We have been interested in the development of rubisco-based biomimetic systems for reversible CO2 capture from air. Our design of the chemical CO2 capture and release systems is informed by the understanding of the binding of the activator CO2 (ACO2) in rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), which is the most abundant enzyme on Earth and it is responsible for carbon fixation in plants. The active site consists of the tetrapeptide sequence Lys-Asp-Asp-Glu (or KDDE) and a hydrated Mg2+ ion that coordinates to the carboxylic acid groups of the Asp and Glu side chains. As part of our studies of the structural chemistry and the thermodynamics of CO2 capture of the KDDE tetrapeptide, we studied aqueous solutions of butylamine to understand the capture mechanism and optimize capture condition. Here, we report the results of 1H NMR and 13C NMR analyses of CO2 capture by butylamine and of computational studies of CO2 addition to alkylamines. We measured the pH dependence of the equilibrium between butylamine and butyl carbamic acid/carbamate and determined the best pH value and ΔG0 (pH) values for CO2 capture. We also studied the stereochemistry and the energies of all species involved in the CO2 capture by small alkylamines (R–CH2–NH2, Fig. 1) with density functional theory and including aqueous solvation at the SMD(APFD/6-311G*) level. The thermodynamical data computed for the capture reaction agree very well with the measurements. The data also inform about the pH-dependencies of the ratios between ammonium ion and amine and between carbamic acid and carbamate in solution.

Computational and experimental study of CO2 capture by alkylamines

255th National Meeting (2018)

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