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

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Surface Modification of Indium Tin Oxide

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

Indium tin oxide serve a critical function in many organic devices, such as organic light emitting diodes and organic photovoltaics. To optimize the performances of these devices, it is desirable to tune the interface between the indium tin oxide and the next functional layer of these devices. A common surface modification of transparent conductive oxides is through the use of self-assembled monolayers. This methodology enables a simultaneously tuning of the properties and performance of this interface, including the surface energy, work function and durability of the transparent conductive oxide. Phosphonic acid and silane based monolayers have been extensively studied and used in devices for their ability to tune the interfacial properties of transparent conductive oxide. Herein, alcohol based monolayers are first demonstrated on transparent conductive oxide surfaces. The electrochemical and chemical stabilities of alcohol based monolayers, as well as changes in the optical properties of the Indium tin oxide as a function of their stability were evaluated in comparison to more traditional routes of surface modification, such as through the use of silanes and phosphonic acid based monolayers. The tunability of both work function and surface energy of the modified Indium tin oxide were also determined for assessing their electronic properties.

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

An improved synthesis of gold nanorods with tunable dimensions and localized surface plasmon resonance properties

Author: 
Date created: 
2018-04-19
Abstract: 

Gold nanorods have been pursued due to their unique optoelectronic properties, which have led to potential uses in multiple applications. We sought to prepare gold nanorods that would potentially be used in biomedical applications, such as bio-imaging, photothermal therapies, and drug delivery systems. Typically in biomedical applications, gold nanorods with a localized surface plasmon resonance band that lies in the near infrared window between 650 to 1350 nm is highly desirable to obtain better images and an efficient photothermal effect over a range of depths within biological tissues. In addition, the dimensions of gold nanorods also play an important role in terms of cellular uptake and retention, as well as controlling the ratio between their absorbance and scattering properties. Thus, a primary goal of our study was to regulate dimensions and localized surface plasmon resonance of the gold nanorods to improve their potential utility in applications requiring both cellular uptake and photothermal triggered processes through the use of localized surface plasmon resonance bands in the near infrared “window”. We have modified the seed-mediated method by sequentially varying concentrations of hydrochloric acid and chloroauric acid to tune the dimensions, and thus the properties of the gold nanorods. The average dimensions of the gold nanorods were tuned from 24±4 nm in length and 7±1 nm in width, to 47±10 nm in length and 11±2 nm in width from these adjustments in the concentration of hydrochloric acid and chloroauric acid in the growth solution.

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

Photocatalytic fluorination of benzylic C-H bonds and studies towards the synthesis of salinosporamide C

Author: 
Date created: 
2018-04-18
Abstract: 

Fluorinated pharmaceuticals comprise nearly a quarter of the total pharmaceutical market. However, current fluorination methods and reagents lack a certain range particularly in the fluorination of C-H bonds. The first part of this thesis describes the fluorination of benzylic C-H bonds utilizing the hydrogen abstracting ability of a classic photocatalyst and a bench stable fluorine atom transfer reagent. The simple and straightforward reaction demonstrates a wide range of tolerance to functionalities and provides access to fluorinated compounds in moderate to good yield. The second part of this thesis consists of research towards the synthesis of a marine natural product, salinosporamide C, which was discovered in 2002 and has yet to be synthesized. The true activity of the compound is unknown, however its biogenetically related counterpart salinosporamide A is considered a potent 20S proteasome inhibitor. Though the total synthesis of salinosporamide C was not accomplished, an advanced intermediate was successfully synthesized and the groundwork for a successful synthesis of this natural product was completed.

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

Mechanistic applications of volume profiles for chemical and biochemical processes

Date created: 
2018-04-16
Abstract: 

Pressure has a profound effect on both the speed and direction of chemical reactions; an effect which is inextricably linked to the change in volume of the system. Experimentally, this effect is described by the activation and reaction volumes, defined as the pressure derivatives of rate constants and equilibrium constants respectively. These quantities provide information about the relationships between the partial molar volumes of the reactant, product and transition state (TS). However, mechanistic interpretation of these volumes has posed a challenge due to the lack of an accurate computational technique for relating the geometrical structure of a reaction system to its volume. We have formulated a theoretical methodology that can be used to describe and predict the effects of pressure on reaction systems using the concept of a volume profile. These profiles, which detail how the partial molar volume of a system changes over the course of a reaction, can be calculated using the recently developed Archimedean displacement model of molecular volume. We explore two mechanistic applications of these profiles. The first is the calculation of Gibbs energy profiles at elevated pressures, allowing for the prediction of interesting and potentially useful chemical transformations that can occur with pressure. This technique was used to investigate high pressure structural transformations for a radical hydrogen transfer reaction, and also to examine the feasibility of pressure-driven molecular machines. The second application is the elucidation of TS structures from a comparison of the theoretical volume profile with the experimentally-determined activation volume. This technique is especially useful for systems with a high degree of conformational flexibility whose TSs are not readily identified using standard computational methods. We used this method to identify the TS ensemble for a flexible model chain, and for conformational changes in a cyclophane system. To apply this method to larger, more complex systems such as the unfolding of proteins, a reaction coordinate for the process is required. A proper definition for such a coordinate was investigated and some preliminary results are presented for biological systems.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Michael H. Eikerling
Noham Weinberg
Department: 
Science: Department of Chemistry
Thesis type: 
(Thesis) Ph.D.

