One of the major unsolved questions of modern physics is the nature of dark matter, whose existence is inferred from astronomical observations. There are numerous potential dark matter candidates: one strong contender is the axion. The axion was initially proposed to solve the strong CP problem of quantum chromodynamics but it was later realized that its properties make it simultaneously a good candidate for dark matter. Axions couple to the Standard Model in various ways. In this thesis, we describe experiments which exploit the axion coupling gd to the nuclear electric dipole moment (nEDM). In particular, in the presence of an external electric field, the axion perturbs the magnetization of an ensemble of nuclear spins due to this coupling. In the CASPEr-Electric experiment, the axion dark matter interacts with the nuclear spins of 207Pb and the effective electric field is provided by a ferroelectric crystal in which the 207Pb is embedded. CASPEr-Electric is a resonant search where axion dark matter would perturb the equilibrium magnetization of the 207Pb nuclear spin ensemble. The experiment is calibrated through pulsed nuclear magnetic resonance (NMR) experiments on the 207Pb nuclei. The first generation of the experiment demonstrated the feasibility of this method and established limits on the nEDM coupling in the mass range of 162-166 neV (Compton frequency 39-40 MHz). This thesis primarily focuses on the second generation of the CASPEr-Electric experiment, which probed axion dark matter at a lower frequency range of 4 - 5 MHz using superconducting quantum interference devices (SQUIDs). Our search established upper limits on the coupling for axion masses in the range 19.5-20.5 and 21.5-22 neV (4.6 - 5.0 and 5.2 - 5.3 MHz). The upper bound on the nEDM coupling is |gd| < 4 x 10-4, GeV-2 with 95 % confidence. / 2024-11-07T00:00:00Z

In our previous publication of Thiele cage diols, we describe the first pinacol rearrangement to occur over a C(sp3)–C(sp3). Two mechanisms were initially proposed: a concerted mechanism and a stepwise mechanism, proceeding through a carbocation intermediate. Interestingly, the rearrangement provides only a single diastereomer. The aim of this thesis is to investigate the nature of the reaction by measuring the relative rates of reaction with varying substituents that either stabilize or impede the formation of carbocations. From the relative rates, we can narrow in on whether the mechanism is stepwise or concerted, based on substituent effects, and determine how the reaction may provide a single diastereomer. In Chapter 1, the pinacol rearrangement is introduced, and each analogue that followed after, including stereoselective pinacol rearrangements and a series of different semipinacol rearrangements that provide useful synthetic pathways for chemists with desirable stereochemical outcomes. In Chapter 2, we describe the isolation and characterization of two analogues of a key side product. The structure of each analogue was determined through a series of spectroscopic techniques including 1H-1H COSY, HSQC, HMBC, and 1D-selective gradient NOE NMR. From the solved structures, we proposed a possible mechanism to describe their formation during the main rearrangement reaction – one that shares a carbocation intermediate with the stepwise mechanism already proposed. In Chapter 3, we prepared five Thiele cage diol analogues with aryl substituents with different electronic properties: two substituents that stabilize carbocation intermediates (p-OCH3 and p-CH3), two that destabilize (p-F and 3,5-diOCH3), and the base tetraphenyl Thiele cage diol. We measured the rates of reaction of each diol with p-toluenesulfonic acid at 25°C, 35°C, 45°C, and 52°C via variable temperature quantitative 1H-NMR over time. From the rates of reaction, we found that diols with carbocation-stabilizing aryl substituents reacted faster than the destabilizing analogues, providing evidence that the rearrangement proceeds through a carbocation intermediate. We also found that the diols with electron-deficient aryl substituents showed an increase in the entropy of activation with increasing electron-deficiency in the aryl groups, suggesting an associative pathway for the electron-deficient substituents toward the rearrangement product. Considering the pathway proposed for the side product, we propose an updated stepwise mechanism. Based on computational studies and a previously-isolated X-ray crystal structure, we determined that the diastereoselectivity of the reaction was facilitated by favourable π-π stacking interactions between two aryl substituents. The interaction of the aryl groups twists the geometry of the molecules, placing the migrating aryl substituent in the ideal position for the rearrangement to occur stereoselectively. / Graduate / 2023-10-31

