Polychlorinated biphenyls (PCBs) are toxic and persistent chemicals that have been largely dispersed into the environment. The biological and abiotic transformations of PCBs often generate hydroxylated derivatives, which have been detected in a variety of environmental samples, including animal tissues and feces, water, and sediments. Because of their toxicity and widespread dispersion in the environment, hydroxylated PCBs (OH-PCBs) are today increasingly considered as a new class of environmental contaminants. Although PCBs are known to be susceptible to microbial degradation under both aerobic and anaerobic conditions, bacterial degradation of OH-PCBs has received little attention. The overall objective of this study is therefore to evaluate the transformation of mono-hydroxylated PCBs by the well characterized aerobic PCB-degrading bacterium, Burkholderia xenovorans LB400. In order to achieve our overall objective, a series of model mono-hydroxylated PCBs have been selected and they are used to determine the toxicity of hydroxylated congeners toward the bacterium B. xenovorans LB400. The biodegradation kinetics and metabolic pathways of the selected OH-PCBs by B. xenovorans LB400 are then characterized using GC/MS. To understand further the molecular basis of the metabolism of OH-PCBs by B. xenovorans LB400, gene expression analyses are conducted using reverse-transcription real-time (quantitative) polymerase chain reaction (RT-qPCR) and microarray technology. More formally, the specific aims of the proposed research are stated as follows: (1) To evaluate the toxicity of selected mono-hydroxylated derivatives of lesser-chlorinated PCBs toward the bacterium B. xenovorans LB400. (2) To assess the degradation of the selected OH-PCBs by B. xenovorans LB400. (3) To gain further understanding of the molecular bases of the metabolism of the selected OH-PCBs by B. xenovorans LB400. Three hydroxylated derivatives of 4-chlorobiphenyl and 2,5-dichlorobiphenyl, including 2'-hydroxy-, 3'-hydroxy-, and 4'-hydroxy- congeners, were significantly transformed by Burkholderia xenovorans LB400 when the bacterium was growing on biphenyl (biphenyl pathway-inducing conditions). On the contrary, only 2'-OH-4-chlorobiphenyl and 2'-OH-2,5-dichlorobiphenyl were transformed by the bacterium growing on succinate (conditions non-inductive of the biphenyl pathway). Gene expression analyses showed that only exposure to 2'-OH-4-chlorobiphenyl and 2'-OH-2,5-dichlorobiphneyl resulted in induction of key genes of the biphenyl pathway, when cells grown on succinate. These observations suggest that 2'OH-PCBs were capable of inducing the genes of biphenyl pathway. These results provide the first evidence that bacteria are able to cometabolize PCB derivatives hydroxylated on the non-chlorinated ring. Genome-wide transcriptional analyses using microarrays showed that 134 genes were differentially expressed in cells exposed to biphenyl, 2,5-dichlorobiphenyl, and 2'-OH-2,5-dichlorobiphneyl as compared to non-exposed cells. A significant proportion of differentially expressed genes were simultaneously expressed or down regulated by exposure to the three target compounds i.e., biphenyl, 2,5-DCB, and 2'-OH-2,5-DCB, which suggests that these structurally similar compounds induce similar transcriptional response of B.xenovorans LB400. Results of this study may have important implications for the natural attenuation of PCBs and fate of OH-PCBs in the environment. The recalcitrance to biodegradation and the high toxicity of some OH-PCBs may provide a partial explanation for the persistence of PCBs in the environment. / Civil Engineering

