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Potential energy surface (PES) analyses at the SMD[MP2/6–311++G(d,p)] level and higher‐level energies up to MP4(fc,SDTQ) are reported for the fluorinated tertiary carbamateN‐ethyl‐N‐(2,2,2‐trifluoroethyl) methyl carbamate (VII) and its parent systemN,N‐dimethyl methyl carbamate (VI). Emphasis is placed on the analysis of the rotational barrier about the CN carbamate bond and its interplay with the hybridization of theN‐lone pair (NLP). All rotational transition state (TS) structures were found by computation of 1D relaxed rotational profiles but only 2D PES scans revealed the rotation‐inversion paths in a compelling fashion. We found four unique chiral minima ofVII, one pair each ofE‐andZ‐rotamers, and we determined theeightunique rotational TS structures associated with every possibleE/Z‐isomerization path. It is a significant finding that all TS structures featureN‐pyramidalization whereas the minima essentially contain sp²‐hybridized nitrogen. We will show that the TS stabilities are affected by the synergetic interplay between NLP/CO₂repulsion minimization, NLP→σ^*(CO) negative hyperconjugation, and two modes of intramolecular through‐space electrostatic stabilization. We demonstrate how Boltzmann statistics must be applied to determine the predicted experimental rotational barrier based on the energetics of all eight rotamerization pathways. The computed barrier forVIIis in complete agreement with the experimentally measured barrier of the very similar fluorinated carbamateN‐Boc‐N‐(2,2,2‐trifluoroethyl)‐4‐aminobutan‐1‐olII. NMR properties ofVIIwere calculated with a variety of density functional/basis set combinations and Boltzmann averaging over theE‐andZ‐rotamers at our best theoretical level results in good agreement with experimental chemical shifts δ(¹³C) andJ(¹³C,¹⁹F) coupling constants ofII(within 6 %).

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 ΔG₁(R) for the reaction R−NH₂+CO₂R−NH−COOH requires the solution of a multi‐equilibrium equation system, which accounts for the dissociation constantsK₂andK₃controlling carbonate and bicarbonate concentrations, the acid dissociation constantK₄of the conjugated acid of the amine, and the acid dissociation constantK₅of 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 ΔG₁(Bu)=−1.57 kcal/mol and ΔG₁(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.