[pt] Os nitretos, carbetos, boretos e óxidos de metais de transição na forma de nanopartículas, têm recebido nos últimos anos uma grande atenção no mundo científico, por apresentar propriedades físicas e químicas bem específicas, com aplicações diretas na indústria de alta tecnologia. Esta tese de doutorado foi motivada pelo desenvolvimento e avaliação experimental de uma nova configuração de reator, tubular e de fluxo cruzado, que promove um melhor contato entre as fases gasosas reagentes, possibilitando a execução da síntese de nanopartículas em temperaturas mais baixas. O reator consiste em um tubo de quartzo e um sistema de alimentação de gás NH3(g), dotado de chicanas que o redireciona promovendo uma distribuição mais homogênea deste nos orifícios de alimentação no reator. O TiCl4, uma vez vaporizado, é arrastado pelo argônio na direção axial do reator e o NH3 é injetado na direção radial central do reator. No aparato experimental desenvolvido foram avaliados os efeitos das variáveis do processo, temperatura, tempo espacial e pressão parcial do TiCl4 sobre o tamanho médio de cristalitos das partículas sintetizadas. Os resultados experimentais obtidos mostraram que no reator proposto foi possível produzir, na temperatura ambiente, nitreto de titânio (TiN) com 100por cento de conversão e tamanhos de cristalitos abaixo de 20 nm. Além da produção do TiN, também observou-se a formação de um co-produto, também particulado, o cloreto de amônio (NH4Cl). Nas análises por difração de Raios-X observou-se a presença de dióxido de titânio (TiO2) na forma de anatásio e de oxinitreto de titânio. O aparecimento destas fases pode ser explicado pela alta reatividade do nitreto de titânio com o oxigênio e vapor de água presentes na atmosfera e a sua elevada superfície específica. / [en] Nitrides, carbides, borides and oxides of transition metals in the form of nanoparticles have received in recent years the attention in the scientific world, by their specific physical and chemical properties, with direct applications to the high technology industry. This thesis was motivated by the development and experimental evaluation of a new reactor concept, tubular and cross-flow, which promotes better contact between the gas-phase reactants, allowing the execution of nanoparticle synthesis at lower temperatures. The reactor consists of a quartz tube and a gas supply system (NH3), equipped with baffles that redirects the gas promoting a more homogeneous distribution of it in the holes that feed the reactor. The TiCl4 vaporized is carried by argon gas, in the axial direction, to the reactor and NH3 is injected in the radial direction in the central region of the reactor. In the experimental apparatus developed were evaluated the effects of process variables, temperature, space time and TiCl4 partial pressure, on average crystallite size of the synthesized particles. The experimental results obtained show that in the proposed reactor was possible to produce, at room temperature, titanium nitride with 100% conversion and crystallite size below 20nm. Besides the production of the titanium nitride was also observed the formation of a particulate co- product, the ammonium chloride (NH4Cl). In the X-ray diffraction analyzes was observed the presence of titanium dioxide (anatase) and titanium oxynitride. The occurrence of these phases can be explained by the high reactivity of titanium nitride with oxygen and water vapor present in the atmosphere and their high specific surface.

