In medical and health physics, we are interested in the effects of ionizing radiation on biological systems, in particular, human biology. The main process by which ionizing radiations causes damage to biological systems, is through the creation of radicals close to DNA strands. The radicals are very reactive and those created within close proximity to DNA will react with the DNA causing damage, in particular single strand or double strand breaks. This damage to the DNA can cause mutations that can kill the cell, either mitotically or apoptotically, or possibly lead to a cancerous formation. Therefore it is important to study how these radicals interact with DNA strands for a correlation between the resultant products of radical reactions and DNA strand breaks. For this study, we look at the most important radical, the OH radical and it's addition to DNA bases. We will study, through quantum chemistry, the thermodynamics of OH radical addition to the four bases, Adenine, Guanine, Cytosine and Thymine. The Jaguar program developed by Schrodinger was used for DFT calculations of the Gibbs free energy of the addition. In addition, calculations for the partial charge, HOMO's and Fukui indices were calculated and compared to experiment.

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. / Engineering and Applied Sciences

The process of radiation induced corrosion of copper is not well understood. The most obvious situation where the knowledge of this process is crucial is in a deep repository for high level spent nuclear fuel where the fuel will be sealed inside copper canisters. The radiation will penetrate the canisters and be absorbed by the surrounding environment. In this study gamma irradiations of polished and pre-oxidized copper cubes in anoxic pure water, air of 60-100 % RH and in humid argon were performed. The copper surfaces were examined using IRAS, XPS, cathodic reduction, SEM, AFM, and Raman spectroscopy. The concentration of copper in the reaction solutions was measured using ICP-OES.  Also the formation of oxidative species caused by radiation absorption of water was studied by numerical simulations using MAKSIMA software. The corrosion of copper during gamma irradiation vastly exceeds what is expected. The production of oxidative species caused by radiation absorption of water is hundreds of times too low to explain the amount of oxidized copper. A possible explanation for this mismatch is an enhanced radiation chemical yield of HO· on the copper surface. Another one is an increased surface area due to oxidation of copper. One speculation is that HO· interacting with the copper oxide can cause oxidation of the metal. If the thermodynamic driving force is large enough then electrons can be conducted from the metal through the oxide to the oxidant. A dramatic increase in surface area together with an increased interfacial yield of HO· might explain the radiation enhanced corrosion process. / <p>QC 20151022</p>

The use of hydroxyl radical based reaction (Fenton reaction) for the destruction of organic pollutants has been widely reported in the literature. However, the low pH requirement and rapid hydrogen peroxide consumption rate make the application of conventional Fenton reaction difficult for in-situ treatment. In this study, we conducted a modified Fenton reaction by introducing a chelating agent into the reaction system that could prevent Fe(OH)3 (s) precipitation even at a neutral pH condition and reduce the H2O2 consumption rate by controlling the Fe2+ concentration. A chelating agent (mono-chelate or poly-chelate) combines with Fe2+ or Fe3+ to form stable metal-chelate complexes in solution. This decreases the concentration of Fe2+ in the solution so that reactions can be carried for longer contact times. Experimental results (citrate was the chelating agent) for 2,4,6-trichlorophenol (TCP) showed that TCP degradations were greater than 95% after 2.5 h and 24 h reaction times at fixed pH 5 and 6, respectively. For the same reaction time, the normalized chloride formations were 85% at pH 5 and 88% at pH 6. Several other chlorinated organic compounds were also chosen as the model compounds for detoxification studies because of their chemical structures: trichloroethylene (unsaturated hydrocarbon), carbon tetrachloride (highly oxidized compound), 2,2-dichlorobiphenyl, and biphenyl (a dual-aromatic ring structure). Poly-chelating agents (such as polyacrylic acid-PAA) provide multiple Fe2+/Fe3+ binding sites in the modified Fenton reaction for the oxidation of contaminants (2,2-dichlorobiphenyl, and biphenyl) at a neutral pH environment. Numerical simulation based on the kinetic model developed from the well known Fenton reaction and iron-chelate chemistry fits experiment data well for both standard and chelate modified Fenton reactions. In this dissertation, it was proven that both monomeric (citrate) and polymeric (PAA) chelate modified Fenton reactions were effective for dechlorination of carbon tetrachloride from aqueous phase by the superoxide radical anion. On the other hand, PAA (a poly-chelating agent) can also be used for solid surface modification by polymerization of acrylic acid (monomer). The successful degradations of biphenyl and trichloroethylene by the PAA functionalized silica particles/membrane demonstrate the versatile applications of the chelate modified Fenton reaction.

