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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Ammonia borane composites for solid state hydrogen storage and calcium-ammonia solutions in graphite

Nathanson, A. S. January 2014 (has links)
The dual problems of worlds growing population, increasing energy demand and global warming, necessitate an alternative to fossil fuels. Hydrogen is plentiful and has a high energy density but storage in high pressure tanks is complex and presents safety concerns. Ammonia borane (AB) is one of the most promising solid state hydrogen storage materials due to its high releasable hydrogen content (13.1 wt%), stability in air, and low toxicity. On heating, however, pure AB releases hydrogen only after long nucleation times and is accompanied by the liberation of gaseous impurities including borazine and ammonia; additionally, extensive material expansion and foaming occurs. AB composites with polyethylene oxide, polystyrene and imogolite have been synthesized. It is concluded that the decomposition of AB is best ameliorated by providing access to functional groups that catalyse alternative dehydrogenation routes. Lowering the onset of hydrogen loss to below the melting temperature limits the overall foam and expansion. The two dimensional confined motion of liquid ammonia in a multi staged ternary calcium ammonia graphite intercalation compound was studied with respect to temperature. Hopping diffusion at 300K gives way to rotation below 100K. The dynamics of this confined calcium ammonia solution are observed as similar to the three dimensional counterpart.

Metal oxide semiconductor gas sensors as an electronic nose for the detection of microbial agents

Newton, E. J. January 2015 (has links)
The problem of rapid detection of bacteria for 'in-field' applications is addressed by way of a portable 'electronic nose' comprised of five metal oxide semiconductor (MOS) gas sensors in an array for the discrimination of volatile organic compounds (VOCs) associated with bacteria species such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). A prototype portable sensor array unit (PSA unit) is presented capable of heating and taking measurements from five MOS gas sensors using a 7-volt power source. An array of five sensors based on zinc oxide (ZnO) is produced suitable for the operational requirements for portable applications. This was achieved be means of zeolite modification where a selection of these microporous aluminosilicalite structures (H-ZSM-5, H-ZSM-22 and H-Y) were incorporated into the ZnO sensor as admixtures, overlayers, admixtures as an overlayer and admixtures with overlayers using commercial screen-printing methods. Unique signal patterns towards ethanol and acetone, two key markers identified for the model bacteria selected for this thesis, were achieved at low ppm concentrations (a detection limit of 2 ppm is reported) using just one MOS material with various zeolite modification strategies.

Plasma electrochemistry : electron transfer at the solid/gas interface

Elahi, A. January 2014 (has links)
The ability to control redox reactions at the solid/gas interface is demonstrated for the first time, by considering gaseous flame plasma as an electrolyte. An innovative method to perform potentio-dynamic experiments in a liquid-free electrochemical system using flame plasma is described. This novel approach can help apply the well-established foundations of electrochemistry developed almost exclusively in liquids, to the new context of gas plasma. There are limited examples using plasmas as media to study redox reactions but no examples of voltammetry in the gas phase at true solid/gas interfaces. Successful electrochemical measurements are illustrated by doping the flame plasma with both inorganic and organic species, and recording distinct faradaic peaks at defined potentials in cyclic voltammograms. The sensitivity of the system is highlighted by the ability to distinguish between several amino acids, pinpointing specific functional groups. The most significant innovation responsible for these measurements is the development of a reference electrode able to function at temperatures over 1300 K. Extensive assessment of several materials has enabled the development and optimisation of a reference electrode, allowing an extension of the potential window to 10 V; an unprecedented value in electrochemistry. After careful experimentation and appropriate control experiments, the features observed are confirmed as specific reduction processes at the solid/gas interface. Undoubtedly, and perhaps expectedly, there are significant departures from the analogous process in condensed phases. The physical origin of these electrochemical signals is discussed and a framework of interpretation upon which a full mechanistic understanding can be based is provided. The scope of commercial and academic impact is extensive. Liquid-free electrochemistry presents access to a plethora of redox reactions, which lie outside potential limits defined by liquids. The prospect of new redox chemistries will enable new technological applications such as electrodeposition and electroanalysis, which have significant economic and environmental benefits.

Modelling phosphate-based glasses for biomedical applications

Ainsworth, R. I. January 2014 (has links)
In this thesis, we present the application of theoretical methodologies to model several compositions of phosphate-based glasses (PBGs) for biomedicine. Quantum mechanical calculations of single crystal phosphorus pentoxide, P2O5, have been conducted using plane wave density functional theory. A rigorous structural, mechanical and electronic characterization of the two most stable phases, o’(P2O5)∞ and o(P2O5), showed both to be highly elastically anisotropic due to structural features. Lӧwdin atomic charge and valence charge density analysis shows mixed ionic and covalent character in both phases. A formal charge, shell-model force field, has been parameterized to reproduce the structural and mechanical properties of o’(P2O5)∞. This has been used to conduct classical molecular dynamics simulations of amorphous P2O5-CaO-Na2O systems, via a melt-quench protocol. Dependent on composition, phosphorus atoms are primarily Q1 and Q2. Moreover, calcium ions coordinate to a significantly higher proportion of non-bonded oxygens than sodium. Born-Oppenheimer and classical molecular dynamics simulations of amorphous P2O5-CaO-Na2O-Ag2O systems reveal a distorted octahedral / trigonal bi-pyramidal coordination environment for silver. An increase in the phosphorus to bonded oxygen bond disorder, and disproportionation in the medium-range structure, following the relation 2 Q2 → Q1 + Q3, is evidenced upon Ag-doping. The influence of titanium on the structural, mechanical and electronic properties of PBG has been investigated via Born-Oppenheimer molecular dynamics and theoretical 31P chemical shieldings calculations. Upon Ti-doping, a depolymerization of the phosphate network is offset by the formation of P-O-Ti and Ti-O-Ti linkages. The reconstructed theoretical 31P NMR spectra compare well to experimental spectra, suggesting that the unimodal spectral peak comprises Q1 - 4 phosphorus. The bulk modulus rises from 38.96 GPa in PBG to 43.94 GPa for Ti-PBG, due to a more cross-linked glass network. Density of states calculations show a reduction in the band gap from ~3.3 eV to ~2.1 eV upon Ti-doping.

Evaluation of strategies for modular assembly of targeted therapeutics and diagnostics

Moody, P. R. January 2014 (has links)
It has become routine to generate proteins that will selectively bind to a targeted cell type. By attaching functional chemical components to these binding proteins, a variety of useful constructs could be generated. For example, attachment of a drug could enable delivery of the drug to the targeted cell type, or attachment of an imaging agent could enable selective visualisation of the cells in vivo. In order to facilitate attachment of multiple functional groups, we aimed to identify a simple and robust strategy for controlled synthesis of multifunctional constructs. The first strategy that we evaluated was attachment of multiple functional components to bromomaleimide linkers. Specifically, we tested a hypothesis that molecules attached to bromomaleimides could be released inside the targeted cell. This hypothesis was tested by generation of bromomaleimide-linked FRET pairs and microinjection of these into cells, which enabled release of components from bromomaleimides to be detected by fluorescence microscopy. We next evaluated a strategy in which multiple components are attached to apo neocarzinostatin (apo-NCS). It has been reported that Holo-NCS internalises into cells and releases its cargo in the nucleus, which raises the possibility that apo‑NCS could also deliver therapeutic ligands into cells. In order to test this possibility, apo-NCS was chemically labelled using rhodamine or biotin to detect internalisation. The final strategy that we evaluated was to react two cysteines on a single protein with dibromodiamide (DBDA). This reaction can generate a uniquely reactive group at each cysteine position, which can each be conjugated to a different functional chemical. We aimed firstly to demonstrate that this strategy could be applied to pairs of cysteines on other proteins. Secondly, we aimed to better understand the reaction of cysteine with DBDA. In an attempt to achieve both of these aims, DBDA was reacted with a library of single cysteine mutants.

