Doctor of Philosophy (PhD), Wright State University, 2021, Biomedical Sciences PhD

The carotid bodies (CB) are peripheral chemoreceptors that detect changes in arterial oxygenation and, via afferent inputs to the brainstem, correct the pattern of breathing to restore blood gas homeostasis. Elucidating the “signal” that couples carotid body sensory type I cell (CBSC) hypoxic mitochondrial inhibition with potassium channel closure has proven to be an arduous task; to date, a multitude of oxygen-sensing chemotransduction mechanisms have been described and altercated (Varas, Wyatt & Buckler, 2007; Gao et al, 2017; Rakoczy & Wyatt, 2018). Herein, we provide preliminary evidence supporting a novel oxygen-sensing hypothesis suggesting CBSC hypoxic chemotransductive signaling may in part be mediated by mitochondria-generated thermal transients in TASK-channel-containing microdomains. Confocal microscopy measured distances between antibody-labeled mitochondria and TASK-potassium channels in primary rat CBSCs. Sub-micron distance measurements (TASK-1: 0.33 ± 0.04µm, n = 47 vs. TASK-3: 0.32 ± 0.03µm, n = 54) provided the first direct evidence for CBSC oxygen-sensing microdomains. Using a temperature-sensitive dye (ERthermAC), hypoxic-inhibition of mitochondrial oxidative phosphorylation in CBSCs was suggested to cause a rapid and reversible inhibition of mitochondrial thermogenesis and thus temperature in these microdomains. Whole-cell perforated-patch current-clamp electrophysiological recordings demonstrated CBSC sensitivity of resting-Vm to temperature: lowering bath temperature from 37°C to 24°C induced consistent and reversible depolarizations (Vm at 37°C: -48.4 ± 4.11mV vs. Vm 24°C: -31.0 ± 5.69mV; n = 5; p<0.01) in isolated, primary rat CBSCs. We propose that hypoxic inhibition of mitochondrial thermogenesis may play a critical role in hypoxic chemotransduction in the carotid body. A reduction in temperature within cellular microdomains will inhibit plasma membrane ion channels, influence the balance of cellular phosphorylation–dephosphorylation, and (open full item for complete abstract)

Doctor of Philosophy, Case Western Reserve University, 2013, Biomedical Engineering

The increase in skeletal muscle oxygen consumption (VO2) at the onset of contraction is an indicator of the ability to do work. The VO2 response to contraction (i.e., VO2 kinetics) is determined by oxygen delivery (convective and diffusive) to tissue, oxygen utilization in muscle myocytes, and intracellular PO2 (iPO2). However, factors determining oxygen diffusion, including permeability-surface area (PS) and the blood-tissue O2 gradient, are difficult to measure during the onset of contraction. Therefore, computational models of O2 transport and metabolism in skeletal muscle can be used to elucidate underlying factors and predict the effects of alterations in oxygen transport and metabolism on VO2 kinetics in skeletal muscle.A computational model of O2 transport and utilization in skeletal muscle, including changes in blood volume fractions at the onset of contraction, can be used to quantify changes in hemoglobin (Hb) and myoglobin (Mb) oxygenation in skeletal muscle at the onset of contraction. The model quantifies the increase in Mb deoxygenation where convective or diffusive oxygen delivery is limited, which increases the relative contribution of Mb to the total change in heme oxidation (measured by near-infrared spectroscopy) as compared to normal physiological conditions.A computational model of O2 transport and utilization, including anaerobic glycogenolysis, is used to investigate VO2 and iPO2 kinetics in response to submaximal and maximal contraction intensity in the canine gastrocnemius. The model is able to predict VO2 kinetics for different blood flow (Q), contraction intensity, and arterial oxygen content in addition to quantifying the role of iPO2 at higher contraction intensity. The model (A) predicts that PS is the major controller of oxygen diffusion and (B) quantifies the relationship between iPO2 and contraction intensity, which depends on transport and metabolic properties of the muscle.This model is also used to explore the effects of convectiv (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2024, Mechanical Engineering

