Doctor of Philosophy, The Ohio State University, 2016, Environmental Science

Triclosan (TCS; 5-chloro-2-(2,4-dichlorophenoxy)phenol) and triclocarban (TCC; 3,4,4'-trichlorocarbanilide) are two antimicrobials ubiquitously found in surface waters. Many studies exist for the photolysis and toxicity of TCS, but not for TCC. Both compounds undergo photolysis, and are commonly found simultaneously in surface waters, yet effects of mixtures of these compounds to aquatic organisms are unknown. The aims of these projects are to determine the relative toxicities of TCS, TCC, and their photolysis products, all with and without dissolved organic matter (DOM), and determine the structure of any TCC photoproducts deemed important due to toxicity. The effects of mixtures of these parent compounds and photoproducts will be studied. Acute toxicities were tested using Daphnia magna in 96-hr LC50 assays for TCS, TCC, and photolyzed compounds with and without DOM in moderately hard EPA water. DOM has no impact on the toxicity of TCS (LC50 of 1.62µM (95% confidence interval (CI) 0.920-2.864) without DOM, 1.76 µM (95% CI 1.174-2.652) with DOM). TCS was significantly detoxified after photolysis (LC50s of 8.48µM (95% CI 6.681-10.77) without DOM, 8.51µM (95% CI 2.700-26.84) with DOM). The toxicity of TCC was not affected by DOM (LC50 of 0.087µM (95% CI 0.040-0.191) without DOM, LC50 of 0.147 µM (95% CI 0.050-0.434) with DOM), and TCC photolyzed in EPA water alone was significantly detoxified (LC50 of 2.67µM, 95% CI 2.067-3.443). When TCC was photolyzed with DOM the toxicity of the photoproducts did not decrease (LC50 of 0.032µM, 95% CI 0.017-0.060), indicating that DOM mediates the transformation of TCC to toxic photoproducts. Using this data, binary mixture concentrations were calculated to assess effects of these compounds and photoproducts simultaneously versus their individual effects. LC50s were the basis for toxic units (TUs), with a mixture of ½ the LC50 of one compound and ½ the LC50 of another compound representing one TU, or LC50, at which 50% mort (open full item for complete abstract)

Committee: Roman Lanno (Advisor); Yu-Ping Chin (Advisor); Christopher Hadad (Committee Member); John Lenhart (Committee Member) Subjects: Aquatic Sciences; Chemistry; Environmental Science; Geochemistry; Toxicology

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2007, Photochemical Sciences

Poly(acene)s, linear poly(benzenoid) hydrocarbons, consist of an aromatic linear array. The largest whose synthesis has been authenticated is hexacene, C26H16. However, all reported syntheses of hexacene are difficult to repeat. Synthesis of higher acenes (seven member and higher) have challenged chemists for a long time. Heptacene has been elusive by the attempted classical synthetic routes because such procedures instantly yield an array of dimers. Recently, pentacene and its derivatives have been shown to be excellent candidates with enhanced π-stacking ability for application in OFET and in other electronic devices. Hexacene and heptacene can be considered potential molecules for opto-electronic applications. A classical synthetic procedure to produce heptacene was followed first, which involved Meerwein-Ponndorf-Verley (MPV) reduction of corresponding quinone. Product appeared to be a mixture of dimers of heptacene. In order to minimize dimerization processes, several reactions to substitute at the carbonyl group of quinone with a bulkier group were attempted. However, none of these reactions was successful. The insolubility of the precursor dione seems to be the primary reason for the failure of these reactions. To enhance the solubility and stability of heptacene and precursors, substituted heptacenes retaining the polyacene backbone were designed. Symmetric quinones were considered as the key synthons. While many reduction methods failed to yield the final product from substituted quinones, the borane-THF complex reduced 6,8,15,17-tetraarylheptacene-7,16-quinones to the 7,16-dihydro derivatives. An alternative approach using coupling between in-situ generated dibenzyne and naphthofuran also failed to yield any heptacene core. Dihydroheptacene derivatives emit in the region of 420 – 428 nm in several solvents (ΦF = 0.15  – 0.21 in CH2Cl2) and in the solid state (ΦF = 0.37  – 0.44). These compounds have good solubility in common organic solvents, ar (open full item for complete abstract)

