Light-Activated Artificial\nCO<sub>2</sub>‑Reductase:\nStructure and Activity

Light-dependent reduction of carbon dioxide (CO<sub>2</sub>) into\nvalue-added products can be catalyzed by a variety of molecular complexes.\nHere we report a rare example of a structurally characterized artificial\nenzyme, resulting from the combination of a heme binding protein,\nheme oxygenase, with cobalt-protoporphyrin IX, with good activity\nfor the photoreduction of CO<sub>2</sub> to carbon monoxide (CO).\nUsing a copper-based photosensitizer, thus making the photosystem\nfree of noble metals, a large turnover frequency value of ∼616\nh<sup>–1</sup>, a turnover value of ∼589, after 3 h\nreaction, and a CO vs H<sub>2</sub> selectivity of 72% were obtained,\nestablishing a record among previously reported artificial CO<sub>2</sub> reductases. Thorough photophysical studies allowed tracking\nof reaction intermediates and provided insights into the reaction\nmechanism. Thanks to a high-resolution crystal structure of the artificial\nenzyme, both in the absence and in the presence of the protein-bound\nCO<sub>2</sub> substrate, a rational site-directed mutagenesis approach\nwas used to study the effect of some modifications of the active site\non the activity.