Doctor of Philosophy, The Ohio State University, 2024, Chemistry

Ultrafast carrier and spin dynamics of photoexcited yttrium iron garnet (Y3Fe5O12, YIG) are studied to demonstrate that it is an efficient photocatalyst for oxygen (O2) evolution half-reaction in the electrolysis of water. Producing hydrogen as an alternative fuel to traditional carbon-based fuels requires efficient catalysis of both H2 and O2 production from water. O2 production is the limiting factor in water splitting as it is a 4e- transfer process. An efficient O2 evolution photocatalyst requires a material with proper band alignment and low carrier recombination. Recent advances have shown that a spin polarized catalyst can enhance water splitting to produce paramagnetic O2 from diamagnetic water. A photocatalyst utilizes the carriers excited by light, preferably sunlight, to perform catalysis. Photoexcitation is an ultrafast process occurring on an attosecond time scale whereas the electron transfer in catalysis between the semiconductor and water is a slow process occurring in millisecond time scale. Therefore, understanding carrier and spin dynamics between photoexcitation and catalysis is necessary to identify a potential efficient photocatalyst such as YIG. For this purpose, we used time resolved extreme ultraviolet (XUV) reflection absorption and magnetic circular dichroism (MCD) spectroscopies to study the photoexcited dynamic of YIG. These techniques allow us to probe the surface sensitive, element specific and spin resolved carrier dynamics that occur in YIG after photoexcitation. The details of the instrumentation for these techniques are discussed in detail in Chapter 2. YIG is a ferrimagnetic n-type semiconductor with a valence band containing majority of O 2p and a conduction band with Fe 3d contributions. The Fe atoms occupy tetrahedral (Td) and octahedral (Oh) lattice sites in a 3:2 ratio formed by O atoms. An above bandgap excitation causes electrons to transfer from O 2p to Fe 3d orbitals. These electrons can be probed with linear trans (open full item for complete abstract)

Committee: Robert Baker (Advisor); Fengyuan Yang (Committee Member); John Herbert (Committee Member) Subjects: Chemistry

Master of Science, The Ohio State University, 2024, Chemistry

Camptothecin-dilysine (CPT-KK) self-assembles into nanotubes which may serve as a pH-responsive drug delivery vehicle. The nanotubes provide a carrier that allows camptothecin to enter the cell before inactivation by hydrolysis. As a drug delivery vehicle, one issue is monitoring drug release in vitro. Co-assembling CPT-KK with a rhodamine B-dipeptide conjugate (RhB-KE) provides a pH-responsive means to track the assembly through endocytosis and eventual release into the cytosol. Since CPT-KK is positively charged and RhB-KE is negatively charged at pH 7.4, electrostatic co-assembly is the preferred means for assembly as the positive charged CPT-KK will interact with RhB-KE than itself. This is due to the stabilizing attractive interactions between CPT-KK and RhB-KE and destabilizing repulsive interactions with itself. Pre-assembling RhB-KE provides a template for CPT-KK to wrap around. Mixing CPT-KK with RhB-KE in equimolar amounts produces co-assemblies within 1 h and produces mature tubes after 24 h. Since the incubation time is established, varying the ratio of CPT-KK/RhB-KE was done in order to optimize the co-assembly for drug loading and CPT-KK templating onto RhB-KE. Centrifugation at 5,000 rpm for 5 min gives the optimal ratio of 1:5 (CPT-KK/RhB-KE), while centrifugation at 13,400 rpm for 15 min gives 1:1 (CPT-KK/RhB-KE) as the ideal ratio. With this knowledge, determining the exact composition of the co-assembly can be determined via analytical high-performance liquid chromatography (HPLC) and further optimized using zeta-potential measurements. Live-cell imaging and cell viability assays will be used to investigate the efficacy of CPT-KK/RhB-KE as a drug delivery vehicle compared to self-assembled CPT-KK.

