Thesis (Ph. D.)--University of Oregon, 2007. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 144-153). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

1,4-Dihydropyridines (DHPs) are a classification of compounds used as calcium channel blockers in the treatment of various conditions. These compounds readily undergo photodegradation. The degradants produced have no pharmaceutical activity and render the drugs ineffective. DHPs also exhibit polymorphism. Nifedipine and Nimodipine are two such drugs. This study aimed to monitor the photodegradation of these two drugs and to establish the effect of particle size, polymorphism and β-Cyclodextrin (β-CD) on the rate of photodegradation. Different polymorphs (namely the amorphous and stable crystalline polymorphs) of the two drugs were prepared for use in the study. Mixtures of each drug with β-CD were also prepared for photostability studies. The mixtures were prepared in a 1:1 molar ratio. The rate of photodegradation was studied with a 500 W metal halide lamp in accordance to ICH guidelines. The study employed samples on a small scale where degradation was analysed with High Performance Liquid Chromatography, and also samples on a larger scale where degradation was monitored with Powder X-ray Diffraction. The two sets of results of observing the degradation process by two analytical techniques where compared in terms of their quantification methods. The extent of photodegradation was suitably modelled and fitted using the Avrami-Erofeyev kinetic equation. Smaller particle size showed increased photodegradation for Nimodipine; the effect was insignificant for Nifedipine however. For both drugs it was found that the amorphous polymorph underwent faster photodegradation. The study showed that β-CD caused an increase in photodegradation for both drugs under these experimental conditions.

Thesis (Ph. D.)--University of Oregon, 2008. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 131-143). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

Decomposition of organic matter is a critical component in global biogeochemical cycling. While decomposition rates have been robustly predicted for mesic systems, modeling decomposition dynamics in drylands has proven to be problematic, reflecting a need to account for processes that may be unique to dryland systems: low and spatially variable vegetation cover, high rates of soil movement, and high levels of radiant energy exposure at the soil surface. Recent empirical evidence suggests that the discrepancies between measured and predicted decomposition rates in drylands may be due to the greater influence of abiotic drivers, such as soil-litter mixing (SLM) and solar radiation, on plant litter decomposition relative to more mesic systems. UV-driven photodegradation may dominate until SLM reaches a threshold, at which point litter is shielded from radiation and microbial processes become predominant. The overarching goal of this dissertation was to examine the influence of SLM and solar radiation on decomposition of foliar and woody plant litter in a dryland ecosystem undergoing woody plant encroachment. A series of four complimentary experiments sought to quantify the effects of these abiotic drivers on decomposition in relation to variables such as vegetation patch type (e.g., beneath a shrub canopy, in a grass patch, on bare ground), radiant energy regime (e.g., full sun vs. shade), geomorphic surface (e.g., sandy, Holocene-age vs. clay-rich, Pleistocene-age soils), seasonality of litter fall (e.g., summer vs. winter), and litter quality (e.g., grass, shrub leaf, woody). Results indicate that interactions between SLM and photodegradation are complex and mediated by variations in ground cover which influence the local radiant energy environment and the movement of soil across the landscape by wind and water. Decomposition rates were significantly influenced by SLM, UV radiation, radiant energy regime, vegetation structure, and initial litter quality. While these results confirmed the importance of SLM and photodegradation as dryland decomposition drivers, they also reinforced the need for additional research to further clarify the relative importance of these processes under field conditions, particularly the interplay between UV radiation and SLM and their relative influence on biotic and abiotic decomposition processes. Given the changes in climate and vegetation projected for drylands, it is critical to further elucidate the influence of these processes on dryland biogeochemical cycling, as their effects may be magnified or dampened under future conditions. A deeper understanding of the processes driving biogeochemical cycling that may be unique to systems undergoing shifts in plant lifeform composition will allow us to better account for the fate of carbon in these globally important ecosystems.

