Free Fluoride Ions Research Articles

Hydration process and fluoride solidification mechanism of multi-source solid waste-based phosphogypsum cemented paste backfill under CaO modification

The large-scale, environmentally friendly utilization of phosphogypsum (PG) remains a global challenge. PG cemented paste backfill (PCPB) is a promising method to manage PG, but using ordinary Portland cement as the binder has drawbacks such as high cost, low mechanical strength, and high fluoride leaching risk. This paper presents a multi-source solid waste-based PCPB (MPCPB) material that enhances mechanical properties and reduces fluoride leaching risks. In MPCPB, industrial waste residues like steel slag (SS) and ground granulated blast furnace slag (GBFS) are used as precursors (SS: GBFS = 1:2). Additionally, 4–8 wt% CaO (relative to the dry weight of PG) is used as a neutralizing modifier and alkaline activator. The results indicate that an optimal amount of CaO can neutralize the residual acidity of PG, provide sufficient Ca(OH)2 for MPCPB hydration, and react with PG to produce significant amounts of AFt. Furthermore, CaO promotes the geopolymerization reaction between SS and GBFS, generating more calcium silicate hydrate (C-S-H) and calcium aluminate silicate hydrate (C-A-S-H) gels. Fluoride stabilization in MPCPB results from synergistic effects involving hydration reactions, complexation, ionic mobility, rearrangement, and physical adsorption. Notably, CaO enhances the conversion of free fluoride ions into stable compounds like fluorapatite, fluorite (CaF2), [AlF6]3-, and [FeF6]3- complexes. This approach offers a cost-effective, environmentally friendly, and efficient solution to the PG stockpiling challenge.

The Trifluorooxygenate Anion [OF3]-: Spectroscopic Evidence for a Binary, Hypervalent Oxygen Species.

Experimental evidence for hypervalent compounds of second-row elements is still scarce in literature. Here, we present the first report of the long-sought binary hypervalent trifluorooxygenate anion [OF3]-. It was isolated in solid Ne matrices under cryogenic conditions after reacting oxygen difluoride with free fluoride ions from laser ablation of alkali metal fluorides MF (M = Li-Cs). As predicted by VSEPR theory and calculations at the CCSD(T) level, and confirmed by FTIR spectroscopy as well as isotopic labeling, [OF3]- exhibits a C2v-symmetric T-shaped structure with one short and two long O-F bond distances. Analysis of the natural local molecular orbitals shows the presence of 2c-2e bond and one 3c-4e bond. Natural resonance theory indicates the importance of the stability of [OF2]•- for the stability of [OF3]-. Although free [OF2]•- was not detected, the species MOF2 (M = Na-Cs) could be observed in the same experiments, which are best described as contact ion pairs of M+[OF2]•-.

The Trifluorooxygenate Anion [OF3]−: Spectroscopic Evidence for a Binary, Hypervalent Oxygen Species

Experimental evidence for hypervalent compounds of second‐row elements is still scarce in literature. Here, we present the first report of the long‐sought binary hypervalent trifluorooxygenate anion [OF3]−. It was isolated in solid Ne matrices under cryogenic conditions after reacting oxygen difluoride with free fluoride ions from laser ablation of alkali metal fluorides MF (M = Li–Cs). As predicted by VSEPR theory and calculations at the CCSD(T) level, and confirmed by FTIR spectroscopy as well as isotopic labeling, [OF3]− exhibits a C2v‐symmetric T‐shaped structure with one short and two long O‐F bond distances. Analysis of the natural local molecular orbitals shows the presence of 2c‐2e bond and one 3c‐4e bond. Natural resonance theory indicates the importance of the stability of [OF2]•− for the stability of [OF3]−. Although free [OF2]•− was not detected, the species MOF2 (M = Na–Cs) could be observed in the same experiments, which are best described as contact ion pairs of M+[OF2]•−.

