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Fluoride Ion (fluoride + ion)
Selected AbstractsRatiometric Fluorescence Sensing of Fluoride Ions by an Asymmetric Bidentate Receptor Containing a Boronic Acid and Imidazolium GroupEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2009Zhaochao Xu Abstract The synthesis of the first examples of anion receptors that utilize boron,fluoride interactions and (C,H)+···F, -type ionic hydrogen-bond interactions in the binding of F ions is reported herein. o -, m -, and p -Phenylboronic acids were linked to naphthoimidazolium through a methylene group. On the basis of fluorescence and 19F NMR studies, we have confirmed that the addition of fluoride to a boron center occurs prior to the formation of (C,H)+···F, -type ionic hydrogen bond with the imidazolium moiety. More importantly, these investigations have demonstrated that only the receptor bearing the ortho -directed boron and imidazolium exhibits enhanced fluoride binding. The increased binding ability of the asymmetric bidentate receptor of ortho -boronic acid and imidazolium towards F, enables it to sense fluoride ions in a 95:5 CH3CN/HEPES aqueous solution. The fluorescence responses to different anions were also explored; the ortho -boron-imidazolium receptor displayed ratiometric fluorescence changes and a high selectivity towards fluoride ions over other anions (Cl,, Br,, CH3CO2,, HSO4,, and H2PO4,).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Thiourea Based Tweezer Anion Receptors for Selective Sensing of Fluoride IonsCHINESE JOURNAL OF CHEMISTRY, Issue 5 2007You-Ming Zhang Abstract Three 3,3,-di(4-substituted-phenyl)-1,1,-isophthaloylbis(thiourea) compounds were designed as novel neutral anion receptors, and synthesized by simple steps in good yields. The single crystal structure of receptor 1 shows that a solvent molecule was captured by the host molecule through intermolecular hydrogen bonding. Moreover, it was self-assembled as a supramolecular system for the presence of abundant inter- and intramolecular hydrogen bonding and ,-, interactions between phenyl groups. Their application as anion receptors has been examined by UV-Vis and 1H NMR spectroscopy, showing that they had a higher selectivity for fluoride than other halides. The host and guest formed a 1:1 stoichiometry complex through hydrogen bonding interactions in the first step, then following a process of deprotonation in presence of an excess of F, in the solvent of DMF. [source] Effect of potential on the corrosion behavior of a new titanium alloy for dental implant applications in fluoride mediaMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2004A. M. Al-Mayouf Abstract The effect of fluoride ion concentration and pH on the corrosion behavior of TCA (60 Ti 10 Ag 30 Cu), which is a new Ti alloy with low melting point, pure Titanium (Ti), and TAV (TiAl6V4) was examined using open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) at different potentials. Results show that the corrosion resistance of TCA and Ti decrease at anodic potentials compared with results obtained at OCP. At one potential the corrosion resistance decrease depends on NaF concentration and pH. TAV shows less resistance against corrosion in fluoride containing saliva. TCA has potentials more positive than Ti and TAV due to surface enrichment of Cu and Ag as Ti dissolves which accelerates the cathodic reaction. Fluoride ion may not hinder the growth of oxide layers on the surfaces of the electrodes. It will have influence on the properties of the oxide layer causing them to be not protective against corrosion in acid media containing fluoride ions. [source] Fluorapatite-Supported Palladium Catalyst for Suzuki and Heck Coupling Reactions of HaloarenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2007M. Lakshmi Kantam Abstract A fluorapatite-supported palladium catalyst (PdFAP) was synthesized by treatment of fluorapatite (prepared by incorporating the basic species fluoride ion into apatite in situ by co-precipitation) with bis(benzonitrile)palladium(II) chloride in acetone. The catalyst displayed high catalytic activity for Suzuki coupling of aryl iodides and bromides with boronic acids at room temperature and chloroarenes at 130,°C in the presence of tetrabutylammonium bromide to give biaryls in excellent yields. Heck olefination of chloroarenes was also successfully carried out by this catalyst. PdFAP was recovered quantitatively by simple filtration and reused with consistent activity. PdFAP was well characterized by XRD, FTIR, XPS, ICP-AES, CO2 TPD and CHN elemental analysis. [source] Skeletal Fluorosis From Instant Tea,,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 5 2008Michael P Whyte MD Abstract Introduction: Skeletal fluorosis (SF) can result from prolonged consumption of well water with >4 ppm