Committee: Douglas Neckers (Advisor); Daniel Pavuk (Other); Thomas Kinstle (Other); Michael Rodgers (Other) Subjects: Chemistry, Organic

Master of Science, The Ohio State University, 2005, Graduate School

Committee: Not Provided (Other) Subjects:

PhD, University of Cincinnati, 2024, Arts and Sciences: Chemistry

This work details various research topics all using distinct types of light to explore the possible mechanisms from sunscreen derivatives to experimental organic azides that have the potential from high magnetic properties to molecular rotors and actuators. The types of light used in different experimental setups range from high-intensive UV lamps to low-intensive UV-visible light-emitting diodes (LEDs). These mechanisms were studied at room temperature and cryogenic temperatures (4 K – 77 K) with multiple characterization techniques in solution and solid-state. Time-resolved methods encompass a range of techniques, including but not limited to NMR, UV-Vis, and IR spectroscopies, as well as nanosecond laser flash photolysis, employed for monitoring excited state reactivity. Cryogenic temperature experiments were used to analyze reactive intermediates using Argon-IR and UV-Vis spectroscopies techniques, and phosphorescence. The plausibility of high-energy photochemical routes and the confirmation of intermediates to validate the reaction mechanisms were assessed using DFT calculations on the Gaussian 16 computational program. The dissertation encapsulates the findings of the subsequent research studies: 1. Photoinduced Triplet Excited State Tautomerization of Ethyl Benzoylacetate: Model Studies for Commercial Sunscreen Application 2. Illuminating the a-Cleavage of 2,2-Diazido-2,3-dihydroinden-1-one in Solution and Cryogenic Matrices 3. Photoexplosivity of 1-Azido-2-Nitrobenzene Crystals In Chapter 2, we explored the mechanism of a sunscreen derivative with a ß-diketone backbone, ethyl benzoyl acetate (EBA), similar to the commonly known filter, avobenzone. This work demonstrated that this sunscreen derivative has triplet reactivity in organic solvents and cosmetic gels, solvents that can be applied to the skin. Furthermore, we have used laser flash photolysis and DFT calculations to confirm the energetic possibility of tautomerization in the t (open full item for complete abstract)

Committee: Anna Gudmundsdottir Ph.D. (Committee Chair); Harshita Kumari Ph.D. (Committee Member); Jeanette Krause Ph.D. (Committee Member); Neil Ayres Ph.D. (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2023, Arts and Sciences: Chemistry

Photochemistry is an outstanding tool to use light energy to achieve synthesis of natural products and applications in developing smart electronics. We have used photochemistry to convert light energy into mechanical energy by investigating photodynamic crystals and explored their real-life applications as actuators. It is vital to understand the underlying causes that are responsible for these crystals to demonstrate photomechanical behavior. Hence, my thesis solely focused on investigating the various factors that are responsible for determining photomechanical behavior upon irradiation. Therefore, mechanistic studies including photoreactions and detection of reactive intermediates in crystals have been investigated by various spectroscopy techniques.

Committee: Anna Gudmundsdottir Ph.D. (Committee Chair); George Stan Ph.D. (Committee Member); Hairong Guan Ph.D. (Committee Member) Subjects: Organic Chemistry