Design and characterization of metal-thiocyanate coordination polymers

Author: 
Date created: 
2018-01-12
Abstract: 

This thesis focuses on exploring the synthesis and chemical reactivity of thiocyanate-based building blocks of the type [M(SCN)x]y- for the synthesis of coordination polymers. A series of potassium, ammonium, and tetraalkylammonium metal isothiocyanate salts of the type Qy[M(SCN)x] were synthesized and structurally characterized. Most of the salts were revealed to be isostructural and classic Werner complexes, but for (Et4N)3[Fe(NCS)6] and (n-Bu4N)3[Fe(NCS)6], a solid-state size-dependent change in colour from red to green was observed. This phenomenon was attributed to a Brillouin light scattering effect by analyzing the UV-Visible spectra of various samples with different sized crystals. Coordination polymers of the type [M(L)x][Pt(SCN)4] were prepared and structurally characterized using a variety of bi- or tri-dentate capping ligands (ethylenediamine, 2,2’-bipyridine, 2,2';6',2"-terpyridine, N,N,N′,N′-Tetramethylethane-1,2-diamine). Overall, structural correlations between the ligand, the metal centre, the coordinating mode of the [Pt(SCN)4]2- building block and the topologies of the coordination polymers were established. Similar systems were synthesized using the ligands N,N’-bis(methylpyridine)ethane-1,2-diamine (bmpeda) and N,N’-bis(methylpyridine)cyclohexane-1,2-diamine (bmpchda) and were revealed to be multidimensional coordination polymers by structural analysis. Five complexes of the type [Cu2(μ-OH)2(L)2][A]x•yH2O (where L = 1,10-Phenanthroline, tmeda and 2,2’-bipyridine) were prepared and have been characterized by spectroscopic and crystallographic structural analyzes and by SQUID magnetometry. Two complexes were revealed to be dinuclear molecular units capped with the SCN- ligand. The complexes involving the [Au(CN)4]- anion were structurally characterized as double salts involving the dinuclear Cu(II) unit with a varying degree of hydration. The complex [Cu2(μ-OH)2(tmeda)2Pt(SCN)4] was revealed to be a 1D coordination polymer with trans- bridging [Pt(SCN)4]2- units. The magnetic susceptibility versus temperature was measured and fitted for each system to obtain J-coupling values that were qualitatively compared to the previously published magnetostructural correlation for dinuclear hydroxide-bridged units. The birefringence and luminescent properties for four new complexes of the type [Pb(4’-R-terpy)(SCN)2] were measured. The complexes presented unique luminescence based on the presence of the SCN unit, whereas the birefringence of the complexes was compared to [Au(CN)2]- analogues and was correlated to the structural properties of the system.

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

Electronic structure and reactivity of transition metal complexes incorporating pro-radical bis-phenoxide ligands

Date created: 
2018-04-05
Abstract: 

Transition metal complexes with pro-radical ligands have received considerable research attention due to their interesting electronic structures, photophysical properties, and applications in catalysis. The relative ordering of metal and ligand frontier orbitals in a complex incorporating pro-radical ligands dictates whether oxidation/reduction occurs at the metal centre or at the ligand. Many metalloenzymes couple redox events at multiple metal centres or between metals and pro-radical ligands to facilitate multielectron chemistry. Owing to the simplicity of the active sites, many structural and functional models have been studied. One class of pro-radical ligand that has been investigated extensively are bis-imine bis-phenoxide ligands (i.e. salen) due to their highly modular syntheses. In this thesis, projects related to the synthesis, electronic structure, and reactivity of mono and bimetallic complexes incorporating the salen framework are explored. Chapter 2 presents a systematic investigation of the effects of geometry on the electronic structure of four bis-oxidized bimetallic Ni salen species. The tunability of their intense intervalence charge transfer (IVCT) transitions in the near infrared (NIR) by nearly 400 nm due to exciton coupling in the excited states is described. For the first time, this study demonstrates the applicability of exciton coupling to ligand radical systems absorbing in the NIR region. Chapter 3 investigates the ground-state electronic structure of a bis-oxidized Co dimer. Enhanced metal participation to the singly occupied molecular orbitals results in both high spin Co(III) and Co(II)-L• character in the ground state, and no observable band splitting in the NIR due to exciton coupling. Finally, Chapter 4 describes a series of oxidized nitridomanganese(V) salen complexes with different para ring substituents (R = CF3, tBu, and NMe2), demonstrating that nitride activation is dictated by remote ligand electronics. Upon one-electron oxidation, electron deficient ligands afford a Mn(VI) species and nitride activation, whereas an electron-rich ligand results in ligand based oxidation and resistance to N coupling of the nitrides. This study highlights the alternative reactivity pathways that pro-radical ligands impose on metal complexes and represents a key step in the use of NH3 as a hydrogen storage medium. The results presented herein provide a starting point for further efforts in reactivity with the salen platform.

