Anion Recognition Research Articles

Tetrel Bonding in Anion Recognition: A First Principles Investigation

Twenty-five molecule-anion complex systems [I4Tt···X-] (Tt = C, Si, Ge, Sn and Pb; X = F, Cl, Br, I and At) were examined using density functional theory (ωB97X-D) and ab initio (MP2 and CCSD) methods to demonstrate the ability of the tetrel atoms in molecular entities, I4Tt, to recognize the halide anions when in close proximity. The tetrel bond strength for the [I4C···X-] series and [I4Tt···X-] (Tt = Si, Sn; X = I, At), was weak-to-moderate, whereas that in the remaining 16 complexes was dative tetrel bond type with very large interaction energies and short Tt···X close contact distances. The basis set superposition error corrected interaction energies calculated with the highest-level theory applied, [CCSD(T)/def2-TZVPPD], ranged from -3.0 to -112.2 kcal mol-1. The significant variation in interaction energies was realized as a result of different levels of tetrel bonding environment between the interacting partners at the equilibrium geometries of the complex systems. Although the ωB97X-D computed intermolecular geometries and interaction energies of a majority of the [I4Tt···X-] complexes were close to those predicted by the highest level of theory, the MP2 results were shown to be misleading for some of these systems. To provide insight into the nature of the intermolecular chemical bonding environment in the 25 molecule-anion complexes investigated, we discussed the charge-density-based topological and isosurface features that emanated from the application of the quantum theory of atoms in molecules and independent gradient model approaches, respectively.

Semicarbazone and thiosemicarbazone appended 4-diethylamino-2‑hydroxybenzyl compounds as highly selective bifunctional chemosensors: An experimental and computational approach

Three bifunctional chemosensors, 2-(4-(diethylamino)-2-hydroxybenzylidene)hydrazinecarboxamide (S1), 2-(4-(diethylamino)-2-hydroxybenzylidene)hydrazinecarbothioamide (S2) and 2-(4-(diethylamino)-2-hydroxybenzylidene)-N-methylhydrazinecarbothioamide (S3) have been designed and synthesized for recognition of inorganic cations and anions in solution at room temperature. The structure of the receptor S2 was confirmed by single crystal X-ray diffraction technique, which crystallizes in the monoclinic P21/n space group. The selectivity and sensitivity of cations (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+ and Pb2+) and anions (F−, Cl−, Br−, I−, HSO4− and H2PO4−) were investigated using colorimetric, UV–vis absorption, emission and 1H NMR studies. The receptors (S1–S3) with ONO/ONS donors allow bare-face recognition of Co2+, Ni2+ and Cu2+ cations, and F− anion in a mixture of solvent, CH3CN:CH3OH (8:2, v/v). The receptor S3 possesses high sensitivity and selectivity in comparison with the receptors S1 and S2. The binding constant and limit of detection of the receptors with sensed cations and anion showed high sensitivity and selectivity towards Co2+ cation with order of magnitude 6, greater than the other sensed cations. In addition, the receptors S3 also shows 6 order of magnitude for Cu2+ cation and F− anion. The optimized geometry determined by DFT studies shows that the receptors in its conjugated state provide binding sites for cations and F− anion. The HOMO-LUMO energy gap between the receptors and the Co2+ cation was found to be the least among the studied receptors-cations binding interaction, possibly due to charge transfer effect.

Chalcogen Bonds: How to Characterize Them in Solution?

Chalcogen bonds (ChBs) occur between molecules containing Lewis acidic chalcogen substituents and Lewis bases. Recently, ChB emerged as a pivotal interaction in solution-based applications such as anion recognition, anion transport and catalysis. However, before moving to applications, the involvement of ChB must be established in solution. In this Concept article, we provide a brief review of the currently available experimental investigations of ChB in solution.

Anti-Hofmeister Anion Selectivity via a Mechanical Bond Effect in Neutral Halogen-Bonding [2]Rotaxanes.

Exceptionally strong halogen bonding (XB) donor-chloride interactions are exploited for the chloride anion template synthesis of neutral XB [2]rotaxane host systems which contain perfluoroaryl-functionalised axle components, including a remarkably potent novel 4,6-dinitro-1,3-bis-iodotriazole motif. Halide anion recognition properties in aqueous-organic media, determined via extensive 1 H NMR halide anion titration experiments, reveal the rotaxane host systems exhibit dramatically enhanced affinities for hydrophilic Cl- and Br- , but conversely diminished affinities for hydrophobic I- , relative to their non-interlocked axle counterparts. Crucially, this mechanical bond effect induces a binding selectivity which directly opposes Hofmeister bias. Free-energy analysis of this mechanical bond enhancement demonstrates anion recognition by neutral XB interlocked host systems as a rare and general strategy to engineer anti-Hofmeister bias anion selectivity in synthetic receptor design.

