Fluoride Source Research Articles

18 F]Ethenesulfonyl Fluoride as a Practical Radiofluoride Relay Reagent.

Fluorine-18 is the most utilized radioisotope in positron emission tomography (PET), but the wide application of fluorine-18 radiopharmaceuticals is hindered by its challenging labelling conditions. As such, many potentially important radiotracers remain underutilized. Herein, we describe the use of [18 F]ethenesulfonyl fluoride (ESF) as a novel radiofluoride relay reagent that allows radiofluorination reactions to be performed in minimally equipped satellite nuclear medicine centres. [18 F]ESF has a simple and reliable production route and can be stored on inert cartridges. The cartridges can then be shipped remotely and the trapped [18 F]ESF can be liberated by simple solvent elution. We have tested 18 radiolabelling precursors, inclusive of model and clinically used structures, and most precursors have demonstrated comparable radiofluorination efficiencies to those obtained using a conventionally dried [18 F]fluoride source.

Catalytic, Enantioselective 1,2-Difluorination of Cinnamamides.

The enantio- and diastereoselective synthesis of 1,2-difluorides via chiral aryl iodide-catalyzed difluorination of cinnamamides is reported. The method uses HF-pyridine as a fluoride source and mCPBA as a stoichiometric oxidant to turn over catalyst, and affords compounds containing vicinal, fluoride-bearing stereocenters. Selectivity for 1,2-difluorination versus a rearrangement pathway resulting in 1,1-difluorination is enforced through anchimeric assistance from a N- tert-butyl amide substituent.

Importance of the Mixing and High-Temperature Heating Steps in the Controlled Thermal Coprecipitation Synthesis of Sub-5-nm Na(Gd–Yb)F4:Tm

In order to achieve a significant size reduction to get ultrasmall upconverting nanoparticles (UCNPs) following a thermal coprecipitation pathway, we identified two critical points: the UCNP precursor mixing and high-temperature heating steps. Significant differences could be observed according to the way the inorganic sodium and fluoride sources were mixed to the rare-earth oleate before the high-temperature heating step. More interestingly, accurate monitoring of the high-temperature heating step using microwave (MW) dielectric heating yielded major improvement toward ultrasmall UCNPs. Thus, hexagonal, Tm-doped sub-5-nm UCNPs with an unusual Na(Yb-Gd)F4 matrix with 53% Yb were produced, displaying satisfactory luminescence. Noticeably, MW heating was achieved in a weakly MW-absorbing oleic acid (OA)/octadecene mixture, and the influence of the OA content composition on the MW heating efficiency is discussed in this report.

Effect of flouride on preparation and pervaporation performance of NaY zeolite membrane for EtOH/ETBE mixture

Good separation performance NaY zeolite membrane was successfully prepared on the tubular mullite support by fluoride-containing precursor synthesis gel. The fluoride source had a great influence on NaY zeolite membrane growth and separation performance for EtOH/ETBE mixture, the NaF containing precursor gel was benefit for preparing high Si/Al ratio, fine reproduction quality and long-term stable NaY zeolite membrane. Solid state 19F MAS NMR characterization results indicated that the fluorine existed in the channel of NaY zeolite crystals. Both flux and separation factor of the NaY zeolite membrane were greatly depended on the separation temperature and composition of EtOH/ETBE mixtures. The NaY zeolite membrane presented eminent long-term stability for separating 20 wt% EtOH/ETBE mixture at 60 °C, even if the test time was prolonged to 80 h, the flux and separation factor were kept 1.30 kg m−2 h−1 and 1100.

Straightforward and Relatively Safe Process for the Fluoride Exchange of Trivalent and Tetravalent Group 13 and 14 Phthalocyanines.

