CO₂ Conversion by a Metal-Coordinated Single Amino Acid Carbonic Anhydrase Enzyme Mimic

The rising atmospheric concentration of carbon dioxide (CO₂) is assumed to be a key factor in global climate change, requiring robust and sustainable carbon conversion technologies. While carbonic anhydrase (CA) is a highly efficient enzyme for CO₂ sequestration, its industrial application is limited by stability, cost, and scalability challenges. To address these limitations, we developed a CA-mimetic metal-amino acid (Phe-Zn(II)) bionanozyme featuring amyloid-like supramolecular cross-β-sheet architecture that provides high structural stability and recyclability. Gas chromatography (GC) analysis of a continuous flow bubble reactor charged with Phe-Zn(II) bionanozyme exhibits a CO₂ conversion efficiency of approximately 18% in an aqueous medium (pH 7.0, 25 °C, ambient pressure), while maintaining remarkable structural integrity as confirmed by postcatalysis PXRD analysis. The amyloid-like supramolecular cross-β-sheet architecture, stabilized by π-π stacking and intermolecular hydrogen bonding, generates a confined catalytic microenvironment that enhances Zn(II) Lewis's acidity and promotes efficient CO₂ hydration, which is crucial compared to previous reports. Next, density functional theory (DFT) calculations reveal a three-step catalytic pathway involving hydroxide ion generation, nucleophilic attack, and carbonic acid formation, with a rate-determining barrier of 12.3 kcal/mol, making the reaction feasible at room temperature. We also investigated the impact of different amino acids coordinated with Zn, finding that Phe-Zn(II) shows higher catalytic activity. This is due to the stronger electron-withdrawing effect of the phenyl group, which enhances the Lewis acidity of Zn²⁺, activates the Zn²⁺-OH₂ bond, and lowers the rate-determining barrier. Taken together, the combination of experimental catalysis, structural robustness, and mechanistic validation highlights Phe-Zn(II) as a promising, cost-effective, and minimalistic catalyst yet efficient carbonic anhydrase mimic for CO₂ conversion, paving the way for scalable and sustainable carbon sequestration strategies critical for mitigating climate change.