Aerosols of nitrate solutions were irradiated in the presence of radical scavengers in an attempt to measure the yield of hydroxyl radical in both the aqueous phase and the gas phase. Carbon monoxide, benzoic acid, benzene and cyclohexane were used as scavengers to trap hydroxyl radical. The products from the reaction of these scavengers with hydroxyl radical were analysed with High Performance Liquid Chromatography and mass spectrometry. The radiant flux in the chamber was measured via ferrioxalate actinometry, both with bulk liquid and aerosol droplets. Many quantitative results were obtained but several anomalies were found. This suggests that Mie theory is not capable of predicting rates of photochemical reactions within droplets.

É urgente o desenvolvimento de novas tecnologias para o tratamento de água nos dias atuais. Neste contexto, os processos oxidativos avançados (POA) tem sido bem-sucedido no tratamento de contaminantes presentes em efluentes industriais e na rede de esgoto doméstico. Neste trabalho, estudamos um dos POA, a fotocatáliseheterogênea por meio da síntese de fotocatalisadores mistos de nióbio e titânio utilizando-se o método Pechini, com uma temperatura de calcinação de 470 oC. Foram sintetizados os fotocatalisadores PNB000, PNB018, PNB030, PNB070, PNB099 e PNB100, onde os números mostram aporcentagem em mols de pentóxido de nióbio presente em cada um deles. Estes fotocatalisadores foram submetidos a um segundo tratamento térmico a 800oC, durante 6 horas, e obtivemoso PNB000_01, PNB018_01, PNB030_01, PNB070_01 e PNB100_01. A caracterização dos fotocatalisadores foi feita por: análise de espectroscopia de energia dispersiva (EDS); área superficial determinadas por isotermas de adsorção e dessorção de nitrogênio, BET; imagens de microscopiaeletrônica de varredura (MEV); difração de raios-X; análises térmicas (termogravimetria e análise térmica diferencial), determinação de band gap por reflectância difusa. O potencial para serem usados como fotocatalisadores heterogêneos para degradação de compostos orgânicos foi avaliado pela eficiência fotônica de geração de radicais hidroxilas(OH)sob radiação de lâmpada UVA (15 W). A análise de EDS confirmou acomposiçãoem mol de TiO2 e Nb2O5presentes nosfotocatalisadoressintetizados. A área superficial obtida por isotermas (BET) do PNB018 (161,7 m²/g), PNB030 (130,8 m²/g), PNB070 (150,5 m²/g) mostraram-se maiores do que ado TiO2 P25 (52,68 m²/g). As imagens de MEV mostrou que estes fotocatalisadoressão constituídos de partículas manométricas. Outra característica dos óxidos com quantidade intermediária de mols de Nb2O5 (18, 30 e 70%) foi a estrutura amorfa determinada por difração de raios-X. Por sua vez, os óxidos tratados a 800oC apresentaram estruturas cristalinas edifratogramas de raios-X completamente diferentes do TiO2 e do Nb2O5, comprovando-se que são novos materiais.As medidas de energia de band gapmostrou diferenças significativas quando comparamos o TiO2 P25 (Egap 3,22eV) e o PNB000 (Egap 2,90eV). Isso leva a concluir que estes fotocatalisadores sintetizados pelo método Pechini necessitam de uma energia menor para que ocorram as transições eletrônicas. O fotocatalisador PNB070, que apresenta 70% em mols de pentóxido de nióbio, apresentouOH de 0,104 da mesma ordem de grandeza do TiO2 P25 (OH 0,134) e ligeiramente menor do que o OH do Nb2O5.nH2O (OH 0,164). Dessa maneira, supõe-se que o PNB070 tenha o mesmo potencial de eficiência que o TiO2 P25 para fotodegradações. Por sua vez, os fotocatalisadores que passaram por um segundo tratamento térmico a 800 oC mostraram valores de rendimento quântico de produção de radicais hidroxilas bem inferiores aos seus originais. Por exemplo, o PNB070_01 teve OH de 0,003. Esses resultados sugerem que o aumento da cristalinidade pode diminuir a atividade fotocatalítica, ou, que o estado amorfo dos fotocatalisadores deste trabalho favorece o aumento da velocidade de transferência de elétrons e a da fotocatálise. / Nowadays, the development of new technologies for the treatment of water is urgent. In this context, the advanced oxidative processes (AOP) has been successful in the treatment of contaminants foundin industrial effluents and domestic sewage. In this work, we have studied an AOP, the heterogenousphotocatalysis, by means the synthesis of niobium and titanium mixedphotocatalysts, employing calcination temperature of 470 oC.The PNB000, PNB018, PNB030, PNB070, PNB099 and PNB100photocatalysts were synthetized, where the numbers show the percentage in mol of Nb2O5content in each of them. These photocatalytswere submitted to a second heat treatment to 800oC during 6 hours, and PNB000_01, PNB018_01, PNB030_01, PNB070_01 and PNB100_01 were obtained. The characterization of the photocatalysts was made by: analysis of the energy dispersive spectroscopy (EDS); the surface area determined by adsorption and desorption isotherms of nitrogen, BET; images of scanning electron microscopy (SEM); X-ray diffraction; thermal analysis (thermogravimetry and differential thermal analysis), determination of the band gap by diffuse reflectance.Their potential to be used as heterogeneous photocatalystsfor degradation of organic compounds was evaluated by means the determination of the photonic efficiency for hydroxyl radical production (OH)under radiation of UV-A lamp (15 W). The EDS analysis confirmed the composition in mol of TiO2 and Nb2O5 present in the synthesizedphotocatalysts. Surface area obtained by isotherms (BET) of PNB018 (161.7 m ²/g), PNB030 (130.8 m ²/g), PNB070 (150.5 m ²/g) were higher than TiO2 P25 (52.68 m ²/g). SEM images showed that these photocatalysts consist of nanoparticles. Another feature of the oxides with intermediate amount of moles of Nb2O5 (18, 30 and 70%) was the amorphous structure determined by X-ray diffraction. On the other hand, the oxides treated to 800 oC showed crystalline structures and X-ray patternscompletely different from TiO2 and Nb2O5, proving that the synthetized oxides are new materials.The band gap energy measurements showed significant differences when we compare TiO2 P25 (Egap 3.22 eV) and the PNB000 (Egap 2.90 eV). This allow us to conclude that thephotocatalysts synthesized by Pechini method require lower energy in order to have electronic transitions. The PNB070 photocatalyst, which has 70% in mols of niobium pentoxide, showed OHof 0.104 of the same order of magnitude of TiO2 P25 (OH0.134) and slightly smaller than the OH of Nb2O5.nH2O (OH 0.164). For this reason, we can assume that PNB070 has the same potential of the TiO2 P25 for organic compound photodegradation. The photocatalyststhat were submittedthrough a second heat treatment at 800 oC showed quantum efficiency of hydroxyl radical production values well below their original. For instance, PNB070_01 showed OHof 0.003. These results suggest that increased crystallinity can reduce the photocatalytic activity, or the amorphous structures of the photocatalysts of this work improve the electron transfer rates and the photocatalysis.

