Laccase-catalyzed oxidative polymerization of aniline dimer (N-phenyl-1,4-phenylenediamine) in aqueous micellar solution of sodium dodecylbenzenesulfonate

We have studied oxidative polymerization of aniline dimer (N-phenyl-1,4-phenylenediamine) catalyzed by high-redox potential laccase isolated from the fungi Trametes hirsuta (Wulfen) Pilát CF-28. Enzymatic aniline dimer polymerization was performed in aqueous micellar solution of sodium dodecylbenzenesulfonate, the atmospheric oxygen serving as an oxidizer. The resultant dispersion was stable for at least 6 months. The products synthesized were characterized using Fourier transform infrared and UV–vis spectroscopies. MALDI TOF analysis has shown that aniline dimers polymerize to mainly form aniline oligomers with the m/z ratio up to 2180, which corresponds to a polymerization degree of 24 (in terms of aniline subunits). Enzymatically formed aniline oligomers consist for the most part of para-directed units in the form of emeraldine salt. The end product structure depends on the reaction medium pH. Transmission electron microscopy has revealed granular nanoparticles of the reaction product.

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► Aniline dimer formation may be the rate-limiting stage of enzyme-catalyzed aniline polymerization.
► MALDI-TOF spectra of tetrahydrofurane-dissolved products of aniline dimer enzymatic oxidation are evidence for aniline oligomers with the polymerization degree 4–22 in terms of aniline subunits.
► Enzymatically formed aniline oligomers consist for the most part of para-directed units in the form of emeraldine salt.
► The final product structure of enzymatic polymerization of aniline dimer depends on the reaction medium pH.