fluoride ion (F,; i.e., >4 mg/liter). Black and green teas can contain significant amounts of F,. In 2005, SF caused by drinking 1,2 gallons of double-strength instant tea daily throughout adult life was reported in a 52-yr-old woman. Materials and Methods: A 49-yr-old woman developed widespread musculoskeletal pains, considered fibromyalgia, in her mid-30s. Additionally, she had unexplained, increasing, axial osteosclerosis. She reported drinking 2 gallons of instant tea each day since 12 yr of age. Fluoxetine had been taken intermittently for 5 yr. Ion-selective electrode methodology quantitated F, in her blood, urine, fingernail and toenail clippings, tap water, and beverage. Results: Radiographs showed marked uniform osteosclerosis involving the axial skeleton without calcification of the paraspinal, intraspinal, sacrotuberous, or iliolumbar ligaments. Minimal bone excrescences affected ligamentous attachments in her forearms and tibias. DXA Z-scores were +10.3 in the lumbar spine and +2.8 in the total hip. Her serum F, level was 120 ,g/liter (reference range, 20,80 ,g/liter), and a 24-h urine collection contained 18 mg F,/g creatinine (reference value, <3). Fingernail and toenail clippings showed 3.50 and 5.58 mg F,/kg (control means, 1.61 and 2.02, respectively; ps < 0.001). The instant tea beverage, prepared as usual extra strength using tap water with ,1.2 ppm F,, contained 5.8 ppm F,. Therefore, the tea powder contributed ,35 mg of the 44 mg daily F, exposure from her beverage. Fluoxetine provided at most 3.3 mg of F, daily. Conclusions: SF from habitual consumption of large volumes of extra strength instant tea calls for recognition and better understanding of a skeletal safety limit for this modern preparation of the world's most popular beverage. [source] Desensitizing Agent Efficacy during Whitening in an At-Risk PopulationJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 1 2004RALPH H. LEONARD Jr. DDS. ABSTRACT Background: Nightguard vital bleaching (NGVB) has gained acceptance among dentists and patients as a simple and effective procedure to lighten discolored teeth. Although the efficacy and predictability of NGVB have been well established, it has been documented that patients undergoing the procedure may experience side effects such as tooth sensitivity (TS) and gingival irritation (GI). A previous NGVB study suggested that selected participants might benefit from a regimen of a desensitizing agent (DSA)to decrease or prevent TS during whitening. Purpose: The purpose of this study was to determine whether the daily use of an active DSA (UltraEZTM, Ultradent Products Inc., South Jordan, UT, USA) during NGVB would decrease TS in a population at risk for TS when compared with a placebo. Materials and Methods: Forty subjects participated in this single-blind randomized clinical trial. All participants had indicated that they had preexisting TS or other risk factors for TS during NGVB. To evaluate TS caused by the tray alone, participants wore custom-fitted maxillary whitening trays containing no DSA or whitening solution during week 1. Next, participants were randomly assigned to apply either the active DSA or placebo daily for 14 days in the trays for 30 minutes prior to whitening. The placebo was the same formulation as UltraEZ but without the desensitizing agents (3% potassium nitrate and 0.11% by weight fluoride ion). The bleaching solution was a 10% carbamide peroxide whitening solution (OpalescenceTM, Ultradent Inc.). Post treatment, participants were followed up for 1 week, during which time they used neither trays nor solutions. Throughout the study, participants completed a daily diary to record their perceptions of TS and the time spent wearing the tray with the whitening solution. Results: Forty-one percent of the active group had at least 1 day of TS during treatment compared with 78% of the placebo group. The difference was statistically significant (p= .027) using the two-tailed Fisher exact test. [source] Automated radiosynthesis of [18F]SPA-RQ for imaging human brain NK1 receptors with PETJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 1 2006Frederick T. Chin Abstract [18F]SPA-RQ is an effective radioligand for imaging brain neurokinin type-1 (NK1) receptors in clinical research and drug discovery with positron emission tomography. For the automated regular production of [18F]SPA-RQ for clinical use in the USA under an IND we chose to use a modified commercial synthesis module (TRACERlab FXF-N; GE Medical Systems) with an auxiliary custom-made robotic cooling,heating reactor, after evaluating several alternative radiosynthesis conditions. The automated radiosynthesis and its quality control are described here. [18F]SPA-RQ was regularly obtained within 150 min from the start of radiosynthesis in high radiochemical purity (>99%) and chemical