Committee: Jonathan Parquette (Advisor); Davita Watkins (Committee Member); Christopher Hadad (Committee Member) Subjects: Chemistry; Organic Chemistry

Doctor of Philosophy, Case Western Reserve University, 2024, Macromolecular Science and Engineering

Helices are abundant and crucial examples of rigidity throughout biology from protein lever arms in molecular motors to collagen type II that assembles into fibrils in the extracellular matrix (ECM). The origin of the collagen fibril radial length scales is not fully understood but is hypothesized to be related to the flexibility of the protofibril and environmental effects. In this work, we systemically investigate both the elasticity of biomacromolecules and their surrounding elastic environments using simple polyacrylamide gels. We determine the persistence length (lp), a measure of elasticity, of model polypeptide single helices and collagen type II triple helices by using static and dynamic light scattering. Using circular dichroism, we observe that the model polypeptide transitions from a random coil to a helix with increasing pH, and lp increases from ~1 - 2 nm to ~20 nm. In addition, we crosslink the model polypeptide to utilize its increase in lp and produce hydrogels with stain stiffening behavior at low crosslink densities. In various pH and ionic strength environments, triple helical lp varies from 60 - 90 nm but has an intrinsic lp of 90 nm when backbone interactions are neutralized. We correlate the triple helical lp to the fibril diameter as determined by transmission electron microscopy (TEM) in various ionic strength solutions and determine that the values are of similar magnitude unless in high ionic strength solutions. We then investigate the environmental elasticity effects on self-assemblies of complex coacervates using light microscopy and collagen type II fibrils using cryogenic TEM. The volume of the complex coacervate droplets is inversely proportional to the modulus of the gel that the complex coacervates are formed in and have a non-monotonic salt resistance as a function of gel moduli. Collagen fibrils in 100 mM PBS solution are ~50 nm in diameter, and the fibril diameter drops to ~30 nm in gels across 63-8700 Pa moduli. Collagen's lp, s (open full item for complete abstract)

Committee: Svetlana Morozova (Committee Chair); Lydia Kisley (Committee Member); Valentin Rodionov (Committee Member); Michael Hore (Committee Member) Subjects: Biophysics; Materials Science; Physics

Doctor of Philosophy, The Ohio State University, 2024, Chemistry

Solar energy attracts increasing attention due to its abundance and high sustainability. Among all the semiconductors that can convert solar energy to electric, chemical and light energy, organic-inorganic halide perovskites (OIHPs) are being widely studied due to its promising optical and photoelectric properties as well as easy processing and fabrication. As a derivative family from 3D OIHPs, low dimensional OIHPs have their unique attributes and applications because of the strong quantum confinement, high tunability and better stability. However, compared with 3D OIHPs, low dimensional OIHPs are still less explored because of their large band gap, poor charge carrier mobility and structural prediction difficulty. In this dissertation, we first report a machine learning (ML)-assisted approach to predict the dimensionality of lead iodide-based perovskites. A literature review reveals 86 reported amines that are classified into ‘2D'-forming and ‘non-2D'-forming based on the dimensionality of their perovskites. Machining learning models were trained and tested based on the classification and descriptor features of these ammonium cations. Four structural features, including steric effect index, eccentricity, largest ring size, and hydrogen-bond donor, have been identified as the key controlling factors. Based on these features, a quantified equation is created to calculate the probability of forming 2D perovskite for a selected amine. To further illustrate its predicting capability, the built model is applied to several untested amines, and the predicted dimensionality is verified by growing single crystals of perovskites from these amines. This work represents a step towards predicting the crystal structures of low dimensional hybrid halide perovskites using ML as a tool. The poor stability of OIHPs against polar solvents highly limited their application for photocatalysis and photoelectrochemistry. Therefore, we report the use of methylviologen lead iodide (MVPb2 (open full item for complete abstract)

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

Doctor of Philosophy, The Ohio State University, 2021, Chemistry

The ability of DNA to resist photodamage has led to extensive study of its excited state properties. Most recently interest in metal coordinated DNA materials have led to a surge in study of the spectroscopic properties of Metallo-DNAs. In particular, Ag+ interactions with DNA have been of great interest to due to the non-canonical base pairs, such as cytosine-cytosine, formed through Ag+ binding and the ability to form reduced silver nanoclusters which could potentially operate as biosensors. In this text the relationship between structure and photophysics is explored for a Ag+ bound all-cytosine oligonucleotide dC20 as well as Ag+ bound cytosine and Ag+ bound cytidine monomers. Using circular dichroism and UV-Vis-NIR transient absorption spectroscopy, in conjunction with TDDFT calculations carried out by our collaborator Prof. Lara Martinez-Fernandez, it is shown that addition of silver nitrate to dC20 (Ag+-dC20) solutions leads to the formation of parallel duplexes which contains Ag+ mediated cytosine-cytosine base pairs with a high degree of propeller twist. The Ag+-dC20 duplexes are found to form an unusually long-lived state which persists beyond our time window (>4 ns). This state is unobserved in i-motif and single stranded forms of dC20. Furthermore, the state is absent in solutions of Ag+ bound cytosine monomers which are expected to form planar base pairs than can potentially form sheets or ribbons, indicating that propeller twisting is leading to the formation of this long-lived state. iii The identity of this long-lived species in Ag+-dC20 was investigated using FTIR and time resolved infrared spectroscopy (TRIR) with aid from QM/MM calculations carried out by our collaborator Prof. Lara Martinez-Fernandez. In addition to Ag+-dC20, Ag+ bound cytidine monomers (Ag+-Cyd) and cytosine monomers (Ag+-Cyt) were studied which are expected to form propeller twisted and sheet like structures, respectively. The long-lived state, which is found to also form in A (open full item for complete abstract)

