The widespread and continuous existence of antibiotic-resistant microorganism is a major worldwide problem. Consequently, many Schiff base complexes derived from aromatic aldehydes, aromatic amines and transition metals has been extensively studied. The presence of electron donating or electron withdrawing substituents on the benzene rings of the Schiff bases have effects on their physical, chemical and biological activities. We examined the effects of substituent on the geometry, electronic and biological activities of cobalt(II) complexes and a series of Schiff bases derived from the condensation of o-vanillin with aniline, 1-aminonaphthalene, 3-aminopyridine, 4-aminopyridine, 2-aminomethylpyridine or 3-aminomethylpyridine. The Schiff bases and the complexes were characterized by elemental analyses, electronic and infrared spectroscopy. 1H NMR and 13C NMR spectral studies were further used to characterized the Schiff bases. The geometry for the Schiff bases and their cobalt(II) complexes were proposed on the basis of data obtained from the various. On the basis of these studies, a four-coordinated distorted tetrahedral complexes have been proposed for all the complexes while the Schiff bases are mixtures of enol-imine or keto-amine tautomers. The cobalt(II) complexes and the Schiff bases were tested for their antibacterial, antifungal and lethality activities against three bacteria, (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and one fungus strain, Aspergillus niger, using the disc diffusion method. Contrary to the general believe that complexation increase activity, it was observed that some of the Schiff bases showed more activity than their cobalt complexes against Gram-negative bacteria, (Pseudomonas aeruginosa, Escherichia coli), and fungus, Aspergillus niger. In addition, lethality activities against brine shrimps were reduced after forming the complexes. However, the complexes showed higher activity against the Gram-positive Staphylococcus aureus than their corresponding Schiff bases.

Synthesis, characterization and biological studies of cobalt(II) Schiff bases derived from o-vanillin with series of aromatic amines

255th National Meeting (2018)

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