Measurements of fluoride production in Resistive Plate Chambers

Resistive Plate Chambers (RPCs) are operated with a gas mixture made of C2H2F4, SF6 and iC4H10. It is well known that under the effect of a high electric field and radiation, the C2H2F4 molecule breaks into several compounds and free fluoride ions, which can accumulate under gas recirculation and could be harmful for the long-term detector operation. Furthermore, if High Pressure Laminate (HPL) electrodes are employed, the gas mixture is humidified and, in presence of water, the free fluoride ions become hydrofluoric acid (HF), a very reactive compound. The F− production depends on several factors such as radiation rate, gas flow, detector current and gas mixture. In this study we developed and tested two different set-ups for the F− concentration measurements by using an Ion Selective Electrode (ISE) station. The measurement on the F− production were performed on 2 mm gas gap bakelite RPC detector irradiated at the CERN Gamma Irradiation Facility (GIF++) with different absorption factors. Several gas mixtures were tested to understand how the formation of HF is affected. The F− production of the standard gas mixture was compared with the one of the standard gas mixture with the addition of 30% CO2 at several gamma rates. Different concentrations of SF6 were also investigated to understand if and how the SF6 could affect the F− production. Finally, two gas mixtures containing HFO1234ze, C2H2F4 and He or CO2 were used to study the RPC F− production in presence of the HFO1234ze, which is less stable in atmosphere with respect to the C2H2F4.

An Analytical Protocol for the Differentiation and the Potentiometric Determination of Fluorine-Containing Fractions in Bovine Milk.

Free fluoride ions are effective in combating caries in children, and their supplementation in milk has been widely used worldwide for this purpose. Furthermore, it is known that ionic fluoride added to milk is distributed among its components, but little is known about their quantitative relationships. This is likely due to the absence of an analytical protocol aimed at differentiating and quantifying the most important forms of fluorine present in milk. For the first time, a comprehensive protocol made up of six potentiometric methods devoted to quantifying the most important fractions of fluorine in milk (i.e., the free inorganic fluoride, the inorganic bonded fluorine, the caseins-bonded fluorine, the whey-bonded fluorine, the lipid-bonded fluorine, and the total fluorine) has been developed and tested on real samples. Four of the six methods of the procedure are original, and all have been validated in terms of limit of detection and quantification, precision, and trueness. The data obtained show that 9% of all fluorine was in ionic form, while 66.3% of total fluorine was bound to proteins and lipids, therefore unavailable for human absorption. Beyond applications in dental research, this protocol could be extended also to other foods, or used in environmental monitoring.

Biodefluorination of Perfluorooctanesulphonate by Ensifer adhaerens M1

A strain of bacteria M1, defluorinating perfluorooctanesulfonic acid (PFOS), was isolated from soil taken from the territory for testing fire extinguishing agents. The analysis of cultural, morphological, physiological and biochemical characters, the 16S rRNA gene sequencing allowed us to identify strain M1 as Ensifer adhaerens. The uniquely skill of the isolated strain to utilize PFOS in a mineral liquid medium for 5 days of cultivation was shown. It was found that E. adhaerens M1 transforms perfluorooctanesulfonic acid into perfluoroheptanoic acid, releasing 152 mg/L of free fluoride ions from 1,000 mg/L of PFOS. The data obtained allow us to recommend E. adhaerens M1 as potential treatment agent of the environment from organofluorine compounds.

Ion Concentration of Silver Diamine Fluoride Solutions

ObjectiveThe aim of this work was to determine the free fluoride and silver ion concentrations and the alkalinity of 4 commercially available 38% silver diamine fluoride (SDF) solutions. MethodsFour common brands of 38% SDF solutions, namely Saforide, Advantage Arrest, e-SDF, and Topamine, were selected. Three bottles of each brand of SDF solution from the same lot were assessed. Measurements of the silver and fluoride content and alkalinity were performed directly when a bottle was opened. Each measurement was repeated to recheck its reliability. The free fluoride ion concentrations were measured using a calibrated ion-selective electrode. The free silver ion concentrations were measured using optical emission spectrometry. The alkalinity of the SDF solution was determined with a pH electrode. ResultsThe mean concentrations of fluoride ions of the Saforide, Advantage Arrest, e-SDF, and Topamine were 43,233 ppm, 44,333 ppm, 51,370 ppm, and 54,400 ppm, respectively; their percentage differences from the expected value (44,800 ppm) were 3.5%, 2.4%, 14.7%, and 21.4%, respectively. The mean concentrations of silver ions of the Saforide, Advantage Arrest, e-SDF, and Topamine were 258,841 ppm, 260,016 ppm, 336,149 ppm, and 319,966 ppm, respectively; their percentage differences from the expected value (253,900 ppm) were 3.2%, 5.8%, 32.4%, and 25.9%, respectively. The 4 products had pH values of 9.2, 9.1, 9.2, and 9.0, respectively. ConclusionsThis study showed differences between the claimed and measured fluoride and silver ion concentrations in 4 common 38% SDF products, which were alkaline with a pH value of 9.