This study reports on the behavior of silica based optical fibers in a hydrogen environment at high temperatures. The hydrogen response in the form of optical loss in the wavelength range of 1000-2500 nm of a germanium doped graded index 50/125 graded index fiber was examined in the temperature range of 20–800 °C. When the fiber was exposed to hydrogen at 800 °C two absorption bands appeared: ~1390 nm assigned to the first overtone of the hydroxyl stretch and ~2200 nm band with complex assignments including the combination mode of the fundamental hydroxyl stretch with SiO4 tetrahedral vibrations and the combination mode of SiOH bend and stretch. The growth rate of the 1390 nm band fits the solution to the diffusion equation in cylindrical coordinates while the 2200 nm band does not. Absorption for both bands persisted as the fiber is cooled to room temperature. Temperature dependent behavior was observed in that as temperature increases from room temperature, the absorption intensity decreases and band shifts slightly to longer wavelengths. Temperature dependence is repeatable and reversible. However, if no hydrogen is present in the environment at temperatures greater than 700 °C, the 1390 nm band will permanently decrease in intensity, while the 2200 nm band does not change. Changes in the structure of the glass appear to be causing this temperature dependent behavior. Other necessary conditions for structural changes to cause this temperature dependent behavior are examined. / Master of Science

Photosäuren sind aromatische Alkohole, sogenannt aufgrund der Erhöhung ihrer Azidität, die aus der elektronischen Anregung folgt. Allerdings muss ein plausibles Verständnis der Prozesse, die zu der Erhöhung der Azidität führen noch etabliert werden. Zu diesem Zweck wird die Photophysik zweier Photosäuren, 1-Naphthol (1N) und 2-Naphthol (2N), untersucht. Mit Hilfe der Femtosekunden-UV-Anrege/IR-Abtast-Spektroskopie wird die OH-Streckschwingung sowohl im Grundzustand als auch im angeregten Zustand gemessen. Die intrinsische elektronische Ladungsverteilung, die aufgrund der Anregung in der Säure auftritt, in apolaren Lösungsmitteln untersucht. Der Vergleich mit Resultaten eines theoretischen Modells stellte einwandfrei fest, dass eine geringe Ladungsverteilung in der Photosäure auftritt. Die OH-Streckschwingung von wasserstoffverbrückten Komplexen zwischen 2N und Acetonitril wird gemessen. Obwohl experimentell gefunden wurde, dass der angeregte Zustand verglichen mit dem Grundzustand eine nahezu doppelt so große solvatochromatische Verschiebung zeigt, scheitern theoretische Modelle daran, diese Ergebnisse wiederzugeben. Die Ladungstransferreaktion im angeregten Zustand von 1N und 2N zu halogenierten Lösungsmitteln wird zur Abfrage der elektronischen Dichte am aromatischen Ring nach Anregung verwendet. Wurde ermittelt, dass verglichen mit dem unkomplexierten Molekül die Elektrontransferrate in einem wasserstoffverbrückten Komplex mit Acetonitril 10 mal höher ist. Auf diese Weise hat sich der Einfluss der Wasserstoffbrückenbindung auf das Ausmaß der Ladungsverteilung gezeigt. Mittels zeitaufgelöster Anisotropie, Fluoreszenz und IR-Messungen war es möglich festzustellen, dass die ultraschnelle ( / Photoacids are aromatic alcohols, characterized by a dramatic increase in acidity upon electronic excitation. A coherent view of the processes giving rise to this increase in acidity has yet to be established. To this effect, the photophysics of photoacids 1-naphthol (1N) and 2-naphthol (2N) are investigated. Using femtosecond UV pump-IR probe spectroscopy, the OH stretch vibration in both the ground and excited-state is measured. The intrinsic electronic charge redistribution in the acid upon excitation is investigated in non-polar solvents where specific interactions are absent. Comparison with results from a theoretical model based on the Pullin-van der Zwan-Hynes perturbative approach established that little charge redistribution occurs in the photoacid. The OH stretch vibration of hydrogen-bonded complexes of 2N with acetonitrile is measured. While it was found experimentally that the excited-state is characterized by a solvatochromic response that is almost twice as large as in the ground-state, the theoretical model failed to reproduce these results. Instead, the calculations predict no significant differences between the behaviour of the two states. The excited-state charge transfer reaction of 1N and 2N to halogenated solvents is used as a probe for the electronic density on the aromatic ring upon excitation. The charge transfer rate for the hydrogen-bonded complex with acetonitrile is found to be ten times higher than for the uncomplexed molecule. In this way, the influence of a hydrogen-bond on the extent of charge redistribution was evinced. Using time resolved anisotropy, fluorescence and IR measurements, it was determined that ultrafast (