This thesis focuses on the development of oxidatively stable cathode and electrolyte materials for sodium-based battery systems. This is primarily achieved through the use of solid-state nuclear magnetic resonance (ssNMR) and pulsed-field gradient (PFG) NMR spectroscopy. ssNMR is used to diagnose the primarily failure mode of the NaOB. It is found through a combined 23Na and 19F study that the main discharge product of the cell, NaO2, oxidizes both the carbon and polyvinylidene fluoride (PVDF) binder of the cathode to produce parasitic Na2CO3 and NaF. In a subsequent study, Ti4O7-coated carbon paper cathodes are implemented in an attempt to stabilize NaO2. The 23Na triple quantum magic angle spinning (3QMAS) and 1H to 23Na dipolar heteronuclear multiple quantum correlation (23Na{1H} D-HMQC) experiments are used to diagnose the failure modes of carbon-coated, and Ti4O7-coated cathodes. It is found that electrochemically formed NaO2 is significantly more stable in Ti4O7-coated cathodes, leading to longer lifetime NaOBs. Oxidatively stable electrolyte materials are also examined. Lithium and sodium bis(trifluoromethansulfonyl)imide (TFSI) in adiponitrile (ADN) electrolytes exhibit extreme oxidative resistance, but are unusable in modern cells due to Al corrosion by TFSI, and spontaneous ADN degradation by Li and Na metal. PFG NMR is used to investigate the transport properties of LiTFSI in ADN as a function of LiTFSI concentration. By measuring the diffusion coefficient of Li+ and TFSI as a function of diffusion time (Δ), diffusional behaviour is encoded as a function of length scale to study the short- and long-range solution structure of the electrolyte. It is found that at high concentrations, LiTFSI in ADN transports Li+ primarily through an ion-hopping mechanism, in contrast to the typical vehicular mechanism observed at low concentrations. This suggests significant structural changes in solution at high concentrations. The NaTFSI in ADN analogue is examined for its electrochemical properties in Na-ion and Na-O2 batteries. It is found that the oxidative resistance of ADN to Na metal is significantly increased at high concentrations, leading to reversible Na deposition and dissolution in cyclic voltammetry (CV) experiments. Linear sweep voltammetry (LSV) and chronoamperometry (CA) experiments on Al current collectors show that Al corrosion by TFSI is similarly suppressed at high concentration. This culminates in high concentration NaTFSI in ADN being able to reversibly intercalate Na3V2(PO4)2F3 (NVPF) cathodes in SIB half-cells for multiple cycles. The knowledge gained from exploring oxidatively stable cathode and electrolyte materials can be used in tandem for the development of a longer lifetime, more oxidatively stable, NaOB in the future. / Thesis / Doctor of Philosophy (PhD) / The continued development of rechargeable batteries is paramount in reducing the world’s reliance on fossil fuels, as they allow for the storage of electrical energy produced by renewable sources. This work primarily examines sodium-based batteries systems, such as the sodium-oxygen battery (NaOB) and sodium-ion battery (SIB), which are possible alternatives to the currently used lithium-ion battery (LIB) system. In order to produce energy, NaOBs produce sodium superoxide (NaO2) during the discharge process, which is formed on the carbon cathode. However, NaO2 is inherently unstable to carbon materials, causing degradation of the battery overtime. Ti4O7 is investigated as a stable coating material in NaOBs, used to coat the carbon cathode to make the system more stable to NaO2 degradation. The degradation processes in NaOBs are characterized by solid state nuclear magnetic resonance (ssNMR) spectroscopy, which uses strong superconducting magnets to probe the magnetic properties of, and consequently identify, the chemical species formed within the battery. It is found that the addition of the Ti4O7 coating inhibits NaO2 degradation, producing longer lifetime NaOBs. Subsequently, both Li-bis(trifluoromethansulfonyl)imide (LiTFSI), and NaTFSI, in adiponitrile (ADN) electrolytes are examined for their use in LIBs and SIBs, respectively. Electrolytes facilitate stable ion transport within the cell, and ADN electrolytes specifically allow for the use of higher voltage cathode materials, which can result in a higher energy density battery. The transport properties of LiTFSI in ADN electrolytes are studied by a pulsed-field gradient (PFG) NMR technique, that allows for the measurement of the rate of ion transport in the electrolyte. It is found that the mechanism of ion transport significantly depends on electrolyte concentration, which suggests significant changes to the electrolyte solution structure at high concentration. The electrochemical ramifications of this are studied for the NaTFSI in ADN electrolyte in SIBs. It is found that the electrolyte becomes substantially more stable at high concentrations, leading to more favourable charging and discharging behaviours when tested in SIBs. The work presented in this thesis illustrates the development of more stable, longer lifetime, batteries over a number of cell chemistries, using a variety of NMR and electrochemical characterization techniques.

