Matching Items (29)
Description
This dissertation examines two topics of emerging interest in the field of organic geochemistry. The topic of the first portion of the dissertation is cold organic geochemistry on Saturn's moon Titan. Titan has an atmosphere and surface that are rich in organic compounds. Liquid hydrocarbons exist on the surface, most famously as lakes. Photochemical reactions produce solid organics in Titan's atmosphere, and these materials settle onto the surface. At the surface, liquids can interact with solids, and geochemical processes can occur. To better understand these processes, I developed a thermodynamic model that can be used to calculate the solubilities of gases and solids in liquid hydrocarbons at cryogenic temperatures. The model was parameterized using experimental data, and provides a good fit to the data. Application of the model to Titan reveals that the equilibrium composition of surface liquids depends on the abundance of methane in the local atmosphere. The model also indicates that solid acetylene should be quite soluble in surface liquids, which implies that acetylene-rich rocks should be susceptible to chemical erosion, and acetylene evaporites may form on Titan. In the latter half of this dissertation, I focus on hot organic geochemistry below the surface of the Earth. Organic compounds are common in sediments. Burial of sediments leads to changes in physical and chemical conditions, promoting organic reactions. An important organic reaction in subsurface environments is decarboxylation, which generates hydrocarbons and carbon dioxide from simple organic acids. Fundamental knowledge about decarboxylation is required to better understand how the organic and inorganic compositions of sediments evolve in response to changing geochemical conditions. I performed experiments with the model compound phenylacetic acid to obtain information about mechanisms of decarboxylation in hydrothermal fluids. Patterns in rates of decarboxylation of substituted phenylacetic acids point to a mechanism that proceeds through a ring-protonated zwitterion of phenylacetic acid. In contrast, substituted sodium phenylacetates exhibit a different kinetic pattern, one that is consistent with the formation of the benzyl anion as an intermediate. Results from experiments with added hydrochloric acid or sodium hydroxide, and deuterated water agree with these interpretations. Thus, speciation dictates mechanism of decarboxylation.
ContributorsGlein, Christopher R (Author) / Shock, Everett L (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Zolotov, Mikhail Y (Committee member) / Williams, Lynda B (Committee member) / Gould, Ian R (Committee member) / Arizona State University (Publisher)
Created2012
Description
Throughout time, compounds from natural sources have provided humans with medicines, and recently become the structural inspiration for semisynthetic drugs. One arena that has benefited greatly from the use of these natural products is the discovery of novel antibacterial agents. Methicillin-resistant Staphylcoccus aureus (MRSA) continues to plague the United States as well as throughout the world, at least in part because of increasing antibiotic resistance. Therefore, scientists continue to scour natural products as potential leads, either directly or indirectly, for antibiotics to treat MRSA. The structure of the indole sesquiterpene, polyalthenol, was discovered in 1976 and recent work shows a 4µg/mL minimum inhibitory concentration (MIC) against a variety of strains of MRSA. Given the unique framework of this natural product and its biological activity against MRSA, the total synthesis becomes the next logical step. Presently a racemic synthesis has successfully afforded an indole ketone with the correct relative stereochemistry of polyalthenol, however, the completion of the total synthesis of polyalthenol presents several challenges. Herein, the work towards the synthesis is described in addition to the proposed completion of the synthesis.
