The dislocation etch pits formed on the cleavage surfaces of lithium fluoride in an aqueous solution containing varying concentrations of ferric ions are investigated by electron microscopy. The results obtained reveal the powerful influence of the inhibitor in the stabilisation of kinks and macroledges. There is some evidence for the nucleation of disso­lution at imperfections other than the dislocations. Dissolution spirals are observed in some cases suggesting the presence of helical dislocations in lithium fluoride. / Thesis / Master of Science (MS)

Fluorescence spectroscopy has been considered to be one of the most important research techniques in modern analytical chemistry, biochemistry, and biophysics. At present, fluorescence is a dominant methodology widely used in a great number of research domains, including biotechnology, medical diagnostics, genetic analysis, DNA sequencing, flow cytometry, and forensic analysis, to name just a few. In the past decade, with the rapid development of fluorescence microscopy, there has been a considerable growth in applying fluorescence technique to cellular imaging. The distinguished merits of fluorescence techniques, such as high sensitivity, non-invasiveness, low cytotoxicity, low cost, and convenience, make it a promising tool to replace radioactive tracers for most biochemical measurements, avoiding the high expense and difficulties of handling radioactive tracers. Among the wide range of applications of fluorescence technique, fluorescent sensing of various cations and anions is one of the most important and active areas. This dissertation is all about developing fluorescent sensors for physiologically significant ions, including F-, K+, Fe3+, and Ca2+. All of these sensors demonstrate fluorescence "turn-on" response upon interacting with their respective ions, which makes them much more appealing than those based on fluorescence quenching mechanisms. In Chapter II, a novel highly selective fluorescence turn-on F- sensor (FS), comprised of a fluorene platform serving as the chromophore, and two 1,2,3-triazolium groups functioning as the signaling moieties, is described. The function of FS is established on the basis of deprotonation of the C-H bonds of 1,2,3-triazolium groups, which makes FS the first reported anion sensor based on the deprotonation of a C-H bond. Easy-to-prepare test strips were prepared for determining F- in aqueous media, providing an inexpensive and convenient approach to estimate whether the concentration of F- contained in drinking water is at a safe level. Chapter III contains an optimized synthesis of a reported K+-selective group (TAC), and the development of two TAC-based fluorescence turn-on K+ sensors (KS1 and KS2). The synthetic route of TAC is shortened and its overall yield is enhanced from 3.6% to 19.5%. Both KS1 and KS2 exhibited excellent selectivity toward K+ over other physiological metal cations, high sensitivity for K+ sensing, and pH insensitivity in the physiological pH range. Confocal fluorescence microscopy experiments demonstrate that they are capable of sensing K+ within living cells. 2PA determination reveals that KS2 has a desirable 2PA cross section of 500 GM at 940 nm, which makes it a two-photon red-emitting fluorescent sensor for K+. Chapter IV describes the development of a novel BODIPY-based fluorescence turn-on Fe3+ sensor (FeS). FeS is a conjugate of two moieties, a BODIPY platform serving as the fluorophore and a 1,10-diaza-18-crown-6 based cryptand acting as the Fe3+ recognition moiety. FeS displays good selectivity, high sensitivity, reversibility, and pH insensitivity toward Fe3+ sensing. Based on its excellent performance in determining Fe3+ and very low cytotoxicity, FeS was effectively applied to sensing Fe3+ in living cells. In Chapter V, a new BODIPY-based fluorescence turn-on sensor (CaS) was designed and synthesized for selectively and sensitively determining Ca2+. CaS is comprised of two moieties, a BODIPY fluorophore and a Ca2+ complexing unit. CaS demonstrated selective fluorescence turn-on response towards Ca2+ over other biological metal cations. Moreover, CaS exhibited desirable sensitivity for Ca2+ detection, which makes it more suitable for extracellular Ca2+ determination. In addition, CaS was insensitive to the pH of the physiological environment, especially in the pH range of blood and serum. Therefore, CaS has potential to be applied to sensing Ca2+ ions in extracellular environments. Chapter VI discusses potential future work of KS2 and CaS, following the results achieved in this dissertation. Based on the desirable performances of both sensors in sensing their respective ions, future work could largely be focused on their applications in cellular imaging.

