Anions In Aqueous Media Research Articles

Inorganic–organic hybrid nonwoven fabrics with colorimetric detection capability for borate ions in aqueous solutions

Abstract A nonwoven fabric sheet with an immobilized colorimetric reagent was prepared to detect borate anions in aqueous media. The fabric comprised immobilized chromotropate and 1-butanesulfonate anions and chromotropate, as the colorimetric reagent, per anion exchange capacity of the layered double hydroxide. The resulting sheet quantitatively detected borate anions through photoluminescence measurements. Thus, it can be used for onsite quantitative analysis of dissolved boron in water, with promising potential for water quality monitoring and, consequently, sustainable and safe water resources globally.

Development of Fluorescent Sensors for Biorelevant Anions in Aqueous Media Using Positively Charged Quantum Dots.

Quantum dots (QDs) have captured the attention of the scientific community due to their unique optical and electronic properties, leading to extensive research for different applications. They have also been employed as sensors for ionic species owing to their sensing properties. Detecting anionic species in an aqueous medium is a challenge because the polar nature of water weakens the interactions between sensors and ions. The anions bicarbonate (HCO3-), carbonate (CO32-), sulfate (SO42-), and bisulfate (HSO4-) play a crucial role in various physiological, environmental, and industrial processes, influencing the regulation of biological fluids, ocean acidification, and corrosion processes. Therefore, it is necessary to develop approaches capable of detecting these anions with high sensitivity. This study utilized CdTe QDs stabilized with cysteamine (CdTe-CYA) as a fluorescent sensor for these anions. The QDs exhibited favorable optical properties and high photostability. The results revealed a gradual increase in the QDs' emission intensity with successive anion additions, indicating the sensitivity of CdTe-CYA to the anions. The sensor also exhibited selectivity toward the target ions, with good limits of detection (LODs) and quantification (LOQs). Thus, CdTe-CYA QDs show potential as fluorescent sensors for monitoring the target anions in water sources.

La-doped MgFe-layered double hydroxides and their sorption properties towards tungsten oxyanions (WO42-) at alkaline pH’s

The present study focuses on the tungsten recovery from alkaline solutions using for the first time La-doped MgFe-LDH type sorbents (pH ≥ 13). A small-scale synthesis procedure was optimized, and further upscaled (20x) to produce up to 200 g batches with reproducibility degree close to 100%. The chemical composition, structural and textural characteristics of the as-synthesized materials were investigated by ICP-OES, X-ray Diffraction, N2 physisorption and IR spectroscopy techniques. The materials were applied for sorption of WO42- anions in aqueous media under relevant conditions. Parameters influencing the sorption process, such as the LDH composition, pH of the sorption media, adsorption capacity, kinetics and desorption solution composition were thoroughly investigated. Multi-cycling tests in different desorption solutions combined with IR and XRD characterization of the La-MgFe-LDH solids in different steps of the process, allowed us to elucidate the WO42- recovery mechanism. Further, the La-doping in the LDH structure increases the sorption capacity and assures the material stability throughout the WO42- recovery process in high pH media. The alkaline stability was demonstrated by powder post characterization by X-ray Diffraction as well as performing alkaline stability test and follow up of any leaching elements by ICP-OES in alkaline solutions. The results indicate that the as-developed La-MgFe-LDH are suitable candidates for WO42- recovery from aqueous solutions, including highly alkaline solutions compatible with the current hydrometallurgical processes.

A charge-neutral organic cage selectively binds strongly hydrated sulfate anions in water.

In biological systems, enzymes and transport proteins can bind anions in aqueous media solely by forming hydrogen bonds with charge-neutral motifs. Reproducing this functionality in synthetic systems presents challenges and incurs high costs, particularly when targeting strongly hydrated anions such as sulfate. Here we report a [2.2.2]urea cryptand (cage), synthesized in one pot, that selectively binds sulfate in a mixture of dimethyl sulfoxide and water and in water with affinities in the micromolar to millimolar range. The neutral cage bearing six urea groups donates 12 strong hydrogen bonds to encapsulate a sulfate anion, showing favourable enthalpy even in pure water. Sulfate binding can be further enhanced by using micelles to provide a low-polarity microenvironment. The cage finds utility in analysing divalent anions in water and beverage samples or in removing sulfate. The work demonstrates the achievability of robust and selective anion binding in water with minimal synthetic efforts, by using neutral NH hydrogen bonds akin to those found in biology.

