Effect of environmental factors on the oxidative transformation of cephalosporin antibiotics by manganese dioxides

Abstract

This study aimed to explore the oxidation and transformation of the cephalosporins cefotaxime (CTX), cephalexin (CFX), cephradine (CFD), cephapirin (CFP) and cefazolin (CFZ) by δ-MnO₂. The results showed that the MnO₂ oxidation rate was promoted by environmental factors such as higher MnO₂ loading, lower initial cephalosporin concentration and lower solution pH. The inhibitory effect occurred in the presence of dissolved organic matter and dissolved cations (inhibitory capacity: Mn²⁺ > Ca²⁺ > Mg²⁺ > Fe³⁺). Total organic carbon analysis indicated that the transformation byproducts of the cephalosporins are less reactive and persistent under MnO₂ oxidation. Twelve transformation byproducts (9 CFP byproducts and 3 CTX byproducts) were identified, and two oxidative transformation pathways were proposed: one occurred in the cephem for CFP, and the other occurred at the substituent at the amine position for CTX. The effect of solar light on the oxidation of the five cephalosporin antibiotics by δ-MnO₂ was also investigated, and the results indicated that the initial dissolution rate of δ-MnO₂ under sunlight was approximately eight times faster than that in the dark in the presence of CFP.