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This thesis presents an experimental study of a novel non-thermal atmospheric-pressure gas plasma with controlled liquid droplet flow as an efficient source of reactive species that can influence fundamental chemistries in many applications. The electrical discharge is ignited within the confined geometry of a cylindrical quartz tube that allowed for small liquid droplets entrained in the gas flow to pass through the plasma region only once. Neon was used to generate the droplets from deionised water or a buffered solution and additional helium transported the droplets from the nebuliser through the plasma. A diffuse, glow-like discharge formed that remained ignited during droplet transport. Droplets that enter the plasma contribute to the formation of reactive species and survive the treatment without complete evaporation. This observation paved the way for attempts to expose bacteria-loaded droplets to the same treatment. When collected in the presence of a hydrogen peroxide scavenger, plasma treatment did not affect cell viability or growth kinetics. A biomarker of lipid peroxidation was detected, suggesting cell interaction with plasma-generated species delivered into the droplet over short timescales i.e. droplet transit time through the plasma region. Due to the omission of oxygen and nitrogen from the plasma, a vast proportion of RONS that are reported in the plasma-liquid literature cannot be generated, therefore simplifying the chemistry. Hydroxyl radical is thought to feature in the onset of cellular oxidative stress and the species is known to be generated from plasma-liquid interactions. The radical was detected in both the gas and liquid phases from the plasma treatment of droplets and remained chemically active far from the core plasma region. Hydrogen peroxide is a well-known biocide generated from plasma-liquid interactions and was detected in the plasma-treated droplet collection liquid. These results suggest the new technique can remotely apply reactive species contained in plasma-activated droplets or bulk liquid to a target that never comes in direct contact with the plasma itself. This has the potential to be able to influence biological systems in a controlled way by fine-tuning the chemistry generated from the interaction between non-equilibrium plasma and low volume liquid droplets.

Cloud droplets in the atmosphere have an organic component which has been shown to form a monolayer film at the air-water interface of the cloud droplet and the atmosphere. The process by which a cloud droplet film will oxidise and the persistence or loss of an oxidised organic film from the air-liquid interface of a cloud droplet is not well quantified. To determine the surface properties of a cloud droplet film during atmospheric oxidation a measurement of a kinetic variable, the concentration of material comprising an organic film, during reaction with atmospheric radicals was required. The coupling of a Langmuir trough with a neutron reflectometer allows the measurement of the surface coverage of a monolayer in unison with measurement of the monolayer surface pressure. The technique of coupling a Langmuir trough with neutron reflectometry is used extensively for research into the properties of surfactants for industrial and medicinal use. This thesis builds on the work of King et al., (2009) and King et al., (2010), whom produced the first neutron reflectivity measurements of atmospheric proxy monolayers reacting with ozone. This is the first thesis detailing the neutron reflectometry measurement from an atmospheric perspective. Measurements were taken of representative fatty acid molecules which have atmospheric relevance (stearic acid, oleic acid and methyl oleate) as well as measurements of phospholipid molecules which are potential parent species for the fatty acids found in atmospheric waters (I ,2-dipalmitoyl-sn-glycero-3-phosphocholine). The mono layers were reacted with aqueous phase OH radical and with gas-phase ozone to assess the kinetics of the oxidation of the monolayers at the air-water interface.

When air pollution particles encounter water, whether in clouds or in the lungs, they partly dissolve, which starts a cascade of reactions. In clouds, this chemistry can change the mass concentration, chemical composition, and size distribution of particulate matter (PM) left behind when the cloud re-evaporates, making it an important process impacting the earth’s climate. In the lungs, particles induce health impacts via mechanisms that are areas of active research. While these two environments are distinct, both are mediated by the reactions of reactive oxygen species (ROS). Excess amounts of ROS formation triggered by the inhalation of PM is believed to be one of the causes of PM-induced diseases. I utilized different oxidative potential (OP) metrics in my research to quantify aerosol particles’ ability to generate ROS. I further combined lab measurements with statistical analysis and kinetics models to determine the most toxic components in PM and dominant emission sources contributing to OP. In this dissertation, I first delved into the chemistry of ascorbate, one of the most abundant antioxidants in the lung. Ascorbate plays a vital role in the mechanism by which particulate air pollution initiates biological responses. I synthesized the literature on ascorbate, trace metals, and ROS interactions. Recognizing the large disagreements on the ascorbate reactions with iron or copper, I developed a chemical kinetics model to constrain the mechanisms and derive key rate constants. The modeling results suggest trace metals iron and copper are efficient sinks for ascorbate. Secondly, I investigated the interactions of PM and ROS with two other OP metrics – the hydroxyl radical (OH) and dithiothreitol (DTT) assays. The source apportionment analysis on OP indicates that vehicular exhaust and brake and tire wear are primary contributors to OP. I further linked the measured PM mass and OP with the CalEnviroScreen database. This is the first study in the US to uncover a disproportionate burden of OP for people in lower socioeconomic position. The correlational analysis also suggests that the OH assay may be promising in predicting particle-induced adverse health outcomes. My study on OH chemistry extends to the cloud water context. The OH burst, a recently discovered fast OH formation phenomenon in nascent cloud droplets, contributes to OH radicals exceeding all conventional aqueous phase processes. This discovery suggests a pivotal role of OH burst in aerosol oxidation and aging, yet our understanding of this chemistry is limited. I conducted field campaigns to measure the OH burst for different types of aerosols using the newly developed Direct-to-Reagent method and investigated the variations in the OH burst. I further assessed the degree to which ambient particles we collected encountered clouds along their backward trajectories with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results highlight that biomass burning organic aerosol is the largest predictor of the OH burst. Strong negative associations between OH formation and cloud processing history indicate the role of cloud water as a critical medium of OH chemistry. These findings on the dominant factors of the OH burst chemistry shed light on a parametrization of the chemistry within global models for evaluating its broader impacts on the global OH budget, aerosol oxidation, and climate.

The synergistic enhancement of oxidative degradation of atrazine (ATZ) using combined electrolysis and ozonation (EO) was investigated in a laboratory-scale system. Initial studies relied on high performance liquid chromatography (HPLC) for analysis of intermediates. These experiments conducted in sulfate electrolyte at pH 2, 7, and 12 for electrolysis only (E), ozonation only (O), and the combination (EO) indicated that the rate constant of ATZ degradation in the (EO) system could not be explained simply from considering the (E) and (O) processes as additive based on rate constants obtained when they were applied separately. At pH 7, the measured first-order rate constant for (EO) was 0.3441 min-1, a rate 4.78 times as large as the estimated additive rate (0.072 min-1) from (E) and (O) separately. Across the pH range, the rate constant increased from 0.0516 min-1 at pH 2 to 0.3441 min-1 at pH 7 and 0.3065 min-1 at pH 12. Use of a radical scavenger elucidated that hydroxyl radical (HO&#9679) oxidation dominated the (EO) treatment at pH 7 and 12.The impact of chloride and bromide ions in the matrix was also investigated using HPLC at pH 7. Bromide and chloride slightly increased the rate of ATZ degradation compared to sulfate alone when (E) was applied. When (O) was applied, the estimated first-order degradation rate of ATZ decreased 20% with chloride and 87% with bromide compared to the rates in sulfate. The degradation rate of ATZ decreased 86% with chloride in (EO) mode and 93% with bromide, both as compared to sulfate. This is significant since (EO) has been shown in previously published works to produce strong synergism for contaminant removal in sulfate. The proposed mechanism for antagonism with a reactive electrolyte such as chloride or bromide is increased competition in the system for (HO&#9679). Free halogen species and bromide are reactive with HO&#9679, decreasing the likelihood of direct reaction between HO&#9679 and ATZ. In addition to the antagonism, all cases except ozonation in chloride generated either bromate or chlorate, undesirable byproducts.Finally, research using Quadrupole Time-of-Flight (QTOF) Mass Spectrometry was used to identify potential degradation products from the application of (E), (O) and (EO) at pH 2, 7, and 12 in a sulfate electrolyte. Dechlorination and dealkylation products were identified in all conditions studied. Detailed reaction pathways for ATZ are proposed. Six distinct oxidative mechanisms are proposed at pH 7: dechlorination, dealkylation, alcohol transformation, imine transformation, acetamide transformation, and aldehyde transformation. In addition to the previous six mechanisms, a carboxyl transformation pathway is proposed at pH 2 and 12 and a deamination pathway is proposed at pH 12. Abstraction of hydrogen atoms by HO&#9679 is notable as it can initiate all oxidative mechanisms except dechlorination and deamination. Molecular ozone (O3), a selective oxidant, is reactive with ATZ, and participates only in the acetamide transformation pathway.

