Unexpected influence of metallamacrocyclic architecture of heterometallic pyrazinehydroximate Cu(II)-Bi(III) and Cu(II)-La(III) complexes on their antibacterial activity against Mycolicibacterium smegmatis

Tuberculosis (TB) continues to be a significant global health threat. Hundreds of pure organic molecules are reported annually as promising anti-TB agents. Currently, the metal compounds have gained increasing attention. Nevertheless, the question remains whether or not metal complexes have any significant advantages over purely organic compounds. Herein we reported the first attempt to examine the antimycobacterial activity of pyrazinehydroximate Bi[15-MCCu(II)Pyzha-5] and La[15-MCCu(II)Pyzha-5] metallacrown complexes. These complexes present a typical 15-MC-5 metallacrown structure with a neutral ring consisting of five [Cu(II)-N-O] repeating units and the Bi(III) or La(III) metal ion in the central cavity. Both complexes exhibited enhanced antimycobacterial activity towards Mycolicibacterium smegmatis as a model for Mycobacterium tuberculosis, whereas the parent free pyrazinehydroxamic acid H2pyzha was inactive. The effect of the central metal ions on the antimycobacterial activity was discussed on the basis of DFT calculations.