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The Fe protein of nitrogenase plays multiple roles in substrate reduction and cluster maturation via its redox-active [Fe 4 S 4 ] cluster. Here we report the synthesis and characterization of a water-soluble [Fe 4 Se 4 ] cluster that is used to substitute the [Fe 4 S 4 ] cluster of the Azotobacter vinelandii Fe protein (AvNifH). Biochemical, EPR and XAS/EXAFS analyses demonstrate the ability of the [Fe 4 Se 4 ] cluster to adopt the super-reduced, all-ferrous state upon its incorporation into AvNifH. Moreover, these studies reveal that the [Fe 4 Se 4 ] cluster in AvNifH already assumes a partial all-ferrous state ([Fe 4 Se 4 ] 0 ) in the presence of dithionite, where its [Fe 4 S 4 ] counterpart in AvNifH exists solely in the reduced state ([Fe 4 S 4 ] 1+ ). Such a discrepancy in the redox properties of the AvNifH-associated [Fe 4 Se 4 ] and [Fe 4 S 4 ] clusters can be used to distinguish the differential redox requirements for the substrate reduction and cluster maturation of nitrogenase, pointing to the utility of chalcogen-substituted FeS clusters in future mechanistic studies of nitrogenase catalysis and assembly., (© 2022 Wiley-VCH GmbH.)

Nitrogenases catalyze the reduction of N 2 to NH 4 + at its cofactor site. Designated the M-cluster, this [MoFe 7 S 9 C(R-homocitrate)] cofactor is synthesized via the transformation of a [Fe 4 S 4 ] cluster pair into an [Fe 8 S 9 C] precursor (designated the L-cluster) prior to insertion of Mo and homocitrate. We report the characterization of an eight-iron cofactor precursor (designated the L*-cluster), which is proposed to have the composition [Fe 8 S 8 C] and lack the "9 th sulfur" in the belt region of the L-cluster. Our X-ray absorption and electron spin echo envelope modulation (ESEEM) analyses strongly suggest that the L*-cluster represents a structural homologue to the l-cluster except for the missing belt sulfur. The absence of a belt sulfur from the L*-cluster may prove beneficial for labeling the catalytically important belt region, which could in turn facilitate investigations into the reaction mechanism of nitrogenases., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Naphthalene oxidation with metal-oxygen intermediates is a difficult reaction in environmental and biological chemistry. Herein, we report that a Mn IV bis(hydroxo) complex, which was fully characterized by various physicochemical methods, such as ESI-MS, UV/Vis, and EPR analysis, X-ray diffraction, and XAS, can be employed for the oxidation of naphthalene in the presence of acid to afford 1,4-naphthoquinone. Redox titration of the Mn IV bis(hydroxo) complex gave a one-electron reduction potential of 1.09 V, which is the most positive potential for all reported nonheme Mn IV bis(hydroxo) species as well as Mn IV oxo analogues. Kinetic studies, including kinetic isotope effect analysis, suggest that the naphthalene oxidation occurs through a rate-determining electron transfer process., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An advanced intermediate: A nonheme iron(IV) oxo complex [Fe(IV)(O)(bqen)(L)](n+) (bqen = N,N'-dimethyl-N,N'-bis(8-quinolyl)ethane-1,2-diamine, L = CH(3)CN or CF(3)SO(3)(-)) activates the C-H bonds of alkanes and alcohols by a hydrogen-atom abstraction mechanism. The catalytic oxidation of these species is proposed to occur through a nonheme iron(V) oxo species, with a high reactivity in oxidation reactions (see picture).

A copper-copper separation of about 2.84 Å is determined by extended X-ray absorption fine structure studies for the (μ-1,2-peroxo)dicopper(II) species 1, which has only a 1,8-naphthyridine unit as an additional bridge. Complex 1 was prepared by the reaction of O 2 with a dicopper(I) complex formed from BPMAN., (© 2001 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)