[ES] La luz solar puede producir daños en el ADN por absorción directa de luz UVB, o por fotosensibilización tras la absorción de luz UVA por parte de fármacos, que pueden actuar como fotosensibilizadores (PS). La benzofenona (BP), presente en la estructura química de una amplia variedad de fármacos, tiene el potencial de fotosensibilizar daño al ADN, especialmente hacia la base de timina (Thy). Este daño puede dar lugar a dímeros de pirimidina de tipo ciclobutano (CPD) y a fotoproductos (6-4) pirimidina-pirimidona ((6-4)PPs), los cuales pueden causar mutaciones graves, melanomas o incluso la muerte celular. En algunos organismos, los (6-4)PPs pueden repararse de manera eficiente por las fotoliasas, en lo que se podría entender como una reacción Paternò-Büchi (PB) inversa a través de un intermedio de oxetano altamente inestable. Con el fin de profundizar en la fotorreactividad de los derivados BP-Thy y en la ruptura fotoinducida de oxetanos, se sintetizaron por primera vez una variedad de diadas en las que Thy y BP están covalentemente unidas por un espaciador lineal de diferente longitud y naturaleza. La fotorreactividad de los diferentes derivados se investigó por fotólisis de destello láser (LFP) y espectroscopía de absorción transitoria a escala de femtosegundo; además, se aislaron y caracterizaron los principales fotoproductos (PPs) derivados de la irradiación en estado estacionario. Los resultados mostraron un alto grado de quimioselectividad en la longitud y conformación del espaciador. En cuanto a la reactividad fotoquímica, se formaron PPs derivados de la PB y de la abstracción formal de hidrógeno; así, las diadas con el espaciador más largo dieron lugar a la formación de oxetanos y de PPs de abstracción de hidrógeno. Por el contrario, las diadas con espaciadores más cortos formaron un fotoproducto de abstracción formal de hidrógeno y/o polimerización. Por tanto, la fotorreactividad se vio influida por la longitud del espaciador, correlacionándose bien con los tiempos de 3BP*, observándose los tiempos más cortos para las diadas de espaciadores largos. En relación con la fotoapertura de oxetanos, la irradiación de los diferentes regio- y estereoisoméros condujo a la formación de la típica banda de absorción triplete-triplete de BP; por tanto, dicho proceso opera de forma adiabática. La fotólisis del oxetano que resulta de la irradiación de la diada con el espaciador más largo mostró una banda de absorción transitoria sobre 400 nm, atribuida a la formación del exciplejo triplete entre BP y Thy covalentemente unidos. Por otro lado, se investigó la reacción PB y la cicloreversión de oxetanos que surgen de la interacción entre Thy o derivados de uracilo (Ura) y BP. Así, se sintetizó una amplia gama de oxetanos Thy-BP y Ura-BP con diferentes sustituyentes en las posiciones 1 y 5 de la nucleobase, incluyéndose los regioisómeros cabeza-cabeza (HH) y cabeza-cola (HT). Los estudios espectroscópicos (absorción transitoria ultrarrápida y LFP), junto con el análisis teórico, coinciden en que la cicloreversión fotoinducida para los isómeros HH y HT implica la formación de un exciplejo en el estado excitado triplete antes de la ruptura. Generalmente, se observó que la reacción fue completamente adiabática para los regioisómeros HH. En el caso del oxetano HH que surge de la interacción entre 1,3-dimetiltimina (DMT) y BP, se observó la formación de una banda ~400 nm, que se atribuyó al exciplejo triplete 3[DMT···BP]*. Su formación fue altamente regioselectiva, siendo más rápida y eficiente para el isómero HH que para HT. Estos resultados fueron confirmados por análisis computacional. En general, se observó adiabaticidad en el proceso de fotorreversión para todos los oxetanos investigados, con un alto grado de regioselectividad y con la participación de exciplejos triplete. / [CA] La llum solar pot produir danys a l'ADN per absorció directa de llum UVB, o per fotosensibilització després de l'absorció de llum UVA per part de fàrmacs, que poden actuar com fotosensibilitzadors (PS). La benzofenona (BP), present en l'estructura química d'una àmplia varietat de fàrmacs, té el potencial de fotosensibilitzar dany a l'ADN, especialment a la base de timina (Thy). Aquest dany pot donar lloc a dímers de pirimidina de tipus ciclobutà (CPD) i a fotoproductes (6-4) pirimidina-pirimidona ((6-4)PPs), els quals poden causar mutacions greus, melanomes o fins i tot la mort cel·lular. En alguns organismes, els (6-4)PPs poden reparar-se de manera eficient per les fotoliases, en el que es podria entendre com una reacció Paternò-Büchi (PB) inversa a través d'un intermedi d'oxetà altament inestable. Amb la finalitat d'aprofundir en la fotoreactivitat dels derivats BP-Thy i en la ruptura fotoinduïda d'oxetans, es van sintetitzar per primera vegada una varietat de diades en les quals Thy i BP estan covalentment unides per un espaiador