PhD, University of Cincinnati, 2022, Arts and Sciences: Chemistry

Photochemistry has an essential rule for the living creatures on this earth being involved in life-associated photosynthesis process, vision, ozone layer, etc. It is becoming of a great value in therapeutics and pharmaceutical industry via providing an access to synthetic routes that can be challenging using classical thermal organic reactions. Organic photochemistry in the solid state is gaining an increasing attention today providing greener ways in synthesis by running the reaction without the use of organic solvents. In addition, selectivity in solid state can be greatly enhanced due to the restricted movement within the crystal. Finally, photochemistry is now used as a great avenue to explore the photo-dynamic behavior of organic crystals using light as an external stimulus, in which the crystal can respond to light irradiation by mechanical movement that can be beneficial in designing artificial muscles, optical sensors, nanorobotics, optical waveguides and so on. In this work, we studied the photochemistry of ester azides and vinyl azides in solution, solid state and in cryogenic matrices. We also focused on investigating the dynamic effect of these crystals upon irradiation and used both the reaction mechanism and crystal structure analysis to explain the observed behaviors.

Committee: Anna Gudmundsdottir Ph.D. (Committee Member); James Mack Ph.D. (Committee Member); Ruxandra Dima Ph.D. (Committee Member) Subjects: Organic Chemistry

PhD, University of Cincinnati, 2020, Arts and Sciences: Chemistry

Applications of vinylic azides and aromatic azides are tailored based on the photo-reactivity which in turn can be influenced by both external factors from temperature, to pressure, solvent and physical state to mention a few. Photochemistry has the potential to provide relatively easy access to a wide variety of highly desirable compounds with complex ring structures and sensitive reactive functional groups through the use of mild conditions such as visible light irradiation. By generating high energy intermediates and excited states upon irradiation, synthetic possibilities are expanded in comparison to more conventional benchtop synthesis with the use of thermal energy. A lot is known about the reactivity of vinylic and arylic azides but gaps in the fundamental understanding of these structures exist specifically in understanding when we observe singlet versus triplet reactivity in these azides. In that, singlet reactivity could result in very different outcomes than those observed from triplet reactivity specifically for these highly reactive compounds, we must gain a better understanding of the effect of substitution on the reactivity these compounds take as well as external and internal factors and how they may limit the observed intermediates and reactivity in vinyl and aryl azides. These are some of the themes my dissertation will address and propose hypotheses to explain unusual photo-reactivity in these types of azides.

Committee: Anna Gudmundsdottir Ph.D. (Committee Chair); Bruce Ault Ph.D. (Committee Member); Ruxandra Dima Ph.D. (Committee Member) Subjects: Physical Chemistry

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2019, Photochemical Sciences

Ever since the discovery of the DNA molecular structure, this molecule became a desirable target for the researchers aiming to develop anticancer drugs and therapies. The main emphasis of this dissertation was placed on the design, development and studies of photochemical properties of a novel photo activated DNA damaging agent. Upon light irradiation of compound the release of highly reactive 9,10-phenanthrenequinone was observed. Studies of phenanthrene dihydrodioxin interaction with DNA demonstrated the intercalative mode of binding and slightly preferential binding affinity to the AT-rich DNA sequences. The synthesized agent induced a partial transition from B to Z form of DNA. The phenanthrene dihydrodioxin compound proved to be an efficient single-strand DNA photocleaver upon visible light irradiation. This further demonstrates the potential of photomasked ortho-quinones as efficient DNA damaging agents. This work also describes an unusual transformation from pyridinium substituted methane to the corresponding gem-diol in the mild conditions in the presence of air. Proposed mechanism of the reaction involves the formation of reactive oxygen species (ROS). ROS are known to be highly toxic to biomolecules, including DNA. It is demonstrated in this work that the production of ROS intermediates in the reaction of the gem-diol formation can lead to DNA damage in the dark. In the continuous interest of our research group, a series of bis(pyridinium) and bis(3-carboxamidepyridinium) alkane salts were synthesized in order to study through-space electron delocalization and formation of dimer radical cation species upon electrochemical and photoreduction. Investigation of photoinduced charge separation is important for the development of artificial photosynthetic systems and molecular electronics. Studies of unsubstituted and meta-substituted pyridines connected by the alkyl linker of different length provided additional information on the efficiency of the pyridi (open full item for complete abstract)

