KF and CsF Recognition and Extraction by a Calix[4]crown-5 Strapped Calix[4]pyrrole Multitopic Receptor

Supramolecular chemistry of liquid-liquid extraction

Liquid-Liquid Extraction (LLE) is a venerable and widely used method for the separation of a targeted solute between two immiscible liquids. In recent years, this method has gained popularity in the supramolecular chemistry community due to the development of various types of synthetic receptors that effectively and selectively bind specific guests in an aqueous medium through different supramolecular interactions. This has eventually led to the development of state-of-the-art extraction technologies for the removal and purification of anions, cations, ion pairs, and small molecules from one liquid phase to another liquid phase, which is an industrially viable method. The focus of this perspective is to furnish a vivid picture of the current understanding of supramolecular interaction-based LLE chemistry. This will not only help to improve separation technology in the chemical, mining, nuclear waste treatment, and medicinal chemistry sectors but is also useful to address the purity issue of the extractable species, which is otherwise difficult. Thus, up-to-date knowledge on this subject will eventually provide opportunities to develop large-scale waste remediation processes and metallurgy applications that can address important real-life problems.

α-Methylbenzylamine Functionalized Crown-Ether-Appended Calix[4]arene Phase Transfer Catalyst for Enantioselective Henry Reaction

In this letter, we designed a highly selective α-methylbenzylamine functionalized crown-ether-appended calix[4]arene derived phase transfer catalyst for asymmetric nitroaldol reaction to provide the desired nitroaldol adducts in high yields (up to 99 % yield) with good to excellent enantioselectivities (up to 99.8 % ee).

Highly Selective Transport and Enrichment of Lithium Ions through Bionic Ion Pair Receptor Nanochannels

Inspired by ion pair cotransport channels in biological systems, a bionic nanochannel modified with lithium ion pair receptors is constructed for selective transport and enrichment of lithium ions (Li⁺). NH₂-pillar[5]arene (NP5) is chosen as ion pair receptors, and the theoretical simulation and NMR titration experiments illustrate that NP5 has good affinity for the ion pair of LiCl through a strong host-guest interaction at the molecular level. Due to the confinement effect and ion pair cooperation recognition, an NP5-based receptor was introduced into an artificial PET nanochannel. An I-V test indicated that the NP5 channel realized the highly selective recognition for Li⁺. Meanwhile, transmembrane transport and COMSOL simulation experiments proved that the NP5 channel achieved the transport and enrichment of Li⁺ through the cooperative interaction between NP5 and LiCl. Moreover, the receptor solution of transmembrane transport LiCl in the NP5 channel was used to cultivate wheat seedlings, which obviously promoted their growth. This nanochannel based on the ion pair recognition will be much useful for practical applications like metal ion extraction, enrichment, and recycle.

Selective Potassium Chloride Recognition, Sensing, Extraction, and Transport Using a Chalcogen-Bonding Heteroditopic Receptor

Chalcogen bonding (ChB) is rapidly rising to prominence in supramolecular chemistry as a powerful sigma (σ)-hole-based noncovalent interaction, especially for applications in the field of molecular recognition. Recent studies have demonstrated ChB donor strength and potency to be remarkably sensitive to local electronic environments, including redox-switchable on/off anion binding and sensing capability. Influencing the unique electronic and geometric environment sensitivity of ChB interactions through simultaneous cobound metal cation recognition, herein, we present the first potassium chloride-selective heteroditopic ion-pair receptor. The direct conjugation of benzo-15-crown-5 ether (B15C5) appendages to Te centers in a bis-tellurotriazole framework facilitates alkali metal halide (MX) ion-pair binding through the formation of a cofacial intramolecular bis-B15C5 M⁺ (M⁺ = K⁺, Rb⁺, Cs⁺) sandwich complex and bidentate ChB···X^– formation. Extensive quantitative ¹H NMR ion-pair affinity titration experiments, solid–liquid and liquid–liquid extraction, and U-tube transport studies all demonstrate unprecedented KCl selectivity over all other group 1 metal chlorides. It is demonstrated that the origin of the receptor’s ion-pair binding cooperativity and KCl selectivity arises from an electronic polarization of the ChB donors induced by the cobound alkali metal cation. Importantly, the magnitude of this switch on Te-centered electrophilicity, and therefore anion-binding affinity, is shown to correlate with the inherent Lewis acidity of the alkali metal cation. Extensive computational DFT investigations corroborated the experimental alkali metal cation–anion ion-pair binding observations for halides and oxoanions.

