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

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Design, synthesis and characterization of novel, lead-free multiferroic and relaxor materials

Author: 
Date created: 
2019-04-11
Abstract: 

New multiferroic solid solutions of (1-x)BiFeO3-xBaHfO3 (BF-BaHf) with x = 0.05 - 0.95 has been prepared by conventional solid-state reaction in the form of ceramics. X-ray powder diffraction revealed that the perovskite structure of BF-BaHf transfers from rhombohedral to cubic symmetry with the increasing concentration of BaHf, resulting in the formation of solid solution. Compared with pure BF, the ferromagnetism in the BF-BaHf solid solution is substantially enhanced by the structural distortion due to A-and B-site co-substitutions, with remanent magnetization Mr = 0.0469 ????" ⁄????. ???? in x = 0.15. Meanwhile, ferroelectric domains were observed by transmission electron microscopy for x = 0.15. This confirms the beneficial role of BaHf substitution in enhancing magnetic properties while maintaining ferroelectric properties of the BF-based multiferroic materials. Another new multiferroic solid solution of pseudo-binary system (1-x)[0.8BiFeO3- 0.2BaHfO3]-xBaTiO3 [(1-x)(0.8BF-0.2BaHf)-xBaT] has been successfully synthesized by solid state reaction with x = 0.15 - 0.95. All the composition studies showed a gradual phase transition from rhombohedral to tetragonal phase as the BaT concentration increases. A morphotropic phase boundary is found in the composition range of 0.70 < x < 0.80. Additionally, weak ferromagnetism at room temperature was observed in the composition range of 0.30 ≤ x ≤ 0.40. The dielectric loss tangent shows a significant decrease as the BaT component increases. Summarily, a phase diagram of the (1- x)[0.8BiFeO3-0.2BaHfO3]-xBaTiO3 solid solution has been established. Single crystals of lead-free BaZr0.275Ti0.725O3 (BZT) have been grown successfully by a high temperature solution growth method after 32 trials. The optimal flux combination to grow the BZT single crystals is a mixture of BaCO3, BaCl2 and B2O3. The size of the as- grown crystals varies from 0.5 to 1 nm. X-ray diffraction indicates a pure perovskite phase. Polarized light microscopy has shown that the crystals are of cubic symmetry at room temperature, suggesting that they are of relaxor behaviour, as initially expected. The BZT single crystal composition is determined by X-ray photoelectron spectroscopy to be consistent with the nominal composition. The atomic concentrations ratio of the elements Ti and Zr are 72.5 % and 27.5%, respectively. This work demonstrates that the BZT single crystal can be grown by high temperature solution growth method and this is the first successful growth.

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

Synthesis and characterization of new Au-Ag plasmonic alloy materials

Author: 
Date created: 
2019-04-10
Abstract: 

Confining the delocalized fields of electromagnetic waves to the nanometer scale of metallic surface regions by exciting surface plasmons enables new methods of information transfer, energy conversion, red-ox chemistry and catalysis. Currently, Ag and Au are the most commonly used plasmonic materials, but neither is ideal. The goal of this work is to synthesize and characterize new Au- and Ag-based alloy materials with improved plasmonic response, low optical losses and high chemical stability by employing an electroless reduction method to deposit the alloys through co-deposition of silver and gold ions. The deposition kinetics of the ions in solution have been examined, followed by characterization of the resulting films to assess their quality, crystallinity and physical and chemical properties. We have employed spectroscopic ellipsometry (SE) to assess the optical and plasmonic properties, X-ray photoelectron spectroscopy (XPS) for film composition and electronic structure, X-ray diffraction (XRD) for film crystallinity, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) for their crystalline structure and morphology. The chemical stabilities of the alloy films have also been addressed by examining their stability upon exposure to various oxidants. Nanostructured alloy films deposited using the same chemistry on films patterned by electron beam lithography (EBL) yield large area, high quality, crystalline nanopillar arrays. These metamaterial arrays demonstrate plasmonic response which is determined by pillar diameter, periodicity and composition. The development of new high quality, crystalline, plasmonic alloy materials will enable new and improved performance in plasmonic and metamaterial research and application.

