Stable thiyl radicals in dried yeast Cu(I)6-thionein.

It was of interest to obtain long-lived thiyl radicals embedded in organic matrices. Solid thiol compounds including penicillamine, glutathione, and cysteine were UV irradiated under anaerobic conditions at 293 K for 60 min. The formed radicals were identified by electron paramagnetic resonance (EPR) (g = 2.0265 +/- 0.0015) at 293 K as thiyl radicals. The blue-colored radical species were subjected to reflection spectrometry (lambda max = 601 +/- 3 nm). The color and the EPR signal remained unchanged for six months. At the same time, the UV irradiation of lyophilisized yeast Cu(I)6-thionein generated stable EPR detectable thiyl was seen when the Cu(I)-thiolate was used. No EPR detectable thiyl radicals radicals at a g-value of 2.026 +/- 0.001. Unlike irradiated cysteine, a five times higher concentration of thiyl radicals were measured in the Cu(I)-thiolates of penicillamine, glutathione, and thiophenole, indicating that the hexanuclear copper arrangement in Cu(I)-thionein is most suitable for both the formation and stabilization of this sulfur radical species.