Copper(II) binding to tobramycin: potentiometric and spectroscopic studies

Protonation and Cu(II) binding by tobramycin, an aminoglycosidic antibiotic, was studied by potentiometry and UV–vis, CD and EPR spectroscopies. A range of mononuclear complexes of a general formula CuHnL was found, with n between 3 and −2. Tobramycin anchors Cu(II) with an {NH2, O−} chelate of the C-ring of its molecule. The amino and hydroxyl groups of the A-ring of tobramycin also participate in the binding at pH 7 and higher. The resulting structure involves both terminal aminosugar rings but eliminates the donors of the central streptamine unit from the coordination. A comparison between tobramycin and its close analog, kanamycin B [M. Jeżowska-Bojczuk, W. Bal and H. Kozłowski, Inorg. Chim. Acta, 275–276 (1998) 541–545] reveals the importance of the A3-OH group for the binding properties of these aminoglycosides.