Chemistry
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Item 2-Aminopurine-modified DNA homopolymers for robust and sensitive detection of mercury and silver(Elsevier, 2017-01-15)Heavy metal detection is a key topic in analytical chemistry. DNA-based metal recognition has advanced significantly producing many specific metal ligands, such as thymine for Hg2+ and cytosine for Ag+. For practical applications, however, robust sensors that can work in a diverse range of salt concentrations need to be developed, while most current sensing strategies cannot meet this requirement. In this work, 2-aminopurine (2AP) is used as a fluorescence label embedded in the middle of four 10-mer DNA homopolymers. 2AP can be quenched up to 98% in these DNA without an external quencher. The interaction between 2AP and all common metal ions is studied systematically for both free 2AP base and 2AP embedded DNA homopolymers. With such low background, Hg2+ induces up to 14-fold signal enhancement for the poly-T DNA, and Ag+ enhances up to 10-fold for the poly-C DNA. A detection limit of 3 nM is achieved for both metals. With these four probes, silver and mercury can be readily discriminated from the rest. A comparison with other signaling methods was made using fluorescence resonance energy transfer, graphene oxide, and SYBR Green I staining, respectively, confirming the robustness of the 2AP label. Detection of Hg2+ in Lake Huron water was also achieved with a similar sensitivity. This work has provided a comprehensive fundamental understanding of using 2AP as a label for metal detection, and has achieved the highest fluorescence enhancement for non-protein targets. (C) 2016 Elsevier B.V. All rights reserved.Item A 30-Year Study of Impacts, Recovery, and Development of Critical Effect Sizes for Endocrine Disruption in White Sucker (Catostomus commersonii) Exposed to Bleached-Kraft Pulp Mill Effluent at Jackfish Bay, Ontario, Canada(Frontiers, 2021-04-22)Jackfish Bay is an isolated bay on the north shore of Lake Superior, Canada that has received effluent from a large bleached-kraft pulp mill since the 1940s. Studies conducted in the late 1980s found evidence of reductions in sex steroid hormone levels in multiple fish species living in the Bay, and increased growth, condition and relative liver weights, with a reduction in internal fat storage, reduced gonadal sizes, delayed sexual maturation, and altered levels of circulating sex steroid hormones in white sucker (Catostomus commersonii). These early studies provided some of the first pieces of evidence of endocrine disruption in wild animals. Studies on white sucker have continued at Jackfish Bay, monitoring fish health after the installation of secondary waste treatment (1989), changes in the pulp bleaching process (1990s), during facility maintenance shutdowns and during a series of facility closures associated with changing ownership (2000s), and were carried through to 2019 resulting in a 30-year study of fish health impacts, endocrine disruption, chemical exposure, and ecosystem recovery. The objective of the present study was to summarize and understand more than 75 physiological, endocrine, chemical and whole organism endpoints that have been studied providing important context for the complexity of endocrine responses, species differences, and challenges with extrapolation. Differences in body size, liver size, gonad size and condition persist, although changes in liver and gonad indices are much smaller than in the early years. Population modeling of the initial reproductive alterations predicted a 30% reduction in the population size, however with improvements over the last couple of decades those population impacts improved considerably. Reflection on these 30 years of detailed studies, on environmental conditions, physiological, and whole organism endpoints, gives insight into the complexity of endocrine responses to environmental change and mitigation.Item 3D printing of soft hydrogels incorporating functional nanomaterials(University of Waterloo, 2017-01-10)Tissue engineering (TE) scaffolds are required to closely mimic the human body environment to enable the study of cell behavior in vitro and allow the fabrication of artificial tissue constructs. The scaffolds should possess controlled structural and mechanical properties, such as stiffness and porosity. In addition, its physical and chemical properties, such as electrical conductivity, should be able to promote cell differentiation and growth. In the search of developing an ideal scaffold, hydrogels that incorporate functional nanomaterials scaffolds are being explored. This study, as a fulfillment for a master’s degree, investigates the ability of cells to survive in a three-dimensional (3D) printed soft hydrogels incorporated with functional materials. In this work, alginate, a natural polymer, was used as the main hydrogel material. It can physically crosslink by adding CaCl2 or chemically crosslink after methacrylation, by introducing carbon-carbon double bonds. However, pure alginate hydrogel is mechanically and rheologically weak. Previous mechanical tests indicated that cellulose nanocrystals (CNC)-incorporated alginate-based hydrogels increased the mechanical strength of the scaffolds, which can contribute to the interactions between CNC and polymeric networks. Rheological tests showed that the incorporation of cellulose nanocrystals into the alginate matrix introduced strong shear thinning behavior and improved shear modulus. The enhancement of rheological properties improved the printability and fidelity of the hybrid pre-gel solution. Finally, cell viability was explored by suspending 3T3 fibroblasts in the bioink. It was shown that the hybrid bioink was nontoxic and the cell viability remained high over a 7-days period. This master’s thesis demonstrates the feasibility of 3D printing of soft hydrogels for the fabrication of 3D scaffolds that mimic real tissues. It is anticipated that a broad array of ink compositions with suitable viscosity can be printed and multiple cell lines can grow in the same scaffold. This research provides a platform for the fabrication of biocompatible polymers and stretchable biosensors