Temporal and spatial distributions of the electric field in an atmospheric pressure, ns pulse, positive and negative polarity helium plasma jets are measured by ps Electric Field Induced Second Harmonic (EFISH) generation. The measurements have been done in a quasi-two-dimensional plasma jet impinging on liquid water, using a laser sheet and a focused laser beam positioned at different heights above the water surface. Absolute calibration of the electric field is obtained by measuring a known Laplacian electric field distribution for the same geometry and at the same flow conditions. The vertical component of the electric field is determined by isolating the second harmonic signal with the vertical polarization. The measured electric field is averaged over the span of the plasma jet, in the direction of the laser sheet or the focused laser beam. The spatial resolution of the laser sheet measurements is approximately 15 μm across the sheet, with the temporal resolution of 10 ns. The spatial resolution of the focused laser beam measurements is approximately 180 um across the beam, with the temporal resolution of 2.5 ns. The results show non-monotonous electric field distribution across the jet, with two maxima produced by the surface ionization waves propagating over water. Considerable electric field enhancement is detected near the surface. Residual charge accumulation on the water surface is detected only in the negative polarity pulse discharge. The results provide new insight into the charge species kinetics and transport in atmospheric pressure plasma jets, and produce data for detailed validation of high-fidelity kinetic models. Ionization wave development during ns pulse breakdown in nitrogen between two parallel plate, dielectric-covered electrodes is studied by ps Electric Field Induced Second Harmonic (EFISH) generation and kinetic modeling. The results indicate formation of two well-defined ionization waves in the discharge gap, which requires a relativ (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2022, Chemical Engineering

For many people with acute organ failure or genetic conditions such as cystic fibrosis, organ transplantation is the only treatment option. The number of patients on the organ transplant waiting list is over 100,000 with thousands of people on the list dying each year while awaiting a life-saving organ transplant. Traditional organ storage is done using static cold storage (SCS) whereby organ allografts are kept in hypothermic conditions to decrease metabolism and slow tissue death. The harsh ex vivo preservation conditions of SCS mandate a high standard for graft utilization with marginal organs often being discarded for fear of causing graft dysfunction upon transplantation. Normothermic machine perfusion (NMP) represents a method of ex vivo organ preservation to reduce ischemic time and hypothermic organ injury such that grafts are better supported before utilization. NMP has been shown previously to also be able to resuscitate marginal organs that would have otherwise been discarded to be viable for transplantation. A current shortcoming of NMP is the steep oxygen (O2) demand of cellular respiration at normothermia and the metabolic debt acquired by organs during ischemic time post-mortem. To ameliorate this problem, O2 carriers have been used in perfusates; however, there is not yet an optimal O2 carrier for NMP. Red blood cells (RBCs) are prone to hemolysis in ex vivo perfusion and previous commercially available RBC substitutes have had large quantities of cytotoxic low molecular weight (LMW) hemoglobin (Hb) species (<500 kDa). This work describes the scale-up of a next generation polymerized human Hb (PolyhHb) as an RBC substitute in NMP. Previous work in this lab has synthesized a safer PolyhHb with LMW species purified out of solution but had only been made at the bench-top scale. Successfully increasing the process scale to the pilot scale makes this PolyhHb feasible for use in large animal NMP and eventually in clinical trial applications. The (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2008, Biophysics

Electron paramagnetic resonance (EPR) oximetry is a useful research technique and a potential clinical tool. The goal of this dissertation was to establish particulate-based EPR oximetry for dynamic pO2 measurements in vivo and widen its applications for cellular and tissue systems. EPR oximetry was compared to a fluorescence technique in an experimental tumor model. The study found EPR oximetry to be a noninvasive, robust and reliable method for repeated measurements in tumors. In addition, the response time of particulate EPR probes was established to be faster than 3.3 ms. Consequently, EPR oximetry was used for measuring temporal oxygen changes in tissue. The study revealed the presence of inherent fluctuations of oxygen in normal and tumor tissue. The frequency of fluctuations was unaltered even if modifiers of oxygen change were used. Lastly, regional pO2 data in mouse and rat hearts were analyzed. A post-processing algorithm was used to determine components in EPR spectra obtained from probe implanted in the infarct heart. Overall, the above developments will help widen the scope of applications for particulate-based EPR oximetry and will further encourage evaluation of the technique as a potential clinical tool for tissue oxygen measurements.

