The effects of 3-hydroxyflavone complexes with transition metal ions on the physicochemical and microbial properties of bacterial cell membranes.

Flavonoids are natural antibacterial agents, and their bioavailability can be improved by metal complexation. This study examines 3-hydroxyflavone complexes with Co(II), Mn(II), and Zn(II) against Staphylococcus aureus and Escherichia coli. Antibacterial activity and membrane permeability were tested in vitro, while Langmuir monolayers modeled physicochemical interactions with bacterial membranes and their major lipid components. The results demonstrated that, particularly at the highest tested molar ratio, the metal complexes of 3HF exhibited greater antibacterial efficacy than the 3HF independently. Escherichia coli demonstrated greater sensitivity to the tested compounds, than S. aureus. The tested 3HF-complexes were identified as bacteriostatic. In E. coli, both physicochemical and microbiological changes were observed following treatment with Co(II)-3HF and Zn(II)-3HF complexes. In contrast, the Mn(II)-3HF complex affected only model membrane properties without notable microbiological effects. For S. aureus, only the zinc(II) complex showed effective microbiological action on the native cell and activity on the inner membrane (in the model studies), with efficacy ranked as follows: Mn(II)-3HF ≥ Co(II-3HF) > Zn(II)-3HF. Increased permeability of E. coli and S. aureus membranes (in vitro assays) has been proposed as a mechanism for the antibacterial action of the Co(II)-3HF and Zn(II)-3HF complexes.