Chemistry - Theses, Dissertations, and other Required Graduate Degree Essays

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Expanding the organocatalyzed α-chlorination-aldol reaction

Author: 
Date created: 
2018-12-14
Abstract: 

Organocatalysis, while still a relatively new field in organic chemistry, now plays an indispensable role in organic synthesis. Transformations not accessible by classical synthetic methods are now not only routine, but mild, high yielding and increasingly sophisticated in what they can achieve. One such reaction is the α-chlorination-aldol reaction developed by the Britton group in 2013. This reaction has been demonstrated to provide access to stereochemically rich chlorohydrins from readily available and achiral starting materials. The reaction has found extensive utility in the concise synthesis of imino-cyclitols and carbohydrate analogues. In this thesis a more general approach to the tandem α-chlorination-aldol with different electrophiles or ketones is investigated. Within, we show that azodicarboxylates can be used as electrophiles to functionalize aldehydes prior to submission to an aldol reaction. These aminated aldol adducts are further investigated for their utility in synthesizing imino-cyclitols, and their ability to form cyclic, polyhydroxylated hydrazones. As well, new substrates are investigated for their propensity to engage in an α-chlorination-aldol reaction. Four new substrates are demonstrated to form the corresponding chlorinated aldol adducts in moderate yields and high enantioselectivity. Furthermore, we demonstrate that these new aldol adducts can provide access to novel, natural product-like scaffolds.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Robert A. Britton
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Fully hydrocarbon ionomer catalyst layers in proton- and anion-exchange membrane fuel cells

Author: 
Date created: 
2018-09-17
Abstract: 

The structure and morphology of fuel cell catalyst layers and concomitant system properties, particularly mass transport, were investigated through electrochemical and physical characterization techniques. Catalyst layers designed for proton-exchange membrane fuel cells (PEMFCs) incorporated a hydrocarbon ionomer (sP4c) soluble in low-boiling solvents. These were used to probe the property alterations effected by increasing ionomer coverage within the catalyst layer, and also to measure the impact an extremely small quantities (0.38 wt%) of a commonly employed high-boiling solvent, DMF, in the catalyst ink. High-boiling solvents are difficult to eliminate during electrode formation, and resultant solvent-annealed catalyst layers lost electrocatalytic surface area, resulting in markedly greater kinetic losses compared to catalyst layers formed without high-boiling solvents. Catalyst layers designed for anion-exchange membrane fuel cells (AEMFCs) incorporating hydrocarbon ionomer in the catalyst layer (FAA-3) requiring high-boiling solvent (NMP, 2.3 wt% of total solvent) were formed over a broad array of conditions. Catalyst layers formed slowly at high temperatures to drive off high-boiling solvent displayed significantly enhanced mesoporosity, relating to enhanced transport characteristics, over solvent-annealed analogues with low mesoporosity, despite comparable total volumes. The impacts of solvent annealing on AEMFC electrode properties and resultant achievable power density and degradation were disproportionate compared to the similar PEMFC study. A new methodology for fuel cell membrane-electrode assembly construction, direct membrane deposition (DMD), enables lower interfacial resistances and enhanced water transport for a given thickness of membrane. These are desired properties for both PEMFCs and AEMFCs. Initially developed with inkjet printers designed for single-cell biological printing applications, this method was adapted to spray-coating systems in order to address issues with fuel and electrical crossover, suitability for hydrocarbon ionomers, and scalability / large-scale reproducibility. A perfluorinated sulfonic acid ionomer reference material (Nafion D520) was employed for direct comparison to initial methods. Highly reproducible DMDs with low fuel and electrical crossover resulted.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Steven Holdcroft
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Exploring substrate specificities of novel Burkholderia sp. isolates towards sustainable energy: benzoate degradation by new B. xenovorans strains

Author: 
Date created: 
2018-12-10
Abstract: 

