Determination of Singlet Oxygen Rate Constants in Aqueous Solutions

Abstract— A very efficient quenching of singlet oxygen ( 1 O 2 ) by N 3 ‐ ions has been applied to the determination of rate constants of reactions of 1 O 2 with various substrates (A). This determination has been made possible by choosing experimental conditions which give simple competition between N 3 ‐ and A for 1 O 2 formed in the steady state irradiation of convenient sensitizing dye (S). The consumption of oxygen by the substrate, as followed with an oxygen analyzer, decreases in the presence of low concentrations of N 3 ‐ . Using neutral air saturated aqueous solutions containing the dye phenosafranine + A and varying concentrations of N 3 ‐ , the 1 O 2 rate constants for reactions with biological substrates and some radiation protective agents have been determined.