Helical opposition in poly(2-methoxyaniline) by tuning the concentration of salts in reaction solution

Abstract

The synthesis and application of helical polyaniline derivatives (PANIs) have attracted much interest. However, most of these syntheses have been carried out in organic solutions. In our previous reports, helical PANIs were successfully realized in aqueous solution. Because helical architecture in the backbones of PANIs is an induced rather than the natural arrangement, it is significant to study the change in helicity in aqueous solution, especially opposition or reversion. One excess-handed helicity was induced in poly(2-methoxyaniline) (PMOA) by electrochemical polymerization of 2-methoxyaniline at pH = 2.5 in the presence of protonated β-cyclodextrin sulfate (CDS− H+). When 0.04 mol L−1 NaCl was added to the reaction solution, the PMOA backbone took on an opposite excess of one-handed helicity, which was confirmed by induced circular dichroism. Such a result originates from the dynamic switch between electrostatic and hydrogen-bonding interactions. The helix-inducing process in PMOA depends on the interaction between PMOA and chiral CDS. Due to the competition of Na+ Cl− with PMOA+ CDS−, the electrostatic interaction between PMOA and CDS is limited or weakened. Thus, the slightly preferred interaction between them switches from electrostatic to hydrogen bonding. Simultaneously, the interaction positions and distance are changed. The changed steric hindrance induces PMOA into adopting an opposite excess-handed helicity. Copyright © 2010 Society of Chemical Industry