Anion Receptor Chemistry

Ditopic Receptors Based on Dihomooxacalix[4]arenes Bearing Phenylurea Moieties With Electron-Withdrawing Groups for Anions and Organic Ion Pairs

Two bidentate dihomooxacalix[4]arene receptors bearing phenylurea moieties substituted with electron-withdrawing groups at the lower rim via a butyl spacer (CF₃-Phurea 5b and NO₂ Phurea 5c) were obtained in the cone conformation in solution, as shown by NMR. The X-ray crystal structure of 5b is reported. The binding affinity of these receptors toward several relevant anions was investigated by ¹H NMR, UV-Vis absorption in different solvents, and fluorescence titrations. Compounds 5b and 5c were also tested as ditopic receptors for organic ion pairs, namely monoamine neurotransmitters and trace amine hydrochlorides by ¹H NMR studies. The data showed that both receptors follow the same trend and, in comparison with the unsubstituted phenylurea 5a, they exhibit a significant enhancement on their host-guest properties, owing to the increased acidity of their urea NH protons. NO₂-Phurea 5c is the best anion receptor, displaying the strongest complexation for F⁻, closely followed by the oxoanions BzO⁻, AcO⁻, and HSO4-. Concerning ion pair recognition, both ditopic receptors presented an outstanding efficiency for the amine hydrochlorides, mainly 5c, with association constants higher than 10⁹ M⁻² in the case of phenylethylamine and tyramine.

The mutual noncovalent interactions based on metallophilic cluster and anions: A theoretical investigation of the molecular structure and spectroscopic properties of Host–Guest complexes

The d[Formula: see text] metallophilic host clusters [Au(NHC)2][Formula: see text] [M(CN)2][Formula: see text] [Au(NHC)2][Formula: see text](NHC [Formula: see text] N-heterocyclic carbene, [Formula: see text], Ag) with high phosphorescence are synthesized recently and their phosphorescent modulation by solvents is investigated in theory. In this paper, the guest anions (F−, Cl−, Br−, NO[Formula: see text], and BF[Formula: see text] are used to elucidate their effects on metallophilic interactions and phosphorescence of hosts, and also they served as the probes to study the recognition characters of metallophilic hosts. The calculation shows that the guest anions can mutually interact with the host clusters and further, which can modulate the metallophilic Au[Formula: see text]M distances and the phosphorescence spectra of the hosts.

Anion Influence on the Packing of 1,3-Bis(4-Ethynyl-3-Iodopyridinium)-Benzene Halogen Bond Receptors

Rigid and directional arylethynyl scaffolds have been widely successful across diverse areas of chemistry. Utilizing this platform, we present three new structures of a dicationic 1,3-bis(4-ethynyl-3-iodopyridinium)-benzene halogen bonding receptor with tetrafluoroborate, nitrate, and hydrogen sulfate. Structural analysis focuses on receptor conformation, anion shape, solvation, and long range packing of these systems. Coupled with our previously reported structures, we conclude that anions can be classified as building units within this family of halogen bonding receptors. Two kinds of antiparallel dimers are observed for these dicationic receptors. An off-centered species is most frequent, present among geometrically diverse anions, and assorted receptor conformations. In contrast, the centered antiparallel dimers are observed with receptors adopting a bidentate conformation in the solid-state. While anions support the solid-state formation of dimers, the molecular geometry and characteristics (planarity, rigidity, and directionality) of arylethynyl systems increases the likelihood of dimer formation by limiting efficient packing arrangements. The significantly larger cation may have considerable influence on the solid-state packing, as similar cationic arylethynyl systems also display these dimers, suggesting.