purity and with an overall decay-corrected radiochemical yield of 15±2% (mean±S.D.; n=10) from cyclotron-produced [18F]fluoride ion. The specific radioactivity of [18F]SPA-RQ at the end of synthesis ranged from 644 to 2140 mCi/µmol (23.8,79.2 GBq/µmol). Copyright © 2005 John Wiley & Sons, Ltd. [source] Substitution-reduction: an alternative process for the [18F]N -(2-fluoroethylation) of anilinesJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 4 2004Emmanuelle Briard Abstract Substitution of a halo atom (chloro or bromo) in easily prepared N -haloacetyl-anilines with no-carrier added (NCA) cyclotron-produced [18F]fluoride ion (18F, t1/2= 109.8 min; ,+=96.9%), followed by reduction with borane,tetrahydrofuran (BH3,THF), provides an alternative route to NCA [18F]N -(2-fluoroethyl)-anilines. This two-step and one-pot process is rapid (,50 min) and moderately high yielding (,40% decay-corrected radiochemical yield (RCY) overall). In the nucleophilic substitution reaction, 18-crown-6 is preferred to Kryptofix® 222 as complexing agent for the solubilization of the counter-ion (K+), derived from an added metal salt, in acetonitrile. Weakly basic potassium bicarbonate is preferred as the added metal salt. Inclusion of a small amount of water, equating to 4,5 molar equivalents relative to 18-crown-6, base or precursor (held in equimolar ratio), is beneficial in preventing the adsorption of radioactivity onto the wall of the glass reaction vessel and for achieving high RCY in the nucleophilic substitution reaction. BH3,THF is effective for the rapid reduction of the generated [18F]N -fluoroacetyl-aniline to the [18F]N -(2-fluoroethyl)-aniline. Copyright © 2004 John Wiley & Sons, Ltd. [source] The first enzymatic method for C,18F bond formation: the synthesis of 5,-[18F]-fluoro-5,-deoxyadenosine for imaging with PETJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 13 2003Laurent Martarello Abstract The use of the key enzyme involved in carbon,fluorine bond formation in Streptomyces cattleya catalysing the formation of 5,-fluoro-5,-deoxyadenosine (5,-FDA) from fluoride ion and S -adenosyl-l-methionine (SAM) was explored for its potential application in fluorine-18 labelling of the adenosine derivative. Enzymatic radiolabelling of [18F]-5,-FDA was successfully carried out starting from SAM and [18F]HF when the concentration of the enzyme preparation was increased from sub-mg/ml values to mg/ml values. The purity of the enzyme had no measurable effect on the radiochemical yield of the reaction and the radiochemical purity of [18F]-5,-FDA. Copyright © 2003 John Wiley & Sons, Ltd. [source] Ortho -[18F]Fluoronitrobenzenes by no-carrier-added nucleophilic aromatic substitution with K[18F]F,K222,A comparative studyJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 13 2002M. Karramkam Abstract The scope of the nucleophilic aromatic ortho -fluorinations from the corresponding ortho -halonitrobenzene precursors (halo-to-fluoro substitutions) with no-carrier-added [18F]fluoride ion as its activated K[18F]F,K222 complex has been evaluated via the radiosynthesis of ortho -[18F]fluoronitrobenzene, chosen as a model reaction. The parameters studied include the influence of the leaving group in the ortho position of the phenyl ring (,Cl, ,Br, ,l), the quantity of precursor used, the type of activation (conventional heating or microwave irradiations), the solvent, the temperature and the reaction time. The iodo-precursor was completely unreactive and the bromo-precursor gave only low incorporation (<10%) in the optimal conditions used (conventional heating at 145°C or microwave activation, 100 W for 120 s). Only the chloro-precursor was found reactive in the conditions described above and up to 70% yield was observed for the formation of ortho -[18F]fluoronitrobenzene ([18F]- 1). In all the experiments, the unwanted ortho -[18F]fluoro-halobenzenes, potentially resulting from the nitro-to-fluoro substitution, could not be detected. These results will be applied for the radiosynthesis of 5-[18F]fluoro-6-nitroquipazine, a potent radioligand for the imaging of the serotonin transporter with PET. Copyright © 2002 John Wiley & Sons, Ltd. [source] Highly Sensitive and Selective Fluoride Ion Chemosensing, Fluoroalkylated Polysilane,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2004Anubhav Saxena Abstract Summary: This paper reports a new and simple approach for the amplified detection of fluoride ions by a polymer-based chemosensor made of stiff fluoroalkylated polysilane, poly(3,3,3-trifluoropropylmethylsilane). This chemosensor exhibited extreme sensitivity and selectivity towards fluoride ions by a decrease in the photoluminescence (PL) intensity with parts per billion concentrations of fluoride ions in solution in tetrahydrofuran (THF). The quenching constant for fluoride ions (K,=,1.35,×,107M,1) was found to be exceptionally high. Schematic representation of the polymer amplification mechanism after addition of fluoride ion in tetrahydrofuran. [source] Fluoride catalyzed rearrangements of polysilsesquioxanes, mixed Me, vinyl T8, Me, vinyl T10 and T12 cagesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2010M. Ronchi Abstract Insoluble mixtures of polyvinylsilsesquioxane, -(vinylSiO1.5)n - PVS, and polymethylsilsesquioxanes, -(MeSiO1.5)n - PMS, in THF at ambient when treated with catalytic amounts (1,5 mol%) of fluoride ion introduced as tBu4 NF will depolymerize and dissolve. The resulting soluble species consist of [vinylxMe8,x(SiO1.5)]8, [vinylxMe8,x(SiO1.5)]10 and [vinylxMe8,x(SiO1.5)]12. Ratios of 1:1 of PVS:PMS greatly favor formation of vinyl rich cages. Only at ratios of 1:5 are the proportions of vinyl:Me in the cages approximately equal. Of the T8, T10 and T12 species produced, all conditions tried, including changing the solvent to EtOH or toluene or at reflux (THF), favor the formation of the larger cages sometimes completely excluding formation of the T8 materials. Efforts to isolate the cage compounds by removal of solvent regenerates polysilsesquioxanes, albeit those containing mixtures of Me and vinyl groups. Introduction of CaCl2 sufficient to form CaF2 prior to workup prevents repolymerization, allowing recovery of the mixed cage systems. The approach developed here provides a novel way to form mixed functional group silsesquioxane cages. The fact that T10 and T12 cage formation is favored appears to suggest that these cages are more stable than the traditionally produced T8 cages. Copyright © 2009 John Wiley & Sons, Ltd. [source] Conformational Structure and Energetics of 2-Methylphenyl(2,-methoxyphenyl)iodonium Chloride: Evidence for Solution ClustersCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2010Dr. Yong-Sok Lee Abstract Diaryliodonium salts allow the efficient incorporation of cyclotron-produced [18F]fluoride ions into electron-rich and electron-deficient arenes to provide potential radiotracers for molecular imaging in vivo with positron emission tomography (PET). This process (ArI+Ar,+18F,,Ar18F+Ar,I) is still not well understood mechanistically. To better understand this and similar reactions, it would be valuable to understand the structures of diaryliodonium salts in organic media, where the reactions are typically conducted. In this endeavor, the X-ray structure of a representative iodonium salt, 2-methylphenyl(2,-methoxyphenyl)iodonium chloride (1), was determined. Our X-ray structure analysis showed 1 to have the conformational M,P dimer as the unit cell with hypervalent iodine as a stereogenic center in each conformer. With the ab initio replica path method we constructed the inversion path between the two enantiomers of 1, thereby revealing two additional pairs of enantiomers that are likely to undergo fast interconversion in solution. Also LC,MS of 1 showed the presence of dimeric and tetrameric anion-bridged clusters in weak organic solution. This observation is consistent with the energetics of 1, both as monomeric and dimeric forms in MeCN, calculated at the B3LYP/DGDZVP level. These evidences of the existence of dimeric and higher order clusters of 1 in solution are relevant to achieve a deeper general understanding of the mechanism and outcome of reactions of diaryliodonium salts in organic media with nucleophiles, such as the [18F]fluoride ion. [source] Computational Study of 19F NMR Spectra of Double Four Ring-Containing Si/Ge-ZeolitesCHEMPHYSCHEM, Issue 5 2006Angeles Pulido Abstract 19F NMR chemical shifts are calculated in order to study the F, environment in double four ring (D4R) containing Si/Ge-zeolites. The calculations with the DFT/CSGT/B3PW91 methodology yielded an agreement within 2 ppm with respect to the experimental peaks corresponding to the D4R units containing 8Si0Ge, 7Si1Ge and 0Si8Ge of the octadecasil zeolite. The optimisation of the 7Si1Ge-, 6Si2Ge-, 5Si3Ge- and 4Si4Ge-D4R units with DFT/B3LYP methodology shows that a covalent GeF bond is formed and therefore a Ge atom in the D4R is pentacoordinated. The displacement of the fluoride ion towards a Ge atom in the Ge-containing D4R units locates four Si/Ge atoms in the close vicinity of the F, and this makes possible a rationalization of the 19F NMR signals in groups according to the number of Si (n) and Ge (m) atoms in the nearest F, environment, F,SinGem (where n+m=4). Thus, the calculated chemical shifts show that higher values are observed when the number of Ge atoms in the nearest F, environment increases. [source] Synthesis and Properties of Poly(vinyl alcohol)/Synthetic F-montmorillonite NanocompositesCHINESE JOURNAL OF CHEMISTRY, Issue 8 2009Junhao ZHANG Abstract F-montmorillonite (F-MMT) was synthesized by a hydrothermal method