Aqueous Fluoride Ions Research Articles

Transition metal complexation assisted stabilization of the deprotonated organic moiety: A strategy for colorimetric and electrochemical recognition of fluoride ion in water medium with organic probe molecules

Excess consumption of fluoride through drinking water causes detrimental effects to human health which has been a serious global concern. This situation demands routine monitoring of fluoride in drinking water in fluoride affected regions around the world. A plethora of organic molecules has been demonstrated as chemosensors based on the fluoride induced deprotonation reaction of the probe molecules. However, most of the probe molecules fail to react with fluoride in aqueous medium which limits their application. Herein, we have demonstrated a metal ion, Ni(II) mediated strategy to retain the reactivity and the sensitivity of the probe molecule towards fluoride ion in aqueous medium with the help of two benzothiazole based probe molecules (R and P). Both the probe molecules showed retention of the affinity towards fluoride ion in aqueous medium in presence of Cu2+ ion but the colorimetric response is not upto the mark. On the other hand, the probe molecule P showed excellent affinity and colorimetric response towards aqueous fluoride ion in presence of Ni2+ ion. The methodology is validated with UV–Vis spectroscopy and Differential pulse voltammetry (DPV) technique. Probe molecule P in presence of Ni2+ ion showed limit of detection values 0.60 ppm and 0.57 ppm w.r.t. UV–Visible spectroscopy and DPV technique respectively. Furthermore, the efficiency of the methodology w.r.t. P was tested with real samples collected from the fluoride affected areas of Assam, India and found that the data corroborates well with the results of ion selective electrode. This methodology can provide a new dimension in the development of a low cost method for routine sensing of fluoride ion with organic probe molecules in drinking water for low resource world.

Rocking-Chair Aqueous Fluoride-Ion Batteries Enabled by Hydrogen Bonding Competition.

Aqueous fluoride ion batteries (FIBs) have garnered attention for their high theoretical energy density, yet they are challenged by sluggish fluorination kinetics, active material dissolution, and electrolyte instability. Here, we present a room temperature rocking-chair aqueous FIBs featuring KOAc-KF binary salt electrolytes, enabling concurrent fluorination and defluorination reactions at both cathode and anode electrodes. Experimental and theoretical results reveal that acetate ions in the electrolyte compete with fluoride ions in hydrogen bonding formation, weakening the excessively strong solvation between H2O and F- ions. This results in the suppression of detrimental HF formation and a reduced desolvation energy of F- ions, enhancing the electrochemical reaction kinetics. The bismuth-based cathode exhibits direct conversion in the optimized electrolyte, effectively suppressing the detrimental disproportionation reactions from Bi2+ intermediates. Additionally, zinc anode undergoes a typical fluorination process, forming solid KZnF3 as the electrode product, minimizing the risks of hydrogen evolution. The proposed aqueous FIBs with the optimized electrolyte demonstrate high discharge capacity, long-term cycling stability and excellent rate capabilities.

Electrochemically Induced Conformational Change of Di‐Boronic Acid‐Functionalized Ferrocene for Direct Solid‐State Monitoring of Aqueous Fluoride Ions

AbstractWhile fluoride ions (F−) are abundant across environmental and biological systems, common procedures and potentiometric sensors for quantifying aqueous F− are inefficient, time‐consuming, and suffer from poor pH resiliency and high detection limits. Herein, this work reports a new di‐boronic acid‐functionalized ferrocene (FDBA) molecular receptor for noncovalent F− recognition, toward the development of a solid‐state miniaturized voltammetric fluoride sensor capable of direct and reversible F− detection in drinking water (DW) (pH 6) and community water (pH 7.6–9.1) over the µg L−1–mg L−1 range. The associated sensing mechanism is enabled by the conformational change of FDBA from the open (charge‐repelled) to closed (π‐dimerized) conformation, which is facilitated by the unique linkage of two electron‐accepting phenylboronic acid moieties with the electron‐donating ferrocene moiety using rigid conjugated amide linkers. The square wave voltammetric (SWV) oxidation current response of the FDBA‐based fluoride sensor is spectroscopically investigated, suggesting a combination of electrooxidation‐triggered conformational change of FDBA on a nanocarbon‐modified electrode, F− anion–π interactions, and resulting electron transfer between F− and FDBA. The performance of the voltammetric fluoride sensor is compared to that of a commercial liquid junction‐based fluoride ion‐selective electrode (F‐ISE), and of a solid‐contact (SC) F‐ISE sensor chip, demonstrating significant advantages versus traditional potentiometric F‐ISEs.

