Os ésteres são importantes compostos orgânicos, obtidos por síntese química ou extraídos de alguns produtos naturais utilizando-se solvente em meio adequado. Estudos mostram que enzimas, em particular lipases, podem ser aplicadas na síntese de diversos ésteres. O principal objetivo deste trabalho foi a obtenção de acetato de butila, um éster de aroma característico de abacaxi, utilizando lipase de Geotrichum candidum produzida em fermentação submersa e imobilizada em matriz polimérica de alginato de bário e gelatina reticulada com glutaraldeído. A caracterização bioquímica foi realizada tanto para a lipase na forma livre como para a lipase na forma imobilizada. O rendimento em conversão molar de substrato foi determinado por cromatografia gasosa. A enzima apresentou atividade enzimática máxima após 48 horas de fermentação de 37,7 U/mL. Os valores ótimos para pH e temperatura da enzima na forma livre e imobilizada foram pH 6,5 e 40 °C e pH 7,5 e 45 °C, respectivamente. A enzima na forma livre foi estável do pH 6,0 ao 8,0 e à temperatura de 35 a 45 °C, já na forma imobilizada, foi estável do pH 5,5 ao 8,5 e na faixa de temperatura de 30 a 55 °C. A lipase imobilizada teve seus parâmetros cinéticos determinados, e os valores obtidos para o Km e Vmax, foram 0,115 mmol e 0,718 µmol.mL-1.min-1, respectivamente. As melhores condições de síntese do bioaroma para a enzima na forma livre foram: temperatura de 30 °C, 12,5% de enzima em relação à quantidade de butanol utilizada, proporção molar do substrato 60% de acetato de vinila em um período de 24 horas. O rendimento alcançado neste caso foi de 97,2 % de conversão molar em acetato de butila. Para a enzima imobilizada as melhores condições foram: temperatura de 45 °C, 12,5% de enzima em relação à quantidade de butanol utilizada, proporção molar do substrato 60% de acetato de vinila em um período de 24 horas. O rendimento alcançado neste caso foi de 99,1%, que demonstra que lipase produzida por Geotrichum candidum na forma imobilizada apresenta excelente capacidade de sintetizar acetato de butila (bioaroma de abacaxi). / Esters are important organic compounds obtained by chemical synthesis or derived from some natural products using a solvent in appropriate medium. Studies have shown that enzymes, particularly lipases, ca be applied in the synthesis of various esters. The main objective of this study was to obtain butyl acetate, a characteristic ester aroma of pineapple, using lipase from Geotrichum candidum produced in submerged fermentation and immobilized in a barium alginate and gelatin polymer matrix crosslinked with glutaraldehyde. The biochemical characterization was performed for both free and immobilized lipases. The yield in molar conversion of substrate was determined by gas chromatography. The enzyme showed maximum enzymatic activity after 48 hours of fermentation of 37.7 U/mL. The optimum values for pH and temperature of the enzyme in free and immobilize form were pH 6.5 and 40 °C and pH 7.5 and 45 °C, respectively. The enzyme was stable in free form from pH 6.0 to 8.0 and at temperatures from 35 to 45 °C, and in the immobilized form from pH 5.5 to 8.5 and at temperatures from 30 to 55 °C. Kinetic parameters of the immobilized lipase were determined, and the values obtained for Km and Vmax were 0.115 mmol and 0.718 µmol.mL-1.min-1, respectively. The best conditions for the synthesis of flavor by enzyme in free form were: 30 °C of temperature, 12.5% of enzyme for the amount of butanol used, and molar ratio of substrate 60% of vinyl acetate in a 24 hours period. The yield achieved in this case was 97.2% of molar conversion in butyl acetate. For the immobilized enzyme the best conditions were: 45 °C of temperature, 12.5% of enzyme for the amount of butanol used, and molar ratio of substrate 60% of vinyl acetate in a 24 hours period. The yield achieved in this case was 99.1%, demonstrating that lipase produced by Geotrichum candidum in immobilized form has an excellent ability to synthesize butyl acetate (pineapple flavor).