Neste trabalho, uma série de curcuminoides monocetônicos foram sintetizados por meio da condensação entre acetona e 11 diferentes aldeídos aromáticos. Esses curcuminoides foram posteriormente convertidos em seus álcoois e cetonas saturados correspondentes por meio de reações de hidrogenação catalítica. Os compostos obtidos foram avaliados quanto às suas atividades antimicrobianas frente a um painel representativo de bactérias cariogênicas empregando o método de microdiluição em microplacas. Além disso, as vias de fragmentação em fase gasosa dos curcuminoides monocetônicos protonados foram investigadas por espectrometria de massas sequencial com ionização por eletrospray (ESI-MS/MS) em combinação com dados de massas acuradas, dados de experimentos de espectrometria de massas de estágios múltiplos (MSn) e de troca de deutério, bem como em dados termoquímicos estimados por Química Computacional. Dentre os 31 curcuminoides avaliados, a curcumina A (10), 1E,4E)-1,5-bis(4-hidroxifenil)penta-1,4-dien-3-ona, e o (1E,4E)-1,5-bis(4-hidroxifenil)penta-1,4-dien-3-ona (11), apresentaram a atividade antimicrobiana mais efetiva, com valores de concentração inibitória mínima (CIM) de 50 g/mL contra Streptococcus mutans e de 50 g/mL contra Streptococcus mitis. Os valores de CIM obtidos foram menores que os valores de CIM previamente relatados para a curcumina, que é o análogo -dicetônico do composto 10. As relações estrutura-atividade inferidas sugerem que o grupo hidroxila ligado aos aneis aromáticos e a ligação dupla entre C2-C3 e C2-C3 e o grupo carbonila e C1 são as características responsáveis pela atividade antimicrobiana. Os resultados mostraram que o íon H e o íon acílio D, resultantes de dois rearranjos de hidrogênio competitivos, são os mais intensos no espectro de íons produtos dos curcuminoides protonados. Além da identificação de alguns íons diagnósticos, este trabalho comprovou que a formação de alguns íons produtos ocorreu a partir de um íon intermediário resultante de uma ciclização de Nazarov da molécula protonada, cuja ocorrência foi reportada previamente na literatura. Os dados termoquímicos suportaram as estruturas dos íons propostos e mostraram que a posição da hidroxila fenólica no anel aromático desempenha um papel fundamental sobre a ciclização de Nazarov. Os resultados deste trabalho poderão contribuir futuramente na identificação dos produtos resultante do metabolismo dos estudos in vitro e in vivo sem a necessidade de padrões ou isolamento desses metabolitos / In this work, a series of monoketone curcuminoids were synthesized by condensation between acetone, and 11 (eleven) different aromatic aldehydes. These curcuminoids were subsequently converted to their corresponding saturated alcohols and ketones by means of catalytic hydrogenation reactions. The obtained compounds were evaluated for their antimicrobial activities against a representative panel of cariogenic bacteria using microdilution plating method. In addition, the gas-phase fragmentation pathways of the protonated monoketone curcuminoids were investigated by ionization tandem mass spectrometry (ESI-MS/MS) in combination with accurate mass data, multi-stage mass spectrometry (MSn), and deuterium exchange experiments, as well as in thermochemical data estimated by Computational Chemistry. Among the 31 curcuminoids evaluated, curcumin A (10), (1E,4E)-1,5-bis(4-hydroxyphenyl)penta-1,4-dien-3-one, and (1E,4E)5-bis(4-hydroxyphenyl)penta-1,4-dien-3-one (11) showed the most effective antimicrobial activity, with minimum inhibitory concentration (MIC) values of 50 g/mL against Streptococcus mutans and 50 g/mL against Streptococcus mitis. MIC values of curcumin A (10) were lower than the previously reported MIC values for its -diketone analog of compound 10. The inferred structure-activity relationships indicated that the hydroxyl group attached to the aromatic rings and the double bond between C2-C3 and C2\'-C3 \'and the carbonyl group and C1 are the characteristics responsible for the antimicrobial activity. The results showed that the ion H and the acylium ion D, resulting from two competitive hydrogen rearrangements, are the most intense in the spectrum of proton curcuminoids product ions. Besides the identification of some diagnostic ions, this work proved that the formation of some product ions occured from an intermediate ion resulting from a Nazarov cyclization of the protonated molecule, whose occurrence has been previously reported in the literature. The thermochemical data supported the structures of the proposed ions and showed that the position of the phenolic hydroxyl in the aromatic ring plays a key role in the Nazarov cyclization. The results of this work may contribute in future to the identification of products from the in vitro and in vivo metabolism studies without the need for standards or isolation of these metabolites

No description available.