lineal de diferent longitud i naturalesa. La fotoreactivitat dels diferents derivats es va investigar per fotòlisi de centelleig làser (LFP) i espectroscopía d'absorció transitòria a escala de femtosegons; a més, es van aïllar i caracteritzar els principals fotoproductes (PPs) derivats de la irradiació en estat estacionari. Els resultats van mostrar un alt grau de quimioselectivitat en la longitud i conformació de l'espaiador. Quant a la reactivitat fotoquímica, es van formar PPs derivats de la PB i de l'abstracció formal d'hidrogen; així, les diades amb l'espaiador més llarg van donar lloc a la formació d'oxetans i de PPs d'abstracció d'hidrogen. Per contra, les diades amb espaiadors més curts van formar un fotoproducte d'abstracció formal d'hidrogen i/o polimerització. Per tant, la fotoreactivitat es va veure influïda per la longitud de l'espaiador, correlacionant-se bé amb els temps de 3BP*, observant-se els temps més curts per a les diades amb espaiadors llargs. En relació amb la fotoapertura d'oxetans, la irradiació dels diferents regi- i estereoisòmers va conduir a la formació de la típica banda d'absorció triplet-triplet de BP; per tant, aquest procés opera de manera adiabàtica. La fotòlisi de l'oxetà que resulta de la irradiació de la diada amb l'espaiador més llarg va mostrar una banda d'absorció transitòria sobre 400 nm, atribuïda a la formació de l'exciplex triplet entre BP i Thy covalentment units. D'altra banda, es va investigar la reacció PB i la cicloreversió d'oxetans que sorgeixen de la interacció entre Thy o derivats d'uracil (Ura) i BP. Així, es va sintetitzar una àmplia gamma d'oxetans Thy-BP i Ura-BP amb diferents substituents en les posicions 1 i 5 de la nucleobase, incloent-se els regioisòmers cap-cap (HH) i cap-cua (HT). Els estudis espectroscòpics (absorció transitòria ultraràpida i LFP), juntament amb l'anàlisi teòric, coincideixen en que la cicloreversió fotoinduïda per als isòmers HH i HT implica la formació d'un exciplex en l'estat excitat triplet abans de la ruptura. Generalment, es va observar que la reacció va ser completament adiabàtica per als regioisòmers HH. En el cas de l'oxetà HH que sorgeix de la interacció entre 1,3-dimetiltimina (DMT) i BP, es va observar la formació d'una banda ~400 nm, que es va atribuir a l'exciplex triplet 3[DMT···BP]*. La seua formació va ser altament regioselectiva, sent més ràpida i eficient per a l'isòmer HH que per a HT. Aquests resultats van ser confirmats per anàlisi computacional. En general, es va observar adiabaticitat en el procés de fotoreversió per a tots els oxetans investigats, amb un alt grau de regioselectivitat i amb la participació d'exciplexes triplet. / [EN] Sunlight light can produce damage to DNA through direct absorption of UVB or, more commonly, by photosensitization upon absorption of UVA light by drugs, that act as a photosensitizer (PS). Benzophenone (BP) as a building-block is present in a wide variety of drugs, and have the potential to photosensitize damage to DNA, specially towards the thymine (Thy) nucleobase. The resulting DNA damage can give rise to bulky dimers, i.e. cyclobutane pyrimidine dimers (CPDs) and pyrimidine-pyrimidone (6-4) photoproducts ((6-4)PPs), which can cause severe mutations, melanomas, or even be fatal for the cell. In some organisms, (6-4)PP can be efficiently repaired by photolyase enzymes, in what could be a reverse Paternò-Büchi (PB) reaction through an unstable oxetane intermediate. With the aim of getting deeper insight into the photoreactivity of BP-Thy derivatives and in the photoinduced cleavage of oxetanes, a variety of dyads where Thy and BP are covalently linked by a linear spacer of different lengths and nature were first synthesized. The photochemical reactivity and the photophysical properties of the different derivatives were investigated by means of laser flash photolysis (LFP) and femtosecond transient absorption spectroscopy; besides, the main photoproducts (PPs) arising from steady-state irradiation were also isolated and characterized. The results showed a high degree of chemoselectivity on the linking bridge length and conformation. Concerning the photochemical reactivity, PPs arising from the PB and from formal hydrogen abstraction were formed. In this context, the PB reaction took place for the dyads with the longest spacer with complete regio- and stereoselectivity, along with a hydrogen abstraction process. Finally, the dyads with shorter spacers gave rise to a formal hydrogen abstraction photoproduct and/or polymerization. Accordingly, the overall photoreactivity was proportional to the spacer length and was well correlated with the 3BP* lifetimes, the longer spacers giving rise to shorter lifetimes. In connection to the oxetane photocleavage, irradiation of the different regio- and stereoisomeric oxetanes led to the formation of the typical triplet-triplet