Além do interesse intrínseco pelos seus aspectos mecanísticos, as reações de hidrólise de compostos carbonílicos apresentam também a interessante particularidade da reação pelo próprio solvente, a água. Dentre estas reações, conhecidas como \"reações de água\" (Robertson, 1967; Johnson, 1967), estudou-se neste trabalho a hidrólise de carbonatos, através do cálculo das energias de transferência da fase gasosa para o solvente, de reagentes (R), estado de transição (ET) e produtos (P). O estudo da solvatação de modelos moleculares para R e ET indica uma correlação entre reatividade e estrutura molecular. Os resultados usando o enfoque de \"super-molécula\" mostram maior concordância com os dados experimentais do que o cálculo de solvatação da molécula simples e indicam que a solvatação dos modelos de ET é mais eficiente que para R e, portanto, há um aumento da reatividade. O estudo mais detalhado das estruturas de R, ET e P, em misturas água/acetonitrila para carbonatos de difenila e bis(2,4-dinitrofenila), sugere a existência de duas ligações de hidrogênio: entre o oxigênio da água do \"cluster\" e um dos hidrogênios dos anéis aromáticos (CF e CDNF), e entre o hidrogênio da água e o oxigênio do grupo nitro do outro anel aromático (CDNF). A consequente diminuição da liberdade conformacional em relação à fase gasosa, provocada por estas ligações de hidrogênio (CF e CDNF), expõe um dos hemisférios da carbonila ao ataque da água, provocando então uma aceleração entrópica do processo. Os efeitos eletrônicos, devidos às ligações de hidrogênio, estão de acordo com a maior acidez esperada dos hidrogênios dos anéis do CDNF em relação ao CF. Também mostram uma compensação no CDNF, pouco contribuindo para alterar a densidade eletrônica no seu carbono carbonílico, enquanto que indica uma soma de efeitos no CF, contribuindo então para um aumento desta densidade eletrônica no CF, de acordo com sua conhecida baixa reatividade. O trabalho permite ainda concluir sobre o relativo sucesso do uso de método semi-empírico PM3 e modelo relativamente simples de solvatação (Cramer & Truhlar, 1991), para o cálculo de energia de transferência em misturas de água/acetonitrila, na faixa de fração molar da água (0,40 a 1,00) onde o método apresenta resultados concordantes com os valores experimentais. / In addition to their intrinsic mechanistic interest, hydrolysis reactions of carbonyl compounds in aqueous media exhibit the interesting peculiarity of direct reaction with the solvent itself, i.e., water. In the present work, we have investigated a representative example of one of these \"water reactions\" (Robertson, 1967; Johnson, 1967), the hydrolysis of carbonates, via quantum chemical ca1culation of the free energies of transfer of the reagents (R), the transition state (TS) and the products (P) from the gas phase to water. A model study of the solvation of R and TS points to a correlation between reactivity and molecular structure. Results using the \"super-molecule\" approach show greater agreement with experiment than solvation ca1culations on the isolated molecule and imply that the solvation of the TS is more effective than that of R in increasing reactivity. A more detailed study of the structures of R, TS and P for diphenyl- (DPC) and bis(2,4-dinitrophenyl)carbonates (DNPC) in acetonitrile/water mixtures suggests the existence of two possible types of hydrogen bonds, i.e., between oxygen of the water c1uster and an aromatic ring hydrogen (DPC and DNPC) or, in the case of DNPC, between the protons of water and the oxygens of the nitro group of the second aromatic ring. The decrease in conformational degrees of freedom reI ative to the gas phase provoked by these hydrogen bonds exposes one of the hemispheres of the carbonyl group to attack by water, resulting in an entropic acceleration of the reaction. The electronic effects on the hydrogen bonds are in line with the greater acidity of the aromatic ring hydrogens of DNPC relative to those of DNP. In DNPC, there is a compensation effect, with very little alteration of the electron density on the carbonyl carbon, while in DPC a sum of effects increases the electron density on the carbonyl carbon, in line with the known lower reactivity of the latter. This work points to the relative success of the semi-empirical PM3 method combined with relatively simple solvation models (Cramer & Truhlar, 1991) for ca1culating free energies of transfer involving acetonitrile/water mixtures in the water mole fraction range from 0.40-1.00.

