Cobalt(III) complexes with thiosemicarbazones as potential anti-Mycobacterium tuberculosis agents

CoIII complexes derived from 2-acetylpyridine N(4)-R thiosemicarbazone (Hatc-R, R = alkyl, aryl) have been characterized by elemental analysis, FTIR, UV-Visible and 1H NMR spectroscopies, cyclic voltammetry (CV), conductimetry measurements and single crystal X-ray diffractometry. The results obtained are consistent with the oxidation of the CoII center to CoIII upon coordination of the monoanionic N,N,S-tridentate thiosemicarbazone ligands, resulting in octahedral ionic complexes of the type [Co(atc-R)2]Cl. Electrochemistry studies show two reversible processes referring to the redox couples CoIII/CoII and CoII/CoI which can be modified by the inductive effects of the substituents groups at the N4 position of the ligands. Two CoIII complexes showed satisfactory activity with minimal inhibitory concentration value under 10 µmol L - 1 and one presented quite low cytotoxicity against VERO and J774A.1 cells (IC50), resulting in high selectivity index (SI > 10).