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.

The photosensitized processes significantly enhance photolysis of various chemicals in the aqueous system with dissolved organic matter (DOM) as sensitizer. The excitation of chromophores on the DOM molecule further generates reactive species as triplet states DOM, singlet oxygen, hydroxyl radical, carbonate radical etc. We investigated the photosensitization properties of Beaufort Fulvic Acid, Suwannee River Fulvic Acid, South Platte River Fulvic Acid, and Jeddah wastewater treatment plant effluent organic matter with a sunlight simulator. DOM photochemical properties were characterized by observing their performances in 3DOM*, singlet oxygen, hydroxyl radical production with indirect probing protocols. Sensitized degradation of 0.1 μM and 0.02 μM 2, 4, 6- Trimethylphenol exhibited higher pseudo-first-order rate constant than that of 10 μM. Pre-irradiated DOMs were found to be depressed in photochemical properties. Photolysis of 5 different contaminants: ibuprofen, bisphenol A, acetaminophen, cimetidine, and caffeine were found to be enhanced in the presence of sensitizers. The possible reaction pathways were revealed. Long time irradiance induced change in contaminants degradation kinetics in some DOM solutions, which was proposed to be due to the irradiation initiated indirect transformation of DOMs. Key Words: Photolysis Dissolved Organic Matter, Triplet State DOM, Singlet Oxygen, Hydroxyl Radical, Contaminants Degradation.

The presence of excess free radicals in the body can result in severe health consequences because of oxidative damage to cells. Spin traps may be used as a probe to examine radical reactions in cells, but there is a need for less toxic and more lipid soluble examples. Melatonin is one of the numerous antioxidants used to scavenge free radicals in the body and reportedly one of the most efficient radical scavengers known. It is relatively nontoxic and easily crosses the lipid bilayer in cell membranes. Melatonin is thought to undergo a multistep oxidation process and this work investigates the potential for it to be used as a spin trap. The presence of electron withdrawing or donating groups added to melatonin may stabilize an intermediate and allow it to function as a spin trap. The essence of this study is to conduct a computational inquiry into the relative stability of melatonin, selected derivatives, and the partial oxidation products formed from the scavenging of hydroxyl radical. To determine this, geometries were optimized for each molecule at the DFT/B3LYP/6-31G(d) and HF/6-31G(d) levels of theory.

