Caged compounds are a class of photosensitive reagents used to stimulate cells with spatial control down to a sub-cellular level, and millisecond temporal control. They comprise of biologically important molecule which is modified with a photolabile protecting group. In the absence of light, caged compounds are physiologically silent but irradiation with light induces the release of biologically active species. Illumination under two-photon conditions is particularly advantageous as it enables restriction of the photolysis volume to ~1 fL and it provides deeper penetration into scattering samples. This thesis reports the development of new protecting groups for two-photon uncaging in neuroscience. Mechanistically, the deprotection in these novel groups is designed to operate via an intramolecular photoinduced electron transfer (PeT) between the absorbing unit (electron-donor) and the release module (electron-acceptor). The modular design of these cages ensures separation of absorption and release steps, and allows each process to be tuned and optimized independently. Chapter 1 provides an introduction to the two-photon absorption phenomenon and a historic overview of the uncaging technique. It also discusses recent advances in the development of two-photon sensitive probes used in neuroscience. Chapter 2 describes the exploration of molecular designs for novel protecting groups. A two-photon absorbing dye (electron-donor; fluorene dye) and three different release units (electron-acceptors; nitrobenzyl, pyridinium and phenacyl) were identified as suitable building blocks for the current project. Efficiency of the intramolecular electron transfer between chosen units was evaluated using model dyads which constitute covalently linked electron-donor and acceptor species. Chapter 3 is devoted to the synthesis and photophysical evaluation of nitrobenzyl-based protecting group. Chapter 4 describes the preparation of pyridinium-derived protecting group and demonstrates PeT-mediated release of tryptophan and GABA under one- and two-photon excitation. Hydrolytic instability of pyridinium esters is highlighted. Chapter 5 reports the synthesis, hydrolytic stability and one-photon uncaging efficiency of phenacyl-based derivatives. Chapter 6 discusses properties of developed caged compounds and compares them with other compounds reported in literature. It contains overall conclusions and outlook for the current project. Chapter 7 details the experimental procedures and the characterization of compounds synthesized during this work.

High-valent iron-oxo intermediates play central roles as active oxidants in enzymatic and synthetic catalytic oxidations. Many transition metal catalysts are designed for biomimetic studies of the predominant oxidation catalysts in Nature, the cytochrome P450 enzymes. In this work, a new photochemical method to generate high-valent iron-oxo porphyrin models was discovered. As controlled by the electronic nature of porphyrin ligands, iron(IV)-oxo porphyrin radical cations (Compound I model) and iron(IV)-oxo porphyrin derivatives (Compound II model) were produced. These observations indicate that the photochemical reactions involve a heterolytic cleavage of O-Br in precursors to give a putative iron(V)-oxo intermediate, which might relax to Compound I through electron transfer from porphyrin to the iron or undergo rapid comproportionation reaction with residual iron(III) to afford the Compound II derivative. Furthermore, visible light photolysis of bis-porphyrins-dimanganese(III)-μ-oxo complexes, [MnIII(Por)]2O, was studied in three porphyrin systems. Direct conversion of manganese(III)-μ-oxo dimers to manganese(IV)-oxo porphyrins [MnIV(Por)(O)] and manganese(III) products was observed in benzene solution upon light irradiation. The spectral signature of [MnIV(Por)(O)] was further confirmed by production of the same species in the reported reaction of the [MnIII(Por)Cl] with PhI(OAc)2. Continuous irradiation of bis-porphyrins-dimanganese(III)-μ-oxo complexes in the presence of pyridine or triphenylphospine gave rise to the formation of [MnII(Por)(Py)] or [MnII(Por)(PPh3)], which are stable to be detected. A photo-disproportionation mechanism similar to that for bis-porphyrins-diiron(III)-μ-oxo complex was proposed to explain above photochemical behaviors of bis-porphyrins-dimanganese(III)-μ-oxo complexes. With iodobenzene diacetate [PhI(OAc)2] as the oxygen source, manganese(III) porphyrin complexes exhibit remarkable catalytic activity towards the selective oxidation of alkenes and activated hydrocarbons. Conspicuous is the fact that the readily soluble PhI(OAc)2 in the presence of a small amount of water is more efficient oxygen source than the commonly used PhIO under same conditions. High selectivity for epoxides and excellent catalytic efficiency with up to 10,000 Turnovers (TONs) were achieved in alkene epoxidations. A manganese(IV)-oxo porphyrin was observed in the oxidation of the manganese(III) porphyrin and PhI(OAc)2. However, catalytic competition and Hammett studies suggested that the more reactive manganese(V)-oxo intermediate was favored as the premier active oxidant, even it is too short-lived to be detected in the catalytic reaction.