Influence of anion variation on dielectric response of amide functionalized benzimidazolium dicationic ionic liquids

The present work centered attention on novel ionic liquid (IL) based on dicationic benzimidazolium ion containing amide group (DBimIL) synthesized using dialkylation of N-ethyl benzimidazole to followed with anion exchange reaction. To explore the potential application of ILs, there is a great need to grasp their structural and physical properties. We have developed three different set of DBimIL based ionic liquids with chloride, hexafluorophosphate and perchlorate anions in aqueous media, respectively. Their structural features were studied using 1H, 13C-NMR, FTIR, and HRMS spectroscopy, respectively. The temperature-dependent dielectric characteristics of ILs were closely examined angular frequency in the range of 0.6–125 rad/s from 30 to 150 °C. The relationship between the structural and dielectric properties of ILs established. The dielectric parameters like dielectric constant, dissipation factor and the real part of ac conductivity were found to be affected significantly with the tuning of anionic moieties of ionic liquids. The ability of materials to store a charge in electromagnetic field was measured. From dielectric and electrical studies, to bring to an end, especially in particular way that the present IL systems have an enormous potential for the designing of modern-day energy storage devices.

Preparation and stability of pegylated poly(S-alkyl-L-homocysteine) coacervate core micelles in aqueous media.

We report development and preparation of synthetic polypeptide based, coacervate core polyelectrolyte complex micelles, PCMs, in aqueous media, which were characterized and evaluated for the encapsulation and in vitro release of a model single-stranded RNA, polyadenylic acid, poly(A). Cationic, α-helical polypeptides pegylated at their N-termini, PEG113-b-5bn and PEG113-b-5cn, were designed to form coacervate core PCMs upon mixing with multivalent anions in aqueous media. Sodium tripolyphosphate (TPP) and poly(A) were used as model multivalent anions that allowed optimization of polypeptide composition and chain length for formation of stable, nanoscale PCMs. PEG113-b-5c27 was selected for preparation of PCMs that were characterized under different environmental conditions using dynamic light scattering, atomic force microscopy and cryoelectron microscopy. The PCMs were found to efficiently encapsulate poly(A), were stable at physiologically relevant pH and solution ionic strength, and were able to release poly(A) in the presence of excess polyvalent anions. These PCMs were found to be a promising model system for further development of polypeptide based therapeutic delivery vehicles.

Colorimetric chemosensors for the selective detection of arsenite over arsenate anions in aqueous medium: Application in environmental water samples and DFT studies

Novel organic receptors N3R1- N3R3 were developed for the selective colorimetric recognition of arsenite ions in the organo-aqueous media. In the 50% aq. acetonitrile media and 70% aq. DMSO media, receptors N3R2 and N3R3 showed specific sensitivity and selectivity towards arsenite anions over arsenate anions. Receptor N3R1 showed discriminating recognition of arsenite in the 40% aq. DMSO medium. All three receptors formed a 1:1 complex with arsenite and stable for a pH range of 6–12. The receptors N3R2 and N3R3 achieved a detection limit of 0.008 ppm (8 ppb) and 0.0246 ppm, respectively, for arsenite. Initial hydrogen bonding on binding with the arsenite followed by the deprotonation mechanism was well supported by the UV–Vis titration, 1H- NMR titration, electrochemical studies, and the DFT studies. Colorimetric test strips were fabricated using N3R1- N3R3 for the on-site detection of arsenite anion. The receptors are also employed for sensing arsenite ions in various environmental water samples with high accuracy.

