| Enrofloxacin is one of the most common veterinary antibiotics, which is widely used in aquaculture, graziery, and agriculture. Because of the extensice use of this antibiotic, residual enrofloxacin is excreted into sewage treatment plants with domestic sewage and medical wastewater. Conventional water treatment processes are inadequate to degrade the contaminant, so residual contaminant discharge to surface waters with wastewater plant effluents. In recent years, enrofloxacin was detected frequently in waters and wasterwater plants, the detection concentrations ranged from ng/L to μg/L. What’s more, its product ciprofloxacin(CIP), as one of the common antibiotics, was also detected frequently. The principal risk of residual enrofloxacin is inducing the generation of antibiotic resistant bacteria, which have serious threat on human health and environment. Currently, the degradation of enrofloxacin mostly by chemical oxidation, the oxidants including permanganate, manganese dioxide, ozone, chlorine dioxide, etc.. Among these oxidants, permanganate has some attractive characteristics, including high selectivity, stability and so on, making it a promising oxidant for removing micropollutions in water, especially in organic-rich matrix. Therefore, this study chose permanganate as the oxidant to react with enrofloxacin. Quadrupole-Time of flight(Q-TOF) tandem mass spectrometer was used to obtain the accurate molecular weights of the oxidation products. It can provide a fast and accurate technology for developing effective degradation methods in the area of water.This study discussed the reaction of enrofloxacin and its main product ciprofloxacin with permanganate. Q-TOF was used to identificate their oxidation products, and reaction pathways of enrofloxacin with permanganate was proposed, providing essential information for the following antibacterial activity experiments. The antibacterial activities of solutions with or without reaction with permanganate were assessed by quantitative biological experiments.The antibacterial activities of solutions were evaluated by both the mixure of products and the isolated product. Both agar plate assays and optical density assays were performed. As one of the main products of enrofloxacin, the mixture products and isolated product after separation of ciprofloxacin with permanganate were also assessed with optical density assays. Finally, the relationship between the structures of enrofloxacin products and their antibacterial activities was analyzed.The reaction of enrofloxacin with permanganate generated four main products with mass-to-charge ratio(m/z) 362.1515(E5), 334.1568(E4), 332.1410(E3 / CIP), 376.1672(E7), respectively, and five minor products with m/z 263.0828(E1), 306.1252(E2), 374.1515(E6), 390.1472(E8) and 392.1622(E9), respectively. One of the main products of enrofloxacin is ciprofloxacin(E3). In this study, a new product of enrofloxacin was also detected, which is an N-oxide. The adding radio of permanganate, reaction time, p H and phosphate buffer have no effect on the species of enrofloxacin main products, but have significant effects on the abundances of the products. The reaction of ciprofloxacin with permanganate generated two main products with m/z 334.1240(C1), and 306.1248(C2), respectively.There are three main pathways of the reaction of enrofloxacin with permanganate, namely N-dealkylation, C-hydroxylation, and amine oxidation. The reaction mainly occurs on the piperazine ring of the compound, the quinolone core remains intact for each product.In addition,this study established a method to separate and concentrate the mixture of products, and quantitative assess on the antibacterial activity of the isolated product. Evaluation of tne antibacterial activities of solutions were employed with agar plate assays and optical density assays, respectively. Agar plate assay is easy to operate, requires less wxperimental equipment, with mature method, and the rate of bacteria growth can also be observed. This method is suitable for limited laboratory conditions; optical density assay has the characters that can assess the antibacterial quantitatively with less work-load, the experimental period is short, repeatability is good. This method is suitable for good laboratory conditions, or experiments which require short experimental time.The antibacterial activities of the mixture of the products indicate that the antibancterial activities of the reacted solutions are barely changed compared to the initial solutions. The antibacterial activity of each isolated main product indicates that the antibacterial activity of each main product decreases slightly compared to their parent compound- enrofloxacin, but doesn’t completely disappear. The log(EC50) of the oxidation products of both enrofloxacin and ciprofloxacin have the positive correlation with moleculat weight. With the increase of molecular weight, the absolute value of the log(EC50) of the oxidation product increases, indicating the enhanced antibacterial activity. For enrofloxacin, although after the degradation by permanganate, all the oxidation products remains the quinolone core intact, but the degradation on the substituent groups of piperazine ring can also change their antibacterial activities. |
PDF Full Text Request