<p> Nuclear magnetic resonance spectroscopy has been used to study donor-acceptor complexes of boron trifluoride with ketones, water, and methanol. Various NMR techniques have been applied which, in certain favourable cases, have yielded information on the stoichiometry, structure, relative stabilities, and reactions of the complexes in solution. A new method is proposed for the detection of BF3 complexes having low formation constants.</p> <p> The magnitude and sign of the B-F coupling constant in the tetra-fluoroborate anion have been found to be dependent on the solvent. This solvent dependence is interpreted in terms of solvation and association of the ion in solution.</p> <p> 19F spectra of 10BF3 over a range of temperatures agree well with line shapes calculated, using Pople's expressions, for coupling of fluorine-19 with boron-10 (I=3) which is undergoing partial quadrupole relaxation.</p> / Thesis / Doctor of Philosophy (PhD)

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Increasing awareness to global climate change has drastically focused attention on finding solutions to reduce environmental impacts while still providing sufficient food for the increasing world population. Beneficial Nitrogen Fixing (BNF) microbes provide a possible solution by delivering biological nitrogen to plants resulting in reduced environmental impacts due to fertilizer runoff and eutrophication. One well studied model is that of Sinorhizobium meliloti and its legume host Medicago sativa (alfalfa), the fourth largest USA crop used for animal feed. Advancing research for this symbiosis model can provide solutions to enhance yield while minimizing environmental impacts. Chapter 2 focuses on the deviation of the S. meliloti chemotaxis system from the enteric paradigm. Quantitative immunoblots determined the cellular amounts of chemotaxis proteins. Overall, chemotaxis protein levels were approximately 10-fold lower in S. meliloti compared to B. subtilis and E. coli. Focusing on cellular stoichiometric ratios, S. meliloti generally exhibits drastically higher values for CheB, CheR, and CheY to the histidine kinase CheA monomer compared to E. coli and B. subtilis. Chapter 3 characterizes the role of McpX to quaternary ammonium compound (QAC) sensing. QACs are exuded by germinating alfalfa seeds. In vitro binding assays were performed to determine ligand binding characteristics. S. meliloti chemotaxis behavior to QACs was analyzed in in vivo capillary assays under real-time imaging. These studies strengthen our knowledge of the chemotaxis system in the symbiosis model of S. meliloti and alfalfa. The data can further be used to create a mathematical model of the dynamics of bacteria-host interaction. The results can be used to optimize chemotaxis to host plants to improve crop yield and protect watersheds. / Master of Science / Increasing awareness of global climate change has drastically focused attention on finding solutions to reduce environmental impacts while still providing sufficient food for the increasing world population. Beneficial Nitrogen Fixing (BNF) microbes may offer a feasible solution in reducing environmental impacts by supplying biological nitrogen to plants, which reduces fertilizer use and ultimately runoff. One-well studied beneficial microbial model is that of Sinorhizobium meliloti and its legume host Medicago sativa (alfalfa), the fourth most cultivated USA crop used for animal feed. Advancing research for this symbiosis model can provide solutions to enhance crop yield while diminishing environmental impacts.

The field of ecological stoichiometry has been dominated by studies focusing on aquatic & benthic microinvertabrates with less attention given to herbivorous insects. These organisms rely on their food source(s) to supply all of the building blocks (elements) they need in order to complete their life cycle. Since insect herbivores do not have the same elemental composition as the plants they use for food the question arises; of how they go about building themselves. We investigated what happened when grasshoppers were fed diets with various macronutrient profiles, their total amounts, and when the protein quality varied. We discovered that under controlled conditions when using a high quality protein source that grasshoppers are able to maintain a strict level of elemental homeostasis, but that the elements directly related to manipulations made in the food seem to vary (carbon, which is associated with carbohydrates and nitrogen, associated with protein). We also discovered that when the quality of protein changes an immature grasshoppers elemental stoichiometry loses some of this strict homeostatic regulation.

Evolution shapes ecosystems but the processes by which this occurs are not well understood. Adaptive change in resource expensive traits may underlie one such process, as evolution altering a species’ resource needs may effect how that species interacts with ecosystem resources. For this, Ecological Stoichiometry (ES) may be a tractable framework, as it simplifies organisms into elemental ratios and then applies mass-balance to predict changes in diet and waste interactions. ES detects variation in resource expensive traits as variation in elemental ratios, and predicts compensation via parallel changes in diet (e.g. high phosphorous individuals consume high phosphorus diets) and/or offsetting changes in waste (e.g. high phosphorous individuals release low phosphorus waste). To test the utility of this framework and improve our understanding of eco-evolutionary dynamics, I studied variation in phenotypic traits, genetics, elemental content and resource interactions within and across natural populations of highly regarded eco-evolutionary model species threespine stickleback (Gasterosteus aculeatus). First, I related heritable variation in phosphorus rich bony traits and genetics commonly under natural selection with variation in elemental content (N:P) to determine the magnitude and basis of intraspecific variation in N:P. Second, I investigated the ecosystem consequences of variation in elemental content by determining whether stickleback compensate through changes in diet choice and excretion rates. I found stickleback vary widely in elemental composition (3.0 – 9.4:1 N:P) which models explained well with four bone related traits: bone mineralization, body size, lateral plating and pelvis size (R2 > 0.52). Additional genetic models linked variation in Eda alleles (which underlie lateral plating) with a 12% shift in stickleback N:P. Stickleback compensated for this variation in N:P demand by altering diet choice rather than excretion rates, and by maximizing dietary inputs through changes in gut morphology. Within and across populations, high phosphorus stickleback consumed a larger proportion of high phosphorus prey and contained longer gastrointestinal tracts that more efficiency process diet resources. These results demonstrate that heritable variation in elemental composition is ecologically relevant with individual traits and genetics having large effects. As individuals compensated by altering resource acquisition rather than release, the direct ecological consequences of evolutionary change in these resource expensive traits is likely larger for food web structure and abundance than nutrient dynamics. / Graduate / 2018-12-19