Anion−π Interactions in Monolayers Formed by Amphiphilic Electron-Deficient Aromatic Compounds at Air/Water Interfaces

Biological systems precisely and selectively control ion binding through various chemical reactions, molecular recognition, and transport by virtue of effective molecular interactions with biological membranes and proteins. Because ion binding is inhibited in highly polar media, recognition systems for anions in aqueous media, which are relevant to biological and environmental systems, are still limited. In this study, we explored the anion binding of Langmuir monolayers formed by amphiphilic naphthalenediimide (NDI) derivatives with a series of substituents at air/water interfaces via anion-π interactions. Density functional theory (DFT) simulations revealed that the binding of anions originating from anion-π interactions is related to the electron density of the anions. At the air/water interfaces, amphiphilic NDI derivatives formed Langmuir monolayers, and the addition of anions caused expansion of the Langmuir monolayers. The anions with larger hydration energies related to electron density showed larger binding constants (Ka) for 1:1 stoichiometry with the NDI derivatives. The loosely packed monolayer formed by the amphiphilic NDI derivatives with bromine groups showed a better anion response. In contrast, the binding of NO3- was significantly enhanced in the highly packed monolayer. These results indicate that the packing of NDI derivatives with rigid aromatic rings influenced the binding of the anions. These results provide insight into ion binding using the air/water interface as a promising recognition site for mimicking biological membranes. In future, sensing devices can be developed using Langmuir-Blodgett films on electrodes. Furthermore, the capture of anions on electron-deficient aromatic compounds can lead to doping or composition technologies for n-type semiconductors.

Praseodymium Metallacrown-Based NMR Probe for Enantioselective Discrimination of Mandelate Anions in Water.

Recently, the enhanced interest in water-soluble aminohydroximate Ln(III)-Cu(II) metallacrowns (MC) is largely due to their fascinating structural chemistry, diverse properties and ease of synthesis. We examined the water-soluble praseodymium(III) alaninehydroximate complex Pr(H2O)4[15-MCCu(II)Alaha-5]·3Cl (1) as a highly effective chiral lanthanide shift reagent for NMR analysis of the biologically relevant (R/S)-mandelate (MA) anions in aqueous media. The R-MA and S-MA enantiomers can be easily discriminated in the presence of small (1.2-6.2 mol %) amounts of MC 1 by the 1H NMR signals of multiple protons exhibiting an enantiomeric shift difference (ΔΔδ) of 0.06 ppm up to 0.31 ppm. Additionally, a possibility of coordination of MA to the metallacrown was investigated by the ESI-MS technique and a Density Functional Theory modeling of the molecular electrostatic potential and noncovalent interactions.

Chaotropic anion induced self-assembly of naphthalimide–glutathione nanohybrids: selective recognition of bisulphate anions in aqueous medium

Anion-induced self-assembly is one of the growing research fields as it provides a better understanding of natural self-assemblies such as DNA, proteins, peptides, etc.

Synthesis of Fumed-Pr-Pi-TCT as a Fluorescent Chemosensor for the Detection of Cyanide Ions in Aqueous Media

In this research, fumed silica scaffolds modified via treatment with (3-chloropropyl)-triethoxysilane, piperazine, and trichlorotriazine groups were deployed for the specific detection of cyanide ions, thus paving the way for the detection of environmental hazards and pollutants with high specificity. Fumed-propyl -piperazine-trichlorotriazine (fumed-Pr-Pi-TCT) was synthesized in three steps starting from fume silica. It was functionalized subsequently using 3-(choloropropyl)-trimethoxysilane, piperazine, and trichlorotriazine, and then, the product was characterized through several methods including Fourier-transform infrared spectroscopy (FTIR) spectrum, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Fumed-Pr-Pi-TCT was exposed as a nanoparticle sensor to a range of different anions in aqueous media. This novel sensor could detect cyanide ions as a hazardous material, with the limit of detection being 0.82 × 10−4 M.