Anti‐Hofmeister Anion Selectivity via a Mechanical Bond Effect in Neutral Halogen‐Bonding [2]Rotaxanes

AbstractExceptionally strong halogen bonding (XB) donor‐chloride interactions are exploited for the chloride anion template synthesis of neutral XB [2]rotaxane host systems which contain perfluoroaryl‐functionalised axle components, including a remarkably potent novel 4,6‐dinitro‐1,3‐bis‐iodotriazole motif. Halide anion recognition properties in aqueous‐organic media, determined via extensive 1H NMR halide anion titration experiments, reveal the rotaxane host systems exhibit dramatically enhanced affinities for hydrophilic Cl− and Br−, but conversely diminished affinities for hydrophobic I−, relative to their non‐interlocked axle counterparts. Crucially, this mechanical bond effect induces a binding selectivity which directly opposes Hofmeister bias. Free‐energy analysis of this mechanical bond enhancement demonstrates anion recognition by neutral XB interlocked host systems as a rare and general strategy to engineer anti‐Hofmeister bias anion selectivity in synthetic receptor design.

A ferrocene‐pyrene dyad for multiple channel sensing of F− and H2PO4−

A new ferrocene‐pyrene dyad Fc‐PYS for anion recognition was rationally designed and synthesized, in which the ferrocene and the pyrene groups were combined by the imidazolium and sulfonamide anion donors. The structure of the probe was characterized by single‐crystal X‐ray diffraction. The anion recognition performance of the probe was studied by fluorescence spectroscopy and electrochemical techniques. In acetonitrile solution, Fc‐PYS can fluorescently recognize F− and H2PO4− with different models. Upon the addition of H2PO4−, the fluorescence of Fc‐PYS was increased. However, the complexation with F− quenched its fluorescence. At the same time, Fc‐PYS showed electrochemical response toward basic anions F−, H2PO4−, and AcO− with the ferrocene‐based red/ox potential a negative shift with H2PO4− > F− > AcO−. Furthermore, the binding mechanism between Fc‐PYS and anion has been investigated in detail by 1H NMR titration.

Bifunctional Receptor Based on Calix[4]arene with Chromone Groups as An Efficient Colorimetric Sensor for Co2+, Cu2+, CN− and F−

AbstractNew calix[4]arene derivatives based on chromone linked through a thiosemicarbazone bridge have been designed and synthesized. It has been determined by UV‐visible absorption and IR‐spectroscopic study that molecular receptors are efficient for recognition of cations (Co2+, Cu2+, Ni2+ and Zn2+) and anions (F− and CN−), because calixarene plays a role as a molecular platform and the interaction is explained by the presence of the thiosemicarbazone bridge bound to chromone. The sensors showed selective colorimetric changes with cobalt (II), copper (II), cyanide and fluoride ions. The detection limits of 0.19 to 0.70 mg L−1 and the association constants ranging between 1.28×104 and 9.87×104 mol−1L can be estimated for these three sensors.

Synthesis and recognition behavior studies of indole derivatives

A series of new indole-based chemical sensor azine derivatives were prepared and characterized by various spectroscopic methods such as 1H NMR, mass spectra, ATR, and elemental analysis. The photophysical properties and ion recognition behavior of compound K derivatives were studied by UV–vis, photoluminescence spectroscopy, and naked-eye sensing. The absorption and emission bands of compound K derivatives were observed at 250–350 and 350–360 nm, and the emission was very low. In CH3CN solution, compound K derivatives show a highly selective “turn-on” fluorescence response to Cu2+ and CN– ions over the other competing ions such as Li+, Ca2+, Cr3+, Hg2+, Ni2+, Zn2+, Cd2+, Pb2+, and Br-, I-, HSO4-, ClO4-, and PF6-. In the presence of Cu2+ and CN– ions, new emission bands were found at 500–550 and 440–460 nm, which indicates the sensor K derivatives have a highly selective recognition behavior of Cu2+ and CN– ions. The sensing mechanism of sensors toward Cu2+ and CN– ions was studied through the 1H NMR titrations method, mass studies, photophysical spectrum, and DFT studies. When Cu2+ was coordinated, a new absorption peak of MLCT appeared at 440 nm, which involved energy release through fluorescence for the excited state. For anion recognition, CN– induced the deprotonation of the indole group, and the conjugated system was affected, which is not conducive to the process of PET. Also, the probability of excited electron density was increased in the indole group.

