Aptamer-based homogeneous protein detection using cucurbit[7]uril functionalized electrode

A new strategy for homogeneous protein detection is developed based on a cucurbit[7]uril (CB[7]) functionalized electrode. The analytical procedure consists of the binding of target protein to its aptamer in the test solution, followed by an exonuclease-catalyzed digestion of methylene blue (MB) tag labeled DNA oligonucleotides. Since CB[7] molecules immobilized on the electrode may efficiently capture the released MB-labeled nucleotides, the MB tags are concentrated to the electrode surface and subsequently yield highly sensitive electrochemical signal, which is related to the concentration of the target protein. The method combines the host–guest properties of CB[7] with the immobilization-free homogeneous assay, providing a powerful tool for protein detection. Taking the detection of osteopontin as an example, the proposed method can have a linear response to the target protein in a range from 50 to 500 ng mL⁻¹ with a detection limit of 10.7 ng mL⁻¹. It can also show high specificity and good reproducibility, and can be used directly for the assay of osteopontin in serum samples.     

以黄连素/葫芦脲[7]包合物为荧光探针测定青霉胺

黄连素能和葫芦脲[7]生成1:1的主-客体稳定的包合物并使其荧光强度显著增强。当加入青霉胺后,黄连素/葫芦脲[7]所形成的包合物的荧光迅速猝灭,据此建立了一种简便灵敏的检测青霉胺的新方法。青霉胺浓度在90～3000μg/L范围内与荧光猝灭值ΔF呈良好的线性关系,相关系数0.9996。检出限为30μg/L。本方法的加标回收率为98.3%～103.6%,相对标准偏差为0.68%～0.95%。本方法成功用于药片中青霉胺的测定。     

pH-Switched fluorescent pseudorotaxane assembly of cucurbit[7]uril with bispyridinium ethylene derivatives

¹H NMR spectra and fluorescence analysis revealed that the molecular shuttle and pseudorotaxane assembly of Q[7] with guest G²⁺ can be significantly switched via protonation and deprotonation of the terminal carboxylates of the guest.     

Fluorescence enhancement and cytotoxicity reduction of bis-viologen biphenyl by complexation of cucurbit[7]uril

The effect of cucurbit[7]uril(CB[7]) on fluorescence properties and biocompatibility of the bis-viologen biphenyl molecule(BPV2~(2+)) was investigated by using ~1 H NMR spectroscopy,fluorescence emission titration,and in vitro cytotoxicity experiments.CB[7] can be combined with BPV2~(2+) in a stoichiometric ratio of 1:1 and 2:1.After the formation of host-guest complex,the fluorescence emission intensity of BPV2~(2+) increased significantly,and the emission spectrum blue shifted.Meanwhile,the host-guest complexes showed better biocompatibility than BPV2~(2+) in cell cytotoxicity studies.Results of this paper lay a foundation for the development of host-guest type of fluo rescent probes,biological imaging and so forth.     

Determination of Paraquat by Cucurbit[7]uril Sensitized Fluorescence Quenching Method

A method for the determination of paraquat by cucurbit[7]uril (CB[7]) fluorescence quenching was developed. The assay was based on the reaction of the CB[7] with acridine orange. The fluorescence intensity of acridine orange regularly increased with the addition of CB[7]. However, while an appropriate amount of paraquat was added to the CB[7]- acridine orange system, the fluorescence intensity of the system was quenched which was employed to determine paraquat. Under the optimum conditions, a linear range of 3.0–800 nmol L^?1 and a detection limit of 1.61 nmol L^?1 for paraquat were obtained. The simple strategy reported here offers great practical potential for the determination of pesticide residues in agricultural products.     

Separation performance of polydopamine-based cucurbit[7]uril stationary phase for capillary gas chromatography

Polydopamine(PDA) coating, a nature-inspired polymer, has attracted great attention in many areas due to its high adhesion strength and stability on almost all types of substrate surfaces. This work presents the first example of using PDA coating as a column pretreatment method in capillary gas chromatography(GC) and its employment in the column fabrication of cucurbit[7]uril(CB7) stationary phase. The fabricated PDA-CB7 column exhibited weakly polar nature and had advantages over CB7 column without PDA for the separations of some critical analytes in GC. This work demonstrates the advantage and potential of using PDA as a facile column pretreatment method in capillary GC column fabrication.     

