Department of Chemistry and Biochemistry Theses and Plan B Project Papers

Persistent link for this collectionhttps://hdl.handle.net/11299/275120

This collection contains some of the final works (theses and Plan B project papers) produced by master's degree students in the Master of Science in Chemistry graduate program. Students in this program complete either a Plan A (thesis-based) program or a Plan B (project-based) program. Additional Plan As (theses) can be found in the University of Minnesota Twin Cities Dissertations and Theses collection.

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    Quantifying the impacts of enzyme hydrolysis to biofilm formation on weathered bioplastics
    (2024) Badzinski, Thomas
    As efforts to address plastic pollution increase, new avenues are opening for the use ofbiologically renewable and biodegradable plastics. With the influx of these new polymer systems, it is crucial to understand the degradation processes of these polymers, particularly through the disposal systems designed to manage their waste (i.e., compost). This work seeks to characterize a multistep biodegradation system by studying how enzymatic hydrolysis impacts the formation of biofilms upon weathered biodegradable aliphatic polyesters to better understand processes that should occur in composting. Poly-L-lactic acid (PLLA), after varying amounts of photochemical weathering, was exposed to the esterase proteinase K followed by exposure to suspended facultative anaerobe, Shewanella oneidensis, whose biofilms were quantified with crystal violet staining. Enzymatic hydrolysis was observed to promote the formation of biofilm regardless of enzymatic concentration, enzyme exposure time, and state of weathering on the polymer. This trend also held true for the less commercially viable polymer poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), which was demonstrated to be recalcitrant to enzymatic hydrolysis. Further, we observed that the state of photochemical weathering caused variable impacts to the biodegradation of PLLA. Polymer characterization suggests that while there are changes in crystallinity and surface accessible ester linkages, increased surface area caused by photodegradation and/or enzyme hydrolysis drove the observed trends. Overall, this work demonstrates that a multi-step, synergistic biodegradation process is more effective at breaking down biodegradable polymers, though polymer weathering influences that to some extent, and offers insights into the importance of managing these waste streams to ensure we optimize their designed biodegradability.
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    Sulfur Cycling in Lake Superior: Characterizing the Role of Organic Sulfur in Oligotrophic Systems
    (2021-07) Petersen, Madelyn
    Microbially mediated sulfate reduction is important in lake sediment due to its impact on numerous other biogeochemical cycles, including phosphorus, iron, and mercury, and its contribution to carbon remineralization in lake settings. Recently, modelling studies in oligotrophic lake settings have demonstrated that organic sulfur is a significant portion of the total sulfur pool, capable of sustaining cryptic sulfur cycling within the sediment. Organic sulfur consists of freshly deposited biogenic sulfur-containing molecules, their degradation products, and abiotic “sulfurized” non-labile organic matter, which may play a significant role in organic matter preservation. Few, if any, studies have quantified these organic forms of sulfur to the total sulfur cycle in oligotrophic lake settings, indicating that characterization of the total sulfur budget in a low-nutrient lacustrine system is warranted. Here, organic and inorganic species of sulfur are characterized in Lake Superior sediment from four offshore locations. Inorganic contributions to the sulfur pool consist of sulfate in porewater; and sulfides, elemental sulfur, and pyrite in the sediments. Organic contributions are determined by difference from total sulfur by mass. Contributions from organic and inorganic sources of sulfur are evaluated from the surface of the sediment at 1-cm depths to 12 cm, then again at 15, 20, and 25 cm. Results show that in low-deposition settings, organic sulfur comprises between 70-90% of total sulfur in Lake Superior sediment, indicating the necessity of further exploration of the contribution of organic sulfur to carbon sequestration in oligotrophic lacustrine settings.
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    Characterization of Microplastics in the Water Column of Western Lake Superior
    (2021-08) Fox, John
    The amount of plastic waste in the natural environment has increased precipitously over the past 60 years and plastic contamination is now ubiquitous in aquatic systems across the planet. Microplastic represents a particularly pernicious form of plastic pollution as it is impossible to practically remediate owing to its size and already extensive distribution throughout the environment. While the reality of microplastic in the Laurentian Great Lakes has received substantial scientific attention, more work is required to fully characterize its behavior and fate in this unique freshwater system. At present, very little is known regarding the vertical distribution of microplastics throughout the water column. Most sampling campaigns in the Great Lakes have to this point focused on surface waters, sediments, and shorelines, leaving the water column conspicuously under sampled and undiscussed in the literature. In this research, we characterized the vertical distribution of microplastics in the water column of Western Lake Superior. We hypothesize the chlorophyll maximum to have the largest abundance of microplastics because it coincides with the depth of the pycnocline where the change in water density may allow trapping of microplastics that become too dense to float yet are not dense enough to reach benthic sediments. To achieve this work, we compared several novel methods for collecting microplastic samples from the water column, including Niskin bottle volume-sampling, in situ pumping, and serial filtration in a custom-built filter tower. In this research, we found evidence that in strongly stratified water columns, microplastic particles aggregate at the depth of the chlorophyll maximum, although this aggregation was not observed at sites with well-mixed water columns. Additionally, subsurface waters tended to have the highest abundance of microplastic particles indicating that buoyant microplastics are likely to preferentially accumulate in surface waters. Beyond characterization of the water column, this thesis work also sought to build a completely automated analytical pipeline for the bias-free characterization and quantification of microplastic particles in natural samples. To this end, a program was developed to count and detect microplastic particles based on two-dimensional spectral data obtained using an FTIR microscope. Computational analysis of the data yielded microplastic counts on the same order of magnitude as the manual analysis and yielded very similar trends. Overall, this research is an important first step towards a better understanding of the distribution of microplastics in the water column of Lake Superior and demonstrated an analytical approach for the bias-free detection of microplastics in natural samples using FTIR microscopy.