Complexes in aqueous cobalt(II)–2-picolinehydroxamic acid system: Formation equilibria, DNA-binding ability, antimicrobial and cytotoxic properties

Abstract The coordination properties of 2-picolinehydroxamic acid towards cobalt(II) in aqueous solution were determined by a pH-metric method and confirmed by spectroscopic (UV–Vis and ESI-MS) studies. The results show the formation of mononuclear complexes, as well as of metallacrowns (MC). All methods indicate a high tendency of 2-picolinehydroxamic acid to form cobalt(II) metallacrown 12-MC-4. ESI-MS additionally confirms 15-MC-5 and 18-MC-6, stabilized by a sodium ion and methanol. The complexes observed in the speciation model at a pH about 7.2 were studied for their DNA-binding ability. The decrease of absorbance in the range of ca 310–400 nm indicates effective binding to calf thymus DNA by 2-picolinehydroxamic acid complexes, via intercalative mode. The antimicrobial properties of 2-picolinehydroxamic acid, cobalt(II) ions and of the complexes formed in the Co(II) – ligand system were determined against Gram-positive bacteria ( Enterococcus faecalis , Enterococcus faecium , Staphylococcus aureus , Bacillus subtilis ), Gram-negative bacteria ( Pseudomonas aeruginosa , Escherichia coli , Helicobacter pylori ) and fungal strains ( Candida , Aspergillus niger ). The results indicate that the complexes demonstrate greater antibacterial and antifungal activity for most strains than the ligand. Both the complexes and the ligand induce a slight decrease in the metabolic activity of cells, while the complexes do not damage the cell nuclei. The 2-picolinehydroxamic acid complexes activate the human monocytic cells, suggesting they have immunomodulating properties, which are particularly important in combating infections caused by strains resistant to other drugs.