Spectroscopic characterization of 2,6-dimethoxyphenol radical intermediates in the Coriolopsis gallica laccase-mediator system

Laccases belong to the multicopper oxidase family that contains four Cu ions classified into three groups according to their spectroscopic features. Due to its low redox potential, laccase can oxidize only low redox potential compounds. To overcome this problem small molecules, named mediators, might act as a sort of electron shuttles between the enzyme and the lignin and laccases are able to oxidize compounds with a redox potential higher than 0.8 V. Multifrequency electron paramagnetic resonance (MF-EPR) using S-(3.8 GHz), X-(9.4 GHz) and W-band (94.8 GHz) performed on Coriolopsis gallica laccase combined with computer simulation allowed to obtain an excellent characterization of the enzyme. Some 2,6-dimethoxyphenols have been studied through EPR spectroscopy thanks to their stable radical intermediate formation and their well-structured and intense EPR signals. A relationship between molecular structure and radical formation during the oxidation process mediated by laccase, has been obtained. The great radical stability of such phenoxy radicals, makes them particularly interesting for biotechnological applications and they represent a good example for the design of new stable laccase mediators.