Fluoride and calcium release from peppermint-flavored fluoride varnish containing dicalcium-phosphate-dihydrate coated with xylitol

Bakground: Fluoride varnish with high initial fluoride and calcium release can help patients with high-risk caries. Ample quantities of free fluoride and calcium ions in the oral cavity can enhance enamel remineralization. This study aimed to investigate the effect of dicalcium phosphate dihydrate coated with xylitol (DCPD-xylitol), in fluoride varnish, on the release of fluoride and calcium ions in the oral cavity. Materials and methodsDCPD powder with xylitol was synthesized by preparing a 60% xylitol solution and mixed it with DCPD solution. The mixture was stirred for 1 h at room temperature and dried at 80 °C for 18 h to reduce the water content. Then, the powder was used in the formulation of peppermint-flavored fluoride varnish as an active agent. The amounts of fluoride and calcium ion released in deionized water at 37 °C for 6 h were assessed with an ion-selective electrode. The cumulative fluoride and calcium ion release data were analyzed using one-way analysis of variance (ANOVA) and the post hoc Tukey test with α = 0.05. ResultsThe results showed that the addition of DCPD coated with xylitol provided better bioavailability of the ions than DCPD without coating. Peppermint-flavored fluoride varnish (PFFV) with DCPD-xylitol 1% gave the highest fluoride ion release (296.90 mg/L) compared to the varnishes with other xylitol concentrations and the positive control. In contrast, PFFV DCPD-xylitol 5% afforded the highest calcium ion release at 111.20 mg/L. ConclusionsThis study concluded that xylitol affects the bioavailability of free fluoride and calcium ions in varnishes. However, the efficacy of fluoride and calcium uptake in enamel and under different in vitro media conditions requires further investigation.

Gas mixture quality studies for the CMS RPC detectors during LHC Run 2

Resistive Plate Chamber (RPC) detectors are widely employed in the muon trigger systems of three experiments at the CERN Large Hadron Collider (LHC). They are operated with gas mixture recirculation systems to reduce operational costs and greenhouse gas emissions since their gas mixture is based on C2H2F4, which has a high global warning potential. It is well known that the C2H2F4 molecule can break down under the effect of radiation and electric field. This leads to the creation of several impurities and free fluoride ions (F-), which could accumulate under gas recirculation and potentially attach to the RPC bakelite electrode inner surface. For these reasons, an extensive gas analysis campaign has been performed during LHC Run 2 for the CMS RPC system to verify gas mixture quality and possible accumulation of impurities.During the entire LHC Run 2 period, a gas chromatograph has been used to analyze the RPC gas mixture at different points of the gas system: quality of pure C2H2F4, fresh gas from the mixer, gas at the output of the detectors, and after the purifier module. Several impurities have been found and identified. Few impurities are already present in the C2H2F4 supply, as residuals of the industrial production. Nevertheless, it was found that some of these impurities, as well as others, are created inside the detector gas gap due to the fragmentation of the C2H2F4 molecule under the effects of electric field and radiation.During the 2018 LHC Run several gas analysis points were added to measure the fluoride ions production in different sectors of the RPC detector system. Indeed the products of the C2H2F4 fragmentation do not always recombine and F- species can stay free in the gas mixture. F- analyses were performed on the gas at the output of the detectors both for barrel and endcap regions, where radiation levels and operational conditions were different. In this way, it was possible to correlate the F- production with integrated charge, and gas mixture flow rate. In parallel, the RPC currents have been constantly monitored to look for possible correlations.Fluoride measurements have also been performed at GIF++ to better understand the correlation between F- production, radiation levels and gas volume exchanges.A comprehensive overview of the results obtained from the different types of gas analyses and possible correlation with RPC currents and LHC luminosity will be presented.

