Carbon Dioxide Capture by Amino Acids through an Arginine-Arginine Carbamate Ion Pair

A novel complex comprising an ion pair of arginine-arginine carbamate is reported herein, which is isolated from an aqueous l-arginine solution after reacting with CO₂. Its structure was unambiguously elucidated via single-crystal X-ray diffraction, and its phase purity was confirmed by powder X-ray diffraction (PXRD) analysis. Nuclear magnetic resonance (NMR) studies suggested that the arginine carbamate complex hydrolyzed in aqueous conditions with a rate directly proportional to its concentration. Furthermore, density functional theory (DFT) calculations revealed how the amino group acted as a nucleophile to attack CO₂to enable the ion-pair formation through a proton transfer between the arginine and arginine carbamate. The discovery of the arginine-CO₂adduct expands our understanding of CO₂fixation and can lead to the development of new methods of implementing l-arginine or other amino acids for CO₂capture technology.