Supramolecular Radical Anions Triggered by Bacteria In Situ for Selective Photothermal Therapy

A supramolecular complex that can be selectively reduced to radical anions in situ by facultative anaerobic bacteria is reported. To this end, a water‐soluble bifunctional monomer bearing perylene diimide was synthesized, and its supramolecular complex with cucurbit[7]uril was fabricated on the basis of host–guest complexation, which could be reduced to forming radical anions in the presence of E. coli . It was found that this supramolecular complex could display different ability of generating radical anions by facultative anaerobic and aerobic bacteria in terms of their various reductive abilities. The selective antibacterial activity of the supramolecular complex could be realized by the photothermal performance of the radical anions under near‐infrared irradiation. It is anticipated that this method may lead to a novel bacteria‐responsive photothermal therapy to regulate balance of bacterial flora.     

Capped Mesoporous Silica Nanoparticles for the Selective and Sensitive Detection of Cyanide

The development of easy and affordable methods for the detection of cyanide is of great significance due to the high toxicity of this anion and the potential risks associated with its pollution. Herein, optical detection of cyanide in water has been achieved by using a hybrid organic–inorganic nanomaterial. Mesoporous silica nanoparticles were loaded with [Ru(bipy)₃]²⁺, functionalized with macrocyclic nickel(II) complex subunits, and capped with a sterically hindering anion (hexametaphosphate). Cyanide selectively induces demetallation of nickel(II) complexes and the removal of capping anions from the silica surface, allowing the release of the dye and the consequent increase in fluorescence intensity. The response of the capped nanoparticles in aqueous solution is highly selective and sensitive towards cyanide with a limit of detection of 2 μm .     

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

The optical and colorimetric properties of a new chemosensor 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino)methyl)phenol (L) for cyanide ions were investigated by the naked-eye detection and UV–vis spectroscopy. This receptor reveals visual changes toward CN⁻ anions in aqueous media. No significant color changes were observed upon the addition of any other anions. The cyanide recognition properties of the receptor through proton-transfer were monitored by UV–vis titration and ¹H NMR spectroscopy. The binding constant (K_a) and stoichiometry of the formed host–guest complex were calculated by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The detection limit of the probe towards CN⁻ was 1.03 × 10⁻⁶ mol L⁻¹, which is lower than the maximum value of cyanide (1.9 × 10⁻⁶ mol L⁻¹) permitted by the World Health Organization in drinking water. Thus, this chemosensor was sensitive enough to detect cyanide in aqueous solutions. ¹H NMR experiments were conducted to investigate the nature of interaction between the receptor and CN⁻ anions. Notably, the designed sensor can be applied for the rapid detection of cyanide anions in the basic pH range and also under physiological conditions, for practical purposes for a long duration. The sensing behavior of the receptor was further emphasized by computational studies. Quantum-chemical calculations and molecular studies via Density Functional Theory (DFT) were carried out to supplement the experimental results.     

A Supramolecular Naphthalene Diimide Radical Anion with Efficient NIR-II Photothermal Conversion for E. coli-Responsive Photothermal Therapy

We report a supramolecular naphthalene diimide (NDI) radical anion with efficient NIR-II photothermal conversion for E. coli-responsive photothermal therapy. The supramolecular radical anion (NDI-2CB[7])⋅⁻, which is obtained from the E. coli-induced in situ reduction of NDI-2CB[7] neutral complex, formed by the host–guest interaction between an NDI derivative and cucurbit[7]uril (CB[7]), exhibits unexpectedly strong NIR-II absorption and remarkable photothermal conversion capacity in aqueous solution. The NIR-II absorption is caused by the self-assembly of NDI radical anions to form supramolecular dimer radicals in aqueous solution, which is supported by theoretically predicted spectra. The (NDI-2CB[7])⋅⁻ demonstrates excellent NIR-II photothermal antimicrobial activity (>99 %). This work provides a new approach for constructing NIR-II photothermal agents and non-contact treatments for bacterial infections.     

Cucurbit[8]uril-mediated phosphorescent supramolecular foldamer for antibiotics sensing in water and cells

A phosphorescent supramolecular foldamer is conveniently constructed by the 1:1 host–guest complexation with cucurbit[8]uril and 1,2-diaminocyclohexane-bridged 4-(4-bromophenyl)-pyridinium salt. The tightly compact host–guest complexation in molecular foldamer can greatly suppress the fluorescence emissive channel and promote the intersystem crossing from singlet to triplet states, thus leading to the green phosphorescence at ambient temperature in aqueous solution. More intriguingly, the phosphorescence emission shows very rapid and sensitive responsiveness to different antibiotics in both inanimate milieu and living cells. Remarkably, the limit of detection of such binary inclusion complex toward sulfamethazine can reach as low as 1.86 × 10^?7 mol/L. Thus, it is envisaged that this supramolecular nanoplatform featuring unique complexation-enhanced phosphorescence emission may hold great promise in sensing and detecting many other biological targets under physiological environment.     

