Doctor of Philosophy, Case Western Reserve University, 2017, Pharmacology

Carotenoid cleavage oxygenases (CCOs) constitute a large group of evolutionarily conserved enzymes that metabolize a variety of carotenoid and apocarotenoid substrates, including retinoids, stilbenes, and related compounds. They typically catalyze the cleavage of non-aromatic double bonds by O2 to form aldehyde or ketone products. Their reaction products, denoted as apocarotenoids, serve critical functions in both prokaryotic and eukaryotic cells, including pigmentation, light harvesting, antioxidation, and cell signaling. An RPE65-subgroup of family members expressed in vertebrates catalyze a non-canonical reaction consisting of concerted ester cleavage and trans-cis isomerization of all-trans-retinyl esters, the product of which is essential for visual function. Our understanding of the biological functions of CCOs have progressed significantly in recent years. However, fundamental questions regarding to their catalytic mechanism remain largely unknown. In this project, we employed Synechocystis ACO that catalyzes canonical cleavage of carotenoids, and Novosphingobium NOV2 which catalyzes the cleavage of stilbene compound, through use of biochemical, structural, and biophysical methods to investigate the conserved catalytic mechanisms. In contrast to findings by others, our biochemical and crystallographic studies of ACO demonstrated that this prototypical CCO member is not an isomerase, as proposed previously. Rather, our results answered the important question of whether isomerase activity is a feature common to all CCOs. Our subsequent structure-directed mutagenesis studies of ACO then provided insights into substrate selectivity and regiospecificity regarding C-C cleavage during catalysis. Furthermore, our structure-function characterization of mutations of iron-coordination ligands demonstrated the biochemical and structural roles of the conserved 3-Glu, iron-outer sphere in metal coordination among CCOs. Finally, our isotope labeling studies of ACO and N (open full item for complete abstract)

Committee: Krzysztof Palczewski PhD (Advisor); Philip Kiser Pharm D, PhD (Advisor); Jason Mears PhD (Committee Chair); Johannes von Lintig PhD (Committee Member); Vivien Yee PhD (Committee Member); Matthias Buck PhD (Committee Member) Subjects: Biochemistry; Biology; Biomedical Research; Biophysics; Pharmacology

Master of Education, Cleveland State University, 2018, College of Education and Human Services

Purpose: The aim of this study was to examine the effects of multiple eccentric workloads generated by a powered rowing machine on muscle activation and metabolic cost. It was hypothesized that the increasing eccentric workloads would result in greater eccentric muscular contractions and increased metabolic cost. Methods: The research design of this study was experimental. Ten subjects (5 male, 5 female) were acquired through a convenience sample. The two exercise trials – full body row (FBR) and low body row (LBR) – each consisted of a 12-minute rowing session that included four stages. The eccentric workload, determined by average power (W), increased with each stage while the concentric workload remained constant throughout the entire test. Electromyography (EMG) data was collected through the Delsys EMG System for eight muscles (rectus femoris (RF), gastrocnemius (MG), tibialis anterior (TA), biceps brachii (BB), trapezius (LT), and latisimus dorsi (LD)). Metabolic data was collected through the COSMED K4b2, while heart rate (HR) was monitored through a Polar heart rate sensor. Results: Oxygen consumption significantly increased between stages 1 and 2 for both the FBR (p = .000(1)) and LBR (p = .004), with no significant increases revealed between the remaining stages. However, heart revealed to significantly increase with each stage (p < .05) for both configurations. Muscle activation also significantly increased in some muscle groups (RF, BB, LD) between stages on the FBR and some muscles (RF, BF, and TA) of the LBR, but not for the others. However, an overall increase in muscle activation was seen for all muscle groups through each increased eccentric workload. Conclusion: The powered rowing machine, through its robust controllable impedance, can be effective in creating a more complete, dynamic, and high intensity mode of exercise. This allows the apparatus to be applicable to exercise equipment needed for both rehabilitation and countermeasures to micrograv (open full item for complete abstract)

Committee: Kenneth Sparks Ph.D. (Committee Chair); Douglas Wajda Ph.D. (Committee Member); Emily Kullman Ph.D. (Committee Member); Kristine Still Ph.D. (Other) Subjects: Anatomy and Physiology; Biomechanics; Health; Mechanical Engineering; Physiology; Rehabilitation; Robotics

