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Abstract Invited for the cover of this issue are Harmeet Bhoday, Nathan Knotts, and Rainer Glaser at the Missouri University of Science and Technology. Joe Miner, the university mascot, is a silent and honorary co‐author and personifies the spirit of the old west and the determination to succeed (our emphasis). The image depicts one (MeO‐Ph, Y)‐azine molecule and a model of a perfectly polar stacked bilayer. The floodlight illumination presents a graphic metaphor of second‐harmonic generation (frequency doubling) by the crystalline ferroelectric materials. Read the full text of the article at 10.1002/chem.202400182. 

Abstract The rotational barrier about the CN carbamate bond ofN‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl)tert‐butyl carbamate1was determined by variable temperature (VT)¹³C and¹⁹F NMR spectroscopy. The −CH₂CF₃ appendage reports on rotational isomerism and allows for the observation of separate signals for the E‐ and Z‐ensembles at low temperature. The activation barrier for E/Z‐isomerization was quantified using Eyring‐Polanyi theory which requires the measurements of the maximum difference in Larmor frequency Δν_max and the convergence temperature T_c. Both Δν_max and T_c were interpolated by analyzing sigmoidal functions fitted to data describing signal separation and the quality of the superposition of the E‐ and Z‐signals, respectively. Methods for generating the quality‐of‐fit parameters for Lorentzian line shape analysis are discussed. Our best experimental value for the rotational barrier ΔG_c^≠(1)=15.65±0.13 kcal/mol is compared to results of a higher level ab initio study of the modelN‐ethyl‐N‐(2,2,2‐trifluoroethyl) methyl carbamate. 

Abstract An improved design is described for ferroelectric crystals and implemented with the “methoxyphenyl series” of acetophenone azines, (MeO−Ph, Y)‐azines with Y = F (1), Cl (2), Br (3), or I (4). The crystal structures of these azines exhibit polar stacking of parallel beloamphiphile monolayers (PBAMs). Azines 1, 3, and 4 form true racemates whereas chloroazine 2 crystallizes as a kryptoracemate. Azines 1–4 are helical because of the N−N bond conformation. In true racemates the molecules of opposite helicity (M and P) are enantiomers A(M) and A*(P) while in kryptoracemates they are diastereomers A(M) and B*(P). The stacking mode of PBAMs is influenced by halogen bonding, with 2–4 showcasing a kink due to directional interlayer halogen bonding, whereas fluoroazine 1demonstrates ideal polar stacking by avoiding it. Notably, (MeO−Ph, Y)‐azines display a stronger bias for dipole parallel alignment, attributed to the linearity of the biphenyl moiety as compared to the phenoxy series of (PhO, Y)‐azines with their non‐linear Ph−O−Ph moiety. The crystals of 1–4 all feature planar biphenyls and this synthon facilitates their crystallization through potent triple T‐contacts and enhances their nonlinear optical (NLO) performance by increasing conjugation length and affecting favorable chromophore conformations in the solids. 

Abstract The front cover artwork is provided by Prof. Rainer Glaser's group at the Missouri University of Science and Technology. The image shows one of four potential energy surfaces generated from our rotation‐inversion study of tertiary carbamates and highlights two of the eight possible transition state pathways between two ensembles of E‐ and Z‐minima. In the context of synthetic studies of fluorinated carbamates R₁O−CO−N(R₂)CH₂CF₃, we unexpectedly observed two sets of ¹³C NMR quartets for the CF₃ group and we needed to understand their origin. Read the full text of the Research Article at 10.1002/cphc.2022005442. 

Abstract The syntheses are reported of N^ϵ‐(2,2,2‐trifluoroethyl)‐D,L‐lysine (^tFK) and N^ζ‐(2,2,2‐trifluoroethyl)‐D,L‐homolysine (^tFK₊₁) from amino alcohols HO−(CH₂)_n−NH₂. The syntheses involve reductive amination, Appel bromination, and the stereoselective bond formation between C_α of the amino acid and the fluorinated alkyl chain in the Schöllkopf bislactim amino acid synthesis. The methyl esters of the fluorinated amino acids are the relevant substrates for oligopeptide synthesis. With theR‐Schöllkopf reagent, we stereoselectively generated methyl N^ϵ‐boc‐N^ϵ‐(2,2,2‐trifluoroethyl)‐L‐lysinate and methyl N^ζ‐boc‐N^ζ‐(2,2,2‐trifluoroethyl)‐L‐homolysinate. Products and intermediates were characterized by ¹H NMR, ¹³C NMR, COSY, HSQC, and LCMS. A variety of N‐functionality may be introduced by reacting hemiacetals with different appendages. This fluorine modification reduces the sidechain N‐basicity by combined ‐I effect of the three fluorines. This effect increases the [amine]/[ammonium ion] ratio of the sidechain amine in lysine to facilitate carbamylation at lower pH conditions. 

Abstract 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. 

Abstract 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 are developing energy-efficient and reversible carbon capture and release (CCR) systems that mimic the Lys201 carbamylation reaction in the active site of ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO). The multiequilibria scenario ammonium ion Xa ⇌ amine Xb ⇌ carbamic acid Xc ⇌ carbamate Xd requires the presence of both free amine and CO₂ for carbamylation and is affected by the pK_a(Xa). Two fluorination strategies aimed at ammonium ion pK_a depression and low pH carbamylation were analyzed with (2,2,2-trifluoroethyl)butylamine 2b and 2,2-difluoropropylamine 3b and compared to butylamine 1b. The determination of K₁ and ΔG₁ of the carbamylation reactions requires the solution of multiequilibria systems of equations based on initial conditions, ¹H NMR measurements of carbamylation yields over a wide pH range, and knowledge of K₂– K₅ values. K₂ and K₃ describe carbonic acid acidity, and ammonium ion acidities K₄ were measured experimentally. We calibrated carbamic acid acidities K₅ based on the measured value K₆ of aminocarbamic acid using isodesmic reactions. The proton exchange reactions were evaluated with ab initio computations at the APFD/6-311+G* level in combination with continuum solvation models and explicit solvation. The utilities of 1–3 will be discussed as they pertain to the development of fluorine-modified RuBisCO-mimetic reversible CCR systems. 

The Cover Feature shows one of four potential energy surfaces generated from our rotation-inversion study of tertiary carbamates and highlights two of the eight possible transition state pathways between two ensembles of E- and Z-minima. More information can be found in the Research Article by Brian Jameson and Rainer Glaser.