Unravelling the origin of long-term stability for Cs+ and Sr2+ solidification inside sodalite

Cesium (Cs⁺) and strontium (Sr²⁺) ions are the main fission byproducts in the reprocessing of spent nuclear fuels for nuclear power plants. Their long half-live period (30.17 years for ¹³⁷Cs and 28.80 years for ⁹⁰Sr) makes them very dangerous radionuclides. Hence the solidification of Cs⁺ and Sr²⁺ is of paramount importance for preventing them from entering the human food chain through water. Despite tremendous efforts for solidification, the long-term stability remains a great challenge due to the experimental limitation and lack of good evaluation indicators for such long half-life radionuclides. Using density functional theory (DFT), we investigate the origin of long-term stability for the solidification of Cs⁺ and Sr²⁺ inside sodalite and establish that the exchange energy and the diffusion barrier play an important role in gaining the long-term stability both thermodynamically and kinetically. The acidity/basicity, solvation, temperature, and diffusion effect are comprehensively studied. It is found that solidification of Cs⁺ and Sr²⁺ is mainly attributed to the solvation effect, zeolitic adsorption ability, and diffusion barriers. The present study provides theoretical evidence to use geopolymers to adsorb Cs⁺ and Sr²⁺ and convert the adsorbed geopolymers to zeolites to achieve solidification of Cs⁺ and Sr²⁺ with long-term stability.

Triazolated calix[4]semitubes: assembling strategies towards long multicalixarene architectures

Cone and 1,3-alternate calix[4]arenes bearing pairs of 2-azidoethyl or propargyl groups, and 1,3-alternate calix[4]arenes having four 2-azidoethyl, four propargyl groups or pairs of 2-azidoethyl and silylated propargyl groups were explored...

Regioisomers of singly bridged calix[6]crown-6 and their heavy alkali metal complexes: a molecular baseball glove for caesium(I)

We report the formation of heavy alkali metal complexes of bicyclic host molecules including the caesium(I) complex that catches the central metal ion with the deep pocket of the host similar to a baseball glove. For this, three regioisomers of singly bridged calix[6]crown-6 [1,2-bridged (H4 L 1,2), 1,3-bridged (H4 L 1,3) and 1,4-bridged (H4 L 1,4)] have been synthesized by alkyl-ation of calix[6]arene with penta-ethyl-ene glycol di-tosyl-ate in the presence of M 2CO3 (M = Na, K, Rb and Cs). The larger the cation size of the metal carbonate, the higher the yield of the H4 L 1,4 isomer, indicating the size-based template effect. A combination of H4 L 1,2 and RbOH allowed isolation of the mononuclear rubidium(I) complex (1) in which the metal center is six-coordinated in a loose fashion, the remaining two oxygen donors in the crown loop and two phenols in the calix rim are uncoordinated. Notably, the complexation of H4 L 1,2 with CsOH yielded the mononuclear caesium(I) complex (2), in which all possible ten binding sites on the deep and good-fit pocket participate in coordination via high cooperativity between the crown loop and calix rim, similar to a baseball glove. In dipolar organic solution, the caesium(I) complex 2 remains intact. H4 L 1,4 afforded a dicesium(I) complex (3) and adjacent complexes are linked by intermolecular cation-π interactions, giving rise to a pseudo one-dimensional coordination polymer. These results provide insight into the metal carbonate-dependent synthesis of calix[6]crowns and the influence of regioisomers on caesium(I) complexation.