within an engineered scaffold.Item Accelerating peroxidase mimicking nanozymes using DNA(Royal Society of Chemistry, 2015-09-07)DNA-capped iron oxide nanoparticles are nearly 10-fold more active as a peroxidase mimic for TMB oxidation than naked nanoparticles. To understand the mechanism, the effect of DNA length and sequence is systematically studied, and other types of polymers are also compared. This rate enhancement is more obvious with longer DNA and, in particular, poly-cytosine. Among the various polymer coatings tested, DNA offers the highest rate enhancement. A similar acceleration is also observed for nanoceria. On the other hand, when the positively charged TMB substrate is replaced by the negatively charged ABTS, DNA inhibits oxidation. Therefore, the negatively charged phosphate backbone and bases of DNA can increase TMB binding by the iron oxide nanoparticles, thus facilitating the oxidation reaction in the presence of hydrogen peroxide.Item Accurate Determination of the Diffusion Coefficient of Proteins by Fourier Analysis with Whole Column Imaging Detection(American Chemical Society, 2015-01-21)Analysis in the frequency domain is considered a powerful tool to elicit precise information from spectroscopic signals. In this study, the Fourier transformation technique is employed to determine the diffusion coefficient (D) of a number of proteins in the frequency domain. Analytical approaches are investigated for determination of D from both experimental and data treatment viewpoints. The diffusion process is modeled to calculate diffusion coefficients based on the Fourier transformation solution to Fick’s law equation, and its results are compared to time domain results. The simulations characterize optimum spatial and temporal conditions and demonstrate the noise tolerance of the method. The proposed model is validated by its application for the electropherograms from the diffusion path of a set of proteins. Real-time dynamic scanning is conducted to monitor dispersion by employing whole column imaging detection technology in combination with capillary isoelectric focusing (CIEF) and the imaging plug flow (iPF) experiment. These experimental techniques provide different peak shapes, which are utilized to demonstrate the Fourier transformation ability in extracting diffusion coefficients out of irregular shape signals. Experimental results confirmed that the Fourier transformation procedure substantially enhanced the accuracy of the determined values compared to those obtained in the time domain.Item Action Mechanism and Structural Studies on the Lipopeptide Antibiotic Daptomycin(University of Waterloo, 2019-07-02)Daptomycin (dap) is calcium-dependent lipopeptide antibiotic that is used clinically to treat systemic infections caused by Gram-positive pathogens. It is thought that dap brings about its antimicrobial effect by binding cytoplasmic bacterial membranes, via a calcium meditated interaction with the lipid phosphatidylglycerol (PG), and subsequent oligomerization. There is consensus that dap oligomerization is required for bactericidal activity, but the exact mechanism by which dap oligomers cause cell death is contested. Significant experimental evidence suggests that dap oligomers form cation-selective pores that cause membrane depolarization halting metabolite transport and resulting in cell death. Other proposed action modes include dap-induced non-selective membrane permeabilization, lipid extraction, and dislodgement of membrane-associated biosynthetic enzymes. The effect of phospholipids acyl tails on dap cation-selective pore formation has not been studied. In this thesis, fluorescence spectroscopy experiments on large unilamellar vesicles were used to study the effects of phospholipid acyl tails on dap cation-selective pore formation in a systematic fashion. It was observed that dap could permeabilize membranes composed of equal parts PC and PG with myristoyl acyl tails, but not those containing palmitoyl and oleoyl acyl tails. Oleoyl lipid acyl tails were found to render membranes insusceptible to dap pore formation regardless of the headgroup they were ligated to and at low concentrations in the membrane (10 mol%). Further studies showed that inhibition of dap pore formation by phospholipid acyl tails is correlated with increased acyl tail length rather than lipid unsaturation. Oleoyl acyl tails were found to restrict dap pore formation by disrupting the final stage of oligomer assembly. Attempts to permeabilize oleoyl lipid acyl tail containing membranes by branching and increasing the length of dap’s acyl tail moiety were unsuccessful. Overall, these findings suggest that lipid acyls affect dap’s action mode and should be a major consideration when designing model membrane systems for future dap action mode studies. Determining dap’s membrane-bound structure at an atomic level would help resolve the debate in literature regarding its action mode and establish dap’s structure-activity relationship. Previous attempts to determine the membrane-bound structure by solution-state nuclear magnetic resonance have failed because no suitable membrane mimetic existed. The latter portion of this thesis investigated the suitability of novel styrene-maleic acid (SMA) co-polymers to create membrane nanodisc suitable for determining dap’s membrane-bound structure. Through dynamic light scattering, fluorescence spectroscopy, and solution-state NMR it was found that this polymer can form membrane nanodiscs, with a diameter small enough for structural studies by solution-state NMR, in the presence of PG (50 mol%) and 3 mM calcium. Further, these PG containing nanodiscs allow for partially dap oligomerization, and are stable on the timescale of NMR experiments. Overall, while the SMA polymer used in this study did not allow for full dap oligomerization, the partial structure of membrane-bound dap could be obtained with this system by solution-state NMR.Item The action mechanism of daptomycin(Elsevier, 2016-12-15)Daptomycin is a lipopeptide antibiotic produced by the soil bacterium Streptomyces roseosporus that is clinically used to treat severe infections with Gram-positive bacteria. In this review, we discuss