Aqueous light driven hydrogen production by a Ru–ferredoxin–Co biohybrid

Abstract

Herein we report the creation of a novel solar fuel biohybrid for light-driven H2 production utilizing the native electron transfer protein ferredoxin (Fd) as a scaffold for binding of a ruthenium photosensitizer (PS) and a molecular cobaloxime catalyst (Co). EPR and transient optical experiments provide direct evidence of a long-lived (>1.5 ms) Ru(III)-Fd-Co(I) charge separated state formed via an electron relay through the Fd [2Fe-2S] cluster, initiating the catalytic cycle for 2H(+) + 2e(-) → H2.

Ru–protein–Co biohybrids designed for solar hydrogen production: understanding electron transfer pathways related to photocatalytic function

“…6). The observed time constant for the initial electron transfer in Ru–ApoFld–CoBF 2 ( τ 1 = 170 ± 30 ns) is similar to what we observed previously in Ru–ApoFd ( τ = 200 ± 10 ns), 22 which also lacks an internal electron acceptor and we presume proceeds through a Ru( i ) intermediate as in eqn (1). By contrast, the observed time constant for initial electron transfer in Ru–Fd–CoBF 2 is more rapid ( τ 1 = 90 ± 20 ns), which is consistent with Ru( ii )* → Ru( iii ) electron transfer to the [2Fe–2S] cluster out competing the diffusionally governed Ru( ii )* → Ru( i ) reductive electron transfer.…”

“…1C) with Cys18. 22 We now have determined the quantum efficiency for the two electron process of H 2 production to be 1.0 ± 0.3% (Table 1). This H 2 production quantum efficiency value compares reasonably well to multimolecular systems with Co polypyridyl 23 and Co polypyrazine 24 catalysts with H 2 production quantum efficiencies of 3.6% and 0.49% respectively.…”

Artificial Hydrogenases Based on Cobaloximes and Heme Oxygenase

“…This observation led to the emergence of projects aiming at developing artificial enzymes and, as a result, several artificial hydrogenases have been recently described that incorporate a molecular synthetic catalyst into a suitable peptide or protein and allow catalysis in water . In particular, cobaloximes have been incorporated into PS1, sperm whale myoglobin (SwMb), and ferredoxin, with the resulting biohybrids showing catalytic activity for hydrogen production. These approaches enable the catalytic performance of the biohybrid system to be tuned and optimized through modification of both the synthetic component and its coordination‐sphere interactions with the protein cavity.…”

Light‐driven catalysis with engineered enzymes and biomimetic systems

“…In the presence of ascorbate in aqueous solution, Ru-Fd-Co facilitates a TON up to 320 (mol H 2 /mol sensitizer) under irradiation, remaining active over 6 H. Spectroscopic evidence indicates that the ruthenium sensitizer could pass electrons to the [2Fe-2S] cluster of Fd. Ru-ApoFd-Co does not produce hydrogen under the same optimum conditions, demonstrating the importance of the [2Fe-2S] cluster for electron transfer from sensitizer to catalyst [169]. The role of the cluster in electron transfer was further confirmed in subsequent work that replaced the [2Fe-2S] cluster iron ions with redox-inactive gallium [170].…”

“…Cobaloxime 1 (Fig. 10) has also been prepared in a complex with electron-transfer protein Fd (Spinacia oleracea) [169]. This Fd contains a [2Fe-2S] cluster used to mediate electron transfer.…”