This thesis is concerned with the exploitation of carbon paste electrodes and heterogeneous mixtures, such as emulsions or solutions only containing miceller structures, for the accumulation or trapping of analytes of interest and their subsequent electroanalysis. In Chapter 4, the reduction of oxygen is studied in aqueous solutions of pH 6.22 - 8.01, at a carbon paste electrode fabricated from dioctyl phthalate (oil) and graphite. Two two-electron voltammetric waves are usually seen on carbon electrodes, associated with the formation of hydrogen peroxide and water, respectively. However, an additional signal is seen on the carbon paste electrode, which is attributed to the initial formation of the superoxide radical anion, O2.-. Data is presented to show that the predominant source of oxygen for this reaction is that dissolved in the carbon paste material, rather than in the aqueous solution, and that the superoxide is likely formed at the graphite/oil/water triple phase boundary. Kinetic and thermodynamic parameters for the O2/ O2.-redox couple are reported. In Chapter 5, a novel electrochemical procedure is developed that allows the amount of oxygen in cetyltrimethylammonium bromide (CTAB) micelles to be effectively titrated and hence the oxygen solubility in the micelles to be determined. The electroreduction of oxygen is studied in aqueous phosphate buffer solutions, using a microelectrode. The addition of micelle forming surfactants to solutions pre-saturated with oxygen leads to a reduction of the oxygen signal allowing the oxygen uptake by the micelles to be measured. For CTAB micelles, a concentration of oxygen of 6.7 ± 0.72 mM was observed, and shown to remain constant with increasing CTAB concentration in the bulk solution. The method has general applicability. In Chapter 6, the electrochemistry of nitroblue tetrazolium chloride (NBTC) is investigated in aqueous solutions of pH 6.97, on a glassy carbon macroelectrode and at a carbon fibre microelectrode; the adsorption properties of the electrochemically produced diformazan are also studied. A reduction and overall mechanism is proposed based on the analysis of the obtained results. A carbon paste electrode, fabricated using dioctyl phthalate and graphite powder, is then used as a non-enzymatic sensor. The sensitivity of the diformazan oxidation signal to the presence of superoxide is taken advantage of to detect superoxide. The paste electrode is first immersed in aqueous superoxide solutions. It is subsequently equilibrated with NBTC, by immersing it into aqueous NBTC solutions. The reduction of NBTC (by superoxide) thus takes place in the paste so allowing the quantification of the superoxide in the aqueous phase by means of the diformazan oxidation signal. A value for the practical limit of detection of 0.059 nM is obtained. In the final chapter (Chapter 7), a carbon paste recipe is optimised for the detection of phenols via a procedure in which phenols are allowed to accumulate in the paste via transfer from an aqueous solution prior to electro-oxidation. Importantly, the use of such paste electrodes is shown to substantially overcome the "self-passivating" behaviour of the phenol oxidation which usually constrains the electrode process to low concentrations and single-shot experiments. Here, 4-phenoxyphenol could be detected in the range from 2.5 to 40 μM, phenol from 2.5 μM to 60 mM and 4-methoxyphenol from 5.0 to 40 μM. The electrodes were re-usable without surface renewal for phenol concentrations up to 1.0 mM. The use of a bulk phenol solution for pre-concentration via absorptive uptake into a bulk phase followed by electrochemical quantification represents a new form of electroanalysis which is here termed "absorptive stripping voltammetry". This novel approach is complementary to "adsorptive stripping voltammetry", where accumulation ii occurs via adsorption on an electrode surface. The value of absorptive stripping voltammetry is demonstrated through the application of the approach to the sensitive detection of Δ9-tetrahydrocannabinol (THC) in both aqueous solutions of pH 10.0 and in synthetic saliva solutions; an optimised carbon paste electrode, fabricated from graphite powder and mineral oil, is here utilised. Practical limits of detection of 0.50 μM and 0.10 μM are determined for THC in stationary and stirred aqueous borate buffer solutions, respectively, while THC concentrations as low as 0.50 μM are detected in synthetic saliva solutions. "Absorptive Stripping Voltammetry" can thus be reliably applied to the detection of ?9-tetrahydrocannabinol, after suitable optimisation of the assay.