Committee: R. Marshall Wilson Prof. (Advisor); Farida Selim Prof. (Other); Pavel Anzenbacher Prof. (Committee Member); Alexander Tarnovsky Prof. (Committee Member) Subjects: Biochemistry; Chemistry; Organic Chemistry; Physical Chemistry

Master of Science, The Ohio State University, 2017, Chemistry

Cutaneous leishmaniasis (CL) is the most common form of the neglected tropical disease leishmaniasis, causing skin lesions and ulcers on exposed parts of the body often leaving life-long scars and serious disability. This disease is caused by protozoan Leishmania parasites that are transmitted via the bite of infected female phlebotomine sandflies, a species native to tropical regions. With 0.7-1.3 million new annual cases worldwide researchers are investigating new ways of combatting the illness before it progresses to its lethal forms. Photochemical therapy (PCT), more generally known as photodynamic therapy (PDT), has recently become an attractive mode of treatment in various medical fields due to the affordability and efficiency of new light sources and its low invasiveness. Ru(II)-polypyridyl complexes possess a unique combination of chemical stability in solution, strong absorption throughout the UV-vis light regions, and long excited state lifetimes, making them important contributors to this field. Ruthenium complexes containing monodentate N-heterocyclic aromatic ligand and a distortion of the pseudo-octahedral geometry have been shown to undergo ligand dissociation upon irradiation via the population of the metal-centered ligand field (3LF) state from the excited triplet metal-to-ligand charge transfer (3MLCT) state. This presents a mode of photoinduced target drug delivery that can be used to kill the parasites inside the CL infected cells. The following new complexes were synthesized and characterized using ESI-MS and NMR spectroscopy, [Ru(tpy)(bpy)(Q)][PF6]2 and [Ru(tpy)(bpy)(CQ)][PF6]2 (tpy = 2,2':6',2''-terpyridine; bpy = 2,2'-bipyridine; Q = quinoline, and CQ = chloroquinoline, chloroquine). The photochemical properties of ligand dissociation for each of these compounds were investigated and compared; additionally, their photoproducts were identified using NMR photolysis. The complexes possess low quantum yields of ligand exchange, but more importan (open full item for complete abstract)

Committee: Claudia Turro (Advisor); James Cowan (Committee Member) Subjects: Chemistry; Inorganic Chemistry

PhD, University of Cincinnati, 2017, Arts and Sciences: Chemistry

In this dissertation, we report the photochemical mechanistic investigations on triplet sensitized and unsensitized organic azides and isoxazoles. Photochemical decomposition of the parent compounds generates carbon and nitrogen centered reactive intermediates leading to remarkable applications. Furthermore, reported synthetically modified photoremovable protecting group (PRPG) system shows significantly high quantum yield and broaden the applicability of the benzophenone based PRPGs. Detection of reactive intermediates were done at room temperature and cryogenic temperatures. Required photon energy for the photochemical processes were provided using various UV light sources depending on the experimental procedures. Femto to nano second transient UV /Vis and resonance Raman has been used in aiding the characterization of the intermediates at room temperature. Detection of cryogenic temperature intermediates were done using Electron spin resonance (ESR), FT-IR matrix isolation, fluorescence, phosphorescence and UV/Vis spectroscopy techniques. Gaussian 09 computations have used to predict favorability of reaction pathways and molecular properties. Our investigation reported in this dissertation outlines three different radical types, 1) Triplet 1,4-biradicals a) Generation of irreversible imine biradical by expelling of a N2(g) by an excited state intermediate b) Applicability of irreversible imine biradical intermediate in high quantum yield applications 2) Triplet nitrenes a) Generation Feasibility of triplet aryl nitrene from unsensitized precursor and sensitized precursor at ambient and cryogenic temperatures b) Revelation of factors affecting the lifetime of triplet vinylnitrenes, rigidity and the ring strain approach 3) Singlet alkyl nitrenes How the immediate molecular environment determines the singlet photoproduct formation In chapter 02, we explore photoreactivity of methyl benzophenone with azido modification to study the behavior of benzoph (open full item for complete abstract)