DNA needs to be accurately copied during DNA replication for a normal cell function. Errors during DNA replication can cause genomic instability that can lead to cancer. To avoid mistakes during the process of DNA replication, nuclease enzymes can act as molecular scissors in removing lethal DNA structures. Therefore, Flap endonuclease 1 (FEN1) is an enzyme that can cleave the 5’flap primer during Okazaki fragment maturation. However, studies have shown that overexpression of FEN1 is associated with different types of cancer. Thus, targeting FEN1 represents a potential for enhancing cancer therapy. However, structural investigation of FEN1 and factors that influence DNA binding need to be comprehensively studied at the molecular level before designing an inhibitor. Thus, this thesis aimed to investigate and compare the catalytic behavior of FEN1wt, FEN1K93A, and FEN1D181A in different experimental conditions. We have found that the activity of FEN1 is affected by the presence of divalent metal ions such as Ca2+ and Mg2+ by performing enzymatic assays. Using the microscale thermophoresis technique, we determined the dissociation constants for FEN1 proteins. Additionally, we performed a thermal shift assay in different conditions which gave us additional insights into the stability of the protein-DNA complex in FEN1. We have found that protein-DNA complex in FEN1D181 is more stable than FEN1wt and FEN1K93A by having a higher melting temperature. Lastly, I used the NMR technique to map the conformational changes within FEN1 proteins upon interacting with divalent metal ions such as Mg2+ ions. To do this, I performed a series of Mg2+ ions titration for FEN1 (WT, K93A, and D181A) using a 2D 1 H 15N TROSY-HSQC experiment to monitor the chemical shifts changes to the chemical environment around the N-H backbone amides of the protein. We have found that both WT and K93A FEN1 proteins interact in a similar way with Mg2+ ions, i.e., explicitly targeting first the higher affinity catalytic site, then spreading around several unspecific low-affinity sites across the protein; however, we observed only the unspecific and weak milli molar binding affinity in FEN1D181A across the entire protein surface upon interacting with Mg2+ ions.

No description available.

The work describes the preparation of some acetylene complexes of nickel, palladium and platinum. The structure of and the bonding in these complexes is discussed in the light of their infrared and nuclear magnetic resonance spectra. Some reactions of the complexes are described. / Thesis / Master of Science (MSc)

The quadrupolar interaction in sodium orthovanadate dodecahydrate, calcium orthovanadate, vanadinite, descloizite, zirconium divanadate, cadmium divanadate, potassium metavanadate and vanadium pentoxide, was studied by nuclear magnetic resonance. The v51 quadrupole coupling constants in these compounds show a strong correlation with the distortion of the tetrahedral symmetry around the vanadium ion. Vanadium pentoxide is an exception and shows a surprisingly small coupling constant. The point multipole model was found to be inadequate for the calculations of the electric field gradients in these compounds. A covalent model provides an explanation of the small magnitude of the coupling constant of vanadium pentoxide. However, because of the numbers of approximations in this model, only a qualitative correlation with the experimental results was achieved. In addition, the chemical shift tensor of the v51 resonance line in a single crystal of vanadium pentoxide was measured to be very large. This result was correlated with a large Van Vleck term in the magnetic susceptibility of vanadium pentoxide. / Thesis / Doctor of Philosophy (PhD)

<p> This thesis is primarily concerned with an investigation of the reaction of tetrakis(tri-p-tolyl phosphite)nickel(0) with strong acids, using 1H, 31P and 2H NMR. The results differ from those previously obtained for similar reactions with other Ni(0) phosphites, in that both five and four-coordinate nickel hydrides are formed in concentrations sufficient for spectroscopic studies. The four-coordinated hydride is believed to be the catalytically active species in a number of reactions catalyzed by Ni(0) phosphites. Variable-temperature studies show that the four-coordinate hydride complex is a fluxional molecule. The exchange process is exclusively intramolecular in nature.</p> <p> A very simple method was used to analyze the NMR data and obtain activation parameters for the exchange process. These parameters were compared with those reported in the literature for related intramolecular and intermolecular reactions. The large negative entropy of activation is interpreted in terms of ion pairing in the transition state. NMR evidence for the structure of the products resulting from the reactions of acids with both the metal complexes and the free phosphite ligands is presented. The conditions necessary for the observation of four-coordinated nickel hydrides are also discussed.</p> / Thesis / Master of Science (MSc)

