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Measurements have been made of the X-ray scatter from an MgO single crystal at low temperatures irradiated by an infra-red laser beam of wavelength 10.6μm. The purpose of these measurements was to obtain information about the anharmonic coupling between the lattice vibrations. The modes investigated were the transverse acoustic phonons in the [100] direction, which it has been suggested have anomalously long lifetimes at very low temperatures. The above method was chosen after considering a variety of possible excitation methods including electron-phonon interactions via the piezoelectric effect and the deformation potential. These other processes had to be rejected because they either excited phonons which were unsuitable for X-ray measurement or required pulsed experiments. The dispersion curves for MgO, obtained from a deformable shell model for the lattice were analysed to provide information as to the most likely positions in reciprocal space for phonon population enhancement to occur. The decay routes for the primary phonons excited directly by the infra-red radiation were predicted from the dispersion curves. A major part of the work involved the design and construction of the helium cryostat on which the sample crystal was mounted and kept at as low a temperature as possible. The standard X-ray detection technique of a scintillating crystal-photomultiplier combination was employed and the infra-red beam was produced by a CO2 gas laser with an output power of up to lOW. Because of the nature of the measurements, the results obtained for the change in X-ray scatter by the MgO crystal when the infra-red beam was shone on the crystal required analysis by statistical methods in order to provide the maximum information. It was possible to set an upper limit to the effects found of a few percent, and to compare the orders of magnitude of the coupling for two different processes.

Nitrifier denitrification is a poorly quantified microbial process leading to emissions of N2O from soils. Nitrous oxide emissions, particularly from agricultural soils, are currently being targeted for reduction due to the contribution of this gas to anthropogenic climate change. Measurements specific to nitrifier-denitrification are hampered by poor culturability of many of the strains involved, and the inability of single isotope labelling methods to distinguish it from denitrification carried out by other organisms, dual-labelling approaches and evidence form pure cultures suggest that its contribution to nitrous oxide emissions may be large. Environmental conditions favouring the pathway are unknown, leading to difficulties in mitigation or modelling. In this thesis data from both dual-labelling isotopic techniques and isotopomer measurements of the nitrous oxide emitted are used to determine whether isotopomer techniques can quantify nitrifier-denitrification in situ, and the conditions under which nitrous oxide emissions from the pathway are increased are investigated. Data is also presented on site preference (isotopomer ratio) from ammonia oxidation in several Nitrosospira strains for which this has previously not been measured. The capacity of Nitrosospira strains in pure culture to reduce N2O to N2, an environmentally neutral product of the nitrogen cycle, are investigated. Site preference results from this research suggest that nitrifier denitrification cannot be distinguished from heterotrophic denitrification by site preference, indicating that previously published data stating proportional outputs of N2O from dentrification may overestimate heterotrophic contributions. Several Nitrosospira strains are found to be capable of a reduction step from N2O to N2 in pure culture conditions. Nitrifier denitrification is found to respond to environmental factors of soil N-level, pH and rainfall events, and changes in site preference also occur under these conditions. Site preference is linked to microbial phylogeny for the strains of Nitrosospira tested, indicating a possible effect of enzyme structure above pathway level determination.

Human activities have doubled the loading of ecosystems with reactive nitrogen (N) contributing to many serious problems such as eutrophication, climate change and pollution. As most anthropogenic reactive N is created to supply plant-available N in agriculture, one of the ways to mitigate the situation is to improve N use efficiency in crop production. It is also potentially more sustainable to supply N to crops using biological N fixation (BNF) rather than synthetic N fertilisers, because BNF does not rely on energy from fossil fuels to create plant-available N. Soil pH affects N transformations (e.g. nitrification is generally slower in low pH), but pH effects during decomposition of green manure and pH interactions with physico-chemical properties of the plant material are not well known. Here, effects of soil pH on N release, mineral-N dynamics and N2O emissions during plant material decomposition were studied. One of the objectives was to establish if regulation of soil pH could be used to manipulate N supply from green manures to crops. It was the first time such study was conducted using a long-term pH gradient (Woodlands Field, Craibstone, Aberdeen, UK). This enabled to avoid short-term effects of pH change on soil biochemical processes and confounding effects of other variables, such as soil texture and organic matter content, which vary when soils from different locations are used. Field and laboratory experiments showed that soil acidification is unlikely to be useful as a means regulate N supply from green manure (e.g. to reduce risk of nitrate leaching) as it did not significantly affect N release and nitrate dynamics. Comparison of different green manure species showed that tannin-rich plant material and purified tannins can interact with soil pH affecting soil microbial community composition and N2O emissions, but the effects were not related causally, which warrants further investigation.