Selective Separation of Lithium Chloride by Organogels Containing Strapped Calix[4]pyrroles

Reported herein are two functionalized crown ether strapped calix[4]pyrroles, H1 and H2. As inferred from competitive salt binding experiments carried out in nitrobenzene-d₅ and acetonitrile-d₃, these hosts capture LiCl selectively over four other test salts, viz. NaCl, KCl, MgCl₂, and CaCl₂. Support for the selectivity came from density functional theory (DFT) calculations carried out in a solvent continuum. These theoretical analyses revealed a higher innate affinity for LiCl in the case of H1, but a greater selectivity relative to NaCl in the case of H2, recapitulating that observed experimentally. Receptors H1 and H2 were outfitted with methacrylate handles and subject to copolymerization with acrylate monomers and cross-linkers to yield gels, G1 and G2, respectively. These two gels were found to adsorb lithium chloride preferentially from an acetonitrile solution containing a mixture of LiCl, NaCl, KCl, MgCl₂, and CaCl₂ and then release the lithium chloride in methanol. The gels could then be recycled for reuse in the selective adsorption of LiCl. As such, the present study highlights the use of solvent polarity switching to drive separations with potential applications in lithium purification and recycling.

Halogen Bonding Heteroditopic Materials for Cooperative Sodium Iodide Binding and Extraction

A series of novel heteroditopic halogen bonding (XB) receptor functionalised silica based materials, containing mono- and bis-iodotriazole benzo-15-crown-5 groups are investigated for the cooperative binding and extraction of sodium halide ion-pair species from aqueous solution. Characterisation of the XB materials by CHN elemental analysis, 13 C CP/MAS NMR and ATR-FTIR spectroscopies confirms and quantifies the successful incorporation of the ion-pair receptor frameworks to the silica material. ICP-MS solid-liquid extraction studies demonstrate the bidentate XB functionalised material is capable of NaI extraction from water. Importantly, cooperative XB-mediated sodium halide ion-pair binding is determined to be crucial to the material's extraction capabilities, impressively demonstrating a two-fold enhancement in sodium iodide extraction efficiency relative to a heteroditopic hydrogen bonding receptor functionalised silica material analogue.

Revealing the Dynamic Process of Ion Pair Recognition by Calix[4]pyrrole: A Case Study of Cesium Chloride

Ion pair receptors based on meso-octamethylcalix[4]pyrrole (CP) have been extensively investigated over recent years. However, the nature of their ion pair recognition has barely been reported, even for CP itself. Herein, cesium chloride was used as a guest ion pair to investigate the dynamic process of ion pair recognition by CP, and the "capture-bind" mechanism for this process is proposed for the first time. The results reveal that Cs⁺ can be first captured by Cl^- at long distances, and then it is bound to the cavity through almost equal contributions of Cl^- and CP. Although the effective charge of Cl^- is obviously reduced by charge-transfer, the electrostatic interactions between Cl^- and Cs⁺ are still strong even at long distances in the presence of CP.

Development of effective potassium acetate extractant

Carboxylates are commonly used in the food and pharmaceutical industry and due to their extensive use, carboxylates present a significant environmental burden. In this context, valine based, heteroditopic receptor 1 was prepared and its ability to bind simultaneously potassium cation and acetate anion in water containing CH₃CN solutions was demonstrated. Under liquid–liquid extraction conditions the receptor 1 was capable of extracting hydrophilic AcOK salt from aqueous solution and was proved to be nearly ten times more effective than the equimolar mixture of monotopic receptors. Furthermore, compound 1 could extract one of the most popular nonsteroidal anti-inflammatory drugs, ibuprofen (IbuOK), from relatively dilute aqueous solutions.

Structurally simple, heteroditopic receptor is capable of extracting hydrophilic potassium acetate and other carboxylate salts from water to organic phase.

