Effect of chelation on therapeutic potential of drugs: Synthesis, structure, antimicrobial and insecticidal activity of 3d-metal complexes involving Schiff-bases

VO(II), Fe(II), Co(II), Cu(II) and Zn(II) metal complexes of Schiff bases derived from 2thiophenecarboxaldehyde with 2,6-dichloro-4-nitroaniline (TDNA) and 4-anisidine (TCA) are reported and characterized based on elemental, FT-IR, UV-visible, molar conductance, FAB-mass, ESR, magnetic susceptibility, thermal and XRD analysis. IR spectra show that TDNA and TCA are coordinated to the metal ions in a bidentate manner with S and N donor sites of azomethine -N and thiophene-S. FAB-mass spectra of [VO(TCA)2].SO4.4H2O have been investigated. FAB-mass and thermal data show degradation pattern of the complexes. The thermal behavior of metal complexes shows that the hydrated complexes loses water molecules of hydration in the first step; followed by decomposition of ligand molecules in the subsequent step. The metal complexes exhibited good microbial screening results against a number of medically important bacterial strains namely Escherichia coli, Staphylococcus aureus, Proteus mirabilis and fungi as Aspergillus niger and Candida albicans. The antimicrobial activity was evaluated using well diffusion technique. The solvent used, was DMSO. Schiff bases and their metal complexes were also evaluated for their insecticidal activity on cockroaches (Periplanata americana) as the test insect. Schiff bases and their metal complexes have been found active as an insecticide. Thus, the aim of this study is to observe the impact of chelation on the therapeutic value of the bioactive organic compounds. The antimicrobial and insecticidal screening results also indicate that the metal complexes are better antimicrobial and insecticidal agents as compared to the Schiff bases.