Free radical scavenging and antioxidant properties of conducting polymers examined using EPR and NMR spectroscopies

Conducting polymers are being considered for a range of applications in which they will come into contact with biological tissues, such as artificial muscles, in drug release, nerve regeneration and as scaffolds for cell attachment. The radical scavenging properties of antioxidants consumed in the diet are often assessed by their ability to neutralise stable free radicals such as α,α-diphenyl-β-picrylhydrazyl (DPPH). Commercially available soluble polyaniline and polypyrrole were found to be efficient and rapid scavengers of DPPH radicals, as monitored by EPR spectroscopy. Further experiments using solid polyaniline samples, in the partially oxidised or fully reduced state, using solid state 13C NMR (CP MAS, NQS and Polarization Inversion) showed that the polyaniline was oxidised through its interaction with DPPH radicals. Aniline and pyrrole monomers also reacted with DPPH radicals but at a much slower rate, consistent with their lower reducing strengths.