Committee: Anna Gudmundsdottir Ph.D. (Committee Chair); Ruxandra Dima Ph.D. (Committee Member); James Mack Ph.D. (Committee Member) Subjects: Organic Chemistry

PhD, University of Cincinnati, 2017, Arts and Sciences: Chemistry

The work outline in this dissertation, we report the possible mechanisms for the photogeneration of carbon and nitrogen reactive intermediates by studying their excited state reactivity at room temperature and cryogenic temperatures (4 K – 77 K) in both solution and solid state.The feasibility of high energy photochemical pathways and the verifications of intermediates to validate the reaction mechanisms are estimated using DFT, Gaussian 09 computational platform. In Chapter 02, we look at the α-phenyl substituted isoxazole in cryogenic matrices with the focus of capturing azirines from vinylnitrenes. We demonstrated that conjugation of the α-phenyl group to the vinylnitrene moiety renders it more flexible and lower the rotational barrier than vinylnitrenes with a-methyl substituents, and therefore facilitate intersystem crossing of vinylnitrene to azirine, rather than ketenimine. In Chapter 03, we rationalizes and provides physical insight into vinylnitrene stability at room temperature and low temperature. We theorize that the unique reactivity of triplet vinylnitrene is due to their flexibility which is a reflection of their 1,3-biradical character. Moreover, triplet vinylnitrenes can be stabilized by limiting the flexibility of the built in sensitizer and the vinyl C=C bond at room temperature and low temperature. In Chapter 04, we explore the thermal and photochemical reactions of (CH3)3Ga and O3 to form metal oxides, using a combination of matrix isolation, infrared spectroscopy and theoretical calculations. The potential mechanisms for the formation of intermediates were discussed. In Chapter 05, we report the photochemistry of β γ-vinylarylketone with a built-in triplet sensitizer. This work demonstrated that intramolecular sensitization of a simple alkenes can be used to form triplet 1,2-biradicals with the two radical centers localized on the adjacent carbon atoms, which can potentially be used for cis-trans isomerization of simple alkenes in (open full item for complete abstract)

Committee: Bruce Ault (Committee Chair); Anna Gudmundsdottir (Committee Member); Hairong Guan (Committee Member); James Mack (Committee Member) Subjects: Organic Chemistry

PHD, Kent State University, 2017, College of Arts and Sciences / Department of Chemistry

Nitroxyl (HNO) has attracted increasing attention because it has important and unique chemical and biological properties distinct from nitric oxide (NO). Especially, prodrugs of HNO show much promise in treating congestive heart failure. However, HNO is a very reactive molecule that rapidly dimerizes and spontaneously dehydrates to yield nitrous oxide (N2O) and H2O. Thus, precursor molecules named HNO donors are required to generate HNO in situ for chemical and biological studies. Current HNO donors release HNO with half-lives of minutes to hours. Due to the rapid reaction between HNO and biomolecules (k ~ 103-107 M-1s-1), the decomposition of current HNO donors to release HNO is invariably the rate-determining step during the mechanistic studies. Therefore, directly obtaining kinetic and mechanistic data for the reactions of HNO with biomolecules is not feasible because of the slow release of HNO (t1/2 ~ minutes to hours) from current available HNO donors. To address this limitation, we have sought to develop a novel family of photoactivatable HNO donors incorporating various photolabile protecting groups (PPG), which rapidly release HNO on demand. Initial work focused on the development of three N-alkoxysulfonamides incorporating the (3-hydroxy-2-naphthalenyl)methyl (3,2-HNM) phototrigger as HNO donors. Photochemical studies of these 3,2-HNM-based HNO donors revealed the presence of a photo-induced redox O-N cleavage pathway, in addition to the desired HNO generation pathway. Trifluoromethanesulfonyl-based donors maximally released ~ 70% HNO under optimal solvent conditions, and decomposed with a half-life ~ 7 s under a direct xenon light source. The HNO generation was found to occur via a concerted fashion rather than a stepwise mechanism. We also explored the role of 2-nitrobenzyl and 4,5-dimethoxy-2-nitrobenzyl phototriggers in these photoactivatable N-alkoxysulfonamides in an effort to improve the selectivity for the desired HNO generation pathway. However, th (open full item for complete abstract)

