Aqueous Solutions Of Sodium Fluoride Research Articles

NMR Spectroscopy and Multiscale Modeling Shed Light on Ion-Solvent Interactions and Ion Pairing in Aqueous NaF Solutions.

The balance between ion solvation and ion pairing in aqueous solutions modulates chemical and physical processes from catalysis to protein folding. Yet, despite more than a century of investigation, experimental determination of the distribution of ion-solvation and ion-pairing states remains elusive, even for archetypal systems like aqueous alkali halides. Here, we combine nuclear magnetic resonance (NMR) spectroscopy and multiscale modeling to disentangle ion-solvent interactions from ion pairing in aqueous sodium fluoride solutions. We have developed a high-accuracy method to collect experimental NMR resonance frequencies for both ions as functions of temperature and concentration. Comparison of these data with resonance frequencies for nonassociating salts allows us to differentiate the influence of solvation and ion pairing on NMR spectra. These high-quality experimental NMR data are used to validate our modeling framework comprising polarizable force field molecular dynamics (MD) simulations and quantum chemical calculations of NMR resonance frequencies. Our experimental and theoretical resonance frequency shifts agree over a wide range of temperatures and concentrations. Structural analysis reveals how both trends are dominated by interactions with water molecules. For the more sensitive 19F nucleus, the NMR resonance frequency decreases as hydrogen bonds between fluoride and water molecules are reduced in number with increased temperature and molality. Through a detailed analysis of the theoretical NMR resonance frequencies for both ions, we show that NMR spectroscopy can distinguish both contact ion pairs and single-solvent-separated ion pairs from free ions. This quantitative framework can be applied directly to other systems.

Adsorption of croconic acid anions at silver electrodes in sodium fluoride solutions. Interplay of DFT calculations and in situ ATR-SEIRAS measurements for the interpretation of experimental spectra of adsorbed species

The adsorption of species coming from the disodium salt of croconic acid (4,5-dihydroxy-4-cyclopentene-1,2,3-trione, H2C5O5) at chemically deposited silver electrodes was studied in aqueous sodium fluoride solutions by combining in situ ATR-SEIRAS (Surface-Enhanced Infrared Reflection Absorption Spectroscopy experiments under Attenuated Total Reflection conditions) and Density Functional Theory (DFT) calculations. Voltammetric experiments suggest the existence of reversible adsorption processes in the potential range between −0.55 and −0.20 V vs Ag/AgCl (KCl 1 M), whereas irreversible reduction is observed for potentials below-0.55 V. ATR-SEIRA spectra show potential-dependent adsorbate bands in the potential range for reversible adsorption, that were assigned according to DFT calculations. Calculated optimized geometry of adsorbed croconate and bicroconate correspond to bonding to the silver surface in a bidentate configuration through two oxygen atoms with the molecular plane perpendicular to the metal surface. The broadening and splitting at high electrode potentials of the CO stretching bands for adsorbates coming from croconic acid can be explained by invoking the existence of collective vibrational modes appearing at high coverage. In overall, the ATR-SEIRA spectra obtained with Ag thin layer electrodes resembles that reported for Au thin layers. As a difference, higher adsorbate coverage seems to be obtained in the case of silver. Moreover, a strong feature at ca. 1580 cm−1 is experimentally observed, that was much weaker on gold samples. The calculated frequencies for adsorbed croconate and bicroconate do not change significantly with the adsorption bonding sites for the optimized geometries. Taking into account the calculated frequencies of both types of species, a better agreement with the experimental behavior (including the splitting/shifting caused by dipole–dipole coupling in high-coverage collective modes) is obtained in the case of bicroconate. The coexistence with some adsorbed croconate species cannot be ruled out.