This dissertation focuses on chemical and biological evaluation of diazeniumdiolate based nitrogen oxide releasing prodrugs. Three projects are described. i. Synthesis and biological evaluation of a series of new nitroxyl (HNO) releasing non-steroidal antiinflammatory drugs (NSAIDs) and comparison to related nitric oxide (NO) releasing NSAIDs A series of HNO releasing isopropylamine-based diazeniumdiolate adducts of NSAIDs and the NO releasing diethylamine diazeniumdiolate counterpart were synthesized. The aspirin derivatives were evaluated for antiinflammatory, cardioprotective and anticancer effects. Both prodrugs demonstrated similar antiinflammatory properties to aspirin but significantly lower gastrointestinal ulceration, which is a common side effect of aspirin. The HNO adduct also improved cardiac contractility. The chemotherapeutic potential of the prodrugs was assessed in vitro and in vivo. Both the prodrugs inhibited growth of cultured carcinoma cells without inducing cytotoxicity towards non-tumorogenic cell lines. The higher cytotoxicity of the HNO adduct was in part due to increased production of reactive nitrogen and oxygen species leading to oxidative damage to DNA, inhibition of glyceraldehydes-3-phosphate dehydrogenase and upregulation of signaling pathways leading to caspase-3 mediated induction of apoptosis. The NO adduct is a promising candidate for reduction of metastasis by increasing E-cadherin levels, which influences cellular adhesion. Both derivatives showed significantly reduced angiogenesis in cultured cells and tumor volume in nude mice. ii. Synthesis and characterization of primary amine based cyclic amine diazeniumdiolates and comparison to their acetoxy methyl ester derivatives. A series of HNO releasing cyclic amine diazeniumdiolates were synthesized to expand upon the few examples of primary amine diazeniumdiolates. An ester derivative of cyclopentylamine NONOate was also synthesized, to increase decomposition half-life and to improve HNO production and better cellular uptake. This modification increased its cytotoxicity compared to ionic NONOates. iii. Evaluation of mechanism of action of JS-K. JS-K (O²-(2,4-dinitrophenyl)-1-[(4-ethoxycarbonyl)-piperazin-1-yl]-diazeniumdiolate) has previously been found to be highly cytotoxic in many cancer cell lines compared to ionic diazeniumdiolates. Thus, the role of NO in cytotoxicity of JS-K was explored. A low intracellular NO flux in combination with a lack of any effect on cyclic guanosine monophosphate (cGMP) dependent pathway suggests that NO is not directly responsible for the cytotoxicity of JS-K.

We have studied a continuous aerosol process for producing oxide nanoparticles with sizes of 10-60 nm that are decorated with smaller 1-3 nm metallic nanoparticles. Such particles may be useful in a number of areas including catalysis and as contrast enhancement agents in biomarkers. To produce the oxide nanoparticle carriers, an aerosol of 1-10 [micrometer] oxide particles are ablated using an excimer laser. The resulting oxide nanoparticle aerosol is then mixed with 1-2 [micrometer] metallic particles and this mixed aerosol is ablated a second time. The oxide nanoparticles are too small to ablate but act as seeds for the nucleation of metallic nanoparticles on the surface of the oxide. The nanoparticle sizes can be varied by changing the gas type or gas pressure in the aerosol. We demonstrate the feasibility of such an approach using two oxides, SiO₂ and TiO₂, and two metals, Au and Ag. / text

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