Evaluation of free and total fluoride concentration in mouthwashes via measurement with ion-selective electrode

BackgroundThe aim of this study was to compare free fluoride concentration and total fluoride concentration in mouthwashes.MethodsFluorine-containing mouthwashes from various companies and manufacturers (Colgate Total Plax Classic Mint®, Colgate-Palmolive, New York, USA; Colgate Total Plax Gentle Mint®, Colgate-Palmolive, New York, USA; Colgate Total Plax Fresh Mint®, Colgate-Palmolive, New York, USA; Oral B Advantage®, Procter&Gamble, Cincinnati, USA; Reach Fresh Mint®, Johnson&Johnson, New Brunswick, USA; Foramen®, Laboratorios Foramen, Guarnizo, Spain; Lacalut Sensitive®, Dr. THEISS, Homburg, Germany; Sensodyne®, GlaxoSmithKline, London, UK; Vesna F®, Vita, Saint Petersburg, Russia; Lacalut Fresh®, Dr. THEISS, Homburg, Germany) were selected as study objects. Fluoride measurements were carried out using the fluoride selective electrode.ResultsFree fluoride:total fluoride ratio was more than 80% for six samples (Colgate Total Plax Gentle Mint® - 88%, Colgate Total Plax Fresh Mint® - 99%, Oral B Advantage® - 92%, Reach Fresh Mint® - 92 and 89% for the mouthwash of another batch, Lacalut Sensitive® - 94%) and less than 63% for three samples (Colgate Total Plax Classic Mint® - 56%, Foramen® - 62%, Vesna F® - 61%). Two samples had more than 70% and less than 80% of unbound fluoride, respectively (Sensodyne® - 77%, another batch of Oral B Advantage® mouthwash - 74%). Rinse containing sodium monofluorophosphate (Na2PO3F) (Vesna F®) had more than 50% of free fluoride, while the rinse containing amine fluoride (AmF) (Lacalut Sensitive®) had 94%. The difference in the free fluoride:total fluoride ratio can be explained by binding of fluoride ions by components contained in mouthwashes, such as coloring agents and polymeric compounds. The lowest concentration of free fluoride ions (0.000093 mol/L) was observed for aluminum fluoride (AlF3) rinse (Lacalut Fresh®), while the total fluoride amount was not determined due to possible generation of strong fluoride complexes. This implies that fluoride ions will not be uptaken by tooth tissue and may even be washed away from it, compromising the efficacy of mouthwashes.ConclusionsThe differences in free fluoride: total fluoride ratio between analyzed mouthwashes reveal a need to develop a method for evaluation of free fluorides in mouthwashes for proper updating of national and international guidelines.

The role of fluoroaluminate complexes on the adsorption of fluoride onto hydrous alumina in aqueous solutions

Activated alumina (AA) has been extensively applied in the defluorination of industrial wastewaters and groundwater. Although the dissolution of AA due to formation of fluoroaluminate complexes (AlFx3−x), especially in acidic condition, has been observed, its role on fluoride uptake by alumina has not been discussed in any previous literature, most of which consider F− as the sole adsorbed species. The present study described the effect of fluoroaluminate complexes on fluoride adsorption onto alumina. Results indicated that fluoroaluminate complexes, major fluoride species at pH < 6, were responsible for total fluoride adsorbed. Free fluoride ions were adsorbed mainly in the alkaline pH region, e.g., pH > 6. The dissolution of AA during defluorination was measured and analyzed by the thermodynamic solubility model. The surface concentration of F− and AlFx3−x were calculated considering electrostatic interactions. Characterization of fluoride-laden AA by XPS revealed that the fraction of surface Al-F species decreased with pH, which suggested the transition of the surface fluorinated species to that of free fluoride ions. The stability constants of four surface complexes, namely, AlOH-FAl2+, AlOH-F2Al+, AlOH2+-F− and AlOH-F−, were 106.88, 105.36, 102.72 and 102.36, respectively. Obviously fluoroaluminate complexes exhibited stronger chemical bonds with the surface hydroxy species than free fluoride.