the mode of action of this important antibiotic. Although daptomycin is structurally related to amphomycin and similar lipopeptides that inhibit peptidoglycan biosynthesis, experimental studies have not produced clear evidence that daptomycin shares their action mechanism. Instead, the best characterized effect of daptomycin is the permeabilization and depolarization of the bacterial cell membrane. This activity, which can account for daptomycin's bactericidal effect, correlates with the level of phosphatidylglycerol (PG) in the membrane. Accordingly, reduced synthesis of PG or its increased conversion to lysyl-PG promotes bacterial resistance to daptomycin. While other resistance mechanisms suggest that daptomycin may indeed directly interfere with cell wall synthesis or cell division, such effects still await direct experimental confirmation. Daptomycin's complex structure and biosynthesis have hampered the analysis of its structure activity relationships. Novel methods of total synthesis, including a recent one that is carried out entirely on a solid phase, will enable a more thorough and systematic exploration of the sequence space.Item An Acyl-Linked Dimer of Daptomycin Is Strongly Inhibited by the Bacterial Cell Wall(American Chemical Society, 2017-03-28)The lipopeptide antibiotic daptomycin is active against Gram-positive pathogens. It permeabilizes bacterial cell membranes, which involves the formation of membrane-associated oligomers. We here studied a dimer of daptomycin whose two subunits were linked through a bivalent aliphatic acyl chain. Unexpectedly, the dimer had very low activity on vegetative Staphylococcus aureus and Bacillus subtilis cells. However, activity resembled that of monomeric daptomycin on liposomes and on B. subtilis L-forms. These findings underscore the importance of the bacterial cell wall in daptomycin resistance.Item Adnectin Solubility and Dynamics(University of Waterloo, 2019-10-28)Rapid growth of the global market for monoclonal antibodies (mAbs) has generated considerable interest in the development of alternative molecules that facilitate rapid discovery and manufacturing, while replicating the low toxicity/immunogenicity and tight, specific binding of mAbs. One such molecule is the tenth human fibronectin type III domain (10Fn3), which has solvent accessible loops resembling the VH complementarity-determining regions H1, H2, and H3 of immunoglobulin. 10Fn3-based binding proteins called Adnectins have been engineered to bind with high affinity to diverse targets using in vitro evolution methods such as mRNA display, yeast display, and phage display. Adnectins are known to vary in aggregation propensity, sometimes despite exceptionally high amino acid sequence identity, and have been used as a basis for protein aggregation/solubility research. Aggregation of therapeutic proteins can provoke a protein-specific immune response, and the solubility of Adnectins is therefore of immediate practical interest. The aggregation of proteins in general is a complicated and incompletely understood phenomenon, the study of which we advance using Adnectins as a model system. We also investigate protein dynamics (which can be related to protein aggregation, but additionally has enormous impact on how we think about protein structure and function) through nuclear magnetic resonance (NMR) spectroscopic and computational study of Adnectins. Here, we first present solubility data for a reference set of 41 Adnectins and use them to screen computational solubility/aggregation prediction methods. On the basis of these results, we select the CamSol prediction method for use in a protein engineering project that applies the principles of consensus design to enhance the solubility of the Adnectin scaffold. Furthermore, we demonstrate that hydrogen/deuterium exchange by hydrogen bonded amides in the C-terminal β-strand of the original scaffold is induced by transient inter-Adnectin association, and that equivalent exchange is not observed in our solubility-enhanced scaffold. Next, we describe the results of variable-temperature solution NMR experiments that probe Adnectin dynamics. Each resonance observable by NMR spectroscopy is composed of contributions from structurally equivalent nuclei in a vast number of proteins, the conformations of which may both differ from each other at any particular instant and evolve over the timescale of the experiment. The temperature dependences of amide proton and nitrogen chemical shifts are due to differences in the conformations sampled and their probabilities of occupation. Empirically, these temperature dependences are well-approximated by fits to a linear model, the slopes of which (known as temperature coefficients) may report on protein dynamics in the vicinity of each backbone amide. We explore possible determinants of amide proton and nitrogen temperature coefficients using a combination of molecular dynamics simulations and quantum chemical (density functional theory) calculations. In the directly detected (high resolution) proton dimension, we also analyze deviations from linearity, which may be attributable to fast exchange between protein conformations with distinct chemical shifts and a temperature-dependent difference in free energy.Item Adsorption and Desorption of DNA on Graphene Oxide Studied by Fluorescently Labeled Oligonucleotides(American Chemical Society, 2011-03-15)Being the newest member of the carbon materials family, graphene possesses many unique physical properties resulting is a wide range of applications. Recently, it was discovered that graphene oxide can effectively adsorb DNA, and at the same time, it can completely quench adsorbed fluorophores. These properties make it possible to prepare DNA-based optical sensors using graphene oxide. While practical analytical applications are being demonstrated, the fundamental understanding of binding between graphene oxide and DNA in solution received relatively less attention. In this work, we report that the adsorption of 12-, 18-, 24-, and 36-mer single-stranded DNA on graphene oxide is affected by several factors. For example, shorter DNAs are adsorbed more rapidly and bind more tightly to the surface