at 493 K for 72 h, in which a little of hydroxyl radical is replaced by fluoride ion in the silicate structure. Poly(vinyl alcohol) (PVA)/F-MMT nanocomposites were prepared using the synthetic F-MMT by a solution-intercalation method. The F-MMT and PVA/ F-MMT nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the flake structured F-MMT is homogeneously dispersed in PVA, forming an exfoliated nanocomposite structure. Thermogravimetric analysis, mechanical performance and UV-visible spectroscopy were applied to test the properties of PVA nanocomposites, which indicate that the thermal stability and mechanical performance are enhanced distinctly, without a sacrifice in optical clarity. The improvement of mechanical and thermal properties was attributed to the homogeneous and good dispersion of F-MMT in polymeric matrix and the strong hydrogen bonding between O,,H of PVA and F,, of F-MMT. [source] Electrochemical Characteristics of Mediated Laccase-Catalysis and Electrochemical Detection of Environmental PollutantsELECTROANALYSIS, Issue 8 2008Ying Liu Abstract Laccase has been immobilized on the carbon nanotubes modified glassy carbon electrode surface by adsorption. As-prepared laccase retains good electrocatalytic activity to oxygen reduction by using 2,2,-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) as the mediator. It can be used as a biosensor for the determination of catechol with broad linear range. Especially, azide, one of inhibitors of laccase, shows sensitive inhibition to catalytic activity of the laccase modified electrode. In addition, the inhibition by fluoride ions has also been studied. These demonstrate that the as-prepared electrode can be used to detect halide and some the toxic pollutants, e.g., catechol and azide based on catalytic or inhibition reaction of laccase. The simple preparation procedure makes the system can be developed as non-inhibition or inhibition biosensor. [source] Ratiometric Fluorescence Sensing of Fluoride Ions by an Asymmetric Bidentate Receptor Containing a Boronic Acid and Imidazolium GroupEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2009Zhaochao Xu Abstract The synthesis of the first examples of anion receptors that utilize boron,fluoride interactions and (C,H)+···F, -type ionic hydrogen-bond interactions in the binding of F ions is reported herein. o -, m -, and p -Phenylboronic acids were linked to naphthoimidazolium through a methylene group. On the basis of fluorescence and 19F NMR studies, we have confirmed that the addition of fluoride to a boron center occurs prior to the formation of (C,H)+···F, -type ionic hydrogen bond with the imidazolium moiety. More importantly, these investigations have demonstrated that only the receptor bearing the ortho -directed boron and imidazolium exhibits enhanced fluoride binding. The increased binding ability of the asymmetric bidentate receptor of ortho -boronic acid and imidazolium towards F, enables it to sense fluoride ions in a 95:5 CH3CN/HEPES aqueous solution. The fluorescence responses to different anions were also explored; the ortho -boron-imidazolium receptor displayed ratiometric fluorescence changes and a high selectivity towards fluoride ions over other anions (Cl,, Br,, CH3CO2,, HSO4,, and H2PO4,).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Comprehensive Modeling of Ion Conduction of Nanosized CaF2/BaF2 Multilayer HeterostructuresADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Xiangxin Guo Abstract Molecular beam epitaxy-grown CaF2/BaF2 heterolayers are a demonstration of the potential of nanoionics. It has been shown that ion conductivities both parallel and perpendicular to the interfaces increase with decrease in interfacial spacing. This size effect was attributed to the thermodynamically necessary redistribution of the mobile fluoride ions (N. Sata, K. Eberl, K. Eberman, J. Maier, Nature 2000, 408, 946; X. X. Guo, I. Matei, J.-S. Lee, J. Maier, Appl. Phys. Lett. 2007, 91, 103102). On this basis, the striking phenomenon of an upward bending in the effective parallel conductivity as a function of inverse interfacial spacing for low temperatures (T,,,593,K) has been satisfactorily explained by application of a modified Mott,Schottky model for BaF2 (X.X. Guo, I. Matei, J. Jamnik, J.