A new magnesium(II) complex of marbofloxacin: Crystal structure, antibacterial activity and acute toxicity

Abstract

In this work, a new magnesium(II) complex was synthesized by solvothermal method using marbofloxacin (MB) as the medicinal ligand. The crystal structure of this complex ([Mg(MB)2(H2O)2], MB-Mg) determined by X-ray single crystal diffraction analysis demonstrates a mononuclear and six-coordinated octahedral configuration, in which two MB ligands chelate with Mg(II) through the 3-carboxyhydroxyl O atom and the 4-carbonyl O atom of MB, respectively, and two water molecules occupy the axial positions of the octahedron. The study on the solution chemistry by means of mass spectroscopy and molar conductivity further indicate that the coordinated species of MB-Mg could be still maintained in aqueous solution. The minimal inhibitory concentration (MIC) of MB and MB-Mg against seven typical species of pathogenic bacteria were tested in vitro. The results showed that MB-Mg exhibited better inhibitory effects on most the tested strains than MB. Furthermore, the acute toxicity was tested by acute toxicity test in mice. The results showed that the LD50 of MB-Mg was 9184.25 mg/Kg, which could be classified to Grade-II toxicity (practical non-toxic) according to the standard of toxicity classification standard. The acute toxicity in vivo, represented by LD50, is significantly lower than which of MB ligands (LD50 = 1249 mg/Kg, Grade-III toxicity). This result strongly suggests that the coordination of MB with the biosafe Mg(II) can effectively reduce its toxicity in vivo, contributing to the research of new metal-based veterinary drug products, with important practical value and scientific significance.