Photo‐Driven Hydrogen Evolution by an Artificial Hydrogenase Utilizing the Biotin‐Streptavidin Technology

Abstract

Photocatalytic hydrogen evolution by an artificial hydrogenase based on the biotin‐streptavidin technology is reported. A biotinylated cobalt pentapyridyl‐based hydrogen evolution catalyst (HEC) was incorporated into different mutants of streptavidin. Catalysis with [Ru(bpy)3]Cl2 as a photosensitizer (PS) and ascorbate as sacrificial electron donor (SED) at different pH values highlighted the impact of close lying amino acids that may act as a proton relay under the reaction conditions (Asp, Arg, Lys). In the presence of a close‐lying lysine residue, both, the rates were improved, and the reaction was initiated much faster. The X‐ray crystal structure of the artificial hydrogenase reveals a distance of 8.8 Å between the closest lying Co‐moieties. We thus suggest that the hydrogen evolution mechanism proceeds via a single Co centre. Our findings highlight that streptavidin is a versatile host protein for the assembly of artificial hydrogenases and their activity can be fine‐tuned via mutagenesis.

Biosynthetic Approaches towards the Design of Artificial Hydrogen‐Evolution Catalysts

“…Biotin‐streptavidin technology has been employed to construct artificial hydrogenases featuring Co and Fe‐Fe cofactors . Biotinylated macrocyclic Co complexes employing pentapyridyl and 1,4‐di(picolyl)‐1,4,7‐triazacyclononane ( H Py 2 tacn) ligands with varying linker lengths have been synthesized followed by investigating the H 2 production activity of protein‐encapsulated cofactors (Figure ). Upon incorporation of the biotinylated pentapyridyl Co complex into streptavidin (Sav), a significant decrease in the activity was observed for photocatalytic H 2 production.…”

Enhanced Photocatalytic Hydrogen Production by Hybrid Streptavidin‐Diiron Catalysts

“…Streptavidin‐based catalysts that interface an organometallic complex with a protein scaffold have been used successfully in particular to impart stereospecificity to a reaction . This approach, however, had been partially successful in the catalysis of proton reduction: incorporation of cobalt catalysts did not enhance activity at neutral pH, although significant effects were observed at high pH when using [Ir(bpy)(ppy) 2 ]PF 6 as photosensitizer and triethanolamine as sacrificial electron donor; these conditions require the use of acetonitrile as co‐solvent . Herein, we chose to explore the incorporation of a different type of hydrogen evolving complex, a biomimetic diiron hexacarbonyl active center.…”

“…In this system, cobalt catalysts for hydrogen production retained or improved catalytic activity, especially when probed at high pH . Mutations close to the organometallic complex improved pH dependence and initial rates/TON as compared to the naked catalyst …”

“…A synthetically convenient strategy to build hybrid metalloproteins is based on the streptavidin‐avidin complex; since its introduction, this strategy has been successfully used to catalyze enantioselective reduction of a variety of organic substrates, indicating that catalysts linked to biotin interact with the protein . In this system, cobalt catalysts for hydrogen production retained or improved catalytic activity, especially when probed at high pH . Mutations close to the organometallic complex improved pH dependence and initial rates/TON as compared to the naked catalyst …”

Artificial Metalloenzymes: From Selective Chemical Transformations to Biochemical Applications

“…Various d 6 -pianostool complexes and protein scaffolds have been combined via the different types of anchoring method mentioned above [ 7 ]. Although several excellent ArMs are known to reduce H + [ 27 , 28 ], CO 2 [ 29 ], and SO 3 − [ 30 ], we have focused herein on ArMs used as catalysts for the reduction of organic molecules.…”