Anion Binding Studies Research Articles

Dual-Hydrogen Bond Donor-Functionalized Carbon Nanotube Fibers: Enhancing Anion-Sensing Performance Through Functionalization Approaches.

In this study, chemiresistive anion sensors are developed using carbon nanotube fibers (CNTFs) functionalized with squaramide-based dual-hydrogen bond donors (SQ1 and SQ2) and systematically compared the sensing properties attained by two different functionalization methods. Model structures of the selectors are synthesized based on a squaramide motif incorporating an electron-withdrawing group. Anion-binding studies of SQ1 and SQ2 are conducted using UV-vis titrations to elucidate the anion-binding properties of the selectors. These studies revealed that the chemical interaction with acetate (AcO-) induced the deprotonation of both SQ1 and SQ2. Selectors are functionalized onto the CNTFs using either covalent or non-covalent functionalization. For covalent functionalization, SQ1 is chemically formed on the surface of the CNTFs, whereas SQ2 is non-covalently functionalized to the surface of the CNTFs assisted by poly(4-vinylpyridine). The results showed that non-covalently functionalized CNTFs exhibited a 3.6-fold higher sensor response toward 33.33mm AcO- than covalently functionalized CNTFs. The selector library is expanded using diverse selectors, such as TU- and CA-based selectors, which are non-covalently functionalized on CNTFs and presented selective AcO--sensing properties. To demonstrate on-site and real-time anion detection, anion sensors are integrated into a sensor module that transferred the sensor resistance to a smartphone via wireless communication.

Unlocking Photocatalytic Activity of Acridinium Salts by Anion-Binding Co-Catalysis.

The in situ generation of active photoredox organic catalysts upon anion-binding co-catalysis by making use of the ionic nature of common photosensitizers is reported. Hence, the merge of anion-binding and photocatalysis permitted the modulation of the photocatalytic activity of simple acridinium halide salts, building an effective anion-binding - photoredox ion pair complex able to promote a variety of visible light driven transformations, such as anti-Markovnikov addition to olefins, Diels-Alder and the desilylative C-C bond forming reactions. Anion-binding studies, together with steady-state and time-resolved spectroscopy analysis, supported the postulated ion pair formation between the thiourea hydrogen-bond donor organocatalyst and the acridinium salt, which proved essential for unlocking the photocatalytic activity of the photosensitizer.

A Cationic Catechol Derivative Binds Anions in Competitive Aqueous Media.

A simple dihydroxy isoquinolinium molecule (3+) was prepared by a modification of a literature procedure. Interestingly, during optimisation of the synthesis a small amount of the natural product pseudopalmatine was isolated, and characterised for the first time by X-ray crystallography. Compound 3+ contains a catechol motif and positive charge on the same scaffold and was found to be a potent anion receptor, binding sulfate strongly in 8 : 2 d6-acetone:D2O and 7 : 3 d6-acetone:D2O (Ka>104 and 2,100 M-1, respectively). Unsurprisingly, chloride binding was much weaker, even in the less polar solvent mixture 9 : 1 d6-acetone:D2O. The sulfate binding is remarkably strong for such a simple molecule, however anion binding studies were complicated by the tendency of the molecule to react with BPh4 - or BF4 - species during anion metathesis reactions. This gave two unusual zwitterions containing tetrahedral boronate centres, which were both characterised by X-ray crystallography.

Evaluation of naked-eye sensing and anion binding studies in meso-fluorescein substituted one-walled calix[4]pyrrole (C4P).

