Add to ORKGiii To my parents iv ACKNOWLEDGEMENTS I would like to express my gratitude to my advisor professor Dr. Pedro Bouchon whose patience, wise guidance and permanent support were invaluable for the successful conclusion of this research. I would like to thank Mr. Ricardo Cayupe and Mr. Ulises Lazo, laboratory assistants, for their unconditional help through the whole research. I would specially want to extend my gratitude to Mrs. Hilda Agurto, for all her help and care not only during this work but also through my entire career. I would also like to thank my colleagues and friends who helped me get through this work, Carolina Moreno, Verónica Dueik and Mariel Farfán with whom I shared long work hours through which they gave me advices and suppor...