Near-Infrared Turn-On Fluorescent Probe for Aqueous Fluoride Ion Detection and Cell Imaging.

Fluoride ions are one of the most essential anions in the human body and have been implicated in various pathological and physiological processes. The detection of fluoride ions in aqueous solution, as well as the imaging of fluoride ions in living cells, remains a challenge. We herein report a BODIPY-based fluorescent probe employing a pinacol borate group as the recognition moiety for the detection of fluoride ions in aqueous solutions. This probe shows high selectivity and sensitivity to fluoride ions with a significant near-infrared fluorescence turn-on response. In addition, this probe was successfully employed in fluorescence bioimaging of fluoride ions in the human cervical cancer cell and mouse mammary cancer cell, demonstrating its good cell permeability and stability under physiological conditions.

Triarylborane-triphenylamine based luminophore for the mitochondria targeted live cell imaging and colorimetric detection of aqueous fluoride.

Bioimaging of subcellular organelles such as mitochondria is crucial for detecting physiological abnormalities induced by fluctuations in the levels of various analytes. Herein, we report the design and synthesis of two novel water-soluble cationic Lewis acid triarylborane-triarylamine conjugates 1 and 2. The optical characteristics of 1 and 2 and their precursor compounds BTPA-NMe2 and BTPA-2NMe2 were evaluated, which show similar absorption and fluorescence spectra, with 1 and 2 exhibiting higher quantum yields of 0.73 and 0.64, respectively, than those of the precursors BTPA-NMe2 and BTPA-2NMe2, indicating the partial disruption of the ICT process and the activation of alternative emission bands in 1 and 2. The live cell imaging ability of compound 2 was examined in HeLa cells using a confocal microscope. Moreover, mitochondrial internalisation using compound 2 was effective and it was found to have high photostability under UV light conditions. Furthermore, compound 2 demonstrated an evident colorimetric response with a colour change to dark yellow in aqueous environments, indicating that it could be used for anion sensing. The spectral changes were observed in UV-visible and fluorescence titration experiments, which were strongly supported by DFT calculations. In short, compound 2 synthesized by us can be exclusively utilized for the selective localization of mitochondria with less cytotoxicity and shows excellent colorimetric response to aqueous inorganic fluoride at levels as low as 0.1 ppm with high selectivity.

Lowest aqueous picomolar fluoride ions and in vivo aluminum toxicity detection by an aluminum(iii) binding chemosensor.

Aluminum toxicity in biological systems is a well-known issue yet remains as a prevalent and unsolvable problem due to the lack of proper molecular tools that can detect free aluminum(iii) or Al(iii) ions in vivo. Herein, we report a water-soluble photo-induced electron transfer (PET)-based turn-ON/OFF fluorometric chemosensor for the dual detection of Al(iii) and fluoride ions in aqueous media with a nanomolar (∼1.7 × 10-9 M) and picomolar (∼2 × 10-12 M, lowest ever detection so far) detection limit, respectively. Fluoride ions in sea water could be detected as well as the recognition of non-contamination in drinking water. In addition, using live-cell microscopy, Al(iii) ions were detected in live biological samples in vivo to aid establishing the aluminum-toxicity effect.

Off/On Amino-Functionalized Polyhedral Oligomeric Silsesquioxane-Perylene Diimides Based Hydrophilic Luminescent Polymer for Aqueous Fluoride Ion Detection.

Fluoride ion detection in water focuses much attention due to the serious healthy impact in human pathologies. For fluoride recognition, the chemical affinity between fluoride and silicon has been developed on the basis of the degradation mechanism. However, most fluorescent probes are the "turn off" type due to the aggregation of the degradational products. Herein, we first developed an "off-on" hydrophilic luminescent polymer composed of amino-functionalized polyhedral oligomeric silsesquioxane (AE-POSS) and perylene diimides (PDIs) for fluoride ion in water. The AE-PDI polymer was "turned off" because of the photoinduced electron transfer (PET) between PDI and AE-POSS, and then after reaction with F-, the fluorescent emission could "turn on" obviously because the PET was blocked by the degradation of the cage. The PET from amino-POSS to PDI was proved by FL spectrum and energies of HOMO and LUMO orbitals. 29Si, 19F NMR, and 1H NMR titration, XRD, FTIR, size analysis, and ion chromatography were applied to demonstrate the degradation mechanism. These results indicated that the higher quantum yield could be obtained by introducing the amide group in the PDI and the products of AE-PDI polymer might exist in the form of complex compounds with partial condensation of organosiloxane. With high selectivity and sensitivity (detection limit of 16.2 ppb), this probe was successfully applied for F- detection in actual water samples.

