Sensitization of Peroxynitrite Chemiluminescence by the Triplet Carbonyl Sensitizer Coumarin‐525. Effect of CO2

Abstract

Abstract— The flash of spontaneous chemiluminescence (CL) that reflects the formation of electronically excited intermediates during the decay of peroxynitrite (ONOO) to nitrate was investigated. The half‐decay time of the CL flash (0.5 ± 0.1 s) was in agreement with the half‐life of peroxynitrite obtained in stopped‐flow experiments. The spontaneous CL intensity was linearly dependent on peroxynitrite concentration. The yield of spontaneous CL from peroxynitrite decay, 2 × 10‐9 photons/peroxynitrite at pH 9.5, was strongly enhanced by a sensitizer of triplet carbonyl CL, coumarin‐525 (C‐525). The maximal yield of sensitized CL was calculated to be 3 × 10‐6 photons/ peroxynitrite molecule for infinite concentration of C‐525. The dependence of both spontaneous and sensitized CL on pH has a maximum at about pH 9.5. Bubbling with CO2 or addition of NaHCO3 considerably enhanced the flash of CL, and it is concluded that the reaction of the peroxynitrite anion with CO2 is a major pathway leading to the formation of an electronically excited intermediate of peroxynitrite.