Sensitization of peroxynitrite chemiluminescence by the triplet carbonyl sensitizer coumarin-525. Effect of CO2

The Bash 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 Bash (0.5 +/- 0.1 s) was in agreement with the half-life of peroxynitrite obtained i n stopped-flow experiments. The spontaneous CL intensity was linearly depen dent on peroxynitrite concentration. The yield of spontaneous CL from perox ynitrite decay, 2 x 10(-9) photons/peroxynitrite at pH 9.5, was strongly en hanced by a sensitizer of triplet carbonyl CL, coumarin-525 (C-525), The ma ximal yield of sensitized CL was calculated to be 3 x 10(-6) photons/peroxy nitrite molecule for infinite concentration of C-525. The dependence of bot h spontaneous and sensitized CL on pH has a maximum at about pH 9.5, Bubbli ng with CO2 or addition of NaHCO3 considerably enhanced the Bash 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 interm ediate of peroxynitrite.