Les 50 dernières années ont été caractérisées par le développement rapide de l’astrochimie. Plus de 150 réactions entre espèces neutres ont déjà été étudiées aux basses températures qui sont celles du le milieu interstellaire et des atmosphères planétaires. Néanmoins, les constantes de vitesse, et la nature des produits, restent inconnus pour de nombreuses réactions potentiellement importantes pour caractériser ces milieux. Nous avons effectué des études cinétiques pour des processus réactifs, et non réactifs, entre des atomes dans un état électronique excité [C(1D), O(1D) et N(2D)] et plusieurs molécules stables afin de quantifier leur importance dans la chimie des atmosphères planétaires. Nous avons aussi étudié la réaction entre les atomes de carbone dans leur état électronique fondamental (3P) et l’eau, confirmant l’importance, pour certaines réactions avec barrière, de l’effet tunnel pour la réactivité à basse température. Les constantes de vitesse et les rapports de branchement pour ces processus ont été déterminés dans la gamme de température entre 50 et 296 K en utilisant un appareil CRESU, les atomes étudiés ont été produits par photolyse à l’aide d’un laser pulsé (PLP) et détectés par fluorescence induite dans l’ultraviolet sous vide (VUV LIF). / The last 50 years have been characterized by the fast development of astrochemistry as a science. To date, more than 150 gas-phase neutral-neutral reactions have been investigated at low temperatures relevant to planetary atmospheres and in cold regions of the interstellar medium. However, the rate constants and nature of the products for many potentially important gas-phase processes remain unknown. We performed kinetic studies of reactive and non-reactive removal processes between electronically excited atoms [C(1D), O(1D) and N(2D)] with several molecules in order to quantify their importance in the chemistry of planetary atmospheres. Furthermore, we also investigated the reaction between carbon atoms in their ground electronic state (3P) with water, providing new evidence of a quantum mechanical tunnelling mechanism at low temperatures, which could play an important role in the chemistry of interstellar clouds. Rate constants and branching ratios for these processes were determined over the 50 - 296 K temperature range using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus coupled with pulsed laser photolysis (PLP) and vacuum ultraviolet laser induced fluorescence (VUV LIF).

Les réacteurs à lit fluidisé (FBR) constituent la seule technologie viable sur le plan commercial pour la production de polyéthylène en phase gaz, car la polymérisation est hautement exothermique et le FBR est le seul type de réacteur en phase gaz offrant des possibilités suffisantes de transfert de chaleur. La nature hautement exothermique de cette polymérisation pose effectivement de nombreux problèmes pour le fonctionnement en phase gaz et peut limiter la production de certains procédés. Au cours des dernières années, les procédés en lit fluidisé ont été améliorés par de nouvelles technologies. En particulier, l'ajout d'hydrocarbures inertes (généralement liquides) permet d'augmenter la quantité de chaleur évacuée du réacteur. Ces composés augmentent la capacité calorifique de la phase gazeuse et, s’ils sont injectés sous forme liquide, s’évaporent également et absorbent ainsi encore plus efficacement la chaleur du milieu réactionnel. C’est ce qu’on appelle le fonctionnement en mode condensé. On y utilise des composés qui peuvent être liquéfiés dans le condenseur de recyclage et qui sont appelés agents de condensation induits (en anglais : Induced Condensing Agents - ICA). L’utilisation de l’ICA est extrêmement importante d'un point de vue industriel. L’injection d’ICA peut avoir de nombreux effets physiques différents au niveau des particules de polymère en croissance. Par exemple, l’ajout de ces composés peut entraîner des modifications de la solubilité et d’autres propriétés physiques, ce qui peut faciliter le transport de l’éthylène et de l’hydrogène vers les sites actifs des catalyseurs. Il est donc très important que les phénomènes physiques liés à l'équilibre de sorption entre la phase gaz et la phase polymère du ou des monomères et