2D Materials Kill Bacteria from Within.

Early work demonstrated that some two-dimensional (2D) materials could kill bacteria by using their sharp edges to physically rupture the bacteria envelope, which presents distinct advantages over traditional antibiotics, as bacteria are not able to evolve resistance to the former. This mechano-bactericidal mode of action, however, suffers from low antibacterial efficiency, fundamentally because of random orientation of 2D materials outside the bacteria, where the desirable "edge-to-envelope" contacts occur with low probability. Here, we demonstrate a proof-of-concept approach to significantly enhance the potency of the mechano-bactericidal activity of 2D materials. This approach is in marked contrast with previous work, as the 2D materials are designed to be in situ generated inside the bacteria from a molecularly engineered monomer in a self-assembled manner, profoundly promoting the probability of the "edge-to-envelope" contacts. The rationale in this study sheds light on a mechanically new nanostructure-enabled antibacterial strategy to combat antibiotic resistance.

Locking Patterned Carbon Nanotube Cages by Nanofibrous Mats to Construct Cucurbituril[n]-Based Ultrapermselective Dye/Salt Separation Membranes.

Surface patterning is a promising strategy to overcome the trade-off effect of separation membranes. Herein, a bottom-up patterning strategy of locking micron-sized carbon nanotube cages (CNCs) onto a nanofibrous substrate is developed. The strongly enhanced capillary force triggered by the abundant narrow channels in CNCs endows the precisely patterned substrate with excellent wettability and antigravity water transport. Both are crucial for the preloading of cucurbit[n]uril (CB6)-embeded amine solution to form an ultrathin (∼20 nm) polyamide selective layer clinging to CNCs-patterned substrate. The CNCs-patterning and CB6 modification result in a 40.2% increased transmission area, a reduced thickness, and a lowered cross-linking degree of selective layer, leading to a high water permeability of 124.9 L·m-2 h-1 bar-1 and a rejection of 99.9% for Janus Green B (511.07 Da), an order of magnitude higher than that of commercial membranes. The new patterning strategy provides technical and theoretical guidance for designing next-generation dye/salt separation membranes.

Cucurbit[6]uril Hyperpolarized Chemical Exchange Saturation Transfer Pulse Sequence Parameter Optimization and Detectability Limit Assessment at 3.0T.

Molecular imaging is the future of personalized medicine; however, it requires effective contrast agents. Hyperpolarized chemical exchange saturation transfer (HyperCEST) can boost the signal of Hyperpolarized 129 Xe MRI and render it a molecular imaging modality of high efficiency. Cucurbit[6]uril (CB6) has been successfully employed in vivo as a contrast agent for HyperCEST MRI, however its performance in a clinical MRI scanner has yet to be optimized. In this study, MRI pulse sequence parameter optimization was first performed in CB6 solutions in phosphate-buffered saline (PBS), and subsequently in whole sterile citrated bovine blood. The performance of four different depolarization pulse shapes (sinusoidal, 3-lobe sinc (3LS), rectangular (block), and hyperbolic secant (hypsec) was optimized. The detectability limits of CB6 in a clinical 3.0T MRI scanner was assessed using the optimized pulse sequences. The 3LS depolarization pulses performed best, and demonstrated 24 % depletion in a 25 µM solution of CB6 in PBS. It performed similarly in blood. The CB6 detectability limit was found to be 100 µM in citrated bovine blood with a correspondent HyperCEST depletion of 30 % ±9 %. For the first time, the HP 129 Xe HyperCEST effect was observed in red blood cells (RBC) and had a similar strength as HyperCEST in plasma.

DMSO-tolerant ornithine decarboxylase (ODC) tandem assay optimised for high-throughput screening.

Ornithine decarboxylase (ODC), the first rate-limiting enzyme in polyamine synthesis, has emerged as a therapeutic target for cancer and Alzheimer's disease (AD). To inhibit ODC, α-difluoromethylornithine (DFMO), an irreversible ODC inhibitor, has been widely used. However, due to its poor pharmacokinetics, the need for discovery of better ODC inhibitors is inevitable. For high-throughput screening (HTS) of ODC inhibitors, an ODC enzyme assay using supramolecular tandem assay has been introduced. Nevertheless, there has been no study utilising the ODC tandem assay for HTS, possibly due to its intolerability to dimethyl sulfoxide (DMSO), a common amphipathic solvent used for drug libraries. Here we report a DMSO-tolerant ODC tandem assay in which DMSO-dependent fluorescence quenching becomes negligible by separating enzyme reaction and putrescine detection. Furthermore, we optimised human cell-line-based mass production of ODC for HTS. Our newly developed assay can be a crucial first step in discovering more effective ODC modulators than DFMO.

