Magister Scientiae Dentium - MSc(Dent) / The prevalence of dental decay is high among lower socio-economic groups in the Southern Cape and Karoo region. 70 - 80% of State employed dentists' time in this region is spent on attempting to reduce the pain and sepsis within the communities for which the primary treatment modality is extraction of the tooth under emergency conditions. In developing countries the prevalence of dental decay is still high. There is a general downward trend of dental decay in developing countries; and it is associated with combinations of exposure to fluoridated water and/ or other forms of fluoride exposure (e.g. in fluoridated tooth paste), the provision of preventive oral health services, an increase in dental awareness through organized oral health education programs and the readily available dental resources. This study looked at the feasibility of implementing community water fluoridation in the Southern Cape and Karoo Region by describing the primary drinking water sources, the population distribution around these sources and the actual levels of fluoride found in the water samples. Each sample was coded and with the use of a global positioning system (GPS), a set of co-ordinates obtained for each. Other options with regard to fluoride supplementation were explored as an attempt to provide an alternative intervention option for exposure to fluoride where community drinking water fluoridation was not the first option. This information will be used to record and update existing tables for fluoride levels in community drinking water of the communities in the Southern Cape and Karoo region that is currently used as a guide for prescribing fluoride supplementation as a means of prophylaxis for the prevention and reduction of dental decay. This study re-iterated the diverse set of variables that communities living in rural areas have to live with. It supports the trend that in developing countries the DMFT (12 years) and dmft (6 years) are higher than those in the same age cohorts of developed countries. This study shows that the fluoride level in borehole water is generally higher than that of dams or reservoirs. Fluoride supplementation is required in the bigger, densely populated areas as the fluoride levels of the water in these areas are below optimal and their water systems can accommodate fluoridation. The long term gains of community water fluoridation at optimal levels for entire communities by far out way the risk of developing fluorosis at above optimal levels. There needs to be a systematic review of treatment needs and treatment modalities for each community so that at some point the need for prevention strategies will be sought out by program managers as best practice for improving the general health (i.e. and oral health) of their communities. There is no single approach for solving issues in communities with different sets of variables determining their needs and so too to the question of community water fluoridation. The recommendation is that at the community level (i.e. the communities should be empowered to do their own situational analysis and prioritize their needs) people need to make decisions for themselves with regard to the type of preventive strategy that they implement. Once they have the data and an intervention option is arrived at, they should lobby with their local health provider to implement that intervention option (e.g. Exposure to fluoride as a means of improving dental health) that they have identified in their towns or villages.

Lithium is one of the most strategically important minerals at the time of writing. The demand for lithium and lithium compounds to be used in lithium-ion batteries is increasing day by day. Zimbabwe possesses a considerable resource of lithium ore, estimated at 23 000 mt Li. Beneficiation of this lithium ore could indeed be a very promising business in the near future. This work focuses on processing of petalite concentrate from the Bikita deposit in Zimbabwe for production of Li2CO3, with subsequent preparation of LiF and LiCl. Analysis performed on the petalite showed that the average Li2O content is 4.10 %. The extraction method used involves roasting the pre-heated concentrate with concentrated H2SO4 followed by water leaching of the resulting Li2SO4, solution purification and precipitation of Li2CO3 with subsequent preparation of LiF and LiCl. Investigation of the roasting and leaching showed that the dissolution rates are significantly influenced by roasting temperature and stirring speed. 97.3 % optimum rate of extraction was attained at 320 rpm and roasting temperature of 300 C. Water-washed lithium carbonate with a purity of 99.21 %( metal basis) and an average particle size of 1.4 ìm was produced. Good quality LiF and LiCl can be produced with purity of 99.36 % and 99.02 % respectively. The pH, concentration and agitation have a great influence on the morphology of the precipitated LiF. Lower pH values and optimum concentration of the Li2CO3 solution results in smaller particle size. High recovery of 96.53 % LiF was realised. Anhydrous LiCl was found to absorb moisture when exposed to air at ambient temperature. The synthesised LiCl melts at 606.2 C with a corresponding enthalpy of fusion of 18.4 kJ mol-1, close to the values reported in the literature. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Chemical Engineering / unrestricted

During the past quarter of a century there has been considerable investigation into the effects of fluorides on living organisms. It has been well established, as a result of these studies, that both small and elevated amounts of fluorides present in the environment may have a marked toxic effect upon gaining entry into the organism. Much of the research involving fluorides and the living organism has been confined to experimentation with animals, although considerable evidence indicates that plants are also subject to injury if fluorides are present in the atmosphere or the soil. The great majority of the research dealing with effects of fluorides on animals has been confined to higher vertebrates, principally domestic farm species. The concentration of fluoride research in this area has been prompted by economic pressures arising from natural, industrial, or accidental fluoridation of livestock. For the most part, these investigations have been confined to determination of toxicity levels to various domestic species, while the mode of fluoride action upon living organisms has often been neglected. Some investigators, however, have postulated "defense mechanisms" within the organism whereby active fluoride ion is removed from systemic circulation and is either deposited in less active tissues of the body, or, is excreted in some manner. Such mechanisms would offer a degree of temporary protection of the organism from harmful effects of the fluoride ion.

