Isocyanide Ligation Enables Electrochemical Ammonia Formation in a Synthetic Cycle for N Fixation.

Transition-metal-mediated splitting of N to form metal nitride complexes could constitute a key step in electrocatalytic nitrogen fixation, if these nitrides can be electrochemically reduced to ammonia under mild conditions. The envisioned nitrogen fixation cycle involves several steps: N binding to form a dinuclear end-on bridging complex with appropriate electronic structure to cleave the N bridge followed by proton/electron transfer to release ammonia and bind another molecule of N. The nitride reduction and N splitting steps in this cycle have differing electronic demands that a catalyst must satisfy.

Targeted Modulation of Photocatalytic Hydrogen Evolution Activity by Nickel-Substituted Rubredoxin through Functionalized Ruthenium Phototriggers.

Light-driven hydrogen evolution is a promising means of sustainable energy production to meet global energy demand. This study investigates the photocatalytic hydrogen evolution activity of nickel-substituted rubredoxin (NiRd), an artificial hydrogenase mimic, covalently attached to a ruthenium phototrigger (RuNiRd). By systematically modifying the para-substituents on Ru(II) polypyridyl complexes, we sought to optimize the intramolecular electron transfer processes within the RuNiRd system.

Evaluating Diazene to N Interconversion at Iron-Sulfur Complexes.

Biological N reduction occurs at sulfur-rich multiiron sites, and an interesting potential pathway is concerted double reduction/ protonation of bridging N through PCET. Here, we test the feasibility of using synthetic sulfur-supported diiron complexes to mimic this pathway. Oxidative proton transfer from μ-η : η-diazene (HN=NH) is the microscopic reverse of the proposed N fixation pathway, revealing the energetics of the process.

Rubredoxin Protein Scaffolds Sourced from Diverse Environmental Niches as an Artificial Hydrogenase Platform.

Nickel-substituted rubredoxin (NiRd) from has previously been shown to act as both a structural and functional mimic of the [NiFe] hydrogenase. However, improvements both in turnover frequency and overpotential are needed to rival the native [NiFe] hydrogenase enzymes. Characterization of a library of NiRd mutants with variations in the secondary coordination sphere suggested that protein dynamics played a substantial role in modulating activity.

Assembly of a Genetically Encoded Artificial Metalloenzyme for Hydrogen Production.

The genetic encoding of artificial enzymes represents a substantial advantage relative to traditional molecular catalyst optimization, as laboratory-based directed evolution coupled with high-throughput screening methods can provide rapid development and functional characterization of enzyme libraries. However, these techniques have been of limited utility in the field of artificial metalloenzymes due to the need for cofactor metalation. Here, we report the development of methodology for production of nickel-substituted rubredoxin, an artificial metalloenzyme that is a structural, functional, and mechanistic mimic of the [NiFe] hydrogenases.