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Now showing 1 - 5 of 37
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    Synthesis and Characterization of Aluminum Complexes Implementing Redox-Active Nitroxide Bidentate Ligands
    (2022) Saleh, Omar; Graves, Christopher R.
    Aluminum is an abundant, sustainable, and non-toxic metal, which would be a great candidate to be used in redox and catalytic chemistry in lieu of the currently used heavy metals. However, aluminum can only exist over one stable oxidation state, which is a major obstacle in this pursuit. To tackle this issue, the Graves Lab has been focusing on incorporating redox active ligands into aluminum complexes. Nitroxide (NO-) is an exceptionally important functional group, as it can reversibly exist over three stable oxidation states. In this work, I synthesized and characterized neutral aluminum complexes, [(OMepyNO)AlMe2]2 (1b) and [(OMepyNO)AlMe2]AlMe3 (2b), with a redox-active pyridyl-based nitroxide ligand (OMepyNO-). These complexes were characterized using XRD crystallography, DFT, and 1H and 13C NMR. We also investigated the redox activity of those complexes using cyclic voltammetry. In addition to that, this project focuses on the reactivity of the dimeric aluminum complexes 1a and 1b with different group 13 metal trihalide Lewis acids (AlCl3, GaCl3, InCl3, GaBr3, AlI3). Those reactions resulted in the formation of novel cationic dinuclear aluminum complexes (3a, 3b, 4a, and 5a), which exhibited an intriguing ligand rearrangement. Herein, we report the synthesis and characterization of those novel complexes, as well as an investigation of their redox activity. We also discuss preliminary detail into the mechanism of the reaction that yields those cationic complexes.
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    Design and Application of Membrane Nanodiscs for Biophysical Studies of Influenza A Proteins
    (2022) Kyaw, Aye; Howard, Kathleen P.
    Membrane proteins play a range of important roles in biological systems, yet they are underrepresented in the data base of high-resolution structures of all proteins. There is intense interest in developing new methodologies for studying membrane proteins. An essential step to membrane protein method development is devising reliable membrane mimics in which to embed membrane proteins. The goal of this thesis was to develop and apply nanodisc membrane mimics to the study of an influenza A membrane protein called M2. Nanodiscs provide a lipid bilayer environment with access to both sides of the bilayer and are smaller than commonly used liposome model membranes whose size provides challenges for some biophysical methods. This thesis shows how the sample composition of M2 containing nanodiscs was optimized. Dynamic light scattering and size exclusion chromatography was used to characterize M2-nanodiscs. Electrophysiological and budding assays showed that M2 in liposomes were in a functionally relevant conformation. Extensive previous work has been done on studying M2 protein in spherical liposome using site-directed spin label electron paramagnetic resonance (SDSL-EPR). We carried out SDSL-EPR studies of M2-nanodiscs and compared them to published work on M2 in liposomes. Our EPR data is consistent with M2 protein in nanodiscs having a similar conformation, mobility and membrane topology as that seen in previously published M2-liposome work. Furthermore, we probed the ability of nanodiscs to allow for conformational exchange by comparing the impact of drug binding on M2-nanodiscs with M2-liposomes.
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    Exploring the kinetics and thermodynamics of O–H bond activation by tripodal tris(nitroxide) aluminum and gallium complexes
    (2022) Scott, Joseph S.; Graves, Christopher R.; Rablen, Paul R.
    Aluminum is one of earth’s most abundant and cheapest metals, and it is also nontoxic and environmentally friendly. This makes it an ideal candidate to be implemented in organometallic chemistry as a greener alternative to metal-based systems based on heavy and/or precious metals. One of the realms in which aluminum and other group 13 elements show promise is metal-ligand cooperative chemistry, which can afford transition metal-reminiscent small molecule activation chemistry. Our studies of organic ligands with nitroxide-functionalities within Al and Ga coordinative systems has led us to the discovery of tripodal tris(nitroxide) Al and Ga complexes with abilities to engage in metal-ligand cooperativity, including in their reaction with small molecule alcohol substrates. In an effort to better understand the mechanism of the O-H bond activation mechanism exhibited by these complexes, we report the results of various kinetics experiments that explore how alcohol O-H acidity (pKa) and metal center (Al, Ga) affect reaction rate, as well as an observable kinetic isotope effect. We also report the results of the screening of various alcohol substrates with these complexes, and find a strong correlation between general reactivity and alcohol acidity.
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    Synthesis and Characterization of α-diimine Complexes of Aluminum
    (2021) Raab, Judah B.; Graves, Christopher R.
    Conventional aluminum complexes are incapable of one- and two-electron redox chemistry. As a result, despite being the most abundant metal on Earth, aluminum is seldom used in redox catalysis—one of chemistry’s most impactful fields. We are motivated to break this barrier to provide a green alternative to the countless redox catalysts built around the toxic, mining-intensive platinum-group metals. To create aluminum complexes that do desirable redox chemistry, we coordinate redox-active α-diimine ligands to the metal center. These ligands are stable across multiple oxidation states, allowing for multi-electron redox chemistry for their aluminum complexes. This thesis will report the synthesis of several α-diimine complexes of aluminum, across various ligand substitution patterns and oxidation states. These complexes have been characterized by combinations of X-ray diffraction, multinuclear NMR spectroscopy, cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory. For our neutral-ligand compounds, we will report their catalytic activity for the epoxidation of cyclohexene by peracetic acid.
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    Kinetics Studies on Isomerization and Unimolecular Decay Processes of the Criegee Intermediate, Methacrolein (MACR) Oxide
    (2021) Lee, Hyun Kyung; Stephenson, Tom
    Alkenes are one of the major components of hydrocarbons in our atmosphere. One of the most common alkenes in our atmosphere is isoprene (2-methyl – 1,3 – butadiene). Currently, it is known that isoprene ozonolysis can lead to the production of Criegee intermediates CH2OO, methacrolein (MACR) oxide, and methyl vinyl ketone (MVK) oxide. In part, we were interested in studying one specific Criegee intermediate, MACR oxide. The competition between the isomerization reactions and the unimolecular reactions became the focus of our study. Rate constants for the relevant reactions were calculated by implementing RRKM theory and using Master Equation modeling to create a scheme for the system. The overall results show that the most favorable reaction of MACR oxide is the isomerization between the cis and trans conformations. Because the transition states between these conformations are relatively low compared to the other transition states in the reaction, the conversions are observed to happen much faster than the others. The next fastest reaction that takes place is the unimolecular decay reactions to the dioxiranes and the dioxole. The decay reactions involved barriers that were higher than the cis⇌trans conversion but still lower than the barrier between the anti⇌syn conversion. With dioxole being our most stable state, our main interest was if different conformers of MACR oxide will decay to this structure in an atmospherically relevant time frame. It was found that substantial fraction (80%) of MACR oxide cannot decompose to dioxole in the relevant time frame as the barrier for the conversion between anti and syn is too high. We saw that there was almost no anti⇌syn conversion in any of our calculations.