Metal‐based antibacterial and antifungal amino acid derived Schiff bases: their synthesis, characterization and in vitro biological activity

A new series of antibacterial and antifungal amino acid derived Schiff bases and their cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, IR and electronic spectral measurements. The spectral data indicated the Schiff base ligands (L1–L5) derived by condensation of salicylaldehyde with glycine, alanine, phenylalanine, methionine and cysteine, to act as tridentate towards divalent metal ions (cobalt, copper, nickel and zinc) via the azomethine-N, deprotonated carboxyl group of the respective amino acid and deprotonated oxygen atom of salicylaldehyde by a stoichiometric reaction of M:L (1:2) to form complexes of the type K2[M(L)2] [where M = Co(II), Cu(II), Ni(II) and Zn(II)]. The magnetic moments and electronic spectral data suggested that all complexes have an octahedral geometry. Elemental analyses and NMR spectral data of the ligands and their Zn (II) complexes agree with their proposed structures. The synthesized ligands, along with their metal complexes, were screened for their in-vitro antibacterial activity against four Gram-negative (Escherichia coli, Shigella flexeneri, Pseudomonas aeruginosa and Salmonella typhi) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and for in-vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glaberata. The results of these studies show the metal complexes to be more antibacterial/antifungal against one or more species as compared with the uncomplexed Schiff base ligands. The brine shrimp bioassay was also carried out to study their in-vitro cytotoxic properties. Only three compounds (2, 11 and 17) displayed potent cytotoxic activity as LD50 = 8.196 × 10−4, 7.315 × 10−4 and 5.599 × 10−4M/ml respectively, against Artemia salina. Copyright © 2007 John Wiley & Sons, Ltd.