ContributorsReichenberg, Erynn Wright (Author) / Madar, David J (Thesis advisor) / Skibo, Edward (Committee member) / Miller, William (Committee member) / Arizona State University (Publisher)
Created2012
Description
Combretastatin A-4 (CA-4) represents one of the most promising antineoplastic and cancer vascular targeting stilbenes that have been isolated from the South African bush willow, Combretum Caffrum Kuntze. In order to further explore the bioactivity of this molecule, a diiodo derivative of CA-4, as well as its phosphate prodrug, was synthesized and analyzed for its biological activity; although only a scale up synthesis of this compound was performed herein for ongoing analysis. In general, no increased specificity was noted for the human cancer cell lines. Antiangiogenic properties were similar to the untreated control. The diiodocombstatin was active against M. luteus, and its phosphate prodrugs were very active against N. gonorrhoeae. Combretastain A-2 is another biologically active stilbene isolated from Combretum Caffrum Kuntze. In an attempt to increase biological activity of this molecule both mono-iodo and diiodo derivatives have been partially synthesized. The initial step involving the iodination of piperonal utilizes a novel, cost effective and mild reaction. The iodo stilbenes were obtained via a Wittig reaction using phosphonium salts 25 and 27 along with 2,3-Bis-[tert-butyldimethylsiloxy]-4-methoxy benzaldehyde 29. Deprotection of the subsequent z-stilbenes, non-isolated mono-iodo stilbene and the diiodo 30 produced two synthetic objective z-stilbenes 16 and 17. Synthesis as well as biological analysis is ongoing.
ContributorsTrickey-Platt, Brindi Brooks (Author) / Pettit, George R. (Thesis advisor) / Moore, Ana (Committee member) / Skibo, Edward (Committee member) / Arizona State University (Publisher)
Created2011
Description
In many natural systems aqueous geochemical conditions dictate the reaction pathways of organic compounds. Geologic settings that span wide ranges in temperature, pressure, and composition vastly alter relative reaction rates and resulting organic abundances. The dependence of organic reactions on these variables contributes to planetary-scale nutrient cycling, and suggests that relative abundances of organic compounds can reveal information about inaccessible geologic environments, whether from the terrestrial subsurface, remote planetary settings, or even the distant past (if organic abundances are well preserved). Despite their relevance to planetary modeling and exploration, organic reactions remain poorly characterized under geochemically relevant conditions, especially in terms of their reaction kinetics, mechanisms, and equilibria.
In order to better understand organic transformations in natural systems, the reactivities of oxygen- and nitrogen-bearing organic functional groups were investigated under experimental hydrothermal conditions, at 250°C and 40 bar. The model compounds benzylamine and α-methylbenzylamine were used as analogs to environmentally relevant amines, ultimately elucidating two dominant deamination mechanisms for benzylamine, SN1 and SN2, and a single SN1 mechanism for deamination of α-methylbenzylamine. The presence of unimolecular and bimolecular mechanisms has implications for temperature dependent kinetics, indicating that Arrhenius rate extrapolation is currently unreliable for deamination.
Hydrothermal experiments with benzyl alcohol, benzylamine, dibenzylamine, or tribenzylamine as the starting material indicate that substitution reactions between these compounds (and others) are reversible and approach metastable equilibrium after 72 hours. These findings suggest that relative ratios of organic compounds capable of substitution reactions could be targeted as tracers of inaccessible geochemical conditions.
Metastable equilibria for organic reactions were investigated in a natural low-temperature serpentinizing continental system. Serpentinization is a water-rock reaction which generates hyperalkaline, reducing conditions. Thermodynamic calculations were performed for reactions between dissolved inorganic carbon and hydrogen to produce methane, formate, and acetate. Quantifying conditions that satisfy equilibrium for these reactions allows subsurface conditions to be predicted. These calculations also lead to hypotheses regarding active microbial processes during serpentinization.
In order to better understand organic transformations in natural systems, the reactivities of oxygen- and nitrogen-bearing organic functional groups were investigated under experimental hydrothermal conditions, at 250°C and 40 bar. The model compounds benzylamine and α-methylbenzylamine were used as analogs to environmentally relevant amines, ultimately elucidating two dominant deamination mechanisms for benzylamine, SN1 and SN2, and a single SN1 mechanism for deamination of α-methylbenzylamine. The presence of unimolecular and bimolecular mechanisms has implications for temperature dependent kinetics, indicating that Arrhenius rate extrapolation is currently unreliable for deamination.