DNA barcoding is a valuable tool for fish species identification by food regulators, however, it does not perform well when multiple species are present within the same food product. PCR cloning has high potential to be used in combination with DNA barcoding to overcome this challenge. The objective of this study was to examine the use of PCR cloning combined with DNA barcoding to identify fish in a mixed-species product that cannot be identified with standard DNA barcoding. A total of 15 fish ball mixtures were prepared with known amounts of Nile tilapia (Oreochromis niloticus), Pacific cod (Gadus macrocephalus), and walleye pollock (Gadus chalcogrammus). The fish balls underwent DNA extraction in triplicate, followed by DNA barcoding across the full barcode (655 bp) and SH-E mini-barcode (226 bp) of the cytochrome c oxidase subunit 1 (CO1) region. Samples that did not pass sequencing according to regulatory standards were further analyzed with PCR cloning. Full barcoding enabled identification of at least one species in 80% of the fish ball mixtures compared to 51% for minibarcoding. The results of PCR cloning with samples that did not pass DNA barcoding showed identification success rates of 61% for clones (54 of 90) that underwent full barcoding and 51% for clones (111 of 220) that underwent mini-barcoding. All fish balls made of just one species tested positive for that species (i.e., tilapia, cod, or pollock).. The combination of standard full barcoding and PCR cloning enabled identification of Nile tilapia in all 12 mixed-species fish balls and Pacific cod in 6 of 12 (50%) of mixed-species fish balls. In comparison, the combination of standard mini-barcoding and PCR cloning enabled identification of Nile tilapia in all 12 mixed-species fish balls and Pacific cod in 9 of 12 (75%) of mixed-species fish balls. Overall, the results of this study show that PCR cloning may be an effective method to identify certain fish in mixed-species products when standard DNA barcoding fails. However, additional research is needed to understand the limitations associated with primer bias.

Kura clover (Trifolium ambiguum) is a perennial legume species that has been found to have exceptional persistence in the United States, Australia and New Zealand. There are two challenges that impede the incorporation of Kura clover into pasture mixtures in Alberta. The first is the lack of available seed, and the second is poor establishment success in mixtures with highly competitive grass species. A series of experiments were conducted to (i) address the potential for seed production in a central Alberta environment and (ii) to determine alternative strategies for establishment in mixtures. Kura clover successfully flowered and produced seed under central Alberta growing conditions. Seed production was greater from the cultivar Endura than Cossack. Kura clover seed production was not affected by row spacing however, yield was greater when clover was planted at 3 or 6 kg/ha versus 9 or 12 kg/ha. Seed yield ranged from 80 kg/ha to 350 kg/ha. Establishing Kura clover with a cover crop reduced flowering and seed production. Corn (Zea mays) was the least competitive cover crop, followed by faba bean (Vicia faba L.). Canola (Brassica napus), peas (Pisum sativum L.), barley (Hordeum vulgare) and triticale (X Tritosecale) reduced Kura clover seed yield and are not recommended as cover crops. Comparison of above and below ground competition between Kura clover and meadow bromegrass (Bromus biebersteinii), indicated that below ground competition has the greatest impact on Kura clover seedling growth. Altering seeding rate and delaying introduction of the grass species by up to two months significantly improved Kura clover establishment in mixtures. Kura clover survival in established pastures was higher with physical than chemical sod suppression of the standing forage. Dry matter yield of Kura clover was greatest when defoliated at 6 week intervals. Challenges still remain regarding seed production and establishment of Kura clover. However, we successfully addressed the major concerns regarding the potential of Kura clover in Alberta. / Plant Science

No description available.