To avoid the use of hydrofluoric acid, a series of fluorinated trivalent and tetravalent metal-containing phthalocyanines (MPcs) were synthesized using a straightforward one-step halide substitution process using cesium fluoride (CsF) as the fluoride source and by reflux in N,N-dimethylformamide for less than an hour. The resulting fluoro MPcs were characterized and compared to the parent chloro MPcs. In some cases, very little change in properties was observed between the fluoro MPcs and the chloro MPcs. In other cases, such as fluoro aluminum phthalocyanine, a blue shift in the absorbance characteristics and an increase in oxidation and reduction potential of as much as 0.22 V was observed compared to the chloro derivative. Thermo gravimetric analysis was performed on all halo-MPcs, indicating that the choice of halo substitution on the axial position can have an effect on the decomposition or sublimation temperature of the final compound. After initial establishment and characterization of the fluoro MPcs, the halide substitution reaction of difluoro silicon phthalocyanine (F2-SiPc) was further explored by scaling the reaction up to a gram scale as well as considering tetrabutylammonium fluoride (TBAF) as an additional safe fluoride source. The scaled-up reactions producing F2-SiPc using CsF and TBAF as fluoride exchange sources were successfully reproducible, resulting in reaction yields of 100 and 73%, respectively. Both processes led to pure final products but results indicate that CsF, as the fluoride exchange reagent, appears to be the superior reaction process as it has a much higher yield.

Distribution, health risk assessment, and anthropogenic sources of fluoride in farmland soils in phosphate industrial area, southwest China

The high concentration of fluoride (F) in soils has become a rising concern for its toxicity to microbes, plants, animals and human health. In the present study, the spatial and vertical distribution, health risk assessment and anthropogenic sources of F in farmland soils in an industrial area dominated by phosphate chemical plants were studied. Concentrations of total fluoride (TF) and water soluble fluoride (WSF) in the surface soils decreased with distance within the range of 2500 m at the prevailing downwind of the industrial area. The soil TF and WSF concentrations in 0–40 cm profiles were higher than those in 40–100 cm layers in the industrial area. At the prevailing downwind of the industrial area within 700 m, the hazard quotient values of human exposure to surface soils were higher than 1, indicating that a potential risk may exist for human health in this area. The main exposure pathway for children and adults was oral ingestion and particulate inhalation, respectively. The source apportionment model of soil F was modified based on years’ historical data and experimental data. The results showed that the proportion of anthropogenic sources of soil F was dustfalls (69%) > irrigation water (23%) > air (5%) > chemical fertilizers (3%) in the industrial area. The high F concentration of dustfalls was mainly due to the phosphate rock, phosphogypsum, and surface soils with high F contents from the factories. In order to safeguard human health and alleviate hazards of F to surroundings, the control of pollutants emission from factories was a basic and vital step to reduce F in the soils in industrial areas.

Comparative Evaluation of the Fluoride Recharge Ability of Two Glass Ionomers Obtained from Fluoridated Dentifrice and CPP-ACFP Paste: An In-vitro Study

Introduction: Glass ionomer cement (GIC) is a restorative material used in pediatric dentistry, which attaches to dental hard tissues and has cariostatic properties due to the ability for fluoride release. The present study aimed to assess the fluoride release and uptake capacity of two GICs in the presence of various fluoride sources. Methods: This in-vitro study was conducted on 120 disks composed of two GICs (Fuji II LC, Equia Forte System), which were prepared with the exact dimensions of 5×2 millimeters. Fluoride release ability of the samples was determined every 24 hours for seven days and weekly (days 7-21) using a combination of ion selective electrodes. The samples in each group were divided into three subgroups and subjected to no fluoride treatment, fluoridated dentifrice (once a day for one minute), and MI Paste Plus (once a day for one minute). After recharging the samples for seven days, the level of fluoride release was measured on days 1-7, 14, and 21. Results: The results of one-way analysis of variance indicated that the fluoride release ability of Fuji II was higher compared to that of EQUIA Forte (P<0.001). In addition, fluoridated dentifrice could recharge both the glass ionomers more significantly than the MI Paste Plus. Conclusion: According to the results, light-cured, resin-reinforced glass ionomers could release significantly higher levels of fluoride compared to EQUIA Forte. Moreover, the fluoride rerelease was higher by the GICs when recharged with fluoridated dentifrice compared to the MI Paste Plus.