Committee: Bern Kohler (Advisor); Robert Baker (Committee Member); James Coe (Committee Member) Subjects: Biophysics; Physical Chemistry

Master of Science (M.S.), University of Dayton, 2020, Chemistry

In the area of photochemistry, many molecules can undergo photoisomerization. Within these photoswitches is a family of molecules derived from azobenzene, which can form what are called supramolecular aggregates. When these molecules are in the presence of one another, they can form large structures. In addition to this, such molecules may also be able to maintain their ability to photoswitch while in a supramolecular structure. These supramolecular photoswitching aggregates have been used in many different applications including hydrogels and sol-gels, and the effort of cataloging and characterization of these molecules is a novel endeavor. Previous testing has concluded that ADA (Azobenzene-4,4'-dicarboxylic acid) and M0423 (4-Dimethylaminoazobenzene4'-carboxylic acid) show aggregation properties as well as photoswitching properties when paired together. When by themselves they show remarkable self-aggregation, however, they both do not show photoswitching properties. ADA shows photoswitching properties while M0423 does not. This data was confirmed through additional tests. The addition of the molecule A1598 (Azobenzene-3,3'-dicarboxylic acid) shows shocking similarities in aggregation to ADA in addition to possessing its own unique attributes. A1598 was confirmed to have formed aggregates with itself and M0423. These tests also confirmed a preferred pH and mixing ratio for the ADA and A1598-M0423 aggregate as well as assessing their photoswitching capabilities and aggregation under the stresses of photoswitching. Showing that both molecules when aggregated, regardless of the high degree of order displayed in the spectra, locked up. This prevented further photoswitching from occurring. This research shows that there is still more that can be learned from these molecules and similar azobenzene derivatives with respect to photoswitching aggregates.

Committee: Angela Mammana Ph.D. (Advisor); Vladimir Benin Ph.D. (Committee Member); Mark Masthay Ph.D. (Committee Member) Subjects: Chemistry; Organic Chemistry

Master of Science, Miami University, 2020, Chemical, Paper and Biomedical Engineering

Protein-surfactant interactions have been studied due to the numerous applications in different industries including hygienic products, cosmetics, pharmaceuticals, and food products. Single surfactant and mixed surfactant systems with protein are of interest to assess the changes in structure and function of protein. Using several different methods to analyze changes in protein structure, surfactant critical micelle concentration (CMC), and protein-bound surfactant, we can understand the interactions between the surfactant and protein molecules. In this study, two different types of surfactants sodium dodecyl sulfate (SDS) and lauryldimethylamine oxide (LDAO) are analyzed to understand their impact on the protein β-lactoglobulin (βLG). The impact of mixtures of the two surfactants on βLG was also explored. SDS has a significant impact on the structure of βLG at low concentrations. In contrast, higher concentrations of LDAO are required to impact the structure of βLG. The mixtures of the two surfactants with the protein showed minimal changes in surfactant aggregation concentration compared to the mixed surfactant solution with no protein. The mixed surfactant system with protein also required a higher concentration of surfactant to impact the protein structure.