An mit Urethan narkotisierten männlichen "Wistar"-Ratten erfolgte die extrazelluläre Einzelableitung der Aktionspotenziale von insgesamt 159 striatalen Neuronen. Mit Hilfe einer Mehrkanalelektrode wurden in die Nähe der Zellen mikroiontophoretisch verschiedene Substanzen appliziert. Die separate Gabe von Serotonin (5-HT), dem 5-HT1A-Rezeptoragonisten 8-OH-DPAT und dem sulfatierten Oktapeptid Cholezystokinin (CCK-8S) führte überwiegend zur Erhöhung der neuronalen Entladungsraten (Wilcoxon-Test signifikant mit p < 0,05), wohingegen der 5-HT2A/2C-Rezeptoragonist DOI nur an wenigen Neuronen einen Effekt induzierte, der hauptsächlich aus einer Reduktion der Entladungsraten bestand. Nach Koapplikation von Serotonin und CCK-8S überwogen ebenfalls aktivierende Effekte (Wt p < 0,05), jedoch wurde die neuronale Responsivität im Vergleich zur Einzelapplikation der beiden Substanzen signifikant reduziert (Chi2 p< 0,01). Da die Serotonin- bzw. 8-OH-DPAT-induzierten Effekte durch die spezifischen 5-HT1A-Rezeptorantagonisten WAY 100635 und S-UH 301 geblockt wurden und eine positive Korrelation der Serotonin- bzw. 8-OH-DPAT-Effekte (p < 0,05) nachgewiesen werden konnte, kann, trotz der entgegengesetzten Ergebnisse früherer Studien, das Vorhandensein von 5-HT1A-Rezeptoren im Neostriatum angenommen werden. Die Grundaktivität der durch Serotonin aktivierten Population war signifikant geringer (p > 0,05) als die der durch Serotonin gehemmten Neurone. Trotzdem zeigte sich keine Abhängigkeit der Responsivität der hier betrachteten Populationen auf die applizierten Serotoninagonisten von der Höhe der neuronalen Ruheentladungsrate. Die meisten der Serotonin-, 8-OH-DPAT-, DOI- bzw. CCK-8S-responsiven Neurone verteilten sich diffus über das gesamte Neostriatum. Nur die durch Serotonin aktivierte Population zeigte eine Präferenz der ventromedialen Bereiche des Neostriatum. Zusammenfassend kann gesagt werden, dass aufgrund der Ergebnisse der vorliegenden Studie die Existenz von 5-HT1A-Rezeptoren innerhalb des Neostriatum der Ratte in hohem Maße angenommen werden kann. Des Weiteren lässt sich vermuten, dass das Zusammenwirken von Serotonin und CCK-8S einen modulatorischen Einfluss auf die normale neuronale Funktion hat. Ob und in welchem Maße dieses letztgenannte Ergebnis eine therapeutische Relevanz zur Behandlung bestimmter Erkrankungen hat, bei denen Störungen im Neostriatum mit ursächlich sind, bleibt zu erforschen. / In rats anaesthetized with urethane single unit activity of 159 neostriatal neurones was extracellularly recorded and several drugs were microiontophoretically ejected. Separate administration of serotonin (5-HT), 8-OH-DPAT (a 5-HT1A/7-receptor-agonist) and the sulfated octapeptide cholecystokinin (CCK-8S) predominantly induced increases in the neuronal discharge rates (Wilcoxon test significant with p < 0,05), whereas the 5-HT2A/2C-receptor agonist DOI affected only a few neurones and mainly reduced firing. After coadministration of CCK-8S and serotonin activating effects also predominated (Wt p < 0,05), but the neuronal responsiveness was significantly reduced (Chi2 p