Sustainable energy technologies demand the use of renewable sources of energy and materials, such as biomass. Remediation of toxic wastes is a related problem. The recalcitrance of the aromatic heteropolymer lignin, commonly found in plant biomass, is a major challenge for its sustainable transformation to energy and biomaterials. Biological approaches for degrading lignin and xenobiotic aromatic pollutants show great promise and are effective in some recent applications. This work aims at investigating the biodegradation activity of the newly discovered Burkholderia sp. isolates in alkali lignin, aromatic hydrocarbons, and n- or iso-alkanes under aerobic condition. Results show that no degradation was observed for alkali lignin inoculated with B. xenovorans. However, the novel B. xenovorans strains were able to grow and utilize benzoate (1 mg mL–1) as the sole carbon source in a minimal medium (M9) at relatively fast rate. HPLC analysis showed the presence of catabolic intermediates that were further used by the bacteria for growth. A 1H NMR analysis confirmed the presence of catechol as the central intermediate having a yield of 31.21 mg after hours of incubation. Furthermore, the new endophytic B. phytofirmans isolates also showed growth on M9 plates containing isooctane as the sole carbon source. More work is needed to determine the mechanism of degradation in isooctane, a recalcitrant branched alkane, by the novel B. phytofirmans. Overall, this study reveals the degradation potential of the new Burkholderia sp. isolates, in which the provided information can be harnessed for advanced applications and biotransformation strategies.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Jeffrey J. Warren
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Dynamic modelling of platinum degradation in polymer electrolyte fuel cells

Author: 
Date created: 
2018-12-10
Abstract: 

Platinum stability in the catalyst layer is vital to the lifetime of polymer electrolyte fuel cells. This thesis uses physical-mathematical modelling to provide a deeper under- standing of platinum degradation. Dissolution, a dominant degradation mechanism under fuel cell operating conditions, is shown to be strongly linked to oxide formation, growth, and reduction. However, since a consistent model that explains this link does not exist, the goal is to understand the platinum oxide processes and relate these to platinum degradation. In the first part, a physical-statistical model of Pt degradation is presented that encompasses the main particle-level degradation pathways namely dissolution, rede- position, coagulation, and detachment. A systematic algorithm is developed to pro- cess experimental inputs and generate outputs on kinetic rate parameters. Once the complete parameter space is explored using Monte Carlo techniques, an optimization routine is run to refine the results. In this way, unique, unambiguous rate parameters pertinent to different degradation mechanisms under various operating protocols have been extracted. It is shown that dissolution/redeposition increase with increasing up- per potential cycling limit; particle detachment increases with increasing surface area of the carbon support, whereas dissolution is independent of the carbon support type. Then a platinum oxide growth and reduction model is developed that implements in- terfacial exchange processes between platinum and oxygen atoms, as well as transport mechanism of oxygen vacancies through diffusion and field migration. A quasi-steady state model of oxide formation, growth, and reduction is developed. Oxide growth is seen to be sensitive to oxygen ion vacancy at the metal-oxide interface and the rate of platinum ion extraction across the interface. The tools this thesis presents provide better understanding to the underlying relations of platinum degradation that can be used to enhance the lifetime of fuel cells. For example, reliable assessments of the prominent degradation mechanism under various operating conditions can be evaluated to set priorities for materials research.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Michael H. Eikerling
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Nitric oxide donating furoxan derivatives and ruthenium(II) complexes as anticancer and antibacterial agents

Author: 
Date created: 
2018-08-27
Abstract: 

Ruthenium(II)-arene complexes were combined with furoxan (1,2,5-oxadiazole 2-oxide) moieties to generate new anticancer and antibacterial drug candidates. Previous studies have shown that Ru(II) organometallic complexes can exhibit significant anticancer activity with low levels of side-effects. Furoxans are heterocyclic molecules capable of releasing nitric oxide (NO), which can induce apoptosis or necrosis. Therefore, furoxans were employed as ligands for Ru(II)-arene complexes to design new drug candidates. Furoxan derivatives were synthesized with different substituents (-NO2, -H, -OCH3, -OPh, -SPh, -SOPh, -SO2Ph), which were found to affect the amount of NO released. NO release was quantified via electron paramagnetic resonance (EPR) spectroscopy. The complexes were found to donate more NO than the ligands; the highest concentration of NO was donated by the complex containing (-SO2Ph) substituent. Furthermore, antibacterial assays were performed, and the complexes exhibited higher cytotoxicity than the corresponding ligands. This work also reports the synthesis of a new heterobimetallic complex combining a Ru(II)-arene with a gold(III) compound.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Charles Walsby
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Development of organic-inorganic nanoparticle hybrid systems for medical applications

Author: 
Date created: 
2018-07-09
Abstract: 

