We have been interested in the development of rubisco‐based biomimetic systems for reversible CO2capture from air. Our design of the chemical CO2capture and release (CCR) system is informed by the understanding of the binding of the activator CO2(ACO2) in rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase). The active site consists of the tetrapeptide sequence Lys‐Asp‐Asp‐Glu (or KDDE) and the Lys sidechain amine is responsible for the CO2capture reaction. We are studying the structural chemistry and the thermodynamics of CO2capture based on the tetrapeptide CH3CO−KDDE−NH2(“KDDE”) in aqueous solution to develop rubisco mimetic CCR systems. Here, we report the results of1H NMR and13C NMR analyses of CO2capture by butylamine and by KDDE. The carbamylation of butylamine was studied to develop the NMR method and with the protocol established, we were able to quantify the oligopeptide carbamylation at much lower concentration. We performed a pH profile in the multi equilibrium system and measured amine species and carbamic acid/carbamate species by the integration of1H NMR signals as a function of pH in the range 8≤pH≤11. The determination of Δ
- Award ID(s):
- 2152633
- NSF-PAR ID:
- 10412905
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 25
- Issue:
- 12
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 8624 to 8630
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract G 1(R) for the reaction R−NH2+CO2R−NH−COOH requires the solution of a multi‐equilibrium equation system, which accounts for the dissociation constants K 2andK 3controlling carbonate and bicarbonate concentrations, the acid dissociation constantK 4of the conjugated acid of the amine, and the acid dissociation constantK 5of the alkylcarbamic acid. We show how the multi‐equilibrium equation system can be solved with the measurements of the daughter/parent ratioX , the knowledge of the pH values, and the initial concentrations [HCO3−]0and [R‐NH2]0. For the reaction energies of the carbamylations of butylamine and KDDE, our best values are ΔG 1(Bu)=−1.57 kcal/mol and ΔG 1(KDDE)=−1.17 kcal/mol. Both CO2capture reactions are modestly exergonic and thereby ensure reversibility in an energy‐efficient manner. These results validate the hypothesis that KDDE‐type oligopeptides may serve as reversible CCR systems in aqueous solution and guide designs for their improvement. -
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Abstract Reaction of {LiC6H2−2,4,6‐Cyp3⋅Et2O}2(Cyp=cyclopentyl) (
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Abstract Reaction of {LiC6H2−2,4,6‐Cyp3⋅Et2O}2(Cyp=cyclopentyl) (
1 ) of the new dispersion energy donor (DED) ligand, 2,4,6‐triscyclopentylphenyl with SnCl2afforded a mixture of the distannene {Sn(C6H2−2,4,6‐Cyp3)2}2(2 ), and the cyclotristannane {Sn(C6H2−2,4,6‐Cyp3)2}3(3 ).2 is favored in solution at higher temperature (345 K or above) whereas3 is preferred near 298 K. Van't Hoff analysis revealed the3 to2 conversion has a ΔH =33.36 kcal mol−1and ΔS =0.102 kcal mol−1 K−1, which gives a ΔG 300 K=+2.86 kcal mol−1, showing that the conversion of3 to2 is an endergonic process. Computational studies show that DED stabilization in3 is −28.5 kcal mol−1per {Sn(C6H2−2,4,6‐Cyp3)2unit, which exceeds the DED energy in2 of −16.3 kcal mol−1per unit. The data clearly show that dispersion interactions are the main arbiter of the3 to2 equilibrium. Both2 and3 possess large dispersion stabilization energies which suppress monomer dissociation (supported by EDA results). -
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