Effect of laser radiation and sodium fluoride on the reactivity of prepared teeth

BACKGROUND: The use of esthetic restorations (metalceramic and metal-free) provides for the preparation of teeth within the enamel and surface or middle layers of the dentin, which entails an increase in the reactivity of teeth. One of the promising directions for increasing the resistance of the prepared teeth in the orthopedic treatment of patients using esthetic dental restorations is the combined and consistent use of fluorides and low-intensity laser radiation.
 AIM: To examine the effect of low-intensity laser radiation and sodium fluoride on the reactivity of dissected vital teeth.
 MATERIAL AND METHODS: A 2% aqueous solution of sodium fluoride was administered by electrophoresis with a portable device Desensitron-II. For laser exposure, a dental laser device Optodan was used in the first (anti-inflammatory) mode of operation. The research material was the results of orthopedic treatment of 120 patients aged 2039 years (57 men and 63 women). To assess the initial state of teeth reactivity and the effect of the therapeutic measures, the sensitivity of the teeth to temperature (thermoreactivity of the teeth), mechanical (sliding tangent test), and electrical (electrodontometry) influences was investigated.
 RESULTS: In the third group, the studied indicators before fixation demonstrated the maximum improvement in indicators relative to the data obtained in other groups.
 CONCLUSIONS: The combined sequential effect of low-intensity laser radiation and sodium fluoride reduces the reactivity of the prepared teeth while significantly improving the indicators of electrical excitability of the pulp and increasing the pain threshold in relation to temperature and mechanical stimuli.

Investigation of Corrosion Performance of Pure Aluminum as Bipolar Plate in PEMFC Environment

The global climate changes occurred because of the emissions of greenhouse gases such as CO2, NO x and SO x that are ongoing throughout the world pose a gradually higher demand for replacing today's fossil fuel based energy system by less pollutant technologies.[1-2] Among the alternative energies available, proton exchange membrane fuel cells (PEFCs) have been considered to power transportation vehicles such as automobiles and buses due to their high power density, relatively quick start-up and low operating temperatures.[3] The bipolar plate is one of the most important parts that impacts the manufacturing cost of the PEFC.[4] The high electrical conductivity, high gas impermeability, good mechanical performance and low cost are some of the desired properties of bipolar plate materials. Also, mainly two types of materials are used as bipolar plates in PEFC as carbon and metals. Carbon materials show a very good corrosion resistance but lower performance in separating reaction gases compare with metals. Among the many candidate materials, aluminum (Al) is considered as better bipolar plate applications in PEFC due to its low cost and low density.[5] Moreover, bipolar plate is required to have sufficient corrosion resistance even with a sulfuric acid solution having a pH of around 3.0, but it is considered that Al cannot tolerate this condition without its well surface modification which is proposed by Yashiro et al.[6] Sulfuric acid solutions are widely used for aluminum anodizing operations. That’s why it was our interest to study the corrosion of Al material for using as a gas separating plate in PEFC environment. Also, the influence of sulfate and fluoride ions on the stability of films formed on Al surfaces in aqueous solutions of sulfuric acid and sodium fluoride particularly at low concentration levels through finding the amount of corrosion was examined. Scanning electron microscopic (SEM), energy dispersive x-ray (EDX) and cross-sectional analyses were also done to observe the surface morphology and elemental composition.In the present investigation, pure Al having 6 cm2 of area were used as the test pieces for immersion in 2.5×10-6M H2SO4 (pH 5.41), 5×10-6M H2SO4 (pH 5.14), 2.5×10-6M H2SO4 + 2ppm F- (pH 5.57) and 5×10-6M H2SO4 + 2ppm F- (pH 5.45) solutions using reagent grade of H2SO4 and NaF. Test pieces were polished by emery paper 4/0, 6/0, 1200 and 2000, rinsed and immersed in around 100 cm3 aqueous solutions for a period of 24h, 48h, 72h, 96h and 120h at 80°C. A potentiodynamic polarization test was performed to check the corrosion resistance of Al in the simulated PEFC environment using 0.05M SO4 2- and 2ppm F- solutions (pH 3.3 and 5.8) and high current density of Al was found. Moreover, a 500h single cell operation was also performed to investigate the corrosion of Al as the gas separating plates. A glassy carbon was used as the channel former and aluminum foil was used as the gas separating plate. The single cell results showed that the corrosion of the gas separation plate was much milder than the corrosion expected in polarization test which showed the possibility of using Al as a gas separating plate in PEFC.Additionally, the oxide film was formed in the Al surfaces because of the oxidized aluminum at the time of immersion. As a result, the corrosion products were formed and graphed as amount of corrosion versus immersion time. Firstly, the amount of corrosion was increased with increasing the concentration of sulfuric acid and increased more after the addition of 2ppmF- ions in the acid solutions. From the results found in this study, it is concluded that pure as-polished Al undergoes severe corrosion in sodium fluoride whereas sulfate ions form much lower corrosion as well as act as inhibitor when Al is used as bipolar plate in the PEFC environment. Acknowledgements This work was supported by the Ministry of Education, Sports, Science and Technology (MEXT), Japan. References Carrette, K. A. Friedrich, U. Stimming, Fuel Cells, 1 (1), 5-39 (2001).O. Collantes, Technol Forecasting Soc. Change, 74(3), 267-280 (2007).Schäfer, J. B. Heywood, M. A. Weiss, Energy, 31 (12), 2064-2087 (2006).Cunningham, D. Baird, J. Mater. Chem, 16, 4385-4388 (2006).A. A. El-Enim, O. E. Abdel-Salam, H. El-Abd, A. M. Amin, J. Power Sources, 177 (1), 131-136 (2008).Yashiro, T. Ichikawa, S. -T. Myung, M. Kumagai, S. Kozutsumi, Zairyo-to-Kankyo, 60 (10), 432-434 (2011).

