Viologen-Cucurbit[7]uril Based Polyrotaxanated Covalent Organic Networks: A Metal Free Electrocatalyst for Oxygen Evolution Reaction

Viologen-based covalent organic networks represent a burgeoning class of materials distinguished by their captivating properties. Here, supramolecular chemistry is harnessed to fabricate polyrotaxanated ionic covalent organic polymers (iCOP) through a Schiff-base condensation reaction under solvothermal conditions. The reaction between 1,1'-bis(4-aminophenyl)-[4,4'-bipyridine]-1,1'-diium dichloride (DPV-NH2) and 1,3,5-triformylphloroglucinol (TPG) in various solvents yields an iCOP-1 and iCOP-2. Likewise, employing cucurbit[7]uril (CB[7]) in the reaction yielded polyrotaxanated iCOPs, denoted as iCOP-CB[7]-1 and iCOP-CB[7]-2. All four iCOPs exhibit exceptional stability under the acidic and basic conditions. iCOP-CB[7]-2 displays outstanding electrocatalytic Oxygen Evolution Reaction (OER) performance, demanding an overpotential of 296 and 332 mV at 10 and 20 mA cm-2, respectively. Moreover, the CB[7] integrated iCOP-2 exhibits a long-term stable nature for 30 h in 1 m KOH environment. Further, intrinsic activity studies like TOF show a 4.2-fold increase in generation of oxygen (O2) molecules than the bare iCOP-2. Also, it is found that iCOP-CB[7]-2 exhibits a high specific (19.48 mA cm-2) and mass activity (76.74 mA mg-1) at 1.59 V versus RHE. Operando-EIS study evident that iCOP-CB[7]-2 commences OER at a relatively low applied potential of 1.5 V versus RHE. These findings pave the way for a novel approach to synthesizing various mechanically interlocked molecules through straightforward solvothermal conditions.

Photo-Controlled Nano-Supramolecular Size and Reversible Luminescent Behaviors Based on Cucurbit[7]uril Cascaded Assembly

Supramolecular luminescent material with switchable behavior and photo-induced aggregation with emission enhancement is a current research hot spot. Herein, a size-tunable nano-supramolecular assembly with reversible photoluminescent behavior was constructed by noncovalent polymerization of diarylethene-bridged bis(coumarin) derivative (DAE-CO), cucurbit[7]uril (CB[7]), and β-cyclodextrin-grafted hyaluronic acid (HACD). Benefiting from the macrocyclic confinement effect, the guest molecule DAE-CO was included into the cavity of CB[7] to give enhanced fluorescence emission of the resulting DAE-CO⊂CB[7]2 with longer lifetime at 432 nm to 1.43 ns, thereby further enhancing fluorescence output and lifetime (1.46 ns) when further assembled with HACD, compared with the free DAE-CO (0.95 ns). In addition, DAE-CO, DAE-CO⊂CB[7]2, and DAE-CO⊂CB[7]2&HACD all possessed characteristics of aggregation-induced emission and reversible photo-switched structural interconversion, exhibiting an obvious photophysical activation phenomenon of self-aggregation into larger nanoparticles with increase in fluorescence emission intensity, lifetime, and size after irradiation, which could be increased step by step with the alternating irradiation of 254 nm (5 min) or >600 nm (30 s) repeated 7 times. These supramolecular assemblies were successfully used in the tumor cells' targeted imaging and anti-counterfeiting because of the capability of HACD for recognizing specific receptors overexpressed on the surface of tumor cells and the excellent photo-regulated switch ability of DAE-CO, providing an approach of constructing photo-induced emission-enhanced luminescent materials.

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.

Modulation of the Fibrillation Kinetics and Morphology of a Therapeutic Peptide by Cucurbit[7]uril

Fibrillation is a challenge commonly encountered in the formulation and development of therapeutic peptides. Cucurbit[7]urils (CB[7]), a group of water soluble macrocycles, have been reported to suppress fibrillation in insulin and human calcitonin through association with Phe and Tyr residues which drive fibril formation. Here, we report the effect of CB[7] on the fibrillation behavior of the HIV fusion inhibitor enfuvirtide (ENF) that contains N-terminal Tyr and C-terminal Phe residues. Thioflavin T fluorescence, CD spectroscopy, and transmission electron microscopy were used to monitor fibrillation behavior. Fibrillation onset showed a strong pH dependency, with pH 6.5 identified as the condition most suitable to monitor the effects of CB[7]. Binding of CB[7] to wild-type ENF was measured by isothermal titration calorimetry and was consistent with a single site (K_a = 2.4 × 10⁵ M^-1). A weaker interaction (K_a = 2.8 × 10³ M^-1) was observed for an ENF mutant with the C-terminal Phe substituted for Ala (ENFm), suggesting that Phe was the specific site for CB[7] recognition. The onset of ENF fibrillation onset was delayed, rather than fully suppressed, in the presence of CB[7]. The ENFm mutant showed a greater delay in fibrillation onset but with no observable effect on fibrillation kinetics in the presence of CB[7]. Interestingly, ENF/CB[7] and ENFm fibrils exhibited comparable morphologies, differing from those observed for ENF alone. The results indicate that CB[7] is capable of modulating fibrillation onset and the resulting ENF fibrils by specifically binding to the C-terminal Phe residue. The work reinforces the potential of CB[7] as an inhibitor of fibrillation and highlights its role in determining fibril morphologies.

