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

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Development of an in vitro method to study heterogeneous particle mimic exposures

Date created: 
2016-04-12
Abstract: 

Particulate matter, a heterogeneous mixture of solid and liquid particles suspended in the atmosphere, has been strongly linked to several respiratory diseases and cardiovascular disease. Due to its impact on human health, epidemiological, in vivo, and in vitro studies are used to assess toxicity of diverse types of particulate matter, and mechanisms behind disease pathogenesis. To enable insight on how particle composition affects cellular response, an in vitro dose-response apparatus and methodology were developed to deliver heterogeneous particles of controlled compositions onto human lung cell mono- and co-cultures. Silica particles, an ambient particle type sourced from crustal matter, were generated using the apparatus and were delivered onto cultures of alveolar epithelial cells (A549) up to an estimated 3.2 µg cm-2. No change was observed in membrane bound protein intercellular adhesion molecule-1 (ICAM-1) expression. In a proof of concept study, tumor necrosis factor (TNF)-α, a potent cytokine, was introduced as a secondary component to silica. This binary particle type was also delivered onto A549 monocultures, and ICAM-1 signal increased with an increase in dose. Silica particles were also delivered onto co-cultures containing A549 cells and macrophages differentiated from blood monocyte cells (THP-1). Cytokine interleukin (IL)-6 was significantly up-regulated in co-cultures, but IL-8 was not. Lipopolysaccharide (LPS), a component of the cell wall in Gram negative bacteria, and nickel, in the form of Ni(NO3)2·6H2O, were introduced as secondary components to silica. These binary particle types were generated at ratios representative of respirable agricultural soils and dosed onto co-cultures. It was observed that silica plus LPS particles caused an up-regulation of IL-6 and IL-8 response relative to silica particles, whereas silica plus nickel particles did not. LPS bioavailability was determined as 10±3% and 1.0±0.6% for silica plus LPS particles at atmospherically-relevant LPS to silica mass ratios of 91 ppm and 910 ppm, respectively. The reduction in bioavailability showed how interactions between compositions in a heterogeneous particle type can affect cellular response.

Document type: 
Thesis
File(s): 
Senior supervisor: 
George Agnes
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Investigations into O-GlcNAcylation through analytical mass spectrometry

Author: 
Date created: 
2014-12-17
Abstract: 

The modification of proteins with O-linked N-acetylglucosamine residues (O-GlcNAc) is found on many proteins in the nucleus and cytoplasm. O-GlcNAc has been implicated in many physiological processes but much remains to be learned about the effects of this modification on protein function. In this thesis I detail two studies aimed to improve our understanding of protein modification by O-GlcNAc. First, I describe a bioinformatics study focused on uncovering the protein structural features that favour O-GlcNAcylation by the enzyme O-GlcNAc transferase. The search for a sequence or structural motif to be found amongst the many substrates O-GlcNAcylated by OGT is a path well-trodden. On the basis of our analysis of site mapping data accumulated from the literature and also through targeted site mapping of an entirely intrinsically disordered protein by mass spectrometry, I counter argue that OGT preferentially targets substrates which can be intrinsically disordered.Second, I describe a study aimed to gain insight into cellular proteomic response due to lowering of O-GlcNAc levels. There is mounting evidence O-GlcNAcylation is both linked with protein folding and intracellular proteome stability. While stability is measured by turnover it is also tied to misfolding. We investigated a possible relationship between lowered O-GlcNAc levels and instability of a segment of the proteome using stable isotope labelling by amino acids in cell culture mass spectrometry.

Document type: 
Thesis
File(s): 
Senior supervisor: 
David Vocadlo
Department: 
Science:
Thesis type: 
(Thesis) M.Sc.