Doctor of Nursing Practice, Mount St. Joseph University , 2024, Department of Nursing

Intubation for acute respiratory illness that often leads to acute respiratory distress syndrome (ARDS) is a common threat to the pediatric population worldwide and at the project site pediatric intensive care unit (PICU). The length of mechanical ventilation is a multifactorial determination for each patient circumstance and is strongly associated with the extensiveness of the respiratory illness. Literature supports postural drainage (PD) positioning as a form of treatment for respiratory illness and ARDS, but it is not a common modality utilized in the project site PICU. Using evidence of best positioning practices for lung health, a two-stepped protocol for patient positioning was developed and implemented based on the severity level of ARDS to decrease the length of mechanical ventilation. The application of the positioning protocol for patients that met inclusion criteria demonstrated notable fluid shifting and decreased opacities on chest radiography, a consistent gradual decline in ventilator pressures, oxygen requirement, and ARDS severity levels, and a decrease in the average length of mechanical ventilation. This evidence-based quality improvement initiative provided a strong testimonial to the value of using PD positioning as a treatment method for patients intubated due to respiratory illness and ARDS.

Doctor of Philosophy, The Ohio State University, 2022, Chemical Engineering

Developing a clinically useful blood substitute has become a major international goal in the last few decades due to limited donor blood and possible complications with transfusion blood. Blood supplies are dependent upon volunteers and has seasonal supply fluxes. This supply problem could further be exacerbated by the limited shelf-life of donor blood. Stockpiling and deliver of blood in military or civilian disaster scenarios as well as roadside rescue is, therefore, a difficult undertaking. Additionally, the transfusion of donor blood may result immunogenicity and toxicity problems. Precious time, also known as golden hours, is often lost during cross-matching of the blood types. Hemoglobin (Hb) is a natural oxygen carrier that resides inside red blood cells (RBCs), which could be easily extracted via RBCs lysis using hypotonic solution. There is no cross-matching concerns associated with cell-free Hb given that the RBC membrane blood group antigens are removed during the process. Unfortunately, cell-free Hb cannot be used as a blood substitute due to short circulatory half-life and toxicity including endothelial injury via NO scavenging, oxidative stress, endothelial activation, and endothelial barrier dysfunction. Further modifications need to be performed to increase its safety and efficacy. In this study, different types of hemoglobin-based oxygen carriers (HBOCs) have been synthesized and comprehensively characterized. In Chapter 2, we have developed improved synthesis and purification methods to produce polymerized bovine hemoglobin in the Tense (T) and relaxed (R) quaternary state with ultrahigh MW (>500 kDa) at varying cross-link densities. We further investigated the effect of MW on key biophysical properties. To further optimize current PolybHb synthesis and purification protocols, we performed a comprehensive meta-data analysis to evaluate correlations between procedural parameters (i.e., cross-linker:bovine hemoglobin (bHb) molar ratio, gas-liqui (open full item for complete abstract)

Doctor of Philosophy, Case Western Reserve University, 2022, Macromolecular Science and Engineering

The oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are critical electrocatalytic reactions for clean and renewable energy technologies, such as fuel cells, metal-air batteries, and water-splitting. Current commercial applications of these reactions utilize noble-metal-based catalysts (e.g., Pt, Pd, RuO2, IrO2). The high cost of these precious metal-based catalysts and their limited reserve have precluded these renewable energy technologies from large-scale applications. Therefore, research efforts have focused on the development of alternative catalysts that are readily available and cost-effective, with superior electrocatalytic performance compared to noble-metal-based catalysts. In 2009, nitrogen-doped carbon nanotubes (N-CNTs) were discovered to demonstrate electrocatalytic ORR activity attributed to the doping-induced charge transfer from carbon atoms adjacent to the nitrogen atoms to change the chemisorption mode of O2. More recent studies have further demonstrated that certain heteroatom-doped carbon nanomaterials can even act as multi-functional metal-free electrocatalysts for ORR/OER/HER, leading to the potential development of low-cost, highly efficient, and multi-functional electrocatalysts for advanced clean and renewable energy technologies. The work presented herein develops new carbon-based metal-free electrocatalysts (C-MFECs) by utilizing different design strategies. Chapter two demonstrates carbonization of a newly-synthesized pair of enantiotopic chiral metal-organic frameworks (MOFs) to produce Co-coordinated N-doped carbon materials with a hierarchical rod-like morphology and remarkable bi-functional electrocatalytic activity and stability for both OER and ORR – comparable to both commercial RuO2 for OER and Pt/C electrocatalysts for ORR. The observed excellent electrocatalytic activities were attributed to their unique hierarchical rod-like structure with homogeneously distributed cob (open full item for complete abstract)

Master of Science in Chemistry, Youngstown State University, 2020, Department of Chemistry

Reactive oxygen species (ROS) are chemically reactive oxygen containing molecules and radicals mainly produced from the partial reduction of molecular oxygen. ROS have been associated with aging and several diseases such as atherosclerosis and cancer. Metal-catalyzed oxidation (MCO) systems are systems that produce free radicals using transition metal ions such as copper or iron and hydrogen peroxide. As such, MCO may cause oxidation of proteins. To study the correlation between protein structure and oxidative damage of proteins by MCOs, different mutants of hen egg white lysozyme (HEWL) have been developed. This research focuses on the optimization of the expression of the mutant HEWL H15S. The Pichia pastoris expression system was adapted for the expression of HEWL H15S. The P. pastoris X-33-pPICZαA-hewlH15S strain was subjected to different growth conditions in a glycerol and methanol buffered media under conditions for small scale expression. Both intracellular and extracellular protein expression were analyzed for enzyme activity. Increasing glycerol concentration from 0.5% to 1% did not show significant increase in yeast growth resulting in low protein concentration and enzyme activity at 28 °C. Also, protein expression at three different methanol concentrations at 28 °C: 0.5% (v/v), 1% (v/v), and 2% (v/v) showed an increase in enzyme activity but only small changes in total protein concentration. The addition of calcium chloride showed a significant effect on the expression of H15S to about 1mg/mL compared to the other conditions without CaCl2. Lysing of the cells grown at 28 °C for intracellular analysis by the Bradford assay showed a significant band of protein corresponding to the size of the H15S mutant. A lower temperature of 22 °C at different growth and expression conditions measured high protein concentration and an increase in enzyme activity for extracellular expression. Intracellular analysis on protein expression at 22 °C measured no lysozyme acti (open full item for complete abstract)

Master of Mathematical Sciences, The Ohio State University, 2019, Mathematics

The delivery of oxygen by blood through blood vessels is a critical process that enables cells and tissue to maintain functionality. This thesis focuses on this process at a small scale in the body. In particular, it examines the flow of blood through capillaries in the brain and how that blood diffuses oxygen into the surrounding tissue. These two models, blood flow and oxygen diffusion, are modeled and the two models are coupled. Two different implementations of this coupled model are used to solve the partial differential equation (PDE). First, an implementation in MATLAB based on the Finite Element Method (FEM) was written for this paper. Additionally, an implementation in C++ is used which is based on Green's Function Methods. This implementation was written by Secomb and can be found at github [3]. These implementations are used to examine oxygen transport and the effects of heterogeneity on it (differences in oxygen content of blood vessels that are close to each other). Heterogeneity tends to occur alongside diseases. We aim to show that this heterogeneity decreases the total oxygen in surrounding tissue. Additionally, we aim to show what the consequences of heterogeneity and the decrease in oxygen in the tissue would be on nearby neurons.