Low cost, high sensitivity detection of waterborne Al3+ cations and F− anions via the fluorescence response of a morin derivative dye

Morin dye is known as a cheap and readily available selective ‘off → on’ fluorescent sensitiser when immobilised in a phase transfer membrane for the detection of Al3+ ions. Here, a morin derivative, NaMSA, which readily dissolves in water with good long-term stability is used in conjunction with a fibre optic transducer with lock-in detection to detect Al3+ in drinking water below the potability limit. The combination of a water soluble dye and the fibre optic transducer require neither membrane preparation nor a fluorescence spectrometer yet still display a high figure-of- merit. The known ability to recover morin-based Al3+ cation sensors selectively by exposure to fluoride (F−) anions is further developed enabling a complementary sensing of either fluoride anions, or aluminium cations, using the same dye with a sub-micromolar limit-of-detection for both ions. The sensor performance parameters compare favourably to prior reports on both aqueous aluminium and fluoride ion sensing.

Electrochemical sequential reduction and oxidation facilitates the continual ambient temperature degradation of SF6 to nontoxic gaseous compounds

An efficient process for the degradation of the potent greenhouse gas, SF6, into non-toxic gaseous products at ambient temperature is still desirable. In this study, consistently generable homogeneous low/high-valent metal ions were used to degrade SF6 to non-toxic gaseous products at ambient temperature. Two homogenous electron mediators, [Ni(I)(CN)4]3− (Ni(I) low-valent) and AgSO4 or Ag(NO3)2 (Ag(II) high-valent), were generated concurrently using a membrane-divided electrolytic cell and quantified by measuring the ORP (oxidation/reduction potential) variations along with a potentiometric titration. The variation of electrogenerated Ni(I) from 6.3 mM to 4.1 mM and Ag(II) from 4.8 mM to 4.3 mM during the removal of SF6 evidenced their concurrent generation, and SF6 removal followed a mediated electrocatalytic reduction (MER) and mediated electrocatalytic oxidation (MEO) process. FTIR online gas analyzer confirmed that using the MER process only, approximately 92% of the SF6 in a gas mixture containing 5 ppm of SF6 at a 0.2 L min−1 flow rate had decomposed to OF2 (7 ppm), SOF2 (2 ppm), and SO2 (2.9 ppm). At the same time, the MER-treated gas passed into Ag(II) generated anolyte solution resulted in the complete removal of SF6, SOF2, OF2, and SO2 by the MEO process. Also, the absence of fluoride containing gases and SO2 gas in the exit gas from the MEO process and the presence of fluoride ions in the anolyte solution demonstrates the aqueous soluble products fluoride and sulfate ions formation. The possible consistent generation of homogenous electrocatalysts and their combined use in SF6 degradation at ambient temperatures is a practical technology that can be scaled up to a more practical level.

A Metallogel Based on a Zwitterionic Spirocyclic Meisenheimer Complex: Sensing of Fluoride Ions in Water and Moisture Content in Organic Solvents

AbstractDesign and synthesis of stimuli‐responsive materials are highly desired for various practical applications. For this purpose, a picric acid and N,N′‐dicyclohexylcarbodiimide based highly rigid zwitterionic spirocyclic Meisenheimer complex has been applied to produce a metallogel. The Meisenheimer complex does not undergo self‐gelation under any condition. But it forms a stable gel only with Fe3+ ion in a 2:1 ratio in chloroform. Interestingly, the Meisenheimer complex shows bright yellow emission under 366 nm UV light. But the Fe3+ based metallogel does not show any emission under UV irradiation. However, in the presence of fluoride contaminated water, the metallogel surface shows bright yellow emission while checking inside a UV chamber. Thus the non‐fluorescent metallogel was utilized as a sensor of aqueous fluoride ion. The sensor is able to detect aqueous fluoride down to 156 ppb concentration. Like the gel, the dried metallogel solution is also non‐fluorescent in different polar as well as nonpolar organic solvent. But the same solution shows bright yellow emission in the presence of water. The fluorescence intensity was found to increase with an increase in the percentage of water. In this way, the xerogel was utilized as a sensor of undesired water content present in different organic solvents which can detect moisture content with a minimum detection limit of 0.04% for dichloromethane.

