Sono-enzymatic polymerization of catechol

Abstract

The potential of laccase enzymes for polymerizing, crosslinking and functionalizing various compounds was studied extensively and increasing interest has been focused on the application of this enzyme as a new biocatalyst in organic synthesis.[1-6] Laccases (EC 1.10.3.2) are a class of multi-copper-containing oxidoreductase enzymes able to catalyze the transformation of various aromatic compounds, specifically phenols and anilines, through the formation of a free cation radical after the transfer of a single electron to laccase. The radical can further react on non-enzymatic oxidation polymerizing various halogen, alkyl-, alkoxy-substituted anilines and phenols.[7-8] The phenolic derivatives resulting in the production of polymeric aggregates are usually less soluble and much stable than their parent compounds.[9,10] Unfortunately the relatively short catalytic lifetime of the laccases in the polymerization processes and the mass transfer limitations, restrict their applications. This effect can be attributed to the inactivation of the enzyme active site due to phenoxy radicals and polymers produced during enzyme treatment.[11] To overcome this limitations the use of ultrasound, under proper conditions, has shown to enhance significantly the mass transfer as well as the structure stability, substrate binding, and activity of the enzyme.[12,13] Ultrasound alone or in combination with other methods is known to enhance a wide variety of chemical and physical processes, mainly due to the phenomenon known as cavitation in a liquid medium that is the growth and explosive collapse of microscopic bubbles.[14-16] These localized ‘‘hot spots’’ generate high local temperature and pressure rise, capable of decompose water to hydrogen atoms and hydroxyl radicals and of break several chemical bonds.[17,18] Therefore in this work laccase from Trametes villosa was tested in combination with ultrasound to improve the radical polymerization of catechol. A solid-state “in situ” sono-enzymatic synthesis of poly(catechol) was also performed by coloration of wool. The results were analyzed by spectrophotometric and HPLC analyses.