Halide anion discrimination by a tripodal hydroxylamine ligand in gas and condensed phases

Electrospray ionization of solutions containing a tripodal hydroxylamine ligand, H3TriNOx ([((2-tBuNOH)C6H4CH2)3N]) denoted as L, and a hydrogen halide HX: HCl, HBr and/or HI, yielded gas-phase anion complexes [L(X)]- and [L(HX2)]-. Collision induced dissociation (CID) of mixed-halide complexes, [L(HXaXb)]-, indicated highest affinity for I- and lowest for Cl-. Structures and energetics computed by density functional theory are in accord with the CID results, and indicate that the gas-phase binding preference is a manifestation of differing stabilities of the HX molecules. A high halide affinity of [L(H)]+ in solution was also demonstrated, though with a highest preference for Cl- and lowest for I-, the opposite observation of, but not in conflict with, what is observed in gas phase. The results suggest a connection between gas- and condensed-phase chemistry and computational approaches, and shed light on the aggregation and anion recognition properties of hydroxylamine receptors.

Theoretical investigation on the interaction of benzazaborole derivatives with iodide ion: Structural, binding and fluorescence properties analysis

The structural, fluorescence properties and binding interaction of benzazaborole derivatives 1-hydroxy-2-(α-methyl) benzyl-1,2-benzo boron nitrogen heterocyclic-3-phosphate diethyl ester (PADE) and 1-hydroxy-2-(2-chloro) benzyl-1,2-benzo boron nitrogen heterocyclic-3-phosphate diethyl ester (PADC) with iodide ion have been investigated utilizing density functional theory (DFT) and Time-dependent density functional theory (TD-DFT) method, in which the PADE and PADC showed strong emission in aqueous solution and fluorescence quenching was observed upon addition of iodide ion. The theoretical study indicates that the strong hydrogen-bond (O-H…I) between benzazaborole derivatives and iodide ion leads to the formation of the benzazaborole-iodide ion complexes. The excited state properties have been explored by theoretical calculation to understand the fluorescent quenching upon introduction of iodide ion. The strong fluorescent emission is originated by the electron transfer from benzyl and phosphate moieties to benzo boron nitrogen fused heterocycle moiety, while the fluorescence quenching is attributed to the electron transfer between the PADE (PADC) and iodide ion. The density difference (EDD) maps and the frontier molecular orbitals diagrams during excitation and de-excitation process demonstrate that the photoinduced electron transfer process between PADE (PADC) and iodide ion leads to fluorescence quenching after a significant internal conversion.

Exploiting 1,4-naphthoquinone and 3-iodo-1,4-naphthoquinone motifs as anion binding sites by hydrogen or halogen-bonding interactions

We describe here the utilization of 1,4-naphthoquinone and 3-iodo-1,4-naphthoquinone motifs as new anion binding sites by hydrogen- or halogen-bonding interactions, respectively. These binding sites have been integrated in bidentate ester based receptors. Emission experiments reveal that both receptors selectively recognize sulfate anions, which induced a remarkable increase of a new emission band attributed to the formation of π-stacking interactions between two 1,4-naphthoquinone units. Absorption spectroscopy and mass spectrometry indicate the disruption of the ester group of the 1,4-naphthoquinone based receptor in the presence of HP₂O₇^3-, H₂PO₄^-, F^-, AcO^- and C₆H₅CO₂^- and in the halogenated receptor with HP₂O₇^3-, F^- and AcO^- anions, while the presence of sulfate anions showed the clasical complexation behaviour. The ¹H-NMR experiment showed a slow exchange process of the receptors with their sulfate complexes. The binding mode of the receptors with sulfate has been studied by DFT calculations along with the Molecular Electrostatic Potential (MEP) surface computational tool that reveals those parts of the receptors which are more suitable for interacting with anions.

Bambusuril analogs based on alternating glycoluril and xylylene units

The glycoluril monomer is a popular building block in supramolecular chemistry as it is used for the synthesis of versatile host molecules which can interact with cationic, anionic or neutral guest molecules. Here we present the design and synthesis of a new hybrid macrocycle containing glycoluril and aromatic units. The reaction afforded a mixture of macrocyclic homologues from which a two-membered macrocycle was isolated as the main product. Two disastereomers of the macrocycle were separated and characterized by means of NMR spectroscopy and X-ray crystallography. Conformational changes of these diastereomers were investigated using DFT models and variable-temperature NMR.