absorption band of BP. Accordingly, the photoinduced cycloreversion also operates as an adiabatic process. Photolysis of the oxetane that results from irradiation of the dyad with the longest spacer showed a transient absorption at ~400 nm, which is ascribed to formation of the purported triplet exciplex between BP and Thy covalently linked. Additionally, the PB reaction and the cycloreversion of oxetanes arising from the interaction between Thy or uracil (Ura) derivatives and BP were also investigated. Thus, a wide range of Thy-BP and Ura-BP oxetanes with varying substituents at positions 1 and 5 of the nucleobase were synthesized, including both the head-to-head (HH) and head-to-tail (HT) regioisomers. Spectroscopic studies, including femtosecond transient absorption and LFP results, as well as theoretical multiconfigurational quantum chemistry analysis, agree that the photoinduced cycloreversion for the HH and HT isomers involved the formation of a triplet excited exciplex before the cleavage takes place. Generally, the photochemical reaction was fully adiabatic for the HH regioisomers. In the case of the HH-oxetane arising from the interaction between 1,3-dimethylthymine (DMT) and BP, an absorption band at ca. 400 nm was formed, and was attributed to the triplet exciplex 3[DMT···BP]*. Its formation was highly regioselective towards the HH regioisomer, being faster and more efficient than for the HT isomer. These results were confirmed by computational analysis. In general, adiabaticity was observed in the photoreversion process for all oxetanes, with a high degree of regioselectivity, which falls in line with the theory of the involvement of a triplet exciplex in the process. / Thanks to the Generalitat Valenciana for the finantial support through the Santiago Grisolía grant. / Blasco Brusola, A. (2021). Mechanistic Studies on the Photochemical Formation and Cleavage of Oxetanes Derived from Pyrimidine Bases [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/165256 / TESIS

No description available.

[ES] Los inhibidores de la tirosina quinasa (TKIs) son fármacos anticancerígenos que actúan atacando selectivamente a las células cancerosas, inhibiendo su crecimiento descontrolado y, por tanto, la consiguiente aparición de tumores. Sin embargo, muchos TKIs presentan un cromóforo en su estructura que les permite interaccionar con luz solar y, consecuentemente, pueden generar reacciones de fotosensibilización. A pesar de ello, existen pocos estudios sobre el mecanismo de reacción asociado a estos eventos. En este sentido, conocer la fotorreactividad de un fármaco en medio biológico es clave para entender dichos mecanismos y correlacionar el comportamiento fotofísico del fármaco con el daño fotobiológico que genera. La espectroscopía de fluorescencia y de absorción transitoria son técnicas altamente sensibles que permiten estudiar las especies transitorias generadas tras la absorción de luz por parte de un fármaco, las cuales podrían ser las responsables de las reacciones de fotosensibilización inducidas por éste. Habiendo estudiado recientemente la foto(geno)toxicidad asociada al TKI gefitinib (GFT) y a sus principales metabolitos fenólicos (GFT-M1 y GFT-M2), se ha llevado a cabo un estudio completo de la fotorreactividad de éstos tanto en disolución orgánica, utilizando disolventes de distintas polaridades, como en medio biológico, utilizando las proteínas transportadoras de origen humano albúmina sérica (HSA) y ¿1-glicoproteína ácida (HAG). Para ello, se han utilizado las técnicas espectroscópicas de absorción, fluorescencia y absorción transitoria, entre otras. Adicionalmente, se han llevado a cabo estudios teóricos de modelización molecular para investigar la unión ligando@proteína, así como las interacciones que tienen lugar en el complejo supramolecular tras la absorción de luz UV-A. Con este trabajo, se ha conseguido establecer una buena correlación entre el comportamiento fotofísico observado para gefitinib y sus dos metabolitos fenólicos con su potencial fototóxico. / [CA] Els inhibidors de la tirosina quinasa (TKIs) són fàrmacs anticancerígens que actuen atacant selectivament a les cèl·lules canceroses, inhibint el seu creixement descontrolat i, per tant, la consegüent aparició de tumors. No obstant això, molts TKIs presenten un cromòfor en la seua estructura que els permet interaccionar amb llum solar i, conseqüentment, poden generar reaccions de fotosensibilització. Malgrat això, existixen pocs estudis sobre el mecanisme de reacció associat a estos esdeveniments. En este sentit, conéixer la fotorreactivitat d'un fàrmac al mig biològic és clau per a entendre estos mecanismes i correlacionar el comportament fotofísic del fàrmac amb el dany fotobiològic que genera. La espectroscopia de fluorescència i d'absorció transitòria són tècniques altament sensibles que permeten estudiar les espècies