Monitoring Fluorine in Metallurgical Fuel

The environmental impact of metallurgical fuel, which includes various types of mineral fuel (such as coke, coal, lignite, peat, fuel shales, and their derivatives) is a continuing concern. In the combustion of metallurgical fuel, harmful materials (chlorine, fluorine, sulfur, and arsenic) are released, with consequent environmental degradation. Safety regulations regarding coal production include restrictions on the content of harmful impurities and their limiting permissible concentrations. On account of the broad distribution of fluorine in nature and industry, it is of special importance to monitor the fluorine content in metallurgical fuel. Physical methods based on the excitation of various radiation spectra permit determination of the fluorine content, without decomposition of the initial solid sample. However, such methods have problems in terms of sensitivity, precision, and the complexity of the equipment required. In the ion-chromatographic, ionometric, and other methods, the samples are broken down, and the fluorine content is determined in solution. Usually, high-temperature processes are used for decomposition of the samples: pyrohydrolysis, combustion in oxygen and in a calorimetric bomb, and alkaline fusion. In the present work, a selective method is developed for the ionometric determination of fluorine, by means of a fluorine-selective electrode. Samples of lignite, gas coal, semicoke, and coke nuts are investigated. The samples may effectively be decomposed by two-stage high-temperature melting with KNCO3. Fluorine is transferred to solution in the form of free fluoride ions by means of hydrolytic codeposition of interfering cations with chloride iron(II). The analytical procedure is described. It consists of decomposition of the sample and the ionometric determination of fluorine. The precision and truness of the proposed method is verified by variation in the sample size. In the samples considered, the fluorine content is within the limits typical of commercial coal. That indicates that the use of the samples in fuel is environmentally acceptable. The proposed method is promising for the monitoring of fluorine impurity in metallurgical fuel. It is selective and simple to use.

Trifluoromethyl group containing C3 symmetric coumarin-triazole based fluorometric tripodal receptors for selective fluoride ion recognition: A theoretical and experimental approach

A series of unique C3 symmetric tripodal receptors, A–E containing hexasubstituted aryl core decorated with an alternate array of coumarin-triazole moieties and methyl groups have been synthesized, characterized and investigated for fluoride ion recognition (tetrabutylammonium salt) in dimethyl sulphoxide (DMSO). A pleothora of spectroscopic studies (fluorescence, UV–vis, 1H NMR and 19F NMR titrations) exhibits that out of the five derivatives synthesized, only one, receptor D displays selective five fold fluorescence enhancement with fluoride ion (TBA salt) at 480 nm wavelength over other anions at a detection limit of 2.6 × 10−5 M. Selectivity may be ascribed to strategical incorporation of trifluoromethyl group in the scaffold of receptor D which modulated the binding ability of the receptor, so that it is able to bind fluoride ion exclusively and selectively in preorganized C3 symmetric cavity formed by its three arms. 1H NMR and 19F NMR titration validate CH⋯F- hydrogen binding interactions via downfield shift of CH peak at δ 8.47 ppm by δ 0.5 ppm and upfield shift of peak at δ −102 ppm due to free fluoride ion 2.98 ppm, respectively. Further, HRMS study of receptor-fluoride complex gave evidence for the formation of 1:1 stoichiometric ratio between receptor and fluoride ion. Computations using density functional theory have shown that in 1:1 complex of receptor and fluoride ion, the three arms are directed in same orientation forming a cavity where it fits fluoride ion by CH⋯F- hydrogen binding interactions.

Sevoflurane for procedural sedation in critically ill patients: A pharmacokinetic comparative study between burn and non-burn patients

BackgroundSevoflurane has anti-inflammatory proprieties and short lasting effects making it of interest for procedural sedation in critically ill patients. We evaluated the pharmacokinetics of sevoflurane and metabolites in severely ill burn patients and controls. The secondary objective was to assess potential kidney injury. MethodsProspective interventional study in a burn and a surgical intensive care unit; 24 mechanically ventilated critically ill patients (12 burns, 12 controls) were included. The sevoflurane was administered with an expired fraction target of 2% during short-term procedural sedation. Plasma concentrations of sevoflurane, hexafluoroisopropanolol (HFIP) and free fluoride ions were recorded at different times. Kinetic Pro (Wgroupe, France) was used for pharmacokinetic analysis. Kidney injury was assessed with neutrophil gelatinase-associated lipocalin (NGAL). ResultsThe mean total burn surface area was 36±11%. The average plasma concentration of sevoflurane was 70.4±37.5mg·L−1 in burns and 57.2±28.1mg·L−1 in controls at the end of the procedure (P=0.58). The volume of distribution was higher (46.8±7.2 vs 22.2±2.50L, P<0.001), and the drug half-life longer in burns (1.19±0.28h vs 0.65±0.04h, P<0.0001). Free metabolite HFIP was higher in burns. Plasma fluoride was not different between burns and controls. NGAL did not rise after procedures. ConclusionWe observed an increased volume of distribution, slower elimination rate, and altered metabolism of sevoflurane in burn patients compared to controls. Repeated use for procedural sedation in burn patients needs further evaluation. No renal toxicity was detected. Trial registry numberClinicalTrials.gov Identifier NCT02048683.