From Heteroditopic to Multitopic Receptors for Ion-Pair Recognition: Advances in Receptor Design and Applications

Ion-pair recognition has emerged from cation and anion recognition and become a diverse and active field in its own right. The last decade has seen significant advances in receptor design in terms of the types of binding motifs, understanding of cooperativity and increase in complexity from heteroditopic to multitopic receptors. As a result, attention has turned to applying this knowledge to the rational design of ion-pair receptors for applications in salt solubilisation and extraction, membrane transport and sensing. This Review highlights recent progress and developments in the design and applications of heteroditopic and multitopic receptors for ion-pair recognition.

Heteroditopic receptor flexibility – an important design principle for effective ion pair extractants based on carboxylate studies

Potassium carboxylate salt binding and extraction experiments of a heteroditopic receptor series reveal that conformational freedom is an important factor affecting salt extraction efficiency.

Monofunctionalized Bambus[6]urils and Their Conjugates with Crown Ethers for Liquid-Liquid Extraction of Inorganic Salts

Bambusurils are a growing family of macrocyclic anion receptors. In this Letter, we present the first syntheses of monofunctionalized bambusurils and their use for the preparation of heteroditopic bambusuril-crown ether conjugates suitable for the extraction of ion pairs from water to chloroform.

Strapped calix[4]pyrroles: from syntheses to applications

Supramolecular chemistry is a central topic in modern chemistry. It touches on many traditional disciplines, such as organic chemistry, inorganic chemistry, physical chemistry, materials chemistry, environmental chemistry, and biological chemistry. Supramolecular hosts, inter alia macrocyclic hosts, play critical roles in supramolecular chemistry. Calix[4]pyrroles, non-aromatic tetrapyrrolic macrocycles defined by sp³ hybridized meso bridges, have proved to be versatile receptors for neutral species, anions, and cations, as well as ion pairs. Compared to the parent system, octamethylcalix[4]pyrrole and its derivatives bearing simple appended functionalities, strapped calix[4]pyrroles typically display enhanced binding affinities and selectivities. In this review, we summarize advances in the design and synthesis of strapped calix[4]pyrroles, as well as their broad utility in molecular recognition, supramolecular extraction, separation technology, ion transport, and as agents capable of inhibiting cancer cell proliferation. Future challenges within this sub-field are also discussed.

Strapped calix[4]pyrrole as a lithium salts selective receptor through separated ion-pair binding

A triazole-bearing strapped calix[4]pyrrole (1) was synthesized as a lithium salt selective ion pair receptor.

Molecular Recognition of Pyrophosphate with Extended Bis(Zn(II)-DPA) Derivatives

A series of pyrophosphate (PPi) receptors were synthesized, and their binding affinities toward both PPi and adenosine triphosphate were evaluated in N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid-buffered solution. The presence of two hydrogen bond donors slightly retarded the reaction rate of anionic guest exchange, while four had a significant retardation effect. A macrocyclic receptor, 17, exhibited superior selectivity toward PPi compared with acyclic receptors, presumably due to effective steric interactions. Isothermal titration calorimetry experiments and potentiometric titration experiments revealed the effect of the substituent structure on the degree of anion guest stabilization and the deprotonation of water molecules bound to zinc(II) ions, as well as the guest binding thermodynamics.

