Singlet oxygen quenching by trolox C in aqueous micelle solutions

Abstract

Singlet oxygen ( 1O 2) quenching by trolox C (TC, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), which is a water-soluble vitamin E analogue, in ethanol–water solutions and in aqueous SDS and CTAC micelles was studied by measuring the time-profiles of 1O 2 phosphorescence at 1274 nm. The second-order rate-constant for 1O 2 quenching by TC was determined in the ethanol–water solution to be 1.03 × 10 8, 6.22 × 10 7 and 6.23 × 10 7 M −1 s −1 at pH 2.0, 7.0, and 8.4, respectively. These values mean that the non-dissociated form of TC under acidic conditions has superior activity to the mono-anion form. In aqueous micelle systems, the decay rate of 1O 2 at first decreased and then increased with increase of the concentration of TC. This behavior is explained in terms of the 1O 2 quenching by TC in the bulk phase and in terms of shifting the environment surrounding 1O 2 to lipophilic by dissolving TC in the hydrophobic region inside the micelle. The present investigation on 1O 2 emission dynamics in inhomogeneous solutions made it possible to detect a little change in the solutions, which affects the environment around 1O 2, such as the micelle formation and dissolving solute in the micelle.