of graphene. The adsorption is favored by a lower pH and a higher ionic strength. The presence of organic solvents such as ethanol can either increase or decrease adsorption depending on the ionic strength of the solution. By adding the cDNA, close to 100% desorption of the absorbed DNA on graphene can be achieved. On the other hand, if temperature is increased, only a small percentage of DNA is desorbed. Further, the adsorbed DNA can also be exchanged by free DNA in solution. These findings are important for further understanding of the interactions between DNA and graphene and for the optimization of DNA and graphene-based devices and sensors.Item Adsorption of DNA Oligonucleotides by Titanium Dioxide Nanoparticles(American Chemical Society, 2014-01-28)Titanium dioxide (TiO2) or titania shows great promise in detoxification and drug delivery. To reach its full potential, it is important to interface TiO2 with biomolecules to harness their molecular recognition function. To this end, DNA attachment is an important topic. Previous work has mainly focused on long double-stranded DNA or single nucleotides. For biosensor development and targeted drug delivery, it is more important to use single-stranded oligonucleotides. Herein, the interaction between fluorescently labeled oligonucleotides and TiO2 nanoparticles is reported. The point of zero charge (PZC) of TiO2 is around 6 in water or acetate buffer; therefore, the particles are positively charged at lower pH. However, if in phosphate or citrate buffer, the particles are negatively charged, even at pH ∼2, suggesting strong adsorption of buffer anions. DNA adsorption takes place mainly via the phosphate backbone, although the bases might also have moderate contributions. Peptide nucleic acids (PNAs) with an amide backbone cannot be adsorbed. DNA adsorption is strongly affected by inorganic anions, where phosphate and citrate can strongly inhibit DNA adsorption. DNA adsorption is promoted by adding salt or lowering pH. DNA adsorption is accompanied with fluorescence quenching, and double-stranded DNA showed reduced quenching, allowing for the detection of DNA using TiO2 nanoparticles.Item Adsorption of DNA onto gold nanoparticles and graphene oxide: surface science and applications(Royal Society of Chemistry, 2012-06-28)The interaction between DNA and inorganic surfaces has attracted intense research interest, as a detailed understanding of adsorption and desorption is required for DNA microarray optimization, biosensor development, and nanoparticle functionalization. One of the most commonly studied surfaces is gold due to its unique optical and electric properties. Through various surface science tools, it was found that thiolated DNA can interact with gold not only via the thiol group but also through the DNA bases. Most of the previous work has been performed with planar gold surfaces. However, knowledge gained from planar gold may not be directly applicable to gold nanoparticles (AuNPs) for several reasons. First, DNA adsorption affinity is a function of AuNP size. Second, DNA may interact with AuNPs differently due to the high curvature. Finally, the colloidal stability of AuNPs confines salt concentration, whereas there is no such limit for planar gold. In addition to gold, graphene oxide (GO) has emerged as a new material for interfacing with DNA. GO and AuNPs share many similar properties for DNA adsorption; both have negatively charged surfaces but can still strongly adsorb DNA, and both are excellent fluorescence quenchers. Similar analytical and biomedical applications have been demonstrated with these two surfaces. The nature of the attractive force however, is different for each of these. DNA adsorption on AuNPs occurs via specific chemical interactions but adsorption on GO occurs via aromatic stacking and hydrophobic interactions. Herein, we summarize the recent developments in studying non-thiolated DNA adsorption and desorption as a function of salt, pH, temperature and DNA secondary structures. Potential future directions and applications are also discussed.Item Adsorption of Nanoceria by Phosphocholine Liposomes(American Chemical Society, 2016-12-13)Nanoceria (CeO2 nanoparticle) possesses a number of enzyme-like activities. In particular, it scavenges reactive oxygen species based on in-vitro and in vivo antioxidation studies. An important aspect of fundamental physical understanding is its interaction with lipid membranes that are the main components of the cell membrane. In this work, adsorption of nanoceria onto phosphocholine (PC) liposomes was performed. PC lipids are the main constituents of the cell outer membrane. Using a fluorescence quenching assay, a nanoceria adsorption isotherm was determined at various pH values and ionic strengths. A non-Langmuir isotherm occurred at pH 4 because of lateral electrostatic repulsion among the adsorbed cationic nanoceria. The phosphate group in the PC lipid is mainly responsible for the interaction, and the adsorbed nanoceria can be displaced by free inorganic phosphate. The tendency of the system to form large aggregates is a function of pH and the concentration of nanoceria, attributable to nanoceria being positively charged at pH 4 and neutral at physiological pH. Calcein leakage tests indicate that nanoceria induces liposome leakage because of transient lipid phase transition, and cryo-transmission electron microscopy indicates that the overall shape of the liposome is retained although deformation is still observed. This study provides fundamental biointerfacial information at a molecular level regarding the interaction of nanoceria and model cell membranes.Item Advanced Electrodes and Electrolytes For Long-Lived and High-Energy-Density Lithium-Sulfur Batteries(University of Waterloo, 2017-05-16)The increasing demand on renewable but intermittent energy and the need for electrified transportation place great emphasis on energy storage. Lithium-sulfur (Li-S) batteries are promising systems due to the high theoretical energy density and natural abundance of sulfur. This thesis presents a thorough investigation on strategies to confine the polysulfides and to build long-lived and high-energy-density Li-S batteries. A