In this paper, we have design, synthesized and fully characterized a new meso-fluorescein substituted one-walled calix[4]pyrrole (C4P7), obtained from simple and easily available starting materials such as fluorescein, 4-hydroxyacetophenone and pyrrole. The anion sensing studies reveal that the C4P7 system displays selective and sensitive naked-eye sensing towards fluoride, phosphate, and acetate anions with the limit of detection of 4.27 mg L-1, 6.4 mg L-1, and 5.94 mg L-1, respectively. Moreover, the C4P7 receptor displays good results of binding (host-guest, 1 : 1) towards a variety of anions. The 1 : 1 binding stoichiometry was further confirmed by means of Job's plots. TD-DFT calculations showed that the HOMO-LUMO gap decreases in all the complexes (C4P7@anions) in comparison to the free C4P7 system. The authors are of the opinion that this work may provide a good platform to explore calix[4]pyrrole chemistry in the arena of recognition/sensing of biologically significant analytes in future studies.

N-Confused strapped calix[4]pyrrole: the missing member of calix[4]pyrrole chemistry.

The first example of N-confused strapped calix[4]pyrrole 5 is presented. The structural integrity of 5 and its regular isomer 4 was unambiguously confirmed by single crystal X-ray diffraction analysis. Anion binding studies using 1H NMR titration carried out in CDCl3 revealed a small but detectable tendency of 5 to interact with an anion. Conversely, the isomeric regular strapped calix[4]pyrrole 4 displayed high selectivity for fluoride anions under similar experimental conditions. The high fluoride selectivity of 4 and unexpectedly low anion affinity of 5 were ascribed to the presence of intramolecular hydrogen bonds within strapping subunits.

Selective sodium halide over potassium halide binding and extraction by a heteroditopic halogen bonding [2]catenane.

The synthesis and ion-pair binding properties of a heteroditopic [2]catenane receptor exhibiting highly potent and selective recognition of sodium halide salts are described. The receptor design consists of a bidentate halogen bonding donor motif for anion binding, as well as a di(ethylene glycol)-derived cation binding pocket which dramatically enhances metal cation affinity over previously reported homo[2]catenane analogues. 1H NMR cation, anion and ion-pair binding studies reveal significant positive cooperativity between the cation and anion binding events in which cation pre-complexation to the catenane subsequently 'switches-on' anion binding. Notably, the heteroditopic catenane displayed impressive selectivity for sodium halide recognition over the corresponding potassium halides. We further demonstrate that the catenane is capable of extracting solid alkali metal salts into organic media. Crucially, the observed solution phase binding selectivity for sodium halides translates to superior functional extraction capabilities of these salts relative to potassium halides, overcoming the comparatively higher lattice enthalpies NaX > KX dictated by the smaller alkali metal sodium cation. This is further exemplified in competitive solid-liquid experiments which revealed the exclusive extraction of sodium halide salts from solid mixtures of sodium and potassium halide salts.

Phosphate selective binding and sensing by halogen bonding tripodal copper(II) metallo-receptors in aqueous media.

Combining the potency of non-covalent halogen bonding (XB) with metal ion coordination, the synthesis and characterisation of a series of hydrophilic XB tripodal Cu(II) metallo-receptors, strategically designed for tetrahedral anion guest binding and sensing in aqueous media is described. The reported metallo-hosts contain a tripodal C3-symmetric tris-iodotriazole XB donor anion recognition motif terminally functionalised with tri(ethylene glycol) and permethylated β-cyclodextrin functionalities to impart aqueous solubility. Optical UV-vis anion binding studies in combination with unprecedented quantitative EPR anion titration investigations reveal the XB Cu(II) metallo-receptors exhibit strong and selective phosphate recognition over a range of other monocharged anionic species in competitive aqueous solution containing 40% water, notably outperforming a hydrogen bonding (HB) Cu(II) metallo-receptor counterpart. Electrochemical studies demonstrate further the capability of the metallo-receptors to sense anions via significant cathodic perturbations of the respective Cu(II)/Cu(I) redox couple.