An optimised nuclear magnetic resonance (NMR) detector design has been developed to allow in situ NMR observation of sub mM concentrations of sample within a 2 l sample volume on a microfluidic chip. The detector is a new design of double micro-stripline detector that is compatible with functional lab-on-a-chip devices. The design has been optimised using nite element analysis taking into account both the shape of the sample chamber and the resonator. The sensitivity of this detector compares favourably with other micro-NMR systems. The ability to observe low concentrations allows direct analysis of cell metabolomics on a chip within 20 minutes of experiment time. The detector has been adapted to resonate at 2 frequencies. This opens the possibility of heteronuclear NMR experiments without compromising the sensitivity of the probe. The sensitivity is sufficient to demonstrate the ability to study changes in the structure of proteins when binding to a substrate. Also explored in this work is another detector design the inductively coupled planar microcoil. Finite element analysis has allowed accurate simulation of these microcoils.

The rise in wind, solar and tidal renewable power generation presents a new challenge for the future stability of electrical networks on the national and international scale. The modal nature of renewable power and its incompatibility with consumer demand necessitates a means for largescale energy storage with high efficiency and relatively low cost. Zinc-air flow batteries represent one possible solution to this problem. The energy is stored in the metallic zinc, and reversed with the oxidation to form zincate releasing the energy on demand. The majority of energy losses in the zinc-air battery are for the O2 evolution and reduction reactions on the air electrode. A stable, durable and low-cost bi-functional air electrode would allow the introduction of zinc-air flow batteries to support the power grids of the future. The work in this thesis will investigate the activity of NiCo2O4 electrocatalysts prepared by various methods, for their use as bi-functional electrocatalysts in the air-electrode. The electrocatalyst prepared on to a gas diffusion electrode, to determine activity in lab-scale half-cells. Improvements to catalyst activity are then considered through the addition of metal nanoparticles to the surface of NiCo2O4, with in-situ X-ray absorbance measurements to determine the oxidation states of ruthenium during the O2 evolution reaction. The activity of NiCo2O4 was compared to alternative perovskite mixed metal oxide electrocatalysts.

The synthesis of three fragrance ingredients currently manufactured at International Flavours and Fragrances (IFF), Benicarló, Spain are primarily investigated herein. After reviewing the literature surrounding each of these, efforts were made to improve upon their current synthesis through the development of new methodology. Assessments of the compatibility of the developed chemistry, as well as other industrially important transformations, with continuous flow processing were also made. Hedione (methyl dihydrojasmonate) was the subject of the first of these three projects. Efforts were focused towards novel dehydrohedione (DHH) syntheses from Hedione. A new copper(II) bromide mediated oxidation was firstly developed that was shown to be capable of oxidising the Hedione enol-acetate to DHH in high yield. The methodology was also applied to a range of other substrates including to the synthesis of a phenol. A catalytic system was also developed and demonstrated on a model substrate derived from desoxyanisoin. A second novel DHH synthesis was achieved by direct Hedione oxidation via an α-chloro intermediate which underwent spontaneous elimination in methanol. Of the chlorinating agents used, sulfuryl chloride was found to be the best, giving DHH yields of 77%, an improvement upon the 71% yield associated with the currently used three-step process. The process was found to be easily scalable and its amenability to flow was demonstrated. The second project involved an assessment of a Diels-Alder reaction currently used by IFF for the synthesis of Isofloriffone, a precursor to δ-Damascone. The reaction is currently catalysed using AlCl3 in high loading and an alternative catalytic system was sought. While none of the alternative methods employed gave yields that came close to those achieved with AlCl3, key factors influencing the yield were identified as the AlCl3 loading and the temperature, which must be kept low enough to prevent a runaway/diene polymerisation. The Lewis acid catalysed reaction, as it stands is not suited to flow, however, it is proposed that many thermal Diels-Alder processes in the flavour and fragrance industry would benefit from continuous flow manufacturing protocols. The final project involved the synthesis of α-dehydroherbac, a precursor to a fragrance ingredient known as Galbascone. The current process used by IFF gives rise to a mixture of products and was poorly understood prior to this work. Following mechanistic studies, a proposed overall mechanistic pathway for the reaction was outlined that accounted for the products formed and their ratios. Following this, two novel routes towards the desired α-dehydroherbac isomer were investigated. The first of these failed to give the desired product but revealed unprecedented conjugate addition reactivity of a Wittig reagent. The second route developed made use of an irregular nitro-aldol reaction followed by a Nef reaction. High selectivity towards the desired isomer was successfully achieved through steric control of an imine intermediate. The resultant process, offered both an improved yield (51% vs 38% both over two steps) and selectivity (84% vs 50% isomeric purity) over the process used currently and was demonstrated for a range of substrates. In summary, three new reactions were discovered; an irregular conjugate addition reaction of a Wittig reagent, a catalytic and non-catalytic CuBr2 mediated oxidation of ketones and enol acetates and a one-pot chlorination-elimination oxidation process which is well suited to flow and currently being trialled at pilot plant scale at IFF Benicarló. Key features of the Isofloriffone and α-dehydroherbac industrial processes were also established and a new process based on known chemistry was developed that resulted in higher yields and selectivities than the currently used α-dehydroherbac synthesis.

