Functionalized Tyrosinase-Lignin Nanoparticles as Sustainable Catalysts for the Oxidation of Phenols

Abstract

Sustainable catalysts for the oxidation of phenol derivatives under environmentally friendly conditions were prepared by the functionalization of lignin nanoparticles with tyrosinase. Lignin, the most abundant polyphenol in nature, is the main byproduct in the pulp and paper manufacturing industry and biorefinery. Tyrosinase has been immobilized by direct adsorption, encapsulation, and layer-by-layer deposition, with or without glutaraldehyde reticulation. Lignin nanoparticles were found to be stable to the tyrosinase activity. After the enzyme immobilization, they showed a moderate to high catalytic effect in the synthesis of catechol derivatives, with the efficacy of the catalyst being dependent on the specific immobilization procedures.

Keywords: lignin nanoparticles; oxidation of phenols; sustainable catalyst; tyrosinase.

Scheme 1

Schematic representation for the preparation of catalysts I–IV.

Figure 1

SEM images of catalyst I and catalyst II. (a) General overview of catalyst I; (b) Selected magnification of catalyst I; (c) General overview of catalyst II.

Figure 2

Representative particle diameter distributions of OL nanocapsules and Catalyst I–IV.

Figure 3

Confocal images of (a) Catalyst I; (b) Catalyst II.

Figure 4

Zeta potential values of OL nanoparticles, OL PDDA nanoparticles, and catalysts I–IV.

Figure 5

SEM images of catalyst III in the first panel (a) and of catalyst IV in the second panel (b).

Figure 6

Cyclic voltammograms of OL nanocapsules (black line, A–D), Catalyst I (red line, (A)), Catalyst II (red line, (B)), Catalyst III (red line, (C)), and Catalyst IV (red line, (D)) performed in 250 µM catechol solution (50 mM PBS buffer pH 6.5 + 100 mM KCl) at a scan rate of 5 mV s⁻¹.

Scheme 2

Oxidation of phenols 1–4 with catalysts I–IV.