Identification of Copper( II ) Binding Sites in the Aminoglycosidic Antibiotic Neomycin B

Protonation and copper( II ) coordination properties of neomycin B were studied in solution by potentiometry, NMR, UV/Vis, CD, and EPR spectroscopy, XAS and mass spectrometry. Mono‐ and dinuclear complexes were found depending on the metal‐to‐ligand molar ratio. Neomycin B anchors Cu II ions above pH 5.0 with an NH 2 group from ring B. Simultaneously, the second amino group of the same ring and the hydroxyl group of ring A complete the binding set of donors. With an increase in pH the remaining –NH 3 + functional groups in the neomycin B molecule are deprotonated without affecting the complexation pattern. However, these groups, particularly the ones located in the D ‐ring of the antibiotic, may coordinate the second copper( II ) ion when the metal is present in excess. We have proved this process with the use of potentiometry, CD and especially mass spectrometry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)