New approaches to remediation of nanoscale contaminants in the workplace

Date created: 
2014-12-15
Abstract: 

It is important that all workers understand the health and safety risks of their work environment. It has been demonstrated that exposure to nanoparticles can lead to potential health concerns. A 1 mL nanoparticle solution spill can contain >10^9 nanoparticles, with the particles invisible to the human eye. This nanoparticle spill can cause further contamination in the work environment as workers transfer the particles from one area to another if the nanoparticles are not properly remediated. Therefore, it is essential that effective methods be developed for early identification and clean-up of such spills to avoid potential hazards to those working with these particles. One goal of this research is to develop a methodology that is simple to implement on a global scale to rapidly detect the presence of nanoparticles in different workplace environments to accompany methods for the remediation of spills containing nanoparticles. X-ray fluorescence spectroscopy was identified as a portable solution to potentially identify the presence of and the extent of a spill containing nanoparticles. Many other techniques could also be utilized, but the ease of use at the point of contamination without the requirement of sample preparation makes this an attractive solution in nanoparticle remediation. Another goal of this research is to develop an efficient, effective and inexpensive means to remediate spills containing nanoparticle contaminants. The implementation of these remediation procedures would change how nanoparticles are treated in the workplace and promote a healthy work environment when using materials that would otherwise go unnoticed due to their small size. Remediation of nanoparticles spilled in the workplace requires a method of acknowledging that these unseen particles are appropriately being removed and to avoid spreading these particles to a wider extent throughout the workplace. Analytical techniques were used to monitor the presence of nanoparticle contaminants and, in combination with techniques to encapsulate nanomaterials within a spill, were used to assess the appropriateness of these remediation techniques for cleaning up simulated spills. These studies demonstrate a series of methods to progressively remove nanoparticle contamination from countertops in the workplace.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Byron D. Gates
Department: 
Science: Chemistry
Thesis type: 
(Thesis) M.Sc.

Establishing the Quality of Molecular Coatings on Gold Nanoparticles

Author: 
Date created: 
2014-12-16
Abstract: 

The surface chemistry of nanoparticles imparts colloidal stability to nanoparticles by acting as barriers between their surrounding environment and the nanoparticles. Gold nanoparticles (AuNPs) are an ideal platform for many studies because of localized surface plasmon resonant properties, chemical stability, and the relative ease of modifying their surfaces with a wide variety of molecular coatings (e.g., alkanethiolates). Understanding and improving the physicochemical stability of these surface-modified nanoparticles is essential for their reproducible use in each application. The long-term colloidal stability of AuNPs relies on the resistance of their surface modifications to thermal degradation, chemical attack and oxidizing conditions. For this purpose, my research has been focused on determining the quality of molecular coatings on gold nanoparticles, and developing techniques, which are complementary to each other, to assess the quality factor of these coatings. Gold nanoparticles with varied qualities of molecular coatings were prepared and tested for their relative stabilities under various physical (e.g., temperature, time, laser irradiation) and chemical (e.g., in presence of metal etchants) conditions. We found that the quality of molecular coatings on AuNPs depends on the process conditions such as solution composition (e.g., the presence of co-surfactants, concentration of excess surfactants), density of capping molecules, and process time, used to form these coatings. We found that higher quality molecular coatings on the gold colloids increased the chances that the particles would remain stable over the over the duration of their intended use. Those colloids modified with relatively higher quality self-assembled monolayers were also more resistant to cyanide etching. These results highlight the importance of methodology for preparing high quality monolayers on nanoparticles and testing their ability to remain stable over the duration of their intended use, for example, during photothermal processes. In addition, the loading of DNA molecules onto AuNPs was tuned to achieve varying densities of DNA, and through this work, achieved the highest reported loading of single-stranded DNA (ss-DNA) molecules on gold nanorods. These high loadings of DNA oligonucleotides could enable a high loading of therapeutics onto the nanorods, which could translate into a higher or more prolonged delivery of therapeutic doses when actived by photothermal or other processes.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Byron D. Gates
Department: 
Science:
Thesis type: 
(Thesis) Ph.D.