Novel approaches to the synthesis of Wieland-Miescher ketone analogues

Turner, R. L. January 2014 (has links)
Important for the regulation of bodily glucose levels and within the fight-or-flight response, the glucocorticoid receptor has become an interesting pharmaceutical target, with the discovery that both natural and synthetic glucocorticoids induce a significant anti-inflammatory effect. Current research focuses on the synthesis and identification of novel selective glucocorticoid receptor modulators, which lack the debilitating side effects associated with these drugs. Building upon the work of previously successful glucocorticoid modulators, pyrazole 2 is the target for this work. The first part of this thesis describes investigations into the synthesis of the Wieland-Miescher ketone (WMK) analogue 1; an important intermediate in the prospective synthesis of pyrazole 2. The traditional route towards WMK analogues via a Robinson annulation proved to be unsuccessful, with a range of catalysts trialed for the key Robinson annulation step and with difficulties arising from the synthesis of the key pyran-3,5-dione precursor. The second route proved to be more successful with the methoxy-protected WMK being afforded, via a 6-step route with a key Birch reduction step. Alpha-Aminosulfonamides are a relatively unknown functionality, which possess the ability to mimic natural amino acids and behave as peptidomimetics. Previous literature has described this advantageous functional group as both synthetically challenging and an unstable moiety. Employing novel radical reaction conditions developed within the Wilden group, a selection of both the unusual alpha-aminosulfonamide and the more readily available beta-aminosulfonamide have been synthesised in significant yields.

B(OCH2CF3)3-mediated amidation reactions

Lanigan, R. M. January 2014 (has links)
This thesis describes the further development of a borate ester, B(OCH2CF3)3, as a reagent for amidation with a focus on carboxylic acids, including N-protected amino acids, and on the amidation of unprotected amino acids. In addition, a novel methodology for the determination of enantiomeric ratio in chiral amines is reported. The B(OCH2CF3)3-mediated direct amidation of carboxylic acids furnishes the amide product in generally excellent yield (A). A formylation method using DMF as the formyl donor was also developed (B). The B(OCH2CF3)3-mediated amidation method allows the amidation of α-chiral acids (for example, N-protected amino acids) in good yield with excellent retention of enantiopurity (C). Importantly, a solid-phase work-up procedure was developed which enables the purification of all of these amide products without the need for column chromatography or aqueous work-up. The application of B(OCH2CF3)3 to the amidation of unprotected amino acids is described (D). This covers an optimisation study and an investigation into the scope of the reaction. As a result of this study a new method for the determination of enantiomeric purity of chiral amines was developed. Using an aldehyde derived from lactic acid the enantiopurity of chiral amines can be determined by NMR, circumventing the need for chiral HPLC. Additionally, a mechanistic study of the direct amidation reaction is discussed. A reaction intermediate as well as a tentative mechanism are proposed based on the results of this mechanistic study and preliminary experimental evidence.

Antibody conjugates via disulfide bridging : towards therapeutic and diagnostic applications

Hull, E. A. January 2015 (has links)
Antibodies play a prominent role in chemical and biological research and the largest application of chemical bioconjugation reagents is in the production of antibody conjugates. These conjugates provide a means of highly sensitive detection, for example in enzyme-linked immunosorbent assay (ELISA) systems. In therapeutics, such conjugates have enabled the development of bispecifics and antibody-enzyme directed prodrug therapy (ADEPT). Long-established chemical modification techniques for the conjugation of antibodies yield highly heterogeneous products. This heterogeneity is far from optimal and for therapeutic use antibody conjugates must be of a defined composition. Recently the site-specific introduction of chemical linkers has been reported through unnatural amino acid insertion. In this approach however, each protein must undergo successful mutation and expression prior to conjugation. To avoid this, an ideal site-directed conjugation technique would use residues natural to the protein. A new class of chemical bioconjugation reagents, the 3,4-substituted maleimides, allow the selective modification and bridging of naturally occurring protein disulfide bonds. In this thesis, the generation of homogeneous antibody-protein conjugates using 3,4-substituted maleimide based cross-linkers is investigated, with a focus on producing conjugates for ADEPT and bispecific therapeutics. A range of direct and indirect chemical cross-linking strategies via disulfide bridging are explored and the consequences of each approach examined. Ultimately, a new chemical platform to generate site-specific, homogeneous, antibody-antibody conjugates by targeting and bridging disulfide bonds was developed. A bispecific antibody construct was produced in good yield using a readily synthesised bis-dibromomaleimide cross-linker. Binding activity of antibodies was maintained, and in vitro binding of target antigens was observed. This technology is demonstrated through linking scFv and Fab antibody fragments, showing its potential for the construction of a diverse range of bispecifics. Finally, the ability of 3,4-substituted maleimide based reagents to functionalise antibodies for diagnostic applications is investigated. A strategy for the modification of a scFv-Fc construct with commercially available fluorophores is achieved and a synthetic route towards reagents suitable for immuno-PET applications determined.