transitòries generades després de l'absorció de llum per part d'un fàrmac, les quals podrien ser les responsables de les reaccions de fotosensibilització induïdes per aquest. Havent estudiat recentment la foto(geno)toxicitat associada al TKI gefitinib (GFT) i d'els seus principals metabòlits fenòlics (GFT-M1 i GFT-M2), s'ha dut a terme un estudi complet de la fotorreactivitat d'estos tant en dissolució orgànica, utilitzant dissolvents de diferents polaritats, com al mig biològic, utilitzant les proteïnes transportadores d'origen humà albúmina sèrica (HSA) i ¿1-glicoproteïna àcida (HAG). Per a això, s'han utilitzat les tècniques espectroscòpiques d'absorció, fluorescència i absorció transitòria, entre altres. Addicionalment, s'han dut a terme estudis teòrics de modelització molecular per a investigar la unió lligant@proteína, així com les interaccions que tenen lloc en el complex supramolecular després de l'absorció de llum UV-A. Amb este treball, s'ha aconseguit establir una bona correlació entre el comportament fotofísic observat per a gefitinib i els seu dos metabòlits fenòlics amb el seu potencial fototòxic. / [EN] Tyrosine kinase inhibitors (TKIs) are anticancer drugs that target cancer cells, inhibiting their uncontrolled growth and thus the subsequent development of tumours. However, many TKIs contain a chromophore in their structure that allows them to interact with sunlight and, consequently, to induce photosensitivity reactions. Despite this, there are few studies on the reaction mechanism associated with these events. In this regard, a better understanding on the photoreactivity of a drug in a biological environment is key to correlate the photophysical behaviour of the drug with the photoinduced damage it can induce to biomolecules. Fluorescence and transient absorption spectroscopies are very sensitive techniques that allow the study of the transient species generated after drug excitation, which could be responsible for drug-induced photosensitivity reactions. Having recently studied the photo(geno)toxicity associated with the TKI gefitinib (GFT) and its main phenolic metabolites (GFT-M1 and GFT-M2), a complete study of their photoreactivity has been carried out both in organic medium, using solvents of different polarities, and in a biological environment, using transport proteins such as human serum albumin (HSA) and human ¿1-acid glycoprotein (HAG). For this purpose, absorption, fluorescence and transient absorption techniques, among others, have been used. In addition, molecular dynamics simulation studies have been carried out to investigate the ligand@protein binding, as well as the interactions arising in the supramolecular complex after absorption of UV-A light. Therefore, a good correlation between the photophysical behaviour of gefitinib and its two phenolic metabolites and their phototoxic potential has been established in this research work. / Tamarit Mayo, L. (2024). Fotorreactividad de gefitinib y sus metabolitos fenólicos en disolución y en proteínas transportadoras [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/204145

Rhodopsin ist der Photorezeptor der Stäbchenzellen in der Retina von Vertebraten und wird als Prototyp für die gesamte Gruppe der GPCRs beforscht. Trifft ein Photon auf das Protein, so wird der über eine Schiffbase kovalent gebundene Chromophor von seiner 11-cis- in die All-trans-Konfiguration isomerisiert und setzt infolgedessen den Aktivierungsprozess in Gang. Dieser mündet in der aktiven Rezeptorkonformation, die das G-Protein Transducin aktivieren kann und dadurch eine Kaskade weiterer Aktivierungsschritten einleitet, die letztlich ein Nervensignal verursachen. Das Ziel dieser Arbeit war die Aufklärung der späten Aktivierungsschritte und ihrer Ursache-Wirkungs-Beziehungen. Zu diesem Zweck wurden Blitzlichtphotolyse, Elektronenspinresonanz (EPR) mit Spinlabeling (SDSL), UV/vis-Spektroskopie, FTIR-Spektroskopie und Fluoreszenzspektroskopie angewandt. Kinetische Messungen wurden unter identischen Bedingungen durchgeführt, um die Abfolge der mit den unterschiedlichen Techniken zugänglichen Aktivierungsschritte aufzuklären. Nach der Bildung des absorptionsspektroskopisch definierten Meta-II-Zustands bewegt sich die Helix TM6 in einem späteren Schritt als ganzes nach außen und markiert damit den Übergang von Meta-IIa zu Meta-IIb. Dadurch wird die bis dahin in der Membran verborgene D(E)RY-Region für das Umgebungsmedium zugänglich und nimmt ohne Zeitverzögerung ein Proton auf, wodurch der Meta-IIb*H+-Zustand gebildet wird. Die verfügbaren Daten sprechen dafür, dass das D(E)RY-Motiv bei der Aktivierung des Transducins sowohl die Alpha- als auch die Gamma-Untereinheit desselben bindet. Die Bindung von zu Transducin-Abschnitten analogen Peptiden kann dann erfolgen, wenn die Helix TM6 im nach außen bewegten Zustand ist, und führt zur Abgabe von bis zu zwei