An enzymatically synthesized polyaniline: A solid-state NMR study

The variation in molecular and electronic structure of doped (as synthesized) conducting, dedoped base, and redoped conducting forms of polyaniline (PANI) prepared by oxidative enzymatic polymerization of aniline with and without the presence of polyelectrolyte template was analyzed by solid-state C-13 and N-15 CP/MAS NMR spectroscopy. Polyanilines were enzymatically synthesized using a natural biocatalyst such as horseradish peroxidase (HRP) at pH 4.3 and a synthetic biomimetic catalyst, specifically poly(ethylene glycol)-coupled hematin (PEG-hematin), at pH 1.0. The HRP-catalyzed enzymatic polymerization of PANI was carried out in the presence of macromolecular polyelectrolyte templates such as poly(vinylphosphonic acid) (PVP), poly(4-styerenesulfonate) (SPS), and dodecylbenzenesulfonic acid (DBSA). C-13 and N-15 CP/MAS NMR spectral features indicate that the PANI obtained by PEG-hematin-catalyzed enzymatic polymerization resembles most with chemically synthesized analogues in its doped (as synthesized) conducting form than other forms of PANI. A systematic experiment involving a redoping process at different pH levels shows the structural changes during the transformation from dedoped base form to redoped conducting form. Solid-state NMR data also indicate a decrease of polaronic contribution at the higher doping level. End-group analysis from IN CP/MAS NMR data provides information on the molecular weight of the enzymatically polymerized PANI sample.