Committee: Jason Berberich (Advisor); Justin Saul (Committee Member); Jason Boock (Committee Member); Neil Danielson (Committee Member) Subjects: Analytical Chemistry; Biochemistry; Chemical Engineering

Doctor of Philosophy, The Ohio State University, 2019, Chemistry

Iron-sulfur clusters are one of the most primitive protein cofactors, present in all three kingdoms of life and performing diverse functions such as electron transfer, DNA repair and replication, gene regulation and catalysis. The biosynthesis of such iron-sulfur clusters involves highly regulated cluster assembly pathways, which include ISC (Iron-Sulfur Cluster), SUF (Sulfur Utilization Factor), CIA (Cytosolic Iron-sulfur Assembly) and NIF (Nitrogen Fixation) pathways. The ISC pathway is the most important cluster assembly pathway in mammals as it is responsible for cluster maturation of mitochondrial as well as cytosolic proteins. The ISC pathway involves de novo synthesis of a [2Fe-2S] cluster on scaffold protein Isu, which is then trafficked and delivered to apo protein targets. It has been well established that homodimeric monothiol glutaredoxins Grx5 (mitochondrial) and Grx3 (cytosolic) play a crucial role as intermediary cluster carriers by binding a [2Fe-2S] at the dimer interface with glutathione also coordinating to Fe center. Monothiol glutaredoxins can also bind [2Fe-2S] cluster in the form of a heterodimeric complex with another partner protein belonging to the BolA family. Though exact role of the BolA proteins is not known, previous studies have proposed that the [2Fe-2S]-bound bridged complexes of glutaredoxin Grx5 with BolA1 and BolA3 may have distinct and essential physiological roles in humans. Genetic mutations in BolA3 cause the fatal disease Multiple Mitochondrial Dysfunctions Syndrome 2 (MMDS2), though the molecular reason for the disease condition remains unknown. The focus of this work is to understand the mechanistic details of [2Fe-2S] cluster trafficking by monothiol glutaredoxin along with its partner BolA protein. The seemingly simple process of cluster exchange involving such entities potentially involves multiple Fe-cysteinyl bond dissociation and formation events, accompanied by simultaneous exchange of glutathione molecules. Herei (open full item for complete abstract)

Committee: James Cowan (Advisor); Ross Dalbey (Committee Member); Hannah Shafaat (Committee Member) Subjects: Biochemistry; Chemistry

PhD, University of Cincinnati, 2019, Medicine: Molecular Genetics, Biochemistry, and Microbiology

The human skin commensal, Staphylococcus epidermidis, is the bacterium most commonly responsible for hospital-acquired infections. This microbe has a very strong capacity for forming bacterial communities known as biofilms. These communities are well-structured and often involve a slime-like matrix of extracellular polysaccharide which assists in bacterial accumulation. A well-known protein factor, the accumulation-associated protein (Aap), can also mediate intercellular adhesion, contributing the biofilm formation. Interestingly, Aap has been shown to be critical for infection in a rat catheter model, whereas the extracellular polysaccharide was irrelevant in infection. Aap is a large, multi-functional, cell wall-anchored protein expressed by S. epidermidis. The N-terminus of the protein contains a region of short repeats called the A-repeats, followed by a globular lectin domain. The lectin domain can mediate attachment of bacteria to a surface. A proteolytic cleavage site downstream of the lectin domain leads to the release of the A-repeats and lectin domain, allowing Aap to function in accumulation. There are 5 - 17 B-repeats downstream of the cleavage site, which can assembly with Aap on adjacent cells in the presence of Zn2+. At the C-terminus of Aap lies a region of low complexity, which is rich in proline and glycine residues. After this region is a cell wall-anchoring motif that results in the covalent attachment of Aap to the bacterial cell wall. Much of the progress made toward understanding the structure and biological function of the B-repeats has utilized a minimal construct containing one and a half B-repeats (Brpt1.5). Previous members of the Herr Lab have determined that Brpt1.5 can assemble into an anti-parallel dimer in the presence of Zn2+. Interestingly, while the Brpt1.5 dimer would disassociate in the presence of Zn2+-chelator, mature biofilms were unaffected by addition of the chelator. This led members of the Herr Lab to express and ch (open full item for complete abstract)

Committee: Andrew Herr Ph.D. (Committee Chair); David Haslam M.D. (Committee Member); Rhett Kovall Ph.D. (Committee Member); Mark Rance Ph.D. (Committee Member); Thomas Thompson Ph.D. (Committee Member) Subjects: Biophysics

BS, Kent State University, 2019, College of Arts and Sciences / Department of Chemistry and Biochemistry