Protonen vom aktivierten Rhodopsin. Sowohl das D(E)RY- und das NPxxY(x)5,6F-Motiv als auch die beiden Zustände Meta-IIb und Meta-IIb*H+ könnten relevant für den sequenziellen Transducin-Aktivierungsmechanismus sein. / Rhodopsin is the photoreceptor in the rod cells of the vertebrate retina. It is considered as a prototype of the whole group of GPCRs. Upon absorption of a photon the chromophore, which is covalently bound through a Schiff base, is isomerized from its 11-cis into the all-trans configuration. This initiates the activation process and finally results in the active receptor conformation which is capable of activating the G protein transducin and thereby triggers a cascade of further activation steps which finally cause a nerve signal. The aim of this work was the clarification of the late activation steps and their cause-and-effect chain. For this purpose flash photolysis, electron paramagnetic resonance (EPR) with spin labeling (SDSL), UV/vis spectroscopy, FTIR spectroscopy and fluorescence spectroscopy were applied. Kinetic measurements were executed under identical conditions in order to elucidate the sequence of activation steps, which are accessible with the different techniques. After formation of the spectroscopically defined Meta-II state helix TM6 moves outward as a rigid body, thereby marking the transition from Meta-IIa to Meta-IIb. Therefore the D(E)RY region, which is until then buried in the membrane, gets accessible to the surrounding solution. It consequently takes up a proton without delay, thus forming the Meta-IIb*H+ state. Available data argue for the D(E)RY motif binding both the Alpha and the Gamma subunit of transducin during activation of the latter. The binding of peptides which are analogous to sections of transducin is possible when helix TM6 is in the outward position. It causes the release of up to two protons from the activated rhodopsin. Both the D(E)RY motif and the NPxxY(x)5,6F motif as well as both the states Meta-IIb and Meta-IIb*H+ are potentially relevant for the sequential transducin activation mechanism.

Artificial photosynthesis is often considered to have great potential to provide alternative, renewable fuels by harvesting, conversion and storage of solar energy. One promising approach is the development of modular molecular photocatalysts inspired by natural photosynthetic enzymes. The first part of this thesis deals with artificial mimics of the water oxidizing photosystem II composed of a chromophore and an electron relay as synthetic counterpart of the P680-TyrZ/His190 ensemble of photosystem II. Three ruthenium polypyridyl - imidazole - phenol complexes with varying position of a methyl group on the phenol ring (Ru-xMe) were synthesized and characterized by electrochemical and photophysical methods. As an improvement compared to earlier complexes the increased redox potential (~0.9 V vs. Ferrocene) of the phenol groups makes their function as an electron relay in a photocatalytic system for water oxidation thermodynamically possible. Time-resolved absorption studies revealed fast intramolecular electron transfer (<5-10 µs in aprotic solvent and <100 ns in water) despite the low driving force and the importance of the hydrogen bond between the phenol and the imidazole group was put in evidence. Slight differences between the three Ru-xMe complexes and investigation of the effect of external bases allowed to derive a mechanistic picture in which the imidazole is involved in a "proton domino" reaction. Accepting the phenolic proton upon ligand oxidation (within the H-bond) renders its second nitrogen site more acidic and only deprotonation of this site pulls the overall equilibrium completely towards oxidation of the ligand. Another part of this thesis comprises a chromophore-tryptophan construct synthesized using a click chemistry approach. Light-induced oxidation of Trp in this Ru-tryptophan complex was shown to follow ETPT mechanism. Depending on the pH conditions tryptophan radicals, either Trp* or TrpH*⁺ were detected and spectral measurement at different time showed the transition between the two forms. Deprotonation of the radical was dependent on the concentration of water as proton acceptor. Later part of the thesis deals with efforts to covalently bind a catalytic unit to the previously characterized chromophore-electron relay module. The click chemistry approach was not successful to obtain the final photocatalytic assembly. Therefore bimolecular activation of a Mn salen catalyst was performed and formation of Mn(IV) species was observed. As a step towards utilization of these types of photocatalysts in a photoelectrochemical cell a [Ru(bpy)₃]²⁺ chromophore with phosphonate anchoring groups (Ru-Phosphonate) was synthesized and grafted on the surface of a TiO₂ mesoporous semiconductor surface anode to perform photocurrent measurements.