The presence of persistent organic pollutants in water/wastewater has caused a rising public concern and become a major issue for the sustainable development of society. Electrochemical advanced oxidation processes (EAOPs), which can ultimately mineralize recalcitrant organic compounds to CO2 and H2O, have attracted increasing interest in recent years. While many studies have been conducted on the oxidation effectiveness of a wide variety of organic compounds using various anodes, more efforts should be paid on understanding direct electron transfer (DET) and •OH generation mechanisms in anodic oxidation systems to facilitate the design of electrochemical oxidation systems and decrease the energy consumption. In this thesis, DET and •OH generation mechanisms are investigated using fixed and flow electrodes in different electrochemical oxidation systems. A review of recent progress in understanding the DET and •OH generation mechanisms of the most commonly used anodes is followed by studies on the impact of the presence and state of carbon-containing materials on fixed TinO2n-1 electrodes. There has been considerable recent interest in use of electrodes constructed from this conducting material with studies of DET processes in a traditional flow-by cell showing that the oxygen-containing functional groups play an important role in interfacial electron transfer. In addition to studies on TinO2n-1 fixed electrode systems, attention has also been given to development and use of a novel flow anode system in which a suspension of TinO2n-1 is used as a “flow anode” with the particles charged via contact with the anode current collector. Initial studies focussed on the oxidation of H2O to adsorbed OH* at only 1.5 V vs SHE with the ability to perform oxidation of organic target compounds at this low potential suggesting that flow anodic oxidation represents a viable electrochemical technology for water decontamination. Following studies of the indirect oxidation of organic compounds via generation of adsorbed OH*, we investigated DET processes in the flow anode system in a configuration in which carbon black was utilized as the flow anode material. The results indicate that the potential drop and mass transfer processes at the solid-liquid interfaces play critical roles in DET processes in such suspension systems. Finally, the long-term performance of a continuously operated flow anode system with particles retained in the system using an ultrafiltration membrane (UF). Results showed that the flow anode/UF system was capable of continuously oxidizing perfluorocarboxylic acid for 12 days with a high efficiency and a reasonable energy consumption compared to other technologies.

The oxidative capacity of the troposphere – primarily characterized by the burden of the most abundant and reactive of oxidants, the hydroxyl radical (OH) – determines the lifetime of many trace gases of importance to climate and human health, including air pollutants and the greenhouse gas methane. In the upper troposphere, there is large uncertainty in the oxidative capacity associated with the lightning NOx production, for which reported results range from 16-700 mol NO flash-1. I implemented a lightning parameterization which significantly improves the representation of lightning in one chemical transport and and showed that this parameterization should be more effective in any model. I combined the model simulations configured with this new lightning parameterization with the satellite observations of NO2 column to yield a better estimate of lightning NOx production over the continental US. In cities, urban OH controls the removal rate of primary pollutants and triggers the production of ozone. Interannual trends of OH in urban areas are not well documented or understood due to the short lifetime and high spatial heterogeneity of OH and of OH precursors. Here I synthesized a machine learning technique, satellite observations and simulations from a state-of-art chemical transport model to estimate OH trends between 2005 and 2014 in 49 North American cities. I described trends in the summertime OH with wide variation among different cities. The variation of OH is explained by the shift in chemical regime from one where additional NOx slows chemistry to one where additional NOx speeds chemistry over the years. The identification of chemical regime, in turn, sheds light on the effective policy for controlling ozone.

Atmospheric waters – including fog/cloud drops and aerosol liquid water (ALW) – are important sites for the transformations of atmospheric species and the formation of aqueous secondary organic aerosols (aqSOA). These chemical processes largely occur through reactions with photoformed oxidants such as hydroxyl radical (●OH), singlet molecular oxygen (1O2*), and oxidizing triplet excited states of organic matter (3C*). Despite this, there are few measurements of these photooxidants, especially in extracts of ambient particles. Moreover, ALW – which has high solute concentrations – has great potential to produce aqSOA, but the chemistry in ALW is poorly understood. To address this gap, in this work we measured photooxidant concentrations and formation kinetics in dilute aqueous particle extracts and extrapolated the results to ALW conditions. We also studied the kinetics of triplet reactions with biomass burning phenols under ALW conditions.In chapter 2, we investigated kinetics of six highly substituted phenols that are potentially important in ALW with the triplet excited state of 3,4-dimethoxybenzaldehyde. Second-order rate constants at pH 2 are all fast, (2.6-4.6) × 10^9 M-1 s-1, while values at pH 5 are 2-5 times smaller. Rate constants are reasonably described by a quantitative structure-activity relationship with phenol oxidation potentials. Triplet-phenol kinetics are unaffected by ammonium sulfate, sodium chloride, galactose (a biomass-burning sugar), or Fe(III). In contrast, ammonium nitrate increases the rate of phenol loss by making ●OH, while Cu(II) inhibits phenol decay. Our results suggest that phenols with high KH can be an important source of aqSOA in ALW, with 3C* typically the dominant oxidant. In chapter 3, we evaluated how dissolved organic matter (DOM) and Cu(II) inhibit 3C* probe decay, which can cause an underestimation of 3C* concentrations. Our overarching goal is to find a triplet probe that has low inhibition by DOM and Cu(II), and low sensitivity to 1O2*. We tested 12 potential probes from a variety of compound classes and found that (phenylthiol)acetic acid (PTA) seems well suited for ALW conditions, with mild inhibition and fast rate constants with triplets. We evaluated the performance of both PTA and syringol (SYR) as triplet probes in several aqueous extracts of particulate matter. While PTA is less sensitive to inhibition than SYR, it measures lower triplet concentrations, possibly because it is less sensitive to weakly oxidizing triplets. In chapter 4, we measured photooxidant concentrations in illuminated aqueous particle extracts as a function of particle dilution and used the resulting oxidant kinetics to extrapolate to ALW conditions. Extracts were prepared from winter (WIN) and summer (SUM) particles from Davis, California. As particle mass gets more concentrated, ●OH concentrations in WIN remain relatively unchanged, while they increase in SUM. In both winter and summer samples, 3C* concentrations increase rapidly with particle mass concentrations and then plateau under more concentrated conditions. 1O2* in WIN increases linearly with particle mass while in SUM it approaches a plateau. Under ambient aerosol liquid water conditions we predict a ratio of concentrations of 1O2*: 3C*: ●OH of 10^3 – 10^2: 10^2: 1 with ●OH concentrations on the order of 10^-14 M (including mass transport from the gas phase). Although ●OH is often considered the main sink for organic compounds in the aqueous phase, the much higher concentrations of 3C* and 1O2* in aerosol liquid water suggest these photooxidants are more important sinks for many organics in particle water. In chapter 5, we investigate the seasonal variation of photooxidants by measuring their concentrations in dilute aqueous extracts of ambient particles. Based on UV/Vis and aerosol mass spectrometer data, we categorized our 18 samples into four groups: Winter & Spring (Win-Spr) influenced by residential wood combustion; Summer & Fall (Sum-Fall) without wildfire influence; summer fresh biomass burning particles from wildfires (FBB), and aged biomass burning plumes (ABB). The concentration ratio of 1O2*: 3C*: ●OH in dilute particle extracts is (150 – 1500) : (10 – 300) : 1, respectively, while this ratio in ALW is predicted to be (100 – 1000): (10 – 150): 1. FBB has the highest mass absorption coefficient (MAC) and highest average 1O2* concentration but lowest average quantum yields (Φ) for formation of all three photooxidants. Win-Spr and ABB have similar MAC and higher average Φ of oxidants, indicating aging tends to enhance quantum yields. Sum-Fall has the lowest 1O2* due to low DOC, but highest Φ1O2*. 1O2* and 3C*determined by SYR are linearly correlated with DOC and appear to be independent of sample type.