Multisite Binding of Drugs and Natural Products in an Entropically Favorable, Heteroleptic Receptor

The cavities of artificial receptors are defined by how their components fit together. The encapsulation of specific molecules can thus be engineered by considering geometric principles; however, intermolecular interactions and steric fit scale with receptor size, such that the ability to bind multiple guests from a specific class of compounds remains a current challenge. By employing metal-organic self-assembly, we have prepared a triangular prism from two different ligands that is capable of binding more than 20 different natural products, drugs, and steroid derivatives within its prolate cavity. Encapsulation inflates the host, enhancing its ability to bind other guests in peripheral pockets and thus enabling our system to bind combinations of different drug and natural product cargoes in different locations simultaneously. This new mode of entropically favorable self-assembly thus enables central encapsulation to amplify guest-binding events around the periphery of an artificial receptor.

Construction and interconversion of anion-coordination-based ('aniono') grids and double helicates modulated by counter-cations

‘Aniono’ double helicates and grids were constructed using PO₄^3– anions and a bis–tris(urea) ligand and interconverted by changing the counter-cation.

Supramolecular assembly of well-defined discrete architectures has been of great interest due to the tunable properties of these structures in functional materials and bio-mimicking. While metal-coordination-driven assembly has been extensively studied, anion-coordination-driven assembly (ACDA) is just emerging for constructing complex supramolecular structures. Herein two A_2nL_2n (A = anion, L = ligand; n = 1 or 2) ‘aniono’-supramolecular assemblies, i.e. double helicates and the first anion grid, have been constructed based on the coordination between phosphate (PO₄^3–) anion and a bis–tris(urea) ligand. Moreover, the aniono-grid and double helicate motifs can be readily interconverted under ambient conditions by simply changing the counter-cation. These results redefine the power and scope of ACDA, which may represent a new approach in the assembly of well-defined architectures in parallel with the metal coordination-driven assembly of metallo-supramolecules.

Squaramide-Naphthalimide Conjugates as "Turn-On" Fluorescent Sensors for Bromide Through an Aggregation-Disaggregation Approach

The syntheses of two new squaramide-naphthalimide conjugates (SQ1 and SQ2) are reported where both compounds have been shown to act as selective fluorescence "turn on" probes for bromide in aqueous DMSO solution through a disaggregation induced response. SQ1 and SQ2 displayed a large degree of self-aggregation in aqueous solution that is disrupted at increased temperature as studied by ¹H NMR and Scanning Electron Microscopy (SEM). Moreover, the fluorescence behavior of both receptors was shown to be highly dependent upon the aggregation state and increasing temperature gave rise to a significant increase in fluorescence intensity. Moreover, this disaggregation induced emission (DIE) response was exploited for the selective recognition of certain halides, where the receptors gave rise to distinct responses related to the interaction of the various halide anions with the receptors. Addition of F^- rendered both compounds non-emissive; thought to be due to a deprotonation event while, surprisingly, Br^- resulted in a dramatic 500-600% fluorescence enhancement thought to be due to a disruption of compound aggregation and allowing the monomeric receptors to dominate in solution. Furthermore, optical sensing parameters such as limits of detection and binding constant of probes were also measured toward the various halides (F^-, Cl^-, Br^-, and I^-) where both SQ1 and SQ2 were found to sense halides with adequate sensitivity to measure μM levels of halide contamination. Finally, initial studies in a human cell line were also conducted where it was observed that both compounds are capable of being taken up by HeLa cells, exhibiting intracellular fluorescence as measured by both confocal microscopy and flow cytometry. Finally, using flow cytometry we were also able to show that cells treated with NaBr exhibited a demonstrable spectroscopic response when treated with either SQ1 or SQ2.

Arylpyrrolyldiketone Boron Complexes Exhibiting Various Anion-Binding Modes Based on Dynamic Conformation Changes

Arylpyrrolyldiketone boron complexes as anion-responsive π-electronic molecules were synthesized by Claisen condensations of acetylpyrrole and corresponding aryl esters. The synthesized π-electronic molecules exhibited anion-binding behavior with various binding modes including pyrrole-inverted and non-inverted [1+1]-type anion complexes as well as [2+1]-type complexes owing to the presence of only a single pyrrole ring. Furthermore, solid-state ion-pairing assemblies, comprising receptor-anion complexes and countercations, were constructed based on fairly planar [2+1]-type complexes.

Sigma-holes from iso-molecular electrostatic potential surfaces

Visualization of the halobenzene σ-hole region of molecules (PhX, X = Cl, Br, I) was conducted to investigate the nature of the σ-hole present between covalently bonded elements of groups IVB-VIIB (known as halogen bonding for group VIIB) and corresponding negative sites, such as Lewis base lone electron pairs, π-electrons, or anions. The σ-hole consists of a region of poor electron density and often relatively positive electrostatic potential surrounding the outermost portion of the halogen atom along the A-X bond axis. In this work, molecular electrostatic potential (MEP) isosurfaces for PhX obtained from ab initio calculations are examined to determine the σ-hole in 3D, showing the surfaces of corresponding positive and negative regions. Surfaces were mapped for isopotentials of PhX molecules as low as 0.003 V and scaled up by factors of 10 up to 3 V. The σ-hole is revealed as a positive region exposed underneath a predominantly negative MEP isosurface. As isopotential values move away from zero, this hole grows in radius; conversely, its presence completely fades as potential approaches zero with increasing distance from the molecule. This technique can also be used to compare behaviors of neutral molecules and their ionic counterparts like the case of neutral PF₆ (not observed experimentally) and the hexafluorophosphate anion, PF₆^-, a typical counter-ion in commercial Li-ion batteries. The pnictogen halide PF₅ features similar MEP trends as the neutral PF₆, which features reactive sites, shown as negative potential caps, at specific points in the molecule, similar to those of PF₅. The portrayal of MEP behavior in iso-surfaces at specific and practical values of chemical interest is crucial when defining lump parameter sets for Coulombic force fields for molecular dynamics simulations to be used in systems that go from biological macromolecules to crystal engineering to devices to final products. Active chemical sites can be described by the MEP function, V(r), more proficiently than just wavefunctions or electron densities that intrinsically contain the same information, and this is fully enhanced when color-coding electron densities on isopotential surfaces are shown. Graphical abstract The hidden features of orbital holes depicted by iso-potentials.

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.

Anion coordination chemistry using O-H groups

This review covers significant advances in the use of O-H groups in anion coordination chemistry. The review focuses on the use of these groups in synthetic anion receptors, as well as more recent developments in transport, self-assembly and catalysis.

Low Molecular Weight Fluorescent Probes (LMFPs) to Detect the Group 12 Metal Triad

Fluorescence sensing, of d-block elements such as Cu2+, Fe3+, Fe2+, Cd2+, Hg2+, and Zn2+ has significantly increased since the beginning of the 21st century. These particular metal ions play essential roles in biological, industrial, and environmental applications, therefore, there has been a drive to measure, detect, and remediate these metal ions. We have chosen to highlight the low molecular weight fluorescent probes (LMFPs) that undergo an optical response upon coordination with the group 12 triad (Zn2+, Cd2+, and Hg2+), as these metals have similar chemical characteristics but behave differently in the environment.

The road to aryl CHanion binding was paved with good intentions: fundamental studies, host design, and historical perspectives in CH hydrogen bonding

Throughout the design and development of supramolecular receptors for anion binding, many different non-covalent anion-binding motifs have been employed. One motif seen in many host-guest systems is the sometimes weaker, 'non-traditional' aryl CH hydrogen bond. From June Sutor's discovery of the interaction and its subsequent dismissal by the field in the 1960s to today's use of the aryl CH hydrogen bond in synthetic anion receptors, the path our lab took to begin studying this interaction has been influenced by many other researchers in the field. This feature article highlights the history and properties of the CH hydrogen bond, with a particular focus on aryl CH hydrogen bonds in anion recognition. We highlight select recent developments in the field of anion receptors utilizing aryl CH hydrogen bonds, with an emphasis on how this has influenced the evolution of our approach in designing fundamental studies on CH hydrogen bonding and exploiting this interaction in efforts aimed toward preferential anion binding.