Synthesis, structural characterization, and anion binding studies of bisamide functionalized molecular clefts

The utilization of amide functional groups as anion-binding sites in the structure of synthetic anion receptors has received significant attention. In this study, three new compounds, namely, N,N′-bis(2-(pyridin-2-yl)ethyl)pyridine-2,6-dicarboxamide (L1), N,N′-bis(2-(pyridin-3-yl)ethyl)pyridine-2,6-dicarboxamide (L2), and N,N′-bis(2-(pyridin-4-yl)ethyl)pyridine-2,6-dicarboxamide (L3), have been successfully synthesized. These compounds were fully characterized using a combination of spectroscopic techniques such as Fourier transform infrared spectroscopy, gas chromatography–mass spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, elemental analysis, and ultraviolet–visible (UV–Vis) spectroscopy. Further investigation on the potential of these compounds to bind with anions, such as chloride, nitrate, chromate, and phosphate, has been conducted using UV–Vis titration and a fluorescence titration method, and the results revealed that compound L2 has high potential to bind with chloride, chromate, and phosphate anions compared with other investigated hosts and analytes. This has opened a good opportunity for further application bisamide compound as anion sensing materials in the future.

A hexapyrrolic molecular cage and the anion-binding studies in chloroform

An ester–imine cage was synthesized from hexapyrrolic tripodal precursor and characterized with NMR spectroscopy and X–ray crystallography. This novel molecular cage displays good stability in wet organic solvents and exhibits moderate to strong affinity (103–106 M–6) for anions in chloroform. Theoretical calculations support the relative strong binding between the cage and SO42−.

Carbazole Integrated Tetrakis-(1H-pyrrole-2-carbaldehyde): A Highly Selective Fluorescent Probe for HP2O73.

A new carbazole-coupled tetrakis-(1H-pyrrole-2-carbaldehyde) anion receptor 1 has been designed and synthesized. Anion binding studies in organic media using fluorescence and UV-vis spectroscopy revealed that receptor 1 is capable of sensing HP2O73- with high selectivity. Addition of HP2O73- to THF solution of 1 resulted in the emergence of a new broad band at longer wavelength along with quenching of the original emission band forming a ratiometric response. Based on dynamic light scattering (DLS) experiment and fluorescence lifetime measurement, we propose that the emergence of new emission band in the presence of HP2O73- ion is due to the aggregation-induced excimer formation.

Novel synthesis and evaluation of anion-π interactions in one-walled meso-cyanophenyl substituted calix[4]pyrrole (C4P): Experimental and computational insights

A novel one-walled meso-cyanophenyl functionalized calix[4]pyrrole (4) was synthesized from cyanophenyl appended dipyrromethane (3) through conventional strategy and also by utilizing deep eutectic solvent of N,N'-dimethyl urea (DMU) & L-(+)-tartaric acid (TA) in a ratio of 7:3. The structural confirmation of 4 was done through 1H-NMR, 13C-NMR, FT-IR, and HRMS spectral data. Anion binding studies of the receptor 4 with several anions (halides, trigonal oxoanions, tetragonal oxoanions, etc.) used as tetrabutylammonium (TBA) salts, were successfully investigated by virtue of UV–Vis spectroscopy and time dependent density functional theory (TD-DFT). Notably, the UV–Vis absorbance titrations performed in CH3CN solvent, revealed significantly higher anion binding of receptor 4 with F¯, Cl¯, Br¯, and SCN¯ in comparison to the simple C4P. This can be ascribed to the fact that the cyanophenyl moiety is π-acidic in nature which participates in anion complexation through weak anion-π interactions (observed through 1H-NMR spectroscopy) and hence modulates anion binding through cooperative effect of preliminary NH-hydrogen bonding due to C4P scaffold and anion-π contacts due to cyanophenyl moiety.

Experimental and computational anion binding studies of meso-substituted one-walled phthalimide-based Calix[4]pyrrole

Anion binding studies of meso‑substituted one-walled phthalimide-based calix[4]pyrrole (m-PC4P, 6) were investigated through UV–vis spectroscopy in acetonitrile and corroborated by time-dependent density functional theory (TD-DFT) calculations using 6–311G(d) basis set. Notably, to our expectation, the m-PC4P (6) displayed higher anion binding affinities in comparison to the parent C4P system, probably due to the additional weak CH-anion interactions besides four NH-hydrogen bonds of the C4P framework (supported by 1H NMR evidence). Herein, we have observed the usual trend with halide anions (used as their tetrabutylammonium salts), i.e. with increase in size of the halides from fluoride to iodide, the anion binding affinity decreases. Moreover, with the nitrate anion, appreciable better binding was observed in the case of m-PC4P (6) as compared to the simple C4P (1).

