Charge separation related to photocatalytic H2 production from a Ru–apoflavodoxin–Ni biohybrid

• Published in: ACS energy letters 2016-12, Vol.2 (1)
• Main Authors: Soltau, Sarah R., Niklas, Jens, Dahlberg, Peter D., Mulfort, Karen L., Poluektov, Oleg G., Utschig, Lisa M.
• Format: Article
• Language: English
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; SOLAR ENERGY
• ISSN: 2380-8195; 2380-8195

The direct creation of a fuel from sunlight and water via photochemical energy conversion provides a sustainable method for producing a clean source of energy. Here we report the preparation of a solar fuel biohybrid that embeds a nickel diphosphine hydrogen evolution catalyst into the cofactor binding pocket of the electron shuttle protein, flavodoxin (Fld). The system is made photocatalytic by linking a cysteine residue in Fld to a ruthenium photosensitizer. Importantly, the protein environment enables the otherwise insoluble Ni catalyst to perform photocatalysis in aqueous solution over a pH range of 3.5–12.0, with optimal turnover frequency 410 ± 30 h–1 and turnover number 620 ± 80 mol H2/mol hybrid observed at pH 6.2. For the first time, a reversible light-induced charge-separated state involving a Ni(I) intermediate was directly monitored by electron paramagnetic resonance spectroscopy. As a result, transient optical measurements reflect two conformational states, with a Ni(I) state formed in ~1.6 or ~185 μs that persists for several milliseconds as a long-lived charge-separated state facilitated by the protein matrix.