Exploring the Biological Activity of Organically Ligated Metal–Peroxo Complexes

Metal-based complexes have attracted considerable attention due to their diverse biological activities and potential applications as antimicrobial agents. In this study, a series of previously synthesized metal complexes of Molybdenum(VI), Uranium(VI), Zirconium(IV), and Thorium(IV) were systematically evaluated to investigate their antifungal, antibacterial, and cytotoxic properties. The primary objective of this work was to assess the bioactive potential of these complexes and to identify promising candidates for antimicrobial applications. The antifungal activity of the complexes was examined against <i>Aspergillus</i><i> </i><i>niger</i>, <i>A. </i><i>fumigatus</i>, and <i>A. </i><i>flavus</i> using the agar diffusion method. Antibacterial efficacy was determined by minimum inhibitory concentration (MIC) assays against both Gram-negative (<i>Pseudomonas </i><i>aeruginosa</i> and <i>Escherichia coli</i>) and Gram-positive (<i>Streptococcus</i> β-haemolyticus and <i>Bacillus </i><i>subtilis</i>) bacterial strains. Cytotoxicity was evaluated using the brine shrimp lethality assay as a preliminary indicator of biological safety. The results demonstrated that all tested complexes exhibited varying degrees of antifungal and antibacterial activity. Notably, the Mo(VI) complex 2 showed the highest antifungal activity against <i>A. </i><i>flavus</i>, producing a zone of inhibition of 14 mm. In antibacterial studies, Mo(VI) complex 4 displayed the lowest MIC values, indicating superior antibacterial potency, followed by the U(VI) complex 8, while Th(IV) complexes showed comparatively weaker activity. Cytotoxicity assessment revealed that Mo(VI) complex 5 exhibited the highest toxicity, whereas complexes 1 and 2 were comparatively less toxic. Overall, the findings suggest that Mo(VI) complexes possess significant antimicrobial potential and represent promising candidates for further development as bioactive agents.