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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.
1

Development of environmental water monitors based on hydrostatic and flourescence detection techniques

Scott, Robin M. January 2009 (has links)
The research for this thesis led to the development of two environmental detectors, whose function was to identify predetermined threshold levels of the analyte. The research centred onto two types of analyte; immiscible and dissolved, both occurring in water based locations. The first detector was developed to detect the accumulation of oil within an oil/water interceptor. Pollution from oil spillages is a major contaminate of water systems and the control of this potentially hazardous material has legal obligations. This liquid, which naturally separates from water, accumulates within the interceptor enclosure and can be removed once the quantity of oil reaches the desired level. However, the often unpredictable nature of oil leaks and spillages means that the accumulation of oil within an interceptor is an irregular occurrence. Interceptor detectors based upon electrical techniques already exist. This research specifically developed a detection system that operated without any electrical devices within the interceptor. The research explored several possible avenues, eventually pursuing a technique based upon pressure change, based on the density differential between water and oil. The final system was capable of identifying when the oil had reached a depth of 200 to 250 mm within the interceptor. The second detection system, a portable microfluidic fluorimeter, was intended for placement in locations for the direct analysis of water. Glutathione was chosen as a model analyte, associated with a sex pheromone and prior to the onset of spawning may be found in high concentrations. The system that has been developed is capable of selectively sensing glutathione to below 10 μM. However, the threshold concentration in the proximity of its release as a pheromone is greater than 100 μM and within this range the fluorimeter produced a linear response. The fluorimeter used an LED light source with a PMT detector. An analysis could be made every seven minutes, using 150 μL each of analyte and reagent for every cycle. Through assessment of a pre-made standard, the viability of the microfluidic system could be assured with regards to blockages or other malfunctions of the system.
2

Fabrication of novel functional anisotropic micro-particles for foam stabilisation and structuring in food formulations

Campbell, Andrew Lee January 2009 (has links)
This thesis is concerned with the fabrication of novel food-grade anisotropic solid particles for foam stabilisation and applications in food formulations. Two main techniques were employed for the fabrication of these particles. Acidic hydrolysis of Nata de Coco bacterial cellulose was used to form cellulose nano-rods which were applied as a foam scaffolding material. Characterisation and modification of Nata de Coco nano-rods was also carried out. It was found that cellulose nano-rods modified with a surface layer of ethyl cellulose exhibited good foamability.Secondly, a combination of in-shear-flow dispersion and solvent attrition techniques were employed to form micro-rods from the edible polymeric materials shellac, ethyl cellulose and zein. Characterisation of the properties of shellac, ethyl cellulose and zein micro-rods was carried out, together with assessments of their foam stabilisation ability. Stable aqueous foams were produced using shellac, ethyl cellulose and zein micro-rods as stabilisers, and ethyl cellulose micro-rods were also used to form water-in-oil emulsions.An extension of this technique was used in the fabrication of novel functional anisotropic food-grade micro-rods with micro-particle inclusions giving altered morphology. Enhanced foamability and drainage retardation was achieved using lumpy yeast-shellac micro-rods to stabilise aqueous foams. The method was extended to the production of aqueous dispersions of ballooned micro-rods, formed by two different protocols.This procedure also allowed the formation of novel, dual-function micro-rod capsules or ‘micro-ampules’ for stabilisation and encapsulation by inclusion of oils into the dispersed phase prior to micro-rod fabrication. The oils became trapped within the micro-rods resulting in micro-ampules with a range of morphologies which were characterised by fluorescence doping and microscopy.
3