Hydrothermal experiments with benzyl alcohol, benzylamine, dibenzylamine, or tribenzylamine as the starting material indicate that substitution reactions between these compounds (and others) are reversible and approach metastable equilibrium after 72 hours. These findings suggest that relative ratios of organic compounds capable of substitution reactions could be targeted as tracers of inaccessible geochemical conditions.
Metastable equilibria for organic reactions were investigated in a natural low-temperature serpentinizing continental system. Serpentinization is a water-rock reaction which generates hyperalkaline, reducing conditions. Thermodynamic calculations were performed for reactions between dissolved inorganic carbon and hydrogen to produce methane, formate, and acetate. Quantifying conditions that satisfy equilibrium for these reactions allows subsurface conditions to be predicted. These calculations also lead to hypotheses regarding active microbial processes during serpentinization.
ContributorsRobinson, Kirtland J (Author) / Shock, Everett L (Thesis advisor) / Herckes, Pierre (Committee member) / Hartnett, Hilairy E (Committee member) / Anbar, Ariel D (Committee member) / Arizona State University (Publisher)
Created2017
Description
Guided by cognitive, socio-cognitive, and socio-cultural learning theories, large-scale studies over multiple semesters, multiple instructors and at two different institutions have been performed in order to understand the factors that contribute to student performance in general organic chemistry. Students’ cognitive abilities were assessed in a new way based on a categorization of problem types in a standard organic chemistry curriculum. Problem types that required higher cognitive load were found to be more predictive of overall course performance. However, student performance on high cognitive load problems was different when compared in terms of non-cognitive factors, e.g. whether they were pre-health students or not. These results suggested that organic chemistry performance may be significantly influenced by non-cognitive factors. Students’ motivation and related self-regulation factors were then studied using an instrument specifically designed for general organic chemistry, the Organic Chemistry Motivation Survey. Of all the factors examined, self-efficacy was found to be the most significant predictor of performance. Socio-cultural factors were also studied using a newly developed instrument for measuring college students’ cultural and social capital, the Science Capital Questionnaire (SCQ). Of the different socio-cultural variables measured by the SCQ, students’ social connections in college were found to be most predictive of organic chemistry performance. Finally, cognitive and socio-cognitive variables were studied together in the context of gender differences in organic chemistry. Females were found to underperform in comparison to the males. This gap was found to be alarmingly large on the basis of final letter grade, in some semesters the percentage of males earning an A grade was twice as large as that for females. Spatial ability was not a factor that contributed to this difference, nor was the gender of the instructor. Instead, self-efficacy was found to be both significantly different between males and females, and also the factor that connected most strongly to course performance. It is suggested that sociocultural factors be the subject of further study in college science courses.
ContributorsAustin, Ara Cho (Author) / Gould, Ian R. (Thesis advisor) / Atkinson, Robert K. (Committee member) / Williams, Peter (Committee member) / Arizona State University (Publisher)
Created2018
Description
Minimally invasive endovascular embolization procedures decrease surgery time, speed up recovery, and provide the possibility for more comprehensive treatment of aneurysms, arteriovenous malformations (AVMs), and hypervascular tumors. Liquid embolic agents (LEAs) are preferred over mechanical embolic agents, such as coils, because they achieve homogeneous filling of aneurysms and more complex angioarchitectures. The gold standard of commercially available LEAs is dissolved in dimethyl sulfoxide (DMSO), which has been associated with vasospasm and angiotoxicity. The aim of this study was to investigate amino acid substitution in an enzyme-degradable side group of an N-isopropylacrylamide (NIPAAm) copolymer for the development of a LEA that would be delivered in water and degrade at the rate that tissue is regenerated. NIPAAm copolymers have a lower critical solution temperature (LCST) due to their amphiphilic nature. This property enables them to be delivered as liquids through a microcatheter below their LCST and to solidify in situ above the LCST, which would result in the successful selective occlusion of blood vessels. Therefore, in this work, a series of poly(NIPAAm-co-peptide) copolymers with hydrophobic side groups containing the Ala-Pro-Gly-Leu collagenase substrate peptide sequence were synthesized as in situ forming, injectable copolymers.. The Gly-Leu peptide bond in these polypeptides is cleaved by collagenase, converting the side group into the more hydrophilic Gly-Ala-Pro-Gly-COOH (GAPG-COOH), thus increasing the LCST of the hydrogel after enzyme degradation. Enzyme degradation property and moderate mechanical stability convinces the use of these copolymers as liquid embolic agents.