O comportamento emocional tem sido considerado fundamental para a sobrevivência dos animais, sendo o medo uma se suas mais primitivas e importantes formas. A substância cinzenta periaquedutal dorsal (SCPD) tem-se destacado como uma estrutura importante na organização das respostas defensivas. Estudos usando estimulação elétrica e química da SCPD e microinjeções de drogas agonistas e antagonistas de receptores serotoninérgicos mostraram uma mediação serotoninérgica através dos subtipos de receptores 5-HT1A e 5-HT2A na regulação do comportamento defensivo organizado nesta estrutura. O objetivo deste trabalho foi examinar a mediação serotoninérgica na SCPD através de receptores 5-HT1A nas respostas defensivas de animais sem e com experi~encia aversiva prévia. Para isto, os limiares de congelamento e fuga foram determinados em ratos implantados com uma cânula acoplada a um eletrodo na SCPD, antes e após microinjeção local do agonista 8-OH-DPAT (4 e 8 nmol) e do antagonista WAY100635 (10 nmol). Os efeitos destas drogas injetadas na SCPD foram avaliados também sobre o tempo de congelamento pós-estimulação em animais ingênuos e também em animais colocados em um contexto no qual receberam choques inescapáveis nas patas 24h antes (medo condiconado contextual). O 8-OH-DPAT, de maneira dose dependente, produziu um efeito anti-aversivo sobre os limiares de congelamento e fuga em ratos sem experiência aversiva prévia, mas não nos animais com experiência aversiva prévia quando comparado com seus controles. Por outro lado, este agonista 5-HT1A reduziu o tempo de congelamento contextual. Já o WAY100635 não produziu alterações significativas sobre os limiares aversivos em ratos ingênuos ou com experiência aversiva prévia, mas elevou o tempo de congelamento contextual nestes aniamis (efeito pró-aversivo). Estes resultados estão em concordância com a idéia de uma modulação fásica exercida pela 5-HT sobre os substratos neurais do medo organizado na SCPD. Por outro lado, mecanismos mediados pelos receptores 5-HT1A não são alterados em animais com experiência aversiva prévia. Acreditamos que estes resultados trazem uma contribuição importante para a nossa compreensão sobre a integração de estados aversivos no SNC e, particularmente sobre o funcionamento destes substratos neurais de defesa na SCPD de animais com experiência aversiva prévia. / It is well established that 5-HT1 mechanisms modulate the defensive behavior produced by stimulation of the dorsal periaqueductal gray (dPAG). However, in spite of the notion that past stressful experiences play a role in certain types of anxiety only few studies with stimulation of the dPAG of rats without previous aversive experience have been conducted so far. In this study, we examined the mediation of 5-HT1 receptors of the dPAG in rats naive and in rats previously submitted to contextual fear conditionong (CFC). Defensive behaviors induced by activation of the dPAG were assessed by measuring the lowest intensity of electric current applied to this structure (threshold) able to produce freezing and escape responses during testing sessions of CFC, in which animals were placed in a context previously paired to footshocks. The persistence of the freezing behavior after the interruption of the dPAG electrical stimulation was also evaluated. The 5-HT1 function of the dPAG in this condition was evaluated by local injectinos of 8-OH-DPAT (4 and 8 nmol/) and WAY100635 (10nmol), selective agonist and antagonist of 5-HT1 receptors, respectively. In accordance with previous studies, 8-OH-DPAT increased the aversive thresholds (antiaversive effects) and injection of WAY100635 into the dPAG did not produce significant effects in naive rats. On the contrary, both serotonergic drugs 8-OH-DPAT and WAY100635 did not produce any significant effects on the aversive thresholds. Post-stimulation freezing was not affected by any treatment given to animals before or after CFC. However, the contextual conditioned freezing was attenuated or enhanced by intra-dPAG of 8-OH-DPAT and WAY100635, respectively. The present results suggest that 5-HT1 receptor-mediated mechanisms exert a phasic inhibition on the neural substrates of fear in the dPAG in naive rats whereas past stressful experience does not produce significant changes in the synaptic function of 5-HT1 receptors within the dPAG.