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First-year chemistry was identified by the North West University Potchefstroom Campus as one of the modules with a low pass rate. It is clear that students often memorise definitions and formulae, without understanding the underlying concepts which are necessary for problem solving. It is important that these and other related problems are addressed, before any significant change in the through-put rate for first-year students is reached. Conventional forms of lectures as teaching approach had little impact on the performance of students’ exam results. Much research has already been done on students’ misconceptions of stoichiometry, as well as problem solving strategies regarding stoichiometric problems. In addition, several alternative approaches concerning the teaching of chemistry have already been developed. Students still see this subject as very difficult and challenging. This study handles the systematic integration of visualization during lectures and the development of critical thinking and metacognition in assignments in stoichiometry teaching of first-year students at a South African University with the purpose of improving conceptual understanding. A quantitative research approach was followed. A one-group pre-test-post-test design was initiated to determine if there were practical significant differences in the conceptualisation of students at the beginning and at the end of the study. The intervention consisted of the implementation of specific teaching techniques, which included visualization and the development of critical thinking. Slideshows, a document camera, assessment tasks, a mini-project as well as thinking skills tasks were used. The study indicated that visualization, metacognition and critical thinking had a positive influence on the learning and conceptualisation of stoichiometry in students. The promotion of the learning of by the implementation of visualization, metacognition and critical thinking techniques, was successfully applied to help first-year students of this university realise stoichiometric-conceptualisation. / MSc (Natural Science Education), North-West University, Potchefstroom Campus, 2015

First-year chemistry was identified by the North West University Potchefstroom Campus as one of the modules with a low pass rate. It is clear that students often memorise definitions and formulae, without understanding the underlying concepts which are necessary for problem solving. It is important that these and other related problems are addressed, before any significant change in the through-put rate for first-year students is reached. Conventional forms of lectures as teaching approach had little impact on the performance of students’ exam results. Much research has already been done on students’ misconceptions of stoichiometry, as well as problem solving strategies regarding stoichiometric problems. In addition, several alternative approaches concerning the teaching of chemistry have already been developed. Students still see this subject as very difficult and challenging. This study handles the systematic integration of visualization during lectures and the development of critical thinking and metacognition in assignments in stoichiometry teaching of first-year students at a South African University with the purpose of improving conceptual understanding. A quantitative research approach was followed. A one-group pre-test-post-test design was initiated to determine if there were practical significant differences in the conceptualisation of students at the beginning and at the end of the study. The intervention consisted of the implementation of specific teaching techniques, which included visualization and the development of critical thinking. Slideshows, a document camera, assessment tasks, a mini-project as well as thinking skills tasks were used. The study indicated that visualization, metacognition and critical thinking had a positive influence on the learning and conceptualisation of stoichiometry in students. The promotion of the learning of by the implementation of visualization, metacognition and critical thinking techniques, was successfully applied to help first-year students of this university realise stoichiometric-conceptualisation. / MSc (Natural Science Education), North-West University, Potchefstroom Campus, 2015

This thesis focuses on ecological processes among plankton organisms. It especially questions the influence of food quality on growth and survival of freshwater plankton. I focused on the influence of various ratios of nitrogen and phosphorus in available food. I am also interested in finding out the food requirements of chosen consumer Daphnia longispina. Within this broad topic, I specify a question, whether various quality and quantity of food influences the life history parameters of the species Daphnia longispina and whether the absence of common species of Cladoceran Daphnia longispina in Plešné Lake is caused by unsuitable quality of food. I have bred Daphnia longispina in laboratory conditions for two years. I fed it by algae Monoraphidium dybowskii isolated from Plešné Lake and grown in two media P-limited (C:P 1174), P-unlimited (C:P 290) and three concentration (1,2, 4 mg C/L). Cladocerans fed by food from medium that had a C:N:P ratio approximately the same as can be found in Plešné Lake (C:P 1174) lived for a singificantly shorter period of time and during the experiment they did not reproduce even in the case with the largest amount of food (4 mg C/L). This is a possible reason why Daphnia longispina did not return to Plešné Lake after the period of strong acidification, climax of...

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