Ce mémoire décrit l'utilisation de la spectrométrie de masse en mode électrospray pour l'étude mécanistique de réactions catalytiques.Dans le premier chapitre, le mécanisme de la réaction de Wacker est étudié ; l'implication d'espèces dinucléaires en palladium, dans le cas de l'utilisation de la benzoquinone comme oxydant, est mise en évidence. La réoxydation du palladium avant la décomplexation du produit a également été établie.Le deuxième chapitre est consacré à l'étude mécanistique de l'oxydation de l'allylphénole en milieu aqueux. La détection d'un intermédiaire epoxyde confirme un mécanisme en cascade : isomérisation, epoxydation et solvolyse.L'étude du mécanisme de réactions de type Heck déshydrogénant représente le dernier chapitre, quatre intermédiaires clefs du cycle catalytique proposé, ont été détectés. / This thesis describes the use of electrospray spectrometry for mechanistic studies of catalytic reactions. The mechanism of the Wacker reaction has been studied in the first chapter ; the implication of dinuclear palladium species, using benzoquinone as oxidant, has been demonstrated. The reoxidation of the palladium before the decoordination of the product has also been established. The second chapter focuses on the mechanism study of the oxidation of allylphenol in aqueous media. The detection of an epoxyde as intermediate corroborates the proposed mechanism : isomerisation, epoxydation solvolysis. The mechanism of a Dehydrogenative Heck reaction is described in the last chapter. Four key intermediates of the catalytic cycle have been identified.

Arsenic is a widespread environmental contaminant whose toxicity depends on its valence and its chemical form. Arsenic species have been typically determined using high pressure liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICPMS), however ICPMS cannot differentiate the co-eluting arsenic species. This thesis explores the use of electrospray mass spectrometry (ESI-MS) with HPLC separation for arsenic speciation and demonstrates applications of various HPLC-ESI-MS methods for the determination of toxicologically and environmentally relevant arsenic compounds. The trivalent arsenicals, such as arsenite (AsIII) and its metabolites monomethylarsonous acid (MMAIII) and dimethylarsinous acid (DMAIII) are not easily detected using ESI-MS due to their poor ionizability, but they are known to have high affinity for thiols. Thus, the easily ionizable dithiol dimercaptosuccinic acid (DMSA) was used to derivatize the trivalent arsenicals prior to ESI-MS. Selection of the derivatizing reaction was based on studies of arsenic-thiol interactions. An HPLC-ESI-MS/MS method was developed for the detection of derivatized AsIII, DMAIII and MMAIII and underivatized arsenate (AsV), monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV), and was used to analyze multiple types of samples including urine, plasma and water. One set of groundwater samples from the site of a former pesticide manufacturing plant contained concentrations of MMAIII as high as 3.9-274 mg/L, the highest ever observed in the environment. Another HPLC-ESI-MS/MS method, without the need of derivatization, was developed for the detection of the toxic thio-arsenicals dimethylmonothioarsinic acid (DMMTAV) and monomethylmonothioarsonic acid (MMMTAV). DMMTAV was present in rat plasma and human urine and both DMMTAV and MMMTAV were detected in rat urine. The method of derivatization and ESI-MS/MS detection was extended to the speciation of inorganic SbIII and SbV. The use of the HPLC-ESI-MS/MS method using DMPS derivatization enabled the speciation of SbIII and SbV in water samples from mine waste.

No description available.