Os ésteres são importantes compostos orgânicos, obtidos por síntese química ou extraídos de alguns produtos naturais utilizando-se solvente em meio adequado. Estudos mostram que enzimas, em particular lipases, podem ser aplicadas na síntese de diversos ésteres. O principal objetivo deste trabalho foi a obtenção de acetato de butila, um éster de aroma característico de abacaxi, utilizando lipase de Geotrichum candidum produzida em fermentação submersa e imobilizada em matriz polimérica de alginato de bário e gelatina reticulada com glutaraldeído. A caracterização bioquímica foi realizada tanto para a lipase na forma livre como para a lipase na forma imobilizada. O rendimento em conversão molar de substrato foi determinado por cromatografia gasosa. A enzima apresentou atividade enzimática máxima após 48 horas de fermentação de 37,7 U/mL. Os valores ótimos para pH e temperatura da enzima na forma livre e imobilizada foram pH 6,5 e 40 °C e pH 7,5 e 45 °C, respectivamente. A enzima na forma livre foi estável do pH 6,0 ao 8,0 e à temperatura de 35 a 45 °C, já na forma imobilizada, foi estável do pH 5,5 ao 8,5 e na faixa de temperatura de 30 a 55 °C. A lipase imobilizada teve seus parâmetros cinéticos determinados, e os valores obtidos para o Km e Vmax, foram 0,115 mmol e 0,718 µmol.mL-1.min-1, respectivamente. As melhores condições de síntese do bioaroma para a enzima na forma livre foram: temperatura de 30 °C, 12,5% de enzima em relação à quantidade de butanol utilizada, proporção molar do substrato 60% de acetato de vinila em um período de 24 horas. O rendimento alcançado neste caso foi de 97,2 % de conversão molar em acetato de butila. Para a enzima imobilizada as melhores condições foram: temperatura de 45 °C, 12,5% de enzima em relação à quantidade de butanol utilizada, proporção molar do substrato 60% de acetato de vinila em um período de 24 horas. O rendimento alcançado neste caso foi de 99,1%, que demonstra que lipase produzida por Geotrichum candidum na forma imobilizada apresenta excelente capacidade de sintetizar acetato de butila (bioaroma de abacaxi). / Esters are important organic compounds obtained by chemical synthesis or derived from some natural products using a solvent in appropriate medium. Studies have shown that enzymes, particularly lipases, ca be applied in the synthesis of various esters. The main objective of this study was to obtain butyl acetate, a characteristic ester aroma of pineapple, using lipase from Geotrichum candidum produced in submerged fermentation and immobilized in a barium alginate and gelatin polymer matrix crosslinked with glutaraldehyde. The biochemical characterization was performed for both free and immobilized lipases. The yield in molar conversion of substrate was determined by gas chromatography. The enzyme showed maximum enzymatic activity after 48 hours of fermentation of 37.7 U/mL. The optimum values for pH and temperature of the enzyme in free and immobilize form were pH 6.5 and 40 °C and pH 7.5 and 45 °C, respectively. The enzyme was stable in free form from pH 6.0 to 8.0 and at temperatures from 35 to 45 °C, and in the immobilized form from pH 5.5 to 8.5 and at temperatures from 30 to 55 °C. Kinetic parameters of the immobilized lipase were determined, and the values obtained for Km and Vmax were 0.115 mmol and 0.718 µmol.mL-1.min-1, respectively. The best conditions for the synthesis of flavor by enzyme in free form were: 30 °C of temperature, 12.5% of enzyme for the amount of butanol used, and molar ratio of substrate 60% of vinyl acetate in a 24 hours period. The yield achieved in this case was 97.2% of molar conversion in butyl acetate. For the immobilized enzyme the best conditions were: 45 °C of temperature, 12.5% of enzyme for the amount of butanol used, and molar ratio of substrate 60% of vinyl acetate in a 24 hours period. The yield achieved in this case was 99.1%, demonstrating that lipase produced by Geotrichum candidum in immobilized form has an excellent ability to synthesize butyl acetate (pineapple flavor).