series of sulfur host materials and a class of sparingly solvating electrolyte are presented. Chapter 3 presents an approach to confine polysulfides within a cobalt sulfide material, which exhibits both metallic conductivity and high polysulfide adsorptivity. First-principles calculations and X-ray photoelectron spectroscopy studies consistently demonstrate the coupled interaction between the ionic components of cobalt sulfide and lithium polysulfides. The interconnected nanosheets form 3D networks and enable high sulfur loading electrodes with stable cycling. Chapter 4 presents a novel dual-doping strategy on porous carbon for effective binding of polysulfides. The N and S heteroatoms respectively bond with the Li cations and S anions in the polysulfides. The synthesis is based on liquid-crystal driven self-assembly of bio-sustainable cellulose nanocrystals. Chapter 5 reports a light-weight graphitic carbon nitride material that incorporates high concentration of active N-doping sites for polysulfide binding. Excellent long-term cycling performance of the sulfur electrode is achieved with only 0.04% capacity fading per cycle over 1500 cycles. Chapter 6 further reports a comprehensive strategy on coupling a hybrid sulfur host with an in-situ cross-linked binder in order to construct high loading electrodes while using a low electrolyte volume. Alternative stacking of graphitic carbon nitride and graphene offers both Li-N based adsorption for polysulfide and high electronic conductivity. Benefiting from the high elasticity of the cross-linked binder, crack-free high loading electrodes are fabricated at an electrolyte/sulfur ratio of 3.5:1 (µl:mg). Chapter 7 presents a comprehensive study on the ACN2-LiTFSI-TTE electrolyte with sparing solubility for polysulfides at elevated temperature. A quasi-solid state reaction is demonstrated by the distinct Li-S voltage profiles and sulfur/lithiu sulfide phase evolution as probed by operando XRD measurements. This discovery will inspire further studies into modifying the local structure of electrolytes to control the reaction pathways of dissolution-precipitation electrochemistry.Item Advanced Electrolyte Design for Long-Life and High-Areal-Capacity Divalent Metal Batteries(University of Waterloo, 2024-01-22)Net-zero carbon dioxide emission demands clean renewable energy, while harnessing it requires electrochemical storage devices with high energy density, safety and affordability. To achieve decarbonization, much effort is being devoted to new battery technologies beyond lithium-ion batteries (LIBs), which suffer from limited lithium resources and low safety. Rechargeable batteries based on divalent metal anodes (Zn, Mg and Ca) are promising systems due to their high abundance, high volumetric capacity and potentially high safety. Zn anode has a high standard redox potential (-0.76 V vs. standard hydrogen electrode (SHE)), resulting in its relatively good compatibility with aqueous electrolytes. Such inherent safety and potential low-cost make aqueous Zn metal batteries (AZMBs) desirable candidates for small and large-scale stationary grid storage. Mg or Ca anode, on the other hand, has a much lower standard redox potential (-2.37 V or -2.87 V vs. SHE, respectively) that is even comparable to lithium (-3.04 V vs. SHE). Therefore, high-voltage rechargeable Mg or Ca metal batteries (MMBs or CMBs) are potential alternatives to LIBs in a variety of areas ranging from portable electronic devices to electrical vehicles. However, the study of these divalent metal batteries is still at the early stages. Among many unaddressed challenges for practical divalent metal batteries, designing better electrolytes is one key to their successful commercialization. This thesis presents a comprehensive investigation on designing new electrolytes for both AZMBs (chapters 3, 4 and 5) and MMBs (chapters 6 and 7), by tuning the solvation structure of Zn2+ or Mg2+ ions and their interaction with solvents or anions. A series of electrolytes with precisely controlled interfacial electrolyte/electrode chemistry are developed to achieve rechargeable AZMBs and MMBs under practical conditions. Chapter 3 reports a novel additive - N,N-dimethylformamidium trifluoromethanesulfonate (DOTf) - in a low-cost aqueous electrolyte that enable near 100% coulombic efficiency of Zn plating/striping at a combined high current density of 4 mA cm-2 and areal capacity of 4 mAh cm-2 over long-term cycling. The water-assisted dissociation of DOTf into triflic superacid creates a robust nanostructured SEI - as revealed by operando spectroscopy and cryo-microscopy - which excludes water and enables dense Zn deposition. Zn||Zn0.25V2O5·nH2O (ZVO) full cells based on this modified electrolyte retain ~83% of their capacity after 1000 cycles with mass-limited Zn anodes. By restricting the depth of discharge, the cathodes exhibit less proton intercalation and LDH formation with an extended lifetime of 2000 cycles. Chapter 4 presents the electrochemical degradation mechanism of LiV2(PO4)3 (LVP) as a host cathode in AZMBs. Phase conversion of LVP induced by H+ intercalation is observed in 4 m Zn(OTf)2 whereas dominant Zn2+ insertion is confirmed in ZnCl2 water-in-salt electrolyte (WiSE). This disparity is ascribed to the complete absence of free water and the strong Zn2+-H2O interaction in the latter that interrupts the H2O hydrogen bonding network, thus suppressing H+ intercalation. Based on this strategy, a novel PEG-based hybrid electrolyte is designed to replace the corrosive ZnCl2 WiSE. This system exhibits an optimized Zn2+ solvation sheath with a similar low free water content, showing not only much better suppression of H+ intercalation but also highly reversible Zn plating/stripping with a CE of ~99.7% over 150 cycles. Chapter 5 reveals the competition between Zn2+ vs proton intercalation chemistry of typical ZVO cathode using ex-situ/operando techniques, and alleviate side reactions by developing a cost-effective and non-flammable hybrid eutectic electrolyte. A fully hydrated Zn2+ solvation structure facilitates fast charge transfer at the solid/electrolyte interface, enabling dendrite-free Zn plating/stripping with a remarkably