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

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Time-resolved gamma-ray spectroscopy with the GEARS detector: Applications in environmental radionuclide monitoring and neutron activation analysis

Date created: 
2017-08-17
Abstract: 

The Simon Fraser University Nuclear Science Laboratory (SFU NSL) joined into two collaborations, each with an interest in monitoring Fukushima-derived cesium-134 and cesium-137 in various environmental samples. The first investigated Fukushima-derived contamination in soil and three species of Pacific salmon, sockeye, chum, and Chinook. The second investigated Fukushima-derived contamination in sockeye salmon, Dungeness crab, and kelp. In both of these monitoring campaigns, the maximum radiocesium activity concentrations observed were significantly below Health Canada's regulatory limits with the conclusion drawn that there is no health risk to the average Canadian seafood consumer. The Neutron Generator Facility at SFU NSL has recently acquired a Thermo Scientific P 385 neutron generator capable of activating samples, inducing radioactivity in them which may be studied via time-resolved gamma-ray spectroscopy. Recording timing information is a prerequisite of these studies therefore, a new data acquisition (DAQ) system was installed with the Germanium detector for Elemental Analysis and Radioactivity Studies enabling timing measurements to take place. The new DAQ system was benchmarked via the measurement of two neutron activated metals, verifying its stability and precision.

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

Exploring gold(I) as a luminophore for emissive coordination polymers

Author: 
Date created: 
2017-07-27
Abstract: 

This thesis focuses on the incorporation of gold(I) as a luminophore in photoluminescent materials via coordination polymer (CP) methodology. This is explored via two avenues: (i) the use of dicyanoaurate, [Au(CN)2]– as a building block with lanthanide metals and (ii) the design of electron-rich gold(I) building blocks containing the ‘aurothiolate’ motif. A series of dicyanoaurate/lanthanide CPs [nBu4N]2[Ln(NO3)4Au(CN)2] (LnAu) Ln = Ce, Nd, Sm, Eu, Gd, Tb, and Dy were synthesized. LnAu CPs are strongly luminescent at room temperature and this behaviour is primarily lanthanide-based. These results contrast those reported for Ln[Au(CN)2]3·3H2O (LnAu3), which is only faintly emissive at room temperature. Solid-solutions of Eu(III)/Tb(III) were prepared to explore these differences. The emission colour in LnAu could be varied between red and green corresponding to Eu/Tb ratio, whereas in LnAu3 only red Eu(III) emission is observed. Short Ln–Ln contacts in LnAu3 enable energy transfer, whereas in LnAu the long Ln–Ln distances preclude this, allowing for colour tunable emission. Colour tuning was explored to find the maximum available gamut, and it was found that white emission, and multiple emission colours is possible at room temperature. Design considerations for an electron-rich gold(I) building block were evaluated and the dithiocarbmate building block [Au2(dopdtc)2] was synthesized. The would-be building block is hindered in its ability to form CPs but its luminescence proved to be interesting; the pressure dependent emission energy is significantly lower than for similar materials, despite similar Au–Au distances. The role of geometry becomes clear when probed using DFT; deviations from linearity in aurophilic chains result in the transition becoming MLCT in nature, which is less sensitive to applied pressure. To improve the utility of an electron rich Au(I) building block, [Au2(i-mnt)2]2– (i-mnt = S2C=C(C#N)22–) was explored for its ability to form intermolecular aurophilic interactions. Aurophilic materials were prepared via substituting [nBu4N]+ cations with those containing the N-H+ functional group, illustrating that [Au2(i-mnt)2]2– is a good candidate for aurophilic CPs. To that end, some preliminary results in the preparation of [Au2(i-mnt)2]2– CPs are reported.

