Constants of acid‒base equilibria in an aqueous amikacin aminoglycoside solution at 298 K

Abstract

The acid dissociation constants of form pK1 = 7.34 ± 0.01, pK2 = 7.84 ± 0.01, pK3 = 8.77 ± 0.01, pK4 = 9.49 ± 0.01, and pK5 = 10.70 ± 0.02 of cationic amikacin are determined by pH-metric titration at 25°C against the background of 0.1 mol/L KNO3. K1, K2, K3, and K4 correspond to the dissociation of protons coordinated to amino groups, while K5 characterizes the dissociation of the hydroxyl hydrogen atom, testifying to the amphoteric character of amikacin molecules. Applying density functional theory (DFT) with the B3LYP hybrid functional and the 6-311G**++ basis set, the partial charges on the atoms of an amikacin molecule are calculated. It is concluded that the dissociation of H(55)hydrogen atom occurs with a greatest partial charge of +0.53631.