Doctor of Philosophy, The Ohio State University, 2019, Chemical Engineering

A major constraint in improving the effectiveness of traditional chemo- and radiotherapeutic approaches to cancer treatment is inadequate oxygenation of solid tumors. Hypoxic conditions in the tumor microenvironment induce quiescence in cancer cells which can reduce the therapeutic effect of chemo- and radio-therapies. Consequently, alleviating hypoxia in solid tumors is considered a promising target for improving the efficacy of anti-cancer therapeutics. Motivated by this vision, this work aimed to examine how polymerized human hemoglobin (hHb) (PolyhHb) can be applied to increase solid tumor oxygenation and potentially improve the effectiveness of chemo- and radio-therapy used in oncology. In vascularized solid tumors, the microcirculatory environment is complex. Rapid and uncontrolled angiogenesis is responsible for the aberrant vascularization of solid tumors that display dramatic macro and microscopic heterogeneities compared to normal vasculature. These heterogeneous features include multi-scale variations in capillary density and blood flow throughout the tumor mass. Furthermore, PolyhHb can be produced under different conditions. Thus, the increased efficacy of PolyhHb transfusion as a chemo- and radio-sensitizing strategy is dependent on defining the appropriate conditions for olyhHb transfusion. Using in silico and in vivo models of tumor vascularization, we utlined how PolyhHb transfusions function as oxygen modulators within the umor microenvironment. We began by synthesizing a library of PolyhHb with various sizes and oxygen binding affinities. By careful manipulation of the reaction conditions, the size of the resulting PolyhHb can be controlled. This results in solutions with low polydispersity. Additionally, the oxygen saturation of the PolyhHb within the reactor can be controlled to effectively lock the PolyhHb in either the relaxed state (R-State) or the tense state (T-State). By locking PolyhHb in the R-State, oxygen offloading at low oxyge (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2019, Mechanical Engineering

Metal-oxygen batteries are an emerging class of energy storage devices that have some of the highest energy densities among secondary batteries. These batteries are unique because molecular oxygen is the active cathode material and is not stored in the cathode structure. During discharge, oxygen diffuses to an active cathode site, gets reduced on the surface on the cathode, and forms a metal oxide with the cation. The regulation of molecular oxygen concentration throughout the battery therefore becomes critical for battery performance. In particular, oxygen should be present in the cathode in sufficient concentrations but be prevented from diffusing to the anode. The process of oxygen diffusion to anode is known as oxygen crossover and poisons the anode surface, limiting the cycle life of the battery. The goal of this dissertation is to increase the cycle life of potassium-oxygen batteries by preventing molecular oxygen crossover and is achieved with conducting polymer membranes and functionally-graded cathode architectures. This work demonstrates that polypyrrole (PPy) electropolymerized on a porous membrane serves an effective oxygen barrier and increases cyclability. Dopant selection is found to have a strong influence on both ion transport properties and cycle stability in the DME-based electrolyte used for K-O2 batteries. PPy membranes doped with dodecylbenzenesulfonate (DBS-) increase the cycle life from 4 to 18 cycles by transporting K+ and blocking oxygen. However, electrochemical cycle stability of PPy(DBS) cathodes in DME is found to be poor. Bilayer bending studies are performed, and it is determined that the cycle stability depends on the mechanical boundary condition (free versus fixed). The free membrane has improved cycle stability compared to the fixed membrane, which is attributed to the higher cyclic compressive stresses in fixed membrane as estimated by a beam bending model. The presence of oxygen causes further degrades the cyclabi (open full item for complete abstract)

Master of Science (MS), Wright State University, 2018, Earth and Environmental Sciences

