Silica nanoparticles-supported heterometallic Mo₆Ag₆nanoclusters with enhanced antibacterial and antibiofilm...

In this work, we present the heterometallic polynuclear complex [Mo₆I₈(BTA-Ag(tBuXPhos))₆](OTf)₄ as an antibacterial agent. This complex binds six lipophilic Ag(I) phosphine (tBuXPhos) complexes to the photodynamically active {Mo₆I₈}^4 + cluster via the apical 1,2,3-benzotriazole (BTA) ligand. We showed that the insufficient solubility of this complex in water leads to the formation of its self-aggregates, which exhibit further aggregation in saline and nutrient media, and this is a factor limiting the Gram-selective antibacterial activity of the complex. We also demonstrate that electrostatically mediated adsorption of the complex on the surface of silica nanoparticles is a convenient tool for enhancing the antibacterial activity of the complex, which is most pronounced against S. aureus and is further enhanced upon light irradiation due to the photodynamic activity of the {Mo₆I₈}⁴⁺ cluster core. As demonstrated for S. aureus, both the bacteriostatic and bactericidal effects of the complex are primarily due to depolarization rather than cell membrane lysis, which is characteristic of ion-channel-forming antimicrobial agents. The complex, both in self-aggregated form and as silica nanoparticles modified with the complex, exhibits high antibiofilm activity, significantly inhibiting biofilm formation and destroying existing biomass even at concentrations below the minimum inhibitory concentration (MIC).