Ambient synthesis of single-atom catalysts on catalytically active cells for chemoenzymatic cascades.

While microbial cells have emerged as a versatile platform for the synthesis of metal nanoparticles, their application for the production of single-atom catalysts (SACs) has been rarely studied yet. Here, we develop a facile method for the ambient synthesis of SACs with a high loading of >4.0 wt% by in-situ reduction of metal ions on the cells overexpressing a catalytically active enzyme, producing chemo-bio bifunctional catalysts (SAC@cell). Computational investigations unlock that the coordination between SACs and the oxygen atoms on cell surface is responsible for SAC formation. The alcohol dehydrogenase (ADH)-overexpressed cells growing with single-atom palladium (SA-Pd) as a heterogeneous catalyst (SA-Pd@cell-ADH) demonstrate high regio- and enantio-selectivity in the fully asymmetric reduction of α,β-unsaturated enones, a challenging transformation for single metal- and bio-catalysts. Silica-coating is also conducted on cell surfaces to enhance the stability and reusability of the chemo-bio hybrids. This work presents the versatility of microbial cells for the fabrication of SACs and metal-enzyme integrated catalysts.