A Combination of Bio-Orthogonal Supramolecular Clicking and Proximity Chemical Tagging as a Supramolecular Tool for Discovery of Putative Proteins Associated with Laminopathic Disease

Protein mutations alter protein-protein interactions that can lead to a number of illnesses. Mutations in lamin A (LMNA) have been reported to cause laminopathies. However, the proteins associated with the LMNA mutation have mostly remained unexplored. Herein, a new chemical tool for proximal proteomics is reported, developed by a combination of proximity chemical tagging and a bio-orthogonal supramolecular latching based on cucurbit[7]uril (CB[7])-based host-guest interactions. As this host-guest interaction acts as a noncovalent clickable motif that can be unclicked on-demand, this new chemical tool is exploited for reliable detection of the proximal proteins of LMNA and its mutant that causes laminopathic dilated cardiomyopathy (DCM). Most importantly, a comparison study reveals, for the first time, mutant-dependent alteration in LMNA proteomic environments, which allows to identify putative laminopathic DCM-linked proteins including FOXJ3 and CELF2. This study demonstrates the feasibility of this chemical tool for reliable proximal proteomics, and its immense potential as a new research platform for discovering biomarkers associated with protein mutation-linked diseases.

A Fluorescent Unnatural Mannosamine Derivative with Enhanced Emission Upon Complexation with Cucurbit[7]uril

Metabolic incorporation of unnatural functionality on glycans has allowed chemical biologists to observe and affect cellular processes. Recent work has resulted in glycan-fluorophore structures that allow for direct visualization of glycan-mediated processes, shining light on their role in living systems. This work describes the serendipitous discovery of a small chemical reporter-fluorophore. Investigations into the mechanism of fluorescence arising from (trimethylsilyl)methylglycine appended on mannosamine suggest rigidity and restriction of lone pair geometry contribute to the fluorescent behaviour. In fact, in situ cyclization and encapsulation in cucurbit[7]uril enhance fluorescence to levels that can be observed in live cells. While the reported unnatural mannosamine does not traverse the sialic acid biosynthetic pathway, this discovery may lead to small, "turn-on" chemical reporters for incorporation in living systems.

Supramolecular Interfaces and Reconfigurable Liquids Derived from Cucurbit[7]uril Surfactants

Nanoparticle surfactants (NPSs) offer a powerful means to stabilize the oil-water interface and construct all-liquid devices with advanced functions. However, as the nanoparticle size decreases to molecular-scale, the binding energy of the NPS to the interface reduces significantly, leading to a dynamic adsorption of NPS and "liquid-like" state of the interfacial assemblies. Here, by using the host-guest recognition between a water-soluble small molecule, cucurbit[7]uril (CB[7]) and an oil-soluble polymer ligand, methyl viologen-terminated polystyrene, a supramolecular NPS model, termed CB[7] surfactant, is described. CB[7] surfactants form and assemble rapidly at the oil-water interface, generating an elastic film with excellent mechanical properties. The binding energy of CB[7] surfactant to the interface is sufficiently high to hold it in a jammed state, transforming the interfacial assemblies from a "liquid-like" to "solid-like" state, enabling the structuring of liquids. With CB[7] surfactants as the emulsifier, O/W, W/O and O/W/O emulsions can be prepared in one step. Owing to the guest-competitive responsiveness of CB[7] surfactants, the assembly/disassembly and jamming/unjamming of CB[7] surfactants can be well controlled, leading to the reconfiguration of all-liquid constructs.

Cucurbit[7]uril-Mediated Supramolecular Bactericidal Nanoparticles: Their Assembly Process, Controlled Release, and Safe Treatment of Intractable Plant Bacterial Diseases

A safe, biocompatible, and stimuli-responsive cucurbit[7]uril-mediated supramolecular bactericidal nanoparticle was fabricated by encapsulating a highly bioactive carbazole-decorated imidazolium salt (A₁, EC₅₀ = 0.647 μg/mL against phytopathogen Xanthomonas oryzae pv oryzae) into the host cucurbit[7]uril (CB[7]), thereby leading to self-assembled topographies from microsheets (A₁) to nanospheroidal architectures (A₁@CB[7]). The assembly behaviors were elucidated by acquired single-crystal structures, ¹H NMR, ITC, and X-ray powder diffraction experiments. Complex A₁@CB[7] displayed lower phytotoxicity and could efficiently switch on its potent antibacterial ability via introducing a simple competitor 1-adamantanamine hydrochloride (AD). In vivo antibacterial trials against rice bacterial blight revealed that A₁@CB[7] could relieve the disease symptoms after being triggered by AD and provide a workable control efficiency of 42.6% at 100 μg/mL, which was superior to bismerthiazol (33.4%). These materials can provide a viable platform for fabricating diverse stimuli-responsive supramolecular bactericides for managing bacterial infections with improved safety.

Selective Homocysteine Assay with Cucurbit[7]uril by pH Regulation

We report the effect of pH on the supramolecular complexation of two biothiols, viz., homocysteine (Hcy) and cysteine (Cys), with cucurbit[7]uril (CB[7]). Under basic pH conditions, Cys did not complex with CB[7], whereas Hcy efficiently complexed with CB[7], as confirmed by ¹H NMR spectroscopy and Ellman's reagent (5,5'-dithio-bis(2-nitrobenzoic acid), DTNB) assay. ¹H NMR and Raman spectroscopic studies revealed that, in the absence of CB[7], Hcy auto-oxidized slowly (~36 h) to homocystine (HSSH) under basic pH conditions. However, the rate of Hcy oxidation increased by up to 150 fold in the presence of CB[7], as suggested by the DTNB assay. Thus, supramolecular complexation under basic pH conditions led to the formation of a HSSH-CB[7] complex, and not Hcy-CB[7]. The results indicate that Hcy is rapidly oxidized to HSSH under the catalysis of CB[7], which acts as a reaction chamber, in basic pH conditions. Our studies suggest that Hcy concentration, a risk factor for cardiovascular disease, can be selectively and more easily quantified by supramolecular complexation with CB [7].