Dans le cadre des recherches menées dans le domaine de la sûreté des réacteurs nucléaires, la problématique de la formation des oxydes d'iode dans l'enceinte de confinement par la destruction d'iodures organiques lors d'un accident grave a été étudiée avec les moyens du domaine de la chimie atmosphérique.La cinétique de destruction d'iodures organiques (tels que CH3I, CH2I2, CHI3, C2H5I, n-C3H7I et i-C3H7I) par les radicaux OH et O a d'abord été étudiée avec un système de Photolyse Flash – Résonance Fluorescente, dans des conditions représentatives de l'enceinte d'un accident de réacteur nucléaire accidenté. Des constantes cinétiques et leurs énergies d'activation ont été déterminées, dont certaines pour la première fois dans la littérature. Les mécanismes d'oxydation par OH et O des iodures organiques sont soit par abstraction d'un atome d'hydrogène, soit par la formation d'un complexe, menant à l'arrachement de l'atome d'iode. Ensuite, une analyse avec le code IODAIR a permis de réactualiser certaines cinétiques et de compléter ce code avec l'ajout de nouvelles réactions publiées récemment. Une comparaison de la cinétique globale de destruction de CH3I par OH et O dans le code IODAIR et de la constante cinétique globale inclue dans le code ASTEC/IODE a mis en évidence une différence d'un facteur environ 2, ce qui montre l'influence de ces deux radicaux (et principalement de O) sur la destruction des iodures organiques. L'autre voie de destruction majoritaire serait par rayonnement électronique. Les autres radicaux comme H ou N ne contribueraient que très peu à leur disparition. / Within the framework of the research in the nuclear reactor safety field, the iodine oxides formation by organic iodides destruction in the containment has been studied with the means of the atmospheric chemistry field. The destruction kinetics and their activation energy of organic iodides by OH and O radical has been quantified by a Flash Photolysis system able to monitor the oxidant radicals by resonance fluorescence. Those results have been published and some of them for the first time in the literature. The mechanisms leading to the organic iodides destruction are either by a hydrogen atom abstraction, either by the formation of a complex, depending on the organic iodide involved. Then, certain kinetics reactions have been updated in the IODAIR code. Other reactions have been added based on the recent literature available. A comparison of the kinetics destruction of CH3I by OH and O with IODAIR and the global kinetics of destruction in ASTEC/IODE showed a difference of about 2 which shows the importance of these two radicals (and mainly O) in those destruction processes. The other main path of destruction would be by electron radiation. Other radicals like H and N would not contribute significantly to organic iodides destruction. A sensitivity analysis highlighted that organic iodides would mostly be destroyed into iodine oxides with a almost complete conversion within a few hours. Finally, an atmospheric chamber has been used to quantify iodine oxides growth, density and composition. Under the conditions studied, their formation is fast. Particles sizes of about 200- 400 nm are formed within a few hours.