<p> A kinetic and mechanistic study on catalytic decomposition of n- and sec-butyl acetate was carried out. The catalysts were silica-alumina and synthetic zeolites including type A, X, Y and mordenite. The reactions were performed in the temperature region of 140° to 290°C at atmospheric pressure using a fixed-bed flow reactor.</p> <p> The esters decomposed to acetic acid and n-butenes. The isomerization of butenes occurred consecutively. The mechanism of ester decomposition was different from that of pyrolysis. The catalytic activity was effected by acidity, cations and pore size. The Langmuir-Hinshelwood rate equation corresponding to the surface reaction on dual-sites correlated data satisfactorily. Strong adsorption of acetic acid, crystal collapse and the blocking of pores with organic deposit caused aging of catalysts.</p> / Thesis / Doctor of Philosophy (PhD)

Objective: Twenty-two million Americans or roughly 8% of the population are hearing impaired. This affects more than just the ability for one to hear. In the last three decades, younger Americans have shown a sharp increase in hearing impairment. Hearing loss affects social and emotional well being and thus has the ability to decrease one's quality of life. This study was designed to examine the association between smoking, workplace chemical exposure, and hearing loss.Methods: This cross-sectional population-based study was conducted in an occupational health clinic setting in Virginia. The study population consisted of employees from local businesses who visited the clinic during the period of 1/1/03 to 1/1/05 for pure tone audiometry. Chart reviews supplemented by telephone interviews were conducted to extract data for analysis. All study subjects were eligible to participate except for those who were unable to communicate due to a language barrier. Prevalence and crude prevalence ratios were calculated. Adjusted prevalence ratios and prevalence odds ratios were calculated using Cox and logistic regression models. Data entry and statistical analysis were accomplished with the SPSS Data Builder and the SPSS 13.0 statistical software. SAS statistical software was also used for a portion of the statistical analysis.Results: In a Cox regression model controlling for many potential confounding factors (age, race, smoking, chemical exposure, military service, as well as others) cigarette smoking was not associated with hearing loss PR(95% CI), 1.0 (0.7, 1.3). Similarly, exposure to chemicals was not associated with hearing loss 1.1 (0.7, 1.6).Conclusion: This study did not find an association between cigarette smoking and hearing loss and exposure to industrial chemicals and hearing loss in persons who worked in a noisy occupational environment.

La production mondiale de solvants représente environ 28 millions de tonnes, dont 5 millions en Europe. L’industrie des peintures et des revêtements en est la principale consommatrice (46 % des solvants produits). Dans ce domaine, les solvants les plus utilisés sont l'acétate d'éthyle, l'acétate de butyle et la méthyl éthyl cétone. Ces molécules sont actuellement synthétisées industriellement à partir de substrats d’origine pétrochimique en présence de catalyseurs homogènes et dans des conditions énergivores. Afin de réduire l’impact environnemental des peintures et revêtements, la substitution de ces solvants issus du pétrole par leurs équivalents bio sourcés a été étudiée dans le cadre du projet européen ECOBIOFOR (FP7/2007-2013/Grant Agreement no 605215), dans lequel se sont inscrits ces travaux de thèse. Ainsi, l’objectif de cette thèse a été de développer, à partir de synthons renouvelables, des procédés de production de ces trois solvants simples à mettre en oeuvre, peu coûteux et respectueux des principes de la chimie verte. Pour la production des acétates d’éthyle et de butyle, deux voies de synthèse ont été étudiées en présence d’une résine échangeuse d'ions comme catalyseur hétérogène. La première voie utilise de l'acide acétique et l’alcool biosourcé correspondant (éthanol ou le butan-1-ol); la seconde met en jeu l’anhydride acétique à la place de l’acide acétique. Dans ces synthèses, quatre résines ont été testées. Des études cinétiques et thermodynamiques ont permis de choisir la résine la plus performante et les conditions de réaction les plus adaptées. Cette étude a finalement permis de proposer un procédé de coproduction des deux acétates efficace et innovant dans lequel la purification des acétates est facilitée, la production de déchets et coproduits est réduite et le recyclage de la résine est possible. L'évaluation des performances des acétates synthétisés dans des formulations de laques nitrocellulosiques et de vernis polyuréthanes