively employed to describe the enthalpic-entropic compensation principle of the molecular recognition process of cucurbituril hosts, but the synergistic contribution of experimental data is required for accurate results to be obtained. This paper proposes the first fully theoretical model able to reconcile the calculated thermodynamics of the complexation process with the experimental data obtained by calorimetry (ITC) for cucurbit[7]uril. The model allows the isolation and estimation of all of the enthalpic and entropic contributions coming from solute and solvent alike to the whole host-guest binding event and enables the straightforward calculation of the contribution of the solvation entropy to the binding.

pH-Mediated Single Molecule Conductance of Cucurbit[7]uril

Recognition tunneling technique owns the capability for investigating and characterizing molecules at single molecule level. Here, we investigated the conductance value of cucurbit[7]uril (CB[7]) and melphalan@CB[7] (Mel@CB[7]) complex molecular junctions by using recognition tunneling technique. The conductances of CB[7] and Mel@CB[7] with different pH values were studied in aqueous media as well as organic solvent. Both pH value and guest molecule have an impact on the conductance of CB[7] molecular junction. The conductances of CB[7] and Mel@CB[7] both showed slightly difference on the conductance under different measurement systems. This work extends the molecular conductance measurement to aqueous media and provides new insights of pH-responsive host-guest system for single molecule detection through electrical measurements.