Study of Complex Ferroelectric and Antiferroelectric Systems

Author: 
Date created: 
2014-12-12
Abstract: 

Rhombohedral (R), monoclinic (MA/MC) and tetragonal (T) phases are found in coexistence in a compositionally segregated xPb(In1/2Nb1/2)O3- yPb(Mg1/3Nb2/3)O3- zPbTiO3 (PIN-PMN-PT) (nominal composition x/y/z = 30/35/35) single crystal. Polarized light (PLM) measurements and X-ray diffraction (XRD) on both single crystal and ceramic series confirms the existence of 2 different monoclinic phases. A phase diagram in the MPB region of the PIN-PMN-PT solid solution is proposed based on both single crystals and ceramic material.Further study on the temperature driven rhombohedral (R) (R3m)  monoclinic (MA) phase transition in the single crystals and ceramics with MPB composition are carried out. It was found that the rhombohedral domain is able to return to its original state after annealed at above the RMA phase transition temperature (TR-M) but below the Currie temperature (TC). A polarization reversal model is proposed based on the polarization rotation theory.Solid solutions of (1-x)Pb(Mg1/2W1/2)O3-xPb(M1/2W1/2)O3(M = Zn2+ and Mn2+) have been prepared by solid state reaction with composition x up to 30% for Zn and 50% for Mn. The influence of Zn2+ and Mn2+ on structure, electrical and magnetic properties are revealed. (1-x)PbZrO3-xPb(Mn1/2W1/2)O3 (x = 0 - 0.1) as another new solid solution system was also prepared by the solid state reaction method. Its crystal structure, dielectric properties and antiferroelectricity were investigated and it was proven to be an excellent candidate for energy storage devices.In summary, the study for PIN-PMN-PT ternary solid solution near its MPB composition shall provide a general guideline for designing high performance peizocrystals. The study of PZ-based and PMW-based antiferroelectric solid solutions provided better understanding of antiferroelectric perovskites and provides a different approach for the design of soft antiferroelectric material with high energy density.

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

Studies toward the biosynthesis of chimonanthine in chimonanthus praecox

Author: 
Date created: 
2016-01-18
Abstract: 

Chimonanthine is the building block of a series of natural products found in terrestrial plants including members of Psychotria in the family of Rubiaceae. Studies have shown that alkaloids containing the chimonanthine core display interesting analgesic, inhibition of melanogenesis, and anti-cancer activities. The goal of this study is to explore the precursor directed biosynthesis of chimonanthine and the enzymes involved in the biosynthesis of chimoanthine as well as to identify these enzymes for potential use as biocatalysts that can generate libraries of modified natural products. Herein we report the identification of a suitable plant containing these enzymes and demonstrate the feasibility of new assays by showing that feeding of plants with synthetic precursors leads to the production of labelled chimonanthine.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Robert Britton
David J Vocadlo
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Alternative Platinum Electrocatalyst Designs for Improved Platinum Utilization

Date created: 
2014-12-10
Abstract: 

Platinum electrocatalysts are important for a number of low and zero-emission energy technologies, including low temperature fuel cells. For reactions such as oxygen reduction at a fuel cell cathode, poor kinetics and harsh operating conditions (which lead to catalyst degradation) dictate the use of large volumes of Pt for efficient electrocatalysis. This need for a large quantity of Pt increases the cost of the fuel cell and makes the technology too expensive to compete with petroleum based energy alternatives typically used in automotive applications. Improving the effective utilization of Pt enables the same performance to be achieved with a smaller mass of Pt. A more effective use of Pt can be achieved through the use of alternative catalyst layer designs. The work presented in this thesis demonstrates three novel Pt catalyst layer designs with the aim of improving the effective utilization of Pt for electrocatalysis. These designs include pure Pt ordered porous electrodes (Pt-OP electrodes), supported Pt nanoparticle ordered porous electrodes (support@PtNP-OP electrodes) and nanobowl supported Pt NPs (support@PtNP nanobowls). These designs aim to enhance Pt utilization by improving: i) mass transport through the use of an open porous design; ii) Pt electrochemical stability via the use of stable materials throughout the electrocatalyst design and/or through support interactions; and iii) Pt catalytic activity via favorable interactions with support materials. The preparation of these new Pt electrocatalyst designs is presented through the use of sacrificial templates. The new materials were extensively characterized by electron microscopy, X-ray spectroscopy, and electrochemical methods. The alternative electrocatalyst designs demonstrated here provide new routes towards enhancing the utilization of Pt for electrocatalytic applications.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Byron Gates
Department: 
Science:
Thesis type: 
(Thesis) Ph.D.