Les processus d'oxydation avancés à base du radical sulfate (SO4•- -) ont prouvé leur efficacité pour l'élimination de nombreux contaminants. Dans ce travail de thèse, nous avons étudié les processus d'oxydation et de dégradation par le radical sulfate activé à partir du persulfate (PS) pour les molécules suivantes : le diatrizoate, molécule utilisée comme produit de contraste radiologique iodé (DTZ), le salbutamol (SAL) et la terbutaline (TBL), agonistes des récepteurs ß2-adrénergiques. En outre, la réactivité de SO4•- avec la matière organique naturelle (NOM) a également été déterminée. Plus précisément, pour déterminer la réactivité de SO4•- avec NOM, une technique de photolyse laser couplée à la spectroscopie (LFP) a été appliquée pour étudier l'évolution de SO4 • ainsi que la formation d'espèces transitoires à partir de la matière organique. Des constantes de vitesses comprises entre 1530 et 3500 s-1 mgC-1 L ont été obtenues par analyse numérique des équations différentielles et des valeurs moyennes de coefficient d'absorption molaires comprises entre 400 et 800 M-1 cm-1 ont été déterminées pour les espèces transitoires générées de la matière organique.Dans le processus de décomposition de DTZ par PS activé par UV, les principales voies d'oxydation sont la dé-iodination-hydroxylation, la dé-carboxylation-hydroxylation et le clivage de la chaîne latérale. Les résultats ont également indiqué que la vitesse de dégradation du DTZ augmentait avec l'augmentation de la concentration en PS. La présence de NOM a inhibé la dégradation de DTZ, tandis que le bicarbonate l'a amélioré. Pour les ions chlorure un effet négatif a été observé pour des concentrations supérieures à 500 mM.Pour la dégradation du SAL et du TBL, il a été montré que les radicaux phénoxy jouaient un rôle majeur en début de réaction. Par ailleurs, le chlorure n'a pas eu d'effet tangible sur l'efficacité d'oxydation de la SAL et du TBL, tandis que les ions bromures, bicarbonates et le NOM présentaient des effets inhibiteurs / Sulfate radical (SO4•-) based advanced oxidation processes (AOPs) has been proved to be effective for the removal of many contaminants. In this thesis, we investigated the oxidation processes of iodinated X-ray contrast media diatrizoate (DTZ), ß2-adrenoceptor agonists salbutamol (SAL) and terbutaline (TBL) by reaction with SO4•- generated from the activation of persulfate (PS); in addition, the reactivity of SO4•- with natural organic matter (NOM) was also estimated.Specifically, to determine the reactivity of SO4•- with NOM, laser flash photolysis (LFP) technique was applied to monitor the SO4•- decay and the formation of the transients from organic matters. Reaction rate constants comprised between 1530 and 3500 s-1 mgC-1 L were obtained by numerical analysis of differential equations and the weighted average of the extinction coefficient of the generated organic matters radicals between 400 and 800 M-1 cm-1.In the decomposition process of DTZ by UV-activated PS, major oxidation pathways include deiodination-hydroxylation, decarboxylation- hydroxylation and side chain cleavage. Results also indicated that DTZ degradation rate increased with increasing PS concentration. The presence of NOM inhibited DTZ removal rate, while, bicarbonate enhanced it, and chloride ions induced a negative effect above 500 mM. For the degradation of SAL and TBL, phenoxyl radicals were proven to play a very important role from the initial step. Chloride exhibited no effect on the oxidation efficiencies of SAL and TBL, while bromide, bicarbonate and NOM all showed inhibitory effects

L'atmosphère est un milieu hautement hétérogène contenant de la matière condensée : les aérosols. Ceux-ci sont des composants importants de l'atmosphère car ils impactent le bilan radiatif planétaire mais aussi la qualité de l'air. En particulier les aérosols organiques secondaires (AOS), produits par la transformation chimique dans l'air de nombreux composés organiques, plus ou moins volatils, représentent une fraction conséquente dans le budget global des aérosols atmosphériques pour laquelle de nombreuses incertitudes persistent. En particulier, leurs voies de formation et de transformation dans la troposphère restent très mal décrites. C'est pourquoi, cette thèse décrit principalement l'étude de trois aspects de la croissance et du vieillissement (transformation) des aérosols : caractérisation de la croissance des AOS par des processus photosensibilisés ; investigations mécanistiques du vieillissement des AOS et de la photochimie des