THE CROCIN ASSAY FOR THE DETERMINATION OF RELATIVE RATE CONSTANTS OF ALKOXYL RADICAL REACTIONS WITH THE PYRIDOINDOLE STOBADINE AND WITH OTHER ANTIOXIDANTS

The water-soluble carotenoid crocin is bleached in aqueous solutions b y tert-butyloxy radicals (t-BuO(.)) photolytically generated from tert -butyl hydroperoxide. Crocin bleaching as measured at 440 nm can be co mpetitively inhibited by antioxidants. This method therefore allows th e determination of the relative reaction rates of these compounds with the t-BuO(.) radicals. In this test system the scavenging effect of t he pyridoindole stobadine, a new antioxidant with potential for the tr eatment of tissue injury caused by oxidative stress, was compared with other known antioxidants. Generally good agreement was observed in tw o different approaches for the evaluation of the experimental data. Th e relative rate constants of the antioxidants tested increased in the order: stobadine, chlorpromazine, isoascorbic acid, trolox, ascorbic a cid. Since it has been shown previously that stobadine can scavenge al koxyl radicals also in a non-polar environment, this antioxidant prope rty may be important in the inhibition of lipid peroxidation.