Synthesis and Characterization of Ferroelectric and Antiferroelectric Complex Perovskite Systems

Author: 
Date created: 
2014-12-09
Abstract: 

Single crystals of Pb(Sc1/2Nb1/2)O3 (PSN) were grown by a high-temperature solution method using (PbO + B2O3) as flux. X-ray diffraction (XRD) indicates a pure perovskite phase without B-site ordering. Polarized light microscopy shows that the crystals are of rhombohedral symmetry at room temperature and become cubic at 112 oC on heating which is the Curie temperature (TC). A relaxor-to-ferroelectric phase transition is confirmed by dielectric spectroscopy. Frequency-dependent permittivity is also observed, revealing relaxor behavior. Poling the crystal at room temperature does not change TC but suppresses the permittivity. A typical ferroelectric hysteresis loop is obtained at room temperature, indicating the ferroelectric nature of the PSN crystal.A new antiferroelectric solid solution ceramics of (1-x)PbZrO3-xPb(Zn1/2W1/2)O3 [(1-x)PZ-xPZnW, with x = 0 - 10%] has been prepared by conventional solid state reaction method. XRD reveals the perovskite structure of the (1-x)PZ-xPZnW ceramics. TC decreases when the percentage of PZnW increases. Meanwhile, another transition related to the transformation from antiferroelectric (AFE) to an intermediate ferroelectric (FE) phase was observed and its transition temperature (TAFE-FE) decreases from 213 oC for x = 0 to 58 oC for x = 0.10. A typical FE hysteresis loop was obtained, indicating the FE nature of the intermediate phase.The 0.97PbZrO3-0.03Pb(Zn1/2W1/2)O3 (97%PZ-3%PZnW) ceramic was used to study the intermediate FE phase. The temperature dependence of dielectric permittivity was studied. TC on cooling and heating are both 212 oC, indicating a second-order phase transition. Another phase transition below TC was observed, from the AFE phase at room temperature to an intermediate phase at higher temperature. This transition shows thermal hysteresis on cooling and heating, representing a first-order phase transition. Within the temperature range of the intermediate phase, ferroelectric hysteresis loops were displayed and a non-centrosymmetric structure was revealed by second harmonic generation, which indicates the FE nature for the intermediate phase. High resolution XRD and the subsequent refinement results show that the intermediate FE phase is rhombohedral (R3m) and the AFE phase is orthorhombic (Pbam). A phase diagram of the (1-x)PbZrO3-xPb(Zn1/2W1/2)O3 solid solution has been established.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Zuo-Guang Ye
Department: 
Science:
Thesis type: 
(Thesis) M.Sc.