Abstract: In northern Alberta, the bitumen extraction process from oil sands ores consumes large amounts of water, resulting in the generation of huge volumes of oil sand process water (OSPW). Currently, the treatment of OSPW is considered a major challenge facing the oil sands industry. Moreover, among the different constituents in OSPW, naphthenic acids (NAs) have attracted increasing attention due to their acute toxicity associated with complexity and persistently, which are great hazards towards several organisms. Therefore, great efforts have been made in developing efficient and effective treatment techniques for the remediation of OSPW. The main objective of this research was to investigate the applicability and effectiveness of using combined electro-oxidation and electrochemically activated peroxymonosulfate (EO-PMS) process for the treatment of OSPW. In the first stage of this study, the coupled EO-PMS process showed high removal efficiency of 5-Phenylvaleric Acid (PVA) as a NA model compound, in which EO was enhanced by the successful electrochemical activation of PMS at different electrodes surface. The removal efficiencies increased with the increase in the PMS concentration and applied current, however, decreased at higher levels. Both sulfate radicals (SO4•‾) and hydroxyl radicals (•OH) were found to be the primary reaction oxidants for PVA degradation. A complete removal of 50 mg/L PVA was achieved within 1 h under optimal conditions of carbon felt (cathode), platinum Pt (anode), PMS = 4mM, and current I= 250 mA. In the second stage of this study, the combined EO-PMS process using Pt, dimensionally stable anodes (DSA), boron-doped diamond (BDD), and graphite plate anodes and carbon felt used as cathode was able to reduce the classical and oxidized NAs as well as aromatics in OSPW. Applying the EO only showed lower removal of NAs compared when adding PMS to the system using the same Pt anode. DSA, BDD and graphite plate anodes achieved higher reduction of 76%, 88.4% and 89.7% of classical NAs (O2-NAs) concentration, respectively, while only BDD was able to completely remove all the oxidized NAs. The combined system of EO-PMS presents an efficient technology for the degradation of NAs and has a great potential to be attractive for wastewater treatment in oil sands industry due to its flexibility and high effectiveness at removing constituents of concern from OSPW as part of reclamation approaches.

This dissertation describes the study of anthracene/DNA interactions with the goal of simulating and understanding the conditions of high ionic strength similar to that of cell nucleus that a DNA photosensitizer might encounter (410 mM). The compounds used for studying the photocleavage reactions were bis 9-aminomethylanthracene dye 2 vs. a mono-anthracene 4, two 9-methylaminoanthracene derivatives. We observed that the addition of sodium and potassium chloride salts into photocleavage reactions containing micromolar concentrations of antharcene triggers the conversion of supercoiled, nicked, and linear forms of pUC19 plasmid into a highly degraded band of DNA fragments, representing a dramatic and unexpected increase in levels of anthracene-sensitized DNA photocleavage (KCl > NaCl; pH 7.0 and 22 °C). Experiments using specific ROS scavengers indicate higher levels of ROS production in presence of chloride salt. Further investigation into the mechanism of ROS production suggests more involvement of type I electron transfer in generation of hydroxyl radicals. In contrast to the chloride salts, anthracene-sensitized DNA photocleavage is inhibited (KI ≥ NaI ≥ KBr ≥ NaBr ≥ KF ≥ NaF). The results of CD spectroscopy suggest unwinding of DNA in presence of high concentration of potassium(I) salts and UV-visible absorption and fluorescence experiments point to the possibility of a heavy atom effect involving Br¯ and I¯ anions. DNA photocleavage and fluorescence probe experiments point to the involvement of photo-oxidized form of anthracene in ROS generation.

Coordination chemistry of imidazole thione and selone compounds with 2nd and 3rd row d-block metals are of considerable interest due to their wide-ranging applications of reducing heavy metal toxicity, catalysis, and antimicrobial and antitumor activity. Antioxidant behavior of some imidazole thiones and selones is attributed to their ability to scavenge hydrogen peroxide or other reactive oxygen species as well as their coordination of redox-active iron and copper to prevent hydroxyl-radical-mediated DNA damage. Chapter 1 of this dissertation provides an overview of 2nd and 3rd row d-block metal complexes with imidazole thione and selone ligands and their applications. Ruthenium complexes with labile solvato ligands represent versatile synthons for entry into Ru(II) coordination chemistry. Thus, homoleptic and heteroleptic solvato Ru(II) complexes were synthesized from readily available RuCl3∙xH2O (Chapter 2). An improved synthesis of [Ru(NCCH3)6][BF4]2 affords higher yields with fewer reaction steps, and the [Ru(NCCH3)2(DMSO)3Cl][BF4]1.5[Cl]0.5[Na], [Ru(NCCH3)4(DMSO)2][BF4]2, and [Ru(NCCH3)5(DMSO)][BF4]2, (DMSO = dimethylsulfoxide) mixed-solvato complexes could be useful for synthesizing heteroleptic Ru(II) complexes. Sulfur and selenium compounds can scavenge reactive oxygen species to prevent oxidative damage, and metal coordination can improve this activity. Therefore, novel homoleptic Ru(III) and Ru(II) complexes with methimazole (MMI), N,N'-dimethylimdiazole thione (dmit) and selone (dmise) ligands of the formula [RuL6]Cl3 and [RuL6][BF4]2 were synthesized (Chapter 3). Heteroleptic complexes RuL4Cl2 were also synthesized with the same three ligands. The [RuL6]Cl3 complexes quickly react with hydrogen peroxide, with the MMI and dmise complexes reacting significantly faster than the dmit complex. [Ru(MMI)6]Cl3 also prevents iron-mediated DNA damage at very low micromolar concentrations. Ruthenium nitrosyl complexes are some of the most investigated compounds for biological NO delivery. Therefore, Ru(II)-nitrosyl complexes [Ru(NO)(L)4Cl][BF4]2 (L = dmit dmise) were synthesized from RuCl3·xH2O with silver nitrate as a simple and convenient nitrosyl source (Chapter 4). This novel method considerably simplifies synthesis of Ru-nitrosyl complexes with good yields and avoids the use of unstable or toxic starting materials to generate nitrosyl complexes. This work develops Ru(II) and Ru(III) chemistry as starting materials and with thione, selone, and nitrosyl ligands that have promising biological applications as antitumor, antimicrobial, and photodynamic therapy agents as well as catalytic applications.

Ultrasonic humidifiers use sound vibrations at frequencies higher than can be heard by humans (> 20,000 Hz) to generate aerosolized water also have potential for inducing sonochemical reactions for chemicals present in water. This research focuses on examining oxidants formed within ultrasonic humidifiers, as well as the oxidants effects of contaminants in water used in the systems. Hydroxyl radicals were found using DMPO as a spin trap. Caffeine and 17β-estradiol, as pharmaceutical contaminants of drinking water, were both emitted from the humidifier when present in the water reservoir and would enter breathing air. Emitted 17β-estradiol was found at 60% of the initial concentration filled in the ultrasonic humidifier after 480 minutes. Caffeine exhibited less degradation than 17β-estradiol. Degradation of both pharmaceuticals was attributed to ultrasonic processes, most likely oxidation with hydroxyl radicals produced. Bromide as a contaminant of the fill water was found to remain constant over time.

Interest in inclusion of titanium dioxide nanoparticles in a multitude of industrial and personal products has driven production over the past two decades. Concurrent with increases in nanoparticle production, an increase in nanoparticle movement from use to environment can be expected. Particular concern is focused on TiO2 nanoparticles moving to freshwater compartments. Inherent photocatalytic nanoparticle properties generate reactive oxygen species upon exposure to water, oxygen, and ultraviolet light. While this particular feature is utilized for surface-cleaning and pollution mitigating applications, it poses a significant risk to organisms exposed to these nanoparticles. This risk can be difficult to quantify, exhibited by the variation in toxicity reports from various labs. These variations are a result of differing conditions. Environmental factors such as presence of natural organic matter (NOM), intensity of ultraviolet (UV) light, and the wavelengths of UV light exposure will affect toxicity as well as physical characteristics of the nanoparticle, including size and crystallinity. These variations impart uncertainty to toxicity measurements creating a knowledge gap regarding conditional effects acting on TiO2 to modulate toxicity. The goal of the present research was to develop a comprehensive understanding of the effects that environmentally relevant conditions have on TiO2 radical generation and correlate these conditionally affected rate changes to toxicity measurements. To accomplish these goals, a systematic approach of a full factorial exposure design to quantify the interacting effects of simulated environmental conditions on irradiated TiO2 nanoparticles at eight TiO2 concentrations, five NOM concentrations (measured as dissolved organic carbon), and four UV-A intensities was utilized. Radicals generated by irradiated TiO2 were characterized as hydroxyl radicals using Electron Paramagnetic Resonance spectroscopy. The exposure conditions were characterized and compared to existing literature and natural conditions. The changes in hydroxyl radical generation rates were monitored using fluorescence spectroscopy. Linear regression techniques were used to determine how the conditional effects regulated hydroxyl generation rate. A number of trends were well correlated with conditions. Rate of hydroxyl generation was positively correlated with concentration of TiO2 nanoparticles as a result of increased total available surfaces for photon impingement. Increases in light intensity were likewise positively correlated to increases in hydroxyl generation rate, a result of a greater number of photons interacting with the nanoparticle surface. The reciprocal interaction of these conditions demonstrates classic phototoxic behavior wherein a low concentration of TiO2 and a high intensity of UV-A generates an equivalent response compared to high concentrations of TiO2 and low intensities of UV-A. This reciprocal effect is complicated by the addition of NOM. Increasing total amounts of NOM to suspensions results in decreased hydroxyl generation rate. Decreased generation rates are related to the large number of oxidizable functionalities that exist within the NOM conglomeration of molecules. Readily available functionalities can competitively quench radicals, resulting in the attenuated hydroxyl generation rate measurements. Additional rate reduction as a result of coating effects and aggregation/agglomeration to reduce available surface area may also occur.