Complexation behavior of cucurbit[6]uril with short polypeptides

The binding properties of cucurbit[6]uril towards various peptides have been investigated in acidic aqueous solution. Stability constants and thermodynamic values of the complex formation between following peptides: glycyl-l-alanine, l-leucyl-l-valine, glycyl-l-asparagine, l-leucyl-l-phenylalanine, l-leucyl-l-tryptophan, glycyl-l-histidine, l-glutathione reduced (γ-l-glutamyl-l-cysteinyl-glycine, GSH), and dl-leucyl-glycyl-dl-phenylalanine) with cucurbit[6]uril in aqueous formic acid (50%, v/v) have been calculated from calorimetric titrations. From these results it can be seen that the peptides form exclusion complexes with cucurbit[6]uril. Due to the polar peptide bond they are not included within the hydrophobic cavity of cucurbit[6]uril. The complex formation is favoured by entropic contributions. The release of water molecules from the polar amino groups of the peptides and the carbonyl groups of cucurbituril are responsible.     

New lanthanide-based complexes constructed from cucurbit[6]uril: Synthesis,structures and properties

Three lanthanide-based complexes, {Gd₂(H₂O)₁₀(CB[6])₂}·CB[6]·6Cl·12H₂O (1), {[Gd₂(H₂O)₈CB[6]₂]·(CuCl₄)·4Cl·46H₂O}_n (2), and {Dy₂(NO₃)₂(H₂O)₁₀(CB[6])}·4NO₃·14H₂O (3) (CB[6] = cucurbit[6]uril), were prepared with cucurbit[6]uril (CB[6]). These complexes were characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR spectroscopy, UV–Vis spectroscopy, thermogravimetric analysis and magnetization measurements. Crystallographic results showed that 1 and 3 are dinuclear and crystallize in the triclinic space group Pī, whereas 2 is a 1-D zigzag supramolecular chain that crystallizes in the monoclinic system in C2/c. The results indicated that temperature has a big effect on the supramolecular assemblies and a different structure inducer also leads to the formation of different coordination polymers. Frequency dependence in the ac susceptibility signals was observed in 3.     

Cucurbit[7]uril as a Supramolecular Artificial Enzyme for Diels–Alder Reactions

The ability to mimic the activity of natural enzymes using supramolecular constructs (artificial enzymes) is a vibrant scientific research field. Herein, we demonstrate that cucurbit[7]uril (CB[7]) can catalyse Diels–Alder reactions for a number of substituted and unreactive N ‐allyl‐2‐furfurylamines under biomimetic conditions, without the need for protecting groups, yielding powerful synthons in previously unreported mild conditions. CB[7] rearranges the substrate in a highly reactive conformation and shields it from the aqueous environment, thereby mimicking the mode of action of a natural Diels–Alderase. These findings can be directly applied to the phenomenon of product inhibition observed in natural Diels–Alderase enzymes, and pave the way toward the development of novel, supramolecular‐based green catalysts.     

A supramolecular fluorescent probe based on cucurbit[10]uril for sensing the pesticide dodine

We report herein a new fluorescent probe for the selective recognition and determination of dodine among 20 different pesticides.This fluorescent probe was assembled through host-guest complexation between cucurbit[10]uril(Q[10]) and aminopropyl-1-pyrenebutanamide(PBA) and is designated as PBA@Q[10].Addition of dodine to PBA@Q[10] results in a dramatic enhancement of fluorescence intensity at 390 nm,accompanied by fluorescence quenching at 488 nm.On this basis,the detection limit is 6.78 × 10^-7 mol/L.The response mechanism is a competitive interaction:dodine occupies the cavity of Q[10] and forces PBA to leave.     

