The Role of Template in the Enzymatic Synthesis of Conducting Polyaniline

It was recently reported that water soluble conducting polyaniline may be prepared using a new template-guided enzymatic approach. To address the mechanistic role of the template in this reaction, various macromolecular and surfactant templates were investigated. It was found that the template provides a necessary type of “local” environment where the pH and charge density near the template molecule is different from that of the bulk solution. 13C and 1H NMR studies showed that this “local” environment serves as a type of nano-reactor that is critical in anchoring, aligning, and reacting the aniline monomers and ultimately controls what form of polyaniline (conducting or insulating) is obtained during reaction. Strong acid polyelectrolytes, such as sulfonated polystyrene (SPS), are the most favorable because they provide a lower, local pH environment that serves to both charge and preferentially align the aniline monomers through electrostatic and hydrophobic interactions to promote the desired head-to-tail coupling. Interestingly, it was found that micelles formed from aggregating, strong acid surfactant molecules such as sodium dodecylbenzenesulfonic acid (SDBS) also provide suitable local template environments that lead to the formation of conducting polyaniline. 1H NMR spectral data showed that the aniline monomers in these micelle systems intercalate between the sulfonated styrene headgroups of the micelles. However, if the reaction media was such that micelles were not formed or if the distance between the sulfonated headgroups in the mixed micelle systems was too large, then the conducting form of polyaniline could not be obtained. The information gained from this study strongly supports the existence and importance of “local” template environments in guiding the enzymatic synthesis of polyaniline. A fundamental understanding of these types of mechanisms should lead to the design and optimization of a broad range of other interesting template-guided reactions.