Thesis (Ph. D.)--Syracuse University, 2008. / "Publication number AAT 3333562."

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6790. Adviser: Thomas B. Rauchfuss. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2008. / Title from PDF t.p. (viewed Dec. 9, 2008). Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 2999. Adviser: P.A. Evans.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3793. Adviser: Yi Lu. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

<p> This dissertation describes the study of transition metal complexes in relation to two types of oxidation catalysis, namely dehydrogenation and water oxidation.</p><p> Chapters 1 and 2 explore dehydrogenation catalysis as a means of glycerol valorization. Glycerol is the major byproduct of biodiesel production (~10%), and there is thus intense interest in developing methods to convert this waste glycerol to more valuable products. One such product is lactic acid, which is commonly used in the food and detergent industries, and is a platform chemical that is seeing increasing demand. All prior methods for convening glycerol to lactic acid employed heterogeneous catalysts, which often require high temperatures and give generally poor selectivity and catalytic activity. In this work, I describe our study of homogeneous catalysts for glycerol conversion to lactic acid. Our Ir bis-NHC (NHC = N-heterocyclic carbene) precatalysts are superior to the previous systems in terms of selectivity and activity, and function in neat glycerol without the need for a co-solvent. These complexes can convert samples of crude glycerol from the biodiesel industry without the need for prior purification, suggesting their possible industrial application. Additionally, hydrogen is produced as a valuable byproduct. Chapter 2, carried out in collaboration with Professor Nilay Hazari (Yale), describes the study of catalysts based on non-precious metals for this reaction. A family of Fe precatalysts with bifunctional PNP pincer ligands give excellent selectivity and activity, and represent the first examples of homogeneous base-metal catalysts for glycerol conversion to lactic acid. In studies of Ir species formed from our Ir bis-NHC precatalysts during glycerol dehydrogenation, we isolated a series of unusual NHC-rich Ir polyhydride clusters (Chapter 3). These compounds are unprecedented in terms of their high NHC content, and were fully characterized using a variety of methods.</p><p> Chapters 4 and 5, carried out in collaboration with Shashi Sinha and Dimitar Shopov, joint BrudvigCrabtree students, describe the study of model complexes related to resting states and high oxidation state intermediates in water oxidation catalysis. Water oxidation has garnered intense interest because of its potential application in the production of solar fuels, but effective catalysts are needed to carry out the reaction with low overpotentials. Our group previously found that upon oxidative activation, the Cp*Ir(pyalk)OH precatalyst (pyalk = 2-pyridyl-2-propanolate) generates one of the most active and robust water oxidation catalysts reported to date. Previous spectroscopic characterization and DFT studies revealed that the Cp* ligand is oxidatively degraded, and the catalyst resting state likely consists of a mixture of related species with a (pyalk)₂Ir^IV-O-Ir^IV(pyalk) core. However, these species completely resisted purification and crystallization by standard methods. Therefore, we developed a protocol to more selectively prepare related CI(pyalk)₂Ir^IV-O-Ir^IV(pyalk)₂CI complexes, which can be isolated and crystallographically characterized. These complexes are unusual examples of well-defined Ir(IV,IV) mono-&mu;-oxo dimers, and are stable under ambient conditions, in contrast to previous examples of Ir(IV,IV) mono-&mu;-oxo dimers containing organometallic ligands. Our study of these complexes sheds light on the resting state of our Ir water oxidation catalyst, and opens the door to future development of well-defined Ir-oxo dimers for water oxidation catalysis.</p><p> In a related study (Chapter 5), we use techniques and insights that build on our Ir oxo-dimer study to synthesize unprecedented Ir(V) coordination complexes with organic ligands. Study of such well-defined high oxidation state complexes is of interest in relation to oxidation catalysis, where Ir(V) species have been proposed as key intermediates. In order to access Ir(V), we developed the ligand dpyp, an N,O,Odonor analogue of pyalk. Importantly, dpyp forms coordination complexes with four coplanar alkoxogroups, an arrangement that favors attainment of high oxidation states based on our previous work. Indeed, oxidation of Ir^IV(dpyp)₂gives Ir^V(dpyp)_⁺2+, which was fully characterized including by X-ray crystallography and DFT methods.</p><p>