a permis de montrer que ces molécules répondent au cahier des charges en terme de séchage, viscosité, formation de film, brillance et adhérence. Enfin, le bénéfice environnemental du processus de coproduction a été mis en évidence par le calcul des métriques de la chimie verte et l'analyse du cycle de vie des esters produits. De plus, l'influence de l'origine des alcools, biosourcés ou pétrochimiques, sur l’impact environnemental a été évaluée. L’impact sur le changement climatique est réduit avec l’utilisation des synthons bio-sourcés. Pour la synthèse de la méthyl éthyl cétone, nous avons décidé d’étudier la réaction de décarboxylation de l’acide lévulinique, molécule plateforme biosourcée disponible et peu coûteuse. Contrairement au principal procédé industriel qui repose sur la déshydrogénation du butan-2-ol d'origine fossile, la méthode développée dans ces travaux utilise des conditions plus respectueuses de l’environnement puisqu’elle est réalisée dans l’eau en présence de persulfate de potassium et d’un sel d'argent à une température raisonnable (100°C). L'évaluation du rôle de chacun des réactifs a permis de proposer un mécanisme réactionnel complexe de cette synthèse. L'étude de l’évolution des espèces en phase solide réalisés par diverses analyses spectroscopiques (RMN du solide, DRX, XPS, AES et MEB) a permis de mettre en évidence les espèces impliquées dans la décarboxylation et finalement de proposer une méthode permettant d’obtenir des conversions et des rendements élevés. / Global solvent production accounts for about 28 million tonnes, including 5 million tonnes in Europe. The paint and coating industry is the main consumer (46% of the solvents produced). In this sector, the most used solvents are ethyl acetate, butyl acetate and methyl ethyl ketone. These molecules are currently synthesized industrially from petrochemical substrates in the presence of homogeneous catalysts and under energy-consuming conditions. In order to reduce the environmental impact of paints and coatings, the substitution of these fossil-based solvents by their bio-based equivalents has been studied in the framework of the European project ECOBIOFOR (FP7/2007-2013/Grant Agreement no 605215), in which this thesis work was inscribed. Thus, the objective of this thesis was to develop production processes for these three solvents that would start from renewable synthons and would be simple to implement, inexpensive and respectful of the principles of green chemistry. For the production of ethyl and butyl acetates, two synthetic routes have been studied in the presence of an ion exchange resin as a heterogeneous catalyst. The first route uses acetic acid and the corresponding bio-based alcohol (ethanol or butan-1-ol); the second involves acetic anhydride instead of acetic acid. Kinetic and thermodynamic studies have led to select the most efficient resin and the most suitable reaction conditions. This study has finally allowed to propose an efficient and innovative coproduction process for the two targeted acetates in which their purification is facilitated, the production of waste and co-products is reduced and the recycling of the resin is possible. The evaluation of the performance of the synthesized acetates in nitrocellulose lacquer and polyurethane varnish formulations has shown that these molecules meet the specifications in terms of drying, viscosity, film formation, gloss and adhesion. Finally, the environmental benefit of the co-production process was highlighted by the calculation of green metrics and the life cycle assessment (LCA) of the produced esters. Furthermore, the influence of the origin of alcohols (bio-based or petrochemical) on the environmental impact was evaluated. The impact on climate change is reduced through the use of bio-sourced synthons. For the synthesis of methyl ethyl ketone, we decided to study the decarboxylation reaction of levulinic acid, which is a bio-based platform molecule available and inexpensive. Unlike the main industrial process, which relies on the dehydrogenation of butan-2-ol from fossil origin, the method developed in this work uses conditions that are more respectful of the environment since the reaction is carried out in water in the presence of potassium persulfate and a silver salt at a moderate temperature (100°C). The evaluation of the role of each of the reagents allowed us to propose a complex reaction mechanism for this reaction. The study of the evolution of the solid phase species carried out through various spectroscopic analyzes (SSNMR, XRD, XPS, AES and SEM) made it possible to highlight the species involved in the decarboxylation and finally to propose a method to obtain high conversions and yields.