The hydroxyl radical (HO•) is a photochemically generated species that is important in the attenuation of organic contaminants in sunlit natural surface waters and in advanced oxidation processes (AOPs) used to treat drinking and wastewater. The steady state concentration of HO•, ([HO•]ss), in photochemical systems is typically measured indirectly using probe compounds. In this work, we investigate the use of caffeine as a photochemical probe for the detection of HO• in the presence of dissolved organic matter (DOM) solutions derived from allochthonous and autochthonous precursors using both the first order and initial rates approach to kinetic analysis to determine [HO•]ss in aqueous solution. Values for [HO•]ss are found to agree within a factor of two of values measured using terepthalic acid (TPA), a well-established probe for the detection of HO•, in the identical DOM solutions. Additionally, we find that caffeine is more selective for HO• than previously believed since it does not appear to undergo reaction with long-lived reactive transients as was formerly presumed.The presence of nitrate in wastewater effluent could play an important role in the formation of HO•, and therefore also in the fate of contaminants in sunlit receiving waters. We investigate the interplay between HO• formation derived from both effluent dissolved organic matter (EfOM) and nitrate (NO3-). The assumption of little to no interaction between NO3- and EfOM during HO• production (RHO•), needed to determine the contribution of DOM to hydroxyl radical formation in waters containing NO3- withoutextracting EfOM from the wastewater, is invalid. We based our findings on measurements of RHO• and [HO•]ss using benzene and caffeine as HO• probes in both whole wastewater effluent and solutions of EfOM isolated by solid phase extraction from the same effluent sample. The RHO• value measured for the isolate in the absence of NO3- (0.074 ± 0.009 (SE) nM s-1) is 1.5 fold higher than that found for bulk, non-isolated EfOM (0.049 ± 0.026 (SE) nM s-1), which was calculated by subtracting the estimated contribution of NO3- to overall HO• production from the RHO• obtained for the Southerly whole wastewater. This difference calculated this way is not significantly different (a=0.05, p=0.39). We find that we are able to reproduce the RHO• found with benzene for Southerly wastewater effluent (0.199 ± 0.022 nM s-1) using a NO3-ROH• curve generated in a Southerly isolate solution (0.178 ± 0.011 nM s-1). Similarly, [HO•]ss values measured in Southerly whole wastewater effluent using caffeine as a probe compound (1.32 ± 0.096 fM) were comparable to measurements made in Southerly EfOM (1.50 ± 0.091 fM). We revise the ratio at which NO3- and DOM contribute equally in solution from the value reported by Vione et al. (2006) of 3.3 x 10-5 [(mol NO3-) (mg-C)-1]) upwards to 8.1 ± 1.5 x 10-5 [(mol NO3-) (mg-C)-1] based on the average of the ratios determined for the three DOM isolates used in this study. Values for [HO•]ss in IHSS isolate solutions and whole wastewater effluent determined by benzene and caffeine are in good agreement, which supports the use of caffeine as a credible HO• probe compound, subject to caveats detailed within this work, in both isolate solutions and whole water containing NO3-.Organic UV-filters are key ingredients found in sunscreens, cosmetics and plastic goods. Concerns have been raised about potential ecological and human health effects of certain organic UV filters that are currently FDA approved for use in the United States. Here, we investigate the photochemical fate of two of these compounds, oxybenzone and sulisobenzone. Both oxybenzone and sulisobenzone have previously been detected in surface waters, seawater, and treated wastewater effluent. Enhanced photodegradation of oxybenzone and sulisobenzone was observed under simulated solar irradiation in solutions of International Humic Substance Society standards (Pony Lake fulvic acid and Suwannee River Natural Organic Matter), filtered wastewater effluent (Southerly Wastewater Treatment Plant in Lockbourne, OH), and Scioto River water (Columbus, OH). Quenching experiments with isopropanol revealed that the main pathway for degradation appears to be reaction with the hydroxyl radical (HO•). Observed degradation rates were 2-3 times slower than estimates calculated using literature reported second-order rate constants and measured hydroxyl radical steady-state concentrations for SRNOM, PLFA and Scioto waters. The Southerly sample, however, exhibited nearly identical expected and observed rate constants, which we take to indicate the presence of unidentified reactive species that can react with oxybenzone and sulisobenzone. Values obtained in this work were used to calculate second-order rate constants for oxybenzone and sulisobenzone with the hydroxyl radical, as well as to estimate environmental half-lives for these compounds. Near surface 24-hour averaged half-lives of 3.0 and 4.0 days were calculated for oxybenzone and sulisobenzone,respectively. When extrapolated to an environmentally representative water column, these same 24-hour averaged half-lives increased to 2.4 and 3.5 years, respectively.

Atmospheric aerosols play an important role in climate by scattering and absorbing radiation and by serving as cloud condensation nuclei. An aerosol’s optical or nucleation properties are driven by its chemical composition. Chemical aging of aerosols by atmospheric oxidants, such as ozone, alters the physiochemical properties of aerosol to become more hygroscopic, light absorbing, and viscous during transport. However the mechanism of these transformations is poorly understood. While ozone is a protective and beneficial atmospheric gas in the stratosphere, it is a potent greenhouse gas in the troposphere that traps heat near the Earth’s surface. It also impacts human heath by irritating the respiratory tract and exacerbating cardiovascular diseases. Additionally, ozone can alter the ecosystem through oxidizing plant foliage which can lead to deforestation and crop losses as well. Both gases and aerosols in the troposphere can react with ozone directly and indirectly with hydroxyl radicals. While daytime aging is thought to be primarily driven by photochemical processes and hydroxyl radicals, ozone is thought to be a key player in nighttime or dark aging processes that can alter the physicochemical properties of aerosols. Measured concentrations of trace gases and aged aerosol components in the field are higher than values predicted based on laboratory studies and computer simulations. Consequently, new experimental approaches are needed to narrow the gaps between observations and mechanistic understandings. In this dissertation, a plume of microdroplets was generated by pneumatically assisted aerosolization and then exposed to a flow of ozone before entering a mass spectrometer. This surface-specific technique allowed for the real-time analysis of reaction products and intermediates at the air-water interface. This work explores the in situ oxidation of iodide, a component of sea spray aerosols, by 0.05 – 13.00 ppmv ozone to explore how heterogeneous oxidation could enhance the production of reactive iodide species. Methods to study the reaction channels and intermediates were also established to not only determine a mechanism of iodide oxidation by ozone, but to enable the study of more complex systems. The developed approach was then applied to examine the oxidation of catechol and its substituted cousins, a family of compounds selected to model biomass burning and combustion emissions, at the air-water interface. While literature suggested that the primary mechanism of catechol oxidation by ozone would be the cleavage of the C1-C2 bond, it was determined that this was only a minor pathway. An indirect oxidation channel dominated heterogeneous processes at the air-water interface, giving rise to hydroxyl and semiquinone radicals that recombine to produce polyhydroxylated aromatics and quinones. This new mechanism of aging represents an overlooked channel by which brown, light-absorbing carbon aerosols are produced in the atmosphere. In addition, the work investigates how reactions on solid particulate aerosols proceed under variable relative humidity. Thin films were developed alongside a novel flow-through reactor to study of how aerosols are transformed by ozone and hydroxyl radicals when exposed to 50 ppbv - 800 ppmv of ozone. This system was employed to probe how catechol reacts with ozone under variable relative humidity. Further work was undertaken to model the adsorption process at the air-solid interface under variable humidity, permitting the estimation of the reactive uptake of ozone by the film at concentrations (50-200 ppbv) seen in rural and urban areas. Together, these results provide an increased understanding of how heterogeneous oxidation of aerosols contributes to aerosol aging processes as well as free radical production in the troposphere.

