The use of Trametes versicolor laccase for the polymerization of aniline in the presence of vesicles as templates

• First laccase/O2-catalyzed synthesis of polyaniline with vesicles as templates.
• Detailed study of the changes occurring during the reaction.
• Characterization of isolated products by FTIR, EPR and XRD measurements.
• Comparison with the same reaction catalyzed by horseradish peroxidase/H2O2.
• First demonstration of inkjet-printability of the obtained polyaniline suspension.

The enzymatic polymerization of aniline to polyaniline (PANI) with Trametes versicolor laccase (TvL) as catalyst and dioxygen (O2) as oxidant was investigated in an aqueous medium containing unilamellar vesicles with an average diameter of about 80 nm formed from AOT (=sodium bis(2-ethylhexyl) sulfosuccinate). Compared to the same reaction carried out with horseradish peroxidase isoenzyme C (HRPC) as catalyst and hydrogen peroxide (H2O2) as oxidant, notable differences were found in the kinetics of the reaction, as well as in the characteristics of the PANI obtained. Under comparable optimal conditions, which are pH 3.5 for TvL/O2 and pH 4.3 for HRPC/H2O2, the reaction with TvL/O2 was much slower than with HRPC/H2O2, i.e. ≈27 days vs. 1 day reaction time to reach equilibrium with >90% yield at 25 °C. Although in both cases, aniline monomer coupling occurred mainly via the carbon atom in para position of aniline, UV–vis–NIR absorption and EPR measurements indicate that the reaction with TvL/O2 yielded mainly overoxidized products (with λmax = 730 nm). These products had a lower amount of unpaired electrons if compared with the products obtained with HRPC/H2O2 (with λmax ≈ 1000 nm, which is characteristic for the polaron state of PANI-ES, the emeraldine salt form of PANI). Similarly to previous findings with HRPC/H2O2, enzyme inactivation occurred during the polymerization also in the case of TvL/O2. Since the aqueous PANI-vesicle suspensions obtained are of high colloidal stability, they can be used directly as ink in a conventional thermal inkjet printer for printing on paper or on surface treated polyimide films. Printed PANI-ES patterns on paper changed colour from green (emeraldine salt) to blue (emeraldine base) upon exposure to ammonia gas, demonstrating the expected ammonia sensing properties.