Antimicrobial salicylaldehyde Schiff bases: synthesis, characterization and evaluation.

As the pathogens soon develop resistance to the existing antibiotics, the demand for new and more effective anti-microbial agents is a continuous phenomenon. In this paper we are reporting synthesis and spectral data of eight Schiff bases of salicylaldehyde with different amines, and evaluation of their anti-microbial activities against different bacterial strains. The bases were synthesized by reflux method, and their structures were determined based FT-IR, 1 H- NMR, 13 C-NMR and Mass spectrometric data. The Schiff bases synthesized included 2-{((Z)-(2-hydroxyphenyl) methylidene) amino}benzoicacid (SB1), 4-{((Z)-(2-hydroxyphenyl) methylidene) amino} benzoic acid (SB2),2- ((naphthalene-2-ylimino)methyl) phenol(SB3),2-2'-(benzene-1,4-diylbis(nitrilomethylylidene))diphenol (SB4), 2-2'- (benzene-1,2-diylbis (nitrile-(E)-methylylidene))diphenol (SB5), 2-((2-phenylhydrazineylidene)methyl)phenol (SB6), 2- 2'-(ethene-1,2-diylbis(iminomethanediyl))diphenol (SB7) and 2-((Z)-(phenylimino)methyl)phenol (SB8). The anti- microbial activities of synthesized Schiff bases were determined in terms of zones of inhibition and minimum inhibitory concentrations (MICs). All the bases showed moderate to good activities against all the tested microorganisms. The MICs of most compounds were 100-200µg/mL against different microorganisms. However, it was 50µg/mL for SB1 against P. aeruginosa (1), SB3 against P. aurantiaca, P. aeruginosa (1), E. coli (2), S. typhi (2) and C. freundii, SB4against E. coli (2), S. typhi (1) and S. maltophilia, SB5 against K. pneumoniae and S. typhi (2), SB6 against P. aeruginosa (3) and C. freundii, SB7 against E. cloacae and A. lipoferum, andSB8against E. coli (2). Considerably active bases may prove to be potential candidates for future antibiotic drugs.