The use of fluoride for the prevention of dental erosion and erosive tooth wear in children and adolescents.

Erosive tooth wear (ETW) has gained increasing clinical relevance. It is estimated that worldwide 30-50% of deciduous and 20-45% of permanent teeth are affected. One of the most important nutritional factors causing ETW is the overconsumption of soft drinks, but also patient-related factors like reflux or eating disorders can lead to erosive lesions. Whether acids lead to erosive demineralisation depends on their degree of saturation with respect to tooth mineral at their actual pH. Fluoride compounds like sodium or amine fluoride seem to be of limited efficacy against erosion, the main reason for this is the missing biofilm in the erosive process as well as the lower pH of the acids compared to bacterial acids. This means that to achieve some kind of preventive effect it would be necessary to use products with higher fluoride concentration, which is not an appropriate option for small children, and/or to increase the frequency of application. In addition, the fluoride compound plays a role as promising effects were found when fluoride is combined with titanium or stannous ions. TiF4 can cause acid-resistant surface coatings and when Sn2+/F- formulations are applied, Sn is not only found on the surface but is also incorporated into enamel and dentine. Both effects make the tooth surface more resistant against acid demineralisation. Different fluoride-containing vehicles have been tested to prevent erosion/ETW, such as toothpastes, rinses, gels and varnishes. Toothpastes offer some degree of protection, especially Sn2+-containing formulations, but effects of the active ingredients are sometimes counteracted by the presence of abrasives. Detecting associated factors and influencing them is the main instrument in arresting erosive tooth wear. Additionally, patients at risk for dental erosion should always use an additional fluoride source preferably containing Sn2+.

Impairing fluoride export of Aspergillus fumigatus mitigates its voriconazole resistance

Fungi have evolved specific export activities to balance intracellular levels of the toxic ion fluoride, while the first-line antimycotic voriconazole contains fluorine. This study aimed to explore whether impaired fluoride export might result in altered susceptibilities of the human pathogenic mould Aspergillus fumigatus towards this antifungal compound. Functional characterization of the putative fluoride exporter in A. fumigatus was performed in the context of azole resistance by generating deletion strains that were assessed for their resistance against fluoride and voriconazole. The FexA fluoride exporter of A. fumigatus appears to be expressed constitutively, and targeting its encoding gene results in significantly increased sensitivity towards this halide. Impaired fluoride export correlates with increased susceptibility of an azole-resistant fexAΔ strain. These results demonstrate that the fexA-encoded gene product is the major fluoride export activity of A. fumigatus, and that voriconazole serves as a source of fluoride. However, these data do not support the application of voriconazole based on fluoride toxicity.

Long term spatial-temporal dynamics of fluoride in sources of drinking water and associated health risks in a semiarid region of Northern China

There is a concern about the increasing prevalence of health problems related to the ingestion of fluoride (F−) in the developing world. Drinking water is one important source of F−, and the concentration of F− needs to be known to ensure the safety of drinking water. In this study, F− levels in drinking water were investigated across Taiyuan in Shanxi Province, China. Spatial-temporal distribution characteristics and potential associated health risks were analyzed using GIS. We collected 485 samples from shallow wells without any defluoridation treatments between 2008 and 2016. After analyzing the samples of F− content we found that mean F− levels of urban areas (0.61 ± 0.39 mg L−1), suburban areas (0.70 ± 0.87 mg L−1) and for all of Taiyuan city (0.63 ± 0.56 mg L−1) were in optimum range based on the recommendation by USEPA. However, individual locations within industrial areas (e.g. Gujiao District) had higher F− levels (1.06 mg L−1). A concerning result showed that 12.37% of tested locations had F− concentrations larger than 1.0 mg L−1. We calculated F− Health Risk Indices (HRIsF) and found that highest were associated with suburban areas, especially in the year 2009 and 2010. However, from 2008 to 2016, overall F− levels and HRIsF of the sampled groundwater in Taiyuan City showed a decreasing trend. HRIsF in suburban areas was higher than urban areas, possible due to the heavily prevalent coal mining industry in those areas. Specific policies should be formulated to address HRIsF.