high average coulombic efficiency of 99.8% at commercially relevant areal capacities of 4 mAh cm-2 and function up to 1600 hours at 8 mAh cm-2. By concurrently stabilizing Zn redox at both electrodes, we achieve a new benchmark in Zn-ion battery performance of 4 mAh cm-2 anode-free cells that retain 85% capacity over 100 cycles at 25 C. Using this eutectic-design electrolyte, Zn||Iodine full cells are further realized with 86% capacity retention over 2500 cycles. The approach represents a new avenue for long-duration energy storage. Chapter 6 reports a low-cost inorganic membrane that forms an effective protection film on the Mg surface to stabilize Mg plating/stripping. It significantly reduces the population (and hence decomposition) of free diglyme (G2) molecules at the Mg/interface, while allowing facile transport of Mg2+ cations, leading to dendrite-free Mg deposition in a magnesium tetrakis(hexafluoroisopropyloxy)borate/G2 electrolyte. We demonstrate very stable Mg plating/stripping performance with a 750-fold extended lifetime (over 6000 hours) with a high coulombic efficiency of ~98%. The prototype Mo3S4 cathode paired with inorganic membrane-protected Mg anode shows 91% capacity retention over 200 cycles. More importantly, this membrane also protects soluble species in a high-voltage organic polymer cathode from being reduced at the anode via shuttling, achieving a full cell with a 3.5 V cutoff voltage and 1.4 V average discharge voltage. This results a high specific energy density of 320 Wh kg-1 and power density of 1320 W kg-1 based on cathode mass. Chapter 7 report a new and easily accessible co-ethereal phosphate electrolyte system for high-voltage rechargeable MMBs, which very effectively solves the difficulty of ion pair dissociation and facilitates fast nanoscale Mg nucleation/growth for the first time, enabling facile interfacial charge transfer at current densities up to 10 mA cm-2. Dendrite-free Mg plating/stripping is achieved for over 6000 hours (8.3 months) at a practical areal capacity of 2 mAh cm-2. The four-volt oxidative stability of these electrolytes - in conjunction with a polyaniline cathode with an upper potential of 3.5 V and a Mg metal anode - enables cells with stable cycling at a 2C rate for over 400 cycles at 25 C. We believe our work opens up new frontiers in developing low-cost and fast-charging MMBs with long life and high energy densities.Item Advanced research on Lithium-Sulfur battery : studies of lithium polysulfides.(University of Waterloo, 2013-10-03T15:52:47Z)This thesis was devised as a fundamental study of the Li-S system by the use of 7Li Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), X-ray Absorption Near- Edge Structure (XANES), and Non-Resonant Inelastic X-ray Scattering (NRIXS). The first part of this thesis reports the first evidence of a stable solid-phase intermediate between elemental sulfur (α-S8) and Li2S, Li2S6, which can be used to understand deeper Li-S battery. The second part of this thesis is based on operando XANES measurements made in the Argonne Photon Source (APS).Linear combination fit (LCF) analyses are performed to interpret the data; and, noticeably, the distinction between short-chain and long-chain polysulfides can be made due to the use of proper reference materials. The results reveal the first detailed observation of typical sulfur redox chemistry upon cycling, showing how sulfur fraction (under-utilization) and sulfide precipitation impact capacity. It also gives new insights into the differences between the charge and discharge mechanisms, resulting in the hysteresis of the cycling profile. Operando XANEs were also performed on het-treated material, which exhibits a particular electrochemical signature, which has never explained. After a preliminary electrochemical study by potentiodynamic cycling with galvanostatic acceleration (PCGA), operando XANES measurements at the sulfur K-edge are performed on heat-treated PCNS. Noticeably, the difference in the XANES signatures of the pristine and the recharged state shows the irreversible process that occurs during the first discharges. At last, electrolytes are investigated by the compilation of quantitative physico-chemical parameters – viscosity, ionic conductivity, and solubility of Li2S and Li2S6 – on novel class of solvents that are glymes with non-polar groups and acetonitrile (ACN) complexed with LiTFSI. 1,1,2,2-Tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) is chosen to decrease their viscosities. (ACN)2:LiTFSI attracts particular attention because of the particularly low Li2Sn solubility and. Its good electrochemical performance when mixed with 50 vol% HFE. Operando XANES proves the formation of polysulfides in this electrolyte, although constrains imposed by this novel electrolyte to the XANES experiment complicate the data analysis. The low energy feature evolution shows a more progressive mechanism involved in this electrolyte, which could be linked to the particularly low Li2Sn solubilityItem Advanced Separation Techniques in the Analysis of Environmental Pollutants(University of Waterloo, 2012-04-30T20:14:54Z)Recent developments in chromatographic supports and instrumentation for liquid chromatography are enabling rapid and highly efficient separations. Various analytical strategies have been recently proposed, for example the use of monolithic supports, elevated mobile phase temperatures, columns packed with sub-2 μm fully porous particles for use in ultra-high-pressure liquid chromatography (UHPLC) and superficially porous particles (fused core). All these approaches could be used to enhance the efficiency and shorten the analysis time. In the presented work, a high efficiency HPLC method was proposed based on coupling three columns packed with fully porous sub-2 µm particles and operating them at high temperature to reduce the solvent viscosity, thus reducing the column backpressure. The developed method could increase the number of theoretical plates compared to a single column at 30 ºC. The approach of column coupling was applicable for both isocratic and gradient mode of separation. Also, fast analysis methods were proposed based on using either a column packed with