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Copper corrosion and its inhibition are often associated with the presence of oxide films. Several studies have demonstrated that copper oxide films, which are normal corrosion products, protect copper substrate from further corrosion. However, little work has been carried out on the chemical formation of copper oxide films. On the other hand, the development of new polymer coatings is needed for corrosion prevention in aggressive environment. Although interest in the use of polypyrrole films for corrosion prevention has arisen recently, no successful utilisation of the polymer for control of copper corrosion has been reported, due to the difficulty in the deposition of the polymer. In this study, two new surface modification techniques, namely chemical formation of copper oxide films and the electrodeposition of polypyrrole on copper, have been developed to address the above issues. The influence of bicarbonate ions on the stability of copper oxide films and pitting corrosion were studied. Various approaches for the electrodeposition of polypyrrole (PPy) film onto copper substrate were investigated. The characteristics and properties of PPy films, particularly for the film formed in sodium tetraborate solution, were investigated. The redox reactions of copper substrate were inhibited completely by the presence of the polypyrrole film, formed in sodium tetraborate solution, in several weak alkaline solutions. The electrochemical behaviour of the Cu-PPy electrode is quite similar to Cu electrode in the presence of an effective corrosion inhibitor, such as benzotriazole, in several solutions. These properties of the PPy film clearly indicate that there is potential for the application of the polymer in the control of copper corrosion. / Doctor of Philosophy (PhD)

Orientador: Mario de Oliveira Neto / Resumo: A biomassa lignocelulósica pode ser usada para a produção de energia ou de novos bioprodutos potenciais substitutos de químicos convencionais. Porém a conversão dos polissacarídeos estruturais presentes na parede celular vegetal das células que compõe a biomassa não é simples. Isto se deve principalmente pela presença da lignina, que juntamente com a hemicelulose, formam uma estrutura coesa de microfibrilas que entrelaçam a celulose. Compostos que inibem as enzimas celulolíticas, incluindo fenólicos solúveis (derivados da lignina), açúcares solúveis, aldeídos de furano e ácidos fracos são gerados durante os diversos pré-tratamentos utilizados atualmente. Neste estudo, observamos como os fenólicos solúveis interagem com -glicosidases. Para isso, combinamos simulações de ensaio enzimático, docking molecular e dinâmica molecular para descrever o processo de ligação. Notavelmente, o ácido tânico, um dos fenólicos solúveis estudados, foi a molécula com maior poder inibitório em comparação com todos os demais fenólicos. Possivelmente devido ao seu comprimento e suas substituições de grupos químicos. A alta presença de anéis aromáticos e grupos hidroxilas no ácido tânico, leva a maior interação entre as moléculas e consequente inibição/desativação das β-glicosidases bacterianas, enquanto os grupos carboxílicos presentes nos demais fenólicos alteram os efeitos físico-químicos aumentando a hidrofobicidade; criando cargas eletrostáticas e aumentando a ligação de hidrogênio, afetando a... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Lignocellulosic biomass can be transformed to chemicals or energy products. However converting polysaccharides present on the cell wall can be limitated due to the high recalcitrance caused by the presence of lignin. Compounds that inhibit enzymes, including lignin-derived phenolics, soluble sugars, furan aldehydes, and weak acids, are generated during the various pre-treatments currently used. In this study was observed how the soluble phenolics generated significantly impede the enzymatic hydrolysis of cellulose. For this were combine enzymatic assay, molecular docking and molecular dynamics simulations to describe the binding process between soluble phenolics and bacterial β-glycosidases. Notably, tannic acid, one of the soluble phenolics generated, was the strongest inhibitory molecule in comparison with all phenolics studied. Possibly because of its length and its substitutions of chemical groups. The high presence of aromatic rings and hydroxyl groups in tannic acid leads to greater interaction between the molecules and consequent inhibition / deactivation of bacterial β-glycosidases. Taken together, our studies of the interaction suggest that there is a high correlation between exposed hydrophobic surface areas and the number of binding sites on the inhibition of βglucosidases. These data may provide a useful basis for future biotechnological applications of microbial β-glucosidases, especially in the field of biofuel production. / Doutor