Foram sintetizados a 5-tia-pentaceno-14-ona (TX-A) e a 5-tia-naftaceno-12-ona (TX-Np), dois compostos derivados da tioxantona, para serem usados como fotiniciadores em reações de polimerização de diacrilatos. Após purificação usando cromatografia em coluna e líquida de alta eficiência, esses compostos foram caracterizados por análise elementar (AE), espectroscopia na região do infravermelho (IV) e de ressonância magnética nuclear de próton (1H RMN). A caracterização do comportamento espectroscópico dos compostos foi feita utilizando-se espectroscopia na região do ultravioleta e visível (UV-vis) e de fluorescência. A UV-vis revelou que a TX-A apresenta maior absorção na região do visível em relação à TX-Np. Os resultados de fluorescência evidenciaram a dependência do solvente na emissão, juntamente com o comportamento das transições presentes. Os tempos de vida das espécies singlete foram determinados como sendo da ordem de nanosegundos, sendo maior em meio de solventes hidroxílicos polares. A fotólise por pulso de laser foi utilizada para estudar a absorção dos transientes, demonstrando que a TX-Np apresenta três máximos de absorção em 340, 450 e 590 nm, que foram atribuídos aos transientes do estado triplete/radical, radical cetila e ao estado triplete respectivamente, cujos tempos de vida se situam na ordem de microssegundos. Já a TX-A apresentou dois máximos de absorção em 415 e 515 nm, que correspondem à absorção do estado triplete do antraceno resultante da transferência de intramolecular de energia entre grupos da molécula. A avaliação do desempenho de ambos os compostos como fotoiniciadores foi feita com o auxílio da Fotocalorimetria Exploratória Diferencial (Foto-DSC) usando-se como modelo uma mistura dos monômeros BisGMa (dimetacrilato de bisfenilglicidila) e TEGDMA (dimetacrilato de trienilo glicol) nas proporções: 70:30; 30:70 e 50:50 (m/m), respectivamente. Estes estudos demonstraram que utilizando-se a TX-Np como fotoiniciador, a polimerização ocorreu com maior velocidade no sistema contendo maior proporção de BisGMA, que torna o sistema mais viscoso. Entretanto, maiores graus de conversão foram obtidos utilizando maiores proporções de TEGDMA, ou seja, misturas menos viscosa. Utilizando a TX-A, o sistema contendo BisGMA e TEGDMA na proporção 70:30 (m/m), apresentou maior velocidade de polimerização, enquanto a mistura contendo quantidades de massa iguais dos dois monômeros foi a que apresentou o maior grau de conversão. Quanto à influência de O2, apenas a TX-A apresentou resultado significativo na polimerização, quando o experimento foi realizado em ar. / The 5-thia-pentacene-14-one (TX-A) and 5-thia-naphthacene-12-one (TX-Np), both derivatives of thioxanthone have been synthesized and evaluated in relation to their performance as photoinitiators in diacrylates polymerization reaction. After purifying by column and liquid chromatography the compounds were characterized by elemental analysis (EA), spectroscopy in the infrared region (IR) and proton nuclear magnetic resonance (1H NMR). The spectral behavior of the thioxanthone derivatives was performed by spectroscopy in the ultraviolet and visible range (Uv-vis) and fluorescence. The UV-vis results revealed that TX-A presents higher absorption in the visible range than the TX-Np. The fluorescence data evidenced a dependence of the solvent nature in the emission. The life time of singlet species was determined as in the nano-seconds level, being higher in polar hydroxilic solvents medium. The laser flash-photolysis was used to investigate the transients absorption, revealing that the TX-Np have three absorption maxima at 340, 450 and 590 nm, which were attributed to the triplet state/radical, cetyl radical and triplet state, respectively, whose lifetimes were in the microseconds scale. Meanwhile, the TX-A showed two absorption maxima at 415 and 515 nm corresponding to the anthracene triplet state absorption from an intramolecular energy transfer between groups of the molecule. The performance of both photoinitiators had been evaluated by Photocalorimetry, using a mixture of bisphenylglycidyl dimetacrilate (BisGMA) and triethileneglycol dimetracrylate (TEGDMA) containing 70:30; 30:70 and 50:50 (w/w) of each monomer respectively. Such studies demonstrated that using TX-Np as a photoinitiator the rate of polymerization was higher when larger amounts of BisGMA is used in the mixture, making the system more viscous. However higher conversion degrees were found when higher amounts of TEGDMA are used, that means in less viscous mixtures. When TX-A is used as a photoinitiator the system containing 70:30 (w/w) of BisGMA and TEGDMA, showed higher rate of polymerizations while the mixture containing equal amounts of both monomers presented a higher conversion degree. Concerning the O2 influence, only the TX-A presented a significant polymerization extent when the experiment was performed in the presence of air.