ArcView and ArcInfo were used to identify and delineate areas contaminated by fluoride, sulfate, chloride, and nitrate in the Woodbine Aquifer. Water analysis data were obtained from the TWDB from the 1950s to 1990s covering 9 counties. 1990s land use data were obtained to determine the relationship with each contaminant. Spearman's rank correlation coefficients and Kruskal-Wallis tests were used to calculate relationships between variables. Land uses had little effect on distributions of contaminants. Sulfate and fluoride levels were most problematic in the aquifer. Depth and lithology controlled the distributions of each contaminant. Nitrate patterns were controlled mainly by land use rather than geology, but were below the maximum contaminant level. In general, contaminant concentrations have decreased since the 1950s.

No description available.

The thesis entitled “New Supramolecular Ion Sensing Probes and their Application in the Detection of Environmentally Relevant Ions” deals with the design and synthesis of several small molecular probes which can specifically sense environmentally relevant ions of (anion or cation) particularly in aqueous or biological medium. The probes have been designed using four different molecular entities which include anthraquinone, oxidized bis-indolyl system, pyrene and rhodamine. The probes afford naked eye detection of a particular ion in the aqueous medium. This work has been divided into six chapters. Chapter 1. Introduction The first chapter gives a brief idea of ion sensor. It provides the description of various approaches used for designing molecular sensors. The chapter further presents an overview of the four different dyes (anthraquinone, oxidized-bis-indole, pyrene and rhodamine) used for designing probes in this work. The properties of these probes, their advantages and disadvantages to use as a signaling subunit have been discussed. This chapter also describes the use of micellar medium for solubilizing different organic dyes in water. Chapter 2. Colorimetric Probes based on Anthraimidazolediones for Selective Sensing of Fluoride and Cyanide ion via Intramolecular Charge Transfer. The second chapter describes the design and synthesis of four different probes based on anthra [1, 2-d] imidazole-6, 11-dione. The anthraquinone part of each molecule has an acceptor moiety whereas substituted nitrogen linked aromatic unit forms the donor site. Each probe acted as strong colorimetric sensor for fluoride and cyanide ion detection and exhibited intramolecular charge transfer (ICT) band which showed significant red-shifts after addition of either the F¯ or CN¯ ion. One of the probes 2 showed selective colorimetric sensing for both cyanide and fluoride ions. In organic medium 2 showed selective color change with fluoride and cyanide, whereas in aqueous organic medium it showed a selective ratiometric response towards cyanide ion. The effect of anionic charge (on the donor moiety) on ICT has been discussed. Among the various donor moieties, the donor site having negative charges on them was found to disperse greater electron density on them. Figure 1. Molecular structures of the sensors Chapter 3 deals with chemodosimetric detection of cyanide ion in water using various oxidized bis-indole based compounds. Chapter 3A. A Chemodosimetric Probe based on a Conjugated and oxidized Bis¬ indolyl System for Selective Naked Eye Sensing of Cyanide ion in Water. The chapter 3A describes the design and synthesis of a new water-soluble bis-indolyl based probe, 5 which possesses two –COOH groups. This probe specifically reacted with the CN¯ ion in pure water at ambient temperature and produced a remarkable change in color from red to colorless. The mechanism of this process was investigated by NMR (1H, 13C and DEPT-135) spectroscopy, mass spectrometry and kinetic studies. The mechanism investigation showed that the cyanide ion reacts with the probe and removes the conjugation of the bis-indolyl moiety of the probe with that of the 4-substituted aromatic ring which renders the probe colorless. Taken together a plausible mechanism of the reaction was presented which showed to operate via a Michael type adduct formation under ambient conditions of pH and temperature in water. The probe gave a