-S. Lee, J. Maier, Phys. Rev. B 2007, 76, 125429). This model was further confirmed by measurements perpendicular to the interfaces that offer complementary information on the more resistive parts. Here a successful comprehensive modeling of parallel and perpendicular conductivities for the whole parameter range, namely for interfacial spacings ranging from 6 to 200,nm and investigated temperatures ranging from 455 to 833,K, is presented. The model is based on literature data for carrier mobilities and Frenkel reaction constants and the assumption of a pronounced F, redistribution. Given the fact that an impurity content that was experimentally supported is taken into account and apart from minor assumptions concerning profile homogeneity, the only fit parameter is the space charge potential. In particular, it is worth mentioning that in BaF2 the low temperature Mott,Schottky space charge zone which is determined by impurities changes over, at high temperatures, into a Gouy,Chapman situation owing to increased thermal disorder. (The situation in CaF2 is of Gouy,Chapman type at all temperatures.) [source] Fluoride pit and fissure sealants: a reviewINTERNATIONAL JOURNAL OF PAEDIATRIC DENTISTRY, Issue 2 2000Tonia L. Morphis There are two methods of fluoride incorporation into fissure sealants. In the first method, fluoride is added to the unpolymerized resin in the form of a soluble fluoride salt that releases fluoride ions by dissolution, following sealant application. In the second method, an organic fluoride compound is chemically bound to the resin and the fluoride is released by exchange with other ions (anion exchange system). This report reviews the literature on the effectiveness of all the fluoride-releasing sealants ,commercial and experimental , that have been prepared using either the former or the latter method of fluoride incorporation. There is evidence for equal retention rates to conventional sealants and for ex vivo fluoride release and reduced enamel demineralization. However, further research is necessary to ensure the clinical longevity of fluoride sealant retention and to establish the objective of greater caries inhibition through the fluoride released in saliva and enamel. [source] Removal of fluoride using some lanthanum(III)-loaded adsorbents with different functional groups and polymer matricesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2003Luo Fang Abstract Although fluoride is beneficial for human beings in small quantities, it causes dental fluorosis when consumed in larger quantities over a period of time. In recent years, considerable work has been conducted for the purpose of developing new and low cost absorbents for adsorptive removal of fluoride, especially chelating resins loaded with metal ions. In the present study, several types of adsorbents with different functional groups loaded with lanthanum(III) were prepared to be used for fluoride removal from water. The optimum conditions for loading lanthanum(III) on the adsorbents and the effects of pH and initial fluoride concentration as well as shaking time and solid,liquid ratio on the removal of fluoride have been investigated. Based on these fundamental data, the removal of fluoride from actual hot spring water was also tested as a practical application by comparing the efficiency of different adsorbents for the removal of fluoride from hot spring water. The following conclusions were obtained. (1) The different chemical composition and chemical structure of the polymer matrix play the most important role in fluoride adsorption, (2) strongly acidic adsorbents are more effective on fluoride removal at neutral pH than weakly acidic adsorbents, (3) the order of fluoride removal in the neutral pH range of 4.5,8.0 by the different La(III)-loaded adsorbents employed in the present work is as follows: 200CT resin > POJRgel > IR124resin > SOJR gel , CPAgel , WK11 resin. The column experiments showed that the 200CT resin loaded with lanthanum(III) at pH 6.0 can be successfully employed for the removal of fluoride ions from actual hot spring water. Copyright © 2003 Society of Chemical Industry [source] Fluoride ion diffusion from a glass,ionomer cementJOURNAL OF ORAL REHABILITATION, Issue 7 2000S.-Y. Lee The aims of this study were to observe the release of fluoride ions (F,) from GC-Fuji Lining-LC® glass,ionomer cement, to assess the diffusion process, and to measure fluoride diffusivity (D) in the set cement. Specimens of various dimensions and shapes, ranging from discs to cylindrical rods, were fabricated for both open and embedded modes of testing. In the open mode studies, specimens with different surface to volume ratios were selected and immersed in 37 °C distilled water. In the embedded mode studies, only one diametral surface of the rod-shaped specimens of different lengths and diameters was exposed. F, concentration was measured using a fluoride electrode. The storage solution was analysed at predetermined intervals hourly, daily, and weekly (up to 10 weeks). Immediately after each sampling, the old storage solution was discarded and replaced with new distilled water. F, release from the set cements was detectable (0·4,3·8 ppm, varied with sample geometry), even after a 10-week sampling interval. F, release was greater in ground set cements (0.37 ppm/mg powder) than in control samples of unmixed powder (0.01 ppm/mg powder) immersed for 1 