Cu(II)-catalyzed degradation of ampicillin: effect of pH and dissolved oxygen
- 270 Downloads
Cu(II)-catalyzed hydrolysis of β-lactam antibiotics has been well-identified and recognized as the key mechanism of antibiotic degradation. However, the overlooked Cu(II) oxidation susceptibly also plays an important role comparably with hydrolysis. This study evaluated the roles of hydrolysis and oxidation in Cu(II)-catalyzed degraded ampicillin (AMP), as a typical β-lactam antibiotic, under relevant environmental conditions (pH 5.0, 7.0, and 9.0; oxygen 0.2 and 6.2 mg/L). Under AMP and Cu(II) molar ratio of 1:1, AMP degradation was the fastest at pH 9.0, followed by pH 5.0 and pH 7.0. The facilitation of oxygen on AMP degradation was notable at pH 5.0 and 7.0 rather than pH 9.0. AMP degradation rate increased from 21.8% in 0.2 mg/L O2 solution to 85.9% in 6.2 mg/L O2 solution at pH 7.0 after 4-h reaction. AMP oxidation was attributed to both oxygen-derived Cu(I)/Cu(II) cycle and intermediate reactive oxygen species (HO. and O2 .−). Several intermediate and final products in AMP degradation were firstly identified by LC-quadrupole time-of-flight-MS analysis. Phenylglycine primary amine on the AMP structure was the essential complexation site to proceed with the oxidation reaction. The oxidation of AMP preferentially occurred on the β-lactam structure. The inherent mechanisms related to pH and oxygen conditions were firstly investigated, which could enhance the understanding of both oxidation and hydrolysis mechanisms in AMP degradation. This study not only has an important implication in predicting β-lactam antibiotic transformation and fate in natural environment but also benefits the developing of strategies of antibiotic control to reduce the environmental risk.
Keywordsβ-Lactam antibiotics Ampicillin Copper redox Complexation Oxidation Hydrolysis
We thank the National Basic Research Program of China (grant 2015CB459000), National Science Foundation of China (grants 21577178 and 21622706), Guangdong’s Natural Science Funds for Distinguished Young Scholars (grant 2015A030306017), and Fundamental Research Funds for the Central Universities (grant 17lgpy93) for their financial support of this study.
- Clarke EGC, Moffat AC, Jackson JV, Moss MS, Widdop B (1986) Clarke’s isolation and identification of drugs in pharmaceuticals, body fluids, and post-mortem material, 2nd edn. The Pharmaceutical Press, LondonGoogle Scholar
- Gunther G (1950) The disintegration of penicillin in the presence of heavy metals. Die Pharmazie 5:577–582Google Scholar