STABLE THIYL RADICALS IN DRIED YEAST CU(I)(6)-THIONEIN

It was of interest to obtain long-lived thiyl radicals embedded in org anic matrices. Solid thiol compounds including penicillamine, glutathi one, and cysteine were UV irradiated under anaerobic conditions at 293 K for 60 min. The formed radicals were identified by electron paramag netic resonance (EPR) (g = 2.0265 +/- 0.0015) at 293 K as thiyl radica ls. The blue-colored radical species were subjected to reflection spec trometry (lambda(max) = 601 +/- 3 nm). The color and the EPR signal re mained unchanged for six months. At the same time, UV irradiation of l yophilisized yeast Cu(I)(6)-thionein generated stable EPR detectable t hiyl radicals at a g-value of 2.026 +/- 0.001. Unlike irradiated cyste ine, a five times higher concentration of thiyl radicals was seen when the Cu(I)-thiolate protein was used. No EPR detectable thiyl radicals were measured in the Cu(I)-thiolates of penicillamine, glutathione, a nd thiophenole, indicating that the hexanuclear copper arrangement in Cu(I)-thionein is most suitable for both the formation and stabilizati on of this sulfur radical species.