Substituent Effect on the Antimicrobial Activity of Schiff Bases Derived from 2-aminophenol and 2-aminothiophenol

Fasina, T.M. ; Ejiah, F.N. ; Dueke-Eze, C.U. ; Idika, N. (2013)


The biological activity of Schiff bases have been of interest in the design of new antimicrobial agents, however relationship between molecular structure and biological activity had been little studied. This study seeks to investigate the role of subtle electronic effect arising from substituent variation on the biological activity of salicyladimines. The effect of substituent variation on the antimicrobial activity of Schiff bases was therefore studied using aminophenol and aminothiophenol compounds. Four Schiff bases derived from condensation of 2-aminophenol or 2-aminothiophenol with 5-bromosalicylaldehyde and 5-nitrosalicyladehyde were synthesized and characterized by IR, NMR and elemental analysis. Electronic absorption spectra of the compounds were recorded in dioxane and methanol as solvents. The presence of absorption bands above 400 nm for the aminophenol compounds reveals the existence of keto-enol tautomerisim. In vitro antimicrobial screening against Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923), Enterococcus feacalis (ATCC 29212) in N,N’-dimethylformamide (DMF) and 1,4-dioxane as solvents show dependence of biological activity on the nature of substituent and solvent. The Schiff bases were active against gram positive bacteria and more potent in DMF with the bromine substituted imines exhibiting higher activity.