Synthesis, recognition and sensing properties of dipyrrolylmethane-based anion receptors

Two tweezer-like anion receptors 2,2'‑bis(2‑cyano‑2‑phenylvinyl)‑5,5'‑dimethyl dipyrromethane (1) and 2,2'‑bis[2‑cyano‑2‑(4‑nitrophenyl)vinyl]‑5,5'‑dimethyl dipyrromethane (2) were synthesized in good yields, via a facile condensation of diformyldipyrromethane and the appropriate phenylacetonitrile. Anion recognition properties of these receptors were studied in detail in DMSO solution, by means of UV-vis and ¹H NMR titration techniques. The obtained results indicated that receptor 2 containing a terminal nitro group exhibited the strong and selective binding to biologically important fluoride and dihydrogenphosphate ions over other anions. In addition, the binding strength of receptor 2 with fluoride was enhanced by a factor of 18, relative to receptor 1 lacking the nitro group. Remarkably, the presence or absence of nitro group within receptor compounds also had a great influence on the anion-binding selectivity. In particular, a distinct color change of DMSO solution of receptor 2 was observed only upon addition of fluoride, showing the potential of 2 acting as an effective colorimetric sensor for the detection of fluoride anion.

1,8-Diamidocarbazoles: an easily tuneable family of fluorescent anion sensors and transporters

The synthesis, structure and anion recognition properties of an extensive, rationally designed series of bisamide derivatives of 1,8-diaminocarbazole and 1,8-diamino-3,6-dichlorocarbazole are described. Despite simple structures and the presence of only three hydrogen bond donors, such compounds are remarkably strong and selective receptors for oxyanions in DMSO + 0.5%H2O. Owing to their carbazole fluorophore, they are also sensitive turn-on fluorescent sensors for H2PO4- and AcO-, with a more than 15-fold increase in fluorescence intensity upon binding. Despite relatively weak chloride affinity, some of the diamidocarbazoles have also been shown, for the first time, to be very active chloride transporters through lipid bilayers. The binding, sensing and transport properties of these receptors can be easily modulated by the usually overlooked variations in the length and degree of branching of their alkyl side arms. Overall, this study demonstrates that the 1,8-diamidocarbazole binding unit is a very promising and synthetically versatile platform for the development of fluorescent sensors and transporters for anions.

Anion Recognition in Water by Charge-Neutral Halogen and Chalcogen Bonding Foldamer Receptors

A novel strategy for the recognition of anions in water using charge-neutral σ-hole halogen and chalcogen bonding acyclic hosts is demonstrated for the first time. Exploiting the intrinsic hydrophobicity of halogen and chalcogen bond donor atoms integrated into a foldamer structural molecular framework containing hydrophilic functionalities, a series of water-soluble receptors was constructed for an anion recognition investigation. Isothermal titration calorimetry (ITC) binding studies with a range of anions revealed the receptors to display very strong and selective binding of large, weakly hydrated anions such as I^- and ReO₄^-. This is achieved through the formation of 2:1 host-guest stoichiometric complex assemblies, resulting in an encapsulated anion stabilized by cooperative, multidentate, convergent σ-hole donors, as shown by molecular dynamics simulations carried out in water. Importantly, the combination of multiple σ-hole-anion interactions and hydrophobic collapse results in I^- affinities in water that exceed all known σ-hole receptors, including cationic systems (β₂ up to 1.68 × 10¹¹ M^-2). Furthermore, the anion binding affinities and selectivity trends of the first example of an all-chalcogen bonding anion receptor in pure water are compared with halogen bonding and hydrogen bonding receptor analogues. These results further advance and establish halogen and chalcogen bond donor functions as new tools for overcoming the challenging goal of anion recognition in pure water.