ContributorsRosas Gomez, Karime Jocelyn (Author) / Vernon, Brent (Thesis advisor) / Weaver, Jessica (Committee member) / Pal, Amrita (Committee member) / Arizona State University (Publisher)
Created2019
Description
Organic reactions in natural hydrothermal settings have relevance toward the deep carbon cycle, petroleum formation, the ecology of deep microbial communities, and potentially the origin of life. Many reaction pathways involving organic compounds under geochemically relevant hydrothermal conditions have now been characterized, but their mechanisms, in particular those involving mineral surface catalysis, are largely unknown. The overall goal of this work is to describe these mechanisms so that predictive models of reactivity can be developed and so that applications of these reactions beyond geochemistry can be explored. The focus of this dissertation is the mechanisms of hydrothermal dehydration and catalytic hydrogenation reactions. Kinetic and structure/activity relationships show that elimination occurs mainly by the E1 mechanism for simple alcohols via homogeneous catalysis. Stereochemical probes show that hydrogenation on nickel occurs on the metal surface. By combining dehydration with and catalytic reduction, effective deoxygenation of organic structures with various functional groups such as alkenes, polyols, ketones, and carboxylic acids can be accomplished under hydrothermal conditions, using either nickel or copper-zinc alloy. These geomimetic reactions can potentially be used in biomass reduction to generate useful fuels and other high value chemicals. Through the use of earth-abundant metal catalysts, and water as the solvent, the reactions presented in this dissertation are a green alternative to current biomass deoxygenation/reduction methods, which often use exotic, rare-metal catalysts, and organic solvents.
ContributorsBockisch, Christiana (Author) / Gould, Ian R (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Shock, Everett L (Committee member) / Arizona State University (Publisher)
Created2018
Description
Metalloporphyrins represent a class of molecular electrocatalysts for driving energy relevant half-reactions, including hydrogen evolution and carbon dioxide reduction. As electrocatalysts, they provide a strategy, and potential structural component, for linking renewable energy sources with the production of fuels and other value-added chemicals. In this work, porphyrins are used as structural motifs for exploring structure-function relationships in electrocatalysis and as molecular building blocks for assembling photoelectrochemical assemblies leveraging the light capture and conversion properties of a gallium phosphide (GaP) semiconductor. These concepts are further covered in Chapter 1. A direct one-step method to chemically graft metalloporphyrins to GaP surfaces is described in Chapter 2. Structural characterization of the hybrid assemblies is achieved using surface-sensitive spectroscopic methods, and functional performance for photoinduced hydrogen production is demonstrated via three-electrode electrochemical measurement combined with product analysis using gas chromatography. In Chapter 3, preparation of a novel cobalt porphyrin modified with 3-fluorophenyl groups at all four meso-positions of the porphyrin ring and a single 4-vinylphenyl surface attachment group at one of the β-positions is described. Electrochemical measurements show the 3-fluorophenyl groups perturb the reduction potentials of the complex to more positive values as compared to non-fluorinated analogs, illustrating synthetic control over the redox properties of the catalysts. The use of grazing angle attenuated total reflectance Fourier transform infrared spectroscopy to characterize chemically modified GaP surfaces containing grafted cobalt fluoro-porphyrins is presented in Chapter 4. In these hybrid constructs, porphyrin surface attachment is achieved using either a two-step method involving coordination of cobalt fluoro-porphyrin metal centers to nitrogen sites on an initially applied thin-film polypyridyl surface coating, or via a direct modification strategy using a cobalt fluoro-porphyrin precursor bearing a covalently bonded 4- vinylphenyl surface attachment group. Finally, Chapter 5 describes binuclear copper porphyrins in which two copper porphyrin macrocycles are doubly fused at the meso-β positions are shown to be active electrocatalysts for the hydrogen evolution reaction. The enhancement in catalytic performance over analogous non-fused copper porphyrins indicates extended macrocycles provide an advantageous structural motif and design element for preparing electrocatalysts that activate small molecules of consequence to renewable energy.