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

Water permeation through polymer electrolyte membranes

Author: 
Date created: 
2017-07-26
Abstract: 

Water management has a major impact on the performance of the polymer electrolyte membrane fuel cells. An understanding of water permeation through polymer electrolyte membranes is crucial to offset the unbalanced water activity within fuel cells. The work presented in this thesis includes contributions that provide insight into internal and interfacial water permeation behavior of membranes, as well as insight into how membranes could be designed to enhance water management. Three types of ex-situ water permeation techniques are used in this thesis work. These are: liquid-liquid water permeation (LLP) in which both sides of the membrane are in contact with liquid water; liquid-vapor permeation (LVP) where one side of the membrane is exposed to liquid, and the other is exposed to vapor; and vapor-vapor permeation (VVP) where both sides of the membrane are exposed to water vapor. Three polymer electrolyte membrane systems were investigated under varied experimental conditions: degraded Nafion®, short side chain (SSC) perfluorosulfonic acid ionomer membrane, and an emerging class of anion exchange membrane, poly(benzimidazolium). Correlations between membrane series were drawn and compared to the commercially-available materials. It was found that membranes of smaller thickness, greater water volume fraction (Xv), and higher ion exchange capacity (IEC) result in a higher overall water permeability. However, the membrane thickness, Xv, and IEC do not dominate the rate of water permeation through the membrane interface. In contrast, the side chain length of the polymer is found to influence the interfacial water permeation, wherein membranes with longer side chain length are more water permeable at the interface.

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

Synthesis of natural and unnatural products by elaboration of alpha-chloroaldehydes

Date created: 
2017-04-21
Abstract: 

Fitting broadly under the category of target-oriented synthesis of complex organic molecules, the work described in this document pertains primarily to exploiting the facile organocatalytic synthesis of enantiomerically enriched α-chloroaldehydes, drawing out their potential through conversion into 1,2-chlorohydrins, and exploring the means by which these substances may be coerced to undergo intramolecular cyclization involving a nitrogen nucleophile. Specific targets and methodology include a successfully completed synthesis of the natural product (+)-preussin and similarly substituted pyrrolidines through the reductive annulation of β-iminochlorohydrins, a formal synthesis of (-)-swainsonine and related alkaloids through a related intramolecular cyclization strategy, and the synthesis and structural analysis of a carbocyclic mechanism-based inactivator of a glycoside hydrolase. As a secondary focus, this thesis also describes the isolation, structural elucidation, and testing of the long-range sex pheromone of the strepsipteran Xenos peckii, which was ultimately determined to be (7E,11E)-3,5,9,11-tetramethyltridecadienal, and of the chemical constituents of the bed bug (Cimex lectularius) aggregation pheromone, which were ultimately determined to be dimethyl disulfide, dimethyl trisulfide, (E)-2-hexenal, (E)-2-octenal, 2-hexanone, and histamine.

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

Oxygen mass transport parameters in ionomer films under controlled relative humidity

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

Mass transport parameters are determined for the oxygen reduction reaction (ORR) at the electrochemical interface of a platinum microdisk electrode and five different series of polymer electrolyte membranes. The series included proton exchange polyfluorosulfonic acid (PFSA) based membranes (Nafion 117, Nafion 211), films cast from PFSA dispersions (DE2020), anion exchange quaternary ammonium based membranes (FAA-3), and films cast from hexamethyl-p-terphenyl polymethylbenzimidazole (HMT-PMBI) dispersions. The membranes differ in chemical structure, morphology, and water content controlled by relative humidity. The series of materials were investigated over a range of temperatures (50-70 °C) and relative humidities (30-98% RH) using a solid state electrochemical cell. Cyclic voltammetry yielded the potentials where ORR is mass transport limited, as well as the electrochemically active surface area of the platinum microdisk electrode. Chronoamperometry was performed at mass transport limiting potentials, where fitting the current transients to analytical models (Cottrell/Shoup-Szabo) allowed for the calculation of oxygen diffusion coefficient (Db), solubility (cb), and permeability (Db*cb) for the applied environmental conditions. A numerical model is also presented which highlights constraints in using the analytical models to determine mass transport parameters when the inherently-assumed infinite electrolyte thickness is not present. During chronoamperometric measurements, where the potential applied results in the generation of liquid water at the membrane/electrode interface (ORR), a reversible time-dependent behaviour was observed where Db and Db*cb increased over time to plateau values. The time-dependency responds to changes in relative humidity and is reversible, where mass transport parameters shift to a vapour equilibrated state over long periods of time. It is suggested that the electrochemically generated liquid water at the membrane/platinum interface during oxygen reduction results in a morphological change over repeated perturbations in the form of chronoamperometric analysis. The presence of interfacial liquid water causes hydrophilic channels, which are not present in substantial amounts at the interface in the vapour equilibrated-state, to reorient toward the surface. The increase in water-filled channels at the interface can explain the increase in Db and Db*cb, which are dependent on water content. Oxygen mass transport parameters for both proton and anion exchange membranes are reported as a function of relative humidity. In order to perform electrochemical measurements at < 70% RH (at 50 °C) for perfluorosulfonic acid membranes and for all conditions for anion exchange membranes, a modified twoelectrode setup was employed and compared to a three-electrode configuration. The oxygen diffusion coefficient is observed to depend on the water content. A lower relative humidity resulted in lower values of Db; significantly so for alkaline anion exchange samples compared to their acidic counterparts. cb was observed to exhibit an inverse relationship, which increases with decreasing relative humidity. The decrease in Db as the relative humidity was lowered was larger than the increase in cb, which lead to a decrease in Db*cb as the relative humidity was lowered for all membranes.

