A tungsten-containing aldehyde:ferredoxin oxidoreductase (AOR) has been purified to homogeneity from Pyrobaculum aerophilum. The N-terminal sequence of the isolated enzyme matches a single open reading frame in the genome. Metal analysis and electron paramagnetic resonance (EPR) spectroscopy indicate that the P. aerophilum AOR contains one tungsten center and one [4Fe-4S](2+/1+) cluster per 68-kDa monomer. Native AOR is a homodimer. EPR spectroscopy of the purified enzyme that has been reduced with the substrate crotonaldehyde revealed a W(V) species with g(zyx) values of 1.952, 1.918, 1.872. The substrate-reduced AOR also contains a [4Fe-4S](1+) cluster with S=3/2 and zero field splitting parameters D=7.5 cm(-1) and E/D=0.22. Molybdenum was absent from the enzyme preparation. The P. aerophilum AOR lacks the amino acid sequence motif indicative for binding of mononuclear iron that is typically found in other AORs. Furthermore, the P. aerophilum AOR utilizes a 7Fe ferredoxin as the putative physiological redox partner, instead of a 4Fe ferredoxin as in Pyrococcus furiosus. This 7Fe ferredoxin has been purified from P. aerophilum, and the amino acid sequence has been identified using mass spectrometry. Direct electrochemistry of the ferredoxin showed two one-electron transitions, at -306 and -445 mV. In the presence of 55 microM ferredoxin the AOR activity is 17% of the activity obtained with 1 mM benzyl viologen as an electron acceptor.

For simple and fast synthesis of a high-performance electrode material for an aqueous magnesium ion battery (AMIB), UV photolysis is applied to prepare the binder-free δ-MnO2/multiwalled carbon nanotube (δ-MnO2/MWCNTs) composite on carbon cloth (CC). The MnO2 nanosheets are directly grown on the surface of CC covered by MWCNTs to form three-dimensional hierarchy construction, which enhances the electrochemical property. The δ-MnO2/MWCNT composite delivers a discharge capacity of 313.2 mA h g–1 at 50 mA g–1 and its capacitance retention at 1000 mA g–1 is near to 100% after 500 cycles. The AMIB system is assembled using δ-MnO2/MWCNTs as a cathode and VO2 as an anode, which displays a charge capacity of 108.4 mA h g–1 at 50 mA g–1. Furthermore, XPS and ex situ X-ray diffraction measurements are carried out to research the reaction mechanism of Mg ion insertion/deinsertion from δ-MnO2 during the electrochemical process. This work provides insights into the synthesis of the high-performance and low-cost electrode material for AMIB systems.