This thesis explores the effects of pH and chloride on Cu transformations in aqueous solutions typical of both natural waters and physiological conditions: i) The effect of pH on the interaction between Cu and H2O2 in 0.7 M NaCl solution was investigated. A speciation-kinetic model was developed to explore the mechanism. While the rate of Cu(I) oxidation by H2O2 did not change with pH, the rate of reduction of Cu(II) by H2O2 was highly pH dependent due to changes in Cu and H2O2 speciation. ii) The production of oxidizing intermediates increased with increasing pH, with their reactivity assessed by phthalhydrazide hydroxylation and formate degradation experiments, both in presence and absence of additional probe compounds. By comparing observed reactivity with that expected for HO• it was shown that a higher oxidation state of copper, Cu(III), not HO•, is the oxidant formed between pH 6 and 8. Model simulations under experimentally inaccessible environmental conditions showed that Cu(III) production rates did not vary strongly with pH, despite large changes in cycling of Cu between its +I and +II oxidation state. iii) The impact of Cu on Menadiol (MNH2Q) oxidation was examined between pH 6.0 and 7.5. The oxidation of MNH2Q occurred in the open air and the autoxidation rate by O2 increased with pH, with Cu significantly accelerating the oxidation. The results were well-described by a kinetic model where mono-deprotonated menadiol caused the pH dependence, Cu(II) initiated the MNH2Q oxidation, and semiquinone and superoxide played important roles. The high [Cu(I)]ss attained in the system and the production of H2O2 also lead to formation of Cu(III). iv) The impact of chloride and the well-characterized Suwannee River Fulvic Acid (SRFA) on Cu-transformations was investigated. High chloride concentrations lead to highly-reactive Cu(II) complexes but more stable Cu(I) complexes with respect to reaction with all reductants/oxidants in the system. In the absence of O2, SRFA acted like a hydroquinone in the reduction of Cu(II); in the presence of O2 additional reactions mediated by superoxide that consumed the SRFA reductant needed to be considered, as well as complexation of Cu(I) by an oxidized SRFA moiety. A kinetic model that incorporated these key features described the key observations.

Devices to produce non-thermal atmospheric-pressure plasma, or NTP, are gaining increasing attention for a wide range of applications. In addition to promising work in the field of plasma medicine, NTP has also been shown to effectively decontaminate food and surfaces, degrade organic pollutants, and open new routes for nanomaterials synthesis. In many of these applications, plasma-liquid interfaces play a key role in influencing reaction pathways and mediating the transport of reactive species to their intended targets in the liquid phase. Understanding the mechanisms by which reactive species are formed in the liquid phase will aid in the rational design of plasma devices for treating aqueous systems or tissues, and may enable the delivery of tailored ‘cocktails’ of reactive species.In order to carry out this research, a device producing a pin-to-target plasma discharge in direct contact with a target solution was developed. NTP discharges in direct contact with an aqueous solution are known to produce reactive oxygen and nitrogen species in solution, including OH•, NO2• and O2•-. The type and geometry of the discharge employed, as well as the properties of the treated solution, affect the quantity and ratio of species produced. The resulting setup can be tuned for solution acidification, greater oxidative power, limited peak current flow or other attributes depending on the research priorities. The relationship between the voltage-current characteristics of the device, the properties of the solution (pH, conductivity), and the reactive species produced in solution was established. Methods to measure reactive species produced by NTP in liquids were reviewed and developed where necessary. This allowed the evolution of reactive species (e.g. H2O2, NO2-, and OH•) produced in solution by NTP to be determined as a function of time and solution pH. Subsequent reactions of these species were considered, and a model of peroxynitrous acid (O=NOOH) formation and degradation was developed and used to investigate the relevant reaction rates. Evidence is provided that near-surface reactions generating hydroxyl radicals (OH•) or other oxidizing species are the predominant source of active species in NTP-treated solution by tracking the degradation of indigo carmine, a common industrial dye. Selective use of buffers or other additives allows inactivation of certain reaction pathways, enabling contributions from either surface or bulk reactions to be identified. The observed rate of indigo oxidation in contact with the discharge far exceeded predictions from modeling reaction networks based on concentrations of species measured in the bulk solution, indicating a high concentration of highly oxidizing species within a very short distance (< 1 µM) of the plasma-liquid interface. The origin of the reactive species produced (gas phase, boundary layer, or bulk solution) and the relative importance of chemical kinetics versus transport were investigated during the oxidation of the target molecule in solution. Competition experiments and analysis of indigo carmine degradation products were used to identify active agents and properties of the NTP-treated solutions. Furthermore, the effects of NTP on simple biomolecules was investigated. The effect of NTP on solutions of free amino acids, nucleic acids, and the anti-oxidant glutathione was assessed to determine the extent to which irreversible oxidation of these species is induced. This work provides initial evidence of key mechanisms for both in vitro and in vivo studies reported in the literature. These results have important implications for NTP device design and operation for future applications of NTP.

This thesis explores the natural forces controlling variability of the tropospheric oxidants on interannual to glacial-interglacial time scales. The oxidants (primarily OH and ozone) determine the lifetime of many trace gases of human interest, including air pollutants and long-lived greenhouse gases such as methane. The oxidants respond to meteorological conditions, precursor emissions (natural and anthropogenic), and surface and overhead stratospheric boundary conditions, all of which have changed since the Last Glacial Maximum (LGM; ~21ka). This dissertation first examines in mechanistic detail the effect of variability in the lightning source of nitrogen oxides \((NO_x)\) precursors on interannual variability (IAV) of the oxidants in the recent past. An optimized technique is presented to constrain the lightning \(NO_x\) source in the GEOS-Chem global chemical transport model (CTM) to time-varying satellite data from the Lightning Imaging Sensor. This constraint improves the ability of the CTM to reproduce observed IAV in 9-year (1998-2006) hindcasts of tropical ozone and OH. IAV in ozone and OH is more sensitive to lightning than to biomass burning, despite greater IAV in \(NO_x\) from the latter source. The sensitivity of OH to lightning reflects positive chemical feedbacks on ozone production, \(HO_x\) recycling, and loss frequencies. This dissertation next introduces an offline-coupled climate-biosphere-chemistry framework for determining oxidant levels at and since the LGM. Detailed simulations of tropospheric composition are performed by GEOS-Chem driven by meteorological fields from the GISS ModelE general circulation model, land cover from the BIOME4-TG global terrestrial equilibrium vegetation model, and fire emissions from the LMfire model. Time slice simulations are presented for the present day, preindustrial, and two different possible representations of the LGM climate. Sensitivity of the results to uncertainty in lightning and biomass burning emissions is tested. Though well-buffered, all simulations find net reduced oxidative capacities relative to the present day. The most important parameters for controlling tropospheric oxidants over glacial-interglacial periods are changes in overhead ozone, tropospheric \(H_2O\), and lightning. The results are discussed in the context of the ice-core record, particularly for methane.

Hydrogen peroxide (H2O2) is a strong oxidizing agent which is renowned for its damaging effects primarily due to the formation of the extremely reactive hydroxyl radical (*OH) upon its reaction with reduced metal complexes such as those of Fe(II). Kinetic and mechanistic studies of the reaction between the important reduced intracellular vitamin B12 complex cob(II)alamin (Cbl(II)) and H2O2 are reported. Rate constants, stoichiometric information on the reaction, and preliminary information on the intermediates and products of the reaction are presented. The second-order rate constant of the initial reaction between Cbl(II) and H2O2 was determined under three pH conditions and it is shown that Cbl(II) is rapidly oxidized by H2O2 in a pH independent reaction (pH 5-10). Through the use of *OH radical scavengers such as acrylonitrile combined with HPLC product analysis, our studies suggest that the initial reaction is a one electron oxidation of Cbl(II) by H2O2 to give aquacobalamin/hydroxycobalamin (cob(III)alamins, Cbl(III)) and *OH, followed by subsequent reactions of *OH with the corrin ring leading to the formation of complexes with spectra similar to the well-known stable yellow corrinoids. Possible reaction pathways are proposed.

Heterogeneous reactions between gas-phase oxidants and particulate-phase organic compounds impact many important atmospheric chemical processes. For example, little is known about the reaction dynamics of gaseous oxidants with organic compounds found in the atmosphere. The first step of the reaction between gaseous ozone and solid pentacene was investigated using Reflection Absorption Infrared Spectroscopy (RAIRS). Ozone was found to add to pentacene non-selectively and form a range of products after heavy ozone exposure. The rate limiting step had an activation energy of 17 kJ/mol, which is consistent with the findings of previous ozone oxidation studies for the cleavage of a carbon-carbon double bond. Unfortunately the products could not be used to distinguish between probable reaction mechanisms. Hydroxyl radicals (•OH) play a major role processing atmospheric hydrocarbons. Due to their short lifetimes, not much is known about the dynamics of the first steps of •OH reactions. To investigate these reactions, a rotational state-selector was constructed to filter a molecular beam of •OH for reaction dynamics investigations with organic surfaces. The rotational state-selector was designed to leverage the linear Stark effect to pass only suitable molecules in a particular rotational state and block the flow of any other atoms, molecules and ions in a molecular beam. The state-selector was validated and used to positively deflect molecular beams of methyl iodide and D₂O via the linear Stark effect. Future studies with the rotational state-selector will investigate the initial steps of •OH reactions with solid organic compounds.

