Singlet oxygen quenching by trolox C in aqueous micelle solutions
Singlet oxygen (1O2) 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 1O2 phosphorescence at 1274 nm. The second-order rate-constant for 1O2 quenching by TC was determined in the ethanol–water solution to be 1.03 × 108, 6.22 × 107 and 6.23 × 107 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 1O2 at first decreased and then increased with increase of the concentration of TC. This behavior is explained in terms of the 1O2 quenching by TC in the bulk phase and in terms of shifting the environment surrounding 1O2 to lipophilic by dissolving TC in the hydrophobic region inside the micelle. The present investigation on 1O2 emission dynamics in inhomogeneous solutions made it possible to detect a little change in the solutions, which affects the environment around 1O2, such as the micelle formation and dissolving solute in the micelle.
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 97, Issue 3, 2 December 2009, Pages 132–137