O comportamento emocional tem sido considerado fundamental para a sobrevivência dos animais, sendo o medo uma se suas mais primitivas e importantes formas. A substância cinzenta periaquedutal dorsal (SCPD) tem-se destacado como uma estrutura importante na organização das respostas defensivas. Estudos usando estimulação elétrica e química da SCPD e microinjeções de drogas agonistas e antagonistas de receptores serotoninérgicos mostraram uma mediação serotoninérgica através dos subtipos de receptores 5-HT1A e 5-HT2A na regulação do comportamento defensivo organizado nesta estrutura. O objetivo deste trabalho foi examinar a mediação serotoninérgica na SCPD através de receptores 5-HT1A nas respostas defensivas de animais sem e com experi~encia aversiva prévia. Para isto, os limiares de congelamento e fuga foram determinados em ratos implantados com uma cânula acoplada a um eletrodo na SCPD, antes e após microinjeção local do agonista 8-OH-DPAT (4 e 8 nmol) e do antagonista WAY100635 (10 nmol). Os efeitos destas drogas injetadas na SCPD foram avaliados também sobre o tempo de congelamento pós-estimulação em animais ingênuos e também em animais colocados em um contexto no qual receberam choques inescapáveis nas patas 24h antes (medo condiconado contextual). O 8-OH-DPAT, de maneira dose dependente, produziu um efeito anti-aversivo sobre os limiares de congelamento e fuga em ratos sem experiência aversiva prévia, mas não nos animais com experiência aversiva prévia quando comparado com seus controles. Por outro lado, este agonista 5-HT1A reduziu o tempo de congelamento contextual. Já o WAY100635 não produziu alterações significativas sobre os limiares aversivos em ratos ingênuos ou com experiência aversiva prévia, mas elevou o tempo de congelamento contextual nestes aniamis (efeito pró-aversivo). Estes resultados estão em concordância com a idéia de uma modulação fásica exercida pela 5-HT sobre os substratos neurais do medo organizado na SCPD. Por outro lado, mecanismos mediados pelos receptores 5-HT1A não são alterados em animais com experiência aversiva prévia. Acreditamos que estes resultados trazem uma contribuição importante para a nossa compreensão sobre a integração de estados aversivos no SNC e, particularmente sobre o funcionamento destes substratos neurais de defesa na SCPD de animais com experiência aversiva prévia. / It is well established that 5-HT1 mechanisms modulate the defensive behavior produced by stimulation of the dorsal periaqueductal gray (dPAG). However, in spite of the notion that past stressful experiences play a role in certain types of anxiety only few studies with stimulation of the dPAG of rats without previous aversive experience have been conducted so far. In this study, we examined the mediation of 5-HT1 receptors of the dPAG in rats naive and in rats previously submitted to contextual fear conditionong (CFC). Defensive behaviors induced by activation of the dPAG were assessed by measuring the lowest intensity of electric current applied to this structure (threshold) able to produce freezing and escape responses during testing sessions of CFC, in which animals were placed in a context previously paired to footshocks. The persistence of the freezing behavior after the interruption of the dPAG electrical stimulation was also evaluated. The 5-HT1 function of the dPAG in this condition was evaluated by local injectinos of 8-OH-DPAT (4 and 8 nmol/) and WAY100635 (10nmol), selective agonist and antagonist of 5-HT1 receptors, respectively. In accordance with previous studies, 8-OH-DPAT increased the aversive thresholds (antiaversive effects) and injection of WAY100635 into the dPAG did not produce significant effects in naive rats. On the contrary, both serotonergic drugs 8-OH-DPAT and WAY100635 did not produce any significant effects on the aversive thresholds. Post-stimulation freezing was not affected by any treatment given to animals before or after CFC. However, the contextual conditioned freezing was attenuated or enhanced by intra-dPAG of 8-OH-DPAT and WAY100635, respectively. The present results suggest that 5-HT1 receptor-mediated mechanisms exert a phasic inhibition on the neural substrates of fear in the dPAG in naive rats whereas past stressful experience does not produce significant changes in the synaptic function of 5-HT1 receptors within the dPAG.

