The rising atmospheric concentration of CO2 has motivated researchers to seek routes for improved utilization, increased mitigation, and enhanced sequestration of this greenhouse gas. Through a combination of bioinformatics, molecular modeling, and first-principles quantum mechanics the binding of carbon dioxide to proteins is analyzed. It is concluded that acid/base interactions are the principal chemical force by which CO2 is bound inside proteins. With respect to regular secondary structural elements, β-sheets show a marked preference for CO2 binding compared to α-helices. The data also support the inference that while either or both oxygens of CO2 are generally tightly bound in the protein environment, the carbon is much less “sequestered.” First principles and more approximate modeling techniques are assessed for quantifying CO2 binding thermodynamics.

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To focus on the identification of potential alternative amine carbon capture compounds, CO(2) with methyl, silyl, and trifluoromethyl monosubstituted and disubstituted amine compounds were studied. Interaction energies of these CO(2)·amine complexes were determined via two methods: (a) an ab initio composite method, the correlation consistent composite approach (ccCA), to determine interaction energies and (b) density functional theories, B3LYP/aug-cc-pVTZ and B97D/aug-cc-pVTZ. Substituent effects on the interaction energies were examined by interchanging electron donating and electron withdrawing substituents on the amine compounds. The calculations suggested two different binding modes, hydrogen bonding and acid-base interactions, which arise from the modification of the amine substituents, echoing previous work by our group on modeling protein·CO(2) interactions. Recommendations have been noted for the development of improved amine scrubber complexes.

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