Anthropogenic CO2 emissions have become exceedingly impactful and atmospheric CO2 concentrations have reached a level that will require CO2 capture from air to effectively address climate change. Most methods for CO2 scrubbing employ amines which capture CO2 by carbamate formation. We have focused on RuBisCO-inspired CO2 capture using oligopeptides which offer the advantages of quantitative capture at ambient temperatures and of energy-efficient reversibility. All models include the active-site tetramer KDDE (Lys-Asp-Asp-Glu) and the free amine in the side chain of lysine binds to CO2 to form a carbamate with catalysis by an Mg2+ ion complexed to the carboxylates of the Asp-Glu moiety. RuBisCo employs an elaborate trick to reduce the pKa of the lysine ammonium ion, so as to ensure a sufficient concentration of free amine for efficient CO2 capture at ambient conditions. For the small biomimetic system, we employed chemical means to lower the pKa of the lysine protonated amino group: N-alkylation with a 2,2,2-trifluoroethyl group. We will show that the 2,2,2-trifluoroethyl N-substituent is able to lower the pKa of protonated N-(2,2,2-trifluoroethyl)-4-aminobutanol and we demonstrate the viability of this system for CO2 capture at ambient pH conditions. In light of these results, we are now employing this concept in the oligopeptide capture systems that include the fluorinated lysine. Here, we report on the syntheses of Nε-(2,2,2-trifluoroethyl)-L-lysine from 4-aminobutanol and of Nz-(2,2,2-trifluoroethyl)-L-homolysine from 5-aminopentanol. The synthesis is outlined in Figure 1 for the lysine derivative.

Synthesis of fluorinated lysine derivatives and application in reversible CO2 capture

ACS Fall 2020 Virtual Meeting

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