Insights into β-amyloid transition prevention by cucurbit[7]uril from molecular modeling

In this study, comparable molecular dynamic (MD) simulations of 1.2 microseconds were performed to clarify the prevention of the β-amyloid peptide (Aβ_1-42) aggregation by cucurbit[7]uril (CB[7]). The accumulation of this peptide in the brain is one of the most harmful in Alzheimer's disease. The inhibition mechanism of Aβ_1-42 aggregation by different molecules is attributed to preventing of Aβ_1-42 conformational transition from α-helix to the β-sheet structure. However, our structural analysis shows that the pure water and aqueous solution of the CB[7] denature the native Aβ_1-42 α-helix structure forming different compactness and unfolded conformations, not in β-sheet form. On the other hand, in the three CB[7]@Aβ_1-42 complexes, it was observed the encapsulation of N-terminal (Asp1), Lys16, and Val36 by CB[7] along the MD trajectory, and not with aromatic residues as suggested by the literature. Only in one CB[7]@Aβ_1-42 complex was observed stable Asp23-Lys28 salt bridge with an average distance of 0.36 nm. All CB[7]@Aβ_1-42 complexes are very stable with binding free energy lowest than ∼-50 kcal/mol between the CB[7] and Aβ_1-42 monomer from MM/PBSA calculation. Therefore, herein we show that the mechanism of the prevention of elongation protofibril by CB[7] is due to the disruption of the Asp23-Lys28 salt bridge and steric effects of CB[7]@Aβ_1-42 complex with the fibril lattice, and not due to the transition from α-helix to β-sheet following the dock-lock mechanism.Communicated by Ramaswamy H. Sarma.

Organic Host Encapsulation Effects on Nitrosobenzene Monomer-Dimer Distribution and C-NO Bond Rotation in an Aqueous Solution

The intermolecular (monomer-dimer equilibrium) and intramolecular (C-NO and C-NMe₂ rotations) dynamics of 4-nitrosocumene (1a) and 4-(N,N-dimethylamino)nitrosobenzene (1b), respectively, were found to be controlled by the medium (water) and the host environment (organic capsules and cavitands). The ability of water to shift the equilibrium toward the dimer appears to result from dipolar stabilization of the polar dimer structure and has a resemblance to water's known ability to favor organic cycloaddition reactions. In an aqueous medium, a range of organic hosts selectively include only the nitrosocumene monomer 1a. Encapsulation in the octa acid duplex (OA₂) selects two 1a monomers rather than a dimer structure. Octa acid encapsulation also results in more restricted intramolecular C-N rotations of the guest 1b.

DFT-D4 Insight into the Inclusion of Amphetamine and Methamphetamine in Cucurbit[7]uril: Energetic, Structural and Biosensing Properties

The host-guest interactions of cucurbit[7]uril (CB[7]) as host and amphetamine (AMP), methamphetamine (MET) and their enantiomeric forms (S-form and R-form) as guests were computationally investigated using density functional theory calculations with the recent D4 atomic-charge dependent dispersion corrections. The analysis of energetic, structural and electronic properties with the aid of frontier molecular orbital analysis, charge decomposition analysis (CDA), extended charge decomposition analysis (ECDA) and independent gradient model (IGM) approach allowed to characterize the host-guest interactions in the studied systems. Energetic results indicate the formation of stable non-covalent complexes where R-AMP@CB[7] and S-AMP@CB[7] are more stable thermodynamically than R-MET@CB[7] and S-MET@CB[7] in gas phase while the reverse is true in water solvent. Based on structural analysis, a recognition mechanism is proposed, which suggests that the synergistic effect of van der Waals forces, ion-dipole interactions, intermolecular charge transfer interactions and intermolecular hydrogen bonding is responsible for the stabilization of the complexes. The geometries of the complexes obtained theoretically are in good agreement with the X-ray experimental structures and indicate that the phenyl ring of amphetamine and methamphetamine is deeply buried into the cavity of CB[7] through hydrophobic interactions while the ammonium group remains outside the cavity to establish hydrogen bonds with the portal oxygen atoms of CB[7].

Encapsulation of Metronidazole in Biocompatible Macrocycles and Structural Characterization of Its Nano Spray-Dried Nanostructured Composite

Due to the great potential of biocompatible cucurbit[7]uril (CB7) and 4-sulfonatocalix[4]arene (SCX4) macrocycles in drug delivery, the confinement of the pharmaceutically important metronidazole as an ionizable model drug has been systematically studied in these cavitands. Absorption and fluorescence spectroscopic measurements gave 1.9 × 10⁵ M⁻¹ and 1.0 × 10⁴ M⁻¹ as the association constants of the protonated metronidazole inclusion in CB7 and SCX4, whereas the unprotonated guests had values more than one order of magnitude lower, respectively. The preferential binding of the protonated metronidazole resulted in 1.91 pH unit pK_a diminution upon encapsulation in CB7, but the complexation with SCX4 led to a pK_a decrease of only 0.82 pH unit. The produced protonated metronidazole–SCX4 complex induced nanoparticle formation with protonated chitosan by supramolecular crosslinking of the polysaccharide chains. The properties of the aqueous nanoparticle solutions and the micron-sized solid composite produced therefrom by nano spray drying were unraveled. The results of the present work may find application in the rational design of tailor-made self-assembled drug carrier systems.

Affinity-Directed Dynamics of Host-Guest Motifs for Pharmacokinetic Modulation via Supramolecular PEGylation

Proteins are an impactful class of therapeutics but can exhibit suboptimal therapeutic performance, arising from poor control over the timescale of clearance. Covalent PEGylation is one established strategy to extend circulation time but often at the cost of reduced activity and increased immunogenicity. Supramolecular PEGylation may afford similar benefits without necessitating that the protein be permanently modified with a polymer. Here, we show that insulin pharmacokinetics can be modulated by tuning the affinity-directed dynamics of a host-guest motif used to non-covalently endow insulin with a poly(ethylene glycol) (PEG) chain. When administered subcutaneously, supramolecular PEGylation with higher binding affinities extends the time of total insulin exposure systemically. Pharmacokinetic modeling reveals that the extension in the duration of exposure arises specifically from decreased absorption from the subcutaneous depot governed directly by the affinity and dynamics of host-guest exchange. The lifetime of the supramolecular interaction thus dictates the rate of absorption, with negligible impact attributed to association of the PEG upon rapid dilution of the supramolecular complex in circulation. This modular approach to supramolecular PEGylation offers a powerful tool to tune protein pharmacokinetics in response to the needs of different disease applications.