Metal complexation induced supramolecular gels for the detection of cyanide in water

ABSTRACT

The role of metal salts in inducing supramolecular gel network formation was analysed by reacting two pyridyl-N-oxide amides with various diamagnetic zinc(II) and cadmium(II) salts. Metal induced supramolecular gelation was observed for zinc(II) and cadmium(II) chloride complexes in water and the morphologies of the xerogels were analysed by scanning electron microscopy (SEM). The relative gel strength was corroborated with various non-bonding interactions observed in the solid-state structures of zinc(II) complexes using X-ray diffraction. The non-bonding interactions of the pyridyl-N-oxide amides and the metal complexes were compared to find the key interactions responsible for metallogel formation. The anion induced stimuli-responsive property of the metallogels was studied in the presence of halides and cyanide anions. The cadmium(II) gels were stable in presence of two equivalents of halides but the network collapsed in presence of cyanide anion in water and this property can be used to detect cyanide anions in water.     

Anion Recognition and Sensing: The State of the Art and Future Perspectives

Anion recognition chemistry has grown from its beginnings in the late 1960s with positively charged ammonium cryptand receptors for halide binding to, at the end of the millennium, a plethora of charged and neutral, cyclic and acyclic, inorganic and organic supramolecular host systems for the selective complexation, detection, and separation of anionic guest species. Solvation effects and pH values have been shown to play crucial roles in the overall anion recognition process. More recent developments include exciting advances in anion-templated syntheses and directed self-assembly, ion-pair recognition, and the function of anions in supramolecular catalysis.     

An Efficient Probe for Rapid Detection of Cyanide in Water at Parts per Billion Levels and Naked‐Eye Detection of Endogenous Cyanide

A new molecular probe based on an oxidized bis‐indolyl skeleton has been developed for rapid and sensitive visual detection of cyanide ions in water and also for the detection of endogenously bound cyanide. The probe allows the “naked‐eye” detection of cyanide ions in water with a visual color change from red to yellow (Δλ_max=80 nm) with the immediate addition of the probe. It shows high selectivity towards the cyanide ion without any interference from other anions. The detection of cyanide by the probe is ratiometric, thus making the detection quantitative. A Michael‐type addition reaction of the probe with the cyanide ion takes place during this chemodosimetric process. In water, the detection limit was found to be at the parts per million level, which improved drastically when a neutral micellar medium was employed, and it showed a parts‐per‐billion‐level detection, which is even 25‐fold lower than the permitted limits of cyanide in water. The probe could also efficiently detect the endogenously bound cyanide in cassava (a staple food) with a clear visual color change without requiring any sample pretreatment and/or any special reaction conditions such as pH or temperature. Thus the probe could serve as a practical naked‐eye probe for “in‐field” experiments without requiring any sophisticated instruments.     

Construction of anion‐responsive crosslinked polypseudorotaxane based on molecular recognition of pillar[5]arene

A pillar[5]arene pendant polymer (Poly‐P[5]A) is synthesized via ROMP using Grubb's first‐generation catalyst. GPC analysis of the polymer suggested ~30 pendant pillar[5]arene units in the polymer. Supramolecular polypseudorotaxane assembly is constructed by intermolecularly crosslinking pendant pillar[5]arene units using a bispyridinium guest via host–guest complexation. Formation of the polypseudorotaxane assembly is characterized by 1D/2D NMR techniques and DLS analysis. Moreover, anion‐responsiveness of the polypseudorotaxane assembly is demonstrated by ¹H NMR spectroscopic analysis using chloride anion as external stimulus. Scanning electron microscopic analysis of the poly‐P[5]A showed breath‐figure assembly and upon crosslinking with G.2PF₆ the polymer self‐assemble to give a supramolecular polymer network. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1508–1515     

Multichannel recognition of hydrogen sulphate anion by a Zn(II)–triazole–pyridine complex bearing a ferrocenyl pendant

Receptors ferrocene–triazole–pyridine triads assembled with Zn(II) or Cd(II) metal cations behave as chemosensor molecules for HSO₄ ^?  anions through electrochemical and optical channels: the redox peak of the ferrocene/ferrocenium redox couple is shifted cathodically by 72–53 mV, and a new absorption band appeared in the UV–vis spectrum upon complexation with the HSO₄ ^?  anion. Association constants, detection limits and stoichiometries of the recognition processes have been determined, whereas ¹H NMR experiments and density functional theory calculations are used to suggest the plausible binding mode taking place in the new supramolecular assembly formed.     