Selective determination of 2,4,6-Trinitrotoluene (TNT) with cysteamine in deep eutectic solvents

2,4,6-trinitrotoluene (TNT) is one of the most widely used explosives for military and civilian purposes. Detection of TNT is very important for both human health and public safety. In this study, TNT determination was carried out using a new solvent medium containing cysteamine (CysN) without the need for noble metal nanoparticles (i.e. CysN-AuNPs used for anchoring CysN through S-atom) or strong alkalinity (i.e. to stabilize TNT-Meisenheimer anions in aqueous medium). CysN was prepared in a deep eutectic solvent (DES) consisting of a mixture of choline chloride and ethylene glycol, and the color of the Meisenheimer complex was derived from the donor–acceptor interaction between the amine group on CysN and the nitro group on TNT. The Lewis base-acid neutralization product, CysN-TNT charge-transfer complex, was stable in the optimized DES solvent unlike that in water. The absorbance of the resulting red complex was measured at 515 nm. The LOD and LOQ values were found to be 67.17 and 223.90 μg L− 1, respectively. The proposed method was not affected by similar explosives, camouflage agents, and possible ion interference in the soil. Finally, the method was validated with an HPLC-DAD analysis. This method is the first study to use DESs in the determination of energetic materials such as TNT and the proposed assay shows excellent selectivity for TNT. The proposed method stands out as it is fast, simple, of low cost, compatible with green chemistry with the potential to convert to a paper-based colorimetric sensor.

Synthesis of oxydiacetate functionalized strontium coordination polymer through gel diffusion technique: A new dual luminescent chemosensor for the detection of Copper(II) ions and Cr(VI) oxyanions in aqueous medium

The current scenario shows the wide applicability of coordination polymers (CPs) in various fields due to their structural topology and tunable properties. The development of these molecules with potential application can be obtained by incorporating active metals with highly functionalized ligands under different synthetic conditions. Here in we report a newly synthesized dual luminescent chemosensor based on oxydiacetate functionalized strontium [Sr(C4H4O5)(H2O)3]n·nH2O by one of the simplest gel diffusion technique at room temperature. The grown crystal was characterized by elemental analysis, FTIR, UV–Visible Spectroscopy, Single Crystal X-ray Diffraction and TG/DTA measurements. Single Crystal X-ray diffraction studies of the synthesized CP revealed a monoclinic crystal system with space group P21/c. The luminescent properties of the synthesized analyte were analyzed from photoluminescence (PL) spectrum. The coordination polymer displayed an emission of 371 nm upon excitation of 313 nm. The luminescence titration experiments showed that the synthesized coordination polymer dispersed in water, can selectively sense Cu(II) metal ions as well as the Cr(VI) oxyanions [CrO42-/Cr2O72-] from the aqueous media with a detection limit of 0.2536 µM and 0.1060 µM respectively. The grown strontium based CP can thus be used as an effective dual luminescent chemosensor for the detection and probing of both Cu2+ and Cr(VI) oxyanions (CrO42-/Cr2O72-) in aqueous medium. The study further suggests the possibility of fabrication of strontium based luminescent chemosensors for the detection of Cu(II) cations and CrO42-/Cr2O72- anions in aqueous medium with high selectivity and sensitivity.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids.

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host–guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Modulation of micellization behavior of imidazolium based surface active ionic liquids by aromatic anions in aqueous medium

Surface active ionic liquids (SAILs) represent a class of ionic surfactants that many times display better surface-active properties as compared to conventional ionic surfactants. The micellization of SAILs can be further tailored by the addition of salts, and aromatic salts comprising hydrotropic anions have never been explored for altering the micellization of SAILs in low concentration range. Considering this, we have investigated the effect of addition of three aromatic salts i.e. Sodium 4-hydroxy benzenesulfonate, sodium benzenesulfonate, and sodium p-toluenesulfonate on the micellization of 1-dodecyl-3-methylimidazolium chloride, [C12mim][Cl] and its amide functionalized counterpart, 3-(2-(dodecylamino)−2-oxoethyl)−1-methyl-1H-imidazol-3-ium chloride, [C12Amim][Cl]. The surface-active behavior of SAILs has been investigated by tensiometry, whereas micellization in bulk has been probed through conductivity, steady-state fluorescence, dynamic light scattering (DLS) and zeta-potential measurements. The possible location of aromatic anions adsorbed on the micellar surface has been probed using 1H NMR measurements. Isothermal titration calorimetry has been utilized to gain insights into the thermodynamic aspects of micellization. The inferences gained from different techniques have been correlated and found to be in good agreement with each other. It has been observed that the functionalization of alkyl chain length of SAIL along with relative hydrophobicity and bulkiness of the aromatic anions control the characteristic properties of micellization.