<p> The addition compounds of selenium tetrafluoride with sulfur trioxide, boron trifluoride, and arsenic, antimony, bismuth, vanadium, niobium and tantalum pentafluorides have been prepared. These compounds have been studied in the solid state using X-ray powder diffraction, and infra-red and Raman spectroscopy; in the molten state using Raman spectroscopy, nuclear magnetic resonance spectroscopy, and conductimetric and viscosity measurements; and in solution using Raman spectroscopy, cryoscopy, conductivity and nuclear magnetic resonance spectroscopy.</p> <p> The compound SeF4SO3 has a fluorosulfate-bridged polymeric structure. The remaining compounds have fluorine-bridged structures, this interaction being the strongest in SeF4BF3 and SeF4VF5 and decreasing in the order SeF4NbF5 SeF4TaF5 SeF4AsF5 SeF4SbF5 SeF4BiF5.</p> <p> The characteristics of the SeF3+ group are discussed. The properties of fluorine bridging and various methods of detecting such interactions are also considered.</p> / Thesis / Doctor of Philosophy (PhD)

At ~662 gigatonnes of carbon (GtC), marine dissolved organic matter (DOM) is the largest reduced pool of actively cycling carbon and nitrogen in the oceans1. Operationally defined as smaller than 0.1µm in size, this carbon reservoir comprises all non-living organic matter smaller than a bacterial cell and comprises organic colloids and molecules spanning as a continuum of sizes ranging from marine viruses and large macromolecules (e.g. DNA, enzymes) to small organic molecules (e.g. polymers and monomers)2. With deep apparent 14C-ages ranging between 4900-6400 ybp 3,4, marine DOM is anomalously old given timescales of global ocean ventilation (1000-1500 years). The great age of DOM has remained one of the most elusive lines of scientific inquiry in Chemical Oceanography for decades. The size and molecular composition of DOM has been shown to be a key variable in determining its biological reactivity (e.g. cycling rate) and long-term persistence in the deep ocean5,6. Despite the importance of DOM in the marine carbon and nitrogen cycles, we lack a detailed understanding of the molecular composition of DOM. Due to the high concentration of salts in seawater relative to DOM, it is difficult to analyze the molecular composition of seawater with conventional chemical- or size- fractionation methods without introducing bias (i.e. isolating only hydrophobic and/or high molecular weight DOM). In fact, it is commonly reported that >80% of DOM remains uncharacterized at the molecular level (e.g. not readily identifiable as an individual known biomolecule)5. Nuclear magnetic resonance (NMR) spectroscopy has been used as a tool for several decades to describe the composition of marine DOM isolates7. For example, 13C-NMR of major high molecular weight DOM functional groups at the molecular-level demonstrated that DOM is largely made up of reactive polysaccharides with low aromaticity compared to terrestrial DOM8. To date, all marine DOM NMR measurements have been made on size-fractionated DOM or chemically-fractionated (e.g. solid phase extracted) DOM isolates. In this thesis, I report the first Proton (1H) NMR composition of total seawater DOM from seawater samples collected from 10 stations in Baffin Bay aboard the CCGS Amundsen (2019). Samples were measured using 1H-NMR at uOttawa following a novel water suppression method established by Lam and Simpson9. The use of this method has allowed for the first molecular composition assessment of total seawater DOM to be measured (e.g. without any chemical or size fractionation). I report the % relative abundance of individual biomarkers and determine molar concentrations of two compound classes of interest. These results are shown in Ocean Data View section plots, and are listed within appendix tables, to provide a comprehensive depiction of the changing concentrations of dissolved organic carbon (DOC), total carbohydrates (TCHO), and carboxyl-rich alicyclic molecules (CRAM). In this thesis, I explore changes in the abundance of these unique DOM compound classes and discuss how the composition of DOM directly determines its bioavailability and thus cycling in Baffin Bay 5. The core objective of my thesis was to measure DOM concentrations for TCHO and CRAM, as well as to calculate the production and removal of these key DOM compounds in Baffin Bay due to either physical and/or biological processes. We found that the concentration of both TCHO and CRAM decreased with depth throughout Baffin Bay. This is consistent with previous work suggesting the rapid cycling of carbohydrates, however it contradicts the current paradigm of CRAM cycling. Our results indicate between 21-43% of CRAM produced in the surface is subsequently removed at depth. Rapid cycling of a surface CRAM population suggests that not all CRAM can be considered recalcitrant DOM We live in a time of unprecedented global change. The Arctic Ocean is warming at a rate at least four times faster than the global average10. The impact of a rapidly warming, freshening and increasingly acidified Arctic Ocean on the biogeochemistry of DOM remains unknown. It is imperative that more DOM research be conducted as early as possible in order to better understand these impacts and inform future research directions. The distribution and cycling of CRAM in Baffin Bay provide novel and fundamental knowledge of DOM cycling in a key Arctic region, but could also potentially occur throughout the global ocean. Such data will no doubt be of use in informing future iterations of Earth System Climate models seeking to forecast how the marine carbon cycle will respond to global change.