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

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

In vivo hyperCEST imaging: Experimental considerations for a reliable contrast.

PURPOSE: HyperCEST contrast relies on the reduction of the solvent signal after selective saturation of the solute magnetization. The scope of this work is to outline the experimental conditions needed to obtain a reliable hyperCEST contrast in vivo, where the "solvent" signal (ie, the dissolved-phase signal) may change over time due to the increase in xenon (Xe) accumulation into tissue. METHODS: Hyperpolarized 129 Xe was delivered to mice at a constant volume and rate using a mechanical ventilator, which triggered the saturation, excitation, and acquisition of the MR signal during the exhale phase of the breath cycle-either every breath or every 2, 3, or 4 breaths. Serial Z-spectra and hyperCEST images were acquired before and after a bolus injection of cucurbit[6]uril to assess possible signal fluctuations and instabilities. RESULTS: The intensity of the dissolved-phase Xe signal was observed to first increase immediately after the beginning of the hyperpolarized gas inhalation and NMR acquisition, and then decrease before reaching a steady-state condition. Once a steady-state dissolved-phase magnetization was established, a reliable hyperCEST contrast, exceeding 40% signal reduction, was observed. CONCLUSION: A reliable hyperCEST contrast can only be obtained after establishing a steady-state dissolved phase 129 Xe magnetization. Under stable physiological conditions, a steady-state dissolved-phase Xe magnetization is only achieved after a series of Xe inhalations and RF excitations, and it requires synchronization of the breathing rate with the MR acquisition.

Nanozyme based on graphene oxide modified with Fe3O4, CuO, and cucurbit[6]uril for colorimetric determination of homocysteine.

A nanozyme based on graphene oxide modified with Fe3O4 NPs, CuO NPs, and cucurbit[6]uril has been successfully fabricated by a simple sonochemical technique. By employing CB[6] as a specific binding pocket and Fe3O4@CuO-GO as a peroxidase mimic, this novel nanozyme (BN I) is equipped with molecular recognition ability and enhanced peroxidase-like activity. On the basis of the inhibition effect of homocysteine (Hcy) towards the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by BN I, a simple colorimetric method is established for the sensitive and selective determination of Hcy. This proposed method displays a good linear response in the range 5-200 µM with a detection limit of 1.8 µM. In the practical assay of human plasma samples, the relative standard deviations (RSD) are lower than 11% and the recoveries are between 98.0 and 104.9%. In the assay of human urine samples, the RSD are below 9.0% and the recoveries range from 94.0 to 103.5%. The colorimetric method presented offers a convenient and accurate way for the determination of biomarkers in point-of-care testing (POCT).

Supramolecular Atropine Potentiometric Sensor.

A supramolecular atropine sensor was developed, using cucurbit[6]uril as the recognition element. The solid-contact electrode is based on a polymeric membrane incorporating cucurbit[6]uril (CB[6]) as an ionophore, 2-nitrophenyl octyl ether as a solvent mediator, and potassium tetrakis (4-chlorophenyl) borate as an additive. In a MES-NaOH buffer at pH 6, the performance of the atropine sensor is characterized by a slope of (58.7 ± 0.6) mV/dec with a practical detection limit of (6.30 ± 1.62) × 10-7 mol/L and a lower limit of the linear range of (1.52 ± 0.64) × 10-6 mol/L. Selectivity coefficients were determined for different ions and excipients. The obtained results were bolstered by the docking and spectroscopic studies which demonstrated the interaction between atropine and CB[6]. The accuracy of the potentiometric analysis of atropine content in certified reference material was evaluated by the t-Student test. The herein proposed sensor answers the need for reliable methods providing better management of this hospital drug shelf-life while reducing its flush and remediation costs.

Cucurbit[6]uril-Derived Sub-4 nm Pores-Dominated Hierarchical Porous Carbon for Supercapacitors: Operating Voltage Expansion and Pore Size Matching.

