A new mixed-ligand lanthanum(III) complex with salicylic acid and 1,10-phenanthroline: Synthesis, characterization, antibacterial activity, and underlying mechanism

A new mononuclear ternary La(III) complex with mixed ligands of salicylic acid (Hsal) and 1,10-phenanthroline (phen), namely [La(sal)3(phen)2], has been synthesized and characterized. The structure of the La(III) complex was studied by elemental analysis, thermal analysis, infrared, UV-visible, and fluorescence spectroscopy, single-crystal X-ray diffraction, and tight-binding quantum chemical calculation. The crystal structure analysis reveals the La center was chelated by two phen and three sal ligands. Comparative studies on the bacteriostatic and bactericidal activities of the La(III) complex, ligands, and the lanthanum salt were completed against gram-positive and gram-negative bacteria. These studies demonstrate that the La(III) complex has efficient antibacterial activities toward the selected bacteria. The safety profile of the complex was studied using mice as animal models. The results show that the La(III) complex has low toxicity. The morphology of bacteria was observed by field emission scanning electron microscopy, showing that the La(III) complex may act on the cell envelope of bacteria to achieve good bactericidal effects. The results suggest that the La(III) complex may be developed as effective antibacterial drug candidates. (C) 2020 Elsevier B.V. All rights reserved.