Positron emission tomography (PET) employs short half-life positron emitting isotopes, typically ¹⁸F, for in vivo measurement of physiological processes. Easy access to structurally diverse radiolabelled probes would accelerate the rapid progress of PET imaging but, to date, radiochemistry is still limited by cost and efficiency. Nucleophilic fluorination with ¹⁸F-fluoride is the preferred “non-carrier-added” methodology in the synthesis of ¹⁸F-labelled pharmaceuticals because it leads to radiotracers with a high specific activity, a key feature allowing for investigations to be performed in sub-toxic doses. Chapter 1 serves as an introduction on radiochemistry, especially focussing on current radiosynthetic methods for the synthesis of ¹⁸F-labelled aromatics. Aromatic compounds without electron-withdrawing groups are notoriously difficult to label with ¹⁸F-fluoride. In this thesis, we present two novel methodologies to deliver ¹⁸F-labelled aromatic compounds from nucleophilic 18F-fluoride. Chapter 2 details the experimental efforts towards “Convergent Radiosynthesis” (Scheme 1). We proposed a convergent synthetic tactic that allows for simultaneous reaction between three or more substrates, including an ¹⁸F-labelled building block. This chemistry has been validated by the radiosynthesis of various structural scaffolds which are not responsive to direct nucleophilic fluorination. Chapter 3 presents our research into “Oxidative Nucleophilic ¹⁸F-Fluorination” (Scheme 2). We proposed that electron-rich aromatics, such as phenols, which are not responsive to nucleophilic fluorination may undergo umpolung reactivity under oxidative conditions. This “umpolung strategy” allows for the direct transformation from ¹⁸F-fluoride to 4-[¹⁸F]fluorophenol. Potentially, this established oxidative fluorination strategy could be adapted to the radiosynthesis of radiotracers containing a 4-fluorophenol sub-motif, such as 6-fluoro-meta-tyrosine. An appropriate precursor has been validated for the prospective radiosynthesis of 6-[18F]fluoro-meta-tyrosine.

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In this work, a pulsed CO₂ laser was used to excite methanol, ethanol, propan-2-ol, butan-2-ol, t-butanol, pentan-2-ol, hexan-2-ol, and 3,3-dimethyloxetane in order to study how these moleCUles absorb laser energy and decompose. The dependence of absorbed energy and fractional yield on laser parameters such as irradiating wavelength.,fluence and pulse type, and on reactant molecular size, pressure and diluent, was examined. The absorbed energy was measured using the optoacoustic (OA) technique. A new method for calibrating the OA cell was developed and is described in full in the thesis. The approach enables calibration to be extended to lower absorption levels (about 200µJ for a signal-to-noise ratio of six) than is possible with the more usual transmission methods, and was found to be capable of measuring as little as 5µJ. A particular advantage of the technique, is that it is simple, rapid, and provides an immediate visual indication of the absorption level. It is observed, for all reactants studied, that the absorption cross-section at low pressure was less than at high pressure, but that the difference diminishes with molecular size with the absorption cross-section taking on a value comparable to that of the small signal, broadband cross-section. These findings are consistent with the explanation that rotational hole-burning exists, but decreases in importance as the molecular size, and hence density of states, increases. As the fluence is varied, the absorption cross-section is found to increase with decreasing fluence towards the small signal, broadband value. With increasing molecular size the increase is less noticeable, and the absorption cross-section takes on the value comparable to that of the small signal, broadband cross-section. With increasing alkanol molecular size, it is observed that the major decomposition products can always be explained in terms of a molecular elimination channel i.e. one of dehydration. Also, the number of minor products and their yields both increase. It is believed that most of the minor products arise as a consequence of carbon-carbon fission processes, with minor contributions due to molecular elimination.

Thesis--University of California, Berkeley, 1959. / "Chemistry General" -t.p. Includes bibliographical references (p. 119-122).

