Glutathione (γ-glutamyl-cysteinyl-glycine, GSH) is a major thiol-containing peptide with cellular levels of up to 10 mM.1 Several recent reports have demonstrated glutaredoxins (Grx) to form [Fe2S2] cluster-bridged dimers, where glutathione provides two exogenous thiol ligands, and have implicated such species in cellular iron sulfur cluster biosynthesis. We report the finding that glutathione alone can coordinate and stabilize an [Fe2S2] cluster under physiological conditions, with optical, redox, Mössbauer and NMR characteristics that are consistent with a [Fe2S2](GS)4 composition. The Fe-S assembly protein ISU catalyzes formation of [Fe2S2](GS)4 from iron and sulfide ions in the presence of glutathione, and the [Fe2S2] core undergoes reversible exchange between apo ISU and free glutathione.

The order and other properties of the magnetic phase transitions in the rare-earth (R)-cobalt Laves phases RCo 2 have been studied for RϭGd, Tb, Dy, Ho, Er, Sm, Nd, and Pr by measuring the temperature dependence of the magnetic hyperfine interaction of the nuclear probe 111 Cd on the cubic R sites using the perturbed angular correlation technique. Both for heavy and light R constituents the transitions change from second order ͑Gd, Tb, Sm͒ to first order ͑Dy, Ho, Er, Nd, Pr͒ at order temperatures of 150-200 K. For heavy R constituents, the order deduced from the hyperfine interaction is in agreement with previous investigations. The observation of first order transitions in NdCo 2 and PrCo 2 , however, is unexpected. In earlier studies the transitions in these compounds are usually classified as second order transitions. Both in the heavy and the light RCo 2 the discontinuous jump of the hyperfine interaction at the first order transitions increases with decreasing order temperature. This trend implies that the Co magnetization at the transition increases with decreasing T C which can be related to the temperature dependence of the coefficient of the M 4 term of the free energy in the Wohlfarth-Rhodes-Shimizu theory of itinerant electron magnetism. All compounds investigated presented a spread of the order temperature of ϳ1 -2 K which results in a coexistence of the paramagnetic and the magnetically ordered phase near the transition and causes a critical increase of the relative linewidth of the hyperfine frequency diverging as ␦ϰ(1ϪT/T C ) with ϭϪ1.0(1).

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This paper deals with a perturbed angular correlation investigation of the microstructure and subsequent thermal evolution of a commercial ZrO2‐2. 8 mol% Y2O3 ceramic powder and of a pellet obtained upon sintering the powder at 1450°C. The perturbed angular correlation results, complemented by those of X‐ray diffraction and Raman spectrometry, indicate that the metastable tetragonal phase exhibits two hyperflne interaction forms instead of the interaction associated with the conventional t‐ZrO2 phase, both having different oxygen vacancy configurations around zirconium sites. While the powder sample exhibits mainly a very defective tetragonal form, the pellet exhibits a slightly distorted one as the major form. As temperature is increased, a reversible transformation between both forms occurs involving a redistribution of the oxygen vacancy. Once the transition is completed, the oxygen vacancy movement is described by a fast relaxation regime with an activation energy Eact= 0. 50 ± 0. 04 eV.