Light has been efficiently used to control molecules and materials. Integration of photo-responsive molecules into larger molecular systems allows for the use of light to regulate the physical and chemical properties of these systems and to control their activity. The way in which a photoresponsive moiety is used depends on its response to the light signal and its interaction with other components in the molecular system. Based on their structure, some chromophores translate light signals into chemical, structural or electronic changes, while others convert the light signal into another type of energy signal (such as heat) that can trigger changes in a molecular system. The work presented in this thesis examines the design, preparation and evaluation of two light-controlled biomedical molecular systems utilizing different types of photo-responsive molecules.In the first study, featured in Chapter 2, light is used to control the activity of a nanoparticle-based MRI contrast agent. The design relies on the photochromic properties of spiropyran ligands to induce photo-control over the ability of the surrounding water molecules to access the surface of NaGdF4 nanoparticles, and consequently affect their proton relaxivity. The optimized structure of the spiropyran ligand was synthesized, and the photoswitching behaviour between the two isomers, with distinct polarities, was evaluated in an aqueous medium for both free and anchored versions. The designed nanoassembly enhanced the relaxivity of water protons, although displayed a small change in activity upon irradiation with visible light, which was attributed to the high magnetic field at which the data was acquired.In the second study, featured in Chapter 3, light is used to activate thermally-responsive enediyne molecules and generate reactive radicals that can potentially be used to destroy cancer cells. The design utilizes the photothermal effect of gold nanoparticles to transform the light energy into localized heat energy. The room temperature stable enediyne ligand was synthesized and then attached to the surface of the gold nanoparticles. Irradiation of the nanoassembly with a nanosecond pulsed green laser for three minutes generated enough heat to trigger the cyclization reaction of the enediyne decorated nanoparticles and release the activated enediyne ligands from gold nanoparticle surface.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Neil R. Branda
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Design and Synthesis of Novel, Lead-reduced Piezo-/Ferroelectric Materials

Author: 
Date created: 
2017-08-24
Abstract: 

Relaxor-based piezo-/ferroelectric materials of complex perovskite structure, represented by (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), have demonstrated excellent piezoelectric performance. However, they also exhibit some inherent drawbacks, such as a low Curie temperature, an even lower de-poling temperature due to the presence of a morphotropic phase boundary (MPB) region, a weak coercive field and a high content of lead, which make them unsuitable for high-temperature and high-field (power) applications and raise environmental concerns. Bismuth-based complex perovskites, such as Bi(Zn1/2Ti1/2)O3 (BZT) seem to be an interesting candidate for the replacement of lead-based compounds because, like Pb2+ ion, Bi3+ also contains the 6s2 lone electron pair which is considered to be essential for the high piezo-/ferroelectric performance in lead-based perovskite. In addition, the solid solution between BZT and PT indeed exhibits larger structural distortion resulting in a higher Curie temperature than PT. However, its coercive field is too large for the material to be poled in order to make its potentially high piezo-/ferroelectric properties useful. Faced with those issues and challenges, outcomes of this thesis are two-fold: Firstly, addition of a non-stereochemically active ion and related complex compound, namely La(Zn1/2Ti1/2)O3 (LZT), as an end-member \"softens\" the structures, chemical bonding and electric properties of \"hard\" ferroelectric materials, to achieve improved electric properties, such as giant dielectric constant, smaller coercive field and switching polarization and excellent piezoelectricity and ferroelectricity.Secondly, addition of BZT as the third component \"hardens\" the structures, chemical bonding and electric properties of PMN-PT binary system in order to increase its coercive field and to improve its piezo-/ferroelectricity. In particular, special efforts have been made to grow the single crystals of the PMN-PT-BZT ternary system. The studies of the single crystals provide invaluable information on the phase symmetry, domain structures, phase transitions and electric properties and allow to gain a better understanding of the relationship between crystal formation, chemical composition, phase symmetry and macroscopic properties.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Zuo-Guang Ye
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Covalent surface modification of silicon oxides

Date created: 
2017-08-30
Abstract: 