The role of van der Waals interactions and nuclear quantum effects in soft layered materials

Graziano, G. January 2015 (has links)
Recent years have seen a surge of interest in layered materials, mainly because of their numerous applications, prominently in gas sorption. These materials are highly anisotropic, because of the coexistence of covalent bonds within the individual layers and weak van der Waals (vdW) interactions between layers. Although the anisotropy makes layered materials appealing for many technological applications, it also makes their full theoretical and experimental description difficult. This study has addressed some of the major gaps in our understanding of layered materials using a combination of theoretical and experimental techniques. Computationally, newly developed functionals able to treat both short and long range interactions within density functional theory have been used to look at the structure, energetics, dynamics and adsorption properties of layered materials. Neutron scattering experiments have been used to further our understanding of the atomic dynamics in graphite and to set up a preliminary study of the hydrogen adsorption in doped graphite. The present results underline strong similarities of the vdW-dominated properties of the systems examined. The interlayer binding energies and the hydrogen adsorption capabilities have been found to be surprisingly similar. Analysis shows that this is due to a fine balance between attractive and repulsive forces and, more specifically between atomic polarizabilities and volumes of the material components. The comparison between experimental and predicted atomic displacements in graphite highlights that the carbon dynamics is affected by nuclear quantum effects at temperatures lower than 300 K. These temperatures are common for many technological applications, especially those related to gas adsorption. Thus, the presented results pose some questions on what could be the correct model and computational technique to use in order to gain a better understanding of the sorptive properties of layered materials, especially carbon based, and move forward in the design of new gas storage materials.

Hetero-junction and nanomaterial systems for metal oxide semiconductor based gas sensing

Naik, A. J. T. January 2015 (has links)
Investigations into a number of hetero-junction and nanoceramic materials systems for metal oxide semiconductor (MOS) gas sensing for potential environmental and bio-sensing applications are presented. The hetero-junction study encompasses investigations into various composite n-n hetero-contact systems such as WO3-ZnO and SnO2-ZnO and a p-n hetero-contact system, specifically CTO (Chromium Titanium Oxide) - ZnO. The facile fabrication of various arrays of hetero-junction MOS gas sensor devices has been demonstrated. A simple change in the compositional contribution of an individual metal oxide within a composite, exhibits the ability to tune the composite’s responsivity and selectivity. The hetero-junction systems were characterized by various techniques including Scanning Electron Microscopy (SEM), Raman spectroscopy, X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) and the influence of the physical and chemical properties of these materials towards the associated gas sensing properties, deduced. Further, the influence of fundamental properties of junctions such as contact potential and packing structure, towards the sensing properties, are also discussed. The nanomaterials study encompasses investigation into ZnO semiconducting oxides fabricated by various emerging fabrication technologies including Continuous Hydrothermal Flow Synthesis (CHFS) and other relatively high temperature routes. The chemical and physical properties of the nanoceramics have been investigated by various techniques including Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Brunauer Emmett Teller (BET) surface area measurements. The investigation demonstrates emerging techniques for the production of nanomaterials, which can be successfully used in MOS gas sensing for the desired applications. Further, the study shows that the behaviour of the nanomaterials is complex and material surface area is not the only deterministic factor of enhanced responsivities, but microstructural factors such as morphology and particle size, as well as heat-treatment conditions are all influential over the overall sensing properties. This thesis presents an overview of emerging material systems for MOS gas sensing applications.

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