Direct Observation of Intermediates in the Reaction of Peroxynitrite with Carbon Dioxide

Peroxynitrite (ONOO⁻, oxoperoxonitrate(1−)) reacts with carbon dioxide to form an adduct that absorbs with a maximum at 640 nm and an extinction coefficient of ca. 2 × 10² M ⁻¹ cm⁻¹. Within 0.1 s at 4°, this absorption decreases while the maximum is shifted to lower wavelengths, which indicates that trioxocarbonate(1−) radicals (CO₃^.−) are formed. This interpretation is supported by the observation of a weak ESR signal at g=2.013.