Theses and Dissertations at Montana State University (MSU)
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Item Catalysis with early and late transition metals: C-H activation at tantalocene hydrides and oxidative addition at palladium solvato complexes(Montana State University - Bozeman, College of Letters & Science, 2021) Rehbein, Steven Mark; Chairperson, Graduate Committee: Sharon Neufeldt; Matthew J. Kania and Sharon R. Neufeldt were co-authors of the article, 'Experimental and computational evaluation of tantalocene hydrides for C-H activation of arenes' in the journal 'Organometallics' which is contained within this dissertation.; Steven M. Rehbein and Sharon R. Neufeldt were co-authors of the article, 'Solvent coordination to palladium can invert the selectivity of oxidative addition' in the journal 'Organometallics' which is contained within this dissertation.Herein we present our work on transition metal catalysis using metals from two sides of the periodic table: C-H activation catalyzed by early transition metals and cross-couplings catalyzed by late transition metals. In the first part, a synergistic experimental and computational approach was employed to investigate the possibility of extending the reactivity of bent tantalocene hydrides beyond aromatic C-H activation to enable activation of aliphatic substrates. In situ monitoring of the characteristic 1 H NMR metal hydride signals in the reaction of Cp 2TaH 3 and related complexes with deuterated aromatic substrates allowed for the evaluation of reaction kinetics of catalyst decomposition, H/D exchange, and off-cycle reactions. The insight gained from in situ reaction monitoring with aromatic substrates, combined with computational analyses, allowed for the extension of this chemistry to intra- and intermolecular aliphatic C-H activation. This work represents the first example of aliphatic C-H activation by homogeneous tantalum hydrides. In the second part, we provide compelling evidence that solvent coordination to palladium during oxidative addition of chloroaryl triflates can result in an inversion of chemoselectivity of this step. Previous investigations attributed a solvent-dependent switch in chemoselectivity to the propensity of polar solvents to stabilize anionic transition states of the type [Pd(P t Bu 3)(X)]- (X = anionic ligand). However, our detailed investigations show that solvent polarity alone is not a sufficient predictor of selectivity. Instead, solvent coordinating ability is selectivity-determining, with polar coordinating and polar noncoordinating solvents giving differing selectivity, even in the absence of anionic ligands 'X'. A solvent-coordinated bisligated transition state of the type Pd(P t Bu 3)(solvent) is implicated by density functional theory calculations. This work provides a new mechanistic framework for selectivity control during oxidative addition.Item The effects of atomic oxygen on silicon-carbon systems in extreme environments(Montana State University - Bozeman, College of Letters & Science, 2021) Chen, David Zuyu; Chairperson, Graduate Committee: Timothy Minton; Chenbiao Xu, Vanessa J. Murray and Timothy K. Minton were co-authors of the article, 'Oxidation of silicon carbide through the passive-to-active transition' submitted to the journal 'The journal of chemical physics' which is contained within this dissertation.; Chenbiao Xu and Timothy K. Minton were co-authors of the article, 'Effect of atomic oxygen on CV-1144-0 and RTV-560 silicones' submitted to the journal 'Acta astronautica' which is contained within this dissertation.; Chenbiao Xu and Timothy K. Minton were co-authors of the article, 'Effect of silicone coating on atomic oxygen reactivity with fiberform and phenolic impregnated carbon ablator' submitted to the journal 'Journal of spacecraft and rockets' which is contained within this dissertation.Vehicles traveling at hypersonic speeds require thermal protection systems (TPSs) that can withstand the extreme temperatures and reactive atomic oxygen species present in these environments. Ultra-high temperature ceramics are candidate TPSs, and many of them contain silicon carbide, allowing them to resist chemical attack by forming a protective oxide-containing layer, called passive oxidation. At very high temperatures, however, the layer will decompose, subjecting the material to ablation from reaction with O-atoms, called active oxidation, through a process called the passive-to-active oxidation transition (PAT). We have conducted molecular beam-surface scattering experiments to investigate the interactions of O-atoms with SiC at high temperatures, which revealed that with a lower fluence of O-atoms above the PAT, the SiC surface undergoes graphitization, while a sufficiently higher fluence of O-atoms promotes active oxidation. Analysis of the oxide layer decomposition revealed a decomposition process that initiated at the oxide-SiC interface. These insights will be useful for the development of more accurate predictive models, but they also aided understanding of the ablation of silicone-coated heat shields for atmospheric entry applications. For these applications, phenolic impregnated carbon ablator (PICA), a material composed of a carbon fiber network (FiberForm) and a resole phenolic resin stable against high heat convection and conduction, is