Enhanced Photocatalytic Hydrogen Production by Hybrid Streptavidin‐Diiron Catalysts

Abstract

Hybrid protein–organometallic catalysts are being explored for selective catalysis of a number of reactions, because they utilize the complementary strengths of proteins and of organometallic complex. Herein, we present an artificial hydrogenase, StrepH2, built by incorporating a biotinylated [Fe–Fe] hydrogenase organometallic mimic within streptavidin. This strategy takes advantage of the remarkable strength and specificity of biotin‐streptavidin recognition, which drives quantitative incorporation of the biotinylated diironhexacarbonyl center into streptavidin, as confirmed by UV/Vis spectroscopy and X‐ray crystallography. FTIR spectra of StrepH2 show characteristic peaks at shift values indicative of interactions between the catalyst and the protein scaffold. StrepH2 catalyzes proton reduction to hydrogen in aqueous media during photo‐ and electrocatalysis. Under photocatalytic conditions, the protein‐embedded catalyst shows enhanced efficiency and prolonged activity compared to the isolated catalyst. Transient absorption spectroscopy data suggest a mechanism for the observed increase in activity underpinned by an observed longer lifetime for the catalytic species FeIFe0 when incorporated within streptavidin compared to the biotinylated catalyst in solution.

An Artificial Metalloenzyme Based on a Copper Heteroscorpionate Enables sp3 C–H Functionalization via Intramolecular Carbene Insertion

“…The remarkable affinity of biotin for streptavidin ( K d < 10 –13 M) offers an attractive means to anchor any biotinylated probe within streptavidin (Sav). Several groups have relied on this tool to assemble ArMs. ,− A common strategy for the synthesis of anchored Tp complexes relies on the introduction of a fourth substituent on the boron, replacing the hydride moiety. − In our hands, however, this strategy proved challenging as tetrasubstituted Tp-derivatives bearing electron-deficient pyrazoles revealed insufficient stability. Inspired by the work of Desrochers and co-workers on heterocycle metathesis, we selected the Tp ( t Bu)2 K 1 as the precursor for the assembly of a biotinylated, electron-deficient TpM-cofactor.…”

Biosynthetic Approaches towards the Design of Artificial Hydrogen‐Evolution Catalysts

“…The 2 Bio ⊂Sav hybrid having a longer and more flexible linker between the biotin and ligand scaffolds, sampled two different conformations with the Co center ending up in close proximity to polar residues and internal H 2 O molecules of Sav, which presumably influenced catalysis by making H‐bonding interactions. A biotinylated Fe‐Fe complex featuring CO and bridging thiols was incorporated into Sav where encapsulation of the Fe‐Fe complex into the protein enhanced its activity . Under photocatalytic conditions, while naked biotinylated Fe‐Fe complex produced H 2 with a TON of ≈6.4 after 3 h, the Fe‐Fe⊂Sav had a TON of ≈48 over 11 h. The parent Fe‐Fe complex was active for 100 min while the protein‐encapsulated complex produced H 2 for 9 h due to the longer lifetime of the catalyst upon its incorporation into the protein scaffold.…”

Designing Artificial Metalloenzymes by Tuning of the Environment beyond the Primary Coordination Sphere

“…Most recently, Ghirlanda and co-workers have employed the Sav-biotin system to generate a synthetic H 2 ase using a biotinylated [Fe­(CO) 3 -(μ-S) 2 -Fe­(CO) 3 ] complex . Use of [Ru­(bpy) 3 ] 2+ to drive catalysis in the presence of visible light and ascorbate resulted in slow H 2 production, reaching ∼48 TON over the course of 11 h, significantly greater than the TON = 6 found in the absence of the Sav scaffold, demonstrating that the presence of a surrounding protein scaffold significantly improves the catalyst integrity.…”