A triply-responsive supramolecular amphiphile fabricated by a thermal-responsive pillar[5]arene-based host–guest recognition motif

A novel molecular recognition motif was built between a neutral water soluble pillar[5]arene and decyltrimethylammonium bromide in water. Its thermal-controlled complexation with G1 in water was investigated. Furthermore, based on this new thermal responsive host–guest recognition motif, we further constructed a supramolecular amphiphile between this pillar[5]arene and a trimethylammonium bromide derivative containing an azobenzene group at the other end. This supramolecular amphiphile showed triply-responsiveness, that is, thermal responsiveness of the host–guest complex, photo-responsiveness of the azobenzene group and chemical-responsiveness by adding β-CD.     

Fluoride anion sensing using colorimetric reagents containing binaphthyl moiety and urea binding site

Four 1,1′-binaphthalene based bis-urea derivatives bearing aryl groups at end-on nitrogen atoms IIIa–d were synthesized as potential sensor molecules. These receptors show characteristic UV-VIS spectral changes on complexation with anions and they exhibit selective recognition of F⁻ over other halide anions. Interaction of a fluoride anion with urea NH groups was confirmed by ¹H NMR data. The presence of an electron-withdrawing nitro group in N′-aryls (receptors IIIa and IIIb) appeared to be necessary for naked-eye colorimetric detection. These receptors show dramatic color change from light-yellow to orange (IIIa) or to orange-red (IIIb) in the presence of guest fluoride anions already at concentrations of 10⁻⁵ mol dm⁻³ of the receptor and host.     

A Supramolecular Vesicle Based on the Complexation of p‐Sulfonatocalixarene with Protamine and its Trypsin‐Triggered Controllable‐Release Properties

Enzyme‐responsive assembly represents one of the increasingly significant topics in biomaterials research and finds feasible applications to the controlled release of therapeutic agents at specific sites at which the target enzymes are located. In this work, based on the concept of host–guest chemistry, a trypsin‐responsive supramolecular vesicle using p‐sulfonatocalix[4]arene as the macrocyclic host and natural serine protease trypsin‐cleavable cationic protein protamine as the guest molecule, is reported. The complexation of p‐sulfonatocalix[4]arene with protamine directs the formation of a supramolecular binary vesicle, which is dissipated by trypsin with high selectivity. Therefore, the present system represents a principle‐of‐concept to build a controlled‐release carrier at trypsin‐overexpressed sites.     

A Supramolecular Tubular Nanoreactor

The extremely strong noncovalent complexation between the rigid host of phthalocyanine‐bridged β‐cyclodextrins and the amphiphilic guest carboxylated porphyrin is employed to construct a hollow tubular structure as a supramolecular nanoreactor. A representative coupling reaction occurs in the hydrophobic interlayers of the tubular walls in pure water at room temperature, leading to an enhancement of ten times higher reaction rate without any adverse effect on catalytic activity and conversion.     

Transformative Supramolecular Vesicles Based on Acid-Degradable Acyclic Cucurbit[n]uril and a Prodrug for Promoted Tumoral-Cell Uptake

Smart supramolecular vesicles constructed by host–guest interactions between “acid-degradable” acyclic cucurbit[n]uril (CB[n]) and a doxorubicin prodrug are reported. “Acid-degradable” acyclic CB[n] is a high-affinity host for several common antitumor drugs, and its degradation leads to a more dramatic decrease in binding affinity than that observed for “acid-sensitive” hosts. Supramolecular complexation between acid-degradable acyclic CB[n] and a doxorubicin prodrug resulted in the formation of negatively charged supramolecular vesicles. The prodrug strategy allowed doxorubicin to be conjugated to vesicles in a stable manner with a high drug-loading ratio of 20 %. The resulting supramolecular vesicles were responsive to tumor acidity (pH 6.5). Induced by mildly acidic conditions (pH 6.5–5.5), acid-degradable acyclic CB[n] could be degraded, and this led to a vesicle-to-micelle transition to form positively charged micelles. This transition resulted in a pH-dependent change in size and surface charge, which improved tumoral-cell uptake for doxorubicin.     

Visible-Light-Switchable Tellurium-Based Chalcogen Bonding: Photocontrolled Anion Binding and Anion Abstraction Catalysis

Exploring new noncovalent bonding motifs with reversibly tunable binding affinity is of fundamental importance in manipulating the properties and functions of supramolecular self-assembly systems and materials. Herein, for the first time, we demonstrate a unique visible-light-switchable telluro-triazole/triazolium-based chalcogen bonding (ChB) system in which the Te moieties are connected by azobenzene cores. The binding strengths between these azo-derived ChB receptors and the halide anions (Cl⁻, Br⁻) could be reversibly regulated upon irradiation by visible light of different wavelengths. The cis-bidentate ChB receptors exhibit enhanced halide anion binding ability compared to the trans-monodentate receptors. In particular, the telluro-triazolium-based ChB receptor can achieve both high and significantly photoswitchable binding affinities for halide anions, which enable it to serve as an efficient photocontrolled organocatalyst for ChB-assisted halide abstraction in a Friedel–Crafts alkylation benchmark reaction.     