Transient absorption spectroscopy was used to study light induced electron transfer processes in Type 1 photosynthetic reaction centers. Flash induced absorption changes were probed at 800, 703 and 487 nm, and on multiple timescales from nanoseconds to tens of milliseconds. Both wild type and menB mutant photosystem I reaction centers from the cyanobacterium Synechocystis sp. PCC 6803 were studied. Photosystem I reaction centers from the green algae Chlamydomonas reinhardtii, and the newly discovered chlorophyll-d containing organism Acaryochloris marina, were also studied. The flash induced absorption changes obtained for menB mutant photosystem I reaction centers are distinguishable from wild type at 800 nm. MenB mutant photosystem I reaction centers displays a large amplitude decay phase with lifetime of ~50 ns which is absent in wild type photosystem I reaction centers. It is hypothesized that this ~50 ns phase is due to the formation of the triplet state of primary electron donor.

Steady state reflectance and emission characteristics of anthracene adsorbed on silica gel and titania-silica mixed oxides have been investigated as a function of sample loading. Titania-silica mixed oxides with 1, 3, 5 and 10 wt. % TiO2 were prepared by two different methods: a dropwise method and a sol-gel route. Ground state diffuse reflectance and fluorescence emission spectra of anthracene adsorbed on titania-silica surfaces show a dependence on titania content. The absorption peaks of anthracene are difficult to resolve at higher titania content due to the increasing red-shift of the titania absorption edge. The absorption edge of titania is shifted to longer wavelengths and the band gap energy decreases with increasing the titania loading. Diffuse reflectance laser flash photolysis at 355 nm produces both the triplet and radical cation of anthracene and gives relevant information regarding the photochemical transients and the kinetics details of the surface photochemical processes. Energy dependence studies confirm the monophotonic nature of the triplet production, whereas the anthracene radical cation is formed by monophoton or multiphoton ionisation in the mixed titania-silica systems. Energy and electron transfer reactions of anthracene co-adsorbed with azulene as electron donor on silica sol-gel and titania-silica mixed oxides prepared by the sol-gel method with different titania content have been studied using the time-resolved diffuse reflectance laser flash photolysis technique. The fluorescence of excited anthracene adsorbed on silica sol-gel is quenched by the addition of azulene, while co-adsorption of azulene on titania-silica mixed oxides resulted in a decrease in the fluorescence intensity of the adsorbed anthracene due to the formation, at the same time, of anthracene radical cation and Ti3+ species on the titania-silica surface. Triplet-triplet energy transfer from the excited anthracene to ground state azulene and electron transfer from azulene to the anthracene radical cation have been investigated using a time-resolved diffuse reflectance laser flash photolysis technique following laser excitation at 355 nm. Bimolecular rate constants for energy and electron transfer between anthracene and azulene have been obtained. Kinetic analysis of the decay of the anthracene triplet state and radical cation show that the kinetic parameters depend on the titania content of the sample and the azulene concentration. This indicates that the rate of energy and electron transfer reactions increases as a function of azulene concentration and decreases with increasing titania content in titania-silica mixed oxides, whereas the observed rate of reaction on silica sol-gel is predominantly governed by the rate of diffusion of azulene. Electron transfer reactions in a ternary system using azulene for hole transfer between 9-anthracenecarboxylic acid radical cation as electron acceptor and perylene as electron donor were also studied in order to demonstrate the mobility of radical cations on the silica sol-gel and titania-silica surfaces. The co-adsorption of azulene as a molecule shuttle with 9-anthracenecarboxylic acid and perylene on both silica sol-gel and titania-silica systems has been shown to enhance the rate of electron transfer in this ternary system. Activation energies for energy and electron transfer on photoinduced bimolecular and termolecular processes on silica sol-gel and titania-silica mixed oxides have been measured. In bimolecular anthracene / azulene systems, at higher azulene loadings, the activation energies and the pre-exponential factors on titania-silica surfaces are the same for both energy and electron transfer and are comparable with the parameters extracted for azulene diffusion on silica Davisil suggesting that azulene diffuses across the silica Davisil and titania-silica mixed oxides surfaces, while at lower azulene loadings, ion-electron recombination dominates and the activation energy extracted is for this process. In a ternary 9-anthracenecarboxylic acid / azulene / perylene system, the activation energy for perylene diffusion is higher than that observed for the anthracene / azulene system, reflecting the lower mobility of the perylene molecule. In this study, a series of titania-silica samples with different loadings of titania (1 10 wt. %) prepared by the sol-gel method and also the pure TiO2 P25 Degussa have been used to study the photocatalytic degradation of 4-chlorophenol in aqueous solution under UV light irradiation. The absorption peak of 4-chlorophenol at 280 nm decreases with increasing titania content and finally disappeared suggesting that titania has a positive influence on the degradation of 4-chlorophenol. The investigated titania-silica mixed oxides prepared by the sol-gel method are less efficient photocatalysts for the degradation of 4-chlorophenol than TiO2 P25.

