Recently,
the sulfate radical (SO4
•
–) has been found to exhibit broad application
prospects in various research fields such as chemical, biomedical,
and environmental sciences. It has been suggested that SO4
•
– could be transformed into
a more reactive hydroxyl radical (•OH); however,
no direct and unequivocal experimental evidence has been reported
yet. In this study, using an electron spin resonance (ESR) secondary
radical spin-trapping method coupled with the classic spin-trapping
agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and
the typical •OH-scavenging agent dimethyl sulfoxide
(DMSO), we found that •OH can be produced from three
SO4
•
–-generating systems
from weakly acidic (pH = 5.5) to alkaline conditions (optimal at pH
= 13.0), while SO4
•
– is the predominant radical species at pH < 5.5. A comparative
study with three typical •OH-generating systems
strongly supports the above conclusion. This is the first direct and
unequivocal ESR spin-trapping evidence for •OH formation
from SO4
•
– over a wide
pH range, which is of great significance to understand and study the
mechanism of many SO4
•
–-related reactions and processes. This study also provides an effective
and direct method for unequivocally distinguishing •OH from SO4
•
–.