Aqueous oxidation degradation of ciprofloxacin involving hydroxyl and sulfate radicals: A computational investigation

Abstract

Aqueous oxidative degradation mechanism of three forms of ciprofloxacin (CIP) involving hydroxyl (OH) and sulfate radicals (SO4−) was investigated by performing density functional theory (DFT) calculation at the M06-2X/6–311 + G(d,p) level. The computational results indicated that hydrogen abstraction (HA) pathways occurring on piperazine ring were the most favorable in all plausible parallel channels. Electron transfer (ET) reactions between CIP and OH (SO4−) were impossible to occur. HA reactivities correlated well with the involved CH bond lengths and atomic charges of the abstracted H atoms. Compared with OH, SO4− was a stronger oxidant in degrading CIP. Piperazine ring cleavage was the main pathway in the early stage of CIP degradation involving OH (SO4−). Dissolved oxygen in water and water molecules could play significant roles in the oxidative degradation of CIP.