Correction: Fast and reliable generation of [18F]triflyl fluoride, a gaseous [18F]fluoride source.

Correction for 'Fast and reliable generation of [18F]triflyl fluoride, a gaseous [18F]fluoride source' by A. Pees et al., Chem. Commun., 2018, 54, 10179-10182.

Persica Chewing Gum Effects on Saliva Fluoride Concentration and Flow Rate: A Triple-Blind Randomized Clinical Trial.

Context:Dental caries is a prevalent disease worldwide. Salvadora persica or Miswak could be a source of fluoride and has caries preventive effects.Aims:The aim of this study was to compare saliva fluoride concentration and flow rate after using Persica and sodium fluoride chewing gums.Settings and Design:In a triple-blind crossover randomized trial, 44 healthy volunteers (21–25 year old) were recruited according to the inclusion criteria and were randomly allocated into two groups (22 each).Participants and Methods:This study was performed within two sets of trial with a 10-day washout period. Participants (subjects) were followed a running period and matched for trial confounders. Saliva samples were collected under controlled conditions at similar time (11 am) within baseline, 5, 10, 20, and 45 min intervals preceded by 5-min chewing of Persica or sodium fluoride chewing gum. Saliva samples were analyzed for fluoride ion using hexamethyldisiloxane diffusion method.Statistical Analysis Used:Saliva flow rate (ml/min) and mean fluoride concentration (ppm) during different time periods in two types of gum were compared using ANOVA-repeated measures (P < 0.05).Results:The difference in total means of stimulated saliva flow rates between two Persica and sodium fluoride gum intervention groups was statistically significant (P = 0.048); however, difference of fluoride concentrations was not statistically significant (P = 0.244).Conclusions:Chewing Persica containing gum released fluoride ions in saliva and increased saliva flow rate comparable with sodium fluoride chewing gum use as a gold standard.

Identification and Analysis of the Fluoride Concentration in Toothpastes Intended for Children

Objective: To identify the commercially available toothpastes intended for children and their total soluble fluoride concentrations (TSF). Material and Methods: Twelve brands of toothpastes intended for children marketed in supermarkets and pharmacies were found and analyzed: Bitufo ® ; Colgate Smile ® ; Lilica Ripilica ® ; Even Baby ® ; Turma da Monica Baby ® ; Loney Tunes ® ; Loney Tunes Baby ® ; Malvatrikds Baby ® ; Oral B Stages ® ; Sanifil Kids ® ; Tandy ® ; Tra-la-la Baby ® . Duplicate samples of each toothpaste were weighed (+/- 90 to 110 mg) and diluted in 10 mL of distilled water under stirring. To evaluate soluble fluoride, duplicate aliquots of supernatant suspensions were evaluated on specific ion fluoride electrode calibrated with fluoride standard solutions and results expressed in ppm F according to established protocol. Results: According to information provided by manufacturers, 5 non-fluoridated toothpastes, 3 toothpastes with less than 1000 ppm F and 4 toothpastes with conventional fluoride concentration (1100 ppm F) were identified. After analysis of soluble fluoride of fluoridated toothpastes, only 02 presented TSF concentration equal to or greater than 1000 ppm F. The TSF concentration (mean ± SD) for all samples ranged from 8.2 ± 0.1 to 1065.9 ± 24.7 ppm F. Conclusion: Few toothpastes intended for children presented soluble fluoride concentrations capable of preventing dental caries. Additionally, regulatory measures need to be implemented for the marketing of toothpastes intended for children with at least 1000 ppm of soluble fluoride, especially in locations without other sources of fluoride (fluoridated water) for the population.