used. Silicone is sprayed onto PICA to reduce dust, but the silicone can also form an oxide layer, which, like on SiC, will resist O-atom attack until it decomposes at very high temperatures, exposing the underlying material to reactive O-atoms. We conducted additional experiments in which a beam of atomic oxygen was directed at silicone-coated and uncoated samples of PICA as well as FiberForm, which revealed high nonreactive O-atom product scattering when the oxide layer was present, while with the decomposition of the oxide, product scattering resembled O-atom scattering from the underlying substrate. Additional studies probed the oxidation layer that is formed on pure silicone during O-atom bombardment, which revealed a three orders of magnitude reduction in erosion yield compared to that of Kapton H, a polyimide. This new data on PICA and FiberForm has been provided to NASA Ames for their development of an ablation model.Item Enzymatic strategies for controlling and harnessing the oxidative power of O 2(Montana State University - Bozeman, College of Letters & Science, 2018) Machovina, Melodie M.; Chairperson, Graduate Committee: Jennifer DuBois; Robert J. Usselman and Jennifer L. DuBois were co-authors of the article, 'Monoxygenase substrates mimic flavin to catalyze cofactorless oxygenations' in the journal 'Journal of biological chemistry' which is contained within this dissertation.; Emerald S. Ellis, Thomas J. Carney, Fikile R. Brushett and Jennifer L. DuBois were co-authors of the article, 'Understanding how a cofactor-free protein environment lowers the barrier to O 2 reactivity' in the journal 'Journal of biological chemistry' which is contained within this dissertation.; Sam J. B. Mallinson, Rodrigo L. Silveira, Marc Garcia-Borras, Nathan Gallup were authors and Christopher W. Johnson, Mark D. Allen, Munir S. Skaf, Michael F. Crowley, Ellen L. Neidle, Kendall N. Houk, Gregg T. Beckham, Jennifer L. DuBois and John E. McGeehan were co-authors of the article, 'A promiscuous cytochrome P450 aromatic O-demethylase for lignin bioconversion' in the journal 'Nature Communications' which is contained within this dissertation.; Sam J.B. Mallinson was an author and Brandon C. Knott, Marc Garcia-Borras, Alexander W. Meyers, Lintao Bu, Japheth Gado, April Oliver, Graham P. Schmidt, J. Hinchen, Michael F. Crowley, Christopher W. Johnson, Ellen L. Neidle, Christina M. Payne, Gregg T. Beckham, Kendall N. Houk, John E. McGeehan and Jennifer L. DuBois were co-authors of the article, 'Enabling microbial syringol conversion through structure-guided protein engineering' submitted to the journal 'PNAS' which is contained within this dissertation.; Dissertation contains one article of which Melodie M. Machovina is not the main author.Dioxygen, one of Nature's most powerful oxidants, is essential for countless biological reactions. To harness this oxidant's power while minimizing toxicity, enzymes evolved to interact with O 2, activate it, and poise it for catalysis with substrates. This dissertation explores how two very different enzyme families, monooxygenases and a new class of cytochrome P450s, utilize this powerful oxidant. Previously, it was thought that cofactors are essential for O 2 activation; however, a subset of O 2-utilizing enzymes that catalyze direct reactions between substrate and O 2 was recently discovered, including nogalamycin monoxygenase (NMO). To probe how the protein environment affects thermodynamic and kinetic barriers of O 2 activation, we used a suite of techniques, including: UV/vis (transient and conventional) and electron paramagnetic resonance spectroscopies, O 2 consumption, high-performance liquid chromatography (HPLC), and cyclic voltammetry. Here, we provide evidence that the NMO mechanism has similar characteristics to that in flavoenzymes; in NMO, the substrate, acting in lieu of flavin, donates an electron to O 2, activating it to superoxide with the protein environment facilitating this by lowering the reorganization energy. The last half of this dissertation describes the discovery and engineering of a new class of cytochrome P450 enzymes that employ heme-iron oxygen activation to demethylate key lignin degradation products, forming central carbon intermediates that are precursors for bioplastics. The P450 GcoAB, comprised of the oxidase GcoA and the reductase GcoB, is efficient at demethylating G-lignin, but shows poor reactivity towards S-lignin. Using a structure-guided mutagenesis approach, we generated a variant, F169A GcoA, that is more efficient than wild-type at demethylating G-lignin and the only enzyme that efficiently degrades S-lignin. We characterized this variant, and the wildtype enzyme, using biochemical (UV/vis spectroscopy, HPLC), structural (X-ray crystallography), and computational (Molecular Dynamics and Density Functional Theory). Currently, we are testing the in vitro efficiency of additional variants evolved using a directed evolution approach. The results presented in the following chapters explore the mechanisms of several enzymes. Understanding how O2 is activated and utilized across diverse enzymatic systems provides valuable knowledge that can aid in future design and engineering of systems that use this 'green' oxidant, particularly for large-scale industrial applications.Item Delineating the