O Ni(OH)2 é amplamente utilizado como principal componente ativo do eletrodo positivo na maior parte das baterias secundárias como: Ni/Cd, Ni/Zn, Ni/Fe, Ni/H2 e, recentemente na pilhas de Ni/MH. Estes acumuladores possuem variadas aplicações como: satélites geoestacionários, alimetação de recarga de computadores, aparelhos portáteis. Apesar do eletrodo de Ni(OH)2 possuir boa durabilidade, após vários ciclos de oxidação/redução ocorre a transformação do par redox &#945;-Ni(OH)2/&#946;-NiOOH para &#946;-Ni(OH)2/&#947;-NiOOH o qual ocasiona uma diminuição na capacidade de carga. Por essa razão, é necessário o estudo do efeito de aditivos para estabilização da capacidade de carga no eletrodo. Neste trabalho, hidróxido de cério foi utilizado como aditivo para estabilizar o &#945;-Ni(OH)2. Os resultados obtidos mostram que os íons cério são incorporados no eletrodo estabilizando a fase &#945;-Ni(OH)2 e com isso aumentando a capacidade de carga do mesmo. Nas análises de espectroscopia no IV e Raman foi possível verificar modificações estruturais causadas pela presença de íons Ce3+ na estrutura, principalmente, a partir de 21,33% em mol do aditivo. Nos estudos de ciclagens sucessivas a fase &#945;-Ni(OH)2 foi estabilizada na presença de 21,33% em mol do aditivo uma vez que a capacidade de carga do eletrodo manteve-se constante ao longo de 90 ciclos de oxidação/redução. / Ni(OH)2 is widely used as main active component for positive electrodes for secondary batteries such as Ni/Cd, Ni/Zn, Ni/Fe, Ni/H2 and recently in cell of Ni/MH. These accumulators show certain characteristics and they have several applications, such as: geostationary satellites, recharge feeding of computers, portable devices. Although the electrode of hydroxide of nickel have a good durability, after several oxidaction/reduction cycles, the material suffer modification from &#945;-Ni(OH)2/&#946;-NiOOH to &#946;-Ni(OH)2/&#947;-NiOOH, decreasing its charge capacity. For this reason, it is necessary to study the role played by some additives for stabilization of charge capacity the electrode. Our results show that the cerium ions are incorporate in the electrode, stabilizing the &#945;-Ni(OH)2 and therefore increasing charge capacity of the electrode. In the IV and Raman Spectroscopy analyses it was possible to verify structural modification caused by the presence of Ce3+ ions in the structure, mainly for 21,33% in mol of the additive. Potentiodynamic cycling experiments have shown that the phase &#945;-Ni(OH)2 was stabilized with 21,33% of additive and the charge capacity of the electrode remains constant throughout 90 oxidation/reduction cycles.