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.

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.

A novel electrochemical aptasensor for exosomes determination and release based on specific host-guest interactions between cucurbit [7]uril and ferrocene

The superior supramolecular recognition ability of macrocyclic compounds will enhance the sensitivity and selectivity of electrochemical detection, which has a great application potential in electrochemical sensing. Herein, we developed a novel electrochemical aptasensor based on the specific host-guest interactions between cucurbit [7]uril and ferrocene (Fc) for capture, determination and release of exosomes. Macrocyclic compounds, cucurbit [7]uril is modified on the surface of the gold nanoparticles composed electrode by self-assembling. CD63 aptamer linked ferrocene is introduced into this platform to capture exosomes specifically by CD63 protein on the exosomes. The dual specificity of macrocyclic compounds and aptamers enables highly selective and sensitive electrochemical detection of exosomes. The limit of detection (LOD) was 482 particles μL^-1. In addition, the captured exosomes could be released on demand in a very mild manner through aminoferrocene (NH₂-Fc) because of its higher affinity to cucurbit [7]uril. The proposed electrochemical aptasensor showed good performance in detecting exosomes even in plasma samples, thus demonstrating its great potential in early clinical diagnosis. Simultaneously, exosomes could be released undamaged by this protocol, exhibiting good applicability in comprehensive studies of exosomes. Moreover, this strategy can be applied to other target biomolecules by changing the recognition pairs.

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].

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.

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.

Supramolecular Encapsulation of a Neurotransmitter Serotonin by Cucurbit[7]uril

pH-dependent host-guest complexation of a monoamine neurotransmitter, Serotonin, with cucurbit[7]uril has been thoroughly investigated. The binding phenomena were explored using steady-state and time-resolved fluorescence spectroscopy at different pH values. At lower pH, i.e., protonated Serotonin, the binding affinity with cucurbit[7]uril was significantly higher compared to higher pH. Furthermore, detailed NMR titration experiments depicted the solution structure of the host-guest complex through the complexation induced chemical shift values. A competitive binding assay with cesium ions at pD 2.8 was subsequently performed for the further manifestation of the binding. Finally, the molecular docking studies provided well-documented proof of the 1:1 inclusion complex and the geometry of the complex. We believe that understanding from such studies can be important for pH-controlled delivery of serotonin for biological applications.

Interaction of Cucurbit[7]uril with Oxime K027, Atropine, and Paraoxon: Risky or Advantageous Delivery System?

Antidotes against organophosphates often possess physicochemical properties that mitigate their passage across the blood–brain barrier. Cucurbit[7]urils may be successfully used as a drug delivery system for bisquaternary oximes and improve central nervous system targeting. The main aim of these studies was to elucidate the relationship between cucurbit[7]uril, oxime K027, atropine, and paraoxon to define potential risks or advantages of this delivery system in a complex in vivo system. For this reason, in silico (molecular docking combined with umbrella sampling simulation) and in vivo (UHPLC—pharmacokinetics, toxicokinetics; acetylcholinesterase reactivation and functional observatory battery) methods were used. Based on our results, cucurbit[7]urils affect multiple factors in organophosphates poisoning and its therapy by (i) scavenging paraoxon and preventing free fraction of this toxin from entering the brain, (ii) enhancing the availability of atropine in the central nervous system and by (iii) increasing oxime passage into the brain. In conclusion, using cucurbit[7]urils with oximes might positively impact the overall treatment effectiveness and the benefits can outweigh the potential risks.

Cucurbit[7]uril-Mediated 2D Single-Layer Hybrid Frameworks Assembled by Tetraphenylethene and Polyoxometalate toward Modulation of the α-Chymotrypsin Activity

Construction of large-scale single-layer two-dimensional (2D) frameworks in water is significant due to their utilities in various fields. Utilizing macrocycle-mediated supramolecular self-assembly represents a promising approach; however, challenges still remain in their practical preparation. Here, we exploited a two-step supramolecular strategy to build 2D organic-inorganic hybrid frameworks at a micrometer scale in water. Taking advantage of the high binding affinity to cucurbit[7]uril (CB[7]), mono-quaternary ammonium tetraphenylethene (MQATPE) derivatives were first included with CB[7] to form a 1:1 complex (MQATPE@CB[7]). Then, just mixing the complex with anionic polyoxometalate Na₉[EuW₁₀O₃₆]·32H₂O (denoted as Eu-POM) in a 3:1 molar ratio leads to the formation of single-layer 2D films with tens of micrometers via electrostatic and π-π stacking interactions. The most unique feature of this strategy is that the steric effect imposed by CB[7] would not only lead the modules to adopt a periodic hexagonal assembly but also forbid stacking between layers through comparison with the merely multilayered 2D nanosheets self-assembled by MQATPE/Eu-POM. Interestingly, the charge interactions between MQATPE and Eu-POM would lead to the aggregation-induced emission (AIE) fluorescence of MQATPE, and white light emission could be obtained through the simple regulation of the contents of Eu-POM and MQATPE. Furthermore, due to the high surface areas and more accessible active sites, the single-layer films can act as an effective enzyme inhibitor to modulate the activity of α-chymotrypsin (ChT). These findings suggest a simple but universal approach for single-layer hybrid materials, which may hold promise for practical applications in photophysical and biomedical fields.