Natrophosphate, Arctic Mineral and Nuclear Waste Phase: Structure Refinements and Chemical Variability

The crystal structures of natural (Mt. Koashva, Khibiny alkaline massif, Kola Peninsula, Russian Arctic) and synthetic (obtained from an aqueous solution of sodium phosphate and sodium fluoride (1:1) by evaporation at room temperature (RT)) natrophosphate, Na7(PO4)2F·19H2O, have been investigated using single-crystal X-ray diffraction analysis. Natrophosphate and its synthetic analogue are cubic, Fd-3c, a = 27.6942(3) Å (natrophosphate at RT), a = 27.6241(4) Å (natrophosphate at 100 K), a = 28.1150(12) Å (synthetic analogue at RT), a = 27.9777(7) Å (synthetic analogue at 100 K). The crystal structure is based upon the super-octahedral [Na6(H2O)18F]5+ polycationic complexes consisting of six edge-linked Na6(OH2)5F octahedra sharing one common fluorine vertex. The A site is statistically occupied by Na and H2O with the prevalence of H2O with the refined occupancy factors O:Na equal to 0.53:0.47 for natrophosphate and 0.75:0.25 for its synthetic analogue. The coordination of the A site in synthetic natrophosphate is enlarged compared to the natural sample, which agrees well with its higher occupancy by H2O molecules. The general formula of natrophosphates can be written as Na6+xHxF(PO4)2·(19 + x)H2O, where x = 0–1. The chemical variability of natrophosphate allows to explain the discrepancies in its solubility reported by different authors. The information-based parameters of structural complexity are equal to 3.713 bit/atom and 2109.177 bit/cell that allows to classify natrophosphate as a structurally very complex mineral.

SUBTOXIC EFFECTS OF SODIUM FLUORIDE ON THE ULTRASTRUCTURE OF PITUITARY GLAND IN RATS

The study aimed at investigating the morphofunctional state of the pituitary gland in white rats under the subtoxic exposure to sodium fluoride. Mature male rats (N = 17), weighing 130-150 g, were intragastrically administered with aqueous solutions of sodium fluoride in a dose of 1/10 LD50 ranged from 20 mg / kg of body weight. The duration of the subacute experiment was 60 days. To assess the morphological rearrangement at the subcellular level of organization of the pituitary gland, electron microscopy was performed. The microscopic study revealed changes in the submicroscopic architecture resulted from dystrophic processes caused by the subtoxic exposure to sodium fluoride. Prolonged sodium fluoride intoxication led to a number of changes in the ultrastructure of the pituitary gland, manifested by the development of intracellular oedema, swelling of mitochondria, changes in the density of their matrix, partial reduction and loss of cristae, vacuolization and expansion of the cisterns of the granular endoplasmic reticulum, an increase in the number of primary lysosomes, in the redistribution of chromatin nucleus and a decrease in the number of ribosomes and glycogen granules. Hemocapillaries showed oedema of endothelial cells, uneven thickening of the basement membrane, vasodilatation with the development of stasis and sludge of erythrocytes. As in the vessels of the hypothalamus, the presence of fibrin and a significant number of platelets has been found. These changes indicate a disruption of bioenergetics associated with the mitochondrial apparatus and the development of hypoxic processes, which lead to a decrease in the activity of redox reactions occurring at the level of intracellular membranes and organelles.