A Tioxantona (TX) e a Benzofenona (BP) são cetonas frequentemente utilizadas como sensibilizadores em reações fotoquímicas. Assim, foi investigada a degradação de filmes de poliestireno (PS) contendo TX e BP como fotossensibilizadores. Os filmes foram irradiados em λ > 350 nm, em condições e tempos diferentes. As mudanças espectrais dos filmes foram acompanhadas por espectroscopia de infravermelho e UV-Vis e as mudanças no peso molecular foram acompanhadas por cromatografia de exclusão por tamanho (SEC). Os espectros UV-Vis mostraram que TX sofre fotobranqueamento após 5 h, ao contrário de BP que é fotoestável. Simultaneamente, os polímeros contendo grupos cromóforos são formados e a luz é absorvida. Os fotoprodutos nos filmes contendo TX e BP mostraram um aumento de absorbância entre 280-360 nm e 310-370 nm, respectivamente. Os picos de IV em torno de 3645 e 1740 cm-1 indicam a geração de hidroperóxidos e espécies carbonílicas, respectivamente. Os resultados mostraram que TX gerou mais fotoprodutos do que a BP. Os filmes de PS irradiados apresentaram uma diminuição no peso molecular indicando que ocorreu a cisão na cadeia polimérica. A fotofísica dos estados excitados de TX e TX quimicamente incorporada no poliestireno (PS-TX I e PS-TX II) foi estudada, com a finalidade de estudar o comportamento como fotossensibilizador na fotodegradação do PS. O triplete-triplete (T-T) e transientes de TX e TX contendo poliestireno foram estudados em diferentes solventes, para verificar o efeito de polaridade do solvente. Uma boa correlação foi encontrada entre o solvente ET(30) e parâmetro de energia do T-T. A constante de velocidade de supressão para a desativação do triplete de TX por trietanolamina diminuiu quando aumentou-se a polaridade do solvente. Essa variação é representada pela escala de polaridade do solvente através dos parâmetros π*, α e β. / Many ketones, quinones and peroxides are initiators of different reactions such as polymerization, degradation, chemical modification that occur in organic compounds. Thioxanthone (TX) and Benzophenone (BP) are ketones often used as photosensitizers in photochemical reactions. The degradation of polystyrene films containing TX and BP was investigated. Films were irradiated at λ > 350 nmin different conditions at different times. The changes were investigated by infrared and UV-Vis spectroscopies and the molecular weight were determined by gel permeation chromatography (GPC). The UV-Vis spectra showed that TX is photobleached after 5 h, unlike BP which is photostable. Simultaneously, polymers containing chromoforic groups are formed and the light is absorbed by them. The formation of photoproducts films containing TX and BP showed an increase of absorbance between 280-360 nm and 310-370 nm, respectively. The IR peaks around 3645 and 1740 cm-1 indicated the generation of hydroperoxide and carbonyl species, respectively. The results showed that thioxanthone has generated more photoproducts than benzophenone. The UV-Vis irradiation of PS films in both samples presented a decrease in the molecular weight after irradiation, indicating that polymer chain scission occurs. The photophysics of the excited states of thioxanthone (TX) and thioxanthone which was chemically incorporated in polystyrene (PS-TX I and PS-TX II) have been studied in order to be able to predict their behavior as photoinitiator in photodegradation of PS. The triplet-triplet (TT) and transient absorptions of thioxanthone and thioxanthone-containing polystyrene (PS-TX I and PS-TX II) has been studied in different solvents in order to ascertain the effect of the solvent. A good correlation is found between the solvent ET(30) parameter and the energy of the triplet-triplet. The quenching rate constants for the deactivation of triplet thioxanthone by triethanolamine decreases when the solvent polarity increases. This variation is represented by the π*, α and β scale of solvent polarity.

O estudo do comportamento de materiais em relação a intempérie, esforços, tempo, temperatura é fundamental para a escolha de materiais para uma dada aplicação. O poliestireno é uma resina polimérica muito aplicada no mercado, pois é transparente e relativamente econômica, mas não é indicada para aplicações com muita exposição a radiações luminosas, já que é muito susceptível a intemperismos, não sendo recomendada para aplicações com excessiva exposição. A adição de borracha (copolímero de estireno e butadieno) melhora algumas de suas propriedades, como resistência ao impacto e ductilidade, mas piora outras características, como a resistência à tração. Em relação ao intemperismo, apesar da borracha degradar-se rapidamente, ela protege o poliestireno da radiação ultravioleta. Este estudo visa comparar as conseqüências da degradação por envelhecimento natural com o envelhecimento artificial acelerado do poliestireno e do poliestireno de alto impacto e a determinação da possível correlação entre eles. Foram utilizados equipamentos de envelhecimento artificial, de ensaio de tração, impacto IZOD, índice de fluidez, uma estação de envelhecimento natural e equipamento de análise térmica (DSC). Os resultados obtidos permitiram correlacionar os envelhecimentos natural e artificial em relação às propriedades medidas, sendo que para o poliestireno comum, o envelhecimento artificial acelerou a degradação em cerca de 4 vezes, enquanto que para o poliestireno de alto impacto, o fator de aceleração foi de cerca de 2 vezes. / The study of weathering materials regarding to climate, stresses, time, temperature, is essential to choose the materials for a purpose. Polystyrene is a polymeric resin with much usage in the market as it is transparent and relatively cheap, but it is not indicated for outdoor purposes with much actinic radiation exposure, as it is very sensitive to weathering, tough not recommended to purposes with much exposure. The addition of rubber (styrene-butadiene copolymer) improves some of its properties, like impact resistance and ductility, but decreases other properties, like tensile strength. Regarding the weathering, although the rubber degrades very quickly, it protects the polystyrene from the ultraviolet radiation. This study aims to compare the consequences of the degradation by natural weathering and accelerated artificial weathering and try to correlate their results. Equipments for artificial weathering, tensile strength, IZOD impact, melt flow, a natural weathering station and DSC thermal analysis equipment were used. The results allowed the correlation between the natural and artificial weathering regarding the measured properties, as for the common polystyrene the artificial weathering accelerated the degradation in approximately 4 times, while for the high impact polystyrene the acceleration factor resulted in approximately 2 times.

