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Gases like H2, N2, CO2, and CO are increasingly recognized as critical feedstock in green energy conversion and as sources of nitrogen and carbon for the agricultural and chemical sectors. However, the industrial transformation of N2, CO2, and CO and the production of H2 require significant energy input, which renders processes like steam reforming and the Haber-Bosch reaction economically and environmentally unviable. Nature, on the other hand, performs similar tasks efficiently at ambient temperature and pressure, exploiting gas-processing metalloenzymes (GPMs) that bind low-valent metal cofactors based on iron, nickel, molybdenum, tungsten, and sulfur. Such systems are studied to understand the biocatalytic principles of gas conversion including N2 fixation by nitrogenase and H2 production by hydrogenase as well as CO2 and CO conversion by formate dehydrogenase, carbon monoxide dehydrogenase, and nitrogenase. In this review, we emphasize the importance of the cofactor/protein interface, discussing how second and outer coordination sphere effects determine, modulate, and optimize the catalytic activity of GPMs. These may comprise ionic interactions in the second coordination sphere that shape the electron density distribution across the cofactor, hydrogen bonding changes, and allosteric effects. In the outer coordination sphere, proton transfer and electron transfer are discussed, alongside the role of hydrophobic substrate channels and protein structural changes. Combining the information gained from structural biology, enzyme kinetics, and various spectroscopic techniques, we aim toward a comprehensive understanding of catalysis beyond the first coordination sphere.

A sub-ångström-resolution X-ray crystal structure of [NiFe] hydrogenase, with direct detection of the products of the heterolytic splitting of dihydrogen into a hydride bridging the Ni and Fe and a proton attached to the sulphur of a cysteine ligand. Hydrogens visualized in hydrogenase enzyme [NiFe] hydrogenases use nickel and iron to catalyse the reversible oxidation of molecular hydrogen. They are the focus of much research worldwide because of their potential in biotechnology and in serving as natural models for biomimetic catalysts in the energy sector for hydrogen production and conversion. In protein X-ray crystallography it is notoriously difficult to detect hydrogens, a particularly significant problem in hydrogenases where hydrogens are involved directly in the reaction. Hideaki Ogata et al. have succeeded in obtaining a sub-ångström resolution X-ray crystal structure of [NiFe] hydrogenase leading to detection of most of the hydrogens even close to the metal ions. Using their technique authors were able to detect the products of the heterolytic splitting of dihydrogen: a hydride that bridges the Ni and Fe ions, and a proton that is attached to the sulfur of a cysteine ligand. The enzyme hydrogenase reversibly converts dihydrogen to protons and electrons at a metal catalyst.sup.1. The location of the abundant hydrogens is of key importance for understanding structure and function of the protein.sup.2,3,4,5,6. However, in protein X-ray crystallography the detection of hydrogen atoms is one of the major problems, since they display only weak contributions to diffraction and the quality of the single crystals is often insufficient to obtain sub-ångström resolution.sup.7. Here we report the crystal structure of a standard [NiFe] hydrogenase (~91.3 kDa molecular mass) at 0.89 Å resolution. The strictly anoxically isolated hydrogenase has been obtained in a specific spectroscopic state, the active reduced Ni-R (subform Ni-R1) state. The high resolution, proper refinement strategy and careful modelling allow the positioning of a large part of the hydrogen atoms in the structure. This has led to the direct detection of the products of the heterolytic splitting of dihydrogen into a hydride (H.sup.-) bridging the Ni and Fe and a proton (H.sup.+) attached to the sulphur of a cysteine ligand. The Ni-H.sup.- and Fe-H.sup.- bond lengths are 1.58 Å and 1.78Å, respectively. Furthermore, we can assign the Fe-CO and Fe-CN.sup.- ligands at the active site, and can obtain the hydrogen-bond networks and the preferred proton transfer pathway in the hydrogenase. Our results demonstrate the precise comprehensive information available from ultra-high-resolution structures of proteins as an alternative to neutron diffraction and other methods such as NMR structural analysis., Author(s): Hideaki Ogata [sup.1] , Koji Nishikawa [sup.1] [sup.2] , Wolfgang Lubitz [sup.1] Author Affiliations: (1) Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, [...]

The article studies the design of a High Temperature Superconducting (HTS) rotating machine with melt-textured Gd-123 bulk pole-field magnets. Findings reveal the stability of the magnetic flux density and its distribution on each bulk with averaged decay of 4 percent for seven hours continuous synchronous operation.

The issue concerning several matters in hydrogenase research, namely the formal oxidation states of nickel in all its paramagnetic intermediate state, the structure of the [NiFe] cluster, including the type of the third bridging ligand between the metals and the functional role of the active center of the enzyme in the hydrogen conversion process is addressed. The various experimental and theoretical considerations indicate a plausible assignment of the g tensors to a specific site.

The carbon monoxide complex of [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F is characterized by X-ray crystallography and absorption and resonance Raman spectroscopy. Nine crystal structures of the of [NiFe] hydrogenase in the CO-bound and CO-liberated forms are determined at 1.2,-1.4 A resolution.