Ce travail a pour objectif d'étudier la formation des aérosols organiques secondaires (AOS) formés dans l'atmosphère à partir de l'oxydation en phase gazeuse de composés organiques volatils en présence d’oxydants atmosphériques (ozone, radicaux hydroxyle, chlore et nitrate). Parmi eux, les hydrocarbures aromatiques polycycliques (HAP) ont été proposés comme étant une source potentiellement importante d’AOS d’origine anthropique. Ainsi, l’oxydation de quatre HAP gazeux majoritaires (naphtalène, acénaphtylène, acénaphtène et phénanthrène) en présence des principaux oxydants atmosphériques a été menée afin de déterminer la formation d’AOS. La caractérisation des phases gazeuse et particulaire par spectrométrie de masse et spectroscopie optique a permis d’identifier les principaux produits d’oxydation afin de proposer des mécanismes réactionnels conduisant à la formation d’AOS. Les différents rendements de formation ont également été déterminés dans le but d'évaluer l'impact de l'oxydation des HAP en phase gazeuse comme source d’aérosols. Les expériences ont été conduites en chambres de simulation atmosphérique ainsi qu'en réacteur à écoulement. L'évolution de l'AOS au cours de son vieillissement a également été étudiée pour identifier les différents processus oxydatifs mis en jeu au sein de l'aérosol organique. / This work deals with the secondary organic aerosol (SOA) formation from gas phase oxidation of volatile organic compounds in the presence of atmospheric oxidants (ozone, hydroxyl radical, chlorine and nitrate radical). Among them, polycyclic aromatic hydrocarbons (PAHs) have been proposed as an important potential source of anthropogenic SOA. The oxidation of 4 main gaseous PAHs (naphthalene, acenaphthylene, acenaphthene and phenanthrene) in the presence of main atmospheric oxidants has been performed in order to investigate the SOA formation. Characterization of both gas and particulate phases has been carried out using mass spectrometry and optical spectroscopy allowing the identification of products in both phases. Then, chemical mechanisms have been proposed in order to explain SOA formation. SOA yields have been also determined to evaluate the impact of the gas phase oxidation of PAHs in SOA formation. Experiments have been carried out using flow tube and atmospheric simulation chambers. SOA fate has been investigated to determine the different oxidation processes involved in SOA aging.

Plusieurs facteurs conduisent à la génération de radicaux libres oxydants dans les organismes qui endommagent les biomolécules et en particulier les protéines du vivant. L’une des cibles de l’oxydation dans les protéines est la méthionine (Met). Son oxydation provoque des effets très dommageables, comme la maladie d’Alzheimer ou les maladies à prion. Nous avons étudié la réaction des radicaux hydroxyle (•OH) et de l’état triplet de la 3-carboxybenzophénone (3CB*) avec ces peptides. Le but de ce travail était de caractériser les espèces transitoires et les produits stables formés après oxydation radiolytique et photolytique de peptides contenant la Met (les dipeptides contenant de la Met et les pepetides plus longs tels que la bradykinine, une hormone humaine importante impliquée dans la diminution de la pression artérielle). Nous avons utilisé la photolyse éclair laser (LFP) et la radiolyse pulsée (PR) (pour les espèces transitoires de courte durée de vie), tandis que la radiolyse gamma et la photolyse continue (pour obtenir une caractérisation des produits stables). Les modifications structurelles ont été caractérisées par des techniques de HPLC et par couplage de la spectrométrie de masse (MS) et la détection par spectrométrie infrarouge couplée à la MS (IRMPD, CLIO laser à électrons libres). En outre, il nous a paru intéressant d’étudier deux autres dérivés de la benzophénone (BP), l’oxybenzone (OXB) et le sulisobenzone (SB), qui sont largement utilisés dans les produits de protection solaire commerciaux. En effet, l’application d’écrans solaires est controversée car certaines études épidémiologiques ont indiqué un risque accru de mélanome malin pour leurs utilisateurs. L’oxydation de dipeptides contenant Met par les radicaux •OH ou photosensibilisée par la ³(CB)* a conduit à la formation de radicaux cations centrés sur le soufre de la Met (>S•⁺) qui ont été en outre stabilisés par la formation de liaison deux centres à trois électrons (S∴Y)⁺, Y étant un atome possédant un doublet libre, ou qui ont subi une déprotonation donnant les radicaux contrés sur le carbone en α (α-S). L’oxydation des dipeptides par •OH a abouti à la formation de sulfoxyde de Met (MetSO) en tant que produit principal. Sans aucun doute, l’identification et la caractérisation des MetSO en solutions désoxygénées contenant la catalase est une étape importante dans la quête de produits stables. Toutefois, dans certains cas, d’autres produits ont été identifiés. En ce qui concerne, les produits stables de photolyse, ce sont des adduits avec le groupement 3CB, probablement résultant de la réaction de recombinaison radical-radical. Un autre produit formé au cours de la photolyse était 3CB-3CB