NMR and EPR Structural Delineation of Copper(II) Complexes Formed by Kanamycin A in Water

The complexes formed by kanamycin A at three different pH values (5.5, 7.4 and 12.0) were investigated by NMR and EPR spectroscopy. The interaction of the Cu(II) ion with the nitrogen of the C ring is apparent at all pH values. At higher pH also the amino group of ring A starts to be involved in the metal coordination sphere. This is accompanied by a switch in conformation of ring C. Structures are consistent with the involvement in the coordination sphere either of the 2 or 4 hydroxyl oxygens at pH 5.5 and the 5 and the 6 hydroxyl oxygens (or the ring oxygen) at pH 12.0.