Ion-pair induced supramolecular assembly formation for selective extraction and sensing of potassium sulfate

Selective extraction of sulfates in the form of alkali metal salts using charge-neutral molecular receptors is one of the holy grails of supramolecular chemistry. Herein we describe, for the first time, a squaramide-based ion pair receptor equipped with a crown ether site that is able to extract potassium sulfate from the aqueous to the organic phase (an analogous monotopic anion receptor lacking the crown ether unit lacks this ability). 1H NMR, UV-vis, DOSY-NMR, DLS, and MS experiments and the solid-state single crystal structure provided evidence of the formation of a supramolecular core-shell like assembly upon interaction of the receptor with potassium sulfate. The presence of monovalent potassium salts, in contrast, promoted the formation of simple 1 : 1 complexes. Unlike the 4 : 1 assembly, the 1 : 1 complexes are poorly soluble in organic media. This feature was utilized to overcome the Hofmeister bias and allow for selective extraction of extremely hydrophilic sulfates over lipophilic nitrate anions, which was unambiguously proved by quantitative AES and ion chromatography measurements. A simple modification of the receptor structure led to a "naked eye" optical sensor able to selectively detect sulfates under both SLE and LLE conditions.

Macrocycles as Ion Pair Receptors

Cation and anion recognition have both played central roles in the development of supramolecular chemistry. Much of the associated research has focused on the development of receptors for individual cations or anions, as well as their applications in different areas. Rarely is complexation of the counterions considered. In contrast, ion pair recognition chemistry, emerging from cation and anion coordination chemistry, is a specific research field where co-complexation of both anions and cations, so-called ion pairs, is the center of focus. Systems used for the purpose, known as ion pair receptors, are typically di- or polytopic hosts that contain recognition sites for both cations and anions and which permit the concurrent binding of multiple ions. The field of ion pair recognition has blossomed during the past decades. Several smaller reviews on the topic were published roughly 5 years ago. They provided a summary of synthetic progress and detailed the various limiting ion recognition modes displayed by both acyclic and macrocyclic ion pair receptors known at the time. The present review is designed to provide a comprehensive and up-to-date overview of the chemistry of macrocycle-based ion pair receptors. We specifically focus on the relationship between structure and ion pair recognition, as well as applications of ion pair receptors in sensor development, cation and anion extraction, ion transport, and logic gate construction.

New dimensions in calix[4]pyrrole: the land of opportunity in supramolecular chemistry

The quest for receptors endowed with the selective complexation and detection of negatively charged species continues to receive substantial consideration within the scientific community worldwide. This study is encouraged by the utilization of anions in nature in a plethora of biological systems such as chloride channels and proteins and as polyanions for genetic information. The molecular recognition of anionic species is greatly interesting in terms of their favourable interactions. In this comprehensive review, in addition to giving accounts of some selected syntheses, we illustrated diverse applications ranging from molecular containers to ion transporters and drug carriers of a supramolecular receptor named calix[4]pyrrole. We believe that the present review may act as a catalyst in enhancing the novel applications of calix[4]pyrrole and its congeners in the other dimensions of science and technology.

The quest for receptors endowed with the selective complexation and detection of negatively charged species continues to receive substantial consideration within the scientific community worldwide.

Recognition and Extraction of Sodium Chloride by a Squaramide-Based Ion Pair Receptor

We synthesized an ion pair receptor 1 consisting of a crown ether cation binding site and a squaramide anion binding domain and compared its binding properties to those of its analogous urea counterpart 2. We studied their salt binding properties using spectrophotometric and spectroscopic measurements in an acetonitrile solution and in acetonitrile/water mixtures. Apart from carboxylate anions, all of the anions tested were found to associate with receptor 1 and 2 more strongly in the presence of sodium cations. A homotopic anion receptor 3, lacking a crown ether unit, was unable to bind sodium salt more strongly than tetrabutylammonium salts. Solution and solid-state X-ray measurements revealed strong sodium chloride coordination to receptor 1, which is able to bind this salt even in the presence of 10% water. In contrast to the urea-based ion pair receptor 2 or anion receptor 3, ditopic receptor 1 is capable of extracting sodium chloride from aqueous media to the organic phase, as was evidenced unambiguously by ¹H nuclear magnetic resonance, mass spectrometry, and atomic absorption spectroscopy analyses.