résultant d’une photo-addition, qui a une structure similaire à celle du produit d’irradiations de la BP. Tous les produits identifiés (MetSO et la photo-adduits) ont été formés à partir des radicaux α-S par l’intermédiaire d’une dismutation ou une réaction avec 3CBH•/3CB•⁻. L’oxydation de la Met-Lys-bradykinine (MKBR) a abouti à la formation de photo-adduits similaires par réaction sensibilisée avec 3CB. L’oxydation induite de MKBR par •OH a abouti à plusieurs produits, en accord avec la non sélectivité des radicaux •OH. L’un des principaux produits est le MetSO et la phénylalanine hydroxylée. Notons que l’arginine n’est pas oxydée. Enfin, la photolyse de SB et OXB a été étudiée à l’aide de photolyse éclair au laser femto-et nanoseconde, ainsi que l’oxydation à un électron de ces molécules par radicaux •OH ont été réalisées en PR. Les résultats obtenus ont été comparés à ceux d’autres dérivés de la BP. L’état singulet excité subit un quenching à 100 % par transfert de proton intraomléculaire à l’état excité (ESIPT) en milieu aprotique et en milieu non polaire. Dans le cas d’un solvant polaire, la formation de radicaux phénoxyles a été identifiée. La réactivité des filtres solaires UV-excité vers dérivés simples de méthionine est également en cours d’étude. / Several factors (radiation, metabolism, pollutants) lead to the generation of oxidizing free radicals in living organisms that damage all biomolecules and especially proteins. One of the protein targets is Methionine (Met). Its oxidation causes highly damaging effects, such as Alzheimer’s or prion disease. The aim of this work was to investigate the transient species and the stable products formed after radiolytic and photolytic oxidation of Met-containing peptides. The reaction of hydroxyl radicals (•OH) and 3-carboxybenzophenone triplet state with Met-residue in peptides was investigated for model compounds (Met-dipeptides) and for longer peptides (e.g. Bradykinin). Laser flash photolysis and pulse radiolysis were used to characterize short-lived transient species, while gamma radiolysis and steady-state photolysis were used for quantitative and qualitative characterization of stable products. The structural modifications induced by oxidation have been characterized by the HPLC coupled with mass spectrometry and Infrared Multi Photon Dissociation Spectroscopy (IRMPD, CLIO Free electron laser). The oxidation of investigated Met-containing compounds by •OH or 3CB* led to the formation of S-centered radical cation >S•+ on Met-residue, that were further stabilized by formation of two-centered three-electron bond (S∴Y)+ or underwent the deprotonation reaction yielding the α-(alkylthio)alkyl radicals (α-S). The oxidation of Met-containing dipeptides by •OH radicals yielded the formation of Met sulfoxide (MetSO) as a main product. Undoubtedly, the identification and characterization of MetSO in deoxygenated solutions containing catalase was a milestone in investigation of stable products. However, in some cases, other products were identified. The stable products of photolysis were adducts with 3-carboxybenzophenone moiety, resulting from radical recombination reaction. Another identified product formed during photolysis was 3CB-3CB benzpinacol photoadduct, which has similar structure to the product of BP irradiations. Identified products (MetSO and the photo-adduct) were formed from the α-S via disproportionation or reaction with 3CBH•/3CBH•⁻. The oxidation of Met-Lys-Bradykinin (MKBR) yielded formation of similar photo-adducts via sensitized reaction with the 3CB*. The •OH induced oxidation of MKBR yielded several products, e.g. the sulfoxide and hydroxylated phenylalanine. In addition, other derivatives of benzophenone (oxybenzone (OXB) and sulisobenzone (SB)) were investigated due. They are widely used in commercial sun-protecting products dp to their unique photophysical properties. However the application of sunscreens awakes controversies because some epidemiological studies indicated an increased risk of malignant melanoma for their users. Photo-instability of sunscreen filters would result in reduced protection and may produce reactive free radicals or mutagens. In addition, the reactions of the sunscreens with oxygen free radicals e.g. hydroxyl radicals are likely to arise and they were not yet sufficiently documented. Finally, the radiolytic and photolytic properties of SB and OXB were investigated using femto-and nanosecond laser flash photolysis. Pulse radiolysis studies of the oxidation of those molecules by •OH radicals were performed. The results obtained for SB and OXB were compared to several other benzophenone derivatives. The results shown the formation of excited singlet state that was deactivated efficiently via the Excited State Intramolecular Proton Transfer (ESIPT). In case of polar solvent, the formation of trace amounts phenoxyl radicals was identified, while for nonpolar media those radicals were not observed. The reactivity of UV-excited sun filters towards simple derivatives of Met was also investigated, however, this topic requires further and more detailed investigations.

