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Browsing by Author "Tigner, Jonathan"

Now showing 1 - 3 of 3
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    Fluorescent Dye Staining as a Tool to Monitor and Quantify Changes in Plastic Surface Hydrophobicity Throughout Photodegradation (2022-04-01)
    (2022) Tigner, Jonathan; University of Minnesota Duluth. Department of Chemistry and Biochemistry
    The widespread use of plastics has resulted in the major environmental challenge of plastic pollution. One solution to minimizing the amount of plastic pollution is to improve reuse and recycling strategies, which are limited by the extent of plastic degradation. A significant pathway of plastic degradation is photo-oxidation resulting from UV light causing chemical changes in the plastic backbone. The incorporation of carbonyl groups into the plastic backbone from photooxidation can lead to chain cleavage with UV light as well as a decrease in surface hydrophobicity. Current techniques for monitoring plastic degradation are limited in their ability to observe the early stages of degradation. To fill this knowledge gap, this research seeks to develop a cheap, reproducible, and non-destructive technique for monitoring photooxidative degradation of polyethylene and polypropylene thin films using Nile Red as a fluorescent probe through measurements of surface hydrophobicity. Changes in Nile Red’s fluorescence spectra were be observed from stained, aged polyethylene and polypropylene samples due to Nile Red solvatochromism. As the surface hydrophobicity of the plastic decreases, the signal obtained from Nile Red’s fluorescence undergoes corresponding signal shifts. Trends with the fluorescent profiling were related to carbonyl index from FTIR measurements and contact angle goniometry, allowing for the correlation of fluorescence signals to current measurements of plastic hydrophobicity. Results demonstrate a linear trend in fluorescence spectra shifts as related to the chemical changes to the backbone, with trends dependent on polymer type but independent of polymer film thickness. Overall, this work establishes a new tool to better characterize the extent of plastics’ degradation, which may ultimately impact our ability to recover plastics and minimize plastic waste.
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    Interdomain Force Dispersion within Spectrin Repeats of Dystrophin and its Influence on Secondary Structure
    (2020-05) Nelson, Eleanore; Amaris, Althea; Nohner, Madison; Olson, Kari; Tigner, Jonathan; Fealey, Michael; Hinderliter, Anne
    Dystrophin is a large protein complex that connects the cytoskeleton to the extracellular matrix and functions to stabilize muscle cells when force is applied. Dystrophin consists of four domains; an actin binding domain (ABD-1), triple helical spectrin domains composed of 24 spectrin repeats (SR’s), and cysteine rich domain, and the C terminal domain. Mutations, even single point mutations, within the dystrophin gene are known to cause muscular dystrophy, a condition characterized by progressive weakness of the muscles. The fact that single point mutations can result in muscular dystrophy support the idea the domains must communicate with each other. It has been hypothesized that dystrophin exhibits negative interdomain coupling mechanism, meaning that as force is dispersed across the domains, domains destabilize each other and adopt multiple conformations. This negative coupling mechanism is being tested on the spectrin repeats of dystrophin and the actin binding domain. This presentation discusses the data analysis method used to calculate free energy using differential scanning calorimetry, the conclusions drawn thus far from data obtained, and analyzes circular dichroism data to predict secondary structures of the constructs.
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    Quantifying Polymer Surface Degradation Using Fluorescence Spectroscopy
    (2023) Tigner, Jonathan
    One solution to minimizing plastic pollution is to improve reuse and recycling strategies. Recycling, however, is limited by the overall degradation of plastics being used. Photochemical or thermal driving forces facilitate the incorporation of oxygen into the backbone and chain cleavage; yet, current techniques for monitoring this plastic degradation fail to observe early stages of degradation, which is key for optimizing reusability. This research seeks to develop a cheap, reproducible, and nondestructive technique for monitoring degradation of polyethylene and polypropylene materials using Nile red as a fluorescent probe. Changes in Nile red’s fluorescence spectra were observed upon exposure to stained, aged polyethylene and polypropylene samples. As the surface hydrophobicity of the plastic decreases, Nile red’s fluorescence signal undergoes corresponding signal shift to longer wavelengths (lower energy). The trends seen in the fluorescent profile were related to more commonly used measurements of plastic degradation, namely carbonyl index from infrared spectroscopy and bulk crystallinity from calorimetry. Results demonstrate clear trends in fluorescence spectra shifts as related to the chemical and physical changes to the plastics, with trends dependent on polymer type but independent of polymer film thickness. The strength of this technique is divided into two defined fits of the fluorescence signal; one fit characterizes the degradation throughout the whole range of degradative oxidation and the other is tailored to provide insight into the early stages of degradation. Overall, this work establishes a characterization tool that assesses the extent of plastics’ degradation, which may ultimately impact our ability to recover plastics and minimize plastic waste.