In situ laccase-assisted overdyeing of denim using flavonoids

A laccase-mediated system for denim overdyeing using phenolic compounds was developed. Laccase from ascomycete Myceliophthora thermophila was able to oxidize phenolic compounds such as catechol and catechin and mediate their attachment to denim surfaces. Laccase-generated polymers gave rise to new coloration states from dark brown to green–yellow and replaced dyes in the overdyeing process. Process parameters, such as enzyme dosage, incubation time and presence of mediator, were studied by considering a compromise between the highest overdyeing level and lower energy/products consumption (2 U/mL laccase; 4 h incubation in the absence of mediator). Enzyme-generated polymers were followed by UV/Vis spectrophotometry and their level of attachment to denim surfaces was evaluated by means of spectral values quantification [k/s, Kubelka–Munk relationship (k=absorption coefficient, s=scattering coefficient)]. Overdyeing of denim with phenolics, such as catechol or catechin, was successfully achieved with acceptable levels in terms of durability.S.Y.K. would like to acknowledge the BIORENEW European Project - Sixth Framework European Program. C.S. would like to acknowledge the Portuguese Fundacao para a Ciencia e a Tecnologia (FCT) for funding under the scholarship SFRH/BPD/46515/2008

Laccase in organic synthesis and its applications

Laccase (benzenediol:oxygen oxidoreductase, EC 1.10.3.2), a multi-copper-containing oxidoreductase enzyme, is able to catalyze the oxidation of various low-molecular weight compounds, specifically, phenols and anilines. Due to their high stability, selectivity for phenolic substructures, and mild reaction conditions, laccases are attractive for fine chemical synthesis. In this study, new green domino syntheses were developed by conducting the reaction in an aqueous medium, an environmentally-friendly solvent, and using laccase as a biocatalyst. The first study presents a work on the synthesis of naphthoquinones in the aqueous medium. Herein, laccase was used to oxidize o- and p-benzenediols to generate o- and p-benzoquinones in situ. These quinones then underwent Diels-Alder and oxidation reactions to finally generate napthoquinone products. This reaction system can yield naphthoquinones in up to 80% yield. The next part of this thesis reports the cascade synthesis of benzofuran derivatives from the reaction of catechols and 1,3-dicarbonyl compounds via oxidation-Michael addition in the presence of laccase and Sc(OTf)3/SDS in an aqueous medium. Depending on the substrates, one-pot yields of benzofurans averaged 50-79%. From an environmental concern, this system still produced a hazardous waste from the transition metal catalyst. Therefore, the development of alternative methodologies to replace the lanthanide metal catalyst in this synthesis is a high priority to enhance the overall green chemistry aspect. As a consequence, lipase was used as a catalyst to replace Sc(OTf)3 for the synthesis of benzofuran derivatives. In addition, this catalytic system was also used to catalyze the reaction of anilines and catechol. In the last part of this thesis, laccase was applied to the modification of high-lignin softwood kraft pulp. This modification demonstrates the potential of laccase-facilitated grafting of amino acids to high lignin content pulps to improve their physical properties in paper products which resulted from the increase of carboxylic acid group of the fibers. In this study, a variety of amino acids were examined. Laccase-histidine treatment provided the best yield of acid groups on pulp fiber and was used in the preparation of handsheets for physical strength testing. Laccase-histidine-treated pulp showed an increase in the strength properties of the resulting paper.Ph.D.Committee Chair: Ragauskas, Arthur; Committee Member: Bunz, Uwe; Committee Member: Cairney, John; Committee Member: Collard, David; Committee Member: Singh, Pree