Novel cells integrated biosensor based on superoxide dismutase on electrospun fiber scaffolds for the electrochemical screening of cellular stress

A novel electrochemical biosensor was developed to monitor fibroblast cells stress levels for the first time in situ under external stimuli based on the recognition of superoxide anion released upon cell damage. The biosensor comprised metallized polycaprolactone electrospun fibers covered with zinc oxide for improved cell adhesion and signal transduction, whilst stable bioconjugates of mercaptobenzoic acid-functionalized gold nanoparticles/superoxide dismutase were employed as recognition bioelements. Biosensors were first tested and optimized for in situ generated superoxide detection by fixed potential amperometry at +0.3 V, with minimal interferences from electroactive species in cell culture media. L929 fibroblast cells were then implanted on the optimized biosensor surface and the biosensor morphologically characterized by scanning electron microscopy (SEM) and fluorescence microscopy, which illustrated the network-type pattern of fibroblasts adjacent to the fiber scaffold. Fibroblast stress was induced by zymosan and monitored at the cells integrated biosensor using fixed potential amperometry (CA) with a sensitivity of 26 nA cm-2 μg mL-1 zymosan and electrochemical impedance spectroscopy (EIS), with similar sensitivity of the biosensor considering the Rs and Z’ parameters of around 0.13 Ω cm2 μg-1 mL and high correlation factors R2 of 0.9994. The obtained results underline the applicability of the here developed biosensor for the electrochemical screening of the fibroblast cells stress. The concept in using low-cost biocompatible polymeric fibers as versatile scaffolds for both enzyme immobilization and cell adhesion, opens a new path in developing biosensors for the in-situ investigation of a variety of cellular events.

Anion Recognition with Antimony(III) and Bismuth(III) Triaryl-Based Pnictogen Bonding Receptors.

The synthesis and characterisation of a library of acyclic antimony(III) and bismuth(III) triaryl pnictogen bonding (PnB) receptor systems are reported. In the first-generation receptor series, quantitative 1 H NMR chloride titration experiments in THF solvent media reveal halide anion binding potency is intimately correlated with both the electronic-withdrawing nature of the aryl- substituent and the polarisability of the PnB donor. Further extensive anion binding investigations with the most potent Sb- and Bi-based PnB receptors: 1⋅Sb2CF3 and 1⋅Bi2CF3 , reveal novel selectivity profiles, both displaying Cl- selectivity relative to the heavier halides and, impressively, to a range of highly basic oxoanions. The synthesis and preliminary chloride anion binding studies of a series of novel tripodal tris-proto-triazole triaryl Sb(III) and Bi(III) mixed PnB-HB receptor systems are also described. Whereas parent triphenyl Sb(III) and Bi(III) compounds are incapable of binding Cl- in THF solvent media, the PnB-triazole HB host systems exhibit notable halide affinity.

Cucurbit[10]uril-Based Orthogonal Supramolecular Polymers with Host-Guest and Coordination Interactions and Its Applications in Anion Classification.

A novel orthogonal supramolecular polymer (Q[10]-TPDPB-Lu3+) in a host-guest ratio of 2:1 was successfully constructed utilizing the specificity and excellent cavity matching of Q[10] with the tripyridine derivatives (TPDPB). Significantly, non-covalent interactions between Q[10]'s hydrophobic cavities and Lu3+ were used to induce charge transfer of TPDPB to TPDPB and TPDPB to Lu3+, resulting in the construction of structurally interesting orthogonal assemblies with excellent fluorescence properties. Finally, the Q[10]-TPDPB-Lu3+ assemblies were shown to have good recognition and classification of strong and weak acid anions as well as iodide anions, and the classification was accompanied by a clear fluorescence emission change allowing visual observation.