Counterion Effects in Metal Hybrid Biopolymer Materials for Sulfate Adsorption: An Experimental and Computational Study

Modification of biomaterials is an active research area in materials and environmental science, where the controlled removal of sulfate is a key goal toward achieving global water security in regions with saline aquifers. In this study, biopolymer-based ternary metal composites (TMCs) were prepared that contain alginate/chitosan/Al(III) with variable counterions: chloride (C), nitrate (N), and sulfate (S), denoted as TMC-C, TMC-N, and TMC-S, respectively. The structure and physicochemical properties of the TMCs were characterized by spectroscopy (NMR, FT-IR, Raman, and XPS) and other complementary methods (thermal gravimetry, potentiometry, and zeta potential) to gain insights on the role of counterion effects related to the adsorption properties of TMCs with inorganic and organic anions in aqueous media. Both equilibrium and dynamic adsorption properties of the TMCs were evaluated with inorganic sulfate (Na2SO4) and two types of anionic organic dyes (methyl orange, MO,; and reactive black-5, RB5) at pH 7 and 295 K. A computational study was carried out to evaluate the structural features of the TMCs related to the coordination of sulfate with the TMC-N system. The charge state of the TMCs for the various counterion systems was estimated according to the pHPZC (5.0 to 5.9) and zeta potential (+8.31 to +35.7 mV) of the composites in aqueous media. The presence of variable counterions (chloride, nitrate, and sulfate) revealed the effects on the equilibrium and kinetic uptake of sodium sulfate and RB5. The Sips isotherm model for sulfate adsorption revealed a value of Qe from 87 to 120 mg/g, which depends on the counterion. The uptake of RB5 (Qm = 77 to 208 mg/g) by the TMCs varied over a wider range due to the role of secondary biopolymer adsorption sites. The incorporation of switchable counterions in TMCs offer a low-cost and bottom-up approach for the design of tailored biopolymer adsorbents with tunable anion uptake properties toward organic and inorganic anions in aqueous media.

Highly Selective and Sensitive Colorimetric and Fluorescent Chemosensors for Rapid Detection of Cyanide Anions in Aqueous Medium: Investigation on Supramolecular Recognition of Tweezer‑shaped Salophenes.

Three tweezer‑shaped salophenes having catechols (1), phenols (2) and anisoles (3) units in conjunction to the dipodal Schiff bases have been applied for the optical sensing of cyanide (CN¯) ions in CH3CN-H2O (7:3) as solvent of choice. Among them, compounds 1 and 2 recognized CN¯, relying on distinct color and spectral changes. They are easy-to-use probes that exhibit extremely high sensitivity (limit of detection = 1-10 nM), rapid response (5s) and excellent selectivity. Moreover, the visual detection and concentration determination of CN¯ by solution test kits of both sensors are the advantages for the practical applications. Based on the fluorescence and NMR spectroscopy, as well as the OH¯ and reversibility experiments, the explicit effect of hydroxyl groups on sensing and as well the different recognition of 1 and 2 toward CN¯ ions was proved. While probe 1 senses CN¯ via deprotonation, probe 2 recognizes it through an intramolecular aldimine condensation cyclization, leading to formation of anions of dihydroxyquinoxaline 4. This chemodosimetry is being reported for the first time in a Schiff's base. Furthermore, the similarity of fluorescence and NMR responses of 2 and 4 toward CN¯ supports the proposed process.

Mechanistic Insight of Sensing Hydrogen Phosphate in Aqueous Medium by Using Lanthanide(III)-Based Luminescent Probes.

