Singlet oxygen reactivity of bilirubin and related tetrapyrroles

Summary The rates of chemical reactivity (k_R) and physical quenching (k_Q) of singlet oxygen by bilirubin IX, mesobilirubin IX, bilirubin IX dimethyl ester, aetiobilirubin IV, biliverdin IX, biliverdin IX dimethyl ester, aetiobiliverdin IV and an oxodipyrromethene have been determined. The k_R and k_Q values approach the diffusion threshold for the bilirubin-like substrates, but k_RQ by about a factor of 10³ for the verdins. A reaction mechanism involving superoxide ion is suggested. Bilirubin appears to quench singlet oxygen by an electron-transfer mechanism.The authors wish to thank the National Science Foundation (CHE 74-20877) and the National Institute of Child Health (HD 09026) for generous support of this work.