Bicarbonate Enhanced Photolysis of 5-Fluorouracil in Aqueous Environment
Date Issued
2014
Date
2014
Author(s)
Lu, Yi-Tsung
Abstract
5-fluorouracil is an antineoplastic drug that has been widely used in colorectal and pancreatic cancer treatment over the past 40 years, and its presence in aqueous environments is a potential risk to ecological systems and humans. Sunlight photodegradation is one of the most significant natural attenuation processes for various emerging contaminants. Dissolved organic matter, nitrates and bicarbonate enhanced nitrate systems are known photosensitizers. In this study, the action of bicarbonate alone was found to increase the direct photolysis rate of 5-fluorouracil for the first time, and the reaction mechanism was investigated. The half-lives of direct and bicarbonate enhanced photolysis were 24.5 ± 4.6 h and 11.5 ± 1.3 h (at pH 7), respectively. The reaction was fastest at pHs 9 and 8, followed by pHs 7 and 6.
The primary pathway for the direct photolysis of 5-fluorouracil was photohydration, which resulted in a hydration product, 5-fluoro-6-hydroxyhydrouracil (5FUHy). 5FUHy is resistant to direct and indirect photolysis and was degraded by less than 20% in Jingmei River (JMR) water. The yields of 5FUHy by direct photolysis at pHs 6, 7, 8 and 9 were 64%, 63%, 53% and 12%, respectively. In bicarbonate enhanced photolysis, the 5FUHy yields decreased to 59%, 40%, 14% and 1.3% at pHs 6, 7, 8 and 9, respectively. A model of 5-fluorouracil photolysis was developed and used to predict that the bicarbonate directly reacted with the excited state of 5-fluorouracil but did not enhance the photohydration process. Other photodegradation byproducts and pathways were also proposed. The presence of bicarbonate was found to increase the 5-fluorouracil photolysis rates through pathways other than photohydration by changing the proportions of the photodegradation byproducts and the fate of pollutants. The model predicted the yield of 5FUHy in JMR water accurately, demonstrating that the actions of nitrate and dissolved organic matter in the photohydration process were not as significant as those of bicarbonate and pH.
The phenomenon of bicarbonate enhanced photolysis was also shown with methotrexate. However, its degradation mechanism was different from that of 5-fluorouracil, indicating that the enhancement was compound dependent.
Subjects
抗癌藥物
五氟尿嘧啶
碳酸氫根離子
光解
光水解
SDGs
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-103-R01541132-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):55dc2744e9c7ab3e5fafaf7697366584