The intrinsic properties of carbon-based material and the voltage window of electrolyte are the two key barriers to restrict the energy density of carbon-based supercapacitors (SCs). Herein, a cucurbit[6]uril-derived nitrogen-doped hierarchical porous carbon (CBCx) with unique pore structure characteristics is synthesized and successfully applied to construct SCs based on different electrolyte systems. Owing to narrow pore size distribution (0.5-4 nm), colossal ion-accessible pore volume, prominent supermesopore volume, and reasonable heteroatom configuration, the CBCx-based SCs demonstrate excellent electrochemical performances with high operating voltages in two distinct systems. The optimal SCs can output a maximum energy/power density of 18 Wh kg-1 (11.1 Wh L-1 )/20 kW kg-1 (12.3 kW L-1 ) with an operating voltage of 1.2 V in potassium hydroxide aqueous electrolyte, as well as an ultralong cycle life of up to 50 000 cycles (0.046% decay per 100 cycles). Furthermore, the optimal SCs deliver an exceptionally high energy/power density of 95 Wh kg-1 (58.4 Wh L-1 )/70 kW kg-1 (43 kW L-1 ) with an ultrahigh operating voltage of 3.5 V in 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte. This work opens up a new application field for cucurbit[6]uril and provides an alternative avenue for optimizing the performances of carbon-based materials for SCs.

A simpler potentiometric method for histamine assessment in blood sera.

Histamine intolerance results from a disequilibrium of accumulated histamine and the capacity for histamine degradation. An impaired histamine degradation based on reduced DAO activity and the resulting histamine excess may cause numerous symptoms mimicking an allergic reaction. For that, the determination of histamine in blood or in food products has great importance to identify risk factors. A new histamine-selective electrode is proposed using cucurbit[6]uril (CB[6]), as ionophore, in the analysis of biological samples. The selection of this smart supramolecular organic framework was based on its apparent stability constant of histamine-CB[6] (log ß) of 4.33. The optimized electrode based on a polymeric membrane (PVC) combines the histamine-selective ionophore with 2-nitrophenyl octyl ether as solvent mediator and potassium tetrakis(4-chlorophenyl)borate as anionic additive. Furthermore, multi-walled carbon nanotubes particles were included in the membrane composition to partly lower the detection limit of the method, while improving stability and lowering the response drift (± 4 mV). The electrodes showed a rapid response (≃ 13 s) in the pH operational range of 2.7-5.4, with a Nernstian slope of 30.9 ± 1.2 mV/dec, a detection limit of (3.00 ± 0.61) × 10-7 mol/L, and a lower limit of the linear range of (3.00 ± 0.00) × 10-7 mol/L. After miniaturization, the electrode was used as a detector in a sequential-injection lab-on-valve flow setup. The optimized flow conditions were achieved for sample injection volumes of 197 µL propelled towards the cell under detection, at a flow rate of 30 µL/s during 100 s, making the analysis of 30 samples per hour possible. The developed system was used to analyze spiked blood serum samples previously cleaned by using solid-phase extraction. The sample pretreatment of the serum samples using Oasis MCX cartridges showed outstanding efficiency for histamine determination. The recovery values for three different levels of histamine concentration (1 × 10-4 mol/L, 1 × 10-5 mol/L, and 1 × 10-6 mol/L) were (97 ± 6)%, (103 ± 1)%, and (118 ± 9)%, respectively, showing that this method was suitable for biological samples.

Visual and spectrophotometric detection of metformin based on the host-guest molecular recognition of cucurbit[6]uril-modified silver nanoparticles.

A simple, sensitive, and naked-eye assay of metformin (MET), based on the host-guest molecular recognition of cucurbit[6]uril (CB[6])-modified silver nanoparticles, has been developed for the first time. The molecular recognition between CB[6] and MET is initially demonstrated and the related recognition mechanism is further discussed. CB[6]-modified AgNPs were first synthesized and then characterized by UV-vis spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. The solution behavior of CB[6] in the presence of AgNO3 was also studied, and the correlative result revealed that AgNPs could combine with the carbonyl portals of CB[6]. On the basis of the molecular recognition of CB[6] and the surface plasmon resonance effect of AgNPs, CB[6]-modified AgNPs were used as visual probes to detect MET. In CB[6]-modified AgNP solution, the aggregation of CB[6]-modified AgNPs induced by MET triggered changes of color and the UV-vis absorption spectrum, which laid the foundation for the visual identification and spectrophotometric determination of MET. Under the optimized detection conditions, the UV-vis spectral assay had a good linear relationship in the range from 3 to 750 µM, and the limit of detection was 1 µM. According to the color changes, the minimum concentration recognized by the naked eye was about 75 µM. Furthermore, this assay has high selectivity for coexisting interferents and was also applied to MET detection in human urine samples. This strategy provides a novel and facile tool for highly selective and sensitive detection of MET. Graphical abstract.

