Improvement of enzymatic synthesis of conducting polyaniline in anionic surfactant AOT stabilized bicontinuous microemulsion by adding zwitterionic surfactant SB-12
The horseradish peroxidase (HRP) mediated synthesis of conducting polyaniline (PANI) was investigated in detail in the bicontinuous microemulsion stabilized by both sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and dodecyl sulfobetaine (SB-12). The addition of zwitterionic surfactant SB-12 not only reduces the phase inversion temperature of the anionic surfactant AOT stabilized microemulsion, but also enhances the catalytic performance of the solubilized HRP. Compared with the previously reported AOT/SDS stabilized bicontinuous microemulsion, the present AOT/SB-12 stabilized bicontinuous microemulsion is much more suitable for the expression of the catalytic activity of HRP; moreover, the conductivity of the resulting PANI improves greatly (a 15-fold increase in conductivity). The present results indicate further that the catalytic activity of HRP and its stability are crucial for the biosynthesis of PANI in bicontinuous microemulsions. To understand the underlying mechanism of the medium effects, electron spin resonance (ESR), UV–vis-NIR and small-angle X-ray scattering (SAXS) spectroscopies were used to investigate the effects of the oil-to-water ratio ( α ) and the surfactant concentration ( γ ) of the present bicontinuous microemulsion on the conductivity of resulting PANI. Results show that the bicontinuous microemulsion stabilized by both AOT and SB-12 still has a template role in the biosynthesis of PANI and the PANI conductivity is mainly determined by the microstructure of the template and by the microstructure-dependent activity and stability of the solubilized HRP. Lower α and γ values are beneficial to the enzymatic synthesis of high-quality PANI. The present study is of great help not only to deepen the understanding of the template role of anionic surfactant aggregates in the biosynthesis of conducting PANI, but also to develop new strategies for the biosynthesis of high quality PANI.
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