O ácido fólico, a forma mais estável entre os folatos, é indicado como forma de prevenção sendo encontrado em forma de suplementação medicamentosa e alimentos fortificados, como leite e derivados. O folato pode reagir com a riboflavina singlete excitada, 1kq = 4,8·1010 L·mol-1·s-1, como determinado por desativação da fluorescência do estado estacionário, e com a riboflavina triplete excitada, com uma reação um pouco mais lenta, 3kq= 4,8·108 L·mol-1·s-1, como determinado por fotólise de pulso de laser e espectroscopia de absorção de transientes verificando-se que ambos os processos são competitivos e próximos ao limite de difusão. A preferência cinética de um a outro depende da matriz alimentar. O rendimento quântico para solução de riboflavina e de folato preparado em solvente aquoso e deuterado e em meio anaeróbico e aeróbico mostrou a prevalência do mecanismo fotoreacional do Tipo I. A voltametria cíclica apresentou um processo irreversível anódico de dois elétrons para o ácido fólico (E= 1,14 V vs. NHE). Os principais produtos da fotodegradação do folato sensibilizado pela riboflavina foram identificados por LC-IT-MS/MS como: 6-carboxipterina,p-aminobenzoil-L-ácido glutâmico e oxaziridina derivada do ácido fólico, como confirmando a desativação química do estado triplete excitado da riboflavina por transferência de elétrons com subseqüente clivagem oxidativa entre N(10) e C(9) no ácido fólico. / Folic acid, the most stable among folate, is recommended as prevention and it is found in supplementation and fortified foods such as milk and dairy products. The folate can react with singlet-excited state of riboflavin, 1kq= 4.8·1010 L·mol-1·s-1, as determined by steady-state fluorescence quenching, and with triplet-excited state of riboflavin in a slower reaction with 3kq= 4.8·108 L·mol-1·s-1, as determined by laser flash photolysis and transient absorption spectroscopy, verifying that both the processes are competitive and they are near limited diffusion. The kinetic preference depends on the matrix food. The quantum yield for the solution of riboflavin and folate prepared in aqueous and deuterated solvents and in anaerobic and aerobic medium showed the prevalence of the mechanism Type I. The cyclic voltammetry showed an irreversible two-electron anodic process for folate (E = 1.14 V vs. NHE). The main products of folate photodegradation sensitized by riboflavin were identified by LC-IT-MS/MS as: pterin-6-carboxylic acid, p-aminobenzoyl-L-glutamic acid and oxaziridine derivative of folic acid, as confirming chemical quenching of the triplet-excited state of riboflavin by electron transfer with subsequent oxidative cleavage between N(10) and C(9) in folic acid.