ContributorsKhusnutdinova, Diana (Author) / Moore, Gary F. (Thesis advisor) / Moore, Ana L. (Committee member) / Petuskey, William T. (Committee member) / Arizona State University (Publisher)
Created2019
Description
The search for highly active, inexpensive, and earth abundant replacements for existing transition metal catalysts is ongoing. Our group has utilized several redox non-innocent ligands that feature flexible arms with donor substituents. These ligands allow for coordinative flexibility about the metal centre, while the redox non-innocent core helps to overcome the one electron chemistry that is prevalent in first row transition metals. This dissertation focuses on the use of Ph2PPrDI, which can adopt a κ4-configuration when bound to a metal. One reaction that is industrially useful is hydrosilylation, which allows for the preparation of silicones that are useful in the lubrication, adhesive, and cosmetics industries. Typically, this reaction relies on highly active, platinum-based catalysts. However, the high cost of this metal has inspired the search for base metal replacements. In Chapter One, an overview of existing alkene and carbonyl hydrosilylation catalysts is presented. Chapter Two focuses on exploring the reactivity of (Ph2PPrDI)Ni towards carbonyl hydrosilylation, as well as the development of the 2nd generation catalysts, (iPr2PPrDI)Ni and (tBu2PPrDI)Ni. Chapter Three presents a new C-O bond hydrosilylation reaction for the formation of silyl esters. It was found the (Ph2PPrDI)Ni is the most active catalyst in the literature for this transformation, with turnover frequencies of up to 900 h-1. Chapter Four explores the activity and selectivity of (Ph2PPrDI)Ni for alkene hydrosilylation, including the first large scope of gem-olefins for a nickel-based catalyst. Chapter Five explores the chemistry of (Ph2PPrDI)CoH, first through electronic structure determinations and crystallography, followed by an investigation of its reactivity towards alkyne hydroboration and nitrile dihydroboration. (Ph2PPrDI)CoH is the first reported cobalt nitrile dihydroboration catalyst.
ContributorsRock, Christopher L (Author) / Trovitch, Ryan J (Thesis advisor) / Kouvetakis, John (Committee member) / Pettit, George R. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Non-photochemical quenching (NPQ) is a photoprotective regulatory mechanism essential to the robustness of the photosynthetic apparatus of green plants. Energy flow within the low-light adapted reaction centers is dynamically optimized to match the continuously fluctuating light conditions found in nature. Activated by compartmentalized decreases in pH resulting from photosynthetic activity during periods of elevated photon flux, NPQ induces rapid thermal dissipation of excess excitation energy that would otherwise overwhelm the apparatus’s ability to consume it. Consequently, the frequency of charge separation decreases and the formation of potentially deleterious, high-energy intermediates slows, thereby reducing the threat of photodamage by disallowing their accumulation. Herein is described the synthesis and photophysical analysis of a molecular triad that mimics the effects of NPQ on charge separation within the photosynthetic reaction centers. Steady-state absorption and emission, time-resolved fluorescence, and transient absorption spectroscopies were used to demonstrate reversible quenching of the first singlet excited state affecting the quantum yield of charge separation by approximately one order of magnitude. As in the natural system, the populations of unquenched and quenched states and, therefore, the overall yields of charge separation were found to be dependent upon acid concentration.
ContributorsPahk, Ian (Author) / Gust, Devens (Thesis advisor) / Gould, Ian (Committee member) / Mujica, Vladimiro (Committee member) / Arizona State University (Publisher)
Created2015