Light-Activated Artificial CO₂-Reductase: Structure and Activity

Light-dependent reduction of carbon dioxide (CO₂) into value-added products can be catalyzed by a variety of molecular complexes. Here we report a rare example of a structurally characterized artificial enzyme, resulting from the combination of a heme binding protein, heme oxygenase, with cobalt-protoporphyrin IX, with good activity for the photoreduction of CO₂ to carbon monoxide (CO). Using a copper-based photosensitizer, thus making the photosystem free of noble metals, a large turnover frequency value of ∼616 h^-1, a turnover value of ∼589, after 3 h reaction, and a CO vs H₂ selectivity of 72% were obtained, establishing a record among previously reported artificial CO₂ reductases. Thorough photophysical studies allowed tracking of reaction intermediates and provided insights into the reaction mechanism. Thanks to a high-resolution crystal structure of the artificial enzyme, both in the absence and in the presence of the protein-bound CO₂ substrate, a rational site-directed mutagenesis approach was used to study the effect of some modifications of the active site on the activity.