O estudo do comportamento de materiais em relação a intempérie, esforços, tempo, temperatura é fundamental para a escolha de materiais para uma dada aplicação. O poliestireno é uma resina polimérica muito aplicada no mercado, pois é transparente e relativamente econômica, mas não é indicada para aplicações com muita exposição a radiações luminosas, já que é muito susceptível a intemperismos, não sendo recomendada para aplicações com excessiva exposição. A adição de borracha (copolímero de estireno e butadieno) melhora algumas de suas propriedades, como resistência ao impacto e ductilidade, mas piora outras características, como a resistência à tração. Em relação ao intemperismo, apesar da borracha degradar-se rapidamente, ela protege o poliestireno da radiação ultravioleta. Este estudo visa comparar as conseqüências da degradação por envelhecimento natural com o envelhecimento artificial acelerado do poliestireno e do poliestireno de alto impacto e a determinação da possível correlação entre eles. Foram utilizados equipamentos de envelhecimento artificial, de ensaio de tração, impacto IZOD, índice de fluidez, uma estação de envelhecimento natural e equipamento de análise térmica (DSC). Os resultados obtidos permitiram correlacionar os envelhecimentos natural e artificial em relação às propriedades medidas, sendo que para o poliestireno comum, o envelhecimento artificial acelerou a degradação em cerca de 4 vezes, enquanto que para o poliestireno de alto impacto, o fator de aceleração foi de cerca de 2 vezes. / The study of weathering materials regarding to climate, stresses, time, temperature, is essential to choose the materials for a purpose. Polystyrene is a polymeric resin with much usage in the market as it is transparent and relatively cheap, but it is not indicated for outdoor purposes with much actinic radiation exposure, as it is very sensitive to weathering, tough not recommended to purposes with much exposure. The addition of rubber (styrene-butadiene copolymer) improves some of its properties, like impact resistance and ductility, but decreases other properties, like tensile strength. Regarding the weathering, although the rubber degrades very quickly, it protects the polystyrene from the ultraviolet radiation. This study aims to compare the consequences of the degradation by natural weathering and accelerated artificial weathering and try to correlate their results. Equipments for artificial weathering, tensile strength, IZOD impact, melt flow, a natural weathering station and DSC thermal analysis equipment were used. The results allowed the correlation between the natural and artificial weathering regarding the measured properties, as for the common polystyrene the artificial weathering accelerated the degradation in approximately 4 times, while for the high impact polystyrene the acceleration factor resulted in approximately 2 times.

O ácido fólico, a forma mais estável entre os folatos, é indicado como forma de prevenção sendo encontrado em forma de suplementação medicamentosa e alimentos fortificados, como leite e derivados. O folato pode reagir com a riboflavina singlete excitada, 1kq = 4,8·1010 L·mol-1·s-1, como determinado por desativação da fluorescência do estado estacionário, e com a riboflavina triplete excitada, com uma reação um pouco mais lenta, 3kq= 4,8·108 L·mol-1·s-1, como determinado por fotólise de pulso de laser e espectroscopia de absorção de transientes verificando-se que ambos os processos são competitivos e próximos ao limite de difusão. A preferência cinética de um a outro depende da matriz alimentar. O rendimento quântico para solução de riboflavina e de folato preparado em solvente aquoso e deuterado e em meio anaeróbico e aeróbico mostrou a prevalência do mecanismo fotoreacional do Tipo I. A voltametria cíclica apresentou um processo irreversível anódico de dois elétrons para o ácido fólico (E= 1,14 V vs. NHE). Os principais produtos da fotodegradação do folato sensibilizado pela riboflavina foram identificados por LC-IT-MS/MS como: 6-carboxipterina,p-aminobenzoil-L-ácido glutâmico e oxaziridina derivada do ácido fólico, como confirmando a desativação química do estado triplete excitado da riboflavina por transferência de elétrons com subseqüente clivagem oxidativa entre N(10) e C(9) no ácido fólico. / Folic acid, the most stable among folate, is recommended as prevention and it is found in supplementation and fortified foods such as milk and dairy products. The folate can react with singlet-excited state of riboflavin, 1kq= 4.8·1010 L·mol-1·s-1, as determined by steady-state fluorescence quenching, and with triplet-excited state of riboflavin in a slower reaction with 3kq= 4.8·108 L·mol-1·s-1, as determined by laser flash photolysis and transient absorption spectroscopy, verifying that both the processes are competitive and they are near limited diffusion. The kinetic preference depends on the matrix food. The quantum yield for the solution of riboflavin and folate prepared in aqueous and deuterated solvents and in anaerobic and aerobic medium showed the prevalence of the mechanism Type I. The cyclic voltammetry showed an irreversible two-electron anodic process for folate (E = 1.14 V vs. NHE). The main products of folate photodegradation sensitized by riboflavin were identified by LC-IT-MS/MS as: pterin-6-carboxylic acid, p-aminobenzoyl-L-glutamic acid and oxaziridine derivative of folic acid, as confirming chemical quenching of the triplet-excited state of riboflavin by electron transfer with subsequent oxidative cleavage between N(10) and C(9) in folic acid.