Conductive polypyrrole via enzyme catalysis

Abstract

Laccase catalyzes the polymerization of pyrrole into a conducting polymer using dioxygen as the terminal oxidant. This finding is significant, because it identifies an enzymatic route, and thus an environmentally benign method, for preparing a technologically important polymer. In addition, the rate of oxidation of pyrrole increases when the redox molecule, ABTS [2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate)], is included in a reaction medium that contains laccase. This increase in rate occurs because laccase catalyzes the oxidation of ABTS to ABTS. In addition to laccase, the biocatalytically generated ABTS oxidizes pyrrole to its corresponding radical cation to yield polypyrrole. Moreover, oxidation of pyrrole by ABTS regenerates ABTS for subsequent biocatalytic turnover. Including ABTS in the reaction medium has two important consequences for the final product: (a) The reaction proceeds rapidly enough to form polymeric films instead of oligomeric precipitates, and (b) ABTS remains within the polymeric film as a redox-active dopant. The charge transport properties of the resulting polymers, both with and without ABTS as the counteranion, are compared to those of other conducting materials including polypyrrole prepared electrochemically or chemically.