fully porous sub-2 μm particles and operated at high temperature or a column packed with superficially porous particles as a tool to increase the analysis speed. An ultra-fast green method was also proposed by using a short narrow bore column packed with fully porous particles. In addition, the chromatographic performance of columns packed with fused-core particles was investigated and compared to that of fully porous particles (sub-2 µm) at elevated temperature and extended column lengths. The study involved a comparison of chromatographic parameters such as retention, selectivity, resolution, efficiency and pressure drop. This study demonstrated that the fused-core particles can produce key advantages over the sub-2 µm particle columns in terms of separation speed, resolution and efficiency. All the developed methods were validated and applied to the analysis of environmental pollutants in surface water and/or waste water. The fast and efficient methods developed could be used as an alternative to the traditional ones for the environmental analysis of many pollutants.Item Advances in Biamperometry with Applications in Ocular Toxicology(University of Waterloo, 2013-10-02T17:03:26Z)This thesis presents advances in biamperometry, together with applications cyclic biamperometry, in in vitro ocular cytotoxicity assessment. For the cytotoxicity/viability assessment, cultured human corneal epithelial cells have been used as a model. The assay involves electrochemical measurement of the respiratory activity of the cells, and relating the extent of cell respiration to cell viability. This measurement is done by capturing electrons from the components of the respiratory chain and transferring these electrons to a non-native terminal recipient. In this study, three lipophilic redox mediators, including 2,6-dichlorophenolindophenol,menadione (vitamin K3) and N,N,N',N'-tetramethyl-p-phenylenediamine were evaluated. The mediators were compared with each other under their optimal conditions and 2,6- dichlorophenolindophenol was selected for further studies. To demonstrate the cytotoxicity assessment, three well-characterized toxicants, including benzalkonium chloride, sodium dodecylsulfate, and hydrogen peroxide, were used and it has been shown that the electrochemical assay is able to detect the cytotoxicity of the test chemicals near their cytotoxicity threshold reported in the literature. In addition, culturing human corneal epithelial cells on growth inserts, in an attempt to construct 3D corneal tissues to be used in ocular cytotoxicity assessment, is discussed. Diff erential pulse biamperometry is also introduced. This electrochemical method involves application of diff erential pulse waveforms in the biamperometric electrochemical cells. Various parameters aff ecting the response of the method as well as potential applications for future studies are discussed.Item Advances in Multidimensional Chromatography(University of Waterloo, 2012-07-23T16:34:37Z)Comprehensive two-dimensional gas chromatography (GC×GC) is among the most powerful methods used to separate complex samples. Two columns of different selectivities are coupled in series through a special interface (modulator). The main role of the modulator is to trap and/or sample the primary column effluent and inject it into the secondary column. This results in an enhanced sensitivity, increased peak capacity and structured chromatograms. Practically all thermal modulators in use today are equipped with two trapping stages to prevent problems related to analyte breakthrough, which makes their design more complicated. In this work, The sensitivity of GC×GC coupled to two different detectors, time-of-flight mass spectrometer (GC×GC-TOFMS) and flame ionization detector (GC×GC-FID) was compared to the sensitivity of conventional one-dimensional gas chromatography (GC-TOFMS and GC-FID) by determining the limits of detection (LOD) for a series of different compounds such as n-alkanes and alcohols using both approaches. Different modulation periods were used for GC×GC ranging from 2 to 8 seconds. In addition, different types of inlet ferrules were used to study their effect on both systems. In general, the LODs in GC×GC were lower by at least an order of magnitude. A new liquid nitrogen-based single-stage cryogenic modulator was developed and characterized. In addition, a new liquid nitrogen delivery system was developed. Band breakthrough was prevented using changes in the carrier gas viscosity with temperature to reduce the carrier gas flow during desorption. Injection band widths for n-alkanes of 30-40 ms at half height were obtained. Most importantly, even the solvent peak could be perfectly modulated, which is impossible with any commercially available thermal modulator. Moreover, the newly developed liquid nitrogen supply system reduced liquid nitrogen consumption to ~30 L per day versus 50-100 L per day for commercially available modulators. Evaluation of the newly developed system for the GC×GC separation of some real samples such as regular gasoline and diesel fuel showed that the analytical performance of this single-stage modulator rivals that of the more complicated dual-stage designs. The technique was tested in various applications. Headspace solid phase microextraction in combination with GC×GC coupled to time-of-flight mass spectrometry (HS-SPME-GC×GC-TOFMS) were used for the detailed investigation of the impact of malolactic fermentation (MLF) using three commercial Oenococcus oeni strains on the volatile composition of Pinotage wines. The technique was also applied for the characterization of Pinotage wine volatiles and blue honeysuckle berries volatiles.Item Advances in solid-phase microextraction as sample preparation method for food analysis.