A novel UV-photolysis approach with acetone and isopropyl alcohol for the rapid determination of fluoride in organofluorine-containing drugs by spectrophotometry

A UV photolysis decomposition (UVPD) method for the determination of fluoride in fluorine containing pharmaceuticals by spectrophotometry is reported. It is based on the use of high intensity UV-irradiation in the presence of a digesting solution comprising a mixture of acetone and isopropanol. For the optimization of the UVPD procedure, three bulk drugs (levofloxacin, nebivolol and efavirenz) were chosen as representatives of three diverse compounds containing a single fluorine atom, two fluorine atoms, and trifluoromethyl groups respectively. Operational conditions of the UVPD method, such as concentration and volume of reagents (acetone and isopropyl alcohol), and UV irradiation time (1–6 minutes) were optimized. The efficiency of digestion was evaluated by the determination of fluoride in sample digests. Using the developed method, it was possible for complete conversion of the organofluoride to free fluoride ion for its subsequent determination by spectrophotometry based on bleaching of Zr–xylenol orange-color complex. Quantitative recovery (>98%) of the fluorine in the drug samples could be achieved using a mixture of 2% acetone + 2% isopropyl alcohol + 0.003% Na2CO3 in just 5 minutes of UV irradiation, which can be considered an important aspect considering the difficulties involved in the cleavage of the CF bond. Accuracy was evaluated by comparison of results obtained by the UVPD method with the values estimated using formula weight of the compound and no statistical difference was observed between the results. Therefore, the proposed method is suitable for application in routine analysis of fluoride in organofluorine-containing drugs.

Pentavalent tantalum reduction mechanism from 1-butyl-3-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid

In this paper, we report and discuss the reduction mechanism of pentavalent tantalum salt (TaF5) in a room temperature ionic liquid (RTIL) by coupling two complementary electrochemical techniques: the cyclic voltammetry and the electrochemical quartz crystal microbalance (EQCM). The experiments were performed in the hydrophobic 1-butyl-3-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide ([BMPyr][TFSI]) RTIL used both as a solvent and as an electrolyte. Four different reduction peaks are present in the obtained voltammogram in the range from 0V (vs Pt-Fc/Fc+) to −3.5V (vs Pt-Fc/Fc+). The existence of the first reduction peak depends mainly on the nature of the substrate of the working electrode and is therefore not related to the reduction of the tantalum salt. The second reduction peak is ascribed to the direct tantalum salt reduction to its metallic state. During this reduction, free fluoride ions are produced in the electrolyte in the vicinity of the electrode surface. These ions can then react with diffusing TaF5 to form TaF5+x−x complexes and thus the reduction peaks occurring at lower potential are referred to the reduction of such complexes. This hypothesis was confirmed by addition of LiF in the electrolyte.

Free fluoride determination in honey by ion-specific electrode potentiometry: Method assessment, validation and application to real unifloral samples

Surprisingly, a reliable method for measuring the concentration of free fluoride ions in honey is still missing from the literature, notwithstanding the generally recognized importance of the analyte and the matrix. To fill this gap, this study proposes and validates a straightforward ion-specific electrode potentiometric method for this task. The method offers very low detection and quantification limits (6.7μgkg−1 and 25μgkg−1, respectively), good linearity (R2>0.994), good sensitivity (typically 55±3mV for an order of magnitude of concentration) in an unusually low concentration interval (between 0.020 and 1mgL−1), and acceptable precision and bias. The method was applied to 30 unifloral (thistle, eucalyptus and strawberry tree) honey samples from Sardinia, Italy. The amount of free fluoride ions found in these honeys appears to be lower than the range usually found in the literature; indeed, early results suggest a possible dependence of the analyte concentration on the honey’s botanical origin.

