Fluorination of Rubisco-Mimetic CO2 Capture Systems. Theoretical and Experimental Studies of Ammonium Ion Acidity Depression and Carbamylation
"RuBisCO-inspired CO2 capture and release (CCR) systems featuring amines have been developed for the purpose of reversable CO2 capture from air. The enzyme active site consists of the tetrapeptide sequence Lys-Asp-Asp-Glu. The Lys sidechain amine undergoes carbamylation and an Mg2+ cation stabilizes the resulting carbamate. The Na-acyl-lysinyl-aspratyl-aspartyl-glutamide (Lys-Asp-Asp-Glu, KDDE) peptide featured maximum capture at pH ≈ 10; a pH region too high for Mg2+ ions to remain in solution. This work aims to achieve pKa depression by introducing fluorine in the proximity of the lysine’s sidechain amine. A comparative analysis was made of butylamine, (2,2,2-trifluoroethyl) butylamine, and 2,2-difluoropropylamine to examine fluorination strategies aimed at ammonium ion pKa depression and carbamylation at reduced pH (CH. 1). CF3-functionalized lysines tFKn were synthesized for the purpose of embedding the amino acids into the larger KDDE tetrapeptide (CH. 2). Two 13C NMR rotamer quartet signals were observed for the CF3 carbon of tert-butyloxycarbonyl (boc) protected intermediates. To understand the rotational dynamics, we analyzed the potential energy surface (PES) of a fluorinated tertiary carbamate model system (CH 3). The rotation-inversion barrier was measured to create a direct connection to experimentation (CH. 4). The CO2 addition pathway of the fluorinated tFLys-Asp-Asp-Glu (tFKDDE) tetrapeptide was analyzed to understand its carbamylation mechanics (CH. 5). The CF3-functionalized lysine tFK was embedded into the tetrapeptide and its carbamylation, both with and without Mg2+, was analyzed as a function of pH to determine maximum carbamylation, the pH of maximum carbamylation, and its Gibbs’ free energy (CH 6)"--Abstract, p. iv
Carbamylation, CO2 Capture, Fluorinated Amines, pKa Depression, RuBisCO-mimetic, Unnatural Amino Acids, Chemistry, Physical Chemistry, Physical Sciences and Mathematics
Missouri University of Science and Technology
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