Supramolecular Nano-Encapsulation of Anabasine Reduced Its Developmental Toxicity in Zebrafish

Anabasine (ANA), a major piperidine alkaloid originally isolated from wild tobacco trees (Nicotiana glauca), has been known to induce serious developmental toxicities such as skeletal deformities in livestock and humans. In this study, we thoroughly investigated the supramolecular nano-encapsulations of ANA by an artificial nanocontainer, cucurbit[7] uril (CB[7]), and examined the influences of the nano-encapsulation on ANA's inherent developmental toxicities on a zebrafish model. We have shown that CB[7] formed 1:1 host-guest inclusion complexes with ANA via a relatively high binding strength [K_a of (7.45 ± 0.31) × 10⁴ M⁻¹] in an aqueous solution, via UV-vis and ¹H nuclear magnetic resonance spectroscopic titrations, as well as isothermal titration calorimetry titration. As a consequence, CB[7] significantly attenuated the developmental toxicity of ANA on zebrafish in vivo. In contrast, for a comparative purpose, β-CD didn't exert any influence on the toxicity of ANA due to its weak binding with ANA, which was not even measurable via either spectroscopic methods or ITC titration. This is the first head-to-head comparison of this pair of nanocontainers, CB[7] and β-CD, on their potential roles in influencing the toxicity of guest molecules and the results suggested that CB[7] could become a more promising functional excipient for reducing the inherent toxicities of active pharmaceutical ingredients, particularly alkaloids that may form relatively strong host-guest binding species with the host.

Cucurbit[7]uril-Based Metal-Organic Rotaxane Framework for Dual-Capture of Molecular Iodine and Cationic Potassium Ion

Metal-organic rotaxane frameworks (MORFs) attracted much attention in the past years for construction of intelligent functional materials. Herein, a one-pot synthesis is reported of a three-dimensional (3D) cucurbit[7]uril (Q[7])-based MORF under hydrothermal conditions, namely Q[7]-MORF-1, formed by encapsulating the anionic benzoate moieties of the tricarboxylate ligand into the cavity of Q[7]. Furthermore, Q[7]-MORF-1 shows dual-capture capacity for iodine and K⁺ selectively among the alkali metal ions. The captured molecular iodine is included in the cavity of Q[7] through halogen-bonding interactions and the K⁺ cations are positioned at the carbonyl port of the Q[7] through K-O coordination interactions.

Encapsulation of oxime K027 into cucurbit[7]uril: In vivo evaluation of safety, absorption, brain distribution and reactivation effectiveness

Oxime-based acetylcholinesterase reactivators (briefly oximes) regenerate organophosphate-inactivated acetylcholinesterase and restore its function. Poor blood-brain-barrier passage and fast elimination from blood limit their actual use in treatment of patients exposed to organophosphates. Previous in vitro results implicated further testing of cucurbit[7]uril as a delivery vehicle for bisquaternary oximes. The present paper focuses on cell toxicity, in vivo safety and influence of cucurbit[7]uril on oxime pharmacokinetics and pharmacodynamics. Neither the K027 nor the complex caused any cell toxicity, changes in blood biochemistry or hepato- or nephrotoxicity in tested concentrations. The encapsulation of K027 increased and accelerated the blood-brain-barrier penetration. The peripheral oxime exposure also increased, supporting the suggestion that cucurbit[7]uril protects the circulating oxime from rapid renal clearance. Contrary to the comparable in vitro reactivation power of K027 and the encapsulated K027, we failed to confirm this in vivo. In theory, this might result from the non-specific binding of molecules to the cucurbit[7]uril or the interaction of K027 with cucurbit[7]uril being too strong for acetylcholinesterase reactivation. Precise explanation requires additional in silico, in vitro and also in vivo experiments.

An Eco- and User-Friendly Herbicide

The increasing use of pesticides in agriculture and gardening has caused severe deterioration to both the ecosystem and the health of users (human beings), so there is an urgent need for eco- and user-friendly pesticides. Among a variety of herbicides, paraquat (PQ), frequently used as an effective herbicidal agent worldwide, is well-known for its serious toxicity that has killed, and harmed, thousands of people and countless wildlife such as fish. Herein, we present a facile supramolecular formulation of PQ@cucurbit[7]uril (PQ@CB[7]), prepared by simply mixing PQ with equivalent (molar) CB[7] in water. With addition of CB[7], PQ's cellular uptake was dramatically inhibited. The reactive oxygen species (ROS) generation and the associated apoptosis otherwise induced by PQ in cellular models were both reduced, resulting in increased cellular viability. In a wildtype zebrafish model that is a typical fragile wildlife species in the ecosystem, the supramolecular formulation exhibited significantly reduced hepatotoxicity and increased survival rate, in comparison with those of the fish exposed to free PQ. In a mouse model that is clinically relevant to human being, the administration of PQ@CB[7] significantly alleviated major organ injuries and unusual hematological parameters that were otherwise induced by free PQ, resulting in a significantly increased survival rate. Meanwhile, this formulation maintained effective herbicidal activity that was equivalent to that of free PQ. Taken together, this facile supramolecular PQ formulation is providing not only an extremely rare example of an eco- and user-friendly herbicide that has been desired for decades but also a practical solution for green agriculture.

Fabrication, characterization and adsorption properties of cucurbit[7]uril-functionalized polycaprolactone electrospun nanofibrous membranes

The fabrication of electrospun nanofibers comprising cucurbit[7]uril (CB[7]) and poly(ε-caprolactone) (PCL) is reported. Various techniques such as SEM, FTIR, XRD, DSC and TG were utilized to characterize the morphology, composition and properties of the nanofibers. Uniform bead-free electrospun nanofibers were obtained from PCL/CB[7] mixed solutions and the average fiber diameter of the nanofibers increases with the increase of CB[7] content. The nanofibers are composed of a physical mixture of PCL and CB[7], and CB[7] itself is present in the PCL fiber matrix in an uncomplexed state. The static adsorption behavior of the PCL/CB[7] nanofibers towards methylene blue (MB) was also preliminary investigated. The results indicate that the adsorption of MB onto the nanofibrous membranes fits the second-order kinetic model and Langmuir isotherm model.

