Carotenoid radical anions and their protonated derivatives,

Abstract:In this study, we report the protonation reactions for astaxanthin and canthaxanthin radical anions in methanol, alkaline methanol, and aqueous 2% Triton X-100 at different pH values. The pK_a values for the corresponding a-hydroxy radical derivatives of astaxanthin, canthaxanthin, and b-apo-8′-carotenal were estimated in 2% Triton X-100. Also, the effects of the microenvironment and the structure of the carotenoids on the protonation rate constant are discussed.