Committee: Paul Sampson (Committee Chair); Nicola E Brasch (Committee Co-Chair); Songping Huang (Committee Member); Mietek Jaroniec (Committee Member); Derek S Damron (Committee Member); Gail C Fraizer (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2015, Arts and Sciences: Chemistry

Organic compounds containing a chromophore can be excited from its ground electronic state to higher excited states. This photochemistry of organic compounds can be done in two medium one of which is solution and another is solid state. In solution, the intermediates can be stabilized by solvent molecules and can also freely rotate and thus most of the time there is a loss of stereochemistry. Whereas in solid state due to restricted rotation of the intermediates in the crystal lattice, the stereochemistry is intact. Thus there is much more interest in the solid state photochemistry. To understand the mechanism in solid state it is much needed to identify the intermediates formed in solid state.

Committee: Anna Gudmundsdottir Ph.D. (Committee Chair); Sivaramakrishnan Muthukrishnan Ph.D. (Committee Member); Hairong Guan Ph.D. (Committee Member); James Mack Ph.D. (Committee Member) Subjects: Organic Chemistry

PhD, University of Cincinnati, 2015, Arts and Sciences: Chemistry

In order for a chemical transformation to occur, enough energy must be placed in the system to overcome the activation barrier, making energy the key component of all chemical reactions. Although thermal energy is more traditionally used in this capacity, photochemical and now mechanochemical energy has played a prominent role in promoting chemical reactions to occur. This work will focus on extending the fundamental chemistry of corannulene in both photochemical as well as mechanical environments, where studies on nitrogen based corannulene derivatives such as, nitrocorannulene, azidocorannulene, and azoxycorannulene dimer were performed. Where the photochemistry of 1-nitro corannulene better resembles 2-nitropyrene not 1-nitropyrene; and the photochemistry of 1-azidocorannulene better resembles vinyl azides rather than phenyl azides. In the case of the azoxycorannulene dimer, this represents first corannulene-based molecule synthesized in a mechanochemical ball milling environment and studied photochemically. To further the study of energy of a Spex 8000M mixer/mill we determined a way to measure the relative amount of energy generated in this environment using Diels-Alder reactions and found the conditions were equivalent to roughly 90 °C thermally.

Committee: Anna Gudmundsdottir Ph.D. (Committee Chair); James Mack Ph.D. (Committee Chair); Bruce Ault Ph.D. (Committee Member) Subjects: Chemistry

BS, Kent State University, 2015, College of Arts and Sciences / Department of Chemistry and Biochemistry

HNO (nitroxyl) is a biologically relevant unstable small molecule which rapidly dimerizes in aqueous solution. Thus, there is a need for HNO donors that can quickly release HNO “on demand”. Our group has developed a first generation family of HNO donors which generate HNO rapidly through photolysis. However, some competition from a photoredox side reaction reduces the utility of these molecules. The goal of this thesis was to explore the impact of incorporating a methyl substituent on the rate and selectivity of HNO generation.