O Ni(OH)2 é amplamente utilizado como principal componente ativo do eletrodo positivo na maior parte das baterias secundárias como: Ni/Cd, Ni/Zn, Ni/Fe, Ni/H2 e, recentemente na pilhas de Ni/MH. Estes acumuladores possuem variadas aplicações como: satélites geoestacionários, alimetação de recarga de computadores, aparelhos portáteis. Apesar do eletrodo de Ni(OH)2 possuir boa durabilidade, após vários ciclos de oxidação/redução ocorre a transformação do par redox &#945;-Ni(OH)2/&#946;-NiOOH para &#946;-Ni(OH)2/&#947;-NiOOH o qual ocasiona uma diminuição na capacidade de carga. Por essa razão, é necessário o estudo do efeito de aditivos para estabilização da capacidade de carga no eletrodo. Neste trabalho, hidróxido de cério foi utilizado como aditivo para estabilizar o &#945;-Ni(OH)2. Os resultados obtidos mostram que os íons cério são incorporados no eletrodo estabilizando a fase &#945;-Ni(OH)2 e com isso aumentando a capacidade de carga do mesmo. Nas análises de espectroscopia no IV e Raman foi possível verificar modificações estruturais causadas pela presença de íons Ce3+ na estrutura, principalmente, a partir de 21,33% em mol do aditivo. Nos estudos de ciclagens sucessivas a fase &#945;-Ni(OH)2 foi estabilizada na presença de 21,33% em mol do aditivo uma vez que a capacidade de carga do eletrodo manteve-se constante ao longo de 90 ciclos de oxidação/redução. / Ni(OH)2 is widely used as main active component for positive electrodes for secondary batteries such as Ni/Cd, Ni/Zn, Ni/Fe, Ni/H2 and recently in cell of Ni/MH. These accumulators show certain characteristics and they have several applications, such as: geostationary satellites, recharge feeding of computers, portable devices. Although the electrode of hydroxide of nickel have a good durability, after several oxidaction/reduction cycles, the material suffer modification from &#945;-Ni(OH)2/&#946;-NiOOH to &#946;-Ni(OH)2/&#947;-NiOOH, decreasing its charge capacity. For this reason, it is necessary to study the role played by some additives for stabilization of charge capacity the electrode. Our results show that the cerium ions are incorporate in the electrode, stabilizing the &#945;-Ni(OH)2 and therefore increasing charge capacity of the electrode. In the IV and Raman Spectroscopy analyses it was possible to verify structural modification caused by the presence of Ce3+ ions in the structure, mainly for 21,33% in mol of the additive. Potentiodynamic cycling experiments have shown that the phase &#945;-Ni(OH)2 was stabilized with 21,33% of additive and the charge capacity of the electrode remains constant throughout 90 oxidation/reduction cycles.

Le radical hydroxyle OH est un oxydant puissant qui intervient, entre autre,dans de nombreux processus photochimiques atmosphériques. L'objectif de cette thèse était de développerun système de mesure desradicaux OH dédié aux études de laboratoire. Celui-ci est basé sur la spectroscopie d'absorption en cavité résonante hors d'axe (OA-ICOS,Off-Axis integrated Cavity Output Spectroscopy).Notre système repose sur le couplaged'une diode laser fibrée (DFB) émettant dans le proche infrarouge (∼1435 nm) au sein d'une cavitéoptique àhaute finesse de 50 cm. Le parcours d'interaction du faisceau avec le milieu atteint 1263 m. Le couplage hors de l'axe permet d'atteindre une limite de détection à 2,12 x 10¹¹ OH / cm³. La spectroscopie par modulation de la longueur d'onde (WMS) en modulant l'intensité de la diode laser à 10 kHz est utilisée conjointement à la cavité OA-ICOS. Cette technique permet de s'affranchir du bruit en 1/f. La WM-OA-ICOS atteint alors une limite de détection de 5,7 x 10¹⁰OH/cm³. Les effets de la Modulation Résiduelle d'Amplitude (RAM) occasionnés par la modulation de l'intensité laser ont ensuite été supprimés. L'implémentation d'une boucle de contrôle de l'intensité laser en amont de la cavité optique a permis de réduire les variations d'intensité de la source et les effets de RAM. Ceci se traduit par une limite de détection plus basse à 5,7 x 10⁹ OH/cm³ pour 100 secondes d'intégration. La suppression des effets de RAM par moyen optique est utilisée pour la première fois pour réduire la limite de détection de systèmes WM-OA-ICOS. Ceci nous permet d'atteindre une valeur de NEAS qui est parmi les meilleures au monde et offre des perspectives intéressantes. / The hydroxyl free radical (OH) plays a central role in atmospheric chemistry due to its high reactivity with VOCs and other trace species. In this thesis, we demonstrate the feasibility of OH radical detection by means of a compact sensor based on off-axis integrated cavity outpout spectroscopy (OA-ICOS) dedicated to laboratory studies. The developed system requires the coupling of a distributed feedback diode (DFB) emitting in near infrared (∼1435 nm) to a 50 cm long spherical high finesse cavity. The effective interaction path length reaches 1263 m. The off-axis injection of the laser beam allows a detection limit of 2,12 x 10¹¹ OH / cm³. The OA-ICOS is used in combination with wavelength modulation spectroscopy (WMS) by modulating the diode current at 10 kHz. This technique is efficient to remove 1/f noise in the signal. The developed WM-OA-ICOS setup achieves alower detection limit at 5,7 x 10¹⁰OH/cm³. While modulating DFB current, Residual Amplitude Modulation occurs. This background contribution was removed at the optical level by the implementation of a control-loop on the laser intensity before its onjection to the cavity. This stabilisation loop on WM-OA-ICOS achieves a detection limit 5,7 x 10⁹ OH/cm³ for an integration time of 100 s. RAM suppression at the optical level was first used to enhance the detection limit of WM-OA-ICOS setup. It makes our OA-ICOS system one of the most efficient in Noise Equivalent Absorption Sensitivity in the world and provides great opportunities for future development.

