Recently, a variety of thiolated gold alloy clusters with well-defined compositions have been synthesized, and the effect of doping on their properties and stability has been studied extensively. We examined the occupation site of the Pd dopant within Au 24 Pd 1 (SC 12 H 25 ) 18 by probing complementarily the local environments of Au and Pd elements using 197 Au Mossbauer and Pd K-edge EXAFS spectroscopy, respectively. The experimental results suggest that the doped single Pd atom is preferentially located at the center of Au 24 Pd 1 (SC 12 H 25 ) 18 to form the superatomic Pd@Au 12 core, which supports recent theoretical predictions. These spectroscopic measurements also clarified intracluster electron transfer from the Pd atom to the surrounding Au atoms.

57 Fe Mössbauer spectroscopy was applied to an iron-based layered superconductor LaFeAsO 0:89 F 0:11 with a transition temperature of 26 K and to its parent material LaFeAsO. Throughout the temperature range from 4.2 to 298 K, a singlet pattern with no magnetic splitting was observed in the Mössbauer spectrum of the F-doped superconductor. Furthermore, no additional internal magnetic field was observed for the spectrum measured at 4.2 K under a magnetic field of 7 T. On the other hand, magnetically split spectra were observed in the parent LaFeAsO below 140 K, and this temperature is slightly lower than that of a structural phase transition from tetragonal to orthorhombic phase, which accompanies the electrical resistivity anomaly at around 150 K. The magnetic moment is estimated to be $0:35 B /Fe from the internal magnetic field of 5.3 T at 4.2 K in the orthorhombic phase, and the spin disorder appears to remain in the magnetically ordered state even at 4.2 K. The lack of a magnetic transition in LaFeAsO 0:89 F 0:11 down to 4.2 K suggests that this system exhibits a paramagnetic state or that the magnetic moment is small. The present results show that F doping effectively suppresses the magnetic and structural transitions in the parent material, leading to the emergence of superconductivity in the F-doped system.

The Rieske dioxygenases are a major subclass of mononuclear nonheme iron enzymes that play an important role in bioremediation. Recently, a high-spin FeIII–(hydro)-peroxy intermediate (BZDOp) has been trapped in the peroxide shunt reaction of benzoate 1,2-dioxygenase. Defining the structure of this intermediate is essential to understanding the reactivity of these enzymes. Nuclear resonance vibrational spectroscopy (NRVS) is a recently developed synchrotron technique that is ideal for obtaining vibrational, and thus structural, information on Fe sites, as it gives complete information on all vibrational normal modes containing Fe displacement. In this study, we present NRVS data on BZDOp and assign its structure using these data coupled to experimentally calibrated density functional theory calculations. From this NRVS structure, we define the mechanism for the peroxide shunt reaction. The relevance of the peroxide shunt to the native FeII/O2 reaction is evaluated. For the native FeII/O2 reaction, an FeIII–superoxo intermediate is found to react directly with substrate. This process, while uphill thermodynamically, is found to be driven by the highly favorable thermodynamics of proton-coupled electron transfer with an electron provided by the Rieske [2Fe-2S] center at a later step in the reaction. These results offer important insight into the relative reactivities of FeIII–superoxo and FeIII–hydroperoxo species in nonheme Fe biochemistry.

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