Abstract
The oxidation of cefalexin (CFX), a commonly used cephalosporin antibiotic, was investigated by permanganate (PM) in water. Apparent second-order rate constant of the reaction between CFX and PM was determined to be 12.71 ± (1.62) M−1·s−1 at neutral pH. Lower pH was favorable for the oxidation of CFX by PM. The presence of Cl− and HCO3− could enhance PM-induced oxidation of CFX, whereas HA had negligible effect on CFX oxidation by PM. PM-induced oxidation of CFX was also significant in the real wastewater matrix. After addition of bisulfite (BS), PM-induced oxidation was significantly accelerated owing to the generation of Mn(III) reactive species. Product analysis indicated oxidation of CFX to three products, with two stereoisomeric sulfoxide products and one di-ketone product. The thioether sulfur and double bond on the six-membered ring were the reactive sites towards PM oxidation. Antibacterial activity assessment indicated that the activity of CFX solution was significantly reduced after PM oxidation.
Highlights
The β-lactam antibiotics, including penicillins and cephalosporins, are among the most extensively used antibiotics in human and veterinary medicine [1]
We further investigated the impact of Humic acid (HA) on the oxidation of CFX by PM, and the result showed that PM-induced oxidation of CFX was not affected by various concentrations of HA (Figure 3C)
To investigate whether the products possess biological activity, we further evaluated the antibacterial activity of the transformation products of CFX by PM with E. coli as the tested bacteria
Summary
The β-lactam antibiotics, including penicillins and cephalosporins, are among the most extensively used antibiotics in human and veterinary medicine [1]. Because β-lactam antibiotics developed at early stage, e.g., penicillin G, are susceptible to acid/β-lactamase catalyzed hydrolysis, their occurrence in the environment is scarcely reported. With the development of pharmacology, some β-lactam antibiotics are designed to be acid-stable and β-lactamase resistant, they are frequently detected in the environment [2]. Cefalexin (CFX), one of the most frequently used first generation cephalosporins, is relatively stable in aquatic environments. It has been widely detected in different water matrices, such as wastewater, surface water and even coastal water with the concentration up to μg·L−1 [3,4,5]. The residual antibiotics in the environment could lead to adverse effects on non-target organisms, pose risk to drinking water supplies and increase the bacterial resistance [6]
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