School of Chemistry - Theses
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ItemBiomaterial porous networks of hydroxyapatite and titanium dioxide( 2014)A gap in a bone that exceeds 2.5 times the bone radius is termed a critical size bone defect and will not heal naturally. The defect needs to be filled with a synthetic bone substitute (a biomaterial scaffold). \(\textit{In situ}\) delivery of medicinal drugs may assist with treating a bone defect, but current drug delivery vehicles (DDVs) are neither able to controllably release drug molecules nor allow for targeted delivery. Porous networks of either hydroxyapatite (HA) or anatase titanium dioxide could be used as biomaterial scaffolds or DDVs. Using sol-gel chemistry and a templating technique, the preparation of such networks, with potential as materials for biomedical applications, forms the research objective. Polyurethane sponge (PU), polyethylenimine-modified polyurethane sponge, polyurethane-agarose gel composite sponge (AG) and natural sea sponge were used as templates for open-celled, porous HA networks. Two concentrations of sol-gel precursor solutions were employed; the higher concentration obscured the template structure in the final network. The choice of template, multiple sol-gel coating, and the rate of temperature increase when removing the template by calcination led to evolution of the HA fibre surface. PU-templated and AG-templated HA networks were contrasted against each other, with the agarose gel component influencing results. All final networks were HA, but other calcium species were present as well. As an initial alternative to the HA networks, titanium dioxide networks were templated on PU sponge, but these lacked both high surface area and mesoporosity. Next, a Type I collagen gel was employed as a template for anatase titanium dioxide networks composed of mesoporous fibres. A standard method for titanium dioxide network preparation is firstly described, where selective solvothermal treatment preceded calcination. This is followed by modified preparations exploring the morphological transition from the collagen to titanium dioxide network structures, and solvothermal fluids containing varying solvent ratios or ammonia. The collagen fibres were 50-100 nm thick, while the titanium dioxide fibres had walls up to 300 nm thick but retained the collagen structure. Compared to networks that only underwent calcination, solvothermal treatment altered the fibre morphology and enhanced the textural properties (surface area, mesopore diameter and total pore volume). Three titanium dioxide networks, previously templated on collagen gel, and spanning a large surface area range were studied for possible biomedical applications. Biomineralisation took place in a simulated body fluid. Apatite grew on each network indicating in vitro bioactivity, but surface area may affect sustained biomineralisation. Ibuprofen drug delivery was monitored by two methods, with a loading of 58.9 mg/g achieved on the highest surface area network. The drug release was modelled as a sustained diffusion mechanism. Ibuprofen could be stored in mesopores or adsorb to the titanium dioxide fibre surface. Overall, HA and titanium dioxide porous networks were fabricated by sol-gel chemistry and templating. In general, morphology and textural properties were influenced by the choice of template, precursor concentrations and processing conditions, including the rate of heating, calcination time and solvothermal treatment. The collagen-templated titanium dioxide networks have potential as materials for biomedical applications.
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ItemSynthesis, structure and reactivity of ligand stabilized coinage metal nanoclusters( 2013)The coinage metal nanoclusters (CMNCs), defined as copper, silver or gold, constitute an intermediate state of matter that exist between molecules and bulk material. The properties of CMNCs differs to that of molecules and bulk material due to quantum confinement effects. These nanostructured materials have attracted significant attention owing to their fundamentally interesting architectures, and unique properties with applications in areas such as catalysis, optical materials, medical imaging, models for hydrogen storage. Tailoring the properties of such promising materials has proven challenging and requires a fundamental understanding of their assembly, structure and reactivity. The aim of this thesis is: (i) the primary application of mass spectrometric techniques to monitor the formation of CMNCs which result from the addition of sodium borohydride to a solution consisting of a coinage metal salt and the bidentate ligand, bis(diphenylphsphino)methane (dppm) under various synthetic conditions; (ii) to apply this information in developing synthetic approaches to optimize clusters of interest and apply a mass spectrometry (MS) directed synthesis leading to the isolation of crystalline material suitable for structural characterization by X-ray crystallography (iii) apply MS based analysis methods to provide information on the reactivity of CMNCs in solution and the reactivity and structure of mass selected CMNCs in the gas phase. Electrospray ionization mass spectrometry (ESI-MS) and UV-Vis spectroscopy were used to monitor the formation of gold nanocluster cations in the condensed phase via the sodium borohydride (NaBH4) reduction of methanolic solutions containing AuClPPh3 and dppm. ESI-MS highlights the formation of complexes prior to the addition of NaBH4 as [Au2(dppm)2]2+, [Au(PPh3)2]+, [Au2(dppm)3]2+, [Au(dppm)2]+,[Au2Cl(dppm)2]+. The cationic complex product distribution can be monitored over a range of metal to ligand ratios to minimize the colloid precursor [Au(PPh3)2]+. The addition of NaBH4 where the optimized metal to ligand ratio was determined as AuClPPh3:dppm is 1:2 results in the formation of the following types of gold nanoclusters [Au9(dppm)4]3+, [Au9(dppm)5]3+, [Au5(dppm)3(dppm-H+)]2+, [Au10(dppm)4]2+, [Au11(dppm)5]3+, [Au11(dppm)6]3+, [Au13(dppm)6]3+ and [Au14(dppm)6(Ph2PCHPPh2)]3+. The gas phase unimolecular chemistry of these cations was examined by (i) collision induced dissociation (CID) and electron capture dissociation resulting in the gas phase synthesis of the novel clusters [Aux(dppm)y]z+ (x = 2,3 , 6–13; y = 1–6 and z = 1–3) and [Aux(dppm)y(dppm-H+)]z+ (x = 5,14; y= 2,5; z = 2,3) via ligand loss and core fission fragmentation channels. (ii) electron capture dissociation (ECD) of mass selected multiply charged gold cluster cations where an additional fragmentation channel arises due to C-P bond activation. ESI-MS was also applied to study the reactivity that results from silver salts in the presence of dppm, that are treated with sodium borohydride. It was observed by ESI-MS that no all metallic silver clusters had formed. Instead there existed abundant and relatively monodisperse trinuclear silver(I) hydride clusters. The synthesis could be refined by careful MS based analysis to result in the isolation of crystalline material of (i) [Ag3(μ3-H)(μ3-Cl)(dppm)3]BF4, and (ii) [Ag3(μ3-H)(dppm)3](BF4)2. These clusters could be mass selected to generate novel gas phase clusters in the gas phase. The multiply charged cation [Ag3(μ3-H)(dppm)3]2+ was also investigated by ECD and EID. The silver hydride cluster cation [Ag10H8(dppm)6]2+ was observed during the synthesis of trinuclear silver clusters. This cluster has yet to be isolated.