No description available.

The reactions of thiolate anions with α-substituted 2-nitropropanes have been studied. The products of these reactions are the corresponding disulphides, α-nitrothioethers, and 2,3-dimethyl-2,3-dinitropropane. The ratio of the products in relation to the structure of the starting materials is discussed. The α-nitrothioethers are formed by the SRN1 mechanism, while the available evidence suggests that the disulphides are formed by a non-radical mechanism. Some α-nitrothioethers have been reacted with a series of anions. Several of these reactions have been shown to proceed by the SRN1 mechanism, with displacement of thiolate anion. The reaction of nitronate anions with aromatic disulphides has been shown to give α-nitrothioethers under mild conditions. The reaction has been shown by kinetic studies to be second order overall.

Hydrogen peroxide is made commercially by the cyclic reduction and oxidation of solutions containing alkyl-substituted anthraquinones. Such solutions contain not only the alkyl anthraquinone, but also certain oxidation and reduction products which do not revert to the active compounds in the plant working solution, and which thus reduce the efficiency of the plant for the production of hydrogen peroxide. Section 2 examines the chemistry involved in the hydrogen peroxide manufacturing process and degradation routes of the various active materials. The identification and quantitation of the components of the working solution is thus of considerable significance in the economic production of industrially important hydrogen peroxide.

The aim of this study was to investigate hydrophilic interaction chromatography (HILIC) and its application to metabolic profiling. The effect of different mobile phase modifiers on the retention behaviour of acidic and neutral test probes was studied on silica gel based columns which confirmed the hypothesis that HILIC is due to a combination of hydrophilic interactions and electrostatic interactions. Among the acidic probes tested, the more negatively charged maleic acid was not strongly retained until the strength of the ammonium ion in the mobile phase was high enough to shield the acid from repulsion by charged silanol groups on the silica gel surface. The neutral test probes were increasingly retained with increasing ionic strength of the mobile phase suggesting that the thickness of the water layer on the surface of the silica gel increased with the strength of the ionic modifier. The utility of three silica hydride columns, Cogent silica C, Cogent Phenyl Hydride and Cogent UDC cholesterol, for separating mixture of metabolites was successfully assessed with an alternating gradient from high organic to high aqueous and then from high aqueous to high organic, thus permitting two orthogonal selectivities to be obtained on the same column. A method for the reductive amination was developed for the analysis of sugars and sugar phosphates. This method was very successful with deuterated aniline as a tag which led to the separation of the three common hexoses glucose, galactose and mannose. The method was applied to the profiling of sugars in milk and in brain tissue. An extensive study of seal milk in comparison with other mammalian milks was also conducted which found that unlike the milks of terrestrial mammals, seal milk had very little lactose. Thus seal pups appear to rely on fat metabolism to produce energy. A notable feature of the milk was that it contained high levels of nicotinamide, an essential precursor for the production of the cofactor NAD+ which is required for the β-oxidation of fats.