A polymer monolith composed of a perovskite and cucurbit[6]uril hybrid for highly selective enrichment of phosphopeptides prior to mass spectrometric analysis.

A hybrid monolith was prepared from perovskite and cucurbit[6]uril [poly(hydroxyethyl methacrylate-pentaerythritol triacrylate) monolith] for the enrichment of phosphopeptides. By coupling with mass spectrometry, three goals were simultaneously realized, viz. (a) selective enrichment of phosphopeptides from non-phosphopeptides, (b) identification of mono- and multi-phosphopeptides, and (c) recognition of tyrosine phosphopeptides. The perovskite introduced into the monolith warrants high selectivity for phosphopeptides even at a high (10,000:1) ratio of non-phosphopeptides to phosphopeptides, and and enables identification of eight mono- and multi-phosphopeptides from standard ß-casein tryptic digests. Tyrosine phosphopeptides were specifically detected via the recognition capability of cucurbit[6]uril integrated into the monolith. The method has remarkably specific enrichment capacity for phosphopeptides from samples including human serum, nonfat milk, and human acute myelocytic leukemia cell lysate. Graphical abstractSchematic representation of a monolith integrated with perovskite and cucurbit[6]uril. The monolithic column was coupled with mass spectrometry and applied to the enrichment of phosphopeptides. The method has remarkably specific enrichment capacity for phosphopeptides from complex biological samples.

Rotaxane Probes for the Detection of Hydrogen Peroxide by 129 Xe HyperCEST NMR Spectroscopy.

The development of sensitive and chemically selective MRI contrast agents is imperative for the early detection and diagnosis of many diseases. Conventional responsive contrast agents used in 1 H MRI are impaired by the high abundance of protons in the body. 129 Xe hyperCEST NMR/MRI comprises a highly sensitive complement to traditional 1 H MRI because of its ability to report specific chemical environments. To date, the scope of responsive 129 Xe NMR contrast agents lacks breadth in the specific detection of small molecules, which are often important markers of disease. Herein, we report the synthesis and characterization of a rotaxane-based 129 Xe hyperCEST NMR contrast agent that can be turned on in response to H2 O2 , which is upregulated in several disease states. Added H2 O2 was detected by 129 Xe hyperCEST NMR spectroscopy in the low micromolar range, as well as H2 O2 produced by HEK 293T cells activated with tumor necrosis factor.

Efficient Room-Temperature Phosphorescence of a Solid-State Supramolecule Enhanced by Cucurbit[6]uril.

Efficient emission of purely organic room-temperature phosphorescence (RTP) is of great significant for potential application in optoelectronics and photobiology. Herein, we report an uncommon phosphorescent effect of organic single molecule enhanced by resulting supramolecular assembly of host-guest complexation. The chromophore bromophenyl-methyl-pyridinium (PY) with different counterions as guests display various phosphorescence quantum yields from 0.4 % to 24.1 %. Single crystal X-ray diffraction results indicate that the chromophore with iodide counterion (PYI) exhibits the highest efficiency maybe due to the halogen-bond interactions. Significantly, the nanosupramolecular assembly of PY chloride complexation with the cucurbit[6]uril gives a greatly enhanced phosphorescent quantum yield up to 81.2 % in ambient. Such great enhancement is because of the strict encapsulation of cucurbit[6]uril, which prevents the nonradiative relaxation and promotes intersystem crossing (ISC). This supramolecular assembly concept with counterions effect provides a novel approach for the improvement of RTP.

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer.

A series of hetero [4]-, [5]- and [6]rotaxanes containing both cucurbit[6]uril (CB[6]) and γ-cyclodextrin (γ-CD) as the macrocyclic components have been synthesized via a threading-followed-by-stoppering approach. Due to the orthogonal binding of CB[6] to ammonium and γ-CD to biphenylene/tetra(ethylene glycol), the [n]rotaxanes display a specific sequence of the interlocked macrocycles. In addition, despite of the asymmetry of γ-CD with respect to the orthogonal plane of the axle, only one stereoisomer of the [6]rotaxane was obtained.

Multilayer Cucurbit[6]uril-Based Magnetic Nanoparticles Prepared by Host-Guest Interaction: Remarkable Adsorbent for Low Density Lipoprotein Removal from Plasma.

