Catalytic Reduction of CN−, CO,and CO2 by Nitrogenase Cofactors in Lanthanide‐Driven Reactions

Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN⁻), carbon monoxide (CO), and carbon dioxide (CO₂) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI₂) and 2,6‐lutidinium triflate (Lut‐H) are employed as a reductant and a proton source, respectively. Driven by SmI₂, the cofactors catalytically reduce CN⁻ or CO to C₁–C₄ hydrocarbons, and CO₂ to CO and C₁–C₃ hydrocarbons. The C C coupling from CO₂ indicates a unique Fischer–Tropsch‐like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN⁻, CO, and CO₂ by isolated cofactors suggests the possibility to develop nitrogenase‐based electrocatalysts for the production of hydrocarbons from these carbon‐containing compounds.     

Synthesis,structure and physical properties of trinuclear M3tdt3(PEt3)3 (M = Fe,Co) clusters containing metal–metal bonds

Trinuclear M₃tdt₃(PEt₃)₃ (M = Fe^II for I, Co^II for II) clusters have been synthesized from the reaction between M(PEt₃)₂Cl₂ and Na₂tdt (tdt = toluene-3,4-dithiolate) in MeCN. Both complexes have been characterized by elemental analyses, FT-IR, UV–Vis, FAB-MS, ¹H NMR and cyclic voltammetry. Structures of Fe₃tdt₃(PEt₃)₃ (I) and Co₃tdt₃(PEt₃)₃ (II) were determined by single crystal X-ray crystallography. The Fe₃ triangular core of the 48-electron complex I, with an isosceles triangular geometry, showed very short Fe–Fe distances of 2.4014(13) and 2.4750(12) Å, which are comparable to the extensive M–M frameworks found in the FeMo-cofactor in nitrogenase. The isostructural Co₃tdt₃(PEt₃)₃ (II), with an analogous Co₃ coordination geometry, showed short Co–Co distances of 2.4442(9) and 2.5551(10) Å. The slightly longer M–M distances in complex II were explained by a total valence electron counting argument. Cyclic voltammetry of Fe₃tdt₃(PEt₃)₃ (I) showed robust reduction waves compared to Co₃tdt₃(PEt₃)₃ (II). Temperature-dependent effective magnetic moment measurements of I and II showed both clusters behave similarly and the magnetic property of the M₃ equilateral triangle core with extensive metal–metal interactions was characterized as degenerate frustration.     

固氮酶活性中心结构模型的EHMO研究

应用群分解EHMO程序,研究了基于MoFe-蛋白X射线衍射结果的固氮酶活性中心结构模型.对比和分析了该模型中尚未确定的配体Y分别为S、O、N、C、H和H…H时的总能量和电荷分布等.结果表明Y=O量为有利.本文进一步提出了Y=O的模型在底物活化过程中Y(O)的邻位加氢后作为活性中心吞吐底物与产物窗口的可能作用方式.     

On the Synthesis of the FeMo Cofactor of Nitrogenase: Gene-Controlled in Nature versus Laboratory-Produced by Man

One of the primary challenges of chemistry is the controlled synthesis of compounds with tailor-made structures and properties. Natural products serve as inspiration in this quest, ranging from biocatalysts with optimal selectivity and activity to “inorganic materials” with exceptional properties, whose generation can be described by the term biomineralization. It is of fundamental importance to comprehend the courses of events at the interface between gene expression and the subsequent processes of epigenesis that are no longer under gene control. Chemistry has been able to achieve many goals; however, in the area of controlled syntheses of highly complex, tailor-made metal clusters, there is a lack of fundamental theories and principles. This is especially true for the fascinating metal–sulfur cluster of nitrogenase, which, in this enzyme, functions as the active center for the N₂ reduction and, so far, has eluded all attempts to be synthesized in the laboratory. To understand the biosynthesis of this cluster, information from genetics and chemistry must be combined.     

An organometallic approach to the synthesis of high nuclearity Mo-Fe-S clusters as potential models for the iron-molybdenum cofactor of nitrogenase

Reaction of the [Fe₂S₂(CO)₆]^2– dianion with molybdenum reagents produces a number of high-nuclearity Mo-Fe-S carbonyl clusters with Fe/Mo ratios 5, as well as a variety of new Fe-S carbonyl clusters. The former are particularly relevant as models or precursors to models for the iron-molybdenum cofactor [FeMo-cofactor] of nitrogenase. General strategies for the synthesis of FeMo-cofactor models are briefly reviewed, and the structures of clusters produced in the [Fe₂S₂(CO)₆]^2–/Mo systems examined to date are described.     

固氮酶中N2键合位的研究

用乙烯作为株针，从Ｎ＿２还原Ｈ＿２和体系的总电子数可以看出，乙烯不能与Ｎ＿２在固氮酶体系中相竞争，表明Ｎ＿２在固氮酶中的键合位很可能是蛋白键合ＦｅＭｏ－ｃｏ笼内的６Ｆｅ［μ＿６（η￣２，ε＿４）］模式和３Ｆｅ＋ｌＭｏ［μ＿４（η￣３，ε＿１）模式。而不是笼口的２Ｆｅ模式，     

Characterization of nitrogen-fixing moderate halophilic cyanobacteria isolated from saline soils of Songnen Plain in China

Twenty out of 200 isolates of cyanobacteria mainly from saline soils of Songnen Plain of China were successfully grown on BG11 N-free medium. The nitrogen-fixing activity was then demonstrated for the 20 isolates in modified BG 11 medium using the acetylene reduction assay. All of them possessed appreciable nitrogenase activity （acetylene reduction） under non-saline conditions; however, at 5% NaCl only 60% of the isolates exhibited a high rate of this activity and 25% were completely negative under these conditions. The cyanobacteria isolates grew well in BG11 medium; nevertheless, growth of the majority of isolates was reduced by about 25-85% in the same medium containing 5% NaCl. Cellulolytic activity was detected in 50% of the 20 strains, amylolytic in 45%, and pectinolytic in 10%o of the isolates. The cyanobacteria isolates showed also enzymatic activity under saline conditions （6%）. The preliminary identification indicated that seven isolates were Nostoc, two were Microcystis, four were Oscillatoria, six were Anabaena, and one isolate was Synechococcus.     

Wie entstand das Leben auf der Erde?: Ammoniak aus Stickstoff unter präbiotischen Bedingungen

This article discusses natural and technical nitrogen fixation. Additionally, a possible scenario of prebiotic nitrogen fixation is presented. The way how ammonia is generated in this scenario could have been the basis for the formation of early amino acids, which are the fundamental building blocks of all nitrogen‐containing bio‐molecules.