Les travaux de cette thèse reposent sur l’étude des processus hétérogènes à la surface desparticules minérales en présence d’irradiation UV-A. Nous savons que les poussièresminérales contiennent des oxydes métalliques pouvant absorber la radiation solaire et ainsiactiver une chimie très différente de celle observée à l’obscurité. Un réacteur à écoulementd’aérosols a été utilisé pour étudier les interactions des gaz (SO2, NO2 et O3) avec devéritables poussières minérales, évitant ainsi les artéfacts de mesure liés à la naturemacroscopique des films comme dans les études précédentes.La mise en suspension des poussières minérales a permis d’observer une formation inattenduede nouvelles particules ultrafines en présence de SO2. Le mécanisme proposé pour expliquerce phénomène de nucléation suggère une désorption de radicaux OH photoproduits à lasurface des minéraux vers la phase gazeuse. Ce mécanisme a pu être corroboré par descampagnes de mesure en atmosphère réelle. Nous avons étudié la chimie des échantillons de réelles cendres volcaniques issus de la dernière éruption du volcan Eyjafjallajökull en Islande (2010). Ceci nous a permis d’élaborerdes cinétiques de capture du SO2 sur des films macroscopiques de cendres aboutissant à descoefficients de capture de l’ordre de 10-7. Ces cinétiques couplées à des analyses chimiquesont permis de proposer un mécanisme réactionnel expliquant la formation de sulfate de fer àla surface des cendres. Finalement, nous avons étudié les interactions photochimiques de O3 et NO2 sur les poussièresminérales dans le réacteur à écoulement mettant en évidence un bon accord avec des étudesantérieures sur des surfaces macroscopiques / The objective of this work is to study the heterogeneous processes of mineral dust surfacesunder UV-A radiation. It is know that mineral dust containing metal oxides which can absorbsolar radiation and therefore activate a different chemistry compared to that observed in thedark. In order to avoid measurement artifacts related to the nature of macroscopic films, anaerosol flow tube was developed during this work and applied to study the interactions ofSO2, NO2 and O3 with real mineral dust.An unexpected formation of new particles in the presence of SO2 was observed. In order toexplain this phenomenon, we suggest the desorption of OH radicals from the mineral dustsurface to the gas phase. This mechanism has also been supported by field campaigns.Using real samples of volcanic ash from the last eruption of Eyjafjallajökull in Iceland (2010)allowed us study capture of SO2 on macroscopic ashes films with uptake coefficient around10-7. Associated kinetic experiments combined with chemical analysis allowed us to propose areaction mechanism explaining the formation of iron sulfate on the surface of ashes.Finally, we investigated the photochemical interactions of O3 and NO2 with minerals dustaerosols in the flow tube reactor showing a good agreement with previous data obtained onmacroscopic surfaces.