detection limit of 0.38 ppm for detection of cyanide ion in water. Figure 2. Molecular structure of the probe 5. Chapter 3B. Micelle Assisted ppb level Detection of Cyanide ion in Water by Chemodosimetry and Visual detection of the Endogenous Cyanide. The chapter 3B deals with the synthesis of a bis-indole based colorimetric probe 6. The probe showed selective detection of the cyanide ion in water at ppb level and a visible detection of endogenous cyanide from cassava (a major staple food in the developing world) by chemodosimetry. The cyanide ion binds with the probe 6 in a chemodosimetric fashion and follows pseudo first-order kinetics in water under appropriate conditions. It showed a highly sensitive detection of the cyanide ion in water with a detection limit of 0.33 ppm. The use of the micellar medium improved the detection limit drastically and a ppb level detection limit was achieved. The probe also showed the detection of the endogenously bound cyanide in cassava both visually and by spectrophotometer. Figure 3. Molecular structure of the probe 6. Chapter 3C. Ratiometric Cyanide ion probe in Water and for the detection of the Endogenously bound cyanide. Chapter 3C presents the synthesis of two new bis-indolyl (7 and 8) based probes for colorimetric detection of cyanide ion in pure water. Compound 8 showed a ratiometric response with cyanide in water and a visual detection of the endogenously bound cyanide ion in cassava. Using compound 8 the selective detection of the cyanide ion in water was achieved with a detection limit of ~ 17 ppb which is almost 13 times lower than the permitted limit as specified by EPA, United States. 7; R = H 8; R = -(OCH2CH2)3CH3 Figure 4. Molecular structures of the probes 1 and 2. Chapter 4 deals with the colorimetric and ratiometric detection of the Cu2+and Hg2+ions using different small synthetic molecular probes. Chapter 4A. Colorimetric Sensors for Ratiometric Detection of Copper and Mercury ions in Biological media and below ppm level in Water. The chapter 4A deals with the synthesis of two novel colorimetric probes (9, 10) using bispicolyl unit as the binding moiety and anthraimidazolediones and bis-indolyl system as a signaling sub-unit. Using the two sensors, Cu2+ion can be detected below the permitted limit (1.3 ppm) in both drinking water and at physiological pH 7.4. Sensor 9 can detect both Cu2+and Hg2+ in water with very low detection limit. It showed specific binding with Cu2+ at physiological pH 7.4 and in presence of serum albumins. Chemosensor 10 can be used for the specific detection of both Cu2+and Hg2in water as well as for the contamination in microorganisms. Figure 5. Molecular structure of the sensors 9 and 10. Chapter 4B. A New Molecular Probe for the Selective Sensing of Cu2+ and Hg2+ ions in Micellar Media and in Live ells.This chapter describes a synthesis of a novel bispicolyl based sensor 11 which can detect Cu2+ ion specifically in water medium and both Cu2+ and Hg2+ ions selectivelyin Brij-58 micellar medium. In micellar medium both the ions can be detected in the ppb level. Using fluorescence spectroscopy these two metal ions can be discriminated.The probe is also be useful for checking metal ion contamination in cellular samples. Figure 6. Molecular structure of the sensor 11. Chapter 4C. Rhodamine based Sensors for Cu2+ and Hg2+ ions in Water and in Biological media. The chapter 4C presents the synthesis and the sensing properties of the three positional isomers of the pyridine end of the rhodamine-pyridine compounds (12-14). The three isomers only differ in the position of nitrogen of the pyridine moiety. Sensor 12, which contains the pyridine nitrogen at the ortho-position showed selective sensing toward Cu2+ ion in both pure water and in buffered physiological media of pH 7.4. It gave a detection limit of ~13 ppb which is 100 times lesser than the EPA permitted limit. The other two sensors 13 and 14, which possessed the pyridine ends with the nitrogen atom at the meta- and the para- positions respectively showed the selective sensing of Hg2+ ion in water and did not show any interaction with the Cu2+ ion. Probes 2 and 3 showed ‘turn-on’ detection of Hg2+ ion both in the UV-vis and the fluorescence emission spectroscopy. Compound 2 and 3 showed a