Time-Resolved EPR Investigation of the Photo-initiated Intramolecular Antioxidant Reaction of Vitamin K−Vitamin E Linked Molecule

The models of vitamin K and vitamin E linked molecule, (1-(1,4-naphthoquinone-2-oxy)-6-(hydroxy-2,5,7,8-tetramethylchroman-2-carbonyloxy)-hexane), was synthesized as a model of vitamin K and vitamin E which coexist in biological membranes. The time-resolved EPR (TR-EPR) spectra of this molecule could be assigned to vitamin K and E radicals and showed that the excited triplet state of the vitamin K moiety was rapidly quenched by abstraction of hydrogen from the vitamin E moiety. The broad and emissive CIDEP spectra observed in ethanol suggested that the intramolecular interaction between vitamin K and vitamin E radicals was strong there. The relatively resolved spectra observed in a TX-100 micelle system, on the other hand, indicated that the interaction between these radicals was very weak. These results suggest that the vitamin K and E radicals existed around the water−oil interface of the micelle independently. The absence of a deuterium effect in our experiments showed that tunneling does not contribute significantly to the quenching reaction.