The kinetics of reactions of nanomolar concentrations of Cu(I) and Cu(II) with H2O2 have been investigated in 0.7 M NaCl and 2.0 mM NaHCO3 at pH 8.0. At these low concentrations of Cu(II), the reaction between Cu(II) and H2O2 was found to occur via the free radical mechanism in which Cu(II) was utilized through one-electron reduction that converted H2O2 into the intermediate reactive radical species O2 with a rate constant of 4.6 x 102 M-1s-1. Measurements of both hydroxylated phthalhydrazide (PhthOH) CL product and the degradation of radiolabelled formate in the absence and presence of known HO scavengers indicated that the reaction between Cu(I) and H2O2 did not occur via a Fenton-like mechanism under the experimental conditions investigated here but involved the formation of a higher oxidation state of copper, Cu(III), with a rate constant of 74 M-1s-1. HO plays an insignificant role because the decomposition of Cu(III) to yield HO is very slow (occurring with an upper limit of 1.6 x 10-4s-1). Cu(III) however, acting as the dominant oxidant, reacts with the substrates that were present (although at much lower rates compared to those of HO ). A kinetic model based on the CuL approach has been developed and shown to satisfactorily describe the reaction kinetics of the inorganic Cu(I)/Cu(II)/H2O2/O2 system over a range of experimental conditions. Key reactions in this kinetic model have been determined by sensitivity analysis.

The oxidation kinetics of ferrous iron, Fe(II), in natural aquatic systems is of interest due to both its importance to the biogeochemistry of iron, a critical micronutrient, and also due to the formation of reactive oxygen species (ROS) during these oxidation reactions. The most important oxidants of Fe(II) are O2 and H2O2, with the H2O2-mediated oxidation process of particular interest due to the potential formation of hydroxyl radical, HO , a powerful oxidizing agent, during this process. The impact of natural organic matter (NOM) upon the H2O2-mediated oxidation of Fe(II) has been explored under both circumneutral freshwater and seawater conditions, with addition of NOM resulting in markedly slower Fe(II) oxidation rates compared to inorganic Fe(II). The formation of less-readily oxidized Fe(II)-NOM complexes is proposed to explain this, with the results quantitatively described by a kinetic model incorporating such complexes. The ability of NOM to complex Fe(II) is lower in seawater due to both ionic strength effects and the presence of cations such as Mg2+ and Ca2+ which compete with Fe(II) for NOM binding-sites, as such, the impact of NOM in seawater conditions was much lower, with the same kinetic model applicable after a decrease in the effective formation constant between Fe(II) and NOM. The question of whether HO is formed during Fe(II) oxidation at circumneutral pH was explored using phthalhydrazide as a probe for HO , with this method extensively characterized and validated for quantitative measurements in natural systems. Initial studies employed the well-characterized ligands EDTA, DTPA and citrate, where it was shown that at pH 8 HO was only formed when Fe(II) was organically complexed; when inorganic Fe(II) is oxidized by H2O2 a species other than HO is formed. Similar results were found when Fe(II) is complexed by NOM, with the HO production data able to be modelled using the same kinetic model developed to describe the Fe(II) oxidation process if it is assumed that only Fe(II)-NOM complexes yield HO . Overall, under circumneutral conditions Fe(II)-NOM complexes, although only slowly-oxidized by H2O2, yield HO , whereas the more-rapidly oxidized inorganic Fe(II) species produce some other unidentified intermediate.

The atmospheric chemistry of cities depends strongly on the concentration of the hydroxyl radical (OH). OH removes organic molecules (τ = minutes - days), nitrogen oxides (NOx: NO + NO2; τ = 2 - 20 h), and sulfur dioxide (τ = 2 - 3 d) from the atmosphere and forms ozone and particulate matter in the process. The spatial and temporal variability of OH is not fully understood due in large part to its strong nonlinear dependence on the concentration of NOx. In this dissertation, I use measurements of the NO2 column from the Ozone Monitoring Instrument (OMI), a satellite-based UV/Visible spectrometer, and calculations from chemical transport models to investigate the relationship of OH and NOx in urban regions. I characterize the instrumental and model performance necessary to accurately infer OH concentration from space-based measurements of the NO2 column. I use the OMI observations and the WRF Chem model to investigate the spatial variability of the NO2 column over a variety of emission sources. I find, not surprisingly, that a result of the nonlinear dependence of OH on NOx is that the lifetime of NOx depends on the spatial distribution of NOx. Where the nonlinear NOx-OH feedbacks are most important, I find that a spatial resolution of 4 - 8 km is necessary for both model simulations and measurements to accurately capture variations of the NO2 column. Although this result is expected, quantitative analyses of the nonlinear coupling were not previously available and the calculations presented in this dissertation serve as a guide to interpretation of coarse-resolution measurements and models. I investigate the response of the NO2 column observed by OMI to variations of wind speed and day-of-week emission patterns. I find that these high spatial resolution measurements (13 × 24 km2 at nadir) contain independent information on both NOx emissions and removal.

Oxidative processes are linked to a number of major disease states as well as the breakdown of many materials. Of particular importance are reactive oxygen species (ROS), as they are known to be endogenously produced in biological systems as well as exogenously produced through a variety of different means. In hopes of better understanding what controls the behavior of ROS, researchers have studied radical chemistry on a fundamental level. Fundamental knowledge of what contributes to oxidative processes can be extrapolated to more complex biological or macromolecular systems. Fundamental concepts and applied data (i.e. interaction of ROS with polymers, biomolecules, etc.) are critical to understanding the reactivity of ROS. A detailed review of the literature, focusing primarily on the hydroxyl radical (HO•) and hydrogen atom (H•) abstraction reactions, is presented in Chapter 1. Also reviewed herein is the literature concerning high density polyethylene (HDPE) degradation. Exposure to treated water systems is known to greatly reduce the lifetime of HDPE pipe. While there is no consensus on what leads to HDPE breakdown, evidence suggests oxidative processes are at play. The research which follows in Chapter 2 focuses on the reactivity of the hydroxyl radical and how it is controlled by its environment. The HO• has been thought to react instantaneously, approaching the diffusion controlled rate and showing little to no selectivity. Both experimental and calculational evidence suggest that some of the previous assumptions regarding hydroxyl radical reactivity are wrong and that it is decidedly less reactive in an aprotic polar solvent than in aqueous solution. These findings are explained on the basis of a polarized transition state that can be stabilized via the hydrogen bonding afforded by water. Experimental and calculational evidence also suggest that the degree of polarization in the transition state will determine the magnitude of this solvent effect. Chapter 3 discusses the results of HDPE degradation studies. While HDPE is an extremely stable polymer, exposure to chlorinated aqueous conditions severely reduces the lifetime of HDPE pipes. While much research exists detailing the mechanical breakdown and failure of these pipes under said conditions, a gap still exists in defining the species responsible or mechanism for this degradation. Experimental evidence put forth in this dissertation suggests that this is due to an auto-oxidative process initiated by free radicals in the chlorinated aqueous solution and propagated through singlet oxygen from the environment. A mechanism for HDPE degradation is proposed and discussed. Additionally two small molecules, 2,3-dichloro-2-methylbutane and 3-chloro-1,1-di-methylpropanol, have been suggested as HDPE byproducts. While the mechanism of formation for these products is still elusive, evidence concerning their identification and production in HDPE and PE oligomers is discussed. Finally, Chapter 4 deals with concluding remarks of the aforementioned work. Future work needed to enhance and further the results published herein is also addressed.

Numerous chemical species are important to the health of biological systems. Some species can be beneficial at low doses and harmful at high doses. Other species are highly reactive and trigger serious cell damage. Improved methods to detect the presence and activity of such species are needed. In this work, several biologically important species were studied using appropriate analytical techniques. Fluoride is an important species in human physiology. It strengthens teeth and gives protection against dental caries. However, elevated concentrations of fluoride in the body can lead to health problems such as dental and skeletal fluorosis. Reported fluoride sensors used fluorescence quenching methods in determining fluoride concentration. Our study explored synthesis and characterization of 1,8-bis(phenylthioureido) naphthalene (compound 1) as a fluoride sensing molecule. Compound 1 showed a remarkable 40 fold enhancement in fluorescence with 5 eq of fluoride addition. Compound 1 also showed possibility of visual colorimetric sensing with fluoride. Free radical mediated oxidations of biomolecules are responsible for different pathological conditions in the human body. Superoxide is generated in cells and tissues during oxidative burst. Moderately reactive superoxide is converted to peroxyl, alkoxyl and hydroxyl radicals by various enzymatic, chemical, and biochemical processes. Hydroxyl radical imparts rapid, non specific oxidative damage to biomolecules such as proteins and lipids. Superoxide also reacts with nitric oxide in cells to yield peroxynitrite, which is highly reactive and damages biomolecules. Both hydroxyl radical and peroxynitrite readily react with amino acids containing aromatic side chains. Low density lipoprotein (LDL) carries cholesterol in the human body. Elevated concentration of LDL is a potential risk factor for atherosclerosis. Previous research drew a strong correlation between oxidized low density lipoprotein (ox-LDL) and plaque formation in the arterial wall. More importantly, oxidative damage causes structural changes to the LDL protein (apo B-100) which might facilitate the uptake of LDL by macrophages. In this study LDL was exposed to various concentrations of hydroxyl radical peroxynitrite and hypochlorite. Thereafter oxidized amino acid residues in apo B-100 were mapped by LC-MS/MS methods. We found widely distributed oxidative modifications in the apo B-100 amino acid sequence.

