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

Abstract

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.

Mechanistic Understanding of Superoxide Radical-Mediated Degradation of Perfluorocarboxylic Acids

“…The in situ long-path spectroscopic approach used to generate O 2 •– in aqueous solutions was described in our previous study in great detail. , Briefly, O 2 •– was generated by 30 s UV irradiation of a buffered solution containing 5 μM DTPA, 5 mM H 2 O 2 , and 5 mM FA at pH 8. Because small quantities of metal ions ( e.g., Fe 3+ , Cu 2+ , etc. )…”

“…The identification of O 2 •− generated in the aqueous solutions has been confirmed by both comparing the UV spectra under pulse radiolysis and chromogenic reactions with nitro-blue tetrazolium (NBT), which has been discussed in great detail in our previous studies. 31,32 Generation of O 2…”

Response to Comment on “Mechanistic Understanding of Superoxide Radical-Mediated Degradation of Perfluorocarboxylic Acids”

“…reported the k value of sulfacetamide (SCT), a representative antibiotic, and O 2 •– to be fast with the rate constant k of 7.0 × 10 7 M –1 s –1 . We reevaluated this k value in a recent study, and all experimental and theoretical evidence indicated that the measured k value is 6 orders of magnitude smaller than the reported one . In addition, two studies reported that O 2 •– is linked to fast degradation of PFOA, , which is contradictory to the study by Javed et al .…”

“…22 We reevaluated this k value in a recent study, and all experimental and theoretical evidence indicated that the measured k value is 6 orders of magnitude smaller than the reported one. 23 In addition, two studies reported that O 2…”

Effect of cold plasma on different polyphenol compounds: A review

“…The various radicals and anions formed by the two pathways are shown in Figure 3b,c. The nucleophilic nature of superoxide radicals would inhibit a radical/nucleophilic attack on the benzene ring (Bai et al, 2021; Luo et al, 2021). Moreover, the benzene ring has a high electron density due to the hydroxide group that would enhance repulsion to the negatively charged superoxide radical anion, thereby slowing the reaction (Min et al, 2022).…”