h. Two mechanisms for F, release were proposed. One was short-term and involved rapid dissolution from the cement surface. The other was more gradual and resulted in the sustained diffusion of ions through the bulk cement, which can be modelled by applying a mathematical technique known as separation of variables to Fick's Second Law of Diffusion. The mean D of F, in embedded set cements of glass,ionomer was (1·4±0·5)×10,11 cm2/s, with higher apparent D observed in open mode samples [(7·6±1·4)×10,11 cm2/s]. [source] Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structuresJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2008Michiya Fujiki Abstract Strong chemical forces such as covalent and ionic bonds are responsible for building discrete molecules, nature dwells on noncovalent forces weaker by three orders in magnitude, like the hydrophobic effect, hydrogen bonding, and van der Waals forces. Despite being weak, they possess the potential to drive spontaneous folding or unfolding of proteins and nucleic acids and the recognition between complimentary molecular surfaces. The power of these forces lies in the cooperativity with which they act, thereby generating a cumulative effect of many bonding interactions occurring together. Many ongoing research aims to translate the potential of these forces to the synthetic world to create desired structures with specific chemical functions. Achieving this offers unlimited opportunities for designing and synthesizing the most complex structures with specific applications. This highlight aims to reflect the critical role these noncovalent forces play in controlling macromolecular structures, which hold immense untapped potential for applications defying conventions, and briefly touches on the concept of homochirality in nature based on chiral and weak noncovalent interactions in synthetic nonpolar Si-catenated polymers. It sheds some light on the discovery and characterization of Si/F-C interactions in fluoroalkylated polysilanes in chemosensing of fluoride ions and nitroaromatics with a great sensitivity and selectivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4637,4650, 2008 [source] Fatigue and Fluoride Corrosion on Streptococcus mutans Adherence to Titanium-Based Implant/Component SurfacesJOURNAL OF PROSTHODONTICS, Issue 5 2009Cassia Bellotto Correa DDS Abstract Purpose: The influence of fatigue and the fluoride ion corrosion process on Streptococcus mutans adherence to commercially pure Titanium (Cp Ti) implant/component set surfaces were studied. Materials and Methods: Thirty Nobel implants and 30 Neodent implants were used. Each commercial brand was divided into three groups. Group A: control, Group B: sets submitted to fatigue (105 cycles, 15 Hz, 150 N), and Group C: sets submitted to fluoride (1500 ppm, pH 5.5) and fatigue, simulating a mean use of 5 years in the oral medium. Afterward, the sets were contaminated with standard strains of S. mutans (NTCC 1023) and analyzed by scanning electronic microscopy (SEM) and colony-forming unit counts (CFU/mL). Results: By SEM, bacterial adherence was verified only in group C in both brands. By CFU/mL counts, S. mutans was statistically higher in both brands in group C than in groups A and B (p < 0.05, ANOVA). Conclusion: The process of corrosion by fluoride ions on Cp Ti implant/component sets allowed greater S. mutans adherence than in the absence of corrosion and with the fatigue process in isolation. [source] Highly Sensitive and Selective Fluoride Ion Chemosensing, Fluoroalkylated Polysilane,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2004Anubhav Saxena Abstract Summary: This paper reports a new and simple approach for the amplified detection of fluoride ions by a polymer-based chemosensor made of stiff fluoroalkylated polysilane, poly(3,3,3-trifluoropropylmethylsilane). This chemosensor exhibited extreme sensitivity and selectivity towards fluoride ions by a decrease in the photoluminescence (PL) intensity with parts per billion concentrations of fluoride ions in solution in tetrahydrofuran (THF). The quenching constant for fluoride ions (K,=,1.35,×,107M,1) was found to be exceptionally high. Schematic representation of the polymer amplification mechanism after addition of fluoride ion in tetrahydrofuran. [source] Effect of potential on the corrosion behavior of a new titanium alloy for dental implant applications in fluoride mediaMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2004A. M. Al-Mayouf Abstract The effect of fluoride ion concentration and pH on the corrosion behavior of TCA (60 Ti 10 Ag 30 Cu), which is a new Ti alloy with low melting point, pure Titanium (Ti), and TAV (TiAl6V4) was examined using open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) at different potentials. Results show that the corrosion resistance of TCA and Ti