The development of synthetic lanthanide luminescent probes for selective sensing or binding anions in aqueous medium requires an understanding of how these anions interact with synthetic lanthanide probes. Synthetic lanthanide probes designed to differentiate anions in aqueous medium could underpin exciting new sensing tools for biomedical research and drug discovery. In this direction, we present three mononuclear lanthanide-based complexes, EuLCl3 (1), SmLCl3 (2), and TbLCl3 (3), incorporating a hexadentate aminomethylpiperidine-based nitrogen-rich heterocyclic ligand L for sensing anion and establishing mechanistic insight on their binding activities in aqueous medium. All these complexes are meticulously studied for their preferential selectivities towards different anions such as HPO42−, SO42−, CH3COO−, I−, Br−, Cl−, F−, NO3−, CO32−/HCO3−, and HSO4− at pH 7.4 in aqueous HEPES (2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid) buffer. Among the anions scanned, HPO42− showed an excellent luminescence change with all three complexes. Job’s plot and ESI-MS support the 1:2 association between the receptors and HPO42−. Systematic spectrophotometric titrations of 1–3 against HPO42− demonstrates that the emission intensities of 1 and 2 were enhanced slightly upon the addition of HPO42− in the range 0.01–1 equiv and 0.01–2 equiv., respectively. Among the three complexes, complex 3 showed a steady quenching of luminescence throughout the titration of hydrogen phosphate. The lower and higher detection limits of HPO42− by complexes 1 and 2 were determined as 0.1–4 mM and 0.4–3.2 mM, respectively, while complex 3 covered 0.2–100 μM. This concludes that all complexes demonstrated a high degree of sensitivity and selectivity towards HPO42−.

Conducting polyaniline nanotubes with silver nanoparticles in the separation of thiocyanate from aqueous media

Thiocyanate anions represent serious environmental hazards and the ways for their extraction from ecosystem are sought. In the testing of new adsorbents, polyaniline nanotubes have been utilized as a host polymer in which silver nanoparticles were distributed to produce polyaniline nanotubes/silver nanocomposite. The interaction of thiocyanate anions in aqueous medium with the nanocomposite deposited on the quartz-crystal microbalance was studied. The results indicated that polyaniline nanotubes adsorb thiocyanate anions, and silver nanoparticles are suspected in addition to catalyze the transformation of thiocyanate. The extraction of thiocyanate anions using nanocomposites from the aqueous solution was then monitored with the UV–visible spectroscopy. The effect of different parameters including concentration, adsorbent dose, and pH has been mentioned. The pH effect demonstrated that ion exchange and electrostatic interaction as well as chemisorption mechanisms are involved in the adsorption. The results were fitted into various kinetic models. It was concluded that pseudo-second-order kinetic model best matched the adsorption and the extraction capacity of thiocyanate anions, 112 mg g−1, exceeds the results reported so far in the literature. In addition, the results showed that the separation of SCN− depends on a synergetic effect of interaction and reduction of SCN− with polyaniline nanotubes/silver nanocomposite.

Turn-on fluorescence sensor for selective detection of fluoride ion and its molecular logic gates behavior

Loutonin based emissive probe (L) for the dual sensing of fluoride (F−) and bisulphate (HSO4−) anions in aqueous media. The development is based on reports that the interaction between fluoride and loutonin based fluorescent probe exhibits rapid and remarkable color changes in both colorimetrically as well as fluorimetrically. More amusingly, on the introduction of bisulphate ion into the medium containing loutonin fluoride ion complex (L-F−) which shows both the color and fluorescence has been recovered. The limit of detection for fluoride ions by the probe was determined as 8.62 × 10−7 M by fluorescence titrations. Further the probe L can be employed for the removal of fluoride ions. The need for a dual anion detection system with such an outstanding reversible and reproducible process characteristics led us to consider loutonin as a feasible nominee for the construction of molecular keypad lock and molecular logic circuits. The fluorescence change of loutonin after appendage of fluoride ions is mainly due to the hydrogen bonding interaction. Further, the probe could be potentially incorporated into the test strips and silica gel plates, with better selectivity for fluoride and bisulphate anions in aqueous media.