Laccase-catalyzed controlled radical polymerization of N-vinylimidazole
Laccase from Trametes versicolor is a multi-copper-containing oxidoreductase which was found to catalyze the polymerization of N-vinylimidazole under conditions of atom transfer radical polymerization (ATRP) in aqueous solution (pH 4, 100 mM acetate buffer) at ambient temperature by using sodium ascorbate as a reducing agent. The reaction followed first order kinetics and resulted in polymers with controlled number-average molecular weights (between 1660 and 9970 g mol−1) and relatively narrow, monomodal molecular weight distributions (Đ between 1.27 and 1.56) according to gel permeation chromatography. Purified polymers were also analyzed by mass spectrometry which revealed a Đ of 1.07. The enzyme could be separated quantitatively from the polymer, lowering the metal content of the purified polymers below the detection limit of ICP-OES of 9 ppb. The enzyme retained its polymerization activity for more than eight hours, but formed electrostatic complexes with the polymer and underwent conformational changes at the beginning of the reaction. Biocatalytic controlled radical polymerization allows the synthesis of poly(N-vinylimidazole) with a well-defined molecular weight. Such polymers will be useful building blocks in many applications, such as drug- and gene-delivery, fuel cell membranes and polyionic liquids.