Fundamentals and electrochemical applications of [Ni–Fe]-uptake hydrogenases

Abstract

Hydrogenases are found in a wide range of archaea, prokaryotes and eukaryotes as soluble and membrane-bound enzymes and are generally classified by the structure of the catalytic site. From a biotechnological perspective, hydrogenases have been examined for their role in the production of biohydrogen; for co-factor regeneration in coupled enzyme reactions; for environmental applications, and for the electrochemical oxidation of molecular hydrogen. Hydrogenases, with their ability to readily oxidise hydrogen or reduce protons into hydrogen, have huge potential as biocatalysts in many emerging technologies based on the use of hydrogen as a clean energy vector. This review will focus on the hydrogenases associated with the oxidation of molecular hydrogen (so-called ''uptake hydrogenases'' (EC 1.12.99.6)), covering their properties, structure, isolation, and remaining barriers for potential industrial applications, including bio-fuel cells, photocatalytic water splitting and hydrogen sensors.

Pd(II)-Directed Encapsulation of Hydrogenase within the Layer-by-Layer Multilayers of Carbon Nanotube Polyelectrolyte Used as a Heterogeneous Catalyst for Oxidation of Hydrogen

“…These peaks could be assigned to the elements of Br(3d), S(2p), Cl(2p), C(1s), Pd(3d), N(1s), O(1s), I(3d), Fe(2p), and Ni(2p), among which the elements of Pd and Cl were from the connector; the other elements were from the nanolinker. Hence, the XPS data confirmed the coordination of PdCl 4 2− with the MWNT-PVPMe@H 2 ase bionanocomposites. Figure 6 shows an FE-SEM image for the gold substrate covered by three layers of the (Pd/MWNT-PVPMe@H 2 ase) 3 LBL films together with a "naked" gold surface (covered by the SAM of -SPy).…”

“…Except for Na 2 PdCl 4 , we also tried to construct the LBL multilayers with the salts of AgNO 3 and CdCl 2 as connectors, but the quality of the LBL multilayers was not so good. A possible reason may be that the PdCl 4 2− ions could coordinate with pyridine substituents more efficiently than those reported previously at the interfaces. 39 The assembling process was monitored by measuring the absorption spectra, XPS, FE-SEM, and AFM images as described below.…”

“…39 The absorption intensity at 290 nm was proportional with the layer numbers assembled (see the graph inserted in Figure 5), which indicated that similar amounts of the nanolinkers and Na 2 PdCl 4 connectors were assembled for each bilayer. A close inspection of the absorption increase could find a relatively larger increase for the coordination of the PdCl 4 2− ions, together with a smaller one for the coordination or adsorption of the bionanocomposites. On the basis of the absorption intensity of the bionanocomposites as well as the absorption coefficient of H 2 ase and MWNT-PVPMe, the surface density of the H 2 ase within each layer was roughly estimated to be about 0.2 μg/ cm 2 .…”

“…26 Then the MWNT-PVP nanohybrid was reacted with methyl iodide (MeI) to produce positively charged MWNT-polyelectrolyte (MWNT-PVPMe) that could interact with the H 2 ase to form MWNT-PVPMe@ H 2 ase bionanocomposites. The pyridine substituents of PVPMe were not fully converted to the pyridinium salts (controllably by adjusting the amount of MeI added); they could act as coordinative units to react with transition metal ions such as PdCl 4 2− , Ag + , and Cd 2+ , thus resulting in the MWNTPVPMe@H 2 ase bionanocomposites capable of binding with these metal ions. Finally, MWNT-PVPMe@H 2 ase was used as the nanolinker (like a multidentate ligand), and inorganic salt of Na 2 PdCl 4 was used as the connector to construct the metaldirected (Pd/MWNT-PVPMe@H 2 ase) n multilayers by the LBL technique.…”

Reductive Dehalogenases Come of Age in Biological Destruction of Organohalides

“…Heterologous expression of functional RDases is not trivial, although the genetic requirement is not as complex as for some oxidoreductases (such as uptake hydrogenases) where coexpression of numerous structural, accessory, and maturation genes is essential [66]. Only a handful of efforts to overexpress PceA in a heterologous host have been reported; however, for the most part, the purified enzymes remain catalytically inactive [8,67,68].…”