Highly Specific and Sensitive Naked-Eye Fluoride Ion Recognition via Unzipping a Helical Poly(phenylacetylene)

Fluoride anion (F–) recognition has attracted much attention in recent years due to its significant role in biological, medical, environmental, and industrial processes. Although many artificial receptors show high sensitivity toward F–, they still lack the specificity for such an anion. It still remains a great challenge to endow the receptors with high specificity and sensitivity toward F– at the same time. Herein, a contracted cis-cisoid poly(phenylacetylene) derivative (Poly-1) has been synthesized, whose preferred-handed helix can be stabilized by intramolecular hydrogen bonding networks among neighboring pendant amides. The average layer distance between its side chains of 3.88 Å can provide a small pocket, which is suitable to accommodate the smallest anion F– with high basicity, but excludes other anions. When the first F– binds to the pendant amides via intermolecular hydrogen bonding, the main chain conformational transition into a stretched cis-transoid nonpreferred-handed helix is triggered, which facilitates the subsequent F– binding. Such an unzipping effect gives rise to an ultralow detection limit of 2.85 × 10–8 M (0.54 ppb) for F–. Meanwhile, the solution color change from colorless to yellow can be observed because of the conjugated cis-transoid conformation of Poly-1. As a result, a highly specific and sensitive naked-eye recognition toward F– is realized. This work lays a solid foundation for the development of smart materials on the basis of stimuli-responsive cascade processes.

A Charge-Neutral Self-Assembled L2Zn2 Helicate as Bench-Stable Receptor for Anion Recognition at Nanomolar Concentration.

The field of anion recognition chemistry is dominated by two fundamental approaches to design receptors. One relies on the formation of covalent bonds resulting in organic and often neutral host species, while the other one utilizes metal-driven self-assembly for the formation of charged receptors with well-defined nanocavities. Yet, the combination of their individual advantages in the form of charge-neutral metal-assembled bench-stable anion receptors is severely lacking. Herein, we present a fluorescent and uncharged double-stranded hydroxyquinoline-based zinc(II) helicate with the ability to bind environmentally relevant dicarboxylate anions with high fidelity in dimethyl sulfoxide (DMSO) at nanomolar concentrations. These dianions are pinned between zinc(II) centers with binding constants up to 145 000 000 M-1. The presented investigation exemplifies a pathway to bridge the two design approaches and combine their strength in one structural motif as an efficient anion receptor.

Highly Efficient and Selective Recognition of Dicyanoaurate(I) by a Bambusuril Macrocycle in Water.

Dicyanoaurate(I) anion, [Au(CN)2 ]- , plays a central role in the current industrial production of gold, as its extraction from crude ore samples represents the most money-consuming step. Herein, we present the strongest host-guest recognition of dicyanoaurate anion using the bambusuril receptor in water, a highly competitive solvent. The micromolar stability of such a complex facilitated the up to date most efficient supramolecular stripping of dicyanoaurate from activated carbon at ambient temperature. Thermodynamic characteristics of bambusuril binding with [Au(CN)2 ]- differing from binding of other inorganic chaotropic anions are rationalized, as well as the bambusuril selectivity for [Au(CN)2 ]- over [Ag(CN)2 ]- .

Highly Efficient and Selective Recognition of Dicyanoaurate(I) by a Bambusuril Macrocycle in Water

AbstractDicyanoaurate(I) anion, [Au(CN)2]−, plays a central role in the current industrial production of gold, as its extraction from crude ore samples represents the most money‐consuming step. Herein, we present the strongest host–guest recognition of dicyanoaurate anion using the bambusuril receptor in water, a highly competitive solvent. The micromolar stability of such a complex facilitated the up to date most efficient supramolecular stripping of dicyanoaurate from activated carbon at ambient temperature. Thermodynamic characteristics of bambusuril binding with [Au(CN)2]− differing from binding of other inorganic chaotropic anions are rationalized, as well as the bambusuril selectivity for [Au(CN)2]− over [Ag(CN)2]−.

Methotrexate recognition by the human reduced folate carrier SLC19A1.