d'autres espèces, ainsi que leur diffusion dans la matrice polymère au niveau des sites actifs, soient pris en compte. En plus d'avoir un effet sur la cinétique, ces phénomènes peuvent également impacter la structure des molécules de polymère et par conséquent changer les caractéristiques du polymère. Identifier le comportement de ces phénomènes dans les conditions de la procédé et les variables de contrôle du rapport hydrogène / éthylène et du rapport comonomère / éthylène avec l'ICA sont les objectifs centraux de cette étude. Une série d’homo- et co-polymérisations d’éthylène en phase gazeuse a été réalisée en utilisant un catalyseur commercial Ziegler-Natta en présence de l’ICA (propane, n pentane et n-hexane). Nous avons étudié l’effet des températures, de la pression partielle de l’ICA, de l'hydrogène et des comonomères sur le comportement de la polymérisation. Il a été constaté que l’ajout de l’ICA augmentait significativement la vitesse de réaction ainsi que les poids moléculaires moyens à une température donnée. De manière inattendue, il a également été observé que l’augmentation de la température du réacteur en présence d’ICA entraînait en réalité une diminution de la vitesse de réaction globale. Ces résultats ont été attribués à l’effet de cosolubilité. Dans les réactions en présence de différentes concentrations en hydrogène, pour un rapport ICA/C2 beaucoup plus grand que le rapport H2/C2, l'effet de l’ICA sur la solubilité de l’éthylène peut compenser la diminution en taille des molécules provoquée par la présence d’hydrogène. L’impact de l’ICA sur les taux de réaction de copolymérisation est plus prononcé aux stades initiaux, perdant de son efficacité en raison de l'effet de comonomère. Enfin, une évaluation de la cinétique de cristallisation dans des conditions isothermes pour des mélanges de différentes concentrations ICA: HDPE a montré que le temps de cristallisation est significativement plus long pour les systèmes riches en ICA que pour les polymères secs / Fluidized bed reactors (FBR) are the only commercially viable technology for the production of polyethylene in the gas phase since the polymerization is highly exothermic and the FBR is the only type of gas phase reactor that offers adequate possibilities of heat transfer. The highly exothermic nature of this polymerization effectively poses many problems for gas phase operation and can limit the production of a certain process. However, in recent years the fluidized bed processes have been improved with new technologies. In particular, the addition of inert (usually liquefied) hydrocarbons allows one to increase the amount of heat removed from the reactor. These compounds increase the heat capacity of the gas phase and, if injected in liquid form, also evaporate and thus absorb even more heat from the reaction medium efficiently. This is known as a condensed mode operation. In it, one uses compounds that can be liquefied in the recycle condenser, and which are called Induced Condensing Agents (ICA). The use of ICA is extremely important from an industrial point of view. The injection of ICA can have many different physical effects at the level of the growing polymer particles. For instance, adding these compounds can cause changes in solubility and other physical properties, which can facilitate the transport of ethylene and hydrogen to the active sites of the catalysts. It is thus very important that the physical phenomena related to the sorption equilibrium of the monomer(s) and other species from the gas phase to the polymer phase, and their diffusion on the polymer matrix at the active sites should be accounted for. In addition to having an effect on the kinetics, these phenomena can also impact the structure of the polymer molecules and consequently qualify the characteristics of the polymer. Identifying the behavior of these phenomena under process conditions and control variables of the hydrogen/ethylene ratio and the comonomer/ethylene ratio with ICA are central objectives of this study. A series of ethylene homo- and co-polymerizations in the gas phase were carried out using a commercial Ziegler-Natta catalyst in the presence of ICA (propane, n-pentane, and n-hexane). We investigated the effect of