Within the past century, several strains of bacteria have developed resistance to common antibiotics, such as methicillin and vancomycin, making it increasingly difficult to treat and prevent infections. Thus, development of novel antibiotics has become a necessity. The goal of our research is to disrupt ribosomal assembly mechanisms by inhibiting ribosomal modification enzymes. Protein RsmC (ribosomal RNA small subunit methyltransferase C), which binds to the 3' helix 34 (3'-h34) of the 16S 3'-major domain rRNA and methylates a guanine at position 1207 (G1207; E. coli numbering), is the focus of this research. Transverse mutations at position 1207 resulted in a lethal phenotype, perhaps due to the formation of a nonfunctioning ribosome. We have discovered a 7-mer peptide that binds tightly to 3'-h34 RNA using phage display. Tryptophan quenching experiments confirmed the binding of the peptide to 3'-h34, in addition to several 3'-h34 model RNAs. Furthermore, the binding of the peptide to the RNA was found to be sequence dependent. Circular dichroism was used to verify the structure of the model RNAs during the quenching experiments.

Committee: Sanjaya Abeysirigunawardena (Advisor); Soumitra Basu (Committee Member); Gary Koski (Committee Member); Suzy D'Enbeau (Committee Member) Subjects: Biochemistry

Doctor of Philosophy (PhD), Ohio University, 2018, Physics and Astronomy (Arts and Sciences)

Nanoscale materials have demonstrated unique properties in condensed matter studies and played a crucial rule in modern devices. Fundamental research on nanoscale systems provides deep understanding into science and enables advancing and reshaping of nanotechnology. Scanning tunneling microscopy is a comprehensive tool which is capable of characterizing topographic and electronic properties of nanoscale materials in real space down to atomic scale. To date many emerging techniques have been combined with scanning tunneling microscopy to discover and explore new phenomena. This dissertation explicitly demonstrates novel application of synchrotron X-ray scanning tunneling microscopy which combines synchrotron X-ray and scanning tunneling microscopy to study magnetic, electronic, and structural properties of materials interfaces. A scanning tunneling microscope tip is used to capture X-ray magnetic circular dichroism and near edge X-ray absorption fine structure signals, which explain charge transfer and magnetic properties of oxide materials interfaces with chemical and elemental sensitivities. Using X-ray absorption spectroscopy and spectroscopic imaging with a scanning tunneling microscope tip, the effect of charge transfer at the interfaces formed by transition metals of cobalt and nickel in nanoscale clusters and islands on a Cu (111) surface has been explored. Finally, X-ray standing wave formed by the interference of the incident and diffracted X-ray beams is used to characterize the structural properties of a cobalt thin film grown on a Au (111) surface. These results open novel research directions where material characterizations will be able to perform simultaneous chemical, structural and magnetic contrast potentially down to atomic scale.

Committee: Saw-wai Hla (Committee Chair); Nancy Sandler (Committee Member); Gang Chen (Committee Member); Hugh Richardson (Committee Member); Volker Rose (Committee Member) Subjects: Materials Science; Nanoscience; Physics

Master of Science (M.S.), University of Dayton, 2017, Chemistry

Bacteriorhodopsin (BR) is a purple trans-membrane protein which constitutes the color and biological function of the purple membrane (PM) found in the salt–loving bacterium H. Salinarium. BR monomers consist of a covalently bound retinyl chromophore that is elliptically surrounded by seven alpha–helices. These monomers aggregate as individual trimers which arrange in a rigid, hexagonal crystalline lattice in PM. A two–photon one–monomer process allows for the photoconversion from PM to a laser–induced blue membrane (LIBM), stimulated by exposure to intense 532 nm laser pulses. Furthermore, the exposure of PM to diffuse 254 nm ultraviolet light results in a one–photon one–monomer process which dictates the PM photoconversion to an ultraviolet–induced colorless membrane (UVCM). The color changes observed in PM in the following studies are due to either the wavelength of light exposure or the concentration of divalent cations in the membrane. A highly debated issue surrounding PM is the origin of the bisignate circular dichroism (CD) signal associated with the achiral retinyl chromophore of BR. The initial purpose of this research was to address light scattering evident in PM solutions, which would provide an improvement in the analysis of the spectral behaviors of PM. A reduction in the light scattering was achieved by adding glycerol to the suspension solvent. A secondary principle of the following studies was to further investigate the influence of cation concentration on the color changes of PM before and during photo–induced degradation. Specifically, the photodegradation of calcium saturated purple membrane (CSPM) and cation–free blue membrane (CFBM) were studied upon exposure to intense 532 nm laser pulses and diffuse 254 nm ultraviolet light. Though these aspects are significant in providing new insights into the mechanism of degradation of PM, the central purpose of this research was to address the origin of the bisignate CD signal. Improvements in the l (open full item for complete abstract)