A matrix isolation study of transition metal halides and their structure

Wilson, Antony January 2009 (has links)
The work within this thesis has concentrated on the formation and isolation of titanium, vanadium, palladium, and mercury halides, with emphasis on the fluorides.TiF, TiF2, TiF3, and TiF4 have all been isolated within an argon matrix and infrared spectra obtained. From the titanium isotope splitting pattern a bond angle has been determined for TiF2 for the first time of 165o, or effectively linear. This work is also the first time that TiF has been isolated within an argon matrix. Work has also been conducted with vanadium which has lead to the isolation of VF5, VF4, VF3, and VF2, with VF4 undergoing Fermi Resonance. This is the first time that VF4 and VF2, consistent with a linear structure, have been isolated within a matrix.Work conducted upon palladium led to the isolation of numerous palladium fluorides, identified by the palladium isotope patterns in their IR spectra. Due to the similarity of the calculated stretching frequencies of PdF2, PdF3, PdF4, and PdF6 the assignment was challenging and so identification of these bands was conducted based photolysis and annealing behaviour in conjunction with computational calculations. This has allowed for the assignment of the bands present to PdF6, PdF4, PdF3, PdF2, and PdF.The bond length of molecular HgF2 has also been determined for the first time at 1.94(2) Å using the Hg L3-edge with EXAFS. Although the initial aim of this work was to isolate HgF4, using IR, UV/Vis, and XANES, no evidence could be found for oxidation states of mercury higher that HgII. The work also developed a new clean way of making HgF2 in a matrix. The identification of a new Hg…X2 complex was also discovered which when photolysed forms the HgX2 compound, this has only been proven for HgF2. This was achieved by isolating mercury atoms in an argon matrix doped matrices, photolysis of this matrix the led to the formation of HgF2 in significant amounts.
4

Integrated DNA extraction and amplification on a microfluidic device

Shaw, Kirsty Jane January 2009 (has links)
An evaluation of DNA extraction and amplification performed in microfluidic systems was carried out, with the aim of integrating the two processes in a single microfluidic device. This integrated device will then be incorporated upstream of capillary gel electrophoresis and fluorescence-based detection for development of a completely integrated genetic analysis system. DNA extraction was performed using a silica substrate with both hydrodynamic and electro-osmotic pumping (EOP), resulting in maximum DNA extraction efficiencies of 82% and 52% respectively under optimised conditions. While the DNA extraction efficiency was lower using EOP, this method eliminates the need for external pumps and ensures easier mechanical connection to the microfluidic device. The use of thermally activated silica monoliths as the solid-phase resulted in superior DNA extraction efficiencies compared to when photo-initiated monoliths and silica beads were used. DNA amplification of up to nine forensically relevant loci was successfully achieved on the microfluidic device in volumes as low as 1.1 microlitres using Peltier heating. A combination of silanisation and dynamic passivation was required to prevent PCR inhibition resulting from DNA polymerase adsorption. A custom-built microwave heating system was also evaluated, which was capable of heating and cooling rates of 65degC/second and 58degC/second, respectively. EOP was used in the generation of an integrated microfluidic device, for DNA extraction and amplification. The silica monolith used as the solid-phase for DNA extraction also acted as a pump for electrokinetic movement. All necessary reagents for carrying out both DNA extraction and amplification were encapsulated in agarose gel and pre-loaded onto the microfluidic device creating a self-contained, ready-to-use system. Following addition of the biological sample to the microfluidic device, all electrokinetic movement and thermal cycling was controlled using a custom-built operating system.
5