An Aqueous Rechargeable Fluoride Ion Battery with Dual Fluoride Electrodes

An anion flow battery has recently emerged as an option to store electricity with high volumetric energy densities. In particular, fluoride ions are attractive for these batteries because they have the smallest size among anions, which is beneficial for charge transport. To date, reported fluoride ion batteries either operate with an ionic liquid, organic electrolyte or solid-state electrolyte at high temperatures. Herein, an aqueous fluoride ion flow battery is proposed that consists of bismuth fluoride as the anode, 4-hydroxy-TEMPO (TEMPO) as the cathode, and NaF salt solution as the aqueous electrolyte. During the charging process, bismuth fluoride electrochemically releases fluoride ions with the formation of bismuth metal, while TEMPO captures the fluoride ions. A reversible and stable discharge capacity of 89.5 mAh g−1 was achieved at 1000 mA g−1 after 85 cycles. The fluoride ion battery possesses excellent rate performance. To the best of our knowledge, this is the earliest demonstration that fluoride ion batteries can work in aqueous solutions, which can be used for future clean energy applications.

A two-photon fluorescent probe for imaging aqueous fluoride ions in living cells and tissues

Fluoride ions are extensively found in aqueous solution, body fluids and tissues, and play an important function in life, so the detection and stable imaging of fluoride ions in living organs is of considerable importance. Herein, we designed and synthesized a new two-photon probe TXS to detect fluoride ions in aqueous solution with turn-on fluorescence. The chemical probe was constructed from tetrahydroxanthenone with a SiO bond to provide excellent selectivity for fluoride ions. Based on the emission properties of tetrahydroxanthenone, two-photon microscopy (TPM) was applied to image fluoride ions in the organs, and the results showed good images in liver tissue at a depth of 60 μm. TPM images of TXS supported a feasible application in biological analyses.

A silica-based SERS chip for rapid and ultrasensitive detection of fluoride ions triggered by a cyclic boronate ester cleavage reaction.

Chemical sensing for the convenient detection of trace aqueous fluoride ions (F-) has been widely explored with the use of various sensing materials and techniques. It still remains a challenge to achieve ultrasensitive but simple, rapid, and inexpensive detection of F- for environmental monitoring and protection. Here we reported a novel surface-enhanced Raman scattering (SERS) nanosensor, fluorescein phenylboronic acid covalently linked to 1,4-dimercapto-2,3-butanediol modified Au@Ag NPs by a cyclic boronate ester (Flu-PBA-Diol-Au@Ag NPs), for the rapid and ultrasensitive detection of F-. Once the Flu-PBA approached the surface of Au@Ag NPs, the Raman signals of Flu-PBA were remarkably enhanced due to the strong SERS effect. However, the presence of F- will induce the cleavage reaction of the cyclic boronate ester into the trifluoroborate anion (3F-Flu-PBA) and diol. The 3F-Flu-PBA molecules exfoliated from the surface of Au@Ag NPs, and the SERS signals of the nanosensor were quenched. Following the sensing mechanism, a silica-based SERS chip has been fabricated by the assembly of Flu-PBA-Diol-Au@Ag NPs on a piece of silicon wafer. The silica-based SERS chips showed high sensitivity for aqueous F-, and the limit of detection (LOD) could reach as low as 0.1 nM. Each test using the SERS chip only needs a droplet of 20 μL sample and is accomplished within ∼10 min. The silica-based SERS chip has also been applied to the quantification of F- in tap water and lake water.

Fluorescence and visual detection of fluoride ions using a photoluminescent graphene oxide paper sensor.

The instant and on-site detection of trace aqueous fluoride ions is still a challenge for environmental monitoring and protection. This work demonstrates a new analytical method and its utility of a paper sensor for visual detection of F(-) on the basis of the fluorescence resonance energy transfer (FRET) between photoluminescent graphene oxide (GO) and silver nanoparticles (AgNPs) through the formation of cyclic esters between phenylborinic acid and diol. The fluorescence of GO was quenched by the AgNPs, and trace F(-) can recover the fluorescence of the quenched photoluminescent GO. The increase in fluorescence intensity is proportional to the concentration of F(-) in the range of 0.05-0.55 nM, along with a limit of detection (LOD) as low as 9.07 pM. Following the sensing mechanism, a paper-based sensor for the visual detection of aqueous F(-) has been successfully developed. The paper sensor showed high sensitivity for aqueous F(-), and the LOD could reach as low as 0.1 μM as observed by the naked eye. The very simple and effective strategy reported here could be extended to the visual detection of a wide range of analytes in the environment by the construction of highly efficient FRET nanoprobes.