Environmental photodegradation processes are important in the breakdown of pollutants, as well as in the global element cycles. This thesis will describe several physical organic chemistry projects aimed at increasing our understanding of photodegradation processes as they pertain to specific environmental concerns and potential future technological applications. Following this introductory chapter, a reaction-diffusion theory of singlet oxygen is developed. This theory was developed to improve our understanding of photochemical reactions in systems that contain microenvironments. By thinking of these systems on the nanoscale, we are able to explain the enhanced photochemical reactivity of hydrophobic probe molecules and accurately estimate the physicochemical characteristics of the respective local microenvironment. Chapter 3 applies the reaction-diffusion theory towards explaining the observed enhanced inactivation of waterborne pathogens within wastewater stabilization ponds. The next chapter describes the synthesis of nanoscale photoreactors, a step towards a possible technological application, and a test of the reaction-diffusion theory. The final chapter focuses on another photochemically produced reactive intermediate, hydroxyl radical, and describes the development of fluorescent hydroxyl radical probes.

Oxidative protein surface mapping has gained popularity over recent years within the mass spectrometry (MS) community for gleaning information about the solvent accessibility of folded protein structures. The hydroxyl radical targets a wide breadth of reactive amino acids with a stable mass tag that withstands subsequent MS analysis. A variety of techniques exist for generating hydroxyl radicals, with most requiring sources of radiation or caustic oxidizing reagents. The purpose of this research was to evaluate the novel use of electrochemistry for accomplishing a comparable probe of protein structure with a more accessible tool. Two different working electrode types were tested across a range of experimental parameters, including voltage, flow rate, and solution electrolyte composition, to affect the extent of oxidation on intact proteins. Results indicated that the boron-doped diamond electrode was most valuable for protein research due to its capacity to produce hydroxyl radicals and its relatively low adsorption profile. Oxidized proteins were collected from the electrochemical cell for intact protein and peptide level MS analysis. Peptide mass spectral data were searched by two different “hybrid” software packages that incorporate de novo elements into a database search to accommodate the challenge of searching for more than forty possible oxidative mass shifts. Preliminary data showed reasonable agreement between amino acid solvent accessibility and the resulting oxidation status of these residues in aqueous solution, while more buried residues were found to be oxidized in “non-native” solution. Later experiments utilized higher flow rates to reduce protein residence time inside the electrochemical flow chamber, along with a different cell activation approach to improve controllability of the intact protein oxidation yield. A multidimensional chromatographic strategy was employed to improve dynamic range for detecting oxidation of lower reactivity residues. Along with increased levels of oxidation around “reactive hotspot” sites, the enhanced sensitivity of these measurements uncovered a significant level of background oxidation in control proteins. While further work is needed to determine the full utility that BDD electrochemistry can lend protein structural studies, the experimental refinements reported here pave the way for improvements that could lead to a high-throughput structural pipeline complementary to predictive modeling efforts.

Coronary heart disease is one of the leading causes of death worldwide. After an acute myocardial infarction, timely and effective reperfusion is one of the treatment strategies for limiting the size of the infarct. Reperfusion injury is a serious pathological process that is induced by the restoration of blood flow to previously ischemic tissue. When ischemic myocardium is reperfused and oxygen reintroduced, there is a sudden burst of oxygen free radical production (OFR). Hydroxyl radicals (OH*) are one of the most aggressive species of OFR that attack many molecules in the human body. It is documented that two different sub-cellular defects: deranged calcium handling and alterations of myofilament responsiveness contribute to the development of acute myocardial dysfunction. Although the phenotype of the acute injury response is rather well documented, the underlying mechanism and the relative importance of these two factors remains incompletely understood. To elucidate the mechanism that are responsible for the phenotypical dysfunction after IR injury, we propose to test the following hypothesis: The mechanism of oxidative stress injury is the cummulative effect of a deranged calcium handling and changes in myofilament function, but they exert their maximal impact at distinctly different time-points during the injury phase. To assess the role of altered calcium handling, we investigated whether up-regulation of SR-Ca2+ATPase function (SERCA), can attenuate OH* induced dysfunction. We found out that OH* induced injury is substantially less in transgenic mice with higher SERCA activity, and aggravated in mice with a reduction in SERCA activity. Next we focused on the role of altered myofilament responsiveness at different time points of IR injury. After the exposure of OH*, initially there is a marked increase in diastolic force in parallel with an increase in diastolic calcium. After 45 min of injury diastolic calcium had returned to near-normal, pre-OH* levels, whereas diastolic force remained markedly elevated. Assessment of the myofilament responsiveness confirmed an increased calcium-sensitivity after OH*-induced injury. Our results indicate that the acute injury that occurs after OH* exposure is mainly, if not entirely due to calcium overload, while the later sustained myocardial dysfunction is mainly due to the altered/increased myofilament responsiveness.

The presence of biochemically active compounds (BACs) such as endocrine disrupting chemicals (EDCs) and antimicrobial compounds in the aquatic environment is an issue of great concern. For example, EDCs can cause gender bending in aquatic life, and antimicrobial compounds may lead to the evolution of antimicrobial resistant bacteria. The principal objective of this research was to quantify the effectiveness of combining UV/H2O2 and biological oxidation processes for the mineralization of BACs that commonly occur at trace levels in municipal wastewater and in drinking water sources. Initially, the photolysis and UV/H2O2 photooxidation rates of six BACs [the antimicrobial compounds sulfamethoxazole (SMX), sulfamethazine (SMZ), sulfadiazine (SDZ), and trimethoprim (TMP), the EDC bisphenol-A (BPA), and the analgesic diclofenac (DCL)] were determined. Experiments were conducted in ultrapure water, lake water (Lake Wheeler, NC) and wastewater treatment plant effluent (North Cary Water Reclamation Facility, Cary, NC). Photolysis and UV/H2O2 oxidation rates of BACs were quantified with a quasi-collimated beam (QCB) apparatus equipped with low pressure UV lamps, and the effects of the following factors on the BAC oxidation rates were evaluated: (1) pH, (2) H2O2 concentration, and (3) presence/absence of background organic matter. With the QCB apparatus, parameters such as quantum yields and second order rate constants describing the reaction between hydroxyl radicals and BACs were determined. With these parameters the level of BAC transformation at different UV fluences and H2O2 concentrations was predicted. For example, at treatment conditions used at a full-scale UV/H2O2 plant in the Netherlands (UV fluence = 540 mJ cm-2, H2O2 dose = 6 mg L-1), the following BAC transformation percentages would be obtained in NC lake water: ∼98% for DCL, ∼79% for SMX, ∼60% for SMZ, ∼51% for SDZ, ∼43% for TMP, and ∼46% for BPA. In wastewater treatment plant effluent, predicted BAC transformation percentages were lower at the same treatment conditions because hydroxyl radical scavengers were present at higher concentrations. Apart from determining parent compound removal rates in UV photolysis and UV/H2O2 photooxidation processes, antimicrobial activity removal was quantified by conducting growth inhibition assays. Using the Enterobacteriaceae organism E. coli ATCC® 25922, growth inhibition assay data showed that the antimicrobial activity in photochemically treated water samples was principally a result of the parent compound concentration that remained upon treatment. Therefore, no measurable antimicrobial activity was exerted by the photolysis and UV/H2O2 oxidation products of the studied sulfonamides and TMP. These results were consistently obtained for the different background water matrices and solution pH values that were studied. Finally, the mineralization potential of three 14C-labeled BACs (sulfadiazine, bisphenol-A, and diclofenac) after UV/H2O2 treatment was examined with a consortium of lake water bacteria and with bacteria associated with lake sediments. Upon UV/H2O2 oxidation, mineralization of 14C-labeled BAC oxidation intermediates by lake water bacteria was extremely slow (

