Activity assays of NnlA homologs suggest the natural product -nitroglycine is degraded by diverse bacteria.

Linear nitramines (R-N(R')NO; R' = H or alkyl) are toxic compounds, some with environmental relevance, while others are rare natural product nitramines. One of these natural product nitramines is -nitroglycine (NNG), which is produced by some strains and exhibits antibiotic activity towards Gram-negative bacteria. An NNG degrading heme enzyme, called NnlA, has recently been discovered in the genome of strain JS1663 ( NnlA).

Reduction of a Heme Cofactor Initiates -Nitroglycine Degradation by NnlA.

Linear nitramines are potentially carcinogenic environmental contaminants. The NnlA enzyme from sp. strain JS1663 degrades the nitramine -nitroglycine (NNG)-a natural product produced by some bacteria-to glyoxylate and nitrite (NO).

Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe-N-C Catalysts.

Fe-N-C catalysts with high O reduction performance are crucial for displacing Pt in low-temperature fuel cells. However, insufficient understanding of which reaction steps are catalyzed by what sites limits their progress. The nature of sites were investigated that are active toward H O reduction, a key intermediate during indirect O reduction and a source of deactivation in fuel cells.

Experimental Observation of Redox-Induced Fe-N Switching Behavior as a Determinant Role for Oxygen Reduction Activity.

The commercialization of electrochemical energy conversion and storage devices relies largely upon the development of highly active catalysts based on abundant and inexpensive materials. Despite recent achievements in this respect, further progress is hindered by the poor understanding of the nature of active sites and reaction mechanisms. Herein, by characterizing representative iron-based catalysts under reactive conditions, we identify three Fe-N4-like catalytic centers with distinctly different Fe-N switching behaviors (Fe moving toward or away from the N4-plane) during the oxygen reduction reaction (ORR), and show that their ORR activities are essentially governed by the dynamic structure associated with the Fe(2+/3+) redox transition, rather than the static structure of the bare sites.

Improved Oxygen Reduction Activity and Durability of Dealloyed PtCo Catalysts for Proton Exchange Membrane Fuel Cells: Strain, Ligand, and Particle Size Effects.

The development of active and durable catalysts with reduced platinum content is essential for fuel cell commercialization. Herein we report that the dealloyed PtCo/HSC and PtCo/HSC nanoparticle (NP) catalysts exhibit the same levels of enhancement in oxygen reduction activity (~4-fold) and durability over pure Pt/C NPs. Surprisingly, ex situ high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) shows that the bulk morphologies of the two catalysts are distinctly different: D-PtCo/HSC catalyst is dominated by NPs with solid Pt shells surrounding a single ordered PtCo core; however, the D-PtCo/HSC catalyst is dominated by NPs with porous Pt shells surrounding multiple disordered PtCo cores with local concentration of Co.

Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal-nitrogen coordination.

Replacement of noble metals in catalysts for cathodic oxygen reduction reaction with transition metals mostly create active sites based on a composite of nitrogen-coordinated transition metal in close concert with non-nitrogen-coordinated carbon-embedded metal atom clusters. Here we report a non-platinum group metal electrocatalyst with an active site devoid of any direct nitrogen coordination to iron that outperforms the benchmark platinum-based catalyst in alkaline media and is comparable to its best contemporaries in acidic media. In situ X-ray absorption spectroscopy in conjunction with ex situ microscopy clearly shows nitrided carbon fibres with embedded iron particles that are not directly involved in the oxygen reduction pathway.

Elucidating Oxygen Reduction Active Sites in Pyrolyzed Metal-Nitrogen Coordinated Non-Precious-Metal Electrocatalyst Systems.

Detailed understanding of the nature of the active centers in non-precious-metal-based electrocatalyst, and their role in oxygen reduction reaction (ORR) mechanistic pathways will have a profound effect on successful commercialization of emission-free energy devices such as fuel cells. Recently, using pyrolyzed model structures of iron porphyrins, we have demonstrated that a covalent integration of the Fe-N sites into π-conjugated carbon basal plane modifies electron donating/withdrawing capability of the carbonaceous ligand, consequently improving ORR activity. Here, we employ a combination of X-ray spectroscopy and electrochemical methods to identify the various structural and functional forms of the active centers in non-heme Fe/N/C catalysts.