Tuning electropolymerization of boronate-substituted anilines: Fluoride-free synthesis of the advanced affinity transducer

Boronate-substituted polyanilines are able to serve as advanced affinity transducers if synthesized at their highest conductivity and remind properties (particularly, cyclic voltammograms in acidic media) of common conductive polyaniline. This presumes growing conditions, when the substituent promotes electrophilic substitution in para-position relatively amino-group. Thus electropolymerization of 3-aminophenylboronic acid (3-APBA) requires free fluoride ions to convert boronic acid residue to trifluoroborate serving as electron donor. On the contrary, when in ortho-position to amino-group, boronic acid does not hamper the polyaniline-type growth, but its conversion to trifluoroborate inhibits the polymerization. Accordingly, optimal media for electropolymerization of 2-aminobenzeneboronic acid (2-APBA) are strong acidic solutions similar to unsubstituted aniline. Conducting polyaniline-type polymers synthesized from both isomers generate an increase in their conductivity as a response to polyols (saccharides and hydroxy acids) according to the mechanism of self-doping by freezing negative charges in ring substituents upon complexation. This comprises the novel detection principle for reagentless affinity sensors, allowing to discriminate the specific affinity interactions from non-specific bindings.

Crystal structure of bis-(propane-1,3-di-ammonium) hexa-fluorido-aluminate fluoride trihydrate.

The title compound, (C3H10N2)2[AlF6]F·3H2O, was obtained using the solvothermal method with aluminium hydroxide, HF and propane-1,3-di­amine as precursors in ethanol as solvent. The structure consists of isolated [AlF6]3− octa­hedra, diprotonated propane-1,3-di­amine cations [(H2dap)2+], free fluoride ions and water mol­ecules of solvation. The Al—F bond lengths in the octa­hedral [AlF6]3− anions range from 1.7690 (19) to 1.8130 (19) Å, with an average value of 1.794 Å. Each [AlF6]3− anion is surrounded by three water mol­ecules and by six diprotonated amine cations. The ‘free’ fluoride ion is hydrogen bonded to four H atoms belonging to four dications and has a distorted tetra­hedral geometry. The three water mol­ecules are connected by hydrogen bonds, forming trimers that connect the AlF6 octa­hedra and dications into a three-dimensional framework.

Fluoride Ion Sensing and Caging by a Preformed Molecular D4R Zinc Phosphate Heterocubane

Double-4-ring (D4R) zinc phosphate [Zn(dipp)(DMSO)]4 (1, dipp = 2,6-di-iso-propylphenylphosphate, DMSO = dimethyl sulfoxide), on treatment with a free fluoride ion source, exhibited ability to sense and capture fluoride ions from a variety of sources, as evidenced by extensive solution (31)P and (19)F NMR spectral titration studies. The fluoride ion-encapsulated cage [(n)Bu4N][F@{Zn(dipp)(DMSO)}4] (2) was isolated in good yield from an equimolar reaction between 1 and (n)Bu4NF in methanol and characterized by analytical and spectroscopic methods. When 1-methyl-4,4'-bipyridin-1-ium fluoride (MeQ-F) was used as the fluoride ion source a zwitterionic cage [F@{Zn4(dipp)4(MeQ)(DMSO)3}] (3) was isolated. Crystal structure determination for 3 confirmed not only fluoride incorporation inside the D4R cage but also a weak interaction of the central fluoride ion with all four zinc centers of the cubane, resulting in a trigonal bipyramidal geometry around the zinc centers. To establish the selectivity, cubane 1 was treated with 2 equiv of MeQ-X (X = various anions) under similar conditions to isolate [F@{Zn4(dipp)4(MeQ)2(MeOH)2}][X] (X = I 4; BF4 5; PF6 6) in good yields. The crystal structure determination of 4 and 5 showed that the iodide and tetrafluoroborate anions are found outside the cage while fluoride ion has entered the cavity. The final fluoride encapsulated D4R cage is anionic in 2, neutral in 3, and cationic in 4-6, showing the versatility of the cubane framework to stabilize fluoride ions in all three forms. NMR titrations showed that 1 can sense even 1 ppm level of fluoride ions and sequester them from fluoridated water and toothpaste extract.