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

The G-quadruplex-hemin DNAzyme can tag itself with the reactive substrate biotin tyramide

Date created: 
2017-04-19
Abstract: 

Genomic database searches suggest that there are a large number of potentially G-quadruplex forming sequences present in the human genome, in addition to their well-established localization in telomeres. Novel imaging techniques support these data and have begun to indicate the extent to which G-quadruplexes are present in vivo. Information on any biological function of these sequences is less clear. This thesis presents the creation of an assay that could target G-quadruplexes for imaging or pulldown and potentially give information on their biological relevance. We utilize the inherent peroxidase activity of the quadruplex-hemin interaction to initiate a tagging reaction based upon a reactive tyramide substrate.

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

New Directions for Bis-Adamantane Chemistry and Reactivity

Author: 
Date created: 
2017-01-27
Abstract: 

Bulky chiral ligands have gained tremendous attention in metal coordination chemistry as they influence greatly coordination geometry and reactivity and are critical features of asymmetric catalysts. In this thesis, the design and synthesis of sterically congested chiral alcohol and amine ligands based on a bis-adamantane framework, are explored. Optimization of the ligand synthesis and purification were conducted on the racemic ketone, while the chiral synthetic pathway utilized an enzymatic hydrolysis as the key step. In another aspect of bis-adamantane chemistry, the bromonium ion of adamantylideneadamantane (Ad=Ad) has provided valuable mechanistic information about electrophilic addition of bromine and undergoes a fast “Br+” transfer process to alkenes. However, the Ad=Ad isomer SesquiAdAd only reacts with [AdAdBr+] and not with Br2. This thesis also investigated the rearrangement of SesquiAdAd to Ad=Ad catalyzed by [AdAdBr+] via the formation of the potentially high energy intermediate SesquiAdAdBr+, probed by 1H NMR spectroscopy and kinetics. Data analysis involved a series of 1H NMR spectral deconvolutions.

Document type: 
Thesis
Senior supervisor: 
Daniel B Leznoff
Andrew J Bennet
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Development of tools and methods for studying glycan processing proteins in living systems

Date created: 
2016-05-12
Abstract: 

Carbohydrates are a class of biomolecules present in all domains of life that provide energy for cellular processes, afford structural support, and take part in molecular recognition and signalling. Given the ubiquity of carbohydrates in living systems, gaining an improved understanding of the proteins that process them – glycosyl transferases, glycoside hydrolases, lectins, and sugar transporters – is of key interest. Compared to in vitro assays, few live-cell or in vivo assays of carbohydrate-processing proteins have been developed, despite the wealth of knowledge that they provide. This discrepancy is largely due to the difficulties associated with live-cell and in vivo examination of protein function, namely issues of substrate selectivity, sensitivity, reactivity, and cell permeability. This thesis aims to develop substrates and methods to study two carbohydrate-processing proteins: human O-GlcNAcase, a glycoside hydrolase involved in Alzheimer’s disease, cancer, and the stabilization of nascent proteins; and bacterial AmpG, a sugar transporter implicated in β-lactam antibiotic resistance. In doing so, I hope to not only provide insight into the function of these proteins, but to also lay a foundation for live-cell or in vivo study of these and related proteins in the years to come.

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

Design and synthesis of a photoaffinity labelling analogue of ivacaftor to probe its putative binding site on mutant CFTR

Date created: 
2017-03-06
Abstract: 

The cystic fibrosis (CF) therapeutic, ivacaftor, restores activity to certain cystic fibrosis transmembrane regulating protein (CFTR) mutations; however, the nature of ivacaftor's interaction with mutant CFTR is still under investigation. This study aimed to generate photoaffinity labelling (PAL) probes that will be used to elucidate putative ivacaftor binding sites on mutant CFTR. Structure activity relationship studies indicated retention of ivacaftor's potentiating activity despite deletion of either of the t-butyl groups from the ivacaftor structure. These results initiated a synthesis program to prepare PAL probes incorporating a carbene-generating diazirine moiety in place of a t-butyl group on the ivacaftor scaffold. Initial synthetic approaches towards creating the diazirine PAL probe were devised with the ability to afford diversification at a late stage in the synthesis to allow incorporation of reporter tags into the PAL probe. While these approaches were unsuccessful, ultimately a linear synthetic approach successfully afforded the target diazirine PAL probe.

Document type: 
Thesis
Senior supervisor: 
Robert Young
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) M.Sc.

Growth and Characterization of Lead Zirconate-Titanate (PbZr1-xTixO3)-Based Novel Piezo-/Ferroelectric Single Crystals

Author: 
Date created: 
2016-04-18
Abstract: 

Piezo-/ferroelectric materials form an important class of functional materials that can transduce mechanical energy to electrical energy and vice versa. PbZr1-xTixO3 (PZT) ceramics are the most extensively used piezoelectric materials owing to their good piezoelectric and electromechanical properties near the morphotropic phase boundary (MPB). However, the microstructures of this class of materials and the atomistic phenomena that cause the outstanding performance have not been thoroughly understood yet. Therefore, it is of particular interest to grow single crystals of PZT, which are not only necessary for thorough characterization of the anisotropic properties of this system, but also are expected to exhibit superior piezo-/ferroelectric performance over their ceramic counterparts. In this work, PZT single crystals with compositions of x = 0.54 and 0.45 were grown successfully by a top-seeded solution growth (TSSG) method, and characterized by X-ray diffraction, polarized light microscopy (PLM), piezoresponse force microscopy (PFM), and dielectric, ferroelectric, and piezoelectric measurements. On the other hand, given that PZT ceramics used in industry are always chemically modified to obtain desired and enhanced properties for specific applications, we extended our work to grow donor (La3+ and Bi3+)- and acceptor (Mg2+ and Mn2+)-doped PZT single crystals and to investigate the effects of the doping on the structure and properties. The compositions and homogeneity of the as-grown doped PZT single crystals were investigated by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and energy dispersive spectroscopy (EDS). The dielectric, ferroelectric and piezoelectric properties of these single crystals were investigated. These very first set of data on doped PZT single crystals not only provide a better understanding of structure-property relationship of PZT-based single crystals and their doping mechanisms, but also points to the possible applications of doped PZT single crystals as a new high-TC, high-performance piezo-/ferroelectric material. Moreover, there have been pressing demands for lead-free or lead-reduced replacement materials because of the environment concerns arising from the potential toxicity of the lead in high-performance piezo-/ferroelectric material such as PZT. In our search for high-temperature, lead-reduced piezoelectric materials, novel ferroelectric single crystals of complex perovskite ternary solid solution Bi(Zn0.5Ti0.5)O3-PbZrO3-PbTiO3 (BZT-PZ-PT) have been grown for the first time. The structure and properties of these crytals suggest that the BZT-PZ-PT ternary single crystals constitute a new family of high-TC ferroelectric materials, which are promising for various applications such as high-power electromechanical transducers that can operate in a wide temperature range.

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