Sulfite oxidising enzymes are found in all forms of life and play an important role in detoxification of sulfite produced through biochemical processes. All known sulfite oxidising enzymes share a common molybdenum active site. The sulfite dehydrogenase (SDH) from the soil bacterium Starkeya novella differs from the vertebrate sulfite oxidases (SO) in that the heme and Mo subunits are tightly associated rather than connected by a flexible hinge. This structural integrity makes SDH an ideal model enzyme for the study of enzymatic sulfite oxidation without the complications of structural changes underlying catalysis. In human sulfite oxidase (HSO) the substitution of a conserved active site amino acid residue, Arg-160 for Gln, results in a lethal disease. A number of independent studies have been carried out in order to understand the effects of this substitution on catalysis in both human (HSO) and chicken sulfite oxidising enzymes (CSO). The focus of this work is the analogous residue in SDH, Arg 55. A number of active site substitutions have been investigated, including SDHR55Q, an analogous substitution to the lethal mutation identified in humans. In addition, the properties of the Arg residue have also been probed using a substitution to a hydrophobic residue, Met (SDHR55M) and a substitution to the positively charged Lys (SDHR55K). A fourth active site substitution, SDHH57A, was also investigated as the crystal structure of this variant indicated that His-57 plays a role in stabilising the position of Arg-55 in SDH. It was of interest to determine the effect of the instability in the position of Arg-55 on the catalytic parameters of the SDHH57A. The kinetic properties of the substituted enzymes were investigated using steady-state assays with cytochrome c as an electron acceptor. When the positive charge was lost in the case of SDHR55M and SDHR55Q, a dramatic increase in the KM (sulfite - app) of 2 – 3 orders of magnitude resulted. This indicates that the positive charge on Arg-55 is important for substrate binding. All the Arg-55 variants studied were found to have lower turnover numbers than the wild type, in particular, SDHR55Q was found to have a reduced kcat (108 s-1 vs 345 s-1 for SDHWT at pH 8). The changes in the Mo centre underlying the altered kinetic properties were investigated in detail using EPR spectroscopy of the intermediate MoV oxidation state in SDHR55Q and SDHH57A. Similar to what has been noted for HSOR160Q, a sulfate blocked form was observed at pH 6 using pulsed EPR experiments, suggesting that this substitution causes an inhibition of the hydrolysis step required to release the reaction product, sulfate. This could be a further reason for the poor catalytic activity of SDHR55Q, in particular, a reason for the low turnover rate of this variant. Unlike what was noted in HSOR160Q, where the substituted enzyme showed a dramatic decrease in rate of intramolecular transfer by three orders of magnitude compared to HSOWT, the rate of electron transfer was found to be 3 times faster in SDHR55Q relative to the wild type enzyme. These results indicate that Arg-55 is not involved in the pathway of electron transfer between the Mo and heme centres, but rather assists with the the docking of the heme group in HSO. As this process is not required in SDH, our results suggest that intramolecular electron transfer (IET) in HSOR160Q decreases because it is crucial for docking of the heme domain. Through potentiometric redox titrations, the effect of the active site amino acid substitutions on both the Mo and Fe redox potentials was investigated. No significant change was determined for the MoVI/V redox potentials, however, the heme potentials for SDHWT and SDHR55K were 40 mV higher than those of the other variants, with the lowest potentials belonging to SDHR55M and SDHH57A. Of further interest was that the MoVI/V couple is significantly lower than the heme couple (175 mV vs 240 mV respectively) in SDHWT. It appears that the positive charge of the Arg is important in regulating the heme redox potentials and could thereby contribute to modulating enzymatic activity. When SDH was immobilised on a modified pyrolytic graphite electrode, stable and high catalytic currents were observed, indicating facile heterogeneous electron transfer between the enzyme and the electrode. This