Committee: Paul Sampson Ph.D. (Advisor); Alexander Seed Ph.D. (Advisor); Ruth Leslie Ph.D. (Committee Member); Heather Caldwell Ph.D. (Committee Member) Subjects: Chemistry; Organic Chemistry

PhD, University of Cincinnati, 2015, Arts and Sciences: Chemistry

The work outlined in this dissertation, we report Excited State Intramolecular Proton Transfer (ESIPT) of ortho-hydroxy acetophenone derivatives and aromatic Schiff bases occurred on their triplet-excited states. Comparatively, only a little research has shown its triplet reactivity while majority reported to undergo ESIPT on the singlet surface. Enol-forms of these compounds converted to the keto-forms after being transferred the H atom on the hydroxyl group to the electronegative atoms at the γ position (N and O) in the excited states. Moreover, we have compared the ESIPT in solution and solid-states of Schiff bases. Alkyl substituent in the aniline moiety of the aromatic Schiff bases is suggested to act as space-opener, which makes twisted geometries on their ground and excited states and hence play a significant role in controlling the reactivity of the excited species. In contrast, in non-crystalline media, molecular geometries become less predominant in determining the reaction rates as molecules experience free molecular motions compared to the crystalline media. Nanosecond laser flash photolysis of aromatic Schiff bases showed the formation of triplet 1,4-biradicals (triplet excited state of the cis keto-form) in methanol with several microseconds. Nano-crystal suspension in water produces transient absorption spectra of the triplet-excited states of enol-form with the lifetime of ~1-4 µs. Crystal structure analysis and theoretical calculations revealed that these molecules are properly aligned for ESIPT and twisted-geometry of triplet-excited state of enol-form makes them longer-lived compared to the solution. Interestingly, dual phosphorescence was observed for Schiff bases corresponding to the triplet-excited state of the enol-form (n,ϖ*) and triplet-excited states of keto-form (ϖ,ϖ*) generated after ESIPT process. We extended this study to design novel sunscreens agents with broad UV absorption spectrum and high photostability. Proposed compounds, α,β (open full item for complete abstract)

Committee: Anna Gudmundsdottir Ph.D. (Committee Chair); Peng Zhang Ph.D. (Committee Chair); Sivaramakrishnan Muthukrishnan Ph.D. (Committee Member); James Mack Ph.D. (Committee Member); Thomas Ridgway Ph.D. (Committee Member) Subjects: Organic Chemistry

Doctor of Philosophy, The Ohio State University, 2015, Geological Sciences

Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardant that is ubiquitous in the environment and detected in a variety of both biotic and abiotic samples. Mounting concern over the last several decades over the toxic effects of PBDEs has resulted in a global cessation in their production. Nonetheless, PBDEs will continue to be detected in the environment due to their emission from ongoing use and recycling of PBDE-containing products. PBDEs are distally transported to the Arctic, but little is known about the fate of these compounds in Arctic surface waters, especially in the presence of dissolved organic matter (DOM). The present study is focused on quantifying the influence of DOM in the binding (i.e. dissolved organic carbon—water partition coefficients, KDOC) and abiotic photodegradation rates, mechanisms, and product formation of PBDEs under environmentally relevant conditions. My results indicate that PBDEs strongly bind to DOM, whereby the measured KDOC were nearly an order of magnitude lower than previously reported values for the same PBDE congeners in soil or commercially available organic matter. The KDOC values measured in the present study range from 103.97 to 105.16 L Kg-1 of organic carbon, which increase with congener hydrophobicity. This association with DOM facilitates PBDE photodegradation, resulting in at least a factor of 2 increase in rate constants for the indirect relative to direct photolysis of BDE-47. Photodegradation rates are strongly positively associated with DOM aromaticity and negatively correlated to dissolved oxygen. As such, photodegradation likely occurs via reduction reactions with excited triplet DOM and is expected to be insensitive to reactive oxygen species. Finally, the efficacy of fluence-based rate constants is explored for the direct comparison of experiments conducted under variable natural and artificial sunlight. Using the irradiance normalization method, discussed in t (open full item for complete abstract)

Committee: Yu-Ping Chin (Advisor); Kristopher McNeill (Committee Member); William B. Lyons (Committee Member); John Lenhart (Committee Member) Subjects: Environmental Science

MS, University of Cincinnati, 2013, Arts and Sciences: Chemistry

Photoremovable protecting groups are used to release molecules of interest such as drugs and signaling molecules in biochemistry, as protecting groups in synthesis and to release fragrance in household goods. Photolysis of 1 resulted in formation of 2 and release of methanol. In comparison, 3 is photostable. We used laser flash photolysis, phosphorescence, product studies, and density functional theory calculation to elucidate the mechanism for the release from 1 and to explain why 3 is photostable. Intramolecular H-bonding control the reactivity of 1 and 3.

