Barrett

Barrett, The Honors College at Arizona State University proudly showcases the work of undergraduate honors students by sharing this collection exclusively with the ASU community.

Barrett accepts high performing, academically engaged undergraduate students and works with them in collaboration with all of the other academic units at Arizona State University. All Barrett students complete a thesis or creative project which is an opportunity to explore an intellectual interest and produce an original piece of scholarly research. The thesis or creative project is supervised and defended in front of a faculty committee. Students are able to engage with professors who are nationally recognized in their fields and committed to working with honors students. Completing a Barrett thesis or creative project is an opportunity for undergraduate honors students to contribute to the ASU academic community in a meaningful way.

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Dating Deep-Sea Pelagic Clays with Osmium Isotopes to Reconstruct Sources of Iron to the South Pacific Gyre over 90 Million Years

Description
Iron (Fe) scarcity limits biological productivity in high-nutrient low-chlorophyll (HNLC) ocean regions. Thus, the input, output and abundance of Fe in seawater likely played a critical role in shaping the development of modern marine ecosystems and perhaps even contributed to past changes in Earth’s climate. Three sources of Fe—wind-blown dust,…

Iron (Fe) scarcity limits biological productivity in high-nutrient low-chlorophyll (HNLC) ocean regions. Thus, the input, output and abundance of Fe in seawater likely played a critical role in shaping the development of modern marine ecosystems and perhaps even contributed to past changes in Earth’s climate. Three sources of Fe—wind-blown dust, hydrothermal activity, and sediment dissolution—carry distinct Fe isotopic fingerprints, and can therefore be used to track Fe source variability through time. However, establishing the timing of this source variability through Earth’s history remains challenging because the major depocenters for dissolved Fe in the ocean lack well-established chronologies. This is due to the fact that they are difficult to date with traditional techniques such as biostratigraphy and radiometric dating. Here, I develop age models for sediments collected from the International Drilling Program Expedition 329 by measuring the Os (osmium) isotopic composition of the hydrogenous portion of the clays. These extractions enable dating of the clays by aligning the Os isotope patterns observed in the clays to those in a reference curve with absolute age constraints through the Cenozoic. Our preliminary data enable future development of chronologies for three sediment cores from the high-latitude South Pacific and Southern Oceans, and demonstrate a wider utility of this method to establish age constraints on pelagic sediments worldwide. Moreover, the preliminary Os isotopic data provides a critical first step needed to examine the changes in Fe (iron) sources and cycling on millions of years timescales. Fe isotopic analysis was conducted at the same sites in the South Pacific and demonstrates that there are significant changes in the sources of Fe to the Southern Ocean over the last 90 Ma. These results lay the groundwork for the exploration of basin-scale sources to Fe source changes, which will have implications for understanding how biological productivity relates to Fe source variability over geological timescales.
ContributorsTegler, Logan Ashley (Author) / Anbar, Ariel (Thesis director) / Herckes, Pierre (Committee member) / Romaniello, Stephen (Committee member) / Department of English (Contributor) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
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Synthesis of Enzyme-Mimetic Catalysts

Description
The synthesis of the bis(2-diphenylphosphinoethyl)amine chelating ligand (1) was a crucial component in the preparation of non-canonical amino acids (NCAAs) throughout the project. Studies in this project indicated the need to isolate the ligand from its hydrochloride salt form seen in (1) which led to the synthesis of the brown…

The synthesis of the bis(2-diphenylphosphinoethyl)amine chelating ligand (1) was a crucial component in the preparation of non-canonical amino acids (NCAAs) throughout the project. Studies in this project indicated the need to isolate the ligand from its hydrochloride salt form seen in (1) which led to the synthesis of the brown oil, (Ph2PCH2CH2)2NH, (2). The ligand features a phosphine-nitrogen-phosphine group that is not observed in existing NCAAs. Phosphine groups are rarely seen in existing NCAAs and avoided by biochemists because they tend to oxidize before metal addition. In this project, (1) was used in a 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU) mediated method and palladium-catalyzed method to tether an amino acid to the nitrogen atom of the ligand framework. Both methods were monitored through the use of Nuclear Magnetic Resonance (NMR) spectroscopy. While the palladium catalyzed method exhibited little to no coupling, the 31P NMR spectrum obtained for the HATU mediated method did reveal that some coupling had occurred. The unsuccessful attempts to tether an amino acid to (1) led to the hypothesis that the phosphine groups were interfering with the palladium catalyst during the cross-coupling reaction. In an effort to test this hypothesis, (2) was reacted with the dimer, [Rh(nbd)Cl]2, to coordinate the rhodium metal to the free phosphorous arms and the nitrogen atom of the isolated PNP ligand. The PNP-based metal complex was used in the palladium catalyzed method, but cross-coupling was not observed. The new PNP-based metal complex was investigated to demonstrate that it exhibits moisture and air stability.
ContributorsManjarrez, Yvonne (Author) / Trovitch, Ryan (Thesis director) / Stephanopoulos, Nicholas (Committee member) / Herckes, Pierre (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05

Transition Metal Catalyzed Depolymerization of Polyethylene Terephthalate and Synthesis of a Novel Redox-Active Ligand

Description

Post-consumer plastic and polymer waste accumulation in recent years continues to become more of a problem. One of the common polymers that has become ubiquitous to modern life is polyethylene terephthalate, a polymer that makes up 6.2% of all polymers produced and only 39% of which is recycled in the…

Post-consumer plastic and polymer waste accumulation in recent years continues to become more of a problem. One of the common polymers that has become ubiquitous to modern life is polyethylene terephthalate, a polymer that makes up 6.2% of all polymers produced and only 39% of which is recycled in the US annually.1,5 In this study a new catalyst was for the methanolysis of PET and compared to a common organic base, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), that has been used in academia and industry for the depolymerization of PET. In this study it was concluded that yttrium (III) acetylacetonate hydrate was a more active catalyst for the methanolysis of PET at 120 °C in comparison to TBD. It was also determined that there is no co-catalytic effect between yttrium (III) acetylacetonate hydrate and TBD when used in combination. The use of manganese (II) acetate tetrahydrate was also explored as a potential catalyst and was found to shown significant reactivity. However, it was concluded that the optimal conditions for PET methanolysis had not been reached and that further research into reaction times as well as co-solvents needs to be conducted. The synthesis of a novel o-phenylenediamine ligand functionalized with a labile phosphine substituent was also explored with the end goal of metalation and implementation in the methanolysis of PET. It has been assumed through nuclear magnetic resonance spectroscopy (NMR) characterization that the N,N’-(1,2-phenylenediamine)bis[3-(diphenylphosphanyl)-propanamide]-borane precursor was successfully synthesized and isolated. The subsequent deprotection of the N,N’-(1,2-phenylenediamine)bis[3-(diphenylphosphanyl)-propanamide]-borane complex was performed but has not been fully characterized. The 31P NMR does indicate a fully deprotected tertiary organophosphine. Through this work a detailed procedure for the ligand precursor has been laid out and developed so that the synthesis may now be scaled up, further characterized, metalated, and used to support catalysis.
ContributorsMarch, Elizabeth (Author) / Trovitch, Ryan (Thesis director) / Long, Timothy (Committee member) / Herckes, Pierre (Committee member) / Barrett, The Honors College (Contributor) / School of Molecular Sciences (Contributor)
Created2023-05