The theme that is central to this thesis, connecting the three experimental chapters, is the synthesis and characterization of hybrid inorganic-organic nanocomposites, facilitated through inorganic and biological self-assembly.

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Molecules pack in accordance with Kitaigorodsky's theory of close packing to minimise empty space between molecules. The mode of packing is dependent on molecular shape, such that the bumps on one molecule fit roughly into the grooves of a neighbouring molecule. It is possible to extend the close packing theory to ask the following question: Is it possible to interchange substituents of similar shape and size, such as chlorine and methyl (Cl-Me interchange), on a molecule without causing it to adopt a different crystalline structure? This thesis summarises attempts to answer this question. Chapter 2 summarises methods for finding the frequency of isostructural Cl-Me interchange by retrieving as many examples as possible from the Bath Information and Data Services and the Cambridge Structural Database (CSD). However, given the large number of crystal data entries within the CSD, the frequency was approximated from that database. Approximately 23% of all examples retrieved from the CSD are isostructural, which illustrates that factors other than the size and shape of interchanged substituents determine crystal structure. Chapter 3 summarises attempts at finding intermolecular and molecular factors that govern isostructural CL-Me interchange and concludes that minimising the intermolecular interactions of Cl and Me can facilitate isostructurality. Chapters 4, 5 and 6 go on to summarise three approaches for reducing the intermolecular contacts of Cl and me with successful examples of forced isostructurality through co-crystallisation. Finally, chapter 7 discusses the formation of supramolecular tapes - common structures formed by crystal engineers, and illustrates how small changes in the size and shape of acid spacers can effect tape structure and crystal structure.

This thesis describes studies of the kinetics of N₂O₅ hydrolysis using proxies for tropospheric aerosols, measured using an atmospheric pressure aerosol flow tube. The rate of N₂O₅ hydrolysis has been shown previously to depend on particle phase and water content so these physical properties were characterised in detail for some aerosols. The N₂O₅ hydrolysis reaction was initially studied on sulphate aerosols, specifically sulphuric acid, ammonium sulphate and ammonium bisulphate. Good agreement was found between this work and previous studies in the literature. The effect of the organic component of tropospheric aerosol on the N₂O₅ hydrolysis reaction was then considered. Two classes of atmospherically relevant organic species were investigated: dicarboxylic acids and polycarboxylic acids (represented by humic acid). For single-component dicarboxylic acid aerosols, uptake was found to depend on aerosol liquid water content. It was shown that the reactivity of mixed dicarboxylic acid/sulphate aerosols can be predicted based on a knowledge of the liquid water content of the single-component aerosols. The phase transitions of aerosols containing humic acid and mixtures of humic acid and ammonium sulphate were studied prior to an investigation of their chemical reactivity. Ammonium sulphate phase transitions were modified when humic acid was present. The growth of these mixed aerosols could be predicted assuming that the organic and inorganic components take up water independently. The reactivity of ammonium sulphate aerosol was significantly lowered in the presence of humic acid. The results from these experimental measurements are considered within the context of NO_x chemistry in the troposphere.

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This thesis describes a study of the synthesis and characterisation of a new family of cationic alkane-thiolate and -selenolate compounds bearing a phosphonium (or phosphine oxide) head group, and the applications as ligands for the stabilisation of gold nanoparticles. The ability of these cationic phosphonium gold nanoparticles as substrates for the detection of negatively charged biomolecules has also been explored. In chapter 1, topics concerning the synthesis of functionalised gold nanoparticles, their biorecognition properties, the application of these nanoparticles in the biomedical field and gold nanoparticles stabilised with phosphorus-containing ligands, are outlined in a literature review. Instrument details of the analytical methods employed to characterise all the compounds and nanoparticles obtained in the study are outlined in Chapter 2. The syntheses and structural characterisation by NMR, ESMS and X-ray crystallography of cationic phosphonium-containing ligands are described in Chapters 3 to 5. Chapter 3 contains the description of the synthesis of phosphonioalkylthiosulfate zwitterions. The synthesis of related phosphonioalkylselenide compounds is presented in Chapter 4, and Chapter 5 is concerned with the synthesis of phosphonioalkylthioacetate and related phosphine oxide ligands. In Chapter 6, the preparation of the cationic phosphonium-functionalised gold nanoparticles using the phosphonium-containing compounds as protecting ligands, in a two-phase liquid-liquid (DCM-H[2]O) and one phase (ethanol) systems, is described. This chapter also contains details of characterisation of these nanoparticles by NMR, XPS and TEM. The ability of the cationic phosphonium gold nanoparticles to interact with RNA and cDNA, and the potential of using these nanoparticles as biorecognition systems was investigated by the Biacore Surface Plasmon Resonance technique and this work is described in Chapter 7. Finally, a summary of conclusions and some suggestions for future work are presented in Chapter 8.

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S-nitrosothiols undergo homolytic decomposition in aqueous solution to release NO and are also able to transfer the NO+ group to other thiolates to generate Snitrosothiols, which may undergo more facile homolysis. These reactions are probably of some significance in intracellular processes, while the use of S-nitrosothiols as sources of NO is well known, although the possibility of transnitrosation has not always been considered. However, it is possible that some of the biochemistry of Snitrosothiols takes place in cell walls and that their lipophilicity is an important factor in controlling reactivity. Fo/ these reasons, a major part of this thesis has been concerned with the study of the kinetics of decomposition S-nitroso-Nacetylpenicillarnine (SNAP) in a number of non-aqueous solvents, including Noctanol, which is often used to model the lipophilicity of cell membranes. Octanolwater partition coefficients have been measured for SNAP and GSNO (Snitrosoglutathione) and shown to be 0.36 and -1.87 respectively. The reactions of the linear tetrapyrroles biliverdin and bilirubin with some reactive nitrogen oxide species has also been studied. Bilirubin was once regarded as a waste product from the break down of the haem group that is catalysed by the enzyme haem oxygenase. However it now appears that bilirubin acts as a major antioxidant, undergoing oxidation to biliverdin. It has been shown in this thesis that bilirubin also reacts with reactive nitrogen species that cause nitrosative stress. This suggests that bilirubin is a major factor in combating cellular stress in general.