A cucurbit[8]uril recognized rigid supramolecular polymer with photo-stimulated responsiveness

A rigid supramolecular polymer was constructed in aqueous solution via cucurbit[8]uril(CB[8]) host recognition with a rigid monomer containing an azobenzene unit and two 4,4'-bipyridin-1-ium(BP)moieties in the two ends, which also exhibited photo-responsiveness owing to the photoinduced trans–cis isomerization of azobenzene group.     

Switchable peptide-equipped protein/cucurbit[7]uril supramolecular assembly for targeted drug delivery

ABSTRACT

Herein, we develop a switchable peptide-equipped protein/cucurbit[7]uril (CB[7]) supramolecular assembly as novel targeted drug vector. Specifically, bovine serum albumin (BSA) is used to interact with CB[7], serving as the core of drug vector. Then, a peptide shield layer is formed on the surface of BSA/CB[7], yielding peptide-equipped supramolecular assembly (Pep@BSA@CB[7]). The equipped peptide shield layer is composed of switchable peptide probes consisting of a polycationic cell-penetrating peptide (CPP) motif, a polyanionic motif and a linking motif, and therefore provides a variety of desirable properties. First, the CPP motif displays excellent cell penetration ability and can facilitate internalisation of the drug vector. Secondly, the polyanionic motif performs intramolecular electrostatic interaction with CPP motif and thereby can reduce non-targeted delivery towards normal cells. Thirdly, the linking motif can be specifically cleaved by matrix metalloproteinases 2 that is up-regulated in tumour microenvironment, thus enabling precise cancer-targeting. As a consequent, Pep@BSA@CB[7] can serve as a promising drug vector that exhibits superior targeting ability and high uptake efficiency towards cancer cells, which may be of great potential in cancer-targeted treatment.     

A cucurbit[7]uril-based supra-amphiphile: Photo-responsive self-assembly and application in controlled release

A photo-responsive host–guest molecular recognition between a cucurbit[7]uril host and an azobenzene-containing guest was investigated. Based on this recognition motif, a photo-responsive supra-amphiphile was constructed. This supra-amphiphile can self-assemble into vesicles in water, which can be destroyed by UV irradiation. Depending on this photo-responsive assembly, its application in controlled release was further performed.     

Reviving chloroquine for anti-SARS-CoV-2 treatment with cucurbit[7]uril-based supramolecular formulation

The wide-spreading SARS-CoV-2 virus has put the world into boiling water for more than a year, however pharmacological therapies to act effectively against coronavirus disease 2019 (COVID-19) remain elusive. Chloroquine (CQ), an antimalarial drug, was found to exhibit promising antiviral activity in vitro and in vivo at a high dosage, thus CQ was approved by the FDA for the emergency use authorization (EUA) in the fight against COVID-19 in the US, but later was revoked the EUA status due to the severe clinical toxicity. Herein, we show that supramolecular formulation of CQ by a macrocyclic host, curcurbit[7]uril (CB[7]), reduced its non-specific toxicity and improved its antiviral activity against coronavirus, working in synergy with CB[7]. CB[7] was found to form 1:1 host-guest complexes with CQ, with a binding constant of ∼10⁴ L/mol. The CQ-CB[7] formulation decreased the cytotoxicity of CQ against Vero E6 and L-02 cell lines. In particular, the cytotoxicity of CQ (60 μmol/L) against both Vero E6 cell line and L-02 cell lines was completely inhibited in the presence of 300 μmol/L and 600 μmol/L CB[7], respectively. Furthermore, the CB[7] alone showed astonishing antiviral activity in SARS-CoV-2 infected Vero E6 cells and mouse hepatitis virus strain A59 (MHV-A59) infected N2A cells, and synergistically improved the antiviral activity of CQ-CB[7], suggesting that CB[7]-based CQ formulation has a great potential as a safe and effective antiviral agent against SARS-CoV-2 and other coronavirus.     

pH-Responsive supramolecular DOX-dimer based on cucurbit[8]uril for selective drug release