Caries is one of the most common diseases in dentistry. The key to preventing caries is the balance between demineralization and remineralization. Dental delivery methods such as toothpaste, gels, and varnishes are commonly applied as preventative methods against caries. With the advancement of nano-technology, dentistry can supplement traditional diagnostic and treatment methods with more advanced, efficient, and personalized dental care. Hydroxyapatite (HA) is a biomimetic agent that aims to remineralize and protect the enamel from erosion. It is formed by nanoparticles similar to apatite crystals of tooth enamel. Furthermore, it is one of the most biocompatible and bioactive materials. Because HA is present in our enamel, it will be proven as an effective biomimetic agent for the prevention and remineralization of caries. The Caries Management by Risk Assessment (CAMBRA) tool helps dental care professionals identify high-risk patients more susceptible to caries. With the addition of biomimetic agents such as hydroxyapatite, dentists can effectively provide treatment to detect early-stage lesions and correctly intervene with remineralization techniques in all patient types. Studies have shown that HA toothpastes have anti-bacterial properties against S. mutans caries causing bacteria, and inhibit demineralization, similar to fluoride. In orthodontic patients, no significant difference was found between fluoride and HA dentifrice on caries progression nor between HA and fluoride gel in remineralizing initial caries. Similar reports found non-inferiority of hydroxyapatite toothpaste compared to fluoride toothpaste. Fluoride's mechanism of action differs from HA in that hydroxyapatite protects enamel by creating a new layer of enamel, and fluoride hardens the existing enamel layer. A comparison of three biomimetic agents, Casein Phosphopeptides Amorphous Calcium Phosphate (CPP-ACP), Tricalcium Phosphate (TCP), and hydroxyapatite found hydroxyapatite to have the highest amount of remineralization with nHA being more effective in managing early caries and decreasing lesion depth. Hydroxyapatite toothpaste was also shown to be a favorable alternative to oxidizing bleaching agents and zinc-carbonate hydroxyapatite being more effective than a fluoride/potassium nitrate dentifrice in reducing dentin hypersensitivity. With the high consumption of acidic food and beverages, a Zinc-nHA toothpaste was to be more effective than fluoride toothpaste in remineralization and protection after the acid attack and demineralization from Coca-Cola. In conclusion, with the reported results of the studies in this paper, it is known that nano- hydroxyapatite is an effective and safe alternative to fluoride. Many studies have proven nano-hydroxyapatite effective in helping to remineralize early carious lesions. In some studies, it is just as promising as fluoride is. It is especially beneficial for high-risk patients to implement nHA into their oral care routine. Nano-hydroxyapatite (nHA) has been proven to promote remineralization, inhibit demineralization, whiten teeth, protect against dental erosion, and reduce dentin hypersensitivity.

Randomized complete block designs with three replications were utilized to evaluate the effects of fumigation with sulfuryl fluoride (SF) (0, 12, 24, 36 and 72 mg/L), phosphine (PH3) (0, 200 and 1000 ppm at 48 hr), methyl bromide (MB) (0, 4, 8, 16, and 32 mg/L for 48 hr), carbon dioxide (CO2) (0, 60% at 48 hr and 60% at 96 hr) and ozone (O3) (0 ppm and 175 ppm for 48 hr) on the volatile flavor compound concentrations in dry cured ham. Fluoride and SF concentrations increased (P < 0.05) in dry cured hams as SF fumigation concentration increased, but all samples contained fluoride and SF concentrations below the legal limits of 20 and 0.01 ppm, respectively. Also, as phosphine fumigation concentration increased, the residual concentration of phosphine also increased in the hams (P < 0.05), but all samples contained levels that were lower than the legal limit of phosphine in stored food products (0.01 ppm). Minimal differences existed in the presence and concentration of aroma active compounds in fumigated hams when compared to the control. Triangle tests indicated that consumers could not discern (P > 0.75) between the control hams and the fumigated hams. This study revealed that there were minimal aroma/flavor differences among control hams and hams that were fumigated with SF, PH3, MB, CO2 or O3 and that fumigation of dry cured ham with SF and PH3 were safe and met legal requirements for consumption. This reveals that SF, PH3, CO2 and O3 could be tested at the industrial level to determine their efficacy as potential alternatives to methyl bromide to treat dry cured hams for insect pests.

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Yes / The syntheses of three series of complexes designed with self-complementary motifs for formation of halogen bonds between an iodotetrafluorophenyl ligand and a halide ligand at square-planar nickel are reported, allowing structural comparisons of halogen bonding between all four halides C6F4I⋯X–Ni (X = F, Cl, Br, I). In the series trans-[NiX(2,3,5,6-C6F4I)(PEt3)2] 1pX and trans-[NiX(2,3,4,5-C6F4I)(PEt3)2] (X = F, Cl, Br, I) 1oX, the iodine substituent on the benzene ring was positioned para and ortho to the metal, respectively. The phosphine substituents were varied in the series, trans-[NiX(2,3,5,6-C6F4I)(PEt2Ph)2] (X = F, I) 2pX. Crystal structures were obtained for the complete series 1pX, and for 1oF, 1oCl, 1oI and 2pI. All these complexes exhibited halogen bonds in the solid state, of which 1pF exhibited unique characteristics with a linear chain, the shortest halogen bond d(C6F4I⋯F–Ni) = 2.655(5) Å and the greatest reduction in halogen bond distance (I⋯F) compared to the sum of the Bondi van der Waals radii, 23%. The remaining complexes form zig-zag chains of halogen bonds with distances also reduced with respect to the sum of the van der Waals radii. The magnitude of the reductions follow the pattern F > Cl ∼ Br > I, 1pX > 1oX, consistent with the halogen bond strength following the same order. The variation in the I⋯X–Ni angles is consistent with the anisotropic charge distribution of the halide ligand. The temperature dependence of the X-ray structure of 1pF revealed a reduction in halogen bond distance of 0.055(7) Å on cooling from 240 to 111 K. Comparison of three polymorphs of 1oI shows that the halogen bond geometry may be altered significantly by the crystalline environment. The effect of the halogen bond on the 19F NMR chemical shift in the solid state is demonstrated by comparison of the magic-angle spinning NMR spectra of 1pF and 1oF with that of a complex incapable of halogen bond formation, trans-[NiF(C6F5)(PEt3)2] 3F. Halogen bonding causes deshielding of δiso in the component of the tensor perpendicular to the nickel coordination plane. The results demonstrate the potential of fluoride ligands for formation of halogen bonds in supramolecular structures. / We acknowledge an Overseas Research Scholarship from the University of York to VT. We also acknowledge support from EPSRC (grants EP/J012955/1 and EP/ J012998/1).