detection limit of ~ 9 and 4 ppb respectively. The NMR titration showed the change in color was due to the opening of the spirolactam ring of the rhodamine. The sensors can also be used for the detection of Cu2+ and Hg2+ ion in real life water samples and in the live cells. Figure 7. Molecular structure of the sensors 12, 13 and 14. Chapter 5. Ratiometric and ppb level Detection of Toxic Transition Metal ions using a Single Probe in Micellar media. This chapter describes the selective sensing of multiple ions using a single probe 15. The probe incorporates pyrene and pyridine as signaling and interacting moiety respectively. The sensor showed different responses towards different metal ions just by varying the medium of detection. In organic solvent (acetonitrile), the probe showed selective detection of Hg2+ ion. In water the fluorescence quenching was observed with three metal ions, Cu2+, Hg2+ and Ni2+. Further just by varying the surface charge of different micellar media, the probe showed selective interaction with Hg2+ ion in neutral micelles (Brij-58). However, in anionic micellar medium (SDS), the probe showed selective changes with both Cu2+ and Ni2+ in the UV-vis spectroscopy. The discrimination between these two ions was achieved by emission spectroscopy, where it showed selective quenching only with Cu2+. Thus using a single probe all the three metal ions Cu2+, Hg2+ and Ni2+ can be detected and discriminated just by varying the surface charge of the micellar medium. Figure 8. Molecular structure of the sensors 15. Chapter 6. Highly sensitive Rhodamine Based Dual Probes for the Visual detection of F¯ and Hg2+ ions in Water. This chapter deals with the design and synthesis of two new rhodamine based probes (16-17) which act as dual probes for the ppb level selective detection of Hg2+ and F¯ ions in water and at physiological pH 7.4. The two probes were synthesized by coupling tert-butyldiphenylsilyl (TBDPS) protected forms of 4-hydroxybenzaldehyde and 2, 4- dihydroxy benzaldehyde with rhodamine hydrazone. The F¯ ion detection is based on the desilylation of the probe, whereas the spirolactam ring opening leads to the detection of Hg2+ ion. The two probes gave turn-on detection of both Hg2+ and F¯ ion selectively in aqueous medium with the detection limit well below the EPA permitted limits. The probes showed detection of both the ions by dual mode with visibly different color and fluorescence under UV-lamp. The F¯ ion interacts with the silyl bond of probe and the cleavage results into yellow color whereas; the addition of Hg2+ ion to the probe solution opened the spirolactam ring and resulted into appearance of pink color. Figure 9. Molecular structure of the probes 16 and 17. (For structural formula pl see the abstract file)

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / The majority of currently marketed fluoride varnishes (FV) have not been evaluated for their effectiveness in preventing dental caries. Fundamental research on FVs and how different formulations affect adherence to teeth, fluoride release into saliva and uptake by teeth is virtually non-existent. The objective of this work was to investigate the anti-caries potential, measured as fluoride release into saliva, change in surface microhardness of early enamel caries lesions, and enamel fluoride uptake, of multiple commercially available FVs. We have found that FVs differed in their release characteristics, rehardening capability, and ability to deliver fluoride to demineralized lesions. In addition to our in vitro work, we have conducted a clinical study that aimed to compare saliva and plaque fluid fluoride concentrations following the application of three commercially available FV treatments at predetermined post application time points. We also investigated the change in fluoride concentration in saliva and plaque fluid fluoride from baseline to each post application predetermined time point. We found that FVs varied in their release of fluoride into saliva and plaque fluid but shared common trends in release characteristics. The outcomes of our in vitro and in vivo investigations demonstrate a great variation in anti-caries potential of FVs. This may be attributed to different compositions and physical properties of the tested FVs.