MORPHOFUNCTIONAL STATE OF HEPATOCYTES UNDER THE EXPOSURE TO SODIUM FLUORIDE

The article provides the data on the morphofunctional state of hepatocytes in the liver of white rats under the subtoxic action of sodium fluoride. Mature rats of the Wistar population (N = 17), weighing 180-210 g, were intragastrically injected with aqueous solutions of sodium fluoride in a dose of 1/10 LD50 at the ratio of 20 mg / kg of animal body weight daily. The subacute experiment lasted 60 days. Studying hepatocytes in the rat liver and assessing their morphological rearrangement at the subcellular level of organization was carried out by electron microscopy. The study of ultrastructural organization of the liver under the influence of sodium fluoride revealed changes in the submicroscopic architecture characteristic of the development of dystrophic processes. Prolonged intoxication with sodium fluoride caused a number of changes in the liver ultrastructurer, manifested by the development of intracellular edema in hepatocytes, swelling of mitochondria, changes in the density of their matrix, partial reduction and loss of cristae, vacuolization and expansion of the cisterns of the granular endoplasmic reticulum, an increase in the number of primary lysosomes, redistribution chromatin of the nucleus and a decrease in the number of ribosomes and glycogen granules. These changes indicate a disruption of bioenergetics of hepatocytes associated with the mitochondrial apparatus and the development of hypoxic processes, which lead to a decrease in the activity of redox reactions occurring at the level of intracellular membranes and organelles.

Using Shungite in Water Defluoridation by Galvanocoagulation

Fluorine is a natural component of many sources of drinking water. An excess of fluorine in drinking water leads to metabolic disturbances in bone tissues. In this context, the International Drinking Water Quality Standards recommend adhering to a fluoride content of drinking water of no more than 1.5 mg/dm3. If this value is exceeded, water requires defluoridation. In this work, defluoridation by galvanocoagulation in a drum-type galvanocoagulator was studied. The half-cells of the galvanic couple were aluminum and shungite mined at the Polezhaevskii deposit, Karelia, Russia. The occurring electrochemical processes result in anodic dissolution of aluminum to form the corresponding hydroxides. The fluoride ion forms aluminofluoride complexes with them, which are adsorbed on freshly formed hydroxide flakes. The ratio between the half-cells of the galvanic couple as a significant factor of controlling the process efficiency was studied. It was shown that the fluoride ions were removed most completely at an aluminum : schungite ratio of 1 : 1.5. Experiments on model aqueous solutions of sodium fluoride detected a significant dependence of the process on the initial pH value. The experimental results enabled one to choose a mode of defluoridation of water with various fluoride contents. By the example of treatment of artesian water with a fluoride content of 9.1 mg/dm3 from Mashevka, Poltava oblast, Ukraine, a high efficiency of the studied process was demonstrated: the fluoride ion content of the water treated for 5 min decreased to 0.9 mg/dm3. In addition, when using shungite as a half-cell of the galvanic couple, its disinfecting effect was observed: whereas the initial content of coliform bacteria was 700 in 100 cm3, they were absent in the treated water. The redox potential was also reduced from 340 to 255 mV, which is noteworthy because this parameter has recently received considerable attention as being one of the most important parameters of water in its interaction with the human body.

Chitosan Curcumin Film as a Sensor for Detection of O-Nitrophenol and Fluoride Ion Using Fluoresce Quenching Technique

Curcumin was immobilized in chitosan films fabricated by solvent casting method. The amount of curcumin immobilization was more when methanol was used as a solvent to dissolve curcumin than the butanol solvent. The maximum amount of curcumin immobilized per gram of chitosan film was 0.023 g. Immobilized curcumin was not released back in water even after prolong contact of the films with water. Fluorescence intensity of the films got quenched when these films were in contact with an aqueous solution of o-nitrophenol (ONP) and sodium fluoride (NaF). The extent of quenching depended on the concentration of these attributes. Fluorescence intensity was highly pronounced even when the concentration of ONP and fluoride (FL) was as low as 2.0 x 10–6 M and 2.5 x 10–5 M, respectively. UV-vis spectroscopy could not detect 2.5 x 10–6 M ONP; similarly, ion chromatography was not sensitive towards 2.5 x 10–5 M FL. Since the extent of quenching varies linearly with the concentration of ONP and FL in aqueous solution, the Stern-Volmer equation can be used for quantification of these.