The western basin of Lake Erie experiences annual non-nitrogen (N) fixing harmful algal blooms (HABs), while the central basin experiences seasonal hypoxia in bottom water. In the western basin, water column oxygen respiration rates were quantified at four stations throughout the 2016 and 2017 field seasons, including the proportions of total oxygen consumption accounted for by sediments and by water column nitrification (measured in parallel; Hoffman, unpublished data). Water column respiration rates in the central basin of Lake Erie also were measured in July 2017 during seasonal bottom-water hypoxia. Volumetric water column respiration in the western basin in 2017 (0.011–1.227 mol O2/L/hr) was significantly lower than in 2016 (0.275–1.859 mol O2/L/hr; ANOVA, p < 0.001). In July 2017, western basin respiration rates (0.524 ± 0.124 mol O2/L/hr) were not significantly different from those measured on the same day throughout the central basin water column (0.428 ± 0.089 mol O2/L/hr). Lower rates of water column respiration and sediment oxygen demand (SOD), measured in parallel (Boedecker, 2018), in 2017 coincided with a larger contribution of cyanobacteria to the phytoplankton community relative to 2016. The contribution of nitrification to water column oxygen consumption in the western basin was significantly lower than reported in a previous study. Microbially-mediated transformations occurring in aquatic sediments contribute to in situ N concentrations and availability for primary producers, including cyanobacterial HAB organisms performing photosynthesis. Sediment subsamples were collected in the western basin of Lake Erie in 2016 and 2017, and DNA was extracted to quantify functional gene copies as a proxy for the abundance of microbes capable of denitrification (nirS), N fixation (nifH), and dissimilatory nitrate reduction to ammonium (DNRA; nrfA). The gene copy abundance of nirS was significantly correlated (p = 0.002) with denitrification rates measured i (open full item for complete abstract)

Doctor of Engineering, Cleveland State University, 2017, Washkewicz College of Engineering

The dairy industry generates abundant milk waste waters characterized by high biochemical oxygen demand (BOD) and chemical oxygen demand (COD) concentrations that can be very harmful to the environment, if left untreated. Electrocoagulation (EC) has been in use for waste water treatment. The treatment application uses aluminum electrodes and iron or the combined hybrid Al/Fe electrodes. Milk waste water contains high concentration organic pollutants and the main constituents of those organics are carbohydrates, proteins and fats, originating from the milk. The process of separating the flocculated sludge from waste water that has been treated using the electrocoagulation process can be accomplished by the flotation processes. The electroflotation technology is effective in removing colloidal particles, oil, grease, as well as organic pollutants from waste water. This study uses electrochemical and electroflotation treatment of milk waste water by means of an aluminum electrode with specific parameters including total organic carbon (TOC), pH, turbidity, transmittance, and temperature. Even though the electrochemical and electroflotation treatment processes have been around for some time, it has not been thoroughly studied. This study is going to highlight the importance of this technique as a pre-treatment method of milk waste water and its contribution to the reduction of pollutants in the milk processing industry. Furthermore, the process of electroflotation and electrochemical flotation continuously prove to be effective in remediation of varieties of pollutants of different chemical compositions and have the ability to achieve a very high treatment efficiency.

Doctor of Philosophy, The Ohio State University, 2017, Chemical Engineering

In the United States, millions of people are affected by chronic wounds every year. Chronic wounds are characterized by low levels of oxygen (O2) and high levels of pro-inflammatory macrophages that fail to transition to the anti-inflammatory, pro-healing macrophages. There is a need for a therapeutic that simultaneously targets multiple deficiencies of chronic wounds in order to promote healing and avoid devastating outcomes. The main goal of this dissertation is to engineer the oxygen affinity of pure tense state (T-state) and relaxed state (R-state) polymerized hemoglobin (Hb) (PolyHb) mixtures. These mixtures could be topically administered to a chronic wound in order to accelerate the wound healing process by increasing the oxygen flux and exerting additional therapeutic effects by attracting and promoting pro-healing, anti-inflammatory macrophages. To our knowledge, none of the Hb wound healing therapeutics currently in existence use PolyHb mixtures. The partial pressure of oxygen (pO2) of a chronic wound can range from 2-20 mm Hg. By controlling the oxygen affinity (P50 ) of the PolyHb mixture, it is possible to control the pO2 range where the majority of oxygen delivery occurs at the wound site. Therefore, engineering PolyHb mixtures possessing a P50 range of 2-30 mmHg should elucidate the role P50 plays in accelerating wound healing and increasing wound pO2. This dissertation focuses on the development, characterization, and oxygenation potential of human and bovine PolyHb mixtures consisting of pure R-state and T-state PolyHb. This work presents analysis of the biophysical properties of R-state and T-state mixtures for both human and bovine polymerized Hb (PolyhHb and PolybHb) (Chapter 2). In addition, presented is the oxygenation potential of PolyHb mixtures using Comsol Multiphysics to simulate O2 transport in a hepatic hollow fiber bioreactor (Chapter 3). We produced PolyHb by polymerizing Hb using the chemical crosslinker glutar (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 1964, Graduate School

