THE PHOTOPEROXIDATION OF UNSATURATED ORGANIC MOLECULES—XV. O₂1δg QUENCHING BY BILIRUBIN AND BILIVERDIN

Abstract —The use of competitive methods with rubrene as reference acceptor provides values of the rate constants k B Q = 2.3 times 10 9 / mol ‐1 s ‐1 and k v q = 3.3 times 10 9 mol ‐1 s ‐1 for the physical quenching of O 2 1 δg, by bilirubin (in CCl 4 ) and biliverdin (in CHCl 3 ) respectively attributed to electron and energy transfer processes. The rate constant k B R = 1.7 times 10 8 / mol ‐1 s ‐1 for bilirubin reaction with O 2 1 δg is considerably greater than that k v R 3 times 10 8 mol ‐ s ‐1 for the reaction of biliverdin which has identical O 2 1 δa, acceptor sites, and is attributed to a primary Type I oxidation process followed by a slower Type II addition of O 2 1 δg to the primary products.