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

Synthesis and characterization of BiFeO3-based multiferroic solid solution systems

Author: 
Date created: 
2018-02-09
Abstract: 

Bismuth ferrite BiFeO3 (BFO) is one of the most studied single-phase multiferroic materials with both ferroelectricity and G-type antiferromagnetism above room temperature. It undergoes a ferroelectric-paraelectric phase transition at TC = 830°C and an antiferromagnetic-paramagnetic phase transformation at Néel temperature TN = 370 °C. Despite these wonderful properties of BFO, there are some drawbacks associated with this material including the formations of impurity phases, weak magnetic properties, weak magnetoelectric coupling, and large leakage current density. Therefore, the appropriate chemical modifications are required to improve the electrical and magnetic properties of BFO. In this work, the substitutions of rare earth (RE) ions, such as Dy3+, Er3+, Yb3+, etc., for the A-site Bi3+ ion have been performed and the structures and physical properties of the resulting solid solutions have been investigated.First, new multiferroic materials (1−x)BiFeO3-xDyFeO3 (denoted BDF-x) and (1-x)BiFe(1-y)Ti(y)O(3+y/2)-xDyFeO3 (denoted BDFT-x-y) were synthesized by solid-state reactions. Compared with pure BFO, the ferromagnetism in the BDF-x solid solution is substantially enhanced by the structural distortion and unpaired electrons due to A-site substitution of Dy3+ for Bi3+. The electrical properties, including the ferroelectric and dielectric properties, are further improved by the substitution of Ti4+ for Fe3+ on the B-site, which substantially diminishes the conductivity and consequently the dielectric loss. Well-developed ferroelectric hysteresis loops are displayed in BDFT-x-y with a large remnant polarization Pr = 23 μC/cm2 at room temperature, which is significantly higher than the previously reported Pr = 3.5 μC/cm2 in pure BiFeO3 ceramic. Moreover, weak ferromagnetism is found in it at room temperature (Ms = 0.1 μB/f.u.). The structure-composition phase diagram of the BiFeO3-DyFeO3 system is established.The chemically modified (1-x)BiFe(1-y)Ti(y)O(3+y/2)-xLuFeO3 ceramics exhibit ferromagnetism with a saturated magnetization (Ms = 0.03 μB/f.u) and a remnant polarization of 0.30 μC/cm2 at room temperature. In the (1−x)BiFeO3-xYbFeO3 solid solution, a calculated spontaneous polarization of 7.7 μC/cm2 is obtained for the x = 0.11 ceramics which exhibit a weak ferromagnetism with Ms = 0.025 μB/f.u at roomivtemperature. Interestingly, an unusual magnetization reversal behavior is discovered in the (1−x)BiFeO3-xErFeO3 solid solution. At x = 0.12, the magnetic pole inversion occurs at 30 K. Lastly, the (1−x)BiFeO3-xEuFeO3 solid solution is found to exhibit an interesting magnetization behavior, with the magnetic properties undergoing a crossover from an antiferromagnetic to ferromagnetic state at x = 0.12.