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

Evaluation of small molecules and metal complexes that modulate amyloid-beta aggregation of relevance to Alzheimer’s disease

Author: 
Date created: 
2019-11-28
Abstract: 

Alzheimer’s disease (AD) is the most common form of dementia, representing 50-75% of all cases worldwide. AD is a multifaceted disease that is characterized by increased oxidative stress, metal-ion dysregulation, and the formation of intracellular neurofibrillary tangles and extracellular amyloid-B (AB) aggregates. Cu(II), Zn(II) and Fe(II) have been shown to play a role in the aggregation and toxicity of the AB peptide, leading to the formation of reactive oxygen species (ROS) for Cu(II) and Fe(II). Different approaches have been used in this thesis to decrease the formation of ROS, modulate peptide aggregation and the interaction between bioavailable metal ions and the AB peptide. In the first approach, metal-protein attenuating compounds (MPACs) were designed to bind dysregulated metal ions thereby limiting metal ion binding to the AB peptide. The ability of 8-hydroxyquinoline Schiff-base ligands to inhibit peptide aggregation in the presence of Cu(II), and their antioxidant activity measured by a Trolox equivalent antioxidant capacity (TEAC) assay are described. The ligands were shown to form complexes with Cu(II), 8-H2QT in a 1:1 metal:ligand ratio, and 8-H2QH and 8-H2QS in a 1:2 metal:ligand ratio. The second approach investigated herein describes the use of metal complexes that are able to bind to the peptide, with potential to modulate aggregation and limit ROS formation. We report the high affinity binding of the Fe(III) 2,17-bis-sulfonato-5,10,15-tris(pentafluorophenyl)corrole complex FeL1 to the AB peptide (Kd ~ 10-7) and the ability of the bound FeL1 to act as a catalytic antioxidant in both the presence and absence of Cu(II) ions. Overall, FeL1 is shown to bind to the AB peptide, and modulate peptide aggregation. In addition, FeL1 forms a ternary species with AB-Cu(II) and impedes ROS generation. Finally, we report a series of four Ru(III) complexes, inspired by the antimetastatic NAMI-A complex. These complexes bind to AB, and were shown to modulate peptide aggregation. Overall, we highlight the promise of discrete metal complexes to limit the toxicity pathways of the AB peptide.

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

Synthesis of conformationally constrained inhibitors for glycoside hydrolases

Author: 
Date created: 
2019-09-10
Abstract: 

Glycoside hydrolase (GH) enzymes are clinically relevant biological targets for drug development. Disfunction of the two lysosomal GHs β-glucocerebrosidase and α-galactosidase can lead to Gaucher and Fabry’s disease, respectively. With knowledge of their mechanisms of action it is possible to create compounds that would effectively modulate their activity and potentially restore the activity of dysfunctional enzymes. Therefore, this work considers the approach to the synthesis of such compounds and determination of their mode of action. In the future, these compounds can be used for the development of drug candidates.

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

Development and evaluation of a library of thiazoline-sugar based inhibitors

Author: 
Date created: 
2017-04-20
Abstract: 

Thiazoline-sugar based inhibitors are known transition state analog inhibitors of N-acetylhexosaminidases that utilize a substrate assisted catalysis mechanism. Although selective inhibitors have been developed with modifications at the 2-OH and 6-OH positions, modifications at the 3-OH and 4-OH positions have not been explored. Many endo-N-acetylglucosaminidases that act on oligosaccharide or polysaccharide substrates comprised of monosaccharides glycosylated at the 4-OH position have fascinating roles in disease. A library of inhibitors were developed by selectively alkylating the 4-OH position of NAG-thiazoline and tested for inhibition against bacterial virulence factors Endo D, Auto, and FlgJ. These thiazoline based inhibitors were found ineffective in inhibiting Endo D and unsuited to the acidic pH profile of Auto and FlgJ. Hex D is a mammalian N¬-acetylgalactosaminidase that hydrolyzes O-GalNAc substrates. Although the mechanism and substrate selectivity of this enzyme is known, the exact biological substrates and functions of this enzyme are unknown. Gal-thiazoline is known to inhibit Hex D competitively (K¬I = 420 nM) and a recent co-crystal structure of Gal-thiazoline bound to Hex D showed a pocket near the 3-OH position of the inhibitor. To further study the physiological role of Hex D, more potent and selective inhibitors with modifications at the 3-OH position of Gal-thiazoline were synthesized and tested for inhibitory potential. Unfortunately, modifications at this position resulted in decreased inhibition. We hypothesize that the 3-OH position is responsible for a key hydrogen bonding interaction that is compromised upon alkylation.

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

Epitaxial growth of single crystal noble metals for plasmonic and nanophotonic applications

Date created: 
2019-01-17
Abstract: 