Facile synthesis and anion binding studies of fluorescein/benzo-12-crown-4 ether based bis-dipyrromethane (DPM) receptors.

Two novel fluorescein as well as benzo-12-crown-4 ether functionalized dipyrromethane receptors (DPM3 and DPM4) have successfully been synthesized. The anion (used as their TBA salts) binding studies of thus prepared DPM3 and DPM4 receptors were evaluated by the UV-visible spectrophotometric titrations. Binding affinities as well as the stoichiometry were determined through the UV-visible titrations data with the involvement of the BindFit (v0.5) package available online at https://supramolecular.org. Moreover, binding events were validated by means of the comparison of the partial 1H-NMR spectrum of the simple host molecule with that of the host-guest complex, and the 1 : 1 stoichiometry were further confirmed by the Job's method of continuous variation. From the results, we observed the binding constant (Ka) values of DPM3/DPM4 with various tested anions in the range of 516.07 M-1 to 63789.81 M-1, depending upon the nature/shape/size of the anions. Moreover, the anion-π interactions were confirmed by the partial 1H-NMR spectral data, and further supported by the literature reported systems. The authors hope that such types of valued receptors will be benefitted in future for the recognizing/binding of a variety of biologically important anions.

Relevance of the Cation in Anion Binding of a Triazole Host: An Analysis by Electrophoretic Nuclear Magnetic Resonance.

Triazole hosts allow cooperative binding of anions via hydrogen bonds, which makes them versatile systems for application in anion binding catalysis to be performed in organic solvents. The anion binding behavior of a tetratriazole host is systematically studied by employing a variety of salts, including chloride, acetate, and benzoate, as well as different cations. Classical nuclear magnetic resonance (1H NMR) titrations demonstrate a large influence of cation structures on the anion binding constant, which is attributed to poor dissociation of most salts in organic solvents and corrupts the results of classical titration techniques. We propose an approach employing electrophoretic NMR (eNMR), yielding drift velocities of each species in an electric field and thus allowing a distinction between charged and uncharged species. After the determination of the dissociation constants KD for the salts, electrophoretic mobilities are measured for all species in the host-salt system and are analyzed in a model which treats anion binding as a consecutive reaction to salt dissociation, yielding a corrected anion binding constant KA. Interestingly, dependence of KA on salt concentration occurs, which is attributed to cation aggregation with the anion-host complex. Finally, by the extrapolation to zero salt concentration, the true anion-host binding constant is obtained. Thus, the approach by eNMR allows a fully quantitative analysis of two factors that might impair classical anion binding studies, namely, an incomplete salt dissociation as well as the occurrence of larger aggregate species.

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.

A Benzimidazolium-Based Organic Cage with Antimicrobial Activity

Considering the wide interest in (benz)imidazolium-based drugs, we here report our study on a benzimidazolium-based organic cage as potential antimicrobial and antifungal agent. Cytotoxicity studies on a human derived cell line, SH-SY5Y, showed that the cage is not cytotoxic at all at the investigated concentrations. Anion binding studies demonstrated that the cage can bind anions (chloride and nitrate, in particular) both in organic solvent and 20%v D2O/CD3CN mixture. The cage was also tested as anionophore, showing a weak but measurable transport of chloride and nitrate across LUVs vesicles. Nonetheless, the compounds have antimicrobial activity towards Staphylococcus aureus (Gram-positive bacteria). This is probably the first organic cage studied as anionophore and antimicrobial agent.

