Photosynthesized silver-polyaminocyclodextrin nanocomposites as promising antibacterial agents with improved activity

Ag nanocomposites were prepared by photoreduction of ammoniacal silver acetate in the presence of poly-{6-[3-(2-(3-aminopropylamino)ethylamino)propylamino]}-(6-deoxy)-β-CD (amCD). The obtained systems were characterized by means of various complementary techniques (UV-vis, FT-IR, TEM, SAED). In particular, FT-IR spectroscopy evidenced a partial oxidative degradation of the polyamine branches of the capping auxiliary, due to the fact that these groups function as a sacrificial reducing agent in the photoinduced formation of the Ag metal core. TEM and SAED micrographs showed that the Ag cores possess a relatively low polydispersity and a significantly crystalline character. The Ag-amCD systems were assayed for antibacterial activity, using Escherichia coli and Kocuria rhizophila as Gram-negative and Gram-positive tester strains respectively. In addition, the systems function as supramolecular drug carriers, able to bind the β-lactam antibiotic ampicillin, as demonstrated by polarimetric measurements. Antimicrobial assays revealed MIC90 values against E. coli and K. rhizophila as large as a 5 and 1 μg mL-1 respectively. Moreover, the interaction of the Ag-amCD with ampicillin resulted in a synergistic improvement of the antibacterial activity. This study provides insights on the attractive possibility to use a photochemical methodology to produce bioactive supramolecular systems to be employed as powerful and tunable antimicrobial agents.