Microwave radiation was utilized as a tool to modify surface properties of silicon oxides. Covalent surface modification of silicon oxides has been widely pursued in the areas of material science, electronics, microfluidics, biology, and separation science. Chemical surface modifications are often achieved through the formation of organic monolayers, often referred to as self-assembled monolayers (SAMs). While these organic monolayers have been proposed as an effective surface modification strategy, the defects in these organic monolayers compromise the effectiveness on their ability to alter surface properties. For example, in the case of passivation of microscale electronic devices, the surfaces that are not covered by the organic monolayers are susceptible to environmental stress or corrosion, which can cause detrimental failures of the devices. Traditional methods of formation of monolayers often cause many defects including formation of multilayers or micelles, physically adsorbed organic film, and/or voids. In this thesis, microwave radiation is utilized as a tool to accelerate the formation of uniform monolayers. In particular, the formation of silane based monolayers and alcohol based monolayers on silicon oxide surfaces have been extensively studied. Microwave heating, unlike the traditional heating methods, delivers the thermal energy to the substrate surfaces. It can effectively accelerate the formation of both silane and alcohol based monolayers. Alcohol based reagents, in particular, is proposed as an alternative building blocks for their widespread availability and minimal reactivity with moisture. Tuning of surface chemistry of silicon oxides have been achieved with alcohol based regents with different functional groups. Furthermore, the formation of mixed monolayers has been proposed as means of controlling oleophobicity of the silicon oxide surfaces. Finally, the film thickness of the alcohol based monolayers has been characterized with angle-resolved X-ray photoelectron spectroscopy (ARXPS). The film thickness can be precisely tuned by choosing the alcohol based reactants with particular lengths of alkyl chains. A variety of surface chemistry can be designed towards many practical applications requiring surface functionalized silicon oxides using the research presented herein.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Byron D. Gates
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Nuclear isobar separation for Penning trap mass measurements at TRIUMF

Author: 
Date created: 
2018-04-10
Abstract: 

Nuclear mass values are an important experimental input for research in nuclear theory, astrophysics, and fundamental symmetries. Penning trap experiments such as TRIUMF’s Ion Trap for Atomic and Nuclear Science (TITAN) have produced the most precise mass values available for many exotic nuclei. TITAN has measured masses for nuclei with half-lives as short as 8 ms with a relative precision down to 10 −8 . TITAN has recently installed a multiple reflection time of flight (MR-ToF) mass separator to isolate rare isotopes for mass measurements even when they are obscured by intense isobaric backgrounds. The MR-ToF can act as a mass filter, producing isobarically pure samples, and it can also operate as a mass spectrometer, destroying a sample to rapidly produce a mass spectrum of an entire ion beam. In the following I provide a pedagogical introduction to the operating principles of the system and report on the results of initial commissioning.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Corina Andreoiu
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Crystal chemistry and properties of bismuth-modified complex oxide perovskites

Date created: 
2017-08-23
Abstract: 

There is a great interest in developing new high-performance piezo-/ferroelectric materials that are lead-reduced or lead-free. This work focuses on using bismuth as a lead alternative, and studies solid solutions based on the end-member Bi(Zn2/3Nb1/3)O3 (BZN). First, ceramics of the (1-x)PbTiO3-xBi(Zn2/3Nb1/3)O3 [(1-x)PT-xBZN] solid solution were synthesized. The tetragonality (c/a ratio) and A-site displacement increase with increasing BZN content, as revealed by X-ray diffraction analysis. Dielectric measurements show that the Curie temperature TC increases with increasing BZN up to a maximum of 520 °C for the composition of x = 0.20. These results indicate the structural origin of the enhanced tetragonality and properties that arise from the increased anisotropy in the Bi-bonding environment with the increased substitution of Bi3+, with its 6s2 stereochemically active lone electron pair. Synchrotron X-ray pair distribution functions (PDFs) reveal that the tetragonal distortions are preserved down to the local scale, suggesting that studies of the average structure provide reasonable insight into the structure-property relationships in this system. These results provide guidance for designing new materials with high TC. Single crystals of (1-x)PT-xBZN were then successfully grown using the high-temperature solution growth (HTSG) method. The dielectric measurements indicate the ferroelectric-paraelectric phase transition at an average TC of 436 °C. Polarized light microscopy reveals the domain structure of tetragonal symmetry, with domain walls oriented along the <100>cub directions, and birefringence measurements as a function of temperature confirmed the first order phase transition. HTSG allows for a higher BZN content to be incorporated into the crystals in comparison to their ceramic counterpart. Moving toward lead-free materials, ceramics of a novel solid solution, (1−x)BaTiO3 xBi(Zn2/3Nb1/3)O3 (BT-BZN) were synthesized. With increasing BZN content, the materials show a decrease in tetragonality and undergo a transition to pseudocubic symmetry, which is accompanied by a crossover from normal ferroelectric to relaxor behaviour. This crossover is explained by increased cationic disorder that disrupts the ferroelectric order. Synchrotron X-ray PDF analysis reveals that all the compositions show local tetragonal distortions that decrease at larger scales to reach the average structure, demonstrating the striking difference between the local and long-range structures.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Zuo-Guang Ye
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.