Committee: Anna Gudmundsdottir Ph.D. (Committee Chair); Bruce Ault Ph.D. (Committee Member); James Mack Ph.D. (Committee Member) Subjects: Chemistry

PhD, University of Cincinnati, 2010, Arts and Sciences : Chemistry

This dissertation is divided to two main categories. The first part of dissertation focuses on direct detection and characterization of triplet vinyl nitrene, a high spin reactive intermediates that have never been identified. The second part focuses on photorelease from triplet excited state by using photoinduced cis-trans isomerization mechanism. The common theme that connects the two categories is the reactivity of triplet alkene 1,2 biradicals that are generated from acyclic nonaromatic carbon center. The first chapter gives a detailed report on direct detection and characterization of long-lived triplet alkene 1,2 biradical from such system. The reactivity of triplet alkene 1,2 biradical has been used to form triplet vinyl nitrene, which is characterized using time-resolved techniques. The final chapter of the dissertation presents a new photoprotecting group which will release carboxylic acid derivatives by photoinduced cis-trans isomerization and has shown the release of methanol from this system. The mechanism of release involves triplet alkene 1,2 biradical as a key intermediate in the photorelease.

Committee: Anna Gudmundsdottir PhD (Committee Chair); James Mack PhD (Committee Member); Bruce Ault PhD (Committee Member) Subjects: Organic Chemistry

PhD, University of Cincinnati, 2007, Arts and Sciences : Chemistry

In this thesis we have investigated the photochemical reactivity of alkoxy carbonyl azides 1-4 and 2-Benzoyl-3-Methyl-2H-Azirine 39 in different chemical environments. Our results show that photolyzing azides 1-4 in methanol results in intramolecular energy transfer to form triplet alkoxy carbonyl nitrenes 1n-4n that decay mainly by H-atom abstraction from the solvent. Our data also support the postulate that triplet nitrenes 1n-4n absorb another photon and cleave to form alkoxy radicals that abstract an H-atom from the solvent to form the corresponding alcohols 8-12. Photolyzing azides 1-3 in argon matrices at cryogenic temperature yields isocyanic acid from secondary photolysis of triplet nitrenes 1n-3n. Similarly, photolyzing azide 4 in matrices yields isocyanate 4i via secondary photolysis of triplet nitrene 4n. Thus, triplet alkoxy carbonyl nitrenes can be formed selectively via intramolecular photosensitization, but these intermediates are themselves highly photoreactive. The solid state photochemistry of azide 3 reveals a unique bimolecular reactivity leading to the formation of 34. We speculate that formation of 34 can be explained in terms of both singlet as well as triplet nitrene reactivity. We have selectively formed an oxaziridine ring via solid state reactivity, which is the discovery of a new chemical reaction for alkoxy carbonyl azides. In case of azide 4, we observed a different reaction pathway of the nitrene in the solid state as compared to its solution photolysis. We investigated the photoreactivity of 2-benzoyl-3-methyl-2H-azirine (39) and found that irradiation above 300 nm selectively cleaves the C-N bond to form triplet vinyl nitrene 42, which decays into 40. In comparison irradiation with light below 300 nm breaks the C-C bond to form ylide 41, which yields 46 as the final product. Laser flash photolysis (wavelength = 355 nm) produces a transient with wavelength of maximum absorption at 400 nm that we assign to 42, whereas laser flash photo (open full item for complete abstract)

Committee: Dr. Anna Gudmundsdottir (Advisor) Subjects: