Nanostructured silver(I) complexes with a novel azo-quinoline ligand: Synthesis, characterization, and antibacterial activity

In this study, a novel azo-quinoline ligand, 5-[(E)-(3,4-dimethylphenyl)diazenyl]quinolin-8-ol (HQ), was synthesized via conventional diazotization and coupling reactions. The ligand was subsequently utilized to prepare a silver(I) coordination compound, [Ag(HQ)(Q)] (1), both as a bulk powder and in nanostructured form via a sonochemical synthesis using varying reagent concentrations. Characterization of the HQ ligand and compound 1 was carried out using FT-IR, UV-Vis, NMR, elemental analysis, and X-ray powder diffraction (XRD), confirming the successful synthesis and structural integrity of both the bulk and nanostructured materials. These nanoparticles exhibited inhibitory effects on the growth of Escherichia coli ( E. coli ) at concentrations of 0.0050, 0.0035, and 0.0025 mg/mL. However, they did not demonstrate inhibition against Staphylococcus aureus ( S. aureus ). The minimum inhibitory concentrations (MICs) for E. coli were determined to be 50, 35, and 25 μg/mL, respectively. The diameter of the E. coli growth inhibition zones caused by the nanoparticles decreased with decreasing concentrations, indicating a dose-dependent response. Antibiotics produced larger inhibition zones compared to the nanoparticles, suggesting superior antibacterial efficacy of the antibiotics. These findings underscore the selective antibacterial activity of the nanoparticles toward Gram-negative bacteria. Silver nanoparticles were successfully synthesized via solid-state thermal decomposition of the diazo compounds, used as novel precursors, at 500 °C and 600 °C in an electric furnace for 15 min, without employing any surfactant or reducing agent. Thermal decomposition of the nanocomplex resulted in phase-pure silver nanoparticles with a face-centered cubic (fcc) crystal structure, exhibiting particle sizes of approximately 26 nm at 500 °C. This study demonstrates a facile method for the synthesis of multifunctional silver-based nanomaterials with promising antibacterial properties and tunable physicochemical characteristics, highlighting their potential applications in nanomedicine and advanced materials.