Solubility of ammonium fluoride in aqueous sodium fluoride solutions of various concentrations from dilute to saturated at 298.15 K for fluorine recovery from wet-process phosphoric acid

Recovery of fluorine from wet-process phosphoric acid (WPA) to produce ammonium fluoride (NH4F) and sodium fluoride (NaF) provides an environmentally-friendly route to purify WPA and produce high value-added fluoride salt. The solubility data and the related electrolyte thermodynamics are essential for a rational separation design of pure NH4F from aqueous NaF solution by crystallization. In this contribution, the solubilities of NH4F in aqueous NaF solutions of different concentrations from dilute to saturated were systematically measured at 298.15 K using a dynamic synthesis method. Experimental results show that the presence of NaF in the solution could significantly decrease the solubility of NH4F due to the common-ion effect which was decreased by 72.4% when the molality of NaF was only around 0.015 mol/kg. The data can be used to determine the yield of NH4F and liquid composition in the vacuum evaporative crystallization of NH4F. The mean activity coefficients of NH4F at saturation were determined from the experimental solubility data and then correlated with the extended Debye-Hükel equation and the Pitzer model. With four adjustable parameters, both models are able to accurately calculate the experimental data over a wide range of salt concentrations. The average relative deviations between the experimental and calculated logarithm of mean activity coefficients of NH4F from the two models are 1.43% and 2.29%, respectively. The binary and ternary ionic parameters for the Pitzer model are found to be concentration dependent and the correlations of them as functions of ionic strength are proposed.

Патофизиологические механизмы иммунной реактивности печени в условиях длительного экспериментального воздействия на организм фторида натрия