determinants of carboxylation in 2-ketopropyl coenzyme M oxidoreductase/carboxylase: a unique CO 2-fixing flavoenzyme(Montana State University - Bozeman, College of Letters & Science, 2018) Prussia, Gregory Andrew; Chairperson, Graduate Committee: John W. Peters; George H. Gauss, Florence Mus, Leah Conner, Jennifer L. DuBois and John W. Peters were co-authors of the article, 'Substitution of a conserved catalytic dyad causes loss of carboxylation in 2-KPCC' in the journal 'Federation of European Biochemical Societies letters' which is contained within this dissertation.; Jennifer L. DuBois and John W. Peters were co-authors of the article, 'A role for hisitidine 506 in carboxylate stabilization of 2-ketopropyl coenyzme M oxidoreductase/carboxylase' which is contained within this dissertation.; Gregory Andrew Prussia is not the main author of an article which is contained in this dissertation.Global CO 2-emissions are continuously rising, accelerating the impact of associated environmental processes such as climate change, deforestation, and ocean acidification. As a consequence, there is great interest in processes that can mitigate the increase in anthropogenic CO 2. The biological incorporation of a CO 2 molecule into an organic substrate is catalyzed by enzymes known as carboxylases. Although carboxylases employ diverse CO 2-fixing mechanisms and play broad physiological roles in Nature, they follow three general paradigms: 1). The formation of a reactive ene-intermediate nucleophile. 2). Protection of this reactive nucleophile from potential competing electrophiles (other than CO 2) by excluding solvent from the active site. 3). Electrostatic complementation of the negatively-charged carboxylation intermediate and product. 2-ketopropyl coenzyme M oxidoredutase/carboxylase (2-KPCC) is the only known carboxylating member of the FAD-containing, NAD(P)H-dependent disulfide oxidoreductase (DSOR) enzymes. The members of this family catalyze redox reactions and several well-characterized members catalyze the reductive cleavage of disulfide substrate. 2-KPCC performs the reductive cleavage of a thioether bond and subsequently carboxylates it's intermediate. How 2-KPCC has integrated the paradigms of carboxylation using a scaffold purposed for reductive cleavage is unknown. In this work, the paradigms mentioned above are identified in 2-KPCC and the methods by which 2-KPCC integrates carboxylation chemistry with reductive cleavage are discussed. Essential to the redox chemistry catalyzed by many DSOR members is a conserved His-Glu catalytic dyad, which serves to stabilize the electronic interaction between the FAD cofactor and the redox-active cysteine pair in the reactive state. 2-KPCC has substituted the catalytic His and Glu with Phe and His, respectively. We show that the Phe substitution is critical for excluding protons (as competing electrophiles) from the active site and the downstream His substitution acts to stabilize the negative charge on the carboxylated product, acetoacetate. Individually, each substitution plays an essential role in carboxylation. We show through a detailed spectroscopic study that by substituting both catalytic dyad residues the protonated and electronic state of the redox-active cysteine pair and FAD cofactor are affected, altering the DSOR active site to accommodate the unique cleavage and CO 2-fixation reaction catalyzed by 2-KPCC. Thus, this research has furthered the understanding of how the prototypical reductive cleavage reactions catalyzed by DSOR enzymes can be coordinated with a carboxylation reaction by a mechanism analogous to that shared by established carboxylase enzymes.Item Gas-surface interactions with sp 2 carbon in extreme environments(Montana State University - Bozeman, College of Letters & Science, 2018) Murray, Vanessa Jean; Chairperson, Graduate Committee: Timothy Minton; Brooks C. Marshall, Philip J. Woodburn and Timothy K. Minton were co-authors of the article, 'Inelastic and reactive scattering dynamics of hyperthermal O and O 2 on hot vitreous carbon surfaces' in the journal 'Journal of physical chemistry C' which is contained within this thesis.; Eric J. Smoll Jr. and Timothy K Minton were co-authors of the article, 'Dynamics of graphite oxidation at high temperature' in the journal 'Journal of physical chemistry C' which is contained within this thesis.; Marcin D. Pilinski, Eric J. Smoll, Jr., Min Qian, Timothy K. Minton, Stojan M. Madzunkov and Murray R. Darrach were co-authors of the article, 'Gas-surface scattering dynamics applied to concentration of gases for mass spectrometry in tenuous atmospheres' in the journal 'Journal of physical chemistry C' which is contained within this thesis.; Neil A. Mehta is an author and Chenbiao Xu, Deborah A. Levin and Timothy K. Minton were co-authors of the article, 'Scattering dynamics of N 2 from highly oriented pyrolytic graphite' in the journal 'Journal of physical chemistry C' which is contained within this thesis.; Chenbiao Xu, Savio Poovatthingal and Timothy K. Minton were co-authors of the article, 'Scattering dynamics of nitromethane and methyl formate on HOPG' submitted to the journal 'Journal of physical chemistry C' which is contained within this thesis.Molecular beam scattering experiments can determine the relative importance of reactive and non-reactive processes