The introduction of P–F bonds using aqueous fluoride ion and a water soluble carbodiimide: a convenient alternative synthesis of phosphorofluoridates and phosphonofluoridates

The chemistry of ribonucleotides and other phosphates is extended to include their reactions with potassium fluoride in aqueous solution in the presence of a water soluble carbodiimide. High yields (>98%) of phosphorofluoridates are formed. A combination of HPLC, mass spectrometry, and NMR confirms the identities of the products. The methodology is applied, with equally satisfactory outcomes, to the physiologically active phosphonates Adefovir® and Tenofovir®, providing new compounds. Detailed NMR studies of the new phosphonofluoridates are reported.

The reaction of activated RNA species with aqueous fluoride ion: a convenient synthesis of nucleotide 5′-phosphorofluoridates and a note on the mechanism

The chemistry of 5′-phosphorimidazolides of ribonucleosides is extended to include their reaction with alkali metal fluorides in aqueous solution. High yields of 5′-phosphorofluoridates are formed, especially with potassium fluoride, but no detectable oligomerization products were formed. A combination of HPLC, mass spectrometry, synthesis, kinetics, and NMR confirms the identities of the products. Judicious control of pH leads to higher yields in shorter reaction times. This new methodology contrasts favorably with other synthetic routes involving non-aqueous chemistry or aqueous chemistry with a nucleotide triphosphate.

Highly selective fluoride sensing via chromogenic aggregation of a silyloxy-functionalized tetraphenylethylene (TPE) derivative

A silyloxy-functionalized tetraphenylethylene (TPE) derivative shows a remarkable change in the absorption spectrum on deprotection with fluoride ions. The reaction process is highly selective for fluoride and the resulting charge transfer band results in a bright green solution. A simple selective visual assay of aqueous fluoride ions was also obtained by the impregnation of cellulose strips with the TPE derivative.

Aqueous fluoride ion sensing by a new perylenediimide derivative: Interaction between the hydrated fluoride and the aromatic molecule

Fluoride ions can be detected ultra sensitively and selectively by using a new sensor, γ-butyric acid containing perylenediimide (PDI) in water. EPR studies show the involvement of radical formation during sensing. Density functional theory also supports the electrostatic interaction between hydrated fluoride and the sensor molecule. Fluoride sensing is visible through naked eyes and fluorometrically. Moreover, this sensor can be regenerated by oxidizing the sensor-fluoride complex using NOBF4. This study convincingly demonstrates the complex formation of hydrated fluoride with PDI based sensor molecule in sensing of aqueous fluorides as it is evidenced by MALDI-TOF analysis and computational studies.

Expulsion of Ions from Hydrophobic Hydration Shells

Raman spectroscopy is combined with multivariate curve resolution to quantify interactions between ions and molecular hydrophobic groups in water. The molecular solutes in this study all have similar structures, with a trimethyl hydrophobic domain and a polar or charged headgroup. Our results imply that aqueous sodium and fluoride ions are strongly expelled from the first hydration shells of the hydrophobic (methyl) groups, while iodide ions are found to enter the hydrophobic hydration shell, to an extent that depends on the methyl group partial charge. However, our quantitative estimates of the corresponding ion binding equilibrium constants indicate that the iodide concentration in the first hydrophobic hydration shell is generally lower than that in the surrounding bulk water, and so an iodide ion cannot be viewed as having a true affinity for the molecular hydrophobic interface, but rather is less strongly expelled from such an interface than fluoride.

Interactions between halide anions and a molecular hydrophobic interface

Interactions between halide ions (fluoride and iodide) and t-butyl alcohol (TBA) dissolved in water are probed using a recently developed hydration-shell spectroscopic technique and theoretical cluster and liquid calculations. High ignal-to-noise Raman spectroscopic measurements are combined with multivariate curve resolution (Raman-MCR) to reveal that while there is little interaction between aqueous fluoride ions and TBA, iodide ions break down the tetrahedral hydration-shell structure of TBA and produce a red-shift in its CH stretch frequency, in good agreement with the theoretical effective fragment potential (EFP) molecular dynamics simulations and hybrid quantum/EFP frequency calculations. The results imply that there is a significantly larger probability of finding iodide than fluoride in the first hydration shell of TBA, although the local iodide concentration is apparently not as high as in the surrounding bulk aqueous NaI solution.