В условиях непрерывного воздействия неблагоприятных факторов окружающей и производственной среды на человека особую актуальность приобретает изучение механизмов, поддерживающих гомеостаз организма. Длительное поступление фторидов в организм приводит к формированию хронической фтористой интоксикации, патогенез которой вызывает многочисленные споры и дискуссии. До сих пор недостаточно внимания уделяется изучению висцеральной патологии, обусловленной нарушениями иммунного статуса в условиях воздействия на организм соединений фтора. Практически отсутствуют исследования по изучению иммунной реактивности, определяющей морфофункциональный характер ответной реакции печени на ранних стадиях развития фтористой интоксикации. Цель работы - изучение действий патофизиологических механизмов иммунной реактивности печени при субхроническом действии на организм соединений фтора. Методика. Опыты проведены на 210 лабораторных крысах-самцах массой 180-220 г., разделенных на 2 группы: контрольную (n=80) и группу животных с субхроническим действием фторида натрия (n=130). Экспериментальные животные в течение 12 нед имели свободный доступ к водному раствору фторида натрия (концентрация 10 мг/л, что составляет суточную дозу фтора 1,2 мг/кг массы тела). Для изучения иммунологических и биохимических показателей забирали кровь из хвостовой вены через 1, 3, 6, 9, 12 нед от начала эксперимента. Для оценки состояния гуморального звена иммунитета определяли уровень сывороточных иммуноглобулинов (IgA, IgG, IgM) иммуноферментным анализом с помощью наборов реактивов ЗАО «Вектор-Бест» (Новосибирск). Уровень сывороточных цитокинов: TNF-α, IL-1β, 2, 4, 6, 10 определяли на анализаторе Multiskan EX методом иммуноферментного анализа с использованием наборов «Вектор Бест» (Новосибирск). Подсчет общего количества лейкоцитов произведен классическим способом в камере Горяева, анализ лейкоцитарной формулы - в окрашенных мазках периферической крови. Метаболические изменения оценивали по активности ферментов в ткани печени: щелочной фосфатазы (ЩФ), аланин- и аспартатаминотрансфераз (АЛТ, АСТ), лактатдегидрогеназы (ЛДГ), гаммаглутамилтранспептидазы (γ-ГТ). Активность ферментов определяли унифицированными методами с помощью наборов реактивов ЗАО «Вектор-Бест» (Новосибирск) на фотометре PM-750 (Германия). Гистологические исследования печени осуществляли после декапитации крыс, проводимой под эфирным наркозом. Результаты. Показано, что субхроническое воздействие фторида натрия сопровождается формированием внутриклеточных и внутрисосудистых повреждений печени. Активация медиаторов воспаления и развитие иммунологических нарушений в динамике эксперимента способствуют формированию системной воспалительной реакции, которая приводит к появлению стойких морфологических нарушений в печени и изменению активности ферментов основных метаболических путей. Заключение. Полученные результаты могут быть использованы при разработке и проведении профилактических мероприятий в условиях воздействия на организм высоких концентраций фтора с последовательным применением детоксикационной, иммуномодуляторной и органопротекторной коррекции. Studying mechanisms, which maintain the body homeostasis, is particularly important in the conditions of continuous impact of adverse environmental and manufacturing factors. Long-term exposure to fluorides leads to chronic fluoric intoxication, the pathogenesis of which is a subject of multiple controversy and discussions. Not enough attention is still paid to elucidating the visceral pathology associated with fluorine-induced immune disorders. There are virtually no studies of immune reactions that define the morphofunctional nature of the liver response to early stages of fluoric intoxication. Aim. To study pathophysiological mechanisms of hepatic immune reactivity in subchronic exposure of the body to fluorine compounds. Methods. Experiments were performed on 210 male rats weighing 180-220 g. The animals were divided into two groups: 1) control (n=80) and 2) subchronic exposure to sodium fluoride (n=130). The rats had free access to a 10 mg/l aqueous solution of sodium fluoride (daily dose, 1.2 mg/kg body weight) for 12 weeks. Blood was withdrawn from the caudal vein at 1, 3, 6, 9, and 12 weeks of the experiment for immunological and biochemical tests. Histological study of the liver was performed after decapitation of rats under ether anesthesia. Results. The subchronic exposure to sodium fluoride was associated with intracellular and intravascular damage of the liver. Activation of inflammatory mediators and development of immunological disorders during the experiment contributed to a systemic inflammatory reaction, which resulted in persistent morphological injuries of the liver and changes in enzyme activities in major metabolic pathways. Conclusion. The study results can be used for development and implementation of preventive measures against the effects of high fluorine concentrations, which would include a successive use of detoxification, immunomodulation and organ protection.

Characterization of a trans–trans Carbonic Acid–Fluoride Complex by Infrared Action Spectroscopy in Helium Nanodroplets

The high Lewis basicity and small ionic radius of fluoride promote the formation of strong ionic hydrogen bonds in the complexation of fluoride with protic molecules. Herein, we report that carbonic acid, a thermodynamically disfavored species that is challenging to investigate experimentally, forms a complex with fluoride in the gas phase. Intriguingly, this complex is highly stable and is observed in abundance upon nanoelectrospray ionization of an aqueous sodium fluoride solution in the presence of gas-phase carbon dioxide. We characterize the structure and properties of the carbonic acid–fluoride complex, F–(H2CO3), and its deuterated isotopologue, F–(D2CO3), by helium nanodroplet infrared action spectroscopy in the photon energy range of 390–2800 cm–1. The complex adopts a C2v symmetry structure with the carbonic acid in a planar trans–trans conformation and both OH groups forming ionic hydrogen bonds with the fluoride. Substantial vibrational anharmonic effects are observed in the infrared spectra, most notably a strong blue shift of the symmetric hydrogen stretching fundamental relative to predictions from the harmonic approximation or vibrational second-order perturbation theory. Ab initio thermostated ring-polymer molecular dynamics simulations indicate that this blue shift originates from strong coupling between the hydrogen stretching and bending vibrations, resulting in an effective weakening of the OH···F– ionic hydrogen bonds.