<p> Two series of novel phosphors based on parent compound CaYGaO₄ were developed. The first series was created by doping trivalent europium into the yttrium position in percentages ranging from 0.50&ndash;20. The samples exhibit one strong emission in the orange region of the visible spectrum one medium emission in the yellow and several weak emissions in the green and red. This series preforms well in elevated temperatures, which makes them good candidates for solid state lighting purposes. The second series was created by doping terbium into the yttrium position at percentages ranging from 0.50&ndash;20. This latter series exhibits two strong emissions in the green portion of the visible spectrum, and a few weak ones in the red. These, however have high thermal quenching which makes them not suitable for solid state lighting purposes. It should be noted that using just this host lattice alone, there are still many more possibilities for the development of other phosphors, and this work is only the very beginning.</p><p>

<p> This thesis encompasses a suite of coordination-driven self-assembled porphyrin prisms differing in the molecular clips linking two porphyrin faces in a cofacial arrangement. The goal of this work was to apply the facile synthesis methods to rationally design cofacial catalysts and analyze the activity towards the oxygen reduction reaction (ORR). Specifically, we have explored how different molecular clips affected the prisms&rsquo; activity, selectivity, overpotential, and kinetics. High selectivity towards H₂O and low overpotential are key requirements of an oxygen reduction catalyst for applications in fuel cells. </p><p> We have demonstrated the first coordination-driven self-assembled porphyrin catalyst (<b>Benzo-Co</b>) used for small molecule activation, specifically ORR. The first report includes the characterization, along with catalytic chemical and electrochemical reduction studies. The selectivity and rate constants of this catalyst (H₂O vs. H₂O₂) were compared to the mononuclear <b>CoTPyP</b>. After these findings, the goal was to optimize the catalyst using alternative bridging ligands in the molecular clips that held the porphyrin subunits in a cofacial offset and analyze the selectivity towards H₂O. We hypothesized that if the metal centers of <b>CoTPyP</b> were held at a shorter distance, the selectivity of the catalyst would improve. The distance of the metals is critical to the O&ndash;O bond cleavage step. If there is not a secondary metal to interact with O₂, for example mononuclear <b>CoTPyP</b>, O&ndash;O cannot be cleaved. If the M&ndash;M distance is too large, the secondary metal may not interact with O₂ to participate in the bond cleavage step. The catalyst series were immobilized on the electrode surface and the selectivities of <b>Ox-Co</b>, <b>Oxa-Co</b>, and <b>Benzo-Co</b> prisms towards H₂O₂ as determined by rotating ring-disk electrode studies. Rotating disk electrode studies showed Levich current responses. Kouteck&yacute;-Levich and Tafel analyses, were used to obtain kinetic information and estimation of rate constants. This thesis highlights how coordination-driven self-assembly can be used to address difficult multi-electron multi-proton transformations, like oxygen reduction, using cofacial polynuclear catalyst. </p><p>

