Theses and Dissertations - Department of Chemistry & Biochemistry

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Browsing Theses and Dissertations - Department of Chemistry & Biochemistry by Author "Bara, J. E."

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    Anionic polymerization of activated aziridines
    (University of Alabama Libraries, 2018) Mbarushimana, Pierre Canisius C.; Rupar, Paul A.; University of Alabama Tuscaloosa
    Polyethyleneimine, also referred to as polyaziridine, is a polymer that has a repeat unit of (-CH2CH2NH-). Due to its high amine density, PEI finds application in several domains including gene transfection, antimicrobial/antibacterial medicine, CO2 capture, thin film metal deposition, industrial wastewater treatments, and more. Commercially, PEI is obtained via the uncontrolled polymerization of aziridine and the cationic ring opening polymerization (CROP) of oxazolines. However, the available cationic polymerization techniques of aziridines are poorly controlled. In order to synthesize well-defined PEIs, recent literature approaches have used the anionic ring opening polymerization (AROP) of various N-substituted aziridines. The present research, done at The University of Alabama, has focused on the synthesis and AROP of N-substituted aziridines, without the substitution at the 2-position of the aziridine ring. The studied monomers include three tert-butylcarboxy-protected aziridine monomers, specifically tert-butyl aziridine-1-carboxylate, tert-butyl 2-methylaziridine-1-carboxylate, tert-butyl 2-decylaziridine, and six 1-(alkylsulfonylsulfonyl) aziridine monomers, i.e. 1-(methylsulfonyl)aziridine, 1-(toluenesulfonyl)aziridine, 1-(octylsulfonyl)aziridine, 1-(sec-butylsulfonyl)aziridine, 1-((2-nitrophenyl)sulfonyl)aziridine, and 1-((4-nitrophenyl)sulfonyl)aziridine. After characterization, the synthesized monomers were homopolymerized by AROP using various nucleophilic initiators. Except for BOCDecAz, all the synthesized monomers were successfully converted into the corresponding polymers. However, only short oligomers of the resulting homopolymers were formed, as high molecular weight polymer chains were insoluble. The synthesized polymers can potentially be used as precursor to pure linear polyamines A single sulfonyl aziridine, namely1-((ortho-nitrophenyl)sulfonyl)aziridine (oNsAz) was found to produce high molecular weight poly(oNsAz) that was soluble in DMF and DMSO. This is significant as it is the first example of a soluble poly(1-sulfonylaziridine) homopolymer; prior examples were limited to random copolymer. The deprotection of poly(oNsAz) was also attempted in effort to synthesize linear PEI. Although evidence was found for the formation of linear PEI, satisfactory purification of the linear PEI was not achievable.
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    Catalytic small molecule reduction using late transition metal complexes of carbon and nitrogen donor chelates
    (University of Alabama Libraries, 2017) Siek, Sopheavy; Papish, Elizabeth T.; University of Alabama Tuscaloosa
    Hydrogenation reactions can be used to store energy in chemical bonds, and if these reactions are reversible that energy can be released on demand. A new bidentate chelating ligand was designed and synthesized for this project, using an N-heterocyclic carbene ring bound directly to a pyridinol ring (NHC-pyOR). This new ligand was used to make iridium complexes that were studied as catalysts for the hydrogenation of CO2 and dehydrogenation of formic acid. For comparison, analogous bipy derived iridium and ruthenium complexes were also tested. In general, the NHC-pyOR complexes demonstrated modest activity, where hydroxyl-pyridines found in the bipy derived systems are more active for CO2 hydrogenation under basic conditions. However, the trends were quite different for formic acid dehydrogenation reaction which will be discussed in Chapter 2. Other ruthenium (II) and iridium (III) complexes of the NHC-pyOR ligand with difference counter anions from above complexes were also synthesized. The ruthenium complexes were tested for their ability to accelerate CO2 (de)hydrogenation, but our studies show that these complexes all undergo transformations in solution and thus they are not true catalysts, but rather pre-catalysts. The use of new tridentate pincer ligands derived from NHC and pyridinol is also described. A new ligand containing (NHC-pyOR-NHC) rings binding to a metal with the pyridinol derivative were synthesized. A series of metal complexes of the type LnM were synthesized (n = 1 and 2; M = Fe2+, Co3+, and Ru2+). Preliminary results of photocatalytic reduction of CO2 to CO show that ruthenium complexes are the most active catalysts followed by cobalt and iron, respectively. The activation of carbon dioxide and nitrite utilizing bio-inspired and proton responsive catalysts were also studied with tris(triazolyl)hydroborate (Ttz) complexes of zinc(II) and copper(II). For the biomimetic zinc complexes for CO2 activation, the synthetic result was found to be greatly depend on the steric bulk of Ttz ligand which will be discussed in detail in Chapter 6. Moreover, the electrochemical reduction of Ttz-Cu(II) complexes in the presence and absence of a proton source shows processes that are relevant to enzymatic nitrite reduction which also will be studied in Chapter 7.