Evaluation of novel nanoscaled metal fluorides on their ability to remineralize enamel caries lesions

The aim of this in vitro study was to evaluate the ability of two nanoscaled metal fluorides (NMF) to remineralize shallow (SL) and deep (DL) artificial enamel caries lesions. NMF are synthesized via a non-aqueous fluorolytic sol-gel-synthesis and dissolve low fluoride concentration in aqueous solutions (n-CaF2: 7 ppm, n-MgF2: 70 ppm), whilst containing a nominal fluoride concentration of 3,400 ppm. For comparison, an aqueous sodium fluoride solution (NaF: 3,400 ppm), a sodium fluoride containing varnish (Duraphat: 22,600 ppm) and a fluoride-free negative control were investigated. Bovine enamel specimens with SL (n = 86, 4649–4795 vol%xμm) or DL (n = 145, 9091–9304 vol%xμm) were prepared and allocated to five groups each. In each group the respective agent was applied and pH-cycling was performed for 14 days (SL) and 90 days (DL), respectively. Mineral loss and lesion depth were assessed by transversal microradiography. For SL, all fluoride agents significantly remineralized the specimens compared to baseline (p > 0.05; Mann-Whitney test) to a similar extent. For DL, both NMF showed significantly higher mineral gain compared to the other fluoride agents (p < 0.05). In conclusion, the novel NMF- showing relatively low free fluoride concentrations- bear at least the similar potential for remineralization of early caries lesions as highly fluoridated agents being commonly used.

Synthesis of NaYF4 compounds from sulfide precursors

The synthesis of NaYF4 compounds via the “soft chemistry” of sulfide precursors (a simple Y2S3 and a complex NaYS2) was performed. Hydrofluoric acid solution (HF) at a concentration of 3–45% and different contents of a saturated aqueous solution of sodium fluoride that was acidified by hydrofluoric acid (NaF+HF) were used as fluorinating components. When the fluorination proceeded using different concentrations of hydrofluoric acid, yttrium fluoride (YF3) formed. NaYF4 was obtained via different synthesis conditions as a mixture of cubic and hexagonal phases in nanoparticle dimensions (α=30–100nm, β=28–60nm).

Instantaneous and Selective Bare Eye Detection of Inorganic Fluoride Ion by Coumarin–Pyrazole‐Based Receptors

A series of rationally designed coumarin–pyrazole‐based scaffolds, equipped with N―H and C―H hydrogen bond donors (R1–R5) and containing various electron‐withdrawing groups at key positions, are synthesized and characterized in order to investigate their inorganic fluoride binding properties in highly competitive media (1:1 DMSO–water). Only one, 3‐{4‐[(2,4‐dinitrophenyl)‐hydrazonomethyl]‐1‐phenyl‐1H‐pyrazol‐3‐yl}‐chromen‐2‐one (R1), of the five compounds synthesized, is found to be capable to selectively detect inorganic fluoride via naked eye amongst other anionic species in aqueous media. Qualitative and spectroscopic studies exhibit that receptor R1 has the potential of showing instantaneous change of color from yellow to pink upon addition of sodium fluoride (0.95 ppm) in aqueous media, at concentration lower than that recommended by World Health Organization (1 ppm). Intensity of color increases with increasing fluoride concentration till 5 ppm, beyond which intensity of color change becomes saturated. This has established the applicability of this receptor for assessment of the level of fluoride in water. Anion binding studies carried out by UV–visible titration portrayed substantial bathochromic peak shift from 410 to 495 nm, upon addition of varying concentrations of aqueous sodium fluoride solution, which has validated the color change. Jobs plot data confirmed 1:1 stoichiometry between R1 and fluoride ion. 1H‐NMR investigation reveals that the deprotonation of N―H hydrogen donor group of receptor R1 and its interaction with fluoride ion is responsible for the observed color change.

The possible doping of Al3+ and F− modification onto CdS in montmorillonite

The doping of aluminum (Al3+) and the co-doping of aluminum (Al3+)/fluoride (F−) into cadmium sulfide-montmorillonite were investigated. The Al3+ doping was achieved by the reactions between Al3+/Cd2+-montmorillonite and an aqueous solution of sulfide (S2−). The doping of F− was conducted by the reactions between the Al3+ doped sample and an aqueous solution of sodium fluoride (NaF) at room temperature. The products were characterized by powder X-ray diffraction, transmission electron microscopy, as well as Raman, UV–visible and photoluminescence spectroscopies. The blue-shift of the absorption onset and the emission band, as well as the increase in the photoluminescence intensity of the Al3+ doped and Al3+/F− co-doped CdS in montmorillonite if compared with pure CdS and CdS in montmorillonite were ascribed to quantum size effect and Burstein–Moss effect.