that occur when a surface is bombarded with high energy atoms and molecules. The mechanisms by which these processes proceed are inferred by analyzing the angle-resolved flux and energy distributions of the scattered products. The studies presented in this thesis have been conducted with a crossed molecular beams machine reconfigured for surface scattering. Two molecular beam sources were used. One uses a laser detonation process to produce high translational energy O atoms in the ground electronic state, and the other uses a supersonic expansion to produce continuous beams of N 2, nitromethane, or methyl formate. In the first two studies presented in this thesis, the oxidation of dynamics vitreous carbon and highly oriented pyrolytic graphite (HOPG) held at surface temperatures in the range of 800 - 2300 K by O atoms with a translational energy of ~ 500 kJ mol -1 are presented. These two studies revealed that the reactivity is suppressed at high temperature because O atoms desorb from the surface before they react to form CO and CO 2. Even though the translational energy of the O atoms was high, the surface reactions proceeded primarily through reactions that occurred in thermal equilibrium with the surface. The third study focuses on the scattering dynamics of O, O 2, and Ar with the surfaces of a gold thin-film, SiO 2, and HOPG. The results of the experiments were used to evaluate the efficacy of a proposed gas concentrator. The strong forward scattering on the HOPG surface made it the most suitable surface for the gas concentrator. The fourth study examines the non-reactive scattering dynamics of N 2 with HOPG. At high surface temperature, the residence time of N 2 is too short for the molecule to fully accommodate to the surface. Thus, even if the molecule suffers multiple collisions with the surface, it will scatter into the vacuum before it can come into thermal equilibrium with the surface. The results have been used in conjunction with theoretical calculations by a collaborator to investigate the relationship between the potential energy surface and the scattering dynamics. In order determine the usefulness of an HOPG concentrator with complex molecules, the scattering dynamics of methyl formate and nitromethane on HOPG were studied. These molecules do not shatter upon impact with the surface and they both scatter strongly in the forward direction through direct and indirect mechanisms, suggesting that the proposed HOPG concentrator should perform as desired. In all studies described in this thesis, the fundamental gas-surface scattering dynamics were elucidated from molecular beam experiments, and these fundamental results have direct links to modeling the performance of hypersonic vehicles and designing a gas concentrator for mass spectrometry in tenuous atmospheres.Item Partitioning of reactive oxygen species via the re-oxidation of electron transfer flavoprotein(Montana State University - Bozeman, College of Letters & Science, 2019) Austvold, Chase Kennor; Chairperson, Graduate Committee: Edward DratzThe biology of Reactive Oxygen Species are poorly understood. Within a healthy cell, Reactive Oxygen Species behave as signaling molecules, although overproduction leads to oxidative damage. In order to understand when the overproduction of Reactive Oxygen Species takes place, or leads to oxidative damage, the elementary step of quantification becomes necessary. Electron Transfer Flavoprotein is a known Reactive Oxygen Species producing enzyme and was studied. Electron Transfer Flavoprotein is a key-player within the production of energy within the eukaryotic mitochondria. The redox nature of Electron Transfer Flavoprotein's catalytic cofactor, flavin adenine dinucleotide produced two types of ROS; the superoxide anion (O 2 °-) and hydrogen peroxide (H 2 O 2). Electron Transfer Flavoprotein produced roughly five-fold more O 2 °-compared to H 2 O 2 as the enzyme became oxidized. It has been put forward that the production of these two Reactive Oxygen Species is dictated by the formation of a radical pair between the flavin adenine dinucleotide of Electron Transfer Flavoprotein and molecular oxygen. Two types of radical pairs can be formed, either in a triplet or singlet state, and the rate in which these states occur can be influenced by a static magnetic field. Therefore, the effect of a magnetic field on these products was also studied. Upon the suppression of magnetic field strength, the production of H 2 O 2 decreased and a proportional increase of O 2 °-was observed.Item Some aspects of the oxidation of delta-3-carene, 3, 7, 7-trimethyl bicyclo- (4.1.0) hept-3-ene(Montana State University - Bozeman, College of Letters & Science, 1975) Lai, Ching-EItem Mechanistic studies on the chemical oxidation of substituted tetrahydrobenzofurans(Montana State University - Bozeman, College of Letters & Science, 1985) Manfredi, Kirk PaulItem Mechanistic studies on the oxidation of alkyl substituted tetrahydrobenzofurans with m-chloroperbenzoic acid(Montana State University - Bozeman, College of Letters & Science, 1983) Gingerich, Samuel BerylItem A study of the kinetics of the oxidation of maleic hydrazide by ferricyanide in basic aqueous solution \ Robert Baxter Miller.(Montana State University - Bozeman, College of Letters & Science, 1969) Miller, Robert Baxter