We have constructed a database of hydroxyl radical (•OH) cleavage patterns of DNA in order to investigate the relationship between the sequence of a DNA molecule and its three-dimensional structure. The hydroxyl radical cuts DNA at every nucleotide, with the amount of cutting proportional to the solvent accessible surface area (SASA) of the deoxyribose hydrogen atoms. Cleavage fragments are quantified by a fluorescence sequencer, followed by normalization and deposition into the database. Our database currently contains 151 DNA sequences with lengths ranging from 35 to 41 nucleotides. These data have enabled us to develop some general rules regarding the sequence-dependence of DNA structure as well as to predict the cleavage pattern of any given DNA sequence with remarkable precision. Using this prediction algorithm, it is possible to construct structural maps of entire genomes. As there are many examples of DNA binding proteins with highly degenerate binding sites, the use of structural information to locate these sites may be helpful. There also exists other signals, including the signal for nucleosome positioning, which have no apparent consensus, making it likely that the structure of DNA is of critical importance. We have developed algorithms to identify regions of conserved structure using •OH cleavage intensity as a proxy. Within a set of DNase I hypersensitive sites (DHS) obtained from the ENCODE Consortium, we were able to identify a stretch of 12 nucleotides for which the structural conservation is much greater than the sequence conservation. These sites have been dubbed Conserved •OH Radical Cleavage Signatures, or CORCS. Upon further analysis, these CORCS were found to be 17-fold enriched for DHS as compared to shuffled elements. Through the continued analysis of hydroxyl radical cleavage data and development of algorithms to employ the data in biologically meaningful ways, we hope to further our understanding of the relationship between DNA sequence and structure, and how the local structural heterogeneity of genomic DNA contributes to biological function.

Both nanosecond and ultrafast laser flash photolysis with UV-visible and infrared detection were used to observe the transient species generated photochemically from a number of photosensitizers. The reactions of these transient species were monitored spectroscopically with the aid of theoretical computation.In the study of photochemical reactions of riboflavin and nucleosides, it was found that triplet riboflavin can be quenched by a silylated guanosine derivative. TRIR spectroscopy demonstrated that a hydroflavin radical is formed by an electron transfer-proton transfer mechanism. This sequential electron transfer-proton transfer between triplet riboflavin and guanosine derivative provides the direct observation of the photoinduced oxidative damage of riboflavin to the DNA nucleobase. The triplet states of isoquinoline N-oxide and benzocinnoline N-oxide react sluggishly with electron, proton and hydrogen atom donors. These triplets will react with hydroquinone by hydrogen atom transfer (proton coupled electron transfer). Triplet 4-nitroquinoline N-oxide reacts readily with electron donors to from the radical anions as previously reported. The radical anion is protonated on the oxygen atom of the N-oxide group to from a neutral radical. The three N-oxides of this study are not expected to serve as photochemical sources of hydroxyl radical. Singlet states of tirapazamine and desoxytirapazamine were identified by picosecond time-resolved absorption spectroscopy. The lifetimes of the S1 states and fluorescence quantum yields of aromatic N-oxides were found to be controlled by reversible cyclization to an oxaziridine. The S1 states of TPZ and dTPZ are reduced to radical anions by KSCN, KI and NaN3. Using LFP-based methodology, we have determined the rate coefficients for the reaction of hydroxyl radical with a number of monocyclic and polycyclic aromatic hydrocarbons in acetonitrile. We observed the reactivities of hydroxyl radical in acetonitrile. For simple aromatic hydrocarbons, the predominant reaction pathway in acetonitrile is the addition of the hydroxyl radical to the aromatic ring, rather than hydrogen-atom abstraction from the phenyl or benzylic C-H positions. Structure-reactivity analysis, based upon frontier molecular orbital and state correlation models indicate that charge-transfer interactions between hydroxyl radical and a given arene play an important role in the stabilization of the transition state for the reaction. Alpha-Alkoxy and hydroxy radicals were generated through thermal and photochemical reactions. Both the product analysis of the thermal reaction and the direct observation of the transient species involved suggest that alpha-hydroxy radical can very efficiently react with TPZ to form the TPZ-H radical, probably through a direct hydrogen atom exchange between TPZ and ketyl radicals. Alpha-alkoxy radicals can not proceed through this mechanism.

Oxidative modifications to vital cellular components have been described in association with Alzheimer’s disease (AD). Cytoplasmic RNA oxidation is a prominent feature of vulnerable neurons in AD affected regions. However, the role of RNA oxidation in the pathogenesis of AD is unknown. This dissertation examined the magnitude of oxidized mRNAs in AD, identified oxidized mRNA species, and characterized the consequence of mRNA oxidation. An immunoprecipitation method was developed to isolate, characterize and quantify oxidized mRNAs in AD brain. The data showed that 30-70% of mRNAs are oxidized in frontal cortices of AD as compared to age-matched normal control. Identification of oxidized mRNA species revealed that mRNA oxidation in AD is not random but selective. Many identified oxidized mRNA species have been implicated in the pathogenesis of AD. Quantitative analysis revealed that some mRNA species are more susceptible to oxidative damage for which the relative amounts of oxidized transcripts reach 50-70%. To understand whether oxidation of mRNAs is involved in the pathogenesis of AD, the consequence of mRNA oxidation was studied using in vitro translation system and cell lines. mRNA oxidation may have deleterious effects by interfering with normal translational process or by a toxic gain-of-function. Examination of the protein expression from oxidized mRNAs revealed that mRNA oxidation causes a decrease of protein level and associated activity, which may result from the abnormal association of polyribosomes with oxidized mRNAs during the process of translation. Furthermore, we observed that microinjection of oxidized mRNAs into neuronal cells caused cell death, suggesting that increased mRNA oxidation could be lethal to cells. Studies in primary neuronal cultures revealed that RNA oxidation is an early event far preceding cell death induced by insults associated with AD. Neurons are specifically susceptible to RNA oxidation. Some mRNA species highly oxidized in AD brain are also present in oxidized mRNA pool of oxidative insult-treated cultures. A decrease of protein level was observed to oxidized mRNA species in cultures. Taken together, these studies indicate the possibility of oxidized mRNAs to interfere with physiological functions of cells and also implicate the potential contribution of RNA oxidation in the pathogenesis of AD.

Reactive oxygen species are implicates in a variety of diseases and disorders including: Alzheimers disease, immunological disorders and cancer. However, certain ROS, such as superoxide and nitric oxide, play a vital part in the immune defense and in intercellular signaling. In order to develop effective treatments for the diseases in which the production of ROS is insinuated, the amount and identity of the specific ROS that is responsible needs to be known. For this reason, there is a need to develop specific and sensitive techniques for the detection of ROS in biological systems. PEBBLEs (Probes Encapsulated By Biologically Localized Embedding) are nanometer sized optical sensors that have been developed for a variety of analytes. The development of one PEBBLE probe for the detection of the hydroxyl radical (·OH) and two PEBBLE sensors for the detection of hydrogen peroxide (H2O2) and superoxide (O2 -) are discussed in this thesis. Also discussed are some of the problems and possible solutions that have been encountered in the development of the ·OH PEBBLE probe, H2O2 PEBBLE sensor and O2- PEBBLE sensor.

Gas-phase combustion synthesis (GPCS) of nanostructured materials is a powerful synthesis method, capable of generating high purity materials with controlled particle size, size distribution, morphology and composition. However, the fundamental mechanisms governing the formation of nanosized materials are not well understood, particularly the process of particle nucleation. Experimental methods and diagnostic tools, which can be used to improve our knowledge of the physical and chemical processes important in GPCS, are vital to developing combustion synthesis technologies and realizing the potential of nanostructured materials. The research presented in this work demonstrates experimental methods and diagnostic tools that are used to improve our knowledge of the physical and chemical processes that occur in GPCS. In particular, an uv absorption diagnostic is developed for use in measuring hydroxyl radical mole fractions and temperature in the harsh conditions found in GPCS systems. This diagnostic offers a non-intrusive method of making in situ measurements of key radical species in flames with high particle loadings. Additionally, a free-piston rapid-compression facility (RCF) has been modified for use in generating conditions representative of the high temperatures found in GPCS systems. The RCF is used to generate a sustained (∼50 ms) high temperature/pressure environment in which the early steps of SiO2 particle nucleation and growth phenomena are explored. The test times achievable with the RCF are more than an order of magnitude greater than achievable via shock tube experiments and allow the study of particle nucleation and growth over a much longer period. The aforementioned uv absorption diagnostic is used in conjunction with RCF experiments to obtain time dependant concentrations of OH, a radical thought to play a key role in of the kinetics of SiO2 particle formation and growth. The experimental data, combined with thermo-fluid modeling of the RCF, and chemical kinetic modeling of SiH4 combustion, are used to further develop our understanding of particle nucleation and growth in silicon based GPCS systems.