Electro-catalytic reactions

Lledo-Fernandez, Carlos January 2009 (has links)
This thesis discusses and demonstrates the utility and advantages of redox catalytic reactions and small scale synthetic applications. In particular electro-catalytic reactions are investigated along with electrogenerated chemiluminescence (ECL). ECL is used both as a probe for investigating the redox reactions and as an analytical method. The first chapter reviews the current techniques and achievements found in the area of dynamic electrochemistry and electrogenerated chemiluminescence and discusses occurrence, mechanism and potentially useful reactions worthy of further investigation for analytical applications. In Chapter 3 the electrocatalytic ECL reaction of Ru(bpy)32+ with tertiary amines in particular with codeine as a model compound was investigated. The aim of the work was to develop a portable drug testing device, that gave good sensitivity and reproducibility. The Ru(bpy)32+ was immobilized within the sol-gel matrix to develop a sensor which could be used directly for measuring tertiary amine containing drugs in buffer solution without the need to add reagents. A system of three electrodes was used in which Ru(bpy)32+ was immobilised on to a glassy carbon working electrode. Initial work involved physical entrapment of the Ru(bpy)32+ within the sol-gel matrix however, problems occurred with leaching of the reagent from this matrix. This problem was overcome by the covalent attachment of a novel Ru(bpy)32+ derivative to the sol-gel matrix. Using this approach a calibration was obtained using ECL for the determination of codeine over the range 1E-3 to 1E-7 M in aqueous buffer with a limit of detection of 2.65E-6 M for codeine. Covalent attachment, as compared to the physical entrapment of CL reagent, was advantageous as it ensured homogeneous distribution of the reagent within the matrix and prevented leaching. This reduced analysis costs, extended sensor lifetime and gave a reproducible analyte responses. This method was, however, only suitable for drugs that were soluble in aqueous solution and an alternative approach was needed for insoluble compounds. Chapter 4 describes an alternative approach for ECL reaction of tris(2,2’-bipyridyl)ruthenium(II) with tertiary amine compounds. In this approach the electrode was modified using microdroplets of a highly hydrophobic tertiary amine (trioctyamine). As well as allowing for the analysis of compounds that were insoluble in aqueous solution, this setup allowed the investigation of the electron transfer reaction occurring on liquid|liquid interfaces. This mechanism was studied in fully protonated and deprotonated conditions. The extent of the electrochemiluminescence production was shown to be dependent on the degree of the interfacial protonation. Moreover, the data obtained enabled the estimation of the biphasic pKa, which was found to be approximately 10.8. Furthermore, the mechanism was studied in fully deuterated and dedeuterated conditions, in order to investigate the effect of the deuterium on the biphasic pKa. Results suggest that the pKa increases to 13.18 when deuterium is used instead of protons. In Chapter 5 a further electrocatalytic reaction was investigated. The reaction was that of vitamin B12a with trans 1,2-dibromocyclohexane (DBCH) in a homogeneous dimethylformamide media. The reaction was studied by cyclic voltammetry. Four peaks were seen due to the two chemically reversible redox (two electron process) couples for vitamin B12a/B12r (Co(III)/CO(II)L) and B12r/B12s (Co(II)L/Co(I)). When the bulk electrocatalytic reaction was tried in a “one pot” system, the reduction could not, however, be achieved; the cathodically synthesised Co(I)L was thought to be reoxidised at the anode. A “two pot” system did not have sufficient potential control and, therefore, chemical reduction was investigated instead. Four reducing agents (Na/amalgam, NaBH4/NaOH, DL-cysteine/alkali solution and Zn dust/NH4CL) were studied to reduce B12 to B12s for a simple biphasic batch reaction of vitamin B12s with DBCH. The mild reducing agent Na/amalgam was not successful but the other three methods were shown to give 100% yield if the reaction vials were rigorously shaken. This simple type of green, surfactant free reaction has not been previously reported. The reaction was then investigated in a microfluidic system. For this work the vitamin B12 was reduced before being introduced into the microfluidic device. NaBH4/NaOH and DL-cysteine/alkali solution were selected as the most compatible reducing agents for the microfluidic device. Two types of microfluidic device were employed, one with a T-shape channel, and one with a serpentine channel. The conversions obtained with the microfluidic device were much lower (approximately 10%) than for the simple batch reactions (100%). The yield increased as the flow rate decreased, and the residence time increased. Using the serpentine channel made no noticeable difference to the conversion rate. Problems were also seen due to the use of excess reducing agent prior to introduction of the reduced vitamin B12 into the microfluidic device, as this could cause blockages and bubbles. The main problem was, however, the lack of mixing in the device. One way to overcome this would be to use an ultrasonic transducer with the microfluidic device but although preliminary experiments were carried out, there was not time to fully investigate this approach.
6