On the Relationship between the Rate of Salivary Flow and Salivary Fluoride Clearance

The amount of fluoride retained in the mouth following the application of dentifrices, mouthwashes, etc. may be important in determining their anticaries efficacy. In this study we investigated the relationship between the salivary flow rate and salivary fluoride clearance. Ten adults tested six mouthrinses, consisting of aqueous sodium fluoride solutions (0.013, 0.026 mol/l) with and without added sodium chloride (1.28 mol/l) or sucrose (0.44 mol/l), in a randomised order. Prior to each test, subjects swallowed, rinsed for 2 min with 2 ml water and then expectorated into a preweighed container to obtain a measure of initial saliva flow rate. Next, the procedure was repeated using one of the test rinses. Finally, samples of unstimulated whole saliva were collected for up to 3 h after each mouthrinse application and analysed for fluoride. Salivary fluoride concentrations were significantly lower after application of mouthrinses that contained either sucrose or NaCl, both of which compounds markedly enhanced salivary flow, than after the use of corresponding mouthrinses without any additive. Area under the salivary fluoride clearance curve (AUC) values were inversely correlated with salivary flow rate on an individual basis (p < 0.01). The observed behaviour could not be completely attributed to treatment dilution by saliva at the time of application.

High concentration aqueous sodium fluoride certified reference materials for forensic use certified by complexometric titration

Sodium fluoride in concentrations of 1 to 2% is used to prevent the formation of ethanol in blood and urine samples that are to be analysed for ethanol content. The majority of such samples form part of forensic investigations into alleged drunken driving. In South Africa, the laboratory performing the tests is required to prove that the sodium fluoride concentration in the blood samples is above 1g/100ml on receipt. This is done by using a fluoride ion-selective electrode calibrated with external aqueous solutions of sodium fluoride. The National Metrology Institute of South Africa (NMISA) prepares sodium fluoride solutions in concentrations from 0.3 to 3.0g/100ml. No other certified sodium fluoride reference solutions in these concentrations are available commercially. The sodium fluoride is certified by precipitation of the fluoride as lead chlorofluoride (PbClF) through the addition of a known excess of lead nitrate. The excess lead is back-titrated with ethylenediamine tetraacetic acid (EDTA) using a photometric electrode to detect the endpoint. Aqueous sodium fluoride solutions are prepared and the concentrations verified by the precipitation/back-titration method. This paper shows the application of a classical complexometric method to the certification of reference materials and describes the procedures for the preparation of the sodium fluoride solutions, verification of the concentrations, homogeneity and stability by primary titrimetry. It also briefly covers the calculation of uncertainty, the establishment of traceability and the quality control measures applied to ensure the quality of the certified reference materials (CRMs).

Synthesis and gas sorption properties of halogen-doped mesoporous chromium(iii) terephthalate

Mesoporous chromium(iii) terephthalate MIL-101 was treated with aqueous solutions of sodium fluoride, chloride, and bromide. The properties of the resulting compounds to sorb nitrogen, hydrogen, and methane were studied. The methane sorption was shown to depend on the nature of the inserted halide ion. The treatment with a sodium chloride solution leads to an increase in the methane uptake by MIL-101.

Identification of Fluoride and Phosphate Binding Sites at FeOOH Surfaces

Iron oxyhydroxide minerals occur widely in nature and play important roles in environmental and industrial processes. Owing to their high reactivity, these minerals can act as sinks and/or transformation centers for a variety of inorganic and organic ions. Interfacial reactions are often mediated by surface (hydr)oxo groups. These groups can be singly, doubly, or triply coordinated with respect to underlying Fe atoms. In order to investigate the reactivity of these differently coordinated groups, Fourier transform infrared (FTIR) spectroscopy was used to examine adsorption products formed on iron oxyhydroxide surfaces. The absence of water was required to probe the O–H stretching region after initial reactions in aqueous media. This work was specifically focused on synthetic, submicrometer-sized lepidocrocite and goethite particles reacted with aqueous solutions of sodium fluoride and monosodium phosphate. Langmuir–Freundlich adsorption isotherms were calibrated on adsorption data in aqueous media at vari...