Effects and mechanisms of eugenol, isoeugenol, coniferylaldehyde and dihydroeugenol on the riboflavin-sensitized photooxidation of alpha-terpinene in methanol

摘要

The effects of eugenol, isoeugenol, coniferylaldehyde, and dihydroeugenol on the riboflavin-sensitized photooxidation of alpha-terpinene in methanol were studied. Riboflavin greatly accelerated alpha-terpinene oxidation in methanol during light illumination, resulting in two major oxidation products (p-cymene and ascaridole). The results clearly showed the involvement of Type I and II mechanisms. All the eugenols exerted strong protective activity on riboflavin sensitized photooxidation of alpha-terpinene. Dihydroeugenol showed the highest protective activity, followed by isoeugenol, coniferylaldehyde, and eugenol, in a decreasing order. Dihydroeugenol greatly inhibited the production of ascaridole, but showed relatively low inhibitory activity on the formation of p-cymene. The protective activity of dihydroeugenol was higher than those of BHA, BHT and sodium azide. Sodium azide, a specific singlet oxygen quencher, showed strong inhibitory activity on the formation of ascaridole, but very low inhibitory activity on the formation of p-cymene, verifying the feasibility of mechanism study with the present model system. (C) 2016 Elsevier Ltd. All rights reserved.