Infrared (IR) photodepletion spectroscopy coupled with mass spectrometry has been applied in the investigation of size-specific alkali metal-solute complexes. IR spectra have been recorded in the N-H stretching region for Li(NH3)n (4 = n = 7) and Na(NH3)n (3 = n = 8) and in the N-H and C-H stretching regions for Li(NH2CH 3)n (3 = n = 5), with supporting ab initio calculations. All clusters display a red-shift of the N-H stretching modes, consistent with partial electron transfer from the nitrogen to the alkali metal atom. For Li(NH3)n, the IR spectra indicate that the first salvation shell is found to be completed with four ammonia molecules, which is in agreement with conclusions drawn from previous photoionisation studies. This finding is given credence from DFT and MP2 ab initio calculations carried out in the present work, where the lowest energy isomer for n = 4 is adopts a tetrahedral structure. The IR spectra for Na(NH3)n clusters are less definitive, but indicate a completed inner salvation shell with six ammonia molecules, a conclusion in disagreement with some previous experimental and theoretical investigations, but which is consistent with high-level ab initio calculations carried out in the present study. Ab initio investigations into the localisation of the alkali metal valence electron in the three systems determined that not only are a critical number of solvent molecule required to permit formation of a solvated electron, but also a specific geometrical configuration is required. For lithium-ammonia and sodium-ammonia clusters, formation of the solvated electron was found to coincide with an ammonia molecule entering the second salvation shell, whereas for lithium-methylamine, electron salvation was not observed for the largest cluster studied, Li(NHCH3)4.

The aim of this thesis is to provide updated, accurate kinetic (and where possible mechanistic) information regarding the oxidation pathways of various volatile organic compounds (VOCs) and trace gas species within the troposphere. The vast majority of the experiments discussed were conducted using a pulsed laser photolysis, photoionization mass spectrometry (PLP-PIMS) set-up, which operated at low pressures (p = 2 Torr). PLP-PIMS is a time-resolved technique can be used to directly monitor multiple species simultaneously and with time; details of this method are found in Chapter II. Initially, one shortcoming of the PLP-PIMS technique was that it could not detect OH radicals (due to the ionization potential of OH). However, in Chapter III a 1 + 1’ multiphoton ionization (MPI) scheme was implemented, making OH detection possible. In Chapter IV, kinetic and mechanistic information regarding the oxidation of acetaldehyde, CH3CHO, by OH is reported. From this study a rate coefficient of kOH = (1.6 ± 0.2) × 10-11 cm3 molecule-1 s-1 was measured, this is in good agreement with other literature values. Additionally, it was observed that a small yield of methyl radicals (YCH3 ≈ 15%) was also produced. Methyl radicals were an unexpected product from this reaction and it is hypothesised that they are formed from the dissociation of nascent, chemically activated acetyl radicals. Notably, the yield of methyl radicals observed is significantly lower than would be expected from a statistical distribution of the energy between the products. Therefore, a post-reaction complex is proposed to allow for the redistribution of energy. In Chapters VI, reactions of the C1 and C2 Criegee intermediates (CH2OO and CH3CHOO, respectively) with SO2 and NO2 are reported. For the C1 Criegee intermediate (CI), rate coefficients of kC1SO2 = (3.8 ± 0.3) × 10-11 cm3 molecule-1 s-1 and kC1NO2 = (1.2 ± 0.3) × 10-12 cm3 molecule-1 s-1 are reported for the reactions with SO2 and NO2 respectively. For the C2 CI, rate coefficients of kC2SO2 = (1.8 ± 0.3) × 10-11 cm3 molecule-1 s-1 and kC2NO2 = (7.0 ± 1.6) × 10-13 cm3 molecule-1 s-1 were measured. Moreover, in the C2 CI + SO2 reaction, acetaldehyde was positively identified as a product from this reaction at low pressures. Finally, in Chapter VII the reactivity of Criegee intermediates towards different organic species was investigated. From these experiments it was observed that the C1 CI had significant rate coefficients with carboxylic acids, and rate coefficients of kC1FA = (3.7 ± 0.6) × 10-11 cm3 molecule-1 s-1 and kC1AA = (7.1±1.1) × 10-11 cm3 molecule-1 s-1 measured for the reactions with formic and acetic acid, respectively. However, the reactivity of CIs towards alkenes is thought to be considerably slower with upper limits of kC1ethene < 2 × 10-14 cm3 molecule-1 s-1 and kC1isoprene < 3 × 10-13 cm3 molecule-1 s-1 measured for the reactions of the C1 CI with ethene and isoprene.