Cobalt (II), zirconium(IV), calcium(II) complexes with dipicolinic acid and imidazole derivatives: X-ray studies, thermal analyses, evaluation as in vitro antibacterial and cytotoxic agents

Four coordination complexes, [2-mimH]2[Co(pydc)2][ClO4]. H2O (1), [2-mimH]2[Zr(pydc)3] (2), [imiH]2[Zr(pydc)3].4H2O (3) and [Ca(pydcH2)2(H2O)]2[Co(pydc)2]2·6H2O (4) have been prepared from the reaction between proton-transfer compounds containing pyridine-2,6-dicarboxylic acid (pydcH2) with 2-methylimidazole (2-mim) and imidazole (imi) in 1:2 M ratio and metal salts. These compounds have been characterized by spectroscopic methods and single crystal X-ray diffraction technique was used to determine their structures. Also, thermal analyses (TGA/DTA) were carried out on all the synthetic compounds. Then the agar dilution and diffusion methods were used to determine the antibacterial activity of the ligands and their complexes on the growth profile of two pathogenic Gram-positive bacteria namely Staphylococcus aureus and Bacillus cereus and also two Gram- negative bacteria namely Escherichia coli and Klebsiella oxytoca. The highest antibacterial activity was exhibited by (pydcH2) and complex (2) at MIC values between 75 and 175 μg/mL. These two compounds exhibited stronger effects than gentamicin as a standard drug toward Klebsiella oxytoca. The anti-proliferative activity of compounds was evaluated in vitro using oxaliplatin as a positive control against MCF7 (a human breast cancer), HL60 (a human lymphocyte) and HT29 (a human colon adenocarcinoma) cell lines. Selective and significant cytotoxic effect of complex (4) was observed on MCF7 cells (IC50 = 10 μM, Cell viability 62.12%).