Este trabalho relata um estudo da fotólise de 4-clorometil-6,8-dimetil-azuleno (1), 4-bromometil-6,8-dimetil-azuleno (2) e 4-clorometil-1-metil-7-isopropilazuleno (3), em solventes polares e apoiares. Os fotoprodutos foram analisados e identificados ou por cromatografia a gás, comparando-se com padrões autênticos, ou por espectrometria de massas. Em solventes polares, foram obtidos somente produtos provenientes de clivagem heterolítica da ligação C-halogênio, enquanto, em solventes apoiares foi observada somente a presença de fotoprodutos de origem radicalar. O produto majoritário na fotólise de 1 em solventes apoiares, em todas as condições experimentais, foi identificado como 1-cloro-4,6,8-trimetil-azuleno, um isômero do reagente, cuja formação não é afetada pela presença de doadores de hidrogênio. Entretanto, este isômero não foi observado em solventes polares, em nenhuma condição experimental. Resultados similares foram obtidos nas fotólises de 2 e de 3. Com base nestas observações, foi possível formular um mecanismo geral para a fotólise dos derivados de azuleno estudados. Em solventes apoiares ocorre clivagem homolítica, levando exclusivamente a produtos provenientes de reações radicalares. Em solventes polares, ao contrário dos mecanismos propostos na maioria dos trabalhos de literatura, ocorre clivagem heterolítica direta, sem o envolvimento de um par radicalar inicial que levaria à formação do carbocátion via transferência de elétron. Foram feitos, ainda, estudos de fotólise por pulso de laser utilizando-se soluções do derivado 1 em solventes apoiares e polares. Entretanto, em nenhuma condição experimental foi possível detectar absorção transiente. / This work reports a study on the photolysis of 4-chloromethyl-6,8-dimethylazulene (1), 4-bromomethyl-6,8-dimethylazulene (2) and 4-chloromethyl-1-methyl-7-isopropylazulene (3) in polar and apolar solvents. The obtained photoproducts were analyzed and identified by gas chromatography, in comparison to authentic standards or by mass spectrometric analysis. In polar solvents, only products formed by the heterolytic cleavage of the C-X (X = Cl and Br) bond are obtained, whilst, in apolar solvents, only photoproducts originated from radical reactions are observed. The major product in apolar solvents in the photolysis of 1, in all experimental conditions, was identified as 1-chloro-4,6,8-trimethylazulene, an isomer of the reagent, whose formation is not affected by the presence of hydrogen donors. However, this isomer is not observed in polar solvents in any experimental conditions. Similar results are obtained in the photolysis of 2 and 3. These observations allowed us to formulate a general mechanism for the photolysis of the azulene derivatives studied. In apolar solvents, homolytic bond cleavage occurs leading exclusively to the formation of products originated from radical reactions. However, in polar solvents direct heterolytic bond cleavage occurs, without the involvement of an initial radical par which would lead to carbocation formation by electron transfer, in oposition to the mechanism proposed in most of the literature works. Flash photolysis studies with 1 in apolar and polar solvents were also performed. However, it was not possible to detect any transient absorption in all experimental conditions used.

