Oxidation of 8-hydroxyquinoline catalyzed by laccase from Trametes pubescens yields an antioxidant aromatic polymer

We report for the first time the enzyme-catalyzed production of poly (8-hydroxyquinoline) using laccase from the white rot fungus Trametes pubescens (CBS 696.94). The oxidative polymerisation of 8-hydroxyquinoline was catalyzed by laccase in a reaction medium containing 8% acetone, 0.01–0.05 mg/ml 8-hydroxyquinoline and sodium acetate buffer (0.1 M, pH 5.0) at 30 °C. The average molecular weight of the polymeric product, as determined by matrix-assisted laser desorption/ionization coupled with time-of-flight mass spectrometry (MALDI-TOF) analysis, was 789 m/z. Further structural characterisation of the product was achieved using Fourier transform infrared (FT-IR) spectroscopy. The potential for application of poly (8-hydroxyquinoline) as an antioxidant was investigated by evaluating its ability to quench the stable free radical 2,2′-diphenyl-1-picrylhydrazyl (DPPH). The antiradical efficiency (AE) was calculated to be 2 × 10−3, a value which is comparable to the AE values for gallic acid (2.6 × 10−3) and ascorbic acid (11.4 × 10−3), and greater than that of polymeric lignin fractions of similar molecular weight (5 × 10−4).