Anion Recognition Properties Research Articles

Synthesis, X-ray structures, and anion binding properties of 1,8-disulfonamidocarbazole-di(thio)amide hybrid macrocycles

An easy-to-prepare 1,8-disulfonamidocarbazole-diamide hybrid macrocycle 1 and its thioamide analogue 2 were reported, along with their anion recognition properties as determined by UV–vis and 1H NMR spectroscopic titrations as well as single crystal X-ray diffraction analyses. The conversion of amides into thioamides in the macrocyclic structures generated notable effects on the anion-binding affinity and selectivity. For example, amide-bearing macrocycle 1 was found to bind H2PO4- over one order of magnitude more strongly than thioamide-containing macrocycle 2, despite having more acidic NH groups for the latter. Additionally, macrocycle 1 displayed the highest affinity for PhCOO- in DMSO (Ka >105 M-1 for the formed 1:1 complex) followed by H2PO4- and AcO- ions, whereas a different binding order AcO- > PhCOO- >> H2PO4- was observed for macrocycle 2. More importantly, the single crystal X-ray diffraction analysis clearly revealed that macrocycle 1 indeed formed a 1:1 complex with PhCOO- ion in the solid state.

Amino acid – Squaramide conjugates as anion binding receptors

Squaramides have garnered significant attention as anion binding motifs and have become a popular supramolecular synthon owing to their unique structural features and propensity to form strong hydrogen bond interactions particularly with anionic species. However, their conjugation to biomaterials to form biomimetic receptors remains underexplored even though such species would combine the biocompatibility of amino acids with the strong hydrogen bonding propensity of squaramides and may prove useful across broad applications in the chemical and biological sciences. In this study, we present the design and synthesis of a series of amino acid – squaramide conjugates (AASqs) 1 – 5, as well as studying their anion recognition properties. 1–5 were prepared using facile synthetic methods and their anion binding properties were investigated via 1H NMR titrations with a range of anions in 0.5 % H2O in DMSO‑d6. Our findings constitute a cautionary tale, where it was shown that the presence of the C-terminal carboxylic acid of the amino acids complicate the binding behaviour of the receptors towards anions. We show that the C-terminal carboxylates compete with other anionic species for the squaramide binding site leading to complex binding equilibria in solution. However, upon esterification of the C-termini to afford compound 5, a simplification of the binding profile was observed and was easily fitted to a 1:1 (Receptor:Anion) binding stoichiometry. This work sheds light on the potential of AASqs as anion binding receptors whilst underlining the influence of the C-terminus on anion recognition. It also provides a direct solution to mitigate the complex binding behaviour of 1–4 through esterification and will prove useful in the design of more complex squaramide bioconjugates.

Halogen Bonding Tripodal Metallo-Receptors for Phosphate Recognition and Sensing in Aqueous-Containing Organic Media.

The anion recognition and electrochemical anion-sensing properties of halogen-bonding (XB) tripodal zinc(II) receptors strategically designed and constructed for tetrahedral anion guest binding are described. The XB tris(iodotriazole)-containing hosts exhibit high affinities and selectivities for inorganic phosphate over other more basic, mono-charged oxoanions such as acetate and the halides in a competitive CD3 CN/D2 O (9 : 1 v/v) aqueous solvent mixture. 1 H NMR anion binding and electrochemical voltammetric anion sensing studies with redox-active ferrocene functionalised metallo-tripodal receptor analogues, reveal each of the XB tripods as superior anion complexants when compared to their tris(prototriazole)-containing, hydrogen bonding (HB) counterparts, not only exemplifying the halogen bond as a strong alternative interaction to the traditional hydrogen bond for molecular recognition but also providing rare evidence of the ability of XB receptors to preferentially bind the "harder" phosphate oxoanion over the "softer" and less hydrated halides in aqueous containing media.

Synthesis, Characterization, and Phosphate Anion Recognition Properties of Triethylene Glycol Bridged Oligourea Receptors

Synthesis, Characterization, and Phosphate Anion Recognition Properties of Triethylene Glycol Bridged Oligourea Receptors

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.

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.

