Available online www.jocpr.com Journal of Chemical and Pharmaceutical Research, 2013, 5(10):177-181 Research Article ISSN : 0975-7384 CODEN(USA) : JCPRC5 177 Substituent effect on electronic absorption and biological properties of Schiff bases derived from aniline Tolulope M. Fasina* and Raphael O. Dada Chemistry Department, University of Lagos, Akoka _____________________________________________________________________________________________ ABSTRACT The effect of substituents on biological activity of Schiff bases was investigated using Schiff bases derived from the condensation of aniline with salicyaldehyde, 5-methoxysalicyaldehyde, 5-nitrosalicyladehyde and 2- hydroxynaphtaldehyde. The electronic absorption spectra of the compounds in DMF and ethanol reveal that compounds containing the electron withdrawing nitro or naphtyl groups exist in the keto-amine form in both solvents. The compounds were screened against some clinically important bacteria namely Escherichia coli (ATCC 25922), Proteus mirabilis (ATCC 13315), Enterococcus feacalis (ATCC 29212) and Staphylococcus aureus (ATCC25923) using the agar ditch method and results show that 5-methoxysalicyaldehyde Schiff base exhibited highest activity. Keywords: Aniline, Schiff base, Substituent effect, biological activity, electronic spectra _____________________________________________________________________________________________ INTRODUCTION The design of new ligands is crucial to formation of novel metal complexes with interesting properties and applications as the Chemistry of a metal complex is greatly influenced by the properties of the ligand. Since the electron donating and accepting properties of the ligand and presence of structural functional groups affects the nature of metal complex obtained, a knowledge of ligand properties can afford synthesis of metal complexes with tuneable properties. Schiff bases are considered an important class of organic compounds, which have wide applications. In recent years, they have gained significant interest in the area of drug research and development owing to the broad bioactivities such as insecticidal[1], antibacterial[2], antituberculosis[3] and antimicrobial[4-5] reported for the compounds and their metal complexes. These compounds play an important role in biological systems and are observed in various enzymes such as transaminases, tryptophan synthase etc. The important physical and biological properties of these compounds are related to the presence of the intramolecular hydrogen bond and proton transfer equilibrium. Schiff bases have also been utilized as ligands to synthesize metal complexes with interesting applications[6-7]. The steric and inductive effects introduced by substituents present on the aromatic portion of the Schiff base can influence the properties of the ligand significantly. In continuation of our efforts in understanding the role of subtle electronic variations such as substituent effects on Chemistry and activity of Schiff bases and their metal complexes, we herein report the effect of substituents on the antimicrobial activity of Schiff bases derived from aniline and substituted salicyaldehyde.