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

The copper (II) complex of amikacin in water solution at pH 5.5 was investigated by 13C-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 (tau 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.