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.

Magnetite (Fe 3 O 4) nanoparticles are proper materials for Magnetic Fluid Hyperthermia applications whenever these conjugate stability at physiological (neutral pH) medium and high specific dissipation power. Here, magnetite nanoparticles 9-12 nm size, electrostatically

Cubic-like shaped Zn x Fe 3−x O 4 particles with crystallite mean sizes D between 15 and 117 nm were obtained by co-precipitation. Particle size effects and preferential occupation of spinel tetrahedral site by Zn 2+ ions led to noticeable changes of physical properties. D 30 nm particles displayed nearly bulk properties, which were dominated by Zn concentration. For D 30 nm, dominant magnetic relaxation effects were observed by Mössbauer spectroscopy, with the mean blocking size D B ∼ 13 to 15 nm. Saturation magnetization increased with x up to x ∼ 0.1-0.3 and decreased for larger x. Power absorbed by water and chitosan-based ferrofluids from a 260 kHz radio frequency field was measured as a function of x, field amplitude H 0 and ferrofluid concentration. For H 0 = 41 kA m −1 the maximum specific absorption rate was 367 W g −1 for D = 16 nm and x = 0.1. Absorption results are interpreted within the framework of the linear response theory for H 0 41 kA m −1 . A departure towards a saturation regime was observed for higher fields. Simulations based on a two-level description of nanoparticle magnetic moment relaxation qualitatively agree with these observations. The frequency factor of the susceptibility dissipative component, derived from experimental results, showed a sharp maximum at D ∼ 16 nm. This behaviour was satisfactorily described by simulations based on moment relaxation processes, which furthermore indicated a crossover from Néel to Brown mechanisms at D ∼ 18 nm. Hints for further improvement of magnetite particles as nanocalefactors for magnetic hyperthermia are discussed.