Master of Science, The Ohio State University, 2016, Chemistry

One of the major limitations of fuel cell is its sluggish kinetics for oxygen reduction reaction (ORR) occurring at the cathode and the expensive, but efficient Pt-based catalysts still remains the best catalyst for ORR. The first part of the thesis will discuss the activation energy measurement of ORR on polycrystalline Pt and PtCu/C in basic condition followed by the mechanism study via Tafel slope analysis. The results show that the activation energy of ORR at 0.8 VRHE is 23.2 ± 3.9 kJ/mol on polycrystalline Pt and 17.0 ± 3.1 kJ/mol on PtCu/C in alkaline media. The Ea obtained are relatively constant under different temperature (27 to 31 °C) and potential (0.7 to 0.95 VRHE) ranges. Tafel slope analysis gives ~ 120 mV/dec at high current density region (hcd) and ~ 60 mV/dec at low current density region (lcd) on both polycrystalline Pt and PtCu/C in alkaline media. The results indicate that the rate determining step of ORR on both polycrystalline Pt and PtCu/C is the first electron transfer step at hcd region and either the chemical dissociation step or the proton transfer step at lcd region. Also, the kinetics of Cu, Au and CuAu/C have also been studied and compared to the Pt-based catalysts. Results show that CuAu/C predominantly goes through a four-electron pathway to produce water and only produces ~10% peroxide as side product. When normalized to geometric area, the kinetic current of Au is 4-fold of CuAu/C and 120-fold of Cu. Among all five catalysts discussed in this thesis, PtCu/C has the highest ORR activity, showing that Pt-based catalyst still exhibits highest ORR activity compared to the other catalysts.

Committee: Anne Co (Advisor); Yiying Wu (Committee Member) Subjects: Chemistry

Doctor of Philosophy (PhD), Ohio University, 2013, Chemistry (Arts and Sciences)

A series of new environmentally and catalytically significant bioinorganic redox active pseudotetrahedral Ni(II) thiolate and Ni(II) phenolate (S=1, d8) complexes were synthesized and fully characterized as small molecular models in order to study the coordination mode of the Ni-S bond that is biologically significant in anaerobic and archaebacterial enzymes. During this characterization a unique Ni-S ligation mode was discovered and modulated by steric titration and details were further investigated. Nickel thiolate bond reactivity towards electrophilic alkylation with methyl iodide (MeI) is briefly discussed. A series of new Ni(II) phenolate complexes were synthesized and characterized as well as their O2 activation activity were investigated as a model for nickel substituted Copper Amine Oxidase (CAO). During this O2 reduction investigation, depending on the ligand bulk on the parent TpPh,Me/TpMe,Me ligand (where, TpPh,Me= hydrotris{3-phenyl-5-methyl pyrazol-1-yl}borate; TpMe,Me= hydrotris{3,5-dimethyl pyrazol-1-yl}borate) either a C-H or a C=C bond activation was observed. In addition, surprisingly where C-H activation was not possible, a CO2 capture activity was observed by a reactive intermediate nickel species.

Committee: Micahel Jensen PhD (Committee Chair); Jeffrey Rack PhD (Committee Co-Chair); Hugh Richardson PhD (Committee Member); Alexander Govorov PhD (Committee Member) Subjects: Biochemistry; Chemistry; Inorganic Chemistry; Organic Chemistry

PhD, University of Cincinnati, 2004, Arts and Sciences : Chemistry

Ni(II) complexes containing amidates and thiolates have been shown to react with O2 via irreversible ligand oxidation. We have constructed a series of Ni(II) complexes based on a tripodal amine bis(oxime) ligand framework. These complexes display oxygen reactivity upon deprotonation of the oximes without requiring irreversible ligand oxidation. This project investigated the reaction involving one of the complexes in the library, [Ni(TRISOXH 3 )(NO 3 )(H 2 O)](NO 3 )· (H 2 O), where TRISOXH 3 = (tris(1-propan-2-onyl oxime)amine). It was discovered that the reaction of this complex with molecular oxygen is contingent upon the presence of a source of hydrogen atoms. This two-hydrogen atom donor acts as a substrate. Several primary alcohols, including the relatively inert methanol, and amines were catalytically oxidized by this reaction. Spectroscopic analysis using a variety of techniques has demonstrated that reversible oxidation occurs on the oximate nitrogen to form an iminoxyl radical. Many of the other complexes in the series were also investigated to examine their electronic structure, their electrochemical properties, and their ability to oxidize methanol.

Committee: Dr. Michael Baldwin (Advisor) Subjects: Chemistry, Inorganic

PhD, University of Cincinnati, 2002, Arts and Sciences : Chemistry

Ligands containing two oxime donor groups with a variable third group in a tripodal amine motif have been designed and synthesized. Their Ni(II) complexes, and some Zn(II), Cu(II), and Fe(III) complexes, have been structurally and spectroscopically characterized. Deprotonation of the oxime groups gives Ni(II)-polyoximate complexes that form bis(N-O) oximate bridged dimers with significantly low oxidation potentials for Ni(II). These Ni(II)-polyoximate complexes react with dioxygen, consuming multiple equivalents. This is unusual chemistry for Ni(II), especially in the absence of ligand oxidation. The Ni(II) / O 2 reaction system promotes oxidation of triphenyl phosphine, with oxygen atom transfer, benzyl alcohol, and 3,5-di-tert-butylcatechol. Reaction of the Ni(II)-polyoximate complexes with o-quinones causes the formation of high-valent nickel complexes of the reduced dioxolenes, semiquinones and catecholates.

Committee: Dr. Michael Baldwin (Advisor) Subjects: