This project was aimed at the synthesis of some Schiff base compounds and their transition metal complexes of biological significance. Thus, the Schiff bases (109)-(112)were synthesized by the reactions of 2-aminoniconitic acid and salicyaldehyde, 5-bromosalicyaldehyde, 5-nitrosalicyaldehyde and 5-methoxysalichyladldehyde, respectively. Similarly, the Schiff vases (113)-(115) were prepared by condensing the amino component, 2-amino-1,3,4-thiadiazole with the respective aldehydes i.e furfuraldehyde, thiophene-2carboxaldheyde and pyrrole-2-carboxaldehyde. In a similar fashion, the Schiff bases(116)-(121) were derived from 5-amino-1,3,4-thiadiazole-2-thiol and the respective aldehydes i.e furfuraldehyde, thiophene-2-carboxaldehyde, 4-bromothiophene-2-carboxaldehyde, pyrrole-2-carboxaldehyde, salicylaldehyde, and pyrindine-2-carboxaldehyde. The chemical structures of all the Schiff bases were determined by analytical and spectral (IR, 1H-NMR) methods.
Of these Schiff bases,(113)-(112) were used as potential ligands for synthesizing their cobalt(II), nickel(II) and zinc(II) complexes, whereas the Schiff bases (109)-(112) were used for complexation with metal ions viz. cobalt(II), nickel(II) and zinc(II) only, the synthesized metal complexes were characterized by elemental analyses, molar conductance, magnetic moment, IR and electronic spectral data.
The synthesized Schiff bases and their transition metal complexes were screened for their in vitro antibacterial activity against four Gram-negative (Escherichia coli, Pseudomonas aeruginosa, typhi, Shigella flexneri)and two Gram-positive (Bacillus subtilis, Staphylococcus aureus) bacterial strains by the agar-well diffusion method. The synthesized Schiff bases were found exhibit no or low to moderate activity against one or more bacterial species. On the contrary, all the metal complexes exhibited varied activity against different bacteria. The Schiff bases, which were inactive before complexation became active and less active ones, became more active upon coordination with metal ions. The metal complexes(150)-(151),(154)-(155), (157)-159), and (166)-(167) showed comparatively much higher activity. However, the metal complex(155) was found to be the most active one.