Colorimetric probe and optical behaviours of new azomethine derivatives of sulfonamide

Syntheses, colorimetric anion probe properties, density functional theory (DFT) studies, and optical properties of the Schiff bases; 4-fluoro-N-(2-hydroxy-5-methylbenzylidene) benzenesulfonamide (1), 4-fluoro-N-(2-hydroxy-5-nitrobenzylidene)benzenesulfonamide (2) and 4-fluoro-N-[(2-hydroxynaphthalen-1-yl)methylene]benzenesulfonamide (3) were reported. The structure of the compounds was elucidated using MS, FTIR, and UV-visible spectroscopic techniques. Their structures were examined by theoretical calculations using density functional theory (DFT). The colorimetric response of the Schiff base receptors in DMSO was investigated before and after the addition of an equivalent amount of each anion to evaluate the anion recognition properties. The ultrafast transient absorption spectroscopy measurements were performed to investigate the energy transfer dynamics and decay kinetics of the compounds 1-3. The fluorescence and wavelength-dependent pump-probe measurements of the compounds showed that the excited state lifetime of compound 2 is shorter than compounds 1 and 3. The fluorescence properties of compounds 1-3 were compatible with the pump-probe spectroscopy measurements. The compounds with longer ESA lifetimes showed higher fluorescence.

Carbazole sulfonamide-based macrocyclic receptors capable of selective complexation of fluoride ion.

Two carbazole sulfonamide-based macrocycles 1 and 2 were facilely synthesized and carefully evaluated for their anion recognition properties. The obtained results revealed that macrocycle 1 with a 1,3-xylyl linker was able to bind fluoride ion more strongly and selectively in acetonitrile medium than its strong competitors (like acetate and dihydrogen phosphate anions), with a large binding constant (Ka) of 50 878 M−1. More importantly, an exclusive fluoride recognition was achieved for macrocycle 1 in the more polar DMSO-d6 solution, albeit with a moderate affinity of Ka = 147 M−1. Compared with macrocycle 1, macrocycle 2 bearing a 2,6-lutidinyl linkage exhibited a remarkable change not only in the anion affinity but also in the anion selectivity, although with only a slight difference in their molecular structures.

New naphthoquinone-imidazole hybrids: Synthesis, anion recognition properties, DFT studies and acid dissociation constants

The two new naphthoquinone-imidazole based dyes containing indole and pyrene moiety were synthesized and their molecular structures were confirmed by FT-IR, 1H/13C NMR, and HRMS. The anion selectivity and sensitivity of dyes were studied with selected TBA salts in DMSO and binary mixture DMSO:Water (1:1, v/v). These interaction mechanisms were verified by spectrophotometric, spectrofluorometric, and 1H NMR titration methods. While the both dyes interact with F−, AcO−, CN−, and H2PO4− in DMSO, only CN− interact with dyes in the aqueous solution. In addition, the experimental results were explained by DFT calculations. The acid dissociation constants of the dyes were determined in 25.0 ± 0.1 °C, 0.1 M NaCl ionic strength in 40% (v/v) DMSO-Water aqueous solution, and acid dissociation constants relating protonated carbonyl group and nitrogen atoms were determined for each dye.

Synthesis of new chromogenic sensors containing thiourea and selective detection for F–, H2PO4–, and Ac– anions

Two new chromogenic sensors 1-(2-hydroxyphenyl)-3-(4-nitrophenyl)thiourea 1 and 1-(3-hydroxypyridin-2-yl)-3-(4-nitrophenyl)thiourea 2 bearing nitrophenyl and thiourea groups were designed and synthesized by one-step procedure and characterized through 1H NMR, 13C NMR, FTIR, and MS. The anion recognition property of the receptors was studied via naked-eye detection, UV–vis, and 1H NMR. Based on the existence of amino gen and hydroxyl moieties in receptors, receptors 1 and 2 exhibit obvious selectivity by the redshift of UV–vis signals, colour changes through naked-eye detection, and binding effects for F–, H2PO4–, and Ac–. Surprisingly, the detection limits of receptor 1 for F– and Ac– were calculated to be 5.45 × 10−7 and 2.11 × 10−7 (mol/L)−1, respectively, which indicated that F– and Ac– can be identified with high sensitivity by receptor 1. Besides, simple “test strips” were developed and were used as sensors for recognition of F–, H2PO4–, or Ac– in DMSO solution. Lastly, the mechanisms of the recognition process were studied through DFT calculation and 1H NMR titration.

