Distinct Photolytic Mechanisms and Products for Different Dissociation Species of Ciprofloxacin

As many antibiotics are ionizable and may have different dissociation forms in the aquatic environment, we hypothesized that the different dissociation species have disparate photolytic pathways, products, and kinetics, and adopted ciprofloxacin (CIP) as a case to test this hypothesis. Simulated sun...

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Bibliographic Details
Published in:Environmental science & technology 2013-05, Vol.47 (9), p.4284-4290
Main Authors: Wei, Xiaoxuan, Chen, Jingwen, Xie, Qing, Zhang, Siyu, Ge, Linke, Qiao, Xianliang
Format: Article
Language:English
Subjects:
Anti-Bacterial Agents - chemistry
Antibiotics
Applied sciences
Aquatic ecology
Biological and physicochemical phenomena
Chromatography, High Pressure Liquid
Ciprofloxacin - chemistry
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Kinetics
Mass Spectrometry
Natural water pollution
Oxidation
Photochemistry
Photolysis
Pollutants
Pollution
Pollution, environment geology
Reaction kinetics
Water treatment and pollution
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Summary:As many antibiotics are ionizable and may have different dissociation forms in the aquatic environment, we hypothesized that the different dissociation species have disparate photolytic pathways, products, and kinetics, and adopted ciprofloxacin (CIP) as a case to test this hypothesis. Simulated sunlight experiments and matrix calculations were performed to differentiate the photolytic reactivity for each dissociation species (H4CIP3+, H3CIP2+, H2CIP+, HCIP0, and CIP–). The results prove that the five dissociation species do have dissimilar photolytic kinetics and products. H4CIP3+ mainly undergoes stepwise cleavage of the piperazine ring, while H2CIP+ mainly undergoes defluorination. For H3CIP2+, HCIP0, and CIP–, the major photolytic pathway is oxidation. By density functional theory calculation, we clarified the defluorination mechanisms for the five dissociation species at the excited triplet states: All the five species can defluorinate by reaction with hydroxide ions (OH–) to form hydroxylated products, and H2CIP+ can also undergo C–F bond cleavage to produce F– and a carbon-centered radical. This study is a first attempt to differentiate the photolytic products and mechanisms for different dissociation species of ionizable compounds. The results imply that for accurate ecological risk assessment of ionizable emerging pollutants, it is necessary to investigate the environmental photochemical behavior of all dissociation species.
ISSN:0013-936X
1520-5851
DOI:10.1021/es400425b