Synthesis, antioxidant and antibacterial activity of azo dye-stilbene hybrid compounds

Abstract

Purpose The purpose of this paper is synthesis and evaluation of antioxidant and antibacterial activities of a series of new azo dyes derived from 4-aminostilbene. Design/methodology/approach First, the starting material 4-aminostilbene was prepared via two successive Wittig and reduction reactions from 4-nitrobenzyl bromide. The obtained 4-aminostilbene was then reacted with some phenols under the normal azo coupling reaction conditions to give five new azo products. Antioxidant activity of the azo compounds was determined by radical scavenging assay using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. Also, the antimicrobial activity of the compounds against one gram-positive and eight gram-negative strains was evaluated based on the inhibition zone using disc diffusion assay. Findings The structures of the azo dyes were identified and characterized by fourier-transform Infrared, 1H nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-V) is spectroscopic methods. All the compounds showed higher antioxidant activity than ascorbic acid (Asc) and butylated hydroxytoluene (BHT) as positive controls. Moreover, the compounds showed lower antibacterial activity than the standard antibiotic vancomycin. Research limitations/implications Excellent antioxidant activity, along with antibacterial activity against Streptococcus pneumoniae and Pseudomonas aeruginosa, was observed for the two synthesized azo dyes. Originality/value Five novel azo dyes based on 4-aminostilbene were synthesized. The dyes have a highly p-extended conjugated structure comprising the phenolic and stilbenic segments, and they indicated good antioxidant activity, so that the two dyes (2c and 2d) even showed much more scavenging activity compared to BHT which is used as an antioxidant agent in food industries. These compounds with highest antioxidant activity also inhibited the growth of S. pneumoniae and P. aeruginosa.