Simple and Novel Assay of the Host-Guest Complexation of Homocysteine with Cucurbit[7]uril

This paper introduces three ways to determine host-guest complexation of cucurbit[7]uril (CB[7]) with homocysteine (Hcy). After preincubating Hcy and cysteine (Cys) with CB[7], Ellman's reagent (DTNB) was used to detect Hcy and Cys. Only Cys reacted with DTNB and Hcy gave a retarded color change. This suggests that the -SH group of Hcy is buried inside CB[7]. Human cystathionine γ-lyase (hCGL) decreased the level of Hcy degradation after preincubating Hcy and CB[7]. These results suggest that the amount of free Hcy available was decreased by the formation of a Hcy-CB[7] complex. The immunological signal of anti-Hcy monoclonal antibody was decreased significantly by preincubating CB[7] with Hcy. The ELISA results also show that ethanethiol group (-CH₂CH₂SH) of Hcy, which is an epitope of anti-Hcy monoclonal antibody, was blocked by the cavity in CB[7]. Overall, CB[7] can act as a host by binding selectively with Hcy, but not Cys. The calculated half-complexation formation concentration of CB[7] was 58.2 nmol using Ellman's protocol, 97.9 nmol using hCGL assay and 87.7 nmol using monoclonal antibody. The differing binding abilities of Hcy and Cys towards the CB[7] host may offer a simple and useful method for determining the Hcy concentration in plasma or serum.

A Synthetic Receptor as a Specific Antidote for Paraquat Poisoning

Accidental or suicidal ingestion of the world's most widely used herbicide, paraquat (PQ), may result in rapid multi-organ failure with a 60% fatality rate due to the absence of an effective detoxification solution. Effective, specific antidotes to PQ poisoning have been highly desired.

Methods: The binding constant of PQ and a synthetic receptor, cucurbit[7]uril (CB[7]), was first determined in various pH environments. The antidotal effects of CB[7] on PQ toxicity were firstly evaluated with in-vitro cell lines. With in-vivo mice models, the pharmacokinetics and the biodistribution of PQ in major organs were determined to evaluate the influence of CB[7] on the oral bioavailability of PQ. Major organs' injuries and overall survival rates of the mice were systemically examined to evaluate the therapeutic efficacy of CB[7] on PQ poisoning.

Results: We demonstrate that CB[7] may complex PQ strongly under various conditions and significantly reduce its toxicity in vitro and in vivo. Oral administration of PQ in the presence of CB[7] in a mouse model significantly decreased PQ levels in the plasma and major organs and alleviated major organs' injuries, when compared to those of mice administered with PQ alone. Further studies indicated that oral administration of CB[7] within 2 h post PQ ingestion significantly increased the survival rates and extended the survival time of the mice, in contrast to the ineffective treatment by activated charcoal, which is commonly recommended for PQ decontamination.

Conclusion: CB[7] may be used as a specific oral antidote for PQ poisoning by strongly binding with PQ and inhibiting its absorption in the gastrointestinal tracts.

Cucurbit[7]uril-Carbazole Two-Photon Photoinitiators for the Fabrication of Biocompatible Three-Dimensional Hydrogel Scaffolds by Laser Direct Writing in Aqueous Solutions

We have introduced a novel water-soluble two-photon photoinitiator based on the host-guest interaction between 3,6-bis[2-(1-methyl-pyridinium)vinyl]-9-pentyl-carbazole diiodide (BMVPC) and cucurbit[7]uril (CB7) because most of the commercial photoinitiators have poor two-photon initiating efficiency in aqueous solutions. The binding ratio of BMVPC and CB7 was determined as 1:1 by isothermal titration calorimetry and quantum chemical calculation. The formation of the host-guest complex increases the two-photon absorption cross-section about five times, and improves the water solubility required as the photoinitiator for hydrogel fabrication. The BMVPC-CB7 inclusion complex was used as the one-component photoinitiator, and the polyethylene glycol diacrylate with promising biocompatibility was used as the hydrogel monomer to form the aqueous-phase photoresist system applied to two-photon polymerization microfabrication. A relatively low laser threshold of 4.5 mW, a high fabricating resolution of 180 nm, and the true three-dimensional (3D) fabricating capability in the aqueous solution have been obtained by using the as-prepared photoresist system. Finally, 3D engineering hydrogel scaffold microstructures with low toxicity and good biocompatibility have been fabricated and cocultured with living HeLa cells, which demonstrates the potential for further application in tissue engineering.

Magnetic Regulation of Thermo-Chemotherapy from a Cucurbit[7]uril-Crosslinked Hybrid Hydrogel

The fabrication, characterization, and therapy efficiency of a noncovalent-bonded hydrogel network, which is assembled by utilizing cucurbit[7]uril as a supramolecular linker to "stick" superparamagnetic γ-Fe₂ O₃ nanoparticles onto the polymer backbone of catechol-functionalized chitosan are described. The unique barrel-shaped structure of cucurbit[7]uril not only facilitates host-guest recognition with the catechol derivatives, but also forms robust electrostatic interactions between its carbonyl portals and the γ-Fe₂ O₃ nanoparticles in a supramolecular manner, which leaves the physical and chemical properties of the nanoparticles intact. The γ-Fe₂ O₃ nanoparticles display vibrational movement and heat generation under an alternating magnetic field, endowing the formed hybrid supramolecular hydrogel with both thermo- and chemotherapy modalities, which are demonstrated both in vitro and in vivo. Here, a facile strategy is introduced to construct noncovalent interactions between a polymer matrix and the incorporated nanoparticles, which is amendable to a wide range of biomedical and industrial applications.

Alleviation of Polycation-Induced Blood Coagulation by the Formation of Polypseudorotaxanes with Macrocyclic Cucurbit[7]uril

Hexadimethrine bromide (HB), a polycation to neutralize heparin and control internal bleeding, may also cause serious blood coagulation that may be life-threatening. Reversal of HB by heparin and vice versa might potentially lead to a vicious circle of alternative bleeding and blood coagulation. In this Letter, a biocompatible synthetic nanoreceptor, cucurbit[7]uril (CB[7]), was demonstrated to dramatically alleviate HB-induced blood coagulation in vitro as well as in vivo, through the formation of HB@CB[7] polypseudorotaxanes. This discovery, for the first time, suggests the significant clinical potential of a synthetic receptor in alleviating the side effects and toxicity of a polycationic drug.

