Singlet oxygen reactivity in water-rich solvent mixtures

Abstract

The 3-methylindole (3MI) oxygenation sensitized by psoralen (PSO) has been investigated in 100%, 20% and 5% O2-saturated water/ dioxane (H 2O/Dx) mixtures. The lowering of the 1O2 * chemical rate when water (kchemΔ3MI = 1.4 × 109 M-1 s-1) is replaced by deuterated water (kchemΔ3MI = 1.9 × 108 M-1 s -1) suggests that hydrogen abstraction is involved in the rate determining step. A high dependence of the chemical rate constant on water concentration in H2O/Dx mixtures was found showing that water molecules are absolutely essential for the success of the 3MI substrate oxidation by 1O2 * in water-rich solvent mixtures.