Insight into Mn(II)-mediated transformation of β-lactam antibiotics: The overlooked hydrolysis

Manganese II (Mn(II)) is a common metal ion in the environment, but its role in the transformation of beta-lactam antibiotics is still unknown. This work found that Mn(II) could induce the transformation of beta-lactam antibiotics in aqueous solutions. Mn(II)-mediated degradation of ampicillin (AMP) followed first-order kinetics in the initial 12 h at pH 9.0, but gradually slowed down in the presence of oxygen owing to the oxidation of Mn(II) by oxygen. The initial rate constants of AMP linearly increased with increasing Mn(II) concentration, but was independent of AMP concentration. Degradation of AMP induced by Mn(II) was observed at neutral and slight alkaline pHs, but not at acidic pH. The Mn(II)promoted degradation was also significant in real water matrices. Product identification indicated that only the isomers of hydrolysis products were observed without detection of oxidation products. The promoted degradation likely occurred via complexation of carboxyl group and tertiary nitrogen on beta-lactam antibiotics and subsequent hydrolytic cleavage of beta-lactam ring catalyzed by Mn(II). This study elucidates the role of Mn(II) in the environmental transformation of beta-lactam antibiotics which has not been recognized before. This new discovery further supports the important role of Mn species in the environmental fate of beta-lactam antibiotics. (C) 2017 Elsevier B.V. All rights reserved.