decrease at anodic potentials compared with results obtained at OCP. At one potential the corrosion resistance decrease depends on NaF concentration and pH. TAV shows less resistance against corrosion in fluoride containing saliva. TCA has potentials more positive than Ti and TAV due to surface enrichment of Cu and Ag as Ti dissolves which accelerates the cathodic reaction. Fluoride ion may not hinder the growth of oxide layers on the surfaces of the electrodes. It will have influence on the properties of the oxide layer causing them to be not protective against corrosion in acid media containing fluoride ions. [source] Orthorhombic aluminium oxyfluoride, AlOFACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Alexander D. Vasiliev Crystals of the title compound were extracted from the bulk of grown SrAlF5 crystals as unexpected inclusions that were identified as the long sought after aluminium oxyfluoride. The structure of AlOF is built up from tetrahedral and octahedral polyhedra. Each tetrahedron is bisected by a mirror plane, with the Al atom and two vertex anions in the plane. All tetrahedral vertices are positions of competing oxide and fluoride ions and are shared with octahedra. These shared vertices belong to two octahedral edges which join the octahedra to form infinite zigzag chains. The chains are strung along twofold screw axes that run parallel to the unit-cell b axis. The remaining two octahedral vertices are occupied only by fluoride ions. A small deficiency in the occupation of the octahedral Al position was suggested by the refinement. However, the stoichiometry of the compound is AlOF within experimental uncertainty. The Al,F(O) distances are separated into three groups with average values of 1.652,(3) (tetrahedra), 1.800,(2) (octahedra) and 1.894,(2),Å (octahedra). This structure differs widely from the reported tetragonal phase Al1,xO1,3xF1+3x (x = 0.0886) [Kutoglu (1992). Z. Kristallogr.199, 197,201], which consists solely of octahedral structural units. [source] Conformational Structure and Energetics of 2-Methylphenyl(2,-methoxyphenyl)iodonium Chloride: Evidence for Solution ClustersCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2010Dr. Yong-Sok Lee Abstract Diaryliodonium salts allow the efficient incorporation of cyclotron-produced [18F]fluoride ions into electron-rich and electron-deficient arenes to provide potential radiotracers for molecular imaging in vivo with positron emission tomography (PET). This process (ArI+Ar,+18F,,Ar18F+Ar,I) is still not well understood mechanistically. To better understand this and similar reactions, it would be valuable to understand the structures of diaryliodonium salts in organic media, where the reactions are typically conducted. In this endeavor, the X-ray structure of a representative iodonium salt, 2-methylphenyl(2,-methoxyphenyl)iodonium chloride (1), was determined. Our X-ray structure analysis showed 1 to have the conformational M,P dimer as the unit cell with hypervalent iodine as a stereogenic center in each conformer. With the ab initio replica path method we constructed the inversion path between the two enantiomers of 1, thereby revealing two additional pairs of enantiomers that are likely to undergo fast interconversion in solution. Also LC,MS of 1 showed the presence of dimeric and tetrameric anion-bridged clusters in weak organic solution. This observation is consistent with the energetics of 1, both as monomeric and dimeric forms in MeCN, calculated at the B3LYP/DGDZVP level. These evidences of the existence of dimeric and higher order clusters of 1 in solution are relevant to achieve a deeper general understanding of the mechanism and outcome of reactions of diaryliodonium salts in organic media with nucleophiles, such as the [18F]fluoride ion. [source] Selective organic synthesis through generation and reactivity control of hyper-coordinate metal speciesTHE CHEMICAL RECORD, Issue 6 2008Tamejiro Hiyama Abstract This paper is a review of my 40 years of research at Kyoto, Sagamihara, and Yokohama, all based on the generation of hyper-coordinate metal species such as ate complexes and pentacoordinate silicates. The topics are: (i) carbenoid reagents for carbon,carbon bond-forming reactions, (ii) nucleophilic substitution at acetal carbons using aluminate reagents, (iii) preparation of magnesium enolates and its reaction with nitriles, (iv) Cr(II) reagents for reduction of organic halides and highly selective carbon,carbon bond formation, (v) organic synthesis with organosilion reagents/fluoride ions, (vi) cross-coupling reaction of organosilicon compounds, and (vii) silicon-based conjugate addition to ,,,-unsaturated carbonyl acceptors. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 337,350; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20162 [source] | ||||||||||||||||||||||||||||