Reevaluation of the Reactivity of Superoxide Radicals with a Sulfonamide Antibiotic, Sulfacetamide: An Experimental and Theoretical Study

• Published in: ACS ES&T water Vol. 1; no. 11; pp. 2339 - 2347
• Main Authors: Luo, Zonghao, Spinney, Richard, Wei, Zongsu, Hu, Wei-Ping, Villamena, Frederick A, Song, Weihua, Dionysiou, Dionysios D, Xiao, Ruiyang
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12.11.2021
• Subjects: reactivity; sulfonamide antibiotic; in situ long-path spectroscopic technique; DFT; superoxide radicals
• ISSN: 2690-0637; 2690-0637
• DOI: 10.1021/acsestwater.1c00193

Superoxide radical (O2 •–) is a ubiquitous reactive oxygen species in sunlit natural waters. Here, we selected sulfacetamide (SCT) as a representative sulfonamide antibiotic to investigate its reactivity with O2 •–, as this reaction was reported to be fast with the rate constant k of 7.0 × 107 M–1 s–1. The degradation kinetics of SCT were first studied in the classic McDowell systems (i.e., ultraviolet, acetone, and alcohols) for optimal O2 •– productivity. Comparison of the apparent first-order degradation rates (k app) revealed that 70 mM acetone and 1 M isopropanol were optimal for k app, but it was only ∼10% faster than the control. The small degree of enhancement of k app led us to suspect its high reported reactivity with O2 •–. Therefore, we reevaluated this reaction in organic and aqueous solutions by a suite of spectroscopic techniques, and all evidence indicated that the measured k values were 6 orders of magnitude smaller than the reported one. The low reactivity was also confirmed by theoretical calculations at the M06-2X level of theory. Our results are of practical and scientific importance for the holistic assessment of the role of O2 •– in remediation and attenuation of organic contaminants in natural and engineered waters.