Calixarene alpha-ketoacetylenes: versatile platforms for reaction with hydrazine nucleophile

Late stage diversification of calix[4]arenes and thiacalix[4]arenes with heterocycles remains a significant synthetic challenge and hampers further exploitation of the scaffolds. Here we describe the development of a short and facile synthetic route to conformationally diverse novel calix[4]arene and thiacalix[4]arene ynones using a palladium cross coupling approach (5% Pd(ii) + 10% Cu(i)) with benzoyl chloride. Their successful conversion to heterocycles to afford pyrazoles was demonstrated through treatment with hydrazine. Functionalisation is calixarene conformation and linker independent enabling access to a library of structures.

Late stage diversification of calix[4]arenes and thiacalix[4]arenes with heterocycles remains a significant synthetic challenge and hampers further exploitation of the scaffolds.

Control over multiple molecular states with directional changes driven by molecular recognition

Recently, ligand-metal coordination, stimuli-responsive covalent bonds, and mechanically interlinked molecular constructs have been used to create systems with a large number of accessible structural states. However, accessing a multiplicity of states in sequence from more than one direction and doing so without the need for external energetic inputs remain as unmet challenges, as does the use of relatively weak noncovalent interactions to stabilize the underlying forms. Here we report a system based on a bispyridine-substituted calix[4]pyrrole that allows access to six different discrete states with directional control via the combined use of metal-based self-assembly and molecular recognition. Switching can be induced by the selective addition or removal of appropriately chosen ionic guests. No light or redox changes are required. The tunable nature of the system has been established through a combination of spectroscopic techniques and single crystal X-ray diffraction analyses. The findings illustrate a new approach to creating information-rich functional materials.

Functionalised tetrathiafulvalene- (TTF-) macrocycles: recent trends in applied supramolecular chemistry

Tetrathiafulvalene- (TTF-) based macrocyclic systems, cages and supramolecularly self-assembled 3D constructs have been extensively explored as functional materials for sensing and switching applications.

Tritopic ion-pair receptors based on anion–π interactions for selective CaX2 binding

Selective ion-pair binding of CaX₂ (X = Br⁻ and I⁻) was realized by a tritopic receptor incorporating two homoditopic anion–π binding sites and a pentaethylene glycol moiety.

Using anion recognition to control the folding and unfolding of a single chain phosphorescent polymer

We report here the use of anion recognition to control the folding and unfolding of a single polymeric chain consisting of a PMMA bearing pendant calix[4]pyrrole and Pt(ii) porphyrin subunits.

Molecular Recognition Under Interfacial Conditions: Calix[4]pyrrole-Based Cross-linkable Micelles for Ion Pair Extraction

An anthracene-functionalized, long-tailed calix[4]pyrrole 1, containing both an anion-recognition site and cation-recognition functionality, has been synthesized and fully characterized. Upon ion pair complexation with FeF₂, receptor 1 self-assembles into multimicelles in aqueous media. This aggregation process is ascribed to a change in polarity from nonpolar to amphiphilic induced upon concurrent anion and cation complexation and permits molecular recognition-based control over chemical morphology under interfacial conditions. Photoirradiation of the micelles serves to cross-link the anthracene units thus stabilizing the aggregates. The combination of ion pair recognition, micelle formation, and cross-linking can be used to extract FeF₂ ion pairs from bulk aqueous solutions. The present work helps illustrate how molecular recognition and self-assembly may be used to control the chemistry of extractants at interfaces.

Surveying macrocyclic chemistry: from flexible crown ethers to rigid cyclophanes

This review features the progress made in the development of macrocycles since Pedersen's ground-breaking discovery of the crown ethers in 1967.

Liquid membrane transport of potassium fluoride by the organotin-based ditopic host Ph2FSnCH2SnFPh-CH2-[19]-crown-6

A novel tin-based ditopic host efficiently transports KF through an organic membrane.