Contamination of surface and ground water from industrial wastes and anthropogenic activities represents one of the greatest challenges to the sustainable development of human society. Heterogeneous photocatalysis, a kind of advanced oxidation process characterized by the production of highly oxidative hydroxyl radicals, is a relatively novel subject with tremendous potential in water treatment applications.     The purpose of this research was first to develop feasible hydroxyl radical detection methods, which can be used to evaluate efficiency of photocatalytic process, and second to prepare immobilized TiO2 films with high photocatalytic activities by the sol gel method.     The feasibility of Indigo carmine and phthalic hydrazide as OH-radical probes was investigated. The organic dye Indigo carmine absorbs visual light strongly at 610 nm and its destruction can be monitored conveniently in a spectrophotometer. Results showed that both ·OH and HO2· can bleach Indigo carmine, and the bleaching yield of ·OH was pH independent. The photocatalytic dye bleaching in black light UV illuminated Degussa P25 TiO2 aerated suspensions was then investigated. A strong pH dependency of the bleaching yield was found.  This implies that the quantum yield of OH radical at pH 3 is one fourth compared to that at pH 10. The reaction of the OH radical with phthalic hydrazide will form strongly chemiluminescent 3-hydroxyphthalic hydrazide. Using the more specific phthalic hydrazide as OH radical probe, an even stronger pH dependent quantum yield of OH radical was found. At pH 10 the quantum yield reached the same magnitude as that obtained by using Indigo carmine, whereas the quantum yields at acidic pH were close to zero. However it was found that the addition of phosphate and fluoride anions can substantially enhance the OH radical yield at acidic pH by blocking the adsorption of phthalic hydrazide onto the TiO2 surfaces. Hence the adsorption of phthalic hydrazide to TiO2 is an important factor to consider when this method is used.     Photocatalytic TiO2 films coated on metal plates were prepared by a sol gel method using titanium isopropoxide as TiO2 precursor and isopropanol as solvent. The photocatalytic activity of the obtained films was evaluated by bleaching of indigo carmine at pH 9 under black light UV irradiation. The effect of the molar ratio of isopropanol, water and hydrochloric acid to titanium isopropoxide was studied. It was also shown that the activities of TiO2 films are considerably influenced by calcination temperature, coating cycles and the supporting materials. / Förorening av yt- och grundvatten från industrier och humana aktiviteter utgör en av de största utmaningarna för en hållbar utveckling av det mänskliga samhället. Heterogen fotokatalys, en slags avancerad oxidations process som kännetecknas av att starkt oxidativa hydroxylradikaler produceras, är en relativt ny teknik med stor potential för vattenrening.     Ett syfte med detta licentiatarbete var först att utveckla och genomföra olika metoder för att detektera bildningen av hydroxylradikaler såväl i laboratoriet som i tekniska miljöer. Det andra syftet med arbetet var att syntetisera immobiliserade TiO2 filmer med hög fotokatalytisk effektivitet med en sol-gel metod.     Möjligheten att använda indigokarmin och ftalhydrazid som OH-radikalprob undersöktes. Det organiska färgämnet indigokarmin absorberar synligt ljus starkt vid 610 nm vilket gör att dess nedbrytning lätt kan följas i en spektrofotometer. Resultaten av gammaradiolys visade att båda •OH och HO2• kan bleka indigokarmin och att den blekning som härrör från •OH var oberoende av pH. Fotokatalytisk blekning av indigokarmin med blacklight UV bestrålning av  Degussa P25 TiO2 suspensioner undersöktes sedan. Ett starkt pH-beroende av blekningsutbytet erhölls vilket tolkas som att kvantutbytet av OH-radikaler vid pH 3 är en fjärdedel jämfört med det vid pH 10.     När ftalhydrazid reagerar med OH-radikaler bildas starkt kemiluminiscent 3-hydroxy-ftalhydrazid. Med denna  specifika OH-radikalprob, erhölls ett ännu starkare pH beroende. Vid pH 10 var kvantutbytet i paritet med det som erhölls med indigokarmin, medan kvantutbytet vid lågt pH var nära noll. Tillsats av fosfat-  och fluoridjoner visade sig avsevärt öka OH-radikalutbytet vid lågt pH-värde genom att blockera adsorption av ftalhydrazid på TiO2 ytorna. Adsorptionen av ftalhydrazid på TiO2 är således en viktig faktor när denna metod används.     Fotokatalytiskt verksamma TiO2-filmer på metallplattor framställdes med sol-gel metoden med titan-isopropoxide som TiO2-prekursor och isopropanol som lösningsmedel. Den fotokatalytiska aktiviteten av TiO2-belagda plattor utvärderades genom blekning av indigokarmin vid pH 9 under blacklight UV-bestrålning. Effekten av olika proportioner mellan isopropanol, vatten och saltsyra till titan isopropoxide undersöktes. Det visade sig att denfotokatalytiska aktiviteten av TiO2-plattorna i hög grad påverkades av kalcineringstemperatur, beläggningscykler och materialet i plattorna.