Functionalized Chiral Bambusurils: Synthesis and Host-Guest Interactions with Chiral Carboxylates.

Bambusurils are a class of macrocyclic anion receptors that exhibit notable anion recognition properties, able to bind various inorganic anions as well the carboxylates or sulfonates. Recently, we reported enantioselective recognition of chiral carboxylates using non-functionalized chiral bambusuril derivatives. Herein, we report the synthesis and host-guest properties of two new representatives of chiral bambusuril macrocycles bearing ester functional groups, differing by the substituents attached to their portals. Their supramolecular properties in terms of carboxylate binding were studied by means of NMR in DMSO-d6 . The reported bambusurils bind selected chiral carboxylates with enantioselectivity factors up to 3.1. The results indicated that the selectivity towards different carboxylates is governed by the steric constraint of the substituents surrounding bambusuril portals. No clear trend in the binding affinities and their enantioselectivities was found.

Encapsulation of Azaphosphatranes and Proazaphosphatranes in Confined Spaces.

Proazaphosphatranes (also named Verkade's superbases) and their azaphosphatrane conjugated acids have been recently been shown to be confined in either covalent or self-assembled molecular cages, or immobilized in nanopores of hybrid materials. The encapsulation of these phosphorus moieties turns out to strongly affect both their acid-base, catalytic, and recognition properties. The thermodynamics and kinetics of the proton transfer as well as the selectivity and catalytic activities of Verkade's superbases were strongly changed upon their confinement in a hemicryptophane cavity. Moreover, self-assembled cages, including azaphosphatrane moieties, were found to display remarkable anion recognition properties in water. In this Minireview, these new aspects of the chemistry of aza- and proaza-phosphatranes are presented, in order to highlight the great potential of such an approach.

Cyanostar: Anion Recognition Property and Modulation of Lithium Ion Conductivity in Battery Electrolyte

Cyanostar: Anion Recognition Property and Modulation of Lithium Ion Conductivity in Battery Electrolyte

Synthesis and Characterization of Positively Charged tris‐Imidazolium Calix[6]arene Hosts for Anion Recognition

AbstractThe syntheses of new tripodal ligands with effective C3 symmetry and anion recognition properties, are reported herein. The ligands have a 1,3,5‐tris‐methoxy‐2,4,6‐tris‐(α,ω‐bromoalkoxy)calix‐[6]arene as a backbone, and were prepared from 1,3,5‐tris‐methoxy‐p‐tert‐butyl‐calix[6]arene by alkylation with a series of α,ω‐dibromo‐alkanes [Br(CH2)nBr] of different chain lengths (n=2, 4 or 6). Further substitution of the bromo groups, via the use of 1‐methyl‐, 1‐mesityl‐or 2,6‐diisopropylphenyl‐1H‐imidazole, led to alkylation by imidazole units and afforded tripodal and tricationic 1,3,5‐tris‐methoxy‐2,4,6‐tris‐imidazolium‐p‐tert‐butyl‐calix[6]arenes. These scaffolds provide a framework for H‐bonded and electrostatic interactions with various anions and their anion binding properties were investigated by 1H NMR and UV‐visible spectroscopy. A sizeable selectivity for HSO4– (present as the n‐Bu4N+ salt) was demonstrated for most of the tripodal ligands considered in this work. Other anions such BF4–, ClO4–, PF6–, NO3–, Cl– exhibited weak to medium associations with the investigated ligands. A single crystal X‐ray study, unfortunately of poor quality, corroborated the geometry of the calix[6]arenes that was previously established by 1H NMR spectroscopy. The binding‐site geometry was more definitively probed by DFT calculations.Introduction

Synthesis of chiral tripodal receptors under solvent-free conditions using microwave irradiation for investigation of anion and cation recognition properties

Synthesis of chiral tripodal receptors under solvent-free conditions using microwave irradiation for investigation of anion and cation recognition properties

Selective azo dye-based colorimetric chemosensor for F-, CH3COO- and PO43.