none

Electrospray ionization mass spectrometry (ESI-MS) has been applied to the real time study of air-sensitive homogenous organometallic catalytic reactions due to its soft ionization properties. Therefore, fragile molecules and complexes in these reactions were characterized. The kinetic studies of these reactions have also been done by following the relative abundance of different species including starting material(s), products, by-product(s) as well as intermediates. Based on the results, reaction pathways and mechanisms were proposed and numerical models were built to accurately mimic the reactions under specific condition. In order to make the reactions detectable by ESI-MS, many charged ESI-MS friendly substrates were synthesized as tracking tags, including 1-allyl-1-(prop-2-yn-1-yl)piperidin-1-ium hexafluorophosphate(V), 1-allyl-1-(prop-2-yn-1-yl)pyrrolidin-1-ium hexafluorophosphate(V), (4-ethynylbenzyl)triphenylphosphonium hexafluorophosphate(V), hex-5-yn-1-yltriphenylphosphonium hexafluorophosphate(V) etc. The method for continuously monitoring water- and oxygen-sensitive reactions in real time named pressurized sample infusion (PSI) was developed, optimized and applied throughout all the projects in the thesis. These techniques were applied to detailed studies of the intramolecular Pauson-Khand reaction (PKR) with Co2CO8 under different temperatures. The kinetic study results gave the entropy and enthalpy of the reaction and evidence suggested that the ligand dissociation step was the rate-determining step of the reaction. Hydrogenation of alkynes with Wilkinson’s catalyst and Weller’s catalyst were also studied using PSI. The behaviour of starting materials and products were tracked, then various reactions were carried out by using different temperatures and concentrations. Furthermore, competition reaction and kinetic isotope effect study, mechanisms were proposed based on experimental results, numerical models were built, and rate constants for each step were estimated. Different Si-H activation reactions were studied including hydrolysis of silanes, hydrosilation, dehydrocoupling of silanes, alcoholysis of silane and silane redistribution by using (3-(methylsilyl)propyl)triphenylphosphonium hexafluorophosphate(V). A variety of collaborative projects were also carried out including hydroacylation, fast-activating Pd catalyst precursor, catalyst analysis for Cu-mediated fluorination, CdSe - NiDHLA analysis, Ru catalyzed propargylic amination reaction, Zn catalyzed lactide polymerization, and Fe4S4 clusters. / Graduate / jingwei@uvic.ca

A novel application of ionic liquid as a charge carrier for the analysis and detection of neutral organometallic complexes using a mass spectrometer has been presented. The mass spectrometer detects only charged compounds which raise a difficulty in analyzing a neutral molecule that lacks a basic site to associate with charge. Therefore, an effective way of providing charge has always been an area of keen interest in the field of mass spectrometry. Ionic liquids have a very fascinating property of forming a cation-? interaction with other molecules to give a charged complex. In order to take advantage of this, it is important to know the geometric structure of the complex. Advanced methodologies like hydrogen-deuterium exchange and computational calculations have been used assisting in better understanding of the structure of the ionic liquid complexes.

none

none

none

Insects represent very useful experimental model in various branches of biological research. The investigation is driven by economic importance of many insect species, and also by biological features of insects as model organisms such as short period of reproduction, easy breeding and manipulation and, in particular, the minimal regulatory requirements which are associated to the management of vertebrates. Here we report robust and efficient LC/MS/MS methodology for the determination of the physiologically important lipid molecular species in insects. The target metabolites represent polar glycerophos-phopholipids (GPL) and nonpolar lipids diacylglycerols (DG) and triacylglycerols (TG). Combination of the LC/MS data with the subsequent GC fatty acid analysis enables complete structural elucidation of particular lipid species including their fatty acid compositions. The developed methodology was applied to studies of the chill tolerance of the firebug Pyrhocorris appterus. Fields and laboratory experiments were conducted to separate the triggering effects of low temperature, desiccation and diapause progression on the physiological characteristics related to chill tolerance with emphasis on the restructuring of GPL composition. The same effect on the GPL composition was observed during acclimatization in the field and cold acclimation in laboratory. By contrast, the GPL changes related to desiccation and diapause progression were relatively small (Tomčala et al, 2006). In adults of Drosophila melanogaster it has been found that acclimation at 15, 20 and 25°C during preimaginal development affects thermal tolerance and composition of membrane GPLs. Low temperature acclimation was associated with increase in proportion of ethanolamine at the expense of choline in GPLS. Relatively small, but statistically significant changes in lipid molecular compositon were observed with decreasing acclimation temperature (Overgard et al, 2008). Hormonal treatment studies on insect model Locusta migratoria showed a heterogeneous distribution of individual DGs in haemolymph after the hormone application and revealed that mobilization of the DGs is molecular species-specific with the highest proportion of DG 16:0/18:1 and forming in summary about 20% of the total mobilized DG content. Additional analysis of fat body triacylglycerols revealed that the AKH mobilizes the DGs specifically with the preference of those possessing the unsaturated C18 fatty acids (FAs). The fat body FAs with more than 18 carbons did not participate on the mobilization (Tomcala et al, 2009). The LC/MS methodology was further applied to lipid composition studies of several samples with very diverse biological origin (fish, human blood etc.) and was proved to be universally applicable to the wide scope of biological samples.