temperatures, the partial pressure of ICA, hydrogen, and comonomers on the behavior of the polymerization. It was found that adding ICA significantly increased the reaction rate and average molecular weights at a given temperature. It was also unexpectedly observed that increasing the reactor temperature in the presence of an ICA actually led to a decrease in the overall reaction rate. These results were attributed to the socalled cosolubility effect. In reactions in the presence of different hydrogen concentrations, for an ICA/C2 ratio much larger than the H2/C2 ratio, the effect of ICA on ethylene solubility can counteract the decrease in average molecular weight caused by the presence of hydrogen. The impact of ICA on the rates of copolymerization reactions is more pronounced in the initial stages, losing strength due to the effect of the comonomer. Finally, an evaluation of the kinetics of crystallization under isothermal conditions for mixtures of different ICA:HDPE concentrations showed that the crystallization time is significantly higher for systems rich in ICA than for dry polymer

Nas últimas décadas, o desenvolvimento das técnicas de ionização à pressão atmosférica impulsionou a espectrometria de massas, na caracterização e elucidação estrutural de compostos de grande massa molecular. O surgimento dessas técnicas foi o responsável pela amplitude nas aplicações e estudos de espectrometria de massas, sendo a ionização por electrospray a mais versátil dentre essas fontes de ionização. O caráter eletrolítico da fonte de ionização por electrospray permite-se obter íons provenientes de três processos químicos: i) ácido-base; ii) redox e iii) complexação. A extensão com que cada um desses processos ocorrerá dependerá de fatores relacionados à operação da fonte de ionização e grandezas termoquímicas do analito. O notável progresso em técnicas experimentais, processamento de dados e integração entre as mais diversas áreas de aplicação da química, tem estimulado e beneficiado a aplicação da química teórica em estudos de reações em fase gasosa. A aplicação da química computacional fornece uma compreensão quantitativa das variações estruturais e energéticas dos possíveis íons formados durante a ionização da amostra, permitindo também a compreensão das possíveis vias de dissociação. É neste sentido, que o sinergismo entre a aplicação de conceitos derivados da química quântica pode auxiliar nas análises de espectrometria de massas. O objetivo desta tese foi o de se aplicar os modelos fundamentados na mecânica quântica para obtenção de grandezas termoquímicas relacionadas aos fenômenos que ocorrem durante as análises de espectrometria de massas por electrospray. Inicialmente, a comparação entre métodos ab initio, modelos compostos e aqueles embasados na teoria do funcional de densidade foram empregados nos cálculos das grandezas termoquímicas para a -butirolactona e 2-pirrolidinona, com a finalidade de se obter parâmetros termoquímicos de alta qualidade. Os modelos compostos G2, G2(MP2), CBS-Q, CBS-QB3 e os métodos B3LYP, B3P86, B98, PW91PW91 e MP2 foram testados. Os valores obtidos para a entalpia de formação, afinidade protônica e basicidade em fase gasosa para essas duas moléculas foram comparados aos dados experimentais disponíveis na literatura. Os melhores resultados para os valores de entalpia de formação foram obtidos ao se empregar o modelo B3LYP/6-31+G(d,p). A afinidade protônica e basicidade em fase gasosa foram mais bem descritas por B3LYP e G2(MP2). Posteriormente, foram estudadas a 1,4-benzoquinona, 1,4-naftoquinona, bem como seus derivados (2-acetilamina-1,4-naftoquinona; 2-propionilamina-1,4-naftoquinona; 2-butirilamina-1,4-naftoquinona, 2-benzoilamina-1,4-naftoquinona, 2-succinilamina-1,4-naftoquinona e lapachol). A escolha do modelo teórico empregado foi realizada por se comparar as geometrias, afinidade protônica, basicidade em fase gasosa, energia de ionização e afinidade eletrônica obtidos para a 1,4-benzoquinona com aqueles disponíveis na literatura. O modelo B3LYP/6-31+G(d,p) foi o mais exato com relação as grandezas termoquímicas supracitadas, assim, este modelo foi empregado no cálculo dessas mesmas grandezas para a 1,4-naftoquinona e seus derivados. A influência do