Materials representative of those found in a Geological Disposal Facility (GDF) for the long-term storage of nuclear waste have been investigated for their ability to retard the movement of ionic species found in nuclear waste. Fe1-xO, Fe2O3, Fe3O4 (from steel corrosion) and sandstone (bedrock) used as physical barriers in the GDF have been treated using solutions of pH 7-13 which are representative of the leachate expected from concrete encapsulation of waste in contact with ground water. A mimic of portlandite cement, Ca(OH)2 was also prepared carbonate-free via a sacharate method for use in these leachate experiments. Materials have been characterised using a mixture of techniques such as Powder X-ray Diffraction (PXRD) and Infra-red Spectroscopy which focus on the bulk, short range techniques such as Extended X-ray Absorption Fine Structure (EXAFS), Scanning Electron Microscopy(SEM) and Nuclear Magnetic Resonance(NMR) and physical measurements such as diffusion experiments and fluorescence spectroscopy. Characterisation of the bulk materials before and after treatment using PXRD and SEM indicates that high purity iron oxides are affected differently by the solutions of varying pH. While not detectable by bulk techniques, SEM analysis evidence of the surface of the materials showed that Fe1-xO was deleteriously affected by solutions with pH > 7 more than the more oxidised materials. Initially needle-like crystals formed on the surface of Fe1-xO that are characteristic of goethite which at long aging times up to 168 h, showed transformation to crystal morphologies characteristic of Fe2O3. As the alkalinity increased, the transformation of Fe1-xO to Fe2O3 slowed. Dissolution of the iron surfaces in the solutions of pH 7-13 were determined by measuring the concentration of dissolved iron using ICPMS. While Fe1-xO and Fe3O4 followed first order kinetics, the dissolution kinetics for Fe2O3 appeared more complex. As the alkalinity increased, the rate constant for dissolution decreased in all cases indicating that higher pH is better for containment due to the formation of a passivated surface layer evidenced by SEM. The sorption of uranium to the iron oxide surfaces was investigated as a function of pH (7-13). In all cases, there was evidence of uranium sorption. The greatest sorption was evidenced when Ca(OH)2 was present which is most likely due to the precipitation of the known phase, calcium uranate. In the absence of calcium hydroxide, the sorption of uranium to the iron oxide surfaces decreased as the pH increased, reflecting the increase in formation of the anionic uranium species. In the presence of carbonate, the sorption of uranium onto the surfaces also decreases reflecting the formation of the soluble uranyl carbonate species. NMR spectroscopy of uranyl species in solution indicates that the chemical shift is strongly affected by pH shifting from 163 ppm to 175 ppm as the pH changes from 7 to 13 and allowing the uranium speciation to be used as a pH probe. A much -2- smaller shift in respect of temperature of less than 0.5 ppm was observed in the temperature range studied between 25 and 50°C. The quality of fluorescence spectra has been shown to be strongly affected by complexing species present in solution, the best spectra achieved with non-complexing species such as perchlorate. Migration experiments of the radionuclides uranium, thorium and technetium has been investigated by placing sandstone cores in alkaline solution and analysing both the water itself and the core to examine retention and transport. The results determined that the technetium diffused readily through the sandstone matrix. The uranium and throrium did not achieve breakthrough. This was attributed to the low solubilities and the formation of stable precipitates.

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M.Sc. (Chemistry) / Secondary cancer tumour formation, often called metastasis, remains one of the great scientific challenges in public health. Patients with skeletal metastases have a low survival rate, with great discomforts experienced by the sufferers. Pain, decreased mobility, pathologic bone fractures are some of the effects that these patients have to live with. Significant inroads have been made in using radio pharmaceuticals as a pain palliation treatment for bone metastases. They comprise of a bone seeking phosphonate ligand and a radionuclide. The structural variation of the phosphonate affects to a great extend the effectiveness of the radiopharmaceutical with the greatest shortfall being myelosuppression at high doses. In this study an attempt is made at synthesizing novel bisphosphonates, APDDAM and APDDPE. After several synthetic steps from the protected β-alanine tert butyl ester, the free acid precursor was achieved (as shown in the NMR and elemental analysis) in good yields. Unfortunately the final reaction step to form the bisphosphonate ligand was unsuccessful, with the free acid precursor dissociating in the acidic conditions to form salts. A polymer ligand poly-HEDP was synthesized from its free acid form in relatively low yields. The ligand was used in potentiometric studies with the metal ions Ca(II), Mg(II), Cu(II), Zn(II), Sn(II) and Sn(IV) to evaluate its potential as radiopharmaceutical candidate. The ESTA model formation constants obtained were used in the ECCLES blood plasma model to evaluate the competitive stability of the complexes against biological metal ions and ligands. The Sn(IV)-poly-HEDP complex was shown to be unstable, with a 100 % dissociation. On the other hand the Sn(II)-poly-HEDP showed much improved stability with 100 % of the metal ion remaining bound to the ligand.