La structuration des réseaux neuronaux est un processus fondamental qui assure le bon fonctionnement du cerveau. Afin de comprendre la formation et l’activité de ces réseaux, nous souhaitons développer une méthode qui permette de contrôler in vivo sous l’action de la lumière l'expression de gènes ciblés impliqués dans ce phénomène,à l’échelle d’une cellule neuronale individuelle. Pour ce faire, nous utilisons une réaction de photo-clivage permettant de libérer de façon contrôlée un inducteur d’expression de gène sous l’action de la lumière, à l’aide de groupements photo-labiles sensibles aux excitations bi-photoniques développés au laboratoire et favorables aux applications in vivo. Afin de photo-réguler l'expression des gènes in vivo et avec un contrôle spatiotemporel élevé, nous combinons le système d’expression de gène inductible par la tétracycline « Tet-on » à une variété de précurseurs photo-activables d’analogues de tétracycline que nous avons synthétisés. Ceci devrait nous permettre de disposer d’un système efficace pour l’expression in vivo d’un gène d’intérêt par excitation lumineuse,et plus précisément dans le but de photo-réguler le gène Kir2.1 impliqué dans la régulation de l’activité électrique des neurones. / The structural neural network’s is a fundamental process that ensures the proper functioning of the brain. To understand the formation and activity of these networks, we are developing a method which spatio-temporally controlled in vivo, the expression of targeted genes involved in this process at individual neuron cells scale by light. To achieve this in vivo tests, it is necessary to work with methods which are orthogonal to their cellular environment. Photochemical activation by photo-cleavage of an inert biological precursor offers a unique orthogonal way to attain this spatio-temporal control. Therefore, we have recently developed a new family of photoremovable group which are sensitive to two-photon (TP) excitation sensitive, in order to irradiate at favorable wave-lengths for in vivo applications. Moreover, to photo-regulate the expression of genes with high spatial and temporal resolution, we are combining the inducible gene expression system by tetracycline called « Tet-on » system to different photo-activable precursors of tetracycline analogs obtained by hemi-synthesis. All this, should allow us to get an effective system for the in vivo expression of a gene of interest by light excitation in order to photoactivate Kir2.1, a gene that cell autonomously silences the electrical activity of neurons in a subset of cells.

Hydrogen fuel is one of the most important areas of research in the field of renewable energy development and production. Hydrogen gas can be generated by fuel cells, water electrolyzers, and heterogeneous nanoscale catalysts. It can be burned to directly release chemical energy or condensed for storage and transport, providing fuel for combustion devices or storing excess energy generated by renewable sources such as wind turbines and concentrated solar power assemblies. While platinum is the most active catalyst for hydrogen reduction, its high cost significantly deters its utilization in advanced photocatalytic materials. One approach to mitigating this expense is optimizing the morphology and placement of nanostructured platinum catalysts. Highly crystalline, morphologically-controlled platinum nanoparticles (Pt NPs) have been effectively utilized to increase hydrogen generation efficiency in a variety of nanocomposite materials. However, synthesis routes to high-quality Pt NPs can be dangerous and difficult to replicate. Furthermore, utilization of the Pt NPs in nanocomposite materials is hindered by lack of control over catalyst placement. Nanopeapods are versatile nanocomposites that offer a high degree of control over catalyst placement as well as the potential for interesting new properties arising from the interaction between the catalyst and a semiconductor. Platinum@hexaniobate nanopeapods (Pt@HNB NPPs) consist of linear arrays of Pt NPs encapsulated within the scrolled semiconductor hexaniobate. Pt@HNB NPPs offer significant advantages over similar composites by utilizing the isolated reduction environment of the encapsulated Pt NP arrays to decrease kinetic competition and surface crowding. This work describes the design, fabrication, and implementation of the new nanocomposite platinum@hexaniobate nanopeapods for sensitized hydrogen production under visible light irradiation. The following chapters present facile microwave heating syntheses of highly crystalline Pt nanocubes and Pt@HNB NPPs with consistent morphology and high catalyst loading. A detailed study is also presented of the optical properties of the Pt nanocubes, which produced a UV-range absorbance band that indicates the formation of a localized surface plasmon resonance. Most significantly, preliminary results from visible light photolysis indicate that sensitized Pt@HNB NPPs produce hydrogen in quantities comparable to published systems, and that alteration of experimental parameters may result in even greater yields.

