Allergic products from penicillin G transformation driven by Cu^II species-catalyzed sequential hydrolysis and...

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 Cu^II ions also play an oxidative role of Cu^II 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 Cu^II speciation and quantitative analysis of transformation products, especially for the allergic hydrolysate penicilloic acid, were lacking. Hence, this study systematically investigated the Cu^II-mediated transformation of PG under anoxic conditions. The results indicated that PG degradation was significantly pH-dependent in relation to the speciation of Cu^II-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 Cu^II 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.