Parallel kinetic resolutions using active esters

Coulbeck, Eliot January 2009 (has links)
Obtaining enantiomerically pure compounds is of major importance in modern organic chemistry; the resolution of racemic compounds is a very useful and practical method of achieving this. Parallel kinetic resolutions are an interesting variation on the more classical resolution methods; this method has been recently introduced to the scientific community by Vedejs and there are currently very few examples of successful parallel kinetic resolutions in the literature.The aim of the project, outlined in this report, was to investigate the use of parallel kinetic resolution methodology to resolve racemic carboxylic acids and secondary alcohols. This aim was achieved and in total four distinct parallel kinetic resolution methods were developed; one for the resolution of carboxylic acids, one for the resolution of secondary alcohols, and two that can be used to resolve either carboxylic acids or secondary alcohols. The development process is described for each of these distinct resolutions and their relative scope and limitations are discussed. This report also details the possible reasons for the levels of selectivity found in these reactions, and discusses what effect the reaction conditions have on the level ofstereocontrol. Similarities between all four of the resolutions are described, and the possibility of a generic stereoselective pathway is discussed.This report however is not limited only to findings directly related to parallel kinetic resolutions; it also encompasses all findings from the above mentioned studies. As such, it also describes an unusual observation; the fact that the sign of optical rotation for the common resolving agent 4-isopropyl oxazolidinone is solvent dependant. The discovery and further exploration of a method for synthesising a range of optical pure secondary alcohols from the commercial available (S)-enantiomer of 1- (2-bromo-phenyl)-ethanol is also described. An interesting method for the determination of enantiomeric excess of carboxylic acids is also discussed.
7

Towards the total synthesis of calyciphylline A-type Daphniphyllum alkaloids

Michaelides, Iacovos Neal January 2014 (has links)
This thesis details the studies towards the total synthesis of the calyciphylline A-type Daphniphyllum alkaloids, with a particular focus on daphniyunnine D (23). Chapter 1 introduces these biologically and synthetically interesting polycyclic natural products and describes our designed approach towards their synthesis. Separate studies targeting the construction of two tricyclic ring systems have been developed. These provide rapid entry to synthetically versatile intermediates, allowing for the potential synthesis of numerous members of the alkaloid family. Chapter 2 describes the first study which focuses on the construction of the main tricyclic [6‒5‒7] ACD core 172 via a proton transfer/IMDAF reaction cascade as the main step. Large scale synthesis of the precursor to this cascade 164 has allowed for the successful investigation of an asymmetric variant giving rise to an enantioenriched adduct 104. Chapter 3 describes a novel design for the construction of the [7‒5‒5] DEF tricycle common to 100+ Daphniphyllum alkaloids. An IMPKR, double-bond migration, allylic oxygenation protocol was first validated on a model system and later applied in combination with the synthetic route developed in chapter 2 to achieve the construction of the [6‒5‒7‒5‒5] ACDEF pentacycle 249. Chapter 4 focuses on the construction of the piperidine ring B via an intramolecular gold-catalysed 6-exo-trig hydroalkylation. During the development of the route to daphniyunnine D, various intermediates were afforded which were further elaborated to provide appropriate cyclisation substrates for this study. Their synthesis combined with proof of principle experiments for the desired cyclisation conclude this dissertation work.
8

Ammonia borane and its derivatives : high weight percentage hydrogen storage materials