good electron transfer allowed the catalytic properties of SDH and its substituted enzymes to be investigated as a function of potential. A pH dependence ( 59 mV/pH) in the catalytic operating potential was noted for SDHWT and SDHR55K, which appears to follow the pH dependence of the MoVI/V couple. This catalytic potential is pH-independent in the R55M and H57A variants, where the catalytic operating potentials appeared to follow the FeIII/II redox couple. It is proposed that two distinct pathways of electron transfer from the Mo centre to the electrode are likely to exist. The first is direct transfer from the Mo centre to the electrode at lower potential (~ 175 mV) while the second proceeds via the heme group (320 mV). The pathway followed is determined by the oxidation state of the heme group. A slight difference in the electron transfer rates of these two processes was seen, with direct transfer (from Mo) being the faster, which accounts for the unusual peak shape noted in the voltammogram for SDHWT at high sulfite concentrations, where the rate of catalytic activity slows at a higher potentials despite the greater thermodynamic driving force. This work provides new insights into the mechanism of enzymatic sulfite oxidation. Arg-55 has been shown to play an important role in the catalytic functioning of SDH in both substrate affinity and product release. Unlike what has been previously proposed, Arg-55 does not play a part in the pathway of electron transfer, but is rather involved in the regulation of the redox potentials of the metal centres in the enzyme.

Três macroiniciadores foram sintetizados baseados em tioxantona; MMa-co-TXA, BMa-co-TXA e HMa-co-TXA. Estes macroiniciadores possuem vantagens em relação aos compostos de baixa massa molar apesar do seu alto custo. A fotoatividade destes macroiniciadores e da tioxantona para a polimerização de monômeros monofuncional (MMA) e multifuncionais, 2,2-bis[4-(2-hidroxi-3-metacriloxipropoxi)fenil]propano (Bis-GMA) e dimetacrilato de trietilenoglicol (TEGDMA) foi examinada com as técnicas de Fotocalorimetria Exploratória Diferencial e Espectroscopia de Infravermelho por Transformada de Fourier com acessório de ATR. Os co-iniciadores usados foram as aminas EDB, TEA e DMAEMA. Todos os sistemas foram estudados na ausência de solvente. Os resultados mostraram que os macroiniciadores são mais eficientes do que o composto de baixa massa molar. Medidas de fotólise por pulso de laser permitiram obter o espectro de absorção de transientes dos compostos estudados, bem como a constante de supressão do estado triplete pelas aminas e pelo monômero. A polimerização fotoiniciada pelos macroiniciadores na presença de aminas e dos monômeros foi estudada com o objetivo de se determinar o mecanismo que leva à formação dos radicais iniciadores. Expressões para o rendimento quântico de radicais ativos foram deduzidas a partir do mecanismo proposto. Resultados mostraram que a produção de radicais ativos para os macroiniciadores é maior do que a tioxantona. / In this work three macroinitiators based on thioxanthone were synthesized and characterized; MMA-co-TXA, BMA-co-TXA and HMA-co-TXA. Macroinitiators offer some advantages when compared with their corresponding low molecular weight analog. The photopolymerization initiated by macroinitiators and thioxanthone of methyl methacrylate (MMA) and mixtures of 2,2-bis[4-(2-hydroxy- 3-metacryloxipropoxi)phenyl]propane (Bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA) was studied through Photocalorimetry (Photo-DSC) and Fourier Transform Infrared Spectroscopy with ATR accessory. All systems were studied in the absence of solvent (bulk) using EDB, TEA and DMAEMA, as co-initiators. Measures of Laser Flash Photolysis determined the transient absorption spectra of the compounds and also the bimolecular rate constants for the triplet quenching of the compounds. The polymerization reaction of the macroinitiator in presence of amine and monomer was studied in order to determine the mechanism leading to the formation of radical initiators. Expressions for the quantum yield of radicals assets were deducted from the proposed mechanism. Results showed that the radical production assets to macroinitiator is greater than the thioxanthone, making macroinitiators more efficient than the low molecular weight compound.