Self-Assembled Gels Formed in Deep Eutectic Solvents: Supramolecular Eutectogels with High Ionic Conductivity

1,3:2,4-Dibenzylidene-d-sorbitol (DBS), a simple, commercially relevant compound, was found to self-assemble as a result of intermolecular noncovalent interactions into supramolecular gels in deep eutectic solvents (DESs) based on choline chloride combined with alcohols/ureas. DBS formed gels at a loading of 5 % w/v. Rheology confirmed the gel-like nature of the materials, electron microscopy and X-ray diffraction indicated underpinning nanofibrillar DBS networks, and differential scanning calorimetry showed the DES nature of the liquid-like phase was retained. The ionic conductivities of the gels were similar to those of the unmodified DESs, thus proving the deep eutectic nature of the ionic liquid-like phase. Gelation was tolerant of ionic additives Li⁺ , Mg²⁺ , and Ca²⁺ ; the resulting gels had similar conductivities to electrolyte dissolved in the native DES. The low-molecular-weight gelator DBS is thus a low-cost additive that forms gels in DESs from readily available constituents, with conductivity levels suitable for practical applications.

Shape-Selective Recognition of Quaternary Ammonium Chloride Ion Pairs

Synthetic receptors that recognize ion pairs are potentially useful for many technical applications, but to date there has been little work on selective recognition of quaternary ammonium (Q⁺) ion pairs. This study measured the affinity of a tetralactam macrocycle for 11 different Q⁺·Cl^- salts in chloroform solution. In each case, NMR spectroscopy was used to determine the association constant ( K_a) and the structure of the associated complex. K_a was found to depend strongly on the molecular shape of Q⁺ and was enhanced when Q⁺ could penetrate the macrocycle cavity and engage in attractive noncovalent interactions with the macrocycle's NH residues and aromatic sidewalls. The highest measured K_a of 7.9 × 10³ M^-1 was obtained when Q⁺ was a p-CN-substituted benzylic trimethylammonium. This high-affinity Q⁺·Cl^- ion pair was used as a template to enhance the synthetic yield of macrocyclization reactions that produce the tetralactam receptor or structurally related derivatives. In addition, a permanently interlocked rotaxane was prepared by capping the end of a noncovalent complex composed of the tetralactam macrocycle threaded by a reactive benzylic cation. The synthetic method provides access to a new family of rotaxanated ion pairs that can likely act as anion sensors, molecular shuttles, or transport molecules.

A unique benzimidazole-naphthalene hybrid molecule for independent detection of Zn2+ and N3- ions: Experimental and theoretical investigations

Single crystal X-ray structurally characterized benzimidazole-naphthalene hybrid (NABI) functions as a unique dual analyte sensor that can detect Zn²⁺ cation and N₃^- anion independently. The NABI forms chelate with Zn²⁺ to inhibit internal charge transfer (ICT) and CHN isomerisation resulting chelation enhanced fluorescence (CHEF). On the other hand, the sensing of N₃^- is based on formation of supramolecular H-bonded rigid assembly. The association constant of NABI for Zn²⁺ and N₃^- ions are 19 × 10⁴ M^-1 and 11 × 10² M^-1, respectively. Corresponding limit of detections (LOD) are 6.85 × 10^-8 and 1.82 × 10^-7 M, respectively. NABI efficiently detects intracellular Zn²⁺ and N₃^- ions with no cytotoxicity on J774A.1cells under fluorescence microscope. DFT studies unlock underlying spectroscopic properties of free NABI and Zn²⁺/N₃^- bound forms.

Two macrocycle-based sensors for anions sensing

Two macrocyclic bis-benzimidazolium salts 2 and 4 (23-membered for 2 and 25-membered for 4) were prepared, and their structures were confirmed by X-ray crystallography, 1H NMR and 13C NMR spectroscopy. The research of anion recognitions using 2 or 4 as hosts were carried out with the methods of fluorescence and ultraviolet spectroscopy, 1H NMR titrations, MS and IR spectra. The experiment results show that 2 can detect acetate anion and 4 can detect nitrate anion with favorable selectivity and sensitivity.