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    Computational studies of Lewis acidic gas adsorption to transition metal oxide nanoclusters and metal organic frameworks
    (University of Alabama Libraries, 2017) Flores, Luis Antonio; Dixon, David A.; University of Alabama Tuscaloosa
    Computational studies of the interaction of Lewis acid gases with metal oxide clusters and metal organic frameworks show how these gases interact with and degrade these materials at the molecular level. The calculations were done at the levels of density functional theory and correlated molecular orbital theory ((CCSD(T))). Group VI metal oxides clusters physisorb CO_2 near or below to 298K, and chemisorption of CO_2 by carbonate formation is an endothermic process. SO_2 physisorbs to Group VI clusters near or below 298K. Group VI metal oxides chemisorb SO_2 by forming sulfites with positive free energies of binding at 298K. The formation of sulfates is thermodynamically allowed for Cr clusters because Cr clusters have a higher reducibility than do Mo or W clusters. Group IV metal oxide clusters prefer chemisorption of both gases by carbonate and sulfite formation. Mo and W oxides may function as long lived sorbents for these gases, whereas Cr and Group IV metal oxides would degrade upon exposure to these gases as sulfites, sulfates, or carbonates form on their surfaces. Uranium trioxide clusters are predicted to chemisorb CO_2 by uranyl carbonate formation. The exposure of nuclear waste to CO_2 could cause uranium oxides to degrade leading to ground water contamination. The physisorption of the Lewis acid gases (CO_2, SO_2, H_2O, H_2S, CO, and NO_2) to M-MOF-2 systems (M = Zn, Cu, Co), was investigated. The MOFs are predicted to bind H_2O, H_2S, and SO_2 more strongly than the other gases. The binding energies are larger for Zn and Co than for Cu. Zn-MOF-2 clusters will degrade faster than Cu.
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    Synthesis, characterization and applications of metal nanoparticles supported on porous carbon
    (University of Alabama Libraries, 2017) Thambiliyagodage, Charitha Jayaruk; Bakker, Martin G.; University of Alabama Tuscaloosa
    Porous carbon incorporating metal nanoparticles has been synthesized by nanocasting. The main two methods of synthesis were used: the formation of nanoparticles during the carbonization of carbon, and the formation of nanoparticles by metal precursor infiltration and reduction on porous carbon. The catalytic activity of nickel nanoparticles incorporated onto hierarchically porous carbon monoliths for the reduction of p-nitrophenol was studied. p-Quinoimine was identified as the stable intermediate. Catalytic graphitization of monolithic hierarchically porous carbon by iron, cobalt and nickel nanoparticles was investigated. The catalytic graphitization of amorphous carbon increased with increasing pyrolysis temperature. Iron was capable of graphitizing carbon more effectively than cobalt and nickel, with cobalt being higher in activity than nickel. Oxygen and nitrogen rich mesoporous carbon were used to support gold nanoparticles and their catalytic activity was investigated for oxidation of benzyl alcohol in water. The catalysts showed significant catalytic activity, but loss of activity were found, resulting in decreasing conversion of benzyl alcohol on subsequent cycles.