Solvent influence on the kinetics of the photodynamic degradation of trolox, a water-soluble model compound for vitamin E

S. Nonell, L. Moncayo, F. Trull, F. Amat-Guerri, E. A. Lissi, A. T. Soltermann, S. Criado, N. A. García

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Resum

The kinetics of the aerobic dye-sensitized photo-oxidation of 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), a water-soluble model compound for vitamin E, has been studied in aqueous solutions of pH values 6 and 12 and in organic media of different polarity. Experimental evidence indicates that the process largely occurs through a Trolox-singlet molecular oxygen O2(1Δg) interaction, the photo-oxidation rates increasing with the pH value and the polarity of the medium. Low polarity solvents favour the physical quenching of O2(1Δg) by Trolox, as already observed in other tocopherols. High polarity solvents drive the interaction predominantly towards a reactive pathway that yields the same substituted p-benzoquinone that can be obtained by thermal oxidation of Trolox. Overall rate constants for the quenching of O2(1Δg) by Trolox (determined by time-resolved phosphorescence spectroscopy) and reactive rate constants (obtained by relative methods) are both in the range 107-108 M-1s-1. On the basis of these and their results and their comparison with previous results on the photo-oxidation of tocopherol derivatives, the role of the solvent in the behaviour of vitamin E is discussed.

Idioma originalAnglès
Pàgines (de-a)157-162
Nombre de pàgines6
RevistaJournal of Photochemistry and Photobiology, B: Biology
Volum29
Número2-3
DOIs
Estat de la publicacióPublicada - d’ag. 1995

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