Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

M.Sc. / This study is an investigation of environmental impacts caused by airborne fluorides around an industrial uranium and chemical facility in South Africa, the Necsa Pelindaba site. The literature study in Chapter 2 illustrates that industrial atmospheric fluoride emissions can have negative environmental impacts, including accumulation in surface soil horizons, necrosis in leaves, and fluorosis in plants and animals. Fluorides from this site are from two sources – stacks and evaporation pans. Samples to measure fluoride concentration in air, soil and vegetation and deposition rate were taken and analysed from February to August 2007. Standard analytical methods were used for the analysis of fluorides in all samples. Evaluation of historical environmental monitoring at Pelindaba showed that stack emissions were high in the year 2002 followed by a dramatic decrease in 2003 and 2004. In 2005, there was a sharp increase in emissions, with further slight increases until August 2007. For all media and sample types taken (air concentration, deposition, soil and vegetation), samples from nearby the evaporation pans had the highest fluoride concentrations. Results from sampling sites close to the stacks were lower, but still well above off-campus background sites, and above values from Pelindaba sites distant from the stacks. Fluoride concentrations in animal bones from previous studies done at the site showed enhanced fluoride concentrations compared to control samples. The project hypothesis was that fluoride emissions from Necsa Pelindaba site do not have a negative impact on the environment. This hypothesis is proven correct to the extent that no off-site adverse impacts or concentrations were observed. Limited on-campus impacts were observed localised around the evaporation pans and to a lesser extent around the stacks. Airborne fluoride concentration values around the pans only were above the South African guideline values. Deposition values were highest around the pans. The only visible leaf damage attributable to fluoride was on a Karee tree ~50 m from the edge of the pan. Soil fluoride concentrations from the current study were within the range of natural fluoride concentrations in soil. Despite evidence of local deposition, there was no evidence of fluoride accumulation in surface or subsurface soils. No impacts were observed elsewhere around the site or off-site. Based on the results of this work, fluoride emissions from the stacks do not pose a threat to the environment, provided that efficiency of the gas scrubbing equipment is maintained at current levels. Emissions from the pans pose a minor localised problem that nevertheless requires investigation and mitigation.

Proton and fluorine nuclear magnetic resonance spectroscopy was used to investigate the favoured forms of several furanosyl fluorides. The low energy barrier to pseudo-rotation in these systems precludes the assignment of only one favoured conformation for each molecule. A systematic study of five membered ring sugar conformations was undertaken by examining three types of systems, varying from a relatively rigid molecule involving three fused rings, to more flexible molecules involving a "free" furanosyl fluoride ring. The spectral assignment was greatly facilitated by heteronuclear fluorine decoupling and computer analysis. 5-fluoro-3,6-anhydro-α-L-idofuranose was synthesized in good yield from several precursors and the molecule's furanose ring conformation of ₂T³was assigned on the basis of vicinal ¹H-¹H coupling constants. Using the values for vicinal ¹H- ¹⁹F couplings obtained from this molecule, together with data from other workers, a partial Karplus type curve was constructed relating vicinal ¹H- ¹⁹F couplings to dihedral angles. This curve - which was found to be more asymmetric than the Karplus relationship for vicinal ¹H-¹H couplings - was then used, together with the known Karplus curve for vicinal ¹H-¹H couplings, to determine the conformations of the triester furanosyl fluorides of ribose, arabinose and xylose. Assuming pure sp³ hybridization and maximum ring puckering, the conformations for most of the sugars studied were found to involve the displacement of C₂ and/or C₃ positions out of the plane of the ring formed by the other atoms. The conformation for α-fluoro-ribo-furanosyl triester ( ₃T⁴ ) was found to be different than that of the β-fluoro-ribofuranosyl triester (₃T⁴). A significant and apparently stereospecific long-range ⁴J[subscript H].₄,F coupling through oxygen of ca. 6.5 Hz, is observed when H₄ and F are in a trans arrangement, while a much smaller coupling for ⁴J[subscript H].₄,F of ca. 1.0 Hz. is observed when these two nuclei are in a cis or approximately "planar M" arrangement. On the other hand, ⁴J[subscript H].₃,F couplings were found to have a value of ca. 2.2 Hz. in the cis or "planar M" geometry, while in the trans geometry, ⁴J[subscript H].₄,F is ca. 0.5 Hz. / Science, Faculty of / Chemistry, Department of / Graduate

New preparative routes to chromyl fluoride were sought. It was found that chlorine monofluoride reacts with chromium trioxide and chromyl chloride to produce chromyl fluoride. Attempts were made to define a mechanism for the reaction of ClF and Cr03 in light of by-products observed and previous investigations. Carbonyl fluoride and chromium trioxide react to form chromyl fluoride and carbon dioxide. A mechanism was also proposed for this reaction. Chromium trioxide with MoF6 or WF6 to produce chromyl fluoride and the respective oxide tetrafluoride.