Foram sintetizados a 5-tia-pentaceno-14-ona (TX-A) e a 5-tia-naftaceno-12-ona (TX-Np), dois compostos derivados da tioxantona, para serem usados como fotiniciadores em reações de polimerização de diacrilatos. Após purificação usando cromatografia em coluna e líquida de alta eficiência, esses compostos foram caracterizados por análise elementar (AE), espectroscopia na região do infravermelho (IV) e de ressonância magnética nuclear de próton (1H RMN). A caracterização do comportamento espectroscópico dos compostos foi feita utilizando-se espectroscopia na região do ultravioleta e visível (UV-vis) e de fluorescência. A UV-vis revelou que a TX-A apresenta maior absorção na região do visível em relação à TX-Np. Os resultados de fluorescência evidenciaram a dependência do solvente na emissão, juntamente com o comportamento das transições presentes. Os tempos de vida das espécies singlete foram determinados como sendo da ordem de nanosegundos, sendo maior em meio de solventes hidroxílicos polares. A fotólise por pulso de laser foi utilizada para estudar a absorção dos transientes, demonstrando que a TX-Np apresenta três máximos de absorção em 340, 450 e 590 nm, que foram atribuídos aos transientes do estado triplete/radical, radical cetila e ao estado triplete respectivamente, cujos tempos de vida se situam na ordem de microssegundos. Já a TX-A apresentou dois máximos de absorção em 415 e 515 nm, que correspondem à absorção do estado triplete do antraceno resultante da transferência de intramolecular de energia entre grupos da molécula. A avaliação do desempenho de ambos os compostos como fotoiniciadores foi feita com o auxílio da Fotocalorimetria Exploratória Diferencial (Foto-DSC) usando-se como modelo uma mistura dos monômeros BisGMa (dimetacrilato de bisfenilglicidila) e TEGDMA (dimetacrilato de trienilo glicol) nas proporções: 70:30; 30:70 e 50:50 (m/m), respectivamente. Estes estudos demonstraram que utilizando-se a TX-Np como fotoiniciador, a polimerização ocorreu com maior velocidade no sistema contendo maior proporção de BisGMA, que torna o sistema mais viscoso. Entretanto, maiores graus de conversão foram obtidos utilizando maiores proporções de TEGDMA, ou seja, misturas menos viscosa. Utilizando a TX-A, o sistema contendo BisGMA e TEGDMA na proporção 70:30 (m/m), apresentou maior velocidade de polimerização, enquanto a mistura contendo quantidades de massa iguais dos dois monômeros foi a que apresentou o maior grau de conversão. Quanto à influência de O2, apenas a TX-A apresentou resultado significativo na polimerização, quando o experimento foi realizado em ar. / The 5-thia-pentacene-14-one (TX-A) and 5-thia-naphthacene-12-one (TX-Np), both derivatives of thioxanthone have been synthesized and evaluated in relation to their performance as photoinitiators in diacrylates polymerization reaction. After purifying by column and liquid chromatography the compounds were characterized by elemental analysis (EA), spectroscopy in the infrared region (IR) and proton nuclear magnetic resonance (1H NMR). The spectral behavior of the thioxanthone derivatives was performed by spectroscopy in the ultraviolet and visible range (Uv-vis) and fluorescence. The UV-vis results revealed that TX-A presents higher absorption in the visible range than the TX-Np. The fluorescence data evidenced a dependence of the solvent nature in the emission. The life time of singlet species was determined as in the nano-seconds level, being higher in polar hydroxilic solvents medium. The laser flash-photolysis was used to investigate the transients absorption, revealing that the TX-Np have three absorption maxima at 340, 450 and 590 nm, which were attributed to the triplet state/radical, cetyl radical and triplet state, respectively, whose lifetimes were in the microseconds scale. Meanwhile, the TX-A showed two absorption maxima at 415 and 515 nm corresponding to the anthracene triplet state absorption from an intramolecular energy transfer between groups of the molecule. The performance of both photoinitiators had been evaluated by Photocalorimetry, using a mixture of bisphenylglycidyl dimetacrilate (BisGMA) and triethileneglycol dimetracrylate (TEGDMA) containing 70:30; 30:70 and 50:50 (w/w) of each monomer respectively. Such studies demonstrated that using TX-Np as a photoinitiator the rate of polymerization was higher when larger amounts of BisGMA is used in the mixture, making the system more viscous. However higher conversion degrees were found when higher amounts of TEGDMA are used, that means in less viscous mixtures. When TX-A is used as a photoinitiator the system containing 70:30 (w/w) of BisGMA and TEGDMA, showed higher rate of polymerizations while the mixture containing equal amounts of both monomers presented a higher conversion degree. Concerning the O2 influence, only the TX-A presented a significant polymerization extent when the experiment was performed in the presence of air.

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