substituinte na estrutura eletrônica dessas moléculas protonadas, desprotonadas, oxidadas, reduzidas e cationizadas foi estudada utilizando-se análises energéticas, geométricas, eletrônicas e topológicas. O desenvolvimento desses estudos compreendeu as análises das grandezas termoquímicas e análises da densidade eletrônica pelos métodos NBO (Natural Bond Orbital), NSA (Natural Steric Analysis), NRT (Natural Resonance Theory) e AIM (Atoms in molecules). A ionização por electrospray e a dissociação induzida por colisão foram realizadas para os derivados da 1,4-naftoquinona, sendo analisados suas moléculas protonadas, desprotonadas, reduzidas, oxidadas e cationizadas com Na+. As vias mecanísticas de dissociação foram embasadas nas análises da superfície de energia obtidas pelo cálculo das energias de Gibbs e entalpias. / In recent decades, the development of atmospheric ionization techniques improved mass spectrometry, principally for characterization and structural elucidation of high-molecular weight compounds. The development of spray ionization was responsible for the spread of applications and studies of mass spectrometry, where the electrospray ionization is the most versatile among the ionization sources. The electrolytic character of electrospray source allows obtaining ions by three different chemical processes: i) acid-base; ii) redox and, iii) metal complexation. These processes will occur through several factors which can be related to the ionization source and thermochemical parameters of analyte. The notable progress of experimental analyses, computational data and the integration between several areas of chemical application have stimulated the use of theoretical chemistry at gas-phase studies. Computational chemistry can furnish a quantitative understanding of the structure and energy of possible ions during the ionization process. For this reason, the synergism between the concepts from quantum chemistry and gas-phase chemistry can help mass spectrometry analysis. The main purpose of this thesis was the application of several quantum mechanical models to obtain thermochemical parameters which can be related to mass spectrometry phenomena. Firstly, the comparison between ab initio, composite model and DFT methods were employed to obtain the thermochemical parameters to -butyrolactone e 2-pyrrolidinona, in order to obtain high performance of thermochemical parameters. The composite G2, G2(MP2), CBS-Q and, the B3LYP, B3P86, B98, PW91PW91 and MP2 methods were tested. The calculated values were compared to experimental values reported in the literature. The best results for enthalpies of formation were obtained when B3LYP/6-31+G(d,p) model was employed. The proton affinity and gas-phase basicity were better described by using of B3LYP and G2(MP2). Secondly, the studies with quinones were performed, where the 1,4-benzoquinone, 1,4-naphthoquinone and its derivatives (2-acylamino-1,4-naphthoquinone; 2-propyonilamino-1,4-naphthoquinone; 2-butyrilamino-1,4-naphthoquinone; 2-benzoylamino-1,4-naphthoquinone; 2-succynilamino-1,4-naphtoquinone and, lapachol) were studied. A search for a theoretical model was made to compare the geometries, proton affinity, gas-phase basicity, ionization energy and electron affinity to 1,4-benzoquinone with those reported in the literature. The most accurate results were obtained by using of B3LYP/6-31+G(d,p). Thus, this model was applied in all studies with 1,4-naphthoquinone derivatives. The influence of substituent groups on electronic structure of protonated, deprotonated, reduced, oxidized and cationized molecules were studied by energetic, geometrics, electronics and topological analyses. The development of these studies and the determination of the thermochemical parameters and wave function analysis was achieved by means of Natural Bond Orbitals, Natural Steric Analysis, Natural Resonance Theory and Atoms in Molecules The electrospray ionization and gas-phase collision-induced dissociation were made for the 1,4-naphtoquinone derivatives by analyzing their protonated, deprotonated species, the radicalar and sodiated ones. The main fragmentation pathways were elucidated on the basis of the energy surface by using Gibbs energies and enthalpies.

