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

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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.

Electrochemical protein detection exploring redox cation-DNA interaction for signal enhancement

Author: 
Date created: 
2015-12-08
Abstract: 

A simple DNA-redox cation interaction enhancement strategy has been developed for improving the sensitivity of electrochemical immunosensors for protein detection. Instead of labeling with fluorophores or redox-active groups, the detection antibodies were tethered with DNA single strands. Based on the electrostatic interaction between redox cations ([Ru(NH3)6]3+) and negatively charged DNA backbone, enhanced electrochemical signals were obtained. Human chorionic gonadotropin (hCG) detection has been performed as a trial analysis. A linear response up to 25 mIU/mL and a detection limit of 1.25 mIU/mL have been achieved, both comparable with standard enzyme-linked immunosorbent assay (ELISA) tests. The method also shows remarkable selectivity towards hCG over other hormones such as thyroid stimulating hormone (TSH) and follicle stimulating hormone (FSH). By and large, our approach bears the merits of cost effectiveness and simplicity of instrumentation in comparison with conventional optical detection methods.

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

Spectroscopic investigations of fluorinated Ru(III) anticancer theranostics

Date created: 
2015-12-03
Abstract: 

Trifluoromethyl derivatives of the Ru(III) anticancer complexes indazolium [trans-RuCl4(1H-indazole)2] (KP1019), sodium [trans-RuCl4(1H-indazole)2] (NKP-1339), and their imidazole- and pyridine-based analogues have been synthesized and characterized. The aqueous solution behaviour of these compounds and their interactions with proteins were investigated using 19F nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and UV-Visible spectroscopies. Furthermore, the lipophilicity of the new CF3 complexes was quantified using the distribution co-efficient (logD). Fluorescence competition studies and EPR showed that CF3 functionalization enhances non-coordinate interactions with human serum albumin (HSA), correlating with increased hydrophobicity. EPR and 19F NMR experiments demonstrated coordination of Ru(III) to the protein at longer incubation times. The more hydrophobic complexes also exhibited higher cytotoxic activity against the HT-29 human colon carcinoma and A549 non-small cell lung carcinoma cell lines. Proof-of-principle 19F magnetic resonance imaging (MRI) experiments show that these compounds can be used to monitor the tissue penetration behaviour and oxidation state of Ru(III) anticancer compounds.

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

GEANT4 Simulations of Electron Capture Branching Ratio Measurements for the TITAN Facility

Author: 
Date created: 
2015-09-28
Abstract: 

A novel technique has been developed to measure the electron capture branching ratios (ECBRs) of key intermediate nuclei involved in double-b decay using the TITAN facility, TRIUMF’s Ion Trap for Atomic and Nuclear Science Facility. Knowledge of ECBRs is essential to evaluate the nuclear matrix elements of double-b decay for both two-neutrino double-b decay (2nbb) and neutrino-less double-b decay (0nbb) processes. In most of the cases of interest the ECBRs are poorly known or completely unknown because the EC process is suppressed by several orders of magnitude relative to their b-decay counterpart due to energy consideration. In addition, traditional methods of measuring these ratios suffer from large backgrounds due to the many orders of magnitude more intense b-decay. A new method for measuring EC branching ratios was implemented by using the TITAN ion trap at the TRIUMF ISAC (Isotope Separator and Accelerator) radioactive beam facility. In these experiments the Electron Beam Ion Trap (EBIT) is used as a spectroscopy Penning trap, where the electrons from b-decay will be confined by trap’s magnetic field and transported out of the trap, while the x-rays from EC are detected by Si(Li) x-ray detectors that are radially installed around the trap through seven open ports towards the trap’s center. A comprehensive GEANT4 based Monte-Carlo simulation has been developed to optimize the TITAN-EC experimental set-up and measurements at TRIUMF as analytical tool. The developments, evolution and validation of this Monte-Carlo simulation tool are described in this thesis.

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