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

Abstract

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.