Complex chemical mixtures may be released into the environment from a variety of sources including hazardous waste sites. Components of chemical mixtures and their metabolites may be genotoxic leading to cancer and heritable gene mutations. Chemical analysis alone does not always provide the most accurate information from which to estimate the risk of adverse effects associated with exposure to mixtures. Current methods to estimate the human health risk for complex mixtures assume additive effects of the components. Although it is assumed that this approach is protective of human and ecological health, it is also recognized that chemical mixtures may induce a variety of interactions including potentiation, synergism, and antagonism. A combined testing protocol, using chemical analysis coupled with a battery of in vitro, in vivo, and in situ bioassays, provides the most accurate information from which to estimate risk. Such a combined testing protocol provides information to describe the major organic and inorganic constituents, as well as the pharmacokinetics and potential interactions of chemical mixtures. This research was conducted to investigate the potential genotoxic effects of complex chemical mixtures of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated aromatics (PCA) using microbial bioassays (Salmonella/microsome assay and the E. coli prophage induction assay), the 32P-postlabeling assay in mice, and in situ measurements of genotoxicity using flow cytometry. Samples of environmental media and wildlife tissues were collected from four National Priority List Superfund sites within the United States. In general, chemical analysis was not always predictive of mixture toxicity. Although biodegradation reduced the concentration of total and carcinogenic PAHs in soils and groundwater, the genotoxicity of extracts from environmental media did not display a corresponding reduction. Mixtures of polychlorinated biphenyls (PCBs) extracted from sediments were found to inhibit the genotoxicity of PAH mixtures when administered dermally to rodents. This inhibition exhibited a dose-response relationship, with the adduct frequency reduced at increasing doses of sediment extract. Finally, PAH concentrations in environmental media and tissues were found to correlate with DNA damage in wildlife receptors. An integrated approach, combining in vitro and in vivo methods to characterize genotoxicity provides more accurate information from which to estimate uptake and risk associated with exposure to complex mixtures and should be considered in both the human and ecological risk assessment process.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Dust and hybrid mixture explosions continue to occur in industrial processes that handle fine powders and flammable gases. Considerable research is therefore conducted throughout the world with the objective of both preventing the occurrence and mitigating the consequences of such events. In the current work, research has been undertaken to help advance the field of dust explosion prevention and mitigation from an emphasis on hazards to a focus on risk. Employing the principles of quantitative risk assessment (QRA) of dust and hybrid mixture explosions, a methodological framework for the management of these risks has been developed. The Quantitative Risk Management Framework (QRMF) is based on hazard identification via credible accident scenarios for dust explosions, followed by probabilistic Fault Tree Analysis (using Relex – Reliability Excellence – software) and consequence severity analysis, represented by maximum explosion pressure, (using DESC – Dust Explosion Simulation Code – software). Identification of risk reduction measures in the framework is accomplished in a hierarchical manner by considering inherent safety measures, passive and active engineered devices, and procedural measures. Dust explosion tests to determine icing and granulated sugar dust explosibility characteristics have been achieved in a 20-L Siwek chamber, and, accordingly, DESC fuel files were built and DESC has validated. Three industrial case studies are presented to show how the QRMF could has been helpful in reducing dust and hybrid mixture explosion risk at the Imperial Sugar refinery, the Semabla grain storage silo, and a hypothetical 400-m3 polyethylene storage silo. DESC simulations and Probit equation for structural damage provide the destructive percentage of each pressure zone in the simulations, followed by probabilistic FTA that were achieved for the first two case studies, before and after applying the framework. Detailed individual and societal risks calculations were made and F-N curves plotted for the two processes. The polyethylene silo case study is presented to show how inherent safety measures can be helpful in reducing dust and hybrid mixture explosion risk. The framework showed significant risk reduction to the point where the residual risks are acceptable for both processes. Finally, assessment results are compared and improvements measured. / The research main objective is: to manage the risks of any expected dust or hybrid mixture explosion in industrial complexes (large-scale).

We introduce a dimension reduction method for model-based clustering obtained from a finite mixture of t-distributions. This approach is based on existing work on reducing dimensionality in the case of finite Gaussian mixtures. The method relies on identifying a reduced subspace of the data by considering how much group means and group covariances vary. This subspace contains linear combinations of the original data, which are ordered by importance via the associated eigenvalues. Observations can be projected onto the subspace and the resulting set of variables captures most of the clustering structure available in the data. The approach is illustrated using simulated and real data. / Paul McNicholas

No description available.

Nanotechnology as a science is emerging rapidly. As materials are synthesized and utilized at the nanometer size scale, concerns of potential health and safety effects are arising. In an effort to elucidate the physicochemical characteristics of nanoparticles influential in toxicological studies, surface properties of metal oxide and carbonaceous nanoparticles were measured. These properties include zeta potential, dissolution and surface-bound chemical components. Subsequently, the role of these properties in oxidative stress was examined in vitro. This work identifies the influence that pH has on the zeta potential of nanoparticles. The zeta potential has the ability to alter colloidal stability, as the largest nanoparticle agglomerate is seen at or near the isoelectric point for each of the particles tested. Furthermore, it was observed that metal oxide nanoparticles which exhibit a charged surface at physiological pH, lead to decreased in vitro cellular viability as compared to those that were neutral. Thus, nanoparticle zeta potential may be an important factor to consider when attempting to predict nanoparticle toxicity. Real world exposure to nanoparticles is a mixture of various particulates and organics. Therefore, to simulate this particle mixture, iron oxide (Fe2O3) and engineered carbon black (ECB) were utilized in combination to identify potential synergistic reactions. Following in vitro exposure, both nanoparticle types are internalized into endosomes, where liberated Fe3+ reacts with hydroquinone moieties on the ECB surface yielding Fe2+. This bioavailable iron may then generate oxidative stress through intracellular pathways including the Fenton reaction. As oxidative stress is common in particulate toxicology, a comparison between the antioxidant defenses of epithelial (A549) and mesothelial (MeT-5A) cell lines was made. The A549 cell line exhibits alterations in the NRF2-KEAP1 transcription factor system and therefore retains high basal levels of phase II antioxidants. Both cell types were exposed to 33 nm silica where intracellular oxidant generation coupled with markers of oxidative stress were observed. While the MeT-5A cells exhibited a decrease in cell viability, the A549 cell line did not. Therefore, proper characterization of both material and biological systems prior to toxicity testing will help to further define the risks associated with the use of nanotechnology.