Material quality and crystallinity play an important role in the activity of plasmonic devices. Plasmonic structures made from monocrystalline metals may be expected to display much higher efficiency and stability than polycrystalline devices which are subject to many losses due to the presence of grain boundaries and defects. With the help of a novel epitaxial electroless deposition (EED) chemistry, ultrasmooth gold films can be grown on monocrystalline silver surfaces. In this approach, the electrochemical incompatibility of gold and silver can be overcome in concentrated sodium hydroxide (NaOH) solution (1 M), where the presence of OH⁻ causes a decrease in the reduction potential of gold cations by forming Au(OH)4⁻ complexes (E≈0.56 V), an increase in the oxidation potential of the silver electrode (E≈1.40 V), and acts as a reducing agent. As a result, ultrasmooth monocrystalline gold films are grown with the same crystalline orientation as the underlying silver film. This chemistry enables the growth of gold from a few monolayers up to few hundreds of nanometers uniformly over a large area. Furthermore, this approach enables the fabrication of large area metasurfaces made of gold and silver epitaxially grown nanostructures that can be used in a variety of different applications. The growth of gold films and nanostructures can also be manipulated by the introduction of anionic species during the deposition, and leads to the formation of surface nanostructures with specific shape, due to preferential interaction of the anions with certain facets of the growing crystalline structures. Subtractive fabrication of bowtie nanoantenna devices by focussed ion beam milling of gold films deposited by EED chemistry are compared to those deposited by conventional physical vapour deposition (PVD) methods using two-photon photoluminescence spectroscopy and imaging methods, employed as a proxy for plasmonic excitation. The monocrystalline EED gold films demonstrate excellent pattern transfer characterisitics, functional device yield, improved tailoring of local near fields, as well as increased thermal and mechanical stability compared to devices patterned identically on polycrystalline PVD films. Taken together, the work described in this thesis represents a novel and powerful new approach to the fabrication of monocrystalline noble metal films and nanostructures useful for plasmonic and metamaterial research and application.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Dr. Gary W. Leach
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Elucidation of glycoside hydrolase mechanisms by measuring kinetic isotope effects using direct NMR method

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

Enzymes that catalyze the removal of carbohydrate units from biological molecules are called glycoside hydrolases (GH). These enzymes have been categorized into more than 150 different families. This thesis presents an analysis of the mechanistic aspects of three glycoside hydrolases elucidated by measuring kinetic isotope effects (KIEs) by a direct nuclear magnetic resonance (NMR) spectroscopic method. A review of scope and limitations of the NMR method for competitive heavy atom (13C, 18O, 15N) and secondary deuterium KIEs measurement in biological systems is provided. A method for continuous monitoring of isotopically enriched materials is described in detail including the current state of instrumentation and computer programs for data acquisition and analysis. In order to refine the mechanistic understanding of the glycoside hydrolase family 4 (GH4) α-galactosidase from Citrobacter freundii (MelA), leaving group effects were measured with various metal cations and competitive deuterium KIEs were measured with singly and doubly deuterated activated substrates, 2-fluorophenyl and 4-fluorophenyl α-D-galactopyranosides, in the presence of Sr2+, Y3+, and Mn2+. The observations are consistent with hydride transfer at C-3 to the on-board NAD+, deprotonation at C-2, and a non-chemical step contributing to the virtual TS for V/K. The α-D-glucopyranosyl fluoride (α-GlcF) hydrolysis catalyzed by GH15 inverting α-glucoamylases from A. niger and Rhizopus sp. has been studied by use of multiple competitive kinetic isotope effect measurements. The experimental KIEs are consistent with the enzymatic reaction occurring via an SN1-type mechanism, in which the transition state has significant pyranosylium-ion like character and is late with respect to C−F bond cleavage. α-D-Glucopyranosyl fluoride is hydrolyzed by the family 55 inverting exo-1,3-β-glucanase from Trichoderma virens via the Hehre resynthesis–hydrolysis mechanism. The transition state for the Hehre resynthesis-hydrolysis mechanism for the GH55 catalyzed hydrolysis of α-GlcF has been studied by the use of multiple kinetic isotope effect measurements. The transition state for the Hehre resynthesis-hydrolysis reaction is late with respect to both C–F bond cleavage and proton transfer.

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

On-site detection of total arsenic in water with DNA aptamer/CeO2 nanoconjugates on arrayed paper strips

Author: 
Date created: 
2019-07-04
Abstract: 

An on-site fluorometric method for the qualitative detection of major arsenic species, arsenite, As(III), and arsenate, As(V), in water is presented in this thesis. Both As(III) and As(V) are toxic ions that are found in drinking water or water effluents worldwide. Building upon DNA-capped metal oxide nanoparticles, it has been shown that both As(III) and As(V) can be quantitated with a paper-based fluorometric assay. In particular, fluorescently labelled DNA aptamers were first adsorbed onto CeO2 nanoparticles where the fluorescence was initially quenched. After the addition of either As(III) or As(V), the DNA strands were released from the surface due to strong and specific DNA (aptamer)-As(III/V)(ligand) interactions which resulted in fluorescence recovery. It was demonstrated that such a detection scheme can be realized on an arrayed paper substrate; glass fiber filter paper was first modified to be superhydrophobic and then patterned photochemically to create arrayed reaction sites. The signal readout is based on smartphone-imaging, i.e., analyze the RGB intensities of the assay photo taken under UV irradiation with a smartphone. These paper assays provided great performance for testing water samples containing As(III) and As(V), with detection limits of 29 nM and 38 nM, response ranges from 20 nM to 100 µM and from 10 nM to 100 µM, respectively. The satisfactory detection sensitivity (below the WHO standard, 80 nM), high selectivity, and wide response range augment the potential application of these paper-based fluorometric assays for on-site arsenic detection in water.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Hua-Zhong Yu
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Metalloporphyrins bearing a single proton relay or rhenium-diimines for electrochemical reduction of oxygen and carbon dioxide