A Post‐Synthetically Modified MOF for Selective and Sensitive Aqueous‐Phase Detection of Highly Toxic Cyanide Ions

Selective and sensitive detection of toxic cyanide (CN^?) by a post‐synthetically altered metal–organic framework (MOF) has been achieved. A post‐synthetic modification was employed in the MOF to incorporate the specific recognition site with the CN^? ion over all other anions, such as Cl^?, Br^?, and SCN^?. The aqueous‐phase sensing and very low detection limit, the essential prerequisites for an effective sensory material, have been fulfilled by the MOF. Moreover, the present detection level meets the standard set by the World Health Organization (WHO) for the permissible limit of cyanide concentration in drinking water. The utilization of MOF‐based materials as the fluorometric probes for selective and sensitive detection of CN^? ions has not been explored till now.     

Artificial Neural Networks for Guest Chirality Classification through Supramolecular Interactions

A novel strategy for classification of guest chirality based on the combination of artificial neural networks and anion‐receptor chemistry is reported. The receptor reported herein forms supramolecular complexes with a variety of biologically important carboxylates, in which the chemical shift changes during addition of anions result in complex guest‐stereochemistry‐dependent patterns as followed by ¹H NMR spectroscopy. The neural network had learnt these patterns from a training set of 12 anions, and successfully identified the “unknown” chirality of 14 guests present in the test set. Additionally, principal component analysis could discriminate most of the guests studied (26) and allowed for identification of the receptor protons, which are responsible for information transfer of guest chirality.     

Supramolecular photoswitch with white-light emission based on bridged bis(pillar[5]arene)s

White light-emitting (WLE) switches have greatly promising and worthy applications in the field of controllable lighting, display, and sensing. Here, we unprecedentedly construct a photocontrollable light-harvesting supramolecular nanoassembly (G/H@NiR) with rarely switchable white light emission, which comprised oligo(phenylenevinylene)-bridged pillar[5]arenes (H), photochromic diarylethene (G), and Nile red (NiR), through host–guest complexation. In the nanosystem, color-tunable photoluminescence such as cyan, orange red, and especially white with chromaticity coordinates (0.33, 0.34) is achieved through altering the proportions of the energy donor (H in assembly G/H) and acceptor center (NiR). Importantly, G, acting as a modulator, can controllably change the energy-transfer (ET) pathway between H and NiR, when the G/H@NiR nanoassembly was exposed to distinct light, achieving reversible switching of multicolor photoluminescence including white-light emission. In addition, the designed intelligent supramolecular assembly G/H@NiR with captivating characteristics has extremely valuable application as erasable multicolor fluorescent inks to be filled in the groove of a three-dimensional model and further form a high-security-level chromatic anticounterfeiting quick response (QR) code, which can be completely hidden and revealed under stimulation of distinct light. Besides, the erasable fluorescent inks can also be used to record data information in mixed fiber film, which can be completely wiped off and rerecord by distinct light. The study provides a controllable supramolecular light-harvesting strategy (the photo-modulating ET pathway in the light-harvesting process) for developing photo-responsive intelligent photoluminescence materials, particularly photosensitive WLE materials, possessing potential applications in photosensitive lighting and display, multicolor imaging, light-manipulative data storage, and high-security-level anticounterfeiting.     

Self‐Assembly and Disassembly of Vesicles as Controlled by Anion–π Interactions

Anion–π interactions have been widely studied as new noncovalent driving forces in supramolecular chemistry. However, self‐assembly induced by anion–π interactions is still largely unexplored. Herein we report the formation of supramolecular amphiphiles through anion–π interactions, and the subsequent formation of self‐assembled vesicles in water. With the π receptor 1 as the host and anionic amphiphiles, such as sodium dodecylsulfate (SDS), sodium laurate (SLA), and sodium methyl dodecylphosphonate (SDP), as guests, the sequential formation of host–guest supramolecular amphiphiles and self‐assembled vesicles was demonstrated by SEM, TEM, DLS, and XRD techniques. The intrinsic anion–π interactions between 1 and the anionic amphiphiles were confirmed by crystal diffraction, HRMS analysis, and DFT calculations. Furthermore, the controlled disassembly of the vesicles was promoted by competing anions, such as NO₃^?, Cl^?, and Br^?, or by changing the pH value of the medium.