Efficient removal of low density lipoprotein (LDL) is a key challenge due to its high level in plasma as a primary risk factor in the pathogenesis of atherosclerotic cardiovascular disease. In this work, a facile synthesis strategy based on host-guest interactions was developed to prepare multilayer cucurbit[6]uril-based magnetic nanoparticles, MNPs-(HA-DAH5 /HA-CB[6]5 ). The compound was employed as a blood purification material for the removal of LDL from plasma because it had good blood compatibility and could be easily separated with an external magnet. The efficient removal of LDL was attributed to the electrostatic interactions between the positive charged apoB-100 domain of LDL and the negative charged adsorbent. Moreover, the prepared material exhibited high recyclability and could release LDL in physiological saline for recyclable use. MNPs-(HA-DAH5 /HA-CB[6]5 ) offered promising perspectives and broad applications in extracorporeal treatment for the removal of LDL.

Time-resolved monitoring of enzyme activity with ultrafast Hyper-CEST spectroscopy.

We propose a method to dynamically monitor the progress of an enzymatic reaction using NMR of hyperpolarized 129 Xe in a host-guest system. It is based on a displacement assay originally designed for fluorescence experiments that exploits the competitive binding of the enzymatic product on the one hand and a reporter dye on the other hand to a supramolecular host. Recently, this assay has been successfully transferred to NMR, using xenon as a reporter, cucurbit[6]uril as supramolecular host, and chemical exchange saturation transfer with hyperpolarized Xe (Hyper-CEST) as detection technique. Its advantage is that the enzyme acts on the unmodified substrate and that only the product is detected through immediate inclusion into the host. We here apply a method that drastically accelerates the acquisition of Hyper-CEST spectra in vitro using magnetic field gradients. This allows monitoring the dynamic progress of the conversion of lysine to cadaverine with a temporal resolution of ~30 s. Moreover, the method only requires to sample the very early onset of the reaction (<0.5% of substrate conversion where the host itself is required only at µM concentrations) at comparatively low reaction rates, thus saving enzyme material and reducing NMR acquisition time. The obtained value for the specific activity agrees well with previously published results from fluorescence assays. We furthermore outline how the Hyper-CEST results correlate with xenon T2 measurements performed during the enzymatic reaction. This suggests that ultrafast Hyper-CEST spectroscopy can be used for dynamically monitoring enzymatic activity with NMR.

Efficient catenane synthesis by cucurbit[6]uril-mediated azide-alkyne cycloaddition.

We report here the efficient synthesis of a series of [3]catenanes featuring the use of cucurbit[6]uril to simultaneously mediate the mechanical and covalent bond formations. By coupling the mechanical interlocking with covalent macrocyclization, formation of topological isomers is eliminated and the [3]catenanes are formed exclusively in good yields. The efficient access to these [3]catenanes and the presence of other recognition units render them promising building blocks for the construction of other high-order interlocked structures.

Synthesis of star poly(N-isopropylacrylamide) with a core of cucurbit[6]uril via ATRP and controlled thermoresponsivity.

A series of CB[6]-based macroinitiators with "n" bromo-initiation sites on the "equator" of CB[6] is developed for the synthesis of CB[6]-star poly(N-isopropylacrylamide) (CB[6]-star PNIPAM) by atom transfer radical polymerization. By taking advantage of the exceptional binding affinity of the CB[6] core, CB[6]-star PNIPAM is used as a host macromolecule to construct large compound vesicles in the presence of protonated n-butylamine at pH 5.63. The deprotonated n-butylamine is detached from the CB[6] core at pH 11.1, which destructs the vesicular structures. For CB[6]-star PNIPAM, the thermoresponsive properties can be adjusted by simply changing the formation and destruction of the inclusion complexes of the CB[6] core with n-butylamine. These results suggest that the prepared CB[6]-star PNIPAM shows pH and temperature responsiveness, which has great potential for the design of a dual response smart material.

Perhydroxylcucurbit[6]uril as a highly selective gas chromatographic stationary phase for analytes of wide-ranging polarity.

This work describes the separation performance of a perhydroxylcucurbit[6]uril stationary phase for capillary gas chromatography. The perhydroxylcucurbit[6]uril stationary phase exhibits higher resolving capabilities for critical analytes with better peak shapes than cucurbit[6]uril and conventional stationary phases. The advantageous separation feature of the perhydroxylcucurbit[6]uril stationary phase may originate from its unique structure and favorably balanced interactions with the analytes. Also, the perhydroxylcucurbit[6]uril column shows good separation repeatability with relative standard deviations in the range of 0.01-0.13% for intraday, 0.37-0.82% for interday, and 1.0-4.7% for column-to-column repeatability.