TY - JOUR
T1 - Pitfalls in Probing Singlet Oxygen by Electron Paramagnetic Resonance Spectroscopy in Engineered Environmental Systems
AU - Zong, Yang
AU - Chen, Long
AU - Wu, Jing Hang
AU - Liu, Fuqiang
AU - Guan, Xiaohong
AU - Lei, Zhendong
AU - Xu, Jun
AU - Wu, Deli
AU - Liu, Wen
AU - Yu, Han Qing
PY - 2026/1/13
Y1 - 2026/1/13
N2 - Sterically hindered amine (SHA)-based electron paramagnetic resonance spectroscopy (EPR) is still widely used to detect singlet oxygen (1O2) in engineered environmental systems. Nevertheless, the reliability and interpretability of EPR are limited by the insufficient knowledge of the mechanism of SHA transformation to the nitroxide radical (the 1O2 indicator). Here, we systematically investigate the pitfalls and limitations of EPR in detecting 1O2. We find that multiple non-1O2 species, including sulfate radical (SO4•-), hydroxyl radical (HO•), iodate radical (IO3•), high-valent iron, direct electron transfer (DET), etc., could drive the SHA-to-nitroxide radical transformation, hence severely interfering with 1O2 detection. The nitroxide radicals are generated via two distinct patterns dependent on the steric hindrance of non-1O2 species. One is SO4•-/IO3•/DET-driven single electron transfer with H2O and ground-state O2 participation. The other is HO•/high-valent iron-mediated hydrogen atom abstraction and radical coupling/oxygen-rebounding. Unexpectedly, pH, rather than 1O2, governs the EPR results by modulating the SHA probe distributions and controlling the deprotonation processes, further contributing to the invalidity of EPR in probing 1O2 under environmental-relevant conditions. This study uncovers the fundamental flaws of EPR for 1O2 detection, enabling a more accurate interpretation of EPR data for 1O2 identification.
AB - Sterically hindered amine (SHA)-based electron paramagnetic resonance spectroscopy (EPR) is still widely used to detect singlet oxygen (1O2) in engineered environmental systems. Nevertheless, the reliability and interpretability of EPR are limited by the insufficient knowledge of the mechanism of SHA transformation to the nitroxide radical (the 1O2 indicator). Here, we systematically investigate the pitfalls and limitations of EPR in detecting 1O2. We find that multiple non-1O2 species, including sulfate radical (SO4•-), hydroxyl radical (HO•), iodate radical (IO3•), high-valent iron, direct electron transfer (DET), etc., could drive the SHA-to-nitroxide radical transformation, hence severely interfering with 1O2 detection. The nitroxide radicals are generated via two distinct patterns dependent on the steric hindrance of non-1O2 species. One is SO4•-/IO3•/DET-driven single electron transfer with H2O and ground-state O2 participation. The other is HO•/high-valent iron-mediated hydrogen atom abstraction and radical coupling/oxygen-rebounding. Unexpectedly, pH, rather than 1O2, governs the EPR results by modulating the SHA probe distributions and controlling the deprotonation processes, further contributing to the invalidity of EPR in probing 1O2 under environmental-relevant conditions. This study uncovers the fundamental flaws of EPR for 1O2 detection, enabling a more accurate interpretation of EPR data for 1O2 identification.
KW - 18O isotope tracing
KW - advanced oxidation process
KW - nitroxide radical
KW - reactive oxygen species
KW - singlet oxygen detection
UR - https://www.scopus.com/pages/publications/105027372727
U2 - 10.1021/acs.est.5c09862
DO - 10.1021/acs.est.5c09862
M3 - 文章
C2 - 41422401
AN - SCOPUS:105027372727
SN - 0013-936X
VL - 60
SP - 1392
EP - 1402
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 1
ER -