<p>This thesis evaluates several solid-state NMR spectroscopy approaches to studying lithium ion dynamics in solid-state electrolytes. With the goal of reducing the risks associated with current liquid electrolytes, solid-state electrolytes provide non-flammable materials that are also stable against attack by cathode and anode materials. Solid-state NMR spectroscopy offers a versatile method to determine structural details and can also provide information about ion mobility in solid-state electrolytes. Challenges involved in the study of solid-state electrolytes include the difficulty in distinguishing between ^6,7Li resonances due to the small chemical shift range of diamagnetic lithium species. The NMR methods selected in this thesis aim to circumvent some of these issues in order to determine structural and dynamic properties in solid-state electrolytes. Several different electrolytes have been examined including LaLi_0.5Fe_0.2O_2.09 and related materials, which exhibit intricate structural properties. ¹³⁹La NMR spectroscopy, in combination with ⁷Li MAS NMR spectroscopy, was used to determine the nature of this disorder. In addition, studies of the quadrupolar framework ⁸⁷Rb nucleus, which take advantage of its large electric field gradient, have been used to indirectly probe the activation energy for Ag⁺ ion hopping in the solid-state silver ion electrolyte RbAg₄I₅. Alternatively, dipolar coupling between ⁶Li and ⁷Li has been used to compare lithium ion hopping rates in Li₆BaLa₂M₂O₁₂ (M = Ta, Nb) using ⁶Li{⁷Li}-REDOR NMR studies. Finally, T₂ relaxation studies have been used to probe ion dynamics in Li₃V₂(PO₄)₃ and LiVO₃ in order to determine if this is a viable method to study dynamics in these materials.</p> / Doctor of Philosophy (PhD)

Heteropolymeric O antigen (O-Ag)-capped lipopolysaccharide is the principal constituent of the Gram-negative bacterial cell surface. It is assembled via the integral inner membrane (IM) Wzx/Wzy-dependent pathway. In Pseudomonas aeruginosa, Wzx translocates lipid-linked anionic O-Ag subunits from the cytoplasmic to the periplasmic leaflets of the IM, where Wzy polymerizes the subunits to lengths regulated by Wzz1/2. The Wzx and Wzy IM topologies were mapped using random C-terminal-truncation fusions to PhoALacZα, which displays PhoA/LacZ activity dependent upon its subcellular localization. Twelve transmembrane segments (TMS) containing charged residues were identified for Wzx. Fourteen TMS, two sizeable cytoplasmic loops (CL), and two large periplasmic loops (PL3 and PL5 of comparable size) were characterized for Wzy. Despite Wzy PL3–PL5 sequence homology, these loops were distinguished by respective cationic and anionic charge properties. Site-directed mutagenesis identified functionally-essential Arg residues in both loops. These results led to the proposition of a “catch-and-release” mechanism for Wzy function. The abovementioned Arg residues and intra-Wzy PL3–PL5 sequence homology were conserved among phylogenetically diverse Wzy homologues, indicating widespread potential for the proposed mechanism. Unexpectedly, Wzy CL6 mutations disrupted Wzz1-mediated regulation of shorter O-Ag chains, providing the first evidence for direct Wzy–Wzz interaction. Mutagenesis studies identified functionally-important charged and aromatic TMS residues localized to either the interior vestibule or TMS bundles in a 3D homology model constructed for Wzx. Substrate-binding or energy-coupling roles were proposed for these residues, respectively. The Wzx interior was found to be cationic, consistent with translocation of anionic O-Ag subunits. To test these hypotheses, Wzx was overexpressed, purified, and reconstituted in proteoliposomes loaded with I−. Common transport coupling ions were introduced to “open” the protein and allow detection of I− flux via reconstituted Wzx. Extraliposomal changes in H+ induced I− flux, while Na+ addition had no effect, suggesting H+-dependent Wzx gating. Putative energy-coupling residue mutants demonstrated defective H+-dependent halide flux. Wzx also mediated H+ uptake as detected through fluorescence shifts from proteoliposomes loaded with pH-sensitive dye. Consequently, Wzx was proposed to function via H+-coupled antiport. In summary, this research has contributed structural and functional knowledge leading to novel mechanistic understandings for O-Ag biosynthesis in bacteria. / Bookmarks within the document have been provided for ease of access to a particular section in the body of the thesis. Each entry in the Table of Contents, List of Tables, and List of Figures has been "linked" to its respective position and as such can be clicked for direct access to the entry. Similarly, each in-text Figure or Table reference has been "linked" to its respective figure/table for direct access to the entry. / 1.) Canadian Institutes of Health Research (CIHR) Frederick Banting and Charles Best Canada Graduate Scholarship doctoral award, 2.) CIHR Michael Smith Foreign Study Award, 3.) Cystic Fibrosis Canada (CFC) doctoral studentship, 4.) University of Guelph Dean's Tri-Council Scholarship, 5.) Ontario Graduate Scholarship in Science and Technology, 6.) Operating grants to Dr. Joseph S. Lam from CIHR (MOP-14687) and CFC