Rapid access to sulfate-encapsulated symmetrical and asymmetrical capsules based on silver–pyrazole complex cations

A new class of sulfate-encapsulated symmetrical and asymmetrical capsules is developed through ion-pair complexation.

Encapsulation of dihydrogenphosphate ions as a cyclic dimer to the cavities of site-specifically modified indolocarbazole-pyridine foldamers

Site-specifically modified aromatic foldamers can encapsulate dihydrogen phosphate ions as a cyclic dimer via the formation of twelve hydrogen bonds.

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.

Revisiting the fluoride binding behaviour of dipyrrolylquinoxaline in aqueous medium: a copper ion mediated approach

An ion detection methodology employing synergistic interaction between copper(ii) ions and fluoride with 2,3-dipyrrol-2′-yl-quinoxaline (SR1) is investigated with a particular target to detect fluoride in an aqueous environment.

19F-GEST NMR: studying dynamic interactions in host–guest systems

GEST NMR provides dynamic information on host–guest systems. It allows signal amplification of low concentrated complexes, detection of intermolecular interactions and quantification of guest exchange rates.

Selective binding of (thio)sulfate and phosphate in water by quaternary ammonium functionalized oligo-ureas

Functionalization of oligo-ureas with quaternary ammonium groups leads to water soluble receptors for selective binding of adenosine phosphates in water.

Controlled nitrite anion encapsulation and release in the molecular cavity of decamethylcucurbit[5]uril: solution and solid state studies

Nitrite anion encapsulation was realized using molecular cavitands of decamethylcucurbit[5]urils as molecular receptors.

A benzimidazole-based non-symmetrical tripodal receptor for the ratiometric fluorescence sensing of fluoride ions and solid state recognition of sulfate ions

A novel tripodal receptor has been reported as a fluorescent chemosensor for fluoride ions. Moreover, in solid state, seven units of the protonated receptors form a pseudo-capsular cavity to encapsulate two pairs of sulphate anions.

Synthesis and anion recognition studies of new oligomethylene bis(nitrophenylureylbenzamide) receptors

A new series of oligomethylene bis(nitrophenylureylbenzamide) receptors were synthesized varying the relative position of the urea and amide groups (ortho4 and meta8) and the length of the oligomethylene chain (C₂ to C₈). An anion recognition study was performed with TBAX salts (X = AcO⁻, BzO⁻, F⁻, H₂PO₄⁻, and HP₂O₇³⁻) by UV-vis and ¹H NMR. The flexibility of these receptors allows a cooperative effect of both ureylbenzamide units in the receptors. Noteworthy, the ortho position favored the 1 : 1 stoichiometry in the complexes with the carboxylates. The formation of 2 : 1 receptor–anion complexes with both types of receptors 4 and 8 and with hydrogen pyrophosphate and high log K values obtained were very significant in this work. The NMR studies evidenced the formation of supramolecular complexes, even in a competitive solvent, such as DMSO.

Synthesis and supramolecular interaction of new oligomethylene bis(4-nitrophenylureylbenzamide) receptors with different anions.

Fluoride binding by an anionic receptor: tuning the acidity of amide NH groups for basic anion hydrogen bonding and recognition

Here we report the first family of bis-amide receptors able to bind fluoride in their anionic form.

Native Quercetin as a Chloride Receptor in an Organic Solvent

The binding properties of quercetin toward chloride anions were investigated by means of 1H-NMR, 13C-NMR, and electrospray ionization mass spectrometry (ESI-MS) measurements, as well as computational calculations. The results indicate that quercetin behaves primarily as a ditopic receptor with the binding site of the B ring that exhibits stronger chloride affinity compared to the A ring. However, these sites are stronger receptors than those of catechol and resorcinol because of their conjugation with the carbonyl group located on the C ring. The 1:1 and 1:2 complexation of this flavonoid with Cl− was also supported by ESI mass spectrometry.