New liquid supports in the development of integrated platforms for immobilization of oxidative enzymes and polydopamine production

• Autor(a) principal: Pereira, Ana Filipa Soares
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33290
• topic: Laccase; Polymerization of dopamine; Polydopamine; Aqueous biphasic systems; Ionic liquids; Integrated process

Enzymatic biocatalysis contributes to more sustainable processes, compared with the traditional chemical processes, as it leads to the production of less toxic residues and side-products. Among the existing enzymatic applications, the polymerization of dopamine is a promising application since it originates polydopamine (PDA), an added-value biopolymer with several applications in different fields. Amongst the several existing applications of PDA, the following should be highlighted: (i) modification and functionalization of surfaces for the immobilization of biomolecules and cell adhesion; (ii) synthesis of polydopamine nanoparticles, important in photothermal therapy (an emergent technique for the treatment of cancer); and (iii) in the field of biomedicine, for drug delivery. However, the conventional method of dopamine polymerization is a time-consuming process and produces PDA films with poor stability, which limits its applications. In contrast, dopamine polymerization by laccase, an oxidative enzyme with applications in various sectors of biotechnology, is a fast and efficient process. Nonetheless, in economic and sustainability terms, the reuse of the biocatalyst is crucial. Based on the exposed, the main objective of this study is the development of an integrated and sustainable platform for the production of PDA, by using laccase as the biocatalyst, allowing the simultaneous separation of this product and the reuse of the enzyme. For this purpose, five aqueous biphasic systems (ABS) composed of polymers, salts and ionic liquids were studied. Preliminary tests of the optimization of some reaction conditions of the enzymatic polymerization, such as pH, temperature and initial dopamine concentration, were performed. It was demonstrated that the higher enzymatic activity is achieved at pH 5.5, 30°C and initial dopamine concentration of 2 mg/mL. It was found that the enzymatic method is a more efficient process when compared with the non-enzymatic one, since for the same reaction time and lower dopamine concentrations it allowed a significantly superior polymerization. It was concluded that the most-promising ABS is composed of polypropylene glycol 400 (PPG 400) and K2HPO4, allowed the separation of laccase and PDA to opposite phases. In addition, it was possible to reuse the laccase, at least in four consecutive cycles, with a polymerization yield of 68.9% in the last cycle.