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Three Schiff base ligands, L1H = (2-((benzo[d]thiazol-6-ylimino)methyl)-6-nitrophenol), L2H = (2-((benzo[d]thiazol-6-ylimino)methyl)-4,6-diiodophenol), L3H = (2-((benzo[d]thiazol-6-ylimino)methyl)-4-bromo-6-methoxyphenol) and their binary metal complexes, 1 [Cu(L1)2], 2 [Co(L1)2], 3 [Cu(L2)2], 4 [Co(L2)2], 5 [Cu(L3)2] and 6 [Co(L3)2], have been synthesized and characterized by elemental analysis, NMR, ESI mass, FT-IR, ESR, UV–Visible, magnetic susceptibility and TGA studies. The analytical and various spectral data suggested a square-planar geometry around the metal for all complexes with N2O2-donor atoms from the Schiff base ligands. Antimicrobial study was investigated against two Gram-positive, Bacillus amyloliquefaciens and Staphylococcus aureus, and one Gram-negative, Escherichia coli, bacteria as well as against two fungal species, Macrophomina phaseolina and Sclerotium rolfsii, by using Streptomycin and Mancozeb as standard drugs, respectively. The results revealed that metal complexes show more potent activity than free ligands and moderate compared to standard drugs. The free-radical scavenging ability of the complexes was evaluated by DPPH and ABTS assay methods using ascorbic acid as a standard antioxidant, complexes 1 and 2 showed good scavenging activity. DNA-binding titrations were also performed and indicated that all complexes bind to calf-thymus DNA via an intercalation mode. Additionally, the complexes exhibited good cleavage ability against the pBR322 DNA even at low concentrations in the presence of activators, H2O2 as well as UV light. [ABSTRACT FROM AUTHOR]

Three isoxazole Schiff bases 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-6-methoxyphenol (L1), 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-4,6-diiodophenol (L2), 2-((E)-(3,5-dimethylisoxazol-4-ylimino)methyl)-6-bromo-4-chlorophenol (L3), and their Cu(II) complexes [Cu(L1)2] (1), [Cu(L2)2] (2) and [Cu(L3)2] (3) were synthesized. All the complexes have been characterized by elemental analysis, FT-IR, ESI mass, UV-Visible, ESR, TGA, magnetic moments, and single-crystal X-ray diffraction analysis. Based on analytical data, a square planar geometry is assigned to the Cu(II) complexes with N2O2donors from the Schiff base ligands. The single-crystal X-ray diffraction measurements of1and2confirmed the square planar geometry. DNA binding studies from electronic absorption titrations, viscosity measurements, and fluorescence quenching studies indicated an intercalation mode of binding of Cu(II) complexes with CT-DNA. DNA cleavage experiments of Cu(II) complexes with supercoiled plasmid pBR322 DNA have also been investigated by agarose gel electrophoresis in the presence of H2O2(oxidative cleavage) and UV light (photolytic cleavage). The synthesized compounds were screened for antibacterial (Escherichia coli,Pseudomonas putida,Klebsiella pneumoniae,Bacillus subtillisandStaphylococcus aureus) and antifungal (Candida albicansandAspergillus niger) activities by the paper disk method. The Cu(II) complexes showed better activity than corresponding Schiff bases. [ABSTRACT FROM PUBLISHER]