Doctor of Philosophy, The Ohio State University, 1961, Graduate School

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

Sulfur-substituted purine and pyrimidine nucleobases—also known as thiobases—are among the world's leading prescriptions for chemotherapy and immunosuppression. Long-term treatment with some of the purine derivatives of these drugs has recently been correlated with the photo-induced formation of carcinomas. Establishing an in-depth understanding of the photochemical properties of these thiobase drugs may provide a route to overcoming these carcinogenic side effects, or, alternatively, may provide a basis for developing highly-effective compounds for targeted photochemotherapy. In this thesis work, a broad investigation is undertaken, surveying the excited-state dynamics and photochemical reactions of nearly every sulfur-substituted analog of the canonical DNA and RNA nucleobases. The thiobase derivatives are investigated using time-resolved absorption and emission spectroscopies in the femtosecond (10-15 s) to microsecond (10-6 s) time window. Coupling these experiments with quantum chemical calculations, we have developed a molecular-level understanding of how sulfur-substitution so drastically perturbs the photochemical properties of the nucleobases. The structure-property relationships established by this work demonstrate the impact of site-specific sulfur substitution on the population and reaction dynamics of the excited triplet state. Some of the most photoreactive derivatives identified are applied to human epidermoid carcinoma cells and shown to effectively decrease their proliferation upon exposure to a low dose of light. The results presented in this body of work demonstrate the utility of fundamental photochemical investigations for driving the development of next-generation photochemotherapeutics, while simultaneously elucidating overarching principles for the impact of sulfur substitution (thionation) on the photochemical properties of organic chromophores.

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)

Doctor of Philosophy, The Ohio State University, 2015, Chemistry

This dissertation focuses on three projects involving the development of harsh environment gas sensors. The first project discusses the development of a multipurpose oxygen sensor electrode for use in sealing with the common electrolyte yttria stabilized zirconia. The purpose of the sealing function is to produce an internal reference environment maintained by a metal/metal oxide mixture, a criteria for miniaturization of potentiometric oxygen sensing technology. This sensor measures a potential between the internal reference and a sensing environment. The second project discusses the miniaturization of an oxygen sensor and the fabrication of a more generalized electrochemical sensing platform. The third project discusses the discovery of a new mechanism in the electrochemical sensing of ammonia through molecular recognition and the utilization of a sensor taking advantage of the new mechanism. An initial study involving the development of a microwave synthesized La0.8Sr0.2Al0.9Mn0.1O3 sensor electrode material illustrates the ability of the material developed to meet ionic and electronic conducting requirements for effective and Nernstian oxygen sensing. In addition the material deforms plastically under hot isostatic pressing conditions in a similar temperature and pressure regime with yttria stabilized zirconia to produce a seal and survive temperatures up to 1350 oC. In the second project we show novel methods to seal an oxygen environment inside a device cavity to produce an electrochemical sensor body using room temperature plasma-activated bonding and low temperature and pressure assisted plasma-activated bonding with silicon bodies, both in a clean room environment. The evolution from isostatic hot pressing methods towards room temperature complementary metal oxide semiconductor (CMOS) compatible technologies using single crystal silicon substrates in the clean room allows the sealing of devices on a much larger scale. Through this evolution in bonding te (open full item for complete abstract)