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

The Study of ¹¹⁶Sn via Conversion-Electron Spectroscopy and γ-γ Angular Correlations

Date created: 
2017-12-06
Abstract: 

The β– decay of 116m1In (Iπ = 5+), studied using the 8π array at TRIUMF-ISAC, predominantly populated 4+ states in the semi-magic daughter 116Sn, with 50 protons and 66 neutrons. The resulting electromagnetic decays to the ground state were studied through conversion-electron spectroscopy and through angular correlations of coincident gamma rays. Conversion-electron spectroscopy allowed measuring K-shell internal conversion coefficients (αK), and angular correlations of coincident gamma rays allowed determinations of E2/M1 mixing ratios (δ). These values are reported and used to infer aspects of the underlying nuclear structure of 116Sn. In the course of the analysis, several αK values were measured, of which three were measured for the first time in decay spectroscopy. Additionally, ten mixing ratios were measured, eight of which were not previously reported.The 819 keV mixing ratio was re-measured with excellent agreement to literature results, whereas the 931 keV mixing ratio re-measurement indicates that the previously reported measurement requires a sign change. The 138 keV mixing ratio and αK were combined to measure an E0 component, a possible signature of shape coexistence.Measured transition mixing ratios between 4+ states reveal that these highly-mixed states have similar M1 transition strengths among them, but the E2 transition strengths to lower-lying 2+ states suggest underlying wavefunction differences that should be explored and interpreted with current and improved theoretical models of tin nuclei.

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

Recoil distance method lifetime measurements of the 2⁺₁ excited states in ⁸⁴Kr and ⁹⁴Sr

Date created: 
2017-12-13
Abstract: 

Intense re-accelerated beams delivered by the Isotope Separator and Accelerator (ISAC-II) facility at TRIUMF, Canada’s national laboratory for particle and nuclear physics, permit access to nuclear structure information for a wide range of radionuclides via in-beam γ-ray spectroscopy with the TRIUMF-ISAC Gamma-Ray Escape Suppressed Spectrometer (TIGRESS), a high-efficiency and Compton-suppressed segmented high-purity germanium (HPGe) detector array. Electromagnetic transition rates measured via Doppler-shift lifetime techniques such as the recoil distance method (RDM) are recognized as a sensitive probe of collective behavior and shape deformation and can be used to discriminate between model calculations. To take advantage of this opportunity, the TIGRESS Integrated Plunger (TIP) has been constructed at Simon Fraser University (SFU). The TIP infrastructure supports Doppler-shift lifetime measurements via the RDM using a 24-element TIP CsI(Tl) wall for charged-particle identification. A commissioning experiment aimed towards a high-precision measurement of the lifetime of the 2⁺₁→ 0⁺₁ transition in ⁸⁴Kr was performed using Coulomb excitation (Coulex) coupled with an RDM lifetimem easurement of the stable ⁸⁴Kr beam. A rare isotope beam (RIB) experiment was also performed to measure the lifetime of the 2⁺₁→ 0⁺₁ transition as well as the reduced transition probability B(E2; 2⁺₁ → 0⁺₁) in ⁹⁴Sr near the shape transition region around A = 100 and N = 60. A Monte Carlo code for simulating γ-ray spectra has been coupled with a likelihood ratio χ2Λ data analysis method in order to determine the lifetime in the two presented experiments. The device, experimental approach, analysis, and results are presented and discussed.

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

Investigation of H atom and free radical behavior in gas hydrates

Author: 
Date created: 
2017-12-15
Abstract: 

Gas hydrates (or clathrate hydrates) are solid crystalline materials composed of a framework of hydrogen-bonded water molecules arranged to form cages which can contain small guest molecules. They have been a subject of research in the oil and gas industry, for carbon dioxide sequestration, gas storage and separation. In order to better understand the applications of hydrates, there is a need to study them at the molecular scale, but there has been relatively little investigation of chemical reactions of the guest molecules. In this thesis project, muon spin spectroscopy was used for the first time to investigate the behavior of muonium (a light isotope of hydrogen) and free radicals in hydrates. Muonium (Mu) and muoniated free radicals were observed in the hydrates of cyclopentene, furan, 2,5- and 2,3-dihydrofuran, pyrrole, thiophene, isoxazole, benzene and acetone. In order to confirm that hydrates were formed, they were characterized by PXRD and solid state 129Xe-NMR and 13C-NMR. The free radicals were formed by addition of Mu to unsaturated organic compounds that reside as isolated guests in the hydrates. Muon and other nuclear hyperfine coupling constants (hfcs) were extracted from μSR spectra of the radicals and compared to liquid-phase data. DFT calculations of hfcs were used to guide the spectral assignments and distinguish between competing radical products where applicable. An extra μ-LCR resonance was seen in the spectra of radicals in the hydrate, indicating that they have restricted motion compared to the liquid state. Muonium and muoniated free radicals were observed simultaneously in the hydrates of acetone and benzene. This was previously only observed in C60 powder and shows that Mu and the radical are in physically separated environments in the hydrates. The Mu amplitude decreases while the radical amplitude increases with temperature. This is consistent with Mu diffusion from the small cage to the large cage in the hydrates, where it can react with the guest. The diffusion occurs at a lower temperature in the acetone hydrate compared to the benzene hydrate.

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