Release of Fluoride in Saliva the Use Chewing Gums with Different Fluoride Compounds NaMFP, SnF2 and Naf

The goal of search determine the effect of use commercially chewing gums on fluoride kinetics in saliva. Using of three commercially chewing gums with fluoride from local markets, contains 3.38 mg of fluoride as marketed sodium mono fluorophosphates (NaMFP), Stannous fluoride (SnF2) and sodium fluoride (NaF) which are the three most common sources of fluoride used in currently fluoride dentifrices. Fifteen 7–9 year-old volunteers were instructed to chew the fluoridated gums. After starting chewing saliva collected at 0, 3, 6, 9 and 15 minutes. The Salivary fluoride analyzed by using of fluoride-specific electrode (201Fluoride E. Hanna instruments) after acid hydrolysis. The fluoride amount in the saliva samples after the use of chewing gum which contains Sodium mono-fluorophosphates (NaMFP) and Stanous fluoride (SnF2), were 0.328 mg and 0.258 mg respectively which higher than after the use of chewing gum contains sodium fluoride (NaF) which was 0.041mg in all experimental periods. The high fluoride presence in saliva after the use of chewing gum of (NaMFP) and (SnF2), are significant to prevent dental caries and this should be evaluated in clinical researches.

A Polyol-Mediated Fluoride Ions Slow-Releasing Strategy for the Phase-Controlled Synthesis of Photofunctional Mesocrystals.

There are only a few inorganic compounds that have evoked as much interest as sodium yttrium fluoride (NaYF4). Its extensive applications in various fields, including transparent displays, luminescence coding, data storage, as well as biological imaging, demand the precise tuning of the crystal phase. Controlling the emergence of the desired α-phase has so far remained a formidable challenge, especially via a simple procedure. Herein, we represented a polyol-assisted fluoride ions slow-release strategy for the rational control of pure cubic phase NaYF4 mesocrystals. The combination of fluorine-containing ionic liquid as a fluoride source and the existence of a polyalcohol as the reactive medium ensure the formation of uniform α-phase mesocrystallines in spite of a higher temperature and/or higher doping level.

Facile construction of three-membered rings via benzyne-promoted Darzens-type reaction of tertiary amines

A range of tertiary amines having electron-withdrawing groups were activated in situ by benzyne, generated from 2-(trimethylsilyl)phenyl triflate and a fluoride source, and participated in the Darzens-type reaction with carbonyl compounds, imines, and vinyl ketones to afford structurally diverse epoxides, aziridines, and cyclopropanes, respectively, in moderate to excellent yields with high trans-selectivity. The reaction involves in situ formation of unstrained ammonium ylides from tertiary amines and benzyne, proceeds in the absence of transition metals and strong bases, and tolerates a wide variety of functional groups.

Selective Photocatalytic C-F Borylation of Polyfluoroarenes by Rh/Ni Dual Catalysis Providing Valuable Fluorinated Arylboronate Esters.