Hore, Katie January 2013 (has links)
Ammonia borane and ammonium borohydride have been considered extensively as potential hydrogen storage materials. This thesis reports their structure and functional properties, emphasising the key role that dihydrogen bonding plays in both materials. The formation of a 'mobile phase' is considered to be the preliminary step in the decomposition of ammonia borane. The formation of this mobile phase has been studied using neutron diffraction, inelastic neutron spectroscopy and NMR. It has been found that in the mobile phase, 'end-to-end' flipping of the ammonia borane molecule occurs. This is an important precursor to the next step in the decomposition: the formation of the diammoniate of diborane. The dihydrogen bonding networks which occur in both the orthorhombic and the tetragonal phases of ammonia borane, and are the controlling factor in the decomposition process, were investigated using Density Functional Theory Molecular Dynamics (DFT-MD) simulations. It was hence shown that in the high-temperature tetragonal phase of ammonia borane, dihydrogen bonding is still an important stabilising interaction and there is little to distinguish between the three crystallographically distinct dihydrogen bonds. A closely related hydrogen storage material, ammonium borohydride, was also studied using the same techniques. Its low temperature phase progression was examined using variable temperature neutron diffraction. The vibrational modes of ammonium borohydride were assigned by comparing vibrational spectra determined using inelastic neutron spectroscopy with the results of DFT-MD simulations. Quasielastic neutron spectroscopy was used to show that both the ammonium and borohydride groups in ammonium borohydride perform discrete 'hopping' reorientational motions at a wide range of temperatures, and that the ammonium group has a mean residence time approximately 100 times less than that of the borohydride group. Hydrogen atom densities in the ammonium group were determined from DFT-MD simulations, and from refinements of high-resolution neutron diffraction data using cubic harmonic basis functions.
9

Cation-controlled diastereo- and enantioselective synthesis of indolines : an autocatalytic process

Sharma, Krishna January 2014 (has links)
Asymmetric phase-transfer catalysis is a powerful technique that enables a wide range of transformations under mild conditions, often using inexpensive and environmentally benign reagents. By extending the applications of phase-transfer catalysis we have developed a highly diastereo- and enantioselective synthesis of functionalized indolines bearing two contiguous stereocentres, one of which is quaternary and all carbon, in a single synthetic step. The reaction proceeds with complete diastereoselectivity and with high levels of enantioselectivity (up to 99% ee). Despite the development of phase-transfer catalysis as a primary synthetic tool in organic synthesis, the mechanistic understanding of these reactions still remains a challenge, due mainly to the difficulty of studying the complex multi-phase systems. Therefore, a further aim of this project was to understand the reaction mechanism of our phase-transfer catalysed transformation. Investigations into the mechanism of our phase-transfer catalysed reaction have been carried out by studying the reaction kinetics. These have shown that the reaction follows a sigmoidal curve with an induction period present. A detailed kinetic investigation was carried out which demonstrated that an autocatalytic mechanism is operational.
10

Asymmetric synthesis of α-alkylated aldehydes using chiral enamines

Kaka, Naeem Shabbir January 2008 (has links)
Direct generation of enantioenriched mono-α-alkylated aldehydes by intermolecular nucleophilic substitution is a general and long-standing problem in synthesis, and is of importance due to the diverse reactions such aldehydes undergo for introducing asymmetry into molecules. The work described in this thesis initially details the development of the first lithium amide capable of efficiently converting terminal epoxide into enamine functionality, where the latter also demonstrates effective C-alkylation activity. Not only addition to Michael acceptors, but more notably substitution using activated organohalides (α-bromoacetates, benzyl, allyl and propargyl bromide) gave the corresponding α-substituted aldehydes in good to excellent yields. Alkylation with propargyl bromide yielded only the propargyl-substituted aldehyde with none of the corresponding allene observed; this result shows that N-alkylation followed by [3,3] sigmatropic rearrangement is not occuring. Importantly, a range of short-, longer-chain and secondary unactivated alkyl iodides also proved viable. Significantly, with chiral lithium amides, the corresponding chiral enamines could be alkylated with strongly electrophilic benzyl, allyl and propargyl (no allene seen) bromides in very good yields, and with short chain alkyl iodides – MeI and EtI in satisfactory yields, to provide the first direct access to α-alkylated aldehydes with high asymmetric induction by intermolecular nucleophilic substitution.

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