Synthesis and characterization of azobenzene derivatives and azobenzene-imidazolium conjugates with selective antimicrobial potential

Abstract

Five new non-fluorinated and fluorinated azo derivatives, as well as a new series containing five azoimidazolium conjugates of varying alkyl chain length in the imidazolium head group were prepared and characterized using FTIR and NMR spectroscopy, and elemental microanalysis. Antimicrobial activities of these compounds against pathogenic Gram positive bacterium Staphylococcus aureus and Gram negative bacteria Escherichia coli, Salmonella enterica serovar Typhimurium, as well as yeasts Candida albicans and Saccharomyces cerevisiae were evaluated using the disc diffusion method. The azo derivatives and their imidazolium conjugates were selectively active against the tested microorganisms with zone of inhibition diameters ranging from 10mm-21mm. Their biological efficacy was dependent on the chain length and level of fluorine substitution. The presence of long alkyl chains is essential for the azo derivatives to exhibit microbial efficacy. Active azo-imidazolium conjugates on Staphylococcus aureus contained 16 and 18 carbons in the alkyl chains while Gram negative strains exhibited a cut-off effect at chain length C16. Difference in antimicrobial behavior of the azo derivatives could be due to the different cell wall between the Gram positive and negative bacteria. Fluorination had no effect on the activity against E. coli and Salmonella. However, a clear correlation between the level of fluorine substitution and the antimicrobial activity against Staphylococcus aureus, Candida albicans and Saccharomyces cerevisiae was observed.