A supramolecular dimer of doxorubicin (DOX) was constructed via ternary host-guest interactions between cucurbit[8]uril (CB[8]) and tryptophan modified DOX (DOX-Trp, connected with an acid-labile bond) and we demonstrate for the first time that a supramolecular dimer of DOX can be formed upon homo-dimerization by CB[8], which may act as a stimuli pH-responsive, supramolecular DOX dimer prodrug system. This supramolecular DOX dimer transported DOX efficiently and selectively to cancer cells, thereby exhibiting significantly minimized cytotoxicity against noncancerous cells while maintaining effective cytotoxicity against cancer cells. Under this strategy, many other anticancer drugs could be chemically modified and loaded as a dimeric “ammunition” into CB[8] as supramolecular dimer prodrug systems (or a “jet fighter”) for improved cancer therapy.     

Solvent-free self-assembly of C60 and cucurbit[7]uril using high-speed vibration milling

The synthesis of a cucurbit[7]uril-[60]fullerene supramolecular complex using a simple, green, and efficient pathway is reported for the first time. In the complex, which was found to be of the 1:2 type, the compounds interact weekly with each other. Since the complexation can be achieved by a solid-solid reaction without solvent both the waste and contact with harmful solvents can be reduced to a minimum. A significant increase of reaction rate and yield compared to the heterogeneous complexation was observed.     

七元瓜环对阿糖胞苷稳定性的影响

研究了七元瓜环(Q[7])与抗癌药物阿糖胞苷(Ara-C)的不同质子化存在形式之间的超分子相互作用, 探讨了超分子包合作用对药物电离平衡常数及药物稳定性的影响. 结果表明, Q[7]使得Ara-C的pK_a降低了约0.3个单位, Q[7]与Ara-C的2种存在形式(Ara-C⁺及Ara-C)均可形成1∶1的主客体包结配合物, Ara-C以其嘧啶环进入Q[7]空腔, 而核糖环位于瓜环端口发生相互作用; Q[7]与Ara-C作用后对药物起到保护性载体的作用, 从而提高了药物的稳定性.     

Inclusion complex of riboflavin with cucurbit[7]uril: study in solution and solid state

The aqueous solution of riboflavin and cucurbit[7]uril complex has been studied based on fluorescence and ¹H NMR spectroscopic results. Upon addition of cucurbit[7]uril, the fluorescence intensity of riboflavin was quenched and a slight red shift was observed for the maximum emission peak. These results indicated that the cucurbit[7]uril–riboflavin complex was formed at a 1:1 mole ratio. The temperature-dependent inclusion constants were calculated, from which ΔH and ΔS values were calculated. Meanwhile, rationale of the interaction mechanism was also discussed based on ¹H NMR results. The solid inclusion complex was prepared from co-evaporation method and characterised by differential thermal analysis and fluorescence lifetime analysis methods. The experimental results indicated that riboflavin and cucurbit[7]uril formed stable host–guest inclusion complex in both solution and solid states.     

葫芦脲[7]与核黄素包结物的可能结构和光谱性质

利用密度泛函理论对葫芦脲[7]和核黄素包结物的可能结构进行了理论计算.从5种可能结构分析主客体在包结物中的作用得出:核黄素作为客体分子与主体葫芦脲[7]分子通过不同官能团作用可形成稳定性不同的包结物,其中以核糖醇的羟基插入到葫芦脲[7]分子的腔体与其端羰基氧原子形成较多的氢键最稳定.在理论上证明了此包结反应为一放热反应的实验事实,并进一步说明了包结物分子的相对稳定性受主客体分子的几何畸变能和主客体之间作用能的影响,说明了成键能和稳定性之间的区别.在此基础上利用时间相关的密度泛函理论进行了不同构型包结物的激发态计算并对光谱性质进行了理论预测.比较了包结物中核黄素分子的跃迁轨道的组成变化,分析得出:葫芦脲[7]的包结作用改变了核黄素分子的电子跃迁性质,使其吸收光谱发生红移.并预测出其荧光猝灭的微观机理,此理论计算结果很好地解释了相应的实验现象.