Copolymerization of aniline and gallic acid: Novel electroactive materials with antioxidant and antimicrobial activities

Abstract

Novel electroactive PANI-GA micro/nanostructured functional copolymers/co-oligomers were synthesized by the oxidative copolymerization of aniline and gallic acid (GA) in an aqueous solution, using ammonium peroxydisulfate (APS) as an oxidant and different initial mole ratios of GA to aniline ([GA]/[aniline]=0.1, 0.25, 0.5 and 1.0). It was found that the yield, molecular structure, morphology, electrical conductivity, electrochemical behavior, antioxidant and antimicrobial properties of PANI-GA strongly depend on [GA]/[aniline] ratio. The highest conductivity (3.8 × 10–3 S cm−1) showed PANI-GA with dominant polyaniline (PANI) emeraldine salt segments and nanorod morphology, synthesized at [GA]/[aniline] = 0.1. FTIR spectroscopy confirmed the presence of covalently bonded GA and PANI-type structural segments in PANI-GA. The antioxidant activity of PANI-GA was explored by the spectrophotometric 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assay and electrochemical test for superoxide anion radical, •O2−. All protonated PANI-GA showed good scavenging activity toward ABTS•+ and •O2− radicals, whereby the highest activity exhibited PANI-GA produced at [GA]/[aniline] = 1. The radical scavenging activity of protonated PANI-GA samples toward ABTS•+ was much higher than that of PANI. The antimicrobial properties of the PANI-GA against bacteria S. aureus and E. coli, as well as against fungus C. albicans were evaluated. All synthesized protonated PANI-GA were more effective as S. aureus growth inhibitors than pristine GA and PANI. Highest effectiveness against E. coli and C. albicans, higher than that of pristine GA and PANI, showed conductive PANI-GA synthesized at [GA]/[aniline]= 0.1. Based on the obtained experimental results the mechanism of GA and aniline oxidative copolymerization is proposed.