Indiana University-Purdue University Indianapolis (IUPUI)

Indiana University-Purdue University Indianapolis (IUPUI) / The purposes of this study were twofold: (1) to determine whether applying zirconium silicate prophylaxis paste (containing nine per cent stannous fluoride) prior to topical application of 10 per cent aqueous solution of stannous fluoride would promote a significantly greater enamel fluoride uptake than when the solution was applied alone; and (2) to determine whether rinsing the mouth with tap water immediately after these procedures would significantly affect enamel fluoride uptake. A modification of an in vivo, acid-etched enamel biopsy technique was used to measure fluoride and calcium contents of the outermost layer of enamel in first permanent molars and primary cuspids of 89 children. Four sites were biopsied prior to treatment. Treatments involved prophylaxes with a zirconium silicate paste either containing or not containing nine per cent stannous fluoride, followed by either a four-minute topical application of 10 per cent stannous fluoride in an aqueous solution or no such topical application. Some participants were instructed not to rinse for one-half hour; others were immediately offered unlimited quantities of tap water. Four other sites were biopsied one week after treatment; four more were biopsied two weeks after treatment. Pre- versus post-treatment differences were measured via a fluoride-sensitive electrode and atomic absorption spectrophotometry. Results were inconclusive. Enamel fluoride uptakes for most treatment groups appeared to be negative. Due to this seeming disagreement with the findings of many other investigators, and due to the very small numbers within treatment groups and biopsy sites, it was felt that uptake comparisons from group to group would be misleading. Tentative explanations for the unexpected results were offered.

Indiana University-Purdue University Indianapolis (IUPUI) / This study was designed to evaluate a dental alloy containing stannous hexafluorozirconate at 0.5 percent by weight, to determine how the fluoride additive might affect the physical properties of the alloy and the clinical performance of the amalgam restorations. Using established methodology, the fluoride containing alloy was evaluated in the laboratory for fluoride release, enamel uptake and solubility, strength, hardness, flow, dimensional change, corrosion resistance, and marginal leakage. Clinically, 98 pairs of test and control restorations were placed and evaluated for marginal adaptation, surface characteristics, and recurrent caries. The results indicate that the fluoride containing alloy meets the ADA specifications for amalgam alloys, though the strength properties of the amalgam are reduced. The increased susceptibility to corrosion noted in the laboratory for the fluoride-containing amalgam did not correlate with the clinical performance of the restorations, which showed no deleterious affects resulting from the addition of the fluoride compound. The reduced enamel solubility observed in the laboratory can be considered an adjunct in the prevention of recurrent caries, though no recurrent caries was reported for either the test or control restorations. Again, the prevention of recurrent caries must begin with appropriate cavity design, care in manipulation of materials and responsible diet and hygiene practices.

Thesis (M.Sc.D.)--Boston University. School of Graduate Dentistry, 1969. / Bibliography, tables included. / An investigation of the fluoride concentration of cementum of rat molars was performed utilizing sixty Sprague-Dawley rats, averaging eighty grams, thirty-one to thirty-six days of age at the onset of the project. The experimental period was from twenty-two to thirty-five days. The rats were randomly placed into seven groups and were fed Purina Laboratory chow and tap water, to which had been added either none, 50, or 100 ppm fluoride. At the conclusion of the study the first and second maxillary and mandibular molars were extracted and the apical one millimeter of each root was collected for analysis. The samples were ashed and then dissolved in l ml of 0.5 M HC10 [subscript 4] and 4 ml of 0.5 M Na Citrate. The fluoride concentration of the samples was obtained by use of the Ionalyzer (Orion Research, Inc., Mode1 401) with its component specific fluoride ion activity electrode and essential reference electrode and standardizing solutions. The results were statistically significant (p <.00l) and the mean fluoride values ranged from 500 ppm to 2,100 ppm for the controls and from 3,900 ppm to 6,500 ppm for the experimental rats ingesting 100 ppm fluoride in their drinking water. The experimental design and significance of the results are discussed.

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