Poly 3-Hexylthiophene as a photocathode for solar water splitting

Date created: 
2015-10-22
Abstract: 

The focus of this research is to determine the extent to which poly 3-hexylthiophene (P3HT) can be used as a photoelectrode for solar water splitting. Research in the area of solar water splitting mostly focuses on inorganic materials but conjugated polymers, such as P3HT, offer several advantages. Most metal oxides used as photoelectrodes are only able to carry out water oxidation, require thick films to absorb significant amounts of light, and absorb light mainly in the ultraviolet part of the sun’s spectrum. Conjugated polymers are able (thermodynamically) to reduce protons, require thinner films, and absorb mostly in the visible region of the electromagnetic spectrum. Additionally, conjugated polymers are processed from solution at room temperature and pressure, and can be cast onto many different types of substrates (rigid or flexible). The ability of P3HT, on its own, to produce hydrogen gas (H2) from acidic aqueous solution is first examined. Figures of merit such as photocurrent and incident photon to current efficiency as a function of thickness are determined through photoelectrolysis in a homemade cell. In addition, the oxidation state of the polymer film in contact with aqueous acid area investigated using spectroelectrochemistry. Platinum was also employed as a hydrogen evolution reaction (HER) catalyst, either by photoelectrochemical deposition of nanoparticles directly on the polymer or as a colloidal dispersion.Thermodynamically, P3HT should reduce protons following light absorption. However, no H2 was detected in the absence of a HER catalyst. Hydrogen was produced when platinum was photoelectrochemically deposited. This deposition technique resulted in the formation of Pt nanoparticles on the polymer film. Also, this demonstrates that a single layer conjugated polymer device is capable of performing H2 evolution under illumination.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Steve Holdcroft
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

The Use of Light to Control Photo-thermoresponsive Systems

Date created: 
2015-10-21
Abstract: 

Integration of light and chemical reactivity is potentially beneficial for developing new materials with chemical and physical properties that can be regulated by light. Molecular switches based on the 1,2-dithienylethene (DTE) architecture are a class of photochromic molecules that can integrate light and chemical reactivity, providing a platform to develop these new materials. Photochromic dithienylethene derivatives can toggle between two electronically and structurally unique isomers when irradiated with light of an appropriate wavelength. The electronic and structural changes of dithienylethene derivatives can be employed to regulate chemical reactivity using light, which makes them very attractive for many applications such as controlled drug delivery, catalysis and imaging. Alternatively, chemical reactivity can be used to regulate the photochromic properties of dithienylethenes, making them useful in applications such as monitoring and detection. This thesis describes the success in integrating light and chemical reactivity to develop new thermoresponsive materials having the ability to respond to changes in temperature that also can be controlled by light. In a first study (Chapter 2), the concept of the reactivity-gated photochromism is expanded using the Diels-Alder reaction between a series of photoswitchable dienes and dienophiles. It is shown that the electronic changes that occur during the isomerization of a cleavable dithienylethene derivative “gates” the reversibility of the Diels-Alder reaction. An external heat source can only trigger the reverse Diels-Alder reaction when the molecule is first irradiated with light of an appropriate wavelength. In a second study (Chapter 3), a new thermally self-healing polymer is developed by the Diels-Alder reaction between dithienylfuran (DTF) and maleimide monomers to generate a photoresponsive dithienylethene. Results show that UV and visible light “gate” the reversibility of the Diels-Alder reaction and turn the self-healing properties of the polymer ‘off’ and ‘on’, respectively. The thermoresponsive polymer developed in this chapter requires an external heat source to trigger the reverse Diels-Alder reaction. In a third study (Chapter 4), a thermoresponsive anthracene endoperoxide ligand is anchored on the surface of gold nanoparticles. Results show that the indirect heat generated during the photothermal effect of gold nanoparticles triggers the bond-breaking reaction and releases singlet oxygen. In a fourth study (Chapter 5), a new strategy to control the photothermal release of small molecules from the surface of SiO2−Au core-shell nanoparticles is presented. It is shown that irradiation of the nanosystem with visible light triggers the ring-opening reaction of a dithienylethene chromophore then the indirect heat generated by the NIR light induces the reverse Diels-Alder reaction and releases small molecules. Similar to AND logic gate, this system requires both inputs (NIR and visible light) to be present to achieve the desired output (bond-breaking and release).

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