Developing anionic receptors is a huge challenge, especially those using hydrogen bonds to interact with the analytes. Azobenzene-derivative selective chemosensor has been evaluated for anion recognition properties. 2‑(4‑Hydroxiazobenzene)benzoic acid (HABA) has two hydrogens groups available for interaction; one is the phenol group and the other is the carboxylic acid group, enabling interaction with cations and anions. Subsequently titrations of chromophore 2‑(4‑hydroxiazobenzene) benzoic acid were performed with cations and anions; however, only the interactions with fluoride, acetate, and phosphate were significant. These data demonstrated the sensitivity of the ligand HABA by these anions, characterized by the displacement of the absorbance bands at 372nm to 491nm in acetonitrile. The association constants found to fluoride, acetate, and phosphate were 1.56×104±0.28, 1.25×104±0.60, and 1.90×104±0.67mol-1dm3 respectively. 1H NMR titrations data confirmed association constants values in agreement with those of UV-Vis, besides showing evidence of the analyte interaction by the hydrogen-bonding of the carboxylic acid group. Overall, UV-Vis limit of detection data for fluoride (1.05×10-7moldm-3), acetate (3.77×10-8moldm-3) and phosphate (3.00×10-8moldm-3), support that HABA can detect low concentration of these anions.

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.

Novel 1,4-naphthoquinone N-aroylthioureas: Syntheses, crystal structure, anion recognition properties, DFT studies and determination of acid dissociation constants

In this paper, five novel 1,4-naphthoquinone N-aroylthiourea derivatives were synthesized, by the reaction of 2,3-diaminonaphthalene-1,4-dione and aroylisothiocyanates, in excellent yield (88–96%) and characterized by using FT-IR, 1H/13C NMR and HRMS. In addition, the molecular structure of one of the 1,4-naphthoquinone N-aroylthiourea compounds was characterized by single crystal X-ray diffraction studies. The absorption spectra of the compounds were determined in DMSO and the dyes have absorption in visible region in the range of 464–477 nm. The chemosensing ability of each of the prepared dyes was assessed by titrating them towards the anions; F−, Cl−, Br−, I−, AcO−, CN−, ClO4−, H2PO4−, HSO4−, and NO3−, using spectrophotometric and 1H NMR titration techniques in DMSO, experimentally. The results obtained from the experimental investigation were explained by employing theoretical calculations. The molecular structure and absorption spectra of the compounds and their deprotonation forms were obtained using Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) at B3LYP/6311 g(d) level of theory. The computed results are in good agreement with the experimental. Finally, the acid dissociation constants of the 1,4-naphthoquinone N-aroylthioureas were determined potentiometrically in 50% (v/v) DMSO-H2O hydro-organic solution at 25 ± 0.1 °C, at an ionic background of 0.1 mol/L of NaCl using the HYPERQUAD computer program.

Chromogenic and fluorogenic detection of selected anions by bis-terpyridine Fe(II) complex through displacement approach

Abstract This paper deals with synthesis, characterization and anion recognition properties of a homoleptic bis-terpyridine Fe(II) complex covalently coupled with diarylethene unit. The recognition event was examined in both organic as well as mixed aqueous–organic medium through different optical channels and spectroscopic techniques by taking advantage of metal–ligand interaction in the complex. The complex acts as sensor for \(\hbox {F}^{-}\), \(\hbox {OAc}^{-}\) and \(\hbox {CN}^{-}\) among the other studied anions (\(\hbox {F}^{-}\), \(\hbox {Cl}^{-}\), \(\hbox {Br}^{-}\), \(\hbox {I}^{-}\), \(\hbox {CN}^{-}\), \(\hbox {OAc}^{-}\), \(\hbox {H}_{2}\hbox {PO}_{4}^{-}\), \(\hbox {SCN}^{-}\), \(\hbox {BF}_{4}^{-}\) and \(\hbox {ClO}_{4}^{-})\) without selectivity. In contrast to acetonitrile, the complex acts as highly selective chromogenic and fluorogenic sensor for only \(\hbox {CN}^{-}\) in water. Detection limit of the metalloreceptor towards \(\hbox {CN}^{-}\) was determined from the absorption and emission titration data and the observed values lie in the order of \(10^{-9}\) M in acetonitrile and \(10^{-8}\) M in mixed aqueous–organic media.Graphical AbstractSYNOPSIS Anion sensing property of a bis-terpyridine Fe(II) complex was thoroughly investigated in both acetonitrile and water–acetonitrile (100:1, v/v) media through different optical channels and spectroscopic techniques. Interestingly, the complex acts as chromogenic and fluorogenic receptor for cyanide in predominantly aqueous medium with very low detection limit.