(University of Waterloo, 2015-02-25)Within all steps involved in the analytical process, sample preparation is considered the most time-consuming step. Therefore, substantial efforts have focused on the search for automated sample preparation strategies that minimize sample handling and errors associated with human interference. Solid phase microextraction (SPME) addresses well the necessity for simple and automated sample preparation, with the integration of sampling, extraction, clean up and instrumental introduction into a single step. In SPME, selective extraction of compounds takes place based on the degree of distribution of the analyte between the SPME coating and the sample matrix. For this reason, the correct choice of SPME coating for a given application has great influence on the acquisition of reliable analytical data. In spite of its great potential, the implementation of SPME in the analysis of complex matrices, such as food, has been hindered by the lack of suitable SPME coatings that possess compatibility with complex matrices while maintaining sufficient sensitivity for trace applications. The main problem resides in the fact that the most matrix compatible coating, PDMS, has limited extraction efficiency towards less hydrophobic analytes, whereas the coating that exhibits best extraction efficiency towards pesticides, in general, is PDMS/DVB. PDMS/DVB as a solid coating suffers from the attachment of matrix components onto the coating surface, known as fouling. Fouling does not only considerably shorten coating reusability, but it also causes significant changes in extraction efficiency, skewing the reliability of the data obtained. Therefore, in this thesis, a new approach to fabricate a matrix-compatible SPME coating for GC-based analysis of food matrices is presented. The developed matrix-compatible coating was evaluated for its reusability in complex matrices, namely grape pulp and Concord grape juice, as well as for its extraction capabilities towards various analytes bearing different physicochemical properties. First, a method to impart matrix-compatibility to commercially available solid SPME coatings was developed. The method consists of applying a thin layer of PDMS onto the solid coating, in this case PDMS/DVB. The main premise behind this approach was to create a coating that presents the matrix compatibility of PDMS, while maintaining the sensitivity obtained with PDMS/DVB. The reusability of the obtained PDMS-modified coating was evaluated in grape pulp, and rewarding results were obtained since the coating could be reused for over 100 extractions. Moreover, the PDMS-modified coating presented a similar extraction efficacy to that presented by the original PDMS/DVB coating towards the triazole pesticides, used as model analytes. The developed PDMS-modified coating was then employed to develop a simple and fast DI-SPME-GC-ToFMS method for determination of ten triazole fungicides in grapes and strawberries. The method was successfully validated, and the figures of merit obtained with the SPME method were compared to those obtained with the QuEChERS method. The limits of quantitation reached by SPME were at least one order of magnitude lower than those achieved by the QuEChERS method, whereas precision and accuracy were comparable for both methods. Subsequently, given the vast option of commercial PDMS blends available, different types of PDMS were compared for their reusability in complex matrices, and parameters associated with the PDMS-overcoated fiber fabrication were investigated in regards to their effect on fiber longevity. Results showed that the long-term reusability of such coatings is a function of the coating’s fabrication process, such as achievement of smooth and uniform PDMS surface, and sealing of both fiber ends by PDMS layer. Regarding PDMS type, best results were obtained with Sylgard ® 184. Since one of the most important branches of food analysis involves the simultaneous analysis of pesticides with a wide range of polarities and from different classes, the PDMS-modified coating was evaluated for the extraction of analytes of different polarities (log P = 1.43 to 6) from water samples in order to understand the mass transfer of analytes within the PDMS outer layer during the mass uptake process. Results showed that for hydrophobic analytes, the kinetics of extraction of the PDMS-modified coating are quite similar to that of the original PDMS/DVB. However, for more polar analytes, the rate-limiting step is the diffusion through the coating; therefore, the PDMS layer affects the kinetic uptake. The main implication of these results is quite evident if a method aiming at simultaneous determinations of both polar and non-polar analytes is to be developed, such as is the case in multiclass pesticide analysis, since the sensitivity of the method at too short extraction times might not be enough for polar analytes. Finally, once the PDMS-overcoated fibers were proven to be robust and compatible for use in fruit pulp, the DI-SPME-ToFMS method for multiresidue pesticide determination in grapes was developed and SPME parameters that can affect extraction efficiency were optimized via multivariate methods. Despite a thorough investigation during optimization, the most polar pesticides, acephate and omethoate, could not be detected. Next, a careful evaluation of internal standards was presented and attentively discussed. The results showed that two pairs of internal standards, interchangeable amongst them (i.e. only two internal standards were needed) were sufficient to ensure reliable, precise and accurate analytical data. Interestingly, only two internal standards at the time were needed, and among the choices presented, the use of non-deuterated compounds presents an affordable, cost-effective solution for the method. Next, the method was fully validated for 40 pesticides in compliance to EU/SANCO requirements (R2 > 0.995, RSD < 20%, and 80% < accuracy < 120%). The validated method exhibited excellent performance for pesticides such as chlorothalonil, dicofol, and folpet, which are considered the weak link in QuEChERS-based multiresidue methods. Pyrethroid pesticides were not validated due to their non-specific adsorption onto the vial walls. For pyrethroids, a solvent pre-extraction step should be incorporated in order to avoid losses due to the interaction of these compounds with glassware. Overall, despite the challenges and limitations encountered, it is evident that the practical aspects of the PDMS-modified coating demonstrated in this thesis create new opportunities for SPME applied in food analysis.