Popular catalytic cycles, such as the Heck, Suzuki, and Negishi, utilize metal centers that oscillate between two oxidation states (II/0) during the three main steps of catalysis: reductive elimination, oxidative addition, and transmetallation. There has been a push to use less toxic, cheaper metal centers in catalytic cycles, leading to interest in first-row transition metals, such as nickel and cobalt. With these metals, the cycles can potentially pass through the +1 oxidation state, which acts as reactive intermediates, undergoing oxidative additions to form products, potentially with radical characteristics. The oxidative addition steps of catalytic cycles are critical to determining overall rates and products, however in many cases, these steps have not been amenable to study, in either condensed phase or gas phase, in the past. Through the use of electron transfer dissociation (ETD) technology on a modified Thermo Electron LTQ XLTM mass spectrometer, it is possible to generate intermediates in these catalytic cycles, including those in unusual oxidation states. Using sequentially coupled ion/ion-ion/molecule reactions, the reduced, reactive intermediate can be readily generated, isolated, and studied.As a model set of reactions, the mono- and bis-phenanthroline complexes of Fe(I), Co(I), Ni(I), Cu(I), and Zn(I) were formed by reduction of the corresponding M(II) species in an ion/ion reaction with the fluoranthenyl radical anion. The chemistry of the M(I) species was probed in ion/molecule reactions with allyl iodide. In order to explore ligand effects and the scope of oxidative addition reagents further, bipyridine and terpyridine were studied with these five first-row transition metal complexes while using an acetate series and other substrates for oxidative additions. Through these studies, the roles of the metal and ligand in dictating the product distributions and reaction rates were assessed. Metal electron count, ligand flexibility, and coordination number are critical factors. The overall reactivity is in accord with density functional theory calculations and mirrors that of proposed intermediates in condensed-phase catalytic cycles. In addition, second- and third-row transition metals (Ru(I), Pd(I), and Pt(I)) were explored with bipyridine, mono- and bis-triphenylphosphine, and 1,2-bis(diphenylphosphino)benzene ligation schemes. A variety of oxidative addition reagents were surveyed to determine the scope of reactivity and preference toward metal-carbon bond formation or carbon radical formation.

Over the last decade our understanding of mercury cycling has dramatically changed. Evidence of rapid atmospheric oxidation has been observed in the Arctic, Antarctic, the MBL, coastal environments, saline lakes, and the upper troposphere/lower stratosphere. These results show that, Hg0, can undergo rapid gas-phase oxidation under standard atmospheric conditions. However, the mechanism and importance of this transformation is still unclear. The goal of this work was two-fold: to investigate of the kinetics of potential pathway for the gas phase oxidation of atmospheric mercury and to develop new laser based techniques, which can be employed for both laboratory and field studies of Hg(0) and the products of mercury oxidation. First and foremost, this work determined kinetic rate coefficients for the potentially important mercury reactions. Rate coefficients were determined using a Pulse Laser Photolysis - Laser Induced Fluorescence (PLP-LIF) technique monitoring one or more of the following species, Hg(0), Cl, Br, HgCl, and HgBr. The concentrations of these species were measured by LIF as the reaction occurred and a concentration vs. time profile was generated. From these profiles a rate coefficient for the reaction can be obtained. In the course of this work kinetic rate coefficients for the following mercury reactions were measured. Hg(0) + Cl + M --> HgCl + M Hg(0) + Br + M --> HgBr + M HgBr + M --> Hg(0) + Br + M HgBr + Br --> products HgCl + O2 --> products This work is the first direct measurement of a kinetic rate coefficient for these reactions, and the first work which employed one photon LIF to monitor the HgCl and HgBr products. The second aspect of this work was the development of new laser based techniques to detect atmospheric mercury and its oxidation products for both laboratory and field application. In this work a LIF technique was develop to detect HgCl and HgBr. In addition, a two photon LIF technique initially developed by Bauer et al., 2002 was verified and expanded. The two photon LIF technique was used to directly monitor Hg(0) atoms in-situ, to monitor Hg(0) evolving form a gold tube, and to monitor the Hg(0) evolving from the thermal decomposition of reactive gaseous mercury collected on a KCl coated or uncoated denuder. This work represents a significant advance in the development of a viable method the detect mercury and the mercury oxidation products in the laboratory and in the field and is the first study to observe clear differences in the characteristic desorption profiles of HgO and HgX2. This work has broad implications, it enhanced our current knowledge concerning the biogeochemical cycling of mercury, broadened our understanding of the mercury chemistry in high halogen environment, and provided new techniques which can be applied in future field and laboratory studies.