Folates are essential nutrients with important roles as cofactors in one-carbon transfer reactions, being heavily utilized in the synthesis of nucleic acids and the metabolism of amino acids during cell division1,2. Mammals lack de novo folate synthesis pathways and thus rely on folate uptake from the extracellular milieu3. The human reduced folate carrier (hRFC, also known as SLC19A1) is the major importer of folates into the cell1,3, as well as chemotherapeutic agents such as methotrexate4-6. As an anion exchanger, RFC couples the import of folates and antifolates to anion export across the cell membrane and it is a major determinant in methotrexate (antifolate) sensitivity, as genetic variants and its depletion result in drug resistance4-8. Despite its importance, the molecular basis of substrate specificity by hRFC remains unclear. Here we present cryo-electron microscopy structures of hRFC in the apo state and captured in complex with methotrexate. Combined with molecular dynamics simulations and functional experiments, our study uncovers key determinants of hRFC transport selectivity among folates and antifolate drugs while shedding light on important features of anion recognition by hRFC.

High-fidelity Recognition of Organotrifluoroborate Anions (R-BF3 - ) as Designer Guest Molecules.

The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R-BF3 - ). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R-BF3 - , by cyanostar macrocycles that are size-complementary to the inorganic BF4 - progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R-BF3 - anions.

An Electrochemical Sensor for Detection of Neuroblastoma Markers: Complexation Studies as a Tool for the Selection of a Suitable Receptor for Electrode Coating.

Homovanillate (HVA) and vanilmandelate (VMA) are recognized markers of diseases, including neuroblastoma. However, their detection in urine represents a challenging task due to the complexity of the matrix. Here, a design, synthesis and thorough investigation of polymerizable urea-based receptors interacting with HVA and VMA are reported. The selection of receptor with the best anion recognition properties for electrode coating is based on 1 H-NMR and UV-Vis complexation studies. The sensor is prepared by electropolymerization with progress monitoring by cyclic voltammetry. The deposited layer is characterized by IR and scanning electron microscopy. The obtained sensor shows an electrochemical impedance spectroscopy response to VMA with linear range 9.9×10-6 to 1.2×10-3 M and LOD of 3.4×10-6 M. The sensor selectivity was demonstrated by the determination of VMA level in the presence of 16 μM HVA and in artificial urine with and without phosphates, with standard deviations of 0.11, 0.17 and 0.09, respectively.

An AB2 -Type Hyperbranched Supramolecular Polymer Based on Calix[4]Pyrrole Anion Recognition: Construction, Stimuli-Responsiveness, and Morphology Tuning.

An AB2 -type monomer comprised of a calix[4]pyrrole skeleton and alternating bis-carboxylate units is reported and used for the construction of a novel supramolecular hyperbranched polymer based on anion recognition ability of calix[4]pyrrole. 1 H-, DOSY-NMR spectroscopy, viscosity measurements, and dynamic light scatteringtechniques are used for the characterization of the supramolecular hyperbranched polymer exhibiting thermo-, pH-, and chemical responsiveness, as well as concentration dependent morphology tune as inferred from electron microscopy analyses. The present study enriches the field of supramolecular polymers with a new construction motif, building block, and provides a simple approach for the fabrication of smart polymer material with multi-responsiveness and -morphologies.

TD-DFT investigation on anion recognition mechanism of anthraldehyde-based fluorescent thiosemicarbazone derivatives.

The mechanism of host-guest interaction of receptors towards fluoride ion has been investigated using computational methods. To distinguish the effect of aromaticity in host-guest interaction, we investigated unsubstituted (ATSC) and phenyl-substituted (APTSC) anthracene thiosemicarbazones towards different ions. In the ground state of receptor-fluoride complex, the added fluoride ion made hydrogen bond through N - H…F…H - N, whereas the intramolecular hydrogen bonding was through F - H…N in the excited state of receptor-fluoride complex. Experimental absorption and emission spectra were well reproduced by the calculated vertical excitation energies. The transition state (TS) calculations were performed to understand the thermodynamic features and mechanism of host-guest interaction. The natural bond orbital analyses show that the second perturbation energy for donor-acceptor interaction of F- with hydrogen is more than 300kcal/mol-1 at the excited state of receptor-fluoride complex, which indicates the strong single bond between fluoride and hydrogen atom. The PES scan confirms that deprotonation took place at the excited state of receptor-fluoride complex. The results indicate the excited-state proton transfer (ESPT) process from N-H group nearby the anthracene moiety. The APTSC is a better chemosensor than ATSC. This infers that the aromaticity will increase the efficiency of fluorescence receptor towards fluoride ion. A schematic representation of sensing mode of anthracene-based thiosemicarbazones toward fluoride ion. The fluoride ion first makes a hydrogen bond with NH proton nearby anthracene moiety. The excited state proton transfer mechanism was confirmed by PES and NBO studies.