Heteronuclear Complexes of Hg(II) and Zn(II) with Sodium Monensinate as a Ligand

Abstract

The commercial veterinary antibiotic sodium monensinate (MonNa) binds mercury(II) or zinc(II) cations as thiocyanate [Hg(MonNa)2(SCN)2] (1) or isothiocyanate [Zn(MonNa)2(NCS)2] (2) neutral coordination compounds. The structure and physicochemical properties of 1 and 2 were evaluated by the methods of single crystal and/or powder X-ray diffraction, infrared, nuclear magnetic resonance, X-ray photoelectron spectroscopies, and electrospray-mass spectrometry. The primary cores of the two complexes comprise HgS2O2 (1) and ZnN2O2 (2) coordination motifs, respectively, due to the ambidentate binding modes of the SCN–ligands. The directly bound oxygen atoms originate from the carboxylate function of the parent antibiotic. Sodium cations remain in the hydrophilic cavity of monensin and cannot be replaced by the competing divalent metal ions. Zinc(II) binding does not influence the monensin efficacy in the case of Bacillus cereus and Staphylococcus aureus whereas the antimicrobial assay reveals the potential of complex 2 as a therapeutic candidate for the treatment of infections caused by Bacillus subtilis, Kocuria rhizophila, and Staphylococcus saprophyticus.