Mineral dust aerosols play an important role in atmospheric chemistry through photolysis and heterogeneous uptake. Both mechanisms strongly depend on the size and composition of mineral dust. Because of the complex nature of dust, chemistry modeling commonly relies on simplified assumptions about the properties of dust particles relevant to physiochemical processes. The goal of this thesis is to investigate the impact of size-resolved composition of dust aerosols on atmospheric photochemistry. The relative importance of dust characteristics in photolysis and heterogeneous loss and the relative roles of the two mechanisms on atmospheric photochemistry are investigated. A new block of spectral aerosol optical properties was developed and incorporated into the tropospheric ultraviolet and visible radiation transfer code in order to calculate spectral actinic fluxes and photolysis rates, J-values. The Fuchs-Sutugin approximation was employed to compute mass transfer from gas to dust mineral species and heterogeneous loss rate, kloss,j. The J-values and kloss,j were incorporated into a one-dimensional photochemistry model to simulate the diurnal cycle of a vertical profile of photochemical species. Several cases of dust loading were considered in the clean and polluted marine environments. A size-resolved mineralogical composition was constructed by selecting a range of the mass fraction of the three main mineral species such as iron oxide-containing clay minerals, carbonate-containing species, and quartz. This work demonstrates that differences in microphysical and chemical properties of mineral dust lead to the important changes in spectral optical properties, J-values, and kloss,j. It also shows that non-linear relationships of photochemical species with two mechanisms result in various changes in the photochemical oxidant fields and that the most important factor controlling the photochemistry field is the dust size distribution, followed by the amount of mineral species with high uptake coefficients and the amount of iron oxide-clay aggregates. This work demonstrates that accounting for regional differences in microphysical and chemical properties of mineral dust will improve the assessment of the impact of mineral dust on tropospheric photochemistry. In addition, it suggests that the size and composition of mineral dust will lead to a deeper understanding of the impact of mineral dust on the global climate system.

Veterinary pharmaceuticals are routinely used in livestock production to treat diseases, prevent infections, and promote growth. However, the potential release of pharmaceuticals from agricultural activities has raised concerns because they may pose detrimental effects to the ecosystems and human health, for example fostering the evolution of antibiotic-resistant bacteria in the natural environment. A better understanding of the environmental fate of veterinary pharmaceuticals is critical to properly assess and mitigate their risks. This dissertation focuses on a major group of veterinary pharmaceuticals, ionophore antibiotics (IPAs), which is sold at over 4 million kilograms per year and constitutes more than one third of the total antibiotic consumption by the livestock industry in the U.S. Despite the extensive usage of IPAs, their environmental fate was not well-understood. Therefore, this study aimed at achieving a comprehensive understanding of the occurrence, persistence, and transformation of IPAs from poultry litter before and after applications to the agricultural lands. Three of the most commonly used members of IPAs were investigated in this study: monensin (MON), salinomycin (SAL), and narasin (NAR). Based on the common management practices of poultry litter, the potential abiotic and biotic transformation reactions of IPAs were examined under varying conditions relevant to the water-soil-litter systems. This dissertation consists of three sections. First, a robust analytical method was developed to quantify IPAs in various environmental compartments, especially in high organic-containing matrices such as poultry litter, and soil and runoff from litter-fertilized lands. Efforts were made to optimize the analytical method with respect to improving extraction recovery, reducing matrix effects, and validating a surrogate standard. Second, lab-scale experiments were set up to determine the chemical properties of IPAs in aqueous environments and to study the abiotic transformation of IPAs, including hydrolysis and photolysis. The results showed that IPAs are prone to hydrolytic transformation in acidic environments, which are likely to be encountered in acidic soils, alum-amended litter (alum: Al₂(SO₄)₃•12H₂O), and acidic runoff. Multiple transformation pathways were proposed based on the identified hydrolysis products. It is also noteworthy that the hydrolysis products of MON still exhibited a toxic effect on the selected microorganism (Bacillus subtilis). SAL and NAR were found to undergo direct photolysis under both UV light and sunlight irradiation. In natural water matrix, IPAs were also degraded by indirect photolysis with hydroxyl radicals generated by light-excited nitrate. Dissolved organic matter can shield IPAs from light and slow down their photolysis. Third, the biodegradation potential of IPAs was first tested in litter and soil microcosms. Factor analysis was conducted to delineate the interaction of water and temperature on IPA degradation in the litter. Litter-fertilized and non-fertilized soil microcosms were compared on the degradation of MON and SAL. Furthermore, the inhibition and biotransformation potential of IPAs were assessed under different redox conditions with litter-enriched cultures. Inhibition tests focused on examining IPAs’ impact on microbial community functions, including denitrification, sulfate-reduction, and methane production. Biodegradation tests were conducted with different electron acceptors, including oxygen, nitrate, sulfate, and organic carbons, with efforts to elucidate primary biotransformation products. On the basis of the results obtained in this study, several recommendations on litter management and IPA selection were made to help mitigate the release and transport of IPAs, as well as enhance their degradation. Overall, this study significantly improved the understanding of the environmental fate of IPAs and the obtained knowledge can aid proper selection of IPAs and management strategies in future applications to minimize the risks of antibiotic micropollutants in the environment.