The Cucurbit[7]Uril-Based Supramolecular Chemistry for Reversible B/Z-DNA Transition

As a left-handed helical structure, Z-DNA is biologically active and it may be correlated with transcription and genome stability. Until recently, it remained a significant challenge to control the B/Z-DNA transition under physiological conditions. The current study represents the first to reversibly control B/Z-DNA transition using cucurbit[7]uril-based supramolecular approach. It is demonstrated that cucurbit[7]uril can encapsulate the central butanediamine moiety [HN(CH2)4NH] and reverses Z-DNA caused by spermine back to B-DNA. The subsequent treatment with 1-adamantanamine disassembles the cucurbit[7]uril/spermine complex and readily induces reconversion of B- into Z-DNA. The DNA conformational change is unequivocally demonstrated using different independent methods. Direct evidence for supramolecular interactions involved in DNA conformational changes is further provided. These findings can therefore open a new route to control DNA helical structure in a reversible way.

A Highly Selective and Strong Anti-Interference Host-Guest Complex as Fluorescent Probe for Detection of Amantadine by Indicator Displacement Assay

Amantadine (AMA) and its derivatives are illicit veterinary drugs that are hard to detect at very low concentrations. Developing a fast, simple and highly sensitive method for the detection of AMA is highly in demand. Here, we designed an anthracyclic compound (ABAM) that binds to a cucurbit[7]uril (CB[7]) host with a high association constant of up to 8.7 × 10⁸ M⁻¹. The host-guest complex was then used as a fluorescent probe for the detection of AMA. Competition by AMA for occupying the cavity of CB[7] allows ABAM to release from the CB[7]-ABAM complex, causing significant fluorescence quenching of ABAM (indicator displacement assay, IDA). The linear range of the method is from 0.000188 to 0.375 μg/mL, and the detection limit can be as low as 6.5 × 10⁻⁵ μg/mL (0.35 nM). Most importantly, due to the high binding affinity between CB[7] and ABAM, this fluorescence host-guest system shows great anti-interference capacity. Thus, we are able to accurately determine the concentration of AMA in various samples, including pharmaceutical formulations.

Constraining the Teratogenicity of Pesticide Pollution by a Synthetic Nanoreceptor

The teratogenicity of the pesticide nereistoxin (NTX) and its derivative thiocyclam (THI) towards aquatic life was dramatically constrained by a synthetic nanoreceptor, cucurbit[7]uril, through selective encapsulation of the pesticides (K_CB[7]-NTX of 3.24(±0.31)×10⁶  m^-1 and K_CB[7]-THI of 7.46(±0.10)×10⁵  m^-1 ), as evidenced by the rate of hatchability, morphology development, and tyrosinase activity of zebrafish larvae incubated with the pesticides (3-300 μm) in the absence and in the presence of 300 μm cucurbit[7]uril, demonstrating the significant potential of the nanoreceptor in managing ecological pollution of these pesticides.

Confinement induced thermodynamic and kinetic facilitation of some Diels-Alder reactions inside a CB[7] cavitand

The effect of geometrical confinement on the Diels-Alder reactions between some model dienes viz. furan, thiophene, cyclopentadiene, benzene, and a classic dienophile, ethylene has been explored by performing density functional theory-based calculations. The effect of confinement has been imposed by a rigid macrocyclic molecule cucurbit[7]uril (CB[7]). Results indicate that all the reactions become thermodynamically more favorable at 298.15 K temperature and one atmospheric pressure inside CB[7] as compared to the corresponding free gaseous state reactions. Moreover, the rate constants associated with the reactions experience manifold enhancement inside CB[7] as compared to the "unconfined" reactions. Suitable contribution from the entropy factor makes the concerned reactions more facile inside CB[7]. The energy gap between the frontier molecular orbitals of the dienes and dienophiles decrease inside CB[7] as compared to that in the free state reactions thereby allowing facile orbital interactions. The nature of interaction as well as bonding has been analyzed with the help of atoms-in-molecules, noncovalent interaction, natural bond orbital as well as energy decomposition analyses. Results suggest that all the guests bind with CB[7] in an attractive fashion. Primarily, noncovalent interactions stabilize the host-guest systems. © 2017 Wiley Periodicals, Inc.

Cucurbit[7]uril: an emerging candidate for pharmaceutical excipients

Cucurbit[7]uril (CB[7]), belonging to the cucurbit[n]uril family (CB[n], n = 5-8, 10, or 13-15), may form host-guest complexes with a variety of small molecules of biomedical interest. The physical and chemical properties of the complexed drugs are often improved as a result of this complexation, suggesting the potential application of CB[7] as a pharmaceutical excipient. This review has summarized the most recent research progress reported between 2011 and early 2017 regarding the biocompatibility of CB[7] and the influence of CB[7] on the stability, solubility, biouptake, and biological activities (including therapeutic efficacies and toxicities) of guest drug molecules. Through this systemic summary and analysis, we intend to stimulate further research efforts in this area and promote the use of CB[7] as an emerging pharmaceutical excipient to improve various properties of drug molecules (or active pharmaceutical ingredients).

Interactions between photoacidic 3-hydroxynaphtho[1,2-b]quinolizinium and cucurbit[7]uril: Influence on acidity in the ground and excited state

3-Hydroxynaphtho[1,2-b]quinolizinium was synthesized by cyclodehydration route and its optical properties in different media were investigated. The absorption and emission spectra of this compound depend on the pH of the solution. Thus, at higher pH values the deprotonation yields a merocyanine-type dye that exhibits significantly red-shifted absorption bands and causes a dual emisson, i.e., a combination of emission bands of the hydroxyquinolizinium and its deprotonated form. Whereas this compound is a weak acid in the ground state (pK_a = 7.9), it has a strongly increased acidity in the excited state (pK_a^* = 0.4). As a result, the blue-shifted fluorescence of the hydroxyquinolizinium becomes dominant only under strongly acidic conditions. In addition, it is shown that 3-hydroxynaphtho[1,2-b]quinolizinium binds to cucurbit[7]uril (CB[7]) with moderate affinity (K_b = 1.8 × 10⁴ M^-1, pH 5) and that the pK_a and pK_a^* values of this ligand increase by about two to three orders of magnitude, respectively, when bound to CB[7].

