SINGLET OXYGEN REACTIONS IN AQUEOUS SOLUTION. PHYSICAL AND CHEMICAL QUENCHING RATE CONSTANTS OF CROCIN AND RELATED CAROTENOIDS

Article abstract of DOI:10.1016/S0040-4039(00)95585-0

Thermal decomposition of 3-(1,4-epidioxy-4-methyl-1,4-dihydro-1-naphthyl)propionic acid (2) has been used to measure both the physical and chemical quenching rate constants of ¹O2 (k_Q and k_R, respectively) by water-soluble 8,8'-diapocarotenoids such as crocin (1a) and its derivatives (1b,c).The value of k_Q was found to be slightly lower than the diffusion controlled rate constant in all the solvents examined, whereas k_R showed strong dependence on the medium, going from ca. 10⁸ in H2O to 10⁶ M^-1s^-1 in DMF and DMSO.These findings suggest that both energy- and electron-transfer mechanisms are involved in the quenching of O2 (¹Δ_g) by crocinoids.