photosensibilisateurs ; analyse chimique des composés issus du vieillissement des AOS / Aerosols are important constituents of the atmosphere and secondary organic aerosols (SOA) represent a main fraction of the organic aerosols in the total budget. This thesis mainly reports the investigation of three aspects of the growth and aging of SOA: the photosensitized SOA growth ; the mechanistic investigation of SOA aging and of the photochemistry of photosensitizers ; the analysis of the chemical composition of aged SOA. The photosensitized growth and aging processes of SOA were investigated using an aerosol flow tube coupled with various aerosol and gas sensing instruments. For further analysis of the aerosol composition and a better understanding of the formation and growth of SOA in these experiments the aerosols produced in the dark and in the light were sampled on filters at the exit of the flow tube

No description available.

The critically important nature of radical and radical ion mechanisms in biology and chemistry continues to be recognized as our understanding of these unique transient species grows. The work presented herein demonstrates the versatility of kinetic studies for understanding the elementary chemical reactions of radicals and radical ions. Chapter 2 discusses the use of direct ultrafast kinetics techniques for investigation of crucially important enzymatic systems; while Chapter 3 demonstrates the value of indirect competition kinetics techniques for development of synthetic methodologies for commercially valuable classes of compounds. The mechanism of decay for aminyl radical cations has received considerable attention because of their suspected role as intermediates in the oxidation of tertiary amines by monoamine oxygenases and the cytochrome P450 family of enzymes. Radical cations are believed to undergo deprotonation as a key step in catalysis. KIE studies performed by previous researchers indicate N,N-dimethylaniline radical cations deprotonate in the presence of the bases acetate and pyridine. By studying the electrochemical kinetics of the reaction of para substituted N,N-dimethylaniline radical cations with acetate anion, we have produced compelling evidence to the contrary. Rather than deprotonation, acetate reacts with N,N-dimethylaniline radical cation by electron transfer, generating the neutral amine and acetoxyl radical. Transport properties of reactants and solvent polarity changes were investigated and confirmed not to influence the electrochemical behavior forming the basis for our mechanistic hypothesis. To reconcile our conclusion with earlier results, KIEs were reinvestigated electrochemically and by nanosecond laser flash photolysis. Rather than a primary isotope effect (associated with C-H bond cleavage), we believe the observed KIEs are secondary, and can be rationalized on the basis of a quantum effect due to hyperconjugative stabilization in aromatic radical cations during an electron transfer reaction. Product studies performed by constant potential coulometry indicate N,N-dimethylaniline radical cations are catalytic in carboxylate oxidations. Collectively, our results suggest that aminyl radical cation deprotonations may not be as facile as was previously thought, and that in some cases, may not occur at all. Interest in design and synthesis of selenium containing heterocycles stems from their ability to function as antioxidants, anti-virals, anti-inflammatories, and immunomodulators. To establish synthetic feasibility of intramolecular homolytic substitution at selenium for preparation of selenocycles, we set out to determine what factors influence cyclization kinetics. A series of photochemically labile Barton and Kim esters have been syntheisized and employed as radical precursors. The effect of leaving radical stability on kinetics has been investigated through determination of rate constants and activation parameters for intramolecular homolytic substitution of the corresponding radicals via competition experiments. Notable leaving group effects on measured kinetic parameters show more facile reactions for radical precursors with more stable leaving radicals. Moreover, cyclizations to form six-membered (as opposed to five- membered) ring systems exhibited order of magnitude decreases in rate constants for a given leaving radical. Our results are congruent with expectations for radical cyclizations trends for the varied experimental parameters and suggest homolytic substitution affords a convenient means for synthesis of selenocycles. / Ph. D.

