Allergic products from penicillin G transformation driven by CuII species-catalyzed sequential hydrolysis and oxidation: Mechanism and kinetic model.

In aquaculture wastewater, both penicillin G (PG) and heavy metal ions, used as animal feed additives, often coexist and can be transported as complexes into groundwater. Previous studies have found some metal ions can enhance hydrolysis of β-lactam antibiotics, while CuII ions also play an oxidative role of CuII on the transformation of phenylglycine penicillins and cephalosporins in the presence of oxygen. PG was suggested to undergo hydrolysis followed by oxidation according to the reaction mechanism; however, some detailed evidence regarding the effect of CuII speciation and quantitative analysis of transformation products, especially for the allergic hydrolysate penicilloic acid, were lacking. Hence, this study systematically investigated the CuII-mediated transformation of PG under anoxic conditions. The results indicated that PG degradation was significantly pH-dependent in relation to the speciation of CuII-PG complexes at pH 5.0-9.5. Transformation products mainly included penicilloic acid (PA) as hydrolysis product and 2-phenylacetamide (PAA) as oxidation product. Complexation spectral analysis indicated that CuII coordinates with the carboxyl group on the five-membered ring of PG and the amide nitrogen of the lactam ring, which is responsible for rapid hydrolysis of β-lactam ring. Meanwhile, a species-dependent kinetic model supported the hypothesis of sequential hydrolysis followed by oxidation with quantitatively global kinetic fitting of PG-PA-PAA pathway.