Committee: Mark Masthay (Advisor); Angela Mammana (Advisor); Judit Beagle (Committee Member) Subjects: Biochemistry; Biophysics; Chemistry; Physical Chemistry

Doctor of Philosophy (PhD), Ohio University, 2017, Physics and Astronomy (Arts and Sciences)

Research on plasmonics science and study of optical properties of photonic devices at the nanoscale have become extremely prominent and desirable among scientists over the past few decades owing to the introduction of innovative plasmonic devices and their vast applicability. The quest for light manipulation in metallic nanostructures and harvesting energy at the nanoscale have grown greatly due to the creation of novel optical devices for applications ranging from functional metamaterials and cloaking to optical sensing and plasmonic waveguides. This dissertation presents a rigorous study of different nanostructures for specific purposes. Circular dichroism of chiral nanostructures, optical activity of metamaterials, thermal properties and heat dissipation in nanosytems, and directional radiation are main categories which are studied in this work. Theoretical understanding of the behavior of nanostructures involves physics models along with a variety of computational tools such as the point dipole approximation, the discrete dipole approximation, the finite difference method, and the finite element method. In most cases where the experimental observations are available, the informed calculations showed good agreement with observations. In other cases, efficient and appropriate arrangement of nanoparticles are proposed for custom-made and distinct experimental applications. Some of the models represent novel approaches that offer new experimental and measurement possiblities.

Committee: Alexander O. Govorov Distinguished Professor (Advisor); Nancy Sandler Professor (Committee Member); Eric Stinaff Dr. (Committee Member); Savas Kaya Professor (Committee Member) Subjects: Condensed Matter Physics; Nanoscience; Nanotechnology; Optics; Physics

Doctor of Philosophy, The Ohio State University, 1984, Graduate School

Committee: Not Provided (Other) Subjects: Biology

Doctor of Philosophy (PhD), Ohio University, 2015, Electrical Engineering & Computer Science (Engineering and Technology)

The field of spintronics is considered as the next generation of spin-based electronics rather than the flow of charges utilized in electronics. It is expected that it will have some advantages in areas of information storage densities, switching speed, power consumption, manufacturing costs and others. One of the alternatives in developing a successful spintronics materials is the transition metal (TM)-doped III-V diluted magnetic semiconductors (DMSs) and GaMnAs is the proto-type ferromagnetic DMSs. Currently, the origin of ferromagnetism in GaMnAs is not fully clarified yet due to the complexity of an electronic band structure after doping of the Mn into GaAs. However, the magneto-optical characterization, especially, magnetic circular dichroism (MCD), is a very powerful technique to investigate DMS because one can obtain the information of the electronic band structure. Thus, we have performed systematic investigations of the MCD spectra and optical absorption spectra of the Ga1-xMnxAs with different concentrations of Mn. In this project, we have conducted the measurement using the transmission-mode MCD, the reflection-mode MCD and the magneto-optical Kerr effect (MOKE) for three different kinds of GaMnAs samples fabricated with the same growth conditions; GaMnAs on sapphire, GaMnAs on InP, and free-standing GaMnAs, respectively. We have successfully estimated the Zeeman splitting energy of both L (E1 and E1+delta1) and G (E0 and E0+delta0) critical points (CPs) for these materials. We utilized an energy derivative of the Gaussian function to decompose the MCD spectrum into the impurity band (IB) related background and two dispersion components around L-CPs which are expected in theory. Then, using the rigid band shift model we calculated the Zeeman splitting energy of E1 (L-CP). The Zeeman splitting energy at E1 (L-CP) was estimated to be larger than ~ 4 meV in Ga0.97Mn0.03As on sapphire, ~ 0.6 meV in Ga0.97Mn0.03As on InP, and ~ 6.5 meV in free-standing Ga0.9 (open full item for complete abstract)

Committee: Wojciech Jadwisienczak (Advisor); Savas Kaya (Committee Member); Avinash Kodi (Committee Member); Faiz Rahman (Committee Member); Martin Kordesch (Committee Member); Arthur Smith (Committee Member) Subjects: Chemical Engineering; Engineering; Materials Science; Optics; Physics