Anion binding studies with anthraimidazoledione-based positional isomers: A comprehensive analysis of different strategies for improved selectivity

In the present work, we have reported the design of three different positional isomers of anthraimidazoledione-based charge transfer probes and their anion-binding properties under various conditions. In the acetonitrile medium, the meta isomer showed ratiometric optical response towards basic anions, such as F−, CN−, AcO− and H2PO4−. Based on the differences in the hydrogen bonding ability of these anions, we observed distinguishable output signal, particularly in fluorescence. Though meta and para isomers showed effective interaction with anions, the response was relatively weak for the ortho isomer. We suspected that the presence intramolecular hydrogen bond between pyridine nitrogen and imidazole –NH group might be responsible for such poor performance. Further, we have employed two different strategies to improve the selectivity towards anions. In the first case, selective recognition of anions was achieved using suitable metal ions (Cu2+, Zn2+, Ca2+, and Al3+) as masking agents. On the contrary, we have varied the water content (0, 10, 30 and 50% v/v) in the acetonitrile-water mixture in the second case. The anions with relatively large hydration enthalpy showed no detectable interaction with probe in presence of water. Finally, we used the present system to detect cyanide ion in various natural water samples (tap, pond, and seawater). Also, low-cost reusable paper strips were developed as an alternative method for rapid, on-location detection of CN− ions.

Fine-tuning the acceptor–donor ability of star shaped triarylborane–triphenylamine conjugates: synthesis, characterization and anion binding studies

A modest approach to design and synthesize functionalized triarylborane–triarylamine based donor–acceptor systems, compounds1–3, and the investigation of the photophysical, solvatochromic, solid state emissive and anion binding properties.

Carbazole-Based Colorimetric Anion Sensors.

Owing to their strong carbazole chromophore and fluorophore, as well as to their powerful and convergent hydrogen bond donors, 1,8-diaminocarbazoles are amongst the most attractive and synthetically versatile building blocks for the construction of anion receptors, sensors, and transporters. Aiming to develop carbazole-based colorimetric anion sensors, herein we describe the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents, i.e., 3,6-dicyano and 3,6-dinitro. Both of these precursors were subsequently converted into model diamide receptors. Anion binding studies revealed that the new receptors exhibited significantly enhanced anion affinities, but also significantly increased acidities. We also found that rear substitution of 1,8-diamidocarbazole with two nitro groups shifted its absorption spectrum into the visible region and converted the receptor into a colorimetric anion sensor. The new sensor displayed vivid color and fluorescence changes upon addition of basic anions in wet dimethyl sulfoxide, but it was poorly selective; because of its enhanced acidity, the dominant receptor-anion interaction for most anions was proton transfer and, accordingly, similar changes in color were observed for all basic anions. The highly acidic and strongly binding receptors developed in this study may be applicable in organocatalysis or in pH-switchable anion transport through lipophilic membranes.

Naked eye detection and measurement of fluoride concentration in groundwater using novel synthesized receptor

In this communication, a novel receptor (E)-N-methyl-2-(1-(2-oxo-2H-chromen-3 yl)ethylidene)hydrazinecarbothioamide), R was synthesized using microwave irradiation that acts as a highly selective and sensitive receptor towards fluoride detection in aqueous media. Receptor (R) shows naked eye color change from pale yellow to pink towards fluoride ions. Anion binding studies were performed by UV–vis, Mass (ESI-MS) and 1H NMR spectroscopy. Using the Benesi–Hildebrand equation the binding constant of the receptor for fluoride was found to be 1.565 × 104 M−1 and lowest detection limit was 0.18 mg/L (9.024 × 10-6 M) lower than WHO guidelines. To check the applicability of receptor for the detection of fluoride in groundwater samples, preliminary investigations were carried out with synthetic water and groundwater collected from high fluoride content regions in Rajasthan (India). Studies were also carried out using Ion-selective electrode and the results were found to be in good agreement with the results from UV–vis spectroscopy using synthesized receptor.