Nitrate and perchlorate have considerable use in technology, synthetic materials, and agriculture; as a result, they have become pervasive water pollutants. Industrial strategies to chemically reduce these oxyanions often require the use of harsh conditions, but microorganisms can efficiently reduce them enzymatically. We developed an iron catalyst inspired by the active sites of nitrate reductase and (per)chlorate reductase enzymes. The catalyst features a secondary coordination sphere that aids in oxyanion deoxygenation. Upon reduction of the oxyanions, an iron(III)-oxo is formed, which in the presence of protons and electrons regenerates the catalyst and releases water.

Reaction of tetrabutylammonium nitrite with [N(afa(Cy))3Fe(OTf)](OTf) cleanly resulted in the formation of an iron(III)-oxo species, [N(afa(Cy))3Fe(O)](OTf), and NO(g). Formation of NO(g) as a byproduct was confirmed by reaction of the iron(II) starting material with half an equivalent of nitrite, resulting in a mixture of two products, the iron-oxo and an iron-NO species, [N(afa(Cy))3Fe(NO)](OTf)2. Formation of the latter was confirmed through independent synthesis. The results of this study provide insight into the role of hydrogen bonding in the mechanism of nitrite reduction and the binding mode of nitrite in biological heme systems.

Significance Methanobactins (Mbns), copper-binding peptidic compounds produced by some bacteria, are candidate therapeutics for human diseases of copper overload. The paired oxazolone-thioamide bidentate ligands of methanobactins are generated from cysteine residues in a precursor peptide, MbnA, by the MbnBC enzyme complex. MbnBC activity depends on the presence of iron and oxygen, but the catalytically active form has not been identified. Here, we provide evidence that a dinuclear Fe(II)Fe(III) center in MbnB, which is the only representative of a >13,000-member protein family to be characterized, is responsible for this reaction. These findings expand the known roles of diiron enzymes in biology and set the stage for mechanistic understanding, and ultimately engineering, of the MbnBC biosynthetic complex.

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1901912 (1 of 10) Herein, Ti 4+ in P′2-Na 0.67 [(Mn 0.78 Fe 0.22 ) 0.9 Ti 0.1 ]O 2 is proposed as a new strategy for optimization of Mn-based cathode materials for sodium-ion batteries, which enables a single phase reaction during de-/sodiation. The approach is to utilize the stronger Ti-O bond in the transition metal layers that can suppress the movements of Mn-O and Fe-O by sharing the oxygen with Ti by the sequence of Mn-O-Ti-O-Fe.It delivers a discharge capacity of ≈180 mAh g −1 over 200 cycles (86% retention), with S-shaped smooth charge-discharge curves associated with a small volume change during cycling. The single phase reaction with a small volume change is further confirmed by operando synchrotron X-ray diffraction. The low activation barrier energy of ≈541 meV for Na + diffusion is predicted using first-principles calculations. As a result, Na 0.67 [(Mn 0.78 Fe 0.22 ) 0.9 Ti 0.1 ]O 2 can deliver a high reversible capacity of ≈153 mAh g −1 even at 5C (1.3 A g −1 ), which corresponds to ≈85% of the capacity at 0.1C (26 mA g −1 ). The nature of the sodium storage mechanism governing the ultrahigh electrode performance in a full cell with a hard carbon anode is elucidated, revealing the excellent cyclability and good retention (≈80%) for 500 cycles (111 mAh g −1 ) at 5C (1.3 A g −1 ).reactions. [3][4][5] Although SIBs have intrinsic drawbacks, such as their low operation voltages relative to those of LIBs and the difficulty of ready insertion of sodium ions because of the larger size of Na + ions (1.02 Å) compared with Li + ions (0.76 Å), these difficulties can be mitigated with a high capacity to compensate for the low operation voltage. [5] Layered cathode material for SIBs (Na x MeO 2 ) has received particular attention owing to their relatively high capacity and structural stability. Layered Na x MeO 2 (x = 0.5-1 and Me; transition metal) consist of MeO 2 layers sharing edges with MeO 6 octahedra were classified into two groups based on structure: trigonal prismatic (P type: P2, P3, and P′2) and octahedral (O type: O3). [6] The differences in these structures are attributed to sodium ions being respectively located at the district trigonal prismatic or octahedral crystallographic sites sandwiched between the MeO 2 sheets. Among them, many works have introduced Mn-based cathode materials, mainly P2-type materials, in which sodium ions are located at prismatic sites with an AABB oxygen stacking sequence, because of their low cost, good performance, and nontoxicity. [7,8] Recently, many works about P2-type materials have been investigated such as Na x MnO 2 , [7,9] Na x CoO 2 , [10] Na x VO 2 , [11] Na x [Ni,Mn] O 2 , [12] Na x [Fe,Mn]O 2 , [13] Na x [Ni,Fe,Mn]O 2 , [14] Na x [Mg,Mn] O 2 , [15] Na x [Ni,Mg,Mn]O 2 . [16] P2-type materials crystallize in a hexagonal structure; however, the transition metal layers can be distorted at higher temperature with stabilization in an orthorhombic structure (represented as P′2) albeit with the same chemical composition. [17,18] Many works have introduced Mn-based c...