Master of Science (M.S.), University of Dayton, 2015, Chemistry

The purple membrane (PM) of the salt‐loving bacterium H. Salinarium owes both its color and physiological function to the protein bacteriorhodopsin (BR). The PM is comprised of BR trimers arranged in a crystalline hexagonal lattice. PM converts to an ultraviolet‐induced colorless membrane (UVCM) upon exposure to diffuse ultraviolet (UV) light through a 1‐monomer 1‐photon process and to a laser‐induced blue membrane (LIBM) upon exposure to intense green laser pulses through a 1‐monomer 2‐photon process. The color changes which BR molecules undergo depend on the (1) BR aggregation state (e.g. crystalline trimeric PM and monomers) (2) wavelength of light (3) intensity of the light and (4) divalent cations, as earlier results indicate that calcium ions Ca2+ are removed from the PM surface during the PM → LIBM photoconversion. The origin of the unconventional biphasic band in CD spectrum has caused much debate. The principle purpose of the research is to further elucidate the mechanisms responsible for the well known PM → LIBM and PM → UVCM photoconversions. Both of these processes have significant implications regarding potential photocooperative processes and exciton coupling between BR molecules within the PM. They also have important implications for the long‐standing debate about the unusual "bisignate" circular dichroism (CD) spectrum of PM in the visible region of the spectrum, which has been attributed to both exciton coupling between the BR molecules and BR protein heterogeneity within the trimer. To accomplish this objective, I characterized the changes in the absorption and CD spectra of five separate BR species upon irradiation with intense 532 nm laser pulse and diffuse 254nm‐UV‐light: Native PM, Delipidated PM, Monomeric BR, cation‐free blue membrane and calcium saturated PM. Conclusions were drawn about the relative roles of inter‐trimer and intra‐trimer photocooperativity, exciton coupling and BR protein heterogeneity in the photochemistry and color (open full item for complete abstract)

Committee: Mark Masthay (Advisor); Angela Mammana (Committee Member); Shawn Swavey (Committee Member); Matthew Lopper (Committee Member) Subjects: Chemistry

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

Double perovskites have proven to be highly interesting materials, particularly in the past two decades, with many materials in this family exhibiting strong correlations. These materials are some of many novel complex oxides with potential spintronics application. Sr2CrReO6, in particular, is a double perovskite with one of the highest Curie temperatures of its class (> 620 K in bulk and ∼510-600 K in thin films), as well as high spin polarization, ferrimagnetic behavior, and semiconducting properties. This dissertation covers recent work in exploring and tuning physical properties in epitaxial films of Sr2CrReO6. It starts by providing a background for the field of spintronics and double perovskites, bulk and thin film synthesis of Sr2CrReO6, and standard and specialized characterization techniques utilized in both university and national laboratories, and then provides reports of work on Sr2CrReO6 epitaxial films. Examples of exploration and engineering of properties of Sr2CrReO6 include: (1) tuning of electrical resistivity, such as at T = 7 K by a factor of 18,000%, via control of oxygen partial pressure during film growth; (2) enhancement of interfacial double perovskite ordering, demonstrated with high-angle annular dark-field scanning transmission electron microscopy, via the use of double perovskite buffer layer substrates; (3) measurement of magnetization suppression near film/substrate interfaces via polarized neutron reflectometry, which reveals a reduction of thickness (from 5.6 nm to 3.6 nm) of the magnetically suppressed interface region due to buffer layer enhancement; (4) strain tunability of atomic spin and orbital moments of Cr, Re, and O atoms probed with x-ray magnetic circular dichroism, which demonstrates ferrimagnetic behavior and reveals important magnetic contributions of the oxygen sites (∼0.02 µB/site); (5) strain tunability of large magnetocrystalline anisotropy via applied epitaxial strain, revealing anisotropy fields of up to 10s of te (open full item for complete abstract)

Committee: Fengyuan Yang (Advisor); P. Chris Hammel (Committee Member); Ciriyam Jayaprakash (Committee Member); Richard Hughes (Committee Member) Subjects: Condensed Matter Physics

Master of Science (MS), Wright State University, 2011, Biochemistry and Molecular Biology

