Study on the protein and peptide absorbents for capture and storage of CO2 : Interactions bwteen CO2 and amino acids

Abstract Interactions between amino acid side chains and CO2 molecules are systematically evaluated using quantum chemical calculations and NMR experiments. The binding energies of CO2 in three proteins (phosphoenolpyruvate carboxykinase, rhodobacter capsulatus, and carbonic anhydrase II) are analyzed based on QM and MD simulations. In the 20 natural amino acids of proteins 13 charged or polar amino acids possess remarkable ability of electrostatic interaction with CO2 molecules. Aromatic amino acids (Phe, Tyr, and Trp) can form π–π stacking interactions with CO2 molecules that are comparable with common hydrogen bonds (ཞ20 kJ/mol). The best binding sites for CO2 molecules are the three alkaline amino acids (cations Arg+, Lys+, and His+). The acidic amino acids (anions Asp− and Glu−) could maintain a suitable pH condition that is necessary for CO2 releasing from proteins. Histidine may deliver CO2 molecules in proteins through the changes form His+ to His. The CO2 molecules also can form hydrophobic interaction with hydrophobic amino acids, and to be stored in hydrophobic pocket in proteincs. Two peptide absorbents are designed and synthesized, and measured by NMR technique. The study results may help to develop more powerful protain and peptide absorbents for CO2 capture and storage.