4f delocalization in Gd: inelastic x-ray scattering at ultrahigh pressure

We present resonant inelastic x-ray scattering and x-ray emission spectroscopy results on Gd metal to 113 GPa which suggest Kondo-like aspects in the delocalization of 4f electrons. Analysis of the resonant inelastic x-ray scattering data reveals a prolonged and continuous delocalization with volume throughout the entire pressure range, so that the volume-collapse transition at 59 GPa is only part of the phenomenon. Moreover, the Lgamma1 x-ray emission spectroscopy spectra indicate no apparent change in the bare 4f moment across the collapse, suggesting that Kondo screening is responsible for the expected Pauli-like behavior in magnetic susceptibility.     

Solution-phase photochemistry of a [FeFe]hydrogenase model compound: evidence of photoinduced isomerisation

The solution-phase photochemistry of the [FeFe] hydrogenase subsite model (μ-S(CH(2))(3)S)Fe(2)(CO)(4)(PMe(3))(2) has been studied using ultrafast time-resolved infrared spectroscopy supported by density functional theory calculations. In three different solvents, n-heptane, methanol, and acetonitrile, relaxation of the tricarbonyl intermediate formed by UV photolysis of a carbonyl ligand leads to geminate recombination with a bias towards a thermodynamically less stable isomeric form, suggesting that facile interconversion of the ligand groups at the Fe center is possible in the unsaturated species. In a polar or hydrogen bonding solvent, this process competes with solvent substitution leading to the formation of stable solvent adduct species. The data provide further insight into the effect of incorporating non-carbonyl ligands on the dynamics and photochemistry of hydrogenase-derived biomimetic compounds.     

Superconducting gap structure of the 115s revisited

Density functional theory calculations of the electronic structure of Ce- and Pu-based heavy fermion superconductors in the so-called 115 family are performed. The gap equation is used to consider which superconducting order parameters are most favorable assuming a pairing interaction that is peaked at (π, π, qz)—the wavevector for the antiferromagnetic ordering found in close proximity. In addition to the commonly accepted dx2?y2 order parameter, there is evidence that an extended s-wave order parameter with nodes is also plausible. We discuss whether these results are consistent with current observations and possible measurements that could help distinguish between these scenarios.     

Structural characterization of the zinc site in protein farnesyltransferase

X-ray absorption spectroscopy has been used to determine the structure of the Zn site in protein farnesyltransferase. Extended X-ray absorption fine structure (EXAFS) data are consistent with a Zn site that is ligated to three low-Z (oxygen or nitrogen) ligands and one cysteine sulfur, as predicted from the crystal structures that are available for farnesyltransferase. However, in contrast with the crystallographic results the EXAFS data do not show evidence for significant distortions in the Zn-ligand distances. The average Zn-(N/O) and Zn-S distances are 2.04 and 2.31 A, respectively. Addition of a farnesyl diphosphate analogue causes no detectable change in the structure of the Zn site. However, addition of peptide substrate causes a change in ligation from ZnS(N/O)(3) to ZnS(2)(N/O)(2), consistent with ligation of the C-terminal cysteine to the Zn. There is no significant change in Zn-ligand distances when a substrate binds, demonstrating that the Zn remains four-coordinate. Addition of both peptide and farnesyl diphosphate to give the product complex causes the Zn to return to ZnS(N/O)(3) ligation, indicating that the product thioether is not tightly coordinated to the Zn. These spectroscopic experiments provide insight into the catalytic mechanism of FTase.     

On carboxylate as a leaving group at the active site of Mo nitrogenase: electrochemical reactions of some MO and W carboxylates, formation of mono-, di- and tri-hydrides and the detection of an MoH2(N2) intermediate

A carboxylate ligand can function as a leaving group at a reduced molybdenum dihydride centre and this exposes a site at which dinitrogen or other small molecules can bind ; dihydrogen loss occurs after substrate binding ; protic attack intercepts carboxylate loss affording a trihydride intermediate which can partake in a hydrogen evolution cycle : it is suggested that carboxylate loss from the reduced Mo centre of nitrogenase might similarly lead to substrate binding and thence obligatory evolution of H₂.