Cyclo[4]carbazole, an Iodide Anion Macrocyclic Receptor

A novel preorganized and rigid iodide anion macrocyclic receptor, cyclo[4]carbazole (Cy[4]C), is reported here. The structure of Cy[4]C was confirmed by single-crystal X-ray analysis. The binding affinity of Cy[4]C for iodide anion was investigated by UV-vis and ¹H NMR spectroscopic techniques. The crystal structure of the complex between Cy[4]C and chloroform also provided evidence for the recognition ability of Cy[4]C toward iodide anion. Furthermore, the 1:1 complexation stoichiometry between Cy[4]C and iodide anion was confirmed by high-resolution mass spectrometry and molecular modeling.

3-(Dicyanomethylidene)indan-1-one-Functionalized Calix[4]arene-Calix[4]pyrrole Hybrid: An Ion-Pair Sensor for Cesium Salts

A chromogenic calix[4]arene-calix[4]pyrrole hybrid ion pair receptor bearing an indane substituent at a β-pyrrolic position has been prepared. On the basis of solution-phase UV-vis spectroscopic analysis and (1)H NMR spectroscopic studies carried out in 10% methanol in chloroform, receptor 1 is able to bind only cesium ion pairs (e.g., CsF, CsCl, and CsNO3) but not the constituent cesium cation (as its perchlorate salt) or the F(-), Cl(-), or NO3(-) anions (as the tetrabutylammonium salts). It thus displays rudimentary AND logic gate behavior. Receptor 1 shows a colorimetric response to cesium ion pairs under conditions of solid-liquid (nitrobenzene) and liquid-liquid (D2O-nitrobenzene-d5) extraction.

Development of Ion Chemosensors Based on Porphyrin Analogues

Sensing of metal ions and anions is of great importance because of their widespread distribution in environmental systems and biological processes. Colorimetric and fluorescent chemosensors based on organic molecular species have been demonstrated to be effective for the detection of various ions and possess the significant advantages of low cost, high sensitivity, and convenient implementation. Of the available classes of organic molecules, porphyrin analogues possess inherently many advantageous features, making them suitable for the design of ion chemosensors, with the targeted sensing behavior achieved and easily modulated based on their following characteristics: (1) NH moieties properly disposed for binding of anions through cooperative hydrogen-bonding interactions; (2) multiple pyrrolic N atoms or other heteroatoms for selectively chelating metal ions; (3) variability of macrocycle size and peripheral substitution for modulation of ion selectivity and sensitivity; and (4) tunable near-infrared emission and good biocompatibility. In this Review, design strategies, sensing mechanisms, and sensing performance of ion chemosensors based on porphyrin analogues are described by use of extensive examples. Ion chemosensors based on normal porphyrins and linear oligopyrroles are also briefly described. This Review provides valuable information for researchers of related areas and thus may inspire the development of more practical and effective approaches for designing high-performance ion chemosensors based on porphyrin analogues and other relevant compounds.

Multicavity macrocyclic hosts

Multicavity macrocyclic hosts are host molecules comprising more than one macrocyclic guest binding components connected through multipoint linkages.

Ordered co-encapsulation of chloride with polar neutral guests in a tetraurea calix[4]pyrrole dimeric capsule

A calix[4]pyrrole tetraurea, a polar guest and methyltrioctylammonium chloride quantitatively self-assemble in two different complexes in response to the components' stoichiometry.

In this work, we describe the stoichiometrically controlled self-assembly process of tetraurea calix[4]pyrrole 1 with a polar neutral guest, trimethylamine N-oxide or beta-alanine betaine, and methyltrioctylammonium chloride (MTOACl) salt into two supramolecular architectures which differ in morphology and stoichiometry. Whereas an equimolar solution of tetraurea calixpyrrole 1, polar guest and MTOACl produces a four-particle inclusion assembly, a mixture of the same components in a 2 : 1 : 1 molar ratio induces the formation of a dimeric capsular assembly displaying multiple guests which are orderly co-encapsulated. The influence of other polar guests and ammonium salts on the self-assembly process is also described.