Ao ser excitado do estado fundamental para o estado singlete excitado, o Pka do equilíbrio ácido-base das antocianinas apresenta um deslocamento de ca. 4 para ca. -1. Esta característica de superfotoácido, aliado à técnica de fotólise por pulso de laser, permite a perturbação da posição do equilíbrio ácido-base no estado fundamental. O acompanhamento da cinética de reestabelecimento do equilíbrio inicial, existente antes do pulso do laser, permite a determinação das constantes de desprotonação kd e protonação kp no estado fundamental. Este método foi aplicado para a determinação das constantes de protonação e desprotonação das seguintes antocianinas sintéticas e naturais: 4-metil-7-hidroxiflavílio (HMF), 4\', 7-dihidroxiflavílio (DHF), malvidina-3-glucosídeo (Oenina), malvidina-3,5-diglucosídeo (Malvina), pelargonidina-3,5-diglucosídeo (Pelargonina) e cianidina-3 ,5-diglucosídeo (Cianina). Assim, as constantes de desprotonação do estado fundamental são: kd = 1,4 x 106 s-1 (HMF), 3,1 x 106 s-1 (DHF), 5, 1 x 106 s-1 (Oenina), 3,8 x 106 s-1 (Malvina), 1,3 x 106 s-1 (Pelargonina) e 1,8 x 106 s-1 (Cianina). As constantes de protonação do estado fundamental são:kp = 3,56 x 1010 L mol-1 s-1 (HMF), 3,06 x 1010 L mol-1s-1 (DHF), 2,51 x 1010 L mol-1s-1 (Oenina), 2,9 x 1010 L mol-1s-1 (Malvina), 3,6 x 1010 L mol-1s-1 (Pelargonina) e 2,2 x 1010 L mol-1s-1 (Cianina). Nosso método é a única técnica que permite a determinação direta destas constantes. Este método também permite a determinação de kd e kp em meios micro-heterogêneos. Através de medidas de kd , foi possível provar que ocorre a estabilização do cátion flavílio de HMF em micelas aniônicas de SOS (dodecilsulfato de sódio). Em micelas não iônicas e catiônicas, por outro lado, ocorre a desestabilização do cátion flavílio, que se manifesta através do aparecimento de reatividade ausente em solução aquosa. Os resultados da aplicação deste método revelam ainda que o principal processo de dissipação da energia da luz, absorvida pelas antocianinas, é a transferência de próton no estado excitado e não a fluorescência. / Upon excitation from the ground state to the first excited singlet state, the pKa of the acid-base equilibrium of anthocyanins exhibits a large shift, from ca. 4 to ca. -1. This characteristic of super-photoacidity, coupled with the technique of laser flash photolysis, can be employed to perturb the position of the acid-base equilibrium in the ground state. Monitoring the kinetics of relaxation back to the initial equilibrium position that existed prior to the laser pulse permits determination of the rate constants for protonation (kp) and deprotonation (kd) in the ground state. This method was applied to the following natural and synthetic anthocyanins: 4-methyl-7-hydroxyflavylium (HMF); 4\', 7-dihydroxyflavylium (DHF); malvidine-3-glucoside (Oenin); malvidine-3,5-diglucoside (Malvin); Pelargonidine-3,5-diglucoside (Pelargonin); and. cyanidine-3,5-diglucoside (Cyanin). Thus, the ground state deprotonation rate constants (kd) for the acid form were found to be: 1.4 x 106 s-1 (HMF); 3.1 x 106 s-1 (DHF); 5.1 x 106 s-1 (Oenin); 3.8 x 106 s-1 (Malvin); 1.3 x 106 s-1 (Pelargonin); 1.8 x 106 s-1 (Cyanin). The corresponding rate constants for protonation of the ground state of the base (kp) were: 3.6 x 1010 M-1s-1 (HMF); 3.1 x 1010 M-1s-1 (DHF); 2.5 x 1010 M-1s-1 (Oenin); 2.9 x 1010M-1s-1 (Malvin); 3.6 x 1010 M-1s-1 (Pelargonin); 2.2 x 1010 s-1 (Cyanin). Our method is currently the only one that permits direct determination of these rate constants. This method also allows the determination of kpand kd in microheterogeneous media. Thus, employing measurements of kd, it was possible to demonstrate that anionic SDS (sodium dodecyl sulfate) micelles stabilize the flavylium cation form of HMF. In cationic and nonionic micelles, however, the flavylium cation is destabilized, which manifests itself via the appearance of reactivity that is absent in aqueous solution in the absence of these surfactants. Finally, the results of the application of this method show that the primary energy wasting process for radiant energy absorbed by anthocyanins is excited state proton transfer rather than fluorescence.