A highly selective and general photocatalytic C-F borylation protocol that employs a rhodium biphenyl complex as a triplet sensitizer and the nickel catalyst [Ni(IMes)2] (IMes = 1,3-dimesitylimidazoline-2-ylidene) for the C-F bond activation and defluoroborylation process is reported. This tandem catalyst system operates with visible (blue, 400 nm) light and achieves borylation of a wide range of fluoroarenes with B2pin2 at room temperature in excellent yields and with high selectivity. Direct irradiation of the intermediary C-F bond oxidative addition product trans-[NiF(ArF)(IMes)2] leads to very fast decomposition when B2pin2 is present. This destructive pathway can be bypassed by indirect excitation of the triplet states of the nickel(II) complex via the photoexcited rhodium biphenyl complex. Mechanistic studies suggest that the exceptionally long-lived triplet excited state of the Rh biphenyl complex used as the photosensitizer allows for efficient triplet energy transfer to trans-[NiF(ArF)(IMes)2], which leads to dissociation of one of the NHC ligands. This contrasts with the majority of current photocatalytic transformations, which employ transition metals as excited state single electron transfer agents. We have previously reported that C(arene)-F bond activation with [Ni(IMes)2] is facile at room temperature, but that the transmetalation step with B2pin2 is associated with a high energy barrier. Thus, this triplet energy transfer ultimately leads to a greatly enhanced rate constant for the transmetalation step and thus for the whole borylation process. While addition of a fluoride source such as CsF enhances the yield, it is not absolutely required. We attribute this yield-enhancing effect to (i) formation of an anionic adduct of B2pin2, i.e., FB2pin2-, as an efficient, much more nucleophilic {Bpin-} transfer reagent for the borylation/transmetalation process, and/or (ii) trapping of the Lewis acidic side product FBpin by formation of [F2Bpin]- to avoid the formation of a significant amount of NHC-FBpin and consequently decomposition of {Ni(NHC)2} species in the reaction mixture.

Cross‐Coupling Reactions of Aryltriethoxysilanes and Diaryldiselenides ‐ A New Route for the Synthesis of Diarylselenides

AbstractThe present work reports, the new route for the synthesis of diarylselenides by coupling of aryltriethoxysilanes with diaryldiselenides. Various ligands were screened for the said coupling in presence of a copper salt. Cu(II)/bpy in DMSO showed excellent activity for the coupling of aryltriethoxysilanes with various diaryldiselenides. In the present work, no fluoride source was used for the activation of aryltriethoxysilanes and also a possible mechanism was proposed for the said reaction. Moreover, diaryldisuphides and diarylditellurides were also effectively coupled with aryltriethoxysilanes using proposed catalytic system. Importantly, use of non‐precious metal based catalytic system, makes the protocol interesting.

Ph3P+CF2CO2− as an F− and :CF2 source for trifluoromethylthiolation of alkyl halides

As trifluoromethylthiolation has received increasing attention recently, many CF3S-reagents and trifluoromethylthiolation methods have been developed. Herein we describe trifluoromethylthiolation of alkyl halides by using Ph3P+CF2CO2− as a fluoride and difluorocarbene source. Difluorocarbene is a versatile intermediate, but its side reactions are usually ignored and the by-products would therefore be discarded. In this work, a side reaction of difluorocarbene, the generation of a fluoride anion from difluorocarbene, was developed into a synthetic tool. Although the trifluoromethylthiolation reaction involved multi-sequential steps, the cleavage of C–F bond, the formation of CF2=S bond, F-C(S)F2 bond, and C-SCF3 bond, the conversion proceeded fast and was completed within 10 min.

The Fluoride Debate: The Pros and Cons of Fluoridation.

Fluoride is one of the most abundant elements found in nature. Water is the major dietary source of fluoride. The only known association with low fluoride intake is the risk of dental caries. Initially, fluoride was considered beneficial when given systemically during tooth development, but later research has shown the importance and the advantages of its topical effects in the prevention or treatment of dental caries and tooth decay. Water fluoridation was once heralded as one of the best public health achievements in the twentieth century. Since this practice is not feasible or cost effective in many regions, especially rural areas, researchers and policy makers have explored other methods of introducing fluoride to the general population such as adding fluoride to milk and table salt. Lately, major concerns about excessive fluoride intake and related toxicity were raised worldwide, leading several countries to ban fluoridation. Health-care professionals and the public need guidance regarding the debate around fluoridation. This paper reviews the different aspects of fluoridation, their effectiveness in dental caries prevention and their risks. It was performed in the PubMed and the Google Scholar databases in January 2018 without limitation as to the publication period.