Delineation of conformational and structural features of the amikacin–Cu(II) complex in water solution by 13C-NMR spectroscopy

The copper (II) complex of amikacin in water solution at pH 5.5 was investigated by 13 C-NMR. The temperature dependence of spin–lattice relaxation rates was measured and fast exchange conditions were shown to apply. The motional correlation time of the complex was approximated by the pseudo-isotropic rotational correlation time of free amikacin in water solution ( τ c =0.17 ns at 300 K). Formation of a pseudo-tetrahedral 1:1 complex was demonstrated by relaxation rates analysis and also by UV–Vis spectrophotometry. Two amino nitrogens of amikacin, together with the amide nitrogen and the hydroxyl in the hydroxyl–aminopropyl carbonyl side chain, were assigned as the copper-binding sites and a model of the complex was built by using copper–carbon distances obtained by NMR analysis as input parameters.