Molecular Encapsulation of Histamine H₂-Receptor Antagonists by Cucurbit[7]Uril: An Experimental and Computational Study

The histamine H₂-receptor antagonists cimetidine, famotidine and nizatidine are individually encapsulated by macrocyclic cucurbit[7]uril (CB[7]), with binding affinities of 6.57 (±0.19) × 10³ M(-1), 1.30 (±0.27) × 10⁴ M(-1) and 1.05 (±0.33) × 10⁵ M(-1), respectively. These 1:1 host-guest inclusion complexes have been experimentally examined by ¹H-NMR, UV-visible spectroscopic titrations (including Job plots), electrospray ionization mass spectrometry (ESI-MS), and isothermal titration calorimetry (ITC), as well as theoretically by molecular dynamics (MD) computation. This study may provide important insights on the supramolecular formulation of H₂-receptor antagonist drugs for potentially enhanced stability and controlled release based on different binding strengths of these host-guest complexes.

Manifesting Subtle Differences of Neutral Hydrophilic Guest Isomers in a Molecular Container by Phase Transfer

Achieving strong host-guest interactions between synthetic hosts and hydrophilic guests in solution is challenging because solvation effects overwhelm other effects. To resolve this issue, we transferred complexes of cucurbit[7]uril (CB[7]) and monosaccharides to the gas phase and report here their intrinsic host-guest chemistry in the absence of solvation effects. It was observed that effective host-guest interactions in the gas phase mediated by ammonium cations allow the differentiation of the monosaccharide isomers in complex with CB[7] upon vibrational excitation. The potential of the unique observation was extended to a quantitative supramolecular analytical method for the monosaccharide guests. The combination of host-guest chemistry and phase transfer presented in this study is an effective approach to overcome current limitations in supramolecular chemistry.

pH and Glutathione Dual-Responsive Dynamic Cross-Linked Supramolecular Network on Mesoporous Silica Nanoparticles for Controlled Anticancer Drug Release

A dynamic cross-linked supramolecular network of poly(glycidyl methacrylate)s derivative chains was constructed on mesoporous silica nanoparticles via disulfide bond and ion-dipole interactions between cucurbit[7]urils and protonated diamines in the polymer chains. This kind of multifunctional organic-inorganic hybrid material with pH- and glutathione- (GSH-) stimuli responsiveness can be applied to anticancer drug delivery and controlled release. Good release performance toward doxorubicin hydrochloride (DOX) was achieved under the simulative tumor intracellular environment (pH = 5.0, CGSH = 2-10 mM). Significantly, the release amount of DOX increased upon lowering the solution pH value and increasing the concentration of GSH, as demonstrated by a series of controlled release experiments. Furthermore, the DOX-loaded hybrid nanomaterials displayed apparent cell-growth inhibition effects to cancer cell lines, as evidenced by MTT assay and confocal laser scanning microscopy.

Mimicking Positive and Negative Copigmentation Effects in Anthocyanin Analogues by Host-Guest Interaction with Cucurbit[7]uril and β-Cyclodextrins

Copigmentation and the anti-copigmentation effects can be mimicked by the interaction of anthocyanin's model compounds respectively with cucurbit[7]uril (CB7) and β-cyclodextrin (β-CD). The complex network of chemical reactions displayed by this family of compounds includes the colored flavylium cation, AH(+), and quinoidal base, A, along with the colorless hemiketal, B, cis-chalcone, Cc, and trans-chalcone, Ct. Whereas AH(+) is stable only at very acidic pH values, the remaining species are formed at slightly acidic and neutral conditions. However, under these conditions, for most of the natural and synthetic flavylium salts, the colorless species predominate (B, Cc, and Ct) at the expense of A. The host CB7 was found to improve the color of solutions in two different ways: first, it stabilizes AH(+) at higher pH values by decreasing its acidity and, second, it enhances the mole fraction of A due to selective complexation of this species in the pH range where the flavylium cation is no longer stable. In contrast, β-CD increases the acidity of AH(+), favoring the formation of Ct at the expense of all the other multistate species (Bası́lio et al. New J. Chem. 2013, 37, 3166-3173; Petrov et al. J. Phys. Chem. A 2013, 117, 10692-10701; Gago et al. Dyes Pigments 2014, 110, 106-112; and Lopes-Costa et al. Photochem. Photobiol. Sci. 2014, 13, 1420-1426). Although both hosts have a large effect on the hydration rate and pH domain of the flavylium cation, the effect on the degradation kinetics of anthocyanidins is modest. CB7 decreases the hydration rate and decreases the acid-base (AH(+)/A) equilibrium constant (Ka), leading respectively to a slowing and a speeding of the anthocyanin degradation rate. On the other hand, β-CD increases the hydration rate but increases Ka, both effects acting in opposite directions.

Binding Studies of Cucurbit[7]uril with Gold Nanoparticles Bearing Different Surface Functionalities

Host-guest interactions between a synthetic receptor, cucurbit[7]uril (CB[7]), and gold nanoparticles (AuNPs) have been quantified using isothermal titration calorimetry. AuNPs were functionalized with ligands containing tertiary or quaternary benzylamine derivatives, with electron donating or withdrawing groups at the para position of the benzene ring. Analysis of binding interactions reveals that functional groups at the para position have no significant effect on binding constant. However, headgroups bearing a permanent positive charge increased the binding of AuNPs to CB[7] ten-fold compared to monomethyl counterparts.