Author: 
Date created: 
2019-04-15
Abstract: 

Electrochemical reduction of dioxygen (O2) and carbon dioxide (CO2) are two examples of redox reactions that have captured interest as renewable energy solutions. For example, fuel cell technologies demand improvement for reduction of O2 to H2O selectively at low energy costs. The basic requirements for transformations of O2 and CO2 are input of multiple protons (H+) and electrons (e–) (e.g., 4H+/4e– for O2 to H2O). The first half of this thesis focuses on the O2 reduction reaction (ORR) using heterogeneous catalytic platforms. The work starts from Fe-tetra(aryl)porphyrins, which are known ORR catalysts (producing H2O). However, they exhibit high overpotentials and poor stability, making them ill-suited for application. In comparison, heterogeneous Co-derivatives show ORR at lower overpotentials but make mostly H2O2. This is undesirable for fuel cell applications. Following an introduction to proton-coupled redox catalysis (Chapter 1), Chapter 2 presents my work on asymmetric Fe-porphyrin derivatives bearing a single pendant proton relay. Work on heterogeneous ORR shows improvement in catalytic stability on graphite electrodes without compromising selectivity. Chapter 3 shows that Co-derivatives are better catalysts than Fe analogs and use of asymmetric porphyrins shifts selectivity from production of H2O2 to H2O. The electrochemical CO2 reduction reaction (CO2RR) provides a route to turn a greenhouse gas into value-added products. The 2H+/2e– reduction of CO2 to CO is the central attention because CO could be used as a precursor to produce many products, including fuels. Benchmark Fe-porphyrins bearing up to 8 proton relays are known for homogeneous CO2RR. In Chapter 4, I show that an iron porphyrin with one proton relay at a meso-position can achieve a similar benchmark depending on the choice of solvent. Chapter 5 presents that these asymmetric metalloporphyrin derivatives are excellent heterogeneous CO2RR catalysts once immobilized on graphite surfaces, with activation of CO2 near the thermodynamic potential. Another family of CO2RR catalysts, based on ClRe(CO)3 fragments, is described in Chapter 6. Here, I show that Re complexes containing derivatives of 2,2’-pyridylimidazole reduce CO2 at rates that are competitive with state-of-the-art Re derivatives. Immobilization strategies for these Re-complexes onto electrodes are also proposed.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Dr. Jeffrey J. Warren
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Study of 28Mg and 22Ne using fusion-evaporation and Doppler shift techniques

Date created: 
2019-04-25
Abstract: 

Investigations of nuclear structure via high precision measurements of energies and lifetimes of excited nuclear states has been the focus of an ongoing experimental program carried out at TRIUMF, Canada’s particle accelerator centre, using the TIGRESS Integrated Plunger (TIP) infrastructure. As part of this work, methods have been developed to determine energies and lifetimes of excited states in nuclei populated using the fusion-evaporation reaction mechanism and measured using the Doppler-shift attenuation method (DSAM). These methods include a comparison of experimental data to Monte-Carlo simulations in order to determine lifetimes of observed states. Methods were validated using data collected for the benchmark nucleus 22Ne at the ISAC-II facility at TRIUMF. Additionally, an array of 128 CsI(Tl) charged particle detectors has been constructed at Simon Fraser University. This new ‘CsI ball’ array replaces a 24-detector array used in previous TIP experiments and offers improved charged particle detection efficiency due to its increased solid angle coverage (nearly 4π in the lab frame). A subset of the CsI ball array was used to study excited states of 28Mg in an experiment at ISAC-II/TRIUMF, with the goal of investigating the evolution of nuclear shells and searching for evidence of the lowering in energy of pf negative parity orbitals predicted in this region. For the first time 28Mg was investigated using a fusion-evaporation reaction, leading to preferential population of states at high spin and excitation energy where the influence of the pf negative parity orbitals is expected. Analysis methods developed for 22Ne were applied to the 28Mg DSAM data to extract lifetimes of observed states. 3 new excited states of 28Mg were identified. Multiple candidates for negative parity states were also observed, providing an explicit indication of pf negative parity orbital population. Underlying principles and theories of nuclear structure, a technical overview of the CsI ball array and other TIP infrastructure, along with results from the 22Ne, CsI ball commissioning, and 28Mg experiments are presented. A comparison of the data to the predictions of various theoretical models is shown and implications for the structure of 28Mg are discussed.

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