Semiartificial Photoelectrochemistry for CO<sub>2</sub>-Mediated Enantioselective Organic Synthesis
Tessel Bouwens, Samuel J. Cobb, Celine W. S. Yeung, Yongpeng Liu, Guilherme Martins, Inês A. C. Pereira, Erwin Reisner
Abstract
High Resolution Image Download MS PowerPoint Slide Photoelectrochemical (PEC) cells are under intensive development for the synthesis of solar fuels, but CO 2 reduction typically only results in simple building blocks such as HCOO – . Here, we demonstrate that CO 2 -converting PEC cells can drive integrated enzymatic domino catalysis to produce chiral organic molecules by using CO 2 /HCOO – as a sustainable redox couple. First, we establish a semiartificial electrode consisting of three enzymes co-immobilized on a high surface area electrode based on carbon felt covered by a mesoporous indium tin oxide (ITO) coating. When applying a mild cathodic potential (−0.25 V vs the reversible hydrogen electrode (RHE)), CO 2 is reduced to HCOO – using a W-formate dehydrogenase (FDH NvH ) from Nitratidesulfovibrio vulgaris Hildenborough, which then enables the reduction of NAD + to NADH by an NAD + -cofactor-dependent formate dehydrogenase from Candida boidinii (FDH CB ). Subsequently, an alcohol dehydrogenase (ADH) uses NADH generated from CO 2 /HCOO – cycling to reduce acetophenone to chiral 1-phenylethanol in good enantiomeric excess (93%) and conversion yields (38%). Depending on the specific ADH (ADH S or ADH R ), either ( S )- or ( R )-1-phenylethanol can be synthesized at pH 6 and 20 °C. To illustrate solar energy utilization, we integrate the three nanoconfined enzymes with a PEC platform based on an integrated organic semiconductor photocathode to allow for enantioselective synthesis (at +0.8 V vs RHE) based on a solar fuel device. This proof-of-principle demonstration shows that concepts and devices from artificial photosynthesis can be readily translated to precise and sustainable biocatalysis, including the production of chiral organic molecules using light.