The objective of this thesis is to investigate the photocatalytic activity in nanosized TiO2 structures. Two different structures were used for two different reaction systems. In the first part of the study, TiO2 coated on glass beads by a sol-gel procedure were used to test the photocatalytic CO2 reduction reaction with H2O and H2 in the gas phase. The results of photocatalytic CO2 reduction reaction revealed that CO2 reduction step of the overall reaction proceeds in dark / while illumination is required for water splitting reaction. In the second part of the study, Photocatalytic oxidation activity of the commercial TiO2 powders mixed with grout and plaster were studied for a potential commercial self cleaning material. A method based on gas phase benzene oxidation was developed for testing TiO2 added cement based self cleaning surfaces. This method was used to screen 15 commercial TiO2 samples with and without cement. Based on this method a commercial TiO2 sample (S9) was selected for further use. Surface of 15 commercial TiO2 samples were characterized by using NO and CO2 as probe molecules. Photocatalytic benzene oxidation experiments showed that using TiO2 on the surface lead to more effective surfaces in terms of photocatalytic activity. TiO2 was bound to surface by inorganic materials without much activity loss. This kind of amount optimization is of commercial importance.

Chemical dynamics in the vadose zone are poorly understood due to the transient nature of chemical and hydrologic conditions, but are nonetheless critical to understanding contaminant fate and transport. This work explored the effects of soil structure (i.e. layers, lenses) on linked geochemical, hydrological, and microbiological processes under changing hydrologic conditions (e.g. rainfall, introduction of groundwater, and fluctuating water table heights). A homogenized medium-grained sand, homogenized organic-rich loam and a sand-over-loam layered column were constructed for the first series of experiments. The second series of experiments employed two soil columns with lenses that were packed identically with sterilized and untreated sediments. Each consisted of two lenses of organic-rich loam in a medium-grained sand matrix. Lenses were located at different vertical depths and were horizontally offset. In-situ collocated probes collected soil hydrologic and chemical data. In the layered column, enhanced biogeochemical cycling was observed over the texturally homogeneous soil columns. Enumerations of Fe(III) and SO42- reducing microorganisms also show 1-2 orders of magnitude greater community numbers in the layered column. The greatest concentrations of aqueous FeS clusters (FeSaq) were observed in close proximity to the soil interface. To our knowledge, this was the first documentation of FeSaq in partially saturated sediments. Mineral and soil aggregate composite layers were also most abundant near the soil layer interface; the presence of which, likely contributed to an order of magnitude decrease of hydraulic conductivity. In the live lens column, Fe-oxide bands formed at the fringes of the lenses that retarded water flow rates by an order of magnitude compared to the sterilized column. Microbial activity also produced insoluble gases and that led to the creation of a separate gas phase that reduced hydraulic conductivity. This limited the interaction between groundwater with soil-pore waters that led to the formation of geochemically distinct water masses in relatively close proximity to one another. No such changes were observed in the sterilized column. When compared to homogenous columns, the presence of soil heterogeneities altered biogeochemical and hydrologic processes considerably which highlights the need to consider soil heterogeneity in contaminant fate and transport models. These findings suggest that quantifying coupled hydrologic-biogeochemical processes occurring at small scale soil interfaces is critical to accurately describing and predicting chemical changes at the larger system scale.