Peroxisome proliferator-activated receptors (PPAR) and liver X receptors (LXR) are known to play important roles in fatty acid metabolism, interact with each other, and function as heterodimeric partners. Although previous studies indicate that PPARα is activated by long chain fatty acyl-CoA thioesters (LCFA-CoA) and polyunsaturated fatty acids, little is known about the effects of these ligands on the function or interaction of PPARα and LXRα. In this study, hPPARα and hLXRα were shown to directly interact by circular dichroism, fluorescent binding assays, and co-immunoprecipitation. Further experiments suggested that although fatty acids resulted in small structural changes, they significantly altered binding affinities; while LCFA-CoAs decreased the binding affinities, no observable trend was seen with respect to the number of carbon atoms or bonds. In addition, transactivation assays in the presence of certain fatty acids suggested that the combination of PPARα and LXRα increased the activity of the PPARα regulated gene - ACOX, while downregulating the LXRα regulated gene SREBP. As high levels of fatty acids are associated with certain metabolic disorders and also serve as natural ligands for PPARα, changes in structure and/or interaction between PPARα and LXRα may have significant effects on the normal functioning of a cell.

Committee: Heather Hostetler PhD (Advisor); Steven Berberich PhD (Committee Chair); Lawrence Prochaska PhD (Committee Member) Subjects: Biochemistry; Molecular Biology

PhD, University of Cincinnati, 2011, Arts and Sciences: Chemistry

Part I. Heterogeneous, sulfated polysaccharides have attracted significant attention in light of their various biological activities. Of these, heparin has been used extensively as an anticoagulant for decades and is thought to have numerous additional, therapeutic activities. The work detailed in Part I of this dissertation describes several investigations designed to advance the state of heparin analysis through the use of various circular dichroism (CD) based methods. Each of the chapters in Part I, and throughout this dissertation, are meant to provide complementary information while also standing independently. Part II. Modern nuclear forensic investigations are heavily dependent on the use of a wide variety of analytical techniques. These methods are useful in determining the key features for seized nuclear materials, including elemental composition, isotopic enrichment, and age. Such information is invaluable in determining the source of a material, the route it has traveled since production, and its intended use. The ability to conduct nuclear forensic investigations proficiently represents a significant deterrent to groups seeking to carry out a nuclear attack and would be required in responding to an event, should one take place. Several issues exist, however, that will challenge the success of future nuclear forensic efforts. These challenges range from political considerations to the need for new field deployable measurement technologies. Chapter 7 provides a brief overview of several analytical approaches used in nuclear forensics. The introduction to these methods highlights several of the laboratory challenges facing nuclear forensics as well potential future directions for the field. Discussed concepts include separations, counting techniques, mass spectrometry, and alternative approaches to fully characterizing nuclear materials. Chapter 8 discusses the use of alpha spectrometry to critically evaluate a 233U standard reference material as a potenti (open full item for complete abstract)

Committee: Apryll Stalcup PhD (Committee Chair); Thomas Beck PhD (Committee Member); Thomas Ridgway PhD (Committee Member); Henry Spitz PhD (Committee Member) Subjects: Analytical Chemistry

Doctor of Philosophy, The Ohio State University, 2009, Chemistry

Studies on chiral prolinamide-terminated dendrons and dendrimers for their catalytic and chiroptical properties were undertaken. During the course of this research, a convenient multigram preparation of 4-chloropyridine-2,6-dicarbonyl dichloride was developed. This material was utilized in constructing intramolecularly folded pyridine-2,6-dicarboxamide-based dendrons and dendrimers with chiral prolinamide termini. The design of these supramolecular catalysts was based on concepts of preorganization and cooperativity, which stems from the interworking of natural enzymes. The chiral dendron catalysts were synthesized up to their 3rd generation and tested for their catalytic properties in asymmetric direct aldol reactions. Some selected catalysis experiments showed positive dendritic effects in terms of enantioselectivity and diastereoselectivity. In addition, structurally modified dendron catalysts using the 1,3-isophthalamide branching unit as well as 1st generation dendrimer catalysts were prepared. These catalysts also exhibited notable positive dendrimer effects. Circular dichroism (CD) spectroscopic data on benzyl amine derivatives of these dendrons and dendrimers indicated the presence of a generation-dependent helical bias. The helical conformation was determined to be P from the CD analysis together with computational CD investigations conducted in collaboration with the Hadad research group. Crystal structure of 1st and 2nd generation dendrons confirmed the syn-syn conformations of pyridine-2,6-dicarboxamide focal point as well as the P helical arrangement of the terminal prolinamide dendron for G1.

Committee: Jon Parquette Ph.D. (Advisor); Thaliyil RajanBabu Ph.D. (Committee Member); Christopher Hadad Ph.D. (Committee Member) Subjects: Chemistry