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 ran ge of mononuclear complexes of a general formula CuHnL was found, with n be tween 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 tobr amycin also participate in the binding at pH 7 and higher. The resulting st ructure involves both terminal aminosugar rings but eliminates the donors o f the central streptamine unit from the coordination. A comparison between tobramycin and its close analog, kanamycin B [M. Jezowska-Bojczuk, W. Bal a nd H. Kozlowski, Inorg. Chim. Acta, 275-276 (1998) 541-545] reveals the imp ortance of the A3-OH group for the binding properties of these aminoglycosi des. (C) 1998 Elsevier Science Ltd. All rights reserved.