High temperature anhydrous proton conducting polymer and optoelectronic based organic compounds are promising materials for use in renewable energy applications. Fundamental understanding of better proton and charge transport properties are required to achieve desirable alternative energy materials. In this thesis, we focus on molecular design, synthetic approaches, and understanding structure-property relationships to improved proton conductivity and optoelectronic properties. In proton conducting polymers, we tethered N-heterocycles (imidazole and benzotriazole) as proton carrier in two polymer systems; dendritic-linear block copolymers and helical polymers. Dendritic-linear block copolymers functionalized with imidazole and benzotriazole are designed to self-organize into nano scale assemblies that would increase local charge density and enhance proton conductivity. We found that microphase separation within disordered structure of imidazole-based block copolymers could relate to the higher conductivity compared to benzotriazole-based block copolymers that do not have phase separation in the same length scale. In the second system, we have focused on effect of chirality on proton conductivity in helical polymer. We functionalized L-histidine and histamine on poly(phenylacetylene) and poly(4-vinylbenzoate). Poly(phenylacetylene) is known as dynamic helical polymer while poly(4-vinylbenzoate) is a random polymer. Effects of backbone chirality, side chains and doping acids on proton conductivity are evaluated in this work. We found that a single handed conformation of poly(phenylacetylene) bearing L-histidine can enhanced proton conductivity compared to those of containing histamine. Whereas, vinyl backbone, poly (4-vinylbenzoate) bearing L-histidine exhibited lower conductivity due to a higher Tg of the polymer. Cyclopentadithiophene (CPDT) derivatives are often used as an active layer in optoelectronic devices. However, CPDT is known to have a low absorption at the lower energy band. To solve this issue, we proposed to change the conformation of heteroatom at the bridgehead. We incorporated ketone and imine functionalities at the bridgehead positions, anti and syn. We found that by changing heteroatom position to syn-position increased absorption intensity in the lower energy band. Incorporation of a ketone at anti-position provides good mobility of 0.003 cm2/Vs while, changing the ketone group at the syn-position significantly decrease charge mobility.

Oxygen homeostasis is essential to the life of aerobes, which is regulated in humans by Hypoxia Inducible Factor-1α (HIF-1α). Under hypoxic conditions, HIF-1α transactivates over a hundred genes related angiogenesis, erythropoiesis, etc. HIF-1α level and function is regulated by four HIF hydroxylase enzymes: three isoforms of prolyl hydroxylase domain (PHD1, PHD2 and PHD3) and factor inhibiting HIF-1α (FIH). PHD2 is the focus of this research. PHD2 is a non-heme Fe(II) 2-oxoglutarate dependent dioxygenase, which controls HIF-1α levels by hydroxylating two proline residues within the ODD domain of HIF-1α, then the hydroxylated prolines are recognized by pVHL, which targets HIF-1α for proteasomal degradation. Under hypoxic conditions PHD2 cannot hydroxylate HIF-1α and its level rises in cells. The aims of this research include understanding how PHD2 chooses its substrate, how the O2+ activation occurs, and how certain transition metals inhibit PHD2. Our results revealed that electrostatics play a role in substrate selectivity of PHD2 by provoking a change in the opening and closing rate of β2β3 loop for NODD and CODD substrates. Mutational studies of second coordination sphere residues combined with kinetic studies indicated that decarboxylation of 2OG is the slow step in the chemical mechanism. The removal of a hydrogen-bond by the Thr387→Ala mutation revealed a rate 15 times faster than WT-PHD2 by making O2 a better nucleophile. Our results indicate that this hydrogen bonding is essential for proper O2 activation. Previous reports show that certain metals increase HIF-1α levels by inhibiting PHD2. However there are conflicts about how this inhibition occurs, either through metal replacement from the active site or metals binding to a different site causing inhibition. Our competitive and non-competitive kinetic assays showed different inhibition profiles. Under competitive conditions Zn2+, Co2+, Mn2+, and Cu2+ can bind to the enzyme active site and lead to inhibition but under non-competitive conditions Zn2+, Co 2+, and Mn2+ partially inhibit PHD2 suggesting that these metals cannot displace the Fe2+ from the active site. XAS experiments with Zn2+ and Fe3+ indicate that Zn2+ binds to the surface of PHD2 in a six-coordinate manner composed of two Cys 201, 208, His205, Tyr197 and two water ligands.

Droplet-interface bilayers (DIBs) have been developed as a miniature model membrane system with distinct advantages over cell-based and other artificial membrane systems. This dissertation will describe a number of projects relating to DIB research, including: (i) the creation of new devices that allow the repeated addition and mixing of reagents to one side of a droplet-based membrane system; (ii) measurements of peptide and polymer mediated protein translocation across lipid bilayers; (iii) efforts to synthesize eukaryotic ion channels in DIBs; (iv) investigations on the asymmetric lipid dependence of the potassium channel KirBac1.1.