A [RuRu] Analogue of an [FeFe]‐Hydrogenase Traps the Key Hydride Intermediate of the Catalytic Cycle

The active site of the [FeFe]‐hydrogenases features a binuclear [2Fe]_H sub‐cluster that contains a unique bridging amine moiety close to an exposed iron center. Heterolytic splitting of H₂ results in the formation of a transient terminal hydride at this iron site, which, however is difficult to stabilize. We show that the hydride intermediate forms immediately when [2Fe]_H is replaced with [2Ru]_H analogues through artificial maturation. Outside the protein, the [2Ru]_H analogues form bridging hydrides, which rearrange to terminal hydrides after insertion into the apo‐protein. H/D exchange of the hydride only occurs for [2Ru]_H analogues containing the bridging amine moiety.     

The Catalytic Mechanism of Protein Phosphatase 5 Established by DFT Calculations

In order to elucidate the catalytic mechanism of the Mn–Mn containing serine/threonine protein phosphatase 5 (PP5), we present a density functional theory study with a cluster model approach. According to our results, the reaction occurs through an in‐line concerted transition state with an energy of 15.8 kcal mol^?1, and no intermediates are formed. The important role played by His304 and Asp274 as stabilizers of the leaving group has been shown, whereas the role played by the metal ions seems to be mostly electrostatic. The indispensable requirement of having a neutral active center has been demonstrated by testing different protonation states of the cluster model. We have shown also the importance of describing properly the electronic configuration of the Mn–Mn binuclear centers.     

Revealing the Absolute Configuration of the CO and CN− Ligands at the Active Site of a [NiFe] Hydrogenase

Combined molecular dynamics (MD) and quantum mechanical/molecular mechanical (QM/MM) calculations were performed on the crystal structure of the reduced membrane‐bound [NiFe] hydrogenase (MBH) from Ralstonia eutropha to determine the absolute configuration of the CO and the two CN^? ligands bound to the active‐site iron of the enzyme. For three models that include the CO ligand at different positions, often indistinguishable on the basis of the crystallographic data, we optimized the structures and calculated the ligand stretching frequencies. Comparison with the experimental IR data reveals that the CO ligand is in trans position to the substrate‐binding site of the bimetallic [NiFe] cluster.